Vol. 19 No. 7 December 6, 2011



EPA Requires Green Infrastructure
in Washington, DC

On September 30, 2011, the U.S. Environmental Protection Agency (EPA) authorized the Municipal Separate Storm Sewer System permit (MS4 permit) for Washington, D.C. (the District), effective from October 7, 2011, to October 7, 2016. Developers should familiarize themselves with the authorized MS4 permit, which includes new requirements for stormwater retention and green infrastructure implementation. These requirements will likely be mandated by EPA in other jurisdictions in the future and will affect the design of most development projects within the District. Some of the MS4 permit requirements that will affect the development community are outlined below:

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1.2" Rainfall Retention Section 4.1.1 requires "the design, construction and maintenance of stormwater controls to achieve on-site retention of 1.2" of stormwater from a 24-hour storm with a 72-hour antecedent dry period ;through evapotranspiration, infiltration and/or stormwater harvesting and use for all development greater than or equal to 5,000 square feet." This means that approximately 90% of all rainfall must not leave the site.1

Additionally, Section 4.1.5.5 of the permit will require retention2,3, for retrofit projects that disturb less than 5,000 square feet when structures with a footprint greater than 5,000 square feet undergo substantial improvement.4 This requirement will impose stormwater management requirements on developers who are seeking to retrofit buildings within the District, in addition to those who disturb ground.

It should be noted that Chesapeake Bay Executive Order 13508 Section 502 Draft Guidance for Federal Land Management in the Chesapeake Bay Watershed (discussed in further detail in Field Notes Vol. 18, No. 5) requires projects to retain the 95th percentile rainfall event, which equates to 1.7" of rainfall in the Washington, D.C. metro area. The 1.7" retention requirement was originally applied to Federal lands in the District's draft MS4 permit but was subsequently removed from the final issued permit. Now, both Federal and non-Federal projects must comply with the 1.2" retention requirement, but it is unknown at this time if future MS4 permits will require additional retention to comply with the Section 502 Guidance.

• Green Landscaping Section 4.1.4 requires the District to create a "green landscaping incentive program" to encourage developers to specify green roofs, vegetated walls, and permeable pavements, and to preserve existing trees and specify larger plants, among others. This will potentially benefit developers who specify green infrastructure practices on their projects, but the benefits will not be quantifiable until the District has created the program.
• Impervious Area Retrofit Section 4.1.5 requires the District to retrofit 18 million square feet of impervious surfaces (including at least 1.5 million square feet within transportation rights-of-way) during the permit term. This requirement will likely affect all re-development projects within the District.
• Tree Canopy Section 4.1.6 requires the District to expand tree canopy (in an effort to achieve 40% canopy coverage by 2035) by achieving a net planting rate of 4,150 trees per year within the MS4 area (click for map). This requirement will likely mean that all new and re-development projects will need to specify a greater number of trees than was previously required.
• Green Roofs Section 4.1.7 requires the District to install a minimum of 350,000 square feet of green roofs on District-owned properties over the five-year course of the permit term. This requirement will only affect projects seeking to redevelop District-owned properties.
• Stormwater Management Guidebook Section 4.2.3 requires the District to finalize and publish a Stormwater Management Guidebook which will include specifications for the integration of on-site retention and other stormwater management technologies. The District must also create a training program to provide information regarding "objectives and specifications of green infrastructure practices contained in the Stormwater Management Guidebook." This will benefit the development community because it will give developers a definitive set of standards for the implementation of green infrastructure in the District.

With the issuance of DC's MS4 permit, EPA is underscoring its intention to begin mandating Green Infrastructure to manage stormwater runoff from development. This will affect projects throughout the District, and developers should familiarize themselves with the permit language. Additionally, the development industry should be prepared for similar measures to be enacted by EPA in other jurisdictions in the future.

For more information on DC's authorized MS4 permit, please contact Mike Rolband, Jennifer Brophy-Price, or Bethany Bezak.

 

1Per e-mail correspondence between Robert Goo (EPA) and Jennifer Brophy-Price (WSSI) on April 6, 2010, retention means "that the water will be evapotranspired, infiltrated or used onsite and not temporarily detained and discharged slowly over some predetermined period" (emphasis added).

2The permit requires the District to develop an enforceable mechanism to require retention for such projects no later than 18 months following the issuance of the permit, or April 2013.

3Due to the site constraints associated with retrofit development, EPA acknowledges that the District may be justified in setting the retrofit retention performance standard at less than 1.2".

4Substantial improvement is defined as being consistent with District regulation 12J DCMR Section 202: any repair, alteration, addition, or improvement of a building or structure, the cost of which equals or exceeds 50 percent of the market value of the structure before the improvement or repair is started.