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`JSite Assessment Work Plan <br /> 1022 Frontage Road, Ripon,California <br /> 04��CONESTOGA-ROVERS March 7,2008 <br /> &ASSOCIATES <br /> 3.0 PREVIOUS INVESTIGATIONS <br /> Below is the chronology of site assessment, feasibility testing and interim remedial activities at the site. <br /> Historical soil and groundwater analytical data are presented in Tables 1 and 2, respectively. <br /> October 1996: In October 1996,AGE drilled borings *1314 through *1316 along the southern border of <br /> the site(not to be confused with borings B-14 through B-16 drilled in 1999). These borings were part of <br /> AGE's delineation of a hydrocarbon plume originating from the adjacent Ripon Farm Services property, <br /> located south of the site. TEC Accutite collected split soil and grab groundwater samples on behalf of <br /> Olympian Oil. Total petroleum hydrocarbons as diesel(TPHd)was detected only in boring*1315 at 20 ft <br /> bgs at a concentration of 1,300 milligrams per kilogram (mg/kg). Total petroleum hydrocarbons as <br /> gasoline (TPHg) was detected in all three borings at concentrations ranging from <0.5 to 160 mg/kg. <br /> Benzene was detected in borings *B 15 and *B 16 at concentrations ranging from <0.005 to 0.11 mg/kg. <br /> Grab groundwater samples were collected from borings*1314 and*1316 only. The highest dissolved-phase <br /> TPHd,TPHg,and benzene were detected at concentrations of 15,000; 12,000;and 9 micrograms per liter <br /> (µg/L),respectively, in boring*B 14 located near the southern site boundary. <br /> iV'a $y\ <br /> �,. May 1998: In May 1998,AGE oversaw the installation of groundwater monitoring wells MW-6,MW-7, <br /> ry and 1�IV W-8 to assess the extent of a hydrocarbon plume related to the adjacent Ripon Farm Services <br /> property located south of the site. A 20 ft bgs soil sample was collected from each of the well pilot <br /> borings. TPHd was detected in each sample and concentrations ranged from 1.1 to 490 mg/kg. The <br /> highest TPHd concentration detected was from the pilot boring for well MW-6. No benzene was detected <br /> in any of the soil samples. The only sample analyzed for TPHg was from the pilot boring for well MW-7 <br /> and TPHg was detected at a concentration of 6 mg/kg. <br /> June 1998: In June 1998,Walton Engineering(Walton)of West Sacramento,California removed six fuel <br /> dispenser islands and associated piping. Soil samples were collected by Grayland Environmental <br /> (Grayland) of Davis, California during the fuel dispenser and product piping removal activities (FD1 <br /> through FD6,PL1 through PL4). TPHd was only analyzed and detected in soil samples FD4 through FD6, <br /> and PL3 and PL4 at concentrations ranging from 3.3 to 13,000 mg/kg. TPHg was detected in six out of <br /> the 10 soil samples at concentrations ranging from 3.4 to 5,1.00 mg/kg. Benzene was detected in three out <br /> of the 10 samples at concentrations ranging from 0.022 to 0.12 mg/kg. <br /> July 1998: In July 1998, Walton installed a new gasoline UST, ten dispensers (eight diesel and two <br /> gasoline dispensers),and new product piping to connect the new dispensers with the new gasoline UST <br /> and existing diesel ASTs. _— <br /> 3 <br /> Worldwide Engineering,Environmental,Construction,and IT Services <br />