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i INTERNATIONAL TECHNOLOGY CORPORATION Ms Mary Maeys 5 January 15, 1996 M. Contaminant Data Issue A Report all contaminant data for site Response A Attachment 1.0 of this letter contains a summary table for all analytical data ' collected beneath the building basement floor, near the abandoned USTs. Attachment 3.0 of this report contains two summary tables for all analytical data collected beneath the Lindsay Street sidewalk. One of the Attachment 3.0 table was generated by Reidel Environmental Services following tank removal activities and the other table was generated by IT Corporation following the iinstallation of two vapor observation wells in the Lindsay Street sidewalk area. Issue B Justify the selection of data used in residual mass determination. ' Response B For the basement area (Location 1), an average of the ten detected petroleum concentrations was multiplied by an assumed area of impact (based on known data points and the migratory behavior of petroleum) to determine residual mass This calculation includes all detected quantities and can be referenced in Section 6.3 1 of the IT Corporation "Site Closure Recommendation Report," dated April 1995 For the sidewalk area (Location 2), only the current analytical data collected by i IT Corporation was employed in residual mass calculations The areal extent was defined by known data points (soil sampling locations). A revised residual mass calculation which includes all known analytical data was completed and ' is included in Attachment 3.0 of this letter The V-Leach model was re-run using all detected diesel concentrations for the area (which includes all original detections from this area, the presence of which was not confirmed during recent sampling activities conducted by IT). Even when the greater concentrations are employed, the results remain the same — that little to no residual diesel impact to groundwater will result within the modeled 50-year period. The revised model input data and results are included in Attachment 4.0 of this letter. IV. Discuss Organic Carbon Value Used for Modeling Purposes Issue A Relate how the one measured organic carbon concentration compares to the ivalues used in the model (e g , measured 63; modeled a range of .2 to .5) Fraction of organic carbon content vanes with soil type. Analytical samples were tested for total organic matter (TOM) To determine the fraction which is due to carbon only, you divide TOM/1.724