A Municipal Separate Storm Sewer System (MS4) is a conveyance or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains) that is:
- Owned by a state, city, town, village, or other public entity that discharges to waters of the U.S.;
- Designed or used to collect or convey stormwater;
- Not a combined sewer; and
- Not part of a Publicly Owned Treatment Works (POTW) (sewage treatment plant).
The State Water Resources Control Board issued a Phase II Small MS4 General Permit (Permit Number CA000004, Water Quality Order No. 2013-0001 DWQ) which was adopted then became effective on July 1, 2013. The General Permit requires regulated small MS4s in urbanized areas, as well as small MS4s outside the urbanized areas that are designated by the permitting authority, to obtain National Pollutant Discharge Elimination System (NPDES) permit coverage for their stormwater discharges. Each regulated MS4 is required to develop and implement a stormwater management program/approach to reduce and/or eliminate the discharge of pollutants from the MS4 to the maximum extent practicable (MEP) and effectively prohibit discharges of non-stormwater into its MS4, unless such discharges are authorized.
The Storm Water Management Program (SWMP) was implemented to limit, to the MEP, the discharge of pollutants from the Merced Storm Water Group’s (MSWG) storm sewer systems. The MSWG is a coalition of municipalities consisting of the City of Atwater, City of Merced, and Merced County. The development and implementation of the SWMP is to fulfill requirements of storm water discharges from Small MS4 operators in accordance with Section 402(p) of the Federal Clean Water Act (CWA). The SWMP was developed to also comply with the General Permit.
The overall goals of the Permittee’s SWMP are to a) reduce the potential impact(s) of pollution from urban areas on waters of the State and waters of the United States (U.S.) and protect their beneficial uses; and b) develop and implement an effective stormwater program that is well-understood and broadly supported by stakeholders.
The core objectives of the stormwater program are to:
- Identify and control those pollutants in urban runoff that exceed water quality objectives (WQOs), as measured in the waters of the State and waters of the U.S., and protect the beneficial uses of the receiving waters;
- Comply with the federal and State regulations to eliminate or control, to the MEP, the discharge of pollutants associated with urban runoff from the stormwater drainage system;
- Develop a cost-effective program which focuses on the prevention of pollution in urban stormwater;
- Seek cost-effective alternative solutions where prevention is not a practical solution for exceedances of WQOs; and
- Coordinate the implementation of control measures with other agencies.
To learn more about the Merced Stormwater Program you may review the document “Program Effectiveness Assessment and Improvement Plan” below.