This Minimum Control Measure emphasizes the reduction or elimination of pollutants to the municipal separate storm sewer system that may come from post-construction runoff after new development and redevelopment projects. The term post-construction is used to categorize runoff from a site with impermeable surfaces, such as buildings, roads and parking lots that remain after construction ends.
If unchecked, the increased impervious surface associated with development may increase stormwater volume and degrade water quality, which can harm lakes, rivers, streams, and coastal areas. Methods to mitigate stormwater impacts from new development include 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 a few ways to achieve the goals of reducing flows and improving water quality.
Either separately or in combination with the Minimum Control Measure for Construction Site - Stormwater Runoff Control, the MS4 (with land use control capabilities) is required to adopt a new local law, amend existing local laws and ordinances, or establish equivalent regulatory mechanisms to reduce discharge of pollutants in stormwater runoff after completion of construction projects. MS4s without land use control capabilities are encouraged to develop necessary policies and procedures, and include such requirements in lease agreements, bid specifications, contracts, and/or permits.
In addition to post-construction requirements that MS4's place on developers, post-construction stormwater controls are also required of developers directly in Stormwater Pollution Prevention Plans (SWPPPs) under the SPDES General Permit for Stormwater Discharges from Construction Activity. However, the information presented on this webpage will focus on Post-Construction Stormwater Management practices and activities implemented by the regulated MS4.
In general, the MS4's post-construction stormwater management program should: provide for the review of post-construction stormwater management measures in SWPPPs; ensure stormwater management practices used are consistent with technical standards in the New York State Stormwater Management Design Manual; address ongoing maintenance of structural and non-structural management measures; provide for inspection of stormwater management measures and practices; maintain and inventory of post-construction practices; and, address compliance and enforcement activities.
Additionally, in certain areas that have current Watershed Improvement Strategies and/or Total Maximum Daily Load (TMDL) requirements, the regulated community may also be required to undertake additional activities such as: requiring post-construction stormwater management controls designed in accordance with Enhanced Phosphorus Removal Design Standards or with emphasis on the particular pollutant of concern; and, developing and implementing a Retrofit Program including identification of sites with erosion and/or pollutant loading problems; establishment of policies for project permitting, design, funding, construction and maintenance; schedules for retrofit plans; and cooperation with other permittees. The details associated with these additional requirements are further described, and should be referenced, in the SPDES General Permit for Stormwater Discharges from MS4s.