SITE INFORMATION AND CORRESPONDENCE

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Mr. William J. Marshall February 11, 1992 Page 2 Clean up Goal Establishment We propose to establish a clean up goal of 100 µ/1 in accordance with criteria described in the recently revised Article 5 of Chapter 15 in California Code of Regulations, Title 23, Division 3. The following factors were considered in establishing the potential for any adverse effects on surficial and ground water quality and beneficial uses: • The physical and chemical characteristics of the chloroform in the management unit • The hydrogeological characteristics of the facility and surrounding land • The quantity of ground water and direction of ground water flow • Current and potential users in the ground water area • Existing quality of the groundwater and other potential sources of contamination • The potential for health risks to human and wild life to vegetation and structures. • The persistence and permanence of potential affects. The physical and chemical characteristics of the presence of chloroform in soils and groundwater, the hydrogeologic characteristics of the facility and surrounding land, quantity of groundwater and flow direction have been presented in detailed reports prepared by Brown and Caldwell (1985-1991). Current and potential users of water for domestic purposes are prohibited by a local city municipal code, section 11-1.16, from installing a private well within 200 feet of a city water hook up. The city water supply is obtained from the 10 City of Tracy wells that are sealed in the upper 120 foot depth and screened within the lower aquifer. Water for irrigation, according to Mr. Ernie Pombo, is currently being obtained from the Old River by the West Side Irrigation District. Thus, groundwater from the monitored zone is not used for domestic or irrigation with the area affected by the chloroform down gradient (report, April 4, 1985). Existing groundwater quality is presented in condensed form in the attached table, and other potential sources of contamination are described above. Potential risk to a biological receptor would have to occur by an exposure pathway of inhalation, dermal contact, or ingestion. The potential receptor population includes personnel associated with groundwater sampling activities, and those involved in any remedial activities at the site (safety trained well drillers and geologists). The receptor population does not include local residents or employees at the facility because they are not exposed to the chloroform by any of the above mentioned exposure pathways. Chloroform is effectively volatilized when exposed to air, and thereby becomes less likely to reach a potential biologic receptor.