TECHNICAL SUPPORTFOR ROCKY MOUNTAIN ARSENAL

Offpost Operable Unit Endangerment Assessment/Feasibility Study Final Report Volume IIIofVIII (EA Sections 4.0, 5.0, 6.0, 7.0)

November 24, 1992 Contract Number DAAA15-88-0021 Task RIFS1 (Delivery Order 0001)

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

PREPARED FOR PROGRAM MANAGER FOR ROCKY MOUNTAIN ARSENAL

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

# M9200036TABLE OF CONTENTS Page VOLUME I- INTRODUCTION LIST OFTABLES ..................................................... xix LIST OFFIGURES .................................................... xxv PREFACE ........................................................... P-1 EXECUTIVE SUMMARY .............................................. ES-I INTRODUCTION ...................................................... 1-1 GLOSSARY .......................................................... G-1

VOLUME II - ENDANGERMENT ASSESSMENT PREFACE ........................................................... II - P-1 1.0 IDENTIFICATION OF CHEMICALS OFPOTENTIAL CONCERN ........... Il - 1-1 1.1 GENERAL SITE DATA EVALUATION CONSIDERATIONS .......... 11-1-4 1.2 STATISTICAL PROCEDURES FOR COMPARISON WITH BACKGROUND ............................................. 11- 1-8 1.3 SELECTION OF CHEMICALS OF CONCERN ...................... II - 1-15 1.3.1 Groundwater ......................................... 11- 1-15 1.3.2 Surface Water/Sediment ................................. 11- 1-17 1.3.3 Surficial Soil .......................................... 11- 1-21 1.3.4 Biota ................................................ 11

- 1-22 1.4 SUMMARY ................................................ 11- 1-24 1.5 UNCERTAINTIES ........................................... 11- 1-26 2.0 EXPOSURE ASSESSMENT ......................................... 11-2-1 2.1 PROPERTIES AND PROBABLE ENVIRONMENTAL FATES OF CHEMICALS OF CONCERN ................................ 11-2-1 2.1.1 Equilibrium Partitioning Properties ofChemicals ofConcern ..... 11- 2-2 2.1.1.1 Information Sources .............................. Il - 2-3 2.1.1.2 Data Evaluation ................................ 11- 2-5 2.1.1.3 Results ....................................... II - 2-7 2.1.2 Offpost Environmental Fate ofChemicals ofConcern ........... 11- 2-9 2.1.2.1 Organochlorine Pesticides ......................... 11- 2-9 2.1.2.2 Benzene Compounds ............................. II - 2-15 2.1.2.3 Halogenated Aliphatic Compounds .................. II - 2-19 20000,317.10 - 1-toc 0306111892 iTABLE OF CONTENTS (Continued) Page 2.1.2.4 Compounds Containing Sulfur ...................... II - 2-23 2.1.2.5 Compounds Containing Phosphorus .................. II - 2-24 2.1.2.6 Ionic Chemicals ................................. Il - 2-26 2.1.2.7 Miscellaneous Compounds ......................... Il - 2-30 1.3 Uncertainties ......................................... Il - 2-31 2.2 CHARACTERIZATION OF EXPOSURE SETTING .................. II - 2-32 I Site Characteristics Affecting Contaminant Migration ........... II - 2-32 2.2.1.1 Site Description and History ....................... II - 2-32 2.2.1.2 Environmental Setting ............................ II - 2-33 2.2.1.3 Sampling Locations and Media ..................... Il - 2-34 2.2.1.4 Summary ofOffpost Operable Unit Contamination ...... Il - 2-36 4.2.2 Potentially Exposed Populations ........................... Il - 2-37 2.2.2.1 Residential Land Use ............................ Il - 2-38 .".-.2.1.1 Procedures ........................... 11- 2-38 2. 1. 2 Results .............................. 11 - 2-41 2.2.22.2 Commercial/Industrial Land Uses 11- 2-42 2.22. 2.3 Qualitative Assessment ofthe Likelihood ofOccurence ofthe Selection ofFuture Land Use for the Offpost Endangerment Assessment/Feasibility Study ........... 11 - 2-44 2.2.2.4 Water Use ..................................... 11- 2-45 2.2.2.4.1 Existing Groundwater Use ............... 11- 2-45 2.2.2.4.2 Projected Future Use ofGroundwater ....... 11-- 2-49 2.2.2.4.3 Surface-Water Use ..................... II - 2-50 2.3 EXPOSURE PATHWAYS ...................................... 11- 2-51 2.3.1 Potential Sources, Release Mechanisms, and Transport Media ..... 11- 2-51 2.3.1.1 Groundwater ................................... 11- 2-51 2.3.1.2 Surface Water and Sediment ....................... 11-2-54 2.3.1.3 Atmospheric ................................... Il - 2-55 2.3.1.4 Biotic ........................................ 11 - 2-55 2.3.2 Potential Exposure Points ................................ 11-2-56 2.3.3 Potential Exposure Pathways and Routes ..................... 11 - 2-57 2.3.3.1 Inhalation Route ................................ 11- 2-57 2.3.3.2 Dermal Route .................................. 11-2-60 2.3.3.3 Ingestion Route ................................. 11-2-61 2.3.4 Uncertainties ......................................... Il - 2-64 2.4 QUANTIFICATION OF EXPOSURE ............................. 11 - 2-64 2.4.1 Identification ofZones Having Distinct Exposure Concentrations and/or Pathways ....................................... II - 2-66 2.4.2 Exposure Assessment Procedures and Exposure Point Concentrations ........................................ Il - 2-71 2.4.2.1 Statistical Procedures Used toEvaluate Monitoring Data ......................................... Il - 2-72

20000,317.10 - 1-toc 0306111992TABLE OF CONTENTS (Continued) Page 2.4.2.2 Model Used toEstimate 30-Year Groundwater Exposure Point Concentration ............................. II - 2-73 2.4.2.3 Models Used to Estimate Concentrations in Agricultural Products .... .... II - 2-74 2.4.2.3.1 icken gs ......................... 11- 2-75 2.4.2.3.2 Vegetables ............................ 11- 2-75 2.4.2.3.3 Beef ................................ 11 - 2-81 Z.4.2.3.4 Dairy ............................... II - 2-82 2.4.2.4 Summary ofNonchemical-specific Parameters ......... 11 - 2-83 Groundwater Fraction Used for Irrigation (GWF) ....................... II - 2-83 ,(-.4.2.4.2 Fraction Exposed (fe) ................... 11 - 2-83 2.4.2.4.3 Partition Coefficient Deposited from Spray (Kd,p)) .......................... 11- 2-83 2.4.2.4.4 Cattle Water/Feed Intakes (IPWM and Ipwd) .... 11 - 2-84 ".4.2.4.5 Cattle Feed/Soil Intake (I ') ............... 11- 2-84 2 P 2.4.2.5 Sample Calculations and Comparison With the Available Monitoring Data ................................ 11- 2-84 2.4.2.6 Results ...................... I................. II - 2-86 2.4.3 Estimation of Chemical Intakes ............................ 11 - 2-90 2.4.3.1 Chemical-specific Parameters ...................... 11 - 2-94 2.4.3.2 Exposure Factors ................................ II - 2-95 2.4.3.3 Results ....................................... II - 2-98 2.4.4 Estimation ofChemical Intakes forCommercial/ Industrial Scenario ............................................. 11

- 2-99 2.4.4.1 Estimation ofChemical Intakes ..................... 11-2-100 2.4.5 Uncertainty Analysis (Residential) ......................... 11-2-100 2.4.5.1 Preliminary Sensitivity Analysis .................... 11-2-101 2.4.5.2 Additional Scoping Considerations .................. 11-2-102 2.4.5.3 Procedures .................................... 11- 2-103 2.4.5.4 Determination ofInput Parameter Distributions ........ 11 - 2-104 2.4.5.5 Results ............. 11-2-106 2.4.5.5.1 Input Parameters ....................... 11-2-106 2.4.5.5.2 Example Results ....................... 11- 2-108 2.4.5.5.3 Summary ofResults .................... 11-2-110 2.5 SUMMARY OFEXPOSURE ASSESSMENT ........................ 11 -2-112 2.5.1 Residential Scenario ...... - - - *I*III**III*IIIII*I*1 11- 2-113 2.5.2 Commercial/ Industrial Scenario ........................... 11-2-116 2.6 UNCERTAINTIES ........................................... 11 - 2-116 3.0 TOXICITY ASSESSMENT .......................................... II - 3-1 3.1 HUMAN REFERENCE DOSES ................................. II - 3-1 3.2 POTENTIAL CARCINOGENICITY OF CHEMICALS OF CONCERN .... 11- 3-5

20000,317.10 - 1-toc 0306111892TABLE OF CONTENTS (Continued)

PU.e 3.2.1 Weight ofEvidence ..................................... 11- 3-5 3.2.2 Slope Factor .......................................... II - 3-6 3.3 NONHUMAN RECEPTOR TOXICITY REFERENCE VALUES ........ 11- 3-7 3.3.1 Vegetation ........................................... 11 - 3-8 3.3.2 Aquatic Organisms ..................................... 11- 3-8 3.3.3 Terrestrial Organisms ................................... IT- 3-9 3.3.3.1 Derivation of a No-Observed- Adverse-Effect Level ..... 11 - 3-10 3.3.3.2 Phylogenetic Differences .......................... 11- 3-13 3.3.3.2_.1 Intraspecies Differences ................. II - 3-16 3.3.3.2.2 Genus and Species Differences ............ II - 3-16 3.3.3.2.3 Family/Order Differences ................ 11 - 3-18 3.3.3.2.4 Threatened orEndangered Species .......... II - 3-19 3.4 MAXIMUM ACCEPTABLE TISSUE CONCENTRATIONS ............ II - 3-19 3.5 UNCERTAINTIES IN TOXICITY ASSESSMENT .................... 11- 3-20 3.5.1 Human Toxicity Assessment .............................. 11- 3-20 3.5.2 Toxicity Reference Values ............................... II - 3-21

VOLUME III - ENDANGERMENT ASSESSMENT 4.0 HUMAN RISK CHARACTERIZATION ............................... 111-4-1 4.1 RESIDENTIAL SCENARIO .................................... 111 -4-2 4.1.1 Hypothetical Future Exposures ............................ 111- 4-3 4.1.1.1 Hypothetical Carcinogenic Risks Related to Background . . III - 4-4 4.1.1.2 Child Chronic Hypothetical Future Hazard Indices ...... III - 4-5 4.1.1.3 Adult Chronic Hypothetical Future Hazard Indices ...... 111-4-6 4.1.1.4 Hypothetical Future Carcinogenic Risk ............... III - 4-6 4.1.1.5 Zone-specific Risks ............................. 111-4-6 4.1.1.6 Acute/Subchronic Effects ......................... 111-4-10 4.1.2 Hypothetic Current Risks Versus Hypothetical Future Risks ...... 111 -4-12 4.1.3 Health Risk atMost Likely Exposure Intakes ................. 111-4-12 4.1.4 Alternative Risk Estimate Based on Predicted Decline in Groundwater Concentrations .............................. 111 -4-14 4.2 COMMERCIAL/INDUSTRIAL SCENARIO ........................ 111-4-14 4.2.1 Adult Chronic Hypothetical Future Hazard Indices ............. III - 4-15 4.2.2 Hypothetical Future Carcinogenic Risks ..................... III - 4-15 4.2.3 Carcinogenic Risk at Most Likely Exposure Intakes ............. III - 4-15 4.3 RISK CHARACTERIZATION SUMMARY ........................ III - 4-15

20000,317.10 - 1-toc 0306111992 ivTABLE OFCONTENTS (Continued) Page 4.4 UNCERTAINTIES IN THE HUMAN HEALTH ASSESSMENT ......... 111 -4-18 5.0 ECOLOGICALASSESSMENT ....................................... III - 5-1 5.1 SITECHARACTERIZATION ................................... III- 5-1 5.1.1 Study Area Definition ................................... III - 5-1 5.1.1.1 Terrestrial Systems .............................. III - 5-2 5.1.1.2 Aquatic Systems ................................ Ill- 5-3 5.1.2 Ecological Characterization ofthe Offpost Operable Unit ........ III - 5-4 5.1.3 Contamination Pertaining to Offpost Biota ................... III - 5-5 5.1.4 Selection ofChemicals ofConcern for Biota .................. III - 5-6 5.2 EXPOSURE ASSESSMENT ..................................... Ill- 5-7 5.2.1 Potential Biological Receptors and Sensitive Subpopulations ...... III - 5-7 5.2.1.1 Terrestrial Receptors ............................. III - 5-8 5.2.1.2 Aquatic Receptors ............................... III- 5-10 5.2.2 Potential Exposure Pathways .............................. III - 5-11 5.2.3 Exposure Point Concentrations ............................ III - 5-14 5.2.4 Ecological Assessment Endpoints .......................... III - 5-15 5.2.4.1 Terrestrial ..................................... III - 5-15 5.2.4.2 Aquatic ....................................... Ill - 5-16 5.2.5 Bioaccumulation Exposure ............................... III - 5-17 5.2.5.1 Terrestrial Food Web Ingestion Pathways .............. III - 5-17 5.2.5.2 Terrestrial Food Web Predicted Tissue Concentrations .... III - 5-19 5.2.5.3 Aquatic Food WebIngestion Pathways ................ 111-5-20 5.2.5.4 Aquatic Food Web Predicted Tissue Concentrations ...... III - 5-21 5.2.6 Direct Exposure toChemicals ofConcern .................... 111-5-21 5.2.6.1 Surface-Water Ingestion Pathway ......... *,*, ,*,, ,, 111- 5-21 5.2.6.2 Direct Contact with Surface Water or Sediment ......... III - 5-23 5.2.6.3 SoilIngestion .................................. III - 5-23 5.2.6.4 Dietary Ingestion forWildlife ...................... 111- 5-24 5.2.6.5 Dietary and Soil Ingestion Pathways for Livestock ....... III - 5-24 5.3 RISK CHARACTERIZATION .................................. 111- 5-26 5.3.1 Terrestrial Food Web Ecological Risk ....................... Ill- 5-26 5.3.2 Aquatic Food Web Ecological Risk ......................... Ill- 5-29 5.3.3 Underwater Aquatic Life ................................ III - 5-30 5.3.4 Agricultural Life ...................................... 111- 5-30 5.3.5 Ecological Risk Assessment Uncertainty ..................... III - 5-31 5.3.5.1 SiteCharacterization ............................. III - 5-31 5.3.5.2 Exposure Assessment ............................ III - 5-32 5.3.5.3 Risk Characterization ............................ Ill- 5-34 5.4 SUMMARY ................................................ III - 5-34

20000,317.10 - 1-toc 0306111892 vTABLE OF CONTENTS (Continued) Page 6.0 CONCLUSIONS .................................................. 111-6-1 7.0 REFERENCES ................................................... 111- 7-1

20000,317.10 - 1-toc 0306111892 viTABLE OF CONTENTS (Continued)

VOLUME IV - ENDANGERMENT ASSESSMENT LISTOF APPENDIXES A RELEASE OFVOLATILE CONTAMINANTS FROM GROUNDWATER WITH SUBSEQUENT EXPOSURE IN BASEMENTS: SCREENING LEVEL ANALYSIS B ESTIMATE OFAMBIENT PARTICULATE MATTER IMPACT DUE TOWIND EROSION NEAR ROCKY MOUNTAIN ARSENAL C EXPOSURE CONCENTRATIONS D ESTIMATED REASONABLE MAXIMUM EXPOSURE INTAKES E UNCERTAINTY ANALYSIS F TOXICOLOGICAL PROFILES * ESTIMATED REASONABLE MAXIMUM EXPOSURE RISKS AND HAZARD INDICES * SUPPORTING INFORMATION FOR THE ECOLOGICAL ASSESSMENT HI - ANIMAL SPECIESOF POSSIBLE OCCURRENCE IN RMA OFFPOST AREA H2 - BIOACCUMULATION FACTORS, BIOMAGNIFICATION FACTORS, AND PREDICTED TISSUE CONCENTRATIONS

- TERRESTRIAL FOOD WEB

- AQUATIC FOOD WEB H3 - EXPOSURE POINT CONCENTRATIONS OF CHEMICALS IN SURFACE WATER AND PREDICTED CHEMICAL INTAKE FOR AVIAN SPECIES H4 - HAZARD QUOTIENT SUMMARY TABLES FOR CATTLE H5 - MAXIMUM ALLOWABLE TISSUE CONCENTRATION VALUES H6 - SPATIAL WEIGHING ADJUSTMENT FACTORS H7 - ONPOST HHRC SOFTWARE BLUE VERSION 1.0 PREPARED FOR THE PROGRAM MANAGER RMA EBASCO SERVICES, INC., MARCH 1992

20000,317.10 - I-toe 0306111892 viiTABLE OF CONTENTS (Continued) Page VOLUME V - FEASIBILITY STUDY PREFACE ........................................................... V - P-1

1.0 FEASIBILITY STUDY PURPOSE AND ORGANIZATION ................. V - 1-1 1.1 STEPI - DEVELOPMENT OFREMEDIAL ACTION OBJECTIVES ..... V - 1-1 1.2 STEP11 - DEVELOPMENT AND SCREENING OF ALTERNATIVES .... V - 1-2 1.3 STEPIII - DETAILED ANALYSIS OF ALTERNATIVES ............. V - 1-2 1.4 STEPIV - SELECTION OF THE PREFERRED SITEWIDE ALTERNATIVE ............................................. V - 1-3 2.0 DEVELOPMENT OF REMEDIAL ACTION OBJECTIVES AND SCREENING OF TECHNOLOGIES .............................................. V - 2-1 2.1 OVERVIEW OF REMEDIAL ACTION OBJECTIVES DEVELOPMENT .. V - 2-1 2.2 NATIONAL CONTINGENCY PLAN AND ACCEPTABLE RISK RANGE CONSIDERATIONS .......................................... V - 2-2 2.2.1 Comparison ofCumulative RiskWith the Acceptable Risk Range . . V - 2-2 2.2.2 Identification ofMedia Requiring Remedial Action Objectives .... V - 2-4 2.2.3 Site-specific Factors Considered for Groundwater Remedial Action Objectives Development .................... V - 2-6 2.3 DEVELOPMENT OFGROUNDWATER REMEDIAL ACTION OBJECTIVES ............................................... V - 2-6 2.3.1 Development ofRemedial Action Objectives, Step 1: Identification ofChemicals ofConcern ............................ ''*** V - 2-7 2.3.2 Development ofGroundwater Remedial Action Objectives Step 2: Identification ofPotential Exposure Pathways ................. V- 2-7 2.4 GROUNDWATER REMEDIAL ACTION OBJECTIVES ............... V - 2-8 2.4.1 Groundwater Remedial Action Objectives .................... V - 2-9 2.4.1.1 Human Health .................................. V - 2-9 2.4.1.2 Environmental Protection ......................... v - 2-9 2.5 DEVELOPMENT OF GROUNDWATER PRELIMINARY REMEDIATION GOALS ..................................... V - 2-10 2.5.1 Effects ofFuture LandUse on the Development of Preliminary Remediation Goals ........................... V - 2-11 2.5.2 National Contingency Plan and PointofDeparture Considerations for Development ofPreliminary Remediation Goals ............ V - 2-12 2DO00,317.10 - 1-toc 0306111892 viiiTABLE OF CONTENTS (Continued) PaS& 2.5.3 Types ofGroundwater Preliminary Remediation Goals .......... V - 2-15 2.5.3.1 Identification ofApplicable or Relevant and Appropriate Requirements ............. V - 2-15 2.5.3.1.1 Chemical-specific Applicable or Relevant and Appropriate Requirements .... V - 2-17 2.5.3.1.2 Location-specific Applicable or Relevant and Appropriate Requirements ............ V - 2-19 2.5.3.1.3 Action-specific Applicable or Relevant and Appropriate Requirements .... V - 2-18 2.5.3.2 Health-based Criteria ............................ V - 2-18 2.5.3.3 Background Concentrations ........................ V - 2-20 2.5.3.4 Ecological Criteria ..................... : *,, ,*... V -2-20 2.5.4 Development and Identification ofPreliminary Remediation Goals - Groundwater ......................................... V - 2-20 2.5.4.1 Groundwater Chemical-specific Applicable or Relevant and Appropriate Requirements ... V - 2-20 2.5.4.2_ Groundwater Health-based Criteria .................. V - 2-21 ";..5.43 Selection ofGroundwater Preliminary Remediation Goals . V - 2-21 2.6 QUANTITIES OF GROUNDWATER REQUIRING REMEDIATION ..... V - 2-22 2.7 GENERAL RESPONSE ACTIONS ............................... V - 2-22 2.7.1 No Action ............................................ V - 2-23 2.7.2 Institutional Controls ................................... V - 2-23 2.7.3 Containment .......................................... V - 2-23 2.7.4 Removal ............................................. V - 2-24 2.7.5 Treatment ............................................ V - 2-24 2.7.6 Disposal ............................................. V - 2-24 2.8 IDENTIFICATION AND SCREENING OF TECHNOLOGY TYPES AND PROCESS OPTIONS .......................................... V - 2-25 2.8.1 Universal Screening .................................... V - 2-26 2.8.2 Evaluation and Screening ofSelected Process Options ........... V - 2-26 2.8.3 Nonmedia-specific ProcessOptions ......................... V - 2-27 2.8.3.1 NoAction ..................................... V - 2-27 2.8.3.2 Institutional Controls ............................. V - 2-28 2.8.3.2.1 Access Restrictions ..................... V - 2-28 2.8.3.2.2 Alternative Water Supplies ................ V - 2-29 2.8.3.2.3 Monitoring ........................... V - 2-29 2.8.4 Groundwater Process Options ............................. V - 2-30 2.8.4.1 Removal ...................................... V - 2-30 2.8.4.1.1 Groundwater Extraction ................. V - 2-30 2.8.4.2 Disposal .......... V - 2-33 2.8.4.2.1 Subsurface bis*p'o'sa'l* V - 2-33 2.8.4.2.2 Aboveground Discharge ................. V - 2-35 2.8.4.3 In-vessel Treatment ofGroundwater ................. V - 2-37 2.8.4.3.1 Solids Removal ........................ V - 2-37 20000,317.10 - I-toc 0306111892 ixTABLE OF CONTENTS (Continued) Page 2.8.4.3.2 Phase Transfer ........................ V - 2-39 2.8.4.3.3 Sorption ............................. V - 2-40 2.8.4.3.4 Oxidation ............................ V - 2-42 2.8.4.3.5 Radiation ............................ V - 2-44 2.8.4.3.6 Biological Treatment .................... V - 2-45 2.8.4.4 In SituTreatment ............................... V - 2-46 2.8.4.4.1 Water Flushing ........................ V - 2-46 2.8.4.4.2 Enhanced Biological Treatment ............ V - 2-47 2.ý.4.5 Containment ........ .......................... V - 2-48 2.8.4.5.1 Subsurface Barriers ..................... V - 2-48 2.9 SUMMARY OF PROCESS OPTION SCREENING ................... V - 2-50 2.10 SELECTION OFREPRESENTATIVE PROCESS OPTIONS ............ V - 2-50 .2.10.1 Representative Process Options for Groundwater Remediation .... V - 2-51 VOLUME VI - FEASIBILITY STUDY 3.0 DEVELOPMENT OFREMEDIAL ALTERNATIVES ..................... VI - 3-1 3.1 FEASIBILITY STUDY OVERVIEW .............................. VI - 3-1 3.1.1 U.S. Environmental Protection Agency Guidance for Alternatives Development and Evaluation .................... VI - 3-1 3.2 ALTERNATIVES IDENTIFICATION ............................. VI - 3-3 3.2.1 Approach ............................................ VI - 3-3 3.2.1.1 Groundwater Model Input Into Alternatives Development ................................... VI - 3-4 3.2.1.1.1 Chemicals ofConcern .................. VI - 3-4 3.2.1.1.2 Use ofthe Model in Alternatives Development .......................... VI - 3-5 3.2.1.2 Groundwater Alternative Types .................... VI - 3-9 3.3 LAND OWNERSHIP IMPLICATIONS FOR IMPLEMENTING REMEDIAL ALTERNATIVES ............................................ VI - 3-10 3.4 COMMONALITIES OF ALTERNATIVES ......................... VI - 3-10 3.4.1 Commonalities ofGroundwater Remedial Alternatives .......... VI - 3-11 3.4.1.1 Groundwater Alternatives Institutional Controls ........ VI - 3-11 3.4.1.1.1 Provision ofan Alternative Water Supply (Exposure Control) ..................... VI - 3-11 3.4.1.1.2 Monitoring Networks ................... VI - 3-12 3.4.1.1.3 Site Review .........

