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LIGHT, AIR & SPACE CONSTRUCTION ENVIRONMENTAL,SERVICES COMPANY State Contractor's License Number 445403 State EPA R.E.A.Number 04072 Office 408.979-0661 j On the basis of the water data from the pits, the SJC/EHD requested further assessment of the groundwater and the site by installing groundwater monitoring wells. Three monitoring well locations were discussed and approved with a representative of EHD and the wells were installed in 2008. Also, ten four-point composite soil samples were also collected in October 2008 from the soil stockpile aeration area for chemical analysis and are presented in this report. Soil samples were obtained from approximate depths of 6- to 12 inches and 18 to 24 inches at pre- selected grid locations and the samples were composited by depth for analysis by the lab. An EHD representative observed portions of this field work. ' The results of the tank removal soil sampling, stockpile soil sampling and soil and groundwater sampling for monitoring wells are presented in Tables 3, 4, 5 and 6. Contaminants were not detected in any soil sample collected from the monitoring well boreholes next to the former UST pits. The groundwater monitoring well data showed that only 69 micrograms per liter (Ug/1) of Total Petroleum Hydrocarbons as Gasoline and 3.99 Ug/l Methyl-tert-Butyl Ether(MTBE) were detected; the laboratory reported that the TPHG did not resemble atypical gasoline pattern. A second round of well sampling on March 17, 2009 revealed that TPHG, BTEX, and fuel oxygenates were not detected, and only one detection of MTBE in MW-3 at 4.0 Ug/l. The 2008 and 2009 Well MW-3 MTBE detections were below the current State Maximum Contaminant Limit(MCL). 2.0 Site Geology and Hydrogeology The project site is located near Manteca near the northwestern edge of the San Joaquin Valley and Delta area. Quaternary and Holocene alluvial fan and stream sediments composed of sand, gravel, silt and clay deposited by the San Joaquin River underlie the region. Surficial soils in the region are mapped by the U. S. Department of Agriculture as Delhi-Veritas-Tinnin soil association composed of sandy loam to sand forming on low alluvial fans, interfan basins and stream terraces and locally having "hardpan' and moderate to rapid permeability. The deeper underlying alluvium at depth may consist of weakly consolidated and irregularly interbedded sand, silt and clay strata and these strata may be of variable lateral and vertical continuity and extent. Very large groundwater aquifers underlie the Manteca region that produce very large quantities of water used for agricultural and drinking water sources. The regional groundwater flow direction is estimated to the west and northwest in this region. Historic pumping has locally drawn down the groundwater levels in the area and aquifer recharge and discharge may affect the local groundwater flaw direction. Three exploratory borings were drilled on-site on October 8, 2008 to a maximum depth of 22 feet below the surface. The borings revealed brown to yellow brown sandy silt and silty sand that locally may be weakly cemented. ' These strata are underlain by interbedded sandy silt clayey silt, sand and silty sand and appear laterally and vertically discontinuous and compose the Page 3 of 16 MAIN OFFICE •1707 LITTLE ORCHARD STREET,SurrE A-SAN JOSE-CA-95125 MAILING ADDRESS•P.O.Box 36303 r SAN JOSE•CA•95158-0303•4081979-0661 •408/979-0621 FAX•LASCONST r@AOL.COM E-MAIL GENERAL AND ENGINEERING CONTRACTOR•HAZARDOUS SUBSTANCE REMOVAL CONTRACTOR•SITE ENVIRONMENTAL ASSESSMENTS WETLAND AND RIPA PIAN HABITAT-ASSESSMENT-DESIGN-RESTORATION-CONSTRUCTION-MITIGATION MONITORING