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aCalifornia Ros8ional Water Quality (�ntrol Board <br /> iCentral valley Region <br /> Pet"K ROOMY Sacramento Main office Ed J.Schnabel <br /> seem aryfor Internet Address: bq://www.swrcb.cagovl-Twgcb5ftmc huW Chair <br /> &WraaMental 3443 Rou6er Road,Suite A,Sacramento.California 95927-3003 <br /> Prow Phone(916)255-3000•PAX(916)255-3015 <br /> TO.• Gordon L.Boggs FROM: Mark R.List <br /> UST Program Manager Engineering Geologist <br /> DATE: 11 December 1998 SIGNATURE: <br /> SUBJECT- FILE REVIEW FOft CLOSURE CONCURRENCE,LOCKEFORD BEACON, <br /> fMpfrHWy. 88, LOCKEFORD, SAN JOAQUIN COUNTY <br /> At the request of the San Joaquin County Environmental Health Division (SJCEHD), a file review was <br /> completed to determine if Regional Board staff agree with the SJCEHD determination of no further <br /> action required at this site.This information was obtained during my review of the Regional Board <br /> casefile,for the Lockeford Beacon site. <br /> Background: <br /> On 1 June 1987, a pre-UST removal site assessment, and installation of four groundwater monitoring <br /> wells was completed. Groundwater samples collected from all four-monitoring wells contained elevated <br /> concentrations of petroleum hydrocarbons. The groundwater sample collected on 15 June 1987 from <br /> monitoring well MW-2 contained 2,749 gg/L(ppb)Total Volatile Hydrocarbons and 147 w.glL benzene. <br /> Four USTs,two 8,000-gallon and two 5,000-gallon gasoline tanks,were removed from the site on <br /> 21 March 1990. Soil contamination was encountered below both USTs during tank removal activities, <br /> and approximately 800 cubic yards of petroleum impacted soil was excavated prior to the installation of <br /> three new 10,000-gallon dual walled USTs in the same excavation. Prior to installation of the new <br /> tanks,slotted PVC was placed horizontally in the bottom of the excavation, and attached to vertical <br /> sections of blank PVC, installed to the surface,in anticipation of future site cleanup activities. <br /> Based on soil and groundwater sample analytical results, SJCEHD directed the RP to define the lateral <br /> and vertical extent of soil and groundwater contamination below the site. On 11 January 1994,four soil <br /> borings and two monitoring wells were installed at the site. Two additional soil borings were completed <br /> on 10 April 1995. The results of soil boring and monitoring well drilling activities revealed high <br /> concentrations of soil contamination between 30 and 45 feet bgs, in the vicinity of MW-2. The highest <br /> concentrations of soil contamination include TPHg and BTEX constituents in soil samples collected <br /> from the MW-2 boring, and soil boring SB-9,located approximately 15 feet northwest of MW-2. <br /> The lateral and vertical extent of soil contamination is defined by the six monitoring well borings and <br /> three soil borings located on-site. Low concentrations of TPHg contamination in soil were encountered <br /> between 25 and 60 feet below ground surface (bgs) in the borings for monitoring wells MW-1 and <br /> MW-3,located near the UST excavation, and between 35 and 60 feet bgs in MW-2. <br /> California Environmental Protection Agency <br /> �.1 Recycled Paper <br />