# 6................. VI - 3-12 3.4.1.2 'Groundwater Pretreatment Process ptions ............ VI - 3-13

20000,317.10 - 1-toc 0306111892 XTABLE OFCONTENTS (Continued) Page 3.4.1.3 Continued Operation ofthe Boundary Systems and Compliance With Offpost Operable Unit Preliminary Remediation Goals .............................. VI - 3-13 3.5 GROUNDWATER REMEDIAL ALTERNATIVES IDENTIFICATION ... VI - 3-13 3.5.1 Identification ofGroundwater Alternatives: North Plume Group .................. :***'*''*****'***"*''** VI - 3-14 3.5.1.1 Alternative No. N-1: No Action .................... VI - 3-14 3.5.1.2 Alternative No. N-2: Continued Operation ofthe North BoundaryContainment System With Improvements as Necessarv ................... VI - 3-14 3.5.1.3 Alternative No. N-3: Land Acquisition and Use Restrictions ........... :*- **- '- *********** VI - 3-15 3.5.1.4 Alternative No. N-4: Interim Response Action A ....... VI - 3-16 3.5.1.5 Alternative No. N-5: Expansion I to Interim Response Action A ..................................... VI - 3-18 3.5.1.6 Alternative No. N-6: Expansion 2 to Interim Response Action A ......... ''*''*''** ...... VI - 3-19 3.5.1.7 Summary ofAlternatives Identified for the North Plume Group ............. VI - 3-21 3.5.2 Identification ofGroundwater Alternatives: Northwest Plume Group ...................... :*,*''*,****'** ...- - 1 VI - 3-22 3.5.2.1 Alternative NW-1: No Action ...................... VI - 3-22 3.5.2.2 Alternative NW-2: Continued Operation ofthe Northwest Boundary Containment System ..................... VI - 3-22 3.5.2.3 Alternative No. NW-3: Land Acquisition With Use Restrictions .................................... VI - 3-23 3.5.2.4 Alternative No. NW-4: Northwest PlumeGroup Extraction/Recharge System ....................... VI - 3-24 3.5.2.5 Summary ofAlternatives Identified for the Northwest Plume Group .................................. VI - 3-25 4.0 SCREENING OFALTERNATIVES ................................... VI - 4-1 4.1 M ETHODOLOGY ............................................ VI - 4-1 4.1.1 Effectiveness Evaluation ................................. VI - 4-1 4.1.2 Implementability Evaluation .............................. VI- 4-2 4.1.3 CostEvaluation ............. VI - 4-3 4.2 SCREENING OF ALTERNATIVES .............................. VI - 4-4 4.2.1 Screening ofAlternatives - North Plume Group ............... VI - 4-4 4.2.1.1 Alternative No. N- 1: No Action .................... VI - 4-4 4.2.1.1.1 Effectiveness .......................... VI - 4-5 4.2.1.1.2 Implementability ....................... VI - 4-6 4.2.1.1.3 Cost ................................ VI - 4-6

20000,317.10 - 1-toc 0306111892 xiTABLE OF CONTENTS (Continued) Page 4.2.1.2 Alternative No. N-2: Continued Operation ofthe North Boundary Containment System With Improvements as Necessary ..................................... VI - 4-6 4.2.1.2.1 Effectiveness .......................... VI - 4-7 4.2.1.2.2 Implementability ....................... VI - 4-8 4.2.1.2.3 Cost ...... ......................... VI - 4-8 4.2.1.3 Alternative No. N-3: Land Acquisition and Deed Restrictions .................................... VI - 4-9 4.2.1.3.1 Effectiveness .......................... VI - 4-9 4.2.1.3.2 Implementability ....................... VI - 4-10 4.2.1.3.3 Cost ....... :*,,*, *,*,**,**....*,*, * VI - 4-11 4.2.1.4 Alternative No. N-4: Interim Response Action A ....... VI - 4-11 4.2.1.4.1 Effectiveness .......................... VI - 4-11 4.2.1.4.2 Implementability ....................... VI - 4-12 4.2.1.4.3 Cost ................... : *,, *,**,*, II VI - 4-13 4.2.1.5 Alternative No. N-5: Expansion I to Interim Response Action A .............................. VI -4-13 4.2.1.5.1 Effectiveness .......................... VI - 4-13 4.2.1.5.3 Implementability ....................... VI - 4-14 4.2.1.5.3 Cost ....... ........................ VI - 4-15 4.2.1.6 Alternative No. N-6: Expansion 2 to Interim Response Action A .............................. VI - 4-15 4.2.1.6.1 Effectiveness .......................... VI - 4-15 4.2.1.6.2 Implementability ....................... VI - 4-16 4.2.1.6.3 Cost ..... .......................... VI - 4-17 4.2.1.7 Alternative Screening Summary andRecommendation .... VI - 4-17 4.2.2 Screening ofGroundwater Alternatives - Northwest Plume Group ............................................... VI - 4-18 4.2.2.1 Alternative No. NW-I: No Action .................. VI - 4-18 4.2.2.1.1 Effectiveness .......................... VI - 4-19 4.2.2.1.2 Implementability ....................... VI - 4-20 4.2.2.1.3 Cost ................................ VI - 4-20 4.2.2.2 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements As Necessary ....................... VI - 4-20 4.2.2.2.1 Effectiveness .......................... VI - 4-21 4.2.2.2.2 Implementability ....................... VI - 4-22 4.2.2.2.3 Cost ................................ VI - 4-22 4.2.2.3 Alternative No. NW-3: Land Acquisition and Deed Restrictions .................................... VI - 4-23 4.2.2.3.1 Effectiveness .......................... VI - 4-23 4.2.2.3.2 Implementability ....................... VI - 4-24 4.2.2.3.3 Cost ................................ VI - 4-24 4.2.2.4 Alternative No. NW-4: Northwest Plume Group Extraction/Recharge System ....................... VI - 4-25 4.2.2.4.1 Effectiveness .......................... VI - 4-25 4.2.2.4.2 Implementability ....................... VI - 4-26 4.2.2.4.3 Cost ................................ VI - 4-27 4.2.2.5 Alternative Screening Summary and Recommendation .... VI - 4-27 20000,317.10 - I-toc 0306111892 xiiTABLE OF CONTENTS (Continued) Page 5.0 DETAILED ANALYSIS OF ALTERNATIVES ........................... VI - 5-1 5.1 CRITERIA ................................................. VI - 5-2 5.1.1 Overall Protection ofHuman Health and the Environment ....... VI - 5-2 5.1.2 Compliance With Applicable orRelevant and Appropriate Requirements ..... ......................... VI - 5-2 5.1.3 Long-term Effectiveness and Permanence .................... VI - 5-3 5.1.4 Reduction ofToxicity, Mobility, orVolume .................. VI - 5-3 5.1.5 Short-term Effectiveness ................................ VI - 5-3 5.1.6 Implementability ....................................... VI - 5-4 5.1.7 Cost ................................................ VI - 5-4 5.1.8 State Acceptance ....................................... VI - 5-4 5.1.9 Community Acceptance ................................. VI - 5-5 5.2 MODELING RESULTS SUMMARY ............................. VI - 5-5 5.3 FURTHER DEFINITION OF ALTERNATIVES ..................... VI - 5-7 5.3.1 Alternative No. N-1: No Action ........................... VI - 5-7 5.3.2 Alternative No. N-2: Continued Operation ofthe North Boundary Containment System With Improvements as Necessary ... VI - 5-8 5.3.3 Alternative No. N-4: Interim Response Action A .............. VI - 5-8 5.3.4 Alternative No.N-5: Expansion I toInterim Response Action A ............................................ VI - 5-10 5.3.5 Alternative No.NW- 1: No Action ........................ VI - 5-11 5.3.6 Alternative No.NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements as Necessary VI - 5-11 5.4 DETAILED ANALYSIS OFALTERNATIVES ..................... VI - 5-12 5.4.1 Overall Protection ofHuman Health and the Environment ...... VI - 5-12 5.4.1.1 Alternative No. N-1: No Action ..... :* *******'*'' VI - 5-12 5.4.1.2 Alternative No. N-2: Continued Operation of the North Boundary Containment System With Improvements as Necessary ....................... VI - 5-13 5.4.1.3 Alternative No. N-4: Interim Response Action A ...... VI - 5-14 5.4.1.4 Alternative No. N-5: Expansion I toInterim Response Action A ............................. VI - 5-15 5.4.1.5 Alternative No. NW-1: No Action ........... *****' VI - 5-15 5.4.1.6 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements as Necessary ....................... VI - 5-16 5.4.2 Compliance With Applicable orRelevant and Appropriate Requirements . **'*''* :**--'---- VI - 5-16 5.4.2.1 Alternative No. N-1: No Action ................... VI - 5-17 5.4.2.1.1 Chemical-specific Applicable or Relevant and Appropriate Requirements ... VI - 5-17

20000,317.10 - 1-toc 0306111892 xiiiTABLE OF CONTENTS (Continued) Page 5.4.2.1.2 Action-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-17 5.4.2.1.3 Location-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-17 5.4.2.2 Alternative No. N-2: Continued Operation ofthe North Boundary Containment System With Improvements asNecessary ................................... VI - 5-17 5.4.2.2.1 Chemical-specific Applicable or Relevant and Appropriate Requirements .... VI - 5-17 5.4.2."2.2 Action-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-18 5.4.2.2.3 Location-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-18 5.4.2.3 Alternative No. N-4: Interim Response Action A ....... VI - 5-18 5.4.2.3.1 Chemical-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-18 5.4.21. 3.2 Action-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-18 5.4.2.3.3 Location-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-18 5.4.2.4 Alternative No. N-5: Expansion I to Interim Response Action A .............................. VI - 5-18 5.4.2.4.1 Chemical-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-18 5.4.2.4.2 Action-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-19 5.4.2.4.3 Location-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-19 5.4.2.5 Alternative No. NW- 1: No Action ................. VI - 5-19 5.4.2.5.1 Chemical-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-19 5.4.2.5.2 Action-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-19 5.4.2.5.3 Location-specific Applicable or Relevant and Appropriate Requirements ....*,****, , VI - 5-19 5.4.2.6 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements asNecessary ............... VI - 5-19 5.4.2.6.1 Chemical-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-19 5.4.2.6.2 Action-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-20 5.4.2.6.3 Location-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-20 5.4.3 Long-term Effectiveness and Permanence ................... VI - 5-20 5.4.3.1 Alternative No. N-1: No Action .................... VI - 5-20 5.4.3.2 Alternative No. N-2: Continued Operation ofNorth Boundary Containment System With Improvements as Necessary ..................................... VI - 5-20 20000,317.10 - I-toe 0306111892 xivTABLE OF CONTENTS (Continued) Page 5.4.3.3 Alternative No. N-4: Interim Response Action A ....... VI - 5-21 5.4.3.4 Alternative No. N-5: Expansion I to Interim Response Action A ... VI - 5-21 5.4.3.5 Alternative No. NW-1: No Action ................. VI - 5-22 5.4.3.6 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements as Necessary ........................ VI - 5-22 5.4.4 Reduction ofToxicity, Mobility, or Volume .................. VI - 5-23 5A.A.1 Alternative No. N-1: No Action .................... VI - 5-23 5.4.4.2 Alternative No. N-2: Continued Operation ofthe North Boundary Containment System With Improvements asNecessary ............ *'*''**'  VI - 5-23 5.4.4.3 Alternative No. N-4: Interim Response Action A ....... VI- 5-23 5.4.4.4 Alternative No. N-5: Expansion I to Interim Response Action A Vl- 5-24 5.4.4.5 Alternative No. NW- 1: No Action .................. VI- 5-25 5.4.4.6 Alternative No. NW-12: Continued Operation of Northwest Boundary Containment System With Improvements as Necessary ........................ Vl- 5-25 5.4.5 Short-term Effectiveness ................................ VI- 5-25 5.4.5.1 Alternative No. N-1: No Action .................... Vl- 5-26 5.4.5.1.1 Protection ofCommunity and Workers ...... VI- 5-26 5.4.5.1.2 Adverse Environmental Impacts ........... VI- 5-26 5.4.5.1.3 Implementation Period .................. VI - 5-26 5.4.5.2 Alternative No. N-2: Continued Operation of North Boundary Containment System ................ VI - 5-26 5.4.5.2.1 Protection of Community andWorkers ...... VI - 5-26 5.4.5.2.2 Adverse Environmental Impacts ........... VI- 5-26 5.4.5.2.3 Implementation Period .................. VI- 5-26 5.4.5.3 Alternative No. N-4: Interim Response Action A ........ VI- 5-27 5.4.5.3.1 Protection ofCommunity and Workers ...... VI- 5-27 5.4.5.3.2 Adverse Environmental Impacts ........... V1- 5-27 5.4.5.3.3 Implementation Period .................. VI- 5-27 5.4.5.4 Alternative No. N-5: Expansion Ito Interim Response Actoin A .............................. VI- 5-27 5.4.5.4.1 Protection ofCommunity and Workers ...... VI- 5-27 5.4.5.4.2 Adverse Enviornmental Impacts ........... VI - 5-27 5.4.5.4.3 Implementation Period .................. VI- 5-28 5.4.5.5 Alternative No. NW-I: No Action .................. VI - 5-28 5.4.5.5.1 Protection ofCommunity andWorkers ...... VI - 5-28 5.4.5.5.2 Adverse Environmental Impacts ........... VI- 5-28 5.4.5.5.3 Implementation Period .................. VI- 5-28 5.4.5.6 Alternative No. NW-2: Continued Operation of Northwest Boundary Containment System With Improvements as Necessary ........................ VI- 5-28 5.4.5.6.1 Protection ofCommunity and Workers ...... VI- 5-28 5.4.5.6.2 Adverse Environmental Impacts ........... VI- 5-29 5.4.5.6.3 Implementation Period .................. VI- 5-29

20000,317.10 - I-toc 0306111892 xvTABLE OF CONTENTS (Continued) Page 5.4.6 Implementability ....................................... VI - 5-29 5.4.6.1 Alternative No. N-1: No Action .................... VI - 5-29 5.4.6.2 Alternative No. N-2: Continued Operation ofNorth Boundary Containment System With Improvements as Necessary ..................................... VI - 5-29 5.4.6.3 Alternative No. N-4: Interim Response Action A ....... VI - 5-30 5.4.6.4 Alternative No. N-5: Expansion I to Interim Response Action A .............................. VI - 5-30 5.4.6.5 Alternative No. NW-1: No Further Action ............ VI - 5-30 5.4.6.6 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements as Necessary ........................ VI - 5-31 5.4.7 Cost .......... ** - **- - - :''**''*'***'******** ** VI- 5-31 5.4.7.1 Alternative No. N-1: No Action .................... Vl- 5-31 5.4.7.2 Alternative No. N-2: Continued Operation ofthe North Boundary Containment System With Improvements as NecessarN .................. .................. Vl

- 5-31 5.4.7.3 Alternative No. N-4: Interim Response Action A ....... VI- 5-32 5.4.7.4 Alternative No. N-5: Expansion I to Interim Response Action A .............................. VI - 5-32 5.4.7.5 Alternative No. NW-1: No Action .................. VI - 5-32 5.4.7.6 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements as Necessary ........................ VI - 5-32 5.5 COMPARATIVE ANALYSIS OFREMEDIAL ALTERNATIVES ........ VI - 5-33 5.5.1 Comparison ofAlternatives - North PlumeGroup .............. Vl- 5-33 5.5.1.1 Overall Protection ofHuman Health and the Environment ................................... VI - 5-33 5.5.1.2 Compliance With Applicable orRelevant and Appropriate Requirements ........................ VI - 5-34 5.5.1.3 Long-term Effectiveness and Permanence ............. VI - 5-34 5.5.1.4 Reduction in Toxicity, Mobility, and Volume .......... VI - 5-34 5.5.1.5 Short-term Effectiveness .......................... VI - 5-35 5.5.1.6 Implementability ................................ VI - 5-35 5.5.1.7 Cost ................... ****'*6r***' *******''' VI - 5-36 5.5.2 Comparison ofAlternatives - Northwest Plume oup .......... VI - 5-36 5.5.2.1 Overall Protection ofHuman Health and the Environment ................................... VI - 5-37 5.5.2.2 Compliance With Applicable or Relevant and Appropriate Requirements ........................ VI - 5-37 5.5.2.3 Long-term Effectiveness and Permanence ............. VI - 5-37 5.5.2.4 Reduction inToxicity, Mobility, and Volume .......... VI- 5-37 5.5.2.5 Short-term Effectiveness .......................... VI - 5-38 5.5.2.6 Implementability ................................ VI - 5-38 5.5.2.7 Cost ......................... VI - 5-38 5.5.3 Ranking ofAlternatives - North Plume Group and Northwest Plume Group ................................. VI - 5-39 20000,317.10 - 1-toc 0306111892 xviM

TABLE OF CONTENTS (Continued) Page 6.0 SELECTION OF THE PREFERRED SITEWIDE ALTERNATIVE ........... VI - 6-1 6.1 IDENTIFICATION OF THE PREFERRED SITEWIDE ALTERNATIVE . . VI - 6-1 6.1.1 Preferred Sitewide Alternative Description ................... VI - 6-3 6.1.1.1 Alternative No. N-4: Interim Response Action A ....... VI - 6-3 6.1.1.2 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Control System With Improvements as Necessary ........................ VI - 6-6 6.2 CONSISTENCY WITH THE REQUIREMENTS OF CERCLA AND THE NATIONAL CONTINGENCY PLAN .................... VI - 6-7 6.2.1 Principal Threats Addressed by the Preferred Sitewide Alternative VI - 6-7 6.2.2 Consistency With the Statutory Requirements ofCERCLA in Section 121 ........................................... VI - 6-7 6.2. 1 Protection ofHuman Health and the Environment ....... VI - 6-7 6.2- Compliance With Applicable orRelevant and Appropriate Requirements ........................ VI - 6-8 6.2.2.3 Cost-effectiveness ...................... *''***'*' VI - 6-8 6.2.21.4 Utilization ofPermanent Solutions to the Maximum Extent Practicable .................................... VI - 6-8 6.2.3 Consistency With the National Contingency Plan ............... VI - 6-8 6.3 SUMMARY ................................................ VI - 6-9 7.0 REFERENCES ................................................... VI - 7-1

20000,317.10 -1-toc 0306111892 xviiTABLE OF CONTENTS (Continued)

VOLUME VII - FEASIBILITY STUDY LIST OFAPPENDIXES A APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARs) ANALYSIS B WETLAND DELINEATION AND ASSESSMENT C DERIVATION OF HEALTH-BASED CRITERIA AND ECOLOGICAL CRITERIA D SECOND LEVEL PROCESS OPTION SCREENING E GROUNDWATER MODELING RESULTS SUMMARY F COST ESTIMATES

VOLUME VIII - RESPONSES TO COMMENTS U.S. ENVIRONMENTAL PROTECTION AGENCY U.S. FISH AND WILDLIFE SERVICE COLORADO DEPARTMENT OF HEALTH SHELL OIL COMPANY

20000,317.10 - I-toc 0306111892 xviiiLIST OFTABLES

Table No. Volume II - ENDANGERMENT ASSESSMENT 1.0-1 Data Needs inEach Medium 1.3.1-1 Statistical Comparison With Background - Groundwater 1.3.1-2 Chemicals ofConcern - Groundwater 1.3.1-3 Summarv ofAvailable Information on Toxicity and Essentiality ofCalcium, Iron, Potassium, Magnesium, and Sodium 1.3.2-1 Statistical Comparison With Background - Surface Water (First Creek) 1.3.2-2 Chemicals ofConcern - Surface Water (FirstCreek) 1.3.2-3 Statistical Comparison With Background - Surface Water (Canals) 1.3.2-4 Statistical Comparison With Background - Surface Water (Barr Lake) 1.3.2-5 Statistical Comparison With Background - Sediment (First Creek) 1.3.2-6 Statistical Comparison With Background - Sediment (O'Brian Canal) 1.3.2-7 Statistical Comparison With Background - Sediment (Barr Lake) 1.3.3-1 Statistical Comparison With Background - Surficial Soil

2.1-1 Henry's Law Constant (Dimensionless) for Organic Groundwater Chemicals of Concern 2.1-2 Molecular Diffusivity in Air andWater (m2/day) 2.1-3 Solubility (mg/1) and Vapor Pressure (torr) for Organic Groundwater Chemicals ofConcern 2.1-4 Octanol/Water Partition Coefficients (log KOW) 2.1-5 Adsorption Coefficient (1/kg) for Chemicals Elevated inSoil or Sediment 2.1-6 Uptake to Roots, K,,, (1/kg), for Organic Groundwater ChemicalsofConcern 2.1-7 Uptake to Plants, Kwp (1/kg), for Organic Groundwater Chemicals ofConcern 2.1-8 Plant Uptake Coefficients, K., (Dimensionless), for Chemicals ofConcernin Offpost Surficial Soil 2.1-9 Plant Uptake Coefficients, K.., for Chemicals ofConcern inOffpost Surficial Soil

20000,317.10 - I-toc 0306111892 xixLIST OF TABLES (Continued)

2.1-10 Beef Bioaccumulation Coefficients, KPM1 for All Chemicals ofConcern 2.1-11 Milk Bioaccumulation Coefficients, Kpd, for All Chemicals ofConcern 2.1-12 Fish Bioaccumulation Coefficients, K,,f (1/kg), forSurface-Water Chemicals of Concern 2.2.2.1.2-1 Population by Land-Use Area

--. 2.1.2-2 Land Use by Land-Use Area (in acres) 2.2.2.1.2-3 Potentially Sensitive Subpopulations 2.2.2.4.1-1 Well-Use Data From Colorado State Master Extract Register 2.2.2.4.1-2 Well-Use Data From Consumptive Use Phase 1,11, and III Studies Preliminarv Estimate ofthe Number ofWells b,, Well Use in the Offpost Operable Unit 2.2.'( '_.

4.1-4 Well Use Data From the Tri-Countv Health Department Survey 2.2.2.4.1-5 Combined Estimate ofthe Number ofWells bv Well Use inthe Offpost Operable Unit 2.3.3.1-1 Exposure Pathways: Inhalation Route 2.3.3.2-1 Exposure Pathways: Dermal Route 2.3.3.3-1 Exposure Pathways: Ingestion Route 2.4.2.4-1 Nonchemical-specific Parameters Used inBioaccumulation Models 2.4.2.5-1 Concentration ofAldrin Plus Dieldrin in Zone 3 2.4.2.5-2 Chemical-specific Properties ofAldrin and Dieldrin 2.4.2.6-1 Exposure Concentrations, Groundwater, Zone 1 2.4.2.6-2 Exposure Concentrations, Groundwater, Zone 2 (Northern Paleochannel) 2.4.2.6-3 Exposure Concentrations, Groundwater, Zone 3 (96th Avenue and Peoria Street) 2.4.2.6-4 Exposure Concentrations, Groundwater, Zone 4 (First Creek Paleochannel) 2.4.2.6-5 Exposure Concentrations, Groundwater, Zone 5(Northwest Boundary) 2.4.2.6-6 Exposure Concentrations, Groundwater, Zone 6

20000,317.10 - 1-tot 0306111992 xxLIST OF TABLES (Continued)

2.4.2.6-7 Estimated Future Exposure Concentrations for Aldrin and Dieldrin, Groundwater, Zones 3 and 4 2.4.2.6-8 Exposure Concentrations in Surface Water 2.4.2.6-9 Exposure Concentrations in Surficial Soil and Sediments (mg/kg) 2.4.2.6-10 Reasonable Maximum Exposure Concentrations in Vegetables: Maximum Concentrations Estimated in Anv Zone 2.4.2.6-11 Reasonable Maximum Exposure Concentrations in Dairy and Meat Products: Maximum Concentration Estimated in Any Zone 2.4.2.6-12 Reasonable Maximum Exposure Concentration in Eggs (Zones 1,2, and 6) 2.4.3-1 Summary ofLand Use Scenarios Used to Estimate Reasonable Maximum Exposure Intakes by Zone 2.4.3.1-1 Dermal Absorption from Soil/Sediment 2.4.3.2-1 Exposure Factors: Ingestion Rates 2.4.3.2-Ia Parameters Used in Time-weighted Average Intakes Calculation (Milk and Soil Ingestion) 2.4.3.2-2 Exposure Factors: Exposure Frequency and Duration 2.4.3.2-3 Exposure Factors: Physiology 2.4.4-1 Exposure Factors: Commercial/Industrial (Reasonable Maximum Exposure) 2.4.4-2 Exposure Factors: Commercial/Industrial (Most Likely Exposure) 2.4.5.1-1 Sensitivity Analysis Summary 2.4.5.5.3-1 Uncertainty Analysis Results

3.1-1 Hierarchy ofDocuments Referenced Regarding Toxicity Data 3.1-2 Toxicity Data for Rocky Mountain Arsenal Offpost Chemicals ofConcern 3.1-3 Noncarcinogenic Reference Doses and Potential Noncarcinogenic Effects 3.1-4 Cancer Slope Factors and Potential Carcinogenic Effects ofCarcinogenic Operable UnitOffpost Chemicals ofConcern 3.1-5 Regulatory Criteria for Rocky Mountain Arsenal Offpost Operable Unit, Chemicals ofConcern

20000,317.10 - 1-toc 0306111992 xxiLIST OF TABLES (Continued)

3.3.1-1 Reference Media Concentrations for Vegetation and Aquatic Organisms 3.3.3-1 Toxicity Reference Values for Avian and Terrestrial Vertebrate Species of Concern Identified at Rocky Mountain Arsenal 3.3.3-2 References for Critical Toxicity Studies Used to Derive Terrestrial Toxicity Reference Values Listed inTable 3.3.3-1 3.3.3.2.1-1 Nonprimate Mammalian Oral LD50 Data

Volume III 4.0-1 Target Organ- or System-specific Chemicals ofConcern 4.1.1-1 Summary ofResidential Hypothetical Future Carcinogenic Risks: Reasonable Maximum Exposure 4.1.1-2 Summarv ofResidential Child Chronic Combined Noncarcinogenic Hazard Indices (H]s >1) 4.1.1-3 Contribution of Dieldrin and Other Chemicals tothe Child Acute Hepatic Hazard Index 4.1.1-4 Summary ofResidential Hypothetical Future Reasonable Maximum Exposure Subchronic Hazard Indices: Children 4.1.1-5 Summary ofResidential Hypothetical Future Reasonable Maximum Exposure Subchronic Hazard Indices: Adult Females 4.1.1-6 Comparison ofResidential Reasonable Maximum Exposure and MostLikely Exposure Hypothetical Future Carcinogenic Risks byZone

5.1.2-1 Wildlife Species Observed inOffpost Operable Unit: Winter 1989-90 5.1.4-1 Chemicals ofConcern and Tissue Chemicals ofConcern for the Offpost Ecological Risk Assessment 5.2.1-1 Terrestrial Species Selected asIndicators ofEcological Impacts 5.2.1-2 Aquatic/Wetland Species in Relation to Indicator Species Selection Criteria 5.2.2-1 Potential Exposure Pathways for Biota 5.2.3-1 Exposure Point Concentrations for Soil, Surface Water, and Sediment Used for the Offpost Ecological Assessment 5.2.5.1-1 Dietary Fractions for Each ofthe Species in the Terrestrial Food Web 20000,317.10 -1-toc 0306111992 xxiiLIST OF TABLES (Continued)

5.2.5.2-1 Predicted Tissue Concentrations (mg/kg) for the Terrestial Food Web Ecological Receptors 5.2.5.4-1 Predicted Tissue Concentrations (mg/kg) for the Aquatic Food Web Ecological Receptors on the Basisof Surface-Water Concentrations 5.2.5.4-2 Predicted Tissue Concentrations (mg/kg) for the Aquatic Food Web Ecological Receptors on the Basisof Sediment Concentrations 5.3.1-1 Summarv ofIntakes from Zone 3 Soil, Surface Water, and Diet for the Bald Eagle 5.3.1-2 Summarv ofIntakes From Zone 3 Soil, Surface Water, and Dietfor the American Kestrel 5.3.1-3 Summary ofIntakes From Zone 3 Soil, Surface Water, and Dietfor the Great Horned Owl 5.3.1-4 Summarv of Intakes From Zone 3 Soil, Surface Water. and Diet for the Deer Mouse 5.3.1-5 Summary of Intakes From Zone 3 Soil. Surface Water, and Diet for the Prairie Dog 5.3.2-1 Summarv ofIntakes From Zone 3 Sediment, Surface Water, and Diet for the Great Blue Heron 5.3.2-2 Summary ofIntakes From Zone 3 Sediment, Surface Water, and Dietfor the Mallard Duck 5.3.4-1 Summary ofChicken Hazard Quotient by Zone, Offpost Operable Unit

Volume V - FEASIBILITY STUDY 2.2.1-1 Offpost Operable Unit Carcinogenic Risks for Each Medium 2.3.1-1 Offpost Operable Unit Groundwater Chemicals ofConcern 2.5.2-1 Preliminary Chemical-specific Applicable or Relevant and Appropriate Requirements for Groundwater 2.5.2-2 Health-based Criteria for Groundwater Chemicals ofConcern Without Applicable or Relevant and Appropriate Requirements 2.5.2-3 Preliminary Remediation Goals for Offpost Operable Unit Groundwater 2.8.1-1 Screening ofProcess Options forGroundwater 2.10.1-1 Selection ofRepresentative Process Options for Groundwater

20000,317.10 - 1-toc 0306111992 xxiii

### LISTOFTABLES (Continued)

Volume VI 3.5.1-1 Groundwater Alternatives forthe North PlumeGroup 3.5.1.7-1 Summary ofPreliminary North Plume Group Groundwater Alternatives 3.5.2-1 Groundwater Alternatives forthe Northwest Plume Group 3.5.2.5-1 SummaryofPreliminary Northwest Plume Group Groundwater Alternatives

4.2.1.7-1 SummaryofScreening ofGroundwater Alternatives; North Plume Group 4.2.2.5-1 SummaryofScreening ofGroundwater Alternatives; Northwest Plume Group 5.5.3-1 Summarv ofthe Detailed Analysis andRanking ofGroundwater Alternatives for the North Plume Group 5.5.3-2 Summary ofthe Detailed Analysis andRanking ofGroundwater Alternatives for theNorthwest PlumeGroup

20000,317.10 -1-toc 0306111892 xx1vLIST OF FIGURES

Figure No. Volume I- INTRODUCTION I Location Map ofOnpost Operable Unit, Rocky Mountain Arsenal 2 Offpost Area, Rocky Mountain Arsenal 3 Distribution ofDiisopropylmethyl Phosphonate (DIMP) in theOffpost Unconfined Flow System 4 Distribution ofDicyclopentadiene in theOffpost Unconfined Flow System 5 Distribution ofDieldrin inthe Offpost Unconfined Flow System 6 Distribution ofEndrin in the Offpost Unconfined Flow System 7 Distribution of Chloroform in theOffpost Unconfined Flow System 8 Distribution of Chlorobenzene in the Offpost Unconfined Flow System 9 Distribution ofDibromochloropropane inthe Offpost Unconfined Flow System 10 Distribution ofTrichloroethene (TRCLE) inthe Offpost Unconfined Flow System II Distribution ofTetrachloroethene in theOffpost Unconfined Flow System 12 Distribution ofArsenic in the Offpost Unconfined Flow System 13 Distribution ofChloride inthe Offpost Unconfined Flow System 14 Distribution ofFluoride in the Offpost Unconfined Flow System 15 Offpost Operable Unit Confined Denver Formation Monitoring Well Network 16 Distribution ofOrganochlorine Pesticides Detected in Offpost Soil 17 Distribution ofOrganochlorine Pesticides Detected in96th Avenue Area Offpost Soil 18 Distribution ofOrganic Compounds Detected in Offpost Operable Unit Surface Water 19 Distribution ofOrganic Compounds Detected in Offpost Operable Unit StreamBottom Sediment

20000,317.10 - 1-toc 0306111892 xxvLIST OF FIGURES (Continued)

Volume Il - ENDANGERMENT ASSESSMENT 1.0-1 Preliminary Site Conceptual Model, Pre-Remedial Investigation, Offpost Operable Unit 1.2-1 Offpost Operable UnitBackground Surficial Soil Sampling Locations 1.2-2 Offpost Operable Unit Designated Surficial Soil Data Sets for Comparison With Background 1.

