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KLEINEELDER investigation because ACLS cannot be established if the source of ground water contamination is still releasing contaminants to ground water. Release Characterization - Testing soil cores as part of Source Characterization activities will give information on the leachability of soil contaminants, if present. If soil contamination is found in either WMU B or the old solar evaporation pond areas, computer modeling using the HELP model will be conducted to estimate the amount of leachate generated by these areas that could potentially mobilize soil contaminants. The migration of contaminants through the vadose zone will be assessed using soil/water partition coefficients. Contaminant migration in ground water will be assessed using historical ground water direction and gradient data in addition to the slug test results. If the modeling indicates that the plume may have emerged from beneath WMU B undetected, ground water sampling will be conducted using temporary wells employing BAT sampling technology. Attenuation and degradation characteristics of the contaminants will be evaluated based on data obtained from a literature search. Potential Receptor Identification - Land and water use in the immediate vicinity of the landfill is primarily agricultural with a few residential users. Existing data will be analyzed to identify potential receptors and additional investigatory work will be initiated to close gaps in existing data. Exposure routes will be described and the potential for human, animal, and plant exposure will be assessed. Alternate Concentration Limits - Alternate Concentration Limits (ACLs) are chemical concentration "triggers" that are used by regulators to determine when corrective action is required. To establish ACLs, it must be demonstrated that hazardous constituents detected in ground water will not pose a substantial present or potential hazard to human health or the environment at the ACL levels. If results of investigations indicate that setting ACLS is feasible, a health risk assessment will be prepared based on contaminant type, mobility, and potential receptors. Using results of the health risk assessment and data collected during the first four phases, Kleinfelder will propose ACLs for the constituents of concern. If the initial phases of the RFI reveal that ACLs cannot be set, the remainder of the RFI will focus on preparing recommendations for dealing with the contamination. After the investigation is complete, a final RFI report will be prepared. It will present results of the investigation and will discuss a proposed course of action regarding how to deal with ground water contamination detected in MW-SA. C7-90-99 2