D.C. Mun. Regs. tit. 21, r. 21-524

Current through Register Vol. 71, No. 50, December 13, 2024

Rule 21-524 - 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

An AWDZ site shall employ each Best Management Practice (BMP) and land cover necessary to meet the requirements of this section until site redevelopment that follows a Department-approved Stormwater Management Plan 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

An AWDZ site that undergoes a major land-disturbing activity shall achieve treatment of the rainfall from a 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 1.7 inch WQTv equal to the difference between:

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

(2) The 1.2 inch SWRv;

(b) Calculating the WQTv in subsection (a) as follows:

WQTv= (P × [(Rv_I × I) + (Rv_C × C) + (Rv_N × N)] × 7.48 /12)-SWRv

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

SWRv = volume, in gallons, required to be retained

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

Rv_I = 0.95 (runoff coefficient for impervious cover)

Rv_C = 0.25 (runoff coefficient for compacted cover)

Rv_N = 0.00 (runoff coefficient for natural cover)

I = post-development site area in impervious cover

C = post-development site area in compacted cover

N = post-development site area in natural cover

where site area includes substantially improved building footprint plus land disturbance and where the surface area under a BMP shall be calculated as part of the impervious cover (I); and

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

524.5

An AWDZ site that undergoes a major substantial improvement activity and does not undergo a major land-disturbing activity shall:

(a) Comply with the performance requirements for major substantial improvement activity, except that the SWRv shall be equal to the post-development runoff from a 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) Achieve treatment of the rainfall from a 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 each BMP necessary to treat the 1.7 inch WQTv equal to the difference between:

(A) The post-development runoff from the 1.7 inch rainfall event; and

(B) The 1.0 inch SWRv;

(2) Calculating the WQTv in subsection (b) as follows:

WQTv = (P × [(Rv_I × I) + (Rv_C × C) + (Rv_N × N)] × 7.48 /12)-SWRv

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

SWRv = volume, in gallons, required to be retained

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

Rv_I = 0.95 (runoff coefficient for impervious cover)

Rv_C = 0.25 (runoff coefficient for compacted cover)

Rv_N = 0.00 (runoff coefficient for natural cover)

I = post-development site area in impervious cover

C = post-development site area in compacted cover

N = post-development site area in natural cover

where site area includes substantially improved building footprint plus land disturbance and where the surface area under a BMP shall be calculated as part of the impervious cover (I); and

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

524.6

A major regulated project in the AWDZ may achieve on-site treatment for WQTv with:

(a) On-site treatment designed to remove eighty percent (80%) of Total Suspended Solids;

(b) On-site retention; or

(c) Direct conveyance of stormwater from the site to an approved shared BMP with sufficient available treatment or retention capacity.

524.7

An AWDZ site may achieve part of the WQTv or SWRv by using off-site retention 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;

(b) The Department approves an application for relief from extraordinarily difficult site conditions; and

(c) The off-site retention is from outside the CSS.

524.8

An AWDZ site that achieves a gallon of Off-Site Retention Volume (Offv) by using Stormwater Retention Credits (SRCs) certified for retention capacity located outside of the Anacostia watershed shall use 1.25 SRCs for that gallon of Offv.

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;

(b) Where compatible with groundwater protection, non-vegetated infiltration BMPs;

(c) Other low impact development practices;

(d) Collection and use of stormwater for on-site irrigation and other purposes; and

(e) Other on-site BMPs or design methods approved by the Department.

D.C. Mun. Regs. tit. 21, r. 21-524

Final Rulemaking published at 60 DCR 10640 (July 19, 2013); amended by Final Rulemaking published at 67 DCR 844 (1/31/2020)

Authority: Department of Consumer and Regulatory Affairs Civil Infractions Act of 1985, effective October 5, 1985, as amended (D.C. Law 6-42; D.C. Official Code §§ 2-1801.01 et seq. (2007 Repl. & 2012 Supp.)); District Department of the Environment Establishment Act of 2005, §§ 101 et seq., effective February 15, 2006, as amended (D.C. Law 16-51; D.C. Official Code §§ 8-151.01 et seq. (2008 Repl. & 2012 Supp.)); National Capital Revitalization Corporation and Anacostia Waterfront Corporation Reorganization Act of 2008, effective March 26, 2008 (D.C. Law 17-138; 55 DCR 1689), as amended by the Anacostia Waterfront Environmental Standards Amendment Act of 2012, effective October 23, 2012 (D.C. Law 19-192; D.C. Official Code §§ 2-1226.31 et seq.) (2012 Supp.)); The Soil Erosion and Sedimentation Control Act of 1977, effective September 28, 1977 (D.C. Law 2-23; 24 DCR 792), as amended by the Soil Erosion and Sedimentation Control Amendment Act of 1994, effective August 26, 1994, (D.C. Law 10-166; 41 DCR 4892; 21 DCMR §§ 500 -15); Uniform Environmental Covenants Act of 2005, effective May 12, 2006, as amended (D.C. Law 16-95; D.C. Official Code §§ 8-671.01 et seq. (2008 Repl.)); Water Pollution Control Act of 1984, effective March 16, 1985, as amended (D.C. Law 5-188; D.C. Official Code §§ 8-103.01 et seq. (2008 Repl. & 2012 Supp.)); and Mayor's Order 2006-61, dated June 14, 2006, and its delegations of authority.