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1 t � CLEARWATER G R O U P, Z N C . • Environmental Services ..0 t-'!C1 V 15 Pill 19 Ms. Mary Meays November 12, 1996 San Joaquin County Public Health Services/Environmental Health Division P.O. Box 388 Stockton, CA 95201-0388 Re: Revised Remedial Action Plan Ruiz Grocery, 4491 W. Durham Ferry Road, Tracy, CA Dear Ms. Meays, It was good to meet with you and Mrs. Stella Ruiz last week regarding corrective action at the referenced site. This letter follows up on that discussion, during which, we settled upon a conceptual corrective action plan. As you know, this plan differs from that originally proposed by Clearwater Group, Inc. (Clearwater) in our Problem Assessment Report, Feasibility Study, and Remedial Action Plan dated February 21, 1996 in which we recommended first performing dual-phase groundwater and soil vapor extraction and air sparging. Concurrent groundwater pumping with soil vapor extraction was proposed in order to keep the water table depressed so that well screens would be occluded, especially during periods of high water table conditions. However, in letters dated May 23 and August 15, 1996, the San Joaquin County Public Health Services/Environmental Health Division (SJCPHS/EHD) indicated they did not approve of the concept of groundwater extraction at this site. This difference in opinion precipitated our meeting last week, at which Clearwater proposed a compromise in order to move forward with corrective action, which is especially important because of the threat of gasoline constituents entering the domestic well and posing health risks to the residents at the site. The domestic well is located approximately 15 feet beyond the approximate downgradient edge of the dissolved plume. This well provides water for domestic use (except drinking) to four residences around the site. In addition to the threat to the well, the footprint of soil and groundwater contamination resides partially beneath the residence at the site, and thus there is a need to mitigate the potential exposure hazard which may result from volatilized contaminants. The spatial relationship between extent of soil contamination and the aforementioned receptors is shown on Figure 1. The revised corrective action plan proposed by Clearwater consists of performing air sparging and soil vapor extraction using vertical wells during periods of low water table conditions, and air sparging and soil vapor extraction from a proposed horizontal vapor well (to be installed beneath the utility trench needed to connect vertical wells to the remedial compound) during periods of high water table conditions. Use of the horizontal vapor extraction well during periods of high 520 Third Street,Suite 104 • Oakland,California 94607 w Telephone 510-893-5160 + Fax 510-893-5947