, QiiPont Chemicals .... 3'f Wilmmglon, DE 13898 ''fyr/>. DuPont Chemicals March 14, 1994 Delivery by FAX Fax #(215) 597-3150 Hard Copy to Follow Mr. Randy Sturgeon, Remedial Project Manager US EPA, Region III 841 Chestnut St. Bldg. Philadelphia, PA 19107-4431 Re: DuPont Newport Superfund Site DuPont Remedial Action Proposal 3/25/94 Dear Mr. Sturgeon: This letter isin response to your letter of March 2, 1994requesting a more detailed description of DuPont's proposed remedial action alternative for the South Landfill and sampling proposal for the Christina River. Attached to this letter is a document providing the detail on the South Landfill remedial proposal based on conversations between you and Joel Karmazyn of DuPont Environmental Remediation Services ("DERS"). We would be happy to supplement this information if necessary. With regard to the Christina River, you indicate in your letter that DuPont's dredging proposal, in your opinion, falls short of adequately protecting aquatic life in the river, but that EPA understands DuPont's concern about the "...potential for significant cost overruns..." for this component of the Newport Site remedy. Before we address this, we would like to clarify that DuPont's position was not based solely on the issue of costs. DuPont believes that there isno technical justification for an open-ended river dredging remedy that would place DuPont in the position of cleaning up sediment problems caused by other sources or that have no significant impact on the river. The issue of whether DuPont should be held responsible for an undetermined stretch of the Christina River is a basic component of DuPont's objection to this remedy. 4R322676 :<,a Nemours anrl Compjnv ' • (^ rwwc on Recycled-
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,QiiPont Chemicals .... 3'fWilmmglon, DE 13898 ''fyr/>.
DuPont Chemicals
March 14, 1994
Delivery by FAXFax #(215) 597-3150Hard Copy to Follow
Mr. Randy Sturgeon,Remedial Project ManagerUS EPA, Region III841 Chestnut St. Bldg.Philadelphia, PA 19107-4431
This letter is in response to your letter of March 2, 1994 requesting amore detailed description of DuPont's proposed remedial action alternative for theSouth Landfill and sampling proposal for the Christina River. Attached to this letter isa document providing the detail on the South Landfill remedial proposal based onconversations between you and Joel Karmazyn of DuPont Environmental RemediationServices ("DERS"). We would be happy to supplement this information if necessary.
With regard to the Christina River, you indicate in your letter thatDuPont's dredging proposal, in your opinion, falls short of adequately protectingaquatic life in the river, but that EPA understands DuPont's concern about the".. .potential for significant cost overruns..." for this component of the Newport Siteremedy. Before we address this, we would like to clarify that DuPont's position wasnot based solely on the issue of costs. DuPont believes that there is no technicaljustification for an open-ended river dredging remedy that would place DuPont in theposition of cleaning up sediment problems caused by other sources or that have nosignificant impact on the river. The issue of whether DuPont should be heldresponsible for an undetermined stretch of the Christina River is a basic component ofDuPont's objection to this remedy.
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EPA's position that it would be willing to negotiate a consent decree forthe complete Re-ROD (change in South Landfill remedy included), but provide in thedecree (but not in the ROD) that the area of potential dredging be limited to betweenone-quarter mile upstream of the north drainageway (as opposed to the one milerequired by the ROD) and one-quarter mile downstream of the James Street bridge (asopposed to the two miles in the ROD) is partially acceptable to DuPont.
If EPA is willing to amend the extent of the dredging as noted in theprevious paragraph, then EPA should be willing to insert that amendment in the RODas well as the consent decree. DuPont would want the ROD changed consistent withthe consent decree. The March 2, 1994 letter contemplates that if further samplingreveals the need to dredge further than the distances noted in the previous paragraph,DuPont would not be required to perform such activities under the consent decree. Weaccept that premise. But if this proposal is designed to say that the parties will "startover" with regard to expanded sections of the river beyond those noted above, thenthere should be no hesitancy to amending the ROD.