2'

-3 Offpost Operable Unit First Creek Surface-Water Sampling Locations 1.2-4 Offpost Operable Unit First Creek Sediment Sampling Locations 1.2-5 Offpost Operable Unit Surface-Water Sampling Locations 1.2-6 Offpost Operable Unit Sediment Sampling Locations

2.2.2.1.1-1 Offpost Operable Unit Land Use Areas and Consumptive Use Phase 11 Study Area 2.2.2-.1.2-1 Offpost Operable Unit - Future Land Use 2.2.2.1.2-2 Offpost Operable UnitStudy Area Selected Current Zoning Map, 1991 2.3.1-1 Site Conceptual Model Offpost Operable Unit 2.4.1-1 Offpost Operable Unit Zones Major Pathways ofGroundwater Contaminant Transport 2.4.1-2 Offpost Operable Unit Endangerment Assessment Zones 2.4.2.6-1 Estimated Future Exposure Concentrations for Dieldrin, Groundwater, Zones 3 and 4 2.4.2.6-2 Estimated Future Exposure Concentrations for Aldrin, Groundwater, Zones 3 and4 2.4.3.3-1 Offpost Operable Unit Chronic Intake ofChloroform by Pathway and Groundwater Zone - Residential Scenarios 2.4.3.3-2 Offpost Operable Unit Intake ofDieldrin by Zone and Pathway - Residential Scenario 2.4.5-1 Offpost Operable Unit Histograms Describing the Distribution ofIngestion Rate ofLocally Produced Milk (IRd, kg/day) for the Child Chronic and Lifetime Scenarios - Residential

20000,317.10 - 1-toc 0306111992 xxviLISTOF FIGURES (Continued)

2.4.5-2 Offpost Operable Unit Histograms Describing the Distribution ofIngestion Rate ofLocally Produced Vegetables (IRv, kg/day) for the ChildChronic and Lifetime Scenarios - Residential 2.4.5-3 Offpost Operable Unit Histograms Describing the Distribution ofIngestion Rate ofLocally Produced Meat (IRm, kg/day Fresh Weight) for the ChildChronic and Lifetime Scenarios - Residential 2.4.5.5.2-1 Offpost Operable Unit Distribution ofLifetime Oral Intake ofDieldrin in Zone 3 (mg/kg/day) - Residential 2.4.5.5.2-2 Off'post Operable Unit Uncertainty inthe Mean Concentration ofDieldrin in Groundwater (mg/1) in Zone 3 2.4.5.5.2-3 Offpost Operable Unit Uncertainty inthe Mean Concentration ofDieldrin in First Creek Surface Water (mg/1) 2.4.5.5.2-4 Offpost Operable Unit Uncertainty in the Mean Concentration of Aldrin and Dieldrin in Surface Soil ofZone 3 (mg/1) 2.4.5.5.2-5 Offpost Operable Unit Uncertainty in the Mean Concentration ofDieldrin in Vegetables (CFv, mg/kg, Fresh Weight) inZone 3 2.4.5.5.2-6 Offpost Operable Unit Distribution ofChildChronic Oral Intake ofDIMP in Zone 4 (mg/kg/day) - Residential 2.4.5.5.2-7 Offpost Operable Unit Distribution ofLifetime Oral Intake ofChloroform in Zone 2 (mg/kg/day) - Residential 2.4.5.5.2-8 Offpost Operable Unit Distribution ofLifetime Inhalation ofChloroform in Zone 2 (mg/kg/day) - Residential

3.3.1-1 Methodology for Determining Water and Soil Reference Media Concentrations for Vegetation and Aquatic Organisms 3.3.3-1 Methodology to Derive Toxicity Reference Values (TRVs) From Class-specific Toxicity Data

Volume III 4.1.1-1 Offpost Operable Unit Combined Carcinogenic Risks (All Pathways) by Groundwater Zone - Residual Scenarios 4.1.1-2 Offpost Operable Unit Child Resident Hazard Indices Described forToxic Chemicals and Exposure Pathways - Residential Scenarios 4.1.1-3 Offpost Operable Unit Contributors to Carcinogenic Risks - Residential Scenario

20000,317.10 - 1-toc 0306111992 xxviiLIST OFFIGURES (Continued)

4.1.1-4 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone IA, Lifetime Rural Resident, RME 4.1.1-5 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone 113, Lifetime Rural Resident, RME 4.1.1-6 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone IC,Lifetime Rural Resident, RME 4.1.1-7 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone 2. Lifetime Rural Resident, RME 4.1.1-8 Carcinogenic Risks Described by Chemical, Medium. and Exposure Pathway - Zone 3, Lifetime Urban Resident, RME 4.1.1-9 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone 4. Lifetime Urban Resident, RME 4.1.1-10 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone 5, Commercial/Industrial, RME 4.1.1-11 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone 6, Lifetime Rural Resident, RME 4.1.1-12 Child Acute Liver Hazard Indices 4.1.1-13 Subchronic Child Liver Hazard Indices, Maximum and Minimum ofRange 4.2.1-1 Noncarcinogenic Hazard Indices Zone 5;Adult Commercial/Industrial; Chronic RME

5.1.1-1 Offpost Operable Unit BiotaSampling Locations 5.1.1-2 Habitat Map for First CreekPortion ofOffpost Operable Unit 5.2.2-1 Ecological Site Conceptual Model Offpost Operable Unit 5.2.5.1-1 Offpost Operable Unit Terrestrial Food Web 5.2.5.3-1 Offpost Operable Unit Aquatic Food Web 5.2.6.5-1 Offpost Operable Unit Agricultural Food Web

20000,317.10 - 1-toc 0306111892 xxviiiLIST OF FIGURES (Continued)

Volume V - FEASIBILITY STUDY 2.5.1-1 Offpost Operable Unit Feasibility Study Contaminant Distribution Zones 2.6.1 Areas ofExceedances of Groundwater PRGs in the Offpost Unconfined Flow System 2.8-1 Groundwater Process Options 2.8.1-1 Results ofUniversal Screening ofGroundwater Process Options 2.9-1 Results oftheSecond Level Screening ofGroundwater Process Options 2.10.1-1 Selected Representative Process Options for Development ofGroundwater Remedial Alternatives

Volume VI 3.2.1-1 Offpost Operable Unit Groundwater Plume Groups 3.5.1.4-1 Alternative No. N-4: Interim Response Action A 3.5.1.5-1 Alternative No. N-5: Expansion I toInterim Response Action A 3.5.1.6-1 Alternative No. N-6: Expansion 2 toInterim Response Action A 3.5.2.4-1 Alternative No. NW-4: Northwest Plume Group Extraction/Recharge System

20000,317.10 - 1-toc 0306111892 xxix4.0 HUMAN RISK CHARACTERIZATION

This section integrates, summarizes, and interprets information from the exposure and toxicity assessments for the 0) rural residential and (2) commercial/industrial and recreational scenarios, The procedures used are presented in RAGS (EPA, 1989a) and include the following: 1. Determine Hazard Indices (HI) bycomparing chronic and acute/subchronic intake estimates to RfDs to evaluate the potential for noncarcinogenic effects. An HI greater than 1.0 may warrant further evaluation. 2. Multiply estimated lifetime intakes by cancer SFs to estimate the UL95 ofindividual lifetime cancer risk under the RME assumptions. 3. Add His and cancer risks ofmultiple contaminants that are expected to cause similar effects. 4. Interpret the results by identifying chemical pathways and media contributing substantial]y to the overall risks and characterizing the uncertainties associated with the assessment.

Based on information presented in the toxicity assessment, COCs were categorized with respect to the target organ,'system that was affected in the critical study, or studies, used to define the RfD. Some chemicals affect more than one organ or system at similar doses and may be placed in multiple categories. His are summed within categories. The target organ-specific COCs

are presented in Table 4.0- 1. The majority ofchemicals presenting noncarcinogenic effects (i.e., HI >I) affect the liver, so additivity of chemical-specific His ismost significant to the liver. Individual lifetime cancer risks are summed forall carcinogens regardless oftarget organ and weight-of-evidence classification (EPA, 1989a) to estimate theadditive individual lifetime cancer risk. It is appropriate, however, to distinguish between carcinogens on the basis oftarget organ and weight of evidence as part ofthe risk management process, as presented and described in Section 4.3. Uncertainties in the risk characterization represent the combined uncertainties ofthe exposure and toxicity assessments. Overall, these uncertainties were resolved by conservative assumptions. The quantitative uncertainty analysis ofthe estimated intakes indicates that the RME intake estimate is at the 98th to 99.8th percentile ofthe expected range ofhypothetical

20000,317.10(3) - OEA 0306111892 111 - 4-1intakes among the exposed population. Hypothetically, most individuals would experience much lower intakes. For the Offpost OU, the 50th percentile ofthe uncertainty analysis resultant distribution is 10 to 100times lower than the RME, and the95th percentile is a factor of3 lower than the calculated RME. This is an important finding to consider in the evaluation ofthe hypothetical risks described in subsequent sections since it suggests that exposures may be at or above the 99th percentile and therefore meets the definition ofan RME (EPA, 1989a). The quantitative uncertainty analysis did not address the uncertainty associated with infrequently detected chemicals. The uncertainty is resolved conservatively by the replacement method, which assumes nondetections areequal to one-half the CRL (Haas and Scheff, 1990). A substantial portion ofthe estimated carcinogenic risk is attributable to EPA category B2 (probable human) carcinogens, particularly chloroform, and dieldrin. Category B2 designates chemicals for which there is sufficient evidence that the chemicals cause cancer in laboratory animals, but insufficient data that they are carcinogenic in humans. Because much ofthe total carcinogenic risk isbased on the extrapolation ofanimal data to an assessment ofhuman health effects, it is possible that these chemicals are not carcinogenic to humans at the estimated exposure levels. Amajor fraction ofthe estimated noncarcinogenic HIs also rests on RfDs derived from extrapolation of laboratory animal data to an assessment ofhuman health effects. Considering uncertainties associated with such extrapolation, as well as other factors (Section 3.1), the RfDs that critically determine the higher HIs reported here (e.g., liver toxicants and DIMP) incorporate uncertainty factors ranging from 100 to 1000.

4.1 RESIDENTIAL SCENARIO As required by the NCP and RAGS (EPA, 1990a; EPA, 1989a), this section focuses on the estimation of an RME for the residential scenario, including the potential for future exposures that are not occurring currenfly. The alluvial aquifer is used fordomestic supply only in zones IA, I C, and 6. Local agencies plan to develop a community water system, and the water supplied would come from uncontaminated sources or would be treated in compliance with the Safe

20000,317.10(3) - OEA 0306111892 111 - 4-2Drinking Water Act (SACWSD, 1991). Consequently, it is unlikely that residents ofthe Offpost OU are being orwould be exposed tochemicals in groundwater at the RME intake rates. Groundwater is the ultimate source ofapproximately 80 to 90percent ofchemical intakes estimated under the RME scenario. Nonetheless, itwas assumed conservatively that useofthe alluvial aquiferas the primary domestic water supply could occur; therefore, the EA evaluated the

use ofthe alluvial aquifer. Parts ofthe offpost operable unit are expected toremain rural for the foreseeable future. In these areas, specifically zones 1,2, and 6, arural residential scenario in which residents keep chickens and/or cattle and consume theireggs, milk, and meat, is the land use likely to result in RME exposures. In otherareas (zones 3 and 4), an urban residential land use, excluding farm animals, is possible and represents the RME. Finally, zone 5 is notexpected to develop residentially, and commercial/ industrial scenarios represent the RME. Chemical intakes will vary widely among a potentially exposed residential population. The degree ofvariability isshown by the quantitative uncertainty analysis results presented in Section 2.4.5.5 (Volume II). Hypothetically, 91 to99.8 percent ofthe population would experience intakes less than the calculated RME. According to the results ofthe quantitative uncertainty analysis (Section 2.4.5), the calculated RMEs for theOffpost OU have been found tobe in the range ofthe 99th percentile and toexceed the 95th percentile by approximately 3-fold. Recognizing the conservative aspects ofthis assessment, consistent with relevant guidance, most ofthis section is devoted to characterization ofthe risks at RME intake levels.

4.1.1 Hypothetical Future Exposures Hypothetical future HIsand carcinogenic risks were calculated by zone, chemical, and pathway. Consistentwith guidance (EPA, 1989a), zonecarcinogenic risks have been rounded to

one significant figure inthe text and tables. The term "hypothetical future"is intended to address the conditions thatexposure is only assumed (hypothetical) for the future scenario, thatadditional remediation is absent, and that the risks and HIs are derived from risk assessment methodologies, including low-dose and interspecies extrapolation, that are difficult toverify for humans.

20000,317.10(3) - OEA 0306111892 111 - 4-3Additive risks foreach chemical (all pathways) and each pathway (all chemicals) were determined foreach zone, leading to grand totals by zone for each target organ (noncarcinogenic) and total individual lifetime cancer risk. Results ofthese calculations are presented in a series ofmatrices in Appendix G. With respect to cancer risk, thecancer SFs used in these calculations are established at the UL95. Based on the uncertainty analyses, hypothetical risks cited in this section

are likely overstated by 3-fold compared tothe 95th percentile. Results ofthe assessment for carcinogens are summarized in Figure 4.1.1 - 1,which illustrates the data presented in Table 4.1.1 - 1. Hypothetical future RME cancer risksmay exceed I X 10-4 in zones 2, 3, and 4 with maximum risksof approximately 3 x 10-4 in zone 3. The hypothetical future combined risks from exposure to aldrin, arsenic, atrazine chloroform, and dieldrin account for more than 82percent of the additive risk in each zone. The results of the assessment of noncarcinogenic hypothetical future His are summarized in Table 4.1.1-2, which lists all child chronic combined His that exceed 1. Child chronic His are shown because His are greater for children than adults based on intake rates. Acute/subchronic results will be described separatel\. Chlordane, chloroform, dicyclopentadiene, dieldrin, DIMP, and manganese are the only chemicals that contribute significantly to hypothetical future His greater than 1. Reviewing these results, it is apparent that only a fewCOCs contribute substantially to hypothetical future cancer risks and His. The majority ofthediscussion will emphasize the COCs, arsenic, chloroform, DIMP, and dieldrin.

4.1.1.1 Hyvothetical Carcinogenic Risks Related toBackground As indicated in Section 2.4.2.5, dieldrin concentrations in surficial soil outside zones 3 and 4 do not appear to be attributable to RMA but instead to agricultural practices. However, the risk associated with the dieldrin soil data was quantified. The hypothetical risk associated with dieldrin in soil in zones IA, IB, IC, '41, 5, and 6 may be as great as4 x 10-5. Thisrisk may notbe attributable to RMA sources.

20000,317.10(3) -OEA 0306111892 111 - 4-4Naturally occurring arsenic also contributes to carcinogenic risk in several zones. The UL95 concentration of arsenic in the Offpost OU comparison dataset was 1.86 ug/l; an additional comparison group located in theonpost southeastern tier had an UL95 arsenic concentration of 3.13 AgIll. The additive carcinogenic risk associated with these concentrations ranges from 4.4 x 10-5 to 7.4 x 10-5 forthe offpost and onpost comparison data sets. Combining the hypothetical risks from dieldrin in soil outside ofzones 3and 4 (4 x 10-5) and from arsenic in groundwater (4.4 x 10-5) yields arisk of8 x 10-5 from sources thatare either non-RMA related or naturalIN: occurring background risks.

4.1.1.2 Child Chronic Hwothetical Future Hazard Indices The hypothetical future HI for liver toxicants exceeds I in zones 2, 3, and 4, with a maximum HI of2 in zone 3. Therefore, particularly in zones 2, 3, and 4, there is ahypothetical hazard of liver toxicity from future chronic exposure at RME intake levels. The hypothetical hazard of liver toxicity is predominantly attributable to exposure to chloroform, chlordane, dicyclopentadine, and dieldrin. The OCPs and the chlorinated aliphatics are included in the listof liver toxicants. Figure 4.1.1-'.2 shows the chemicals and pathways that pose the greatest hypothet-ical occurrence of liver toxicity. No single chemical or single pathway yields a hazard quotient greater than 1. Exposure by inhalation and ingestion routes to chloroform in shallow groundwater assumed to be used for domestic supply contributes significantly tothe combined liver hazard index of 2 estimated for zone 2. Exposure to dieldrin in vegetables is the largest contribution to the combined liver hazard index of 2 in zone 3, and exposure to chlordane in groundwater is the largest contributor in zone 4. Two chemicals have the potential to affect the CNS for which the hypothetical future RME HI exceeds I in zones 2 and 4 (Table 4.1.1-2). DIMP attains a maximum hypothetical future HI of 3.1 in zone 4 (Appendix G) and, in combination with manganese, produces an RME HI of3.7 in

zone 4. These chemicals are elevated in groundwater, and all exposure isoral. Uptake by vegetable crops when groundwater is used for irrigation contributes to exposure and HIs for these chemicals.

20000,317,10(3) - OEA 0306111892 111 - 4-54.1.1.3 Adult Chronic Hvvothetical Future Hazard Indices As presented in Section 2.4.3, adult chronic intakes are consistently less than child chronic intakes, and His are also lower in direct proportion. Thegreatest hypothetical future HI for the adult chronic scenario is 1.3 for liver toxicants in zone 3, with dieldrin the largest contributor, and is approximately one-half the value of2 estimated forchildren in the same zone. Hypothetical future adult chronic His greater than I occur for liver toxicants in zones 3 and 4. DIMP is the majorcontributor to a hypothetical future HI of2.4 in zone 4.

4.1.1.4 HvI)othetical Future Carcinogenic Risk The hypothetical future risk associated with each carcinogenic chemical by zone isshown in Figure 4.1.1-3. These risks may be overstated by a factor of3, according to the results ofthe uncertainty analysis. These results are based on the RME assumptions and an UL95 for thecancer SF. Clearly, hypothetical future carcinogenic risks are greater in zones 2, 3, and 4 than in other

zones. Chloroform, arsenic, and dieldrin present the highest incremental risks. Chloroform risks are limited primarily to zone 2, and risk attributable to dieldrin is distributed more uniformly. Figure 4.1.1-3 further supports the identification ofarsenic, chloroform, and dieldrin

as thecarcinogenic COCs of greatest concern.

4.1.1.5 Zone-svecific Risks In this subsection, the contribution ofthe most important exposure pathways to carcinogenic risk by COC is described for each zone. Several exposure pathways contribute to total carcinogenic risk, depending on chemical and zone. The hypothetical future carcinogenic risk in each

zone is attributable to the following pathways: ingestion ofshallow groundwater (47 percent), consumption ofhomegrown vegetables (average contribution to total carcinogenic risk - 26percent), ingestion of locally produced milk (9 percent), consumption oflocally produced eggs (6 percent), inhalation ofvolatiles via domestic use ofgroundwater (7 percent), and consumption of locally produced meat (3 percent). Dermal exposure does not contribute significantly to carcinogenic risk, nor does incidental ingestion of soil and sediment. The oral route accounts for

20000,317.10(3) - OEA 0306111892 111 - 4-6more than 90 percent oftotal hypothetical future carcinogenic risk, with the remainder predomi7 nantly by inhalation. As indicated previously, riskspresented in this section may be overstated by

a factor of 3as indicated by the uncertainty analysis. Zone IA. north ofO'Brian Canal, is an area ofrelatively low groundwater and soil contamination (Figure 2.4.1-2). Atrazine and arsenic in groundwater and dieldrin in soil are the largest contributors to hypothetical future carcinogenic risk in zone IA. Dieldrin hypothetical future risks result from several exposure pathways because aldrin and dieldrin are bioaccumulated effectively by root vegetables, milk, meat, and eggs. The method for estimating exposure concentrations in foods assumes that agricultural products can bioaccumulate chemicals from soil and surface water and that aldrin is converted to dieldrin upon uptake. Groundwater and surface

water in zone IA do not contain large concentrations of dieldrin, thus, the dieldrin residues estimated in foods are attributable predominantly to uptake from soil. An alternative way ofcharacterizing the sources ofthe estimated risk is to disaggregate risk associated with the abiotic media (groundwater, surface water, and soil) from which each of the agricultural products may accumulate chemicals (Section 2.4.2). In zone IA, surface water is uncontaminated, groundwater contributes approximately 60 percent oftotal potential risk, and soil contributes approximately 40 percent. Zone IB, south of O'Brian Canal, between the northwest boundary plume and the First Creek paleochannel (Figure 2.4.1-2), is an area of relatively low groundwater and soil contamination. No permanent surface-water features are in zone IB, and agricultural water supply is assumed to be exclusively by alluvial groundwater. Otherwise, exposure conditions are identical

in zones IA and IB. Results in these two zones differ (Figures 4.1.1-4 and 4.1.1-5) because agricultural water supplies were assumed to have higher concentrations of COCs because they are

not diluted by uncontaminated surface water. As a result, future hypothetical risks are slightly higher in zone IB. Zone IC is identical to IA except that irrigation water is drawn from O'Brian Canal and the Burlington Ditch upstream of the outfall of First Creek and is not affected by RMA

20000,317.10(3) - OEA 0306111892 111 - 4-7(Figure 2.4.1-2). In fact, nocarcinogenic COCs were detected atelevated concentrations inthe canals downstream ofFirst Creek, resulting in identical results for carcinogenic risks in zones ]A and IC(compare Figures 4.1.1-4 and 4.1.1-6). As described in Section 4.1.1.1, background concentrations ofarsenic in groundwater and dieldrin in surficial soil may contribute as much as8 x 10-5 carcinogenic risk to the totals shown in Table 4. 1.1-1. The contribution ofbackground risk to Zones IA, IB, IC, 2, 5, and 6 should be considered when evaluating total risks in the Offpost OU. Zone 2 is located directly north ofthe RMA northern boundary (northern paleochannel, Figure 2.4.1-2) and south ofO'Brian Canal. No permanent surface-water features are in zone 2,

an area with relatively high concentrations ofCOCs in groundwater but relatively low concentrations in surficial soil. Approximately 30 percent ofthe hypothetical future carcinogenic risk,In zone 2is attributable to the domestic use of groundwater containing chloroform and (Figure 4.1.1-7). Consistent with EPA guidance, inhalation intakes of volatile chemicals such as chloroform were assumed to equal intakes from ingestion ofgroundwater. Chloroform has a much higher slope factor by the inhalation route than the ingestion route, so hypothetical future risks by the groundwater inhalation pathway were estimated to be much greater than the groundwater ingestion pathway. More than 80 percent ofthe hypothetical future carcinogenic risk estimated for zone 2 'Isultimatelv attributable to the use of groundwater. The inhalation route ofexposure contributes approximately 30 percent oftotal hypothetical future carcinogenic risk in zone 71 (the highest relative contribution ofthe inhalation route for any zone, related to the dominance of volatile COCs in zone 2 groundwater). Zone 3 is the area within approximately 0.5 mile ofthe intersection ofPeoria Street and 96th Avenue (Figure 2.4.1-2). First Creek traverses zone 3, which is an area with relatively high concentrations ofCOCs in surficial soil, groundwater, and surface water. No human receptors currenfly reside in zone 3. Figure 4.1.1-8 presents RME estimates ofhypothetical future risk under the hypothetical urban residential land use scenario for zone 3. Hypothetical future carcinogenic risk would be dominated by exposure to dieldrin by vegetable and groundwater

20000,317.10(3) - OEA 0306111892 111 - 4-8ingestion pathways. The oral route would account for approximately 97 percent ofthe total risk. Total hypothetical future carcinogenic risk for zone 3under the hypothetical urban residential scenario would be attributable primarily to chemical concentrations in shallow groundwater (60 percent), with significant contributions from surface water (150 percent) and soil (30 percent). Arsenic and dieidrin are the predominant contributors to hypothetical future carcinogenic risk in zone 4 (Figure 4.1.1-9). Zone 4 (First Creek paleochannel) is northwest ofzone 3 and traversed by First Creek (Figure 2.4.1-2) and isan area ofrelatively high surface-water and groundwater contamination and relatively low surficial soil contamination. No human receptors reside in zone 4 at this time. COCs in groundwater ultimately are the source ofapproximately 80 percent ofthe total hypothetical future carcinogenic risk. Surface water contributes approximately 10 percent oftotal risk, and 10 percent ofthe hypothetical future carcinogenic risk is ultimate]\ attributable to OCPs in surficial soil. As shown in Figure 4. 1.1 -10, dieldrin and arsenic have the greatest contribution to total hypothetical future carcinogenic risk in zone 5, an area downgradient ofthe NWBCS and south of the canals (Figure 2.4.1-2). Nosurface-water features are in zone 5, soil concentrations are relatively low, and groundwater concentrations are moderate. Groundwater ingestion is the most important pathway, accounting for 89percent ofhypothetical risk. In zone 5, 99percent ofthe hypothetical future RME risk is attributable to groundwater and less than Ipercent to soil concentrations. Zone 6 is the extension ofthe northwest boundary plume north ofthe canals (Figure 2.4.1-2). Hypothetical future carcinogenic risks are predominantly attributable to dieldrin (Figure 4.1.1-11). Soil and groundwater each contribute approximately 50 percent ofthe hypothetical future risk. A summary ofthe contributions to hypothetical future carcinogenic risk by chemical, exposure pathwaý, exposure route, and source media follows: 1.The contribution ofdieldrin to total carcinogenic risk is greater than that ofany other chemical in zones 1,3, and 6. Chloroform poses the greatest risk in zone 2and arsenic in zone 4.

