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_l h 'S.TATE OF CALIFORNIA PETE WILSON Governor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— ,•�=:,, CENTRAL VALLEY REGION 3443 ROUTIER ROAD. SUITE A SACRAMENTO, CA 95827.3098 PHONE: (916) 361.5600 " FAX: (916) 361-5686. c 16 September 1991 SEP Mr. Michael Miller Department of Public Works City of Stockton 425 N. E1 Dorado Street Stockton, CA 95202-1991 APPROVAL OF CORRECTIVE ACTION PLAN, AUSTIN ROAD LANDFILL, CITY OF STOCKTON, SAN JOAQUIN COUNTY (CASE# 2148) We have reviewed the August 1991 Corrective Action Plan (CAP) prepared by EMCON Associates (EMCON) on behalf of the City of Stockton (City) . We find the CAP acceptable and the City may proceed with CAP activities as described in the submittal . However, there were several issues about the CAP which need to be addressed by the City. Drawing 1 and Section 2.4.2 of the CAP indicate that there is a ground water divide in which ground water flow passing under the landfill goes in both a northwesterly and northeasterly direction. Flow in the northeasterly direction, which contains the volatile organic contaminant (VOC) plume, appears to the have an adequate ground water monitoring and detection well system in place. While the only monitoring well, MW1, located on the northwest corner of the landfill is dry, the City should propose additional monitoring or detection wells in that area to ensure that the VOC plume is not spreading to the northwest. The CAP did not discuss the reasons why MW1, MW2, MW3, MW4 were dry during the July 1991 sampling event. Did the pumping tests conducted have any effect on these shallow monitoring wells or was this a result of seasonal fluctuation in the water table? Review of the well logs show that several monitoring wells with less than ten feet of well screen have been installed at the facility. Given the water table fluctuations and future extraction well pumping, the City may need to drill additional wells to adequately monitor ground water. Pages 2- 4 state that monthly water levels and hydrographs will be collected using data from the onsite wells. This information should be submitted either on a monthly or quarterly basis. The CAP implies that only VOCs are constituents of concern. Review of data submitted to date indicates the pH, electrical conductivity (EC), and total dissolved solids (TDS) should be included on the list of constituents of concern. Also, data submitted in the Verification Monitoring Plan indicates that there were constituents of concern in M143 and MW5 on the south portion of the landfill . MW3 had elevated levels of total dissolved solids (TDS) and electrical conductivity (EC), and MW5 had trace levels of VOCs. The CAP did not address either of these issues and no further action has been proposed by the City to date.