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GINN, INC. CONSULTING ENGINEERS June 7,1990 Mr. Ron Whitehead. City Manager Town Of Addison Post Office Box 144 Addison, Texas 75001 Re: Drainage Basin Analysis Farmers Branch/Addison
Interceptor Sewer Tunnel Dear Ron: Attached is a final copy of our Addison Drainage Basil! Analysis report which recalculates the projected wastewater flows from the Town of Addison
to the Farmers Branch/Addison Interceptor Tunnel. After receipt of our draft report, the City of Farmers Branch revised their projected flows using the same criteria. We have met with
the Farmers Branch Engineering Department and jointly concur on the percentage of participation for the interceptor tunneL We are currently recalculating the percentages of participation
for the related collector lines. Ifyou have any questions regarding this analysis, we will be happy to meet with you at your convenience. Sincerely, Sanford W. Case, P.E. cc: Don Preece,
Director of Utilities Randy Moravec. Director of Finance Jerry Murawski, P.E., City of Farmers Branch H. Wayne Ginn, P.E. File 90373 17103 Pr",>ton Rood. Suite 100 • LB 118 • Dallas,
Texas 7524R • Phone 214/248·4900 
ADDISON DRAINAGE BASIN ANALYSIS for the Town of Addison Farmers Branch/Addison Interceptor Sewer Tunnel June 1990 Ginn, Inc. Consulting Engineers 17103 Preston Road, Suite 100 Dallas,
Texas 75248 
Executive SUmmary After re-analyzing the drainage basins within the Town of Addison, the revised projection of ultimate wastewater flow from the Town of Addison to the Farmers Branch/Addison
sewer interceptor tunnel is an average day flow of 7.626 MOD and a peak day flow of 16.099 MOD. These revised flows are based on several assumptions; • Population projections were based
on 100% of actual net acreage minus Rightof-Ways instead of 95% of gross acreage. • 239.8 acres on the east side ofAddison Airport, including the runways, taxiways, and clear zones was
removed from Basin A-2 and will be shifted to the Dallas Water Utilities system prior to completion of the tunnel. • Industrial area populations were based on the same FAR's a, the Farmers
Branch areas of similar development. 􀁾􀀠 • The actual square footage of existing high rise office buildings (4 stories or greater) was used in population projections. • Down zoning
to Single Family (5 units/acre) was applied to the Multi-Family area of the Les Lacs development. The City of Farmers Branch has simultaneously re-analyized their basins to the same
criteria contained herein. The Farmers Branch revisions are necessitated in part to remove the current residential areas from the proposed Public Improvement District (PID). This reduces
the projected Farmers Branch flow to 12.248 MOD. Therefore, the projected total flows and percentages of ownership for the tunnel system are as follows; Addison 16.099 MOD 56.79% Farmers
Branch 12.248 MOD 43.21% Total 28.347 MOD 100.00% 1 
Background In early 1987, the Town of Addison and City of Farmers Branch authorized Freese and Nichols (F&N) to evaluate alternatives for relieving the overloaded interceptors conveying
the two municipalities wastewater to the Trinity River Authority (TRA) system. A major portion of the Farmers Branch/Addison Wa5tewater Study was the analysis of existing population
and land use of the study area and the projection of the future populations, land use, and wastewater flows. The total projected peak flows from the Addison drainage basins in the F&N
study area was 16.95 MGD. The total projected flow from the Farmers Branch basins in the study area was 15.40 MGD. The total projected flow for the interceptor system in the F&N report
was 32.34 MGD (52.4% Addison, 47.6% Farmers Branch). The Freese and Nichols report was then used as the basis for the July 1989, Preliminary Engineering Report For Sanitary Interceptor
Sewer by Consoer, Townsend & Associates, Inc. (CTA). The CTA report dealt with preliminary design of of a 4.2 mile wastewater interceptor tunnel from the Marsh Lane/Spring Valley area
to the TRA interceptor s)\'>tem. In the interim, the Town of Addison commissioned Espey, Huston & Associates, Inc. to evaluate alternatives for wastewater flows from the Midway basin
which were flowing to the City of Carrollton. The November 1988 report entitled, Town Of Addison Evaluation Of Strategic Altematives For Transporting Wrutewater To The TRA System, concluded
that the Midway basin flows should be diverted to the proposed Farmers Branch/Addison tunnel. As negotiations for cost sharing and percentage of participation in the tunnel project proceeded
between the two cities, it became necessary to adjust the projected flows from several of the basins. To equitably accomplish this, the F&N report was analyzed to determine the criteria
to be used for adjustments. The subsequent review yielded several other areas requiring adjustments to the projected wastewater flows. As a result, this analysis was necessitated to
