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KAPREALIAN ENGINEERING, INC. K E I Consulting Engineers P. O. BOX 913 BENICIA, CA 94510 (415)676-9100 (707)746-6915 KEI-P86-084A-2 January 20, 1988 Mobil Oil Corporation P. O. Box 127 Richmond, CA 94807 Attn: Mr. Jim Brendle Re: Supplemental Assessment of Soil and Groundwater Mobil Station #10-NP4 located at the corner of Tracy Blvd. and Grant Line Road in Tracy, California Dear Mr. Brendle: The following report covers Kaprealian Engineering, Inc. (KEI) recent activities at the referenced site. Monitoring and sampling of the seven wells has been conducted on a monthly basis since September 21, 1987 in accordance with our recommendations of April 15, 1987 . Eight monitoring wells (designated MW-1 to MW-8 on the attached Location Map) were installed in September 1986, and January 1987. Subsequent sampling of the monitoring wells revealed no free product but did reveal the presence of dissolved gasoline constituents in five of the wells (MW-4 to MW- 8) . The results of these investigations were described in our reports dated September 12 , 1986 and April 15, 1987 . The purpose of the current investigation is to define the extent of the dissolved constituent plume. GROUNDWATER SAMPLING Monitoring wells MW-1, MW-2 and MW-4 to MW-8 were inspected for the presence of free-floating product using a clear acrylic bailer. During sampling, neither free product or gasoline sheen was noted in any of the wells. Prior to sampling, each well was purged a minimum of four casing volumes. Groundwater samples were subsequently collected from MW-1, MW-2 and MW-4 to MW-8 using a teflon bailer. LABORATORY ANALYSES Soil and water samples were submitted to Sequoia Analytical Laboratory and HAZCAT Organics Lab for analysis. Samples were analyzed using EPA methods 5030 and 602. The analytical results are summarized in Table 1.