TECHNICAL SUPPORT FOR ROCKY MOUNTAIN ARSENAL

Offpost Operable Unit Endangerment Assessment/Feasibility Study

Final Report

Volume VIII of VIII (Responses to Comments)

November 24, 1992 Contract Number DAAA15-88-0021 Task RIFSI (Delivery Order 0001)

PREPARED BY Harding Lawson Associates Environmental Science and Engineering, Inc.

PREPARED FOR PROGRAM MANAGER FOR ROCKY MOUNTAIN ARSENAL

THIS DOCUMENT IS INTENDED TO COMPLY WITH THE NATIONAL ENVIRONMENTAL POLICY ACT OF 1969. THE INFORMATION AND CONCLUSIONS PRESENTED IN THIS REPORT REPRESENT THE OFFICIAL POSITION OF THE DEPARTMENT OF THE ARMY UNLESS EXPRESSLY MODIFIED BY A SUBSEQUENT DOCUMENT. THIS REPORT CONSTITUTES THE RELEVANT PORTION OF THE ADMINISTRATION RECORD FOR THIS CERCLA OPERABLE UNIT.



# M9200041PREFACE TO VOLUME Vill

This volume presents comments regarding the Offpost OU Endangerment Assessment/ Feasibility Study report and responses prepared by Harding Lawson Associates. Four sets of comments and responses are presented in this volume in the following order: Shell Oil Company (Shell) U.S. Environmental Protection Agency (EPA) U.S. Department of the Interior Fish and Wildlife Service (USFWS) Colorado Department of Health (CDH)

Within each set, comments are presented in the same order in which they were received. The comments have not been edited or revised in any way. A Glossary is provided as a list of acronyms and abbreviations used in the responses.

20000,317.10 - viii-pref 0312112092 Vill - P- ISHELL OIL COMPANY COMMENTS REGARDING THE ENDANGERMENT ASSESSMENT/FEASIBILITY STUDY FOR ROCKY MOUNTAIN ARSENAL OFFPOST OPERABLE UNIT - DISPUTE ISSUES

GENERAL COMMENTS Comment No. I - Inat)r)roi)riate Land Use Scenario This EAIFS uses a rural residential(hypothetical subsistencefarmer) scenario in its baseline risk assessment. This hypotheticalpopulationof residents,i.e., subsistencefarmer residents, andthe associatedland uses do not exist in the RMA Offposl Operable Unit. The ruralresidentialcancer risk estimates and hazardindices are based uponflawed dataandfaulty assumptions that do not considerrealistic,reasonablemaximum currentandfuture exposures to compounds of concern as requiredby the NationalContingencyPlan (NCP) and EPA guidance. Moreover, due to various factors it is impossiblefor this scenarioto exist in the RMA Offpost Operable Unit at thepresent time because of the high land values and the over appropriation of alluvialgroundwater. Furthermore, due to the plannedrealignmentof 961h Avenue, if adjacentlands are developed, commercial and industrialland use is most likely, as the Army recognizes in the FS. ResL)onse As a result of dispute resolution, the Organizations agreed to an urban residential scenario for zones 3 and 4, commercial -industrial for zone 5, and rural residential for zones 1, 2, and 6. Attachment A to this set of responses to comments is the dispute resolution agreement letter signed by all parties to the dispute and dated May 5, 1992. Commercial -industrial land use for zone 5 was contingent on the South Adams County Water and Sanitation District's (SACWSD's) certification that it does not plan to use groundwater in this zone during the next 30 years. Attachment B to this set of responses to comments is a letter from SACWSD to the Army, providing documentation that SACWSD does not intend to install water-supply wells in the future in zone 5.

Comment No. 2 - InadeQuate Ecotoxicity Assessment Thefood web n7odel presented in this EAIFS estimates excess risk to the biolapresent in the RMA Offpost Operable Unit due toflawed methodologies anderrors it? logic. The model results are inconsistentwith the observation ofa healthy wildlife population. Furthermore, the model employs unrealistic andphYsically impossibleparametervalues such as those usedfor bioaccumulation factors, bioconcentrati . onfactors, the dietaryintake of aquaticfood items by the great blue heron, and unrealisticall ' v low ioxicit' v reference values. In addition,the uncertaintY associatedwith the food web model is so largethat the resultsare adequateonlyfor screeni .ng purposes. Resvonse As a result of dispute resolution (see Attachment A), the Organizations agreed to use literature values for bioaccumulation factors (BAFs), bioconcentration factors (BCFs), and home range area. The Army considered literature BAFs less than optimal but an acceptable alternative to onpost calibrate BAFs. The Organizations also agreed to use spatial weighting factors determined on the basis of home range area and to modifications to the toxicity reference value (TRV) derivation process.

11788,903 - CR-03 0504112092 Vill - IComment No. 3 - Incorrect Groundwater ExiDosure Point Concentrations The methodology used in this EAIFS to generategroundwaterexposurepoint concentrationsis flawed; therefore, the results are incorrectand inconsistentwith the observed contaminant distribulions. Furthermore,this EAIFS does not present current andfuture contaminantexposuresfor the groundwatercompounds ofconcern, and is therefore inconsistent with the NCP and EPA guidance. Based on Shell's evaluationof the availabledata,the EAIFS overestimates the groundwater exposurepoint concentrationsseveral fold in some areas. Rest)onse Based on dispute resolution (see Attachment A), the Organizations agreed to limit the groundwater database to 1989 to 1991 and to delete gas chromatography/mass spectrometry (GC/MS) and field duplicate data where appropriate (Volume 11, Section 2.0). In addition, a future groundwater exposure scenario was evaluated, and groundwater concentrations were reduced as a result of treatment of groundwater by the boundary containment systems over 30 years.

Comment No. 4 - Incomvlete Dieldrin Toxicolojaical Profile This EAIFS fails to include key toxicological information(identified in our comments on the draft of this document) regardinghuman data in the dieldrin toxicologicalprofile; however, this information was included in the aldrin1dieldrin toxicological profilefor the RMA On-PostFinal Human Health ExposureAssessment. Furthermore,the inclusion of additionalinforrnaiionis preferredper the NCP andEPA guidance, and is important for risk managementdecisions. Resvonse Based on dispute resolution (see Attachment A), the Organizations agreed to include the Shell dieldrin toxicological profile as a separate document in Volume IV, Appendix F of the Endangerment Assessment (EA).

Comment No. 5 - Manganese as a Compound of Concern Manganese should not be a compound of concern (COC) for the RMA Offpost Operable Unit because there is no known source at RMA, the assessment of the analyticaldata is flawed, and manganese, if a COC, would be a pollutant or a contaminant, not a ýaZardoussubstance under CERCLA. Furthermore, manganese is a naturallyoccurring constituent ofthe soils and groundivater. Resnonse Based on dispute resolution (see Attachment A), the Organizations retained manganese as a chemical of concern because groundwater monitoring data indicate manganese is associated with RMA.

Comment No. 6 - ARARs A number of aspects ofthe ARARs anal * ysis in this EAIFS are inconsistentwith the selection criteriaof CERCLA or the NCP. Followingare some ofthe more significantmatters ofconcern.

11788,903 - CR-03 0504112092 VIII - 2With respect to the ARARs basedon the Colorado Basic Standards for Groundwaterand the ColoradoBasic Standards for Surface Water, the EAIFS does not explain why the standardsare applicableor relevantand appropriate. In any event, Shell objects to all state groundwater standardsthat are more stringent than MCLs on the grounds that the standardswere not automaticallyintended to be ARARs by 5 CCR 1002-8.3.1.1](5). We also note that one ofthe most importanttables, 2.4.3.1-1 of Volume V, is missing from this document. rheEAIFS is inconsistentin its treatmentofLand DisposalRestrictions (LDRs). It correctly acknowledges that the reinjection ofgroundwaterdoes not triggerLDRs becauseLDRs are supersededby RCRA Section 3020(a).p. VII-A-9. It also states that LDRs are not ARARs because there are no iisted wastesfrom RMA in the Offpost Operable Unit. p. VII-A-15. Despite these concentrations,the EAIFS then incorrectlystates that LDRs have been identifiedas action -specific ARARs for all treatment alternatives. See p. VII-A-23. With respect to stormwaterdischargeregulations,Shell disagreeswith the conclusion that the stormwaterdischargeregulationsmay be relevantand appropriate, because,among other reasons, the FS alternativesdo not involve the dischargeof stormwaterrunoffto surface water. In certain instances,proposedMCLs have been selected as ARARs ratherthan rBCs. rhis is inconsistent with the NCP. Furthermore,additionalchemical -specific rBCs which were suggested by Shell have been rejected. Resnonse The ARARs analysis presented in Volume VII Appendix A of the Feasibility Study (FS) has been revised to include an explanation for the finding that the Colorado Basic Standards for Groundwater (CBSG) are not applicable or relevant and appropriate. The basis for this finding is in Appendix A and rests primarily on citations from the Statement of Basis and Purpose in the CBSG. The Statement of Basis and Purpose indicates that CDH did not intend that the Table A Interim Organic Standards be applied as cleanup standards for CERCLA, RCRA Subtitle C, or UST actions. Appendix A of Volume VII has been revised to include the language agreed upon in the May 5, 1992, dispute resolution letter concerning land disposal restrictions under RCRA. The dispute relative to stormwater discharge regulations was withdrawn. Appendix A has been revised to include considerations of proposed MCLs as TBCs rather than ARARs.

11788,903 - CR-03 0504112092 VIII - 3U.S. ENVIRONMENTAL PROTECTION AGENCY COMMENTS REGARDING THE ENDANGERMENT ASSESSMENT/FEASIBILITY STUDY FOR ROCKY MOUNTAIN ARSENAL OFFPOST OPERABLE UNIT - DISPUTE ISSUES ENDANGERMENT ASSESSMENT GENERAL COMMENTS Comment No. I - Development of PRGs EPA would invoke dispute concerningthe effects of multiple chemicals within a medium and effects of COCs in multiple media as presentedin the offpost endangermentassessment, and all calculationsthat utilized the resulting values,for the reasonsdetailedbelow, exceptfor the low risk involved it? the specific example. In any other instancewe would not accept thisprocedure. A. Effects ofMultiple Chemicals Within A Medium and Effects of COCs in MultipleMedia. Soil HBCIPRGsdo not adequatelyaddressthe cumulative effects of multiple carcinogensin one medium, nor do they provide protectionagainstcumulative effects of COCs it? multiple media. In its response to cover letter comment No. 4 (VIII-4) the Army "agreesthat the evaluationof multiple media should be included in the derivationofHBC." However, the response only discusses multimedia adjustments for non-carcinogens,which were ultimately ?lot found to be necessarv,and were therefore not made. The document remains silent on the subject of multimeýia adjustments for carcinogens. The approaches for carcinogensand noncarcinogens should be consistent. Since theArmy proposedto divide PRGsfor noncarcillogensby the number of media in which these COC occur, PRGsfor carcinogensshould also be divided by the ?lumber of media in which they occur. Yet, calculatedHBCfor carcinogenswere not adjusted in this manner. Forexample, since severalcarcinogensoccur in groundwater as well as in soil in Zones 3 and 4, and commerciallindustrial workers are exposed to both, soil PRGsfor these carcinogens should have beet? divided by 2. However, no adjustments for multimedia effectsfor carcinogenswere made. VII-C-2 describes the derivation of the residentialsoil PRGfor dieldrinwhich was calculatedto be 0.46 ug/kg at the 10-6 risk level. Insteadof dividing the PRG by 2, the Army chose a concentrationassociatedwith a higher risk level (33 ug/kg at the 7 x 10-5 ris'k level) and presented this approachas the adjustment for additive effects of COCs it? soil andgroundwater. It is unclearto the EPA how the acceptanceof the higher risk level could possibly counteractadditive effects of COCs in multiple media. Furthermore, the proportionmethod does not address the effects of multiple carcinogens within one medium, and no efforts have been made to adjust for this deficiency. EPA calculatedthat 23% of the soil carcinogenicrisk to coninierciall industrialworkers in Zone 3 is attribulableto COCs other than dieldrin,thereforean adjustment to accountfor the additionalrisks is necessary. Response Volume V, Section 2.2 of the FS has been significantly revised to include additional detail concerning development of PRGs in light of comparison of cumulative Offpost Operable Unit (OU) hypothetical cancer risks to the NCP acceptable risk range. Additional detail is also

11788,903 - CR-03 0504112092 VIII - 4presented in this section concerning risk associated with individual media in the Offpost OU, based on the risks presented in Volume III, Section 4.0 of the EA. As discussed in detail in Volume V, Section 2.2, the cumulative Offpost OU hypothetical cancer risk is a maximum of 3 x 10-4, based on risks presented in the EA. As discussed extensively in Volume V, Section 2.2, Offpost OU remedial action is not warranted because the Offpost OU cumulative risk is within the NCP acceptable risk range. Also as discussed in Volume V, Section 2.2, the Army recognizes that there are several site-specific factors that, when considered in totality, suggest remediation of groundwater is preferable to no action in the Offpost OU. The above referenced sections of text concerning PRG development explicitly state the risks corresponding to the groundwater, soil, surface water, and sediment media. Also, justification is given for the conclusion that soil, surface water, and sediment media do not require development of remedial action goals. Remedial action goals were developed for the groundwater medium as discussed in Volume V, Section 2.2, consistent with the methodology presented in detail in Volume VII, Appendix C. Appendix C explicitly describes the development of PRGs, considering the effects of multiple chemicals within the groundwater medium. See response to Part I given above. As described in the response to Part I given above, soil PRGS were not developed. See response to Part I given above. The development of PRGs for groundwater medium explicitly accounts for the effects of multiple carcinogens within groundwater. This information is presented in Volume VII, Appendix C.

B. DerivationofPRGs Some of the soil HBCs differfrom those in the draft final text (as shown in Volume V, Table 2.4.5-1). It appearsa new methodology has been usedfor deriving the HBCs of carcinogens(described in Volume II Appendix C). We have difficulty duplicatingthe new HBC numbers. PRGs were adjustedbased on observed contaminantdistributionand with the intent of achieving low aggregaterisk (as perfootnote to Volume V. Table 2.4.5.5-1, that "some preliminaryremediationgoals are different than HBC presented in Table 2.4.4-1."). Which PRGs were adjusted,and why? The soil HBCfor the "AdjustedResidential"RME ofAldrin and Dieldrinare31 ppb and .5 ppb respectively (listed in Volume V Table 2.4.5-1). Since these two compounds are very similar,to make the document more defensible it would help to explain why theirHBC differ by such a largeamount (a factor of over 60). To enable the layman readerto betterfollow the derivations,we suggest that the Army include thefollowing in itsfinal version of the EAIFS:

i. Aflow chart showing how the PRGsfor each medium was determined. ii. A complete listing ofHBCsfor the COCs in each medium. iii. An addendum or appendix in which the actual step-by-step derivationof the HBCs and PRGs (if differentfrom the HBC) were determined. It should the chemical's slope factorandlor referencedose. It should reflect adjustment effects for multiple media exposure and organ toxicity.

11788,903 - CR-03 0504112092 VIII - 5ResL)onse The response to Part A of this comment states that Volume V, Section 2.2 presents justification based on comparison of cumulative site risk and individual media site risk to the acceptable risk range. Development of remedial action objectives and PRGs for soil was warranted. Selected PRGs differ from HBCs because of the need to consider aggregate risk. A flow chart showing considerations for selecting PRGs has been included in Section 2.4.5.5 of Volume Il. Step-by-step derivation of HBCs is in Appendix C of Volume V11. This appendix accounts for multiple organ toxicity. Slope factors and reference doses are in Tables 3.1-3 and 3.1-4 of Volume II of the EA.

Comment No. 2 - The Use of the 10-4 Cancer Risk as a Point of Denarture for Determination of HBC EPA invokes dispute concerningthe use of the "10 to the minus four"cancer risk as apoint of departure for determinationofHBC aspresented in the offpost endangermentassessment, andall calculationsthat utilized the resulting values,for the reasonsdetailed below. In its response to CoverLetter Comment No. I the Army cites the NCP (55FR 8717) which states "Preliminary remediationgoalsfor carcinogensareset at a 10-6 point of departure,but may be revised to a different risk level within the acceptablerisk range on the basis ofthe considerationofappropriate factors including but not limited to: exposurefactors, uncertainty factors, andtechnical factors..." The Arm), used severalfactors in an attempt tojustify the selection of PRGs whichpresent carcinogenicrisks exceeding 10-6. Forexample, the Army discusses only briefly the groundwater CRLs. There is no explanation ofhow the soil HBCs were derived or why they do not correspondto the PRGpoint of departurerisk level. GroundwaterCRLs are extraneous to soils PRGs. A discussion is requiredtojustify the higherrisk levels selectedfor soils in zones 1, 2, 5 and 6. While EPA agreesthat there are many uncertaintiesin the EA, EPA is not at all convinced that all ofthe uncertaintiescan be interpretedto conclude that the results ofthe EA presentan overestimationof risks. EPA believes thatproblems and uncertaintiesassociatedwith data representiveness,data quality andthe approachesin the EA could also have contributedto an underestimation of risks in the offpost. Examples of specific issues that may have causedan underestimationwere include thefollowing: A. A ke' v pathway (COC intake via eggs) was not addressedexceptfor one chemical (dieldrin). Had the egg pathwa' 1,been addressed for all relevant COCs, some HIs would have shown even greaterexceedances than they did. B. Another source of uncertainty is thefact that some groundwaterCOCs which are currently moving toward the offpost have not been addressedin the EA. These COCs include NDMA. The health risks associatedwith these chemicals would be additive to those already evaluated in the EA. (EPA still has substantive reservationsconcerningthis issue, and reserves the right to invoke dispute at a latertime.) C. The EA (1114-7) states that in Zone ]A 70% of the risks are attributable to COC conlamination of soil. Most ofthis risk stemsfrom the uptake of COCs intofood materials. The fact that soil concentrationswere divided by 5, before COC uptake into vegetables, beefand dairy via soil was assessed.presents a potential for underestimationof risks.

11788,903 - CR-03 0504112092 V111 - 6The Army did not discuss the determinationofbackground contaminationlevels and their incorporation into the development of the appropriate PRGs. A section such be included which discusses the development and incorporationofbackground values. Rest)onse As discussed extensively in Volume V, Section 2.2, development of PRGS for the groundwater medium was performed consistent with the methodology described in the NCP. Groundwater HBC were calculated at the 10-6 level for carcinogens when ARARs were not available and at a HI of less than 1.0 for noncarcinogens without ARARs. These criteria were used as a basis for developing PRGs for groundwater. The NCP states departure from 10-6 may be appropriate considering various factors, including but not limited to exposure factors, uncertainty factors, and technical factors. Exposure factors the Army evaluated in the EA included cumulative effects of multiple contaminants, multiple pathways, population sensitivities, potential impacts on environmental receptors, and cross-media impacts. Additionally, uncertainty factors that evaluate the effectiveness of the alternative, the weight of scientific evidence concerning exposures in cumulative health effects, and the reliability of exposure data were also evaluated by the Army in the EA/FS. Finally, the Army also evaluated technical factors in the selection of PRGs, consistent with the NCP, including detection and quantitation limits, technical limits to the remediation, and the ability to monitor and control movement of the contaminants. In summary, the Army's approach to groundwater PRG development as described in Volume V, Section 2.5 is fully consistent with the approach described in the NCP. As described in the response to EPA Comment No. 1, PRGs were not developed for the soil medium. A. On the basis of dispute resolution (see Attachment A), EPA agreed that the risk assessment would evaluate only dieldrin for the egg pathway. As stated in Volume II, Section 2.1.1.1, dieldrin was the only chemical of concern (COC) detected above the certified reporting limit (CRL) in an egg sample analyzed from the Offpost OU; therefore, inclusion of other COCs was not indicated. B. All the groundwater alternatives include a specific component that calls for improvement or modification of the boundary containment systems, as necessary, to address future chemical plume concentrations. This information is in Volume VI, Section 3.0. C. Without sufficient empirical scientific data, it is difficult to determine whether the division of COC soil concentrations by five actually resulted in an underestimation of risk. The surficial soil concentrations were divided by five to estimate a depth-averaged concentration in the root zone because the soil COCs are strongly adsorbed to soil particles and are unlikely to be readily leached through the soil column. The division of soil concentration by five is discussed further in the response to Comment No. 5. Background concentration levels were not used in the development of groundwater PRGS.

