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PAR-Eckert Cold Storage,Manteca,CA November 25,2002 Page 2 3.0 SITE BACKGROUND • In July 1986 one 500-gallon capacity underground storage tank (UST), identified as TK4, was removed from the site. 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, Analyses of the soil samples collected during the 1988 1 removal of the three remaining USTs did not detect the presence of petroleum contamination. As a result the soil contamination identified in April 1987, the SJCEHD directed Eckert to conduct a site investigation and submit a PAR. As a result of this directive, WHF installed three monitor wells NW-1, MW-2, and MW-3) in January 1995. During initial development of the wells, it was discovered that the MW-2 well casing had been damaged during installation. Because petroleum hydrocarbon contamination was noted in all three monitor well borings, WHF elected to retain MW-2 for water level measurements and install an additional well in the down-gradient direction. Consequently, monitor well MW-4 was installed by WHF on March 22, 1995. On September 18 and 19, 1997 WHF installed three additional monitor wells (MW-5, MW-6, and MW- 7) 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 from 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 began conducting quarterly groundwater monitoring activities at the site on February 27, 2002. Groundwater elevation contours estimated with the depth to water measurements on that date and new monitor well survey data (see below) indicated that the groundwater gradient was generally towards the northwest. 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-i,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 I 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 1 reports. Historical groundwater data collected by WHF indicated a highly variable gradient at the site. Review by Condor of historical groundwater gradient information provided by WHF indicated that there are . potential inconsistencies in the data and possibly components of the interpretation of those data, especially related to MW-5 measurements. However, Condor agreed that the general historical is CONDOR