Clay,
 
I reviewed the attached table sent to me by Chris Robinson with Grantham. There are some discrepancies with the table and what we are allowed to do and that we designed accordingly.
It was my understanding that we did not have to provide detention for any offsite areas and any areas already improved. 
 
The table includes area G, which is offsite (between the lease parcel and Taxiway V pavement). We included this area to offset areas Du and Ou since these two areas were not going through
the detention. The total for G is 0.11 acre and for areas Du and Ou is 0.12 acre. In addition, the runoff coefficient for Area G existing was shown to be 0.5, which should 0.3 for unimproved
conditions. This are will be changing since the access to the taxiway V will be revised to include most of the length adjacent to the lease parcel. This is offsite area and will be handled
in the drainage calculations and system, but will not be detained. 
 
Area Di is within Amelia Earhart Drive which is offsite and is already improved. Areas J and Oi are already improved  (they are paved).Therefore, these areas should not be subject to
detention. Area C is a landscape area and should keep an unimproved runoff coefficient of 0.3. 
 
My calculations provide for the actual unimproved area of 3.01 acres [3.73 acre lease parcel less 0.19 (C) less 0.38 (J) and less 0.18 (Oi)] (some differences due to roundoff), which
makes the allowed release 6.7 cfs (see table on drainage area map), This is the release amount used in my calculation. The volume required by this calculation is as we shown on our plan
which is 25,348 cubic feet.  
 
The submerged orifice calculation as shown on the profile sheet anticipates a release rate of 6.7 cfs which produces an opening of 12.4 inches. The head is the difference between the
water surface in the detention tank less the hydraulic grade elevation in the outfall pipe which is the difference between 635.80 and 633.98 which equals 1.82 feet, not 4.63 feet as
shown for the calculation by Chris. I have also attached the storm sewer profile sheet with the orifice equation shown with more detail. This equation/calculation was added to sheet
4, the DA Map. 
 
I trust this explains and clarifies the issues regarding the detention. Please review and contact me with any questions or comments, or if there is a disagreement with my numbers.  
 
Regards,
L. Lynn Kadleck, PE, RPLS
Kadleck & Associates
555 Republic Drive, Suite 115
Plano, Texas 75074
972-881-0771
lkadleck@verizon.net