TECHNICAL SUPPORTFOR ROCKY MOUNTAIN ARSENAL

Offpost Operable Unit Endangerment Assessment/Feasibility Study Final Report Volume I ofVIII

(Introduction)

November 24, 1992 Contract NumberDAAA15-88-0021 Task RIFS1 (Delivery Order 0001)

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

PREPARED FOR PROGRAM MANAGER FOR ROCKY MOUNTAIN ARSENAL

THIS DOCUMENT ISINTENDED TOCOMPLY WITHTHE NATIONAL ENVIRONMENTAL POLICY ACT OF 1969. THE INFORMATION AND CONCLUSIONS PRESENTED IN THISREPORT REPRESENT THE OFFICIALPOSITION OF THE DEPARTMENT OF THE ARMYUNLESS EXPRESSLY MODIFIED BY A SUBSEQUENT DOCUMENT. THIS REPORT CONSTITUTES THE RELEVANT PORTION OF THE ADMINISTRATION RECORD FOR THIS CERCLA OPERABLE UNIT.


# M9200034TABLE OF CONTENTS Page VOLUME I - INTRODUCTION LIST OFTABLES ..................................................... xix LIST OFFIGURES .................................................... xxv PREFACE ........................................................... P-1 EXECUTIVE SUMMARY .............................................. ES- I INTRODUCTION ..................................................... 1-1 GLOSSARY .......................................................... G-i VOLUME II - ENDANGERMENT ASSESSMENT PREFACE ........................................................... II - P-1 1.0 IDENTIFICATION OF CHEMICALS OF POTENTIAL CONCERN ........... 11- 1-1 1.1 GENERAL SITE DATA EVALUATION CONSIDERATIONS .......... 11-1-4 1.2 STATISTICAL PROCEDURES FORCOMPARISON WITH BACKGROUND ............................................. 11 - 1-g 1.3 SELECTION OF CHEMICALS OF CONCERN ...................... II - 1-15 1.3.1 Groundwater ......................................... II - 1-15 1.3.2 Surface Water/Sediment ................................. 11- 1-17 1.3.3 Surficial Soil .......................................... 11

- 1-21 1.3.4 Biota ................................................ II - 1-22 1.4 SUMMARY ................................................ II - 1-24 1.5 UNCERTAINTIES ........................................... II - 1-26 2.0 EXPOSURE ASSESSMENT ......................................... II - 2-1 2.1 PROPERTIES AND PROBABLE ENVIRONMENTAL FATES OF CHEMICALS OF CONCERN ................................ 11- 2-1 2.1.1 Equilibrium Partitioning Properties ofChemicals ofConcern ..... II - 2-2 2.1.1.1 Information Sources ............................. II - 2-3 2.1.1.2 Data Evaluation ................................ I I- 2-5 2.1.1.3 Results ....................................... 11 - 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 0306111892TABLE OF CONTENTS (Continued) Page 2.1.2.4 Compounds Containing Sulfur ...................... II - 2-23 2.1.2.5 Compounds Containing Phosphorus .................. Il - 2-24 2.1.2.6 Ionic Chemicals ................................. Il - 2-26 2.1.2.7 Miscellaneous Compounds ......................... Il - 2-30 2.1.3 Uncertainties ......................................... II - 2-31 2.2 CHARACTERIZATION OF EXPOSURE SETTING .................. II - 2-32 2.2.1 Site Characteristics Affecting Contaminant Migration ........... II - 2-32 2.2.1.1 Site Description and History ....................... 11- 2-32 2.2.1.2 Environmental Setting ............................ Il - 2-33 2.2.1.3 Sampling Locations and Media ..................... II - 2-34 2.2.1.4 Summary ofOffpost Operable Unit Contamination ...... II - 2-36 2.2.2 Potentially Exposed Populations ........................... 11- 2-37 2.2.2.1 Residential Land Use ............................ 11- 2-38 2.2.2.1.1 Procedures ........................... Il - 2-38 2.2.2.1.2 Results .............................. Il - 2-41 2.2.2.2 Commercial/ Industrial Land Uses ................... II - 2-42 2.2.2.3 Qualitative Assessment ofthe Likelihood ofOccurence ofthe Selection ofFuture Land Use forthe Offpost Endangerment Assessment/Feasibility Study ........... II - 2-44 2.2.2.4 Water Use ..................................... Il - 2-45 2.2.2.4.1 Existing Groundwater Use ............... 11 - 2-45 2.2.2.4.2 Projected Future Use ofGroundwater ....... II - 2-49 2.2.2.4.3 Surface-Water Use ..................... 11 - 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 ................................... Il - 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 ................................ II - 2-56 2.3.3 Potential Exposure Pathways and Routes ..................... II - 2-57 2.3.3.1 Inhalation Route ................................ II - 2-57 2.3.3.2 Dermal Route .................................. 11 - 2-60 2.3.3.3 Ingestion Route ................................. 11 - 2-61 2.3.4 Uncertainties ......................................... 11 - 2-64 2.4 QUANTIFICATION OF EXPOSURE ............................. 11- 2-64 2.4.1 Identification ofZones Having Distinct Exposure Concentrations and/or Pathways ....................................... 11 - 2-66 2.4.2 Exposure Assessment Procedures and Exposure Point Concentrations ........................................ II - 2-71 2.4.2.1 Statistical Procedures Used toEvaluate Monitoring Data ......................................... II - 2-72
20000,317.10 - 1-toc 0306111992TABLE OF CONTENTS (Continued) Page 2.4.2.2 Model Used to Estimate 30-Year Groundwater Exposure Point Concentration ............................. II - 2-73 2.4.2.3 Models Used to Estimate Concentrations inAgricultural Products ...................................... 11 - 2-74 2.4.2.3.1 Chicken Eggs ......................... II - 2-75 2.4.2.3.2 Vegetables ............................ II - 2-75 2.4.2.3.3 Beef ................................ II - 2-81 2.4.2.3.4 Dairy ............................... II - 2-82 2.4.2.4 Summary ofNonchemical-specific Parameters ......... II - 2-83 2.4.2.4.1 Groundwater Fraction Used for Irrigation (GWF) ....................... 11- 2-83 2.4.2.4.2 Fraction Exposed (f.) ................... Il - 2-83 2.4.2.4.3 Partition Coefficient Deposited from Spray (Kd.p)) .......................... II - 2-83 2.4.2.4.4 Cattle Water/Feed Intakes (IPWM and Ipwd) .... Il - 2-84 2.4.2.4.5 Cattle Feed/Soil Intake (1p.) ............... Il- 2-84 2.4.2.5 Sample Calculations and Comparison With the Available Monitoring Data ................................ II - 2-84 2.4.2.6 Results ....................................... II - 2-86 2.4.3 Estimation ofChemical Intakes ............................ II - 2-90 2.4.3.1 Chemical-specific Parameters ...................... II - 2-94 2.4.3.2 Exposure Factors ................................ II - 2-95 2.4.3.3 Results ....................................... 11 - 2-98 2.4.4 Estimation ofChemical Intakes for Commercial/Industrial Scenario ............... II - 2-99 2.4.4.1 Estimation ofChemical Intakes ..................... II - 2-100 2.4.5 Uncertainty Analysis (Residential) ......................... II - 2-100 2.4.5.1 Preliminary Sensitivity Analysis .................... Il - 2-101 2.4.5.2 Additional ScopingConsiderations .................. Il - 2-102 2.4.5.3 Procedures .................................... 11 - 2-103 2.4.5.4 Determination ofInput Parameter Distributions ........ II - 2-104 2.4.5.5 Results II - 2-106 2.4.5.5.1 InputParameters ....................... 11 - 2-106 2.4.5.5.2 Example Results ....................... Il - 2-108 2.4.5.5.3 Summary ofResults .................... Il - 2-110 2.5 SUMMARY OF EXPOSURE ASSESSMENT ........................ II - 2-112 2.5.1 Residential Scenario ...... 11-2-113 2.5.2 Commercial/ Industrial Scenario ........................... II - 2-116 2.6 UNCERTAINTIES ........................................... II - 2-116 3.0 TOXICITY ASSESSMENT .......................................... 11- 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) Page 3.2.1 Weight ofEvidence ..................................... II - 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 ................................... II - 3-9 3.3.3.1 Derivation ofa No-Observed- Adverse-Effect Level ..... 11 - 3-10 33.3.2 Phylogenetic Differences .......................... 11 - 3-13 3.3.3.2.1 Intraspecies Differences ................. 11 - 3-16 3.3.3.2.2 Genus and Species Differences ............ 11 - 3-16 3.3.3.2.3 Family/Order Differences ................ II - 3-18 3.3.3.2.4 Threatened or Endangered Species .......... 11 - 3-19 3.4 MAXIMUM ACCEPTABLE TISSUE CONCENTRATIONS ............ 11 - 3-19 3.5 UNCERTAINTIES IN TOXICITY ASSESSMENT .................... Il - 3-20 3.5.1 Human Toxicity Assessment .............................. II - 3-20 3.5.2 Toxicity Reference Values ............................... 11- 3-21 VOLUME III - ENDANGERMENT ASSESSMENT 4.0 HUMAN RISK CHARACTERIZATION ............................... III - 4-1 4.1 RESIDENTIAL SCENARIO .................................... III - 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 ...... III - 4-6 4.1.1.4 Hypothetical Future Carcinogenic Risk ............... III - 4-6 4.1.1.5 Zone-specific Risks ............................. III - 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 at* Most Likely Exposure Intakes ................. III - 4-12 4.1.4 Alternative Risk Estimate Based on Predicted Decline in Groundwater Concentrations .............................. III - 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 Riskat Most Likely Exposure Intakes ............. III - 4-15 4.3 RISK CHARACTERIZATION SUMMARY ........................ III - 4-15 20000,317.10 - I-toe 0306111992 ivTABLE OF CONTENTS (Continued) Page 4.4 UNCERTAINTIES INTHE HUMAN HEALTH ASSESSMENT ......... 111- 4-18 5.0 ECOLOGICAL ASSESSMENT ....................................... III - 5-1 5.1 SITE CHARACTERIZATION ................................... 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 ...................... :,*****, ** III - 5-3 5.1.2 Ecological Characterization ofthe Offpost Operable Unit ........ III - 5-4 5.1.3 Contamination Pertaining to OffpostBiota ................... III - 5-5 5.1.4 Selection ofChemicals ofConcern for Biota .................. III - 5-6 5.2 EXPOSURE ASSESSMENT ..................................... III - 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 .............................. 111- 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 ....................................... III - 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 Web Ingestion Pathways ................ III - 5-20 5.2.5.4 Aquatic Food Web PredictedTissue Concentrations ...... III - 5-21 5.2.6 Direct Exposure to Chemicals ofConcern .................... III - 5-21 5.2.6.1 Surface-Water Ingestion Pathway ................... III - 5-21 5.2.6.2 DirectContact with Surface Water or Sediment ......... III - 5-23 5.2.6.3 Soil Ingestion .................................. III - 5-23 5.2.6.4 Dietary Ingestion for Wildlife ...................... III - 5-24 5.2.6.5 Dietary and Soil Ingestion Pathways for Livestock ....... III - 5-24 5.3 RISK CHARACTERIZATION .................................. III - 5-26 5.3.1 Terrestrial Food Web Ecological Risk ....................... III - 5-26 5.3.2 Aquatic Food Web Ecological Risk ......................... III - 5-29 5.3.3 Underwater Aquatic Life ................................ III - 5-30 5.3.4 Agricultural Life ...................................... III - 5-30 5.3.5 Ecological Risk Assessment Uncertainty ..................... III - 5-31 5.3.5.1 Site Characterization ............................. III - 5-31 5.3.5.2 Exposure Assessment ............................ III - 5-32 5.3.5.3 Risk Characterization ............................ III - 5-34 5.4 SUMMARY ................................................ III - 5-34

