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�- v kTC A S S O C I A T E S I N C The lateral extent of TPHg and benzene and the presence of these contaminants in the capillary fringe are indicative of groundwater impact and transportation. As stated in Smith Technology Corporation's Additional Soil and Groundwater Report, Fayette Manufacturing Corporation, 7675 West Eleventh Street, Tracy, California, dated January 31, 1997, the lithology of the capillary fringe is primarily silty clay, with clayey sand in some areas. The capillary fringe in the vicinity of wells MW1, MW2, and MW3 was observed to be silty clay. Petroleum hydrocarbons in groundwater would readily adsorb to the clayey soil in the capillary fringe. 2_2 Hvdrogeolozv and Area Groundwater Use Regional groundwater depth is reported to be approximately 8 feet below grade (San Joaquin County Flood Control and Water District, Spring 1995) and the regional inferred groundwater gradient is northwest. This is consistent the results of quarterly monitoring events with the depth to water ranging from 6.34 to 8.99 feet bgs and with a predominantly northwesterly groundwater flow direction(Figures, Appendiz Q. As previously mentioned, water quality differences above and below the confining Corcoran Clay `, layer exist in the Tracy area. In the southwest portion of the County near Tracy an area of good mineral quality exists. This groundwater body can roughly be described as below the Corcoran Clay. The City of Tracy, many industries, and the Tracy Defense Depot (located south of the Site)rely on this deep zone for their supply(DWR Bulletin No. 146, 1967). The water quality in the upper zone (above the Corcorran Clay) is quite variable as a result of several different sources of recharge, however, this upper zone generally consists of inferior water quality. Generally, this water has a lower sodium percentage and higher mineral content than the underlain waters. r The City of Tracy's water system sources include surface water from the Delta Mentoda Canal and groundwater pumped from a network of ten wells located throughout the City. Surface water sources currently make up approximately 66%, or approximately 2.9 billion gallons, of the City's municipal water supply. As mentioned previously, the City's municipal supply wells rely on sources below the confining Corcoran Clay layer. L Furthermore, the City of Tracy is also participating with the cities of Manteca, Lathrop, and ` Escalon and the South San Joaquin Irrigation District to incorporate surface water from the Stanislaus River into the City's municipal water distribution system. This water source will increase the reliability of the City water supplies by having a third source of supply and provide redundancy in treatment facilities by having a second water treatment plant. Water deliveries from this project could occur as soon as 2002. According to City officials contacted by ATC, no municipal drinking water supply is currently available east of MacArthur Drive which is located approximately three-quarters of a mile west of the Site. In addition, the City currently has no plans to extend municipal water services eastward V w:\95122Vvports\ReVeA for NFA-doc 5 r