SITE INFORMATION AND CORRESPONDENCE

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tJ t 7t 83 WEST MARCH LANE 4 ,y',Jlii'i 11TAL s1E. 1 SUITE 12 '.: 'SRF, ;:,� 11C STOCKTON,CA 95207 i PHONE:(209)476-1635 Q,-rP 20 PM 2: 40 MANAGERS DESIGNERSICONSULTANTS .° "`" G• September 15, 1993 Mr. Michael Collins, REHS San Joaquin County Public Health Services Environmental Health Division P.O. Box 2009 Stockton, CA 95201 W.O. No. 06778-003-001 SUBJECT: Summary of Quarterly Groundwater Monitoring Program San Joaquin County Mosquito and Vector Control District 200 North Beckman Road, Lodi, California Site Code: 1849 Dear Mr. Collins, On behalf of the San Joaquin County Mosquito and Vector Control District (the District), this letter summarizes the results of the groundwater investigation and monitoring program which has been conducted by the District on the Beckman Road site. In 1986, the District removed three underground storage tanks (USTs) from the site and excavated soil beneath the gasoline UST to a depth of 31 feet below grade. A soil and groundwater investigation conducted by Weiss Associates on behalf of the District in 1987 consisted of soil borings and the installation of three groundwater monitor wells each to a depth of approximately 50 feet. The results of this investigation indicated the presence of hydrocarbon compounds in soil beneath the former gasoline UST, however, groundwater samples from the three wells indicated there was no detectable hydrocarbon compound presence in the groundwater. The lack of hydrocarbon impact to groundwater was interpreted to be due in part to the presence of a low permeability soil layer at approximately 32 feet below the ground surface which may act as a barrier to downward migration of hydrocarbon compounds. The Weiss Associates study also concluded that groundwater beneath the site flowed in a north- northeasterly direction, based on groundwater elevations in the three monitor wells. In December 1.991, ROY F. WESTON, INC. (WESTON®) began a quarterly groundwater monitoring program on behalf of the District. WESTON's first sampling effort revealed that only one of the three wells contained enough water to sample. Consequently, the San Joaquin County Environmental Health Division (EHD) requested that an additional monitor well be installed on the site northeast of the former tank area to evaluate the possible downgradient migration of hydrocarbons in groundwater. The new well, MW-4, was installer] in July 1992 according to the EHD-approved WESTON work plan. A detailed description of the well installation and sampling activities was presented in the WESTON report entitled Well Installation and Quarterly Groundwater Monitoring Report, dated October 14, 1992. &TK",l<M';W'0LLINS.WPI