revise the projected wastewater flows for the Town of Addison's portion of the interceptor tunnel. Objective The objective of this report is to refine the boundaries and land use assumptions
of each of the Town of Addison's seven drainage basins in the F&N study area plus the Midway basin to determine the projected ultimate wastewater flows from the Town of Addison to the
tunnel system (Exhibit 1). To accomplish this, I" =200' base maps were prepared for each drainage basin. Current zoning and proposed changes were overlaid and acreage totals calculated
for each land use (Exhibit 2). 2 
Criteria Right-of-ways were calculated as a separate land use in the new totals. In the F&N report, the assumption was made for a 95% utilization in commercial and industrial areas and
85% utilization in residential areas. While these utilization figures could possibly be approached in some high rise development areas, the set back, parking and streetscape requirements
within the Town of Addison make these figures unrealistic. Right-of-Ways account for between 9 and 24 percent of the total acreage within the basins. Right-of-Way acreage was included
for the purpose of Infiltration and Inflow calculations. The F&N report based future population projections on Floor Area Ratio's (FAR's). The City of Farmers Branch's Zoning and Master
Land Use Plan are both based on FAR's thus allowing for an accurate conversion to future population. The Town of Addison does not address FAR's in either its Zoning or Master Land Use
Plan. This makes the land use conversion and population projections a difficult and subjective task for the Addison drainage basins. Since only a few tracts in the Town of Addison have
"open zoning", 􀁾􀁭􀁯􀁳􀁴 all developments are platted as planned developments. This process allows the Town additional control over its' growth and development. Setbacks, parking, landscape
requirements, and height restrictions within the Town typically result in a lower FAR than similar tracts in surrounding cities. Development densities within the study area (Addison
and Farmers Branch) appear to be fairly uniform for similar types of land use. The Addison area does appear to have a higher concentration of restraunts and commerciaVlocal retail centers.
The Farmers Branch study area appears to have a higher concentration of high rise office/planned developments. For the purpose ofthis analysis, equal FAR's were applied to areas of similar
land use in each city. For existing high rise office space (4 story or greater), the actual square footages of building space were used. The following FAR's were utilized; 0.70;1 Light
Industrial 1.00;1 Mixed Use -School, Atheltic Facility, etc. 1.75;1 Commercial, Local Retail, Office (3 story or less) 2.10;1 High Rise Office, High Density PD 3.00;1 Single Family (ResidentslUnit)
2.50:1 Multi-Family (ResidentslUnit) It should also be noted that Infiltration and Inflow (1&1) rates are based on the F&N report. Their basis was 14.02 people/acre for both Farmers
Branch and Addison. When the flow rate of84 GPeD is applied, this yiel.ds an 1&1 rate of 1,178 gallons/acre/day which is extremely high considering the age, type of materials, condition
of the sewer system and ongoing rehabilitation projects within the Town of Addison. A figure of600-900 gal!ons!acre/daywould be more realistic; however, for uniformity, the figure of
1,178 gallons/acre/day was utilized in this analysis. 3 
Drainage Basin Analysis Basin A·I Basin A-I consists of approximately 67.5 acres on the west side of the Addison Airport. The entire area is zoned light industrial with approximately
7.7 acres (11.4%) of Right-of-Ways. This revised basin is considerably smaller than in the F&N report. The northern portion of the original A-I basin actually flows to the Midway basin.
Clear zones for the airport prohibit development or buildings within 350 feet of the runway centerline; therefore, the clear zones have also been removed from the drainage basin areas.
Basin A-2 The drainage area for this basin has been reduced by approximately 239.8 acres. When the Arapaho Road Meter Station (City of Dallas) was installed, the station was sized to
accomodate the ultimate flows from the east side of the Addison airport whi& naturally flow to the City of Dallas. The diversion of these flows can be accomplished by the installation
of a new gravity sewer line beginning at the Addison RoadlMiidred intersection. This sewer line is currently under design as a part of the Addison Theater/Mildred Street project. The
revised A-2 basin now consists of three sub-basins. Sub-basin A· 2A consists of 14.45 acres of light industrial, 10.44 acres of commercia)jlocal retail (2 restaurants and 1 hotel), and
3.58 acres of Right-of-Way, totaling 28.5 acres. Sub-basin A-2B consists of 3.05 acres of light industrial, 20.37 acres of offiCe/local retai)jcommercial, and 7.32 acres of Right-of-Ways.
