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1 • • <br /> 1 buried concrete slab along the southeast edge of Alden Park. An accumulation of <br /> oily soil is also present at the 2 foot depth along the west side of Forest <br /> 1 Hills Drive. Several other areas show "spot" concentrations of oil and grease. <br /> Mobility of the oil in the vadose zone (i.e. , the soil above the water table) <br /> appears to be very low, because of the sticky, viscous character of the oil. <br /> Groundwater conditions were investigated through installation of 18 borings, <br /> 1 17 of which were completed as wells to a maximum depth of 22 feet below ground <br /> surface. The water table occurs at depths of 7.4 to 11.4 feet below ground and <br /> ' has a relatively low hydraulic gradient of about 0.005 (1 foot vertical/200 <br /> feet horizontal) to the northwest. Average ground water flow velocity in the <br /> saturated zone was calculated to be in the range of 1 foot/year. Overall <br /> 1 groundwater quality of the water table zone is fresh but hard, with total <br /> dissolved solids and chloride concentrations higher than secondary drinking <br /> 1 water standards. Shallow groundwater use in the immediate site vicinity is <br /> limited. <br /> Liquid oil was observed in the two wells completed within the concrete slab <br /> and in seven of the wells located adjacent to the slab. This assessment is <br /> 1 based both on oil droplets present in soil samples retrieved during drilling and <br /> on product floating on the water table. The slow rate of groundwater flow along <br /> 1 with the viscous nature of the oil has prevented liquid oil from migrating large <br /> distances from Alden Park as a separate phase. Away from the park, visually <br /> 1 clean soil was observed in soil borings within 300 feet of the park edge on all <br /> but the northeast side. The northeast side of the property is bordered by <br /> ' a separate site where an investigation related to oily soil is being conducted <br /> by others. <br /> 1 The distribution of dissolved oil components was assessed through chemical <br /> analysis of groundwater samples. Low concentrations of oil and grease in wells <br /> immediately adjacent to the concrete slab, where liquid oil is present, suggest <br /> that the oil is highly insoluble in water. <br /> ' Selected soil samples and three groundwater samples from wells located up- <br /> gradient, within, and down-gradient of Alden Park were further analyzed for <br /> 1 volatile organic compounds, semi-volatile organic compounds, metals, and several <br /> 1 BFA9/AO <br /> 1 Dames& Moore <br />