ARCHIVED REPORTS_XR0007693 - Laserfiche WebLink

Home Browse Search

1 In August 1988, Woodward-Clyde Consultants (WCC) conducted site assessment activities which consisted of drilling three borings to depths ranging from 52 feet to 64 feet bgs Upon completion, the three borings were converted to groundwater monitoring wells (MW-1, MW-2 and MW-3) TPH was detected only in soil sample collected from MW-2 at 35 feet bgs (2,200 ' mg/Kg), the remaining soil samples were non-detect Benzene concentrations in soil samples were detected at concentrations ranging up to 8 3 mg/Kg (MW-2 at 35') Results of groundwater sample analyses indicated TPH concentrations ranging from 12 2 milligrams per liter (mg/L) in ' well MW-2 to 92 mg/L in well MW-1 Benzene concentrations ranged from 9 7 mg/L in well MW-2 to 15 mg/L in well MW-i In November 1992, Thrifty installed four groundwater monitoring wells (MW-3R, MW-4, MW- 5, and MW-6), two vadose wells (VW-1 and VW-2), and one soil boring (B-5) The groundwater wells were installed to 90 feet bgs to accommodate the drop in the water table from ' approximately 50 feet bgs in 1988 to 75 feet bgs in 1992 Wells MW-3R, MW-4, and MW-6 were screened from 65 to 90 feet bgs and well MW-5 was screened from 20 to 90 feet bgs to allow for future remediation of hydrocarbon-impacted soil in the shallow zone The vadose ' wells were installed immediately adjacent to the USTs to define the extent of soil contamination and to provide access for site remediation Boring B-5 was installed near the pump islands Results of soil sample analyses indicated TPH concentrations ranging from below MDLs to ' 2,100 mg/Kg (MW-5 at 60'), and benzene concentrations ranged from less than the MDL to 66 mg/Kg (MW-5 at 50') Groundwater sample analyses indicated TPH concentrations ranging from 2 4 mg/L (MW-6) to 36 mg/L (MW-4), and benzene concentrations ranged from 0 008 mg/L (MW-6) to 3 8 mg/L (MW-4) ' On October 13, 1994, Thrifty removed the five (5) former USTs and in November 1994 replaced them with new tanks in the northeast corner of the site In conjunction with UST removal/replacement activities, a total of 718 09 tons of hydrocarbon-impacted soil were ' removed from the site on November 17 and 18, 1994, and transported to Forward Inc Landfill in Manteca, California, for disposal A total of 12 soil samples were collected from the tank bottom and analyzed for TPHg, BTEX, and lead The maximum TPHg concentration was 14,000 mg/Kg and the maximum benzene concentration was 23 mg/Kg A total of 20 soil samples were collected from the soil stockpiles with the maximum TPHg and benzene concentrations reported at 6,500 mg/Kg and 0 05 mg/Kg, respectively ' In December 1994, Thrifty installed two vadose wells (TB-4 and TB-6) and three soil borings (TB-3, TB-13, and TB-14) at the site Well TB-4 was located near the northern end of the dispenser island and was drilled to a depth of 50 feet bgs Well T13-6 was located south of TB-4 and was advanced to 25 feet bgs Borings TB-3, TB-13, and TB-14 were located in the pump dispenser island area and were drilled to 15 feet bgs Groundwater was not encountered during drilling activities TPH concentrations in soil samples were detected at concentrations ranging from ND to 4,100 mg/Kg (T134 at 10% and benzene concentrations were detected at concentrations ranging from ND to 5 8 mg/Kg (TB4 at 301) In June 1995, Thrifty installed four groundwater monitoring wells (TB-1, TB-7, TB-8, and TB- 10) and four vapor wells (TB-5, TB-9, TB-11, and TB-12) Wells TB-1 and TB 10 were advanced to 70 feet bgs, vapor wells TB-9, TB-I 1 and TB-12 were advanced to 60 feet bgs and ' 2