ARCHIVED REPORTS XR0010073 - Laserfiche WebLink

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• Groundwater is anticipated to flood the excavations The excavations will be allowed to flood twice and be pumped out twice to remove contaminated water and allow "back flushing" of dissolved contaminants The water will be stored in surface tanks, or pumped directly to vacuum trucks depending upon the operational constraints of the site Verification soil and groundwater sampling will be collected and analyzed for TPHG, BTEX and MTBE and oxygenates Soil samples will be collected at 20-foot intervals along the capillary fringe to ascertain presence of absence of contaminants A groundwater sample will be collected from the flooding following the second dewatenng to ascertain dissolved contaminants presence Samples of the contaminated groundwater and soil will be collected allowing judgment of contaminant mass removal to be estimated Petroleum degrading bacteria or degrading compounds will be placed into the excavation prior to backfilling to assist natural degradation processes This should have an effect of continuing to degrade contanunants and natural groundwater motion should carry the degradation on toward MW-9 and further downgradient MW-9 will be replaced following excavation so the monitoring network will remain to check on the anticipated lowering of contaminant concentrations Option 2 Install a horizontal well along the trend of the dissolved plume axis from the former tank pit to the vicinity of MW-9 The well would be placed at a depth of about 16 feet, so that the well was placed within the upper portion of the aquifer A dual phase extraction approach would be used to capture both dissolved contaminants and soil vapor from the vicinity of the capillary fringe and the dewatered region The extracted vapor and water would be sent to a surface treatment system (assumed to be carbon) The treatment pad could be placed in the corner of the lot, with discharge to permitted outfalls for both air and water Horizontal well installation will be limited by the presence of the irrigation pipeline and proximity of the historically observed plume axis trend (that is along a line from the former tank pit toward monitoring wells MW-3 to MW-9 and MW-2) This placement would affect the region of maximum contaminant location Another possible limitation would be the presence of silty and clayey soils in the capillary fringe of extraction influence is anticipated to be limited to the degree of the air conductivity of that sediment These soils tend to have the higher clay/silt content, grading to sandier sediment below i� Page 9