Comment No. 3 - Land Use EPA invokes dispute concerningthe land use scenariosaspresented in the offpost FS, and all sections and calculationsthat utilized the offpost FS conclusions,for reasonsdetailed below. The discussion in Volume H demonstratesthatthere is uncertainty in regardto the land uses offpost. Uncertainty,per the NCP, would requirea comparisonof land uses, such as residential, commet - cial-industrial and recreational. Scenarios for residentialland use should be evaluatedwhenever there are homes on or nearthe site, or when residentialdevelopment is reasonablyexpected in thefuture. Considerationof historical

11788,903 - CR-03 0504112092 VIII - 7d

land use; suitability for residential development; local zoning; and land use trends should be undertaken. The farmfamily scenarioshould be evaluated if it is known that suchfamilies reside in the area. EPA's concern is that residentialuses were not compared in the FeasibilityStudy (along with the Commercial- IndustrialandRecreationaluses). This should be done, given the present level of discussionand the existing situationin the area. Some examples of uncertaintyin the discussionare: A. PUD is not defined in Figure 7.2.2.1.2-2. A PUD does not support the eliminationof residentialuse between RMA and Route 2, without a specific definition whichprecludes residential. B. There was not informationon the delineation or uses of the wetland it? zones 3 and4 sufficient to eliminate residentialuse. C. The realignmentof 96th Avenue has been presentedas speculation. There is no information on whether there areplans to condemn the property for this route, whether land has been dedicated for this route, whether it is on any officialplanningor transportation plan demonstratingsuch a project. Further,there is not informationsufficient to eliminate residentialuse along a realignedcorridor. D. There was no explanationconcerningtheformat issue ofthe 1990 Census which was describedas helping to define the present use. (P 11-2-40) E. There was no discussionsufficient to conclude that Offpost GroundwaterIRA would render land CommerciallIndustrial.(P 11-2-44). Presently, it cannot be demonstrated thatthe likelihood ofresidentialuse is small, given the discussion of the circumstancesin the Offpost OU, zones 3 and4. These comments arepremised upon page 8710 of the National ContingencyPlan (55FR8710, March 8, 1990), Section 6.2.2 ofthe Risk Assessment Guidance(OSWER Directive 9285.701a;July, 1989), andHuman Health EvaluationManual,Supplemental Guidance: "Standard Default Exposure Factors" (OSWER Directive9285.6-30, March 25, 1991). Rest)onse The topic of this comment was addressed during the dispute resolution process. Refer to Attachment A for additional information in the dispute resolution letter. On the basis of dispute resolution, all Organizations agreed to use a single land use scenario for each zone within the Offpost OU. Zones 1, 2, and 6 were classified as rural residential, zones 3 and 4 as urban residential, and zone 5 as commercial/ industrial. The land use scenarios and potential exposure pathways were further defined as a result of agreements reached by the Organizations during the dispute resolution process, as follows: A. Rural Residential (EA/FS zones 1, 2, and 6) meat* (75 percent) dairy* (75 percent) egg (only evaluated dieldrin) vegetable* (40 percent) groundwater (ingestion) groundwater (inhalation) soil (dermal) soil (ingestion)

11788,903 - CR-03 0504112092 VIII - 8sediments (dermal) surface water (dermal) B. Urban Residential (EA/FS zones 3 and 4) vegetable* (40 percent) soil (dermal) soil (ingestion) sediments (dermal) surface water (dermal) groundwater (ingestion) groundwater (inhalation) *All percents indicate amount of consumption from local sources. Risk estimates for Zones 3 and 4 will be presented in two manners: I. As a baseline risk assessment for all media per EPA guidance. The groundwater portion of the risk assessment will be based on the calculated risks from 1989 to 1991 groundwater data in those zones. 2. The second risk calculations will be based on the continuing beneficial effect of the onpost boundary system operations in a 30-year time. The text will state that these are the expected potential exposures for individuals in those zones and the risks associated with those exposures. C. Commercial/ Industrial (EA/FS zone 5) soil (dermal) soil (ingestions) groundwater (ingestions) groundwater (inhalation) If SACWSD provides appropriate documentation indicating that SACWSD is not planning to install future water wells in zone 5 over the next 30 years, the groundwater pathway will be removed from zone 5. Attachment B to this set of responses to comments is a letter from SACWSD to the Army, providing documentation that SACWSD does not intend to install water-supply wells in zone 5 in the future.

Comment No. 4 - Interpretation of Uncertainties Analysis EPA invokes dispute concerning the interpretation of the uncertaintyanalysisas presented in the offpost EAIFS, and all sections andcalculationsthat involve this interpretation, for the reasons detailedbelow. The response to comments on the uncertaintyanalysis is inadequateto address the agency's concerns, in that itfailed to distinguishbetween propagatingvariabilityandcritical knowledge uncertainties. The uncertaintyanalysis is put togetherin afashion that renders it, in reality,an analysis of uncertainties. Site-specificparameters,such as exposurepoint concentrations, werefound to contribute little to overall variability(i.e. they were "insensitiveparameters") compared to various parametersassociatedwith human behavior (exposure duration,ingestion rates, etc.). This being the case, it is not possible to determine whether the uncertaintyanalysisover- or underestimatesactual exposures which might occur on the site. Stated in another way, any "hypothetical"exposedpopulation in the off-site areamay vary considerably from the "typical"

11788,903 - CR-03 0504112092 Vill - 9case. The logical conclusion is that there is no way to determine whether the RME estimate or the quantitativeuncertaintyanalysis better representspotential upper rangeexposures. The Army maintainthat they accept this conclusion, but the document suggests the opposite. The risk assessment concludes that the uncertaintyanalysis "clearly"shows that the RME overestimates potential exposures and concludes that the risk assessment may be "excessively" conservative. This conclusion is then carriedinto the FeasibilityStudy to helpjustify a target risk substantiallyhigher than I X 10-6 for PRGsfor the residentialscenario. Such conclusions and interpretationsclearly indicatethat the Army accepts the uncertaintyanalysis as a more "accurate" measureofpotential exposures. In view ofthe lack of knowledge of site-specificexposure parametersin these "hypothetical" populations,and the lack of meaningful discussionon them, EPA cannot accept this interpretation. Infact, the analyses seem to suggest thatthe appropriateconclusionmight be almost the opposite. Agreement within afactorof3 or so should be viewed as quite good in theface ofthe many uncertaintieswhich go into risk assessment. EPA feels that the appropriateinterpretation is that estimatesfor maximum exposure are quite reasonablein comparisonwith those expected in a 11 typical" community, and that no substantial "overconservatism" has been documented. In addition,the document does not distinguishbetween a "sensitivesubpopulation"andthe "population-at -risk". An example may serve to demonstratethe point. As one moves awayfrom the Arsenal boundary,concentrationsof contaminantsin soil generallydecreaseuntil some "background"is reached. If datafrom samples taken over this entire areaare averaged,many current orfuture residents on thefringe, or outside of the zone of the higher contaminationwill be included in the exposure estimates. Since such individualsare not among the "at-risk" population, the result will be an underestimateof exposures. The Army has recognized this in dividing the offpost into Zones. However, the document does not recognize that individualsmay also be on the fringe in a temporalas well as spatial fashion. As previously affirmed, many individuals in a populationmaY be exposedfor such short timeperiods that they cannot be considered "at-risk." These individualscan reasonablybe excludedfrom a quantitativeuncertaintyanalysis without changing the basic intent to examine a potential (perhaps "hypothetical") range of exposures in the AT-RISK population. Response The proposed final EA/FS has been revised in response to this comment. Specifically, the Army has concurred with and added EPA suggested wording regarding the interpretation of the uncertainty analysis results, specifically, in Section 2.6 and 4.4. The distinction between propagation of variability and critical knowledge uncertainties was specifically addressed in the previous draft as well as this draft (see Section 2.4.5.5.3), and the Army fails to appreciate how EPA's previous comments require further elaboration on that issue. The Army agrees that the uncertainty analysis is an analysis of uncertainties. The Army agrees that the uncertainty analysis is prone to share certain categories of errors with the reasonable maximum exposure (RME) analysis. Included among these are: 1. Selection of exposure pathways for quantification: The same pathways are included in both the RME and the uncertainty analysis. Some of these pathways may be incomplete now or in the future. Conversely, some pathways that were not quantified may contribute to exposure and risk, but documentation was provided in Section 2.3.3 (and the response to comments incorporated in the March 17, 1992, proposed final report), supporting the conclusion that pathways not quantified contribute negligibly to exposure. 2. Use of national average statistics rather than site-specific data for exposure factors, such as consumption of homegrown vegetables and duration of residency: Additional discussion has been added to respond to EPA's comment on this issue in Section 2.4.5.4.

11788,903 - CR-03 0504112092 Vill - 10Considering these limitations, the primary conclusion that can be drawn from the uncertainty analysis is that consistent selection of upper 90th and 95th percentile values for exposure concentrations, exposure factors, and equilibrium partition coefficients (the procedure used to derive RME intake estimates) tends to compound conservatism to such an extent that the RME intake has a very low probability of exceedance. This finding leads the Army to conclude that selection of a remedial alternative that produces an RME risk near the upper end of the acceptable risk range would be protective of human health per the NCP. The Army disagrees with EPA's interpretation that "agreement" within a factor of 3 is significant of anything more than careful representation of the distributional inputs to the uncertainty analysis. The inputs were designed to represent the same distributional information used to define the point values (90th or 95th percentile) input to the RME calculation, so "agreement" simply confirms that the distributions were represented in a consistent fashion in both the RME and uncertainty analyses. EPA's point regarding the difference between a sensitive subpopulation and the "population at risk" is well taken. The distinction is a difficult issue throughout this and numerous other site risk assessments. The sensitive subpopulation upon which the RME is based is assumed to maintain a backyard garden (and domestic animals in some zones). Although it should be clear that not all, and perhaps relatively few, residents would actually fit this profile, the Army and EPA seek to protect such residents' health should they choose to do so. The uncertainty analysis attempts to represent the population at risk, including these relatively highly exposed few. The Army believes that representation of all the individuals within the population at risk enhances our ability to communicate risks to the public in a balanced and meaningful way. Individuals who reside in the offpost area for only one or two years should not be misinformed that their risk is equal to the RME. Contrary to EPA's comment, the document does address this issue through the uncertainty analysis by incorporating a realistic range of exposure durations (all the way from I year to 70), and this is clearly one of the reasons why the median exposure is much lower than the RME. As derived from the Exposure Factors Handbook, the median duration of residency at a single residence (nationwide) is approximately 10 years, much lower than the RME estimate of 30 years. The distribution used in the uncertainty analysis also reflects the possibility of exposure durations much greater than 30 years, but the probability of longer exposure durations is very low. The Army sees no compelling reason to exclude either short-duration or unusually long-duration residents from the uncertainty analysis.

Comment No. 5 - Division of Soil Concentrations by 5 EPA would invoke dispute concerning the division ofsoil concentrationvalues by thefactorof5 as presented in the offpost endangermentand all calculationsthat used the resulting values,for the reasonsdetailed below, exceptfor the low risk involved in the specific example. In any other instance we would not accept thisprocedure. In its responseto General Comment No. 24 the Army defends the adequacy ofthe subsurfacesoil dataset, which was used to assess COC concentrations in subsurfacesoil. The Arm), claims that 5 sets ofcorrespondingsubsurfaceand surficialsoil data samplepoints were usedfor the comparison. However, subsurfacesample HA 1261 SO, which is mentioned in the Army's response is not included in RI Figure2.5 which gives locationsfor subsurfacesamples. Furthermore, this sample is neithermentioned in the text, nor are any data included in the relevantAppendix. Since the sample appearsto be not documented, it cannot be usedfor the comparison. This would appearto leave 4 soil samplesfor the 0.5 foot depth analysis. Dieldrin was detected in only one of the 4 samples (HA 9085 SO), however, the dieldrinconcentrationin this sample (70 jug/kg) was higher than that ofother surficialsoil samples that were collected relativelynearby (HA 1235 Wb, 30 ILglkg, HA 1229 JVB, 13 pg1kg, and the "collocated"surficialsoil sample HA

11788,903 - CR-03 0504112092 Vill - 110996 WB, 55 ug/kg). Even though dieldrinconcentrationswere below the detection limit in the 3 other subsurfacesamples, EPA believes that the dataare not sufficient tojustify dividing soil concentrationby 5 (or by 4). Furthermore,the text (11-2-77) indicatesthat most of the surficialsoil dataarefrom untilled areas,and that the subsurfacesoil samples were collected "nearby." It seems inappropriate to measure subsurfacesoil concentrationsin areaswhich have not been usedfor agricultural purposes, if these soil concentrationsare then used to determine COC uptake into vegetables. It is obvious that in plowed,filled and irrigated soils COCs would more evenly distributedin the subsurface. Resr)onse Results from sample HA 1261 SO were reported in the remedial investigation (RI) addendum. However, a typographical error in that document resulted in the sample being labelled "HA 1261 S". The results are also part of the Program Manager for Rocky Mountain Arsenal (PMRMA) database wh' ere the sample is labelled HA 1261 SO, and that database is part of the administrative record. EPA appears to be confused that division of concentration by a factor of 5 is somehow related to the fact that five sets of corresponding subsurface and surficial samples were used as supporting documentation. The factor of 5 is derived from the ratio of the depth of the root zone for row crops to the depth interval of surficial samples. At the risk of belaboring our arguments already on the record, we assert that all available evidence supports the conclusion that surficial soil contamination offpost has resulted from deposition of windblown aerosols from onpost sources, that the soil COCs are all organochlorine pesticides that are highly immobile within the soil profile, and consequently that it is likely that untilled soil will contain soil COCs only in the upper one or two inches of the profile. These hypotheses are supported by the fact that detectable concentrations have been observed nearly exclusively in surficial (upper I to 2 inches) samples and that nearby samples of the upper 6 inches have lower or nondetectable concentrations. The portions of the Offpost OU where the highest surficial soil concentrations have been found have predominantly not been used for row crop cultivation but rather have been fallow/pastureland. If, under a potential future land use, they were to be cultivated for vegetables, they would be tilled, thus mixing the contaminants presently found in the upper I to 2 inches through the root zone, resulting in an average root zone concentration approximately 115 of the observed surficial concentrations. EPA's final paragraph suggesting that samples from untilled land not be considered for the vegetable pathway analysis contradicts related EPA guidance that potential future land uses that might result in RME exposures be evaluated. The Army, following EPA guidance, has conservatively assumed that land not currently in cultivation might be cultivated in the future. Areas currently under cultivation for vegetables have substantially lower concentrations of COCs in soil.

Comment No. 6 - Ecological Risk Assessment EPA invokes dispute concerninga) the valuesfor bioaccumulation factors (BAF) and biomagnificationfactors (BMF), and b) the valuefor dieldrinMATC in top predators(eaglelowllkestrell) presented in the offpost ecologicalrisk assessment,and all calculationsthat used thesefactors, such as ecologicalPRGs,for the reasonsdetailedbelow. (See: Volume III, Section 5.0 et sea., Volume IV, Appendix H, and Volume V, EcologicalPRGs, Volume VII, Appendix C.) In addition,EPA still has substantialreservationsconcerningthe methodology used to derive ecological toxic reference (TRV) values. EPA would invoke dispute on the TRV methodologyfor dispute at this time: however, since the TRV values were not used to develop ecologicalPRGs, we

11788,903 - CR-03 0504112092 VIII - 12will not dispute at this time. EPA reservesthe right to invoke disputeon the TRV methodology should it be used in the onpost ecologicalassessment. A. Bioaccumulation factors (BAF) and BiomagnificationFactors(BMF) The valuesfor BAFs andBMFs, andother values calculated from these, cannot be acceptedas presenteddue to seriousconcerns about the methodology used to derive those BAFIBMFs. The offpost ecologicalrisk assessment (ERA), as currentlypresented is a deterministic version of the on post ecological risk characterization (ERC) model. The ERC has not previously been reviewed, andthus constitutes entirelynew information. A set ofcomputer disks were providedto EPA on March 19, 1992, containingthe postcalibration valuesfor on post biota. No supportingdocumentation wasprovided with those disks. EPA will submit detailed comments concerningthe on post biotamodel under separatecover. A careful review of the availabledataset was undertaken for study area1, and indicates that there is no acceptablebasisfor comparingcontaminantconcentrationsin soil, terrestrial plants, andprairiedogs. Although the sample sizes were reasonably large,at leastfor soil andprairiedogs, the number of co-locatedsamples that could be comparedrigorouslyis extremel' 1,small. Thus, these data cannot be used to estimateBAFs or BMFs. The attempt to do so, based on the entirefiles of soil and biota data,involves almost exclusively the comparison ofnon-comparabledata. Response A. The Army elected to use calibrated onpost data because it felt that site-specific parameters were preferable over literature values that were based on controlled experimental studies or field studies conducted in other geographical regions. The Army felt that BAFs derived from both controlled laboratory studies or other field studies would not reflect influences from environmental/ecological conditions within the Offpost OU. Therefore, the Army concluded the onpost values would be preferable because the offpost is environmentally and ecologically similar to the onpost. However, the Army acknowledges that because of different scheduling needs, the onpost values were not adequately reviewed by the Organizations and State (OAS) before their use in the draft final ecological assessment. Therefore, the Army has agreed to incorporate the BAF and BCF values derived during the dispute resolution process. The Army still maintains the literature values are not representative of Offpost OU site-specific conditions.

B. DieldrinMATC in toppredators(eaglelowllkestrel) The dieldrinMATC value of 1.6 ppm cannot be acceptedbecause it relates to lethality in birds of prey. The Army selected an MATC value of 1.6 for both aldrinanddieldrin in birds ofprey. The value of 1.6 ppm is the average concentrationin the carcassesof 101 bald eaglesfound dead between 1971 and 1974. (K.R. Barbehennand W.L. Reichel, Organochlorine concentrationsin bald eajzles: brain1bodi, lipid relationsand hazardevaluation. Journalof Toxicological EnvironmentalHealth 8:325-330, 1981). The value of 1.6 ppm is neither a safe level nor a minimum level: it is an averagelevel in a collection of birdsgroupedtogether for other

11788,903 - CR-03 0504112092 VIII - 13M

reasons. The paperis about the pharmacologyof dieldrin in eagles, not about dose-response relationships. The best experimentaldata on effects ofdieldrin on birds ofprey are those of Wiemeyer gt al. (DDE, DDT+ Dieldrin: Residues in American Kestrels andRelations to Reproduction, 1986). The mean carcassconcentrationsin birds that died was 1.7 ppm (range, 0.7 - 4.5 ppm). Thus, a carcassconcentrationof0.7 ppm is relatedto lethality, and cannot be indicatedas "allowable." To apply these data to other birds ofprey, including eagles, would requirean additionalinterspeciesuncertainty factor. Reportedcases of dieldrin poisoning in bald eaglesfrom several states (Prouty, R.M. et al, 1977. Residues of oreanochlorine pesticidesandpolychlorinatedbiphenyls and autopsy data for bald eagles. 1973-74. Pestic.MonitorJ. 11:134-137, andKaiser,T.E. et al, 1980. Organochlorine pesticide,PCB, and PBB residuesandnecropsydatafor bald ea--Ies from 29 states -- 1975-77. Pestic. Monitor.J. 13:145-149) indicatemedian carcassresidues in bald eagles of0.74, 0.63, 0.60, 0.66, and 0.22 ppm, wet weight. Although it is difficult to use these data to define a minimum or low effect level, it is clear thata populationaverage level of 0.66 ppm is associatedwith deathsfrom dieldrinpoisoning in some individuals. Therefore, EPA cannot accept the MATC value of 1.6 ppm for dieldrin. Resvonse B. The MATC values used in the draft final ecological assessment were obtained from the Onpost Ecological Risk Characterization (ERC). Although these values were not adequately reviewed by the OAS before the release of the draft final ecological assessment, the Army has some serious concerns about the adequacy of the data from the Wiemeyer and others paper cited by EPA for establishing a dieldrin MATC. The Army's concerns include the following: use of a chemical mixture with no single dosing with dieldrin, study not designed to investigate dieldrin toxicity only, the presence of other stressors (e.g., periods of low ambient temperatures and disease episodes of enteritis), study conducted more than 23 years ago, insufficient numbers for an adequate statistical comparison, and the presence of toxicological anomalies. For example, the lowest kestrel carcass concentrations associated with mortality in the low dose groups is 0.7 ppm as cited above by EPA; however, the brain concentration in this kestrel is one of the lowest levels reported, 0.09 ppm, and this animal also has the second highest value reported for carcass lipid percent of dry weight, 36.4 percent. Toxicologically, it is highly unlikely that dieldrin either directly or indirectly caused this animal's death. Additionally, in their summary of dieldrin- related deaths for all study groups, the authors indicate dieldrin was not the cause of death for any animal in the low dosage groups and only contributed to the death of three others. Sixteen birds comprised the low dosage groups. Therefore, the Army cannot accept 0.7 ppm as a suitable MATC. Following a review of several articles published on dieldrin toxicity during the dispute resolution and a conference call with Dr. Stanley Wiemeyer, the Organizations and Army agreed upon a dieldrin MATC value of 1.1 ppm.

Comment No. 7 - Accemance of Ecological Hazard Indices that Exceed I EPA invokes disputeconcerning the acceptanceof ecologicalhazardindices that exceed I as presented it? the offpost risk assessment, and all calculationsthat utilized the resultingvalues,for the reasonsdetailed below.

