ARCHIVED REPORTS XR0001464 - Laserfiche WebLink

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1 65 and 70 feet and subsequently stabilized at a depth of approximately 68 feet. In an earlier letter to Mr. Ed Gotelli., ' dated December 11, 1992 , the PHS/EHD reported that seasonal high groundwater (1986) at this site was estimated to be between 45 and 50 feet. ' 2 . 4 Initial Assessment and Drilling On 9 October 1992 , a soil boring was installed in the center of the ' gasoline tank cavity (Boring #1; see Figure 2) . This boring was advanced to a depth of 60 feet. Samples were collected at five-foot intervals and analyzed for total petroleum hydrocarbons (TPH as ' gasoline) and volatile aromatics (BTE&X) . TPH as gas was detected in samples B1-20 (93 µg/g) , B1-30 (6, 100 ' µg/g) and B1-40 (13 Ag/g) . Benzene, toluene and xylene were detected in all analyzed samples except B1-60, at levels ranging from 0. 007 gg/g (xylene, B1-50) to 520 µg/g (toluene and xylene, B1-30) . Ethylbenzene was detected in samples B1-20 (3 . 5 Ag/g) , Bl- 30 (170 )ug/g) and B1-40 (0. 37 gg/g) . GeoAudit concluded in its Soil Boring installation report dated 16 November 1992 that assessment of the lateral extent of soil contamination could be achieved by further excavation. 2 . 5 Monitoring Well Installation I On 9 and 10 March 1993 , three soil borings were drilled to a depth of 77 feet. Samples were collected at five-foot intervals and selected samples analyzed for TPH as gasoline and BTE&X. The ' borings were completed as groundwater monitoring wells (MW-1 through Wil-3 ) . A benzene concentration of 0. 0079 mg/kg was detected at a depth of 45 feet in MW-2 , just south of the tank pit. Based on I these and prior results, GeoAudit recommended further excavation to remove the contaminated soil. At the request of Mr. Ed Gotelli, GeoAudit subsequently submitted an Interim Remediation Plan for overexcavation. Excavation activities and results are presented in sections 3 . 0 and 4 . 0 below. 2 . 6 Groundwater Monitoring On March 17 and June 24 , 1993 , the water level in each well was measured, each well was purged and samples were collected. In the March sampling event, the gradient direction was determined to be 0 . 0073 ft/ft directed S 70 W; the June sampling event showed a gradient direction of S 700 E. Benzene and xylene were detected at concentrations of 3 .7 Ag/L and 1. 1 ,4g/L in monitoring well MW-2 . Both concentrations are only slightly above the detection limits of 0. 30 µg/L and 0 . 50 gg/L. No contamination was detected in samples collected in June. 4