Grassland Bypass Project

Background Information

The Grassland Bypass Project has been under waste discharge requirements (WDRs) since 1998. Historically, subsurface agricultural drainage water (tile drainage) and surface runoff (irrigation tail water) from the Grassland Watershed was discharged to the San Joaquin River through Salt Slough and/or Mud Slough (north). These two sloughs are tributary to the San Joaquin River and serve as the primary drainage outlets for the Grassland Watershed. With the start of the Grassland Bypass Project in 1996, all tile drainage from a 97,000 acre area known as the Grassland Drainage Area is consolidated and conveyed through San Luis Drain to Mud Slough, eliminating discharges of drainage water from the Grassland Drainage Area into Salt Slough and wetlands. Reducing selenium in wetland channels is the primary goal of the Project, as elevated concentrations of selenium have been documented to be hazardous to wildlife.

For more detailed information and access to annual reports, go to U.S. Bureau of Reclamation Grassland Bypass Project Homepage.

Additional data and reports are available on the San Francisco Estuary Institute's page:

Tentative WDRs for the Grassland Bypass Project

Proposed for consideration at the 5-6 December 2019 Central Valley Water Board Meeting. Persons wishing to submit comments on this action should submit written comments no later than 5:00 pm on 6 November 2019. If you have any questions or comments, please contact Ashley Peters at 916-464-4857 or

WDRs for the Grassland Bypass Project

Waste discharge requirements San Luis & Delta-Mendota Water Authority and United States Department of the Interior, Bureau of Reclamation, Surface Water Discharges from the Grassland Bypass Project

WDRs for Growers in the Grassland Drainage Area

The Central Valley Water Board Irrigated Lands Regulatory Program (ILRP) was initiated in 2003 as a conditional waiver of WDRs program to regulate discharges from irrigated commercial agricultural land to surface waters. As surface water discharges were already regulated under the Grassland Bypass Project WDRs, the growers in the Grassland Drainage Area were not regulated by the ILRP conditional waiver. In 2012, the Central Valley Water Board started issuing waste discharge requirements for discharges to surface water and groundwater for irrigated commercial agricultural land. The General Order for growers in the Grassland Drainage Area regulates discharge to groundwater and is similar to other ILRP general orders.

2010 Basin Plan Amendment

Grassland Bypass Project Documents

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