11788,903 - CR-03 0504112092 VIII - 14A The Army justifies the acceptanceof high HIsfor ecologicalreceptors with the argumentthat the movement of these receptorsto areas outside ofZone 3 will reduce the ecologicalrisk. At the same time the Army dismisses the additionalrisks that ecologicalreceptorsencounter when they move onpost. The Army states (response to GeneralComment No. 6) that "movement of receptorsto the onpost increasesexposure that is more appropriatelyevaluatedit? the onpost." EPA disagreeswith this statement. The physical setting ofRMA and its surroundings suggests that ecological receptorsare more likely to spend time at RMA than in the more developed areasoutside ofRMA. While EPA does not requirethe Army to quantitatively addressthe additionalrisks that animals residingin the offpost encounterdue to movement into the onpost,EPA believes that the additionalexposures are a source ofuncertainty in the ecological risk assessment, which should not be dismissed. The potential for additionaland even greaterexposures make the risks associatedwith Zone 3 very significant,andHazard Indices above I cannot be accepted. While the Army is correct in stating that the home rangeof mobile ecological receptorsmay exceed the size ofZone 3, the Army does not provide any quantitativeinformation on how much time these receptorsspend outside ofZone 3, or what percentageofprey is caught outside ofZone 3. The HIs calculatedin ecologicalrisk assessments are quantitative estimates based on many considerations andfactors. These quantitativedata cannotbe dismissed based on a completely unquantifiedassumption. It should also be noted here, that even though several of the calculatedHIs are high, EPA has many concerns with the input parametersused to calculate the HIs. If more appropriate parameterswere used, resulting HIs would be even higher. B. The results of the EA showed that the eggpathway is an importantcontributorto noncarcinogenic risk. For example,for the child resident in Zone IC the egg pathway contributesan HI of 3.1 x 10-1 to a totalHI of 1.2. Thefact that the eggpathway has not bee evaluated for soil COCs other than dieldrin is especially significant in light ofthefact the HIsfor hepatotoxic effects in children exceed I in all zones. The soil concentrations for endrin,DDTIDDE andchlordaneare similarto those of dieldrin (Table 2.4.2.5-8). Therefore, if the soil to egg partitioningcoefficientsfor these chemicals are similarto the soilleggpartitioningcoefficientfor dieldrin,chemical concentrationsin eggs would be similarto those ofdieldrin,and the egg pathwayfor other soil COCs would contributegreatly to the alreadyexisting calculatedrisk. Forexample, at? estimate shows that the egg pathwayfor chemicals other than dieldrinmight contributean HI of approximately 0.65 to hepatoxic effects it? children in Zone 3. The A rm' v states that it was unable to quantify the egg pathwayfor chemicals other than dieldrin,because no literaturevaluefor the soil to egg partitioningcoefficient could befound for these chemicals. EPA suggested (General Comment No. 26) that a default valuefor K,,,. similarto that ofdieldrinbe used to estimate the concentrationsof soil chemicals in eggs. lit the absence of site-specific data andlorliterature datafor the K.', parameter,the approach recommendedby EPA would have been reasonablyconservative. To not addresspotentially importantpathways because ofthe lack of data is unacceptable in a human health risk assessment, when use ofparallel informationwould at leastyield qualitativeinformation for the uncertaintyanalysis. Remonse A. The movement of mobile ecological receptors to onpost areas potentially could result in additional exposure and increased risks; however, the Army cannot quantitatively determine

11788,903 - CR-03 0504112092 VIII - 15the additional risk that may occur because the onpost ERC is not yet complete. The HI is the result of a comparison of an estimate close to a benchmark, in this case, a toxicity reference value. A numeric result greater than one does not indicate the potential magnitude or severity of effect, only that the benchmark dose was exceeded. The EPA appears to accept an HI of one as an absolute reference point and any exceedance above one as totally unacceptable. This defies biological reality and the uncertainty associated with biological systems. Compared to the physical sciences, biological outcomes are less predictable, and a range of acceptability is appropriate. Although sufficient monitoring/analytical data are lacking, it is highly unlikely that the HIs, as determined for this ecological assessment, underestimate the potential risk and ecological receptors. The Army strongly disagrees with the statement, "If more appropriate parameters were used, resulting HIs would be even higher." In fact, on the basis of dispute resolution, the parameters agreed upon by the Army and Organizations resulted in lower HIs. These parameters included a spatial adjustment factor to account for the receptor's dietary intake fraction obtained from zone 3 and/or zone 4 relative to the receptor's home range.

Comment No. 8 - General Comment Concerninp, ARARs Analysis EPA invokes dispute concerningthe adequacy of the ARAR analysisas presented in the offpost EAIFS, and all calculationsand conclusions that utilizedthe analysis, for the reasons detailed below. The discussion ofARARs in the EAIFS is inadequate. Compliancewith ARARs is a threshold requirement for comparing and selecting remedial alternatives,yet the ARAR discussion in Appendix A provides no basisfor differentiatingalternatives. The ARARs analysis shouldhave consideredthe universe ofARARs as they appliedto each remedial alternative,providingdetailed discussion with respect to the preferredalternative. EPA's "CERCLA Compliance with OtherLaws Manual," OSIVER Dir. 9234.1-01 (August, 1988), specifies theprocessfor completing an ARAR determination. (See CERCLA Compliance with Other Laws Manual,pp 1-55 to 1-56). In addition,Appendix E to EPA's "Guidance for ConductingRemedial InvestigationsandFeasibilit ' i Studies Under CERCLA," OSWER Dir.9355.3-01 (October, 1988), provides a suggestedformal for the summary ofARARs. EPA recommends that thisformal be used. Even if thisformat is not followed, a substantivel ' 1,equivalent discussionis required. EPA believes that the EAIFS does not sufficiently addressARARs, and therefore objects to the entireproposedARAR determination. It is not sufficient to lump together entire statutes orgroups of regulationswithout analyzing the portions thereofthat may be applicableor relevant and appropriate. Forexample, on p. VII-A-14, the Armv's ARAR analysis states: "To the extent that hazardouswastes do exist, 40 CFR Part264 will be an ARAR." This statement is so vague that it cannot reasonablyconstrued to constitute an anal ' ysis. Infact, it is clearthat some sections of Part264 may be ARARs, and some may not. As just one example, 40 CFR Part264.281 relatingto ignitableor reacti .ve wastes is not likely to play a role in this remedial action, but 40 CFR 264.100, which establishesa ground water monitoring program,may well be relevantand appropriate. In light of the lack of adequateidentificationand discussionof individualARARs, EPA is unable to provide a comprehensive list ofthe deficiencies ofAppendix A. Instead,EPA requiresthat a thoroughARAR analysisbe performedtaking into account the universe of Federaland Slate ARARs. In addition,EPA has disagreedwith particular ARAR conclusions that were reachedin the Army's Response to Comments. These are describedin more detailbelow.

11788,903 - CR-03 0504112092 VIII - 16Response Volume VII, Appendix A of the FS, ARARs analysis, has been revised to address EPA's concern that sufficient detail was not provided. Specifically, additional detail was provided in the section describing each of the major categories of chemical -specific, action -specific, and locationspecific ARARs. Additionally, as requested by EPA, a table summarizing the ARARs analysis was added. Additional text was added to Volume VII, Appendix A, specifically addressing sections within 40 CFR, Part 264, and discussing which sections of Part 264 may be ARARs. Additional text has been added to Volume V11, Appendix A, including and addressing the universe of Federal and State ARARs.

A. Specific Inaccuraciesin ARARs Analysis EPA invokes dispute concerningspecific inaccuraciesinARAR analysisas presentedin the offposl EAIFS that EPA can now identify, and all calculationsand conclusions that utilized the analysis, for the reasonsdetailedbelow. i. Response to Comments on Volume VII: The portion ofthis response that states: "ARARs do not discusssurface water and sediments because the preferredalternativedoes not requireremedial actionfor th6se specific media," is inconsistentwith CERCLA and the NCP. CERCLA requiresthat remedialaction.-

attaina degree of cleanupof hazardoussubstances,pollutants,and contaminants releasedinto the environment and of control offurther releaseat a minimum which assuresprotectionof human health and the environment. 42 U.S.C. s'9621(d). In order to assurethat remedies areprotective ofhuman health and the environment, section 121 of CERCLA requiresthat the remedy attainARARs. If there is any exposure pathwayfor humans, ARARs must be consideredto establishprotectiveness. If site conditionsdo not meet ARARs, remedialalternativesmust be developed. Even if surface water and sediment are determinedto have no exposurepathwayfor humans, in light of the EndangeredSpeciesAct, the Bald and Golden EagleProtectionAct and the MigratoryBird Treaty Act, surface water and sediment must be consideredas potential exposurepathwaysfor migratorybirds and eagles. If ARARs have not been considered for surface water and sediment, the selected remedy cannot be shown to be protective and cannot meet the thresholdcriteriarequired for comparisonof remedies in the NCP. See 40 CFR § 300.430. Resi)onse With regard to the EPA inquiry on the Endangered Species Act (ESA), the Bald and Golden Eagle Protection Act (BGEPA), and the Migratory Bird Treaty Act (MBTA), Appendix A in Volume V11 has been revised to include in totality the language agreed upon in the dispute resolution process and communicated in a letter from EPA to the other parties, dated September 18, 1992, regarding these three federal acts (see Attachment Q.

11788,903 - CR-03 0504112092 VIII - 17ii. Response to Comment No. 17: This response states that reports availableat EPA or RMA are "publiclyavailable"and may be cited without constraint. EPA disagrees. The Army has relied on old reportsthat may no longer be available,as well as draft reportsthat may be subject to privilege. These and any other reports that may not be publicly available,shouldbe included as appendicesto the EA, or, at the very least, added infull to the AdministrativeRecord. Resr)onse The Army stands by its response that reports available at EPA or RMA are "publicly available" and may be cited without constraint. In appropriate appendixes in the Final EA/FS, the Army has included information that is not yet available, e.g., some ecological risk assessment parameters that were obtained from the unfinalized Onpost ERC are in Appendix H.

iii. Response to Comment No. 25: This response is incorrect insofaras it suggests that the MigratoryBird Treaty Act does not requireprotectionof individualbirds. 16 U.S.C. s' 703 clearly states that it is unlawful to "kill... any migratory bird... or any egg of any such bird..." This statute was amended in 1974for the specific purpose ofchanging a reference to "birds"(plural) to "bird"(singular). The languageof the statute "makes it clearthat killing a single bird is sufficient to create criminalliability..." United States v. Corbin Farm Service, 444 F. Supp. 510 (E.D. Cal. 1978). For furtherdiscussion of the MigratoryBird TreatyAct as an ARAR, see Response to Comment No. 216, below. Resr)onse Refer to response to Ad. given above, regarding the dispute resolution agreement for the three Federal Acts.

iv. Response to Comment No. 114: This response suggests that EPA may not dispute the valuesfor the chemical-specified absorption factor(ABS) because EPA hadpreviously been informed of these values in a RMA subcommittee meeting and expressed no opposition at that time. Thisposition is insupportable. EPA is in no way bound by its silence at a time when the Agency was under no affirmativeduty to raiseobjections. EPA has not waived its right to pursue dispute resolution on this issue. Rest)onse Comment acknowledged.

v. Response to Comment No. 216: The response to this comment, which states that the EndangeredSpecies Act, 16 U.S.C. s' 1531, et sea., the Bald and Golden EagleProtectionAct, 16 U.S.C. s' 668, et sea., and the MigraloryBird Treat),Act, 16 U.S.C. s" 701 et sea., are not ARARs is both incorrectand

11788,903 - CR-03 0504112092 VIII - 18inadequate. Contraryto assertionsmade in the Army's response,the EndangeredSpecies Act, the MigratoryBird TreatyAct and Baldand Golden EagleProtectionAct contain substantive requirementsapplicableto circumstances present at this site. With respectto the EndangeredSpecies Act, we note that 16 U.S.C. s' 1538 (1)(B) states: [i]l is unlawfulfor anyperson subject to thejurisdictionof the UnitedStates to take any such species within the United States... and "take" is defined at s' 1532(19) as "to harass,harm,pursue, hunt, shoot, wound, kill, trap,capture,or collect, or to attempt to engage in any such conduct." The Agency interprets "harm"as any harm resulting from contaminantpollution.

The MigratoryBird Treaty Act slates: Unless andexcept aspermittedby regulationsmade as hereinafter provided in this subchapter,it shall be unlawful at any time, by any means or in any manner, to pursue, hunt, take, capture,kill... any migratory bird, anypart, nest, or egg of any such bird... 16 U.S.C. s' 703. The UnitedStates Court ofAppealsfor the Second Circuithas interpretedthis statute to apply to a situationin which migrator ' y birds were killed by the release of chemicals into a pond. United States v. FMC Corp.,572 F.2d 902 (2d Cir. 1978). Similarly,the Bald and Golden EagleProtectionAct makes it unlawful to kill bald or golden eaglesby poisoning. See 16 U.S.C. s' 668d: "As used in this subchapter..."take" includes also pursue, shoot, shoot at, Doison, wound, kill, capture, trap..." (emphasis added). According to the NCP, ARARs are: [c]leanup standards, standardsofcontrol, and other substantiverequirements,criteria, or limitationspromulgated under federal environmentalor state environmentalor facility siting laws that specifically addressa hazardoussubstance,pollutant,conlaminani, remedial action, location, or othercircumstance found at a CERCLA site. 400 CFR § 300.5 (emphasis added). The EndangeredSpecies Act, the Bald and Golden EagleProtectionAct and the MigratoryBird Treaty Act, clearly set up substantive requirementsandlorlimitations(i.e. protection ofcertain species) undercircumstancesthat arepresent at this site. The statement it? the ARAR analysis (Appendix A) that "the alternativeswill have no adverse impact on any endangeredspecies or migratorybirds" is insufficient. Not only are the EndangeredSpecies Act, Bald and Golden Eagle ProtectionAct andMigratoryBird Treaty Act ARARs, but they must also be used to set standards for remediationthat will be protective ofendangeredspecies, migratorybirds and bald andgolden eagles. Resvonse

Refer to response to Part I above regarding the dispute resolution agreement with respect to the three Federal Acts.

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## Pages VIII-20 through Vill-26 are missing from the original.FEASIBILITY STUDY GENERAL COMMENT Comment No. I - Alternative Selection EPA invokes dispute concerningthe groundwateralternativeselected in the offposl FS, and all areasof this document and future documents that areeffected by the selection,for the reasons detailedbelow. Since all ofthe alternativespresented for the remediation ofthe groundwater (excepting the No-Action alternative)are variationson the configurationof the same technology, the alternativesare essentiallyequivalent. All of the alternativesevaluate various arrangementsof a transversepump-and-treatsystem. In order to make the FS comprehensive and in compliance with guidance,axial arrangementsshould also be evaluated. The Guidance for ConductingRemedial InvestigationsandFeasibilityStudies Under CERCLA states, "Foraquifers currently being used as a drinking water source, alternativesshouldbe configuredthat would achieveARARs or risk-based levels as rapidlyas possible." The Offpost FS has not evaluated configurationsthat could potentially achieve a more rapid remediation,such as an axialsystem. The Guidanceon RemedialActions for ContaminatedGround Water at Superfund Sites states, "A LgLýj remedial alternative generallyshould be developedfor ground water that is a currentor potential (emphasis added) source ofdrinking water. This alternativeshould achieve the selected cleanup level throughoutthe area ofattainment within the shortest time technically feasible. Additionalalternativesshould be developed to ensure that a wide range ofdistinctive hazardous waste management strategiesare evaluated at most sites." The FS must be modified to broadenthe range of alternativesto include one which would achieve cleanupin the shortest time possible or demonstrate that a more rapidcleanup is not technicallyfeasible. Remonse The Army strongly disagrees with EPA's contention that an aggressive groundwater alternative was not evaluated in the Offpost FS. As discussed in Volume VI, Section 3.0, Development of Remedial Alternatives, and Volume VI, Section 6.0, Detailed Analysis of Remedial Alternatives, the offpost geology, hydrogeologic systems, contaminant distribution, and contaminant transport properties were studied extensively both analytically and using a groundwater numeric model. The modeling effort is described in both Volume VI, Section 3.0 in terms of development of remedial alternatives and extensively in Appendix E of Volume V11. The results of this analysis are presented in a lengthy discussion in Volume VI, Section 3.0. The controlling hydrogeologic and contaminant transport properties of the Offpost OU.1groundwater system include (1) groundwater seepage velocity of the First Creek pathway relative to the northern pathway, (2) the distribution of the relatively less mobile compound dieldrin compared to the distribution of more mobile compounds such as DIMP and chloroform, and (3) the controlling transport properties of dieldrin as compared to the transport properties of DIMP and chloroform. As described in Volume V1, Section 3.0, Alternative No. N-4 for the North Plume Group was developed through a combination of analytical well field simulation, knowledge of contaminant distribution and contaminant transport properties, and hydrogeology of the North Plume Group. A transverse capture system for the northern pathway was chosen to intercept contaminants moving in the northern pathway. An axial system of collection wells and recharge trenches was selected in the First Creek pathway. Alternative No. N-4 consists of a total of 17 walls and 6 trenches with a total extraction flow rate of approximately 480 gpm. Alternative No. N-5 has a total of 20 extraction wells and 12 trenches. Alternative No. N-6 has a total of 4 extraction wells and 19 trenches. The total linear feet of recharge trenches ranges from 1500 feet in Alternative

11788,903 - CR-03 0504112092 V111 - 27No. N-4 to approximately 4400 feet in Alternative No. N-6. The total extraction flow rate ranges from 480 gpm in Alternative No. N-4 to a total of 690 gpm in Alternative No. N-6. The increasing complexity of Alternative Nos. N-5 and N-6 as compared to Alternative No. N-4 was evaluated to assess the impact of adding a number of extraction and recharge trenches in areas where contaminants were remaining in areas of slower relative groundwater velocity and tighter aquifer materials, and to address less mobile contaminants. The level of aggressiveness of Alternative Nos. N-5 and N-6 reached a practical maximum whereby the maximum practical number of additional extraction wells and recharge trenches was evaluated for remediation timeframe and aquifer drawdown considerations. Model-estimated groundwater mounding and drawdown resulting from the recharge trenches and extraction well arrays reached practical limits in Alternative Nos. N-5 and N-6. The discussion presented in Volume VI, Section 3.0 gives specific information demonstrating the distinct differences in level of complexity and aggressiveness of the remedial alternatives studied in the EA/FS. SPECIFIC COMMENTS Comment No. 2 Response to Comment 201 See dispute item number 2 (land use) above. Response See response to EPA General Comment No. 3 under Endangerment Assessment. Response to Comment 202 The response to this comment is inadequate,but EPA will not dispute this issue at this time. However, the document would be more defensible if thefollowing concerns were addressed. The Army has not adequatelyaddressedthe remediationof the contaminatedsurface water. As presented,the FS evaluates only one alternative for the remediationof surface water, which is the remediation ofthe surface watervia source removal, i.e., remediationof the groundwater. The FS Guidance (OSIVER Directive9355.3-01, October 1988, p. 1-8) states, "As practicable,a rangeof trealmentalternativesshould be developed, varying primarilyin the extent to which they rely on long-term management of residualsand untreatedwastes. The upper bound of the range would be an alternativethat would eliminate,to the extentfeasible, the needfor any long-term management (including monitoring) at the site. The lower bound would consist of all alternativethat involves treatment as a principalelement (i.e., treatment is used to addressthe principalthreats at the site), but some long-term management ofportions ofthe site that did not constitute "principal threats" would be required. Between the upper and lower bounds of the treatment range,alternativesvarying in the type and degrees of treatment and associatedcontainment1disposalrequirementsshould be included as appropriate.In addition,one or more containment option(s) involving little or no treatment should be developed as appropriate, and a no-actionalternativeshould always be developed." The A rm' 1,has notprovidedan objective evaluationofpossible alternatives for the remediationof the contaminatedsurface water other than concluding that the remediatiollof the groundwater would remediatethe surface water. The timeframe and costsfor remediationof surface water are not identified, even within the context ofthe remediation ofthe groundwater,since a portionof

11788,903 - CR-03 0504112092 VIII - 28these elements residein the remediationcosts andtimeframefor the OnpostOU, for which the FS has not yet beenprepared. Even though the surface water contaminationmay not constitutea "principal threat" in the Offpost OU, this contaminatedmedia must be evaluated in the FS. Response See response to EPA General Comment No. I under Endangerment Assessment. Remedial action objectives were not developed for the surface-water medium. Response to Comment 229 See response to specific comment 202 above. Resvonse See response to EPA General Comment No. I under Endangerment Assessment. Response to Comment 230 See response to specific comment 202 above. Rest)onse See response to EPA General Comment No. I under Endangerment Assessment. Response to Comment 231 See responses to specific comments 202 above. Resnonse See response to EPA General Comment No. I under Endangerment Assessment. Response to Comment 242 See responsesto specific comments 202 above. Resr)onse See response to EPA General Comment No. I under Endangerment Assessment. Response to Comment 246 See responses to specific comments 202 above.

11788,903 - CR-03 0504112092 VIII - 29Response See response to EPA General Comment No. I under Endangerment Assessment.