20000,317.10 - 1-toc 0306111892 vm

TABLE OF CONTENTS (Continued) Page 6.0 CONCLUSIONS .................................................. 111-6-1 7.0 REFERENCES ................................................... III - 7-1

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

VOLUME IV - ENDANGERMENT ASSESSMENT LIST OFAPPENDIXES A RELEASE OF VOLATILE CONTAMINANTS FROM GROUNDWATER WITH SUBSEQUENT EXPOSURE INBASEMENTS: SCREENING LEVEL ANALYSIS B ESTIMATE OFAMBIENT PARTICULATE MATTER IMPACT DUE TO WIND EROSION NEAR ROCKY MOUNTAIN ARSENAL C EXPOSURE CONCENTRATIONS D ESTIMATED REASONABLE MAXIMUM EXPOSURE INTAKES E UNCERTAINTY ANALYSIS F TOXICOLOGICAL PROFILES G ESTIMATED REASONABLE MAXIMUM EXPOSURE RISKS AND HAZARD INDICES H 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 POINTCONCENTRATIONS OFCHEMICALS 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-toc 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 STEP I - DEVELOPMENT OF REMEDIAL ACTION OBJECTIVES ..... V - 1-1 1.2 STEP II - DEVELOPMENT AND SCREENING OF ALTERNATIVES .... V - 1-2 1.3 STEP III-,DETAILED ANALYSIS OFALTERNATIVES ............. V - 1-2 1.4 STEP IV - 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 Risk With 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 forGroundwater Remedial Action Objectives Development .................... V - 2-6 2.3 DEVELOPMENT OF GROUNDWATER 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 Land Use on theDevelopment of Preliminary Remediation Goals ........................... V - 2-11 2.5.2 National Contingency Plan and Point ofDeparture Considerations for Development of Preliminary Remediation Goals ............ V - 2-12 20000,317.10 -1-toc 0306111892 viiiTABLE OF CONTENTS (Continued) Page 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 - 2-18 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 orRelevant and Appropriate Requirements V - 2-20 2.5.4.2 Groundwater Health-based Criteria .................. V - 2-21 2.5.4.3 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 Process Options ......................... V - 2-27 2.8.3.1 No Action ..................................... 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 Disposal ..................... 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 ixM

TABLE 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 2.8.4.5 Containment ................................... V - 2-48 2.8.4.5.1 Subsurface Barriers ..................... V - 2-48 2.9 SUMMARY OF PROCESS OPTIONSCREENING ................... V - 2-50 2.10 SELECTION OF REPRESENTATIVE PROCESS OPTIONS ............ V - 2-50 2.10.1 Representative Process Options for Groundwater Remediation .... V - 2-51 VOLUME VI - FEASIBILITY STUDY 3.0 DEVELOPMENT OF REMEDIAL 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 InputInto Alternatives Development ................................... VI - 3-4 3.2.1.1.1 Chemicals ofConcern .................. VI - 3-4 3.2.1.1.2 Use ofthe Model inAlternatives 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 ........................... VI - 3-12 3.4.1.2 Groundwater Pretreatment Process Options ............ VI - 3-13
20000,317.10 - I-toc 0306111892 xTABLE OF CONTENTS (Continued) Page 3.4.1.3 Continued Operation ofthe Boundary Systems and Compliance With Off'post 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 ............. - 3-14
.. ..:. .... .... .... .... .... . VI 3.5.1.1 Alternative No. N- I o Action .................... VI - 3-14 3.5.1.2 Alternative No. N-2: Continued Operation ofthe North Boundary Containment System With Improvements as Necessary ..................................... 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 ............................................... 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 Plume Group Extraction/Recharge System ....................... VI - 3-24 3.5.2.5 Summary ofAlternatives Identified for the Northwest Plume Group .................................. VI - 3-25 4.0 SCREENING OF ALTERNATIVES ................................... 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 ................... : ,,,, ***, *,I* 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 and Recommendation .... VI - 4-17 4.2.2 Screening of Groundwater Alternatives - Northwest Plume Group ............................................... VI- 4-18 4.2.2.1 Alternative No. NW-1: 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 OFCONTENTS (Continued) Page 5.0 DETAILED ANALYSIS OFALTERNATIVES ........................... 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 or Relevant 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 DEFINITIONOF 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 asNecessary VI - 5-11 5.4 DETAILED ANALYSIS OF ALTERNATIVES ..................... 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 to Interim 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 WithApplicable 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) Pa_p& 5.4.2.1.2 Action-specific Applicable or Relevant 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 as Necessary ................................... 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 or Relevant and Appropriate Requirements ............ VI - 5-18 5.4.2.2.3 Location-specific Applicable orRelevant 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 5.4.2.3.2 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 or Relevant and Appropriate Requirements ............ VI - 5-18 5.4.2.4.2 Action-specific Applicable or Relevant 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 or Relevant and Appropriate Requirements ............ VI - 5-19 5.4.2.5.2 Action-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-19 5.4.2.5.3 Location-specific Applicable orRelevant 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 or Relevant and Appropriate Requirements ............ VI - 5-19 5.4.2.6.2 Action-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-20 5.4.2.6.3 Location-specific Applicable orRelevant 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 - 1-toc 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, orVolume .................. VI - 5-23 5.4.4.1 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 as Necessary ..... .................. 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 toInterim Response Action A .............................. VI - 5-24 5.4.4.5 Alternative No. NW-1: No Action .................. VI - 5-25 5.4.4.6 Alternative No. NW-2: Continued Operation of Northwest Boundary Containment System With Improvements asNecessary ........................ VI - 5-25 5.4.5 Short-term Effectiveness . . *'*'***:''******'*****' *...- VI - 5-25 5.4.5.1 Alternative No. N-1: No Action .................... VI- 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 ................ Vl- 5-26 5.4.5.2.1 Protection ofCommunity andWorkers ...... VI- 5-26 5.4.5.2.2 Adverse Environmental Impacts ........... V1- 5-26 5.4.5.2.3 Implementation Period .................. Vl- 5-26 5.4.5.3 Alternative No. N-4: Interim Response Action A ........ VI- 5-27 5.4.5.3.1 Protection ofCommunity andWorkers ...... VI - 5-27 5.4.5.3.2 Adverse Environmental Impacts ........... VI - 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-1: No Action .................. VI- 5-28 5.4.5.5.1 Protection ofCommunity and Workers ...... 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 toInterim 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 .................... VI - 5-31 5.4.7.2 Alternative No. N-2: Continued Operation ofthe North Boundary Containment System With Improvements as Necessary ..................................... VI - 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 toInterim 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 OF REMEDIAL ALTERNATIVES ........ VI - 5-33 5.5.1 Comparison ofAlternatives - North Plume Group .............. VI - 5-33 5.5.1.1 Overall Protection ofHuman Health and the Environment ................................... VI - 5-33 5.5.1.2 Compliance With Applicable or Relevant 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 .......................... Vl- 5-35 5.5.1.6 Implementability ................................ VI- 5-35 5.5.1.7 Cost ......................................... VI- 5-36 5.5.2 Comparison ofAlternatives - Northwest Plume Group .......... 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 ........................ Vl- 5-37 5.5.2.3 Long-term Effectiveness and Permanence ............. VI- 5-37 5.5.2.4 Reduction in Toxicity, 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 xviTABLE OF CONTENTS (Continued) Page 6.0 SELECTION OF THE PREFERRED SITEWIDE ALTERNATIVE ........... VI - 6-1 6.1 IDENTIFICATION OFTHE 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 asNecessary ........................ 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 6.2.2.1 Protection ofHuman Health and the Environment ....... VI - 6-7 6.2.2.2 Compliance With Applicable orRelevant and Appropriate Requirements ........................ VI - 6-8 6.2.2.3 Cost-effectiveness ....... VI - 6-8 6.2.2.4 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 OF APPENDIXES 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 TOCOMMENTS U.S. ENVIRONMENTAL PROTECTION AGENCY U.S. FISH AND WILDLIFE SERVICE COLORADO DEPARTMENT OF HEALTH SHELL OIL COMPANY

