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ATC Associates Inc. 1117 Lone Palm Avenue, Suite B %TC Modesto, California 95351 _ -V0 209-579-2221 A s s o c i A r E s i N c fax:209-579-2225 1988; approximately 350 to 400 cubic yards of soil were excavated from April 25 to 28, 1988. Laboratory analyses of soil samples collected from the sidewalls of the enlarged excavation indicated low concentrations of petroleum hydrocarbons remained at the south and southeastern portion of the excavation. On February 26, 1993, Parker Environmental Services (P.E.S.) advanced seven soil borings (BH1 through BH7). Soil samples were collected from each boring and a groundwater sample was collected from.each boring except BH7. Petroleum hydrocarbons were detected in soil samples collected from all the borings except BHI and BH3. Petroleum hydrocarbons were detected in all of the groundwater samples. Water levels measured at the site on March 2, 1993 indicated the groundwater flow direction was to the southeast. Refer to P.E.S.'s Interim Report on Subsurface Investigation Work at Cheaper! 4 37 dated April 20, 1993 for more details. Froniluly to October 1995,P.E.S. conducted subsurface investigation activities that included installing four monitoring wells (MW5 through MW8) and advancing 14 hand augured soil borings (B8 through B21).; B15 through B21 were advanced off-site to the west, southwest, and south. Groundwater was encountered at approximately 6.5 feet bgs. Soil and groundwater samples were collected from B8,B10 through B18, B20, B21, and MW5 through MW7. A groundwater sample was also collected from MW8. Petroleum hydrocarbons were detected in all of the soil samples except for the samples collected from MWfthrough MW7, B14 located east of the former UST location, and B20 and B21 located off-site to the southwest and south, respectively. Petroleum hydrocarbons were detected in the groundwater samples except for the samples collected from B14, B20, B21, MWI, MW2, MW3, MW6, and MW7. MW4 was not sampled due to the presence of approximately 0.02 inches of free product. The reported groundwater flow direction on September 25, 1995 was approximately due north. Refer to the report prepared by P.E.S. titled Environmental Site Investigation Methods and Findings: Drilling of Soil Borings, Drilling and Installation of Groundwater Monitoring Wells f Collection and Analyses of Soil and Groundwater Samples, dated November 17, 1995 for more information. �4 In a letter dated April 11, 2002, the San Joaquin County Environmental Health Department (EHD) indicated that upgradient monitoring wells, MW2 and MW3, could be reduced to annual monitoring and that the lateral and vertical extent of soil contamination remains undefined. The EHD requested t submittal of a workplan to refine the lateral and vertical extent of soil contamination. In response to the EHD;request, H2OGEOL submitted the Work Plan for Additional Soil Characterization dated June 10, 2003, which proposed advancing 14 hand auger borings at the site for the purpose of collecting soil samples. r On September I I and 12, 2003, a 500-gallon capacity used oil UST was excavated and removed from the site by Walton Engineering, Inc. Petroleum hydrocarbons and metals were detected in a soil sample collected from below the former location of the UST from a depth of approximately seven feet bgs. Refer'to Grayland Environmental's Underground Storage Tank and Fuel Dispenser Removal Report, dated October 16, 2003,for more information. sAery omowW\2584710037,reports\3gr-2005.doe 2 f i i5 '