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PUBLIC ItALTH SERVES SAN JOAQUIN COUNTY ENVIRONMENTAL HEALTH DIVISION Karen Furst, M.D., M.P.H., Health Officer 304 East Weber Avenue, Third Floor • Stockton, CA 95202 , 209/468-3420 DONNA SANTINI GARDNER 1206 STRUCK ORANGE CA 92667 RE: Donna Gardner Property Site Code: 1864 26056/26080 Thornton Road Thornton CA 95686 San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has completed review of the following reports prepared by Smith/ATC: "Workplan Addendum to Implement a Feasibility Study and to Complete the Groundwater Investigation" dated December 15, 1997; "Quarterly Report, July through September 1997" dated October 30, 1997 and revised November 24, 1997; "Work plan to Implement a Feasibility Study and to Complete the Groundwater Investigation" dated October 30, 1997; and "Problem Assessment Report" dated October 21, 1997. PHS/EHD has the following comments for your consideration and response. The Problem Assessment Report which was dated October 21, 1997 included the revised tables that PHS/EHD requested in correspondence dated September 22, 1997. A copy of this correspondence has been placed with the referenced report. PHS/EHD has also reviewed the Groundwater Monitoring Report, July through September 1997 which was dated October 30, 1997 and revised on November 24, 1997 pursuant to PHS/EHD's request. The analytical summary table contained misinformation which has been corrected. The Workplan to Implement a Feasibility Study and to Complete the Groundwater Investigation dated October 30, 1997 proposed to drill six soil borings to be completed as three vapor extraction wells, two monitoring wells, and an air sparge well. The two monitoring wells will be placed in the proximity of the Thornton Municipal Well #2. One of the monitoring wells was to be installed to a total depth of approximately 92 feet below ground surface (bgs) and would serve to determine the extent of the vertical groundwater contamination and as a sentinel well. The Workplan included the recommendation to modify the construction of the Thornton Municipal Supply sentinel well as originally proposed. The Problem Assessment Report had proposed the installation of a nested well which would be screened in the shallow zone and in a deeper zone of groundwater. The Workplan modified the proposed construction to avoid possible cross contamination and included the physical separation of the two wells and conductor casing of the deeper well. Based on the Supply well's construction log, PHS/EHD concurs with the modification to ensure that both zones are monitored and that the deeper well be conductor cased from ground surface to 65 feet bgs. PHS/EHD however, will require that soil samples be collected to better characterize the deeper zone, because the boring/driller's log obtained during the installation of the Supply well was most likely based on observations of the drill cuttings, rather than observations of discrete soil samples. During the project meeting held on December 8, 1997 which was attended by Tom Lutterman of ATC, Dean Gilman of San Joaquin County Public Works, Ron Rail of San Joaquin County Utilities Maintenance District L JAN 0 6 1998 A Division of San Joaquin County Health Care Services