SITE INFORMATION AND CORRESPONDENCE_1988-1991

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• MEMORANDUM • CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALL REGION 3443 Routier Road, Suite A Phone: (91 ) 361-5600 Sacramento, CA 95827-3098 ATSS Phone:8495-5600 TO: Antonia K.J. Vorster FROM: Camilla Williams Senior WRC Engineer Engineering Geologist DATE: 18 December 1990 SIGNATURE: SUBJECT: MINUTES OF MEETING ON CONVERSION OF OXIDATION POND TO STORM WATER RETENTION BASIN, SHARPE SITE, SAN JOAQUIN COUNTY A meeting was held with the Corps of Engineers (COE) and their contractor, The Mark Group, Sharpe and the Department of Health Services (DHS) to discuss the conversion of the oxidation pond to a storm water retention basin at the Sharpe Site. The Mark Group prepared a technical report entitled "Environmental Investigation, Pond Conversion Project" dated 8 November 1990 which summarized the soils investigations conducted in 1988 and in 1990 and the water quality from monitor wells within the vicinit of the ponds. I had previously reviewed the report and attended the pre-design conference to convey my concerns with the data in the report and to provide guidance on cleanup and land disposal . The conversion of the oxidation pond to a storm water retention basin is needed because the South San Joaquin Irrigation District wants Sharpe to control the quantity of storm water runoff during periods of high flows. Currently, the storm water runoff flows to the same outfall as the treated domestic wastewater and into the Irrigation Di trict's canal which then flows to French Camp Slough. Discharges through this outfall are under a National Pollutant Discharge Elimination System (NPDES) permit. The data in The Mark Group's report indicated that there were elevated levels f heavy metals and heavy oils found within the sludge / soil samples taken within the oxidation and holding ponds. The report also revealed that the boring outside the western perimeter of the oxidation pond had low concentrations of volatile organic constituents (VOCs) , specifically Trichloroethylene (TCE) . All of the 1988 and 1990 analytical results were based on total concentrations. The report stated that the soils beneath the ponds did not appear to contain hazardous concentrations of waste constituents. The report also stated that the historical ground water high has been within five feet of the base of the ponds. My concerns with the report revolved around the fact that analyses for soluble concentrations had not been performed to determine if the residual wastes within the unsaturated zone represented a threat to water quality. This concern was particularly pertinent because of the shallow ground water table which is known to fluctuate and historically has been as high as the base of the ponds. Another concern is that the water quality of the storm water runoff itself is unknown. The construction of the basin would be a point source of discharge and could represent a threat to ground water quality if the storm water runoff is contaminated and/or the residual wastes within the unsaturated zone are soluble and are not remediated. Additionally, because the oxidation and holding ponds did not contain hazardous concentrations of waste constituents, they are not regulated by the Toxic Pits Cleanup Act. Based on the discussions with the representatives at the meeting, it was decided that the soils beneath the oxidation pond would be resampled and analyzed for soluble