20000,317.10(3) - OEA 0306111892 111 - 4-92. Groundwater ingestion is the exposure pathway with the greatest contribution tototal risk in all zones except zone 3. Ingestion ofhomegrown vegetables isthe largest pathway in zone 3. Domestic use of groundwater (ingestion and inhalation) accounts for approximately 50 percent ofhypothetical future carcinogenic risk outside zone 2 and 67 percent in zone 2. 3. Consumption of vegetables produced in the Offpost OU isalso an important pathway contributing approximately 25 percent ofthe hypothetical future risk. 4. The oral exposure route contributes more than 90percent ofthe total risk in each zone except zone 2, where inhalation contributes approximately 30percent oftotal risk. 5. Background concentrations ofdieldrin in soil attributable to agricultural practices appear to contribute 20 to 50 percent ofthe total hypothetical future carcinogenic risk in zones 1A, 113, W, 2, and 6. Groundwater is thedominant source medium contributing to total hypothetical future carcinogenic risk. Naturally occurring arsenic in groundwater contributes a risk ofapproximately 4 x 10-5. Surface water contributes less than 15 percent oftotal risk in zones 3 and 4.

4.1.1.6 Acute/Subchronic Effects H\,pothetical future acute effects were evaluated by comparison ofacute intake estimates with Minimal Risk Levels (MRLs) developed by the ATSDR and summarized by EPA (1991b). Reference doses were also estimated from EPA's short-term health advisories (HAs) (shorter than 14 days). Acute intakes were estimated for two potentially sensitive subpopulations: women of childbearing age and children. MRLs were not exceeded for any chemical in any zone. Dieldrin is the only chemical estimated hypothetically to exceed HAs. EPA's one-day HA for dieldrin is exceeded hypothetically in zones 2, 3, and 4. An acute HI has been estimated by dividing acute intakes by acute reference doses. Results from children are illustrated in Figure 4.1.1-12 indicating that dieldrin is the predominant contributor to acute His and that the HI exceeds I in

zones 2, 3. and 4, with a maximum acute HI of4 in zone 3. Table 4.1.1-3 presents these results numerically. Adult female acute His are consistently about 60 percent less than children and less than I in all zones except 3. These results indicate that the potential for adverse health effects exists as the result ofhypothetical future short-term exposure to dieldrin at the RME acute intake level in zones 2, 3, and 4. Available data sources used to define exposure factors (Section 2.4.3.2) do not readily support the estimation ofexposure factors averaged over subchronic exposure durations. Acute

20000,317.10(3) - OEA 0306111892 111 - 4-10and chronic intakes have been estimated. RME intakes over subchronic exposure durations are expected to be less than RME acute intakes and greater than or approximately equal to RME chronic intakes. Exposure assumptions adopted in the residential scenario assume continuous residency over periods encompassing a chronic exposure, and the most important exposure pathways are not expected to result in extreme seasonal variability in exposure. Vegetable consumption may vary seasonally with the availability ofhomegrown produce. Thus, although the RME subchronic intake is clearly less than the RME acute intake and greater than the RME chronic intake, it is probably in the low end of that range (i.e., slightly greater than the RME chronic intake). The method used to estimate subchronic His is asfollows: for the lower range, the RME chronic intake was divided bv the subchronic reference dose; for the upper range, the RME acute intake was divided by the subchronic reference dose. Tables 4.1.1-4 and 4.1.1-5 summarize the zone/chemical combinations that have the potential foradverse effects as a result ofexposures

over subchronic duration for children and adult females, respectively (all chemicals whose RME acute intake exceeds the subchronic reference dose). Figure 4.1.1-13 illustrates the range of hepatic His for children by zone. Dieldrin and manganese are the only chemicals with the potential for noncarcinogenic effects as a result ofexposure ofsubehronic duration. When the upper end ofthe range reported exceeds 1,the potential foradverse effects exists; also, ifthe lower end ofthe range isgreater than 1.the RME chronic intake exceeds the subehronic reference dose. Subchronic reference doses have not been published by EPA for all offpost COCs. For those COCs, RME acute intakes were compared to chronic reference doses and subchronic MRI-s (developed by ATSDR and summarized by EPA, 1991b). This final comparison revealed that no chemicals without subchronic reference doses have significant hypothetical future potential for adverse effects asthe result of exposures over subchronic durations (i.e., RME acute intakes exceeded neither chronic reference doses nor subchronic MRI-s for chemicals without subchronic reference doses).

20000,317.10(3) - OEA 0306111892 111 - 4-114.1.2 HvDothetic Current Risks Versus Hypothetical Future Risks As used in this subsection, the term "hypothetical" refers to the application of risk assessment methodologies that extrapolate from high doses to low doses and from laboratory animals to humans. No residents are in zones 3 or 4 at this time; hence, exposure pathways are not complete, and there are no hypothetical current health risks in these zones for the residential scenario. Residents in zones IB and 2 do not use the alluvial aquifer for domestic use; hence, these pathways are not complete. Based on the consumptive use surveys, alluvial groundwater may still be used as an agricultural water supply in zones IB and 2, and RME intake levels associated with agriculture would result in hypothetical risks of less than 8 x 10-5. These risks were determined by subtracting the hypothetical risks associated with the groundwater oral and inhalation exposure pathways (Volume IV, Appendix G). Background risks due to zone 1, 2, and 6 contaminants in soil alone, regardless of the source or use of water, are approximately 4 x 10-5 for residents who consume agricultural products produced in the Offpost OU at RME intake levels. All cited risks may be overstated bv a factor of 3 as indicated by the uncertainty analysis. By a similar process ofeliminating currently incomplete pathways, the maximum hazard index under existing exposures is less than I in all zones.

4.1.3 Health Risk at Most Likelv Ext)osure Intakes The principal focus of the human risk characterization was to estimate health risks at RME intake levels. An uncertainty analysis was performed to characterize the distribution ofchemical intakes among the potentially exposed population, the uncertainty associated with intake estimates. and the degree of conservatism incorporated in the RME risk estimate. To provide additional perspective on this topic, the MLE intakes as well as chronic HIs and cancer risks at the MLE intakes have been estimated. In calculating MLE risks, the same conservative RFDs and SFs used in the RME risk calculations were used, so the appropriate interpretation ofthe MLE risk estimates would be that they are conservative estimates of risk for individuals experiencing MLE intakes. 20000,317.10(3) - OEA 0306111892 111 - 4-12MLE intakes were estimated for all COCs and completed pathways for the hypothetical future exposure scenario. The chronic MLE intakes were estimated using the same equations used for tile RME intakes. The input parameters selected forthis analysis, however, were mean or median values. Mean values were used for exposure concentrations and parameters used to estimate exposure concentrations in food. Median values were used forexposure factors such as ingestion rates and exposure frequency and duration. As aresult, the MLE intakes represent the best estimate ofthe median intake for the potentially exposed population. Because the toxicity factors were the same in both the MLE and RME analyses, the ratio ofRME intakes to MLE intakes is the same as the ratio of RME risks to MLE risks. Table 4.1.1-6 summarizes the additive hypothetical carcinogenic risks at the MLE intake levels and compares these estimates to the RME risks. At MLE intake levels, hypothetical carcinogenic risks would not exceed 3 x 10-5 (zone 4). Risks at RME intake levels typically exceed MLE risks by a factor of 10. It is estimated that approximately halfofa potentially exposed rural residential population would experience intakes less than the MLE and half would experience higher intakes. Less than 2 percent ofthe population would experience intakes as high as the RME (see Section 2.4.5). With respect to potential noncarcinogenic effects, child-chronic His for hepatic effects at MLE intakes do not exceed I in any zone. Hepatic His at MLE intake levels are approximately one-third ofthe RME His. At MLE intake levels, the CNS HI was estimated to be 4 in zone 4. This result is affected by the unique features ofthedistribution ofobserved concentrations of DIMP in groundwater (see Section 2.4.5.5.2). Selection ofthe sample mean as the best estimate of the population mean, instead ofthe lognormal estimator (Gilbert, 1987) would have resulted in an MLE central nervous system HI <1 for zone 4. An important implication ofthe MLE analysis, which is also supported by the uncertainty analysis, is that risks presented at RME intake levels are not representative ofthe risks faced by the majority ofthe hypothetically exposed population. Although a few individuals might be exposed at RME levels, the MLE intakes are more representative ofthe typical exposure levels. The RME exposure rates and corresponding risks overstate the carcinogenic risk to the typical

20000,317A0(3) - OEA 0306111892 111 - 4-13resident by factors ranging from 8to 12 times. Similarly, the typical child's noncarcinogenic hepatic HI would be three times less than RME HIs reported (MLE hepatic HI :51).

4.1.4 Alternative Risk Estimate Based on Predicted Decline in Groundwater Concentrations As presented in Section 2.4.2.2, groundwater concentrations are declining in zones 3and 4, and may be expected to decline further over chronic 9- and 30-year average concentrations for aldrin and dieldrin. All other organic contaminants may be expected to decline at least asfast as these relative]y immobile groundwater COCs. Over the9-year exposure duration used for the noncarcinogenic assessment. concentrations were predicted to decline to 42 to 48 percent less than the RME concentrations based on 1989 to 1991 monitoring data. Over the 30-year exposure duration, average concentrations were predicted to decline by48 to 74 percent. The effect ofusing these predicted aldrin and dieldrin concentrations while holding other COC concentrations constant is not substantial. Cancer risk in zone 3 would be reduced from 3x 10-4 to 2 x 10-4,and the child chronic hepatic hazard index would remain at 2. In zone 4 the carcinogenic risk is unaffected when rounded offto one significant figure at 2 x 1 0-4, and the child chronic hepatic hazard index would decline from 1.4 to 1.2. If, on the other hand, one

assumes that all organic groundwater COCs would be reduced by similar percentages, the effect would be more significant. Carcinogenic risk would decline from 3x 10-4 to 2 x 1 0-4 in zone 3 and from 2 x 10-4 to I X 10-4 in zone 4. The child chronic hepatic hazard index would decline from 2 to 1.4 in zone 3, and from 1.4 to 0.7 in zone 4. As noted in Section 2.4.2.2, these are conservative assumptions used in the aldrin/dieldrin decline prediction. Actual declines may be greater.

4.2 COMMERCIALANDUSTRIAL SCENARIO The C11 scenario differs from the rural residential scenario in that no agricultural pathways

are present (e.g., dairy, meat, vegetables). For this scenario, exposure pathways relating to groundwater and soil were evaluated. RME-estimated intake scenarios for carcinogenic risks and

20000,317.10(3) - OEA 0306111892 111 - 4-14noncarcinogenic His were quantified forzone 5 because ofthe likelihood of future land uses in this zone (Section 2.2.2.2). The exposure pathways that were evaluated forthe adult C/I worker included ingestion of groundwater and inhalation ofvolatiles from groundwater (including showering) and dermal exposure to and ingestion ofsoil. The sediment and surface-water exposure pathways were not evaluated because the ingestion and dermal exposure routes were not expected to occur in zone 5.

4.2.1 Adult Chronic Hypothetical Future Hazard Indices The additive hypothetical future HI for liver toxicants was <0.1 in zone 5 (Figure 4.2.1-1). The OCPs account for the highest His through the soil and groundwater pathways via the ingestion route of exposure. Because thechronic liver His were less than 1,acute HIs are not presented.

4.2.2 Hvt)o hetical Future Carcinopenic Risks The hypothetical future carcinogenic risks for the CIIscenario range from 1.8 x 10-9 to 1.6 x 10-5 in zone 5. Arsenic is the major contributor to the hypothetical future carcinogenic risks in zone 5. Arsenic accounts for approximately 60 percent ofthe estimated risk in zone 5. Exposure to arsenic by the ingestion of groundwater isthe single largest pathway component to the overall hypothetical future risk.

4.2.3 Carcinopenic Risk at Most Likelv Exposure Intakes For the CII scenario, MLE His are approximately 67 percent less than the RME His. The MLE liver H1 is 0.07 for zone 5. The MLE hypothetical future carcinogenic risks are approximately 30 percent less than the RME risks, with risks of7 x 1 0-6 zone 5.

4.3 RISK CHARACTERIZATION SUMMARY Additive carcinogenic risksfor potential future residential exposures at RME intake levels by zone are summarized in Table 4.1.1-1, which shows that cancer risk is highest in zones 2, 3, and 4. These zones are south of O'Brian Canal and within approximately I mile ofthe north

20000,317.10(3) - OEA 0306111892 111 - 4-15RMA boundary. Hypothetical future cancer risks in each ofthese zones are estimated to be less than 3x 10-4. These risks maybe overstated by a factor of3 as indicated by the uncertainty analvsis. More than 60 percent ofthe riskJn each ofthese zones is attributable to category B2 and C carcinogens. Thus, the carcinogenic risk estimate is critically dependent on the extrapolation of toxicological data from animal to human. Discussions on the potential carcinogenicity of each COC are in the toxicological profiles, including Shell OilCompany's toxicological profile for aldrin and dieldrin, located in Appendix F ofthe EA. Dieldrin isthe dominant contributor to total cancer risk in zones 3 and 6 and is significant in all other zones with an average contribution ofapproximately 50 percent. Chloroform contributes 30 percent in zone 2 and arsenic 30 percent in zone 4. Several exposure pathways contribute to total hypothetical carcinogenic risk, depending on chemical and zone. More than 95 percent ofthe carcinogenic risk in each zone, however, is attributable to the following pathways. listed in order oftheircontribution torisk (highest to lowest): I.Ingestion of shallow groundwater 2. Consumption ofhomegrown vegetables 3. Ingestion of locally produced milk 4. Inhalation of volatiles via domestic use ofshallow groundwater 5. Ingestion of locally produced eggs 6. Ingestion of locally produced meat

Dermal exposures do not contribute significantly to carcinogenic risk, nor does incidental ingestion of soil and sediment. The oral exposure route accounts for more than 90 percent oftotal carcinogenic risk, with the remainder predominantly by inhalation. Shallow groundwater isthe dominant source medium contributing to total hypothetical carcinogenic risk in all zones accounting for 45 to 80percent oftotal risk, depending on the zone. Soil contributes 20 to 60percent ofthe risk in zones IA, IB, IC and 6. Groundwater, surface water. and soil contribute to estimated risks via multiple pathways, specifically those involving

20000,317.10(3) - OEA 0306111892 111 - 4-16M

local food production. Groundwater and surface water were assumed to be used for irrigating vegetable crops and watering livestock. Each ofthe food pathways may also accumulate COCs from soil, and these relationships are quantified via theequilibrium partition models presented in Section 2.4.2. Hypothetical risks from all carcinogens were added to determine total carcinogenic risk, regardless oftarget organ/system or weight-of-evidence category. The dominant contribution to total carcinogenic risk in all zones is from category B2 and C carcinogens, as previously described. Hypothetical future noncarcinogenic effects were evaluated for all COCs. Children are a potentially sensitive subpopulation with the largest potential for adverse noncarcinogenic effects due to higher chemical intakes (mg/kg/day). Considering the target organ/system potentially affected bv each of the COCs, the most probable nonearcinogenic effect would be on the CNS asa result ofhypothetical future exposure to DIMP in zone 4, where the HI is4. The hypothetical additive child chronic HI for livertoxicants has a maximum of2 in zone 3. The probability ofadverse effects to women and fetuses is less than the risk,to children because the adult female intake is less than the child intake based on intake rates and body weight. None of the chemicals with Hls approximately equal to or greater than I (indicating potential for adverse noricarcinogenic effects) demonstrate developmental toxicity effects at doses lower than those that adversely affect the mother. Consequently, the chronic and subchronic RfDs are protective for developmental effects. RMEs of existing exposures and resultant health risks are substantially less than hypothetical future exposures. No human receptors reside in zones 3 and 4 at this time; hence, there is no current risk in these zones. Residences with RME concentrations in shallow groundwater wells in

zones IB. 2, 3, and 4 (before relocation) use water supplies other than shallow groundwater. Consequently, groundwater pathways are not complete in these zones. Residential risks due to existing exposure to soil, regardless ofwater use, range from as little as Ix 10-5 (zone 4), to as much as 8 x 10-5 (in zone 3) for residents who might consume foodstuffs produced in the

20000,317.10(3) - OEA 0306111892 111 - 4-17Offpost OU at RME intake levels. However, the 4 x 10-5 risk associated with soil in zones other than zone 3 and 4 may not be attributable to RMA sources but toagricultural practices. MLE His and carcinogenic risks were estimated forthe residential scenario. The carcinogenic risks were from 8 to 12 times less than corresponding RME risks, depending on the

zone. Hypothetical future carcinogenic risks and noncarcinogenic His were estimated for RME intake levels for the C11 scenario. Dieldrin, aldrin, and arsenic account for the largest portion of risk. approximately 80,percent, through the groundwater ingestion exposure pathway. The chronic His for liver toxicants were all <0.1 for zone 5;the OCPs (chlordane, dieldrin, and aldrin)

are the major HI chemical contributors through thegroundwater ingestion pathway. MLE His and carcinogenic risks forthe C11 scenario are approximately 67 and 33 percent ofthe RME risks, respectively.

4.4 UNCERTAINTIES IN THE HUMAN HEALTH ASSESSMENT Uncertainties in the riskcharacterization represent the combined uncertainties ofthe exposure and toxicity assessments. Overall, these uncertainties were resolved byconservative assumptions. Consideration ofthe risk characterization results permits identification ofthe most important contributors tooverall uncertainty. 1. Identification ofCOCs Potential uncertainties in identification ofCOCs have a minor orinsignificant effect on RME risk estimates. COCs contributing significantly to risk areclearly attributable to migration from RMA, and it is extremely unlikely that excluded chemicals could contribute significantly to the total RME risk. 2. Chemical Fate The quantitative uncertainty analysis documents that identified uncertainties in equilibrium partition coefficients used to estimate exposure concentration in foods do not contribute significantly touncertainty in RME risk estimates. Bioaccumulation of pesticides in agricultural products was estimated from experiments using freshly applied chemicals. Site conditions differ; pesticides have aged in soil for many years. This ýource ofuncertainty cannot be evaluated because oflack ofpertinent research information. Numerous COCs have been shown tobiodegrade over time in soil, surface water, sediment, and groundwater. Biodegradation processes were not quantified due to lack ofpertinent site-specific information. This limitation ofthe assessment maycause chronic and lifetime risks to be overestimated.

20000,317.10(3) - OEA 0306111892 111 - 4-183. Exposure pathways Exposure pathways contributing most ofthe residential RME risk in zones 2, 3, and 4. are not complete at this time. In zone 2, alluvial groundwater is not used for domestic supply, but this pathway contributes 74 percent ofRME total carcinogenic risk and 56 percent ofthe child chronic hepatic HI. Pathways excluded from the quantification, through potentially complete, have the potential to add less than 15 percent tototal carcinogenic risk. 4. Intake Estimation Chemical concentrations are expected to decline over time. Intake estimates are based on monitoring data from 1989 to 1991 and may overestimate current and future exposure concentrations. Exposure and risks may be greater than zonewide average risk estimates in localized (e.g., one to five acres) hot spots (up to twice as high in identified hot spots in zones 2and 3). On the other hand, the risk throughout most ofeach zone is probably lower than the zonewide RME. RME exposure concentrations calculated from monitoring data may differ from actual exposure concentrations due solely to the selection ofthe statisticafcalculation procedure. The effect ofthese differences on carcinogenic riskestimates in any zone is estimated to be less than 40 percent. However, the CNS hazard index in zone 4 may be overstated bv a factor of5 for this reason. The results ofthe quantitative uncertainty analysis indicate that RME intakes achieve the goal ofthe RME in estimating an exposure in the upper range ofthose possible. In fact, RME estimates could significantly exceed the 95th percentile exposure, the lower boundary suggested by EPA for an upper range exposure estimate. The RME intakes consistently fall at or above the 98th percentile ofthedistribution ofintakes and typically exceed the 95th percentile by afactor of3. Most people in the Offpost OU will experience intakes substantially less than the RME. 5. Toxicity Assessment Reference doses typical]\,are set 100to 1000 times lower than the lowest doses found to produce an adverse effect in animal studies. These uncertainty factors are reflective of the uncertainties in risk caused by uncertainties in the toxicity assessment. These uncertainties are resolved conservatively by the EPA-recommended procedures adopted in the assessment. An overwhelming portion (59 to 100percent, depending on zone) oftotal carcinogenic risk estimated for humans is attributable to category B2 and C carcinogens. There is insufficient evidence that these chemicals cause cancer in humans. Thus, it is possible that these chemicals are not carcinogenic to humans.

In summary, the RME risk estimates presented here are sufficiently conservative for use in risk management decisions for the offpost operable unit.

20000,317.10(3) - OEA 0306111892 111 - 4-195.0 ECOLOGICAL ASSESSMENT

The objective ofthe Offpost OU ecological risk assessment wasto evaluate potential adverse effects to the environment and nonhuman receptors as aresult ofpotential exposure to chemicals migrating from onpost sources. This section ofthe EA reviews the sitecharacterization with emphasis on ecological receptors. An ecological exposure assessment is provided that describes two ecological assessment endpoints: (I)residue concentration in tissue thatcould adversely affect function or health and (2) contaminant concentrations in abiotic media at levels that could have an impact on ecological receptors through direct toxicity. Procedures for evaluating each are described. The final section characterizes the risk to ecosystems, with particular reference to

zones 3 and 4 in the Offpost OU. Although the EPA has recently published several documents onecological risk assessment (EPA, 1992a, 1992b, 1992c), guidance similar to that for human health risk assessments (EPA, 1989a) Is not available. Therefore, the procedures the Army used to evaluate the potential effects ofoffpost chemicals of concern in ecological receptors for this ecological assessment have been developed from several sources, including theopen literature, EPA documents, and professional judgement. Because oftheevolving nature of ecological risk assessment methodology, the assumptions and approaches adopted for the Offpost OU Ecological Assessment may notbe applicable for use at sites or locations outside theOffpost OU boundaries. Also, the acceptance of the Offpost OU procedures and values as they appear in this document does not imply that the Offpost procedures and values set precedent for use at other sites and locations.

5.1 SITE CHARACTERIZATION 5.1.1 Studv Area Definition The offpost area is defined as thetriangular region north ofRMA that is bounded by the South Platte River on the west and Second Creek on the east, including the waters ofBarr Lake (Figure 2.4.1-2). Sampling areas for biota in the offpost area are in Figure 5.1.1-1 (HLA, 1992). Two major natural ecosystems occur in the Offpost OU: terrestrial and aquatic. The area isalso

20000,317.10(3) - OEA 0815111892 111 - 5-1

### extensively used for agricultural purposes. Regional topography isrepresented by stream-valley lowlands andgently rolling uplands. A result ofthetopographic reliefis apparent in well-defined surface-water drainage areas, wetland features, andlargeexpanses oftemperate grasslands. The Offpost OU supports many ofthe same wildlife species foundonRMA; however, because biotic

resources differ andbecause oftheoccurrence ofintense agricultural land management practices in the Offpost OU, biotasamples wereprimarily restricted tozones 3and4. The majorecological habitats arepresented in Figure 5.1.1-2 (HLA, 1992). 5.1.1.1 Terrestrial Systems A detailed analysis ofaerial photography ofthe OffpostOU wasconducted to identify site usage patterns andto delineate accurate boundaries ofland usefrom aerial photographs taken in 1950, 1969, and 1983 (Bionetics Corporation, 1984). Since 1950, themajority ofthe Offpost OU has beendominated by agricultural lands, primarily supporting grain cropsand pasture, withsome fallow or idlefields. During 1990, a visualcharacterization oftheOffpost OUwas conducted byESE. The primary field crops grown in theOffpost OU include Winterwheat, hay, barley, cornfor grain,

cornfor silage, sugar beets, andoats. Othercrops in thisarea include avariety ofvegetables, sorghum, dry beans, and Springwheat. Ofthe field cropslisted, Winter andSpring wheat,barley, sugar beets, and drybeans are produced forhuman consumption, and corn, haycrops, sorghum, andoats areproduced for animal feed. In general, areas oftheOffpost OU located north ofO'Brian Canal areirrigated, whereas

areas south ofthecanal rely on dryland farming. Pasture is asignificant resource within the Offpost OUbut accounts formuch less acreage than croplands. Intense grazing was observed along theFirst Creekcorridor and in the FirstCreekImpoundment vicinity(HLA, 1992). Other land usesinclude confined livestock feeding operations, residential, industrial, transportation, and mineral extraction.

20000,317.10(3) - 0EA 0815110892 111 

### - 5-25.1.1.2 Aauatic Systems Because ofthe degree ofnatural surface-water drainage and water resource management (waterways, lakes, ponds, reservoirs), limited, butimportant, wetland resources occur in the Offpost OU. Aquatic systems include Barr Lake, O'Brian Canal, Burlington Ditch, South Platte River, First Creek, Second Creek, and several ponds and reservoirs, as shown in Figure 1.2-5. First Creek Impoundment and First Creek were studied during the Offpost RI for habitat characterization, contamination, and species occurrence because these aquatic ecosystems contain the highest concentration and/or frequency ofdetection ofchemical residues attributed to COCs originating from RMA sources. In addition to First Creek and First Creek Impoundment, surface-water and sediment samples were also collected from O'Brian Canal, Burlington Ditch, and Barr Lake (HLA, 1992). As intermittent streams, First Creek and Second Creek do not supporteconomically or environmentally important fish populations. O'Brian Canal is a manmade channel principally used for irrigation that can be expected to support fish species characteristic ofthe South Platte River. Fathead minnows, white suckers, and green sunfish are the most frequently observed species in these water bodies (Environmental Research and Technology [ERT], 1985). Barr Lake is the largest lentic aquatic habitat ofthe Offpost OU. The Colorado Division of Wildlife stocks Barr Lake with channel catfish, smallmouth and largemouth bass, Sacramento and yellow perch, rainbow trout, crappie, and bluegill. Barr Lake provides important nesting and foraging habitat for a variety ofbirds, including white pelicans, great blue herons, cormorants, mallard ducks, grebes, gulls, and bald eagles. In addition to hosting a large heron rookery, Barr Lake has been the site where a pair ofbald eagles has nested since 1986. Recreational fishing and waterfowl hunting are permitted at Barr Lake State Park. Angler effort and fish catch statistics for Barr Lake indicate thatin 1980, 5000 fish were harvested, including carp, bass, and catfish, representing 24,000 angler hours. Barr Lake has received industrial and sewage effluent and runoff from urban and agricultural land since the lake was constructed more than 80 years ago (DRCOG, 1989).

