:; 
􀀨􀀩􀁾COMMITTEE REPORTS 􀁾􀀡􀀨􀁬􀀶􀀡􀀠GOVERNMENT AFFAIRS -----M .1.... Betty Anl.bi raylor //V""'''' Regulatory Update //On November 8, 19s6, the 1NRCC proposed amendments to:> Chilpter
317, Design Criteria for Sewerage Facilities. The pwpose of the amendments is to reduce the number of plans and specifications required to be sent to the 1NRCC for their review. Under
this proposal, persons subject to the submittal requirements of Texas Water Code Section 26.034, would initially only be required to submit to the 1NRCC summary information regarding
a proposed wastewater collection, treatment or disposal project, eliminating the burden of submitting detailed technical information and blueprints. On October 7, 1996, EPA issued a
Notice and Request for Comments m a number of options to standardize facility data reporting. This is the first step EPA is taking to streamline and consolidate EPA's collection and
maintenance of environmental data. EPA is considering options for establishing a national standard for the reporting and maintenance of information regarding the identification of facilities
that are subject to federal environmental reporting and permitting requirements. Comments are due on orbefore December 23,1996. Legislative Update The State of Texas 75th Regular Legislative
Session will convene on January 14,1997. As of December 9, 1996,277 House Bills and 119 Senate Bills have been filed. To date there have not been any bills filed relating to wastewater
issues. We will be monitoring this session for bills impacting the wastewater industry. Updates will be provided in future issues of the Pipeline. Upcoming Meetings Water Environment
Federation 1997 Washington Briefing, March 18-19,1997, Sheraton Suites, Alexandria, VA. Contact: Jim Sullivan, WEF Manager of State and Regional Affairs 703/684-2436 WEF/ABA/EPA Clean
Water 97 Video Conference, May 29, 1997, Numerous locations throughout the U.S., Contact: Jim Sullivan, WEF Manager of State and Regional Affairs 703/684-2436 We are actively recruiting
members for WEA T's Government Affairs Committee. If you would like to become a member of this Committee, or if you need additional information contact Betty Antebi at (214) 670-3213,
E-mail: bantebi@dwu.ci.dalIas.tx.us. We look forward to hearing from you! 􀁾 INTERNATIONAL LIAISON FemandoRoman Update On Status of Water and Wastewater Operator Training Activities
Between the United States and Mexico The Water Environment Association of Texas and the Texas Section-AWWA have been administering a 5-year, $100,000 EPA grant each for operator training
activities in Mexico. Two seminars have been conducted to date, one in Piedras Negras, Coahuila, Mexico, where 16-hour chlorination and water laboratory classes were imparted, and one
in Monterrey, Nuevo Leon, Mexico where B-hour basic water and basic wastewater dasses took place. The training sessions have been successful in the quality of the teaching, but have
come short of the time needed to qualify them for certification. After extensive discussion with officers from the Mexican organization Sociedad Mexicana de Aquas (SMAAC), and Asociacion
Mexicana de Aquas (AMAAC), we conduded that the Texas format (20-hr designated courses) would not be the most effective way to provide the aid, given the shortage of Spanish-speaking
instructors. Instead, the group decided to approach the training with a site-specific objective, whereby a facility in Mexico is identified and American experts in the field are matched
to the facility; some Spanish is still necessary, bul the emphasis changes, from language first, to expertise first. The grants provide for all training needs, including travel expenses
and a reasonable fee for the instructors; although WEAT and AWWA strongly encourage voluntary services. A plan is under development to establish the qualifications and criteria for the
selection of appJicants on an as-needed basis. NOMINATING Gordon Koblitz The Nominating Committee Wants YOU!!! Time again for us to seek our most talented and deserving members as potential
nominees for the 1997-8 WEA T Vice President and Director positions. The Nominating Committee (Gordon Koblitz, Stephen Jenkins, Joe King, Mary Evans and Carolyn Ahrens) needs your input
by January 31. Call or send your nominees name and preferably, a short bio describing their qualifications, WEAT activities, and any other supportive comments. We will present our "slate"
for consideration in the March Pipeline. Members will have the opportunity to vote at our WEAT business meeting during the Annual Conference in April. More details will follow in the
next Pipeline. 4 
17 DESIGN CRITERIA FOR SEWERAGE SYSTEMS 
Effecti"e date: March J, !9n TEXAS 􀁾􀁁ruRAL RESOURCE CONSERVATION COMMISSION Permanent Rule Change Chapter 317 Design Criteria for Sewerage Systems' §3171 I. PUlJIoses. This change
transmittal provides a new adoption to the Texas Natural Resource Conserration Commission (TNRCC) Volume of PeIIl1lllll!nt Rules. 2. E'l1ianation The TNRCC adopted amendments to §317.1
relating to the General Provisions of the Design Criteria for Sewerage Systems. Section §317.1 is adopted with changes to the proposed text as published in the November 8. 1996. issue
of the Texas Register (21 Te.xReg 10961). Please replace the existing chapter with the attached. A new indel( and history page are attached reflecting any changes brought about by this
adoption. 3. Effect ofCbange. The pmpose olthe amendments is to greatly reduce the volume of plans and specifications that are !1I!quired to be submitted to the executive director and
to eliminate notification procedures for municipalities wbi(:h qualify as plans and specifications review authorities. These changes are necessary to allow limited staff !1I!soom:os
to focus on those plans and specifications which need staff review because of: a proposed innovative teChnology; a history of compliance problems; special considerations associated with
the stream segments which will n:ceive the effluem discharge; and when: no qualified municipalities exist to review plans and specifications pursuant to House Bill 1826 (74th Legislative
Session). Additionally. the rules provide that those pe!Sons subject to the submittal requirements specified in the Texas Water Code. §26.034. will initially only be required to submit
a summary 10 the O1(OCutive director. which includes Ulformation regarding proposed wastewater coUection. treatment. or disposal projects. This summary submittal requirement wiU eliminate
the busdens associated with sending in detailed technical infolIllation and blueprints to the agency when nO agency review will be performed. The actual plans and specifications, and
engineering ll!ll!port will remain on file with the project originators and be available for TNRCC inspection. These amendments also mOll! clearly recognize qualified municipalities
as review authorities for wa5ll!Waler coUection system plans and specifications. As with the existing rules, such projects reviewed and approved by municipalities will not be subject
to any submittal or ll!view by the executive director. 
1 , . 1 1 1 1 1 1 1 1 1 1 1 
CHAPTER JL7 DES1GN CRITERIA FOR SEWERAGE SYSTEMS HISTORY PAGE Amendments to §317 1 and §317,.j. Dale Adopted: December 1l. 1995 Dale Filed with the SecrefID!' of State: December 19,
1995 Date Effecuve: January l. 1996 Amendments to: §317, I Date Adopted: February 5, 1997 Date Filed with the Secretary of State: February 10, 1997 Date Published in the Texas Register:
February 18, 1997 Date Effective: MatCh 3, 1997 
􀁛􀁾􀁩􀁄􀁅􀁘􀀠CHAPTER 317 DESIGN CRITERIA FOR SEWERAGE SYSTEMS 􀁾􀀳􀀱􀀷􀀠L General ProVIsions. §317.2. Sewage Colleellon Svstem. 􀁾􀀳􀀡7J Lift Stations. 􀁾􀀳􀀱􀀷􀀢􀀧􀀮􀀠Wastewater Treatment
Facilities. 􀁾􀀳􀀱􀀷􀀵􀀮􀀠Sludge Processing. §3l7.6. Disinfection. §3\7.7 Safety. 􀁾􀀳􀀱􀀷􀀮􀀸􀀮􀀠Design and Operation Features. §317.9. Appendh A. §3\ 7.10. Appendix B -Overland flow
process. §3l7.! L Appendix C • Hyacinth Basins. §3l7l2. AppendixD. §317.13. Appendix E -SepaIation Distances. §317J 5. Appendix G -General Guidelines forme Design of Constructed Wetlands
Units roruse in Municipal Wastewater Treatment 
Te,as Narural Resource Conservauon CommISsion Page 1 Chapter 31' . DesIgn Cmena for Sewerage Svslems CHAPTER 317: DESIGN CRITERIA FOR SEWERAGE SYSTE:l-1S §J17.1. General Provisions.
i!! Purpose. These design crileria are minimum guidelines 10 be used for the comprehens"'e consideration of domestic sewage collection. treaunent, or disposal sysrems and establish the
minimum design criteria pursuant to existing state statutes pertaining to effluent quality necessary to meet stale waler quality standards. These crileria are intended to promote the
design of facilities in accordance with good public health and water quality engineering practices. These criteria include the minimum requirements for a prelirniIuuy engineering report
which provides the general engineering concepts underlying the proposed project as well as the rmal engineering report detailing the fully developed project along with related plans
and specifications. (I) Authority for Requirement. The Texas Water Code prescribes the duties of the Texas Natural Resource Conservation Commission (commission) relating 10 the control
of pollution including the review and approval of plans and specifications for sewage disposal systems. This authority is found in Texas Water Code §§S.OI3. 12.081-12.083, IS.104, 15.114,
26.023, 26.034, 49.181-49.182, 54.024, and S1.333. (2) Review of plans and specifications. Plans and specifications.baIl meet the design criteria and the operation, maintenance, and
safety requirements for the proposed project as provided by Ibis chapler. Appruval given by the executive director, or a participating municipality with review authority as provided
for in paragraphs (5) and (6) of this subsection, sball not relieve the sewerage sysrem owner or the design engineer of any liabilities or responsibilities with respect to the proper
design, constroctiOIl, or authorized operation of the project in accordance with applicable commission rules. (3) Submittal requirements. (A) "Sanitary sewer collection sysrem projects,"
which will be constructed within the jurisdiction of a municipality which peIfolIllli technical reviews of sanitary sewer collection system projects WIder the Texas Water Code, §26.034,
and which ale 1101 prepared by tile staff oca municipality, need not be submitted to the agency for review. (8) 􀁾􀁓􀁡􀁮􀁩􀁴􀁡􀁲􀁹􀀠sewer co1lection system projects," which are prepared
by the S!aff of a municipality, which will be constructed within the jurisdiction ofa municipality which performs technical reviews ofsanitary sewer collection sysrem projects under
the Texas Water Code, §26.034, and where the entire project falls into one or more ofthe categories outlined in \tents (i) through (iii) of this subparagraph, need not be submitted to
the agency for review. (i) Any COIWentiOnal gravity sewer collection system lines less than 1,500 linear feet in length which are extensions 10 existing sysrems where the existing sysrem
has been completed and in operation at least six months; 
Texas :-';arunl Resoun:e Conservauon CommIsSion Page 1 Chapter' 􀁴􀁾􀀠􀁾􀀠DesIgn Cnlena for Sewer.lge Systems (il) Any duplex lift stations which hav'e a fmn pumping capacity of less
than tOO gallons per minute: (iii) Any conventional gravity sewer piping less than t2 inches in diameter. (C) "Domestic wastewater projects" wmch receive a technical revi!:\V and approv'at
from a Stale agency other than the commission need not be submined to the agency for review, if: (i) the review is perfonned under the supervision of a professional engineer registered
in the Slate of Texas, the review ensures that the project complies with this chapter. and the Slate agency has requested thai the commission not perfonn technical reviews of a wastewater
project or category of projects; or (ti) the slate agency has been granted review authority in lieu of the commission under Stale law. (I) A sunuruuy tranSmittal letter shall be sublllitted,
by certified mail, to the Wastewater PermilS Section, and to the appropriate commission regional office. for all wastewater projects consttucted in the Slate of Texas, which are nol
exempted from the commission's submittal requiremenlS as delailed in subparagraphs (A), (B), or (C) of this panlIlzapb. Ifthe e.'(ecutive director does nol notifY the person who submined
the sunuruuy that a review will occur, under subparagraph (E) of this pamgraph, the project is deemed 􀁡􀁰􀁰􀁲􀁯􀁾􀁥􀁤􀀮􀀠The infonnation in the sunuruuy shall be signed, dated, and
sealed by a professional engineer registered in the State of Teus. All summaries shall include, at a mirumum: (i) the name and address of the design finn; (ii) the name, phone munbel'
and facsimile number of the design engineer; (iii) the County(s) in which the projecl will be located with an identifying name for the project; (iv) the name oftile enlity which proposes
10 own, operate, and maintain the project through ilS design life; , (v) the permit name and permit number of the relevant wastewater treatment facility: (vi) a statement verifying that
the plans and specifications are in substantial compliance with all the requilllmenlS ofthis chapter and which states thai any deviations from the requirements are based on the best
professional judgement ofthe IIlgistellld professional engineer who plllpared the project plans and specifications and final engineering design report; and (vii) a brief description
of the project scope which inl:ludes the specifics of < 1,1/1 the project. a description ofdeviations from the IIlquiremenlS of this chapler, inl:luding the use of non􀁾􀁟'" conforming
or innovative techoo\ogy, and an explanation of the reasons for such devtallons, 
􀁔􀁥􀁾􀁡􀁳􀀠"arural Resoun::e Conservauon CommISSIon Page J Chapter} [7 . Design Ctitena for Sewerage Systems i E) Any project. for wruch a summary is submitted. is subject to review
bv the executive dtrecto r. Factors to be used to determme whether a reVIew will be performed include. bui are not ilmned to. whether or not a nonconforming or lnno"ative technology
is being proposed. the stream segment in which the project is located. and the appticant"s compliance record. lith••xecutive direclorchooses to review a project. the design engineer
wlll be notified in writing or by facsimile of the executive directors intent to review the project. within ten days of receipt of the summary. Upon receIpt of the notifICation of intent
to review, the design engineer shall submit to the executive dhector a complete set of plans and specifications and a complete final engineering design report. These submitted materials
shall be sufficient to satisfy the executive director that the project is in compliance with this chapter. II the executive director reviews a project, any approval may be granted under
pamgrnph (4) of this subseclion. Construction mav not commence until approval has been obtained. . (F) A complete set of plans and specifICations, the final version of such plans and
specifications With engineers certification. a complete engineering design report. all change orders and test results. a copy" of the written summary submitted to the executive director,
and any wrinen approvals granted by the executive director, a muniCipality, or another state agency, shall be maintained and kept by the permittee, or for coliection system projects,
person(s) responsible for managemeru of the coliection system, for at least three years from the date the engineer certifies to the executive director that the project is complete. These
materials shall be submitted to the executive director, another Slate agency, or municipality upon request. Such materials must be readily available for inspeclion by the executive director's
staJf upon request during regular business hours. 􀀨􀁾􀀩􀀠Types of approval. Reganlless of the type of approval, constructed facilities when in operation are required to produce the
quality of effluent specified in their discharge permit(s). The types of approvals described in subparagraphs (A) through (C) of this paragraph will be utilized by the commission or
any other review authority. (A) Standanl approval. Plans and specifications found to comply with all applicable paltS of these criteria and 10 conform to commonly accepted sanitary engineering
design prnctices shall be approved for construction. 􀁾􀁾􀀭􀀺􀀺􀀺􀁲􀀠(B) Approvals of innovative and nonconfonnillg technologies. (i) Technologies 􀁣􀁯􀁮􀁳􀁩􀁤􀁥􀁾to be nollCOnfonnillg
or innovative include ones not confonnillg to or addressed in the design crileria of this chapter. (ii) Ifan approval for oonconfonnillg or innovative technologies is requested, engineering
proposals for processes, equipment, Or construction materials 001 covered in these criteria shall be fully described in the submilllld planning materials and the reasons for their seleclion
clearly outlined. Processes considemd to be oollCOnfolllling or ilUlOVlllive should also be supported by results of piloi or demonstration studies. Wltere similarly designed full scale
processes exist and are known to have operated for a reasonable period of time under conditions similar to those suggested for the proposed design, performartce data from these existing
full scale facilities shall be required to be submitted 10 the executive director in addition 10, or in lieu of, pilol or small scale demonstralion studies. Any wammlies or 
Texas "iatllral. Resou!!:e Conservation Commission Page .\ Chapter j I" • Design Cmena for Sewerage Systems performance bo od agreements offered by the process. equipment. or material
manufacturers shall be full>' descnbed in the request • (Ui) Approvals of processes. equipment. orconsuuction materials which are considered to be innovative or nonconforming will be
granted only in cases where the commission or review authority determines. after an engineering evaluation of the supporting information provided to the submirting engineer's design
repon, that the technology will not result in a threat to public health or the environment. (iv) The exec\1tive director or review authority may require the manufacturer or supplier
to obtain and furrtish evidence of an acceptable two-year performance bond from an approved surety which insures the performance of the innovative or nonconforming teclmology. The performance
bond shall cover the cost of removal or abandonment of the innovative or nonconforming facility and and equipment. replacement with previously agreed upon facilities or 􀁥􀁱􀁲􀁴􀁩􀁰􀁭􀁥􀁮􀁾􀀠and
all associated engineering fees necessruy for the removal and replacement. (v) Approval of innovative and nonconforming technologies may include a condition which states that after some
pll!dmrmined period oftime after the installation and startup of the innovative or nonconforming technology. requiring an engineering repon to he submitted after stan-up, detaillng the
performance of the nonconforming or innovative technology, The engiI!eerlng repon shall include unbiased calculations and data supponing the technology's performance; and written submittals
from the design engmeer and permittee wIUch state that the nonconforming or innovative technology has satisfied its manufactwer's claims. (C) Conditional approval The executive director
or review authority may gram approvals which contain detailed conditions, stipulations or resttictions. Examples of such conditions and stipulations include, but are not limited to,
testing requirements, reporting requirements. operational requirements, and additional installation and design requirements which may be necessruy to ensure compliance with this chapter.
AJ:ty conditional approval granted may be issued for a specific set of flow siruations, wastewater chamcleristics, andlor 􀁾􀁱􀁵􀁩􀁮􀀺􀁤􀀠effluent quality. Ifa conditional approval is
granted, both the sewage system owner and design engiMer, as appropriate. shall be responsible for ensuring that the approval conditions outlined by the commission or review authority
have been mel (5) MWIicipali1ies performing tcclmical reviews of sanitary sewer collection systems under Texas Water Code, §26.034, within 90 days of the effective date of this rule
andIorwithin 90 days of a boundaries change, shall submit maps to the agency's Wastewater PcrmiU Section detailing the boundaries of the review authority. Ifa municipality decides to
perfonn tecbnical reviews ofsanitary sewer collection systems after the effective date of this rule, the municipality shall submit maps detailing the boundaries of the review authority,
within the thirty days 􀁢􀁥􀁦􀁯􀁾􀀠staning these reviews. Ifat any time a municipality, which has chosen to implement this II!view authority, decides to cease review of sanitary sewer
collection system plans and specifications, the municipality shall notify the executive dim:tor within thirty days of the date on which the fmaJ plans and specifications review is expected
to be perfonned. In order to meet the standards specified in the Texas Water Code, §26,034, municipalities shall incotpOrate the items detailed in subparagraphs (A) through (E) of this
paragraph into their review programs: 
Texas :':i.1rural Resource Conservauon Commission Page 5 Chapter} I 􀁾􀀠. Design Cntena for Sewerage 􀁓􀁾􀁳􀁴􀁥􀁭􀁳􀀠lAI The murucipality' s review and approval process shall et1Sllre
compliance WIth the rules of lhis chapter. (B) All reviews performed by an employee of the municipality shall be conducted by a professional engineer, registered in the State of Texas,
or the employee conducting the review shall be under the direct super"ision of a professional engineer, registered in the State of Texas, who is ultimatelv responsible for the review
and approval of each collection system submitted and installed in the . municipality's jurisdiction, (e) The responsible review engineer shall be either an employee of the reviewing
murucipality, or a consultant to the municipality, separate from the private consulting firm charged with the design worl< under review, For purposes oflhis section, the term "separate"
means that the responsible review engineer is not employed by and does not receive compensation from the private consulting frrm and from any of its parent companies. subsidiaries or
affiliates charged with the design. The municipality shall provide on request documentation of its agreements with private consultants sufficient to allow the agency to audit its compliance
with this subsection, CD) A participating municipality may review and approve engineering reports, plans and specifications only for projects which trnnspon primarily domestic waste
Within the boundaries of jurisdiction of that municipality, For each project approved for construction, the municipality shall issue an approvalleneror other indication of the approval
which clearly details the project being approved, (E) The municipality shall maintain complete flies of all review and approval activities carried out under its authority and shall make
any existing project files available to the commission upon request and/or during audits performed in accordance with paragraph (6) of this subsection. (6) The executive director may
perform periodic periodic audits of the review and approval process of municipalities which perform technical reviews of sanitI1y sewer collection systems in lieu ofthe commission. to
ensure thaI the projects approved by the ,municipalities are in compliance with this chapter, Ifthe executive director decides to perform an audit ofa municipality's review and approval
process, the e.xecutive director will provide the municipality with a minimum of fIve wodting days advano:e notice of the pending audit The executive director may, for auditing purposes
only, review specific projects which have previously been approved by the review authority. The municipality shall provide to the executive director, on request, documemation ofall agreements
betWeen the private consultants and the municipality, which relate to the wastewater collection system review program, Ifthe executive director finds through reviews of specific projects
or through audits of the municipality's review and approval process that a municipality's review and approval process does not provide for compliance with the minimum design and installation
requirements detailed in this chapter, the review and approval authority shall address these findings within a time established by the executive director. Ifcompliance cannol be achieved.
the review authority shall be voided for thaI municipality. Ifsuch authority is voided for a municipality, the executive director shall notify the municipality in writing and shall include
the justification for voiding the authority ofthe municipality, If the authority ofa municipality is voided, all new projects proposed to be constructed within thaI municipality's jurisdiction
shall be submitted to the executive director in acconlance with paragraph (3)(D) of this subsection. 
Te.,"s >farural Reso"",e Conse!'l'auon CommISSIOn Page 6 Chapter ) 1 ' • Design emeria for Sewerage Systems \b) Preiiminarv engineering repon. (I) Definition. The preliminary engineering
repon shaH form ,he 􀁾􀁯􀁮􀁥􀁥􀁰􀁴􀁵􀁡􀁊􀀠basis for the collection. treaunenl. andlor disposal system proposed. This document shall bear the signed and dated seal of the registered professional
engineer responsIble for the design. tA) For projects receiving U.S. Environmental Protection Agency construction grants assistance. a facility plan may serve as the preliminary engineenng
repon. . (B) For all olller projects, a preliminary engineering repon pwposing processes, methods. or procedures may be submitted as early in the planning stage as is practical. Submission
of a preliminary engineering repon at this point is only necessary 10 resolve any potential disagreements between the design engineer and Ille commission regarding Ille essential planning
information, design data. popu1ation projections. and olller requirements of the commission. Agreement is desirable to eliminate delays or inconveniences and to avoid the possibility
of having to revise the rmal plans and specifications. (e) The preliminary engineering report may be merged directly with the final engineering report to produce a single engineering
report at the discmion ofthe sewerage system owner. (2) General requirements. The following is 􀁲􀁥􀁾􀁤for each project as applicable. (A) A brief description of the project with maps
showing the area to be served. generalloc31;on of proposed improvements, water and wastewater treatment plant sites, existing and proposed streets. pazks, drainage ditches, creeks, streams,
and water mains sball he provided. The drainage area should be derIDed clearly, either by contour map or otherwise. Where a contour map is not available to the community, one should
be obtained and the contours should be sbownat intervals of not more than 10 feet The maps and plans sball be reproduced on paper not larger than 24 inches by 36 inches in size; bowever.
where variations are netessaIY, all sheets sball be unifOIIll in size. (B) The domestic population of tile area to be served (present and projected) and design population of the project
sball be incinded (C) TIle names of industties contributing any significant wastes, typeS of industry (StandaId Industty Codes), volume ofwastes, cba!actcristics and strength of wastes,
population equivalent, and other pertiDem infotmation sball be incinded It sboukl be emphasized !bat ifsignificant amoWIIS of wastes other than IIOrmai domestic sewage are to be treated
at tile wastewater treatment p1ant, sufficient data on such wastes must be presented to allow an evaluation of tile effect on the treatment process. This would include but IIOt be lintited
to bea:vy metals and toxic materials such as polychlorinated biphenyl's, organic chemicals, and pesticides. (0) The preliminary engineering report sball incinde tile technical infonnation
described in §317.1O of this title (relating to Appendix B -Land Application of Sewage Effluent) for all overland flow projects. 