With regard to the river sediment sampling contained in the ROD,DuPont has the following concern. DuPont does not understand the need to samplesediments at four depths. As a practical matter, dredging equipment cannot accuratelyremove sediment in less than one (1) foot intervals. Therefore, DuPont believessamples from the surface and one-foot depth are adequate to characterize the sedimentsthat could impact the biologically-active sediment zone and, thus, might requireremoval. DuPont believes that sampling at two depths rather than four is appropriate.
DuPont is concerned that the ROD is vague on the location points for thesediment sampling. It is in both party's interests to have clarity in the consent decreeand the ROD regarding the sampling locations. DuPont proposes an initial phase ofsampling for both inside and outside of the potentially dredged area. The phrase"potentially dredged area" is taken from your letter of March 2, 1994 to refer to thenew quarter-mile parameters (in both directions) for the river dredging. The samplingwould involve: (i) ten locations within the potentially dredged area; (ii) two locationsupstream; and (iii) four locations downstream. A confirmatory phase would delineatethe specific location(s) to be dredged.
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DuPont is also concerned about the expanded list of metals analytes thatthe ROD requires. The RD/RA phase must focus on the constituents of concern. TheEPA-approved RI/FFS confirmed that the constituents of concern for Newport Sitesediments are lead, cadmium and zinc. Therefore, further delineation of potential areasto be dredged should be limited to an analysis for these three metals. To confirm theneed to remove sediments, DuPont would conduct toxicity tests with all of the 16surface sediment samples mentioned in the previous paragraph.
DuPont would like to raise again its position/concern that the proposeduse of Hyalella azteca is inappropriate. The indigenous species for this area --chironomus tentans (not Hyalella azteca) ~ should be the basis for judging acquaticimpacts on both the wetlands and the river. EPA is aware of the disappointingexperience with Hyalella in the remedial investigation.
We appreciate EPA's diligence in attempting to resolve any concernsthat the NRC has with regard to the North Landfill. We assume that EPA understandsthat no consent decree can be signed without resolution of the NRC 's concernsregarding the thorium disposal in the North Landfill. DuPont takes this position onlybecause if the NRC insists on removal of the thorium waste, we would need tounderstand the basis for such a decision and have an opportunity to comment. To dootherwise would lead to a remedy that is too open-ended.
Lastly, with all of the above in mind, DuPont confirms that it is willingto begin negotiations towards a consent decree. However, we believe that theremediation of the DuPont Newport Superfund Site is a different issue than addressingnatural resource damages ("NRD"). Thus, DuPont is not willing to agree to negotiateNRD with the trustees at the same negotiating session involving the consent decree.
Pursuant to the extension of time granted by Attorney Walters, ORC, weare submitting this information within the deadlines agreed to by the Agency.
Very truly yours,
Robert Wiederhorn,DirectorRemediation Programs
Attachment
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cc: P. B. Butler, DuPont, CRG, B-12228J. Karmazyn, DERS, BPCC, 390N. D. Griffiths, Esq., DuPont Legal, D-8067J. P. Buczala, Woodward-Clyde ConsultantsW. R. Walters, Esq., USEPA, ORC (3RC21)N. V. Raman, DNREC, Superfund BranchF. H. Schranck, Esq., Counsel to DelDOTJ. Deming, Vice President, Production, CIBA-GEIGY, Newport PlantS. Goldfarb, Esq., Counsel to CIBA-GEIGY Corp.
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SOUTH DISPOSAL SITE REMEDIAL OPTION
SLURRY WALL DESCRIPTION & COST ESTIMATE
A soil-bentonite (SB) slurry trench cutoff wall provides one of the lowest permeabilitybarriers using conventional and proven technology. SB cutoff walls are typical controltechnologies used for remediation of closed landfills and other facilities.
A soil-bentonite slurry trench cutoff wall is excavated by means of a backhoe orclamshell and filled with a slurry fluid. The slurry maintains trench stability similar tothat of drilling fluid maintaining borehole stability. Trench excavation around, the SouthDisposal site would extend to sufficient depths to provide continuity with a clayey unitfound at a depth of 0 to 20 feet below existing grade in the area of the landfill, and istaken to be continuous along the entire wall alignment. The slurry is then displaced witha soil-bentonite backfill which consists of a mixture of soil (the soil excavated from thetrench), bentonite, and water. A successfully constructed soil-bentonite slurry trenchcutoff wall should have a permeability on the order of 1 x 10'7 cm/sec, similar to thepermeability of the low permeability cover system.