20000,317.10(3) -OEA 0815110892 111 - 5-35.1.2 Ecological Characterization ofthe Offoost Onerable Unit Habitatmapping ofthe First Creek portion ofthe Offpost OU (HLA, 1992) identified intensive human land use, including dryland farming, cattle grazing, private dumps, and residences (Figure 5.1.1-2). Small vacant lots, fallowfields, wetlands along FirstCreek, and prairie dogcolonies comprise the balance ofhabitat types inthe immediate offpost study area. Undisturbed habitats werenot identified in theOffpost OU. Wildlife species found in habitats in the offpost area (Table5.1.2- 1)were also common on RMA. However, wildlife species diversity in the Offpost OU is limited by the lack ofvariety in habitats and degree ofhuman disturbance. There are no federally designated critical habitats in ornear the Offpost OU (USFWS, 1990). The weedy forbs (WF) and grasses and weedy forbs (GWF) habitats were described inthe Biota RI (ESE, 1989b). The predominant species in the WFhabitat type include summer cypress (Kochiairanica),prickly lettuce (Lactucaserriola),thistle(CirsiumarvensisandCarduusnulans), Russian thistle (Salsolaiberica),field bindweed (Convolvulusarvense),various sunflowers (Helianthusspp.), and tumble mustard (Sisymbriumallissimum). The GWFhabitat type is similar tothe WFhabitat type but with an increased abundance ofcheatgrass (Bromuslectorum),western wheatgrass (Agropyronsmiihii),and bluegrass (Poa spp.) inaddition tothe forb species. WFand GWF habitat types support cattle and horse grazing in the offpost area, particularly along the channelized portion ofFirstCreek below the FirstCreek Impoundment. The offpost prairie dog (PD) colonyhabitat resembled the onpost RMA prairie doghabitat, with slightly less vegetative cover (field bindweed and bunchgrasses). Thehorse and cattle range appeared overgrazed, withonly a few interspersed forbs and grasses (HLA, 1992). Plowed and unplowed fallow fields (PFF and FF) were lightlyvegetated withremnant crops and grasses. The unplowed corners ofthe fallow fields were covered with WF-type vegetation, including the

common Russian thistle. Shelter belt cottonwood trees and ornamental plants surround the residences and buildings inthe mapped area, as shown in Figure 5.1.1-2. Approximately 250 acres ofwetlands occur along FirstCreek from the northern RMA boundary (North Bog) to the FirstCreek Impoundment. These wetlands have been delineated by

20000,317.10(3) - OEA 0815110892 111 - 5-4the U.S. Fish and Wildlife Service (Feasibility Study, Appendix B). These tall grass wetlands (TG-W) contain quackgrass (Agropyronrepens),intermediate wheatgrass (Agropyronintermediatuni),and cheatgrass. Many forbs found in the WF and GWF habitat types were also found in or adjacent to the wetlands. Cattail (Ti,pha angustifolia)marshes (CTM) and areas dominated by sedges (Carexspp.) and rushes (Scirpusspp.) are interspersed in the First Creek drainage. Below the First Creek Impoundment, the wetland vegetation was limited to the banks ofthe river course, which has been channelized and grazed back to aGWF habitat type. No immersed wetlands occur below the First Creek Impoundment until the creek empties into O'Brian Canal. The wetlands habitat, along with WF and GWF habitat, support most ofthe wildlife species observed in theoffpost area. 5.1.3 Contamination Pertaininp,to Offr)ost Biota Data from the chemical analyses ofcow milk and body fat, chicken tissues and a composite egg sample, and aquatic and terrestrial wildlife species are presented in the RI Addendum (HLA, 1992). Volume 11, Section 1.0 ofthis EA summarizes the contamination in the various media. Biota sampling locations are shown in Figure 5.1.1-1. Although dieldrin wasthe contaminant most often detected among offpost biota (bovine fat, chicken tissues [fat and skin, liver, and eggs], fish, earthworms, deer mice, prairie dogs, and pheasant liver samples), the concentrations detected were low and/or infrequent (HLA, 1992). Arsenic concentrations were detected in algal mats and a composite sample ofcrayfish from the First Creek Impoundment, earthworms, and one of four prairie dog samples (HLA, 1992). Mercury was detected in fathead minnows and carp collected from the First Creek Impoundment and in three offive earthworm samples. The mercury levels were determined to be within the expected range for background, as determined by data from McKay Lake in western Adams County and reported in the Biota RI (ESE, 1989b). DDE was detected in the fat and skin portion ofa chicken collected from a farm north ofRMA (site HA 104213P). Aldrin and DDT were not detected in any biological sample collected in the Offpost OU.

20000,317.10(3) - OEA 0815111892 111 - 5-5The impact ofgroundwater on offpost ecological receptors was limited to areas where livestock and crops maybe exposed to contaminated groundwater via agricultural wells. Exposure tothese receptors may occur ifcontaminated wells are still in use; therefore, chemical concentrations in groundwater were evaluated for potential toxicity to agricultural receptors.

5.1.4 Selection ofChemicals ofConcern for Biota COCs for theecological assessment were selected in a manner consistent with theapproach used in the human health risk assessment (Section 1.0). COCs were considered tobe those chemicals in abiotic media with concentrations significantly elevated with respect tobackground. In addition, for the ecological assessment, the selection ofCOCs was refined further by considering appropriate exposure media by food web (e.g., terrestrial or aquatic). For example, target analytes elevated in groundwater would beconsidered as groundwater COCs, butonly livestock with access to agricultural wells would be exposed. All biota could be exposed to COCs directly from abiotic media, and biota at higher trophic levels could receive additional exposure via bioaccumulation in food chains. Potential COCs for terrestrial and aquatic wildlife receptors were limited to site-related chemicals found in surface soil, surface water, and sediment. Groundwater COCs were used in the evaluation of agricultural receptors only. Tissue analytical data for ecological receptors were also evaluated with respect to the COCs in ablotic media. COCs in tissue (TCOCs) were selected by evaluating the biota data for the seven target analytes (aldrin, dieldrin, endrin, DDT, DDE, arsenic, and mercury) in tissue from the Offpost RI Addendum (HLA, 1992). Six ofthese seven analytes in tissue (aldrin, dieldrin, endrin, DDT, DDE, and arsenic) were also COCs in abiotic media and are thusconsidered TCOCs. Mercury was not elevated in offpost abiotic media (Volume 11, Section 1.0). In addition, arsenic concentrations in earthworms from the Offpost OU were similar to the RMA onpost control samples (ESE, 1989b). Because arsenic in soil is considered to be within the range of background, arsenic was not evaluated further as a COC in a terrestrial ecosystems in the Offpost Ou.

20000,317.10(3) -OEA 0815111892 111 - 5-6TCOCs were evaluated using afood webapproach (dietary ingestion); other COCs were evaluated for direct toxicity (surface water, soil, and prey ingestion). The list ofCOCs tobe evaluated for the ecological assessment ispresented in Table 5.1.4- 1.

5.2 EXPOSURE ASSESSMENT This section describes the potential biological receptors and exposure pathways in the offpost

area. It also describes how exposure point concentrations were used in theexposure assessment. Ecological assessment ýndpoints, residue concentrations, and associated procedures used to quantify exposure for the endpoints are also described.

5.2.1 Potential Biolopical Receptors and Sensitive Subpopulations EPA guidance indicates that biological receptors (ecosystem components expected to reflect adverse effects ofpollutant stress) be selected to represent an), potential adverse effects to all ecosystem components (EPA, 1989f). Several site-related criteria were considered in screening for potential biological receptors. Initial screening was performed to identify receptors as potentially present and important in the Offpost OU. The numbers representing the following criteria correspond to numbers on the matrix presented in Table 5.2.1 -1. I. Species observed or collected offpost during RI activities, which confirms their presence offpost 2. Species presence at RMA, which implies theirpresence offpost 3. Species observed offpost orpotentially within the study area, as noted by other studies or agencies 4. Species presence confirmed and an important component of offpost food chains (this may result in a source ofexposure to higher trophic levels ifspecies isan important forage component; ecosystem stability may alter if population is adversely affected)

EPA guidance states that special consideration be given to rare, threatened, and endangered species; birds listed in the Migratory Bird Treaty Act; and to species ofcommercial or sport value (EPA, 1989f). Representative receptor species and sensitive subpopulations for the Offpost OU

were selected from the list ofpotential biological receptors using suggested EPA criteria and additional information: 20000,317.10(3) - OEA 0815111892 111 - 5-75. Rare, threatened, or endangered species known to occur onpost and inferred also to occur offpost, and birds protected underthe Migratory Bird Treaty Act 6. Potentially affected commercial or sport species 7. Species ofhigh public interest 8. Behavior, lifehistory, or physiological aspects oforganism that may increase exposure or uptake ordecrease threshold fortoxic effects 9. Availability ofecotoxicity data for receptor species orrelated taxa

The representative biological receptors include major trophic levels (e.g., primary producer, predators) ofthe offpo9t ecosystem. In most cases, one ortwoorganisms were usedto represent adverse effects to other related taxa; for example, the bald eagle and great horned owlrepresent other large raptors. Focusing the ecological risk assessment on the selected receptors served two purposes. First, the receptors were arranged into food webs to model bioaccumulation ofcontaminants. Food web modeling was usedto predict contaminant exposure totrophic levels for which sampleswere unavailable from the RI (HLA, 1992). Second, selecting the mostimportant and sensitive organisms helped ensure that if these species are protected in the risk assessment, other less sensitive orimportant organisms will be also protected.

5.2.1.1 Terrestrial Recewors Wildlife species that can beconsidered potential receptors (Table 5.2.1-1) include several species that also occur on RMA asdescribed in the BiotaRI (ESE, 1989b), or which are listed as being observed offpost inTable 5.1.2-1 (HLA, 1992). Receptors ofconcern include rodents, especially mice (Peromyscusspp.) andprairie dogs (Cynomys ludovicianus),which fit site-related criteria 1,2, and 4. Additional small mammals thatare inferred tooccur in theOffpost OU, but

were notcollected during the RI, include shrews, voles, and ground squirrels. Mice andprairie dogs are both burrowing animals, andthus potentially contact contaminated soilduring burrowing activities, as well as duringfeeding and grooming. Micehave varied feeding habits that could

20000,317.10(3) - OEA 0815110892 111 - 5-8increase the overall contaminant exposure rate ascompared to prairie dogs, which are primarily vegetarian. Lagomorphs (rabbits) and deer also occur in theOffpost OU but were not collected for the Offpost Rl. Neither species observed onpost contained elevated tissue residues on a regular basis (ESE, 1989b); therefore, they were determined to be less highly exposed than some other species. Skunks, raccoons, bobcats, fox, and coyotes are other mammals that were inferred tooccur

or were observed in the offpost area (Table 5.1.2-1). However, because ofinherent sampling problems.,these animals were not collected for sample analyses during theOffpost Rl. Species selected as representative biological receptors are highlighted in bold type on Tables 5.2'. 1-1 and 5.2. 1 -12.Itwas assumed that the selection criteria ensured that these species would be representative ofall ecological disturbance. Avian species that are inferred to occur or were observed in the Offpost OU include a variety ofupland species. Pheasants (Phasianuscolchicus)fit site-specific criteria 1,2, and 4. Bald eagles. golden eagles, hawks, falcons, and owls are inferred to occur or have been observed in the Offpost OU (Table 5.1.2-1 ). Bald eagles have nested at nearby Barr Lake since 1986. In addition, bald eagles fit the criterion for sensitive subpopulations because they are endangered and

are potentially more highly exposed because oftheir feeding behavior. In addition, other raptors also fit thecriteria ofhigh public interest, migratory birds, and/or potential high exposure because oftheir feeding behavior. Avian predators are also sensitive to the effects of organochlorine pesticides (ESE, 1989b) and are thus represented more heavily as receptors than other predators. Raptors have large home ranges and may feed extensively outside the immediate First Creek drainage (U.S. Fish and Wildlife Service [USFWS], 1989a). All soil invertebrates observed on RMA were presumed also to inhabit the Offpost OU. Earthworms were collected for the RI Addendum (HLA, 1992). These species are important prey items in terrestrial food chains for both mammalian and avian wildlife. Other invertebrates collected included grasshoppers, which also serve as important food items for both mammalian and avian species.

20000,317.10(3) - OEA 0815111892 111 - 5-9Upland vegetation, reptiles, and amphibians were inferred orwere observed inthe offpost

area but were notcollected as part ofthe RI Addendum (HLA, 1992). The terrestrial species selected as representative indicators ofCOCeffects included earthworms, grasshoppers, mice, prairie dogs, pheasants, great horned owls, American kestrels, andbald eagles. These species fit many ofthe selection criteria shown inTable 5.2.1-1. Adverse effects in bald eagles and great horned owls were considered representative ofeffects inother large raptors. Terrestrial agricultural receptors selected include crops, chicken, and cattle because oftheir role inthe human food chain. Crops represent all terrestrial plants because ofa lack ofspecific data for most noncultivated plant species.

5.2.1.2 Aouatic Recevtors Potential freshwater aquatic receptors (Table 5.2.1-2) have been observed or are believed to be present ina variety ofaquatic habitats, asdescribed inthe RI Addendum (HLA, 1992). Wetland resources were limited in the offpost area toriparian/floodplain areas adjacent to the creeks, rivers, and impoundments. FirstCreek and Second Creek are intermittent streams thatdo not support economically important fishpopulations. Specimens collected from the FirstCreek Impoundment included macrophytes and algae, aquatic insects, crayfish, and fathead minnows (HLA, 1992). Fathead minnows areexpected to provide food items for omnivorous wading birds. Fathead minnow tissuebody burden data from the offpost area are reported in the RI Addendum (HLA, 1992). Carp and bullhead catfish are expected to occur in theO'Brian Canal and other water bodies linked to the South Platte River. Despite seining oftheentire First Creek Impoundment from bank to bank, only fathead minnows were collected (HLA, 1992). The pond is shallow, and Winter kill due to iceis expected tooccur; thus, permanent populations oflarge fish are not anticipated. Previous reports ofcarp inthis waterbody may be attributable to stocking the impoundment with fish collected from other areas. The freshwater aquatic species selected as representative for evaluation ofcontaminant effects and the predominant criteria for their 20000,317.10(3) - OEA 0815110892 111 - 5-10inclusion are summarized inTable 5.2.1-2. Larger fish (carpand bullhead) were notincluded in the food web because they were not found during theecological characterization prepared for the RI Addendum (HLA, 1992). Fathead minnows (Pimephales promelas)were observed in the FirstCreek Impoundment. This organism may have contact with sediments, thus increasing chemical exposure. This species may be an important preyitem for higher trophic level biotasuch asgreat blue herons. Crayfish (Orconectessp.), ascavenging invertebrate, were also found in the First Creek Impoundment. Ecotoxicity data specific to this taxaare more limited, but invertebrate data for other species present atthe sitemay be substituted with consideration ofthe resultant uncertainty inherent with extrapolation among taxa. Other aquatic invertebrates are expected to occurin the OffpostOU but were not collected during the RI Addendum (HLA, 1992). Green algae were present in aquatic habitats oftheOffpost OU and were collected as algal matsfor analysis in the RI Addendum (HLA, 1992). Algae represent primary producers in the aquatic ecosystem. Various waterfowl and shorebird species are common to the aquatic habitats inthe offpost

area. These birds have a variety ofdifferent feeding habits and are potential pathways tohigher trophic level species, including humans. Toxicity data are available for different waterfowl species, butmost datapertain to the mallard duck (Anasplatyrhynchos). The bald eagle, mallard duck, and great blue heron were selected asrepresentative avian species associated with aquatic or wetland systems to evaluate the potential adverse effects ofthe COCs.

5.2.2 Potential Ext)osure Pathways The ecological conceptual site model, as shown in Figure 5.2.2- 1,depicts the sources and pathways ofexposure to the potential receptors. Essentially, the conceptual site model summarizes the exposure scenarios that were considered for each majorreceptor component ofthe ecological risk assessment. The model also indicates whether aspecific pathway considered for evaluation

was quantified.

20000,317.10(3) - OEA 0815110892 111 -Potential exposure pathways in relation to each media source are summarized in Table 5.2.2- 1. It wasdifficult toevaluate some exposure scenarios withrespect to biological receptors because ofthe lackofapplicable exposure factors. For example, evaluating dermal contacttoxicity datafor mammals and wildlife species isnot similarto the types ofdermal exposure studied under experimental conditions. Under experimental (laboratory) conditions, the animal's hair is usually shaved, andthe test compound applied directly to the skin. Under field conditions, only the foot pads ornose directly contact contaminated media. The dermal exposure pathway is expected to,be minor compared to soil, water, orcontaminated prey ingestion. Inhalation ofvapors orfugitive dustsisalso expected tobe a minorexposure pathway for wildlife species and agricultural receptors compared toingestion. Most ofthe Cocs insurface water, sediment, and surface soil are notvolatile. Although the offpost area is expected tobe dusty, especially during agricultural activities, therelatively low levels ofCOCs insurface soil (Mg/kg or ppb)were expected to minimize risk via inhalation because oflow exposure point concentrations. Ingestion exposure pathways were evaluated because wildlife may ingest surface wateror soilas part ofburrowing, feeding, orgrooming activities. Wildlife may also beexposed by ingestion ofcontaminated food items. Directcontact and ingestion ofcontaminated food items

were considered for aquatic life. Exposure pathways are listed in Table 5.2.2-1 and are described below for each ofthe receptor species. For earthworms, direct (i.e., dermal) contact is the mostimportant exposure pathway. As with aquatic organisms, separating ingestion from dermal absorption from the surrounding media is difficult. Therefore, toxicity andbioaccumulation were evaluated in relation to direct contact with soil. Grasshoppers may beexposed by direct contact with soil and ingestion ofcontaminated plants and soil. Quantifying the exposure by direct contact through soilingestion is difficult because oflimited information regarding this exposure route. Therefore, toxicity and bioaccumulation were considered in relation toingestion ofplants.

20000,317.10(3) - OEA 0815110892 111 - 5-12Mice and prairie dogs may be exposed by ingestion ofcontaminated soil with dietary items. Exposure by dermal contact isdifficult to quantify because oflimited information regarding this exposure route for wildlife. Because these species are very effective in conserving body water and receive most oftheir hydration via dietary intake, they consume little or no surface water . Contact with groundwater by these species isunlikely. Toxicity and bioaccumulation were considered in relation to ingestion of surface water, soil, invertebrates, and plants. Pheasants may be exposed by direct or dermal contact with soil or surface water, dietary ingestion. and soil ingestion. Quantifying exposure by dermal contact is difficult because of limited information regarding this exposure route in avian species, but it is unlikely to be a major exposure pathway compared to ingestion. Surface water is consumed by pheasants; however, contact with groundwater is unlikely. Soil is ingested during feeding activities, but the actual exposure rates are uncertain. Toxicity and residue bioaccumulation were considered in relation to ingestion ofsoil, surface water, invertebrates, and plants. Great horned owls, American kestrels, and bald eagles may be exposed by dermal contact, dietary ingestion, and soil and surface-water ingestion. As stated above, dermal contact isnot like]v to be a significant pathway compared to ingestion. Surface water isconsumed by these species. but contact with groundwater is unlikely to occur. Limited quantities of soil may be ingested during feeding activities, but the actual exposure rate to soil is likely to be much less than for ground-feeding birds such as thepheasant. Ecological receptor soil ingestion rates determined for the Onpost EA (Ebasco, 1992 [Appendix H]) were used in this ecological risk assessment for consistency with the onpost ecological risk characterization. Toxicity and bioaccumulation were also considered in relation to surface-water, soil, and dietary (prey species) ingestion. The lower trophic level freshwater aquatic receptors (green algae, crayfish, and fathead minnows) mav be exposed by direct contact with their environment and, for some, via dietary ingestion. The higher trophic level organisms in the aquatic food web (mallard, bald eagle, and great blue heron) may be exposed by dermal contact, surface-water and sediment ingestion, and dietary ingestion ofcontaminated prey. Quantifying the exposure to higher trophic level

20000,317.10(3) - OEA 0815111892 111 - 5-13receptors by dermal contact is difficult because of limited information regarding this exposure route for wildlife. These species consume surface water; however, contact with groundwater is unlikely to occur. Limited quantities ofsediment may be ingested during feeding activities. Toxicity and bioaccumulation were considered in relation to ingestion ofsurface water, sediment, and pre), species. Species in the agricultural food web may be exposed by dietary intake, surface-water intake, soil intake, and intake ofcontaminated groundwater via ingestion from agricultural wells. Toxicity and bioaccumulation forthese species were considered in relation to each ofthese potential exposure pathways.

5.2.3 Exposure Point Concentrations The groundwater exposure point concentrations developed for the human health assessment and presented in Section 2.4 (Table 2.4.2.5) were applied for agricultural biota. However, for wildlife receptors, the soil exposure point concentration forzone 3 was based on the geometric

mean ofthe soil concentration rather than the UCL95 ofthe arithmetic mean used for the human health assessment. Additionally, a re-evaluation ofthe sediment and surface-water data indicated that the most reasonable exposure point concentration would be a geometric mean ofuseable data points because the data are not normally distributed. The data were evaluated in a manner similar to that used for the selection ofappropriate data points for the groundwater exposure point calculations for the human health assessment described in Volume 11, Section 2.0 ofthe EA. Geometric means were calculated for COCs, using all single value data points. In cases where duplicate samples were analyzed by two different methods, data for the method with the higher detection limit were eliminated ifthe following conditions occurred: (I) the eliminated value was

a nondetection, (2) a duplicate sample was analyzed using a method with a lower detection limit, and (3) one-halfthe detection limit ofthe removed value isgreater than the highest detected concentration for that analyte in zones 3 or 4. The exposure point concentrations for surface water, soil. and sediment are listed in Table 5.2.3- 1. Terrestrial species are exposed to soil; some species may also contact surface water via ingestion. Lower trophic level aquatic species are 20000,317.10(3) - OEA 0815111892 111 - 5-14exposed to surface water continually by immersion intheir environment. Toxicity to aquatic life resulting from contact with sediments was evaluated with the surface-water assessment. Livestock and crops may contact soil, surface water, orgroundwater from agricultural wells.

5.2.4 Ecological Assessment Endpoints Ecological assessment endpoints are expressions ofvalues or characteristics that are tobe protected. Ifthese endpoints are determined tobe significantly or adversely affected, remedial action is indicated (EPA, 1989f). The assessment endpoints for the Offpost EA were direct toxicity and bioaccumulation, which are indicated aspotentially useful by EPA (1989f), andones thatcan be addressed with the Offpost RI data and the food webmodels. EPA indicates that its listis not all inclusive and that other assessments endpoints are possible. A measurement endpoint corresponds tooris predictive ofassessment endpoints and can include data ormodels. The assessment endpoints were evaluated withthe measurement endpoints ofobserved tissue concentrations and observed abiotic media concentrations, both ofwhich can be correlated with mortality or sublethal toxiceffects by use ofdata found in the toxicity assessments.

5.2.4.1 Terrestrial Differences in species composition and/or distribution between RMA and the OffpostOU

are influenced by landuse and management, and thus comparison ofpopulation stability or diversity (as measured by species diversity, abundance, and productivity) or ecosystems productive capability (as measured by biomass orproductivity) inrelation toRMA isdifficult, if not impossible. One assessment endpoint considered applicable for theecological risk assessment

was the link between TCOC residues and adverse effects. This assessment endpoint wasevaluated bypredicting TCOClevels, using food web modeling and comparing these levels to MATCs. The MATCs (described inSection 3.4 ofVolume II) are tissue concentrations that correspond tono effect orminimal adverse effect in a few members ofapopulation. Tissue residues may be indicative ofimpacts to sensitive individuals and populations.

20000,317.10(3) - OEA 0815110892 111 - 5-15

### Anotherecological endpoint evaluated in thisassessment wasdirect toxicity. Soil, water, andfood intakeswere evaluated forcontaminant levelsthat couldbecorrelated withdirect toxicity. These intakes were compared withtheTRVs contained in Section 3.3 ofVolume Il. Thisapproach was reliedupon, inpart, because some COCs donotbioaccumulate in food webs and alsoto address exposure directly toabiotic media. TRVs are equivalent in concept toRfDs developed forhumanhealth. TRVs area dailyintake levelthat shouldnotresult in anadverse health effectto apopulation oran endangered species. The ratioofchemical intakesto TRVs is definedas a hazard quotient (HQ) forthe purposes ofthis EA. Althoughother environmental assessment endpoints may exist(EPA, 1988; EPA, 1989f), these endpoints may besubjectto confounding exposures notassociated with RMA. The use of registered insecticides andherbicides in the OffpostOU, thedischarge ofsewage effluent toBarr Lake(DRCOG, 1989), and thepossible presence ofcontaminants inthe South Platte Rivermakes assessing the ecological riskattributable tochemicals fromRMA sources difficulttoseparate from the riskfrom other sources. 5.2.4.2 Aouatic Wetlands andhabitats critical forsurvival ofendangered species are generally considered sensitive habitats (EPA, 1989f). BarrLake is animportant migratory birdhabitatand recreational area, butintense management activities, historical inputofeffluents and runoff(DRCOG, 1989), and humanuse makequantitative evaluation ofRMA contaminant effects uncertain. Because of the level ofhabitat disturbance caused byland usepractices in the OffpostOU, the assessment endpoints considered most applicable forthe aquatic assessment were measured using the following criteria: (1)TCOCconcentrations inbiotausingfood web modeling andMATCs and (2) directtoxicity usingTRVs. Othercriteria includethe AWQC thatwere used todetermine risk toaquaticlife. These measurement endpoints provide thebestindication ofpotential adverse impactsin wetlands andaquatic systemsresulting from site-related contamination.

20000,317.10(3) - OEA 0815110892 

### 111- 5-165.2.5 Bioaccumulation ExL)osure This section describes the procedures used for modelingthe bioaccumulation ofTCOCs in terrestrial and aquatic food webs. Predicted tissue concentrations are compared toMATCs in Sections 5.3.1 and 5.3.2.