Texas :--;arur.:tl Resource Conservation CommissIon Page 7 Chapter 317 • Design Critena for Sewerage Svstems t3) Collection 􀁾􀂷􀁳􀁬􀁥􀁭􀀮􀀠The following information shall be pro"ided
in the preliminruv <ngineering report If applicable to the project. . (A) Present area selVed and furure areas to be served: (B) Terrain data in sufficient detail to establish general
topographical features of present and future areas to be selVed: (el Lift stationsexisting andlor proposed; (D) Effect of proposed system expansion on existing system capacity: and (E) Amount of infiltration/inflow existing and anticipated, and how it is to be addressed
in the collection system design. (4) Treattnent plant. The following inforntation is required in a prellinina.!y engineering repon. (A) Quantity and quality ofexisting sewage influent
and changes in the characteristics anticipated in the future. [f adequate records are not available, analyses shall be made for the existing conditions and such information included
in the report. (B) Design and peak flow rates being considered and the design period. Design flow is defmed as the wet weather maximum 30..:lay average flow. Therefore, when determining
design flow rates, consideration mllSt be given to flows during periods of wet weather in order to 􀁾consistent compliance with discharge permit volume and quality lintitati(!ns. Peak
flow is defined as the highest two hour flow expected to be encountered under any operational conditions, including times of high rainfall (gellllrally the two year, 24 hour storm is
assumed) and prolollged periods of wet weather. For llllW systems the peak flow to average annual flow ratio is normally in the raDge oftIu:I:e • five to one, although other peaking
factors may be warranted. (C) Type of u:eaanent plant proposed and the effluent quality expected. The information should Include basis ofdesign, flow, organic loading, infiltration allowance,
and efficiency deten:ni.nations sufficient to a given level of treattnent. {D} Type of units proposed and their capacities, considerillg the criteria contained herein. The information
should Include detention times. surface loadings, weir loadings, flow diagram, and other pertinent infomtation regarding the design of the plant, Including sludge processing uriits required
for the selected ultimate sludge disposal (E) Treatment plant site infomtation and the smog analysis. The location of the plant, the area included in the plant site, dedicated buffer
zone, and a description oftbe surroundiDg area includiDg a map or a sketch of the area Particular reference should be made as Jo the plant'S proximity to present and future housing developments,
industrial sites, prevailing winds, highways and/or public thoroughfares, water plants. water supplY wells, paIks, schools, recreational areas, and shoppillg centers. If 
Texas Saturn! Resource Conservauon Commission Page 8 Chapter 31-• Design Cntena for Sewemge 􀁓􀁾􀀧􀁳􀁴􀁥􀁭􀁳􀀠the effluent IS to be dis.;;harged to the waters of the State. the immediate
receiving stream. canal. major Water course. etc.. shall be deSignated. The sIting analysIs shaU include: (i) Flood hazard analysis. Provide the 100-year flood plain ele\·ation. Proposed
treatment unirs which are to be located within the 100-year flood plain will not be approved for constructron unless protective measures satisfactory to the commission (such as levees
or elevanon of the treatment unirs) are included in the project design. (til Buffer zone analysis. Demonstrate that the location ofeach proposed treatment unil is consistent with the
buffer zone criteria specified in Chapter 309 of this title (relating to Treatment PIant Siting). (5) Sludge management The preUminary engineering report shall include a discussion of
the method of sludge disposal to be utilized. The report shall assess the following factors: (A) Estimated quanlity of sludge thaI must be handled which. irn:ludes future sludge loads
based on flow projections; (B) Quality and sludge treatment requmments for ultimate disposal; (C) Sludge storage requirements for each. altemaltve considering normal operating requiremenrs
and contingencies; (0) Transportation of sludge; (E) Land use and land availability; and, (F) Reliability of!be various altemaltves, contingencieS and mitigation plans 10 ensure reliable
capacity and opel3li.onal flexibility. (6) Control of bypassing. Infonnalion and data shall be submitted to describe features (au:'CiliaIy power, standby and duplicate units, holding
tanks, Storm water clarifiers, ele.) and opel1ltional arrangements (flexibility of piping and valves to controlflow tbrough !be plant, reliability of power sources, etc.) to pmrent uMltthori2ed
discharges ofuntreated or pattialIy tmated wastewater. An outline ofcontrol measures 10 pmrent unauthori2ed discharges of untreated or pattialIy treated wastewater during constructicn
constructicn (see Subsection (eX') oftbissection) is to be included. (c) Final engineering design report The final engineering design repon shall be submitted with the final plans and
technical specifications. The report shall include calculations and any other engineering information pertaining to the plant deSign as may be necessary in die review of the plans and
specifications by the commissiolL This repon shall bear die signed and dated seal of!be registered professional engineer responsible for !be design. Information should be included to
describe any changes that have been made since a preUminary engineering repon was submitted, along with additicnal informaticn as follows: (I) Collecticn system (if applicable). 
Texas "'antral Resource Conservation Commission Page 9 Chapter 317 • Design Cmena for Sewemge Systems (A) mirumum and maximum grades proposed for each size and type of 􀁰􀁩􀁰􀁥􀁾􀀠(B)
lift stauons (also refer 10 §317.3 of this title (relating to Lift Stations)): (i) the operating characteristics of the stations at minimum. ma.ximum. and design flows (both present
and future). (il) safety considerations. such as ventilation. entrances. wotlting areas. and prevention of explosions: and (ill) means of preventing oveIflow of raw sewage; (e) capability
of existing trunk and interceptor sewers and lift stations to handle the peak flow under anticipated conditions and capability of existing treatment facilities to receive and adequately
treat the anticipated peak flows; (1) type of pipe proposed and its anticipated ped'ormance uruIer the conditions imposed by the particular wastewater quality and loading conditions;
(E) the manllole spacing proposed; (F) areas not served by the present proposed project, and the projected means of providing service to !hese areas, including special provisions inco!pomted
in the present plans for future expansion; (G) amount of in(lltIationfmflow existing and anticipated,. its hydIaulic effect on the proposed and existing system, and an abatement plan
ifapplicable. including a: (i) description of in1iItration allowances and test procedures in the specifications governing design of new saniwy sewer lines; and (ii) description ofcontrol
progmn to reduce in1iItrationiinfiow occurring in the existing sewer system; (H) soil conditions, such as quicksand, that will not support collection system development, and measures
10 be taken to overcome the anticipated difficulties. (2) Treatment plant (A) the fwal decisions as to the method of treatment; (8) types of units proposed and their capacities. considering
the criteria contained herein including: (i) detention times.. sulface loadings. weir loadings, flow diagmm. and 
Texas Natural Resoun:e Consel\'auon Commission Page 10 Chapler ,1"7 • Design Criteria for Sewerage S"stems (ii) other peninent information regarding the design of tile planllncluding
hydraulic profiles for wastewater and sludge which includes a plol of tile hydraulic gradient al peak flow conditions for all grant}· lines: (C) tile anticipated operation mode of tile
planl the degree of treatment expected and any special characteristics of tile plant and (D) the safety features included such as stairways. railing, lighting. insulation mats and walkway
mats. (3) Sludge management system. (A) the fmal decisions as to tile methodes) of managing sludge including fmal disposal; (8) contingency alternatives; and (C) the type and size of
sludge treatment units to provide the quality of sludge for tile selected sludge management method. (d) Final plans and technical specifications. (I) construction dIawings and technical
specifications will not be considen::d for review unless tIley bear the signed and dated seal of the n::giste!ed professional engineer responsible for the design on each sheet of the
plans and on the title page ofthe technical specifications. These shall be the plans and specifications to be used by the comractor forbidding and construction. (2) plans and proflles
for sanitary sewetS, insofar as practical, shall be prepared using one of the foUowing S(;a/es: HOrizontal Venical I" = 20 feet 1"=2 feet I" =40 feet 1"=4feet I" = 50 feet l"=Sfeet (3)
the size, grade, and type of pipe material shall be shown. Alternate materials may be identified in the bid documelll 􀀨􀁾􀀩􀀠the location and structural featt.ues of the sewers, including
manholes to be installed, shall be shown on plans and proflles. The details of the appurtenances sball be provided. 
Texas Narur&l ResoulI:e Conservauon COmllUsslOn Page II Chapter 31' • Design Cmeria for Sewerage S,stems (5) the plans and technical specifications for lift stations shall fullv describe
all pumps. valves. pumpmg control mechanisms. safety and ventilation equipment access operator points. hatches and hoisung eqUipment for installing and removing equipment. (6) the plans
and lechnical specifications for the wastewater treatment plant shall include construction details for all units of the plant as well as equipment and material specifications and inStallation
procedures. The location and details of inlet and outlet structures, valving. and piping arrangements that allow alternate modes of operation during periods of stress such as mechanical
failure. structural repair, or any other activity which requires the removal of one or more treatment elements from service. shall be included. The plans shall include a hydraulic profile
of the treatment facilities at both design and peak flows. The plans shall also show provisions for future expansion of the plant, should such be contemplated. Details of complex piping
should be clarified by the inclusion of an isometric flow diagram as a part of the plans. (e) Other requiIements. (I) Completion. Upon completion of construction, the design engineer
or other engineer appointed hy the owner shall notify the commission of completion and attest to the fact that the completed wolk is substantially in accordance with the plans, technical
specifications and change orders approved by the commission. Ifsubstantial changes have been made to the original plans, record drawings documenting such changes shall be submitted to
the commission. (2) Inspection. During construction, the project may be visited by a represemative of the commission during normal wolking hours to establish general compliance with
the plans and technical specifications approved by the commission. (3) Operation and maintenance manual. Prior to completion ofconstruction of a new wastewater treatn!ent plant or plant
expansion, an operarion and maintenance manual covering the recommended operating procedures and maintenance practices for the entire facility sball be furnished to the sewerage system
owner by the designengineer. The design engineer'sball submit a letter to the commission certifying this action has been performed and sball furnish a copy of the operation and maintenance
manual to the commission upon n:quest (4) Sludge management implementation plan. The design engineer shall prepare an implementation plan for the selected sludge management method. The
plan sball identify regulatory requiIements ofSIatII and federal agencies. The plan sball also include requirements for selected contingency alternatives. (S) Authorization to discharge.
For treatment plant projects the owner is required to secure proper authorization from the commission prior to initiation of construction. No discharge shall be authorized withoW a discharge
permit In no case shall bypassing of partially treated wastewater be authorized during construction withow an order for such discharge from the commission. Also see 􀂧􀀳􀀱􀀷􀀮􀁾􀀨􀁡􀀩􀀨􀀳􀀩􀀠ofthis
title (relating to Wastewater Treatment Facilities), (I) Variance. A variance from the design criteria herein may be granted by the commission ifthe variance would not result in an UIU1:asonable
risk to treatment plant perfOrnlanc;e, public health or the waters 
Texas :--Jatufil! Resou",. Conse,,'auon CommissIOn Page I Z Chapt.r ) I' . Design Cntena for Sewerage Svstems to the stale, Requests for ".nances must be submmed in wtiting by the design
engineer and musL for each affected item, Include a detaIled englneenng jusufication, Adopted February 'l. 1997 Effecth'. March 3, 1997 §Jt7.2. Sewage Collection System. (a) General
Requirements, (I) Design, Sewer lines 5hall be desigrted for the estimated future population to be served, plus adequate allowance for instinnional and commercial flows. The collection
system design shall provide a minimum structural life cycle of 50 yem. The collection system design shal! provide for the minimization of anaerobic conditions, Design procedures for
the minimization of anaerobic conditions outlined in the United States Environmental Prolection Agency (EPA) Design Manual for Odor and Corrosion Conlrol in Sanitaty Sewerage Systems
and Treatment Plants (EPAl625/1-85/0 18). ASCE Manual of Engineering Practice Number 69 􀀨􀁍􀁅􀁐􀁾􀀹􀀩or other appropriate references. sltould be followed.. The owner of the collection
system shal! provide inspection under the direction of a Texas registered professional engineer during construction and testing phases of the project. All collection systems 10 be located
over the recharge zone of the Edwards Aquifer shal! be designed and installed in ac:cordano;e with Cltapter 313 ofthis title (relating to Edwards Aquifer Rules) in addition to these
rules. (2) Pipe Selection. The cltoice ofsewer pipe shal! be based on the chemical characteristics of the waler delivered by public and private water suppliers. the character of industrial
wastes, the possibilities ofsepticity, the exclusion of inflow and infdtration, the external forces. intemaI pressures. abrasion. and C(,rrosion resiSlal1Fe. For all installations. ifa
pipe as a wltole or an integral structural component of the pipe will deteriorate when subjected to cOll'Osive internal conditions, a corrosive resistant coating or liner acceptable
10 the Commission sball be installed at the pipe lIlaIU.Ifacturing facility unless the fmal engineering design repel!, including calculations and data, submitted by the engineer demonstrates
that the design and operational characteristics of the system will maintain the structural integrity of the system during the minimum life cycle. The sewer pipe 10 be used shall be identified
in the plans and technical specifications with its appropriate ASTM, ANSI or A WWA standard numbelS for both quality control (dimensions, loiemnces, etc.) and installation (bedding,
bacldill, etc.). (A) Flexible Pipe. The engineer shal! submit an engineering repen thai. includes the method ofdefining the modulus ofsoil reaction, (E1, for the bedding material. (E',),
and the natural soil (E'J, or other specific information 10 quantifY the effect of the in-situ material on the effective modulus, (E',). The repon sball also include design calculations
for E', , prism load, live loads, long term deflection. strain, bending strain, buckling and wall crushing. The design calc;ulations shal! include all infonnation pertinent 10 the determination
of an adequate design includi1lg. but not limited 10: pipe diameter and material with reference to appropriate standan:ls, modulus of elasticity, tensile strength. pipe stiffitess or
ring stiffness cons!allt converted 10 pipe stiffness as described below, Leooltard.t's zeta faclOr or E',li:om another acceptable method. the conversion factor used 10 obtain veltical
deflection when using the Modified Iowa Equation, trench width. depth of cover, water table elevation. etc, Pipe stiffness shal! be related 10 Ring Stiffness Cons!allt (RSC), when necessaJY.
by the follOWing equation: 
Texas NarurnJ Resource Conservation CommIssIon Page 13 Chapler ) 1" • Design Cnteria for Sewerage Systems PS Pipe Stiffness. psi; C 􀁾􀀠Conversion Factor. (0,80); RSC 􀁾􀀠Ring Stiffness
Constant; and, D 􀁾􀀠Mean Pipe Diameter, in. In all cases the design procedure. such as outlined above, shall dictate the minimum pipe stiffness whether less than or greater than 46
psi, however, direct bury installations of flexible pipe material may consider a minimum stiffness requirement to ensure ease of handling, transponation and construction. Special consideration
shall be given to the pipe stiffness at the expected installation temperature, The resistance of each material to the failure modes of strain, buckling and wall crushing shall be justified
to the satisfaction of the executive director by the engineer. In all siruations, the design methodology shall be consistem with currently accepted design practices and acceptable to
the executive director, In the design ofsanitary sewer systems using trenchless technology, other design methodology may be considered appropriate depending upon the type of pipe selected
and other specific conditions. (8) Rigid Pipe. The engineer shall submit an engineering report that includes the trench width. water table. and depth of cover, etc. For rigid conduits
the minimum strengths for the given class shall be noted in the appropriate standan! for the pipe material, For the purpose of this se.;tion, rigid pipe is defmed as concrete, vitrified
clay, or ductile iron pipe. (C) Other pipe materials may be considered on a case by case basis by the executive director. The design and instaIlaIion ofsuch materials shall generally
follow the guidelines for flexible or rigid pipe with appropriate exceptions. (3) ';ointing MateriaL The materials used and methods to be applied in making joints shall be included in
the technical specifications. Materials used for sewer joints shall have a satisfactory record of preventing infiltration and root entrance. Rubber gaskets, PVC compJ:ession joints,
high compn:ssion polyun>:tIIaDe, welded or other types of factory made joints ale required. (4) Testing of Installed Pipe. An infiltration, exfiltration or 10w·presSUJ:e air test sball
be specified. Copies ofall test results shall be made available to the executive director upon request. Tests shall confonn to the following requinlmelllS: (A) Infiltration or Exfiltration
Tests. The tola! exfiltration as determined by a hydroStatic head test..shall not exceed 50 gallons per inch diameter per mile of pipe per 24 hnurs at a minimum test head of two feet
above the crown of the pipe at the upstream manhole, When pipes ale installed below the groundwater level an inflitration test shall be used in lien of the exfiltration teSt. The tola!
infiltration, as detertnined by a IIydrostatic head test. shall not exceed 50 gallons per inch diameter per mile of pipe per 24 hours at a minimum test head of two feet above the crown
of the pipe at the upstream manhole. or at least two feet above existing groundwater level, whichever whichever is greater. For construction within the 25 year 
T.,"s 􀁾􀁡􀁲􀁵􀁲􀁡􀁬􀀠Resoun:e Conse(\3UOn CommIssIon Page 1-1 Chapter, 17 -Design Criteria for Sewerage Svstems tlood plain, the ,"filtranoo or exfiltrotion shaU oot exceed to gallons
per inch diameter per mde of PIpe per 2-1 hows at the same minimum test head. lfthe quantity of infiltranon or exliltration exceeds the ma.ximum quantity specified. remedtal action shall
be undenaken in order (0 n:duce the infdtrauon or e"flItranon to an amount wIthin the limits speCIfied, (8) Low Pressure Air Test. The procedure for the low pressure air test shaU conform
to the procedures descnbed in ASTM C-828, ASThl C-92-1, ASTM F·1417 or other appropriate procedures. excepl for testing times. The tesl times shall be as outlined in this section. For
secuons of pipe less than 36·inch average inside diameter, the following procedure sball apply unless the pipe is to be joint tested. The pipe shall be pressurized to 3.5 psi greater
than the pressure exerted by groundwater above the pipe. Once the preSSure is stabilized. the minimum time allowable for the presstm: to drop from 35 pounds per square inch gauge to
2.) pounds per square inch gauge sball be computed from the following equation: T. 0,08S xDxK Q T = time for pressure to drop 1,0 pound per square inch gauge in seconds K." Q,000419
xDxL, bUI not less than 1.0 0" average inside pipe diameter in inches L" length of line of same pipe size being tested. in feet Q = rate of loss, 0,0015 cubic feet per minuIe per square
foot internal surface sball be used Since a K. value of less than 1.0 sball not be used. there are minimum testing times for each pipe diameter as follows: Pipe Diameter Minimum Length
for Time for (incbcs) Time Minimum Longer Length (seconds) Time (seconds) (feel) 6 340 398 0,8SS(L) 8 454 298 l.S20(L) 10 567 239 2.374(L) 12 680 199 3.419(L) IS 850 159 S,342(L) IS
1020 133 1.693(L) 21 1190 114 1O.471(L) 24 1360 100 13,676(L) 27 1530 88 17.309(L) 30 1700 80 21.369(L) 33 1810 72 25.8S6(L) 
Texas "arural Resoun:e Conservauon CommisSion Page 15 Chapter; 1"7 • Design Cntena for Sewerage Svsrems The test may be stopped If no pressure loss has occurred during the fjr>t 25%
of the calculated resting time. If any pressure loss or leakage has occurred during the fim 25% of the testing penod. then the rest shaU conunue for the enure test duration as outlined
above or until failure. Lines with a 27-inch average inside diameter and larger may be air tested, a! each joint. Pipe greater than 36 inch diameter must be tested for leakage at eachjoinl,
lfthe joint test is used, a visual inspection of the joint shall be performed Immediatelv after testing, The pipe is to be pressurized to 3.5 psi greater than the pressure exerted by
groundwater 􀁡􀁢􀁯􀁾􀀧􀁥􀀠the pipe. Once the pressure has stabilized. the minimum time allowable for the pressure to drop from 3j pounds per square mch gauge to 2.5 pounds per square
inch gauge shaU be 10 seconds. (C) Deflection Testing. Deflection teSts shall be performed on all flel<ible pipes. For pipelines with inside diameters less than 27 inches, a rigid 'mandrel
shall be used to measure deflection. For pipelines with an inside diameter 27 inches and greater. a method approved by the executive director shall be used to teSt for vemcal deflections,
Other methods shall provide a precision of ± two tenths of one percent (0.2 %J deflection. The test shall be conducted after the fmal backfilJ has been in place at least 30 days. No
pipe shall exceed a deflection of frYe percent Ifa pipe should fail to pass the deflection test, the problem shall be corrected and a second test shall be conducted after the final ba.;kfiU
has been in place an additional 30 days, The tests shall be perfomed without mechanical pulling devices. The design engineer should recognize that this is a maximum deflection criterion
for all pipes and a deflection test less than five percent may be more appropriate for specific types and sizes of pipe, Upon completion of construction, the design engineer or other
Texas Registered Professional Engineer appointed by the owner shall certify, to the Executive Director, that the entire installation has passed the deflection test. This certification
may be made in conjunction with the notice of completion required in §317, I(e)(\) of this title (relaling to General Provisions). This certification shall be provided for the Commission
to consider the requirementS ofthe approval to have been mel (i) Mandrel Sizing. The rigid mandrel shall have an outside diameter (0.0.) equal to 95% of the inside diameter (1.0) of
the pipe. The inside diameter of the pipe, for the purpose of detemtining the outside diameter of the mandrel, shall be the average outside diameter minus two minimum wall !lticknesses
for 0.0. comrolled pipe and the avelage inside diameter for 1.0. comroUed pipe, all dimensions shall be per appropriate standaId. Statistical or other "tolerance packages· shall not
be considered in mandrel sizing. (ii) Mandrel Design. The rigid mandrel shall be 􀁣􀁯􀁮􀁳􀁴􀁴􀁵􀁾􀁤􀀠of a metal or a rigid plastic material that can withstand 200 psi without being defomed.
The mand!el shall have nine or more "1UlUIIl1'S" or "legs" as long as the total number of legs is an odd number. The barrel section ofthe mand!el shall bave a length of at least 75%
ofthe inside diameter of the pipe. A proving ring shall be provided and used for each size mandrel in use. (iii) Method Options. Adjustable or flexible mandrels are prohibited, A television
inspection is not a substitute for the deflection test A deflectometer may be approved for use on a case by case basis. Mandrels with removable legs orrunners may be accepted on a case
by case basis. (5) Bedding. Trenching. Bedding and BackfilJ. The width ofthe trench shall be minimized, but shall be ample to allow the pipe to be laid. and jointed property and to allow
the backfill to be placed and compacted as needed. The trench sides shall be kept as nearly vemcal as possible. As used herein, a trench 
Texas :-iarural ResoUl1:e Conservauon CommISsIon Page 16 Chapter 3 I 7 • DesIgn Cmena for Sewerage Svstems shall be deiined as liIat open cut portion of liIe excavauon up to one foot
above the Pipe, The engineer shall specify the ma,,,mum trench Width. The width of the trench shall be sufficient. but no greater than necessarY. to ensure working room to properly and
safely place and compact haunching materials, The space must be . \\ ider than the compaction equipment used in the pipe zone. A minimum clearance of 􀁾􀀠inches below and on each SIde
of aU pipes to the trench walls and floor shall be pronded. Bedding classes A. B. or C. as described in ASTh! C 12 (ANSI A 106,2). Water Environment Federation (WE!,) Manual of Practice
(MOP) No.9 or American Society of Civil EngineetS (ASCE) MOP 37 shall be used for all rigid pipes. provided that the prooer strength pIpe is used with the specified bedding to support
the anticipated Ioad(s). Embedment classes IA. lB. II or m. as described in ASTM 0-2321 (ANSI K65, 171) shall be used for all flexible pipes. provided the proper strength pipe is used
with the specified bedding to suppon the anticipated load, except that ASTM D-2680 may be used if the pipe stiffness is 200 psi or greatllr. Secondaly backfUl shall be of suitable material
removed from e.xcavation except where other matilrial is specified Debris. large clods or stOnes greater than six inches in diametllr, organic mattllr, or other unstable materials shall
not be used for backfUl. Backfill shall be placed in such a manner as not to disturb the alignment of the pipe. Where mmching encountetS extensive flllcture or fault zones, caves, or
solutional modification to the rock strata, construction shaU be halted and an engineer shall provide direction to accommodate site conditions. Wall!r line crossings shall be governed
by special backflU requirements specified io §317.13 of this title (relating to Appendix ESepamtion Distances). (6) Site Inspections. The Executive Director shall, on a random basis,
perform sitll inspections, (7) Protecting Public Watilr Supply. Watilr lines and sanitary sewers shall be installed no closer to each other than nine feet between outside diametetS.
