by: William Strand, PE, QSD

Whether you are a developer or a public agency, your upcoming project will likely be required to comply with the State Water Resources Control Board’s (SWRCB) new site design, runoff reduction, numeric treatment, retention and hyrdromodification requirements. These requirements are being implemented through local Regional Water Quality Control Board (RWQCB) Municipal Separate Storm Sewer System (MS4) Permits.

The requirements call for the use of low-impact development (LID) techniques such as bio-retention, flow-through planters, infiltration trenches, grass filter strips, downspout disconnection, cisterns, green roofs and other methods that have space and cost impacts on your project. The RWQCBs are also beginning to implement hydromodifictaion controls. Hydromodification occurs when drainage patterns are modified, pervious surfaces are paved and vegetative cover is removed. Hydromodification tends to reduce base flows in streams and rivers, increase peak flows and alter sediment supply. In controlling hydromodification, the RWQCBs are attempting to mitigate the impacts of development on streams and rivers.

Phase II of the National Pollution Discharge Elimination System (NPDES) (small municipalities under 100,000 people and non-traditional MS4s) becomes effective July 1, 2013. Under the new Small MS4 Permit, new permittee’s must comply with the water quality requirements of the Construction General Permit (CGP) until July 1, 2015 at which time they must implement water quality and hydromodification controls using LID site design and runoff reduction measures, numeric runoff treatment and retention controls and hydromodification controls.

What does this mean to your agency or project? YOU CAN NO LONGER IGNORE STORMWATER. Stormwater needs to be integrated into your earliest planning efforts. This is not only a requirement of the new MS4 permits, but is now the most cost-effective method to meeting the new requirements. Several new MS4 permits do not allow proprietary filters unless the project can prove LID is infeasible.

RRM’s multidisciplinary team is ideally suited to assist agencies and developers with our in-house engineers, planners and landscape architects assigned to each and every project. Our team can assist you in developing a plan which is cost-effective, maintainable, aesthetic and meets the regulatory requirements.

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