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1.0 INTRODUCTION This report zrtesents the results of a subsurface investigation of x hydrocarbon contamination conducted at the Stephens Anchorage Property, 4950 West Brookside Road in Stockton, California (Figure . l ) . Three underground storage tanks consisting of two 4, 000 gallon regular gasoline and a 4,000 gallon diesel tank were removed in December, 1988 . A 1, 000 gallon premium gasoline tank was removed in April, 1988 . This tank had also contained 18 :1 gas/oil mixture . The four tanks are approximately 25 years old. Upon removal, strong hydrocarbons odor was detected and a sheen noted beneath the tanks . Soil samples taken from both ends of the 4, 000 gallon tanks and from the :middle of the 1,000 gallon tank recorded elevated concentrations of benzene, toluene, ethyl benzene and xylenes (BTEX) and as well as total petroleum hydrocarbons (gasoline ) . Diesel hydrocarbon contamination- =was 3 recorded in one sample . The obJective of the investigation was to character,lze the extent Oof hydrocarbon, contamination in groundwater and soils beneath azo the site. The work entailed the drilling, logging and sampling of three soil borings located northwest and southeast of the fuel f tanks, and completion of these borings as groundwater monitoring w--115 . The work was conducted in accordance with recommendations 4. contained in our proposal dated January 19, 1989 . This proposal was submitted to the San Joaquin County Health Department for W: review and approval prior to implementation . 2 . 0 INVESTIGATION PROCEDURE 11 2 . 1 Soil Boring On August 14, 1989, three soil borings (MW1, MW2 & MW3 ) were advanced to depths of 25 feet below grade for the purpose of Installing groundwater monitoring wells (Figure 2 ) . Drilling was conducted by Osterberg and Stewart (CA License No. C57-446670 ) using an Ingersol/TN-10 rig with ten-inch (O.D. ) hollow stem augers . The drilling was performed under the direction of a field geologist who maintained a continuous log of the materials h encountered using the Unified soil Classification Systems (Appendix I ) . Sails were sampled at five and eight feet below grade . samples were collected in two inch diameter by six inch long brass tubes using a California modified sampler . The samples were collected, preserved and transported under chain-of-custody requirements in accordance with standard EPA protocol . The samples were delivered within 48 hours of collection to BC Laboratories, a state certified hazardous waste laboratory. The two samples from each boring were analyzed for purgeable aromatic hydrocarbons benzene, toluene, ethyl benzene and xylenes (BTEX) , total purgeable (petroleum) hydrocarbons (TPM) as gasoline and diesel . . 1