Where this cannot be achieved, the sanitary sewer shall be constructlld io accordanc:e with §317.l3 oflhis title (relating to Appendix E -Sepamtton Distances) and 30 TAC Section 290.44(e)(I)
(relating to the location of water lines). Separation distances between sanitary sewer systems and water wells, springs, surface watllr so=es and water stOrage facilities shall be installed
in ac:coldanc;e with the requirementS of§§290.41(c)(I), (d){I), (e)(I){C), (e)(3)(A), and 􀀲􀀹􀀰􀀬􀁾􀀳􀀨􀁢􀀩􀀨􀀳􀀩􀀬􀀠of this title (relating to Water Storage) as appropriate. Where
rules governing separation distance are in conflict, the most s1Iii:t ruIc shall apply. No physical colllleCtion sbaIl be made between a drinking water supply, public or private, and
a sewer or any appunenance. An air gap of a minimum of 13 inches or two pipe diametetS. whiche'Ver is gteatllr, shall be maintained between all potable watilr outlets and the maximum
water surface elevation ofsewer appur1ellllll<:es. All appurtenances shall be designed and 􀁣􀁯􀁮􀁳􀁵􀁵􀁣􀁴􀁾􀀠so as to pmvell[ any possibility of sewage entering the potable watllr
SYStllm. (3) Excluding Surface Watllr. Proposals for the cOllSlIW;tion ofcombined sewelS will not be approved. Roof, stJeet, or other types of drains which will permitenuance of swface water inIo the sanitary sewer SYStllm shall nol be acceptable. (9) Active Geologic Faults. For syStllms to be located in areas ofknown active geolOgic faults. the design
engineer sbaIllOCatll any faults within the area of the collection syStllm and the system shall be laid out to minimize the number of sewers crossing faults. Where crossings are unavoidable,
the engineering report shall specify design features to protect the integrity of the sewer. Considemtion should be given to joiots providing maximum deflection and to providing manholes
on 􀁾􀁨side ofthe fault so thai a 
Texas 􀁾􀁡􀁴􀁵􀁲􀁡􀁬􀀠Resource Conservation CommIssion Page 17 Chapter 31' -Design Criteria for Sewerage Systems portable pump may be used In the event of sewer failures, Servlce connections
within 50 reet of an acUve fault should be aVOIded, (10) Erosion Control. Erosion or sedimentation control that minimizes the effects of runoff hall be provided during the construction
phase of a project. This reqUlrement will be reviewed on a case b\' C3se basis. . (b) CapaCIties, ( I) Sources, The peak flow of domestic sewage, peak flow of waste from industrial plants,
and maximum infiltration rates shall be considered in determining the hydraulic capacity of sanitaty sewets. (2) Existing Systems. The design of extensions to sanitaty sewers should
be based on the data from the existing system. [fthis is not possible, the design shall be based on data from similar systems or paragraph (3)of this subsection, New systems, (3) New
Systems. New sewers shall be sized using an appropriate engineering analysis of existing and and future flow data. The executive din:clOr shall have the authority to deteunine the reliability
and appropriateness of the data utilized for sizing the system. In the absence of local reliable flow data and engineering analysis, new sewer systems shall be designed on the basis
ofan estimated daily sewage flow contribution as shown in the table in §317.4(a) of this title (relating to Wastewater Treatment Facilities). Minor sewers shall be designed such that
when flowing full they will transport wastewater at a rate approximately four times the system design daily average flow, Main tIUnk, interceptor, and outfall sewers shall be designed
to convey the contributed minor sewer flows. (cl Design Details. (ll Minimum size. No sewer other than service laterals and force mains shall be less than six inches in diameter. (2)
Slope. All sewelS shall be designed and constructed with slopes sufficient to give a velocity when flowing full of not less than 2.0 feet per secolld. The grades shown in the fullowing
table are based on Maruting's furmula with an assumed "n factor" of 0.013 and constitute minimum acceptable slopes. The minimum acceptable "n" for design and construCtion shall be 0.013.
The "n" used takes into consideration the slime, grit and grease layelS that will affect hydraulics or hinder flow as the pipe marums. 
T",as 􀁾􀁬􀁡􀁬􀀧􀁊􀁲􀀺􀁕􀀠Resoun:e Conservation CommISSion Page 18 Chapter) 17 -Design Cntena for Sewerage Systems Size of Pipe :Vlinimurn Slope Maximum Slope In Inches I.D. In Pen:eru
In Percent 6 0.50 12.35 8 0.33 SAO 10 0.25 6.23 12 0.20 􀁾􀀮􀁓􀀦􀀠15 0.15 3.62 1& O.ll 2.83 21 0.09 2.30 24 0.08 1.93 27 0.06 1.65 30 0.055 1.43 33 0.05 1.26 36. 0.045 Ll2 39 0.04 LOI
>39 • • • For lines larger than 39 inches in diameter. the slope may be determined by Manning's formula (as shown below) to maintain a minimum velocity greater than 2.0 feet persecond
when flowing full and ama'<.imum velocity less than 10 feet per second when flowing full. 1.49 RO.61 fI!'V=_x h 􀁸􀁶􀁾􀀠n v = velocity (ftlsec) n = Manning's roughness coefficient (0.013)
R. = hydraulic radius (ft) S = slope (ftlft) (3) High Velocity Pmledion. Wbml velocities greater than 10 feet per second will occ\u' when 0.25 the pipe is flowing lWl. at slopes greater
than those listed in pmagraph (2) ofthis subsection, special provisiollS shall be made to protect against pipe displacemettt by erosion of the bedding and/or stlock. (4) Alignmettt.
Sewers shall be laid in straight alignment with uniform grade between manholes unless sligh! deviations from straight alignment and uniform grade are justified to the satisfaction of
the Executive Di1I!ctor. (5) Manhole Use. Manholes shall be placed at all poims of change in alignmem, grade or size of sewer, at the intersection ofall sewers and the end of all sewer
lines that will be extended at a future date. Any proposal which deviates from this requiJ:ement shall be justified to the satisfaction of the Executive Director. Clean-outs with watertight
plugs may be insJallcd in lieu of manholes at the end of sewers which 
Texas :-':arur:l.i Resource Conserlauon CommIssion Page 19 Chapter' I 􀁾􀀠-Destgn Critena for Sewerage Systems are not anuclpated to be extended, Such tns1allations must pass a leakage
test and a deflecuon test for all l1exlble lines, (A) Type, Manholes shall be monolithic. cast-in-place concrete. fiberglass. precast concrete. HDPE or ofequivalent construcuon. Bnck
manholes shall not be used. nor shall brick be used to adjust manhole CO\'er5 to grade (8) Spacing. The maximum 􀁲􀁥􀁱􀁵􀁾􀁤􀀠manhole spacing for sewers with straight a1igrunent and
uniform grades are in the foUowing IMlle. Reduced manhole spacing may be necessary depending on the utility's ability to mamtain its sewer lines. Areas subject to flooding require special
consideration to minimize inflow. Pipe Diameter Maximum Manhole Spacing (inches) (feet) 6 -15 500 18 -30 800 36 --18 1000 54 or larger 2000 (C) Inflow and Inftltralion Conttol. Watertight,
size-on-size resillem connectors allowing for differential settlement shall be used to connect pipe to manholes, Pipe to manhole connectors shall conform to ASiM C-923. Other typeS ofconnectors
may be used when approved by the commission. Manholes should not allow surface water to drain imo them. Ifmanholes are located within the 100-year flood plain. the manhole covers shall
have gaskets and be bolted or have another means of preventing inflow. Where gasketed manhole covers are required for more than three manholes in sequence, an alternate means of ve!l!ing
shall be provided at less than 1.500 fOOl intervals. Vems should be designed to minimize inflow. Impervious material should be utilized for manhole construction in these areas in onier
10 minimize inftltration. (0) Manhole Diameter. Manholes shall be of sufficient inside diameters to allow personneito worlt within them and to aUow proper joining of the sewer pipes
in the manhole wall The inside diameter of manholes shall be IIOt less than 48 inches. (E) Manhole Inverts. The bottom of the manhole shall be provided with a ·U· shaped chaIlllellhat
is as much as possible a smooth continuation ofthe inlel and outlet pipes. For manholes connected to pipes less than IS incbes in diameter the channel depth shall be atleasl half the
largest pipe diameter. For manholes connected to pipes IS to 24 inches in diameter the channel depth shall be at least three fourths the largest pipe diameter. For manholes cOllllllCted
to pipes greater than 24 inches in diameter the channel depth shall be at least equal to the la!gest pipe diameter. In manholes with pipes of different sizes, the tops of the pipes shall
be placed at the same elevation and flow channels in the invert sloped on an even slope from pipe to pipe. The bench provided above the channel shall be sloped at a minimwn of0.5 inch
per foot Where sewer lines emer the manhole higller than 24 inches above the manhole invert, the invert shall be filleted to prevent solids deposition. A drop pipe should be provided
for a sewer emering a manhole more than 30 inches above the invert 
Te,,"s S1!Ur:U Resource Conserntion Commission Page !O Chapler 31" -DesIgn Cnlena for Sewerage Svstems (F) Manhole Covers, Manhole covers of nominal 􀀲􀁾􀀠inch or larger diameter are
to be used for aU sewer manholes, (0) Manhole Access, Design affealUres faremering man.holes shall be guided by the following criteria: (i) It is suggested thaI entrance into manholes
in excess of four feet deep be accomplished by means of a portable ladder, Other designs for ing!ess and egless should be given careful evaluation considering the safety hazards associated
with the use of manhole steps under cenatn conditions, (ii) Where steps are used. they shall be made of a non-<:effOsive material and be in accordance with applicable OSHA specifications
as published by the United States Department of Labor. (H) Testing. Manholes shall be tested for leakage sepruately and independently of the wastewater lines by hydrostatic exfUuation
testing, vacuum testing, or other methods acceptable to the commission, Ifa manhole fails a leak.age test. the manhole must be made water tight and retested, The maximum leakage for
hydrostatic testing shall be 0.02S gallons per foot diameter per foot of manhole depth per hour. Alternative test methods must ensure compliance with the above allowable leakage. Hydrostatic
exftlttatinn testing shall be performed as follows: all wastewater lines cOming into the manhole shall be sealed with an internal pipe plug, then the manhole shall be filled with water
and mainlained fuJI for at least one hour. For concrete manholes a wetting period of 24 hours may be used prior 10 testing in order to aUow saturation of the COIlC!ete. (6) Sag Pipes
(Inverted Siphons). Sag pipes shall have two or more barrels, a minimum pipe diameter of six inches and shall be provided with necessuy appurtenances for convenient flushing and maintenance,
The manholes shall have adequale cleruances for mdding, and in general, sufficient head shall be provided and pipe sizes selected 10 assure velocities of at least three feel per second
at design flows. The inlet and outlet details shall be arranged so that the normal flow is diverted to one barrel Provisions shall be made such that either barrel may be taken out of
service for cleaning. (d) Alternative Wasll:water Collection Systems. Use of alternative wastewater collection systems may be considered whenjustified by !IIIIJSUIIltenain or geological
formations, low population density, difficult consttw:tion, or other ciIl:umstances where an alternative wastewater coUectinn system wouid offer an advantage over a convemional gravity
system. An alternative wastewater collection system will be considered for applOVai only when conditions make a conventional gravity collection system impractical. Alternative wastewater
collection system types include pressure sewelS (septic tank effIuem pumping or grinder pump systems), mtalI diameter gravity sewelS (minimum grade effluent sewelS or variable grade
effluent sewers), vacuum sewers and combinalions thereof. Alternative wasll:water collectinn systems_ systems_ comprised ofboth on-sile (interceptor tanks, pumps, pump tanks. valves,
service laterals) and off-site components (collector mains. force mains, vacuwn stations. clcan-outs, manholes, vems, and lift stations), Pressure sewer systems, small diameter gravity
sewelS and vacuum sewers will be approved on a case-bycase basis, The engineering repon must justify the design of alternative wastewater collection systems to the satisfaction of the
Executive Director. The EPA's "Manual of Alternative Wastewater Collection Systems" 
Texas 􀁾􀁡􀁲􀁵􀁲􀁮􀁊􀀠Resou",e Conservauon CommISSIon Page 21 Chapter) 1 􀁾􀀠• DesIgn Crilena for Sewerage S>stems lEPAJ625il-n lIHl. the WEF's Alternative Sewer Systems (MOP FO-12),
or other appropnate engllleenng lilerature. should be used as the basIS for design. (I) Managemem, A responsible managemem strucrure under the regulatory jurisdiction of the TNRCC shall
be established. to the satisfaction of the Executi"e Director. to be in charge of the operation and maintenance of an alternative wastewater collection system. A legally binding se,,'lce
agreement shall be .required to Insure the alternative wastewater collection system is properly constructed and maintained. The required elements of the servIce agreement are as follows:
(Al The document must be legally binding. (B) Existing septic and pump tanks that are 10 be used as inteICeptor tanks for primary !realment, wastewater storage. or pump tanks prior to
the discharge into an alternative sewer system must be cleaned. inspected. repaired. modified or replaced if necessary, to minimize inflow and infiltration into the collection system
prior to connection. (e) The utility shall have approval authority for the design of the system including all materials and equipment prior to the installation of an inten:eptor tank,
pressure sewer pump tank or vacuum system appurtenances, The materials shall comply with standard specifications submitted to and approved by the e.xecutive director. (0) The utility
must be able to approve the iustaUation of the inteICeptor tank. pressure sewer pump tank or vacuum system appurtenances after constrUction to ensure the installation was as specified.
(E) The utility must be responsible for the operation and maintenance of the system including any 1lI1eICeptor tank, pressure sewer pump tank or vacuum system appunenances incorporated.
(F) The utili.ty must be able to stop any discharges from any collection system appurtenaru:es in oilier to plIWem contamination of State waters. (G) The utility shall submit a maintenance
scbedule scbedule to the E:<ecutive Directorwhich outlines routine service inspections and maintenance for all types of pressure sewers. small diameter gravity sewers, and vacuum sewer
system componems. (H) Pumping units, grinder pumps, vacuum sewer appunenances, interceptor tanks, shall be regarded as integral components of the system and not as a pan oftha home plumbing.
(I) Provision to ensure collection system integrity during a power outage (two-year event) shall be incorporated into the design. Power outage dwation will be determined as described
in §311.3(e)( I) of this title (relating to Lift Stations). (2) Pressure Sewer System Design Considerations. The following shall be submitted to and approved by tha Executive Director:

Texas ;>;mural Resource Conse,v,uon CommlSStOn Page 22 Chapter 31' • DesIgn Critena for Sewerage Systems (A) hydraulic calculations for sizing the pressure sewer pumping system shall
be based on pro\lding the firm capacit)' to pump the expected peak flow. These calculations shall include system and pump cur"es as descnbed in §3 I 7.3(c)(4). wet well capacity calculations
based on minimum cycle times as described in §317J(2)(41(B). and emergency and flow equalizauon storage as necessary. The number of units pumping at anyone time may be estimated based
on appropriate engineering literature: (B) flow velocities in the range of three 10 fiye feet per second; (C) the installation of air relief valves; (D) the provision of means to llusll
aU lines in the system; (E) the installation of clean-<Juts; and . (F) development of procedures whereby ponions of the pressure system may be rerouted with temporary lines in the event
of leaks. construction. or repair. (3) Pipe Selection. Appropriate ASTM. ANSI or AWWA standaIds sIlall be specified for alternative wastewatercoUection system pipe aruljoints. Pipe whicll
will be used in pressure sewer systems sllaU Ilave a minimum sustained worldng pressure rating of 150 pounds per square incll gauge as per appropriate standard. Pipe selection sllaU
also confonn to subsection (a) (I). (2). (3) and (5) of this section. (4) Leakage Testing. All alternative wastewater collection systems componentS sllaU be tested for leakage. Testing
procedures for on-site system componentS, smaU diameter gravity sewer systems and vacuum sewer systems will be approved on a case-by-case basis. Pressure sewer instalJation sllaU be
tested for leakage with a hydrostatic test. Copies ofall test resuI1s sball be made available 10 the Executive Director upon request Leakage in the pressure sewer hydrostatic teSt sbaIl
be defIned as the quantity of water that must be supplied into the pipe or any valved section thereof. 10 maintain presStm: within 5 pounds per square inch of the specified test pressure
after after the air in the pipeline lias been expelled. The test pressure sball be either a minimum of 25 poUDds per squaIl: inch gauge or 1.5 lima the maximum force main design pressure,
whichever is !alger. The maximum aUowable leakage shall be calculated using the fonnuJa below. Ifthe quantity of leakage exceeds the maximum amount caJeulatcd. 1IImedia1 action shall
be taken to reduce the leakage to an amount witIIin the aUowable limit as follows: L = leakage in ga1lhr S = length of pipe in It D = inside diameter of pipe in inches P = pressure in
pounds per square iDl;h 
Texas 􀁾􀁡􀀢􀀬􀁲􀀮􀁬􀁬􀀠Resou",e Conservauon CommIssIon Page 23 Chapter! 17 • DesIgn Critena for Sewerage S, stems (5) Pumps. Pumpmg units and grinder pumps used in pressure sewer systems
should be reliable. easily mamwned. and should have compatible charactenstics. (A) Pumps and grinder pump units shall be provided with two bacldlow preyenllon devices (One check valve
at tank. to protect agamst back drainage into tank. 2nd check valve at connection of semce line to pressure collection line to protect against leaking sewage in case service line is
damaged) and shall be easily accessible for mairuenance. (8) Sufficient holding capacity shall be provided in the pumping compartment to allow for wastewater storage during power outages
and eqUipment failures. Storage volume should be based on power supply outage records and replacement equipment availability. (C) Pumping units shall not be installed in the settling
chamber of an interceptor tank ifthe interceptor tank is to be used for solids reduction. (D) Alarms. warning lights. or other suitable indicators of unit malfunction shall be installed
at each pumping station. (E) Whenever any pumping station handles wasae from fWO or more residential housing units or from any public establishment, dual pump units shall be provided
to assure continued service in the event of equipment malfunction. §J17.J. Lilt Statiolls. (a) Site selection. In the selection ofa site for a lift station consideration shall be given
to accessibi· lity and potential nuisence aspects. The station shall be protfCled from the loo-year flood and shall be accesSIble durtng a 2S-year flood. All lift stations shall be intruder-resistam
with a controlled access. Lift stations shottld be located as remotely as possible from populated areas. (b) Design. .(I) Small lift stations. Lift stations designed for a discharge
capacity ofless than 100 gallons per minute will be reviewed on a case-by-c:ase basis by the commission and shall be used only for instirutional use or other locatiollS where it is necessary
to pump the sewage from a single building, 􀁳􀁣􀁨􀁯􀁯􀁾􀀠or other measwable source establishment into the sanitary sewer lines. Ifthe location of the discharge does not provide a positive
head due to elevation, then·a positive pressure control valve shall be provided. Ejectors may be used for this type of lift station. Whenever a lift station handles waste from fWO or
more residential housing units. or from any public establishment, standby pumps shall be provided. In the case of ejectors or eductors. two air compressors shall be proVided. Grinder
pumps should be used for all small installations. (2) DIY well sump pump. The following design considerations shall be addressed in providing dry well sump pumps: (A) Two separate sump
pumps should be provided for removal ofleakage or water from the dry well floor. 
􀁔􀁾􀁸􀁡􀁳􀀠:>iarural Resoun:e Conset\'auon CommISSion Chapter) I' . DeSIgn Cntena for Sewemge SVstems tS) The discharge pipe level from the sump pumps shaU be above the ma'<lmum liquid
level of the wet well. A check valve should be installed on the discharge side of each sump pump, (C) A.1l floor and walkway sUlfaces shau have an adequate slope to a point of drainage
with sufficient measures taken to maximize traction and safety, (D) Motors to drive sump pumps shau be located above the height of the maximum liquid level in the wet well. A.s an allemale,
sump pumps may be of the submersible type, (3) Pump controls, All lift stations Shau have automatically operaled pump control mechanisms, Pump control mechanisms shau be locared so that
they will not be affected by flow cumnts in the wet well Provisions shaU be made to prevent grease and other floating materials and rags in the weI well from interfering with the operation
of the controls. When a float tube is locared in the dty well. its height shau be suelt as \0 prevent overflow of the sewage into the dty well. Pump control mechanisms w bielt depend
on a bubbler in the wet well shall be equipped with a backup air supply system. All connecuons \0 level controls in the wet well shau be accessible at an times. The cin:uit breakers.
indiCator lights. pump control switches. and other elecmcal equipment should be located on a control panel at least three feet abQve ground sUlface e1evatio n. Ifcontrols are located
in a dty well. the dty well shau be protected from flooding. (4) Wet wells, CA) Wet wells and dty wells, including their superstructuIe, shall be separated by at least a watertight and
gaslight wan with separate lockable entnln!:es pItlvided to each. Equipment requiring regular or routine inspection and maintenance shan not be located in the wet well unless the tnainIllnance
can be accomplished without eruering the wet well (B) Based on design flow, wet weU c:apaQty should pmvide a pump cycle time of not less than six minutes for those lift stations using
submersible pumps and nolless than 10 utinutes for other non-submersible pump lift stations. (C) AU influent gIlIViry lines into a wet weU shau be located where the inven is above the
"oft" setting liquid level oftbe pwnps, and pn:fembly should be locatl:d abQve the lead pump "on" setting. (5) Stairways. Stairways with non-slip steps shall be provided in an underground
dty wells. Removable IaddcIS may be provided in small stations wilen: it is inlpIacticai to instaU stairways. (6) Vemilalion. Ventilation shau be provided for lift stations. including
both wet and dty wells. (A) Passive venti1alion such as gooseneck type or llUbine ventilalOrs designed to prevent possible entIy of insects or birds shau be provided in all wet wells
ifmechanical ventilation is not provided. AU mechanical and elecmcal equipment in wet wells should be explosion-proof and spaIk-proof constrUction if mechanical vemilalion is not provided.

Texas Samra! Resou!l:e Canservaoon Commission Page 25 Chapter .11-• DesIgn Cmena far Sewerage Systems IBl Mechamcal "enulation shall be provided for all dIY wells below the ground surface.
The \ enulauon equipment shall have a minimum capacuy of SIX air changes per hour under continuous operntions. At least a capacity ofthirtV all changes per hour shall be required where
the operauon IS imermment. All intermittently opernted "enling equlpmem shall be inte!l:onnected with the StaUons lightmg system. (7) Wet well slopes. 'The bottom of wet wells shall
have a minimum slope of 10 percent to the pump intakes and shall have a smooth finish. There shall be no projections in the wet well which will allow deposition of solids under ordinary
operating conditions. Anti-vortex baffling should be considered for the pump suctions in all large sewage pumping stations (greater than 5 mgd fum pumping capacity). (8) Hoisting equipment
Hoisting equipment or access by hoisting equipment for the removal of pumps. motors. valves, etc.. shall be incorporated in the station design. (9) DIY wells and valve vault drains.
Drains from dry wells or valve vaults to the wet well shall be equipped with suitable devices to prevent entry of potentially hazardous gases. (c) Pumps. (1) Genera!. All raw sewage
pumps shall be of a 􀁮􀁯􀁮􀁾􀁫􀀾􀁧design, capable of passing 2 \1,inch diameter spheres, and shall have no less than 3·inch diamete, ruction and discharge openings. Inspection and cleanout
plates. located both on the suction and discharge sides ofeach pumping unit. are suggested for all non-submersible pumps so as to facilitate locating and removing blockage causing materials.
Where such openings are not provided on the pumps, a hand hole in the lUst fitting connected to the suctio n of 􀁾􀁡􀁣􀁨􀀠pump shall be provided. All pumps shall be securely supported
so as to prevent movement during operation. For submersible pumps, rail-type pump support systems incorporating manufacturer approved mechanisms designed to allow the operator to remove
and replace any single pump without first entering Or dewatering the wet well should be provided. (2) Lift station pwnping capacity. The firm pumping capacity of all liftstations shall
be such that the expected peak flow can be pumped to its desired destination. Finn pumping capacity is defined as total station maximum pumping capacity with the laJ:gest pumping unit
out of service. (3) Variable capacity pumps. Lift stations or transfer pumping facilities at a wastewater treatmelll p!anl or those discharging directly to the treatment plan1 where
the plants permitted daily average flow is equal to or greater than 100,000 gallons per day shall be provided with three or more pumps or with duplex automatically controlled variable
capacity pumps or other automatic flow conlrOl devices. The pumps or other devices shall be adjusted for actnal flow conditions and cOnlrOlled to operate so as to minimize surges in
the treatment units. No single pumping unit shall have a capacity greater than the design peak flow of the the wastewater treatment plant unless flow splitting/equalization is provided
(4) Pump head calculations, The engineeling design report accompanying the plans shall include system curves, pump curves and head calculations. Calculations and pump curves at both
minimum (all pumps off) and maximum (last normal operating pump on) static heads and for a C value ofboth .100 and I􀁾􀁯􀀠must be provided for each pump and for the combination of pumps
(modified pump curves). Where a 
Texas Sam,;il Resource Conservauon CommISsion rage 26 Chapter 􀁾􀀠\' . Destgn Cnlena for Sewerage 􀁓􀁾􀀧􀁓􀁬􀁥􀁭􀁳􀀠sucuon hf! IS requlfed. the repoll shall mclude a calculation of the
available Det positive suction head (NPSH) and a compansoD of that value to the required NPSH for the pump as funushed by the pump manufacturer. en Self-priming pumps. Only self-priming
pumps or pumps with acceptable priming systems. as demonstIated by a reliable record of satisfactory operation. shall be used where the suction head is negative. All self-priming pumps
shall include a means for venting the air back to the wet well when the pump IS priming. (6) Pump positioning. All raw sewage pumps, other than submersible pumps without "no suction"
Piping and self-priming units capable of satisfactory operation under any negative suction heads anticipated for the lift station under consideration. shall be positioned such that the
pumps always e:<perience. during their normal on-off cyding, a positive static suction head. (7) Grinder pumps. See §3\7.2(d) oftbis title (relating to Sewage Collection System). (d)
Piping. (I) Pump suctions. Eacll pump shall have a separate suction pipe. Cavitation may be avoided by using eccentric reducers in lieu of typical reducers in order to prevent air pockets
from forming in the suction line. (2) V::Uves. Full closing valves shall be installed on the discharge piping of each pump and on the suction of all dry pit pumps. A check valve shall
be installed on the discharge side of eaell pump, preceding the full closing valve. Check valves should be of a swing check type with e:«emallevers. Rubberball check valves may be used
for grinder pump installations in lieu of the swing check type. Butterfly valves, tilting disc check valves, or other valves with a piVoted disc in the flow line are not allowed. The
design shall consider surge effects and provide protection where necessary. Swge relief sllall be contained in the system. (3 ) Valve position indicatOlS. Gate valves should be rising-stem
valves. Ifother !ban rising-stem gate valves and cbe!:1i: valves with extemallevelS are used, the valves shall include a position indicator to show their open and closed positions. (4)
Lift station piping. Flanged pipe and fitting or welded pipe shall be used for exposed piping inside of tift stations. A flexible or flanged cOlllleCtion shall be installed in the piping
to each pump so that the pump may be RIIIoved easily for repails. Provisions shall be made in the design to permit flexure where pipes pass through walls of the statiOIL Piping should
nonnally besized so that the maximum suction velocity does no! exceed five feet per Second and the maximum discharge velocity does not exceed eight feet per second. (5) Force main pipe selection.
