ARCHIVED REPORTS_XR0009087 - Laserfiche WebLink

Home Browse Search

a field decision was made to terminate the collection of soil vapor samples, in lieu of discrete, representative soil samples which would be used to evaluate the offsite Petroleum hydrocarbon migration The initial soil vapor analytical results from Borings SV1 , SV2 and SV3 are included in Appendix B. Soil Sampling Results The soil sample analytical results are presented in Table 2 The results indicate detectable petroleum hydrocarbons at depths of 24 to 28 feet bgs (in the capillary fringe area just above the water table) in all borings except SV2 and SV5 Both SV2 and SV5 were installed along the estimated southerly boundary of the suspected petroleum hydrocarbon plume, and the analytical results from these soil samples confirm this southerly boundary SV6, which was installed approximately ten feet down gradient from the existing under- ground gasoline tanks at 7-Eleven, showed substantially higher BTEX concentrations in both the soil and groundwater samples collected from this location than the other offsite sampling locations SV8, which was installed to confirm the presence of petroleum hydro- carbons at the former Cardlock site, indicated significant petroleum hydrocarbon concen- trations from the bottom of the former excavation at 12 feet, to the bottom of the boring at 25 feet Benzene [so concentration maps at depths of 15 to 16 feet, and 23 to 25 feet, respectively, are presented on Figures 4 and 5 Figure 4 indicates that an onsite source area exists Figure 5, meanwhile indicates that petroleum hydrocarbons, including benzene, have migrated offsite toward the northeast, with concentrations decreasing as the distance from the source increases, until a second source area is encountered near SV6 (located in the vicinity of the 7-Eleven underground storage tanks) Groundwater Sampling Results Groundwater sample analytical results are presented in Table 3 These results indicate that the groundwater plume has migrated offsite toward the northeast, and that a second petroleum hydrocarbon source area appears to be contributing to the TPH and BTEX con- centrations observed in the area near SV6 These results appear to be very consistent 9 IJe6s'.94O549Veaon doe 7 94054900