COMPLIANCE INFO_PRE 2019 - Laserfiche WebLink

Home Browse Search

Aqua Terra Technologies F . DISCUSSION The test boring indicated that the immediate area is underlain at the surface by 1205 feet of fill consisting of Lj granular red brown silty sandy gravel. It is our understanding that this material was used to backfill the tank excavation. Below the fill a layer of stiff silty clay, approximately six feet thick, was encountered. Underlying the clay are interlayered clayey silts, clean sands, and silty sands. Groundwater was encountered at a depth of approximately 32 . 5 feet.. The analytical data presented in .?appendix 2 indicates elevated levels of total petroleum hydrocarbons (14 mg/kg) , toluene (1, 000 mg/kg) , ethylbenzene (740 mg/kg) , and xylene (3 , 700 mg/kg) in the soil sample collected from a depth of 14 feet below grade. The soil samples collected from four feet y below grade contained lower conce:atrations of contaminants including toluene (0. 23 mg/kg) , ethylbenzene (0.83 mg/kg) and xylene (0. 42 mg/kg) . The soil samples collected at nine feet below grade contained no detectable chemical contaminants. These data suggest that the deeper contamination resulted from the historical release of gasoline product from the former underground storage tank. It is possible that the contamination observed at the four foot depth. was the result of minor surface contamination or possibly leaks from piping. chemical contaminants were also olaserved at 19, 24 , and 29 feet although in lower concentrations than those observed at 14 feet. At 24 feet, toluene, ethylbenzene and xylene were detected in concentrations of 0. 36 mg/kg, 0. 032 mg/kg and 0. 63 mg/kg, E' respectively. At 29 feet, xylene was detected in a concentration of 0. 076 mg/kg. No other contaminants were detected at this depth, at the detection limits of the Ei instrumentation used for the analysis. It appears that the clayey soils existing between 13 and 1S feet below grade have provided some barrier to rapid contaminant migration to the underlying water bearing, permeable soil strata beginning around 27 feet. Confirmation that the contaminants have not migrated yet to groundwater is provided by the analytical data obtained for the groundwater sample. No contamination was observed in the groundwater sample collected, at the detection limits of the instrumentation used to perform t::ne analysis. However, the presence of the volatile components of the total petroleum hydrocarbon fraction in soil samples collected to a depth of 29 feet indicate that migration is occurring through 3 r� Li M