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,'•{ SITE BACKGROUND ' In July 1986, a 500-gallon capacity underground storage tank (UST), identified as TK4, was removed from the site. Laboratory analyses of soil samples collected from the UST removal area in April 1987 indicated the soil was impacted with petroleum hydrocarbons. In February 1988, three remaining USTs were removed from the vicinity of the former location of TK4. Laboratory analyses of soil samples collected during removal of the three remaining USTs did not identify petroleum impacted soils. As a result of the soil contamination identified in April of 1987, the San Joaquin County Public Health Department/Environmental Health Division (SJCPHD/EHD) directed Eckert Cold Storage to conduct a site investigation and submit a Problem Assessment Report. In response to the directive from the SJCPHD/EHD, WHF, Inc. (WHF) installed three monitor wells identified as MW-1, MW-2, and MW-3 in January 1995. During initial development of the wells, it was discovered that the well casing of MW-2 had been damaged during installation of the well, such that bailers and pumps could not be placed down ' the well. Because petroleum hydrocarbon contamination was noted in all three borings drilled for MW-1 through MW-3, WHF elected to use MW-2 for groundwater gradient data collection and install an additional well in the down-gradient direction. Consequently, an additional well (MW4) was installed at the site on March 22, 1995. On September 18 and 19, 1997, three additional monitor wells identified as MW-5, MW-6, and MW-7 were installed at the site. A sensitive receptor survey for the site was conducted by WHF in 1998. On November 2 and 3, 1999, WHF advanced four shallow soil borings to depths ranging from 38 to 41.5 feet below ground surface (bgs). Groundwater was reportedly encountered at approximately 23 feet bgs. One of the shallow borings was completed as an additional monitor well (MW-8). Additionally, a deep boring was advanced to a depth of 56.5 feet bgs to evaluate the vertical extent of contamination in the location of the former UST area. Petroleum hydrocarbon constituents were detected in all of the soil samples collected from the deep boring. ' WHF conducted quarterly groundwater monitoring activities at the site from April 1995 to December 2001. Condor conducted quarterly groundwater monitoring activities at the site on February 27, 2002, and prepared the First Quarter 2002 Groundwater Monitoring Report, dated April 26, 2002, describing the results of the monitoring. On April 8, 2002 Condor representatives re-surveyed the monitoring wells at the site using traditional and global positioning system (GPS) techniques in accordance with recent CRWQCB directives concerning UST site data to be submitted in Electronic Deliverable Format (EDF). The new survey data ' indicated potential discrepancies between the prior and current elevation data, particularly associated with MW-5. The top of casing elevations measured for MW-1,MW-2,MW-3,MW-6, MW-7, and MW-8 identified during the new survey were either 2.28 or 2.29 feet higher than measured by the prior survey ' conducted by WHF. This indicated that there is good agreement between the data from both surveys for the relative elevations of those monitor wells. However, the top of casing elevations measured during the new well survey for MW-4 and MW-5 were 2.34 and 2.52 feet higher, respectively, than the top of casing ' elevations measured during the prior survey. It is therefore possible, for MW-5 in particular, that the previous top of casing elevation was measured to be approximately 0.23 feet too low relative to the other site monitor well top of casing elevations. This may have occurred during the re-survey of the well on April 25, 2000 following repairs to the well as reported by WHF in previous quarterly monitoring reports. 1