Green Infrastructure Digest

Just in case you missed it last week among all of the other pressing news stories, the EPA released a report outlining technical guidelines for implementing the stormwater runoff requirements for federal projects under Section 438 of the Energy and Independence and Security Act (EISA). In effort to afford designers maximum flexibility, the guidance provided is performance-based. The Section 438 of the EISA established the following requirements:

“Storm water runoff requirements for federal development projects. The sponsor of any development or redevelopment project involving a Federal facility with a footprint that exceeds 5,000 square feet shall use site planning, design, construction, and maintenance strategies for the property to maintain or restore, to the maximum extent technically feasible, the predevelopment hydrology of the property with regard to the temperature, rate, volume, and duration of flow.”

On October 5th, the White House issued a Presidential Executive Order addressing this requirement. The Executive Order titled “Federal Leadership in Environmental, Energy, and Economic Performance.” It required the EPA in coordination with other agencies to develop guidelines for implementing Section 438 of the EISA within 60 days. The current publication meets these guidelines.

The guidelines establish two options for meeting Section 438. The first option is to retain 100% of a rainfall event on site that is less than or equal to a 95th percentile. A 95th percentile rainfall event is an event with a volume over a 24-hr period that is equal to or less than the volume of 95% of all rain events for a period of record (i.e. 20 to 30 years). The table from the report provided below shows the size of the 95th percentile events for various cities across the Country. The events range between 0.7 to 1.8 inches of rainfall. These events commonly known as a “first flush” event were identified because they often contain the highest level of pollutants. Option 2 allows designers to conduct their own hydrological analysis and determine the site specific pre-development hydrological conditions. This options states that “temperature of runoff should not exceed the pre-development rates and the predevelopment hydrology should be replicated.”

For both of these options, the guidelines encourage the use of green infrastructure stategies. The guidelines recognize that “runoff event frequency, volume and rate can be diminished or eliminated through the use of green infrastructure (GI)/Low Impact Design (LID) designs and practices, which infiltrate, evapotranspire and capture and use stormwater”. The guidelines provide a number of studies that illustrate how green infrastructure can meet the established criteria. It is exciting to see the continued momentum green infrastructure is experiencing. If your considering working on federal projects, you will need to take a serious look at green infrastructure as an integral part of your site strategy.