SITE INFORMATION AND CORRESPONDENCE 1995-2004

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0- James L. Tjosvold, P.E. August 19, 1996 Page 2 the combined soil and groundwater FS will include the information discussed below. The agency comments are italicized and presented before each response. Responses to DTSC comments (dated December 26,1995): Comment: 1. The FS Workplan has failed to define a criteria to establish soil cleanup levels that would be protective of groundwater. In order to safeguard water quality, a site-specific and resource protective criteria must form the basis for soil cleanup. The criteria then must be applied for all soil analytical data to determine the degree to which the site should be cleaned or remedial action is necessary. The RWQCB "Designated Level Methodology"for cleanup level determination, or its equivalent, must be used to support this criteria for establishing remedial action goals far soil. Based on application of the cleanup criteria, supported by a qualitative site analysis, contaminant source areas can be appropriately characterized and defined for the proposed remedial actions to be applied and remedial action goals to be satisfied. As a result of applying the above criteria, estimated volumes of contaminated soil requiring remediation may change, resulting in the need for re-evaluation of alternatives and thus requiring a major modification to the FS. Response: 1. The draft Soil OUFS report (not FS workplan) did not identify specific cleanup levels because of the nature and distribution of the COPC in the soil at the site. The COPC are immobile and distributed in random pockets throughout the site. The health and environmental risk assessment did not identify any significant(greater than 10-5 cancer risk or hazard index greater than one) human health risks at the site. Therefore, developing a site-specific criterion to be uniformly applied at the site most likely would result in massive treatment or excavation of the site with little or no overall risk reduction. For example, because small isolated concentrations can not be easily identified and treated, applying the beneficial use criteria for water provided by the RWQCB and back calculating soil cleanup criteria from those levels would result in a great amount of clean soil being treated to ensure that any isolated small pockets of contaminants are treated. It should be noted that many of the soil borings are located within ten feet of the next closest boring, thereby providing very detailed analytical coverage of the site. For these reasons, four qualitative criteria were applied to help identify areas requiring treatment. The overall goal was to treat the areas that have the greatest impact on groundwater quality. The qualitative criteria for defining soil source areas for treatment were presented in Section 5.2.2.2 of the draft OUFS as follows: