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Frequently Asked Questions

General Information

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  • What is a watershed and why does it matter?

    Simply stated, a watershed is an area of land that drains into a common water body, such as a river, lake, or the ocean. Water moving through a watershed picks up pollutants such as trash and bacteria and transports them into our waterways. Preventing pollutants from contaminating our water sources is important for everyone’s health and your actions can help protect our waterways.

  • How can I help?

    Good housekeeping practices like sweeping up litter, picking up pet waste, and preventing irrigation runoff can help to keep pollutants out of our waterways. To learn about more ways you can help, visit our Residential and Industrial/Commercial pages. 

  • What is an MS4?

    MS4 stands for Municipal Separate Storm Sewer System and is basically the storm drain system that is owned and operated by a local municipality.

    An MS4 discharges to local water bodies such as creeks, rivers, streams, lakes or reservoirs, is designated or used for collecting or conveying stormwater, is not a combined sewer, and is not part of a Publicly Owned Treatment Works to treat wastewater.

  • What is the MS4 Permit?

    The Municipal Separate Storm Sewer System (MS4) Permit is a regulatory tool used by the Regional Water Quality Control Board (RWQCB) to regulate stormwater and non-stormwater discharges into MS4s and from MS4s into local water bodies.

    The MS4 Permit defines the regulatory obligations that agencies must meet to remain in compliance with the permit and avoid enforcement actions. MS4 Permits are issued to municipalities as owners of the MS4 and are renewed approximately every five years.

  • What is the goal of the Permit and standards to achieve this goal?

    The overarching goal of the Permit is to protect water quality and designated beneficial uses of local water bodies from adverse impacts caused or contributed to by discharges from MS4s (Order R9-2013-0001).

    Copermittees (i.e., agencies regulated by the MS4 Permit) are required to implement water quality improvement strategies and runoff management programs to meet two standards:

    i.      Non-stormwater discharges will be effectively prohibited from entering the MS4, and

    ii.      Pollutants in stormwater will be reduced to the maximum extent practicable (MEP).

    The County's water quality improvement strategies and Jurisdiction Runoff Management Program are available online for review. 

  • What are the municipalities’ responsibilities under the MS4 Permit?

    The primary responsibility that municipalities have to comply with the MS4 Permit is to reduce or eliminate the pollutants entering and leaving their storm drain systems so the discharges do not contribute to pollution of receiving waters.

    This is accomplished through management of three main areas: land use planning (including new development and redevelopment); construction; and existing development (including municipal, industrial, commercial, and residential areas and activities). The approaches used to regulate these sectors have been developed by individual jurisdictions over the past 15-20 years of regulation under MS4 Permits and are described in the agencies’ Jurisdictional Runoff Management Plans (JRMPs).

Reporting Concerns

Where can I...

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Building and Grading Information




In addition to developing plans, guidelines and ordinances Watershed staff works collaboratively with other County departments and other agencies to ensure water quality is protected.  You can read more about these departments and agencies in the resources provided. 

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Awards and Achievements

Visit our Awards page to learn more about awards and achievements that the Watershed Protection Program has been recognized for.