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Ms.Margaret Lagorio, SJCEHD October 21,2003
<br /> Joe's Truck Plaza Project No.2033-15600-01
<br /> Work Plan for Additional Site Assessment
<br /> Page 2
<br /> will be utilized to perform the GWE and DPE feasibility tests. In addition to this
<br /> feasibility testing, Stratus proposes to initiate interim remedial activities consisting of on-
<br /> site and off-site ozone sparge wells, situated approximately perpendicular to the general
<br /> groundwater flow, downgradient of the northern USTs, and within an area of residual
<br /> MTBE identified in soil during previous site assessment activities.
<br /> SITE DESCRIPTION
<br /> The subject site is an active service station located on Harlan Road, south of the
<br /> intersection with J Street in Lathrop, California (Figure 1). The current station
<br /> configuration consists of a station building, four dispenser islands intended for
<br /> automobile refueling, seven dispenser islands intended for large truck refueling, four
<br /> 10,000-gallon above ground tanks used to store diesel, one 12,000-gallon UST, one
<br /> 10,000-gallon UST, and one 4,000-gallon UST used to store gasoline, and one 4,000-
<br /> gallon UST used to store diesel. The current station configuration is shown on Figures 2.
<br /> The nearest surface water appears to be a small, unnamed drainage canal, located
<br /> approximately 900 feet due west of the site. The San Joaquin River is situated
<br /> approximately one mile west of the station.
<br /> PREVIOUS ENVIRONMENTAL INVESTIGATIONS
<br /> The following information was obtained from reports prepared by Advanced
<br /> GeoEnvironmental, Inc. (Advanced) and Avalon Environmental Consultants (Avalon):
<br /> In January 1997, a preliminary site assessment was performed by Advanced. The
<br /> assessment activities consisted of advancing six soil borings in the vicinity of the
<br /> northern and southern tank pits, and one boring in the vicinity of former septic leach
<br /> lines, collecting soil samples, and collecting grab groundwater samples. Total Petroleum
<br /> Hydrocarbons as diesel (TPHD) were reported in one of the soil samples collected from a
<br /> depth of approximately 6 feet below ground surface (bgs) near the southern tank pit at the
<br /> concentration of 1,000 milligrams per kilogram (mg/Kg). Dissolved TPHD, Total
<br /> Petroleum Hydrocarbons as gasoline (TPHG), and MTBE were reported in groundwater
<br /> samples collected from borings near both tank pits, at concentrations up to 320,000
<br /> micrograms per liter(µg/L), 2,700 µg/L,and 95 µg/L, respectively.
<br /> The USTs, product piping, and dispensers were replaced during site renovation activities
<br /> in February and October 1998. Avalon conducted compliance soil sampling for the
<br /> southern tank pit on February 23, 1998, and for the northern tank pit on October 9, 1998.
<br /> TPHD, benzene, and MTBE were reported in compliance samples collected from a depth
<br /> of approximately 10.5 feet bgs, at maximum concentrations of 660 mg/Kg, 0.88 mg/Kg,
<br /> and 0.46 mg/Kg, respectively. The highest reported concentrations were found beneath
<br /> the northern tank pit.
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