Sub-basin A-2C consists of 21.54 acres of light industrial. This tract is the Dallas Water Utilities Beltwood Reservoir. This is an unmanned pumping and storage facility which generates
virtually no wastewater (less than 100 GPD). Basin A·3 This basin consists of approximately 208.46 acres with zoning as follows: 133.24 acres light industrial, 22.65 acres office/local
retail, 2.31 acres of high rise office (100,000 SF actual), and 50.26 acres (24.1 %) Right-of-Ways. 4 
Basin A-4 Basin A-4 consists ofa variety ofland uses and several proposed changes in land use. The current zoninglIand use is 138.66 acres OfficeIPlanned Development, 4.71 acres municipal
facilities, 3.73 acres (63 units) ofTownhouse (PD), 52.1 acres (378 lots) ofSingle Family, 11.84 acres (88 units) of Duplex, 61.19 acres ofTownhouse, and 53.86 ofRight-of-Way. For the
purpose of developing wastewater flows, the actual number of platted lots of residences were determined in the Townhouse, Single Family, and Duplex areas. In addition, the 61.19 acres
ofTownhouse zoning is proposed to be down zoned to single family (5 lots/acre). The revised residential composition of basin A-4 will be as follows: Townhouse -(PD) 63 units Single Family
378 lots Duplex (2 units/lot) 88 units TH to Single Family 260 lots Basin A-5 The southern boundary of this basin was adjusted to properly reflect the actual City Limit line between
Farmers Branch and Addison. This basin now consists of approximately 17.67 acres of high rise office (404,696 SF actual), 75.10 acres of commercial, 34.06 acres of local retail, 3.8
acres (26 lots) single family, 19.23 acres Townhouse (44 units existing townhouse -85 units (17.0 acres) proposed single family), 20.93 acres of Right-of-Ways, and 96.76 acres mixed
use (Loos Field house, Stadium, and Greenhills School). Basin A-6 Basin A-6 consists of approximately 130.31 acres of apartments (1,994 units @18 units/acre), 27.73 acres commerciaViocal
retail, 4.86 acre mixed use (Loos tract), and 18.29 acres of Rightof-Ways. It should be noted that the original F&N report placed 79 single family lots into this basin which actually
belong in Farmers Branch basin F-l. Basin A-7 The boundaries of this drainage basin were also adjusted to reflect the correct City limits boundaries. This basin now consists of approximately
57.49 acres of industrial, 49.25 acres commercial, 23.39 acres of local retail, 45.96 acres (2,124,453 SF actual) high rise office, and 34.62 acres of Right-of-Ways. 5 ( 
Midway Basin The Midway basin consists of approximately 384 acres which currently drain to the City of Carrollton. The Addison Airport covers approximately 120 acres of this basin with
runways, taxiways, and clear zones. Since this portion will not generate future wastewater flows, the Midway basin was split into a North and South basin to allow for the airport and
its clear zones to be removed from the land areas. Midway South Basin -73.56 acres consisting of approximately 64.6 acres of light industrial, 1.59 acres of office, and 7.37 acres of
