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� • i Addendum to Monitoring Well Installation Work Plan - September 2000 PACIFIC PRIDE 3147 South El Dorado Street, Stockton, California ' 1.0. INTRODUCTION At the request of Mr David Atwater of Van De Pol Enterprises Inc ,Advanced GeoEnvironmental, ' Inc(AGE)has prepared this addendum to Monitoring Well Installation Work Plan-September 1999, dated 01 September 1999,for the drilling and Installation of four additional ground water momtonng wells at 3147 South El Dorado Street, Stockton, California(site) Three ground water monitoring ' wells will be Installed at the site to assess the horizontal extent of hydrocarbon-Impacted ground water, one ground water monitoring well will be Installed at the site to determine the vertical extent The location of the site is illustrated on Figure 1 A plan of the site is illustrated on Figure 2 This work plan addendum Is being submitted to define the horizontal and vertical extent of petroleum-Impact to ground water at the site and is In accordance with a letter directive from the San ' Joaquin County Public Health Services -Environmental Health Department (PHS-EHD) dated 10 August 1999 This work plan addendum has been prepared in accordance with PHS-EHD and ' California Regional Water Quality Control Board (RWQCB) guidelines for the investigation of underground storage tanks (UST) sites Background information and a description of prior investigations at the site were included in Preliminary Investigation And Evaluation Report, dated 26 July 1999 In December 1999,four monitoring wells(MW-1,MW-2,MW-3 and MW-4)were advanced on-site ' as part of site assessment activities related to the former USTs at the site Total petroleum hydrocarbons quantified as gasoline, diesel and kerosene (TPH-g, TPH-d and TPH-k, respectively) were detected In soil samples from MW-1 at 20 and 35 feet bsg at concentrations ranging as high ' as 7,000 milligrams per kilogram(mg/kg) BTEX compounds were detected from MW-1 at 20 and 35 feet bsg and at concentrations ranging as high as 54 mg/kg No fuel oxygenates were detected by laboratory analysis The analytical results of selected soil samples are summarized in Table 1 r 1999 March 2000 and June 2000 ground water monitoring and sampling was In December �' g performed at the site on wells MW-1, MW-2, MW-3 and MW-4 Depth to ground water has 1 fluctuated at the site between 25 and 29 feet bsg, ground water flow direction for the area bound by wells MW-1,MW-2,MW-3 and MW-4 was implied to be generally northwest at a gradient of 0 003 fl/fl The core of the dissolved petroleum hydrocarbon plume appeared to be located in the area of ' MW-1, analysis of ground water samples collected from MW-i suggest the core of the plume Is impacted by TPH-g, TPH-d, TPH-k, BTEX, TBA, 1,2-DCA and EDB The analytical results of selected soil samples are summarized in Table 2 The lateral extent of the adsorbed and dissolved petroleum hydrocarbon plume is not known toward the southeast,northeast, east and west of the current area bound by wells MW-1,MW-2,MW-3 and MW-4, the vertical extent of petroleum hydrocarbon-impacted soil is not known at the site r Advanced GeoEnvi ron mental,Inc ' 1