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SENT BY:VTDPN'R/DEP-watergiJl ; 2-27- 2 ; 3:48PW ; VIDPM?/DEP-H'aiergut-' 1212 637 4284;# 2/10 FILE COPY SDMS Document . __ _ ^ 115617 GOVERNMENT OF THE VIRGIN ISLANDS OF THE UNITED STATES Department of Planning <b /Natural Resources Division of Environmental Proiectiort WATER GUT HOMES 1118 B-111/APT, 14-A CHBI3TIANSTED. ST. CROIX 00820-5065 (340) 773-0565 January 26.2001 Ms. Caroline Kwan Remedial Project Manager U.S. Environmental Protection Agency, Region II 290 Broadway, 20th Floor New York, NY 10007-1866 RE: Virgin Islands Chemical Superfund Site St. Croix, USVI Comments on the Final Draft Feasibility Study Report Dear Ms. Kwan: The Department of Planning and Natural Resources (DPNR) has reviewed the Final Draft Feasibility Report (Final Draft FS) for the Virgin Islands Chemical Superfiind Site and is forwarding the following comments. Estimated Cleanup Times The Draft Final FS assumes cleanup to MCLs in 3 to 4 years. Page 48 contains the following paragraph: "Although the minimum estimated cleanup times (3-4 years) for both Areas are relatively shon, the presence of geologic heterogeneities in both the AST and FPP Areas, as well as the presence of significant source mass above the water table in the AST area, could extend the estimated cleanup time by anywhere from a few years to more than 100 yeais and render the cleanup time predictions highly uncertain (National Academy Press, 1994)" DPNR finds this important paragraph in need of fiirther discussion and explanation regarding the source of this quote and how the authors of this paragraph calculate the estimated time for cleanup to MCLs. 4 0 0 1 9 1 SENT BY:VIDPNR/DEP-watergut : 2-27- 2 : 3:48PM : VIDPNR/DEP-Watergut- 1212 637 4284:# 3/10 Geo-Hydrology DPNR is concenied that the entire Final Draft FS is flawed based on a fundamental misinterpretation ofthe site and area geo-hydrology. The Report describes two upper aquifers in the alluvium (sands, gravels and clays) layer. The authors seem to be unable to differentiate between unconsolidated materials in the Gut (which are typically unsaturated) and the fractured marly limestone ofthe Kingshill Marl (aquifer). The fractures in the marl are the water produdng zones while groundwater recharge ofthe marl occurs in the guts through the unconsolidated material above. The United States Geological Survey (USGS) has performed exhaustive studies ofthe Kingshill Aquifer in South Central St. Croix, including the aquifer in the area around the study site. The USGS describes the area as having 10 to 60 feet of alluvium (unconsolidated material) overlaying the Kingshill Marl (water bearing formation). The Final Draft FS describes the deeper zones of the alluvium as "exhibiting confined to semi-confined conditions". DPNR is unaware of any scientific or environmental study describing area conditions ofthe Kingshill Aquifer in the study area as "confmed or semi-confined". The USGS describes the Kingshill Aquifer as a "single, unconfmed, hydrologically connected unit" (or 1 single aquifer), meaning water flows between the units without restriction. Typically loose material (alluvium) is 10-60 foct thick overlaying marly fractured limestone finom 50-100 feet below that. The aquifer is usually not any deeper than 120 feet. Generally, south ofthe highway, the post- Kingshill limestone predominates (highly transmissive). Desaibing "area* geo-hydrology as "two upper aquifers under confined to semi-confined conditions'* is misleading and dramatically affects all ensuing risk assessments, the evaluation ofthe efficacy ofthe proposed treatment system and clean up duration estimates. DPNR is not satisfied with an FS based on a mischaracterization of tlie aquifer and will not accept a theory that is so drastically opposed to long-standing and documented investigations. DPNR urges EPA not to accept this two-aquifer theory or the implications it may have regarding tbe remedial plans/timeline. Due to the multiple consultants historical misunderstanding/mischaracterization of area hydrology, DPNR believes il is essential to rewrite this section on area/site hydrology to reflect the well-documented and scientifically accurate description of area hydrology including, the USGS description ofthe aquifer and area/regional conditions. It is inconceivable that USGS publications on the subject would not be referenced in any ofthe reports produced during 4 0 0 1 9 2 SENT BY:VIDPM?/DEP-wa:ergui : 2-27- 2 ; 3:48PM ; VIDPNR./DEP-Watergut^ 1212 637 4284:* 4/10 the site investigation and leading up to the FS. Specific borehole conditions should be described as such but should not be used to describe the "area aquifer" or to infer conditions beyond the immediate borehole location. Cunent descriptions ofthe site and area are misleading and leaves the reader with the impression that vertical groundwater/contamination movement is nearly impossible due to the inaccurate "two aquifer" scenario. Additional review and comments will be forthcoming on the specifics of anaerobic and aerobic degradation of contaminants at the site, remediation time frames and the risk assessment. In general the Department is disturbed by the tendency ofthe rqxjrt to underestimate potential for lateral and vertical migration and to minimize the potential for off-site migration. We appreciate your consideration of our comments. If you should have any additional questions, please give me a call. 5yed Syeddli. P.G. Project Manager-DEP/DPNR 4 0 0 1 9 3