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2.2 Hydrogeo/ogic Conditions <br /> Ground water is present beneath the site at a depth of 25 to 35 feet below ground surface (bgs), <br /> depending upon time of year and weather history. EI has determined the groundwater elevation pea <br /> at MW- 1 , MW-2, MW-3 and MW4, the direction of flow, and flow gradient, and reported these <br /> data in Quarterly Groundwater Monitoring Reports since November of 2000. Vy <br /> l <br /> It should be noted that groundwater flow gradients are low in this area, and seasonal changes in <br /> water levels can, therefore, have significant effects on the apparent groundwater flow direction. <br /> 3 .0 PURPOSE OF INVESTIGATION <br /> The purpose of this investigation is to determine the vertical and lateral extent of contamination <br /> affecting MW-4, and to try to explain the results of groundwater analyses showing relatively <br /> consistent levels of BTEX and 1 ,2 —DCA contamination since the well was installed in Nov. <br /> 2000, while gasoline levels dropped significantly in late 2003 . <br /> The source of this contamination has not been identified. The adjacent site at 3147 S . El Dorado <br /> Street, operated as a card-lock service station for many years. Three USTs (one 10,000 gal <br /> diesel, two 10,000 gal gasoline) and associated fuel dispensers and piping, were removed in <br /> September 1998 . Advanced GeoEnvironmental, hie. has completed several investigations of the <br /> site and monitored groundwater for several years. Their reports have identified contamination <br /> (gasoline and BTEX) in several wells, but the contamination appears to move in an easterly <br /> direction from the previous location of the fuel dispenser and USTs. A path for contamination to <br /> CTL's MW4 has not been shown to date. <br /> 4.0 DISCUSSION <br /> MWA was installed down gradient (at the time) from MW-2, to detect possible movement of <br /> used oil from the source (former waste oil UST at MW-2). Used oil has never been detected at <br /> MW-4, but gasoline, BTEX and oxygenates contamination has been present since installation of <br /> the well. Diesel contamination was also present from 09/19/01 through 06/25/02. <br /> Previous investigations were conducted on-site and were concerned with the spread of <br /> i <br /> contamination from USTs which were removed in 1990 (Used Oil) and 1998 (Diesel). As such, <br /> attention was directed at these materials. This investigation will be conducted off-site and will <br /> 3 <br /> i. <br /> J <br />