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l GROUND ZERO ANALYSIS, INC. <br /> ii <br /> 1714 Main Street q <br /> EscaIon,California 95320-1927 <br /> Telephone: (209)838-9888 <br /> Facsimile: (209)838-9883 <br /> March 8, 2004 <br /> Mr. Harlin Knoll �I <br /> San Joaquin County Environmental Health Department <br /> 304 East Weber Avenue, Third Floor <br /> Stockton, CA 95202 <br /> i. <br /> Subject: Workplan for Well Destruction <br /> 8960 W. Walnut Grove Road,Thornton,CA <br /> u <br /> Dear Mr. Knoll: <br /> At your request Ground Zero Analysis, Inc. (Ground 2 ero) has prepared this workplan to destroy <br /> groundwater monitoring wells MW 1 through MW7 at the su ject site. a <br /> i <br /> BACKGROUND <br /> The site is located at 8960 W. Walnut Grove Road in Thornton, California. The site is bounded on the north j <br /> by Walnut Grove Road, on the west by Highway 1-5 and itsoff-ramp,on the south by undeveloped land and <br /> on the east multi-family residences. The site location is shown on Figure 1. The site was formerly operated <br /> as a convenience store and retail gasoline station, which utilized one 10,000-gallon underground storage tank <br /> (UST)to store diesel fuel and two 10,000-gallon USTs to store unleaded gasoline. <br /> A limited subsurface assessment conducted by Ground Ze o in December 1996 provided evidence that <br /> petroleum hydrocarbons had impacted soil and groundwater beneath the site. The three USTs and associated <br /> piping were removed under permit from EHD on January 21, 1 99. Analytical results of side wall soil samples <br /> and a groundwater sample collected from the UST excavat' n indicated that elevated levels of petroleum <br /> hydrocarbons were present in the soil and groundwater. Additi nal investigation was required by EHD. <br /> In July 1999, five direct push soil borings were advanced along the perimeter of the UST excavation to <br /> investigate the vertical and lateral extent of soil and groundwater contamination, and four hand augured soil <br /> borings were advanced to investigate the lateral extent of hallow soil contamination. Total petroleums <br /> hydrocarbons as gasoline (TPHg) and total petroleum hydrocarbons as diesel (TPHd) were detected in the' <br /> soil at low to moderate levels. Benzene and methyl-tent-b tyl ether (MTBE) were detected only in one I <br /> boring advanced in the immediate vicinity of the former USTs. Elevated levels of benzene, toluene,! <br /> ethylbenzene xylenes (BTEX), TPHg, TPHd, and MTBE were detected in grab groundwater samples <br /> collected during drilling. The data suggested that the vertical extent of soil contamination did not exceed 15 <br /> feet below ground surface(bgs)and occurred within a relativ ly limited area near the former USTs. i <br /> G:IGROUNDZEIBarnyard-ManserlReportslWKPLANTDESTROY_MW1 -MW7A c <br /> :1 <br />