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• Field observations and analytical results of samples collected after removal of the USTs indicated soil <br /> and groundwater in the vicinity of the USTs has been impacted with petroleum hydrocarbons Soil <br /> samples collected from the limits of the UST basin contained total petroleum hydrocarbons (TPH) <br /> as diesel (TPHd) ranging from 170 to 1100 milligrams per kilogram (mg/kg), TPH as gasoline <br /> (TPHg) ranging from 300 to 1800 mg/kg, benzene ranging from 880 to 2400 micrograms per <br /> kilogram(ug/kg) and methyl tertiary-butyl ether(MTBE) concentrations ranging from 610 to 21000 <br /> ug/kg The UST basin soil samples also contained concentrations of other BTEX compounds ranging <br /> from 82 to 180000 ug/kg Total lead concentrations in the UST basin soil samples ranged from 1 6 <br /> to 4 5 mg/kg The groundwater sample contained a TPI-Id concentration of 120 milligrams per liter <br /> (mg/L), a TPHg concentration of 100 mg/L, a benzene concentration 5100 micrograms per Inter <br /> (ug/L), and an MTBE concentration of 37000 ug/L The groundwater sample also contained <br /> concentrations of other BTEX compounds ranging from 1600 to 7800 ug/L, other oxygenate <br /> compounds ranging from less 200 to 7300 ug/L and a total lead concentration of 0 01 mg/L <br /> IV REGIONAL GEOLOGY AND HYDROGEOLOGY <br /> The site is located in the central portion of the Great Valley geomorphic province of California in the <br /> eastern San Joaquin-Sacramento Delta region The province is a north-northwest-trending <br /> asymmetrical sedimentary trough measuring approximately 400 miles long by 50 miles wide Surface <br /> • sediments in the site area generally consist of unconsolidated Quaternary flood and delta plain silt and <br /> sand deposits Groundwater in the delta region is typically shallow Groundwater at the site has been <br /> measured at approximately nine feet below ground surface (bgs) in the UST excavation <br /> Groundwater flow directions in the site area are generally westward toward the delta but can vary <br /> locally <br /> V SCOPE OF WORK <br /> The following scope of work is designed to obtain pertinent hydrogeologic information and to <br /> investigate the nature and extent of petroleum hydrocarbons in soil and groundwater The work <br /> includes <br /> ❑ drilling of soil borings and collection of soil samples, <br /> ❑ conversion of the soil borings to groundwater monitoring wells, <br /> ❑ monitoring well development, <br /> ❑ measurement of static groundwater levels and collection of groundwater samples, and <br /> ❑ data evaluation and compilation in a report <br /> A Dnlling of Soil Borings and Collection of Soil Samples <br /> . All appropriate permits for the drilling of soil borings and the installation of monitoring wells shall <br /> WORKPLAN FOR LIMITED SOIL AND GROUNDWATER INVESTIGATION <br /> SUNNYSIDE PRODUCE, THORNTON, CALIFORNIA PAGE 2 <br />