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27 May 1992 <br /> (GeoAudit MDC Ukiah-1.9) <br /> Page 1 of 5 <br /> INTRODUCTION/BACKGROUND <br /> The site is located in a relatively flat commercial area (Figure 1 <br /> - Location Map, 7 . 5 Minute Ukiah Quadrangle, USGS Topographic <br /> Series, 1975) . The depth to ground water is approximately 10 feet <br /> based on information from the existing assessment/monitoring <br /> reports on the property. <br /> Three 10, 000 gallon underground gasoline tanks were removed from <br /> the subject site in 1986 (Figure 2 - Site Plan) . Hydrocarbon <br /> contamination in soil and ground water was discovered following the <br /> tank removal. Subsequent investigations included the installation <br /> of five on-site and four off-site groundwater monitoring wells. <br /> A passive monitoring program was performed between the second <br /> quarter of 1990 and the first quarter of 1991. The results of water <br /> sampling performed during the monitoring program indicated <br />• considerable fluctuations of the contamination level. <br /> Existing records do not indicate that any soil mitigation has been <br /> performed at the site. The fluctuating contaminant levels in the <br /> groundwater table may be attributed to contaminated soil in the <br /> tank area, groundwater capillary fringe and seasonal fluctuations <br /> of the water table. We believe that as long as the "contaminant <br /> source" is still present, the contamination level in the ground <br /> water will fluctuate in an unpredictable manner for an extended <br /> period. <br /> The scope of work is to perform an active mitigation by removing <br /> the contaminated soil from the vadose zone and capillary fringe. <br /> Subsequently, the contaminated soil is to be treated by means of <br /> biodegradation. Upon treatment, the soil, at least partly, will be <br /> used as backfill materials. Approximately 2 , 000 cubic yards of <br /> contaminated soils were estimated to exist within the proposed <br /> limits of excavation. <br /> A work plan and a work plan addendum to this matter were submitted <br /> to the Regional Water Quality Control Board - North Coast Region <br /> (RWQCB) on 31 May and 16 July 1991, respectively, and found <br /> adequate. To comply with current air quality regulations, a permit <br /> to bioremediate the contaminated soil was also secured from the <br /> Mendocino County - Air Pollution Control District (Permit No. <br /> A/C91-20) . <br /> I <br />