Force mains sball be a minimum of four inclles in diameter, uuless justified, as with the use of grinder pumps. In no case shall tile velocity be less !ban two feet per second with only
the smallest pump operating, unless special facilities are provided for cleaning the line at specified intelVals or it can be shown that a flushing velocity offIve feet per second or
greater will occur one or more times per day. Pipe specified for force mains shall be ofa type having an expected life at least as 
Texas :--1arural ResoUICe Conservauon CommIssIon Page 27 Chapler ) I" -DesIgn Critena for Sewemge Svstems long as that of the Itft stauon and shall be suitable for the marenal being
pumped and the opemting pressures to \\ hich It" III be subjected. All pIpe shall be Identified in the techmcal specifications with appropnate ASTM..""'1S[ or AWWA specifications numbers
for both quality conuol (dImensions. tolemnces. etc) and Installation (bedding, backfill. etc.). All pIpe and fittings shall have a minimum working pressure rating of 150 pounds per
square inch. (6) Force main tests. Final plans and specifications shall describe and require pressure testing for all installed fotce mains. Minimum test pressure shall be \.5 times
the ma.'<lIllUm design pressure. (7) Air release valves. Air release valves or combination air releaselvacuum valves suitable for sewage service shall be provided at all peaks in elevation.
The final engineering drawings must depict all proposed force mains in both plan and profile. (e) Emergency provisions. Lift stations shall be designed such that there is not a substantial
hazard orsuearn pollution from overflow or surcharge onto public or private property with sewage from the lift station. Options for a reliable power source may include: (I) Power supply.
The conunission will detennine the reliability of the existing conunercial power service. Such determinations shall be based on power outage records obtained from the appropriate power
company and presented to the commission. When requesting outage records for submittal to the commission. it is importanl to note that the records be in writing, bear the signature of
an authorized utility employee, identify the location of the wastewater facilities being served. list the total number ofoutages that have occurred during the past 24 months. and indicate
the duration of each recorded outage. The facillty will be deemed reliable if the demonstrated wastewater retention capacity. in the station's wet well spill retention facility. and
incoming incoming gravity sewer lines, is sufficient to illSUtll that no discharge ofuntreated wastewater will occur for a length of time equal to the longest elecbical outage recorded
in the past 24 months. Ifrecords for the service area cannot be obtained, a 120 minute wom case outage duration will be assumed. Provisions for a minimum wastewater retention period
of 20 minutes sbould be consideR<! even in those cases where power company records indicate no acrual outages of mote than 20 minutcs occurred during the past 24 months. (2). Alternative
power supply. Ifthe eldsting power supply is found to be unreliable, an emergency power supply or detention facility shall be provided. Options include: (A) Electrical service from two
separate commercial power companies, provided automatic switch over capabilities are in effect; (B) Electrical service Iiom two independent feeder lines or substations of the same electric
utility. provided automatic switch over capabilities are in effect; (C) On-site automatic starting electrk:al gelUlralOrs; (0) Reliance on pollable gelUlrators or pumps, Proposals for
the utilization of portable units shall be accompanied by a detailed repon showing conclusively the abillty of such a system to function satisfactorily. POllable units will be approved
only in those cases where the station is equipped with an auto-dialer, telemetry device or other acceptable operalOr notification device, operalOrs knowledgeable in 
Texas "arural Resou",e Conservation Commission Page 28 Chapter 117 -Design Critena for Sewemge Systems acqul5l!lon and slanup of the portable urulS are on Z.·hour cal\. the station is
accessible in all weather conditions. reasonable assurances eXist as to the timely availability and accessibilitv of the proper portable eqUipmenL and the station is equipped with properly
designed and tested qUick connection facilities. ThIs opuon is usually acceptable only for smaller lift stations, (3) Restoration of lift station, Provisions should be made to resto
re the lift station to serVIce Within four hours ofoutage. (.) Spill containment structures. A spill containment structure should be considered together with in-system retention in determining
a total wastewater retention time, Because separate spill retention facilities 􀁾not suitable for all locations. engineers should check with the commission prior to designing such strucrures,
The design shall provide: (A) a minimum storage volume of average design flow from from the contributing area and the longest power outage during the most recent consecutive 24-month
period or. if power records 􀁾not available. an assumed 24·hour outage; (B) an impermeable liner (such as concrete or synthetic fabric (20 mil !hlckness» and should have an energy dissipater
at the point of overflow from the lift station to prevent scour; (C) a fence with a controlled access; and (0) a plan for routine cleaning and inspection. (5) Alann system. An audio-visual
alamt system (red flashing llght and hom) shall be provided for all lift stations. These alamt systems should be telemetered to a facility where 24 hour attendance is available, The
alamt system shall be activated in case of power outage. pump failure or a specified high water level §317.", Wastewater Treatment Facilities. (a) Gener.d requill:melllS. Wbenever possible,
existing data of flows and raw waste strength from the same plant or ne31by plants with similar service 􀁾􀁡􀁳should be used in design of treatment facilities, When using using such
daIa for design pw:poses, the variability of data should be considered and the design based on the bigbest flows aad strengths encountered during normal operating periods taking into
consideration possible infiltration/inflow, In the absence ofexisting data. the foUowing are general*, acceptable parameters to which must be added appropriate allowances for inflow
and infilttation into the collection system to obtain plant influent characteristics. Figure I: 30 TAC §317.4 (a). Daily Wastewater Wastewater Flow -Gallom Strength Source Remarks Per
PelSOn mg/1 BOD, 
Texas Narunl Resource Conservanon Commission Page 29 Chapter; 11 . DeSign Ctitena for Sewerage Systems \ luruclpa.hry Resrdential 100 200 Subdinslon ResKienual 100 200 TraIler Park (Transient)
2 ,/, persons per uailer 50 JOO \ labile Home Pari< 3 persons per trailer 75 300 School with Cafeteria With Showers 20 300 Without showers 15 300 Recreational Parl<s Overnight user 30
200 Day User 5 100 Office Building or Factory 20 300 Motel 50 300 Restaurant PerMeaJ 5 1000 Hospital Per Bed 200 300 Nursing Home PerBed 100 300 (I) Effluent quality. Wastewater treaunent
plants shall be designed to consistentlv meet the effluent concentration and loading requirements of the applicable waste disposal penni!. . (2) Effluent quantity. The design flow of
a treaunent plant is defined as the wet weather, maximum 30 day average flow. The design basis shall include industrial wastewaters which will enterlhe sewerage system. The engineering
report shall state the flow and strength of wastewaters from industries which individually contribute five pett:ent or more of planJ flow or loading and discuss the aspect of hazardous
or toxic wastes. It is the inlem of these deSign criteria that the permit conditions not be <iolated. The engineering report shall list the design influent flow and concentration of
BOD" TSS. or other parameters for the following: (Al dIy weather 30-day average, (QoW); (B) wet weather maximum 30-day average (Qol; and (C) two-hour peak !low (Q,.). (3) Piping. The
piping within all planJs shall be arranged so that when one unit is out of service for repaiIs; planJ operation will continue and emergency treaunem can be accomplisher:l Valves and
piping shall be provided and sized to allow dewatering of any unit, in order thai repairs of !he unit can be completed in as shott a period oflime as possible. Portable pumping units
rna;y be used for dewatering small trearment planJs (design flow of less than 100.000 gallons per day) or imerim facilities. Removed wastes must be Sloted for·,retn:atmem or delivered
to another treatment facility for processing. Consideration shall be given in design for means to clean piping, especially piping canying IlIW wastewater, sludges. scum and grit 􀀨􀁾􀀩􀀠Peak
flow. For treaunent unit design purposes. peak !low is defined as the highest twohour average !low rate expected to be delivered to the trearmem units under any operational condition,
including periOds of high rainfall (generally the two-year, 24-hour storm is assumed) and prolonged periods of wet weather. With pumped int1ow. clarifiers shall have !he capacity ofall
pumps operating at maximum wet well"level unless a coruml system is provided thai will limit the pumping rate to !he "firm capacity". This 
Texas :-JaruraJ ResQu",e Conservauon CommIssIon Page 30 Chapter; I ' -DesIgn Cnteria for Sewerage S)'srems flow mle rna\' also mdude skimmer flow. thickener o\'erflow, filter backwash.
elc, All treaunent plants must be designed to hydraulically accommodate peak flows without adversely affecting the ueaunent processes. The engineer shall detennine. by methods acceplable
to the commission. the appropriate peak flow mle IOcluding the possibility of utilizing standby pumps, The proposed two-hour peak flow rate. togetherWlth a discussion of rationale. calculations
and aU supporting flow rate data shall be. unless presented in the prelimlruuy engineering report. included in the final engineering design report. Special slonn flow holding basIns
or flow equalization facilities can be specifred to panially satisfY the requirements of this section where all treatment units within a plant are not sized for peak flow. See §317.9
of this title (relating to Appendix Ai for referencing a two-year 􀀲􀁾􀀭􀁨􀁯􀁵􀁲􀀠rainfall event. (5) AlL'<iliaty power. The need for auxiliary power facilities shall be evaluated for
each plant and discussed in the preliminary and final engineering reports. Auxiliary power facilities are required for aU plants, unless dual power supply arrangements can be made or
unless it can be demonstrated that the plant is located in an area where electric power reliability is such that power failure for a period to cause detenoration of effluent quality
is unlikely. Acceptable alternatives to auxiliary power include the ability to store influent flow or partially ucated wastewater during power outage. AuxililIIy power may be required
by the commission for plants discharging near drinking water reservoirs, shellfish watets or areas used for contact recreation, and for plants discharging into waters that could be unacceptably
damaged by unaeated or panially aeated effluent ror more infonnation on power reliability determination and emergency power alternatives, refer to §3\7.3 (e) of this title (rela!l:ng
to Emergency Provisiorts.) (6) Component reliability. Multiple units may be requined based upon the uses of the receiving waters and the significance of the treatment units to the ucarment
processes. (7) Stairways, walkways, and guard rails, Basins having vertical walls terminating four or more feet above or below ground level shall provide a stairway to the walkway. Guard
rni\s on walkways shall have adequate clearance space for maintenance operations (see §317.7 of this title (relating to Safety», (8) Public drinking water supply conneaions. There shall
be no water connection from any public drinking water supply system to a wastewater treatment plant facility unless made through an air gap or a backflow prevention device, in acco!dance
with A WW A Stalldartl C506 (latest revision) and AWWA Manual M14. All bac:kflow prevention devices shall be tested 3IIIIWIIIy with their test and maintenance repon forms retained for
a minimum of thme ycars. All washdown hoses using polable water must be equipped with atrnospbelil: vacuum br.:akellllocated above the overflow level of the washdown area. (9) Ground
movement protection. The suuctu!al design of ueaunent plants shall be suffi· cient to accommodate anIicipated ground movement including any active geologic faults and allow for independent
dewatering of all treatment units. Plants should not be located within 50 feet ofgeologic faults. (10) Odor control facilities. The need for odor control facilities shall be evaluated
for each. plant F actots to be considered are the dissolved oxygen level of the incoming sewage and the type of treat· ment process proposed. (b) Preliminaty aeatment units. Bar screens,
screens or shredders through which all wastewater will pass should be provided al all plants with the exception of plants in which septic tanks, Im.hoff tanks, 
Te'3S Natu",l Resource Conser.auon Commission Page) I Chaptet 31' • Design Cn!ena for Sewerage Systems facultau,e. aerated. or parually mi,ed lagoons represent the initial treatment
UIUt. In the event bat screens. ,creens at shredders are located four or more feet below ground leyet appropnate equipment shall be pro\'lded to lift the screenings to ground eleYation.
Where mechanically cleaned bar screens or shredders are uulized. a backup unit or manually cleaned bar screen shall be proyided. A means of di\'erting flow to the backup screen sball
be included in the design. (l) Bar screens. Manually cleaned bar sCreens shall be constructed having a 30 degree to 60 degree slope to a horizontal platform which will provide for drainage
of the screenings. Bar screen openings shall not be less than three-quaners of an inch for manually cleaned bar screens and one·half inch for mechanically cleaned bar screens. The channel
in which the SCreen is placed shall allow a velocity of two feet per second or more at design flow. Velocity through the SCreen opening, should be less than three feel per second at
design flow. (2) Grit removal. Grit removal facilities should be considered for all wastewater treatment plants. Grit washing facilities shall be provided uriless a burial aIea for the
grit is provided Within the plant grounds, or the grit is handled otherwise in such a manner as to prevent odors or fly breeding. Grit removal units shall have mechanical means of grit
removal or other acceptable methnds for grit removal. Plants which have a single grit collecting chamber shall have a bypass around the chamber. All grit collecting chambers shall be
designed with the capability to be dewatered. The method ofvelocity control used to accomplish grit removal in gravity settling chambers shall be detailed in the fmal engineering repolt
(3) Fine screens. Fine screens, ifused, shall be preceded by a bar screen. Fine SCreens shall not be substituted for pIimary sedimentation or grit removal; however, they may be used
in lieu of primal}' treatment if fully justified by the design engineer. A minimum of two fme screens shall be provided, each capable of independent operation at peak 11ow. A steam cleaner
or high pressure water hose shall be provided for daily maintenance offine screens. (4) Screenings and grit disposal. All screenings and grit shall be disposed of in an approved manner.
Sttitable containers with lids shall be provided for holding screenings. Runoff control must be provided around the containers wbere applicable. Fine screen tailings am considered as
infectious waste; then:Core, containers must provide vector control ifwastes am not disposed of daily at a Type I landfill. (5).·Preacmtion. Because preaemtion may be proposed when a
particular problem is anticipated, evaluation oflhese units will be on a case-by-case basis. Diflllser equipment shall be arranged for greatest effidelll:)', with consideration given
III maintenance and inspection. (6)-FIowequalization. Equallzalion should be considered to minimize random or cyclic peaking of organic or Ilydrnulic loadings. Equalization units should
be provided after screening and grit removal. (A) Aemtion. Aeration may be requimi for odor control When required, air supply must be sufficient to maintain 1.0 mg/I of dissolved oxygen
in the wasteWater. (B) Volume. A diumal flow graph with supporting calculations used for sizing the equalization facility must be provided in the engineering repolt Generally, an equalization
facility requires a 
Texas >iarurnl Resource Conservauon CommIssIon Page n Chllpter 'I" . Design Critena for Sewemge S\,stems volume equl\a1en! to 10 % to 20 % of the anticipated d.ty weather 30-day a,'emge
flow. Tankage should be divided into separate compartments to a!low for opemtional flexIbility. repair and cleaning. (c) Flow measuring devices and sampUng paints. A means for measuring
effluent flow shall be provided at all plants. Consideration should be given to pro"iding a means to monitor influent flow. Where average Influent and effluent flows are significantly
different. e.g.. plants Wtth large water surfaces located in areas of high rainfall or e"aparation or plants using a panion of effluent for irrigation. both influent and effluent must
be measured. Consideration should be given to internal flow monitoring devices to measure returned activated sludge andlor to facilitate spUtting flows between units with special attention
being gi"en when units are of unequal size. All plants shall be provided with a readily accessible area for sampling effluent (d) Clarifiers. (1) [niets. Clarifier inlets shall be designed
to provide uniform flow and stilling. Vertical flow velocity through the inlet stilling well shall not exceed 0.15 fee! per second at peak flow. inlet distribution channels shall no!
have deadened comers and shall be designed to prevent the settling of solids in the channels. Inlet structures should be designecilO allow floating material to enter the clarifier. (2)
Scum removal Scum baffles and a means for the collection and disposal of scum shall be provided for primary and final clarifiers. Scum coUected from fmal clarifiers in plants utilizing
the activated sludge process, or any modification thereof, and ae13ted lagoons may be discharged 10 aeration basin(s) and/or digester or disposed of by other approved methods. Scum from
all other final clarifier> and frem primary clarifiers shall be discharged to the sludge digester or other approved method of disposal. Discharge of scum to any open drying area is not
acceptable, Mechanical skimmers shall be used in units with a design flow greater than 25,000 gallons per day. Smaller systems may use ItydJaulic differential skimming provided that
the scum pickup is capable of removing scum from the entire operating surface of the clarifier. Scum pumps shall be specifically designed for Ibis pwpose. (3) Elfluent wells. EIfluent
wells shall be designed to prevent tuIbu1ence or localized high vertical flow velocity in the claritielS. Wells shall be located 10 prevent shon cireuiting flow through the clarifier
and shall be alljustable for leveling, Weir loadings shall not exceed 20.000 gallons per day peak design flow per linear foot of weir length for plants with a design flow of 1.0 mgd
or less, Special consideJation will be given 10 weirloadings for plants with a design flow inel«:ess of 1,0 mgd, but such loadings shall not exceed 30,000 gallons per day peak flow per
linear foot ofweir. (4) Sludge lines. Means for tJansfer of sludge from primary, intermediate. or fmal clarifiers for subsequent processing shall be pmvided so that lKalment efficiency
will not be adversely affected. G13Vity sludge tJansfer lines shall not be less than eight inches in diameter. (5) Basin sizing. Ovelflow 13tes are based on surface area ofclarifiers.
The swface areas required shall be computed using the following criteria The acruaI clarifier size shall be based on whichever is the larger size from the two surface area calculations
(peak flow and design flow surface loading rates). The fmal clarifier solids loading for all activated sludge treatment processes sbaIJ not exceed 50 pounds of 
􀁔􀁥􀁾􀁡􀁳􀀠:-:a'lJral Resource Conservaoon CommIssIon Page J) Chapter 31' -Design Criteria for Sewerage S'stems solids per day per square foot of surface area at peak flow rate. The
fonowlng design critena for clanfiers are based upon a sIde water depth of 10 reet and shall be consIdered acceptable: Clarifier \[axlmum \finlITlum Effct;;tivo!' 􀁾􀁨..'(jmum Surflctf
\Iiolmum Effecnvt Surfacr:' 􀁄􀁥􀁴􀁾􀁮􀁯􀁮􀀠Time Loading '@D':SlgIl [)::teflflOfl Tim¢ Loading @Peak. 􀁾􀀠Peak Flow Flow 􀁾􀀠􀁄􀁾􀁭􀁧􀁮􀀠Flow Flow (bn) (galtday,sq tt) lhrs.) (gaL'aaY"q
ft) Primary & Intenno!diate. 1800 1000 Final: rixed Film S¢cond4ty 1600 1.1 800 2.2 fixed Film Enhanc«l S¢oondarjl' I.roO 1.3 100 ),0 􀀮􀁾􀁴􀁩􀁶􀁡􀁴􀁥􀁤􀀠Sludge (except <!xtended Air)
&condary l.roo \.l 100 2.6 Enh",..d Se<:ondar'l' 1200 U 600 3,0 E:<!end«l Air S<oondary 1000 1.8 500 ),6 E:ttend«l Air Enh_ell Secondarjl' 800 2,2 400 4.5 Second STage Nitrification
1200 1.5 600 3.0 a Does not include tet;irculation b Enhanced Sec:onduy Treatment refers to enhanced solid, removal achieved through reducing the hydraulic and solids !oading to the
clarifier c Overflow",.. and sid. Wlller d.p1l1 (SWD) may b. adjusted, kcepinB 111. d....bOn tim. ""cbanged, over .....g. of8 ft. to 16 ft. ofSI'tU, The detention time is bued on the
effective volume and the overflow rate of 1be t:irtular or fCt,lAI1gUlar clarifier. (Thc 􀁥􀁦􀁦􀁾􀁴􀁩􀀢􀁣􀀠volume intludes all liquid above lit. sludg. blanket). for cone bo!lcm tanks.
lit. top orllt. 'ludge blanke' is con";dcrcd to be &lilt. top of lit. tone. For IIat bottom tanks. • shldp bllnket ofl ft. should be allowed for development ofmlXimum "'tum sludge cont..llation,
(6) Sidewater depth. The minimum sidewater depth for conventional primaIy and intennediate clarifiers is seven feel. All final ClalifielS shall have aminimum side-water depth of 8 feet
Final clarifiers having a swface axea equalm or greater than 1.250 square feet (diameter equalm or gteater than 􀁾􀁯􀀠feet) must be provided with a minimum sidewater depth of 10 feet.
(7) Hopper bottom clarifiers. Hopper bottom CJari(telS without mecbanical sludge collecting equipment will only be approved for those facilities with a pennitted design flow ofless than
25,000 gallons per day. The requiIed sidewater depth (SWD) for hopper bottom clarifiers may be computed using the following equation: SWD z 160 QD + 4, where SWD equals required sidewaterdepth
in feet and QD equals design flow in million gallons per day. 􀁆􀁷􀀺􀁴􀁨􀁥􀁮􀁮􀁯􀁾􀀬􀀠SWD as computed above for any flow may be reduced by crediting the upper one-third of the hopper
as effective sidewater depth ifthe following conditions are met: (A) clarifier sUiface loading rate is reduced by at least IS % from maximum loading rate as per paragraph (5) of this
subsection; 
Texas SarurnJ Resoun::e Conservauon Commission Page J.l Chapter} I' • Design Criteria for Sewerage Systems (B) influent stilting baffie and effluent welf are designed to prevent shon
circuiting: (e) detention time al peak flow is at least 1.8 hours for secondary treatment and 2 .. hours for advanced treatment and (D) an appropriate form of flow equalization is used,
(8) Sludge collection equipment AU conventional clarifier units that treat flow from a treatment plant facility with a design flow of 25,000 gallons per day or greater shall be provided
with mechanical sludge collecting equipment. Hopper bottom clarifiers must have a smooth wall finish and a hopper slope of not less than 60 degrees, (9) BOD, removal. It shall be assumed
that the BOO, removal in a primary clarifier is 35 percent unless satisfactory evidence is presented to indicate that the ef!1ciency will be otherwise, (n plant efficiency calculations,
it shall be assumed that the BOO, removal in intermediate and final clarifiers is included in the calculation for the efficiency of the treatment unit preceding !be intermediate or fmal
clarifier. (e) Trickling filters. (I) General. Trickling filters an: secondary aerobic biological processes which are used for treatment of sewage, (2) Basic design parameters, Trickling
filters an: classified according to applied hydraulic loading in million gallons per day per acre of filter media surface area, (mgdlage) and organic loadings in pounds BOO pel day per
1000 cubic t«tof filter media, (lb BOO/day. 1000 cu fi). The following factors should be considered in!be selection of!be design hydraulic and organic loadings: strength of!be infiuent
sewage, effectiveness of pretreatment, type offilter media, and t1eatment efficiency required. Typical ranges of applied hydraulic and organic loadings for tbe different classes of uicklillg
filtelS an: presented in !be following table for illustrative purposes. The design engineer shall submit sufficient opernting data from existillg tricklillg filtelS of similar conslJ:UCtion
and operation to justify his efficiency calculations for !be filtelS, and a ftlter efficiency formula from a reliable SOUltll acceptable 10 !be commission. The formula of the National
Resean:h CO\llll:il may be lI5Cd when rock media is used intbe trlckIiDg fi1teI(s). 
Texas 􀁾􀀢􀁲􀁵􀁲􀁡􀁬􀀠Resource Conser\'auon Commission Page 35 Chapter) 17 • Design Criteria for Sewerage S)'stems Typical Design Loadings Opt!ranng Standard Rate Intenn<!diate High
Rate High Rat.: RoughmgCharaclens(ics Rate )'I<!dia Rock Rock Rock ).tanufactuf<!rJ Ei.ih.:r Hydraulic Loading: mgd:acre 1-4 .J-tO 􀁉􀁏􀁾􀀠 60·130' -spd/sq ft 25-90 90·230 230.900 350-1000'
t400-4200 Organic loading:: ttl: 􀁂􀁏􀁄􀀯􀁡􀁣􀁲􀁥􀁾􀁦􀁴􀁬􀁤􀁡􀁹􀀠200·tOOO 700·1400 1000·1300 1 b BODld&yll 000 eu fi 5·25 lS.JO 25·JOO up to 300 100+ BOD Removal (%) 30·85 50-70 65.85
65.85 ·Does not in.;lude recir<:ula:oon (3) Pretreatment The trickling filter treatment facility shall be preceded by primary clarifiers equipped with scum and grease removal devices.
