ARCHIVED REPORTS XR0006590 - Laserfiche WebLink

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i 10 INTRODUCTION • BP Oil Company retained Alisto Engineering Group to prepare a case closure submittal report for former BP Oil Site No 11192, 1403 Country Club Boulevard,Stockton, California The property is currently doing business as a 76 service station A site vicinity map is shown on Figure 1 and a site plan as Figure 2 An expanded site plan showing locations of neighboring properties,buildings, and underground utilities is presented as Figure 3 This case closure report was prepared at the request of the San Joaquin County Environmental Health Division (SJCEHD) and in accordance with the guidelines of the California Regional Water Quality Control Board,Central Valley Region (RWQCB) 2 0 SITE DESCRIPTION AND HYDROGEOLOGIC CHARACTERISTICS The site is an operating retail gasoline service station located at the northwestern corner of Country Club Boulevard and Pershing Avenue, Stockton, California The surface topography of the site slopes generally to the west Approximately 1,300 feet to the north of the site is the Smith Canal, which drains to the San Joaquin River 21 Prosect Background The station was constructed in 1976 and operated by Mobil Oil Corporation until purchased by BP Oil Company in 1989 (IT, 1991) A brief summary of the assessment and source removal activities completed to date at the site is discussed below 21.1 Assessment Activities In March 1989,a soil gas survey was conducted at the site by Target Environmental Services for Mobil Oil Petroleum hydrocarbons were detected in the samples collected from 13 of the 24 soil vapor sampling points,primarily in the eastern portion of the site in the vicinity of the underground fuel storage tanks and dispenser islands Concentrations of petroleum hydrocarbons detected in the soil vapor were up to 97110 micrograms per liter (ug/1) total volatile compounds, 2051 ug/1 benzene, and 19760 ug/1 methyl tert-butyl ether and pentane (Target, 1989) In'April 1990, four groundwater monitoring wells, MW-1 through MW-4,were installed to depths of approximately 34 feet Analysis of soil samples collected from each boring detected only 0 82 milligrams per kilogram (mg/kg)benzene and 0 043 mg/kg ethylbenzene in the sample from MW-3 The initial groundwater sampling of the wells was performed on May 1, 1990,whereby petroleum hydrocarbons were detected in the samples collected from MW-1 and MW-3 at concentrations of up to 200 ug/l total petroleum hydrocarbons as gasoline and 33 ug/l benzene (International Technology Corporation, 1990) In February 1991, three 10,000-gallon underground gasoline storage tanks and three 3000- gallon motor oil tanks were removed from the site Prior to tank removal,Monitoring Well MW-2 was destroyed because it was within the area of the replacement underground fuel tanks Compliance soil samples were collected below each end of each former underground fuel tank for laboratory analysis of petroleum hydrocarbon constituents Additionally, soil samples were collected at each corner of the new fuel tank cavity and at four locations along RIND F\00\10-037\close doc 1