5.2.5.1 Terrestrial Food Web Ingestion Pathways Dietary and soil ingestion exposure pathways were evaluated for TCOCs, using food web modeling (ESE, 1989b;Fordham and Reagan, 1991) and analytical data. The food webs were made site-specific by including the offpost terrestrial and aquatic receptors. The food webs also outlined critical exposure pathways foreach ofthe receptor species. The terrestrial food web is presented in Figure 5.2.5.1- 1. Theindicator species thatwere sampled for chemical analysis consisted ofall lower trophic animals. Bioaccumulation factors (BAFs) for each species were developed from the open literature on the basis ofascientific

consensus and are presented in Appendix H (Table H2-1). A BAF isthe ratio ofa chemical concentration between tissue and intake, e.g., Cbi.t.,/Cdi.t- By definition, BAF includes uptake from bothwater and dietary intake. Because soil isfrequently ingested along with diet,residues resulting from soilingestion areconsidered as well. For the terrestrial species in the Offpost OU, many ofwhich do not consume surface water as adrinking water source, the bulkofthe chemical body burden is expected to be derived from soiland food ingestion. Residues resulting from surface-water ingestion are considered in Section 5.2.6.1. The BAFs were developed through literature research and are contained in Appendix H. The BAFs for the species are intended torepresent bioaccumulation by all members ofthe specific trophic compartment. A medium-sized bird BAFwas notprovided in the OnpostEA data; therefore, the BAFfor the small birds was used to represent the pheasant (Table H2-1 of Appendix H). Prairie dogs were considered as medium-sized mammals. The food chains in the terrestrial food web (Figure 5.2.5.1-1)are presented in Table H2-1 of Appendix H, using producer/consumer notation as indicated byarrow symbols (e.g., earthworm - >mouse). The total BAF (product ofall BAFs in the food chain) for each food chain pathway for

20000,317.10(3) - OEA 0815110892 111- 5-17each COCis also reported in Table H2-1 ofAppendix H. The totalBAF values for each food chain pathway were obtained by multiplying each ofthe individual BAFsin each pathway (TableH2-1). Forexample, the calculation ofthe total BAFfor aldrin for asoil pathway is illustrated below. BAFs Total BAF 6 x 3 x 19 342 Soil Earthworm Deer Mouse Owl Dietary fractions for each food chain pathway, as shown in Table 5.2.5.1-1, weremultiplied to obtain anoverall dietary importance value for the food chain for the target organism. The results are shown in the column labeled percent organism inTable 1-12-1 ofAppendix H. For example, food habits data indicate the owl feeds primarily (66.5 percent ofdiet) ondeer mice, a small mammal (Table 5.2.5.1 -1), andthat deer mice eat a mixed diet, ofwhich48 percent is grasshoppers, an insect; therefore, this foodchain contributes 32 percent ofthe owl's dietary intake: Soil Plants Grasshoppers Deer Mouse Owl 1.0 x 1.0 x 0.48 x 0.665 0.32

In general, dietary fractions were estimated from data usedfor the Onpost EA (Eba-sco, 1992 [Appendix H]). Because the bald eagle's diet in theoffpost areaalso includes asmall fraction (0.031) derived from the aquatic food web, the bald eagle dietary fraction does notadd upto 1.0 inthe terrestrial food web. By definition, abiomagnification factor (BMF) isa more general term that implies food chain transfer ofresidues. BMF isused todefine the uptake by higher trophic level organisms caused by feeding in an entire food web. The totalBMF for ahigher trophic level target organism is the sum ofthe products ofthe total BAF multiplied by fraction ofpathway inthe diet ofthe higher trophic level target species

20000,317.10(3) - OEA 0815110892 111 - 5-18(Table H2-1 ofAppendix H). This adjusts the total BMF toreflect the contribution ofthe respective pathways (n) for the target organism (Table 5.2.5.1 -1).

E (total BAF1 x dietary fraction,) = total BMF (5-1) n=1

To summarize, the dietary fraction ofthe pathway was multiplied by the total BAF forthe pathway, andthese values were summed for each species (Table H2-1 ofAppendix H). The sum ofthe food chain pathways asdepicted inTable H2-1 inAppendix H, for each target organism (i.e., bald eagle or owl) was labeled the total BMF. Thetotal BMF represents the overall biomagnification predicted from soil and all the food chains leading to the target organism. The major species group (Table H2-1 ofAppendix H) is presented to provide consistency with the onpost ecological risk characterization. Soil was considered part ofthe dietary intake because soil intake data are frequently expressed as apercent in relation to diet. Contaminant uptake caused by surface-water ingestion

was considered separately because surface-water intake rates for birds may exceed feed intake on aweight or volume basis (Sax, 1984) and are not usually expressed asa percent ofthe dietary intake. Absorption factors for uptake from water or soil were conservatively assumed tobe equivalent to those fordiet.

5.2.5.2 Terrestrial Food Web Predicted Tissue Concentrations The predicted tissue concentrations ofthe five OCPs for the terrestrial food web species are depicted in Table 5.2.5.2- 1. The predicted tissue concentrations were calculated by multiplying the geometric mean soil concentration ofeach OCPfor zone 3 by the species- and chemicalspecific total BMF developed from literature BAF values (Appendix H); also, aspatial adjustment factor wasapplied for the bald eagle, American kestrel, and great horned owl. For example, to determine the predicted tissue concentration ofdieldrin for the American kestrel, the following equation was applied: (0.043 mg/kg x 13) x 0.2 = 0.11 mg/kg

20000,317.10(3) - OEA 0815111892 111 - 5-19

### where: 0.043mg/kg =soildieldrin concentration 13- totalBMFfor dieldrin fortheAmerican Kestrel 0.2=spatial adjustment factor Literature BAFvalueswere used because offpost datawere insufficient todetermine site-specific values, andonpost dataand values, which mayhave been appropriate foruse, were unavailable. Forthose speciesoccupying theupper trophicboxes andhaving a known homerange (i.e., bald eagles, American kestrels, andgreat horned owls), thepredicted tissueconcentrations were spatially adjustedbased onthehome range forthat particularspecies (Appendix H). Thehome range adjustment wasdeemed appropriate because these animals are mobileand willonlyobtain a fraction oftheirpreyitems within zone 3. The spatial adjustment factorisbasedona ratio ofthe known home ranges ofthe species andthe area ofzone3. 5.2.5.3 Aguatic Food Web Ingestion Pathways The aquatic foodweb is presented inFigure 5.2.5.3-1. Theshaded boxes indicate samples collected aspart oftheRI sampling program. Largefish (carp, bullhead)donot appear on the food web (reflecting current conditions). Thus, large fish were notevaluated as partofthe food web model. Herons are assumed to feedprimarily in the aquaticfoodweb. Dieldrin and arsenicwere the onlyTCOCs observed inthe species collected inthe aquatic food web (HLA, 1992). Aquaticbiota samples were collected fromtheFirst Creek Impoundment only because First Creek, anintermittent stream, wasnot foundto support fishduring the ecological characterization. For smallaquatic species suchas invertebrates, itis assumed thatthe surface areatovolume ratioas wellas the exchange ofwater acrossthe gills causes sufficient absorption ofchemical from water tooutweigh uptake from diet. Species higher upthe aquatic food chains obtain chemicals through dietaryintake aswell as fromdirect uptake from water. Bioconcentration factors (BCFs), the ratioofchemical concentration intissueto chemical concentration inwater, were obtained fromthe open literature (TableH2-2 ofAppendix H).

20000,317.10(3) - OEA 0815110892 

### 111- 5-20

### 5.2.5.4 Aguatic FoodWeb Predicted Tissue Concentrations The predicted tissueconcentrations ofthe five OCPs and arsenicforthe aquaticfoodweb species are depicted inTable 5.2.5.4-1. The predicted tissueconcentrations were calculated by multiplying theexposurepointconcentration ofeachchemical in surfacewater bythe speciesand chemical-specific total BMFdeveloped fromliterature BCFvalues (AppendixH) forthe major receptor species inonlytheBCF values foralgae and invertebrates. Literature BCFvalues

were usedbecause offpostdatawere insufficient to determine site-specific values. A spatial adjustment wasapplied in a similarmanner tothat described previously fortheterrestrial food webforbald eagles and the greatblueheron. The spatial adjustment factor included feeding in

zones 3and 4. A spatial adjustment factor was notderived forthe mallardduck because home range datawere not available forconsideration; therefore, thepredicted tissueconcentrations for the mallard duckare likely overestimated based on dietary intake froma singlearea. The predicted tissue concentrations based onthe direct ingestion ofsediment were alsocalculated ina similar manner (Table 5.2.5.4-2). 5.2.6 DirectExr)osure to Chemicals ofConcern Procedures usedto calculate the species' intake from surface-water ingestion, soilingestion, dietary ingestion, and direct contact are discussed in thissection. However, theintakevalues are presented inTables 5.3.1-1 through 5.3.1-5 where theseintakes areevaluated withrespect to TRVs in Section 5.3. 5.2.6.1 Surface-Water Ineestion Pathway Species thatdonotrelyon surface wateras aprimary drinking watersource(e.g., prairie dogs)are less likelyto beexposed to potentially contaminated surface water. Birds, however, often drink surface water. Birdswithlimited home ranges that overlap acontaminated water

sourcemay conceivably obtain alltheir drinking water fromthe contaminated source. Large mammals andraptors witha relatively larger homerange maynothave as high an exposurerate

20000,317.10(3) - OEA 0815111092 111 

### - 5-21because ofthe opportunities toobtain water fromuncontaminated sources. Surface-water ingestion was evaluated for the following species: WaterIntake Sipecies O/ke-bw/day) Ring-necked pheasant 0.25 Great horned owl 0.25 American kestrel 0.25 Bald eagle 0.25 Mallard duck 0.25 Great blue heron 0.25

Water intakerates for terrestrial avian species were estimated from chicken data (Sax, 1984), because similar data were not available for offpost area species. Water intake isexpected to vary among species, locations, and seasons, when different dietary components may supplymore water

orwhen different energy expenditures require more waterintake. Although mallards were reported to consume 0.2 1/kg-bw/day, in exposure intakes, they were conservatively modeled as ingesting 0.25 1/kg-bw/day to account forwater intake during feeding and bathing activities. Great blue herons were also assumed to ingest 0.25 1/kg-bw/day. The other components ofthe terrestrial food web (earthworms, grasshoppers, mice, and prairie dogs) either do not consume surface water as adrinking water source, or they are fairly immobile andcannot access surface water. However, all surface-water intakes were based on avian waterintake rates, and these intake rates were assumed to beprotective ofother species (e.g., small mammals) in the terrestrial foodweb. In general, waterintake per unitbody weight for variousmammalian species varies between approximately 0.05 to0.2 1/kg-bw/day (Sax, 1984). Therefore, the use ofavian intake rates would provide conservative (high)exposure estimates for mammals because deer mice and prairie dogsin the terrestrial food web do not ingestsurface water as adrinking water source. Direct ingestion is considered to beexposure to surface water caused by consumption, and direct toxicity isthe adverse effect resulting from such exposure. Theexposure point COC concentrations in surface water are presented inTable H3-1 ofAppendix H with the estimated chemical intakes by avian species (raptors, heron, mallard, orpheasant). Chemical intake was

20000,317.10(3) - OEA 0815110892 111- 5-22calculated by multiplying the exposure point concentration in surface water (,ug/1) by the daily water intake for birds (0.25 1/kg bw/day). Total chemical intakes viaall appropriate routes of exposure were compared tothe TRVs presented inSection 3.0 tocalculate anHQto estimate potential hazards (Section 5.3).

5.2.6.2 Direct Contact with Surface Water or Sediment Aquatic life (fish and macroinvertebrates) hasdirect contact with surface water and sediment inthe environment; however, toxicity data with respect tocontact with oringestion of contaminated sediments are lacking for many ofthe COCs for the species ofinterest. Toxicity to aquatic life was estimated from direct contact with surface water and ingestion ofsediment. TRVs for aquatic life were compared to the surface water, sediment, and dietary intakes and are addressed in Section 5.3, Risk Characterization.

5.2.6.3 Soil Inpaestion Soil ingestion by terrestrial biotafor residue calculations was addressed previously via the terrestrial food web model. Soil ingestion rates are often presented as afraction ofthe diet; however, as with surface water, direct toxicity as wellas residue accumulation should be considered. Direct toxicity as aresult ofsoil ingestion waspredicted using the exposure point concentrations presented inSection 2.4. Up to2 to 3 percent ofthe daily food intake may be composed of soil (Palmer and Fowler, 1975) (Table 5.2.5.1-1). Total daily food intake was determined to be a percentage oftotal body weight (Ebasco, 1992). Intakes were calculated on these values. In addition, aquatic birds (e.g., mallard orheron) may also ingest soilduring nesting

or feeding activities. The chemical intakes from sediment are assumed torepresent soil intake by these species. The species-specific soil and sediment dietary fractions are listed in Appendix H. Potential exposure tothe terrestrial plant species (crops) in the OffpostOU could result from direct uptake ofchemicals in soil, groundwater, and surface water in the affected areas. Exposure point concentrations ofthe COCs identified are presented inSection 2.4.2. Hazard to plants is addressed inSection 5.3.

20000,317.10(3) - OEA 0815110892 111 - 5-235.2.6.4 Dietary Ingestion for Wildlife Dietary intakes were derived by multiplying the estimated tissue concentrations in prey items (next lower trophic level) for both terrestrial or aquatic life (Tables 5.2.5.2-1 and 5.2.5.4-1 by the dietary fraction (Table 5.2.5.1 -1) to obtain mgchemical/kg diet. Estimated concentrations in prey were obtained by use ofthe food web model. Assuming dailydietary ingestion rates listed in Appendix H (Ebasco, 1992), thefollowing equation was derived. Prey residue x f x r I x SAF = Chemical intake (mg/kg diet) (mg/kg-bw/day) n=1 (5-2)

where: f = dietary fraction ofprey item (unitless)

r = daily dietary ingestion (feed) rate (kg prey/kg-bw) SAF = spatial adjustment fraction (unitless)

The chemical intake from each component ofthe food chain is additive (due tothe dietary fraction term); thus the total dietary intake isthe sum oftheamount ofchemical in relation to each ofn prey items. For example, in the terrestrial food web, the bald eagle consumes prairie dogs (91.5 percent), deer mice (0.5 percent), and pheasants (1.9 percent); therefore, the dietary DDE intake for the eagle is [[(0.03 x 0.915) +(0.54 x 0.005) +(0.27 x 0.019)] x 0.09] x 0.0009 or 2.8 x 10-6 mg/kg-bw/day. The value 0.09 represents the feeding rate, and the value 0.0009 is the spatial adjustment factor for the bald eagle.

5.2.6.5 Dietarv and Soil Inpestion Pathways for Livestock The dietary and soil ingestion pathways were evaluated for chickens and cattle. Only

zones 1,2. and 6, classified as the rural residential scenario, were evaluated for potential COC effects onchickens and cattle. The agricultural food web (Figure 5.2.6.5-1) indicates the potential exposure pathways.

20000,317.10(3) - OEA 0815111892 111 - 5-24Chickens may be exposed to COCs through direct soil consumption. The chicken intake for soil ingestion was calculated as follows: Chicken soil intake = CS xIS (5-3) BW where: CS = concentration in soil (mg/kg) is = soil ingestion rate = 200 mg/day BW = body weight ofchicken = 2.5 kg

Cattle may be exposed to COCs from the soil through incidental soil ingestion while feeding. Exposure to theCOCs in the groundwater and surface water could occur from direct water consumption. Cattle forage may bioaccumulate COCs from soil or irrigation water. Explanation ofthe classification ofthe groundwater and surface-water use patterns is in Section 2.2.2.4. The intake from contaminated media was calculated by a procedure designed to be consistent with the estimates ofconcentrations in meat used in the human health assessment (Section 2.4.2). The procedure was as follows: Cattle plant intake (mg/kg/dav) = CFM x lp (5-4) KPM x BWM where: CFM = concentration ofthechemical in beef (mg/kg, fresh weight) IP = ingestion rate offeed (kg/day, fresh weight) BWm = body weight ofthe cattle (kg) KPM = equilibrium partition coefficient relating chemical concentration in aboveground plant part to concentration in the soil aqueous phase (1/kg) By substituting equation 2.4.2-4 for CFM into equation 5-4 and rearranging terms, it can be shown that equation 5-4 isequivalent to the following: Intake = CPIP +CWIW +Cals (5-5) BWM

20000,317.10(3) -OEA 0815111892 111 - 5-25M

where: Iw = ingestion rate of water by cattle is = ingestion rate ofsoil by cattle CID = concentration ofchemical in plant IP = ingestion rate of feed Cw = concentration ofchemical in water C., = concentration ofchemical in soil BWm = body weight ofcattle (kg) Equation 5-4 was applied using azone-specific estimated concentration in meat and IP= 37.7 kg/day, BWM = 450 kg. The CFM valuesare provided in Table H4-1 ofAppendix H. The KPM values are included in Table 2.1-10.

5.3 RISK CHARACTERIZATION Potential hazards to thedifferent ecological components oftheOffpost OU were addressed by considering the risk to terrestrial, aquatic, and agricultural life separately. Bioaccumulation and direct toxicity endpoints were evaluated for terrestrial and aquatic life; only direct toxicity

was evaluated for underwater aquatic life and agricultural life.

5.3.1 Terrestrial Food Web Ecolopical Risk The toxicity ofTCOC residues was evaluated when data were available. This type of toxicity is applicable only to those contaminants that bioaccumulate; therefore, residue toxicity

was addressed only for the terrestrial food web for higher trophic level organisms. Residue toxicity was estimated by using MATC values that were developed during extensive literature searches (Volume IV, Appendix H). The MATC is based on soil and dietary intake and is also a function ofthe residue assimilated by the top predator species, whereas the TRV considers intake from all media, particularly for noribioaccumulative COCs. The MATC is specific for toxicity relative to an organism's residue body burden, whereas the TRV accounts forany toxicologic response to dose. The MATC's strength is that itallows comparison of observed biota data to 20000,317.10(3) -OEA 0815111892 111 - 5-26tissue concentrations that, if exceeded, predict possible effects for species not included in the sampling program (suchas endangered species). The MATCs are in Appendix H. MATCs were developed after reviewing literature describing tissue concentrations for avian and mammalian species dosed in toxicity studies. In the food web models, multiple food chains lead to atarget organism, or sink species. Chemicals that bioaccumulate tend to concentrate withineach level ofthe food chain such that thesink species are exposed tohigher concentrations than the lower trophic level species. Because avian species are considered the sink species for the offpost food webs (see receptor identification), soil criteria that aredeveloped with the MATCs and BMF for the sink species are assumed to be protective oflower trophic level organisms as well. However, to validate this assumption, a comparison ofestimated intakes for lower trophic levels totheir respective TRVs is necessary. Tissue concentrations were predicted in the higher trophic level organisms inthe terrestrial and aquatic food webs that were notsampled aspart ofthe offpost RI (HLA, 1992) (Table H2-1 andTable H2-2 ofAppendix H). The predicted tissue residues for the avian species were compared tothe MATCslisted in Appendix H. Thepredicted tissue residues inbirds feeding in

zone 3 exceed the endrin MATC for the great horned owl and American kestrel. A summaryof the ratio ofpredicted tissue concentrations to MATCs by birdsfeeding inthe terrestrial web follows: Ratio ofPredicted Tissue Concentrations to MATC Terrestrial Bald Great horned American Ring-necked TCOC Eaple Owl Kestrel Pheasant Aldrin <1 <1 <1 <1 Dieldrin <1 <1 <1 <1 Endrin <1 4 4 <1 DDE <1 <1 <1 <1 DDT <1 <1 <1 <1

Endrin is indicated asa potential concern to the great horned owl and American kestrel; however, it shouldbe noted thatactual sitedata do not support the predicted tissuesconcentrations ofendrin in lower trophic level organisms. Endrin was reported as BCRL (<0.036 mg/kg)

20000,317.10(3) - OEA 0815110892 111 - 5-27in each of the biota samples analyzed (HLA, 1992). Samples were analyzed from members ofthe following species, domestic cattle, domestic fowl, fathead minnows, carp, crayfish, algae, grasshoppers, earthworms, deer mice, prairie dogs, and pheasants. A detailed presentation ofthe various sample types collected from each species is in the RI Addendum (HLA, 1992). Direct toxicity endpoints were also evaluated for the higher trophic level terrestrial species by adding soil, surface water, and dietary intakes toderive a total intake. Total intake was compared toTRVs (Volume 11, Section 3.0and Table 3.3.3-1), and an HQ value was calculated (Tables 5.3.1 -1 through 5.3.1-3). Menzie and others (1992) describe a similar HQ approach to estimate potential health effects on birds. Their approach calculates an HQratio by comparing the dose ofcontaminant received in diet to a dietary dose as a concentration ofcontaminant in the diet associated with the LOAEL or NOAEL fora particular biological endpoint. The HQs were modified by the application of a home range or spatial adjustment factor to adjust for partial dietarv intake from the areas within the Offpost OU potentially having thegreatest impact (zones 3and 4) relative to a particular species' home range. HQratios greater than I indicate a potential for an effect but do not indicate the magnitude (i.e., severity) or provide a measure of potential population level effects. Also, HQs do not represent the probability ofan adverse effect occurring. The HQ ratio simply compares estimated doses to benchmarks. This comparison is very similar to the use of RfDs in the human health risk assessment and tothe manner by which water quality criteria are applied (water concentrations compared to benchmarks, the criteria). The estimated chemical intakes did not exceed theTRVs for bald eagles, based on the geometric mean soil concentration data for zone 3 and the surface-water data for both zone 3 and

zone 4. HQs for the American kestrel and great horned owl were only exceeded for sulfate (HQ equals 2). The American kestrel HQfor dieldrin equaled 1. All remaining 

## HQsfor both species

were less than 1. Home range or spatial adjustment factors were also applied to the calculations for these two species. Additional home range information on the principal receptors isin Appendix H.

20000,317.10(3) - OEA 0815111892 111 - 5-28Exposure estimates for deer mice (Table 5.3.1-4) and prairie dogs (Table 5.3.1-5) exceeded fluoride and sulfate TRVs. The mammal exposure estimates include surface-water and soil ingestion as well as dietary intake. These estimates are highly conservative because the small mammals are unlikely to ingest surface water; however, intake estimates would be protective of mammals not included as receptors in the food web that may ingest surface water (e.g., fox, coyote, skunks, raccoons). The fluoride and sulfate exceedances are probably the result of uncertainties in theTRV derivation process, as presented in Section 5.3.5.3. Only the zone 3and

zone 4 data were evaluated for potential adverse effects on wildlife because exposure concentrations are less for soil in other zones and no COC-contaminated surface water or sediment

occurs in other zones. 5.3.2 Aquatic Food Web Ecolopical Risk The bald eagle and great blue heron occupy the top trophic level oftheaquatic food web. Predicted tissue concentrations (Table 5.2.5.4- 1 )were based on exposure point concentrations in surface water. Predicted tissue concentrations were then compared to MATCs to determine potential health effects to bald eagles, great blue heron, and mallard ducks feeding in the aquatic food web. The direct ingestion ofsediment does not contribute significantly to the predicted tissue concentrations (Table 5.2.5.4-2). MATCs for dieldrin, DDT, and DDE were not exceeded for bald eagles, great blue herons, and for the mallard duck. Aldrin and endrin were not evaluated because they were not detected in surface water. Ratio of Predicted Tissue Concentrations to MATC Aguatic Bald Great Blue Mallard TCOC Eagle Heron Duck Dieldrin <1 <1 <1 DDE <1 I <1 DDT <1 <1 <1

20000,317.10(3) - OEA 0815111892

### Thecombined intakes fromsoil, water, anddiet (Tables 5.3.2-1 and 5.3.2-2) for greatblue heronsand mallard ducks were compared to TRVs(Table 3.3.3- 1)and anHQcalculated. The HQ for sulfate exceeded Iforthemallardducks. The greatblueheronhad no exceedances. The.HQforbaldeagles, including dietaryuptake from boththe aquatic and terrestrial food webs, isreported inTable 5.3.1-1. Asdescribed previously, theintake ofthe COCs didnot exceed theTRVs; therefore, theresulting HQs wereall less than one. Essentially, theaquatic food web pathway did notresultin anypredicted tissueconcentrations forthe COCsin thebald eagle, thus, onlypredicted tissue concentrations via theterrestrial food webcan becompared to the MATC values. The intakesformostoftheCOCsfrom soilorwater ingestion were minimal. 5.3.3 Underwater Aauatic Life Risk to aquaticlife wasalso evaluated byuseofaquaticreference concentrations (Table 3.3-1). The observed concentration in surface waterwas compared toAWQC, LOAEL, or NOEL from the literature (Table3.3- 1). Residue toxicity was notevaluated for aquatic life because dataregarding thetoxicity ofresidues intissue are largelylackingforthese species. In addition, because aquaticlife are continually surrounded intheir exposure medium, it islikely that waterconcentrations areabetterpredictor oftoxic effectsthantissue levels. Chlordane, dieldrin, fluoride, and DDTappear topresent a potentialfor anadverse effectto aquaticlife in FirstCreek, basedonacomparison ofexposurepoint concentrations insurface water toTRVs (chronic AWQCvalues) for aquatic life. Background information forthe aquatic reference concentrations was reviewed todetermine whether any AWQC valueswere hardness dependent to make the criteria more site-specific. The EPAAWQC forthe surface-water COCs are not dependent on water hardness. 5.3.4 Agricultural Life Groundwater and soil exposurepoint concentrations forCOCs(Tables2.4.2.6-1 through 2.4.2.6-9) were comparedtoreference media concentrations forplants (Table3.3- 1). Reference media concentrations ofthe COCs insoil did notindicate anyexceedances except forchloride as 20000,317.10(3) -OEA 0815110892 111- 5-30applied in irrigation water. The total dissolved salts (free ions) in the irrigation waterwere elevated in the Offpost OU. Anevaluation ofwhether exceedances ofColoradogroundwater and surface-water standards occur is included in the ARARs portion ofthe Offpost OU FS. The potential impact ofcontaminants insoil onpoultry was evaluated by calculating the HQ

as aratio between the dose tothe chicken from soil andthe TRVs (Table 3.3.3-1). TheHQs for chickens based on the zones 1,2, and 6 (rural residential) soilconcentration data sets, did not indicate a potential contamination impact on chickens (Table 5.3.4-1). A hazard evaluation was performed todetermine whether cattle maintained in the Offpost OU could potentially be affected as aresult ofexposure toCOCs in soil andirrigation water through dietary consumption. The indirectexposure pathway includes consumption of plants grown in contaminated soil and irrigation water. HQs calculated for cattle for the different chemical compounds identified atthe Offpost OU for zones 1,2, and 6 are presented in Table H4-1 ofAppendix H. No exceedances above Ioccurred; therefore, the potential for adverse health effects occurring to cattle isnot indicated.

5.3.5 Ecoloeical Risk Assessment Uncertainty This section ofthe ecological risk assessment addresses the uncertainty associated with each element ofthe risk assessment and theoverall impact on the risk assessment's conclusions. The elements ofuncertainty include those associated with particular analyses, methods, and techniques. The discussion is limited toa qualitative presentation ofuncertainty.