20000,317.10 - 1-toc 0306111892 xviiiLIST OF TABLES
Table No. Volume II - ENDANGERMENT ASSESSMENT 1.0-1 Data Needs in Each Medium 1.3.1-1 Statistical Comparison With Background - Groundwater 1.3.1-2 Chemicals ofConcern - Groundwater 1.3.1-3 Summary 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 (First Creek) 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 and Water (m2/day) 2.1-3 Solubility (mg/1) and Vapor Pressure (torr) forOrganic 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 toRoots, Kwr (1/kg), for Organic Groundwater Chemicals ofConcern 2.1-7 Uptake to Plants, KwP (1/kg), for Organic Groundwater Chemicals ofConcern 2.1-8 Plant Uptake Coefficients, K., (Dimensionless), for Chemicals ofConcern in Offpost Surficial Soil 2.1-9 Plant Uptake Coefficients, K.P1 for Chemicals of Concern inOffpost Surficial Soil
20000,317.10 - 1-toc 0306111892 xixLIST OF TABLES (Continued)

2.1-10 BeefBioaccumulation Coefficients, KPM1 for All Chemicals ofConcern 2.1-11 Milk Bioaccumulation Coefficients, Kpd, for All Chemicals ofConcern 2.1-12 Fish Bioaccumulation Coefficients, KWf(1/kg), for Surface-Water Chemicals of Concern 2.2.2.1.2-1 Population by Land-Use Area 2.2.2.1.2-2 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 IIIStudies 2.2.2.4.1-3 Preliminary Estimate ofthe Number ofWells by Well Use in the Offpost Operable Unit 2.2.2.4.1-4 Well Use Data From theTri-County Health Department Survey 2.2.2.4.1-5 Combined Estimate ofthe Number ofWells by Well Use in the 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 in Bioaccumulation 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 I 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 - I-toc 0306111992 xxM

LIST 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 Any Zone 2.4.2.6-11 Reasonable Maximum Exposure Concentrations in Dairyand 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 - I Dermal Absorption from Soil/Sediment 2.4.3.2-1 Exposure Factors: Ingestion Rates 2.4.3.2- Ia Parameters Used inTime-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 Effectsof Carcinogenic Operable Unit Offpost Chemicals of Concern 4 3.1-5 Regulatory Criteria for Rocky Mountain Arsenal Offpost Operable Unit, Chemicals ofConcern
20000,317.10 - I-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 of Concern 4.1.1-1 Summary ofResidential Hypothetical Future Carcinogenic Risks: Reasonable Maximum Exposure 4.1.1-2 Summary ofResidential Child Chronic Combined Noncarcinogenic Hazard Indices (HIs >1) 4.1.1-3 Contribution ofDieldrin and Other Chemicals to the Child Acute Hepatic Hazard Index 4.1.1-4 Summary of Residential 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 Most Likely Exposure Hypothetical Future Carcinogenic Risks by Zone 5.1.2-1 Wildlife Species Observed in Offpost Operable Unit: Winter 1989-90 5.1.4-1 Chemicals ofConcern and Tissue Chemicals ofConcern for theOffpost Ecological Risk Assessment 5.2.1-1 Terrestrial Species Selected as Indicators ofEcological Impacts 5.2.1-2 Aquatic/Wetland Species inRelation 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 0306111892 xxiiM

LISTOF 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 Basis ofSurface-Water Concentrations 5.2.5.4-2 Predicted Tissue Concentrations (mg/kg) for the Aquatic Food Web Ecological Receptors on the Basis ofSediment Concentrations 5.3.1-1 Summary ofIntakes from Zone 3 Soil, Surface Water, and Dietfor the Bald Eagle 5.3.1-2 Summary ofIntakes From Zone 3 Soil, Surface Water, and Diet for the American Kestrel 5.3.1-3 Summary ofIntakes From Zone 3 Soil, Surface Water, and Diet for theGreat Horned Owl 5.3.1-4 Summary ofIntakes From Zone 3 Soil, Surface Water, and Diet for the Deer Mouse 5.3.1-5 Summary ofIntakes From Zone 3 Soil, Surface Water, and Diet for the Prairie Dog 5.3.2-1 Summary of Intakes From Zone 3 Sediment, Surface Water, and Diet for the Great Blue Heron 5.3.2-2 Summary of Intakes From Zone 3 Sediment, Surface Water, and Diet for the Mallard Duck 5.3.4-1 Summary of Chicken 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 forGroundwater 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 forOffpost Operable Unit Groundwater 2.8.1-1 Screening ofProcess Options forGroundwater 2.10.1-1 Selection ofRepresentative Process Options forGroundwater
20000,317.10 - 1-toc 0306111992 xxiiiLIST OF TABLES (Continued)

Volume VI 3.5.1-1 Groundwater Alternatives for the North Plume Group 3.5.1.7-1 Summary ofPreliminary North Plume Group Groundwater Alternatives 3.5.2-1 Groundwater Alternatives for the Northwest Plume Group 3.5.2.5-1 Summary of Preliminary Northwest Plume Group Groundwater Alternatives
4.2.1.7-1 Summary ofScreening ofGroundwater Alternatives; North Plume Group 4.2.2.5-1 Summary ofScreening ofGroundwater Alternatives; Northwest Plume Group 5.5.3-1 Summary ofthe Detailed Analysis and Ranking of Groundwater Alternatives for the North Plume Group 5.5.3-2 Summary ofthe Detailed Analysis and Ranking of Groundwater Alternatives for the Northwest Plume Group

20000,317.10 - 1-toc 0306111892 xxivLIST OF FIGURES Figure No. Volume I- INTRODUCTION I Location Map ofOnpost Operable Unit, Rocky Mountain Arsenal 2 Offpost Area, Rocky Mountain Arsenal 3 Distribution of Diisopropylmethyl Phosphonate (DIMP) in theOffpost Unconfined Flow System 4 Distribution ofDicyclopentadiene in theOffpost Unconfined Flow System 5 Distribution of Dieldrin in the Offpost Unconfined Flow System 6 Distribution ofEndrin in the Offpost Unconfined Flow System 7 Distribution ofChloroform in theOffpost Unconfined Flow System 8 Distribution ofChlorobenzene in the Offpost Unconfined Flow System 9 Distribution ofDibromochloropropane in theOffpost Unconfined Flow System 10 Distribution ofTrichloroethene (TRCLE) in theOffpost Unconfined Flow System II Distribution ofTetrachloroethene in the Offpost Unconfined Flow System 12 Distribution ofArsenic in theOffpost Unconfined Flow System 13 Distribution ofChloride in the Offpost Unconfined Flow System 14 Distribution ofFluoride in theOffpost 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 in 96th 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 -I-toc 0306111892 xxvLISTOF FIGURES (Continued)

Volume II - ENDANGERMENT ASSESSMENT 1.0-1 Preliminary Site Conceptual Model, Pre-Remedial Investigation, Offpost Operable Unit 1.2-1 Offpost Operable Unit Background Surficial SoilSampling Locations 1.2-2 Offpost Operable Unit Designated Surficial Soil Data Sets forComparison With Background 1.2-3 Off'post 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 Unit Study Area Selected Current Zoning Map, 1991 2.3.1-1 SiteConceptual 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 and 4 2.4.3.3- i 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 of Ingestion Rate ofLocally Produced Milk (IRd, kg/day) for the Child Chronic and Lifetime Scenarios - Residential
20000,317.10 -I-toc 0306111992 xxviLIST OF FIGURES (Continued)

2.4.5-2 Offpost Operable Unit Histograms Describing the Distribution ofIngestion Rate ofLocally Produced Vegetables (IRv, kg/day) for the Child Chronic 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 theChild Chronic and Lifetime Scenarios - Residential 2.4.5.5.2-1 OffpostOperable Unit Distribution ofLifetime Oral Intake ofDieldrin in Zone 3 (mg/kg/day) - Residential 2.4.5.5.2-2 Offpost Operable Unit Uncertainty in the Mean Concentration of Dieldrin in Groundwater (mg/1) inZone 3 2.4.5.5.2-3 Offpost Operable Unit Uncertainty in the Mean Concentration ofDieldrin in First Creek Surface water (mg/1) 2.4.5.5.2-4 Offpost Operable Unit Uncertainty inthe Mean Concentration ofAldrin 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) in Zone 3 2.4.5.5.2-6 Offpost Operable Unit Distribution ofChild Chronic 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 of Chloroform 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 - I-toe 0306111992 xxviiM