11788,903 - CR-03 0504112092 VIII - 30U.S. DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE COMMENTS REGARDING THE ENDANGERMENT ASSESSMENT/FEASIBILITY STUDY FOR ROCKY MOUNTAIN ARSENAL OFFPOST OPERABLE UNIT - DISPUTE ISSUES

GENERAL COMMENTS Comment No. I The Service is concernedthat the MigratoryBird Treaty Act (MBTA) is being treated inconsistently within the Offpost EAIFS process. In responseto our GeneralComment #2 on the Draft Offpost EAIFS, the Army has stated thatprotection under the MBTA has been included into the screening criteria for biological receptors,however, in the response to Specific Comment #24, the Army states that "there is no need to attempt to protect individualenvironmentalreceptors". Additionally, in response to EPA GeneralComment #23, the Army states that "the MigratoryBird Treat Act does not requireprotection for individualbirds". The Armyfurtherstates that even humans are not protected at the individuallevel. While this may be truefor humans,federal law does requireprotection at the individual levelfor migratorybirds. While protective models may profess to safeguardonly the majorityof individualswithin a population,it is generally recognizedthat theirlevel ofprecision may not reflect absolute reality. Conservatismexercisedat various steps within modelling efforts may actually come nearerto protectingwi entirepopulationthan an admissionof the imperfection of the process would admit. The Service hopes that throughproviding its best professional judgement it will protect the welfare ofits trust species to the greatestextent practicable. Service trust species must be protectedandlor damage assessment for any losses may be initiated. Resvonse The Army has derived toxicity factors (TRVs and MATCs) for use in the ecological assessment that at least provide protection to a population of a species and that are highly likely to beeven more protective. It is impossible to state with absolute scientific certainty that all individuals covered by the MBTA will be protected because there is a lack of sufficient chronic toxicity data for the COCs in wildlife species. The Army has incorporated modeling parameters (e.g., BAFs, BCFs, and MATCs) that have been derived on the basis of input from the Organizations, including the professional judgment of the U.S. Fish and Wildlife Service (USFWS). The Army's professional judgment is that these factors are sufficiently conservative to be protective of healthy animals, including healthy sensitive subpopulations. The emphasis is on "healthy" because the Army cannot predict the risk to animals that are affected by environmental stressors beyond the control of the Army (e.g., climatic changes, bacterial and viral infections).

Comment N . 2 Additionally, the Service strongly objects to introducingnew informationregardingthe Food Web Model developed in the OnpostEA without aformal review of that information. Specifically, information is presented in this document regardingthe inputparametersidentified as Maximum Allowable Tissue Concentrations(MATCs), BioaccumulationFactors(BAFs), Bioconcentration Factors(BCFs), etc. which the Service has not yet had an opportunity to review. Introductionof this material justifies a delay in thefinalizationof this document until all Food Web Model input parametersand calibrationlvalidation processes have been adequately reviewed and subsequent comments have been addressed.

11788,903 - CR-03 0504112092 VIII - 31Response This comment has been addressed through the dispute resolution process (see Attachment A). The Army and Organizations have agreed to use the revised food web modeling parameters presented in the final EA/FS Ecological Assessment (Volume 111, Section 5.0 and Volume IV, Appendix H). The Army agreed to incorporate the values with the understanding that they represent conservative values based on interpretations of literature data and may not be representative of sitespecific conditions present in the Offpost OU.

Comment No. 3 Furthermore,in reference to Food Web Model inputparameters,the Service has seriousconcerns regardingthe incorporation of some ofthe proposedMATC and BAF values. In particular, the dieldrinMATC is too high and some of the BAFs have extremely high standarddeviationswhich can encompass a wide range of values. Additionally, the appendicesprovided in the document are incomplete and therefore the Biornagnification Factorscannot be correctlyderived using the available information. The Service will be providing further comment on these concerns at a later date after a thorough review of this informationhas been completed. Resvonse Refer to the response for USFWS Comment No. 2

Comment No. 4 Finally,the Service is concerned that sediment contaminationwill not be adequatelyaddressed in the FeasibilityStudy. Specifically, the Service is concerned regardingthe high level ofdieldrin (370 mglkg) found at one site along the north boundary of the Arsenal. In response to our Specific Comment #10, the Army slates that "this sample was collectedfrom a groundwaterseep awayfrom the main channel ofFirstCreek and, as such, is not representativeof FirstCreek sediment". While this may be true, it does not abrogatethe potentialneedfor remediationat this site,particularly as it can be attributedto Arsenal contaminants. Otherissues regarding sediment which the Service previously commented on in the draftdocument appearto have been addressedin the response to our comments. Response Section 2.2 in Volume V of the EA/FS describes the PRG development methodology and compares both cumulative offpost risks and individual media risk to the acceptable risk range. The risk corresponding to the sediment medium is a maximum of 8 x 10-7. Remedial action objectives were therefore not developed for the sediment medium. See response to EPA General Comment No. I Endangerment Assessment.

11788,903 - CR-03 0504112092 VIII - 32COLORADO DEPARTMENT OF HEALTH COMMENTS REGARDING THE ENDANGERMENT ASSESSMENT/FEASIBILITY STUDY FOR ROCKY

MOUNTAIN ARSENAL OFFPOST OPERABLE UNIT - DISPUTE ISSUES

GENERAL COMMENTS Comment No. I - Develot)ment of PRGs a) Use ofHealthBased Criteria (HBCs) to develop Preliminary Remediation Goals (PRGs). The parts of the EAIFS thatdeal with derivationof PRGs have become even more confusing than in the previous draft. We requestthat the relevantsections ofthis document be rewritten to permitpublic understandingand to enable more focused review by the parties. Despite our basic inabilityto duplicateorfollow the Army's process, the State has managed to glean the following problems with the approach: Some (but not all) of the soil HBCs (shown in Volume V, Table 2.4.5-1) are differentfrom those in the draftfinal text. The Army has used a different methodologyfor derivingthe HBCs ofcarcinogens(described in Volume II Appendix C) and our efforts to reproducethe ArmY's new HBC numbers have not been successful. The soil PRGs are even further complicatedby the Army's footnote to Volume V Table 2.4.5.5-1 that "[s]ome preliminaryremediationgoals are different than HBCpresented in Table 2.4.4-1. PRGs were adjusted basedon observed contaminantdistributionand with the intent of achieving low aggregaterisk." The meaning and effect of the second part of the footnote are not clear. Which PRGs received this treatment,how were they adjusted,and why? The soil HBC listed in Volume V Table 2.4.5-1for the "AdjustedResidential"RME of Aldrin andDieldrinare31 ppb and .5 ppb respectively. The two compounds have very similar transportandtoxicologicalproperties. We request an explanationof why their HBC differ by a factor of over 60. In an effort to make the derivationclearer,we request that the Arm), include thefollowing in itsfinal version of the EAIFS.

i. A flow chart detailingthe hierarchyof choices and standardswhich were employed in the derivationof the PRGsfor each medium. ii. A complete set ofHBCfor the COCs in each medium. iii. An appendix in which the actual values are written, detailingstep-by-step derivation of the HBC and PRG if differentfrom the HBC. This appendix should start with the chemical'sslopefactor andlorreference dose and detail the effects ofadjustmentfor multiple media exposure, common organ toxicity, etc. If the method ofproportions is used, we request that the detailsof that step be included, too. We request that this be done for each of the groundwaterCOCs that do not haveARARs (11 compounds) or have PRGs that are different thanARARs, and the soil COCs (5). We also request that this derivationbe detailed for the surface waterand sediment PRGs. Rest)onse Volume V, Section 2.0 has been significantly revised to include additional detail concerning development of PRGs in light of comparison of cumulative Offpost OU risks to the NCP

11788,903 - CR-03 0504112092 VIII - 33acceptable risk range. Additional detail is also presented in this section concerning risk associated with individual media in the Offpost OU, based on the risks presented in Volume 111, Section 4.0 of the EA. As discussed in detail in Volume V, Section 2.2, the cumulative Offpost OU hypothetical cancer risk is a maximum of 3 x 10-4 based on risks presented in the EA. As discussed extensively in Volume V, Section 2.2, Offpost OU remedial action is not warranted because the offpost OU cumulative risk is within the NCP acceptable risk range. Also as discussed in Volume V, Section 2.2, the Army recognizes that there are several site-specific factors that, when considered in totality, suggest remediation of groundwater is preferable to no action in the Offpost OU. The above- referenced sections of text concerning PRG development explicitly state the risks corresponding to the groundwater, soil, surface water, and sediment media. Also, justification is given for the conclusion that soil, surface water, and sediment media do not require development of remedial action goals. Remedial action goals were developed for the groundwater medium as discussed in Volume V, Section 2.2, consistent with the methodology presented in detail in Volume VII, Appendix C. Appendix C explicitly describes the development of PRGs, considering the effects of multiple chemicals within the groundwater medium. See response to Part I given above. As described in the response to Part I given above, soil PRGS were not developed. See response to Part I given above. The development of PRGs for groundwater medium explicitly accounts for the effects of multiple carcinogens within groundwater. This information is presented in Volume VII, Appendix C. b) Use ofa 10-6 point of Deqarture. Despite its assertionsto the contrar ' y, the Army appearsnot to havefollowed the expressprescriptionof the NCP, cited both in the revised document itself and in the Army's responses, that a 10-6 point ofdeparturebe used in the development of PRGs. In response to State comments, the Army claimedthat it had used a 10-6 point of departure,but laterarrivedat a 10-4 risk level PRG after reviewing a "numberofelements and criteria" relatedto the selection ofhealth-basedcriteriaand determinationof PRGs. (Arm , 1,response to CDH Cover Letter Comment No. 1; see also Response to CDH CoverLetter Comment No. 3). Unfortunately,there is not enough informationpresentedin either the document or the responsesto comments to enable a reviewer to reproduceand understandthe Army's analysis anddecision making. This omission makes an objective review difficult. The end result, however, indicatesthat the prescriptionof the NCP has not beenfollowed. The Arm' v states in Volume V of the revised text that "in accordancewith the NCP, Section 300.430(e)(1), PRGs were developed considering ARARs, HBC,factors related to technical limitations(e.g. detection limits), backgroundconcentrations,land use and ecological criteria."(40 C.F.R. Part300.430(e)(i)). Absent from? the Army's anal * vsis (with the exception of the cursory and confusing treatment of arsenicin Appendix C) is any detailed discussion of the determinationofbackgroundcontaminationlevels and their incorporation into the development of the appropriate PRGs. Infact, in response to State comments objecting to the determinationof backgroundlevels in soils andgroundwater,the Army specifically assuredus that its background estimations would not be used to establishPRGs. (See CDH FS Specific Comment No. 7 andthe Army's response to Cover Letter Comment No. 8(d)). This, and other statements, therefore,contradictthe assertionsin the responses to comments. Pleaseclarify whether the Army's backgroundcalculationswere used in the derivation of PRGs. The State has previously objected to the ArmY's locations of background sample sites. (See State comments offpost R.I. as well aspri .or comments on the proposed offpost EAIFS).

11788,903 - CR-03 0504112092 V111 - 34Also absentfrom the EAIFS is an adequateexplanationjustifying the deviation from the 10-6 point ofdeparture. All that is provided in a cursorydiscussion of groundwaterCRLs. There is no explanationof how the Army arrivedat soil HBCs which do not correspondto the PRGpoint ofdeparturerisk level. Since groundwaterCRLs are irrelevantto soilsPRGs, some explanationis needed tojustify the higher risk levels selectedfor soils in zones 1, 2, 5 and 6. Response As discussed extensively in Volume V, Section 2.2, development of PRGs for the groundwater medium was performed consistent with the methodology described in the NCP. Groundwater HBC were calculated at the 10-6 level for carcinogens when ARARs were not available and at a HI of less than 1.0 for noncarcinogens without ARARs. These criteria were used as a basis for developing PRGs for groundwater. The NCP states departure from 1 0-6 may be appropriate, considering various factors, including but not limited to exposure factors, uncertainty factors, and technical factors. Exposure factors evaluated by the Army in the EA included cumulative of multiple contaminants, multiple pathways, population sensitivities, potential impacts on environmental receptors, and cross-media impacts. Additionally, uncertainty factors that evaluate the effectiveness of the alternative, the weight of scientific evidence concerning exposures and cumulative health effects, and the reliability of exposure data were also evaluated by the Army in the EA/FS. Finally, the Army also evaluated technical factors in the selection of PRGs, consistent with the NCP, including detection and quantitation limits, technical limits to the remediation, and the ability to monitor and control movement of the contaminants. In summary, the Army's approach to groundwater PRG development, as described in Volume V, Section 2.2, is fully consistent with the approach described in the NCP. c) Land Use. It appearsthat the Army has modifiedportions ofthe document addressingthe land use issuefor zones 3 and 4 of the offpost operableunit area to clarify that it is not basing its decision on the assurancesoffered by Shell Oil Co; rather,it is relying on land use forecastscontained in the documents cited in responseto Stale FS General Comment No. 1, page 65. The State essentially has two problems with this approach. First,by choosing to remediateonly to levels protective ofcommerciallindustrial or recreational uses, the Army is ignoringthefact that current use of the land is, (or would be butfor thefact that Shell acquiredthe property), rural residential. (See also, Figure2.4.5.5-1, "Offpost Operable Unit CurrentLand Use Aýap, 1991" which clearly indicates that, butfor the acquisitionof landby Shell, the zones are currenlly usedfor "Generalagriculture", "Exclusive Rural Family" "Rural Subdivision (10 acres minimum)" and "Irrigated Farming"). Second, projected uses as forecastedin the cited documents do not define all reasonable potential uses; they merely identify predictedor desireddevelopment. Regardingthefirst issue, aspreviously pointedout, the NCP preamble states that "...the baseline risk assessmentshould considerboth actualrisks due to currentconditionsand potentialrisks assuming no remedial actions"(55 Fed.Reg. 8710). Potentialcarcinogeni .c risks to people living andconsuming vegetables in zones 3 and 4 would exceed I x 10 6, thereby indicatingthat soil remediationis appropriate. The Army and Shell, as liableparties, cannot avoid cleanupby merely restrictingaccess to contaminatedmedia. Regardingthe second issue, we believe the Army has misconstruedthe intent and languageof the NCP addressing future landuse. Futureland use considerationsare not intendedto eliminatepathways and reduce exposures, rather,they are mandatedso that a remedy selected today will be protective ofpeople exposed, perhapsto a greaterdegree, in thefuture. The provision is meant to be inclusive, not exclusive.

11788,903 - CR-03 0504112092 VIII - 35Furthermore,the Army does not considerwhether ruralresidentialland uses represent "reasonablyexpected exposures"as requiredby the NCP, (see 55 Fed.Reg. 8710). Instead,in theArmy's own language,they are determinednot to be "a likely probability." (See Response to State FS GeneralComment No. 1.) These are very different tests. Thus, the Army has failedtofollow the prescriptionsof the NCP regardingutilizationof land useforecasts. Factually,the Army's future landuse assumptions ignoreseveral importantconsiderations. Thefirst and most obvious considerationis that the land useforecasts reliedon by the Army explicitly statethat a considerableportion of zones 3 and 4, including section 13, are either currentlyzonedfor residentiallagricultural use or areforecasted to be. (Volume V, Figures2.4.1-2 and 2.4.5.5-1). The exact basis of theArmy's "expectation"that commercial and industrial development will occur in the proximity of the new DenverAirport is also unclear. Stapleton International Airport has an extensive residentialcommunity borderingthe airportandextending well into the Denver metropolitanarea. Roadways leading to andfrom the airport,throughthese residentialareas,are oftenfour lane divided highways. The Army's basic assumptionthat a widening of 96th Avenue, coupled with expected commercial development, will prevent residentialuse in zones 3 and 4 defies simple observation ofexisting land use conditions around the existing airport. The Army's suggestion that in the event of residentialdevelopment, provisionof alternative drinking water will eliminateany potentialexposure, begs the question of whether residential land use is a reasonable potential use. If so, PRGs must be establishedaccordinglyand alternativesdeveloped to meet these PRGs through remediationto the maximum extent practicable. Remonse The topic of this comment was addressed during the dispute resolution process. Refer to Attachment A for additional information contained in the dispute resolution letter. On the basis of dispute resolution, all Organizations agreed to use a single land use scenario for each zone within the Offpost OU. Zones 1, 2, and 6 were classified as rural residential, zones 3 and 4 as urban residential, and zone 5 as commercial/ industrial. The land use scenarios and potential exposure pathways were further defined as follows: A. Rural Residential (EA/FS zones 1, 2, and 6) meat* (75 percent) dairy* (75 percent) egg (only evaluated dieldrin) vegetable* (40 percent) groundwater (ingestion) groundwater (inhalation) soil (dermal) soil (ingestion) sediments (dermal) surface water (dermal) B. Urban Residential (EA/FS zones 3 and 4) vegetable* (40 percent) soil (dermal) soil (ingestion) sediments (dermal)

11788,903 - CR-03 0504112092 V111 - 36surface water (dermal) groundwater (ingestion) groundwater (inhalation) *All percents indicate amount of consumption from local sources. Risk estimates for Zones 3 and 4 will be presented in two manners: 1. As a baseline risk assessment for all media per EPA guidance. The groundwater portion of the risk assessment will be based on the calculated risks from 1989 to 1991 groundwater data in those zones. 2. The second risk calculations will be based on the continuing beneficial effect of the onpost boundary system operations in a 30-year timeframe. The text will state that these are the expected potential exposures for individuals in those zones and the risks associated with those exposures. C. Commercial/Industrial (EA/FS zone 5) soil (dermal) soil (ingestions) groundwater (ingestions) groundwater (inhalation) If SACWSD provides appropriate documentation indicating that SACWSD is not planning to install future water wells in zone 5 over the next 30 years, the groundwater pathway will be removed from zone 5. Attachment A to this set of responses to comments is a letter from SACWSD to the Army, providing documentation that SACWSD does not intend to install water-supply wells in the future in zone 5. d) GroundwaterPRGs. The Stale objects to thefollowing PRGsfor groundwater.-

Chemical PRG Source CBSG aldrin .05 CRL .002 carbontetrachloride .99 CRL .3 chloroform 15 HBC 6 1,2-Dichloroelhane 1.1 CRL .4 dieldrin .05 CRL .002 manganese 200 CBSG (agric) 50 (secondary drinking) (Table 2.4.4.3-1, Offpost PRGsfor Groundwater;all values are in microgramsper liter).

i. Man--aneseARAR. This table lists the groundwaterPRG for manganeseas 200, according to the ColoradoBasic Standards for Ground Water (CBSG). While this number is correct for agricultural uses, the CBSG secondarydrinking water standard for manganese is 50 ppb. The PRG must be adjustedto reflect this lower number. (5 CCR 1002-8, Part3.11, Table 2.) 11788,903 - CR-03 0504112092 VIII - 37ii. ChloroformARAR. The Army has refused to recognize the State chloroform standard of 6 as an ARAR on the grounds that it is not generally applicablethroughoutthe State since municipalitiesexceed the standard. The Army is incorrect in its assertion. In promulgatingthe Basic Standards for Regulation ofgroundwater,the Water Quality Control Commission was clear in addressingthe generalapplicabilityof the standards. The Commission stated: "...The purpose ofthe adoption ofthe statewide standardsis L(Z provide a statewide baseline ofprotectionby establishingstandardsthat will apply broadlyto Coloradogroundwaters,for certaintoxic organicpollutantsand radioactive materials." (Emphasis added). Under 121(d)(4) ARARs may be waived if they arefound to be inconsistently applied. (See also 40 C.F.R. §300.430 (f)(1)(ii)(C)(5)). However, accordingto the NCP, a State standard "ispresumed to have been consistentlyapplied unless there is evidence to the contrary". (55 Fed.Reg. 8749.) It is the burden of the President,and not the State,to submit substantialevidence that the State standardhas been inconsistentlyapplied. The Army has not'met this evidentiarystandardwith its cursory response to CDH Feasibility Study Comment 4(d) and CDH Appendix A Comment No. 16. iii. The other chemicals have PRGs basedoil theArmy's detection limits which are higher than the State's health-basedstandards. As previously asserted,the State's health-based standardsare applicableto the remedialaction and must be achieved or waivedpursuant to CERCLA 121(d)(4). iv. CRL methodolozv. The State has at least since 1987 consistentlyobjected to the Army's use of its CertifiedReportingLimit (CRL) methodology because it results in detection limits that are higher than EPA method detection limits (MDLs) and, in some instances, exceed health-basedlevels. The State again raisedthis issue in its comments on the Offpost OperableUnit RIIEAIFS Workplan, January26, 1990 in which detection limits for a number of the above-listedchemicals were identifiedas exceeding health-based levels. With the exception of carbon tetrachloride, it appearsthat the Army has been unsuccessful at lowering its CRLs. Given thefact that lower detection limits are practicable,the Army has notjustified its deviationfrom a 10-6 point ofdeparturebased on the limitationof its CRL methodology.

v. Arsenic. Arsenic is a uniqueproblem. Although the Army's CRL of2.35 ugll does not exceed the MCL this ARAR, as acknowledged in the Army's response to EPA General Comment No. 1,falls outside ofthe risk rangeprovidedfor in the NCP. See "EPA Risk Assessment Forum SpecialReport oil Ingested InorganicArsenic: Skin Cancer: NutritionalEssentiality,"EPA, July 1980. As previouslypointed out by the State, a concentrationrepresentativeof a 10-r'risk level would be .023 ugll (State Comments oil DraftARARs for the NWBS Long-Term Improvements IRA, submitted 03106191) which is two ordersof magnitude lower than the CRL. Therefore, for this compound, a lower detection limit andPRG is appropriate. Response Response to Comment d) i. - Secondary drinking water standards are nonenforceable standards and are not ARARs. Response to Comment d) ii. - The ARARs analysis presented in Appendix A of Volume V11 describes the ARARs selection process and the treatment of the CBSGs. Based on language presented in the CBSG Statement of Basis and Purpose and on EPA guidance, the CBSGs are not ARARs.

11788,903 - CR-03 0504112092 VIII - 38Response to Comment d) iii. - CDH has referred to previous documentation provided by the Army regarding the Army's CRLs as compared to other detection limits. Response to Comment d) iv. - See response to Comment d) iii presented above. Response to Comment d) v. - See response to Comment d) iii presented above.

