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i <br /> Mr. Ron Rowe Project 20C42-001.026 <br /> June 25, 1998 <br /> Page 3 <br /> 570/9-75-001, prepared under the auspices of the National Water Well association <br /> Committee on Water Well Standards) to permanently seal abandoned wells. <br /> Additionally, the seal was placed within the uppermost aquifer and across the B-C aquitard, <br /> a low permeability silty clay unit encountered at a depth of about 37 to 47 feet . The seal, <br /> placed across and above the aquitard, was designed to seal out water from the uppermost <br /> zone that would potentially migrate downwards. Because there was doubt as to the <br /> construction of the well, the procedures chosen to abandon the well afforded the highest <br /> probability for success for confining water in the upper 55 feet in which it originally <br /> occurred. In particular, the sealing across the aquitard provides the highest probability for <br /> preventing downward flow of groundwater into a lower, more permeable zone. <br /> Stained soil (petroleum odors) observed on the well casing as it was being extracted <br /> (approximately 30 to 40 feet bgs )is cited as a concern for requiring the entire well be <br /> drilled out. Monitoring results for wells in the vicinity of 17A1 show that TS-9 completed <br /> in the first encountered water bearing zone near 17A1 is not impacted by dissolving <br /> petroleum hydrocarbons. Wells SP/WC-ls and -lm located downgradient of 17A1 in the <br /> first and second water bearing zones have not been impacted by dissolved petroleum <br /> hydrocarbons. No known source of soil or groundwater contamination has been identified <br /> at or immediately adjacent to Well 17A1. A source of the soil staining is likely the lube oil <br /> (typically mineral oil) used to lubricate the well pump. An unknown quantity of lube oil <br /> leaked into the well but was removed prior to abandonment. During operation of the well, <br /> it is probable the oil was drawn down in the casing as the well was pumped and migrated <br /> outside the casing through the holes in the corroded casing. EMCON believes that the <br /> staining observed is localized, and the well was successfully sealed, preventing any vertical <br /> movement of groundwater. <br /> SAC�N:\PJPOC4MC420012.6AG-95Vba=s:l <br />