Design engineers may submit opexating data as justification of other alternative pretreatment devices which provide for effective removal of glit, debris, suspended solids and excess
oil and grease. Preaexation shall be provided where influent wastewater contains harmful levels of hydrogen sulfide concentrations. (4) 'Filter media (A) Material specifications for
rock media. The following are minimum requirements. (i) Crushed rock, slag or similar media should not contain more than five percent by weight. of pieces whose longest dimension is
greater than three limes its least dimension. The rock media should be ftee from thin, elongared and flat pieces and should be free from dust. clay, sand, or fme material Rock media
should conform to the following size distribution and,gmding when mecbanically gxaded over a vibrating screen with square openings: (I) passing fIve inch sieve. 100 % by weigh!; (ll)
retained on three inch sieve -9S·100 % by weight; 
T<.xas 􀁾􀀳􀀮􀁮􀀬􀀬􀁾􀀱􀀠Resource Conservation CommIssIon Page 36 Chapler ) I" . DesIgn Crilena for Sewerage Svstems (Ill) passing two inch sIeve" 0.2 % by weight: (IV) passing one inch
sieve" 0.1 % b:"'eight: (V) the loss of weight by a 20"'0'cle sodium sulphate test. as described in Amencan Society of Civil Engineers Manual of Engineering; and Engineering Practice
No. 13. shall be less than 10 %. (ti) Rock media shall not be less than four reel in depth (at the shallowest point) nor deeper than eight feet (at the deepest point of the filter).
(B) Synthetic (manufactured or prefabricated) media. (i) Application ofsynthetic media shall be evaluated on a case-by-case basis. Suitability should be evaluated on the basis of experience
with installations treating similar strength wastewater under similar hydraulic and organic loading conditions. The manufacturefs recommendations . shall be included as well as case
histories involving the use of the media (il) Media shall be relatively insoluble in sewage and resistant to flaking or spalling. ultraviolet degradation, disintegration, erosion, aging,
all common acids and alkalies, organic compounds. biological attack, and shall suppon the weiglu of a person when the media is in operation. (ill) Media depths should be consistent with
the !\lCommendstions ofthe mamUacturer. (C) Placing of media (i) The dumping of media dirIIctly on the !ilter is unacceptable. Instructions for placing media shall be included in the
specifications. (ti) Crushed rock, slag,aDd similar media shall be washed and screened or forked to remove clays, orgllllic material, and fines. (iii) SuchmateriaIs should be placed
by hand til a depth of 12 inches above the undetd:mins and all material sbDuId be carefully placed in a manner which will not damage the undetd:mins. The remaiDderof the material tnaY
be placed by means ofbelt conveyors or equally effective methods approved by the engineers. Trucks, tractllrs, or other heavy equipment should not be driven over the nIler media during
or after construction. (iv) Prefabricated rdter media shall be placed in accordance with IIIcommendstions provided by the manufacturer. (5) Filler hydraulics. 
T"as 'larurn! Rcsoulte Conservauon CommiSSIon Page F Chapter; I ' . Design Criteria for Sewerage S,·stems tAl Dosing. Wastewater may be applied to the flIters by siphons. pumps. or by
gravuy discharge from preceding treaunent units when suitable flow characteristics have been developed. (8) Distribution equipment. Settled wastewater may be distributed over the filter
media bv rota!!', horizontal, or tmvelling distributors. provided the equipment proposed is capable of producing the required continuity and uniformity of distribution over the entire
surface of the flIter. Deviation from a calculated uniformly distributed volume per unit surface area shall not exceed \0 % at an\' portion of the flIter. Filrer distributors shall be
designed to operate properly at all flow rates. Excessive 􀁨􀁾􀁡􀁤􀀠in the center column of rota!!' distributors shall be avoided, and all center columns shaU have adequately sized overflow
ports to prevent the head from building up sufficiently for the water to reach the bearings in in the center column. Distributors shall include deanout gates on the ends of the arms
and shall also include an end nozzle to spray water on the waU of the fllter to keep the edge of the media continuously wet The ftlterwalls shall extend atIeast 12 inches above the top
of the ends of the distributor arms. (C) Seals. The use of mercury seals is prolubiled in the distributors of newly constructed trickling fillers. Ifan existing treatment facility is
to be modified, any mel'CUIY seals in the trickling fllters shall be replaced with oil or mechanical seals. (D) Distributor clearance. A minimum clearance of six inches shall be provided
berween the top of the flller media and the distributing nomes. (E) Recin:u1alion. In order to insure that the biological growth on the filter media remains active at aU times. provisions
shall be included in aU designs for minimwn recircu1ation during periods of 10'" flow. This minimum recin:ulation shall not be considered in the evaluation ofthe effiCiency of the flIter
unless it is pan of the proposed specified colllinuous recirculation rate. Minimum flow to the fLlters shall not be less than 1.0 mgd per acre offiller surface. In addition, the minimum
flow rate must be great enough to keep rotary distributors tunling and the distribution nomes operating properly. For facilities with a design capacity grealer than or equal to O.S mgd
and in which recirculation is included in design computations for BOD, removal. recirt:ulalion shall be provided by variable speed pwnps and a method of conveniently measuring the recycle
flow rate shall be provided. (F) Surface loading, The engineering repol! shall include calculations of the maximum, design, and minimum surface loadings on the flItel{s) in tenos of
millions ofgallons per acre of filter area per day (for the initial year and design year). Hydraulic loadings of fIlters with crushed rock, slag or similar media shall not exceed 40
mgd per acre based on design flow. The minimum SUlface loading shall not be less than 1.0 mgd per acre. Loadings on synthetic (manufactured or prefabricated) filter media shall be within
the ranges specified by the manuf3cttm:r, (6) Underdrain system. (A) U nderdrains, U nderdrains with semicin:ula.r inverts or equivalent shall be provided and the underdrainage system
shall cover the emile floor ofthe trickling filter, Inlet opertings into the underdrains shall provide an unsubmerged gross combinlld area of atleast ISo/. of the SUlfate area of the
fllter. 
Texas Surural 􀁾􀁥􀁳􀁯􀁵􀁲􀁣􀁥􀀠Conservauon Commission Page 38 Chapter, I" -DesIgn Cntena for Sewerage Systems IS) Hydraulics. Underd!'alns and the filter effluent channel floor shall
ha'·e a mmimum slope of one percent Effluent channels shall be designed to produce a mlrumum ,elocitv of two feel per second at average dally flow rate of applicauon to the trickling
filter. . (Cl Drain ule. Underdrains for rock media trickling filters shall be eithenitrified clay or precast reinforce.! concrete. The use of half tile for underdrain systems is unacceplable.
(D) Corrosion. Underdrain systems for synthetic media trickling filters shaU be resistant to corrosion. (E) Ventilation. The underdrain system. effluent channels. and effluent pipe shall
be designed to permit free passage of air, Drains. channels, and effluent pipes shall have a cross-sectional area such that not more than SO % of the cross-sectional area will be submerged
at peak flow plus recin:u\alion. Provision shall be made in the design of the eflluent eflluent channels to allow the possibility of increased hydraulic loading. The underdrain system
shall provide at least one 􀁾fOOl of ventilating area (vent Slacks. ventilating holes, ventilating ports) for every 250 􀁾feel of rock media filter plan area. Ventilating area for synthetic
media underdrains will be provided as recommeMed by the manufacturer. bUI shall be at least one square foot for every 175 square feet ofsynthetic media trickling filter plan area. (F)
Maintenance, All flow distribution devices. underdrains. channels. and pipes shall be designed so they may be maintained. flushed. and properly dmined, The urtits shall be designed to
facililale cleaning of the distributor anns. A gate shal1 be provided in the wall to facililale rodding of the distributor anns, (O) Flooding, Provisions shall be made to enable flooding
of the trtckling filter for filter fly control; however. consideration will be given by the comutission to alternate methods of filter fly control provided that the effectiveness of
the alternate methcd is verified at a full scale installation. This information shall be subutitted witll tile plans and specifications. (H) Flow measurements. Means shall be provided
to measme flow to the fther and recirculation flows, (I) Rotating biological COntaclOlS (RBe). (l) Genellll. (A) RaC urtilS shall be covered and ample ventilation provided. Working cleaxance
of approximately 30 inches should be provided within the cover unless tile covers are removable, ntilizing eqttipmenl normally available on site. Enclosures shall be col\SUl:lCted ofa
suitable corrosion resistant material, (8) The design of the RaC media shall provide for self cleaning action due to the flow of water and air through the media. Careful selection of
media that will not entmp solids should be made, 
Texas Natural Resource Conservauon 􀁃􀁯􀁭􀁭􀀧􀁳􀁳􀀬􀁯􀁾􀀠Page 39 Chapter) I; -DesIgn emeria for Sewemge $vstems te) The RBe tank should be designed to mirumlze zones m which solids WIll
settle out (D) RBe media should be selected which is compatible with the wastewater. Selection of media can be critical whete the wastewater has an industrial waste portion which either
􀁳􀁩􀁧􀁲􀁵􀁦􀁫􀁡􀁮􀁴􀁬􀁾􀂷􀀠increases the wastewater lempemture or contains a chemical consUtuent which may decrease the life of the RBe media. . (2) Design. (A) Ptetreatment. RBe units
shall be preceded by pretreatment 1.0 remove any grit, debris. and excess oil and grease which may hinder the treatment process or damage the RBC units, The design engineer should consider
primary clarifiers with scum and grease collecting devices. fme screens, and oil separntors. For wastes with high hydrogen sulfide concentrations. preaeration shall be provided. (B)
Organic loading. The organic loading for the design of RBe units shall be based on total BOD, BOD, in the waste going to the RBe including any side streams, The design engineer should
consider a maximum loading rate of Sib BOD, per day per 1.000 ft' of media in any stage. depending on the character of the influent wastewater. The maximum loading rate shall not exceed
8 Ib BOD, per day per 1.000 It' of media in any stage, The design engineer should also consider the ratio of soluble BOD, to total BOD, and its possible effect on tequired RBC media
area Allowable organic loading for the entire RBC system shall not e.'(ceed the following criteli.a: Degree of Treatment Maximum Organic Loading (lb. BOD,/dayll,OOO ft' of media area)
Secondary 3.0 Advanced Secondary 2.0 (C) Stages of treatment. The number ofRBC units in series (stages) for BOD removal only shall be a minimum of tlu1:e stages. For BOD removal and
nitrification, there shall be a minimum of four stages. Ifthe plant is designed with less stages than noted above. the engineer must provide justification based on eitber full-scale
operating facilities or pilot unit operational data Any pilot unit data used in the justification must tala: into considelation an appropriate scale-up factor. (0) Drive system. The
drive system for each RBC unit shall be selected for the maximum anticipauia media load. A valiable speed system should be considered to provide additional operator flexibility. "The
RBC units may be mechanically driven or air driven. (i) Mechanical Drives. (I) Each RBC unit shall have a positively connected mechanical drive with motor and speed reduction unit to
maintain the required rpllL 
􀁔􀁾􀁸􀁡􀁳􀀠S;hUai Resourt'e Conser\"flUOn CommlSStOn Poge 􀁾􀁵􀀠Chapter .11--DesIgn Critena for Sewerage Svstems ([[) A fully-assembled spare mechanical drive urut for eactl size shall
be pronded on-site. (lin Supplemental diffused air should be considered for mechanical drive systems to help remove excess biomass from the media and to tlelp mainlain the minimum dissolved
oxygen co ncentlation. (iil Air Drives. <n Each ItBC unit shall have air diffusers mounted below the media and oif-<::enler from the vertical axis of the ItBC uniL Air cups mounted on
the outside of the media shall coUect the air \0 provide the driving force and maintain the required rpm. (m Blowelll shall provide enough air flow for each ItBC unit plus additional
capacity \0 double the airflow tale to any one unit wbile the others are running normally. (III) The blowers shall be capable of providing the required air flow with the largest unit
out of service. (IV) The air diffuser line to each unit shall be mounted such thaI it can be removed without draining the tank or removing the ItBC media (V) An air control valve shall
be installed on the air diffuser line to each ItBC urut (E) Dissolved oxygen. The RaC plant shall be designed to maimain a minimum dissolved oxygen concentl'alion of one milligram per
liter at all stages during the peak organic flow tate. Supplemental aellllion may be required. (F) Nitrification. The design of a RaC plant to achieve nitrifICation is dependent upon
a number offactors including the concellUlltion of ammonia in the influent, effluent ammonia concentration required, BOD, removal required, minimum operational tempemtures, and llIlio
ofpeak \0 design hydraulic flow. Each of these factors will impact the number of stages oftreatmem requin:d and the allowable ammonia llitmgen loading (lb NH'/day/l,OOO It' media) required
to achieve the desired levels of rumlication for a given fal;ility. The engineer sball submit appropriate dati supporting the design. (0) Design flexibility. The designer ofa RaC plant
should consider provisions to provide additional operational flexibilil;y such as controUed flow to multiple first stages, alternate flow and staging arrangements, removable baffles
between stages, and provision for step feed and supplemental aetation. (g) Activated sludge facilities, (1) Organic loading rates. AeIl!lion tank volumes should be based upon full scale
experience. pilot scale studies, or rational calculations based upon commonly accepted design parameters 
Texas Namrnl Resource Conservauon CommISsIon Page -II Chapler ll' . Design Critena for Sewerage Systems such as food 10 mlcroorgarusm muo. mtxed liquor suspended soUds. and the solids
retenUon time. Other factors to be consIdered mclude size of the ueatmenr plant, diumalload variations. return flows and soluble organic loads from digesters or sludge dewatering opemtions
and degree of treatment required. Temperarure. pH, and dissolved oxygen concentration are particularly important to consider when designing for rutrification. As a general rate. minimum
aeration tank volumes shall be as set forth in the following table. Calculations must be submllted to fully justify the basis of design for any aeration basins not conforming to these
minimum recommendations. DESIGN ORGANIC LOADINGS Aeration Tank Organic Loading Process Ib BOD,Iday/IOOO ell It ConventionalA 􀁾􀀵􀀠Complete Mix 􀁾􀀵􀀠Contact Stabilization" 50 Extended
Aeration 15 Oxidation DitchC 15 Single Stage Nillification 35 (Al The conventional activated sludge process is characterized by having a plug flow hydrauliC tegime wherein particles
m diacharged in the same sequence in which they emer the aeration basin. Plug flow may be approximated in long tanks with a high lenglh-to-width ratio. (8) The contact stabilization
process divides the aeration tank volume between the reaeration zone and the contact zone. The ratio of reaeration volume to contact volume ranges from I: I to 2: I. The hydraulic detention
time in tile contact zone shall be sufficient to provide removals ofsoluble substrates to the required levels. For domestic flows IIOtmally two hours is sufficient in the contact zone.
Contact zone volume. shall be based upon acceptable removal kinetics for soluble BOD, and ammonia nitrogen. (C) Oxidation diu:hes (which are organically loaded consistent with §3l74(g)(l)
of this title (relating to Wastewaler TrealmeDt Facilities,» shall have a minimum hydraulic retention time of 20 hrs, based on design flow, These oxidation diu:h systems shall provide
final clarification and return sludge capability equal to that required for tile extended aeration process, There shall be a minimum of two rotors per diu:h, each capable of supplying
tile requiIed oxygenation capacity and maintaining a minimum channel velocity of 1.0 fps with one rotor out of service. The dill:h shall be 1ined with reinforced concrete or other acceptable
erosion resistant liner malerial. Provision shall be made to easily vaJY the liquid level in the ditch to control the immersion depth oftile rotor for fle>tibility ofoperation. A motor
of suffIcient size to maintain the proper rotor speed for continuous operation shall be provided. Rotor bearings should have grease firtings that are readily accessible to maintenance
personneL Gear housing and outboard bearings should be shielded from rotor splash. 
Texas Namr.:!l Resource Canservauan Commission PageH Chap,er' 17. DesIgn Cnlena for Sewerage S"slems (2) Aerauon basin general design considerations. Aeration tank geometry shall be
arranged to provide opllmum 􀁯􀁾􀀺.. gen transfer and mixing for the type aeration device proposed. Aerauon tanks must be constructed of reinforced concn:te. steel with corrosion reSIStant
linings or coatings. or lined eanhen basins. liquid depths shall not be less than 8.0 feet when diffused air is used. AU aeration tanks shaU have a fn:eboard of not less than 18 Inches
at peak flow. Access walkways with properly designed safety handrails shall be provided to all areas that requin: routine maintenance. Where operator.; would be required to climb heIghts
greater lhan four (+) feel properly designed stairways with safety handrails should be provided. The shape of the tank and the installation of aeration equipment should provide a means
to control shan circuiting through the tank. For plants designed for design flows greater than than 2.0 mgd the total aeration basin volume shall be divided among two or mon: basins.
Each treatment facility shall be designed to hydraUlically pass the design two-hour peak flow with one basin out of service. (3) Sludge pumps. piping. and return sludge flow measurement
The pumps and piping for return activated sludge shall be designed to provide variable underflow rates of 200 to +00 gallons per day per square foot for each clantier. Ifmechanical pumps
axe used. sufficient pumping units shall be provided to maintain design pumping rates with the largest single unit out of service. Sludge piping andlor channels shall be so ammged that
flushing can be accomplished. A minimum pipe line velocity of 3 feet per second should be provided at an underflow rate of 200 gallons per day per square foot Some method shall be provided
to measure the return sludge flow from each clarifier. (+) Aeration system design. (A) General design consideration. Aeration systems shall be designed to maintain a minimum dissolved
oxygen concentration of 2.0 mg/l throughout !be 􀁢􀁾􀁮at the maximum diurnal organic loading rate and to prOVIde thorough mixing of the mL'(ed liquor. The design oxygen requirements
for activated sludge facilities are presented in the foUowing table. The minimum air volume requirements may be reduced with appropriate supporting pelforma.nce evaluatioDS from !be
manufacturer. Minimum Minimum' 0, R.equim:I Air Required Process Ib 0,l1b BODj SCFIlbBODj Conventional 1.2 1800 CompielO Mix 1.2 1800 Contact Stabilization 1.2 1800 ExtmIded Aeration
2.2 28'0 Oxidation Ditch 1.6(2.2)" Nitrification 2.2 3200 (i) Mininium air volume requirements axe based upon a transfer efficiency of +.0 percent in wastewater for all activated'sludge
prooesses except extended aeration, for wlticll a wastewater trnnsfer efficiency of 4.5 percent is assumed. (ti) Value in parentheses represents the minimum oxygen requirement for ditch
type systems which will achieve nitrifICation. 
Texas Nanmll Resou!l:e Conservauon Commission Page .3 Chapter J I' . Design Cnteria for Sewerage S"srems (B) Diffused air systems, 0) Volumetric aeration requllements, Volumetric aerauon
requirements shall be as detenmned from the preceding table unless certified diffuser petfonnance data is preSented ",hich demonstrates tranSfer efficiencies greater than those used
in the preparation of the table, Wastewater uansfer efficiencies may be estimated for; (I) coarse bubble diffusers by multiplying the clean water tranSfer efficiency by 0,65: (0) fine
bubble diffusers by multiplying the clean water transfer efficiency by 0,-15, The maximum allowable wastewater transfer efficiency shall be 12,0 percent Plants treating greater than
10 percent industrial wastes shall provide data 10 justify actual wastewater transfer efficiencies, Wastewater oxygen transfer efficiencies greater than 12% are considered innovative
teclmology, See §317, I (a)(2)(C) of this title (relating to General Provisions) for perfonnance bond requirements, Clean water transfer efficiencies obtained at 20 degrees Celsius shall
be adjusted to rellect field conditions (I.e" wastewater transfer efficiencies) by use of the following equation: Air Flowrate = ribs, BOp,/day)(lbs 0, Req'd/!b BOP,! Required (sefm)
Wastewater T,E, x 0,23 x 0,015 x 1440 Where: Wastewater T.E, = Wastewater Transfer Efficiency, % 023 = lb O,IIb air@20 degrees C 1440 = minutes/day O.07S = Ib air/(eub;c foot) (ti) Mixing
requirement Air requirements for mixing should be considered along with those required for the design organic loading, The designer is refern:d 10 Table 14·V, aeraror mixing requirements
in WASTEWATER lREAIMENT PLANT DESIGN, a joint publication of the American Society of Civil Engineers and the Water Pollution Control Federation. (ill) Blowers and compressors, Blowers
and compressors shall be of such capacity to provide the required aeration rate as well as the requirements of all supplemental units such as airlift pumps. Multiple compressor units
shall be provided and shall be arranged so the capacity of the total air supply may be adjusted to meet the variable organic load 10 be placed on the treatment facility, The compressors
shall be designed so that the maximum design air requirements can be met with the largest single unit out ofservice, The blower/compressor units shall automatitally restart after a period
ofpower outage or the operalOr or owner shall be notified by some method such as teleme!ly or an aUIO-dialer, The specified capacity of the blowers or air compressors, particularly centrifugal
bloweIS, should take into account that the air intake tempellltUle may reach 104 degn:es F(40 degrees C) or higber and the pressure may be less than standard 􀀨􀀱􀁾􀀬􀀱􀀠pounds per 5q\lale
inch absolute). The capacity of the motor drive should 
Tosas San.ual ResoUKe Conser\'a1lOn CommISSIOn Page .\.\ CMpter ; 17 • DesIgn Cmeric . 'f Sewerage Systems also take Into accoum that the mtake arr may be 10 degrees F (·12 degrees C)
or less and may requIre ovemzmg of the motor or a means of reducmg the rate of air delivel)' to prevent overheating or damage 10 the motor. (iv) Diffusers and piping. Each diffuser header
shall include a control ,al,·e. These valves are basically for open/close operation but should be of the throttling type. The depth of each diffuser shall be adjustable, The air diffuser
system, including piping, sMU be capable of detivering 150 peKent ofdesign air requirements. The aeration system piping should be designed to minimize head. losses. Typical air ,elodues
in air delivery piping SYStems ale presented in the foUowing table. Pipe Diameter Velocity (Inches) (Feet/min.-Std.AirJ I -3 1,200. 1,800 􀁾􀀠-10 1,800 • 3,000 12·24 2,700 ·4,000 30·60
3,800 -6,500 (5) Mechanical aeration systems, Mechanical aeration devices shall be of such capacity to provide oxygen transfer to and mixing of the tank contents equivalent to that provided
by compressed air. A minimum of two mechanical aeration devices sball be provided, Two speed or variable speed drive units should be consideled. The oxygen transfer capability of mechanical
surface aellllors shall be calculated by the use of a generally accepted fonnula and the calculations presented in the engineering repon. Proposed clean water transfer rates in excess
of 2.0 Ibs. per horsepower-hour shall be justified by performance data. In addition to providing sufficiem oxygen transfer capability for oxygen transfer. the mechanical aeration devices
shall also be Iequired 10 provide sufficiem mixing to proven! deposition of mixed liquor suspended sotids under any flow condition. A minimum of 100 horsepower per million gallons of
aeration basin volume shall be furnished. (h) Nutrient removal (I) Nitrogen removal. Biological systems desigDcd for nitrification and denittilication may be utilized for the conversiolllremoval
of nitrogen. Various physicallcbcmical processes may be considered on a case-by-case basis. (2) Phosphorous lemoval. (A) Chemical treatment. Addition oflime or the salts of aluminwn
or iron may be used for the chemical lemoval of soluble phosphorous, TIle phosphorous reacts with the calcium. aluminum or iron ions to fonn insoluble compounds. These insoluble compounds
may be flocculated with or without the addition ofa coagulam aid such as a polyelectrolyte 10 facilil3le separation by sedirnentatioll When adding salts ofa1wninum or iron, the designer
should evaluate the wastewater 10 ensure sufficiem alkalinity is available 10 prevent excessive depression of the wastewater or effluem pH. This is of particular importance when the
system will also be required 10 achieve nillific:atioll TIle designer is referred 10 NUTRIENT CONTROL. Manual ofPllICtice FD-7 Facilities Design, published by the Water Pollution Comrol
Federation 
Texas :-iaOlr:U Resourte Conseryauon CommIssIon Pnge 􀁾􀁪􀀠Chapter) l' -Design Cntena for Sewemge Svstems and the Process DeSlen 'Iaollal for PhosphoO!s Removal published by the EnVironmental
Protection A.genc\". for addlUoruUmformation. (B) Biological phosphorus removal. Biological phosphorus removal S'<SlemS "ill be consIdered on a case-by..::ase basiS for systems which
call produce operating data which 􀁤􀁥􀁭􀁾􀁮􀁳􀁴􀁲􀁡􀁴􀁥􀀠the capability to remove phosphorus 10 the required levels. All biological systems which are required to meet a 1.0 mg!l effluent
phosphorus concentrauon shall make provision forstand-by chemical oreaunent to ensure the 1.0 mg!l.s achieved. (i) Aerated lagoon. (I) Horsepower. Mecbanical aeration units in aerated
lagoons shall have sufficient power to provide a minimum of 1.6 pounds of oxygen per pound of BOD, applied with the largest unit out of service. If oxygen requirements control the amount
of horsepower needed. proposed oxygen transfer rates in excess of 2 Ibs. per horsepower-hour must be justified by actual performance data The amount of oxygen supplied or the pounds
of BOD, per hour that may be applied per horsepower-hour may be calculated by the use of any acceptable formula. The combined horsepower rating of the aeration units shall not be less
than 30 horsepower per million gallons of aerated lagoon volume. (2) Construction. Eanhen ponds shall have large sections of concrete slabs or equivalent protection under each aeration
unit to prevent scouring of the earth. Concrete scour pads shall be used in all areas where the velocity exceeds I reet per second. Ea!then ponds shall have protection on the slopes
of the embankment at the water line to prevent erosion of the slopes from the turlmlenee in the lagoon. Where the hOlSepower level is more than 200 horsepower per million gallons of
lagoon volume, the pond embankment at the water line shall be protected from erosion with riprap which may be concrele, gunite, a six-inch thick layer of asphalt-saturated or cement-stabilized
earth rolled and compacted into place, or suitable rock rlpmp. The cresl and dry slopes of embankments shall be protected from erosion by planting of grass. (3) SubsequeDl treatment,
discharge systems. Aerated lagoon efilueDl will normally be routed!l) additional ponds for secoDdaly treatment and to provide sufficient detention time for disinfection. The secondary
ponds system sbaIl consist of two or more ponds. SecoDdaly pond sizing shall not exceed 35 pounds of BOD, per acre per day. Hydmulli: detention time in a combined aerated lagoon and
secondary pond system sball be a minimum of 21 days 􀁾􀁤on design flow) in order!l) provide adequate disinfection. In designing the secoDdaly ponds, BOD, removal efficiency in the aernted
lagoon(s) may be calculated using the following formula: E= I I+K(V/Q) E" efficiency ofa complete mix reactOr without recycle K" removal rate COnstanL day.' (generally 0.5 day_' for
domestic sewage) V.. aeration basin volume, million gallons 
Texas :-iaOlrnl Resource Conservation CommISSIon Page .16 Chaple r ' \7 -DesIgn C ntena for Sewerage 􀁓􀁾􀀧􀁳􀁛􀁥􀁭􀁳􀀠Q = wastewater !low rate. in million gallons per day (j) Wastewaler
stabilization ponds (secondary treatment ponds). (I) Pretreatment. Wastewater stabilization ponds shall be preceded by facilities for primary sedimentation oftne raw sewage. Aerated
lagoons or facultative lagoons may be utilized in place of eom'entional primary treatment facilities. (2) Imperviousness: All earthen struerures proposed far use in domestic wastewater
treatment or storage shall be constructed to protect groundwater resources. Where linings are necessary. !he following methods are acceptable. (A) tn-situ or placed clay soils having
!he fohowing qualities may be utilized for pond lining: (i) more than 30% passing a 200-mesh sieve; (ii) liqtild limit greater than 30%; (iii} plasticity index greater than 15; and (iv)
a minimum tbickness of 2 feet (B) membrane lining with a minimum tbickness of 20 mils, and an underdrain leak detection sYstem. (e) other methods with commission approval (3) Oistribtilion
of flow. Stabilization ponds shah be ofsuch shape and size to insure even distribution ofthe wastewall:r now throughout the entire pond. WbiIe the shapes of ponds may be dictated to
some extent by the topography ofthe location, long namlW ponds are preferable and they sbatild be oriented in the 􀁾􀁴􀁩􀁯􀁮ofthe prevailing winds such that debris is blown toward the
inlct. Ponds with narrow inlets or sloughs should be avoided. (4) Access area. Storm water drainage shah be excluded from aU ponds. All vegelation shah beremoved from within the pond area during construction. Access areas shah be cleared and maintained for a distance of at least 20 feet from the outside toes of the pond embankment walls.