Comment No. 2 - Use of Groundwater Model The Army's responses to comments on the development, use, and reportingof the groundwater model fail to address the State's concerns regardingthe absenceof calibrationof the transportmodel, the absence of sensitivity analysesto quantify the model's uncertainties,the omission ofthe unconfined portion of the Denver Formation,and thepoorpresentationofthe results (no spatialpresentationof plumes at different points in time, and no analysisof the removal rates ofcontaminantmass as a function of each simulated remedy). We, therefore,can have no confidence in the modeled results or in the Army's interpretationof the results:nor are we assuredthat the optimal injectionl extraction well locations were even considered. The Army's response was, in essence, that the model was only to be used to estimate the relative effectiveness of the various remedial alternativesand that a rigorousmodeling exercise was not justifiedat this time. The Army further implied that a rigorousmodeling exercise is only warrantedwhen data are obtainedfrom the performancemonitoring of the installed remedy. A model is useful duringperformancemonitoring to updatepredictionson the installedremedy's ability to achieve goals within an acceptabletimeframe; however, now is the timefor a good, sound modeling exercise,before spending millions ofdollars on an inappropriate remedy, andbefore rej .ech. ng more aggressi .ve and effective remedies on the basis ofprojected initial capitaloutlay. Rest)onse Calibration of the transport models would require a large amount of data that is not available for the systems studied in the Offpost OU. Specifically, data that would be required include hydraulic heads near the likely sources of contamination at RMA during and soon after the years that contamination occurred and historical information regarding plume configuration as a function of time, covering the period commencing with the years that contamination occurred. The groundwater flow models have been approximately calibrated to time-averaged conditions during the 1980s, long after the major hydraulic effects of recharge in Basins A through F had occurred. This fact is what permits the flow model to be based on hydraulic conditions observed in recent years. The lack of comprehensive head data before the 1980s severely limits the possibility of viable transport model calibration. For sensitivity analyses to be performed effectively, the sensitivities of selected parameters, such as hydraulic heads, to model parameters, such as hydraulic conductivities, should be calculated directly using the calibrated flow model. These sensitivities would be optimally determined through simultaneous application of automatic calibration techniques. As stated in Volume VII, Appendix E, the FS models were intended to be only approximate and, consequently, were not calibrated with an automatic inverse technique. The Army reconfirms that the groundwater modeling effort conducted is fully sufficient for purposes of analyzing the relative differences between competing groundwater alternatives. As stated in Volume VI, Section 5.2, significant effort has been expended to produce models that incorporate general features of groundwater flow and associated transport phenomena. Nonetheless, the models are sufficiently detailed that predicted flow and chemical transport phenomena in the Offpost OU agree with historical and current hydrogeologic data and observed contaminant distributions.

11788,903 - CR-03 0504112092 VIII - 39Maximum concentration versus time plots was used because this approach gives a conservative estimate of remediation timeframes. The location of selected points used at each time step in the graph reflects the maximum concentration observed within the entire model area. Selection of the point with maximum groundwater contamination assures that remediation timeframe estimates are based on a time when no point within the model area exceeds PRGs. This method is fully capable of comparing the relative effectiveness of remedial alternatives, which is the intent of the groundwater modeling.

Comment No. 3 - Use of Cost Analysis to Eliminate Alternatives The Army's selection of no additionalremediationother than the currentlyplanned IRA intercept system is not sufficientlyjustified in accordancewith the selection criteriain the NCP and CERCLA. The improper relianceon land use projections,the inappropriate analysisof cost effectiveness, and the utilizationof an inadequatemodel result in violationsof these cleanup prescriptions. The land, use and model issues have been addressedin comments Ic and 2 above. The State has several concerns with theArmy's elimination ofalternativesbased on time andcost considerations. Forexample,N-6 andN-5 were eliminated because they would requiregreater initialcapitaloutlay than the selected alternative. This decisionfailed to consider thefact that the rejected alternativeswould be moreprotective ofthe environment,providefor a shorterremedialion timeframe, andbe equally or more cost effective in the long term than the selected alternative. To emphasize short over long term costs in such a manner is not in accordancewith the NCP. In fact, the EPA specifically eliminated language requiringsuch an analysis from its proposedrule. (55 Fed.Reg. 8728-29). In doing so, the EPA found such an analysis "too narrow"andnot reflective of overall effectiveness which "involves a composite of effectivenessfactors, i.e. long term effectiveness andpermanence, toxicity, mobility or volume reductionthrough treatmentand short tern? effect iveness. " Id. Thus, the Army's elimination ofalternativeN-6 based on increased capital costs when the totalpresent worth costs are "essentiallyequivalent" to alternativeN-5, and the eliminationof alternativeN-5 for which totalpresent worth costs are actually less than the selected alternative,contravenesthe NCP and CERCLA prescriptionsto utilizepermanent treatment solutionsto the maximum extent possible andbe cost effective. NW-4, an alternativewhich would provide substantialimprovements to the Northwest Boundar , y ContainmentSystem (NWBCS), was also eliminatedbased on projected remediationtimeframes which, by the Army's own admission, were inherently uncertain. Byfailing to construct a reasonabl * v reliablemodel at this time. the Army is precludingits ability to perform an accurateand objective cost- effectiveness analYsis in accordancewith CERCLA and the NCP. Response CDH has misinterpreted the analysis of groundwater alternatives presented in Sections 4.0, 5.0, and 6.0, in Volume V1. As presented in these sections of the FS, the analysis and comparison of remedial groundwater alternatives focuses on effectiveness, implementability, remedial timeframes, reduction of toxicity, mobility and volume, compliance with ARARs, overall protection of human health and the environment, and cost considerations. The alternatives studied present a wide range of levels of complexity in terms of remedial components, total flow rate from extraction wells, total numbers of recharge trenches, total linear feet of recharge trenches, and selected location of remedial components with respect to observed plume distribution. The Army strongly disagrees with EPA's contention that an aggressive groundwater alternative was not evaluated in the Offpost FS. As discussed in Volume VI, Section 3.0, Development of Remedial Alternatives, and Volume VI, Section 6.0, Detailed Analysis of Remedial Alternatives,

11788,903 - CR-03 0504112092 VIII - 40the offpost geology, hydrogeologic systems, contaminant distribution, and contaminant transport properties were studied extensively, both analytically and using a groundwater numeric model. The modeling effort is described in both Volume VI, Section 3.0 in terms of development of remedial alternatives and extensively in Appendix E of Volume VII. The results of this analysis are presented in a lengthy discussion in Volume VI, Section 3.0. The controlling hydrogeologic and contaminant transport properties of the Offpost OU groundwater system include (1) groundwater seepage velocity of the First Creek pathway relative to the northern pathway, (2) the distribution of the relatively less mobile compound dieldrin compared to the distribution of more mobile compounds such as DIMP and chloroform, and (3) the controlling transport properties of dieldrin as compared to the transport properties of DIMP and chloroform. As described in Volume VI, Section 3.0, Alternative No. N-4 for the North Plume Group was developed through a combination of analytical well field simulation, knowledge of contaminant distribution and contaminant transport properties, and hydrogeology of the North Plume Group. A transverse capture system for the northern pathway was chosen to intercept contaminants moving in the northern pathway. An axial system of collection wells and recharge trenches was selected in the First Creek pathway. Alternative No. N-4 consists of a total of 17 walls and 6 trenches with a total extraction flow rate of approximately 480 gpm. Alternative No. N-5 has a total of 20 extraction wells and 12 trenches. Alternative No. N-6 has a total of 4 extraction wells and 19 trenches. The total linear feet of recharge trenches ranges from 1500 feet in Alternative No. N-4 to approximately 4400 feet in Alternative No. N-6. The total extraction flow rate ranges from 480 gpm in Alternative No. N-4 to a total of 690 gpm in Alternative No. N-6. The increasing complexity of Alternative Nos. N-5 and N-6 as compared to Alternative No. N-4 was evaluated to assess the impact of adding a number of additional extraction and recharge trenches in areas where contaminants were remaining in areas of slower relative groundwater velocity and tighter aquifer materials, and to address less mobile contaminants. The level of aggressiveness of Alternative Nos. N-5 and N-6 reached a practical maximum whereby the maximum practical number of additional extraction wells and recharge trenches was evaluated for remediation timeframe and aquifer drawdown considerations. Model-estimated groundwater mounding and drawdown resulting from the recharge trenches and extraction well arrays reached practical limits in Alternative Nos. N-5 and N-6. The discussion presented in Volume VI, Section 3.0 gives specific information demonstrating the distinct differences in level of complexity and aggressiveness of the remedial alternatives studied in the EA/FS. The Army has not used short-term cost as a basis for rejection of Alternative Nos. N-5 and N-6. As discussed in Volume VI, Section 5.0 and 6.0, the primary reasons for selecting Alternative No. N-4 over Alternative Nos. N-5 and N-6 are summarized below. With respect to longterm effectiveness and permanence, these alternatives are essentially equivalent. All the alternatives would reduce hypothetical risk and address exposure pathways through reducing COC concentrations in the North Plume Group. Due to inherent uncertainties in groundwater modeling, predicted differences between treatment alternatives in the time to achieve PRGs may not be significant. With respect to reduction in toxicity, mobility, and volume, all the alternatives would reduce the toxicity, mobility, and volume of contaminated groundwater through extraction, treatment, and recharge in the North Plume Group. As stated previously, the uncertainty associated with the remediation timeframes estimated by the groundwater modeling suggests that, in practical terms, the estimated timeframes for the alternatives are equivalent.

11788,903 - CR-03 0504112092 VIII - 41With respect to overall protection to human health and the environment, all the alternatives would provide significant protection of human health and the environment by decreasing contaminant concentrations and reducing hypothetical risks within the same approximate time. These alternatives are essentially equivalent with respect to providing protection of human health and the environment because the short-term intensive groundwater monitoring program proposed under Alternative No. N-4 would provide full-scale system performance information that could be used to identify any necessary or beneficial improvements to the system and to provide information on optimal location of these additional systems. See response to CDH Comment No. 3 Parts I and 2, above for information on evaluation of alternatives. Sections 4.0, 5.0, and 6.0 in Volume VI of the FS present information concerning the relative differences between Alternatives Nos. NW-2 and NW-4. As stated previously, the groundwater model is fully capable of analyzing relative differences between competing alternatives. See responses to Parts 1, 2,,and 3 of Comment No. 3, above.

Comment No. 4 - Selection of the N-4 Alternative The State cannot agree that N-4 is superiorto N-5 becauseN-4's short-term intensive monitoring will "...identify any necessary improvements to the system..." andbecause "[u]ncertainties inherent in the groundwatermodeling results make the predictionof remediationtimes imprecise." (Section 5.5.1.1). Short-termperformancemonitoring should logicallybe a partof any remedy to accomplish thefirst goal statedabove. The short term monitoringprogramproposedby the Army (See DraftFinalMonitoringPlanfor the Groundwater Intercept and Treatment System North of the RMA, IRA, February,1992) should also apply to all ofthe alternativesselectedfor evaluation. The State has submitted comments addressingthe proposed monitoringplan and incorporatesits comments by reference (See CDH Letterfrom Edson to Blose, March4, 1992). The Army's second reason (as stated above) for not selecting remedies more aggressive thanN-4 is inconsistent with their response that more aggressiveremediesfor the DIMPplume along First Creek and the dieldrinplume along the NorthernPathway are not neededbecause the model predictsthat PRGs will be achieved it? 5 to 15 years and 30 years, respectively. Eitherthe predicted remedial timeframes are reliableor they are not. The State agrees with theformula statement that acknowledges that the actualtimeframesfor remediationare unknown. Simple logic, however, suggests that a more aggressiveremedy along the plume's axis (N-5 and N-6) will remediatethe plumefaster andtherefore would be a more desirablealternative. In addition,although the Army adopts 2.35 ugll as its PRGfor arsenic,it is not clearthat the selected remedial alternativewill achieve this level. Plume maps indicatedetections ofarsenic along the First Creekpathway exceeding the PRG: however, the chosen carbonfiltrationtreatment technology does not treat arsenic. As arsenicis a major contributorto the carcinogenicrisk posed by exposure to this groundwater,treatmentalternatives for arsenicmust be addedto the design of the treatment facility. Resr)onse See response to CDH Comment No. 3, above. See response to CDH Comment No. 3, above.

11788,903 - CR-03 0504112092 VIII - 42Estimation of anticipated influent concentrations of contaminants for the alternatives studied in the Offpost FS indicate that the PRG for arsenic will not be exceeded in the influent to a treatment plant.

Comment No. 5 - Preferred Alternative for the Northern Plume As stated in ourprevious comments, the preferredalternative for the NorthernPlume ignores current and forecasted land use in an area that will contain contaminatedwater exceeding ARARs. The areathe plume migrates through is, accordingto the Army's current andforecasted land use maps, subject to residential use. (See Volume V, Figures2.4.5.5-1 "Offpost OperableUnit CurrentLand Use Map, 1991": and 2.4.1-2 "Offpost Operable Unit FutureLand Use" andthe corresponding residentialzoning designations for section 13). rhus,use of the unconfined alluvialaquiferas a source ofdomestic water is a reasonable possibility. ro suggest, as the Army has in its response to the Stale's concern, that rapidrestorationis unnecessary because contaminatedwaler is not now used as a drinking watersource, and becausepotential future users would be put on alternative water supplies, ignores the prescriptionofthe NCP which requiresthe rapidrestorationof current andpotentialdrinking watersources. (55 Fed.Reg. 8732). Alternatives that would address groundwaterremediationwithin the plume migrationareashould be considered. Response The preferred alternative for the Northern Plume Group is fully consistent with the most likely future land use scenario presented in the Offpost EA/FS. The most likely future land use scenario is rural residential for zones 1, 2, and 6; urban residential for zones 3 and 4; and commercial/ industrial in zone 5. As stated previously in Sections 4.0, 5.0, and 6.0 in Volume VII and in response to Comment Nos. 2 and 3 above, Alternative No. N-4 is demonstrably superior to Alternative No. N-5.

Comment No. 6 - Ot)erable Unit Areas Not Included in EA/FS Evaluations rhe Army's response to concerns that a significant portion of the Offpost OU areawas not evaluated in the EAIFS was to state that the remainingareas "were not determined to be affected by RMA relatedcontamination"despite thefact that the Offpost OU "asdescribedin the Federal FacilityAgreement (FFA), is where hazardoussubstances,pollutants,or contaminants from RMA are located" (Arm), responses to CDH Cover Letter Comment No. 3, EPA Cover Letter Comment No. 7, and EPA GeneralComment No. 1). rheArmy alsopointed out that concentrat ions detected in these areas were less than one halfofthe dieldrinPRGs. No informationhas been included in the EAIFS (or in the Offpost RI Addendum) discussing or interpretingthe existing data to determine the source of contamination. rheArmy needs to document why it is excludingfrom the EAIFS process nearlyone halfof the Offpost OU area. An analysismust be suppliedfor those areas outside ofzones I through 6, particularlywhere the cumulative risksfrom RMA contaminantsexceed a 10-6 risk level. Such a presentationis necessary before the State could concur with such conclusions. The Arrnv's dismissal ofdieldrindetections identifiedby the State oil the grounds that they do not exceed týe Army's PRG ignores thefact thatPRGs are supposed to be developed basedoil a 10-6 point of departure. No justification for deviatingfrom the point of departureis offered: therefore, remedial alternativesmust be developed to achieve this risk level in these areas.

11788,903 - CR-03 0504112092 VIII - 43

### Resoonse The Offpost EA/FS divides the OU into six zones. These zones were delineated on the basis of the known extent of contamination as presented in the Offpost OU RI Addendum report. Section 2.4.1 in Volume II of the EA describes in detail the rationale and the database evaluated in delineating the zones to be studied in the Offpost EA/FS. Each of these zones was delineated on the basis of distinctions in exposure conditions. The primary factor used to define the zones was a pattern of COC concentrations in groundwater. In addition, the spatial pattern of COCs in surficial soil was also used to set zone boundaries. A broad area extending from the north and northwest boundaries of RMA to the South Platte River exhibits varying levels of COCs. The maximum downgradient extent of this contamination area is defined primarily by low levels of DIMP (i.e., DIMP in excess of CRLs). The existing contaminate distribution in groundwater, surface water, and surficial soil, as well as differences in land and water use were considered in mapping six zones where exposures are expected to be distinct from each other. The outermost boundary defining the six zones is the extent of known contamination associated with RMA, which is defined as the,Offpost OU by the Federal Facility Agreement. In response to CDH's contention that no information has been included in the EA/FS discussing or interpreting the existing data to determine the source of contamination, CDH is referred to Section 1.0 of Volume I for an extensive four-page discussion detailing the conceptual site model that delineates the source of contamination to the Offpost OU in groundwater, surface water, soil, and air. With respect to CDH's comment regarding the aldrin detections, CDH is referred to Section 2.2, which discusses the Offpost OU cumulative risk and risk corresponding to individual media as compared to the NCP-prescribed acceptable risk range. This section of the text describes in detail the rationale for elimination of the soil medium as requiring development of remedial action objectives.

Comment No. 7 - Statistical "Hot Soot" Analysis In its responses to comments, the Army refers to an "additional analysis"that was performed regardinglocalized "hot spots" of carcinogenicrisk. A more complete explanationof this analysis is needed in orderto understandthe Army's decision-makingprocess with respect to the elimination of "hot spots". This explanationshould includethe specifics ofthose areaswhich were ranked accordingto the highesthot spot potential including well identification,soil boringnumbers, the spatialdistancesbetween these sample locations,the maximum concentrationsin comparisonto the exposurepoint concentrations, and a calculationofthe upper boundaggregaterisk at the subsite. Because residentialexposure can be of long durationover a very localizedarea,results ofan analysissuch as the one performed in responseto the EPA comment are important to an understandingofpotentialexposure. The Army has commented to EPA that "[r]isksat localized 'hot spots' within zones 2 and 3 are less than 2 x 10-3". The State requests that the information which has led to this conclusion be included in the document and that the results ofthis evaluation for all zones be describedin the Finalversion ofthe EAIFS. Rest)onse The "additional analysis" referred to is summarized in the response to EPA General Comment No. I (March 27, 1992, Volume VIII). The analysis performed at that time is no longer pertinent to the offpost exposure assessment, however, because the data set used for the assessment has been revised to include only groundwater data collected from 1989 to 1991, and the previous analysis was based on older data (1985 to 1990). Further, it has been discovered that some groundwater 11788,903 - CR-03 0504112092 VIII - 44REFERENCE PAGE FOR 93012RO3 CDH - PAGES 46 THROUGH 5ZARE NOT INCLUDED IN THE DOCUMENT.wells used in that analysis and identified as "hot spots" for zone 3 are actually south of 96th Avenue and not offpost. Our previous analysis provides general support for the conclusion that localized hot spots would not result in individual risks exceeding zone-RME estimates by more than a factor of 2. As described previously in response to CDH General Comment No. 1, a comparison of cumulative Offpost OU hypothetical cancer risks with the acceptable risk range is presented in detail in Volume V, Section 2.2. The cumulative Offpost OU cancer risk is a maximum of 3 x 10-4. Volume V, Section 2.2 also presents several site-specific factors that suggest remediation of groundwater is preferable to no action in the Offpost OU even considering that the accumulative Offpost OU cancer risk is within the acceptable risk range. Additionally, the above -referenced section of the FS presents information supporting the conclusion that soil, surface water, and sediment media do not require development of remedial action goals because the risk corresponding to these media is low. Because the analysis and calculation of risk performed in the EA fully considered localized high concentration (hot spots) of contaminants in soil, any additional analysis of risk corresponding specifically to hot spots is not necessary. The dispute resolution process resulted in agreement by the Organizations on the most likely future land use scenarios to be used in the EA. Because the exposure scenarios evaluated in the EA are different from the exposure scenarios commented on by CDH, this comment is no longer relevant. Comment No. 8 - Environmental Remedial Action Obiectives The Army still has not identifiedany remedialaction objectives nor developed remedial alternatives that are designedto protect the environment as a receptor in and of itself. In its response to the State's comment, the Army slates that biota ("all plants and animalspotentially exposed to Offpost OU contaminants") was consideredin the development ofRAOs and that "environmental receptors"were also consideredin the evaluation ofcertainpathways. (Army response to CDH Cover Letter Comment No. 5). This response ignores the substance ofthe State's comment. To reiterate,the requirementthat remedies protect the environment, as well as human health is made very clear in CERCLA §121(d)(1) andthe NCP (40 C.F.R. §§ 300.430 §§ (a)(]) and (e)(2)(i)(G)). The plain language of CERCLA §101(8)(B) is equally clear in its definition ofthe term "environment" (which includes "surfacewater, groundwater,drinking water supply, land surface or subsurfacestrataor ambient air"). Thus, the EAIFS must include a consideration of measures which areprotective of the environment as defined by CERCLA. These receptorsshould, at a rninin7um, include.-

a. The surface water medium. Variationsin seasonal surface waterflow in the FirstCreek drainage indicatethat surface water runoff is likely to be contaminated fro"? Onpost and Offpost contaminants. A remedialalternativeshould be developed to addressthis medium as a receptorof contamination. b. The groundwatermedium. There are still no remedialalternativesthat address the existing orpotentialcross contaminationamong the Alluvial, Denver andArapahoe aquifers. Although the Army has invited the State to submit a list of wellsfor closure in the offpost well closureIRA, it has not been receptive to the State'sproposals. (See August 2, 1991 Edson (by O'Grady) to Blose letter, re: Criteria for Offpost Abandonment Wells IRA). There are also no alternativeswhich protect the alluvialaquifernorth of the North Boundary ContainmentSystem (NBCS) through section 13 to O'BrianCanal. This areawill contain groundwaterexceeding ARARs migratingnorthfrom the NBCS. The State will submit under separatecover a list of wells that should be closed to protect the lower aquifersfrom furtherdegradation.

