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1.0 INTRODUCTION The subject property is a former cardlock refueling station which is located near the northwest corner of the intersection of Pershing Avenue and Rose Mane Lane in Stockton, California The subject property is bordered to the east by a veterinary hospital, to the south by a car wash, ' to the north by the Venetian Square Shopping Center, and to the west by retail businesses. A 7-11 convenience store which dispenses gasoline is located approximately 100 feet to the east of the subject property, at the northwest corner of the intersection of Rose Mane Lane and North Pershing Avenue, a Shell service station is located approximately 150 feet southeast of the subject property, at the southwest corner of the intersection of Rose Mane Lane and North Pershing Avenue, and an Exxon service station was previously located approximately 200 feet ' to the southeast of the subject property, at the southeast corner of the intersection of Rose Mane Lane and North Pershing Avenue. A site location map is included as Figure 1 ' 1.1 Background Previous investigations have been performed at the site by TreaTek, Inc and by TMC Environmental, Inc Information regarding the prior investigations conducted at the site was provided to McLaren/Hart by Neumiller & Beardslee, and by the San Joaquin County Public Health Services Environmental Health Division (PHS/EHD). Nine soil borings were drilled in June 1991 by TMC Environmental Inc. to maximum depths of 31 feet below ground surface at the subject property. Maximum concentrations of Total Petroleum Hydrocarbons (TPH) as gasoline, up to 310 milligrams per kilogram (mg/kg), were detected in the samples collected approximately 25 feet below ground surface from the borings drilled in the northeast corner of the property Three 12,000 gallon underground fuel storage tanks, one leaded gasoline, one unleaded gasoline and one diesel, were excavated and removed from the property on January 8, 1992 Soil samples were collected and analyzed for concentrations of TPH, benzene, toluene, ethylbenzene and ' xylenes (BTEX), ethylene dibromide(EDB) and total lead. The results of the TreaTek sampling are provided in the Treatek report dated January 28, 1992 ' McLaren/Hart performed soil sampling and monitor well construction at the subject site on November 3 through November 5, 1992 A total of five monitor wells were. installed, MW 1 through MW4 along the perimeter of the former underground storage tank farm, and MW5 at the northeast corner of the subject site in the inferred downgradient direction. Soil borings were drilled to a maximum depth of 45 feet below ground surface, and monitor wells were installed within the boreholes to a maximum depth of 40 feet below ground surface ' The analytical results of the soil samples indicated that concentrations of TPH y p as gasoline (TPH-G) were detected in the soil collected from monitor wells MW2 through MW5 BTEX compounds were detected in the soil samples collected from monitor wells MW2, MW3 and MW4 The maximum concentrations of petroleum hydrocarbons detected in soil samples were from the samples collected at 25 feet below ground surface, at the historical highest seasonal groundwater elevation 07oakd2 1