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ATTACHMENT EPA COMMENTS ON DDRW-TRACY'S EVALUATION OF DETECTION LIMITS The following represents EPA's comments on the DDRW-Tracy contractor [James M. Montgomery's (JMM's)] letter of January 20, 1993 evaluating the detection limits to be utilized during Phase I of the Comprehensive Remedial Investigation and Feasibility Studies (RI/FS) field work. [On February 12, EPA received the DDRW-Tracy (JMM's produced) Work Plan Addendum for the Comprehensive RI/FS, which resolved some of the potential issues that would otherwise have been noted with the January 20, 1993 detection limit evaluation letter.] General Comments 1. EPA does not concur with the proposed soil detection methodology for dioxins/furans. The proposal was to analyze 10 percent of all soil samples for dioxins/Furans. EPA believes the sampling effort can be focused on only those areas of DDRW-Tracy where there is the possibility of producing these compounds, i.e., burn pits. In doing so, fewer samples may be analyzed (27 versus 51) but supply higher assurance that our decisions will be health protective. The method used to analyze for dioxins/furans should be EPA method 8290 which is more sensitive. Again, the smaller sample size and higher quality data will better support the decisions at the end of the RI. 2. When more than one method could have been chosen the rationale for choice of alternative analytical methods is not fully explained, although it appears that acceptable alternatives were generally chosen. The discussion regarding California- EPA's toxicity values versus Federal EPA's toxicity values is irrelevant to the choice of detection limits in cases where Cal-EPA's toxicity values are more stringent; the more stringent values must be utilized if the data is to be used in the baseline risk assessment (BRA). Adeauacv of Detection Limits 3. If DDRW-Tracy wishes to "deselect" some of the potential sources from further investigation using Phase I data, then the most stringent detection limits should be used. [Note: There appears to be conflicting information on the objectives of Phase I sampling. At the meeting of June 14-15, 1992 DDRW-Tracy stated that deselection of potential SMWUs from further investigation was not an objective of Phase I sampling. However, the Comprehensive RI/FS Work Plan in Section 3.1.2.3.6, page 3- 8 (unchanged by the Work Plan Addendum) calls for deselection of some sites based on Phase I sampling results. The "DDRW-Tracy Response to EPA Comments" dated August 4, 1992, states "no sites will be deselected without the approval of the State of California and EPA." DDRW-Tracy needs to be mindful that changes in Data I