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Environmental Protection Agency because it often contains polyaromatic <br /> or heterocyclic hydrocarbon compounds (9). <br /> Also, on December 3, 1982, the U.S. Army Defense Depot in Tracy disposed <br /> of approximately 11,000 pounds of barium hydroxide at the site. Within <br /> two weeks of the dumping incident, the defense depot conducted a cleanup <br /> of the barium hydroxide. This cleanup was declared adequate by the <br /> California Department of Health Services on January 17, 1983 (10). FIT <br /> was unable to obtain sampling data verifying the adequacy of cleanup <br /> efforts at CHSL. <br /> 3.3 GROUNDWATER <br /> The Corcoran Clay Member is present beneath the northern half of the <br /> landfill. The Corcoran Clay is a lacustrine deposit which consists of <br /> sandy silts and clays. The unit pinches out against the foothills of <br /> the Coast Range (approximately halfway through CHSL) and thickens <br /> rapidly eastward toward the center of the valley. It acts as a <br /> confining bed between upper and lower waterbearing zones. In the case <br /> of CHSL, however, the termination of the clay layer beneath the site <br /> indicates that the upper and lower aquifers are interconnected. The <br /> site is on the western boundary of the San Joaquin Valley groundwater <br /> basin. The groundwater reservoir in the Tracy area has been divided <br /> into three water-bearing zones: (1) a lower water-bearing zone that <br /> contains confined fresh water below the Corcoran Clay, (2) an upper <br /> water-bearing zone that contains confined, semiconfined, and unconfined <br /> water above the Corcoran Clay and younger deposits, and (3) a shallow <br /> water-bearing zone that contains unconfined water within about 25 feet <br /> of the ground surface. The upper two zones converge above the Corcoran <br /> Clay and are considered equivalent to the shallow perched aquifer (3). <br /> In general, groundwater in the deep regional aquifer in the Tracy area <br /> moves toward the northeast, away from the Coast Range and towards the <br /> San Joaquin River. Deep groundwater on-site, however, generally flows <br /> in a southeasterly direction. This deviation from the regional trend <br /> 3-8 <br /> sa/tm/chl/si <br />