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' ATC Associates Inc <br /> 1117 Lone Palm Avenue, Suite B <br /> (: <br /> Modesto, California 95351 v kTC <br /> 209-579-2221 <br /> A S S O C I A T E S 1 N C <br /> fax 209-579-2225 <br /> 12. Site Geology and Hydrogeology <br /> ' A boring advanced at the site on December 13, 2001, to 100 feet bgs utilizing CPT methods <br /> indicated variable layers of clayey silt and silty clay with some organic maternal were encountered <br /> ' from the surface to approximately 18 feet bgs Soil from approximately 18 to 33 feet bgs <br /> generally of consisted of silty sand and sandy silt Soil from approximately 33 feet to 40 feet bgs <br /> consisted of clayey silt and silty clay Soil from approximately 50 feet to 55 feet bgs consisted of <br /> clay Soil from approximately 55 feet to 57 feet bgs consisted of very stiff fine-grained material <br /> Soil from approximately 57 to 73 feet bgs generally of consisted of silty sand and sandy silt <br /> ' 3.0 PREVIOUS ENVIRONMENTAL WORK <br /> In February 1987, SEMCO removed and disposed of one 3,000-gallon unleaded gasoline <br /> ' underground storage tank (UST), associated piping, and fuel dispenser from the location shown <br /> on Figure 2 A soil sample collected from 13 feet below ground surface (bgs) contained elevated <br /> concentrations of petroleum hydrocarbon contaminants The excavation was subsequently <br /> ' backfilled and resurfaced <br /> On July 23, 1997, an ATC geologist supervised the advancement of five soil borings (SB 1 <br /> through SBS) ranging in depth from 6 to 46 feet bgs The soil borings were advanced using a <br /> truck mounted Geoprobe® narrow diameter ng employing direct push technology Petroleum <br /> hydrocarbons were detected in soil samples submitted for laboratory analyses Site activities are <br /> ' summarized in ATC's Summary Report for Subsurface Investigation, dated October 20, 1997 <br /> On September 25, 1998, ATC personnel supervised the advancement of soil boring MW i at the <br /> site to a depth of approximately 65 feet bgs to evaluate groundwater for the presence of <br /> petroleum hydrocarbons The soil boring was completed as a groundwater monitoring well and <br /> on September 28, 1998 the well was developed and sampled Analytical data indicated that soil <br /> and groundwater samples contained detectable concentrations of petroleum hydrocarbons Field <br /> activities and analytical results are detailed in ATC's Summary Report of Additional Subsurface <br /> ' hrvesttgation, dated January 8, 1999 <br /> In December 1999, ATC personnel supervised the advancement of soil borings MW2, MW3, and <br /> ' MW4 at the site to depths of approximately 65 feet bgs to evaluate groundwater for the presence <br /> of petroleum hydrocarbons and to determine the gradient direction and magnitude The borings <br /> were completed as monitoring wells Analytical data indicated that soil samples collected from <br /> ' boring MW2 contained detectable concentrations of petroleum hydrocarbons Petroleum <br /> hydrocarbons were also detected in a groundwater sample collected from well MW2 A <br /> groundwater sample collected from MW3 contained very low concentrations of only a few of the <br /> ' requested analytes Petroleum hydrocarbons were not detected in the groundwater sample <br /> collected from MW4 Field activities and analytical results are detailed in ATC's Summary Report <br /> of Additional Subsurface Investigation, dated February 24, 2000 <br /> s\enwtmenldi 62577-Diesel P �i remdc 2 <br /> 1 <br />