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Regional Office INTERNATIONAL 312 Directors Dnve TECHNOLOGY KnoxviHe Tennessee 37923-4799 CORPORATION 61 s^.90-3211 Fox: 615-690-3626 December 19, 1995 Ms. Caroline Kwan New York/Caribbean Superfund Section U.S. Environmental Agency Region II 290 Broadway, 20th Floor New York, NY 10007-1866 Transmitted of Comments and Concerns Related to Calculated Site Specific Soil Cleanup Standard for the O'Henrv Dry Cleaners. Tutu. St. Thomas. U.S. Virgin Islands Dear Ms. Kwan: This letter presents comments and concerns relating to the site specific soil cleanup standard presented by the EPA as applicable to the O'Henry Dry Cleaners, Tutu, St. Thomas. The site specific standard is presented in CDM Federal, Jufy 1995, Final Report, Estimation of Soil Cleanup Concentrations Required to Protect Groundwater as a Source of Drinking Water. This standard was referred to as the applicable standard by the EPA in the CDM Federal, 1995, document but is also presented in the EPA Technical Review Comments on IT, 1995 Soil Remediation Report for the O 'Henry Dry Cleaners, Tutu St. Thomas, presented in a letter to Nancy D'Anna, Esq. from Carole Peterson received July 27, 1995, and in Geraghty and Miller Inc., 1995, Final Feasibility Study for the Tutu Wells site, Tutu, St. Thomas. Materials in the form of calculation sheets and a spreadsheet were supplied by the EPA on October 6, 1995, in response to a FOIA request filed by Nancy D'Anna, Esq. FT Corporation (IT) at the request of L'Henri Inc., has reviewed this computer spreadsheet in addition to the above referenced documents and has the following comments and concerns with the Soil Cleanup Concentration presented by the EPA for the O'Henry Dry Cleaners site: Development of the site specific soil cleanup levels for the Tutu Wells site by CDM Federal was based on an EPA, December, 1994, Technical Background Document for Soil Screening Guidance (Review Draft). Formulae used for the estimation of the mixing zone depths and derivation of the dilution factor in the supplied spreadsheet were cited from the EPA document, however, the EPA document used is a draft review copy that is marked "Do Not Cite or Quote." Since this method is in review draft stage which has not undergone full EPA and public review and comment, we question the use of the method as applied through the spreadsheet by CDM Federal. IT has previously used the one-dimensional, finite difference model VLEACH to L:\u\Dcc\BFOQS\bf IT Corporation is a wholly owned subsidiary of International Technology Corporation *65029* 65029 INTERNATIONAL TECHNOLOGY CORPORATION Ms. Caroline Kwan 2 December 20, 1995 calculate the appropriate site specific soil cleanup standard (IT, 1994, Work Plan for Evaluation and Interim Remediation of Soils, O 'Henry Laundry, Tutu, St. Thomas, U. S.V.I.) and as pointed out in Section 3.4 of IT, 1995, Soil Remediation Report O 'Henry Laundry, Tutu, St. Thomas, U.S. V.I. (Revision 1), use of the site specific Foe in the model would lead to a higher soil cleanup standard than that presented in the Work Plan (IT, 1994). The model VLEACH is listed among those appropriate to be used for site specific soil cleanup standard determination in EPA, December, 1994 Technical Background Document for Soil Screening Guidance (Review Draft). Understanding that the VLEACH model is conservative in that it does not consider chemical or biological degradation, it is reasonable to expect that use of the VLEACH model would result in lower soil cleanup standards than the CDM Federal spreadsheet model using the same site specific parameters. IT believes that use of VLEACH is appropriate for calculating the site specific soil cleanup standards for this site. Notwithstanding the above, assuming that the method applied by CDM Federal is appropriate for the calculation of site specific soil cleanup standards, following is a listing of assumptions which should be amended as indicated for the O 'Henry site: • A composite soil profile generated by CDM Federal for the O 'Henry Dry Cleaners simulating the soils present beneath the contaminated zone is not representative of actual soils present at the site. The generated profile indicates that the site contains clayey sands (SC) and silty sands (SM) and clayey silts at depth intervals of 0 to 2.1 ft, 2.1 to 10.96 ft, and 10.96 to 22 ft respectively. However, visual classification of soils during soil remediation activities for the excavation area and soil boring ITSB-01 indicated that soils are uniform and predominantly sandy silt with clay (ML) from the ground surface to a depth of 8.25 ft. An andesitic unweathered bedrock underlies the silty soils. Because the soil type simulated for the O 'Henry Dry Cleaners was not representative of site soil conditions, model soil parameters including the assumed water content (which was taken to be the effective porosity), total porosity, soil layer