11788,903 - CR-03 0504112092 V111 - 53Response Remedial action objectives developed for the Offpost OU consider both human health and protection of the environment. As described in the response to CDH general comment No. 1, remedial action objectives were not developed explicitly for the soil, surface water, and sediment media. However, as described in Sections 5.1 through 5.4 in Volume II, a rigorous ecological assessment was performed, including the following components: I. Exposure assessment for biological receptors and sensitive subpopulations included, a risk characterization for both terrestrial food web ecological risk and aquatic food web ecological risk, and an ecological risk assessment uncertainty analysis. The results of this analysis were used in the derivation of ecological criteria presented in Volume 11, Appendix C, derivation of Health Based Criteria Ecological Criteria. Data collected in the RI Addendum to characterize Offpost OU surface water in the First Creek drainage and surface-water bodies leading to Barr Lake are representative of seasonal changes to be expected in surface-water flow. As stated in the text of the EA/FS, no remedial action objectives were developed for surface water medium because neither the human health risk nor the ecological risk corresponding to this medium warranted remediation. Data collected during the Offpost RI Addendum program included groundwater samples from 14 offpost confined Denver Formation wells in the Offpost OU. Additionally, information concerning the confined Denver Formation groundwater is presented in Section 3.3.2 of the Final Offpost RI report. As discussed in Volume I, Introduction to the EA/FS, subheading Nature and Extent of Confined Denver Formation Contamination, data were examined from fall 1989 and spring 1991 sampling rounds. Analysis of the data indicated that the detections were not consistent from one sampling event to the next for the same well. The observed detections are indicative of sporadic, isolated occurrences of contaminants in the Offpost OU confined Denver Formation. A similar analysis of available data was performed for the confined Arapahoe Formation. Approximately 30 Arapahoe Formation wells were sampled by the Army with two isolated detections of DIMP and chloroform observed. A majority of samples collected from the Arapahoe Formation did not contain detectable concentrations of contaminant.

Comment No. 9 - Surface Water in First Creek Several State comments were presentedto the Army concerningthe exclusion of surface waterfrom the FS. The Army has not respondedto these comments salisfactoril ' y. The selected remedial alternativedepends on the validity of the assumptionthat PRGs will not be exceeded at the boundariesofRMA. However, theArmy's data call this conclusion into question. The Army concludesfrom four sampling events at the north boundary ofRMA at site (SW24002) that it is in compliance with PRGs. However, these samples, which apparentlyare not representativeof storm events, are totally inadequate for the characterization of a surface waterflow which is highly variableboth in quantity and in quality. The State's FS General Comment No. 17 quotesfrom the R1 stating that chemical concentrationsin FirstCreek are significantlyhigherduring storm events. The Army's response to the State's FS GeneralComment No. 7, similarlystates that "[tjhe secondarysource ofsurface water in FirstCreek offpost is watershed runoff." These Iwo statements indicatethat contaminatedsurface water will enter the offpost OU duringstorm events. This contaminationwill not be addressedby upgradingor closing the sewage treatmentplant. Therefore, additionalmeans of verifying that surface waterPRGs will be met at the RMA north boundary must be provided by the Army.

11788,903 - CR-03 0504112092 VIII - 54Response Surface water was not identified as a medium requiring development of remedial action objectives because the risk corresponding to surface water is 5 x 10-7 . Refer to Section 2.2 in Volume V of the FS and response to CDH general comment No. I for additional information concerning comparison of Offpost OU cumulative cancer risk to the acceptable risk range and discussion of individual media risk. The Army disagrees with CDH's assumption that surface-water data collected is inadequate for characterization of Offpost OU surface water. Data were collected in the Offpost RI Addendum program from offpost surface water in 1988, from two periods in 1990, and from the 1988 and 1989 surface-water comprehensive monitoring program annual report. Sufficient data from Offpost OU surface-water sampling plans was available for characterization of Offpost OU surface water.

Comment No. 10 - Treatment of Chloroform in the NBCS and NWBCS The groundwatertreatmentsystem at the NBCS appearsto effectively remove chloroformfrom its influent; however, the treatmentsystem at the NWBCS does not. The State requeststhat an evaluationbe performed of the two systems to determine what changes are needed to effectively remove chloroformfrom the NWBCS's influent, and to ensure that the proposedoffpost IRA treatmentfacility is operatedso as to effectively remove chloroform. Response The preferred alternative presented in Section 6.0, Volume V for the North Plume Group and the Northwest Plume Group has continued operation of the boundary containment system with modification as necessary to achieve PRGs at the boundary as a major component of the alternative. Additionally, Alternative No. N-4 contains a provision for modification to be made to the IRA A system in the future in the event that PRGs are not being met.

Comment No. II - EA: Human Health Soil Ingestion Data As previouslypointed out in State comments on the onpost soil ingestionparametervalues, there is currentlya great deal of scientific discussion regardingthe interpretationand useabilityof existing soil ingestion data. In recentlypublished articles,Drs. EdwardJ. Calabreseand EdwardStanek, throughthe use ofa precisionof recovery model developed at the UniversityofMassachusetts, demonstratedthat only titaniumand zirconium valuesfrom theirAmherst study could be considered reliable. Resultsfrom other studies were invalidatedby this model. Lately, týe reliabilityof the zirconium values have been called into question due to probable loss during chemical analyses. As a result, new soil ingestion valuesfor childrenare consideredappropriate.Based on the most reliable datafrom the use of titanium as a tracer,the median valuefrom the Amherst study would be 55 niglkglday,- the 951h percent value would be approximately1500 mglkglday. An upper 95th percent value based upon all tracersweighted accordingto their respectiveprecision of recovery, (not includingzirconium), would be approximately640 mglkglday. The Slate again urges the Army to avail itselfof the expertise ofDr. Calabresewho is willing to meet with the partiesto discuss appropriate soil ingestionestimates. Rest)onse The Army has applied RME soil ingestion rates recommended by EPA for CERCLA baseline risk assessments. The Army understands that "there is currently a great deal of scientific discussions

11788,903 - CR-03 0504112092 VIII - 55regarding the interpretation and useability of existing soil ingestion data." It is the Army's understanding that the thrust of Calabrese's research is that existing studies, including his own 1989 research, have significant design flaws such that the studies do not have sufficient sensitivity to detect and/or quantify the rate of soil ingestion for most of the study subjects. Based on Calabrese's concerns, the Army rejected the ingestion rates suggested by CDH because they are insufficiently supported. Calabrese's research may be able to support the conclusion that soil ingestion rates are "less than" some value but not to determine the actual ingestion rate. Further, the published results from all these studies do not provide sufficient detail to define the distribution of ingestion rates and thus, the 90th or 95th percentiles. Calabrese's recent papers focus on the central tendency of the distribution, such as means or medians, because these statistics are more reliably estimated from the available studies. Although suffering from the same flaws identified here, the Army's review of Calabrese and others (1989) and Davis and others (1990) indicates a 90th percentile of 225 mg/day for children, similar to EPA's recommended RME. The considerable debate and uncertainty regarding quantification of soil ingestion rates indicate that EPA guidance specific to CERCLA assessments is the most reliable and authoritative source for this exposure parameter.

Comment No. 12 - EA: Soil to Epm Partitioning Coefficient rhe State specifically requested clarification from theArm' y regardingderivationof the soil to egg partitioningcoefficient (Human HealthEndangermentAssessment general comment number29, page 27). While the Army did respond to this comment, it never supplied information detailinghow Kee was derivedfrom the results in the Putnampaper. rheArmy's RME value of.087 would appearto be about an order ofmagnitude too low based on thefollowing evaluation. Putnamaddedpesticidesto soil so that the "Low level soil" of aldrin+ dieldrinwas 0.068 ppm. After exposure to these soils, the resulting concentrationof dieldrin in bird tissue was 0.037 ppm. If assumptions derivedfrom Putnamare used (i.e. that aldrinwas completely converted to dieldrin, egg and tissue concentrationsare equivalent, andno adjustment for control treatment concentrations is made), a rough estimate of Kee may be derivedas the ratioof soil to bird concentrations, 0.03710.068 = 0.54. rhis i . s approximatelyan orderof magnitude largerthan the Army's RME valuefor Kee, rhe State requests that the Army demonstratehow they derived their value and distribution for Kee, what qualifying assumptionswere made, andexplain why the number was changedfrorn the one give in earlier EA technical meeting handouts. Absent such information, the Stale cannot assess the validity ofthe Army's methodology or have any confidence in the values derived. Remonse Terms: Kee = concentration in epgs concentration in soil fps = ration of soil ingestion to feed ingestion Kpc = concentration in eggs concentration in feed if = ingestion of feed

11788,903 - CR-03 0504112092 VIII - 56--------------

19 = ingestion of grain is - ingestion of soil Cf = concentration in feed C9 = concentration in grain Cs = concentration in soil Ce = concentration in egg

If = 1 19

+ Is (1)

Cf = 19 C9 + Is CS (2) if if

Cf = 19 C9 + Is Cs (3) Then 19 + Is

From Putnam, it is calculated that fps Is 3.1% 1.2 Ig

Then Ig >> I. and (3) reduces to Cf = C9 + Is Cs (4) 19

Then (4) becomes Cf = 1. C. - fps CS (5) 19 By definition KpC = Ce/Cf (6) Substituting for Cf (from [5]) into (6) KpC Ce (7) fps Ca 11788,903 - CR-03 0504112092 VIII 57Thus Kee ý Ce =fps Kpc (8) Ce Kpc is calculated from BAF values 1.13 Cummings and others, 1966 1.5 Kan & Jonker-den Rooyen, 1978a 2.5 Driver and others, 1977 1.67 Graves and others, 1969 1.35 Waldon & Nabor, 1974 1.18 Kan & Jonker-den Rooyen, 1978b 1.67 Kan & Turinstra, 1976

Thus Kpc = 1.57 + 0.17

Kee = (1.57)(0.031 = Kpc fps

= 0.049 To find RME:

(,I Kee 2 Kpc ) 2= (,, fps ) 2

Kee Kpc f ps

8Kse 0.049 (0.17 2 + 0.012 2 1/2

1 ý1 5-7 10.031

0.020

RME = 0.049 = ZOA * 0.02 = 0.049 x 1.96(0.02)

= 0.087 Using this simple ratio of 0.54 for K. from Putnam and others (1974) one is limited to soil ingestion only when in reality there a;e other pathways of concern. The derivations that follow lead to an RMA value of 0.087 for Kse5 which accounts for the grain ingestion pathway plus the incidental soil ingestion pathway.

11788,903 - CR-03 0504112092 Vill - 58Comment No. 13 - Samr)ling of Deever Aauifers In the Army's Response to General Comment No. 7, it refers to various samplingprogramsto assert that the deeperaquifers have been sufficiently evaluated. The State is aware ofthe ArmylTriCounty Health Departmentdomestic samplingprograminitiatedlastyear. While we arepleased with the Army's decision to monitor domestic use of contaminatedgroundwater, we were never informed by the Army that the domestic use programwould be used to characterize Denverl Arapahoeaquifercontamination. When the State was asked to comment on the Army's domestic well samplingplan we were asked to identify residences which appearedto be within contaminant plumes that had not been sampledpreviously, not to identify locations where sampling should be performed to characterize DenverlArapahoecontamination. In addition,it has always been the contention ofthe Army that characterizationofany ground water plumes cannot be achieved through sampling ofdomestic wells. The State's domestic well sampling program was implemented to identify whether contamination(i.e.; DIMP) exists in the deeper aquifers. Based upon our results. we had anticipatedan Army-initiatedmonitoring well network to be installedto better characterize Arapahoe contamination. As was agreedto by allpartiesyears ago,because ofthe largescreen intervalsassociatedwith domestic wells, their use in defining contamination plumes is inappropriate. The State therefore reiteratesits concerns that the deeper aquifersbeneath the offpost operable unit have not ben adequately investigatedand inappropriately omittedfrom the EAIFS programs. Response The Army disagrees with CDH's contentions that deeper aquifers beneath the Offpost OU have not been adequately investigated. Based on a substantial amount of both confined Denver Formation and confined Arapahoe Formation well data, the isolated detections observed are sporadic and not indicative of deep aquifer contamination. Refer to CDH comment No. 8B for more information on the aquifer characterization.

Comment No. 14 - Surface Water PRG Exceedance In the response to CDH CoverLeiter Comment No. 1, the Army states that there is no risk attributable to sediment and surface water in zones otherthan 3 and 4. However, the MaY-June 1990 surface watersampling at Station HAII59SE in Section 12, O'BrianCanal(in zone 2), indicated exceedances of the commerciallindustrialPRGs developedfor zones 3 and4 for DDT andDDE. The exceedancesfor these two compounds are not shown on Figure2.5.3-1 of Volume V (Exceedances of Surface Water PRGs in the Offpost Operable Unit), and are exceedances of surface water PRGs in the Offpost OU. Pleaseexplain this omissionand why risks associatedwith these exceedances were not consideredor mentioned in the text. Remonse Refer to CDH comment No. 9. Section 2.2 and Volume V of the FS present risk corresponding to the soil medium and rationale for concluding that the soil medium does not require development of remedial action objectives. Refer to response to CDH general comment No. I and Section 2.2 in Volume V for additional information.

Comment No. 15 - Aldrin/Dieldrin Soil HBCs The Health Based Soil Criterialisted in Table 2.4.5-1for aldrinand dieldrin underthe Rural ResidentialScenarioare 31 ppb and 0.5 ppb, respectively. Even if the exposures to these analytes

11788,903 - CR-03 0504112092 VIII - 59are due to secondarysources,the values should be similar. Given the very similarchemical and toxicologicalpropertiesofthese two compounds, such divergent criteria(by severalorder of magnitude) indicate aflow in the derivation ofthese values. The State requests that the Army review its methodology with regardto the soil criteria for these two compounds. Rewonse

ECOLOGICAL RISK CHARACTERIZATION (ERC) COMMENTS Comment No. I - Volume VIII. vage 45, Resvonse to ERC General Comment No. 4 The Army assertsthat lower trophic level animals will be protectedby selected TRVs and by the revised food web model. We have not yet had an opportunity to complete our review of the newfood web model, as it was only delivered to us on March 18, 1992. The TRVs, however, clearlydo not adequatelyaddressthe lower trophic levels. Some 87 TRVs have been derivedfor species that were selectedýased on the criteriasetforth in Vol. II, sec. 3.5.2 (p. 11-3-19). Neither this section nor Table 3.3.1-1 addressesTRVs for other than avianand mammalianspecies. No reptilian, amphibians,nor invertebrateand other lower orderspecies are included. Nor has the Army consideredchemical-specific ecosystem TRVs which would be inclusive of most species in an ecosystem regardlessof whether a species-specific TRV has been derived. The latterapproachhas been recommendedby van StraalenandDenneman, 1989 and Okkerman et al. 1991, andhas recently been accepted by Germany as thepreferredapproachto performingecological risk assessment. Rest)onse The Army has derived TRVs protective of lower trophic organisms as well as nonavian and nonmarnmalian species. These values are presented in Table 3.3.1 -1 as reference media concentrations for vegetation and aquatic organisms. Species -specific TRVs were not derived for reptiles, amphibian, or invertebrate species because of the general lack of chronic toxicity data for these animals. The Army also feels that its chemical/species-specific TRVs provide a more appropriate measure of potential adverse effects in the ecosystem than chemical -specific ecosystem TRVs suggested by CDH because of the Army's receptor specificity.

Comment No. 2 - Volume VIII. r)aRe 45. Rest)onse to ERC General Comment No. 5 The Army's assertionthat "ecotoxicity values do notpermit evaluation of multiple chemical exposures" is not consistent with a largebody ofinformation and recommendationspresentedby prestigiousnationaland international organizations,including the NationalAcademy ofSciences and the World Health Organization,as well as leading texts. Attached to these comments is a limited discussion andlisting ofhighly relevant documents which demonstratethe insupportability ofthe Army's ERCprogram. The text is takenfrom Calabrese: Multiple ChemicalInteractions (Lewis; 1991). Rest)onse Although Calabrese is to be commended for his efforts to publish one of the first comprehensive reviews on multiple chemical interactions, the test xeroxed by CDH may not be as applicable to the offpost ecological assessment as CDH would imply. The method described for aquatic ecosystems assumes simple toxicity additivity for chemicals unless proven otherwise. Other 11788,903 - CR-03 0504112092 VIII - 60interactions that are possible include antagonism, synergism, and potentiation. All are very different from additivity, yet no alternative methodology is presented. Also, by xeroxing the references from Chapter 23 of Calabrese's book and making the above comment, CDH implies that there is a tremendous amount of accepted scientific information on multiple chemical interactions. This is hardly the case, especially for ecological receptors. In fact, the study of multiple chemical interactions is in its infancy compared to other types of toxicological studies. Calabrese alludes to this in the opening chapters of his book and points out in Chapter 2 that "over the past two decades, considerable debate has occurred within the biostatistical/epidemiological, pharmacologic, and toxicological communities over the concept of interaction." Certainly, recommendations have been proposed on multiple chemical interaction methodology; however, because of its early investigative stages and lack of scientific consensus, acceptable guidance for use in ecological assessments is lacking.

Comment No. 3 - Volume VIII, t)aRe 45, Response to ERC General Comment No. 6 The Army's argument that the RMA ecosystem is probably in equilibrium,given the length of time that contaminantshave beenpresent at the site, misses the point of the State's comment. The critical question is not whether the environment as a whole is in steady-state,but ratherwhetherthe individualorganismsare in steady-state. This is a function not ofhow long the contaminanthas been in the ecosystem, but rather how long the organismhas been exposed to the contaminant,and how long it takesfor the contaminantto reach steady-state within the organism. This issue must be addressed. Resr)onse The Army understands that an organism can attain steady state if exposure and biological factors affecting the uptake and loss of a chemical remain constant for a sufficient length of time. However, the Army does not have sufficient data for an inclusive statement regarding steady-state conditions in the Offpost OU.

Comment No. 4 - Volume VIII. L)ape 46. Rest)onse to ERC General Comment No. 7 In response to the State's inquiry regardingthe intended relationshipbetween the TRVs and the MATissueCs, the Army has assertedthatMATissueCs "aremost usefulfor bioaccumulative chemicals andforfood sink species. TRVs are more usefulfor nonbioaccumulativechemicals and for lower trophic level species." Yet, TRVs areproposed for lop level predators for highly bioaccumulativechemicals such as organchlorine pesticides. Therefore, the Army's response has not clarifiedthe question, which is how will these values be used in arrivingat cleanup levels. Froma toxicological perspective, the MATissueCs and TRVs should be consistent. One should be derivable from the othergiven knowledge of appropriate toxicokineticfactors. Priorestimated MATissueCs were significantlygreaterthan those that would be predictedby converted TRVs. We have not had an opportunity to interconvertthe new TRVs ad MATissueCs. However, any inconsistency between the two values would undercut confidence in the'Army's methodology. Rest)onse The Army would be interested in reviewing CDH's methodology for interconverting TRVs and MATCs. The Army uses both MATCs and TRVs to derive ecological soil criteria (Volume VII, Appendix C of the FS).

11788,903 - CR-03 0504112092 VIII - 61Comment No. 5 - Volume Vill. page 46. Response to ERC General Comment No. 8 Thefood web model has now been calibratedwith onpost bioladata. The State hasformally objected to the use of the limited RMA data base to deviatefrom peer-reviewed literaturederived values. Specific comments on the new EcologicalRisk Characterization ("ERC") model and calibratedvalues could not be compiled in time to meet the Army's April 6, 1992 deadline;however, preliminaryreview has indicatedthat, for a variety ofreasons, including internalinconsistency and the lack of accord with availablescientific information, the proposedmodel and output cannot be reliedupon to predict ecosystem responsesto contaminants,anddoes not appropriatelyreflect maximum known exposure within the RMA ecosystem. The State intends to transmitdetailed comments on the ERC model by April 21 in accordancewith the Army's request. Since the offpost values are derivedfrom the ERC model, the Statecannot supportthose values at this time. Response Refer to response to USFWS Comments No. I and No. 2.

