ARCHIVED REPORTS XR0010164 - Laserfiche WebLink

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support an interpretation of a relatively degraded plume generally depleted in Benzene compared to TPHG The irrigation and sewer pipelines were surmised to have possibly acted as contaminant preferred pathways and some residual contaminants remain under the pipelines It is possible that during times of high groundwater contaminants right have reached these areas under the pipes due to capillary action. Coarse-grained sediment does underlie the pipelines in some areas. However these coarse-grained strata packages that appear to have held residual contaminants are interpreted as a small stream channel roughly under the pipelines and is another preferred contaminant pathway This stream channel pathway is interpreted present from lithology logged in Bonngs PB-15, PB-14, MW-3, MW-9, PB-9 and PB-7 This tends to align along the historically observed contaminant plume axis It is our opinion that the soil/sediment texture and residual contaminant source contributed TPHG and Benzene into the dissolved groundwater plume tending to keep the dissolved levels high especially at monitoring wells MW-3 and MW-9 6 2 Estimated Contaminant Volume Removed Wright has estimated the quantity of contaminant removed contained either absorbed on soil and dissolved in groundwater The estimate uses a simple calculation that calculates gallons of TPHG and Benzene removed using the chemical sample analysis averaged for the number of sample detections (samples showing none detected were not used in the averaging). Please note these contaminant volumes are rough estimates only of the contaminant quantity removed Excavated soil used the chemical data for the soil loaded onto the trucks The average TPHG and Benzene concentrations in parts per million (as milligrams per liter, and using an average 100 pounds per cubic foot soil density and 900 yards=24300 cubic feet converted to gallons)for soil contairnnant removed used in the following equation, 0.002425(average TPHG concentration) x 24,300 ft3 x 100 IWO x 0 13368 lb/ft3/gal 788 gallons TPHG 0 0000129 (ave Benzene concentration) x 24,300 ft3 x 100 lb1ft3 x 0 13368 lb/ft3/gal 4.2 gallons Benzene The quantity of estimated groundwater TPHG and Benzene contaminant in parts per million contained in the groundwater pumped from the excavation used the following equation, 0.0000377 (average TPHG concentration) x 239,250 gallons x 0 264 liter/gallon 2.3 gallons TPHG 0 00000334(average Benzene concentration) x 239,250 gallons x 0 264 liter/gallon 0.21 gallons Benzene Page 9 of 13