Design and Constuctibility
The South Disposal site is located on an area that was once composed of wetlandsconsisting of organic silts and clays. The depth of this clay appears to be on the orderof 15 to 20 feet deep in the area along the northern, eastern, and western boundariesof the land fill and daylights to the surface in the wetland area to the south of thelandfill. This clay unit thickness ranges from 7 to 15 feet and overlies the ColumbiaFormation. Figure 1 presents a cross-section of the subsurface stratigraphy in the areaof the landfill, and Figure 2 presents, the location of the cross-section relative to theslurry wall. A deeper low permeability unit also exists at,the top of the PotomacFormation; this unit ranges in depth from 30 to 50 feet below existing ground surface inthe area of the landfill. The base elevation of these clay units is fairly consistent, withsome variation in depth due to ground surface topography.
The cuttoff wall would be keyed into the shallower 9f the clay units if it could be shownduring the design phase that the unit is continuous for the length of the wall alignmentand is suitably thick to act as a key for the wall. If this is not the case, the wall will bekeyed into the low permeability unit at the top of the Potomac Formation. The lowpermeability cap that will be installed over the South Disposal site will be keyed into the
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top of the cutoff wall.
A soil-bentonite slurry trench cutoff wall should be constructive within the existingalluvial deposits at the Site. The feasibility of slurry trenching at the Site is directlyrelated to its location and alignment, as discussed subsequently. The possibility ofencountering objects within the fill zone or cobbles within the Columbia Formationcannot be precluded. The construction of a 40-foot wide working pad along the entirecutoff wall alignment will be needed to support construction equipment duringexcavation and backfilling. Portions of the existing access road in the South Disposal sitearea could be utilized for the working pad. A key excavated into the shallow clay unitor the Potomac Formation should not present any unusual difficulties, assumingobstructions are not encountered. The excavated materials can be mixed near thetrench, or loaded into trucks and hauled to a remote mixing area, mixed and returnedto the trench.
The cutoff wall could preliminarily be designed as a 24-inch wide wall with a minimum3-foot key into the designated clay layer. The wall could be excavated with a largebackhoe such as a Koehring 1066 with an "extended stick", which can reach a depth ofabout 50 feet. Soil-bentonite backfill using the excavated soils would probably require1 to 2 percent added dry bentonite, depending on the amount of fines and nature offines available in the excavated soils. It is believed that at least 20 percent plastic finesare needed in a backfill for a low permeability (1 x 10"7 cm/sec) cutoff wall, withoutresorting to additional dry bentonite for improving permeability. A SB slurry trenchcutoff wall provides the lowest permeability and is the most cost effective of thealternative technologies evaluated below.
Final design studies would be necessary for preparation of design and constructiondocuments, including subsurface investigation, compatibility testing, cutoff wall design,and preparation of a construction document.
Compatibility and Permanence
The chemistry of the on-site soils and groundwater does not indicate the presence ofcontaminants which are known to adversely influence a SB cutoff wall. Measured levelsof pH in the Site groundwater range from 5 to 9. These values are not known to haveadversely impacted bentonite behavior. The results of the available groundwaterchemistry data also do not indicate potential adverse impact on bentonite behavior.However, as a part of final mix design study, laboratory testing would be required to-investigate the compatibility of the design soil-bentonite backfill with the on-sitegroundwater.
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The pond in the western area of the South Disposal site will be filled and the lowpermeability cover system (cap) will be extended over this area. This is being done toremove the logistical complexities associated with maintaining the pond in such closeproximity to the slurry wall and the cap. The cost of including the pond area under thecap is summarized in Table 1. The additional area encorporated into the cap, thelocation of the SB slurry cutoff wall alignment, and the area to be excavated relative toBasin Road is presented in Figure 3.