5.3.5.1 Site Characterization Very little uncertainty is associated with the site characterization because onsite investigations were conducted and supplemented with historical data and aerial photographs. The ecological risk assessment site characterization was conducted inconjunction with the RI Addendum (HLA, 1992).

20000,317.10(3) -OEA 0815111092 111 - 5-315.3.5.2 Exposure Assessment The matrix used to select potential receptor organisms relied on site-specific and EPA guidance criteria, thus minimizing the uncertainty associated with this aspect ofthe ecological risk assessment. Receptors were selected from all pertinent trophic boxes to ensure a complete evaluation ofthe food web. The Offpost OU conceptual site model, as shown in Figure 5.2.2-1, indicates that all possible sources and exposure pathways were considered, thus reducing uncertainty. The uncertaintv associated with the food web models, dietary intake calculations, and the predicted tissue concentrations determined by the food web models may be high for reasons discussed below. The sediment intake rate provided for small fish is difficult to validate because ofthe paucity of available information. Tissue residues predicted for the great blue heron can be influenced significantly by the sediment intake of small fish because the small fish constitutes 37 percent ofthe heron's diet. Because thegreat blue heron and mallard duck predicted tissue concentrations ofCOCs found in aquatic ecosystem appear to overestimate the observed data, a large degree ofuncertainty is associated with aquatic food web model and input parameters. The sediment exposure point concentrations used in this assessment are based on a geometric mean of the chemical residues contained in the sediment matrix. Although the geometric mean value is less than the UCL95 ofthe arithmetic mean values used for the human health assessment, the use oftotal sediment concentrations may not be the most appropriate value to use to measure exposure. Recent reports indicate the free or bioavailable fraction ofthe total chemical presentis the most important factor in potential aquatic toxicity (DiToro and others, 1991; Adams and others, 1992). Because the bioavailable fraction is not known forthe Offpost OU sediment samples. it is difficult to determine whether the evaluations overestimated orunderestimated the actual hazard to theaquatic receptors. Additional uncertainty exists for the hazard evaluation for the bald eagle and great blue heron through the application ofthe spatial adjustment based on home range information obtained from the open literature. Again, it isdifficult to determine

20000,317.10(3) - OEA 0815111892 111 - 5-32whether the spatial adjustment resulted in an overestimation or underestimation ofthe potential hazards to these aquatic receptors. The dietary intakes assume that the animal's intake is year round and from a very limited

area in the Offpost OU. Although these assumptions may be valid for small mammals that havea limited home range and foraging area, theassumptions are not valid for more mobile species such

as theavian receptors; thus, more uncertainty is associated with avian dietary intakes. The application ofthe spatial adjustment factor may reduce the uncertainty associated with Taptor mobility relative toprey located in contaminated areas; however, no adjustment wasmade to account for temporal influences. Bald eagles, with few exceptions (e.g., the Barr Lake pair), winter at or near RMA for only a few monthseach year (November- March). During this time of year, the most likely offpost aquatic foraging sites forthe bald eagle areeither intermittent Or frozen, thus reducing intake from the aquatic ecosystem (USFWS, 1989a and 1989b). Likewise, mallard ducks and the great blue heron are migratory. The USFWS report (1989a) indicates that only a fraction ofthe wintering bald eagles may return to RMA onan annual basis, indicating a fairly substantial turnover ofthe bald eagle population at the RMA roost. The report states that possibly 100 or more eagles visited the RMA roost during the 1988- 1989 wintering season and that casual observation ofthe eagles in early November suggests that up to seven oftheeagles may have returned from the previous year. Perhaps with more data, the probability ofan individual eagle wintering in the Offpost OU during its lifetime could be determined to evaluate the temporal aspect ofexposure to contaminated media more accurately. Similar data are also desirable for theother avian species. More definitive temporal and spatial data on the foraging habits ofthe receptors are required to reduce the uncertainty. The exposure assessment for the agricultural receptors (i.e., chickens, cattle, and crops) has less uncertainty because thedatabase onexposure, absorption factors, uptake models, and toxicity is more complete.

20000,317.10(3) - OEA 0815111892 111 - 5-335.3.5.3 Risk Characterization Inherent uncertainty is associated with thecomparisons between the predicted tissue concentrations (food web models) and the MATCsand the dietary intakes compared tothe TRVs (HQs) because the MATCs and TRVs are based on the extrapolation of field and/or experimental data from the open literature. The uncertainties pertaining to these comparisons is a combination ofthe uncertainty contained in the MATC and TRV derivation procedures in addition to uncertainty associated with the food web models and intake parameters. The uncertainties related to TRVs are presented in Section 3.5. Some ofthe HQ exceedances (e.g., sulfate exceedances) may be an artifact ofthe TRV derivation process. The TRV derivation process, by necessity, israther structured, with minimal opportunity for subjective scientific input. Thisapproach was deemed most desirable because it allows a derivation process that can be easily applied by anyone once the critical toxicity study has been identified. A modifying factor addressing the quality ofthe toxicity study and its relevancy to an ecological receptor would reduce the uncertainty associated with the TRVs and their subsequent application to calculate HQs. However, because ofthe complexity ofwildlife toxicity issues and to reduce criticism, such a modifying factor should only be developed by aconsensus of scientific opinion from qualified individuals (a similar process asapplied to RfDs). The overall uncertainty with the ecological riskcharacterization could be reduced ifsitespecific documented temporal and spatial home range data were available as well as more refined MATCs and TRVs. The result ofsuch adjustments would result in outcomes similar to RMEs used in the human health assessment.

5.4 SUMMARY A quantitative assessment ofimportant exposure pathways was performed for nonhuman receptors in the Offpost OU food webs. The results oftheexposure assessment were expressed as tissue residues or as estimated chemical intakes from water, sediment, soil, and diet. The tissue residues were compared to MATCs. The intakes were compared toTRVs as part ofthe risk characterization to obtain an HQfor each higher trophic level receptor and each COC. 20000,317.10(3) -OEA 0815111892 111 - 5-34Significance is only attached to those comparisons that exceeded MATC or TRV criteria. Uncertainties associated with the quantitative ecological risk assessment are related to assumptions, some conservative and others not, made during thecalculation ofexposure point concentrations, intakes, and adverse health effects. These assumptions are presented in the text but are summarized below for clarity. The assumptions are qualitatively assigned in order of impact on the risk characterization results. I.The use ofBAF and BCF values obtained from the open literature rather than sitespecific values introduced uncertainty because biological, chemical, and physical characteristics unique to the Offpost OU may be very different from those present in the studies reviewed from the literature. The application ofthe spatial adjustment factor based on literature home range information is another source ofuncertainty. Although it is difficult to determine ifthe approach presented in this assessment over- or underestimated the potential hazards, itis generally known that the home ranges, per se, are notreflective ofpotential exposure, and foranimals that have a wide home range, such as the bald eagle, the foraging area may only be a fraction ofthe total home range area. 3. Use ofconservative soil, sediment, and surface-water intakes. 4. The equilibrium and steady-state assumptions for modeling are probably high (i.e., conservative), thus resulting in higher exposure estimates than the higher trophic level species will experience because they can move in and out ofthe ecosystem. 5. The use ofuncertainty factors, LOAELs, and NOELs in developing health effects levels forTRVs is conservative. 6. The use of geometric mean exposure point concentrations for soil, sediment, and surface water probably represents a more realistic scenario than the UCL95 values used for the human health risk assessment; therefore, less uncertainty may beassociated with this aspect ofthe hazard evaluation.

The results of the risk characterization indicate that minimal potential for adverse effects to receptor species in the aquatic and terrestrial food webs may exist. The available analytical data

on likely prey for the bald eagles (prairie dogs and pheasants) exhibited fairly low and infrequent detections ofthe COCs (HLA, 1992). Other raptor species feeding in the terrestrial food web are also not likely to be at high concern for risk as predicted body burdens were less than or within an order ofmagnitude ofthe MATCs.

20000,317.10(3) - OEA 0815111892 111 - 5-35Species in the agricultural food web are not expected to be at risk because ofexposure to the COCs. Plant life, cattle, and chickens will be relatively unaffected, based on the results ofthe risk characterization.

20000,317.10(3) - OEA 0815111892 111 - 5-36

### 6.0 CONCLUSIONS

As indicated in the Preface tothe EA, one ofthe objectivesofthe EA was toprovide an analysis ofrisksin the absence ofadditional remediation (baseline risks) andto provide a basis for determining the need forremedial action atasite. TheEA for the Offpost OUhasdetermined the cumulative hypothetical carcinogenic risk isa maximum of3 x 10-4 onthe basis ofthe RME risks. The maximum risk is withinthe acceptable risk range asdefined by EPAin the revised National Contingency Plan(EPA, 1990a) andin the Role ofthe Baseline Risk Assessment in Superfund Remedy Section Decisions (EPA, 1991c). Thecalculated hazard indices presented in the EA andbelow 1.0, with the exception of

zones 2, 3,and 4, where the HIs slightly exceed 1.0. Although the need for Offpost OU remedial action isnot warranted because the OffpostOU cumulative risk is 3x 10-4, the Army recognizes thatthere areseveral site-specific factors, when considered in totality, suggest remediation ofgroundwater ispreferable to no action inthe Offpost OU. Accordingly, a Feasibility Studý; hasbeen prepared asa companiondocument tothe EA for the Offpost OU.

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20000,317.10 - (III) OEA 0306110992 111- 7-25Veith, G.D., DeFoe, D.L., and Bergsted, B.V., 1979. Measuring and Estimating the Bioconcentration FactorofChemicals inFish. J. Fish Res. Board Can., 36: 1040-1048. Verschueren, K., 1983. Handbook ofEnvironmental Data on Organic Chemicals. Van Nostrand Reinhold Co., New York. Voerman, S., andBesemer, A.F.H., 1975. Persistence ofDieldrin, Lindane, and DDTin aLight Sandy Soiland Their Uptake by Grass. Bull. Environ. Contam. Toxicol., 13(4): 501-505. Vogel, T.M., Criddle, C.S., and McCarty, P.L., 1987. Transformations ofHalogenated Aliphatic Compounds. Environmental Science and Technology, 21(8), p. 722 - 736. Vreman, K., Tunistra, L.G.M.T., van den Hoek, J., Baker, J., Roos, A.H., deVisser, H., and Westerhuis, J.H., 1976. Aldrin, Heptachlor and Beta-Hexachlorocyclohexane to Dairy Cows at Three Oral Doses: Residues in Milk and Body FatofCows Early and Late inLactation. Netherlands. Journal ofAgric. Sci., 24(3):197-207. Waldon, A.C., and Nabor, E.C., 1974. Importance ofFeed as anUnavoidable Source ofPesticide Contamination in Poulty, Meat andEggs. Poultry Sci. 53: 1428-35. Walker, H.A., Paul, J.F., and Bierman, Jr., V.J., 1987. Methods for Waste Load Allocations of Municipal Sewage Sludge at the 106-Mile Ocean Disposal Site. Environ. Toxicol. Chem. 6:475-489. Waller, W.T., and Lee, G.F., 1979. Evaluation ofObservations ofHazardous Chemicals in Lake Ontario During the International Field Year forthe Great Lakes. Environ. Sci. Technol., 13:79-85. Walton, G. 1961. Public Health Aspects ofthe Contamination ofGround Water in the Vicinity of Derby, Colorado. In: Ground Water Contamination Symposium: Robert A. Taft Sanitary Engineering Center Technical Report, W61-5, p. 121-125. Watkins III, J.B., and Klaassen, C.D., 1986. Xenobiotic Biotransformation in Livestock: Comparison toOther Species Commonly Used in Toxicity Testing. Journal ofAnimal Science, 63:933-944. Wauchope, R.D., 1975. Fixation ofArsenical Herbicides, Phosphate, and Arsenate in Alluvial Soils. Journal ofEnvironmental Quality, 4(3):355-8. Wauchope, R.D., and McDowell, L.L., 1984. Adsorption ofPhosphate, Arsenate, Methanearsonate, and Cacodylate by Lake and Stream Sediments: Comparison with Soils. Journal ofEnvironmental Quality, 13:499-504. Wheeler, W.B., Moye, H.A., VanMiddelem, C.H., Thompson, N.P., and Tappan, W.B., 1969. Residues ofEndrin and DDT inTurnips Grown inSoil Containing These Compounds. Pesticides Monitoring Journal, 3(2): 72-76. Wiemeyer, S.N., and Porter, R.D., 1970. DDE Thins Eggshells ofCaptive American Kestrels. Nature. 227:737-738. Wiese, I.H., Basson, N.C.J., and Van der Merwe, J.H., 1970. Dynamics ofDieldrin and Its Photoisomerization Product, Photodieldrin, on Veld and inLivestock Exposed to Dieldrin-Treated Veld. Phytophylactica, 2:33-48.

20000,317.10 - (III) OEA 0306110992 111 - 7-26

### Williams, H.C., Dozier, W.A., Jr., Evans, C.E., Carlton, C.C., and Short,K.C., 1983. Growth and YieldResponse of'Correll' PeachTrees to Fumigation with DBCP. Scientific Horticulture, 20:349-354. Williams, R.T. 1974. Inter-Species Variations inthe Metabolism ofXenobiotics. Symposium of the Biochemical Society ofLondon, Eight CIBA Medal Lecture, Delivered on November 6, 1973. Wilson, B.H., Smith, G.B., and Rees, J.F., 1986. Biotransformations ofSelected Alkylbenzenes andHalogenated Aliphatic Hydrocarbons in Methanogenic Aquifer Material: A Microcosm Study. Environmental Science and Technology, 20:997-1002. Wilson, L.L., Kurtz, D.A., Ziegler, J.H., Rugh, M.C., Watkins, J.L., Long, T.A., Borger, M.L., and Sink, J.D., 1970. Accumulations ofCertain Pesticides in Adipose Tissues and Performance of Angus, Hereford, and Holstein Steers Fed Apple-D Processing Wastes. Journal ofAnimal Sci., 31:112-7. Wolf, M.A., Rowe, V.K., McCollister, D.D., Hollingsworth, R.L., and Oyen, F., 1956. Toxicological Studies ofCertain Alkylated Benzenes and Benzene. Archives ofIndustrial Health, 14:387-398. Wood, P.R., Lang, R.F., and Payan, I.L., 1985. Anaerobic Transformation, Transport, and Removal ofVolatile Chlorinated Organics inGroundwater. Ground Water Quality. C.H. Ward, W. Giger, and P.L. McCarty, eds. John Wiley &Sons. New York, NY. p. 493 - 511. Woodhouse, W.W., Jr., and Griffith, W.K., 1978. Soil Fertility and Fertility ofForages. In: Forages: The Science ofGrassland Agriculture, Third Edition. Heath, M.E., Metcalfe, D.S., and Barnes, R.F., eds. IowaState University Press. Ames, IA. Woolson, E.A., Axley, J.H., and Kearney, P.C., 1973. The Chemistry and Phytotoxicity of Arsenic in Soils. 11. Effects ofTime and Phosphorus. Soil-Science Society ofAmerica Proceedings, 37:254-259. Woolson E.A., Isensee, A.R and Kearney, P.C., 1976. Distribution and Isolation ofRadioactivity from NAs-Arsenate and iAC-Methanearsonic Acid inan Aquatic Model Ecosytem. Pesticide Biochemistry and Physiology, 6:261-269. World Health Organization, 1984. Guidelines for Drinking Water Quality, Volume 2. Health Criteria and Other Supporting Information. Geneva, Switzerland. World Health Organization, 1987. Environmental Health Criteria No. 62, 1,2-Dichloroethane. Geneva, Switzerland. World Health Organization, 1989. Environmental Health Criteria No. 91. Aldrin and Dieldrin. World Health Organization. Geneva, Switzerland. Young, R.W., 1969. Residues ofDieldrin and DDT in Peanuts and Turnip Greens Grown inSoil Containing These Compounds. Pesticides Monitoring Journal, 3(2): 94-99. Zach, R., and Mayoh, K.R., 1984. Soil Ingestion by Cattle; A Neglected Pathway. Health Physics, 46(2):426-431. Zoeteman, B.C.J., Harmsen, K., Linders, J.B.H.J., Morra, C.F.H., and Slooff, W., 1980. Persistent Organic Pollutants in River Water and Ground Water in the Netherlands. Chemosphere, 9:231-249. 20000,317.10 - (III) OEA 0306110992 111 - 7-27Table 4.0- 1: Target Organ- or System-specific Chemicals ofConcern

Taraet Orean or System Chemical ofConcern Blood Benzene Toluene Cardiovascular 1,2-Dichloroethane Atrazine Central Nervous System DIMP' 1,4-Dithiane Malathion Manganese Oxathiane Toluene Xylenes, total Gastrointestinal Hexachlorocyclopentadiene Liver Aldrin Carbon tetrachloride Chloroform Chlorobenzene Chlordane, total CPMS CPMSO CPMS02 Dibromochloropropane Dicyclopentadiene Dichlorobenzenes, total DDE DDT Dieldrin 1,4-Dithiane Endrin Ethylbenzene Isodrin Tetrachloroethene Trichloroethene Ocular Toluene Renal Chlorobenzene Dibromochloropropane Ethylbenzene Respiratory 1,2-Dichloroethane Toluene Xylenes, total Skin Arsenic, total

Based on acute effects (EPA, 1989b). 20000,317.10 - OEA 0306111092Table 4.1.1-1: Summary ofResidential Hypothetical Future Carcinogenic Risks: Reasonable Maximum Exposure

Combined Zone Cancer Risk' Maior Chemicals ofConcern ]A <1 X 10-4 Arsenic, atrazine, dieldrin IB <1 X 10-4 Arsenic, atrazine, dieldrin 1C <1 X 10-4 Arsenic, atrazine, dieldrin 2 <2x 10-4 Aldrin, arsenic, atrazine, chloroform, dibro10-4 mochloropropane, dieldrin, tetrachloroethene 3 <3 x Aldrin, atrazine, dieldrin, tetrachloroethene 4 <2x 10-4 Aldrin, arsenic, atrazine, chlordane, 1,2-dichloroethane, dieldrin 6 7 x 10-1 Aldrin, arsenic, dieldrin

I

Risks are rounded to one significant figure (EPA, 1989a).

Includes all chemicals, all pathways, RME intakes, and 95percent upper confidence limit. (The actual risk atthe RME intake may bethree-fold less, based on the uncertainty analysis.) The "less than"symbol (<) indicates risk is upper-bound risk and that the true RME risk is less than the risk indicated. 2 These Chemicals ofConcern account for more than 90 percent ofrisk. RME = reasonable maximum exposure

20000,317.10 - OEA 0306111092Table 4.1.1-2: Summary ofResidential Child Chronic Combined Noncarcinogenic Hazard Indices (HIs >1)

Target Hazard Zone Organ/System Indexi Chemicals ofConcern2

2 Liver 2 Chloroform, dieldrin CNS 1.3 Manganese 3 Liver 2 Dicyclopentadiene, dieldrin 4 Liver 1.4 Chlordane CNS 4 DIMp3

1All chemicals in target system category, all pathways, RME intakes. 2Elimination ofthese Chemicals ofConcern would reduce HI <1. 3CNS effects based on acute effects (EPA, 1989b). CNS = central nervous system RME =reaasonable maximum exposure

20000,317.10 - OEA 0306111092Table 4.1.1-3: Contribution ofDieldrin and Other Chemicals tothe Child Acute Hepatic Hazard Index Hazard Index by Contamination Zone Chemical ]A IB IC 2 3 4 6 Dieldrin 0.76 0.96 0.76 1.0 3.8 1.5 0.76 Other 005 006 005 02 02 L2 2M Total 0.81 1.02 0.81 1.2 4.0 1.7 0.81

20000,317.10 - OEA 0306111092Table 4.1.1-4: Summary ofResidential Hypothetical Future Reasonable Maximum Exposure Subchronic Hazard Indices: Children

RME Subchronic Hepatic Total Chemical Hazard Index Hazard Index Zone Target System (Possible Range)' (Poss ble Ranpe)l

113 Dieldrin (H)

Chloroform (H) 2 - 4 4 - 7 Dieldrin (H)' i.i - 3 Manganese (CNS) 0.9 - 2

3 Chlordane (H) 0.8 - 2 5 - 14 Dieldrin (H) 4 - 10

4 Chlordane (H) 3 - 5 6- 13 Dieldrin (H) 3 - 7 Manganese (CNS) i.i - 2

5 Dieldrin (H) 1.3 -4 2 - 4

6 Dieldrin (H) i - 3 1.2 - 3

Low end ofrange is RME chronic intake divided by subchronic reference dose. High end of range is RME acute intake divided by subchronic reference dose. CNS = central nervous system H = hepatic (liver) RME = reasonable maximum exposure S= skin

20000,317.10 - OEA 0306111892Table 4.1.1-5: Summary ofResidential Hypothetical Future Reasonable Maximum Exposure Subchronic Hazard Indices: Adult Females

RME Subchronic HepaticTotal Chemical Hazard Index Hazard Index Zone Tareet System (Possible Ranjae)l (Possible Range)' 3 Dieldrin (H) 0.5 - 1.5 0.8 -2 4 Dieldrin (H) 0.2 - 0.6 0.6 - 1.3 Manganese (CNS) 0.7 - 1.1

Low end ofrange is RME chronic intake divided by subchronic reference dose. High end of range is RME acute intake by subchronic reference dose. CNS = central nervous system H = hepatic (liver) RME = reasonable maximum exposure

20000,317.10 - OEA 0306111092Table 4.1.1-6: Comparison ofResidential Reasonable Maximum Exposure and Most Likely Exposure Hypothetical Future Carcinogenic Risks by Zone

Zone RME MLE RME: MLE

IA I X 10-4 1 x 10-1 8:1 IB I X 10-4 1 X 10-1 9:1 IC I X 10-4 1 X 10-1 8:1 2 2 x 10-4 2 x 10-1 12:1 3 3 x 10-4 2 x 10-1 12:1 4 2x 10-4 3x 10-1 8:1 6 7 x 10-1 6 x 10-6 12:1

Risks include all chemicals and all pathways atthe upper 95 percent confidence level RME intake. RME risks may be overstated by three-fold, based on the uncertainty analysis. MLE =most likely exposure RME =reasonable maximum exposure

20000,317(6) - OEA 0306111092Table 5.1.2- 1: Wildlife Species Observed inOffpost Operable Unit: Winter 1989-90

Mammals Coyote Canislatrans Striped (Common) skunk Mephitismephitis Red fox Vulpes vulpes Black-tailed jackrabbit Lepuscalifornicus Eastern cottontail Sylvilagusfloridanus Desert cottontail Sylvilagusauduboni Black-tailed prairie dog Cynomys ludovicianus Deer mouse Peromyscusmaniculatus House mouse Mus musculus Meadow vole Microtuspennsylvanicus Northern pocket gopher Thomomys talpoides Mule deer Odocoileushemionus Ramors Northern harrier Circuscyaneus Ferruginous hawk Buteoregalis Golden eagle Aguilachrysaelos Other Bird Svecies Ring-necked pheasant Phasianus colchicus Mallard Anasplatyrhynchos Killdeer Charadrius vociferus American white pelican Pelecanuserythrorhynchos Great blueheron Ardeaherodias Westernmeadowlark Sturnellaneglecia Red-winged blackbird Agelaiusphoeniceus

20000,317.10 - OEA 0306111092

### Table 5.1.4- 1: Chemicals ofConcern andTissue Chemicals ofConcern forthe Offpost Ecological RiskAssessment Media Ground- Surface Analyte water Water Soil Sediment Biota Aldrin x x x Arsenic x x x x Atrazine x Benzene x Carbon tetrachloride x Chlorobenzene x Chlordane x x x Chloride x x Chloroform x CPMS x CPMSO x CPMS02 x 

### Dibromochloropropane x Dichlorobenzene x 1,2-Dichloroethane x Dicyclopentadiene x DDEI x x x x x DDT' x x x x x Dieldrin x x x x x DIMP x x Dithiane x Endrini x x x x Ethylbenzene x Fluoride x x Hexachlorocyclopentadiene x Isodrin x Manganese x Malathion x Oxathiane x Sulfate x x Tetrachloroethene x Toluene x Trichloroethene x Xylene x

1Alsoa tissue chemical ofconcern.

20000,317.10 - OEA 0816110792Table 5.2.1-1: Terrestrial Species Selected as Indicators ofEcological Impacts Svecies Relation toSelection Criteria2 Species' 1 2 3 4 5 6 7 8 9 Earthworm (sp.) x x x x x Grasshopper (sp.) x x X X X Deer mouse (sp.) X x X X x Prairie dog x x x X X x Shrew X x Vole A x x x Ground squirrel x x X Skunk x x Raccoon X Fox X X Coyote x X Mule deer x x x X White-tail deer x x X Bald eagle X X X X x x x Golden eagle X X X x x x Ferruginous hawk x X x x x Burrowing owl x X x X Prairie falcon X X x x Red-tailed hawk x X X x Swainson's hawk x x x X Northern harrier x x X x x Great-horned owl X X x X American kestrel X x X x x x Peregrine falcon x X x X Pheasant x X X X x X

1 Species in bold were selected as representative nonhuman terrestrial wildlife receptors or

indicators. 2 Selection criteria identified in Section 5.2, Exposure Assessment, of this report.

20000,317.10 - OEA 0816110792Table 5.2.1-2: Aquatic/Wetland Species in Relation toIndicator Species Selection Criteria

St)ecies Relation toSelection Criteria Species' 1 2 3 4 5 6 7 8 9 Green algae x x x x x Vascular plants x x Crayfish x x x Fathead minnow x x x Centrarchid fish x x x x Mallard x x x x x x x Pelican x x x x x Great blue heron x x x x x Bald eagle x x x x x x Other waterfowl x x x x x Other shorebirds x x x x Other raptors x x x x x

1Species in bold were selected as representative nonhuman aquatic wildlife receptors.

20000,317.10 - OEA 0816110792Table 5.2.2- 1: Potential Exposure Pathways for Biota

Contaminated Route of Media Exposure Exposure Point Recemor Soil Ingestion Areas near the northboundary where Terrestrial soilhas elevated concentrations with mammals orbirds respect to background Surface water Ingestion From FirstCreek, First Creek Aquatic, Impoundment, orother surface-water terrestrial, avian, bodies or mammalian species Surface water Direct contact From FirstCreek, First Creek Aquatic life Impoundment, orother surface-water by aquatic life Sediment Ingestion From FirstCreek, FirstCreek Aquatic life Direct contact Impoundment, or other surface-water by aquatic life Groundwater Ingestion From shallow wells in the offpost area Livestock Groundwater Direct contact From shallow wells in the offpost area Crops Biota (plant) Plant uptake From contaminated soil and irrigation Crops water Biota (animal) Ingestion of From any area with contaminated Aquatic or biota biota in the offpost area terrestrial consumers

1Refers to receptors from Tables 5.2.1 -1 and 5.2.1-2.

