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x .A ,IN'T'RODUCTION <br /> This report presents the results <br /> of a subsurface investigation of <br /> hydrocarbon contamination conducted at the Stephens Anchorage <br /> Property, 4950 west Brookside Road in Stockton, California <br /> (Figure 1 ) . Three underground storage tanks consisting of two <br /> 4,000 gallon regular gasoline and a 4,000 gallon diesel tank were <br /> removed in December, 1988. A 1,000 gallon premium gasoline tank <br /> was removed in April, 1988. This tank had also contained 18:1 <br /> gas/oil mixture. The four tanks are approximately 25 years old. <br /> Upon removal, strong hydrocarbons odor was detected and a sheen <br /> -� noted beneath the tanks. Soil samples taken from both ends of <br /> the 4,000 gallon tanks and from the middle of the 1,000 gallon <br /> tank recorded elevated concentrations of benzene, toluene, ethyl <br /> benzene and xylenes (HTEX) and as well as total petralleum, <br /> hydrocarbons (gasoline) . D,{3861,•,,,hydrocarbon-contam nstions-waa <br /> recorde!d."°�in' orie" `same"fie." <br /> The objective of the investigation was to characterize the extent <br /> of hydrocarbon contamination in groundwater and soils beneath the <br /> site. The work entailed the drilling, logging and sampling of <br /> three soil borings located northwest and southeast of the fuel <br /> tanks, and completion of these borings as groundwater monitoring <br /> wells. The work was conducted in accordance with recommendations <br /> contained in our proposal dated January 19, 1989. This proposal <br /> s was submitted to the San Joaquin County Health !department for <br /> review and approval prior to implementation. <br /> 2.0 INVESTIGATION PROCEDURE <br /> 2.1 Soil Boring <br /> On August 14, 1989, three soil borings (Mwl, MW2 & MW3) were <br /> �x advanced to depths of 25 feet below grade for the purpose of <br /> installing groundwater monitoring wells (Figure 2) . Drilling was <br /> conducted by Osterberg and Stewart (CA License No. C57-446670) <br /> . using an Ingersol/TH-10 rig with ten-inch (O.D. ) hollow stem <br /> augers. The drilling was performed under the direction of a <br /> field geologist who maintained a continuous log of the materials <br /> encountered using the Unified Soil Classification System <br /> (Appendix I ) . <br /> 501-1- were sampled at five and eight feet below grade. Samples <br /> -- were collected in two inch diameter by six inch long brass tubes <br /> using a California modified sampler. The samples were collected, <br /> preserved and transported under chain-of-custody requirements in <br /> accordance with standard EPA protocol. The samples were <br /> delivered within 48 hours of collection to HC fLdtibrataa; we ., a <br /> state certified hazardous waste laboratory. The two samples from <br /> each boring were analyzed for purgeable aromatic hydrocarbons <br /> benzene, toluene, ethyl benzene and xylenes ( HTEX ) , total <br /> purgeable (petroleum) hydrocarbons (TPH) as gasoline and diesel. <br />