In 2011, the District of Columbia adopted a precedent-setting stormwater permit that requires onsite retention with green infrastructure. Newly developed properties larger than 465 m2 (5000 ft2) will have to retain 30 mm (1.2 in.) of rain onsite for 24 hours, while redeveloped sites must capture a 20-mm (0.8-in.) storm. The redevelopment standards apply only when renovation project costs exceed 50% of the structure’s value before the project.
The permit also mandates a stormwater rule for managing stormwater and sediment and erosion control. The original 2012 proposal drew criticism from the development industry and mixed reviews from environmental groups. In the June 7 District of Columbia Register, the district announced a new proposed rule to be finalized by July 22.
In an effort to reduce compliance costs and increase flexibility for developers, the rule incorporates a stormwater credit trading program. According to the D.C. Department of the Environment, it will be the first of its kind in the U.S. Property owners could halve retention requirements by purchasing credits generated at nonregulated properties with certified green infrastructure installations and at regulated properties that control more stormwater than necessary.
Developers could also take credit for stormwater controls installed on or after May 1, 2009, for the amount exceeding retention requirements in place at the time. Another option would be to pay an in-lieu fee.