|
ti..� `O/Site Assessment Work Plan
<br /> 1022 Frontage Road, Ripon, California
<br /> CONESTO3A-ROVERS March 7,2008
<br /> &ASSOCIATES
<br /> September 1998: In September 1998, Walton removed three steel,single wall USTs,(7,500 gallon and
<br /> 10,000 gallon gasoline USTs and one 12,000 gallon diesel UST), four additional dispensers, and
<br /> associated piping. Twenty four soil samples(T1 through T3,FD7 through FD 10,and PL5 through PL 17)
<br /> were collected by Grayland during the UST, dispensers, and piping removal activities. TPHd
<br /> concentrations ranged between <1.0 and 12,000 mg/kg(FD 10). TPHg concentrations ranged between
<br /> <1.0 and 1,500 mg/kg(T2n). Benzene concentrations ranged between<0.005 and 2.3 mg/kg(T3n). As a
<br /> result, Grayland Environmental recommended that additional assessment be conducted to evaluate the
<br /> extent of hydrocarbon-impacted soil and to determine if groundwater beneath the site was impacted. A
<br /> total of approximately 1,180 tons(600 cubic yards)of hydrocarbon-impacted soil was removed from the
<br /> site and disposed of at Forward Landfill in Stockton, California.
<br /> May to August 1999: Between May and August 1999,AGE oversaw the advancement of soil borings B 1
<br /> through B16,hydropunch borings HP17 and HPI 8 and the installation of groundwater monitoring wells
<br /> MW-1 through MW-5. Based on the analytical results, it was determined that the greatest hydrocarbon-
<br /> impact to soil was in the area immediately adjacent to the former USTs at 20 ft bgs. Hydrocarbon-
<br /> impacted soil appeared to be limited to a depth of approximately 30 ft bgs. The highest TPHg
<br /> concentration was detected in the 20 foot sample from boring B5 (1,300 mg/kg)and the highest TPHd
<br /> concentration was detected in the 20 foot sample from boring B4 (8,200 mg/kg). The highest benzene
<br /> concentration was detected in the 20 foot sample from boring B4(2.6 mg/kg). The highest methyl tertiary-
<br /> butyl ether(MTBE)concentration was detected in the 10 foot sample from boring B1 (12 mg/kg). Grab
<br /> groundwater samples were collected from borings B2, B5, B14, HP17, and HP18. Dissolved-phase
<br /> hydrocarbons extended north and west of the former USTs.TPHg and benzene concentrations appeared to
<br /> attenuate east and south of the former USTs (AGE, 1999). The highest dissolved-phase TPHd, TPHg,
<br /> benzene, and MTBE were detected at concentrations of 580,000; 23,000; 370; and 2,900 µg/L,
<br /> respectively, in boring B2 located on the south side of the former USTs.
<br /> 10)ikch 2002: In I ch 2002,AGE oversaw the installation of groundwater monitoring well MW-9 and
<br /> extraction well EW-1. Well EW-1 was installed in preparation for an aquifer pump test. Soil samples
<br /> collected from the pilot boring for well MW-9 at 15,20,25,and 30 ft bgs were submitted to the laboratory
<br /> for analysis. No soil samples collected from boring EW-1 were submitted to the laboratory for analysis.
<br /> TPHg was detected in soil samples collected from boring MW-9 at 20,25 and 30 ft bgs at concentrations
<br /> of 260,0.36 and 0.24 mg/kg,respectively. No benzene was detected in any of the soil samples analyzed.
<br /> MTBE was detected in samples collected from boring MW-9 at 15,25,and 30 ft bgs at concentrations of
<br /> 0.016,0.54,and 0.27 mg/kg,respectively. TPHd was only detected in the 20 ft sample of boring MW-9 at
<br /> a concentration of 800 mg/kg.
<br /> 4
<br /> Worldwide Engineering,Environmental,Construction,and IT Services
<br />
|