Document Ln6m0ZD8jKqVyJM5aDrZxXm5

DuPont Engineering July 22,2002 AR226-2609 DuPontE n fitiwing Borloy M l PIb s - Bldg. 27 Lancaster Pik & Rts. H t Wkmington, DE 19805 M r. Steven E. Williams, Hydrogeologist Division ofD rinking and Ground Waters Southeast D istrict Office 2195 Front Street Logan, Ohio 4313$ Reply to Response to Comments Revised Proposed Sampling Investigation Plan L ittle H ocking W ater Association W ell R eid W ashington County, Ohio, June 2002 D ear Mr. Williams: DuPont appreciates the review o f the June 2002 Revised Proposed Sampling Investigation Plan by die Division o f Drinking and Ground Waters and the Division o f Surface Water at the Ohio EPA Southeast District Office. DuPont has reviewed the comments offered by the Ohio EPA and the Little Hocking W ater Association, Inc. and their consultants, Bennett & W illiams Environmental Consultants, toe. Our responses to these comments are presented below. For each comment in your letter dated July 8,2002 (shown in italics), specific responses follow. (Figure 2 from the revised plan, titled Proposed Sampling Locations, is attached for reference.) 1, DuPontproposes to collect soil samplesfrom two borings in the vicinity o f . TW-4 at thefollow ing depths: * at the surface at thefirst encountered water (approximately 1 7 to 20fe e t below grade) * at the top o fthe sand and gravel aquifer (estimated a t 30 to 35feet below grade) * at the bottom o fthe sand and gravel aquifer (estimated at 50 to 55 fe e t below grade) I. de Pent da Nemo* and Company EN-33&Rev. 3/7Q ASSQ 28Q 92 E ID 781372 E ID 781372 The Ohio EPA agrees with these sample depths, however, the Ohio EPA believes additional samples are necessary to adequately characterize the vertical distribution o f C-8from the surface to the approximate top o fthe sand and gravel aqu$er. This data w ill assist in evaluating the air to soil to ground water route o f travel and the potential leaching o f C-8from ikefin e grain alluvial soils. Soil samples should be collected atfiv e fo o t intervalsfrom the ground sutface to the top o fthe sand and gravel aquifer. (Le. approximate depths to be sampled include (5,10, IS, and 25feet below the surface at the two selected locations). This w ill add about 8 additional soil samplesfo r analysis. In addition, Ohio EPA request that DuPont collect soil samples at the remaining fiv e foot interval depthsfrom the two selected borings and retain thesefo r possiblefu tu re analysis. The decision to analyze these samples would be based on the corresponding water sample results. We recommend language be incorporated into the Work Plan whereby either DuPont independently could analyze these soil samples or the samples could be analyzed i f requested by Ohio EPA. D uPont Response DuPont agrees to the revisions to the soil sampling plan as described above for the boring located at TW-4. (See Figure 2 for the location o f this boring.) A t this boring, soil w ill be sampled every five feet from the ground surface to the bottom o f the sand and gravel u n it To ensure that soil will be sampled at depth, a rotosonic drilling rig will be used instead of a Geoprobe, As indicated above, soil sampled from five-foot intervals between the top and bottom o f the sand and gravel unit w ill be held and could be analyzed if appropriate based on the results *wJrobtained for groundwater sampled from the same depths. As suggested above, language w ill be incorporated into tire Work Plan whereby either DuPont independently could analyze these soil samples or the samples could be analyzed if requested by Ohio EPA. <However, for the boring located mid-way between TW-4 and TW -5, DuPont proposes a slightly modified approach that will still m eet Ohio EPA's objectives. (See Figure 2 for die location-of this boring.) DuPont believes C-8 concentrations measured in saturated soils may not be truly representative o f soil conditions because the concentration o f C-8 detected may reflect C-8 contributed by the groundwater. Therefore, for this boring, DuPont proposes sampling soil every five feet from the ground surface to the depth o f first water encountered as recommended by Ohio EPA. Soil will also be sampled at the top and bottom o f the sand and gravel unit as was proposed by DuPont b the Revised Proposed Sampling Investigation Plan (June 2002). To ensure that soil from these depths can be sampled, a rotosonic rig will be used, . unru f W - + tyrf- . wdtr rff'toU 5<U / WB.hr ASH028Q 93 EXD781373 E ID 781373 2. A t the two locations where soil is to be sampled, the Work Plan