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1 v i A S S O C I A T E S I N C hydrocarbons were detected in groundwater samples collected from all eight groundwater monitoring wells, except the samples collected from MW-2 and MW-3 in February 2002 and May 2003, respectively A ' northerly groundwater flow direction was reported by H20GEOL during their sampling activities _ In a letter dated April 11, 2002, the San Joaquin County Environmental Health Department (SJCEHD) 1 indicated that up-gradient monitoring wells MW-2 and MW-3 could be reduced to annual monitoring and that the lateral and vertical extent of soil contamination remains undefined The SJCEHD requested submittal of a workplan to define the lateral and vertical extent of soil contamination In response to the SJCEHD request, H20GEOL 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 In a letter dated November 14, 2003, the SJCEHD indicated that the proposed scope in the H20GEOL workplan was not adequate or necessary The SJCEHD requested that a workplan be prepared in the context of a site conceptual model that includes analytical data collected during removal of a waste oil tank from the site in September 2003 1 On September 11 and 12, 2003, a 500-gallon capacity used oil UST was excavated and removed from the site respectively, 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 In September 23 and 24, 2003, H20GEOL collected groundwater samples from MW-1 and MW-4 through MW-8 Petroleum hydrocarbons were detected in groundwater samples collected from these wells The reported groundwater flow direction was to the north Refer to H20GEOL's Third Quarter, 2003 Groundwater Monitoring Report, dated October 31, 2003, for more information ' HYDROGEOLOGY The site is located within the Great Central Valley geomorphic province Groundwater in the Tracy area is present in Recent alluvium Ground water enters the Great Central Valley via surface and subsurface flow and by direct percolation of precipitation, stream flow, and applied water Replenishment of the groundwater occurs by percolation of precipitation, stream flow, and applied water occurs in the forebay areas where permeable sediments are exposed at ground surface 1 According to the United States Geological Survey (USGS) 7 5-Minute Series Topographic Map of the Union Island, California Quadrangle, the site is located at an approximate elevation of 25 feet above mean sea level (Figure 1) The regional surface topographic gradient in the vicinity of the site is towards the north The groundwater flow direction beneath the site is reported to be generally towards the north but has ' historically exhibited seasonal variation in late winter by flowing towards the southeast This variation may be attributable to infiltration at Pescadero Park located northwest of the site Since 1998, depth to ground- water beneath the site has varied from approximately 4 5 to 7 feet bgs A groundwater gradient map for November 26, 2003, is included as Figure 3 Historical groundwater data are included in Table 1 1 i Former Cheaper#37 January 29 2004 ATC Project Number 5425847 0037 Page 3