LIST OF FIGURES (Continued)

4.1.1-4 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone ]A, Lifetime Rural Resident, RME 4.1.1-5 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone IB, 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 Biota Sampling Locations 5.1.1-2 Habitat Map for First Creek Portion 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 xxviiiLISTOF 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 inthe Offpost Unconfined Flow System 2.8-1 Groundwater Process Options 2.8.1-1 Results ofUniversal Screening ofGroundwater Process Options 2.9-1 Results ofthe Second 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 Ito Interim Response Action A 3.5.1.6-1 Alternative No. N-6: Expansion 2 to Interim Response Action A 3.5.2.4-1 Alternative No. NW-4: Northwest Plume Group Extraction/ Recharge System

20000,317.10 - 1-toc 0306111892 xxixPREFACE TO THE FINAL ENDANGERMENT ASSESSMENT/FEASIBILITY STUDY
The Rocky Mountain Arsenal Offpost Operable Unit (OU) Endangerment Assessment/Feasibility Study (EA/FS) is presented in eightvolumes. The contents ofeach volume are outlined below. To assist the reader, thecomplete TableofContents is included at thebeginning ofeach text volume; appendix volumes include alist ofappendixes in the front. Tables and figures foreach volume are included atthe endofthat volume forthe sections included inthe
same volume. The Introduction, EA, FS, and each appendix have separate reference lists.
VOLUMEI

- Table ofContents EA/FS - complete Table ofContents for allvolumes, followed by List ofTables and List ofFigures

- Preface EA/FS - explanation ofthe organization ofthe EA/FS report

- Executive Summary - summary ofinformation presented in the EA/FS

- Introduction to the EA/FS - introductory material common toboth the EA and the FS, including site history and nature and extent ofcontamination at the OffpostOU

- Glossary EA/FS - listofacronyms and abbreviations used in the EA/FS
VOLUME II

- Table ofContents EA/FS - complete Table ofContents is included in each volume

- Preface EA - outline ofthe organization ofthe EA

- Section 1.0 EA - Identification ofChemicals of Potential Concern

- Section 2.0 EA - Exposure Assessment

- Section 3.0 EA - Toxicity Assessment

- Volume II Tables EA - tables forSections 1.0, 2.0, and 3.0 ofthe EA

- Volume 11 Figures EA - figures for Sections 1.0, 2.0, and 3.0 ofthe EA
VOLUME III

- Table ofContents EA/FS - complete Table ofContents is included ineach volume

- Section4.0 EA - Human Risk Characterization

20000,317.10 - I-pref 0306111892 P-1

### - Section 5.0 EA - Ecological Assessment

- Section 6.0EA - Conclusions

- Section 7.0 EA - References

- Volume III Tables EA - tables for Sections 4.0, 5.0, and6.0 oftheEA

- Volume IIIFigures EA - figures forSections4.0, 5.0, and6.0 ofthe EA VOLUME IV

- ListofEA Appendixes

- EA Appendixes (A through H) - All Appendixes forthe EA VOLUME V

- Table ofContents EA/FS,- complete TableofContents is included ineach volume

- Preface FS - outline ofthe organization ofthe FS

- Section 1.0 FS - Feasibility Study Purpose and Organization

- Section 2.0FS - Development ofRemedial Action Objectives andScreening of Technologies

- Volume V Tables FS - tables forSections 1.0 and2.0ofthe FS

- VolumeV Figures FS- figures for Sections 1.0 and 2.0ofthe FS VOLUME VI

- Table ofContents EA/FS - completeTable ofContents is included in each volume

- Section 3.0 FS - Development ofRemedial Alternatives

- Section 4.0FS - Screening ofAlternatives

- Section 5.0FS - Detailed Analysis ofAlternatives

- Section 6.0FS - Selection ofthe Preferred Sitewide Alternative

- Section 7.0 FS - References

- Volume VITables FS- tables for Sections 3.0, 4.0, 5.0, and 6.0 ofthe FS

- Volume VIFigures FS - figures for Sections3.0, 4.0, 5.0, and6.0 ofthe FS

20000,317.10 -I-pref 0306111892 P-2VOLUME VII

- ListofFSAppendixes

- FS Appendixes (A through F) - All Appendixes for the FS VOLUME VIII

- Response toComments

- Glossary - listofacronyms used inthe responses

20000,317.10 - I-pref 0306111892 P-3EXECUTIVE SUMMARY
This Final Endangerment Assessment/Feasibility Study (EA/FS) isconsistent with the National Contingency Plan (NCP), the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), the regulations implementing the National Environmental Policy Act of 1969 (NEPA), and Federal Facility Agreement (FFA). ENDANGERMENT ASSESSMENT An Endangerment Assessment was performed forthe Offpost Operable Unit (OU) ofRocky Mountain Arsenal (RMA). Theoffpost area consists of27 square miles located tothe north and northwest ofRMA. The OffpostOU is defined by the Federal Facility Agreement as that portion ofthe offpost area where the hazardous substances, pollutants, orcontaminants fromRMA are found, and which is subject toremedial action. On the basis ofinformation existing atthe conclusion ofthe offpost remedial investigation (RI) and the beginning ofthe EA/FS, the Offpost OU is assumed to be coincident with the offpost area. It iscurrently characterized by rural agricultural and residential land uses, with some industrial land use. In the future, land use is projected tochange to more commercial, industrial, andrecreational land use in areas adjacent to RMA, with some areas zonedfor residential development (Adams County Planning Commission, 1990). Forthese reasons, a rural residential scenario (including agriculture), an urban residential scenario (excluding farm animals), and a commercial/industrial scenario were evaluated. An ecological assessment was also performed, due in partto the bald eagle habitat and other sensitive environments in the Offpost OU. The major stepsperformed in the EA included data evaluation, identification ofchemicals ofpotential concern, exposure assessment, toxicity assessment, human risk characterization, and ecological assessment. Identification ofChemicals ofPotential Concern Chemicals ofpotential concern (COCs) were identified by medium. The primary criterion for identification ofCOCs was a statistically significant increase in concentration in samples

20000,317.10 - I-es 0306111892 ES- Icollected from the Of f

post OU when compared with samples from locations believed to be unaffected by RMA contamination (i.e., background). The statistical procedures used in this assessment to determine whether chemical concentrations were elevated above background levels contained several conservative elements when compared with procedures recommended by published guidance. These conservative elements
were included to compensate for small sample size and low frequency of detection above certified reporting limits in some ofthe data sets. Theconservative features built into the statistical procedure exceeded published guidance andresulted in the inclusion offour groundwater COCs, two surface-water COCs, and one surface soil COC that would normally have been excluded. Thirty-four COCs were identified forgroundwater, including nine pesticides, five inorganic compounds, and 20 volatile or sernivolatile organic compounds. Ten COCs were identified for surface water, including four pesticides, two organic compounds, and four inorganic compounds. Each is also a COC for groundwater, the primary source of offpost surface-water contamination. The six COCs identified in sediments are all pesticides. These COCs are associated with groundwater and/or surface water that interacts with the sediments in First Creek. Six pesticides
were identified as COCs in surface soils. All ofthe thirty-four COCs were evaluated for biota; however, only those COCs for which a complete pathway ofexposure existed for a specific receptor organism were evaluated in the ecological assessment. Exr)osure Assessment The major elements ofthe exposure assessment included fate and transport ofCOCs, characterization ofthe exposure setting and exposure pathways, quantification ofexposure, and
an uncertaintv analysis of calculated exposure intakes. Chemicals migrated to the Offpost OU as a result ofpast operations at RMA, primarily by shallow groundwater and airborne pathways . Contaminant transport by both pathways has been controlled by onpost interim remedial actions. Offpost OU surface water was contaminated primarily bythe natural interaction with offpost groundwater. Offpost OU surface soil was
20000,317.10 - I-es 0306111892 ES-2contaminated bythe deposition ofairborne contaminants, non-RMA-related intentional agricultural application ofpesticides, and irrigation practices. Air monitoring data indicate that the air pathway does not contribute to human exposure. TheCOCs exhibit great variability in their mobility and persistence in environmental media. Organochlorine pesticides are relatively immobile and persistent, tending to associate with soils and sediments and tending to bioaccumulate in the food chain; the organochlorine pesticides are the only COCs elevated above background levels in soils and sediments. Most ofthe remaining COCs are mobile in groundwater, and the aromatics and aliphatics are volatile in surface waters. The fate properties ofthe COCs tend to determine their distribution in the Offpost OU. Groundwater containing elevated levels ofCOCs exists north and northwest of RMA in three distinct plumes with characteristically different groundwater quality conditions. These flow paths are referred to as the northern paleochannel, due north ofthe RMA north.boundary; the First Creek paleochannel, paralleling First Creek to the northwest from the RMA north boundary; and the northwest paleochannel, west ofthe RMA northwest boundary. The northern and First Creek paleochannels comprise the North Plume Group, and the northwest paleochannel is referred to as the Northwest Plume Group. The alluvial flow system transports most ofthe contamination in paleochannels characterized by coarser sediments. Groundwater traveling through the First Creek paleochannel discharges to First Creek, probably seasonally, resulting in elevated levels of several COCs in FirstCreek. First Creek discharges to O'Brian Canal. Concentrations ofCOCs
are reduced substantially upon discharge to O'Brian Canal; only two COCs (diisopropyl methylphosphonate [DIMP] and fluoride) are elevated in theCanal. Land use in the Offpost OU has been predominantly agricultural and rural residential, with localized commercial/ industrial land uses and open space. The portion ofthe Offpost OU north of O'Brian Canal, where irrigation water is available from Burlington Ditch, contains many vegetable and turffarms. A recent change in land use affecting exposure to COCs was the purchase offormer residential properties near the intersection of96th Avenue and Peoria Street by Shell Oil Company. Based on local planning documents, it is expected that development