Cost
The cost for the soil-bentonite slurry trench cutoff wall, utilizing a backhoe with acapability of excavating to depths of about 20 feet, a 24-inch wide wall, and mixingbackfill adjacent to the trench is estimated to be about $7 per square foot of cutoff wallarea. If a remote batching system is used, instead of mixing along the trench, anadditional cost of about $2 per square foot of cutoff wall would be added. Amobilization and demobilization cost of about $46,000 is also estimated. A workingplatform would be required along the entire alignment of the wall. It is estimated thaton the order of 8800 cubic yards of material at a cost of about $44,000 would.berequired for the platform construction. This does not include the cost for any otherfilling prior to working pad construction. It is assumed that the disposal of any excessmaterial would be at the landfill on-site and there would be no additional cost forhauling and disposal. The quantity of waste material, soil and bentonite, could amountto as much as 1,900 cubic yards for every 1,000 lineal feet of the cutoff wall, assuminga bulking factor of 1.25. The total cost of the slurry wall keyed into the shallow clayunit, including mobilization, demobilization, health and safety, and engineering costs isestimated to be $690,000. Installation of the wall to the Potomac Formation wouldincrease costs by approximately $935,000. A preliminary cost summary is presented inTable 1.
In addition, costs for the excavation of the Basin Road area, and the low permeabilitycover system (including the South Pond) are also included in the preliminary costsummary presented in Table 1.
Alternatives
Cement-bentonite wall: The constructibility of a cement-bentonite (CB) wall would benearly the same as that for the soil-bentonite cutoff wall. There would still be a needfor a working pad and a large backhoe for excavating down to the aquiclude. The keyfor the cutoff wall would still be in the organic clay overlying the Columbia Formationor the low permeability soils of the Potomac formation. The excavated material for theCB wall would be wasted, as the CB itself would become the cutoff wall after hardening.
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Thus, there would be a need to dispose of about 1,900 cubic yards of spoils for every1,000 lineal feet of the cutoff wall, assuming a bulking factor of 1.25.
Problems which are associated with constructibility of a soil-bentonite type cutoff wallalso persist for the CB wall. Additionally, since very little filter cake formation isassociated with the cement-bentonite, extensive slurry loss through the pervious zonesof the cutoff wall could occur.
Typical permeability for CB cutoff .materials is about 1 x 10"6 cm/sec. The short andlong term permeability of the CB wall should be investigated as a part of the final designpackage to study the impact, if any, of the reported chemicals present in the on-sitegroundwater on the cutoff material.
The estimated cost of installing a CB cutoff wall is $891,000 (including mobilization,demobilization, health and safety, engineering, and contingency costs). The unit costwould be $15/sq ft as compared to $11.6/sq ft for installation of the SB slurry cutoffwall.
Deep Soil Mixing: The grout columns created by Deep Soil Mixing are about 24 inchesin diameter each. The .columns would be extended to penetrate into the designatedaquiclude. A set of 1 to 4 rotating mixing shafts advance into the ground and eject acement base grout to create the columns. A series of columns completed in this mannerwould create the cutoff wall. Cutoff wall continuity is created by columns of soilcreteoverlapping each other in adjacent applications, A successfully completed wall can havea permeability on the order of 1 x 10"6 cm/sec. Laboratory testing would be requiredfor selection of the optimum soilcrete mix and to assure that it satisfies the permeabilityand compatibility requirements.
Deep Soil Mixing and CB walls require some compromise on their degree ofeffectiveness (i.e., higher permeability) as a barriers. A cutoff wall installed by thetrenching technique requires an offset from the existing slope edge. Soilcrete columnsby Deep Soil Mixing could be constructed closer to the edge of the landfill slope withoutadversely impacting its slope stability. However, portions of the slope may still remainoutside the barrier.
The estimated cost of installing a DSM cutoff wall is $802,000 (including mobilization,demobilization, health and safety, engineering, and contingency costs). The unit costwould be $13.5/sq ft as compared to $11.6/sq ft for installation of the SB slurry cutoffwall.
