524 STORMWATER MANAGEMENT: PERFORMANCE REQUIREMENTS FOR MAJOR REGULATED PROJECTS IN THE ANACOSTIA WATERFRONT DEVELOPMENT ZONE

524.1 An Anacostia Waterfront Development Zone site (AWDZ site) is a site within the Anacostia Waterfront Development Zone (AWDZ) that undergoes a major regulated project that is publicly owned or publicly financed.

524.2 For an AWDZ site, the property owner shall employ and maintain each Best Management Practice (BMP) and land cover necessary to comply with the requirements of this section until site redevelopment that follows a Department-approved Stormwater Management Plan (SWMP) occurs.

524.3 Except for activities exempted under this chapter, if a provision of this section conflicts with any other provision of this chapter, an AWDZ site shall be subject to the more stringent provision.

524.4 For an AWDZ site that undergoes a major land-disturbing activity, the property owner shall treat the rainfall from a one and seven-tenths (1.7) inch rainfall event, which is the ninety-fifth (95th) percentile rainfall event for the District of Columbia, measured for a twenty-four (24) hour rainfall event with a seventy-two (72) hour antecedent dry period by:

(a) Employing each BMP necessary to treat the one and seven-tenths (1.7) inch Water Quality Treatment Volume (WQTv) equal to the difference between:

(1) The post-development runoff from the one and seven-tenths (1.7) inch rainfall event; and

(2) The one and two-tenths (1.2) inch Stormwater Retention Volume (SWRv);

(b) Calculating the WQTv requirement in § 524.4(a) as follows:

$$WQTv = (P \times [(Rv_N \times N) + (Rv_C \times C) + (Rv_I \times I) + (Rv_B \times B) ] \times 7.48 / 12) - SWRv$$

where:

The surface area shall include the combined total of the substantially improved building footprint and the land disturbance,

WQTv = volume, in gallons, required to be retained or treated, above

Water and Sanitation

and beyond the SWRv requirement,

SWRv = volume, in gallons, required to be retained,

P = 95th percentile rainfall event for the District (1.7 inches),

RvN = .00 (runoff coefficient for natural cover),

RvC = .25 (runoff coefficient for compacted cover),

RvI = .95 (runoff coefficient for impervious cover),

RvB = .95 (runoff coefficient for BMP cover),

N = post-development natural cover surface area;

C = post-development compacted cover surface area,

I = post-development impervious cover surface area,

B = post-development BMP cover surface area; and

(c) Employing each post-development land cover factored into the WQTv.

524.5For an AWDZ site that undergoes a major substantial improvement activity and does not undergo a major land-disturbing activity, the property owner shall:

(a) Comply with the performance requirements for major substantial improvement activity, except that the SWRv requirement shall be equal to the post-development runoff from a one (1.0) inch rainfall event, which is the eighty-fifth (85th) percentile rainfall event for the District of Columbia, measured for a twenty-four (24) hour rainfall event with a seventy-two (72) hour antecedent dry period;

(b) Treat rainfall from a one and seven-tenths (1.7) inch rainfall event, which is the ninety-fifth (95th) percentile rainfall event for the District of Columbia, measured for a twenty-four (24) hour rainfall event with a seventy-two (72) hour antecedent dry period by:

(1) Employing and maintaining each BMP necessary to treat the one and seven-tenths (1.7) inch WQTv requirement equal to the difference between:

(A) The post-development runoff from the one and seven-

tenths (1.7) inch rainfall event; and

(B) The one (1.0) inch SWRv;

(2) Calculating the WQTv requirement in § 524.5(b) as follows:

$$WQTv = (P \times [(Rv_N \times N) + (Rv_C \times C) + (Rv_I \times I) + (Rv_B \times B)] \times 7.48 / 12) - SWRv$$

where:

The surface area shall include the combined total of the substantially improved building footprint and the land disturbance,

WQTv = volume, in gallons, required to be retained or treated, above and beyond the SWRv requirement,

SWRv = volume, in gallons, required to be retained,

P = 95^th percentile rainfall event for the District (1.7 inches),

Rv_N = .00 (runoff coefficient for natural cover),

Rv_C = .25 (runoff coefficient for compacted cover),

Rv_I = .95 (runoff coefficient for impervious cover),

Rv_B = .95 (runoff coefficient for BMP cover),

N = post-development natural cover surface area,

C = post-development compacted cover surface area,

I = post-development impervious cover surface area,

B = post-development BMP cover surface area; and

(3) Employing each post-development land cover factored into the WQTv.

524.6 For an AWDZ site, the property owner may comply with the on-site WQTv requirement with:

1. (a) On-site treatment designed to remove eighty percent (80%) of total suspended solids;
2. (b) On-site retention; or
3. (c) Direct conveyance of stormwater from the site to an approved shared BMP with sufficient available treatment or retention capacity.524.7 For an AWDZ site, the property owner may comply with part of the WQTv or SWRv requirements by using off-site retention pursuant to § 527 if:- (a) Site conditions make compliance technically infeasible, environmentally harmful, or of limited appropriateness in terms of impact on surrounding landowners or overall benefit to District waterbodies; and
4. (b) The Department approves an application for relief from extraordinarily difficult site conditions.524.8 For an AWDZ site, person shall use one and one-quarter (1.25) SRCs to comply with one (1) gallon of an Offv requirement if the SRCs are certified for retention capacity located outside of the Anacostia watershed.524.9 An AWDZ site shall obtain Department approval of an integrated pesticide management plan meeting the requirements of the Department's Stormwater Management Guidebook.524.10 A major regulated project in the AWDZ shall achieve the required level of stormwater management using one or more of the following methods, in the following order of preference:- (a) Vegetated BMPs and land covers designed to retain and beneficially use stormwater;
5. (b) Where compatible with groundwater protection, non-vegetated infiltration BMPs;
6. (c) Other low impact development practices;
7. (d) Collection and use of stormwater for on-site irrigation and other purposes; and
8. (e) Other on-site BMPs or design methods approved by the Department.

SOURCE: Final Rulemaking published at 35 DCR 21 (January 1, 1988); as amended by Final Rulemaking published at 60 DCR 10640 (July 19, 2013); as amended by Final Rulemaking published at 67 DCR 818 (January

31, 2020); as amended by Final Rulemaking published at 72 DCR 012101 (October 31, 2025).