proposes to collect ground water samples at thefollowing depths; at thefirst encountered water (approximately 17 to 20fe e t below grade) at the top o fthe sand and gravel aquifer (estimated at 30 to 35 feet below grade) at the bottom o fthe sand and gravel aquifer (estimated at 50 to 55 fe e t below grade), In order to evaluate the surface water to ground water and the ground waterflo w pathways, the Ohio EPA request that DuPont collect ground water samples a t these two locationsfrom thefirst encountered water to the bottom efthe-sand-and gravel aqutfer atfivefo o t intervals. This will allowfo r evaluation o fpotential differences in concentration along differentflow lines within the aquifer. DuPont Response DuPont agrees to the revisions to the groundwater sampling plan as described above for the boring located at TW-4. (See Figure 2 for the location o f this boring.) A t this boring, groundwater will be sampled every five feet from the first groundwater encountered to the bottom of the sand and gravel unit and all samples w ill be analyzed. To ensure that groundwater w ill be sampled at depth, a sonic drilling rig will be used to acquire groundwater samples instead o f a Geopiobe. For the boring located mid-way between TW-4 and TW-5, DuPont feels that the sampling strategy as was presented in the Revised Proposed Sampling Investigation (June 2002) will allow for the evaluation o f potential differences in C-8 concentration along different flow lines within the aquifer. (See Figure 2 for fee location o f this horing.) DuPont believes it is unlikely feat significant stratified flow paths are present within fee sand and gravel aquifer at fee Little Hocking w ell field. The combined effect o f active pumping and lack o f stratified layering w ill limit fee presence o f separated flow lines. At tins boring, groundwater will be sampled at the first water encountered and at fee top and bottom o f the sand and gravel unit. Again, to ensure feat the groundwater from fee bottom o f fee sand and gravel unit can be sampled, a rotosonic rig will be used to access fee sampling zones. 3. In addition to the indirect measurements o friver stage heightproposed in the WorkPlan, a direct measurement o friver elevation should be collected at Kraton Polymers, Jim Thrall, Senior Environmental Engineer with Kraton, indicated to Ohio EPA that a measuringpointfo r river elevation is located on the Kraton property and with permission, DuPont can access this point. Please contact Jim, in advance, at (740) 423-2273, Page 3 ASH028094 EID781374 EXD781374 D uPont Response D uPont concurs that measuring river elevation directly is preferable over indirect measurements. DuPont appreciates the opportunity to collect this data front the m easuring point located on the Kraton Polymers property. DuPont w ill m ake the necessary arrangements in advance with Jim Thrall, as suggested. As noted in your letter, Ohio EPA and the Little Hocking W ater Association w ould like the investigation to begin as soon as possible. However, the rotosonic rig proposed for use in this investigation is currently being used to install wells at die DuPont's Local Landfill in W est Virginia (one o f the C-8 Plume Idcntification/Groundwater Assessment W ork Plan activities). DuPont proposes that this investigation at Little Hocking commence in early August 2002 during an anticipated break in tire drilling program. DuPont also proposes a slight delay in the quarterly sampling event for little Hocking that was scheduled for July 2002 so that this quarterly sampling event w ill coincide with the proposed sampling investigation. If, at that time, the laboratory is still unable to analyze C-8 in the soil samples, the samples w ill be retained at the laboratory until the laboratory has developed the protocols needed to perform these analyses. Pending approval o f the latest modification in the revised proposed sampling investigation plan, DuPont will update the plan to reflect the agreed upon changes in soil and groundwater sampling strategy, in sampling equipment, in river stage measurement and in schedule. The updated investigation plan w ill then be forwarded to Ohio EPA for final approval. Should you have any additional questions or comments on the responses provided, please feel free to contact m e at (302) 992-6820. Sincerely, Andrew Hartten Project Director cc; David M. Rurak, DuPont Bernard, J. Reilly, DuPont Legal Ann M. Bradley, Spillman Thomas & Battle Laura W alter, DuPont Legal David Waflrins,WVDEP A ttachm ent Page 4 A S H 0 2 B Q 95 EID781375 E ID 781375