Comment No. 6 - Volume VIII. vage 46. Rest)onse to ERC MATissueC Comment No. I The Army, in defending its sink species methodology, has attemptedto avoid its own obligationof proving the protectiveness of its approach,instead challenging the State toprove to the contrary. Such a shifting of the burdenofproofis contraryto the prescriptionsof CERCLA and the NCP which require the Presidentto demonstrateprotectivenessofthe environment as a thresholdcriterion for any remedy selected. The principal premise of the Army's ecologicalrisk assessmentmethod is that relianceon sink species viafood chain modeling will protect all otherspecies, including those species that may be inherentlymore sensitive than the sink species at a similarexposure. This premise assumes that the enhanced exposure in the sink species will more than compensate for any differentialsusceptibilily to the agents ofconcern. To determine the validity ofthis assumption,one must identify the degree of interspecies variation in susceptibilitythat one can expect if the intent is to protect all biota within the ecosystem. Differential susceptibilityat the ecosystem level has been inferentiallyaddressedby Slooff ei al. (1987) in their comparisonof35 species over 11 taxa. Their work involved a largeseries of binar ' v comparisonswhich estimate interspeciesdifferences in susceptibility. The results showed up to 100-fold interspeciesvariability for 60% of the comparisons,and up to 1000-fold variation for 90% of the comparisons. A considerationofpredictedtissue concentrations from the calibratedbiomagnificationvalues (BMF) (Vol. IV, Table H3, Page2 of 2, FirstCreek) reveal that the rangeof tissue concentrations for dieldrinwas 6.1-fold (algae to heron),DDT was 6.1-foldfor algae to the heron and 427.5-foldfor invertebratesto the heron;DDE was 1.8-foldfor the algae to bald eagle and 39.7-foldfor invertebrateto the bald eagle. In addition,the bald eagle was estimatedto bioaccumulate39.4-fold moreDDE, 29.6-fold more DDT, and 5.6-fold more dieldrinthan the smallfish; 22.6-fold more DDE and DDT, and6.0-fold more dieldrinthan the mallardduck; 19.1-fold more DDE, 13.8-fold more DDT, and 3.3-fold more dieldrin for the large fish. In the terrestrial food web (Table H2,page 2 of3) the variationin predictedtissue concentrations ofprairiedogs andthe greathornedowl were 6.2, 4.8, 3.1, and 50.9-fold,for DDE, DDT, dieldrin andendrin, respectively.

11788,903 - CR-03 0504112092 V111 - 62Regardlessofhow one estimates exposure, whether on a mglkgldose-rate basisor tissue concentrationbasis, the Army's existing data indicatethatthe premise of using sink species to compensate for interspeciesvariationin response to toxic substances may be seriouslyflawed. Rest)onse The Army stands by its original response and fails to see where CDH was challenged to prove otherwise. The data presented above simply illustrate the concept of bioaccumulation and biomagnification, and any other interpretation is conjecture.

Comment No. 7 - Volume V111. pape 47. Resr)onse to ERC MATissueC Comment No, 2 To clarify the Slate's ERC GeneralComment 2 regardingendpoint selectionfor biota criteria derivations, "legislative factors"which must be included in cleanupcriteriaare,for example, the requirementsof the EndangeredSpecies Act ("ESA"), the Bald EagleProtectionAct ("BEPA"), and the MigratingBird Treaty Act ("MBTA"). These Acts, as well as the case law construing them, variously define andprohibitharm and harassment. The MigratoryBird TreatyAct (16 U.S.C. § 703) is intended to "aidin the restorationofsuch birds... where [they] have become scarceor extinct." The MBTA, similarto the ESA and BEPA, protects individualbirds and their parts,nests, or eggs, by prohibitinghunting, taking,possession, killing, etc., ofprotectedspecies, except aspermittedby regulation(=, Cg, 50 C.F.R. pts. 20 & 21). Further,the purposes of the ESA, as setforth at 16 U.S.C. 1531(b), includeproviding "a means whereby the ecosi,stems upon which endangeredspecies and threatenedspecies depend may be conserved..." (emphasis added). Any manifestationofstatutory orjudiciallydefined harm must be consideredwhen selecting appropriate endpoints from which to derive action levels, so that these levels are sufficiently protective to prevent such harm to biota. We are disturbedby the Army's assertionthat the MigratoryBird Treaty Act does not require protectionof individualanimals. The purposeof that act is to "aidin the restorationof such birds... where [they] have became scarce or extinct." Legal interprelationin the courts (=, fg., U.S. v. Corbin FarmService, 444 F. Supp. 510 (1978)) supportsprotection of individualswithin a species. Selection ofaction levels that would kill, harm or take individuals(or parts or eggs) of coveredspecies would clearly contravene thepurposeof thatAct. Also, the Army is continuingto ignore the variabilityin endpoints used to deriveMATissueCs. The Arm), states in volume II, page 3-18, section 3.4, secondparagraph, that the MATC values "representtissue concentrationsthatcorrespondto no effect, or minimal effects in afew animals in apopulation." The specific endpoints used in the derivation of the MATissueCs are notprovided with the EAIFS document. We request that a descriptionof the endpoints along with citationsgiven the source literaturebe included in thefinal version. The secondarysource which is cited by the Army (Onpost HHRA software, version 1.0, EBASCO 1992) does not contain this information. The most current list ofMATissueC endpoints which the Army has supplied the partiesis the "MATC supplemental Tables" datedDecember 2, 1991. In these tables, endpoints range from lethality to no effects. This is an unacceptable rangeoftoxic responseson which the Stale has commenled previously (State letters of September 23, 1992 and December 10, 1991). The Army states in section 3.4 that "[w]henthe endpoint was lethality, an appropriate uncertainly factor was applied." However, the EBASCO 1992 citationdoes not appearto containany details of this uncertainly factor. In human health risk assessment methodology an uncertainty factor of 10 is used if an adverse effect ("LOAEL") is observed,-if afrank effect ("FEL") is noted, a modifyingfactor is available 11788,903 - CR-03 0504112092 V111 - 63to adjustfor the additionaluncertainty introduced. An analogousapproachmust be developed to protect biota. Response Regarding CDH's comment on the ESA, BEPA, and MBTA, Appendix A, Volume VII of the FS has been revised to include in totality the language agreed upon in the dispute resolution process and communicated in a letter from EPA to the parties on September 18, 1992. The MATCs have been revised and are discussed in Volume II, Section 3.0 and Volume IV, Appendix H of the EA.

Comment No. 8 - Volume VIII. vage 48, Response to ERC MATissueC Comment No. 3, The Army hasfailed to addressto State's concern that MATissueCs based on sublethaleffects may not even protectpopulationsofexposed biota. The topic of acceptablesublethal effects must be carefully evaluated in both the MATissueC and TRV approaches. The adverse effects arehighly variableandpresentdifferent health consequences to both individualsandpopulations. For example, if the Army accepts a LOAEL for COC No. I at which 30% of the exposed individuals experienced life shorteningphysicaldeformity, a LOAEL for COC No. 2 at which 45% experienced behavioralabnormalitiesthat reduce reproductivesuccess, and a LOAEL for COC No. 3 at which 35% experienced increasedsusceptibilityto acute viraldisease,populationeffects are likely to be observed. Analogous problems could be associatedwith MATissueCs basedon sublethal effects. What criteriahave the Army used tojudge if there would be a populationeffect and have these criteriabeen developed and validated for the species of interest? Until a systematic assessmentof the role ofsublethal effects (both single andmultiple concurrenteffects) on the survival and vitality of the populationis completed, the Army's approachcannot be consideredprotective of populations. Resnonse The MATC values presented in the draft final were obtained from the Onpost ERC. Because the onpost ERC was not finalized at the time of the draft final, several of the MATC values were an item of dispute. On the basis of the dispute resolution process, revised MATC values were derived on a basis of scientific consensus. These revised values are discussed and presented in Volume 11, Section 3.0 and Volume IV, Appendix H of the EA.

Comment No. 9 - Volume VIII. vage 48, Rest)onse to ERC MATissueC Comment No. 5 The Armv uses a relationship between human brain and whole body mercury to establish a constant so that whole body values can be estimatedwhen only brainlevels are measured in a given species. The State'spreviously submitted comments documented that there is considerableinterspecies variabilityin organ to organ ratiosof mercury dependingon the animal species. Since this variabilit ' v can be extreme, it introduces a high degree of uncertaintyin thisprocess. The Army proceduredoes not recognizethis uncertainty;nor does it incorporatea means (L.g, UFs) to compensate for uncertainty. The Army has respondedin part by assertingthat the variabilitynoted in the State's comment is addressedwithin the context ofthe interspeciesUF. However, this assertionis obviously erroneous. First,accordingto the document, only the TRV methodology includes interspecies UFs, not the MATissueC approach. Yet,it is the MATissueC approach which requires whole body extrapolations, not the TRV. Secondly, even if MATissueC interspecies UFs were to be adopted,they would 11788,903 - CR-03 0504112092 VIII -. 64normally be triggeredwhen MATissueCs were derived from a literaturevalue based on different species. Since it appearsthat each MATissueC has been derived from studies oil each target species,no UFfactor would be deemed necessary. However, the source of the toxicity information is irrelevantto the whole body extrapolationissue because the latterextrapolationis based, not on the toxicity information,but rather, for example, on the mercury brainto whole body ratiothat has been determined for humans. Accordingly, the State again maintainsthat this inaccuracymust be addressedin the MATissueC methodology. Resi)onse Refer to response to Comment No. 8.

Comment No. 10 - Volume V111, DaPe 51. Response to Comment No. La The Army hasfailed tojustify its selection ofphylogenetic related interspeciesuncertainty factors. In the interestofdeterminingthe validity of the Army's theory andproposed values, the State has undertaken an evaluation ofexisting datapertainingto interspecies susceptibilityto chemicals. The resultsof this analysis are attachedand demonstratethat the Army's values cannot be supported. Analyses of thousandsofphylogenetic toxicological comparisonssummarizedby Suter and others indicatethat, although the datado generallysupportthe theory ofphylogenetic relatednessto a greaterextent thanpreviously noted, they refule the Army's proposed valuesfor interspecies uncertainty factorvalues. Forexample,for species within genera,at the 99% confidence interval, they observed differentialsusceptibilitiesbetween 6 and 21fold: for orders within classes, there were differences between 17 and 17,534 fold. These datademonstratethat the Army's proposed values of 2 for each level ofphylogenetic difference are not adequate to address interspecies variationin susceptibility to contaminants. Response Contrary to CDH's position, the magnitude of the Army's uncertainty factors applied in the derivation of TRVs is supported by the paper published by Suter and Rosen (1988) as well as Barnthouse and others (1990) as discussed in Volume II, Section 3.0 of the EA. CDH's reference to the uncertainty factors associated with the 99 percent confidence interval is not appropriate and would imply the use of extremely conservative uncertainty factors beyond scientific reason.

Comment No. I I - Volume VIII, page 59. Resnonse to ERC Sr)ecific Comment No. 12 In response to the State'sprevious comment regardingsensitivepopulationsand subpopulalions,the Army states that it selected representativereceptorspecies and sensitive subpopulationsusing EPA criteriaand additionalinformationas listed on page 111-5-7. However, it is still not clear how such species (i.e., species with lower thresholds to toxic substances) were differently addressed. Pleaseexplaiý-how and which species were identified, and the pollutantsto which they had lowered threshold tolerances,andthe magnitudeof differentialsusceptibility. Also, please explain how the ERC methodology was used to derive TRVs andMATissueCs protective of such species. In addition,the selection criteriareferredto relates only to receptorspecies: it does not address sensitive subpopulationswithin a species. Pleaseexplain how considerationsofsuch subpopulations have been incorporatedin the ERC methodology, andprovide examples of the incorporationof such considerationsin the derivationofspecific TRVs andMATissueCs.

11788,903 - CR-03 0504112092 VIII - 65Rest)onse The potential receptors listed in Tables 5.2.1-1 and 5.2.1-2 were qualitatively evaluated against the criteria presented in Section 5.2.1 of Volume Ill. The selection process was according to the professional judgment of the evaluators. The pollutants to which the receptors were assumed to have lowered threshold tolerances were the organochlorine pesticides primarily because of their bioaccumulative properties. Magnitude of differential susceptibility was based on trophic box level. The TRV and MATC methodology, including application to sensitive subpopulations, is presented in Section 3.0, Section 5.0, and Appendix H of the EA.

Comment No. 12 - Volume VIII. page 63. Response to ERC Svecific Comment No. 28 The Army hasfailed to,justify its requirementthat the HI be exceeded by afactor of 10 before remedial action is considered. In response to the rationale presented: (1) The assertionthat the use of UFs,LOAELs andNOAELs in deriving MATissueCs and TRVs is conservative demonstratesa profound lack ofunderstandingof the most fundamentaltenets of risk assessmentacceptednot only by EPA but by majorhealth organizationsthroughout the world. While many debate about the size of UFs, UFs are not inherently conservative but necessary to make valid extrapolations. Infact, the sparsedata base that exists indicatesthat values traditionallyutilized may not be sufficient to accountfor variabilityand other considerationsobsensibly embodied in each UF. In Comment 8 above the Statepoints out that the use ofLOAELs and NOAELs may not be protective,let alone conservative. (2) The fact that mobile species may have had their exposure overestimateddoes not eliminate concern with the organismsof limited mobility. Furthermore,if exposure estimatesare known to be unrealistic, they should be revised. Unquantifiedoverconservationin this assumptiondoes not support the arbitraryuse of, essentially,a 10-fold multiplier ofthe acceptabledoes or tissue concentrationvalue. (3) The Arm* v has not substantiatedits beliefthat modeling assumptions are consistently conservative;regardless,this issue is best dealt with via the constructionof the model itself, which should reflect the best estimatedexposure. (4) The assertionthat soil intakes are "conservative,"especially in light of the high uncertainty in this area,is totally inappropriate and unverified. It thereforecannot be used tojustify the Army's HI approach. The use of aHI of10 is inherently irrational. The denominatorof the hazardindex is suppose to be the scientists'best professionalestimate of an acceptabledose (or, in the case ofRMA, tissue concentration);therefore,any exceedance of such a level shouldbe a cause of concern. If the partiesdo not believe that the TRV orMATissueC is accurate,it should be changed to accordwith the best availablescientific informationandjudgement. To add uncertainty factors on thefront end to accountfor inadequacies, andthen basicallysubtract them in the final analysis, is nonsensical. Essentially,the Arm), is proposingan UF multiplierof 10 which is without supportingdocumentalion or rationale,and is dramaticallydeviantfrom existing risk assessment knowledge and methodology throughoutthe world.

11788,903 - CR-03 0504112092 VIII - 66Resvonse 1. The Army strongly disagrees with CDH. UFs, for the most part, are inherently conservative. This conservatism is eloquently presented in the recent publication by Lewis and others (1990). CDH fails to present evidence from the "sparse database" that traditional UF values (the Army assumes CDH is referring to 10) may not be sufficient to account for variabilities encountered during toxicity extrapolation. The traditional values were initially arbitrarily assigned a value of 10 on the basis of professional judgment. They basically have been accepted by regulatory agencies and organizations as more a matter of convention than a scientific absolute. It is likely that the UFs now applied will be reduced as more useful toxicological data become available. The UF values suggested by EPA for the derivation of human reference doses are not codified. The use of UFs less than 10 at each step of the iterative process in deriving a TRV is supported by the recent literature, including papers cited by CDH. CDH is referred to Volume 11, Section 3.0 of the EA for a further discussion of UFs and is encouraged to read the references cited by the Army. The draft final ecological assessment used MATC values derived for the Onpost ERC. On the basis of dispute resolution, some of these values have changed and are discussed and presented in Volume II, Section 3.0 and Volume IV, Appendix H. 2. Because the exposure estimates were known to be unrealistic when presented in the draft final, they have been revised for the final ecological assessment. 3. Again, revisions have been made to estimate more realistic exposures. 4. Refer to 2 and 3 above.

Comment No. 13 The Arm), previously proposeda reduction factor of5 to account for the unique concern over protectingEndangeredSpecies. In this draft,thefactor has been changedto 2. Neithervalue has been supportedby literatureor rational argument. Much literatureexists on interindividual variationin response to toxic substances. In the case of the highly heterogeneoushuman population, interindividualvariationexceeding 10-fold is commonly encountered. In the case of the highly inbred rodents, interindividualvariationof3- 5-fold is often seen. These commonly recognized occurrences indicatethat a 5-foldfactormay not effectively protect individualeagles. Since the federal legislation'sintent is to protect all individuals,afactor greaterthan or equal to 10 is clearlv warranted. Rest)onse The selection of an uncertainty factor of 2 to provide additional protection to the bald eagle population is supported by the literature. The use of a factor of 2 is identical to that selected in the ecological risk assessment Standard Evaluation Procedures (SEPs) developed by the Office of Pesticide Programs in EPA to protect threatened and endangered species.

SPECIFIC COMMENT Comment No. I Volume IV, Appendix F, "Toxicity ProfilesofChemicals ofConcern"has MATissueC values which do not match the MATissueC values listed in Appendix H of the same volume. Forexample, the Toxicity Profile lists aldrin1dieldrin as having a MATissueC of 10 mglkg. Appendix H lists

11788,903 - CR-03 0504112092 VIII - 67aldrin1dieldrin as having MATissueC values ranging from 1.6 to 3.75. Pleaseupdate the Toxicity Profiles. Rest)onse Comment noted. The toxicological profile has been updated.

11788,903 - CR-03 0504112092 VIII - 68GLOSSARY

ABS absorption factor ARAR applicable or relevant and appropriate requirement BAF bioaccumulation factor BCF bioconcentration factor BEPA Bald Eagle Protection Act BGEPA Bald and Golden Eagle Protection Act BMF biornagnification factor CBSG Colorado Basic Standards for Groundwater CCR Colorado Code of Regulations CDH Colorado Department of Health CERCLA Comprehensive Environmental Response, Compensation, and Liability Act CFR Code of Federal Regulations COC chemical of potential concern CRL certified reporting limit DDE 2,2-bis (para-chlorophenyl)-I,I-dichloroethene DDT 2,2-bis (para-chlorophenyl)- 1,1,1-trichloroethane DIMP diisopropyl methylphosphonate EA endangerment assessment Ebasco Ebasco Services, Inc. EPA U.S. Environmental Protection Agency ERA Ecological Risk Assessment ERC Ecological Risk Characterization ESA Endangered Species Act FFA Federal Facility Agreement FS feasibility study GC/MS gas chromatography/mass spectroscopy

11788,903 - CR-03 1119112092 VIII-G- IHA health advisory HBC health-based criteria IRA Interim Response Action IRA A Additional Interim Response Action LDR Land Disposal Restrictions LOAEL lowest -observed -adverse -effect level MATC Maximum Allowable Tissue Concentration MBTA Migratory Bird Treaty Act MCL Maximum Contaminant Level mg/day milligrams per day NCP National Contingency Plan NOAEL no- observed -adverse -effect level NWBCS Northwest Boundary Containment System OAS Organizations and State OSWER Office of Solid Waste and Emergency Response OU operable unit PC permeability coefficient PCB polychlorinated biphenyl PMRMA Program Manager for Rocky Mountain Arsenal ppm parts per million PRG preliminary remediation goal RCRA Resource Conservation and Recovery Act RI remedial investigation RMA Rocky Mountain Arsenal RME Reasonable Maximum Exposure SACWSD South Adams County Water and Sanitation District SEP Standard Evaluation Procedure

11788,903 - CR-03 1119112092 VIII-G-2TBC to be considered TRV toxicity reference value UF uncertainty factor USFWS U.S. Fish and Wildlife Service UST underground storage tank USC United States Code

11788,903 - CR-03 1119112092 VIII-G-3.. . .. --

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ATTACHMENT ADEPARTMENT OF THE ARMY PROG&RAM MANAGER FOR ROCKY MOtJWrJUN AMMAL C0MNM=CrrV.C0L0PAW MUM= 

# (D,Mnv TO ATTKNTM On May 5, IM Office of the Program Manager

Mr. L4ewis D. Walker Mr. Ray Gerard Deputy Assistant Secretary of the Army Shell Oil Company

. for Installation, Logistics, and Environment P.O. Box 2463 Pentagon, Room 2ES77 Houston, IX 77252 Washington, DC 20310-0103

Mr. Galen Buterbaugh Mr. Jack McGraw Regional Director Deputy Regional Administrator U.S. Fish and Wildlife Service US. Environmental Protection Agency P.O. Box 25486 Suite 500, South Tower Denver Federal Center 999-18th Street Denver, CO 80225 Denver, CO 80202-2405

Dear Sir: Following several weeks of dispute resolution discussions at the RMA Committee and Council levels regarding the Of[post Operable Unit (OU) Endangerment Assessment/Feasibility Study (EA/FS), the Organizations have reached agreement an all but one issue.

The resolutions to the dispute Issues for the Offpost EA/FS are enclosed. The most complex of the resolved issues was the issue regarding the Ecological Risk Assessment. The Army agreed to incorporate the values described in the enclosure with the understanding that they represent conservative values based on interpretations of the literature and may not be representative of site-specific conditions present in the Of[post OU. These values have been accepted by the Army in the spirit of cooperation to facilitate the completion of the Ecological Risk Assessment.