thickness, and soil mass (dry bulk density) were not accurate parameters for the site. Site specific soil parameters obtained during soil remediation activities are as follows: - Volumetric water content = 0.3 - Dry bulk density = 1.53 g/cc - Total porosity = 0.4. • A contaminant source length of 50 ft was used by CDM Federal for the O 'Henry site. This parameter is used in the calculation of the dilution factor. A resulting dilution factor of 0.04 was subsequently used for the calculations of the target soil leachate concentration of < 132 //g/L for the acceptable groundwater MCL of <5 /*g/L. During soil remediation activities conducted in March 1995 at the O'Henry site, field observations indicated that a contaminant source length parallel to the groundwater flow for the site is approximately 25 feet (Note: 25 ft is used conservatively, the actual source length is probably less than 20 feet). Using the source length of 25 feet results in a dilution factor of 0.02. In L:\riDcc\BPOOS\bf 7T Corporation is a wholly owned subsidiary oi International Technology Corporation INTERNATIONAL TECHNOLOGY CORPORATION Ms. Caroline Kwan 3 December 20, 1995 addition, a lower source length results in a lower leachate flux rate of 5.025 ft3/yr instead of the flux rate of 10.05 ft3/yr used by CDM Federal in the soil leaching model. • The allowable contaminant concentration in soil was calculated by CDM Federal using an foe value of 0.006 in soils above 1.6 feet and an assumed foe value of 0.0002. CDM Federal cover letter to the EPA which accompanies the CDM Federal, July 1995, report acknowledges that the model results are very sensitive to the input value for organic carbon content of the soils and states "This represents a significant uncertainty in the model results. CDM Federal recommends that the soil cleanup goals calculated here be recalculated if additional site-specific data becomes available and revised if necessary at that time." The foe obtained by IT for soils at a depth of 5-6 feet at the O'Henry site indicate that foe is 0.008. Therefore, it is appropriate that the soil cleanup concentration be recalculated. Using the Soil Screening framework as described on page 2-22 of EPA, December 1994, the simple site specific soil screening level (SSL) is backcalculated from acceptable groundwater concentrations. First the acceptable groundwater concentration is multiplied by the dilution factor to obtain the target leachate concentration. The partition equation is then used to calculate the equilibrium soil concentration corresponding to this soil leachate concentration. Using this simple methodology (ignoring chemical degradation) and using the site specific parameters as described above for PCE at the O'Henry site yields the following: • Allowable groundwater concentration is 4.9 mg/1 (i.e., <5mg/l), the site-specific dilution factor is 1/0.02, therefore the allowable leachate concentration is 245 mg/1 • Kd is calculated to be 2.18 (foe assumed to be 0.006) for soils above 1.6 feet and 2.91 (foe assumed to be 0.008) for soils below 1.6 feet, therefore the allowable soil concentration is calculated to be 534 mg/kg for soils above 1.6 feet and 713 mg/kg for soil below 1.6 feet. (Note that recalculated values through the CDM Federal spreadsheet accounting for biodegradation should result in higher allowable soil concentrations than those presented here). The site specific soil cleanup standards for the O'Henry site were calculated by CDM Federal based on the assumption that soil remediation activities had not been performed. Soil remediation was conducted in March, 1995 for the O'Henry site. Soil left in place is represented by two distinct profiles; soil left in place at the excavation base overlain by clean backfill material and soil beneath the concrete area on the northern excavation wall. IT has presented an evaluation of impact to groundwater of the soils left in place in the revised Soil Remediation Report (IT, August, 1995) using the VLEACH model. This evaluation indicates soil left at the site will not impact groundwater to greater than the MCL for PCE. IT, therefore, requests that EPA review the method currently used to calculate the site specific soil cleanup standards for the O'Henry site and revise these standards based on the comments presented here. TT Corporation is a wtiouy owned subsidiary of International Technology Corporation TUT COS INTERNATIONAL TECHNOLOGY CORPORATION Ms. Caroline Kwan 4 December 20, 1995 If you have any questions regarding these comments, please contact L'Henri Inc., Counsel Nancy D'Anna, Esq. at (809) 776-6533 or me at (423) 690-3211. Additionally, please note the change of area code for east Tennessee. Sincerely, Belinda K. Price, R.P.G. Project Manager cc: Andrew Praschak Esq., EPA Leonard Reed, DPNR Nancy D'Anna Esq. Jack McBurney, de maximis, inc. n COTporOuonKawKoSy owned subsidiary of International Technology Corporation