20000,317.10 - I-es 0306111892 ES-3resulting from encroachment ofthe Denver suburban fringe from the southwest and the new regional airport to the east will supplant agricultural land uses with residential and commercial/industrial land uses over the next 20 years. The predominant traditional agricultural land use ofthe area supports theevaluation of exposure pathways involving consumption offoods produced in the Offpost OU. A complete pathway must have a source, a mechanism ofrelease, a transport medium, an exposure point, a receptor (e.g., humans must be present to be exposed), and an exposure route (e.g., ingestion). The most important pathways considered under the residential reasonable maximum exposure (RME) scenario, including hypothetical future exposure pathways that may not be complete at this time, are direct ingestion ofgroundwater, inhalation ofvolatile COCs released from groundwater used for domestic purposes (e.g., showering, cooking), and consumption ofvegetables, meat, eggs, and dairy products produced in the Offpost OU. Exposure concentrations in foods were estimated usingequilibrium partition models. Predictions by the models were compared to limited sitespecific sampling and analytical data, and the model results approximated the limited number of observed concentrations in meat and eggs. Data for milk and vegetables were insufficient to verify the models. Current and projected future commercial/industrial land uses in zone 5 suggested that exposure pathways consistent with this land use should be evaluated. The most important pathways considered in the RME commercial/industrial scenario are direct ingestion ofgroundwater and inhalation of volatile COCs from other uses (e.g., showering). For purposes ofthe EA, the Offpost OU was subdivided into six geographic zones, each with distinct exposure conditions. Variations in medium-specific exposure concentrations and land and water use were considered in defining these zones, which are shown in Figure ESI. A separate exposure assessment was performed foreach zone. Hypothetical future intakes under the RME scenario are greatest in zones 2, 3, and 4, directly north ofthe RMA north boundary. Exposure factors used in this EA conformed to U.S. Environmental Protection Agency (EPA) RME guidance wherever applicable factors existed. Where EPA guidance was not

20000,317.10 - I-es 0306111892 ES-4available, RME exposure factors were derived for the 90th percentile ofthe range ofthe exposure factor. COCintakes were estimated for lifetime, chronic, and acute exposure durations. The lifetime scenario begins at age 0 andextends for 30years, considering age-dependent body weight, milk consumption, and direct ingestion ofsoil. Intakes were estimated for children and adult women to address potentially sensitive subpopulations. The child chronic scenario assumes an exposure duration fromages I to9. Children tend tobe exposed at greater rates than adults, so the child chronic scenario represents the RME for chronic noncarcinogenic risk assessment. Commercial/industrial intakes were estimated for adult workers with a 25-year duration. The RME COC intake estimates include hypothetical exposure pathways that have not been complete for several years (i.e., exposure has notoccurred by these pathways). Forexample, previous residents in zones 3 and4 and current residents in zone 5 have water supplies other than shallow wells. There are no current residents in zones 5 and 4. Therefore, residential intake estimates in these zones are conservative because the pathways do not represent existing exposures. A limited quantitative uncertainty analysis was performed to.evaluate the possible exposure variation among the potentially exposed population. The uncertainty analysis implies that upto 99 percent ofa future exposed population would experience intakes less than the RME. Although there are uncertainties in exposure estimates, the EA generally used conservative approaches to limit the potential for underestimating exposures. Thus, itis reasonable to conclude that the RME falls above the 95th percentile ofpossible exposures and is thus in the range ofexposures consistent with the definition ofRME. The uncertainty analysis combines uncertainty indefining exposure concentrations (frommonitoring data and models) and variability in hypothetical exposures. The uncertainty analysis process demonstrates thatmost ofthe variance in intake estimates can be attributed to variability across the population rather than uncertainty in defining the exposure concentrations. Toxicity Assessment Available information on the toxiceffects ofthe COCs, emphasizing information pertinent to the evaluation of subchronic and chronic exposures atrelatively low intakes, issummarized in
20000,317.10 - I-es 0306111892 ES-5the toxicity assessment section of the report. Available reference doses and cancer slope factors published by EPA were used in this EA. When chronic reference doses were unavailable from EPA, they were estimated or identified from other sources, particularly the RMA onpost toxicity assessment contained in the Final Human Health Exposure Assessment (Ebasco, 1990). Two of the COCs, arsenic and benzene, are known human carcinogens (EPA category A). Ten COCs are probable human carcinogens (EPA category B2). Category B2 chemicals have sufficient evidence that the chemical causes cancer in laboratory animals, but insufficient evidence for cancer in humans. Most of the COCs have the potential for noricarcinogenic effects
on the liver (hepatic system), and these chemicals were grouped to evaluate the probability of adverse effects on the liver. The potential effects of the contaminants on terrestrial wildlife, livestock, terrestrial vegetation. and aquatic organisms were also summarized in the toxicity assessment section of this report. Toxicity reference values for biota were developed, which are intended to represent exposure levels that would result in a low probability of adverse effects on a population of nonhuman receptors, rather than to protect every individual animal. The potential for ecological effects was also evaluated by comparing observed tissue concentrations ofCOCs in biota samples to maximum allowable tissue concentrations, which are summarized in the toxicity assessment and ecological assessment.
Human Risk Characterization Additive carcinogenic risks for residential hypothetical future exposures at RME intake levels by zone are highest in zones 2, 3, and 4. These zones are south of O'Brian Canal and within approximately one mile of the RMA north boundary. Based on the uncertainty analysis, the hypothetical risks may be overstated by threefold from intake considerations alone. Future hypothetical cancer risks (assuming pathways are complete and without considering additional remediation) in these zones are estimated to be less than 3 x 10-4. More than 60 percent of the Psk in each of these zones is attributable to category B2 and C human carcinogens. Thus, the risk estimate is critically dependent on the extrapolation of toxicological data from animals to humans.
20000,317.10 - I-es 0306111892 ES-6The largest contributor to total carcinogenic risk is dieldrin. Two toxicological profiles discussing both animal and human data are in Appendix F ofthe EA (page F- I and F- 112). In addition to RMA-related sources, dieldrin in surface soils north of O'Brian Canal appears to be associated with agricultural practices in the Offpost OU. The hypothetical carcinogenic risk associated with dieldrin in soil resulting from agricultural practices in zones other than zone 3 and 4 is 4 x 10-5. In addition, naturally occurring arsenic in groundwater contributes approximately 4.4 x 10-5 risk. Summing these two risks yields a 8 x 10-5 risk that is not attributable to RMA. More than 95 percent ofthe residential hypothetical carcinogenic risk in each zone is attributable to the following pathways. listed in order oftheir contribution to risk: 1. Ingestion ofshallow groundwater

Consumption ofhomegrown vegetables 3. Ingestion oflocally produced milk 4. Inhalation ofvolatiles via domestic use ofshallow groundwater (e.g., showering, cooking) 5. Ingestion oflocallv produced eggs 6. Ingestion oflocally produced meat Dermal exposures for all media do not contribute significantly to carcinogenic risk for the residential exposure, nor does incidental ingestion of soil and sediments. The oral exposure route for all media accounts for more than 70percent oftotal carcinogenic risk, with the remainder predominantly by inhalation. Groundwater is the dominant source medium contributing tototal carcinogenic risk in
zones 4.. 3, and 4 accounting for 60to 80 percent oftotal risk, depending on the zone. In the remaining zones where groundwater concentrations are lower, soil contributes relatively more to total risk (40 to 50 percent), and soil alone contributes a risk from agricultural practices of approximately 4 x 10-5 In all zones. Groundwater, surface water, and soil may contribute to estimated risks via multiple pathways, specifically those involving food production within the Offpost OU. Groundwater and surface water are assumed to be used for irrigation ofvegetable

20000,317.10 - I-es 0306111892 ES-7crops and watering of livestock. Each of the food pathways may also accumulate COCs from soil, and these relationships are quantified via the equilibrium partition models. Hypothetical risks from all carcinogens are added to determine total carcinogenic risk regardless oftarget organ/systern or weight-of-evidence category. The dominant contribution to total carcinogenic risk in all zones is from category B2 and Ccarcinogens, as previously presented. Carcinogenic risks are also posed by arsenic, a category A human carcinogen. Hypothetical future noncarcinogenic effects were evaluated for all COCs by calculating a hazard index (1-11), which is the estimated intake divided by a reference dose. An HI ofgreater than 1.0 warrants further evaluation. Children are a potentially sensitive subpopulation in the residential scenario with the largest potential for adverse noncarcinogenic effects, due to higher intakes. Considering the target organ/system potentially affected by each of the COCs, the most probable noncarcinogenic effect would be to the central nervous system (CNS). The maximum hypothetical future additive child chronic HI for CNS toxicants is 4 in zone 4. Hepatic (liver) effects are also a potential, although smaller, risk, with additive chronic Hl of 2 in zones 2 and 3. RME estimates of hypothetical current carcinogenic risks for residential land use are substantially less than future hypothetical risks. No one resides in zones 3 and 4; hence, there is
no hypothetical current risk for these zones. Residents in zones IB and 2 do not use water from the shallow aquifer. Consequently, the domestic use groundwater pathway is not and has not been complete in these zones for several years. Hypothetical current risks in zones IB and 2 are at least 3 to 4 times lower than the hypothetical future RME estimates. For the commercial/ industrial RME scenario, hypothetical future carcinogenic risks in
zone 5 is approximately 3 x 10-5, with 83 percent of the risk in zone 5 from aldrin, dieldrin, and arsenic. The estimated chronic His (liver toxicants) for the commerctat/ industrial scenario in
zone 5 are less than one.

