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CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION CEASE AND DESIST ORDER R5-XXXX-XXXX FOR SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS CORRAL HOLLOW SANITARY LANDFILL SAN JOAQUIN COUNTY GROUNDWATER CORRECTIVE ACTION REQUIREMENTS The California Regional Water Quality Control Board, Central Valley Region, ("Central Valley Water Board" or "Board") finds that: 1. The San Joaquin County Department of Public Works (hereafter County or Discharger) owns and operates a closed municipal solid waste landfill about five miles south of Tracy, California. Municipal solid waste has been placed on property owned by both San Joaquin County and California Department of Transportation (CalTrans). 2. The facility consists of 57.71 acres, of which 42.79 acres were permitted for landfilling and are shown in Attachment A, which is attached hereto and made part of this Order by reference. The landfill is regulated by Waste Discharge Requirements (WDRs) Order R5-2013-0013 and consists of a single, closed unlined waste management unit (WMU). 3. The Facility began operations as a solid waste disposal site in the 1950's. The Discharger began operating the landfill in 1991 as a Class III landfill. The Discharger ceased accepting waste in 1995 and formal closure was completed in 1996. In 2007, the Discharger determined that an additional 1.6 acres of municipal solid waste existed outside of the original landfill area. 4. The landfill is on the alluvial fan at the mouth of Corral Hollow Creek at the base of the eastern side of the Coast Range. The landfill is bounded to the south by Corral Hollow Creek, which flows intermittently toward the San Joaquin River. Land within 1,000 feet of the facility is dry range land. Groundwater Monitoring 5. Two groundwater zones have been identified beneath the landfill site. The first encountered groundwater is monitored by seven wells (SB-1, MW-4, MW-5, MW-8, MW-9A, MW-10A, and MW-11A), as shown on Attachment A. The groundwater monitored by SB-1, MW-4, MW-5, and MW-8 is considered to be perched water on top of the Corcoran Clay formation. Groundwater flow from these wells appears to move radially from well SB-1. However, groundwater flows northeast of the landfill (toward the valley) when groundwater elevations from all seven wells are considered. The first encountered groundwater ranges from about 12 feet to 65 feet below ground surface (bgs).