Document LRB0KOEpnXDJrdkgdr1X5rdg

DuPont Engineering July 22,2002 AR226-2609 OuPont Engineering BurloyMill PlKt.Blds.27 Lincastrr Pjk6 & Rtg. 141 Wilffiingtmi, DE 1S805 Mr. Steven E. Williams, Hydrogeologist Division of Drinking and Ground Waters Southeast District Office 2195 Front Street Logan, Ohio 43138 Reply to Response to Cuniinents Revised Proposed Sampling Investigation Plan Little Hocking Water Association Well Field Washington County, Ohio, June 2002 Dear Mr. Williams: DuPont appreciates the review of the June 2002 Revised Proposed Sampling Investigation Plan by tile Division ofDrmldng and Ground Waters and tfae Division of Surface Water at the Ohio EPA Southeast District Office. DuPont has reviewed the comments offered by the Ohio EPA and fhe Little Hoeldtig Water Association, Inc. aod their consultants, Bennett & Williams 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. DuPont proposes to collect soil samplesfrom two borings in the vicinity of . TW-4 at the following depths; at the surface at the first encountered water (approximately 17 to 20 feet below grade) at the top of the sand and gravel aquifer (estimated at 30 to 35 feel below grade) at the bottom of the sand and gravel aquifer (estimated at 50 to 55 feet below grade) , \. its Pent d< NemoTO ind Conpany EH.aWBw.aCTaB ASfl02B092 EID'781372 EID7B1372 The Ohio EPA agrees with these sample depths, however, the Ohio EPA believes additional samples are necessary to adequately characterize the vertical distribution of C-8 from the surface to the approximate top of the sand and gravel aquifer. This data will assist in evaluating the air to soil to ground water route of travel and the potential leaching of C-8 from the fine grain alluvial soils. Soil samples should be collected at jive foot intervals from the ground surface to the top of the sand and gravel aquifer. (Le. approximate depths to be sampled include (5, 10, 15. and 25 feet below the surface at the two selected locations). This will add about 8 additional soil samples for analysis. In addition, Ohio EPA request that DuPont collect soil samples at the remaining five foot interval depthsfrom the two selected borings and retain these for possible future analysis. The decision to analyse these samples would be based on the corresponding water sample results. We recommend language be incorporated into the Work Plan whereby either DuPont independentlycould analyse these soil samples w the samples could be analyzed if requested by Ohio EFA. DuPont Response DuPoat agrees to the revisions to the soil sampling plan as described, above for the boring located at TW-4. (Sw Figure 2 for the location of this boring.) At this boring, soil will be sampled vary five feet from tile ground surface to the bottom of die sand and gravel out To ensure that soil will be sampled at depth, a rotosomc drilling rig will be used instead of a Geoprobe. As indicated above, soil sampled from five-foot intervals between the top and bottom of the sand and gravel unit will be held and could be analyzed if appropriate based on the results obtained for groundwater sampled fiom the same depths. As suggested above, ' . j language will be incorporated into tfae Work Plan whereby either DuPont & ^ff^lfw W^Windependently could analyze these soil samples or the samples could be analyzed I AlWt^fWWr- tNTH __ if requested by Ohio EPA. However, for the boring located mid-way between TW-4 sad TW-5, DuPont ^ h l < proposes a slightly modified approachthat will sttU meet Ohio EPA's objectives. (See Figure 2 for the location-oftnis boring.) DuPont believes C-8 concentrations measured in saturated soils may not be truly representative of soil conditions 5 ^ because the concentration of C-8 detected may reflect C-8 contributed by fhe groundwater. Therefore, for this boring, DuPont proposes sampling soil every five feet from the ground surface to the depth of first water encountered as recommended by Ohio EPA. Soil will also be sampled at the top and bottom of the sand and gravel unit as was proposed by DuPont in the Revised Proposed Sampling Investigation Plan (June 2002). To ensure that soil from these depths can be sampled, a rotesonic rig will be used, .wyfc wry rM- ^ ^^ 5^' i^5ile^r ll<^-/'^S^w^^h^r ^AMrf^tC-S^h^ ASH02B093 EID781373 EID7B1373 2. At the two locations