20000,317.10 - I-es 0306111892 ES-8Ecological Assessment The objective ofthe ecological assessment was to determine hypothetical adverse affects of COCs on the environment and nonhuman receptors. Two major natural ecosystem types occur in the Offpost OU: terrestrial and aquatic. There isalso extensive agricultural use ofthe area. Potential hazards to.the different ecological components ofthe Offpost OU were addressed by considering the hazards to terrestrial, aquatic, and agricultural biota separately. Bioaccumulation and direct toxicity endpoints were evaluated for terrestrial and aquatic life. Maximum allowable tissue concentrations (MATCs) were developed to assess risk from tissue residues as a function ofbioaccumulation. The predicted tissue concentrations for endrin for the owl and kestrel exceeded the MATC; however, these predicted tissue concentrations are not supported by actual data from lower trophic levels. In addition, exposure concentrations or intakes were compared to acceptable intakes, such as toxicity reference values or reference media concentrations, resulting in a hazard quotient (HQ). The estimated intake ofDDE, DDT, aldrin, dieldrin, and endrin for the ecological receptors did not exceed the toxicity reference values. However, an HQ equal to I was calculated for the American kestrel forendrin. The results ofthe ecological risk characterization indicate that a minimal potential for adverse effects toreceptor species in the aquatic and terrestrial foodwebs exist. Species 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. Endangerment Assessment Conclusion The objectives ofthe EA were to provide an analysis of risks in the absence of additional remediation (baseline risks) and to provide a basis for determining the need for remedial action at the Offpost OU. The EA for the Offpost OU has identified hypothetical carcinogenic risks that
are within the acceptable carcinogenic risks as defined by the revised NCP (EPA, 1990) and the Role ofthe Baseline Risk Assessment in Superfund Remedy Selection Decisions (EPA, 1991). Hazard indices only exceeded 1.0 in some noncarcinogenic exposure scenarios.

20000,317.10 -I-es 0306111892 ES-9Although these findings indicate that the OffpostOU remedial action is not warranted on a riskbasis, site-specific factors suggest that remedial alternatives for the groundwater medium should beconsidered. Accordingly, a Feasibility Study hasbeen prepared as acompanion document to the EA for the Offpost OU.
FEASIBILITY STUDY Based onthe results ofthe EA, the FSconcurrently developed and evaluated a range of remedial alternatives consistent with the NCP. Based on the evaluation presented in thisFS, the Army selected a preferred sitewide alternative, which is consistent with CERCLA and the NCP. The FSshows that the preferred sitewide alternative meets the statutory requirements ofCERCLA and the NCP. The major steps performed in the FS include development ofremedialaction objectives (RAOs), development and screening ofremedial alternatives, detailed analysis of remaining alternatives, andselection ofthe preferred sitewide alternative. Develot)ment ofRemedial Action Obiectives The development ofRAOs consisted ofthree steps:

- Identification ofCOCs by medium

- Identification ofmedia ofconcern

- Identification ofexposure pathways.
Sixmedia were evaluated in the remedial investigation (RI) for the Offpost OU: groundwater, soil, surface water, sediment, air, and biota. Each medium was evaluated in the Offpost EA with respect to (1) the nature andextent ofcontamination and (2) potential exposure pathways and associated risk characterization. The cumulative Offpost OU hypothetical cancer riskis a maximum of3 x 10-4on the basis ofthe RME risks presented in the EA (Volume 111, Section4.0 andVolume IV, Appendix G). Since the Offpost OU cumulative riskis within the acceptable cancer riskrange specified by EPA, Offpost OU remedial action is not warranted. The Army, nevertheless, recognizes that there are site-specific factors that suggestremediation ofgroundwater is preferable tono-action inthe
20000,317.10 - I-es 0306120392 ES-10Offpost OU. Groundwater contributes approximately 75percent ofthe total hypothetical risk, and the data available showed exceedances ofsome MCLs in groundwater. Additionally, substantial progress has been made toward the construction and startup ofan offpost groundwater treatment system. Since the remaining media contribute a minoramount of riskto the total, the Army concludes thatthese media donotrequire development ofremedial action objectives (RAOs). On this basis, groundwater was identified asa medium ofconcern. Soil, surface water, and sediment were identified asnot requiring remediation due to the lowrisk attributable to these media. Air was notidentified as a mediumofconcern because air monitoring datahave indicated air qualitywithin the Offpost OU is not affected bycontaminants related toRMA. Biotawere notidentified asa medium ofconcern. Direct remediation ofbiota was not included onthe basis thatit is not effective except bymethods that temporarily eliminate receptor species from the contaminated area. However, protection ofbiota was addressed throughthe development of ecological criteria for the protection ofspecies potentially at risk. Groundwater RAOs specifythe attainment ofpreliminary remediation goals (PRGs) for the identified COCs and exposure pathways. In accordance withthe NCP, PRGs were developed considering applicable orrelevant andappropriate requirements (ARARs), health-based criteria, factors related to technical limitations (e.g., analytical detection limits), land use, andecological criteria. Final remediation goals willbe determined whenthe remedy isselected and the Record ofDecision is issued. Groundwater exceedances ofPRGs were identified in two plumegroups, the North Plume Group and the Northwest Plume Group, anarea encompassing approximately 590acres in the Offpost OU. Groundwater alternatives were developed to address the areas ofPRG exceedances. Develot)ment andScreenina ofRemedial Alternatives Remedial alternatives forthe Offpost OU weredeveloped by (1) identifying the media in which COCswere detected atlevels exceeding PRGs, (2) calculating the areas and volumes of media exceeding PRGs, and(3) assembling combinations ofrepresentative process options into alternatives representing a range oftreatment andcontainment combinations thataddress the
20000,317.10 - I-es 0306120392 ES-11RAOs. Consistent with the NCP, arange ofalternatives for groundwater was developed from no action to complete removal or destruction of contaminants exceeding PRGs.
Use ofGroundwater Modeling in Alternatives Development To aid in the analysis ofgroundwater alternatives, two numerical models (North Plume Group and Northwest Plume Group) were prepared to simulate the groundwater flow and dissolved chemical transport in the Offpost OU. Due to the approximate nature ofthe models, and the considerable Uncertainty in theconceptual model and hydrogeologic parameters, none of the modeling results should be construed as accurate predictions offuture contaminant distribution. Rather, the models and modeling results should be viewed as tools forassessing the relative merits of remedial alternatives. Although there are inherent uncertainties in the groundwater model, this is a tool being used by the FS and predicted differences in remediation timeframes are considered with respect to evaluating alternative effectiveness. Simulations of contaminant transport were made corresponding to the No Action alternative and other configurations for both the North and Northwest Plume Groups. Initial conditions were chosen to reflect the contaminant plumes and to reflect contaminant removal at the North Boundary Containment System (NBCS) and Northwest Boundary Containment System (NWBCS) consistent with attainment ofOffpost OU PRGs at the boundary systems.
North Plume Group Alternatives After screening several extraction/ recharge configurations, the following groundwater alternatives were developed for the North Plume Group. The major components ofeach alternative are also listed.
Alternative No. N-1: No Action The components are as follows:

- Long-term groundwater monitoring

- Five-year site reviews

20000,317.10 - I-es 0306111892 ES- 12This alternative was retained for the detailed analysis step as required by the NCP. Common to the following alternatives are long-term groundwater monitoring and five-year site reviews, as well as the Army's commitment to provide alternative water (i.e., exposure control) to any identified future users ofgroundwater exceeding PRGs. Alternative No. N-2: Continued Ogeration ofthe North Boundary Containment System With lmi)rovements asNecessary The major components are as follows:

- Continued operation ofthe NBCS

- Improvements to the NBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control
This alternative was retained for the detailed analysis step. Alternative No. N-3: Land Acouisition and Use Restrictions The major components are as follows:

- Land acquisition

- Access and deed restrictions

- Continued operation ofthe NBCS

- Improvements to the NBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control
This alternative was not retained for thedetailed analysis step. Alternative No. N-4: Interim ReSDonse Action A The major components are as follows:
20000,317.10 -I-es 0306111892 ES- 13- Removal ofcontaminated unconfined groundwater north ofthe RMA boundary in the First Creek and northern paleochannels, using Interim Response Action (IRA) A groundwater extraction wells

- Treatment ofthe organic COCs present in the groundwater, using carbon adsorption

- Recharge oftreated groundwater to the unconfined flow system (UFS), using IRA A wells and trenches

- Continued operation ofthe NBCS

- Improvements to the NBCS and IRA A asnecessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control
This alternative was retained for thedetailed analysis step.
Alternative No. N-5: Expansion I to Interim Response Action A The major components are as follows:

