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GROUNDWATER ASSESSMENT REPORT • II. SITE BACKGROUND The site, as referred to in this report, is the former UST area that was associated with the UOP Physical Plant on the north side of Mendocino Avenue Within the last few years, UOP has relocated the Physical Plant building, Central Receiving Building, and Electric Shop and remodeled the former shop buildings for classrooms UOP had the UST removed prior to the remodeling work and the area of the former UST is now covered with an asphalt parking lot (Figure 2) s The USGS Stockton West, California 7 5 minute topographic quadrangle (1968), shows the site and UOP campus relatively level with an elevation of approximately 5 to 8 feet above mean sea level (amsl) The regional surface gradient as shown on the topographic map appears to be in a northeasterly direction No watercourses or lakes are depicted on or immediately adjacent to the site The Calaveras River is located approximately 1,800 feet north of the site The site is located in the San Joaquin Valley, within the Great Valley Geomorphic Province Based on the soil materials encountered during UST removal,and July assessment activities, shallow soil underlying the site consist generally of brown clayey silt and fine sand(see Soil Boring Logs, Appendix B) The water table is present in these fine-grained alluvial materials at depths ranging from approximately 15 to 30 feet below ground surface III. SUMMARY OF PREVIOUS INVESTIGATIONS UST REMOVAL, APRIL 7, 2000 As part of renovation and construction of new facilities,UOP removed a 4,400 gallon unleaded gasoline UST on April 7, 2000 under permits issued by San Joaquin County Environmental Health Division (#022179)and the City of Stockton Fire Department(#00-91) Excavated soil containing petroleum was removed from the site for landfill disposal while clean soil and imported pea gravel was used as backfill Deltech Geotechnical Inc performed the UST removal and Ground Zero Analysis,Inc conducted the required soil sampling All removal and soil sampling activities were observed by and completed under direction of Michael Kift and Vidal Pedraza of San Joaquin County Environmental Health Division (SJCEHD) Verification soil samples were collected beneath the northern end of the tank at 13 feet below ground surface(bgs)and beneath the southern end of the UST at 13 feet bgs Groundwater was not encountered during UST removal activities The locations of soil sampling locations are shown on Figure 3 As requested by the SJCEHD, soil samples collected from the UST pit were analyzed for total purgeable petroleum hydrocarbons (TPH)as gasoline, aromatic hydrocarbons,benzene, - _ - - -toluene,ethylbenzene and-xylenes(BTEX);-MTBE,--di-isopropyl ether(DIPS)ethyl tertiary butyl - - — - ether(ETBE),tertiary amyl methyl ether(TAME), and tertiary butyl alcohol(TBA) Laboratory analyses detected MTBE, xylenes, and TBA Results of chemical analyses on soil samples are summarized in Table 1,below Groundwater Assessment Report 3 FSA/200252 September 2003