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Soil at the site within 2 feet of ground surface is contaminated with DDT at 4.94 mg/kg. The cancer risk screen concentration for DDT is 1.7 mg/kg. RWQCB soil samples show Endosulfan I at 48,000 ppb. The reference dose screen concentration for Endosulfan is 29 mg/kg (2,4). Five workers are regularly on the site. An estimated 453 nearby residents are within one mile of the Trinkle & Boys site (1,2,11). .� Surface water is not used for domestic purposes within 15 miles downstream of the site. The San Joaquin River, located approximately 3.5 miles to the east is used for agricultural and industrial water supply, recreation, fishing, and wildlife habitat. Surface water runoff from Trinkle & Boys is unlikely to reach the San Joaquin River due to the distance between the site and the river. In addition, the site is outside the 500-year flood plain indicating that flooding of the San Joaquin River is unlikely to affect the Trinkle & Boys site (1,12,13). The region typically has low year round rainfall amounts. The net precipitation during the months of greatest rainfall in December, January and February is 1.75 inches. In January 1967, the maximum 24 hour rainfall experienced in the Stockton-Tracy area was 3.01 inches (2). Air sampling has not been conducted at the site. Contaminated soil and the sump surface impoundment may release gaseous and particulate contaminants into the air. An estimated 2,729 residents live within 4 miles of the Trinkle & Boys site (1,2,11). 5.0 Summary of Site Inspection Activities A Preliminary Assessment was performed by California Environmental Protection Agency-Department of Toxic Substances Control (formerly California Department of Health Services) on the Trinkle & Boys site in February 1988. EPA recommended a lower ._ priority SSI be performed for Trinkle & Boys under CERCLA. Further evaluation of Trinkle & Boys for this SI included a site reconnaissance visit by URS representatives, review of existing and additional file information, contacts with state and county regulatory agencies, and reevaluation of groundwater and surface water data using the Hazard Ranking System (HRS). The pertinent HRS factors associated with the site are: ■ A release of contaminants has occurred to groundwater. ® Soils on the site are contaminated with pesticides. ■ Groundwater in the area is used for drinking. ■ Approximately 2,729 people reside within 4 miles of the Trinkle & Boys site. ® Access to the site is unrestricted. URS Consultants, Inc. Page 6