New Stormwater Control Requirements Part 2

On October 14, 2009 the San Francisco Bay Regional Water Quality Control Board (RWQCB) adopted a revised Municipal Regional Stormwater Permit (MRP). The MRP regulates stormwater discharges pursuant to the National Pollutant Discharge Elimination System (NPDES). The new MRP consolidates and supersedes previous permits issued to cities, towns, and local agencies in Alameda, Contra Costa, San Mateo, and Santa Clara counties, as well as the Solano County cities of Fairfield, Suisun City, and Vallejo. For a copy of the MRP, go to SF RWQCB

In February 2003 the San Francisco Bay RWQCB added Provision C.3 to the NPDES stormwater permits issued to the municipalities under its jurisdiction. Intended to reduce the introduction of urban pollutants into San Francisco Bay and the creeks, streams, lakes, and other water bodies in the region, Provision C.3 requires the onsite treatment of stormwater prior to its discharge into downstream receiving waters. (These requirements are in addition to the new NPDES requirements for erosion and sedimentation controls during project construction that were addressed in the previous DHA eAlert).

Under the old permit, projects subject to Provision C.3 were required to capture and treat onsite all stormwater from the site prior to its discharge, including rainwater falling on building rooftops, to the "maximum extent practicable." This was accomplished via:

Treatment controls, such as bio-retention areas, vegetated swales, and infiltration trenches;

Source control features designed to keep pollution away from stormwater, such as trash and designated wash areas that are plumbed to the sanitary sewer system;

Site Design features reducing impervious areas, increasing pervious areas, and utilizing landscaped areas in between impervious areas as a storm drainage treatment feature; and

Hydrograph Modification Management, also called Hydromodification Management (HM), to ensure that runoff from developed areas matches the flow volume and rate of the pre-project runoff.

What's New?

In brief, the revised Provision C.3 requirements of the new MRP include:

For some land uses-including gas stations, restaurants, and uncovered parking lots-the threshold for onsite treatment requirements drops to 5,000 (from 10,000) square feet of impervious area created or replaced.

Applicants must evaluate feasibility of infiltration or on-site use.

Applicants may propose to provide treatment of runoff from an equivalent amount of impervious area, subject to conditions.

Use of below-ground vaults and filters is still restricted (exceptions to be updated).

Low-Impact Development (LID) design procedures and criteria for treatment and flow-control facilities will stay the same. However, although many municipalities in the Bay Area have, until now, allowed non-LID designs (including detention basins and proprietary devices) to treat runoff, under the MRP, these municipalities must now require LID be used to reduce runoff before discharge off site.

Biotreatment (filtering stormwater through vegetation and soils before discharging to the storm drain system) and/or vault-based treatment measures will be allowed only where LID methods such as harvesting and reuse, infiltration and evapotranspiration are infeasible at the project site.

Applicants for approval of projects smaller than the threshold are encouraged to include site design measures to reduce runoff and source control measures to reduce pollutants in runoff.

Projects larger than 2,500 square feet of impervious area must include at least one site design feature to reduce runoff.

When Will the New Permit Take Effect?

Most of the new MRP requirements are phased in through 2012. Project applicants should assume new projects that start after January 1, 2010 will be subject to the new MRP. As of the date of this eAlert, most Bay Area jurisdictional agencies have not updated their respective guidance documents to incorporate the requirements of the new permit.

We have prepared a white paper providing more detail on the new requirements, which we're providing free of charge to our readers. Among other information, it includes a table summarizing the changes to the stormwater requirements. You can download the document at Stormwater White Paper #4