where soil is to be sampled, the Work Plan proposes to collect ground water Samples at the/allowing depths: at the first encountered water (approximately 17 to 20feet below grade) at the top of the sand and gravel aquifer (estimated at 30 to 35 feet below grade) at the bottom of the sand and gravel aquifer (estimated at 50 to 55 feet below grade). In order to evaluate the surface water to ground water and the ground water flow pathways, the Ohio EPA request that DuFont wiled ground water samples at these two locations from thejvst encountered water to the bottom efthe-sand-atid gravel aquifer at fivefoot intervals. This will allow for equation ofpotential differencesin concentration along differentflow lines within the aquifer. DnPont Response DuPont agrees to the revisions to tfae groundwater sampling plan as described above for the boring located at Tw-4. (See Figure 2 for the location of this boring.) At fcis boring, ground-waterwill be sampled every five feet from the first groundwater encountered to the bottom of the sand and gravel unit and all samples will be analyzed. To ensure that groundwater will be sampled at depth, a sonic drilling rig will be used to acquire groundwater samples instead of 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 of potential differences in C-8 eoneenttation along different flow lines within the aquifer, (See Figure 2 for toe location of this boring.) DuPont believes it is unlikely that significant stratified flow paths are present within the sand and gravel aquifer at the Little Hocking well field. The combined effect of active pumping and lack of stratified layering will limit the presence of separated flow lines. At this boring, groimdwater will be sampled at the first water encountered and at tile top and bottom of the eand and gravel unit. Again, to ensure that the groimdwater from the bottom of the sand and gravel unit can be sampled, a rotosonic rig will be used to access the sampling zones. 3. In addition to the indirect measurements of river stage height proposed in the Work Plan, a direct measurement of river elevation should be collected at Kraton Polymers. Jim Thrall, Senior Environmental Engineer with Kraton. indicated to Ohio EPA that a measuring point for river elevation is located on the Kraton property and with permission, DuPont can access this point. Please contact Jim, in advance, at (740) 423-2278. Page 3 ASH02B094 EID781374 EID781374 DuPont Response DuPont concurs that measuring river elevation directly is preferable over indirect measurements. DuPont appreciates the opportunity to collect this data from the measuring point located on the Kratoa Polymers property. DuPont will make the necessary atrangemente in advance with Jim Thrall, as suggested. As noted in your letter, Ohio EPA and the Little Hoclang Water Association would like the investigation to begin as soon as possible. However, the rotosonie rig proposedfor use in this investigation is ciiirently Wng used to mstall wells at the DuPont's Local Landfill in "West Virginia (one of tile C-8 Plume IdeaitijSearion/Groundwater Assessment Work Plan activities). DuPont proposes that this investigationat Little Hocking commence in early August 2002 daringan anticipatedbreak in toe drilling program. DuPont also proposes a slightdelay in the quarterly sampling event for Little Hocking that was scheduled for July 2002 so that this quarterlysamplingevent will coincide with the proposedsampling investigation. If, at lhat time, the laboratory is still unable to analyze C-8 in the soil samples,the sampleswill be retained at the laboratory until the laboratory has developedthe protocols needed to perform these analyses. Pending approval of the latest modification in the revised proposed sampling investigation plan, DuPont will update the plan to reflect {be agreed upon changes in soil and groundwater samplingstrategy, in samplingequipment,in river stage measurement and in schedule. The updated investigation plan will 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 me at (302) 992-6820. Sincerely, G^^^ST Andrew Hattten Project Director cc: David M. Rurak, DuPont Bernard, J. Reilly, DuPont Legal Ann M. Bradley, Spillman Thomas & Battle Laura Walter, DuPont Legal David Wafldns, WVDEP Attachment Page 4 ASH028095 EID781375 EID781375