- Removal ofcontaminated UFS groundwater north ofthe RMA boundary in the First Creek and northern paleochannels, using IRA A groundwater extraction wells

- Expansion Iof IRA A (additional wells and trenches)

- Treatment oforganic COCspresent in the groundwater, using carbon adsorption

- Recharge oftreated groundwater to the UFS, using wells and trenches

- Continued operation ofthe NBCS

- Improvements to the NBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control
This alternative was retained for thedetailed analysis step. Alternative No. N-6: Expansion 2 to Interim Response Action A The major components are as follows:

20000,317.10 - I-es 0306111892 ES- 14- Removal ofcontaminated UFS groundwater north ofthe RMA boundary in the First Creek and northern paleochannels, using IRA A groundwater extraction wells

- Expansion 2 ofIRA A (additional wells and trenches)

- Treatment ofthe organic COCs present in the groundwater, using carbon adsorption

- Recharge oftreated groundwater to the UFS, using wells and trenches

- Continued operation ofthe NBCS

- Improvements to the NBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure co'ntrol
This alternative was not retained for the detailed analysis step. Northwest Plume GroUD Alternatives After screening several extraction/recharge configurations, the following groundwater alternatives were developed for the Northwest Plume Group. The major components for each alternative are also listed.
Alternative NW- 1: No Action The major components are as follows:

- Long-term monitoring

- Five-year site review
This alternative was retained for thedetailed analysis step as required by the NCP. Common to the following alternatives are long-term groundwater monitoring and five-year site reviews, as well as the Army's commitment to provide alternative water (i.e., exposure control) to ariv identified future users of groundwater exceeding PRGs. Alternative NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements as Necessary The major components are as follows:
20000,317.10 - I-es 0306111892 ES- 15- Continued operation ofthe NWBCS

- Improvements tothe NWBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control
This alternative was retained for the detailed analysis step. Alternative No. NW-3: Land Acouisition WithUse Restrictions The major components are as follows:

- Landacquisition

- Access anddeed restrictions

- Continued operation ofthe NWBCS

- Improvements tothe NWBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control
This alternative was notretained for the detailed analysis step. Alternative No. NW-4: Northwest Plume Groundwater Extraction/Recharge System The major components are as follows:

- Removal ofcontaminated UFS groundwater northwest ofthe RMA boundary, using three groundwater extraction wells

- Treatment oforganic COCs present in thegroundwater, using carbon adsorption

- Recharge oftreated groundwater to the UFS, using five wells

- Continued operation ofthe NWBCS

- Improvements tothe NWBCS as necessary

- Long-term groundwater monitoring

20000,317.10 - I-es 0306111892 ES- 16- Five-year.site reviews

- Exposure control
This alternative was not retained for the detailed analysis step.
Detailed Analysis ofAlternatives The remaining alternatives (Alternative Nos. N-1, N-2, N-4, N-5, NW-1, and NW-2) were evaluated with respect to the threshold and primary balancing criteria required by the NCP. The criteria are listed below
Threshold Criteria

- Overall protection ofhuman health and theenvironment

- Compliance with ARARs Primary Balancing Criteria

- Long-term effectiveness and permanence

- Reduction oftoxicity, mobility, or volume

- Short-term effectiveness

- Implementability

- Cost
Evaluation ofthe modifying criteria (i.e., the state and community acceptance) is deferred untilcompletion ofthe state and public comment periods. A comparative analysis ofthe remedial alternatives identifying the relative advantages and disadvantages ofeach alternative was performed. Based on the analysis, a preferred sitewide alternative was selected.
Selection ofthe Preferred Sitewide Alternative Using the evaluation ofthe alternatives withrespect to thecriteria required by CERCLA and the NCP, the preferred alternative was selected. The preferred sitewide alternative consists of

20000,317.10 - I-es 0306111892 ES-17Alternative No. N-4 (Interim Response Action A) forremediation ofgroundwater in the North Plume Group and Alternative No. NW-2 (Continued Operation ofthe NWBCS with Improvements
as Necessary) forremediation ofgroundwater in the Northwest Plume Group. Redefinition ofthe Offyost Or)erable Unit On the basis ofthe FSanalysis ofand selection ofthe preferred alternative and the Federal Facility Agreement definition ofthe Offpost OU, the offpost area isnot coincident with the Offpost OU. Consistent withthe Federal Facility Agreement definition limiting the Offpost OU to thatportion ofthe off'post area where hazardous substances, pollutants, orcontaminants from RMA are found atlevels subject toremedial action, the Offpost OU isdefined as only zones 2, 3, and 4 in the offpost area.

20000,317.10 - I-es 0306111892 ES- 18INTRODUCTION TOTHE ENDANGERMENT ASSESSMENT/FEASIBILITY STUDY OFFPOST OPERABLE UNIT
The Final EA/FS report complies with guidelines prepared under the provisions ofthe Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (Title 42, United States Code [USC], Sections 9601-9675), the Superfund Amendments and Reauthorization Actof 1986 (SARA), the revised National Contingency Plan (NCP) (Title 40, United States Code (USC) ofFederal Regulations [CFR] Part 300), theregulations implementing the National Environmental Policy Act of 1969 (NEPA), and associated U.S. Environmental Protection Agency (EPA) guidance documents. This introduction provides background information for theOffpost OU including setting, sitehistory and land use, previous investigations, nature and extent ofcontaminants, and response actions for the Offpost OU.
SETTING This section describes the site location, environmental setting, geology, and hydrogeology of the Offpost OU.
Site Location TheRMA National Priorities List (NPL) site is comprised oftwoOUs: Onpost and Offpost. As shown in Figure 1,the offpost areaoccupies 27 square miles insouthern AdamsCounty, Colorado, and lies north ofthe Denver metropolitan area and east ofCommerce City, Colorado. The offpost area is defined as thearea southeast ofthe South Platte River, north of80th Avenue, southwest ofSecond Creek, and northofthe north and northwest boundaries ofRMA, as depicted in Figure 2. The Offpost OU is defined by the Federal Facility Agreement asthat portion ofthe offpost area where hazardous substances, pollutants, or contaminants from RMA are found, and which issubject to remedial action. Additionally, theOffpost OU includes the surface waters of O'Brian Canal and Burlington Ditch as they extend northeast ofSecond Creek and the surface

20000,317.10 - I-intro 0306111192 1-]

twater ofBarr Lake. The Offpost OU encompasses rural residential, agricultural, and commercial/industrial areas located northand northwest ofRMA.
Environmental Settinp The topography ofthe Offpost OU issimilar to thetopography onpost and consists of stream-valley lowlands separated by gently rolling uplands. Themaximum local topographic reliefin the area is about 300feet. The elevation above mean sea level (MSL) ranges from approximately 5330 feet atthe southernboundary ofRMA toabout 5030 atthe South Platte River. Cropland and rangeland provide habitatfor numerous animal species, including game species such as cottontails, ring-necked pheasants, and mourning doves. Lake and wetland areas at Barr Lake provide feeding, breeding, androosting areas for waterfowl and endangered species, including the bald eagle. The climate ofthe offpost area is characterized by sunny, semiarid conditions. Approximately 37 percent ofthe total annual precipitation (16 inches) occurs in the spring, with much of thismoisture falling as snow in theearly spring. Summer is the hottestseason andis characterized by scattered local thunderstorms during afternoons and evenings. Approximately 31 percent of the total annual precipitation occurs during the summer season. Winter is the coldest season, during which time approximately 13 percent ofthe total annual precipitation occurs. The regional surface drainage is to the northeast toward the South Platte River. Surface water originating south ofRMA, onRMA, orin the Offpost OU flows toward the South Platte River. Twomajor canals, O'Brian Canal and Burlington Ditch, and several smaller ditches flow from southwest to northeast between RMA and the South Platte River. O'Brian Canal receives
some drainage fromthe Offpost OU and RMA where the canal intercepts First Creek. Burlington Ditch may receive surface water infrequently from First Creek.