(5) Multiple ponds. The use of multiple ponds in pond sYstems is reqtiIred. The operation of the ponds shah be tle.'Cible, enabling one or more ponds to be taken out ofservice without
affecting the operation of the remaining ponds. The ponds shah be operated in series during routine operation periods. (6) Organic loading. The organic loading on the stabilization ponds,
based on the total surface area oftile ponds. shah not exceed 35 poWlds of BOO, pet ac.e pet day. The loading an the initial stabilization pond shah not exceed "poWlds of BOO, per acre
per day. 
Texas "amra! Resource ConservJuon Commission Page 􀁾􀁩􀀠Chapler ) I 􀁾􀀠-Design Cnlena for Sewerage S'stems (,) Deplh. The srabili2anon ponds or cells shall have a normal water depth
of} to 5 feel. (8) Inlets and outlets. :vtultiple inlets and mUltiple outlets are required. The Inlets and outlets shaH be arranged to prevent sholt circuiting within the pond so that
the flow of wastewater is dlStnbuted evenly woughout the pond. Multiple !filets and outlets shall be spaced evenly. All outlets shall be baffled wilh removable baffles to prevent floating
material from being discharged. and shall be constructed so thaI the level of the pond surface may be varied under nonnal operating conditions. Submerged outlets shall be used to prevent
the discharge of algae. (9) Embankment Walls. The embankmenl walls should be compacted thoroughJy and compaction details shall be covered in the specifications. Soil used in the embankmenl
shall be free of foreign malerial such as paper, brush and fallen trees. The embankmenl walls shall have a lOp width of al leasl 10 feet Interior and exterior slope of the embankment
wall should be one fOOl vertical 10 three feel horizontal. There shall be a freeboan:! of not less than two feet nor more than three feet based on the normal operating depth. All embankment
walls shall be protected by planting grass or riprapping. Where embankment walls are subject to wave action, riprapping should be installed. Erosion stops and water seals shall be installed
on all piping penetrating the embankments. Provisions should be made to change the operating level of the pond so the pond surface can be raised or lowered at least six inches. (10)
Partially Mixed Aerated Lagoons. (A) Horsepower. With partially mixed aerated lagoons. 110 attempt is made to keep all pond solids in suspension. Mechanical or diffused aeration equipment
should be sized to provide a minimum of 1.6 pounds of oxygen per pound of BOO, applied with the largest unit Out of service. Where multiple ponds are used in series, the power input
input may be reduced as the influent BOD, to each pond decreases. Proposed oxygen transfer rales in excess of two pounds per horsepower-hour must be justified by actual performance data.
(8) Pond sizing. Partially mixed aerated lagoons should be sized in accordance with the formula in§311.4(i)(3) ofthis title (relating to Wastewater Treaunent Facilities) using K..o.2S.
Pond length to width ratios should be three to one or four to one. (C) Imperviousness. Requitements for imperviousness. multiple cells, embankment Walls. and inlets and outlets shall
be the same as for other secondiuy treatment ponds. (1::) Facultative lagoon (raw wastewater stabilization pond). (I)Configuralion. The length to width ratio of the lagoon should be
three to one, with flow along the length from inlets near one end to outlets at the opposite end (other configurations may be approved ifadequate means of prevention ofshort cil:cuiling
am provided). The length should be oriented in the direction of the preva1ling winds with the inlet inlet side located such that debris will be blown towan:! the inlet (generally, the
north-northwest side). Inlet baffles shall be provided to collect floatable material. The outlets shall be consuucted so that the water level of the lagoon may be varied under normal
operating conditions. Storm water drainage shall be prevented from entering the lagoon. The design engineer may wish to locate the facultative lagoon in a central location with regan:!
to the SIIlTOunding secondary ponds 10 facilitate 
Texas Natural Resoun:e Conser.auon CommISsIon Page -18 Chapter ll" -Design Cnteria for Sewerage Svstems oompliance \\ I(h the buffer zone reqUIrement specified in Chapter )09 of this
title (relanng to Domesuc Wastewater Effluent Limitations and Plant Siung). (2) Imperviousness. Requirements for imperviousness shaU be the same as those for seconda!y treatment ponds.
(3) Depth. The ponion of the lagoon near the inlets shaU have a 10 to 12 foot depth to provide sludge storage and anaerobic treatment. This deeper ponion should be approximately 25 pen:ent
of the area of the lagoon bottom. The remainder of the pond should have a depth of flve to eight feet 􀀨􀁾􀀩􀀠Organic loading. The organic loading, based on the surface area of the facultative
lagoon. shall not exceed 150 pounds of BOD, per acre per day. (5) Odor control. The facultative lagoon shall have multiple inlets and the inlets should be submerged approximately 24
inches below the water SUIface to minimize odor but not disturb the anaerobic zone. Capabilities for recilCuiation at SO % to 100 % of the design flow should be provided. Care should
be taken to avoid situations where siphoning oflagoon contents through submerged inlets can occur. (6) Embankment waUs. Refer to §317.4(j)(9) of this title (relating to Wastewater Treatment
Facilities). (7) Subsequent treaunent The facultative lagoon effluent will normally be routed to a wastewater stabilization pond system for secondary treatment In designing the stabiJization
pond system, it may be assumed that BOD removal in the facultative lagoon is SO 'Yo. The stabilization pond system shall contain two or more ponds. (I) Filtration. Filtration must be
employed as a unit operation to supplement suspended solids removal for those treatment facilities with tertiary effluent lintitations (suspended solids effluent quality equal to or
less than 10 mg/l). Filtration may be employed as a unit opemtion for those treatment facilities with secondary or advanced secondary effluent limilations. The utilization of filtmtion
filtmtion in the design of the treatment facility normally provides effective removal of suspended biological floc and neutral density trash material which may remain in secondary clarifier
effluent. lnterntittent filter operation is acceptable where on line controls monhor plain perfotlllllllCe or fibers;e not necessary to meet a specifIC discharge lintitation. (1) General.
requitl!ntents. (A) Fi1terunits shall be preceded by fmal clarifiers designed in accordance with §317 A(d) of this title (relating to Wastewater Treatment Facilities) for secondary treatment
criteria. (8) Filtered effluent. and not potable water, shall be utilized as the soUtCe of backwash water. (2) Deep bed, imerntittemly backwashcd granular media fillers. 
Texas :-hrur:ll Resowce Conservauon Commission Page -19 Chapter; I' DeSIgn Critena for Sewerage Systems tA) Single media (sand filters). dual media (Anthracite. sand filters). Or ml,.d
med,a flIter types tnon·suaufied anthracite. sand. garnet or other medial are acceptable for appiicauon: however. smgle media filters shall be designed for maximum fIluation runs of
six hours between backwash penods. (8) Design filtration rates shaD not exceed J gpmJftl for single media filters. -I gpmJft' for dual media filters. and 5 gpmJft' for mixed media fIlters.
The filter area required shall be calculated utilizing the above specified rates at the design flow of the facility. A minimum of tWO filter urulS shall be provided with the required
filter area calculated with one unit out of service. (C) Facilities to provide periodic treaunent utilizing chlorine or other suitable agents. introduced to the infIuem stream of the
filter units, shall be provided as an opetational technique to control slime growth on the filter surface and the backwash storage basin. (0) A graded gravel layer of a minimum of IS
inches or variable thickness of other fIlter media support material shall be provided over the filter underdlain system. Filter media support material other than gtavel will be reviewed
on a case-by-case basis. Normal media depths for the various mter types are as specified below. Media depths significamly different than these must be justified to the commission. The
justification must include an analysis of the backwash rates. Uniformity coefficiem shall be !.7 or less. The particle size distribution for du,al and mixed media filters shall result
in a hydtatilic gtading of material during backwash which will result in a filter bed with a pore space graded progressively coarse to fine from the top of the media to the supporting
layer. Effective Minimum Particle Filter Type Type of Media Depth (Inches) Size (nun) Single Media Sand 24 1.0·4.0 Automatic Backwash Sand 11 1.0·4.0 Dual Media Anthracite &: Sand 16
Anthracite 10 1.0·2.0 Sand 6 0.5·1.0 Mixed Media AntJuaciIe, Sand 16 &:Other AlJ1hraj;ite 10 1.0·2.0 Sand 4 0.6 ·0.8 Gamel or Similar 2 03·0.6 Material (E) The unil piping for the filter
units shall be designed to return backwash waste 10 upstream treaunenl units. In oilier to minimize a Ilydtaulic surge, a backwash tank must be included into !he design for those plants
that do not bave some means of flow equalization or surge control. A backwash tank shall be designed to provide storage for fllter backwash based upon the number ofdesign daily backwash
cvcles and me volume required for each backwash. Calculations must be provided to the commission demon· 􀁳􀁾􀁴􀁩􀁮􀁧that the performance of the plant will not diminish with !he discharging
ofthe backwash water into 
T.,as :-iarurai Resoun:e Cons<rvu!lon CommIssIon Page 50 Chapter 3!" -Design Cnteria for Sewemge Systems the treatment process. Enclosed backwash tanks shall be vented to maintain atmospheric
pressure. Surge control shall be pronded to the backwash system 10 limit flow rate vana!lons to no more than 15 % of the design flow of the treatment units that will receive the backwash
water. for these calculations an influent lift Sla!lon is not considered as a treatment unit and. therefore. is not bound by the IS % design flow requtrement (F) Pumps for backwashing
filter units shall be designed to deli;·er the required mte with the largest pump out of service. The backup pump urnt may be uninstalled provided that the commission is satisfied that
the spare unit can be quickly installed and placed into operatioll Valve arrangement for isolating a filter unit for backwashing shall provide ready access for the operator. Provision
for manual override shall be provided for any backwash system employing automatic control. control. (0) Head loss indicators shall be provided for all filter units. (H) Backwash for
dual or mixed media flIters shall provide a minimum bed expansion of 20 pelCenl A surface scour shall be provided prior to or during the backwash cycle. Backwash flow rates at 15 to
20 gpmlft' and at a cycle time of 10 to 15 minutes should he provided. The backwash cycte shall provide media fluidization at the end of the cycle to rematify the media Backwash for
single media filters should be provided by a surface air scour or combination air-water seour and washwater at recorrunended rates as foUows: Air Scour )-5 sefmlft' Water Scour 0.5 -2
gpmlft' Backwash Water 6-3 gpmlft' (I) The filter underdrain system shall be of a design adaptable to wastewater treatment, providing a uniform distribution of filter backwash and fn:edom
from excessive orifice plUgging. Wash water collection trough bottoms shall be located a minimum of six inches above the maximum elevations of the expanded media. A minimum freeboard
of tluee inches shall be provided in addition to the design upstream depth of the wash water media. A minimum fi1leboard of tluee inches shall be provided in addition to the design upstream
depth of the wash water trough 10 prevelll submerged trough conditions during fIlterbackwashing. (3) Mu1ti-compa:rtmellled low bead filters with colllinuous operation (automatic backwash).
This paragraph contains the design criteria for multi-compartmented low head fihers where the applicable criteria are dilJel1mt than those contained in paragraphs (I) and (2) of Ibis
section. AU other criteria included in paragrnphs (I) and (2) of Ibis section will apply to multicompan-mented low head fIltets with continuous operatiolL (A) Filtration rates. Filtration
rates shall not exceed 3 gpmlft' for single media . flltets and -I-gpmlft' for dual media filters based on the design flow rate applied 10 the filters. The total filter area should be
provided in two or more unilS and the filtration rate shall he calculated on the total available filter area with one cell of each unit olll ofservice. 􀁍􀁾􀁲􀀧􀁳reconuncnded rates should
be utilized if substantiated by test data. 
To,xas 􀁾􀁡􀁴􀀱􀁊􀁲􀁡􀁊􀀠Resource Conservauon Commission Page 51 Chapter 31' • Design Criteria for Sewemge S\ stems IB) Backwash. The backwash rate shall be adequate 10 fluidize and
e,'pand each media layer a muumum of 20 percent. ProvIsion should be made for an approximate rate of 10 gpmJft' over a 30 to 60 second intervaL Manufacrurer's recommended rates should
be utilized if substantiated bv test data Pumps for backwashing filter units shall be adequate to provide the required mte with the largest 􀁰􀁾􀁭􀁰􀀠out of sel'\'ice. It IS pellntssible
for the backup unit to be an uninstalled unil provided that the installed unit can be easily removed and replaced, Waste filter backwash water shall be rerurned to upstream units, preferably
the final clarifiers. for treatment. (C) Backwash surge control, The rate of return of waste filter backwash waler to treatment units shall be controlled such that the rate does not
exceed 15 % of the deSign flow of the treatment uruts. The hydraulic and organic load from waste waste backwash water shall be considered in the overall design of the treatment plant.
Where waste backwash water is renuned for lreallnent by pumping, adequate pumping capacity shall be provided with the largest unit out of service, [t is permiSSible for the backup unit
to be an uninstalled unit. provided that the installed unit can be easily removed and replaced, 􀀨􀁾􀀩􀀠Alternative design foreft1uent polishing. Where filters are proposed to remOve
retoaining visible panicles, other criteria will be considered on a case-by-<:ase basis, Adopted December II, 1995 Effective January 1. 1996 §3t7.5. Sludge Processing. (a) General requirements.
(I) Disposal requirements, agreement with. Sludge processing and treatment shall be in agreement with the requirements of the ultimate fonn of disposal. (2) Control ofsludge and supernatant
Volumes. Provisions shaU be made to insure that waste sludge will be discharged to the sludge digester in such a IIUUII1e1' so as to minimize the volume of digester supernatant liquor.
Provisions shall be made for the return of supernatant from sludge thickeners and digesters to the head of the treatm.ent wolks or to the aeIation system accoWlling for the im.pact on
the treatment units. (3) Piping. All piping from clarifiers to thickeners, digesters, or other sludge processing facilities shaU be ananged for ease of rnaintena:nce and with sufficient
hydraulic gntdient to insure the flow of sludge. Piping under stationaIy stnJCtUm shaU be arranged so that stoppages can be lUdily elirninaled by redding or with sewer cleaning devices.
The sludge piping within the digester. including the sludge drain line, shall be a minimum of fOUl illChes in diameter. Appropriate facilities for ttansfer ofsupernatant liquor shall
be provided. Piping shall include means to observe the quality of the supernatant from each ofthe withdmwal outlets provided. All units shaU be cap1lb1e ofbeing drained independently
of one another, (+) Sludge pumps. Selection of sludge ttansfer pumps shaU be based on both the quantity and character of the anticipated solids load to be handled by them. When: mechanical
pumps are used, a sufficient number ofpumps sllall be provided so that the design pumping capacity is lIVailable with the largest sludge pump out ofservice. Air lift pumps are an acceptable
mechanism for sludge ttansfer, Dupli
Te,as :-.'JruraJ Resou"e Conservauon CommISSion Page 52 Chapler ,1 1 -DeSign Crilena for Sewernge Systems cale deSign pumpmg capac It:)· IS not requIred when air lift pumps are used.
Pumps used for pumping sludge shall be 􀁳􀁰􀁥􀁣􀁾􀁬􀁣􀁡􀁊􀁬􀁹􀀠designed for that purpose. Cemnfugal sludge pumps shall have a positive suction head unless they are self-pnming or equipped
with some other priming deVIce acceptable to the commission. (5) Sludge stabilization. Sludge stabilization is required for all biological treatment processes with the excepuon ofextended
aeration processes (with a solids retention time 0[20 days or more) in which case the sludge may be drawn directly to a sludge dewatering facility. (6) Sizing. Sizing requiIemerus must
be determined using the BOD, and design flow of the raw sewage influent to the plant (b) Aerobic digestelS. (1) Sludge thickening. Aerobic digesters should be provided with sludge thickening
capability . (2) Aeration. Air supplied from air compressolS or blowelS through diffuselS shall be not less than 30 scfm per 1,000 cubic feet of aerobic digester volume. Ifa separate
system of air compressolS or blowers will supply air to the digester, then the compressor or blower system shall be designed so that the air requirements can he met with the largest
single unit out of service. Ifmechanical aeratolS are used. a minimum of 1.5 horsepower per 1000 cubic feet must be provided. (3) Mixing. Adequate mixing of the sludge shall be provided
to keep the solids in suspension and to bring the deoxygenated liquid conlinuously to the aeration device. The amoum of mixing shall be based upon the sludge characteristics, the tank.
geomeay and type of aemtion/mixing devices. (-l-) Volume. A digester shall provide a minimum sludge retention time of 15 days. The design volume of the aerobic digestets may be cak:ulaled
using 20 cubic feet per lb BOD, per day. This volume should be provided in two cells capable of operating as a single or two-step unit. (5) Sludge withdrawal. Provisioll5 shall be made
to include an effective means of removing solids from the digester. (c) Anaerobic digesters. (I) Volume. The following minimum design criteria shall be used in computing the capacity
of digesters with and without facilities for heating the sludge undergoing digestion and without sludge thickening ahead ofthe digester. VariaDces to the below-referenced table for minimum
digester volume may he granted provided that it can be demoll5ttated to the satisfaction ofthe commission that a minimum solids retention time (SRn of 30 days will be provided for urtheated
digesters and a minimum SRT of 15 days will be provided for heated digesters. Heating of the digester means that adequate facilities shall be provided for heating and mixing the sludge
and maintaining a year-round temperature of at least 95 degrees F. Heating coils inside the digester are not acceplable. All heated digesters shall include a thermometer with not less
than a four inch dial to indicate the temperature ofdigester conteuts. The use of ftat-bottomed digestion chambelS is not acceptable. In sewage treatment plan15 employing sludge thickeners,
the volutne ofthe 
Texas 'iaruraJ Resoun:e Conservauon CommISSion Page 53 Chapler ); 1. DesIgn Cntena for Sewerage Svslems dlgesler mav be reduced. wuh suificiemjuslIIication. as a result of the thickeners
reducing the volume of sludge going to the digester. The calculations for the required sludge digesUon "olume shall be based on the mlrumum percent solids in the sludge expecled to be
encountered. Type of Sludge Cubic Feet Per Pound 80D, perda)' Unhealed Digester Heated Digester Sludge from primary clarifiers Sludge from primary clarifiers. including Imhoff tanks.
plus sludge from clarifiers following trickling filters; sludge from chemical precipitation units, either alone or with sludge from biological treatment unit 205 26.5 14.5 19.0 Sludge
from primary clarifiers with waste activated sludge or contact stabilization sludge; sludge from secondary clarifiers 4•.0 29.S (2) Mixing. Adequate mixing of digester contents is reqnired
for all first-stage and all single·stage digesters. Mixing may be performed by mechanical equipment, including external pumps, or by gas recirculatiolt The rate of mixing shall be such
that the flow created in the digester is sufficient to completely nux the incoming sludge with the digester contentS and plllVent the formation of a scum layer. (3) Digester cover.1.
Uncovered anaerobic digesters are not acceptable. The sludge and supernatant withdrawal piping for all single-stage and flrst-stage digesters with fIXed covers shall be ananged In such
a manner so as to minimize the possibility of air being drawn into the gas chamber above the liquid in the digester. All digester covers shall include a gas chamber adequate for the
gas production anticipated. Digester covers shall be gas tight and the specifteations shall require a test of every digester cover for gas leakage. (4) Gas piping and safety equipment.
The gas piping shall be adequalll for the volume of gas to be handled and shall be pressure tested for leakage (at I.S times the design pressure) before the digester is placed into opemion.
All gas piping shall slope at least 118 InCh per foot to provide drainage of coudensation in the gas piping. The maln gas line from the digester shall have a sediment nap equipped with
a drip nap. Drip naps shall be provided at all other low points in gas piping. The gas piping to every gas outlet including the pilot linc to the waste gas burner shall be eqnipped with
flame checks or flame naps. A nanlfal or bottled gas sourte shall be utilized for the burner pilot Flame naps with fusible Shutoffs shall be included in all maln gas lines. The gas line
to the waste gas burner shall inelude a suitable pressure, vacuum and relief valve. Digester covers shall be equipped with an air vent which includes a flame nap, a vacuwn breaker, and
pressure relief valve. The maln gas line shall be provided with a manometer or other acceptable device which nteasttres the gas pressure in inches of water. Manometers may be used to
measure the gas pressure in other gas lines. AU manometers shall be vented to the atmosphere outside digester buildings. A gas meter to measure the rate of gas production is desirable
and is mandatoty on all anaerobic digester sys
Texas Satma! ResolUte Conservation CommISsion Page 􀀵􀁾􀀠Chapler ) 17 • DeSign Cntena for Sewerage Systems lems desIgned for 1.0 :>tGD fac!lities or larger. Ail rooms in digester bu!ldings
wllh floor level below grade shail be venulated. Ventilation may be ellller continuous or intermIttent. Ventilation. ifcontinuous. shall provide at least sL" complete air changes per
hour. if intermillenL at least 30 complete air changes per hour. (5) Other requirements. The discharge end of sludge inlet piping shaU be separated from the overflow of the supemalantliquor
withdrawal point by a minimum distance equal to the radius of the digester tank. Every digester shall be provided with an o,·erflow. A means shall be provided by which the level can
be varied from which supemalant liquor is withdrawn either automatically or by the operator. {fthis means is by withdrawal pipes at different levels in the digester, at least three different
levels of supernalant liquor withdrawal shall be provided. All supernalant liquor withdrawal systems shall be provided with sampling cocks or other means of inspecting and testing the
supemalant liquor tmm each level Piping for hot water heating systems may be of any size adequate for the flow. The fresh water supply to hot water heating Systems shall be tmm a tank
with an air gap between the lOP of the tank and the fresh water supply pipe to prevent a cross connection between the digester hot water system and the fresh water supply system. (6)
Treatment of digester supematant liquor, Supemalalll liquor from anaerobic digeste.. may be treated by chemical means or other acceptable methods before being rel11nled to tile plant
Ifthe commonly used method of dosing with lime is employed, the following criteria shall apply: Lime shall be applied to obtain a pH of I I .5. The lime feeder shall be capable of feeding
2,000 mgll of hydrated lime or its equivalent. The lime shall be mixed with the supernatant liquor by a mpid mixer or by agitation with air in a mixing chamber. After adequate mixing,
the solids shall be allowed to settle. The supemalant liquor treatment system may be a batch or continuous process. Ifa batch process is used, tile mixing and settling may be in the
same tank The sedimentation tank shall have a capacity to hold 36 hou.. of supernatant liquor but nolless than 1.5. gallons per capita. Ifa continuous process is used, the sedimenlation
tank shall have a detention ume of not less than eight hou... Solids settled from the supernalant liquor treatment are to be returned to the digester or conveyed 10 sludge handling facilities,
The cla.tified supernatant liquor shall be returned 10 the head ofthe treatment works or 10 the aeration system. (d) Other stabilization processes. (I) Incincl3lion and beat treatment.
