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MEMORANDUM CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 TO: GREG K. VAUGHN FROM: JAMES BRATHOVDE Senior Engineer Engineering Geologist DATE: 15 May 1991 SIGNATURE: SUBJECT: DELTA TRUCK SALES, INC. , DRAFT HYDROGEOLOGICAL ASSESSMENT REPORT REVIEW, SAN JOAQUIN COUNTY A report titled "Draft Hydrogeological Assessment Report of Former Surface Impoundment" prepared for Delta Truck Sales, Inc. (DTS) , by Environmental Science and Engineering, Inc. (ESE) , was received on 17 December 1990. The following is a review of that report. GENERAL COMMENTS The Hydrogeological Assessment Report (HAR) for Delta Truck Sales, Inc. included vadose zone sampling, ground water quality data, a description of the excavated surface impoundment sludge and sidewalls, and a chemical analysis of the stockpiled waste from the excavated surface impoundment and a partial excavation of the landfilled area. The HAR is complete with the exception of two items: 1) Confirmation sampling of the existing monitoring wells is necessary. The gradient of the water table appears to be toward the northwest and therefore only one monitoring well is down gradient of the former surface impoundment. Additional down gradient monitoring wells may be necessary, if the monitoring wells are shown to be impacted by operation of the former surface impoundment. 2) The lateral extent of the ash layers, blue paint clods, and oily wastes seepage into the sidewalls of the former surface impoundment and landfilled area need to be defined. A work plan for the proposed soil borings or side wall excavation should be submitted to this office. With an additional round of ground water quality sampling and analysis, and a determination of the lateral extent of contaminated layers in the former landfill area or trench, the HAR would satisfy the requirements of Section 25208.8 of the Health and Safety Code. Cleanup and Abatement Order No. 91-722 was issued on 29 April 1991 . The Order required completion of the HAR by 1 September 1991 . The information supplied by the addendum to the HAR will characterize the lateral extent of contaminated material .