Stormwater Management

New Development

Provision C.3 in the Municipal Regional Permit (MRP) requires site designs for new developments and redevelopments to minimize the area of new roofs and paving. Where feasible, previous surfaces should be used instead of paving so that runoff can infiltrate to the underlying soil. Remaining runoff from impervious areas must be captured and used or treated using bio-retention. In some developments, the rates and durations of site runoff must also be controlled.

In addition, project applicants must execute agreements to allow municipalities to verify that stormwater treatment and flow-control facilities are maintained in perpetuity.

Local Application

The California Regional Water Quality Control Board for the San Francisco Bay Region adopted a re-issued MRP in November 2015.

The C.3 requirements are separate from, and in addition to, requirements for erosion and sediment control and for pollution prevention measures during construction.

Through the Contra Costa Clean Water Program, Contra Costa municipalities have prepared a Stormwater C.3 Guidebook (PDF) to assist applicants through the process of submittals and reviews.

Stormwater Issues 101

Urban Runoff

Stormwater runoff is part of a natural hydrologic process. Human activities particularly urbanization and agriculture, can alter natural drainage patterns and add pollutants to:

  • Coastal Bays
  • Estuaries
  • Lakes
  • The Ocean
  • Rivers
  • Streams

Numerous studies have shown urban runoff to be a significant source of water pollution, causing declines in fisheries, restricting swimming, and limiting our ability to enjoy many of the other benefits that water resources provide (USEPA, 1992). Urban runoff in this context includes all flows discharged from urban land uses into stormwater conveyance systems and receiving waters and includes both dry weather non-stormwater sources (e.g., runoff from landscape irrigation, water line and hydrant flushing) and wet weather stormwater runoff. Urban runoff and stormwater runoff are used interchangeably.

Prevention & Control

For many years the effort to control the discharge of stormwater focused mainly on the quantity (e.g. drainage, flood control) and, only to a limited extent, on the quality of the stormwater (e.g. sediment and erosion control). In recent years, however, awareness of the need to improve water quality has increased. With this awareness, federal, state and local programs have been established to reduce pollutants contained in stormwater discharges to our waterways. The emphasis of these programs is to promote the concept and the practice of preventing pollution at the source, before it can cause environmental problems (USEPA, 1992). Where further controls are needed, treatment of polluted runoff may be required.

Municipal Separate Storm Sewer System Maps

Hard copies of the Municipal Separate Storm Sewer System (MS4) maps are available for review at the City's Permit Center counter, located at:
1950 Parkside Drive
Concord, CA 94519