The equipment shall be housed in a fueproofbuilding. Adequate facilities shall be provided for storage of sludge during the longest period that drying and/or incinemtion uni1s might
nonnall:y be oUl of service fur repaiIs or maintenance. Plans for control of odors, insects, fly ash, and for adequate facilities for the disposal of dried sludge or ash shall be provided
to the commission. Prior to collSUUCtion ofan incincmtion or hca:I tmWnent facility, consultation should be made to the Texas Air Conuol Boam fur applicable emission SWIdards and the
possible requilemem for a separate Texas Air Control Boam permit. (2) Composting, wet oxidation and otberprocesses. Design information given to tile commission shall include the demonstrared
level ofstabilizarion achieved by the process to be employed. Test 􀁾􀁕􀁉􀁴􀁓􀀠to verify the degree of stabilization may be requiIed. In addition, design infonnation shall adctIess design
and/or opetational methods to minimize odor, insects and other nuisance conditions. Sludge storage requirements for each process shall be provided to the commission. Also, tile ultimate
disposal method for the processed sludge shall be reflected in the waste disposal application. 
Texas N:uum.i Resource Conser\,':lUO[l ComrmsslOn Page 55 Chapter 3," • Design Critena for Sewerage Systems Ie) Sludge dewatering facilities. Sludge strall be dewaten:d sufficient!;·
to meet the n:qUlremenrs of the ultimate ronn of disposal. ( I) Sludge drying beds. (Al Required area: The area of sludge drying beds to be provided will vary in accordance with the
average rainfall. average humidity. and type of treatment process used. The required area for aerobic sludge dewatering strall be determined from §317. 12 of this title (relating to
Appendix DJ (for anaerobic sludge dewatering, the value obtained from §317. 12 may be reduced 35 % to determine the required area) using a waste load based on sewage strength and the
daily average flow of the IllW sewage. The bed area Sizing requirements shown in §317. 12 of this title (relating to Appendix D) are for sludge drying beds utilizing a continuous underdrain
media as specified in subsection (E) of this section Concrete (or similar impervious material) sludge drying beds which do not use an underdrain media may require additional area and
will be evaluated on a case-by<ase basis; however. in those counties of the State which e"'perience both high rainfall and high relative humidity (Brazoria, Chambers. Fon BeneL Galveston,
Hardin, Harris. Jasper. Jefferson, Liberry, Newton, and Orange), other methods of sludge dewatering shoWd be utilized in lieu ofsludge drying beds. Where sludge drying beds are used
in those counties of high rainfall and humidity, provisiOns shall be made in the design ofthese beds for covering the beds, for means of accelerated dewatering, or for extta storage
capacity and alternate dewatering methods to effectively dewater the sludge dtumg inclement weather. (B) General design features. At least two sludge drying beds shall be provided and
they shall be COllSU"Ucted atelevations above groundwater level Construction shall be such as to exclude surface water runoff from the beds and seepage from the beds into the ground, Channels shall be of sufficient
grade and size to facilitate the flow of the sludge to the various beds. Runners should be provided to facilitate sludge handling. (C) Filtrale. The filtrate (or dminage) from the sludge
drying beds shall be returned to the head of the treatment wodls orto the aellltion system. (0) Sludge mnoval. A splash block or slab shall be provided at the point where digested sludge
is discharged onto each of the beds. Appropriate means shall be provided to facilitate the removal of the dried sludge from the beds for disposal without bed damage resulting. Evety
sludge drying bed should include a removal 􀁧􀁾or stop plallks in one end to provide a;cess for machinety and trucks to remOve and haul away the dried sludge. (E) Media A minimum depth
of 12 inches offiltering material, of which four to six inches is coarse sand, is required. To eKClude SUlfuce water and eroded eanh, the bed shall be protected by a permanent wall which
shall elClend at least 12 inches but not more than 24 inches above the finished surface of the beds .. (2) Vacuum miers, belt filters, belt mterpresses, and other mechanical dewatering
mters. 
Texas 􀁾􀁊􀁭􀁭􀁬􀀠Resou",e Conser\'Ouon CommIssIon Page 56 Chapter .' 17 . DesIgn Crilena for Sewerage Sl"stems (A) Multiple units. Where dewatenng of sludge is proposed. the desIgn
engineer ,hall provide data to document sufficIent capacity. alternate disposal means or storage facilities capable of maintaIning normal daJl,· operations during breakdowns. upsets.
etC, (B) Filuate, The filuate from the filters shaO be returned to the head of the U'eaunem works or to the aeration system, Consideration shan be given to the impact of the returned
filtrate on the U'eaunem units and to providing odor and insect control facilities, (3) Portable dewatering units. [f sludge is to be treated using portable mechanical dewatering units,
proviSiOns shail be made in the facility plan or preliminaly engineering report for the location and connection of the portable dewatering unites) during facility operation. §JI7.o.
Disinfection. (a) General policy, Facilities for disinfection shall be provided to proteCt the public health and as an aid to plant operation. (b) Chlorination facilities. ( I) Chlorination
equipment. Chlorination equipment shall be selected and installed which is capable of applying desired amounts of chlorine continuously to the effluent Chlorination equipment may also
be lIlStalled to control odors and generally assist tlealmeltt. To accomplish these objectives, points of chlorine application may be established 31 the head of the planJ: for prechlorination,
in the effluem chlorine comaC! chamber or other suitable locations. (A) Capacity. Chlorination equipmem shall have a capacity greater than the highest expected dosage to be applied.
Chlorination systems shall be capable of operating uuder all design hydraulic couditiollS. Duplicate equipment with automatic switch over should be considered for standby service, so
that continuous chlorination can be provided. (8) Controls. Means for automatic proportioning of the chlorine amoum to be applied in accordanl:e with the !lite ofeffluent being ueated
is encouraged encouraged for all plants and may be requin:d ifa maximum chlorine residual is requiRd in the applicable discharge permit Manual control will be permi<ted when: the rate
of eflluent flow is mlatively constam and for p!1:-chlorination applications. Consideration shall also be given to controlling chlorine feed by use of demand. (C) Measurements. A scale
for determining the amoum ofcblorine used daily. as weO as the amoum ofchlorine n:maining in the comaiDer, shall be provided. (D) Safety equipmem. Self contained breathing appllJ:3lUS
shall be available for use by plum personrtet The equipment should be located at a safe distance from the chlorine facilities to insure accessibility. Self-contained breathing appamnts
shall be located outside the emrance to the chlorine facility. (E) Housing. Housing of chlorination equipment and cyliuders ofchlorine shan be in separate rooms above grouud level, with
the door opening to the outside, as a measwe of safety, Doors 
Texas Sa!Unl Resource ConseI>aUon CommissIOn Page 51 Chapler 31' -Design Cnlena for Sewerage Svslems should be equipped wllh panic hardware. The chlorinauon room should be separated
from other moms b,· gas tight paruuons and should be equIpped with a clear glass. gas-tight window which pennlts the chlonnalor to be "iewed without entering the room. Forced mechanical
'·enlilation shall be included in chlorination rooms which WIll pronde a complete air change a mirumum of every three minutes. The exhaust equIpment should be automatically activated
by e.\lemallight switches and gas detectors that are pronded WIth comact dosures or relays. No other equipmem shall be installed or stored in the chlorinator mom. Vents from chlorinators.
vaporizers. and pressure reducing values should be piped to the outdoors at a pOint not frequented by personnel. nor near a fresh air intake. Detectors and alarms should be located in
each area contairung chlorine gas under pressure. Ifgas withdrawal chlorine storage cylinders are subjected [0 direct sun. pressure reducing devices must be provided at the cylinders.
Fire 􀁰􀁲􀁯􀁾􀁯􀁮devices and fireproof construction is required for all chlorine storage areas. Electrical controls in chlorine facilities must be replaceable or protected against corrosion.
Separate, trapless floor drains or a drain to an ample dilution poim shall be provided from the chlorine storage mom and from liquid feed chlorinator rooms. (F) Emergency chlorination.
Emergency power should be provided for chlorinalian facilities. (G) Other. Chlorine rooms shall maintain a minimum temperature of 65 degrees F. Chlorinate solution should be prepared
using treated efiluent Ifpotable water is used, the potable water supply system must be pro!el:ted by an adequate bacldlow prevention device. When a booster pump is required, duplicate
equipment should be provided. (2) Pellets. The use of pellet systems will be considered for approval on a case-by-case basis. (3) Chlorine conta<;t cbamber design criteria (A) Initial
mixing. Rapid initial mixing of the chlorine solution and wastewater is essential for effective disinfection. Effective initial mixing can be accomplished by applying the chlorine solution
in a highly turbulent flow regime created by in-linc diffusers, submerged hydraulic structures, mechanical mi.'«!rs or jet mixers. The mean velocity grndi.ent in the aIea of turbulent
flow, or G value. shall exceed SOO sec.-I withmidence times oftlnee to IS seconds. Calculalians supporting the design G value shall be presented in the engineering report Mixing devices
for which the mean velocity gradient is difficult to verify shall be justified by pilot or full-scale pelfonnaru:e data. (B) Contact time. Contact cbambers shall be designed to provide
a minimum average hydraulic residence time (chamber volume divided by flow) of 20 minutes at the design peak hydraulic flow. (C) Contact chamber confIgUration. Pipe contact chambers
shall be sized so !hat a scour velocity ofat least one foot per second will be obtained at the ex:isting maximwn daily dIy weather flow rate. Ifadequate initial mixing is not provided,
contact chambers shall bave a flow pathway length-to-width ratio of at least 40 and a maximum depth-to-width ratio of no gIeatef than 1.0. This length·to.width ralia may be accomplished
by balIling. 
Te.,"s :-iarural ResQun:e Conservauon CommiSSIon Page 58 Chapter II '/. Design Cmena for Sewe"'ge S\ stems ID) Sludge and scum ",mo\·al. Contact chambers shall either be prol'lded with
a means to ",mol'e sludge and scum. such as a small hydraulic dr<:dge and skimmers. wlthoUllaking the ContaCI lank out of serVIce. or shaH be configured so that one·half of the conlact
chamber can be dramed for cleaning without interrupting flow through the olher half. ,., Other means of disinfection. (I) Chemical disinfection is not normally required when the total
residence time in the wastewater treatment system (based on design flow) is at least 11 days. (2) Ultraviolet light N.Y.) disinfection. (A) General. Ultraviolet disinfection systems
are considered applicable to treated wastewaters with daily average BOD, and TSS concentrations consistently less than 20 mg/1. (8) Definitions: (i) Ultraviolet Module -A grouping of
UV gennicidallamps af a specified arc length in a quartz or teflon sleeve, sealed and supported in a single stainless steel or some other noncorrosive frame. (ii) Ultraviolet Bank -A
grouping of UV modules which span the entire width and depth (of flow) of the reactor. (C) Sizing, configuration and required dosage. Ultraviolet disinfection units will be designed
ill accordance with methodologies presented in the U.S. Environmental Protection Agency Design Manual, Municipal Disinfection, EPAJ62S/1-86102L TUIbu1ell1 flow is necessaIy due to non-unifonn
intensity fields in an ultraviolet reactor. Proposed design shall have a Reynolds' number of gIe3ter than 6,000 at average design flows. Disinfection systems shall consist of a minimum
of two ultraviolet banks in series and shall be capable of providing disinfection to penniued fecal colifonn levels at the design daily average flow with the largest bank out ofservice.
(0) System details. The ultraviolet unit shall be confIgnred so that there is adequate space tbr the removal and JIIlIiJ:IIenanI of lamps. One pemm should be able to replace lamps without
the aid of of mechanical lifting devices, special tools or equipment. Drains shall be provided to completely drain the u1:traviolet reactor unless the equiprnelll can be easily removed
from the eff1uelll 􀁣􀁨􀁡􀁮􀁮􀁥􀁾􀀠but lamps shall be replaceable without draining the unil The material$ used to construCt the reactor shall be resistant to uIl!aviolet light. Ballasts
and other electrical components shall be cOnsistelll with the ultraviolet lamp manufacturers recommendations. Temporary screens shall be installed to protect the lamps and other fmgile
componenlS from construCtion debris, (E) Conlrols. Each individual uIl!aviolet lamp shall be provided with a remote operation indicator. Lamp failure alarms shall also be provided for
a pre-determined number of lamp failures. Techniques that result in non-irradiated flow pathways are prohibited. Each ultraviolet bank shall be equipped with at least one uIl!aviolet
intensity meter or some means to monitor changes in ultraviolet 
Texas 'iaMal Resoulte Conservauon Commission Page 59 Chapter' 17 • Design Cntena for Sewerage 5, stems dosage: ho,'ever. imenslty meters shall not be relied upon to automatically control
system operation. A flow control dence. such as an autOmauc level control. shall be prO"ided to ensure that the lamps are submerged in the effluent at all times regardless of flow rate.
The automatic level control shall be arranged so that it w,II allow suspended soltds. which may serue. to be washed out of the area of UV disinfecuon. Proper beaung and "enntation are
critical to ultraviolet system operation. Cabinets containtng ballasts andlor transformers shaU be provided With positive filtered air "enlilation and automatic sbutdown/alarms at high
temperatures. Provisions shall also be made to maintain the ultraviolet lamps at or near their optimum operating temperature and to filter velUllating air so as to linlil ultraviolet
light absoroance by dust accumulations. Elapsed operation time meters shall be provided for each bank of ultraviolet lamps. (F) Cleaning. Provisions for routirte cleaning such as mechanical
wipen;, high pressure sprayers, ultrasonic transducers or chemical cleaning agems are required. Quam sleeve ultraviolet systems shall have a chenlicaJ cleaning capability in addition
to any ultrasonic andlor mechanical wiper systems. Cleaning solution mIl( and storage tanks shall have a volume of at least 125 percent of the reactor volume 10 be cleaned. A spem cleanmg
solution disposal plan shall be included in the engineering report (G) Safety. Operators shall be protected from exposure to u1travioletlignl during normal opemtions. (H) Replacement
parts. Replacement pan provisions shall be based on: (i) the following table which summarizes minimum requirements as a percentage of the total provided in the ultraviolet system; or
(il) a minimum of one uninstaIIed spare module. Pan Description Minimum Percent of Total Lamps 10 Ballast 5 EncloSlml Tubes 5 Modules· 2 • (excluding lamps and enclosure tubes) (3) Disinfection
Disinfection techniques oot in widespread use, such as ozonation, bromine chloride, and chlorine dioxide, will be considered for approval on a case-by-case basis. Full details of application,
opemtion, and maintenanCe, and results of pilot and developmental studies, shall be furnished to the commission by the design engineer for each proposal §317,7. Safety. (a) General policy.
Design of facilities should follow gttidelines establislled under 29 cm Parts 1901.I (OSHA) and other regulatory authorities. 
Texas 􀁾􀁡􀁲􀁵􀁲􀁡􀁬􀀠Resource Consel'auon CommiSSion Page 60 Chapter 317 -Design Cntena for Sewerage Svstems Ib) Ralltngs and Stall',a),s. Rauings should conform with gUidelines contamed
in the Occupational Safer), and Health ACI. Parngrnph 19[0.23. Operungs in railings must have removable chams. Open "alve boxes and PIts must be guarded by railings. Refer to 2317.4(3)(7)
ofthis utle (relallng 10 Wastewater Treatment facIlities) for additional requirements. Steep and vertical ladders are acceptable for Infrequent access to equipment Walkways and steps
must have a nonslip finish. Ladders must have flat safety tread rungs and extensions at least one (I) foot out of a vault Seven feet of c1eamnce shall be provided for overhead piping
unless piping is padded to prevent head injury and warning signs are prOVIded. (c) Electrical code. Electrical design shall confOIm to local electrical codes. Where there are no local
electrical codes. the design shaU confOIm 10 tile National Electrical Code. Where a flammable gas may exis!. aU electrical equipment shall confOIm to the requirements of the National
Electrical Code, Chapter S. Articles 500 through SlO, "Hazardous Locations." The equipment shall beauhe seal of tile Underwriler Laboratories, Inc. or comply with the National Electrical
Code. Adequate lighting must be provided, especiaUy in areas to be serviced by personnel on duly during hours ofdalkness. (d) Unsafe water. When non-potable water is made avaUable to
any pan of the plan!. aU yard hydrants and outlets shall be property marked "Unsafe W-.r," and aU underground and exposed piping shall be identified as specified in subsection (g) of
this section. (e) Plant protection. The plant area shall be completely fenced and have lockable gates at aU access points. Plants containing open clarifiers. aeration basins and other
open tanks. shall be SUIl'Ounded by an eight-foot fence with a minimum single apron baWed wile outrigger. Livestock fence may be provided in lieu of an eight-fout fence for stabilization
ponds. lagoons, overland flow plots, and similar facilities. Hazard signs stating "Danger -Open Tanks -No Trespassing" must be secured to the fence, within visible sighting of each other,
as weU as on aU gates and levees, Plants shall have at least one aU-weather access road WIth the driving surface siruated above the IOO-yr. flood plain or be provided by an alternate
method of access approved by the commission. (I) Other safety equipment. The plant as a whole, and hazanlous areas in particular, shall be posted in accordance with the Hazardous Communication
Act. (g) Color coding of piping. All piping both exposed and to be buried or located out of view, containing gas, chlorine or other bazartlous materials shall be color coded. Other piping
should be color coded. AIlIIOn-metaUic undcri!round plant piping should be installed with tracer 1ype. The non-potable waterline should also be ideDlified with a proper color coding.
This line shall be painted white and be stenciled "NON.pQT ABLE WATER" or "UNSAFE WATER". The following coding is recommended by the Water Pollulion Control FedeJation. Sludge Line Brown
Gas Line Red Potable Water Line Blue Chlorine Line YeDow Sewage Line Grey Compressed Air Line Green Heating Water Lines Blue with 6" red bands spaced 30" apart 
Texas 􀁾􀁡􀁴􀁵􀁲􀁡􀁬􀀠Resou",e Conservauon CommissIOn Page 61 Chapter 317 • Design Cntena for Sewerage S'stems Power Conduit Orange (h) Portable ventilators and gas detection equipment.
Portable gasoline operated ventilators must be provided for ventilating manholes. Personal gas detecto rs are .required for wear by all personnel whose Jobs require emenng enclosed spaces
capable of having accumulations of hydrogen sulfide or other harmful gases. An approved personnel retrieval system should be provided for continued space enuy. (I) Potable water. Potable
water should be provided to the plant site. Double check backflow pleventers mUSt be proVIded at the main plant service. Atmospheric vacuum breakers are required at aU potable water
washdown hoses. (j) Freeze protection. AU surfaces subject to freezing shall be adequately sloped to prevent standing water. (k) Noise levels Noise levels in aU working areas shall be
kept below standards established by the Occupational Safety and Health Act Removable noise anenuators should not be utilized. (I) Safety training. Regular safety training shall be provided
to all employees. §317.1I. Design ADd Operation Features. (a) LaboratOlY control. (I) Facilities. Laboratory capability for operational control and testing shall be provided. The laboratory
should be located on ground level and easily accessible to the treatment plant and sampling points. The laboratory should be located away from vibraling macbinery or equipment which
could have an adverse effect on the pelfonnance of the operation of Iabol'lllory instruments. The extent of the equipment to be provided and the specific tests to be pelfonned will vary
according to capacity and type of plant As a minimum, provisions should be made at all plams so that chemicals and equipment are available for pelforming sucn on-site tests as setlleable
solids (Imhoff cone), 30-minute settleability, dissolved oxygen, pH, and chlorine residual For plams with a design flow of 1.0 mgd to 5.0 mgd, equipment shall also be provided to detennine
suspended solids concentration. All plams with design flows in excess of 5.0 mgd shall have access to fac:ilities to provide aU pennit Iequired compliance monitoring, plus volatile suspended
solids, nitrogen series, and alkalinity determinations (if anaerobic sludge digestion is used). Alternately, such tests may be perfOlD\ed undercontract with other Iabol'lllories. Special
consideration. for treatment plants 10. cated in remote or vandal prone areas, may be given by the commission to methods for storing chemicals and analytical equipment at an off-site
location. Provisions aball be made in aU cases to provide for the requirements of the commission Self-Reporting System procedures and for proper monitoring ofsignificant industrial connections.
These requirements are minimum requirements only; additional provisions may be needed to insure optimum plant operations. Raw waste char.tcterization sbawd be provided for aU facilities
with a design flow in excess of S.O mgd and for aU facilities anticipating a plant e.'qlaIIsion. (2) Air conditioning. AlilaboratDries shall be air conditioned and heated 10 maintain
a constant temperarure. 
Tex;)s Natur:ll Resourt:e Conservauon Comm'ss,on Poge 62 Chapter) 􀁬􀁾􀂷􀀠Design Criteria for Sewemge Systems ,b) Office and tollet faciliues. Hand washing facilines should be provided
for the protection of opemting personnel. Office. showers, tOIlets, heating. proper lighting and ,'enulauon shall be provIded where opemlors are to be stationed at the plant for opemting
stufts, The needs of male and female employees, the handicapped and VIsitors to the plant should be considered in the design of sanitaty facilities, (cJ Tool shed and work. shop, Appropriate
facilities should be pro"ided for me storage of tools and spare pans, and a work. shop should be proVIded to allow repairs and maintenance, (d) Landscaping and beautification. Upon completion
oCme tn;annent planl. the grounds shOuld be properly graded for swfac. draJnage, Asphalt. conCIete, gravel or sheU walkways should be provided for access to a1llrearment units and to
the final sampling point Where possible. steep slopes should be avoided to prevent erosion. Swface waler shall not be allowed to drain into any unit Particular care shall be taken to
protect trickling filter beds, sludge dtying beds. and intermittent sand filters from storm waler runoff, Provision should be made for landscaping and planl site beautification. particularly
when a plant is visible to the public. §317.9. Appendix A. The following map establishes the maximum 24-hour rainfall at a two-year frequency, 
To,as ,<arural Resource Conservauon CommISsIon Page 63 Chapter J \7 • DesIgn Criteria for Sewerage S,·stems lnsen AppendIx .-\. :>Iap Here 
Texas Satur.ll Resource Conservauon CommIssIon Page 6 .. Chapter) I" . DeSIgn (mena for Sewerage Systems §J\7.1O. Appendix B -O,erland flow process. The overland flow process is the
application of wastewater along the upper portion of uniformly sloped and gross covered land and allowing ilto flow in a thin sheel over the vegetated surface to runoff collecllon ditches.
The pnmary objective of this process is treaunent of wastewater. Utilization of this process does result In a dischaIge and therefore a waste discharge permit from the Texas Water Commission
is required. This process is best utilized on soils with low permeability. The performance of the overland flow process is dependent on the detention time of the wastewater on the vegetated
sloped area. Therefore. in order to meet a specified effluent criteria. the hydraulic loading rale. the application rate and the effectiveness of the distribution system are essential
design considerations. For detailed process design guidance. the latest edition of the the Environmental Protection Agency Technology Transfer Process Design Manual for Land Treaunent
of Municipal Wastewater may be used. (I) Hydraulic loading rate. The hydraulic loading rate and applicAtion rate can vary depending on levels of pretreaunent. quality of effluent. temperature
and other climatic conditions. A hydraulic loading rale of U to 2.0 inches per day and an application rate of 6 to 8 gallons per hour per foot ofslope width are suggested as general
guides. The design rates selected and their justification shaH be submitted in the design repon. (2) Wastewater storage. Storage capacity for inclement wealherconditions shall be provided.
To mirumize the impact ofalgae on the treatment perfotmallCe, this storage shall be designed as an off-line basin. used only as needed and emptied as soon as possible by blending with
other pretreated wastewater prior to application. To control OdolS, provisions for aeration in the storage basin sbould be considered. (3) Soil testing. For the overland flow process,
the soil profile evaluation sbould extend to a depth ofat least three (3) feet The soil sampling and testing specified in subsection (b) of this section shall be representative of the
soil to this dep1b. (4) Other design considerations. (A) The overland flow process treatment ;uea shall be subject to the same buffer zone requiJ:ement as a treatmeDl plant. (B) The
minimum slope length for the applied wasteWater shaH be 100 feet (C) The sloped areas to receive wastewater shall be unifonnly graded to eliminate wastewater ponding and soon cilt:uiting
for the length of the flow. Site gr.Iding proceduIes and tolerances shaH be included in the specifications. Minimum slopes shall equal or exceed 2 peltent; maximum slope shall not exceed
8 percent The application site shall be protected from flooding. (0) The application cycle should provide a ma:'Iimum of ten hours for dosing followed by a minimum period of 14 oours
ofresting. (E) The method of application shall provide unifonn coverage of the area. 
