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| Infiltration islands in parking lots can help reduce stormwater runoff.
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For the past two decades the rate of land development across the country has been more than two times greater than the rate of population growth. If unchecked, the increased impervious surface associated with this development will increase stormwater volume and degrade water quality, which can harm lakes, rivers, streams, and coastal areas.
The best way to mitigate stormwater impacts from new developments is to use practices to treat, store, and infiltrate runoff onsite before it can affect water bodies downstream. Innovative site designs that reduce imperviousness and smaller-scale low impact development practices dispersed throughout a site are excellent ways to achieve the goals of reducing flows and improving water quality.
Phase II MS4s are required to address post-construction stormwater runoff from new development and redevelopments that disturb one or more acres. This primarily includes developing:
- Strategies to implement a combination of structural and non-structural BMPs,
- An ordinance to address post-construction runoff, and
- A program to ensure adequate long-term operation and maintenance of BMPs.
Additional information on this minimum measure, including the stormwater Phase II regulatory requirements for post-construction and a fact sheet on the
post-construction minimum measure [PDF - 214 KB - 4 pp], is also available.
Key BMPs and Resources:
MS4s addressing the post-construction minimum measure should focus on the following four key BMPs to help them in
developing a post-construction program. Information on low impact development and smart growth are key resources for MS4s.
The additional BMPs in the next section describe practices that developers could use to comply with an MS4's
post-construction program.
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