ARCHIVED REPORTS_MONITORING WELL INSTALLATION REPORT - SITE ASSESSMENT WORK PLAN

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' Historical Background:gr d. River City Petroleum and Connell Motor Lift Truck ' Page 11 of 13 DISTRIBUTION OF STODDARD SOLVENT WITH BTEX ' 0 A release of stoddard solvents occurred from an unidentified source on the westernp ortion of the site. The most possible source is a set of dry well storm drains. Available data is ' suggestive of a spill or discharge at the western edge of the building in the area of borings P26,P27,CPT32 and various wells including the extraction well EW-1.The highest impact t to soil in the upper vadose zone is present at borings P26, P27, P14, P25 and EW-1. Once released to the subsurface, the contaminants migrated to a vertical depth of approximately 40 feet bsg, at which point the contaminants migrated locally down to a depth of 70 or 80 ' feet bsg.Minor concentrations of 1,2-DCA and tetrachloroethene were detected at the depths of 45 feet to 65 feet bsg, within the stoddard plume area west of the building. The highest impact to soil near the water table and below the water table to a depth of 70 feet bsg occurs ' in the area of boring EW-1,P27 to 55 feet and borings P26 and P32 to a depth of 70 feet bsg. • Total petroleum hydrocarbons quantified as stoddard solvent (TPH-ss) were detected in various ground water samples at maximum concentrations of 20,000 gg/l TPH-ss(MW-16), with moderate concentrations of BTEX at 34 µg/l benzene, 59 gg/l toluene, 120 gg/l ethylbenzene and 560 µg/1 xylene, respectively. ' The vertical and the lateral extent of TPH stoddard has been defined by sample collected. • The aerial extent of the soil contamination in the vadose zone is defined. DISTRIBUTION OF TPH-G AND BTEX-FORMER UST AREA ' 0 A release of petroleum hydrocarbons(TPH-g, TPH-d) and benzene,toluene, ethylbenzene ' and xylene (BTEX) compounds occurred from dispenser line releases. • Petroleum hydrocarbons were not detected in the soil samples collected from below the former UST area, nor excavation, however the most significant mass of hydrocarbons are ' found below the UST area proper. Available data is suggestive of a release that was most severe at the southern most dispenser islands, less at the north dispensers and even less between the dispenser islands.Once released TPH/BTEX to the subsurface,the contaminants ' migrated north under the former UST area then to a vertical depth of approximately 55 feet bsg near the current water table, where the variation concentration in soil samples suggest a smear zone between 50 feet and 60 feet bsg.At this point the TPH contaminants migrated ' locally down to a depth of 75 feet bsg,where non-detect soil samples were collected at the former UST area. Additionally, minor concentrations of 1,2-DCA were detected in soil ' samples collected at the depths of 65 feet to 85 feet bsg, collected below the former UST area. • The highest TPH-g and BTEX impact to soil in the upper vadose zone is present at Advanced GeoEnvironmental,Inc.