559.1 No stormwater fee discount shall exceed the maximum allowable discount, which shall be fifty-five percent (55%) of the otherwise chargeable stormwater fee.

559.2 The stormwater fee discount shall be calculated as follows:

(a) Determine, in gallons, the maximum volume of stormwater runoff retained by the eligible Best Management Practice (BMP) during a one and two-tenths-inch (1.2 in.) rainfall event;

(b) Divide the step “(a)” result by seven hundred ten and seventy-five hundredths gallons (710.75 gal.) per Equivalent Residential Unit (ERU) (the number of gallons of stormwater runoff per ERU that would be generated by a one and two-tenths-inch (1.2 in.) rainfall event);

(c) Multiply the step “(b)” result by the maximum allowable discount percentage; and

(d) Multiply the step “(c)” result by the stormwater fee per ERU specified in § 556;

(e) Except that, for a rain barrel, the Department may allow the calculation method in § 559.6(e) to be used.

559.3 The calculated stormwater fee discount shall be applied to each month’s obligation of the stormwater fee.

559.4 The stormwater fee discount will appear on the customer’s District of Columbia Water and Sewer Authority bill beginning with the billing period that follows the District Department of the Environment’s (Department’s) receipt and processing of a complete application, which processing will include transmittal to DC Water to incorporate the discount in the customer’s billing calculation.

559.5 A customer shall have the right to apply with a Simplified Application for a property with a BMP, or multiple BMPs, that manages a cumulative impervious area of two thousand square feet (2,000 sq. ft.) or less.

559.6 The Department shall calculate the discount eligible for use of the Simplified Application as follows:

(a) Determine the total area that the BMP(s) manages, in square feet, after taking into consideration the runoff coefficients of this chapter for each Water and Sanitation

land cover type;

(b) Divide the step “(a)” result by the original total area of impervious surface, and express the quotient as a percentage;

(c) Multiply the step “(b)” result by the maximum allowable discount;

(d) Multiply the percentage result from step “(c)” by the stormwater fee per ERU specified in § 556; and

(e) For rainwater harvesting, including a rain barrel and a cistern, add:

(1) The product of multiplying the stormwater fee by 0.13 ERU per rain barrel installed; or

(2) The discount calculated using the methodology of § 559.2.

SOURCE: Final Rulemaking published at 60 DCR 10732 (July 19, 2013); as amended by Final Rulemaking published at 63 DCR 9665 (July 22, 2016).