Rights-of-Ways. Midway North Basin -190.42 acres consisting of approximately 39.7 acres oflight industrial, 120.81 acres of commercial, 4.90 acres (112,225 SF actual) high rise office,
11.00 acres of apartments (421 units), and 14.01 acres of Right-of-Ways. Summary of Addison Drainage Basin Acreages Revised F&N A-I 67.48 108.68 A-2 • 80.75 289.35 A-3 208.46 233.69
A-4 326.09 337.49 A-5 267.55 221.08 A-6 181.19 176.40 A-7 193.89 200.42 Midway South 73.56 Midway North 190.42 ----------1,589.39 Acres 1,567.11 Acres * Approximately 239.8 acres (including
runways, taxiways, and clear zones) has been removed and/or shifted to the City ofDallas Arapaho Road Meter Station. 6 
Projected Land Use Gross Gross. F.A.R.or SF/Emp Equiv. Acres Sq.Ft. # oCUnit. Per!UDlt Pop BasinA·1 Industrial 59.78 2,604,017 0.70 750 2,430 R.O.W. 7.70 335,412 0.00 0 0 1&1 946 Sub-Total
67.48 2,939,429 3,376 Basin A·2 A·2A Industrial Commercial R.O.W 1&1 14.45 10.44 3.58 629,442 454,766 155,945 0.70 1.75 0.00 750 350 0 587 2,274 0 399 A·28 Industrial Office Local Retail
Commercial R.O.W. 1&1 3.05 5.78 3.23 11.36 7.32 132,858 251,7TI 140,699 494,842 318,859 0.70 1.75 _ 1.75 1.75 0.00 750 350 350 350 0 􀁾􀀠 124 1,259 703 2,474 0 431 A-2C Ind. (DWU) 1&1
21.54 938,282 0.00 0 4 302 Sub·Total A2 80.75 3,517,470 8,558 Basin A·3 Industrial HR Office OfliceILocal Retail R.O.W. 1&1 . 133.24 2.31 22.6550.26 5,803,934 100,624 986,634 2,189,326
0.70 100,000 1.75 0.00 750 350 350 0 5,417 286 4,933 0 2,923 Sub-Total 208.46 9,080,518 13,558 BasinA-4 Office TH·PD PD·MUNI Single Family DUPLEX THtoSF R.O.W. 1&1 138.66 3.73 4.71 52.10
11.84 61.19 53.86 6,040,030 162,479 205,168 2,269,476 515,750 2,665,436 2,346,142 1.75 63 1.00 378 88 260 0 350 2.5 750 3.0 3.0 3.0 0 30,200 158 274 1,134 264 780 0 4,572 Sub-Total 326.09
14,204,480 37,381 Gross Gross. F.A.R. or SF/Ernp Equiv. 7 
Basin A-S Commercial Local Retail Mixed Usc TH Single Family HR Office R.O.W. 1&1 Acres 75.10 34.06 96.76 223 20.80 17.67 20.93 Sq.Ft. 3,271,356 1,433,654 4,214,866 97,139 906,048 769,705
911,711 # of Units 1.75 1.75 1.00 44 111 404,696 0.00 PerlUnit 350 350 750 2.5 3 350 a Pop 16,357 7,418 5,620 110 333 1,156 a 3,751 Sub-Total 267.55 11,654,478 34,745 Basin A-4i Apartments
Local Retail Mixed Use Commercial R.O.w. 1&1 Sub-Total 130.31 26.99 4.86 0.74 18.29 181.19 5,676,304 1,175,684 211,702 32,234 796,712 7,892,636 1,994 1.75 1.00 1.75 0.00 25 350 750 350
0 " 4,984 5,878 282 161 0 2,540 13,847 Basin A-7 ' Local Retail Commercial HROffice Industrial R.O.W. 1&1 Sub-Tolal 23.39 49.25 45.96 57.49 34.62 193.89 1,018,868 2,145,330 2,002,018
2,504,264 1,508,047 8,445,843 1.75 1.75 2,124,453 0.70 0.00 350 350 350 750 0 5,094 10,727 6,070 2,337 a 2,718 26,263 Basin Midway-South Industrial Commercial R.O.W. 1&1 Sub-Tolal 64.60
1.59 7.37 73.56 2,813,976 69,260 321,037 3,204,274 0.70 1.75 0.00 750 350 a 2,626 346 a 1,031 4,004 Bnsin Midway-North Industrial Commercial HR Office Apartments R.O.W. 1&1 39.70 120.81
