ARCHIVED REPORTS XR0004322 - Laserfiche WebLink

Home Browse Search

Additional Subsurface Investigation And Well Installation Report 8 The Southland 22gn2tiori,Store#19976,1399 N Main St Manteca California November 15 1998 so CONCLUSION AND REQUEST FOR CLOSURE Based on the reported concentrations of BTEX,TPH-g,and MTBE in the soil samples collected during the Installation of the three groundwater monitoring wells on September 2 and 3, 1998, and the GeoprobeTM sod bonngs drilled on April 29, 1998,the lateral and vertical limits of MTBE, BTEX and TPH-g have been delineated Soil Impacted with low hydrocarbon concentrations appears restricted to a limited area between the former tank pit and underlying the former fuel dispensers The highest dissolved BTEX, MTBE, and TPH-g concentrations from the groundwater samples collected September 16, 1998,were reported in monitoring well MW-2, located southwest(slightly upgradient)of the former fuel dispenser island Groundwater monitoring well MW-1, located east(downgradient) of the former USTs, and MW-3 located south (upgradient&crossgradient) of the former USTs,did not contain detectable concentrations of benzene or MTBE and contained low to moderate concentrations of TPH- ' G The benzene to TPH-G ratio is very low indicating that the dissolved hydrocarbon plume is old and being naturally biodegraded over time The lateral extent of dissolved hydrocarbons has been delineated crossgradient and downgradient of the former tank pit area based on non-detectable BTEX and MTBE concentrations in the groundwater samples collected from monitoring well MW-3 and non-detectable to low Benzene and MTBE concentrations in Downgradlent well MW-1 and grab sample GP-2-W Low dissolved oxygen concentrations In wells MW-1A and MW-2 Indicates that natural biodegradation of hydrocarbons Is occurring in the areas containing dissolved hydrocarbon concentrations Intrinsic biodegradation is expected to continue to reduce dissolved hydrocarbon levels at the site Fluor Daniel GTI, on behalf of the Southland Corporation, request site closure/no further action status at the site based on 1)the low to non-detectable benzene and MTBE concentrations in the groundwater and sod samples collected from newly Installed monitoring wells,2) naturally occurring biodegradation of the dissolved hydrocarbon plume which is expected to continue, 3) low benzene to TPH-G ratio Indicating continued biodegradation, and 4)the upgrade of the current fueling system to meet 1998 California requirements esa7e,g„pt FLUOR DANIEL GTI 4Li