SITE INFORMATION AND CORRESPONDENCE

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Antonia Vorster -2- 4 April 1990 not appear complete. The southern and southwestern extent of contamination in the C-zones (along the front formed by wells M-19, 11 , 17 and MW-6) also appears incomplete. Additionally, as noted in previous comments, deep (D-zone) wells are necessary at the downgradient extents of the plumes to verify and monitor over time the deepest point of contamination. This assumes that contamination in the C2-zone is equivalent to the C1-zone and can be treated as an equally contaminated zone. This may not be a valid assumption since there is very limited data for the C2-zone. The above discussion is conditioned on the results of the forthcoming Risk Assessment and proposed remedial actions. The degree of plume definition and subsequent monitoring is dependent upon both the level of cleanup needed and the type of remediation to be implemented. The decision of the number and location of additional monitoring wells may be deferred until these issues are better defined. However, Nestle needs to make it very clear how, and when, these decisions will be made. 2. In conjunction with the issues discussed in the first comment to finalize plume definition, the collective data needs to be reviewed and correlated to ensure no gaps exist. Although this has probably been done internally, the RI report presentation does not make this clear. Specifically, the following need to be addressed in each data area: a. Chemical Data - some chemicals were excluded as contaminants resulting from Nestle' s operations. Pages 3-30 and 31 conclude that positive results for Chloroform, 1 ,1-Dichloroethane, 1 ,1-Dichloroethylene, and 1 ,1 ,1- Trichloroethane are either anomolous or not associated with the site. All of these constituents have been detected multiple times in a number of wells both on- and off-site. Chloroform is a common laboratory solvent, 1,1 , 1- TCA a common industrial solvent, and 1 ,1-DCA and 1, 1-DCE are breakdown products of TCE or 1 , 1 ,1-TCA. Methylene chloride is found only sporadically in the monitoring wells and thus may be anomolous, but cannot be excluded from concern since MC was used at the site for decaffeination for 16 years. The positive results for Carbon Tetrachloride and Tetrachloroethylene do appear to be anomolous. Contaminant contour maps, such as Figures 3-10 through 12, should depict total volatile organics of concern, as well as any individual contaminants that need to be portrayed separately. This is an issue which was raised in previous comments. The need to separate individual chemicals will depend largely on their individual risk levels as determined in the forthcoming Risk Assessment. Trend analysis at individual wells using plots of contaminants over time should also be performed, especially at wells near the plume edges. When total volatile organics (excluding results for Carbon Tet and PCE) are plotted, the results indicate that contamination is more extensive on-site in the B-zone, high levels (apparently due to the source at M-8) extend for some distance off-site to the southwest in the A-zone, and higher levels and a greater extent of contamination exists in the C-zone. b. Stratigraphic Data - cross-sections are best prepared perpendicular and parallel to the groundwater flow directions to better depict flow paths. The marker bed, or beds, should be included and correlated on the sections.