4.90 11.00 14.01 1,729,332 5,262,484 213,444 479,160 610,276 0.70 1.75 112,225 168 0.00 750 350 350 2.5 0 1,614 26,312 321 421 0 2,670 Sub-Total 190.42 8,294,695 31,338 Totals 1,589.39
69,233,828 173,070 8 
Projected Wastewater Flows Equiv. Avg. Flow Peak Peak Flow Pop GPCD MGD Factor (MGD) Basin A·l Industrial 2,430 23 0.056 2.40 0.134 R.O.W. 0 0 0.000 1.00 0.000 1&1 946 84 0.079 1.00
0.079 Sub·Total 3,376 0.135 0.214 Basin A·Z A·2A Industrial Commercial R.OW 1&1 587 2,274 0 399 23 34 0 84 0.014 0.077 0.000 0.034 2.40 2.40 1.00 1.00 0.032 0.186 0.000 0.034 A·28 Industrial
Office Local Retail Commercial R.O.W. 1&1 124 1,259 703 2,474 0 431 23 34 34 34 0 84 0.003 0.043 0.024 0.084 0.000 0.036 2.40 2.40 2.40 2.40 1.00 1.00 '" 0.007 0.103 0.057 0.202 0.000
0.036 A·2C Ind. (DWU) 1&1 4 302 23 84 0.000 0.025 2.40 1.00 0.000 0.025 Sub· Total A2 8,558 0.340 0.682 Basin A·3 Industrial 5,417 23 0.125 2.40 0.299 HR Office 286 34 0.010 2.40 0.023
OffieelLocal Retail 4,933' 34 0.168 2.40 0.403 R.O.W. 0 0 0.000 1.00 0.000 1&1 2,923 84 0.245 1.00 0.245 Sub·Total 13,558 0.548 0.970 Basin A-4 Office 30,200 34 1.027 2.40 2.464 TH·PD
158 138 0.022 2.77 O.ll6O PD·MUNI 274 34 0.009 2.40 0.022 Single Family 1,134 138 0.156 2.77 0.433 DUPLEX 264 138 0.036 2.77 0.101 THtoSF 780 138 0.108 2.77 0.298 R.OW. 0 0 0.000 1.00
0.000 1&1 4,572 84 0.384 1.00 0.384 Sub-Total 37,381 1.742 3.764 Equiv. Avg. Flow Peak Peak Flow 9 
Pop GPCD MGD Factor (MGD) BasinA-S Commercial 16,357 34 0.556 2.40 1335 Local Retail 7,418 34 0.252 2.40 0.605 Mixed Use 5,620 23 . 0.129 2.40 0.310 TH 110 138 0.015 2.77 0.042 Single
F amity 333 138 0.046 2.77 0.127 HR Office 1,156 34 0.039 2.40 0.094 R.O.W. 0 0 0.000 1.00 0.000 r&r 3,751 84 0.315 1.00 0.315 Sub-Total 34,745 1.353 2.829 Basin A-6 Apartments 4,984
138 0.688 2.77 1.905 Local Retail 5,878 34 0.200 2.40 0.480 Mixed Use 282 23 0.006 2.40 0.016 Commercial 161 34 0.005 2.40 0.013 R.O.W. 1&1 0 2,540 0 84 0.000 0.213 1.00 1.00 , 0.000
0.213 Sub-Total 13,847 1.113 2.627 Local Retail 5,094 34 0.173 2.40 0.416 Commercial 10,727 34 0.365 2.40 0.875 HRO£ficc 6,070 34 0.206 2.40 0.495 Industrial 2,337 0.054 2.40 0.129 R.O.W.
0 0 0.000 1.00 0.000 􀁦􀁲􀀮􀀢􀀢􀁾􀀠t)Vl " 23 fl"i? 1&1 2,718 84 0.228 1.00 0.228 r I (1,.I1,00D 1'". 1-" Sub-Total 26,263 1.011 2.106 􀁾􀀠hi Basin Midway-South Industrial Commercial
R.o.W. 1&1 2,626 346 0 1,031' 23 34 0 84 0.060 0.012 0.000 0.087 2.40 2.40 1.00 1.00 0.145 0.028 0.000 0.000 0.087 Sub-Total 4,004 0.159 0.260 Basin Midway-North Industrial 1,614 23
0.037 2.40 0.089 Commercial 26,312 34 0.895 2.40 2.147 HR Office 321 34 0.011 2.40 0.026 Apartments 421 138 0.058 2.77 0.161 R.O.w. 0 0 0.000 1.00 0.000 1&1 2,670 84 0.224 1.00 0.224
Sub-Total 31,338 1.225 2.647 Totals 173,070 7.626 16.099 10 
MIDWAY_""",SOUTH EXHIBIT I '. 
LEGEND III -Light Industrial 􀁆􀀺􀁾􀀺􀀻􀁉􀀠_ Commeriall ..;;;::,.3 Office/Local Retail 􀀡􀁽􀀬􀀮􀁾􀁾􀀠-Single Family v,rT12 _ Multi -family or :lLLlJ Town House/Condo !'\iV\l Exist. High
Rise I:QQS; -Office C::J -Mixed Use EXHIBIT 2 LAND USE