Ile unresolved issue concerns whether the Endangered Species Act (ESA), Migratory Bird Treaty Act (MBTA), and Bald and Golden Eagle Protection Act (BGEPA) are applicable or relevant and appropriate requirements (ARARs) for the Offpost OU, and, if so, what type of ARAR (e.g., location-, action-, or chemical-specific) they are. EPA argues that all three acts should be chemical-specific ARARs. The Army and USFWS

### contend that the acts are not ARARs but are independently enforceable. Shell!s position is that the ESA, MBTA. and BQEPA are not chemical-specific ARARs. The discussion ofthe ARAR issue is now taking place at the national level between the Department of Interior and EPA. However, because the parties have agreed to the ecological parameters for the Offpost OU, the offpost process should go forward while the isme is being resolved at the national level. The resolution to the dispute, as descr:lbed, will require an additional six months to complete. 7be delay in completing the EA/FS win also cause a delay in the'issuance of the OfEpost Record ofDecision ofup to six months. sincerely,

Culgee T-LBisho Co U.S. A=43y Chairman, RMA Council Enclosure Copies Furnished: Major John M. Fomous, U.S. Army Environmental Law Division, 901 N. Stuart

Street, Suite 400, Arlington, Virginia 22203-1837 Mr. Bradley Bridgewater, U.S. Department ofJustice, 999-18th Streetý

Suite 501, North Tower, Denver, Colorado 8MM Mr. Thomas Cope, Holme Roberts and Owen, Suite 4100, 1700 Lincoln Street,

Denver, Colorado 80203 Ms. Victoria Peters, Attorney Generars Office, CERCLA Law Division,

One Civic Center Plaza, 1560 Broadway, Suite 250, Denver, Colorado 80202 Mr. David C Shelton, Director, Hazardous Material and Waste Management

Division, Colorado Department of Health, 4210 East 11th Avenue, Denver, Colorado 80220 Mr. Thomas Looby, Colorado Department of Health, 4210 East 11th Avenue, Denver,

Colorado 8=0 Mr. William Clemmens, U.S. Environmental Protection Agency, Region 

## VIM

One Denver Place, Suite 801, 999-18th Street, Denver, Colorado 80202-2405 Document Tracking Center, AMXRM-IDT, Room 132, Building 111, Rocky

Mountain Arsenal, Commerce City, Colorado 80022^R

### Ofipost Operable Unit Dispute Resolution Agreement 17he resolution to the dispute, as described, will require an additional six months to complete. The delay in completing the EA/FS win also cause a delay in the issuance of the ofipost record of Decision ofup to six monthsApproval:-

tEe!ne=I-=LB op k4beit Dufrey Army EPA

vinfArn M ohn L Sp Shell SFW #= AUS46"

### omosr ENDANGERMENT ASSESsMENT/1-MAMBUM'y M"UDY DISPUM RESOLU71ON

It is the intent of the Orpnizations to achieve resolution on language prior to finallZation ofthe document on November 13, 1992.

1. Development of Preliminary Remediation,Goals (PRGs)

ISSUE: 

### EPA questioned the methodology (but did not dispute given the magnitude of the impact under the current factual situation) whether the effects of multiple chemicals within a medium and whether the effects of chemicals of concern (COCs) in multiple media were considered when PRGs were developed. RESOLUTION: Ile Army will modify the text in Volume V, Section 2.4.5, and in Volume VII, Appendix C. 7te Army modifications will include additional discussion about how soil PRGs were developed and will Incorporate comments provided by EPA

on April 23, 1992. 2. Use of 10'4 

### vs. 10 Risk as Point of Departure

ISSUE: 

### EPA invoked dispute concerning whether 10'4 

### or 10'6 cancer risk was used as the point of departure for determination7of HBC. T%e Army had added sections in the Proposed Final EA/FS that were intended to address an EPA comm nt,but EPA found the changes to be inmfficieut. RESOLUTION: The Army asked EPA to provide specific comments concerning sections of the EA/FS that still need to be clarified. The Army will incorporate those comments (received on April 23, 1992) into the Final EA/FS, specifically Volume H, Sections 2.4 and 2.5, and Volume V, Section 2.432- 3. Uncertainty Analysis ISSUE: EPA invoked dispute concerning the presentation ofthe uncertainty analysis in the EA/FS, particularly (1) the possibility that risks may be underesd=ted in some areas but not discussed and (2) the discussion ofthe uncertainty analysis and its representation of exposure relative to the reasonable maximum exposure OWE). RESOLLMON: The Army wiH incorporate EPA comments (received on April 23, 1992) to clarify the uncertainty discussions in the EA/FS. 4. Division of Soil Concentrations by 5

1

### ISSUE: EPA questioned the methodology (but did not dispute given the magnitude of the impact under the current factual situation) of the Army's modification of soil exposure concentrations for the plant uptake model by a factor of 5. RESOLLMON: The Army will add discussion ofuncertainty to Volume M Section 2.6, to explain why the factor of 5 was used to account for the lower concentrations of COCs available to plant roots (Le., because COCs acammlate,in the surface I to 2 inches of soil). 5. FS Alternative Selected ISSUE: EPA invoked dispute concerning the groundwater alternative selected in the FS, contending that all alternatives were variations of the same technology/configuration and that the alternatives were essentially equivalent. EPA also stated that the FS did not evaluate configurations that potentially could achieve a more rapid reme4diation. RESOLU71ON: ne Army will clarify the methodology used and the basis for the development of remedial alternatives. Specifically, the Army will describe: (1) the controlling contaminant and bydrogeologic considerations, (2) resultant estimated remediation time frames, (3) relative positions of remedial components for each alternative, (4) limitations on additional components, and (5) level of aggressiveness of the remedial alternatives. 6. Surface Water FS

ISSUE: 

### EPA questioned, but did not dispute, whether surface water alternatives should be developed in the FS. RESOLLMON: Following finther discussion on the issue, EPA withdrew its objection. 7. Groundwater Exposure Point Concentrations ISSUE: Shell invoked dispute concerning the Armys use ofthe 1985-1990 groundwater database, use of data with high certified reporting limits (CPU) from gas chromatograph/mass spectrometer (GC/MS) analysis, and inclusion of duplicate analyses. Shell contended that this approach is unrepresentative ofcurrent conditions. RESOLUTION: The groundwater exposure point concentrations will be revised and will be based on 1989-1991 groundwater data excluding nondetections with high CRJs and duplicate data, as well as on the te staý611ý pr6cedura

2

### 8. Dieldrin Toxicity Profile ISSUE: Shell invoked dispute concerning the Army's failure to include Shell's toxicological profile for dieldrin.in the EA/FS. RESOLUTION: Shell's dieldrin toxicity profile Will be included in Volume IV, Appendix F, in addition to the Army's dieldrin toxicity profile already in Appendix F. Sbelrs profile will be added and referenced in the same manner as in the 1991 Onpost Human Health Exposure AssessmenL 9. Manganese as a COC ISSUE: 

### Shell invoked dispute concerning the inclusion of man anese as a COC based on limited data linkinx manganese to RMA. RESOLILMON: Shell withdraw the dispute when the Army presented additional onpost and ofipost groundwater data concerning manganese. 10. Applicable or Relevant and Appropriate Requirements (ARARs) ISSUE: A. EPA disputed the overall completeness/format of the ARARS assessment. B. Shell disputed the inconsistent treatment and use of land disposal restrictions (LDRs) as ARARs. C. Shell disputed the use of stormwater discharge regulations as ARARL D. Shell disputed the use of Colorado groundwater stmdards that are more stringent than federal standards as ARARs rather than as TBCs (to be considereds). E. Shell disputed the selection ofsome proposed MCLs as ARARs instead of TBCS. RESOLUTION: A. The Army will clarify the presentation/screening of ARARS through additional discussion. B. The Army wffl revise Volume VIL Appendix A of the Offpost EA/FS,as agreed to by the partie& (Attachment A).

3

### C. Shell withdrew the dispute. D. Although there is some question whether the Colorado Basic Standards for Groundwater are legally enforceable as ARARs, the Army is evaluating whether those standards are ARARs for the purposes of this document. E. Ile Army will make appropriate changes to the ARARs listings as part of Item A. 11. Hazard Index (HI) > 1 for Egg Pathway ISSUE: EPA disputed the Army's use of only dieldrin to assess the egg pathway for human exposure. RESOLUTION: EPA dropped the dispute, agreeing that the risk assessment will evaluate only dieldrin for this pathway. 1Z Land Use Scenarios ISSUE: 

### Shell invoked dispute concerning the use of the subsistence farmer (rural residential) scenario in the EA/FS. EPA invoked dispute concerning the selection of commercial/indu3trial land use in the FS in zones 3 and 4. RESOLUTION: All o agreed to use one land use scenario per zone. Zones 1,Z and 6 will remain rural residential. Zones 3 and 4 will be urban residential with two presentations of risk estimates in the EA. Zone 5 will be commercialfindustrial. See Attachment B for details of the pathways to be considered in each zone. 13. Ecological Risk Assessment ISSUE.A. Shell invoked dispute concerning the need for a more quantitative assessment of the spatial and temporal (seasonal) factors involved in the higher trophic level organism foraging habits. B. Shell invoked dispute considering the conservative nature of the toxicity reference value (TRV) process. C. EPA invoked dispute concerning the maximum allowable tissue concentration (MATC) value for dieldrim Sbeli disputed MATC values for aldrin/dieldrin, DDT/DDE, and endrin; USFWS disputed the dieldrin MATC and had general concerns about other MATC-values.

4

### D. EPA, USFWS, and Shell invoked dispute concerning the use of onpost calibrated ioacal3amilation factors (BAF) values. Shell requested the use ofBAF values as used in the Draft Funi version of the EA/FS; EPA requested the use of literature BAF values; USFWS supported literature and/or USFWS BAFvalucL 13- Shell and USFWS disputed oconce on factors (BCFs). RESOLLMON: A. All Organi agreed to the a of a spatial weighting factor to adjust the predicted tissue co and hazard indices for the great blue heron, great homed awl, American kestrel, and bald eagle. The spatial weighting factor will be based on the ratio of available acreage of appropriate habitat and the acreage of taxon-specific home range. Shell withdrew the temporal (seasonal) factor portion of the,dispute. B. All 0 agreed thai-the TRV proem will follow the approach as originally presented by the Army with uncertainty factor modifications to derive a no observed adverse effect level (NOAEL) rather than a no observed effect level (NOEL) from the critical exposure dose. 7be Organizations have agreed to accept the aldrin/dieldrin critical exposure dose presented by SheJ1 as the basis for the great blue heron TRV,-the great blue heron TRV value will be 0.06 mg/kg/day. The Army agreed to provide documentation supporting the uncertainty factor modifications in the Final EA/FS. C The following MATC literature values were agreed to by all Organizations: Aldrin/Dieldrin Bald eagle 1.1 PPM Great blue heron Ll ppm Great homed owl 1.1 ppm. American kestrel 1.1 ppm Water birds 1.1 PPM Small birds 1.1 PPI]kEndrin Bald eagle, 0.01 ppm, Great blue heron 0.1 ppm, Great homed owl 0.01 ppm American kestrel 0.01 ppm Water birds 1.0 ppm, Small birds 0.045 ppm. 5

### DDT/DDE Bald eagle 2.0 ppm Great blue heron 2.0 ppm Great homed owl 2.6 ppm, American kestrel 5.1 ppm Water birds 0 ppm, Small birds 1.7 ppm D. 'ne following BAF Utmtwe values (unitlem) were agreed to bY the,Organizations: Aldrin/Dieldrin Small bird 2 Small mammal 3 medium mammal 3 worm 6 Insect 2.4 Plant 0.4 owl 19 Ke=ei 12 Eagle 19 Endrin Small bird 8 Small Msimmal 8 medium 8 Worm 29 bisect 29 Plant 0.06 owl 8 Kestrel 8 Eagle 8 DDT/DDE Small bird 2 Small momm"I 6 Medium mammal 6 Worm 3 Insect 32 Plant 1.4 owl 31 Kestrel 31 Eagle 31

6M 

### An organizations agreed to use USFWS BCFs (unitless) for small (lower) fish 

### (aldrin/dieldrin, 16,716-, DDE/DDT, 70,094) and use literature values for

. . small fish, invertebrates and alpe. USFWS is to supply documentation suppo their BCFs. The Organizations also agreed to use geometric mean soil concentrations to determine predicted time concentrations and/or soil criteria exceedanCOL Miis resolution is considered applicable only to the Oflpost EA. 7Ue Army will incorporate the MATC and BAF values as agreed to by the organizations.

7

### ATrACHUENT A Based upon oflpost sampling process imowledge,and EPA guidance concerning the Land Disposal Restrictions (IDRs) under RCRA, the Army has no reason to believe there is any listed or characteristic hazardous waste in the Offpost OU, or that construction of any alternative would involve placement of a listed or characteristic hazardous waste. If it is determined that a listed or characteristic hazardous waste is present and that placement ofsuch a waste would occur, LDRs will be ARARs and the Army will act in a manner consistent with EPA guidance for themsina ement of such wastes in the context of a CERCLA response action.

8

### ATrACHMENT B A. Rural Residential (EA/FS zones 1.Z and 6) eme,at (75%) -dairy (75%) egg (only mhwed dieldrin) *vegetable (40%) groundwater (ingestion) groundwater (inhalation) soil (dermal) soil (ingestion) sedimuts (dermal) surhm water (dermal) B. Xjrban Residential (EA/FS zones 3 and 4) *vegetable (4096) soil (dermal soil (ingestion) sediments (dermal) surf= water (dermal) groundwater (ingestion) groundwater (inhalation) All iyo indicate amount of consumption from local SOUrCeL Risk estbmtes for Zones 3 and 4 Will be presented in two MAnnCrs: 1. As a baseline risk Lumsment for all me" per EPA guidance. IMO groundwater portion ofthe risk L&wwment will be based on the calculated risks from 1989-1991 groundwater data in those zones. 2. The second risk calculations will be based on the continuing beneficial effect of the onpost boundary system operations in a 30-year tim franic. Tbe text will state that these are the expected potential exposures for individuals in thaw zones and the risks associated with those exposures. C Commercialgndustrial (EA/FS zone 5) soil ( soil (ingestion) groundwater (ingestion) groundwater (inhalation)

9

### if South Adams County Water and Sanitation District (SACWSD) provides appropriate documentation of not planning to install future water wells in Zone 5 over the next 30 years, the groundwater pathway will be removed from Zone 5. In a meeting on April 24, 1997, SACWSD agreed to document that they had no intentions of installing water wells in zone 5 over the next 30 years. The documentation, when received, will remove the groundwater pathway from zone 5.

10ATTACHMENT B

# -ýANITATICJ 6595 EAST 70TH AVENUE P 0. BOX 597 COMMERCE CITY. COLORADO BM37-0597 TELEPHONE 303 288-2646 

### May 21, 1992

Mr. Kevin T. Blose Deputy Program Manager Remedial Planning Branch Rocky Mountain Arsenal Commerce City, CO 80022-2180 Re: Request for confirmation of Districts& Ground Water Development Plans in Zones 3, 4 and S.

Dear Mr. Blose: In response to your letter of April 27, 1992, please be advised that the South Adams County Water and Sanitation District has no current plans to install municipal water wells in the Army's Zones 3, 4 and 5. This planning assumption is, of course, based upon current projections of demand in the immediate vicinity of these zones and existing ground water quality, and therefore could be subject to change if these circumstances also change. The District would certainly make every effort to communicate promptly with the Army if these circumstances do, in fact, change. Also, because ground water supply and quality are so variable throughout the District's existing and potential service areas, please be advised that other requests of this nature will have to be reviewed

on a case-by-case basis. Sincerely, SOUTH ADAMS COUNTY WATER AND SANITATION D.ISTRICT By: Larty-rL,./ Ford Disi:rict Manager cc: Col. Eugene H. Bishop Lt. Col. Jeffrey S. Guilford Mr. Connally E. Mears Hon. Hank Brown/Ms. Julie Cella Lysle R. Dirrim, Esq. David M. Brown, Esq. Mr. James 1. Michael Mr. Lewis D. Walker Mr. Robert L. DupreyATTACHMENT C

### UNITED STATES ENVIRONMENTAI. PROTECTION AGENCY REGION viu 999 18th MF.9r - SUITE 900 VVWZM, COLOIMVO 80202-2466 

# SEP 18 1992

Mf ]EC FM.ýWM 01.7 . WN mr. Lewis D. Walker &R WNX&..jl 

## AY-ý Dftnty AselstaUt Sec=i:9%7 Of the A%M 00W.W2 for Inste.13.etion, Logistics and HnvironM=t Jaw-Ma ON Pentjigon, Room 23577 FILE Vashingt=# D.C. 20310-03.03 

## s ivp2.Z92 bw. Ray Ge=oxd i Lt -:j Vice d abell, "01 ly one Sixell ZL P.O. Ame 2463 zmwCoiý; Twu.w 77252 iftnanweck RezLoval Mxtctor U.S. Fish and Wildlife Service P.O. Box 29486 Dewmr Fedexal Cente'r De=er, Colomado 80223 Re: Off-post; ZVFS D:LmYutG em G=; M. . you I ave all av=e, the Steezing and Policy COMMitt" res. ad a umamimus resoluti= of the Off-PoSt WIFS dinmtG COUG =a3lg 4be g=Umgared Species Act, Migmtory i3ird Treaty Actand Bald and Golden Zqjle Pzvt6ftiOn Act BLt tba September 15, 1 2.992, meeting. ancMosed is etatamBUt of tkat resolution for IMIr review and conc=ence. txf*-yW*adu==Ftbat this otat*MQnt aCcumtel-v Mflscts O= M ?and decision ezd the basis for the dec:LG:Lmj, it- to

-ck*. t ing

ing Regl=a Administrator

znclosure Mi. anRwjakdAVW

### fMni wjt:h encloisure sent tot Col.. Eugene 

## 3. Disbops U.S. A=T W. a. mcxi=ny, shaLl. Oil CO. Rrynal pinle7, U.S. Vish and Wildlife Service ]&=AIGY Bridgmat9r, U.S. Depart=ant of allstieekRTM AM



### The Endangered SpeCiag Act ('BSA'), Migratory Bird TrP_UtY Act kN) and Buld and GOldGA Nagle protection Act (IIDMA') apply to tb?=RcckY VAountaJA Arsez3al . The AXMY shil-I I 613t*bligh reMOdiatiOn goals for site Contam4-nants to majAtain and enbance healthy ]POPul,ations of the species subject to the BSA, MM and IJGBPA and their habitats at tba Arseval. For 

### the off-post cpe=ble vmit, remediation govas for off-post

contau qYMti. t neat the izvmentz of the M, MBT3L and DGMA have been isbed in coo= tion with the U.S. Fish and Wildlife service. 9 will ibe I included as enforceable 1: i 9m adistiOn levels in the 'Propose P, and the Record of Decision. 3por th onýpcot verable unit, remediation goals for roils and sediments a Cons:Lstent with the BSA, MM and BGZPA will be estiblis d usirg a methodology aqTsed to by the A=W, Shell and EPA in c ion, irith the U.S. Fish and Wildlife Service. The A=y will also t with the Fish and*wild'14fe Service to detexmins wbether any A activities or rwadial alte=ativen Might have a a t impact an a subject species or its Mbitat. If SL date=inant made th the Axwrlo activi . jJw = remadial . Xn&tive could impact a subjeci species or its babitatp the A=qY will ccMuslual th the Fish and Wildlife Service to deteruiine whether the activ-i 8 proceed and 

### whaty it agy mitigation measures =a

necess 8 1uht of azy long te= bensfitn'to protection of populations of vubi act species. The Or ations evressly reserve their rights to assext their respective x tiono r-ancirAing the MA, mBTA and z=PA as ApunRa in the future.

3

### Offpost Operable Unit Endangerment Assessment/Feasibility Study, Final Report, Volume Vill of Vill, Task RIFS1 11/24/92, RIC# 93012RO3, Harding Lawson Associates, Environmental Science and Engineering, Inc. Diskette #1, ARES&DOC, ARES&EXE, CHEMRME2.WK1, MASTRMD2.WK1, README can be located in the Diskette Archive.

## Offpost Operable Unit Endangerment Assessment/Feasibility Study, Final Report, Volume Vill of Vill, Task RIFS1 11/24/92, RIC# 93012RO3, Harding Lawson Associates, Environmental Science and Engineering, Inc.

Diskette #2, ARES&DOC, ARES8MLE.EXE, CHEMMLE.WK1, MASTMLE.WK1, README can be located In the Diskette Archive.

## Offpost Operable Unit Endangerment Assessment/Feasibility Study, Final Report, Volume Vill of Vill, Task RIFS1 11/24/92, RIC# 93012RO3, Harding Lawson Associates, Environmental Science and Engineering, Inc. Diskette #3, ARES&EXE, CHEMRME2.WK1, DOCUMENT, MASTRMD2.WK1, READ.ME can be located in the Diskette Archive.

## Oftpost Operable Unit Endangerment Assessment/Feasibility Study, Final Report, Volume Vill of Vill, Task RIFS1 11/24/92, RIC# 93012RO3, Harding Lawson Associates, Environmental Science and Engineering, Inc.

Diskette #4, ARES8.130C, ARES8MLE.EXE, CHEMMLE.WK1, MASTMLE.WK1, README can be located in the Diskette Archive.

## Offpost Operable Unit Endangerment Assessment/Feasibility Study, Final Report, Volume Vill of Vill, Task RIFS1 11/24/92, RIC# 93012RO3, Harding Lawson Associates, Environmental Science and Engineering, Inc. Diskette #5, LASUN.WKI, ADBUN.WKI, CADUN.WK1 CHA2UN.WK1, CHE2UN.WK1, DIMPUN.WK1 can be located In the Diskette Archive.

## Offpost Operable Unit Endangerment Assessment/Feasibility Study, Final Report, Volume Vill of Vill, Task RIFS1 11/24/92, RIC# 93012RO3, Harding Lawson Associates, Environmental Science and Engineering, Inc. Diskette #6, LIMPRECS.DBF, GW1RECS.DBF, GW3RECS.DBF, GW4RECS.DBF, GW5RECS.DBF, GW6RECS.DBF, GW2RECS.DBF, LIMPFORM.DOC, HIMPFORM.DOC, GW1FORM.DOC, GW2FORM.DOC, GW3FORM.DOC, GW4FORM.DOC, GW5FORM.DOC, GW6FORM.DOC, HIMPRECS.DBF can be located In the Diskette Archive.