The project is located in the Grasslands Subarea as defined by the San Joaquin Valley Drainage Program (SJVDP, 1990). The area is a valley floor sub-basin of the San Joaquin River Basin. The Grasslands Subarea is an area of approximately 370,000 acres and is generally bounded on the north by the alluvial fan of Orestimba Creek and by the Westlands Subarea to the south. The San Joaquin River forms the eastern boundary and Interstate Highway 5 forms the approximate western boundary. The San Joaquin River forms a wide flood plain in the region. Approximately 90,000 agricultural acres within the Grasslands Subarea have historically discharged subsurface drainage water through the Grassland Water District channels and ultimately to the San Joaquin River. It is these discharges which are the focus of the Grassland Bypass Project and this Monitoring Plan.
The Grasslands Subarea is comprised primarily of agricultural lands and federal, state and private wetlands. The area is a highly managed hydrologic system due to the diversion of perennial flows out of the basin. Thus, agricultural irrigation water must be supplied via supply canals, as must the wetland irrigation water required to manage the wetlands. Similarly, drainage water must be managed in the absence of perennial receiving water flows and the accompanying assimilative, or dilution, capacity.