Water quality volume (WQV) shall be calculated using the Unified Sizing Criteria as follows:

1. (a) For purposes of this section, “P” means the depth of the 90th percentile storm in inches as defined as follows:

   1. (1) For existing impervious areas that are proposed for redevelopment, P shall be 0.3 inches; and
   2. (2) For all other areas P shall be 1.0 inches;
2. (b) “A” means the total area draining to the design structure;
3. (c) “I” means the percent impervious area draining to the design structure, in decimal form;

4. (d) “Rv” means the unit-less runoff coefficient calculated as the sum of 0.05 plus the product of I multiplied by 0.9, as in the formula below:

   Rv = 0.05 + (0.9 x I)

5. (e) To calculate the WQV, the applicant shall multiply the product of Rv and A by P, as shown in the formula below:

   WQV = P x A x Rv

Source. #9343, eff 1-1-09; renumbered by #9817-A (formerly Env-Wq 1504.09); ss by #12342, eff 8-15-17; ss by #14472, eff 1-19-26, EXPIRES: 1-19-36