Texas !'<alurai Resoun:e Conser,cauon CommISSIon Page 65 Chapter 317 • DesIgn Cnlena for Sewerage Systems (F) A vegetauve co"er shall be provIded on the applicauon sUe. The plantlypes
selected shall be sUllable for o\'erland now conditions and shall proVIde urufonn coverage of soil 10 prevent short circuiting and channeilzauon of the area. (0) Waslewater quality and
disinfection requirements forovertand flow process discharges will be established by the discltarge permit (H) Aneffiuent sampling station shall be provided prior to discharge to surface
waters. The sampling and neporting requ!l'ements will be established by the discharge permit §317.1l. Appendix C· Hyacinth Basins. (a) introduction. (I) Purpose, Hyacintha may be used
for the removal of suspended solids from secondary effiuent Other proposed treatment applications. however, are not excluded by these criteria, and such proposals will be reviewed on
a case-by-<:ase basis. (2) Other permits, The authority to use hyacintha is contingent upon obtaining a possession permit from the Texas Parl:s and Wildlife Department. (3) Location.
Uncovered hyacinth basins will be approved only in Cameron, Hidalgo. Kenedy and WiUacy counties, Hyacinth basins elsewhere shall be covered with a greenhouse structure. A variance will
be considered for systems which are designed for seasonal operation. Greenhouse design shall provide for adequate dike top width for equipment maneuverability, doors for personnel and
equipment access. and openings for ventilation. (b) Design. (I) MUltiple basins. Multiple basins shall be provided. Capacity to treat the design flow with one basin out of selVice shall
be provided. A variance may be considered for systems which are designed for seasonal operation. Average water depth ofbasin shall not exceed 36 inches. (2) Basin sizing and configuration.
Multiple surface inlets and outlets shall distribute flow unifonnly through the basin. This may be accomplished by a weir. openings in a baffle. by a perforated pipe. or other methods.
Basins ofone acre or less in size are required. The bottom of the hyacinth basin shall be sloped to facilitate draining. A surge basin or some other method offlow equalization to achieve
a more constant rate of inflow 10 the basin is desirable. (3) Barrier. A fixed bamer creating a clear zone shall be installed at the outlet to prevent the discharge of hyacintha or hyacinth
seed. While screening may be used as a bamer material., a permeable rock bamer is preferred. Water depth within the outlet area shall not be more than 24 inches with the bottom covered
by a layer of broken rock or washed gravel 
Texas NaMa! Resour<:e Conservauon CommISsion Page 66 Chapler 3 I 7 • Design C mena for Sewerage Systems I􀁾I Loading< Organic loading of hYacinth basins shall no! exceed 100 Ibs/acrelda,<
of BOD, unless supplemental aerauon is provided to consistently maintain an aerobic surface water layer< The maximum hydraulic loading shall not exceed 0<20 mgdlacre< (5) Narural aerators
and mosquito control. Exclosures shall be placed at intervals along basm edges to provide clear zones for aeration and to enhance fish production for mosquito contrOl. Total area of
exclosures should be approximately 20 % of total basin area< 􀁅􀀮􀁾􀁤􀁯􀁳􀁵􀁲􀁥􀁳􀀠shall have a uniform depth of not more than H inches. with bottoms lined with broken rock or washed
gravel. Plastic sheeting covered with a layer of broken rock or washed gravel, extending above and below operating water level, shall be placed all along inner basin berms to prevent
weed growth and eliminate mosquito breeding habitat (c) Operation< (I) Harvesting. Adequate provisions for access, removal. and disposal of the hyacinth plants shall be provided. Removal
shall be done mechanically. (2) Cleaning. Each basin shall be cleaned once each year by dewatering and removing plants and sludge. (3) Coverage. Plant coverage shall be limited to 9O"A.
of the basin area. §317.12. Appendix D. The following map establishes the required area for slndge drying beds with aerobic sludges< For aerobic sludges. the value obtained from the
map maybe reduced by 35%. 
Texas NarurJI Resall!!:e Conservation CommIssIon Page 67 Chapter} l-: -Design Crilena for Sewerage Systems [nsert AppendIx D Map Here. 
Texas ,<alUra! Resource Conservauon CommIssIonPage 68 Chapler ; 􀁉􀁾􀀧􀀠. DeSIgn Cmena for Sewerage Svslems §317.13. Appendix E -Separation Distances. The following rules apply 10 separation distances be"'een potable waler and waS(ewaler
trealment plants. and walerlines and sarutary sewers. (a) Water line/new sewer line separation. When new sanitary sewers are installed, the. shall be installed no closer to walerlines
than nine feet in all directions. Sewers that parallel waterlines must be installed in separate trenches. Where the nine foot separation distance cannot be achieved, the following guidelines
will apply: (I) Where a sanitary sewer par.allels a waterline, the sewer shall be constructed of cast iron. ductile iron or PVC meeting ASTM specifications with a pressure rating for
both the pipe and joints of 150 psi. The vertical separation shall be a minimum of two feet between outside diameters and the horizontal separation shall be a minimum of four feet between
outside diameters. The sewer shall be be located below the waterline. (2) Where a sanitary sewer crosses a wateruM and the sewer is constructed of cast iron. ductile iron or PVC with
a minimum pressure rating of 150 psi, an absolute minimum distance of 6 inches between outside diameters shall be maintained. In addition the sewer shall be located below the waterline
where possible and one length of the sewer pipe must be centered on the waterlillll. (3) Where a sewer crosses under a waterlillll and the sewer is coll.StltU;!ed of ABS truSs pipe.
simIlar semi-rigid plastic composite pipe, clay pipe or concrete pipe with gasketed joints, a minimum two foot separation distance shall be maintained. The initial backfill shall be
cement stabilized sand (two or more bags of cement per cubic yard of sand) for all sections of sewer within nine feet of the waterline. This initial backfill shall be from one quaner
diameter below the centerlillll of the pipe to one pipe diameter (bul not less than 12 inches) above the top of the pipe. (4) Wbete a sewer crosses over a waterline all portions of the
sewer within nine reet of the waterline shall be constructed of cast iron. ductile iron, or PVC pipe with a pressure rating of at least ISO psi using appropriate adapters. In lieu of
this procedure the new conveyance may be encased in a joinl of 150 psi pressure class pipe at least 18 feet long and two nominal sizes larger than the new conveyance. The space aroWld
the camer pipe shall be supported at S feet Intervals with spacers or be filled 10 the springline with washed S3IId. The eDCasement pipe should be centered on the crossing and both ends
sealed with centent grout or manufactured seal (b) Water !Inelmanhole separation. Unless sanitary sewer manholes and the connecting sewer can be made watenighl and tested for no leakage,
they must be installed so as to provide a minimum of nine feet of horizomal clearance from an existing or proposed waterlillll. Where the nine foot separation distance cannot be achieved,
a camer pipe as descnoed In subsection (a)(4) of this section may be used where appropriate, 
Te,as Natural Resource Conservauon CommIssIon Page 69 Chapler 31 􀁾􀀠. D"slgn Cmena for Sewerage Systems §J 17.15. Appendil G • General Guidelines rorthe Design of Conm"cted Wetlands
Units for use in :l-Iunicipal Wastewater Treatment. tal Definitions. The following words and terms. when used in Ibis chapter. shall have the follo"jng mearung, unless the context clearly
indicates otherwise. (I) Constructed wetlands· Constructed Wetlands are designed and man-made complexes of saturated substrates. emergent aDd submergent vegetation. animal life. and
water that simulates narural wetlands. Constructed wetlands as described in these rules are meant to function exclusively as wastewater treatment units. They consist of two varieties:
submerged flow systems and free water surface systems. Combinations orthese varieties may also be acceptable methods of treatment Constructed wetlands are constructed treatment systems
that are inundated or saturated by wastewaler flows at a frequency and duration sufficient to support and under normal cin:umstances do support a prevalence of flora and fauna typically
adapled for life in saturated or inundated soil conditions. i.e., a wetland. Terms thaI are considered svnonymous with constructed wetlands treatemem systems are manmade wetlands. engineered
wetlands. artificial wetlands, rock reed rulers, vertical bio-reactor, submerged flow systems, freewater surface systems. artificial marsh. marsh reed ruter. botanical reactor. lOOted
emergent wetland ftlters and microbial rock plant ruters. (2) Submerged flow -A submerged flow system (SFS) consists of a lined basin or channel filled with a granular rock media. The
media supports the growth of both emergent vegetation on the surface and fixed bio-film on the subsurface. The wastewater flows borizorua1ly, vertically, and transVelSes the subsurface
of the rock media through interstices of the media and vegetation root SlIUCtw:e. Wastewater levels are nominaily maintained at least six inches below the rock media surface. Total rock
media depth shall not exceed 2+ inches. (3) Free waler surface -The free water surface system (FWS) consists of a lined basin or channel partially filled with soil or other media suitable
for supporting rooted emergent and/or submergen! vegetation. Wastewaler flows over the top of the media and through the stalks of the emergent and/or submergent vegetation at an average
depth no greater than 18 inches. (b) General cO.llIIiderations. These guidelines are intended for an exemplary basis. The criteria for design. construetion, and operation should be based
on data collected from operational data of similar facilities. pilot-plant and bellCh-scale studies, and/or proper engineering and scientific mvestigatiollll which should be submitll:d
at the time of review. (I) Algal mat removal. Provisions shall be made for algal mat removal from primary treated effluent prior to entering into the wetland uniTS. These provisiOIlS
may include bar screens, adjustable inlets, baffles, and other methods as approved by the commission. commission. (2) Natural wetlands. The commission will prohibit the use ofany land
defined as a wetland by the U.S. Army Corps of Engineers in +0 Code of Federal Regulations, §122,2 and subject to regulations found in the Clean Water Act, §404, for use in wastewater
treatment. Arrj subsequent construction activity located in a natural wetland may require a permit from the United States Army Corps of Engineers. 
Texas Ciarunl Resource Conservauon CommIssIon Page '0 Chapter) 1" -DesIgn Cmeria for Sewerage S"tems 13) T'PICa] wetlands ,·egelation. Suggested flora for constructed wetlands in the
Slate of Texas mclude the follow mg: (A) Emergent aquatic vegelation such as Typha spp. (cattails). Scirpus spp. (bulrush). Sagittaria spp. (arrowhead). Phragmites spp. (reeds). Juncus
spp. (rushs). Eleocharis spp. (spikerush). caladium spp. (elephant ear). or other acceptable species may be used. (5) Floating aquatic vegetation such as Lemna spp. (duckweed). Hydrocotyle
umbeUata (water pennywort), Limnobium spongia (frogbit), Nymphaea spp. (water lily). Wolffia spp, (water meal). or other acceptable species may be used, (C) The use of indigenous plants
is strongly recommended provided that these species have been proven suitable for use in wasteWater tleatmenl Procurement of these seed plants from natural wetlands should ensure the
natural wetlands are not signifIcantly impacted. (0) The use of all harmful or potentially harmful wetlands plants and organisms, as described in 31 TAC §§S7.1Il,S7,1I8 and 31 TAC §§S7,251·S7.2S8,
must fll'St be approved by the Texas Parles and Wildlife Department. (3) Allowed uses. ConstrllCled wetlands can be used as a: (AJ secondaIy tteatmcnt unit; or (5) advanced secondaIy
tteatmclll unit 􀀨􀁾􀀩􀀠Primaly treatment All systems shall be preceded by primary tleatment Systems may be preceded by secondaIy tteatment Primaly _ can include septic tanks, Imhofftanks,
facultative lagoons, aerated lagoons, stabi1i7ation ponds, and any oilier tteatmcnt process which removes the settleable solids and floating material The design of these pretteatmcnt
units shall conform with applicable State design criteria. (5) Liners. When required in tile facility's permit or by IIIe commission, basins shall be lined with an impermeable liner,
􀁾􀁲soil or synlhetic, as described in subparagraphs (A) and (5) of this ,paragraph. (A) Soil. (i) All placed clay or in-sitIl soils used for basin liners shall be certif1ed by adequate
geotechnicaJ test results. For all in"itu soils, the design engineer shall present adequate soil borings information which ensun:s the homogeneousness of the selected soil. Placed clay
or in-situ soils shall have a measured permeability of less than 10" cmlsec. andIorlile following characteristics: (I) more than 30% passing a 11200 mesh sieve; 
Texas SaPJrnl Resourt:e Conselvauon CommIssIon Page 71 Chapter 317 • Design Criteria for Sewer.lge 􀁓􀁾􀁳􀁴􀁥􀁭􀁳􀀠(lIll plasticity index greater than 15: (IV) no clods larger than two
(2) inches: (V) minimum compacted thickness of two feet for placed clav liners and four feet for in-situ soils. (ti) AU placed clay liners shall be installed accollling to the following
criteria. However. when USUlg in-situ sotls for the required liner. otily the upper six inches should be reworked as fOllows: (f) maximum loose lift of eight inches, SLX inches compacted:
(II) minimum compaction effon of 9S percent Standard Proctor (ASTM D-<598); (III) liners shall be keyed into the existing in-situ soils. (B) Synthetic. NI synthetic liners shall have
a minimum thickness of 30 mils and contain underdrain leak detection which shall consist of leachate collection and detection systems. Proper installation of the materials mentioned
in subpamgxaph (A) of this paragraph shall be described in the project's specifications. The liner liner material shall be resistam 10 or protected from ultra-violet (UV) light degllldation.
(6) Flood hazard analysis. The lOO-year flood plain elevation shall be provided. Proposed treaonent units which are to be located within the lOO-year flood plain will not be approved
for construction utiless protective measures satisfaclOry to the commission (such as levees or elevated treatment units) are included in the project design. Ifconstruction inside the
IOO-year f100d plain is necessary. authorization from the proper coordinating authority must be obtained. All units must either be tJm:e feet above the 100-year flood plain 􀁯􀁾􀀠have
a benn with at least three feet of freeboard above the 100-year flood plaia (7) Benns. Betms sball have side slopes of no steeper than 3: I. Belll1S shall be lined or constructed of
impermeable clay as described in the preceding section penaining 10 solliiners. AJ1 clay berms shall be keyed into the,clay liner. (8) Configuralioa Facilities with permitted avemge
daily flows over over 100.000 gallons per day shall confonn with the folloWing configuration standards. (A) Multiple units. The treatment system shall be divided imo multiple units that
can be operated separately. Each unit shall have the ability to be completely draioed. . . (B) Parallel trains. Design considerations may include parallel treatment streams or trains
which can be operated independemly ofeach other. 
Texas 􀀧􀁜􀁩􀁾􀁬􀁮􀁈􀁮􀁬􀀠Resource ConservauoB CommlSSlon Page 72 Chapter 31 C • :'esign Critena for Sewemge S"tems IC) Length to width ratio. The unilS shaU be designed to operate as
plug flow channels. A proper length to WIdth ratio to achieve tlus condition should be considered in the design of each )·ystem. (D) Switching capability. The design shaU allow for each
unit to be taken out of se!".-ice at any time and ils flows routed 10 another unit. The trealment system must be capable of treating the daily average flow with the largest unil out
of service, (E) Wind prolection. AU FWS systems sl1all be situated so as to minirnJze the adverse effeClS of the prevaIling winds. (F) Minimum slope, All systems should maintain a minimum
slope along the bottom of at least 0,075% to facililllte draining, (9) Flow disUi.bution, (A) Inlets, All treatment units sl1all have multiple inlets (a minimum of three) and provide
a method to mitigate erosion of the media (B) Outlets. All treatment units shau have multiple oudets (a minimum of three), FWS outlets shall be submerged and be able to exclude floating
detrital material and scum, (e) Water levels, The design should aUow inlets and outlets to be raised and lowered, so that water levels within the basin can similarly be varied and provide
the ability to flood the beds when necessazy, (D) Basin hydraulic design. (i) Submerged flow systems: SFS systems should be designed to prevent surface ponding of wastewater, The hydraulic
loading of these systems should be limited to the effective hydraulic capacity of the media in place. This effective hydraulic capacity Will be a flmi:tion of the clean media's hydraulic
capacity n:dIIced by root intrusion, slime layer. detritus. algae, and other blockages. (ti) Free water surface systems. FWS systems should be designed to prevent scour, erosion, and
plaDt damage during peak flow periods. The hydraulic loading ofthese systems should be limited to the open channel canying capacity of the unit at full growth. (IO) Flow equalization.
Flow to the units shall provide for a unifotm environment and growth conducive to wetlands, (11) Initial vegellltion spacing. Plants should be placed no greater than 66·inches apan (center
to center). All plants to be I1SCd should be bealtlty, insect free, and undamaged. A broad diversity of plant species within any unit is recommended. 
Texas >lamral K<source Conservauon Comnusslon Page i3 Chapter 􀁾􀀠17 -Design Cmeria for Sewemge Systems 112) TSS removat The Tara! Suspended Solids (TSS) removal efficiem:v of me wetland
SYstem is dependent on the qUiescence of the system. However. If the facility is unable to meet Its permmed pammeters. alternate means of solids removal must be pursued. (13) Nitrification.
CUlTent wetland technology has not proven the ability to consistently rutnfy typical domestic strenglh sewage to meet average permit limitations below 5 mgil. The deSIgn of any wetland
proposed for use in this type situation will incorporate aseparate rutnfication process. 􀀨􀁉􀁾􀀩􀀠Harvesting. Harvesting of dead wetland vegetation and detritus plant matter is recommended
(e) Submerged flow system design. (1) Basic design parameters. SFS wetlands are sized according to primary and/or secondary treatment efficiency preceding the units. i.e. fm4:tion of
renutining BOD,. and the permitted 30-day average effluent discharge concenlIation of BOD,. The following factors shall be considered in the selection of the design hydraulic and organic
loadings: suenglh of the influem sewage, effectiveness of primary and/or secondary tlIl3tment, type of media. ambient wastewater temperature for winter conditions, and treatment efficiency
required. (Al Rock/media design. The following are minimum requirements for material specifications of the rock media: (i) Crusbed rock, slag or similar media should not contain more
tllan 5.0% percent by weight of pieces whose longest dimension is three times its least dimension. The rock media should be free from thin, elongated and flat pieces and should be free
from clay, sand, organic material. or dirt The media should have a Morns baIdness of at leastS.O. (ii) Rock media. except for the top planting layer, should conform to the following
size distribution and gnldation wben me;;banically grnded over a vibrating SCIeen with square openings: (1) passing six inch sieve· 100% by weight (m retained on two inch sieve' 90-100%
by weight (ill) passing one inch sieve -< 0.1% by weight; (8) Installation of the rock media: . (i) Rock media shall be rinsed or washed to remove sediment. This washing should be sufficient
to remove any signifICant amounts of dirt or accumulated debris. (ii) The proper placemem and installation of media is vital to the success 0 f the system. Undue compaction exerted on
the media's surface, as it is installed and after its installation, can 
Texas 􀁾􀁡􀁴􀁵􀁲􀁡􀁬􀀠Resource Conservauon CommIsSion Page 74 Chapter} I0 • Deslgn Critena for Sewerage Systems f",crure and consol1date the media, The introduction of foreign fine particles
and fracrunng can advenielv affect the system's hvdraulic conducti"ily, Therefore. the following guidelines are recommended: . (I) A layer of smaller rock (0,5 • 1,0 inches) may be used
on the top of the unit to ease planting of the vegetation and aid in vector control. (IT) Media should be gently put in place. avoiding excessive dropping, Jostling, and abusive handling.
(III) Heavy machinery should not be allowed on the surface of the media after fmal placement. If machinery is allowed on the surface, all tire ruts should be smoothed over to prevent
po ruling in ruts. (IV) Provisions should be made priono planting to provide water and nutrients to the plants ifthe system start-up will be delayed. (2) Organic loadings. The foUowing
tables present typical ranges for detention time within the system in days. Each detention time represents combinations of different classes of secondaty and advanced secondary treatment
and different effluent parameters. Design engineers may submit sufficient operating data for similar installations, andIor actual field conditions to justify their efficiency calculations.
These times represent the theoretical detention time of wastewater within the basin. Therefore. the amount of detention volume available is equal to the basin's volume multiplied by
the average porosity of the media. Evapotranspilation and precipitation should also be considered when calculating detention time. The tables are based upon an average effective porosity
media 0020/0, and an average wastewater treatment plant influent 800, of 200 mg/I. (A) Secondaty and Advanced Secondaty treatment The detention times in Table Number I are based on the
fractional80D, remaining in the wetland system's infiuent and the permitted effluent limits. For permitted effluent BOD, concentration and removal efficiencies that fall between the
listed quantities, linear intetpolation is pennissible. Table Number I is based on the foUowing assumptions: (I) ambient winler conditions wastewater temperantre of7,5 degrees Centigrade
(45.5 degrees Fahrenhiet); and ' (2) an average wastewater lRatment plant influent BOD, of 200 mg/I. Ifthe wastewater winter temperatllfe is lower than that indicated above, detention
times must be modified. Table No, I DETENTION TIME (days) SUBMERGED FLOW SYSTEM EractjQMI BOp, Remajnin, After [Mial IreatmeDl Permitted BOD, mgl! 0,70 0.60 0,50 0.30 0.20 0,10 
􀁔􀁾􀁸􀁡􀁳􀀠:-;Jtur.ll '<.esource Conser.auon CommISSIon Page 75 Chapler 1!" . Des!gn Cn!ena for Sewerage Systems .'i () 2.6 2.3 18 ! 3 ! nla 3 7 U 3.0 2.6 2. ! 1.3 nla 5 U 4.4 -1.0
3 -I 2.6 I (8) Advanced secondary treatment following pond systems only. The detenuon ume IS based on the assumption that the treatment facility is composed of a facultative lagoon followed
bv two stabilization ponds. each sized according to the current State design cnteria found in this Chapter. 􀁦􀁾􀁲􀀠applications where pond effluent is to be polished to meet an effluent
BOD, concentration of 30 mgll. a minimum of one day detention time through the wetland system will be required. (3) Oxygen loadings. Since SfS should function in an aerobic envirorunenl
the wastewater dissolved oxygen level is critical. Swiace area needed to maintain suffiCient oxygen transfer through de'ieloped plant roots shall be designed based on approved and acceptable
engineering methods. (d) free water ,wiace system design. (I) Basic design parameters. parameters. FWS wetlands are sized according to prilruuy and/or secondary treatment efficiency,
i.e. fraction of remaining BOD" and the permitted 30-day average effluent discharge concentration of BOD,. The following factors are considered in the selection of the design hydraulic
and organic loadings: strength of the influent sewage, effectiveness of primary andIor secondary treatment type of media. ambient wastewater temperalUIe for winter conditions, and trellIltlent
effICiency required. (2) Organic loading. The following tables present typical ranges for detention time within the wetland system in days. Each detention tinte n:presents combinations
ofdifferent classes of primary and secondary treatment and the diffen:nt effluent parameters. Design engineers may submit sufficient operating data for similar installations, and/or
actual field conditions to justify their efficiency calculations for the wetland system. The tables are based on the following assumptions: Specific swiace area of the media (stems,
stems, toOts, detritus, etc. 15.7) m21m3; ambient winter conditions wastewatertempeIatUre of 7.5 degn:es Centigrade (45.5 degn;es FahIenhiel); and an average wasteWalet treatmelll plant
influent BOD, of 200 mg/l. (A) Secondaly treatment These detenlion times aR: based on the type and efficiency of the primaly treatment unit which precedes the FWS wetlands. (i) Septic
tank: or facultative pond as pIimaIy treatment method: Table No.2 EHluentBOD, Required Detemion CQncenqation (mgt!) Time (days) 30 8 20 11 10 15 
Texas :'-ian:r.)i. Rl!source Conservauon CommIssion Page 76 Chapter, I' -DesIgn Cmena for Sewemge Svstems (Ii) Imhoff rank or cianficauon as pnmary treatment methode Table No.3 Emuent
BOD, Required Detention Concent!lltion rmgllJ Time (days) 30 12 20 15 10 21 (B) Advanced secondary !Ieatment The detention times given in Table Number 􀁾􀀠are based on the fraction or
BOD, remaining after secondary treatment Table Number 􀁾􀀠assumes a wastewater treatment plant influent BOD, of 200 mg/l. For percentages that fan between the listed quantities, linear
interpolation is permissible. Table No.4 DETENTION TIME (days) ADVANCED SECONDARY TREAJMENT FREE WATER SURFACE SYSTEM Fractional BOD, Remajnjng Mer Secondary TnlatmeD! Permined BOD,mg/l
0 . .50 OA5 0.40 0.35 0.30 0.25 0.20 0.15 0.10 )0 S 7 6 6 5 42 nfa nfa 20 11 10 9 8 7 6 5 3 nfa 10 15 14 13 12 11 10 9 7 .5 (C) Vector conttol The 􀁾􀁥of mosquitos and other vectors
bas been . associated with open water. Since the FWS sySlel1lS will have open water 5II1'faces, vector control must be a priority. Vector control mechanisms using natural conttolling
agenlS such as introduction ofGambusia spp. (mosquito fish) have been pmven effective. However. ifthe predatolY fish are used to control vectors, provisions must be made within the basin
for designated open water areas so the fish can swface for oxygen. At least 20% of the basin's swface should be open to the atmosphere. Other methods of vector control may be considered.
However. the introduction of chemil:als (such as pesticides) should be carefully evalUated so that there are no adverse effects on vegetation or on eflluent water quality.