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INITIAL RELEASE DDJC Tracy community, Banta, located about 2.5 miles northeast of the site (Woodward-Clyde Consultants, 1992a). ATSDR obtains demographic information such as location of households, population size, and age and sex of people to determine who is living in the vicinity of a site. This information may be useful in identifying potentially sensitive subgroups or in interpreting relevant health outcome data. ATSDR determined that approximately 3,980 people live within a 1-mile buffer of the site, including approximately 560 children under the age of 7 and approximately 400 adults aged 65 and older (see Figure 3). DDJC Tracy employs approximately 800 people and receives approximately 400 authorized visitors per month. No employees live at the depot (Montgomery Watson, 1996b). Land Use and Natural Resources The depot currently functions as a storage and distribution facility for U.S. military services. Access to the DDJC Tracy site is controlled by a perimeter fence and security guards. A day care center located in the northwest corner of the site provides services to approximately 90 children (see Figure 2) (Montgomery Watson, 1996b). Historically, much of the area surrounding the site has been used for agricultural purposes, although urban/residential growth has occurred since the late 1980s in areas southwest and northeast of the site. Walnut orchards occupy the Tracy Annex and row crops, including beans and tomatoes, are grown in the remaining land north of the orchards (Montgomery Watson, 1995). Flood irrigation is the standard practice for both fruit-bearing trees and crops. Groundwater is the major source of drinking water in the vicinity of the site, serving private, municipal, and agricultural wells in the area. It also has been widely used for irrigation purposes. The Tulare formation is the primary source of groundwater in the San Joaquin Groundwater Basin and is separated into three zones, the Upper Tulare Aquifer, the Corcoran Clay Layer, and the Lower Tulare Aquifer. The Upper and Lower Tulare Aquifers are separated from each other by the impermeable Corcoran Clay layer. Beneath the depot, the water table of the Upper Tulare Aquifer lies approximately 10 to 45 feet below ground surface. The groundwater in this aquifer migrates at an estimated 15 to 150 feet per year toward the north-northeast. The Upper Tulare Aquifer is further subdivided into the Above i Upper Horizon (between 0 and 35 feet below ground surface), Upper Horizon (between 25 and 60 feet below ground surface), Middle Horizon (between 55 and 85 feet below ground surface), and the Lower Horizon (the top begins between 110 and 125 feet below ground surface). Because of the naturally poor water quality (e.g., elevated boron concentrations) in the Above Upper and Upper Horizons of the Upper Tulare Aquifer beneath the site, the groundwater in these horizons 4 j