§ 2–1226.36. Stormwater control standards.

(a) This section shall apply to the new construction and substantial improvement projects identified in § 2-1226.33 that disturb 5,000 square feet or greater of soil or that have a building footprint of 5,000 square feet or greater.

(b) Private and public space, including buildings, sidewalks, streets, and lawns, within a project subject to this part that discharge directly to the waters of the District, or to either a separate or combined sewer system, shall be designed, constructed, and maintained to comply with the following:

(1) Manage stormwater by:

(A) The reduction of the volume of stormwater run-off created during a 24-hour one-inch storm event following 72 hours of dry conditions, via on-site retention through DDOE-approved practices, including those that incorporate one or more of the following: infiltration, evapo-transpiration, and beneficial reuse; and

(B) The improvement of stormwater quality by filtering the stormwater from the 95th percentile storm flowing from a project, by passing the flow through a vegetated filtering medium or other on-site controls designed to remove sediment and pollutants of concern as identified in permits by the DDOE or the District of Columbia Water and Sewer Authority so that, according to DDOE’s determination, the discharge will not cause the exceedance of any water-quality standard applicable to the receiving water or cause interference or pass-through of pollutants at the Blue Plains receiving facility;

(2) Achieve the required level of stormwater control using the following DDOE-approved methods, in the following order of preference:

(A) Vegetated controls designed to retain and beneficially use stormwater;

(B) Where compatible with groundwater protection, non-vegetated controls designed to promote infiltration;

(D) Collection and reuse of stormwater for on-site irrigation; and

(E) Other on-site design methods or practices;

(3) Employ, where feasible, DDOE-approved low-impact development technologies for public spaces regulated by the District Department of Transportation;

(4) Restrict the on-site use of fertilizers, pesticides, and herbicides, through use of a DDOE-approved integrated pest management plan;

(5) Design stormwater controls to prevent migration of stormwater into contaminated underlying soils or groundwater;

(6) Certify that remediation of contaminated soils or groundwater is either completed as part of the development or that properly functioning long-term remedial measures are in place;

(7) Treat any groundwater produced at a project during construction or after completion of construction to remove sediment and pollutants of concern as required by DDOE or the United States Environmental Protection Agency, depending on which agency has jurisdiction; and

(8) Provide that any groundwater discharged from the site into the sanitary sewer system conforms to District of Columbia Water and Sewer Authority requirements designed to ensure that the discharge will not cause or contribute to the exceedance of any water quality standard applicable to the receiving water or cause interference or pass-through of pollutants at the Blue Plains receiving facility.

(c)(1) If DDOE determines that, based on site conditions such as soil or groundwater contamination, local geology, or impacts on surrounding landowners, the substantial weight of the evidence limits the feasibility or appropriateness of the on-site stormwater management required by subsection (b)(1) of this section:

(A) Either off-site mitigation or payment in lieu of mitigation, or a combination thereof, shall be used to satisfy:

(i) The difference between the on-site stormwater reduction volume required by subsection (b)(1)(A) of this section and the volume of on-site stormwater reduction achieved; and

(ii) The difference between the on-site filtration required by subsection (b)(1)(B) of this section, and the volume of filtration achieved;

(B) Off-site mitigation shall be a reduction of stormwater volume equal to the off-site volume and shall be maintained for the life of the primary project; provided, that if the off-site mitigation is located outside the Anacostia Watershed, the volume treated shall equal 1.25 times the volume that would have been required to be treated on site; and

(C) Payment in lieu of mitigation shall be equal to the cost for DDOE to reduce the off-site volume for the life of the primary project. DDOE shall determine this payment based on DDOE’s fully burdened and inflation-adjusted cost of retention to achieve stormwater volume reduction via infiltration, evapo-transpiration, re-use practices, or other methods or practices approved by DDOE, for a site determined by DDOE.

(2) For the purposes of this subsection, the term “off-site volume” shall mean the difference between the requirements of subsection (b)(1)(A) or (b)(1)(B) of this section, and the volume of on-site stormwater management achieved.

(d) A payment in lieu of mitigation shall be:

(1) Deposited in the Anacostia River Clean Up and Protection Fund, established by § 8-102.05; and

(2) Used to achieve stormwater volume reduction in the Anacostia watershed.

(e) Under circumstances described in subsection (c) of this section, transportation projects, or substantially similar projects undertaken by a public utility, in the existing public right-of-way shall be exempt from the requirement for off-site mitigation or payment in lieu of mitigation.