20000,317.10 - OEA 0306110792Table 5.2.3-1: Exposure Point Concentrations for Soil, Surface Water, and Sediment Used for the Offpost Ecological Assessment Soil, Surface Waterl Sediment' COC (iua/kg) (URA) (uelkg) Aldrin 5.08 NA 17 Arsenic NA 3.5 NA Chlordane 17.90 0.18 ND DDE 4.12 0.05 3 DDT 9.49 0.05 5 DIMP NA 11.9 NA Dieldrin 43.45 0.12 18 Endrin 8.55 NA 6 Fluoride NA 1706 NA Sulfate NA 282,840 NA

Geometric mean. pg/kg =micrograms per kilogram jug/l micrograms per liter COC chemical ofconcern DDE 2,2-Bis(p-chlorophenyl)-1,1-dichloroethene DDT 2,2-Bis(p-chlorophenyl)- 1,1,1 -trichloroethane DIMP = diisopropy1methylphosphonate NA = not applicable ND = not detected 200000,317.10(8) -OEA 0820111092Table 5.2.5.1-1: Dietary Fractions forEach ofthe Species in the Terrestrial Food Web Species Diet Fractioni Maior Species Earthworms Soil 0.99 Worm Plants Soil 1.0 Plant Insects Plants 1.0 Insect Deer mice Plants 0.47 Small mammal Earthworms 0.03 Insects 0.48 Soil 0.02 Prairie dogs Plants 0.88 Medium mammal Soil 0.08 Insects 0.04 Pheasants Plants 0.17 Small bird Insects 0.72 Soil 0.06 Earthworm 0.05 Owls Small mammals 0.665 Raptor Medium mammals 0.25 Small bird 0.055 Soil 0.03 Kestrels Small mammals 0.093 Raptor Insects 0.86 Small bird 0.017 Soil 0.03 Eagles Medium mammals 0.915 Raptor Small bird 0.019 Small mammal 0.005 Soil 0.03

1Source: Ebasco, 1992 (See Appendix H7).

20000,317.10 - OEA 0816110792

### Table 5.2.5.2- 1: Predicted Tissue Concentrations (mg/kg) forthe Terrestrial FoodWeb EcologicalReceptors Receptor Aldrin Dieldrin Endrin DDE DDT American kestrel 0.01 0.11 0.04 1.33 3.60 Greathorned owl 0.01 0.10 0.04 0.72 1.66 Bald eagle 0.00 0.00 0.00 0.00 0.00 Prairie dog 0.01 0.06 0.01 0.03 0.07 Deermouse 0.01 0.11 0.12 0.54 1.24 Pheasant 0.01 0.07 0.09 0.27 0.62 Insect 0.00 0.04 0.01 0.18 0.43 Worm 0.03 0.26 0.25 0.01 0.03 Plant 0.00 0.02 0.00 0.01 0.01

DDT=2,2-Bis(p-chlorophenyl)-1,1-dichloroethene DDT - 2,2-Bis(p-chlorophenyl)-1,1,1-trichloroethane mg/kg - milligramsperkilogram

200000,317.10(8) - OEA 0820110392Table 5.2.5.4-1: Predicted Tissue Concentrations (mg/kg) for the Aquatic Food Web Ecological Receptors on the Basis of Surface-Water Concentrations Receptor Aldrin Dieldrin Endrin DDE DDT Arsenic Bald eagle 0.0 0.0 0.0 0.0 0.0 0.0 Great blue heron 0.0 0.2 0.0 1.1 1.1 0.0 Mallard duck 0.0 0.6 0.0 0.4 0.2 4.2 Small fish 0.0 2.0 0.0 3.5 3.5 0.1 Invertebrates 0.0 1.1 0.0 0.5 0.5 0.1 Algae 0.0 0.0 0.0 0.1 0.1 1.5

DDE = 2,2-Bis(p-chlorophenyl)-1,1-dichloroethene DDT= 2,2-Bis(p-chlorophenyl)-1,1,1-trichloroethane mg/kg = milligrams per kilogram

200000,317.10(8) - OEA 0820111092Table 5.2.5.4-2: Predicted Tissue Concentrations (mg/kg) for the Aquatic Food Web Ecological Receptors on the Basis of SedimentConcentrations Receptor Aldrin Dieldrin Endrin DDE DDT Arsenic Bald eagle 0.000 0.000 0.000 0.000 0.000 0.000 Great blue heron 0.000 0.000 0.000 0.000 0.000 0.000 Mallard duck 0.004 0.004 0.000 0.002 0.003 0.000 Small fish 0.000 0.000 0.000 0.001 0.001 0.000

DDE =2,2-Bis(p-chlorophenyl)-1,1-dichloroethene DDT- 2,2-Bis(p-chlorophenyl)-1,1,1-trichloroethane mg/kg - milligrams per kilogram

200000,317.10(8) - OEA 0820110392Table 5.3.1-1: Summary ofIntakes From Zone 3 Soil, Surface Water, andDiet forthe Bald Eagle

Terrestrial Soiland Water Aquatic Dietary Total Intake Dietary Intake Intake Intake TRV COC (mjr/kK-bw1daY) (mjz/kx-bw/daY) (mjz/kjz-bw/day) fmK/kjz-bw/daY) (mg/kg-bw1daY) HQ Aldrin IAE-07 NA 7.5E-07 8.9E-07 2.8E-03 <1 Arsenic 8.8E-04 7.6E-06 NA 8.8E-04 3.OE-02 <1 Chlordane 5.2E-07 NA NA 6.2E-07 4AE-03 <1 DDE 1.2E-07 7.2E-07 2.8E-06 3.7E-06 2.7E-02 <1 DDT 2.7E-07 3.6E-07 6.6E-06 7.2E-06 2.7E-02 <1 DIMP 2.7E-06 NA NA 2.7E-06 3.8E-01 <1 Dieldrin 1.2E-06 IJE-06 4.5E-06 6.8E-06 2.8E-03 <1 Endrin 2.3E-07 NA 9.2E-07 1.1E-06 9AE-03 <1 Fluoridel 3.8E-04 NA NA S.SE-04 6.6E-01 <1 Sulfatel 6AE-02 NA NA 6AE-02 4.7E+00 <1

TRVs reported inTable 3.3.3-1. Otherraptors represented by bald eagle TRV. 1 Cannot be addressed fordietary intake because (1) chemical isa naturally occurring component ofdiet or (2) cannot be

modeledbecause ofa lack ofdata. COC = chemical ofconcern DDE = 2,2-Bis(p-chlorophenyl)-1,1-dichloroethene DDT = 2,2-Bia(p-chlorophenyl)-1,1,1-trichloroethane DIMP = diisopropy1methylphosphonate HQ = hazard quotient mg/kg-bw/day = milligramsper kilogram ofbody weight per day NA = not applicable TRV = toxicity reference value

20000,317.10 - OEA 0309111092Table 5.3.1-2: Summary ofIntakesFrom Zone 3Soil, Surface Water, and Diet for the American Kestrel

Soil and Terrestrial Total Water Intake Dietary Intake Intake TRV COC (mg/kp-bw/day) (mp/kp-bw/day) (mg/kja-bw/day) (mg/kg-bw/day) HO Aldrin 3.OE-05 1.7E-04 2.OE-04 ME-03 <1 Arsenic 1.8E-04 NA 1.8E-04 2AE-02 <1 Chlordane 1.2E-04 NA 1.2E-04 8.8E-03 <1 DDE 2.7E-05 3.7E-03 ME-03 3.1E-02 <I DDT 5.9E-05 8.8E-03 8.9E-03 3.1E-02 <I DIMP 6.OE-04 NA 6.OE-04 7.5E-01 <I Dieldrin 2.7E-04 8.2E-04 LIE-03 ME-03 <I Endrin 5.1E-05 3.8E-04 4.3E-04 3.8E-04 I Fluoridel 8.5E-02 NA 8.5E-02 1.8E+00 <I Sulfatel 1.4E+01 NA 1.4E+OI 9.4E+00 2

TRVs reported inTable 3.3.3-1. Cannot be addressed for dietary intake because (1) chemical isa naturally occurring component ofdiet or (2) cannot be modeled because ofa lack ofdata.

COC = chemical ofconcern DDE = 2,2-Bis(p-chlorophenyl)-I,I-dichloroethene DDT = 2,2-Bis(p-chlorophenyl)-1,1,1-trichloroethane DIMP = diisopropy1methylphosphonate HQ = hazard quotient mg/kg-bw/day =milligrams per kilogram - body weight per day NA = not applicable TRV = toxicity reference value

20000,317.10 - OEA 0311111092Table 5.3.1-3: Summary ofIntakes From Zone 3 Soil, SurfaceWater, and Diet for theGreat Horned Owl

Soiland Terrestrial Total Water Intake Dietary Intake Intake TRV COC (msx/kP,-bw/dav) (mP/kjz-bw/daY) (mp,/kp-bw/day) (mP,/kR-bw/dav) HO Aldrin 9.1E-06 5.2E-05 6AE-05 2.5E-02 <I Arsenic 5.3E-05 NA 5.3E-05 2AE-02 <1 Chlordane ME-05 NA 3.5E-05 8.8E-03 <I DDE 8.2E-06 2.OE-03 2.OE-03 3.OE-02 <I DDT 1.8E-05 4.7E-03 4.7E-03 3.OE-02 <I DIMP 1.8E-04 NA 1.8E-04 7.5E-01 <I Dieldrin 8.OE-05 4.9E-04 5.7E-04 2.5E-02 <I Endrin 1.5E-05 4.7E-04 4.8E-04 3.OE-03 <I Fluoridel 2.6E-02 NA 2.6E-02 1.8E+00 <1 Sulfatel 4.2E+00 NA 4.2E+00 9.4E+00 <1

TRVs reported in Table 3.3.3-1. Cannot be addressed fordietary intake because (1) chemical is anaturally occurring component ofdiet or (2) cannot be modeled because ofalack ofdata.

COC = chemical ofconcern DDE = 2,2-Bis(p-chlorophenyl)-I,I-dichloroethene DDT = 2,2-Bis(p-chlorophenyl)- 1,1,1-trichloroethane DIMP = diisopropy1methylphosphonate HQ = hazard quotient mg/kg-bw/day = milligrams per kilogram - bodyweight perday NA = not applicable TRV = toxicity reference value

20000,317.10 - OEA 0311111092Table 5.3.1-4: Summary ofIntakes From Zone 3 Soil, Surface Water, and Diet forthe Deer Mouse

Soil and Total Water Intake Dietary Intake Intake TRV COC (mg/ke-bw/day) (mg/kg-bw/day) (mp,/ka-bw/day) (mg/kp,-bw/day) HO Aldrin LOE-04 9.OE-05 1.9E-04 2.7E-02 <1 Arsenic 8.8E-04 NA 8.8E-04 9AE-02 <1 Chlordane 4.OE-04 NA 4.OE-04 7.5E-02 <1 DDE 9.5E-05 8.7E-03 8.8E-03 LIE-01 <1 DDT 2.OE-04 2.1E-02 2AE-02 LIE-01 <I DIMP 3.OE-03 NA 3.OE-03 1.9E+01 <I Dieldrin 9.OE-04 2.7E-03 3.6E-03 2.7E-02 <I Endrin L7E-04 1.2E-03 IAE-03 1.8E-03 <I Fluoridel 4.3E-01 NA 4.3E-0I 1.6E-01 3 Sulfatel 7.]E+01 NA 7.1E+OI 9.4E+00 7

Mammals were conservatively assumed to ingest the same amount ofwaterper unit body weight as avian species.

Cannot be addressed fordietary intake because (1) chemical is a naturally occurring component ofdiet or (2) cannot be modeled because ofalack ofdata.

<= less than BAF = bioaccumulation factor COC = chemical ofconcern DDE = 2,2-Bis(p-chlorophenyl)-I,I-dichloroethene DDT = 2,2-Bis(p-chlorophenyl)-1,1,1-trichloroethane DIMP = diisopropy1methylphosphonate HQ = hazard quotient mg/kg-bw/day = milligrams per kilogram - body weight perday NA = not applicable TRV = toxicity reference value 20000,317.10 -OEA 0311111092Table 5.3.1-5: Summary ofIntakes From Zone 3Soil, Surface Water, and Diet for the Prairie Dog

Soil and Total Water Intake' Dietary Intake Intake TRV COC (mR/kR-bw/day) (me/kg-bw/day) (mg/kg-bw/day) (mg/kg-bw/day) HO Aldrin 4.IE-04 O.OE+00 4AE-04 2.7E-02 <1 Arsenic 8.8E-04 NA 8.8E-04 9AE-02 <1 Chlordane 1.5E-03 NA 1.5E-03 7.5E-02 <1 DDE 3AE-04 1.6E-03 1.9E-03 3.8E-02 <1 DDT 7.7E-04 2.6E-03 3AE-03 3.8E-02 <1 DIMP 3.OE-03 NA 3.OE-03 9.4E+00 <1 Dieldrin 3.5E-03 1.9E-03 5AE-03 2.7E-02 <1 Endrin 6.8E-04 4.OE-05 7.2E-04 1.8E-03 <1 Fluoride2 43E-01 NA 4.3E-01 1.6E-01 3 Sulfate2 7. 1E+OI NA 7AE+01 9.4E+00 7

Mammals were conservatively assumed to ingest the same amount of water per unit body weight as avian species. 2 Cannot be addressed for dietary intake because (1) chemical is a naturally occurring component ofdiet or (2) cannot be modeled because of a lack of data.

< = less than BAF = bioaccumulation factor COC = chemical ofconcern DDE = 2,2-Bis(p-chlorophenyl)-I,I-dichloroethene DDT = 2,2-Bis(p-chlorophenyl)-1,1,1-trichloroethane DIMP = diisopropy1methylphosphonate HQ = hazard quotient mg/kg-bw/day = milligrams per kilogram - body weight per day NA = not applicable TRV = toxicity reference value

20000,317.10(4) - OEA 0309111092Table 6.3.2-1: Summary ofIntakes From Zone3 Sediment, Surface Water, and Dietforthe Great BlueHeron

Terrestrial Sediment and Aquatic Dietary Total Water Intake Dietary Intake Intake Intake TRV2 COC fmg/kjz-bw/dayj. (mg/kg-bw/day) fmir/kiz-bw/day) fmg/kjg-bw/daY) fmjz/kjr-bw/daY) HQ

Aldrin 6.8E-04 NA ME-05 7.2E-04 6.OE-02 <1 Arsenic 3.5E-05 3.OE-04 NA 3.3E-04 5.9E-02 <1 Chlordane 1.8E-06 NA NA 1.8E-06 8.8E-03 <1 DDE 5.3E-06 4.9E-03 1.9E-03 6.8E-03 5.5E-02 <1 DDT 8.5E-06 4.9E-03 4.3E-04 5.SE-03 5.5E-02 <1 DIMP 1.2E-04 NA NA 1.2E-04 ME-01 <1 Dieldrin 3.OE-06 3.3E-03 3.9E-04 3.7E-03 6.OE-02 <1 Endrin 9.6E-06 NA 4.3E-04 4AE-04 1.9E-02 <1 Fluoridel 1.7E-02 NA NA 1.7E-02 1.3E+00 <1 Sulfatel 2.8E+00 NA NA 2.8E+00 9.4E+00 <1

Cannot be addressed for dietary intake because (1) chemical isa naturally occurring component of diet or(2) cannot be modeled because ofa lack ofdata. 2 TRVs fromTable 3.3.3-1.

< = lessthan BCF = bioconcentration factor COC = chemical ofconcern DDE = 2,2-Bis(p-chlorophenyl)-1,1-dichloroethene DDT= 2,2-Bis(p-chlorophenyl)-1,1,1-trichloroethane DIMP = diisopropy1methylphosphonate HQ = hazard quotient NA = not applicable TRV = toxicity reference value

20000,317.10 - OEA 0309111092Table 5.3.2-2: Summary ofIntakes From Zone 3 Sediment, SurfaceWater, and Dietfor the Mallard Duck

Sediment and Total Water Intake' Dietary Intake Intake TRV2 COC (mg/ka-bw/day) (mg/ka-bw/dav) (m9/kR-bwJdav) (me/kg-bw/day) HO Aldrin 6.8E-04 O.OE+00 6.8E-04 4.OE-02 <1 Arsenic 8.8E-04 9.7E-02 9.7E-02 4.7E-01 <1 Chlordane 4.5E-05 NA 4.5E-05 6.3E+00 <1 DDE 1.3E-04 LOE-02 LOE-02 LOE-01 <1 DDT 2.1E-04 LOE-02 LOE-02 LOE-01 <I DIMP 3.OE-03 NA 3.OE-03 LOE+OI <I Dieldrin 7.5E-04 BAE-03 9.1E-03 4.OE-02 <I Endrin 2AE-04 NA 2AE-04 1.5E-01 <I Fluoridel 4.3E-01 NA 4.3E-0I LIE+01 <I Sulfatel 7.IE+01 NA 7.IE+01 9.4E+00 7

Cannot be addressed for dietary intake because (1) chemical is a naturally occurring component ofdiet or (2) cannot be modeled because ofa lack ofdata. 2 TRVs from Table 3.3.3-1.

< = less than BCF bioconcentration factor COC chemical ofconcern DDE 2,2-Bis(p-chlorophenyl)-I,I-dichloroethene DDT 2,2-Bis(p-chlorophenyl)- 1, 1,1-trichloroethane DIMP = diisopropy1methylphosphonate HQ = hazard quotient NA = not applicable TRV = toxicity reference value

20000,317.10(4) - OEA 0309111092Table 5.3.4- 1: Summary ofChicken Hazard Quotient by Zone, Offpost Operable Unit

Intake TRV COC (mg/kg/day) (mg/kg/day) Hazard Ouotient Soil Zones 1,2, and 6 Aldrin/dieldrin 1.6 E-06 2.6 E-03 < I DDE/DDT 3.6 E-06 5.5 E-02 < I Endrin 3.3 E-07 5.2 E-03 < I

Indicates the ratio ofintakes toTRVs for chickens.

<= less than COC = chemical ofconcern DDE = 2,2-Bis(p-chlorophenyl)-I,I-dichloroethene DDT = 2,2-Bis(p-chlorophenyl)- 1,1,1-trichloroethane mg/kg/day = milligrams per kilogram per day 20000,317.10 -OEA 0306111092RMAG 1041.21

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## Preparedfor: Figure 4.1.1-1 ProgramManagerfor OFFPOSTOPERABLE UNITCOMBINED CARCINOGENICRISKS (ALL RockyMountainArsenal PATHWAYS) BYGROUNDWATER ZONE -RESIDENTIALSCENARIOS Commerce City,ColoradoRMAG 1041.19



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## Prepared for: Figure 4.1.1-2 ProgramManagerfor OFFPOSTOPERABLEUNITCHILDRESIDENT HAZARD INDICES RockyMountain Arsenal DESCRIBED FORTOXICCHEMICALSAND EXPOSUREPATHWAYS - Commerce City,Colorado 

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## Preparedfor: Figure 4.1.1-9 ProgramManagerfor CARCINOGENICRISKSDESCRIBEDBYCHEMICAL,MEDIUM, AND RockyMountainArsenal EXPOSURE PATHEWAY-ZONE 4,LIFETIME URBAN RESIDENT,RME Commerce City,ColoradoRMAG 1041

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## Preparedfor: Figure 4.1.1-10 ProgramManagerfor CARCINOGENIC RISKSDESCRIBEDBYCHEMICAL,MEDIUM,AND RockyMountainArsenal EXPOSUREPATHWAY-ZONE 5,COMMERCIAIJINDUSTRIAL, RME Commerce City,ColoradoRMAG 1041.16



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### Preparedfor: Figure 4.1.1-11 ProgramManager for CARCINOGENIC RISKS DESCRIBEDBYCHEMICAL,MEDIUM, AND RockyMountainArsenal EXPOSURE PATHWAY-ZONE 6,LIFETIME RURAL RESIDENT,RME CommerceCfty,ColoradoRMAG 1041.22

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## Program Managerfor CHILDACUTE LIVERHAZARD INDICES RockyMountainArsenal Commerce City,ColoradoRMAG 1041.23



### 5- ...................

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............. 0-10 1 1 1 1B 2 3 4 Zone Explanation Ej maximum ES minimum 

## Prepared for: Figure 4.1.1-13 ProgramManagerfor SUBCHRONIC CHILDLIVER HAZARDINDICES, MAXIMUMAND MINIMUM RockyMountain Arsenal OFRANGE CommerceChy,ColoradoRMAG 1041.2

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### Prepared for: Figure 4.2.1-1 ProgramManager for NONCARCINOGENIC HAZARD INDICESZONE5;ADULT RockyMountain Arsenal COMMERCIAIJINDUSTRIAL; CHRONIC RME CommerceCity,ColoradoRMAI 1007.1 HAI" HA10648 EXPLANATION HAI HAI0W8 104thAve HA12546 TerrestrialBiotaSamplingLocations

................ ................................. ......................... ................................................ ..... ...

...................................... FieldMice PrarleDogs Grasshoppers Earthworms ChickenSamplingLocations

ChickenEgg ChickenLiver ChickenFatfSkin 0 ChickenMuscle

14 AquaticBiotaSamplingLocations L3 + Fish 0: WCrayfish Algae ighway 0 650 CowSamplingLocations

OHA10498 CowMilk Scaleinfeet 0 CowFat CowBrain CowMuscle HAIOW + HA10619 HA12508 MAII0629 CowLiver HAI2518 HA 25M ....................... .............. 9 C owKidney PheasantSampling Locations ý FirstCreek PheasantLiver Creelc !Impoundment HA1050"'. +HAO048A PheasantFlesh HAIMN HA125M +iVM936A SampleisaDuplicate 13 SectionNumber

A HAI2558L A HA1255BF 0 KA100AM A (HA12558FO) 0 HAI0106kk 12 0 HAI012BF 13 HA1013BF

HAI0366 .. . . HA10378: In HA103M

HA,03913: woma JHAI0W8 HAI0518 HA12468 HA OUR OHA10178P AR412568L undary HAI ýA 96t - hAve A.HAI2578L.

........... ý HAII= ............... 0 9 4MR......... .......... AM12WF..... ....... ..................... HA12496 WNW 23 111 20 HAI246B ................ ...... ý/WEr-S NDEX 

## Preparedfor: Figure 5.1.1-1 ProgramManagerfor OFFPOSTOPERABLE UNITBIOTASAMPLING LOCATIONS RockyMountain Arsenal Commerce City,ColoradoRMAI 1007.3 EXPLANATION B Buildings,fences.parking areas 100 so 0 100 Scale infeet '000.. T Trashdumps,small abandoneddumps

r= FF FallowField;Notplantedforat FF 0.- leastaseason B PD Prairiedogcolonies

. . . . . . ... (forbsandshortgrasses)

104thAvenue . . . . . . . . . . M SB Shelterbelts,ornamental pants/treesaroun res ences 17777771 WF Weedyforbs FU A PPF Planted,plowedfield;winter 

# ;%;% ED graincrop

%. . . 1 *6 GWF Grasses,weedyforbs, R.

..........

. . . PPF. R. PFF Plowed,fallowfield

........... ...... ....... 2 ' . .......................... ý.-W

F: ........................... .......................... . HCR Horseandcattlerange

..... ......... ............ ....... ........... CTM Cattailmarsh

. . . ............. .. . . . . ... . . ...........

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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. . . . . . . . . . ...... UUMUUUUM . .%. E ] .:.:::GWF

..... . . . . . . . . . . . . . ..

. . . PPF ..... . . . . . . . . .

. . . . . . . . . . . ... . . . . . . . . . . .

. . . . . . . . . . . . 3%4`1 . . . .

. . . . . . . . . . CTM

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :dWF: %

RockyMountainAmenal 

## Prepared for: Figure 5.1.1-2 ProgramManager for HABITATMAPFOR FIRSTCREEKPORTION OF RockyMountain Arsenal OFFPOSTOPERABLE UNIT Commerce City,ColoradoHMA1 1191 

### Secondary Secondary Secondary Exposure Exposure Receptors Quantified? Source Release Transport Media Routes Mechanism Process

From Offsite Groundwater Pumpin Ingestion Livestock Yes, dwater Onpost Flow,Discharge 9 GrounE R PlantUptake Crops Yes Groundwater to SurfaceWater Sorption

Fugitive -Ingestion Livestock Yes From Offsite Dust Deposition Soil Dermal Crops No Onpost Soils tr m 

# H Inhalation TerrestrialWildlife No

Y Ingestion m* Livestock Yes From Offsite Deposition PlantUptake

-- )o Crops Yes Onpost -30 Surface Water Runoff Sorption SurfaceWater DirectContact AquaticLife Yes Sediment Ingestion TerrestrialWildlife Yes Ingestion AquaticLife Yes ),P Sediment Dermal TerrestrialWildlife Yes

iota TerrestrialWildlife Yes "Plants Ingestion "Animals Aquatic Life Yes

Prepared for: Figure 5.2.2-1 Program Manager for ECOLOGICALSITE CONCEPTUALMODELOFFPOST OPERABLE UNIT Rocky Mountain Arsenal CommerceCity,ColoradoRMA1 1105



### Great Horned Owls - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - American Kestrels )o Bald Eagles . K

-- - - - -

A

...

............................

.......... ......... Plants rm rass oDo#.

SurfaceWate. r EXPLANATION

a I,

oudwebpathway Surface wateringestion pathway

-- - -- - Soil ingestionpathway Residuedatafrorn RI addendum 

### Prepared for: Figure 5.2.5.1-1 ProgramManager for OFFPOST OPERABLE UNIT TERRESTRIAL FOODWEB RockyMountain Arsenal Commerce Chy,ColoradoRMA1 1106

r

## - - - - - - - Great Blue BaldEagles Herons

Mallards Ex, 

# A, IBM nt.

.......... ....... , "T



# ..

..

...... ............. ...... . ...... ...

.. (-hp

17- - - - - - - -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

-- -- -- -- -- -- -- -- -- -- -- -- -

- -- -- -- - -- -- -- -- -- - - -- -- -- -- -- -- -- -- - EXPLANATION

Foodwebpathway

-- - - - - Surface water ingestion pathway Sediment ingestion pathway Residue datafrom RI addendum 

## Prepared for: Figure5.2.5.3-1 Program Manager for Rocky MountainArsenal OFFPOSTOPERABLE UNITAQUATIC FOODWEB Commerce City,ColoradoRMAI 110'

-< --- - ------- - - - - - ------- - ------ ------ *:--'M Vf

: .............. 

## .......... ....

..........

Crops

. .. . . .. . ..

. . . . . . . . . . . . . . . M XX2.

..........

EXPLANATION

Food wi-b pathway Sur-face water ingestion pathway

- - - - - - Soi!ingestion pathway

..................... Groundwater ingestion pathway Residue data from RIaddendum 

### Prepared for: Figure 5.2.6.5-1 Program Manager for Rocky Mountain Arsenal OFFPOST OPERABLE UNITAGRICULTURAL FOODWEB Commerce City,Colorado