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r <br /> Ms Vicky McCartney Project No 880-040 1 A <br /> December 8, 2003 <br />' Page 6 <br /> rSITE CONCEPTUAL MODEL <br /> Release Scenario and Plume Characterization <br /> 1 <br /> Shallow soil at the ub ect 1te has be impacted with fuel hydrocarbons at <br /> concentrations up to 20-8-ug/4of TPHg, 0-6272 uytr of benzene, and oY MtBE u ( <br /> r <br /> The highest hydrocarbon concentrations have been present in soil beneath the western IZ�jD y <br /> dispenser islands <br /> Hydrocarbons have been reported in groundwater beneath the site at concentrations up to <br /> 25,700 ug/l of TPHg (well MW-1), 1,820 ug/l of benzene (well MW-1), and 41,000 ug/I <br /> of MtBE (well MW-5) Currently on-site, TPHg are observed in wells MW-1 and <br />' MW-3 at concentrations of 4,400 and 160 ug/l, respectively Benzene at a concentration <br /> of 640 ug/l is reported in well MW-1 While MtBE is reported at concentrations up to <br /> 4,200 ug/1 in all on-site wells (MW-1 through MW-3)? Off-site and downgradient of the <br /> site, MtBE is reported in wells MW-4 and MW-5 at concentrations of 14,000 and <br /> 10,000 ug/l, respectively In borings CPT-3 and CPT-4, groundwater samples collected <br /> at 25 feet bgs had concentration of MtBE at 7,600 and 12,000 ug/l, respectively <br /> Figures 3 and 4 illustrate the extent of the MtBE plume beneath and downgradient of the <br /> subject site based on recent groundwater monitoring well analytical data Given the <br /> depth to water near the base of the upper sand at 15 feet bgs, and no detectable MtBE in <br /> groundwater below 30 feet bgs, the sand located between approximately 28 to 40 feet <br /> bgs appears to be the main migratory pathway downgradient of the site YEs <br /> Potential Environmental Receptors <br />' The hydrocarbon plume extends beneath an area that is currently being used for <br /> commercial purposes (gasoline sale) and transportation (West Hammer Lane) Most of <br />' this area is paved with asphalt or concrete No residential buildings are located within <br /> the probable extents of the plume No water producing wells are located within 2,000 <br /> feet of the subject site <br /> 1 <br />' N\sacDP120031PrM81880040 1A 3aa doe <br />