20000,317.10 - I-intro 0306111192 1-2

### Geology Sediments at the land surface in the Offpost OU consist ofunconsolidated alluvial and eolian deposits ofPleistocene and Holocene age. The composition ofthe unconsolidated sediments varies from claysto coarse gravels, and the thickness varies from lessthan 10 feetto approximately 100 feet. The thickest deposits ofunconsolidated sediments occur in paleochannels eroded into the underlying Denver Formation. The Denver Formation is oflate Cretaceous to early Tertiary age, and consists of250 to 300feet ofinterbedded shale, claystone, siltstone, and sandstone, with a regional dip ofone-half to one degree tothe southeast. The uppermost bedrock unit was subjected toerosion before deposition ofthe overlying unconsolidated units. Paleochannels incised into the bedrock surface
are present in many areas in the Offpost OU. The presence ofpaleochannels in the Denver Formation surface has animpact on groundwater flow in the unconfined flow system(UFS). Two such paleochannels, the First Creek and northern paleochannels, are present north ofthe RMA North Boundary Containment System (NBCS). Anadditional paleochannel, the northwest paleochannel, is present west ofthe RMA Northwest Boundary Containment System (NWBCS). Coarse, unconsolidated materials commonly found within these paleochannels provide for preferential groundwater movement in the UFS. Groundwater contaminant plumes that have historically migrated across the RMA boundaries to the Offpost OU are generally confined to these paleochannels. The Arapahoe Formation lies beneath the DenverFormation at depths of230 to 300 feetat the RMA north boundary and has aregional dipofone-halfto onedegree to the southeast. The formation consists of400 to 700feet ofinterbedded conglomerate, sandstone, siltstone, and shale. The upper portion consists predominantly of200 to 300 feetblue to gray shale with some conglomerate and sandstone beds. The lower portion consists largely ofsandstone and conglomerate with lessprevalent beds ofshale. The lower portion is asource zonefor many water supply wells inthe area. The Arapahoe Formation is the oldestgeologic unit present beneath the sitethat
was investigated in the OffpostRemedial Investigation (RI) and OffpostRI Addendum programs.
20000,317.10
- 1-intro 0306111192 1-3Alluvial and eolian Pleistocene and Holocene deposits form much oftheground surface in the Offpost OU. At some locations, Denver Formation units crop out atthe ground surface. The Arapahoe Formation is notpresent atthe ground surface anywhere in the Offpost OU. Hydrogeology The two principal water-bearing units in the Offpost OU that have been impacted by chemicals originating from RMA arethe unconsolidated alluvial deposits and the underlying Denver Formation. The hydraulic properties ofthese two units, including hydraulic conductivity, porosity, and associated,groundwater flow velocities, aredistinctly different. Hydraulically, these twounits generally behave asdistinct hydrostratigraphic units. Groundwater flow inthe Offpost OU area occurs within anUFS thatoverlies aconfined flow system (CFS). The UFS includes groundwater present inthe unconsolidated materials overlying the Denver Formation, the weathered upper portion ofthe Denver Formation, and, near the South Platte River, the weathered upper portion ofthe Arapahoe Formation. The CFSincludes thedeeper portions ofthe DenverFormation and the underlying Arapahoe Formation. The Final Water RI (Ebasco, 1989), the Final Offpost RI (ESE, 1988a), and the Draft Final OffpostRI Addendum (Harding Lawson Associates [HLA], 1991a) reports provide further information concerning the conceptual model ofgroundwater flow in the unconfined and confined flow systems (UFS and CFS). On the basisofan evaluation ofthe distribution of contaminant plumes inthe Offpost OU area, the UFS isconsidered the principal migration route forgroundwater contaminants from onpost tothe Offpost OU, although some contaminants are present inthe CFS in the DenverFormation andisolated occurrences of afew contaminants have been detected in some domestic Arapahoe Formation wells. Water-level data for the UFS were collected from all Offpost OU monitoring wells during several monitoring events and programs. The UFS potentiometric surface slopespredominantly toward the northwest, indicating groundwater flow in thatdirection. This information is consistent with the interpretation that theSouth Platte River is aregional discharge point for the groundwater system in the Offpost OU. Hydraulic gradients in the Offpost OU range from 20000,317.10
- I-intro 0306111192 1-40.003 to0.02 ft/ft and average approximately 0.004 to0.005 ft/ft. The hydraulic gradients are highest inthe area immediately downgradient ofthe NBCS and in the vicinity ofO'Brian Canal and Burlington Ditch. The hydraulic gradient ofthe UFS near the canals isconsistent with thatreported inthe Final Offpost RI. However, the hydraulic gradient near the NBCS has increased asa result ofthe installation and operation ofrecharge trenches in late 1988. Operation ofthese trenches has increased groundwater recharge in northern portions of Sections 23 and 24, near the northern RMA boundary. The confined DenverFormation isheterogeneous and consists ofinterbedded claystones, siltstones, sandstones, and organic-rich (lignitic) intervals. Water-bearing layers ofsandstone and siltstone occur in irregular beds dispersed within thick sequences ofrelatively impermeable material. Individual sandstone layers commonly are lens-shaped andrange inthickness from a few inches toas much as 50 feet. Confined aquifer conditions are observed in sandstone layers within the deeper portions ofthe DenverFormation. Water-level data collected from three Arapahoe Formation wells installed under the RI Addendum program indicate that the Arapahoe Formation is aconfined aquifer. Data generally indicate that the Arapahoe Formation has anortherly to northwesterly regional groundwater flow direction, as presented in the Final Offpost RI.
SITE HISTORY AND LAND USE This section presents adiscussion offormer RMA and Offpost OU activities andland uses.
Former Disi)osal Practices RMA began operation in 1942. RMA was a sitefor the manufacture anddemilitarization of chemical and incendiary munitions and the manufacture of industrial chemicals, primarily pesticides and herbicides, until 1984. A detailed account ofdisposal practices associated with these operations is presented inthe Onpost Study Area Reports and RI Media Reports for each potential site.

20000,317.10 - 1-intro 0306111192 1-5M

From 1945 to 1950, RMA distilled available stocks ofLevinstein mustard, demilitarized several million rounds ofmustard-filled shells, and test-fired mortar rounds filled with smoke and highexplosives. Also, many different types ofobsolete World War(WW) 11 ordnance were destroyed by detonation or burning. Colorado Fuel and Iron (CF&I) leased facilities atRMA in 1946. JuliusHyman &Company firstleased facilities in 1947, and succeeded to theCF&I leasehold interest, with some modifications and additions in 1949. Shell OilCompany acquired amajority interest in Hyman in 1952, andoperated the plant as the Julius Hyman Company until 1954, when theoperation became the Shell Chemical Company - Denver Plant. RMA was selected as the sitefor construction ofafacility to produce Sarin, anerve agent. The facility was completed in 1953, with the manufacturing operation continuing until 1957 and the munitions-filling operations continuing until late 1969. From 1970until 1984, RMA was involved primarily withthe disposal ofchemical warfare material. This disposal included the incineration ofTX anticrop agent and mustard agent explosive components, and the destruction of Sarin and related munitions casings by caustic neutralization. Chemicals were introduced tothe RMA environment primarily by the burial orsurface disposal ofsolid wastes, discharge ofwastewater to basins, and leakage ofwastewater and industrial fluids from chemical and sanitary sewer systems. Munitions were destroyed and disposed ofin trenches. Wastewater generated by the Army andprivate industry inthe South Plants and North Plants areas was discharged to aseries ofunlined evaporation and holding basins (Basins A, B, C, D, and E) and toasphalt-lined Basin F at various times throughout the history of RMA operations. The primary areas thathave contributed to groundwater contamination at RMA include (1) former manufacturing facilities, (2) former waste storage basins, (3) solid waste disposal areas, (4) the chemical sewer system, and (5) locations with in the rail classification yard, and (6) the motor pool area.

20000,317.10 -I-intro 0306111192 1-6Land Use The current land use within the Offpost OU is predominantly agricultural and rural residential with localized commercial/industrial land uses and open spaces. Areas within the Offpost OU are largely used for rangeland and dryland farming, with some rural residential areas and,scattered areas ofintensive agricultural use. Certain areas within theOffpost OU are currently zoned and developed for commerci.al/ industrial activities. Commerce City, which is located west ofRMA, is the only urban area in the immediate vicinity of RMA and has recently annexed lands within the Offpost OU. Another geographic feature in the Offpost OU is Barr Lake, a state recreation area. Farming in the Offpost OU ranges from large grain operations covering square miles to small subsistence farms to vegetable gardens. A number ofthese farms also maintain livestock. Subsistence and hobbv farmers often consume a large part oftheir diet from locally produced vegetables and livestock produced in theOffpost OU. Intentional application ofpesticides forpest control purposes likely accounts for the presence ofsome concentrations ofpesticides in Offpost OU soil. Many ofthe pesticides detected in Offpost OU soil are or have been commercially available and may have been applied agriculturallv or residentially. These pesticides include cyclodiene compounds and chlorinated hydrocarbon insecticides. The cyclodiene compounds aldrin, endrin, dieldrin, and isodrin detected in Offpost OU soil have been used as insecticides in areas similar to the Offpost OU from the 1940s to the mid- 1970s. Aldrin was used in theearly 1950s to protect cotton against boll weevils and in the 1970s for soil application in grain crops and termite control. In Colorado, dieldrin was used to control insects in field vegetable, grain, and fruit crops (Mullins, 1971) and against termites and locusts. Endrin
was also used to control a wide range ofpests. These insecticides were banned for general uses in 1974 by the EPA. Aldrin and dieldrin may still be used forcertain restricted uses such as subsurface insertion for termite control and dipping ofnonfood roots.

20000,317.10
- I-intro 0306111892 1-7Evaluation ofprojected future land use atthe Offpost OU indicates thatareas ofcommercial/industrial land use will increase (Adams County Planning Commission, 1987). Rural residential (includingagricultural) land use is expected to decrease in the Offpost OU.
PREVIOUS INVESTIGATIONS As aresult ofthe detection ofchemicals inthe Offpost OU, the Army initiated aregional sampling ofhydrogeologic surveillance program requiring the quarterly collection and analysis of samples from more than 100 onpost and offpost wellsand surface-water stations. Thisprogram
was carried outunder the direction ofthe RMA Contamination Control Program, established in 1974 to ensure compliance with federal and state environmental laws. The objectives ofthis program were to evaluate the nature and extent ofcontamination and to develop response actions to control chemical migration. Potential and actual chemical sources were assessed, and chemical migration pathways were evaluated. Tominimize offpost discharge of RMA chemicals via groundwater, three boundary containment systems were constructed, one each atthe northern, western, and northwestern boundaries ofRMA. All three systems are currently inoperation to intercept and treat contaminated groundwater and torecharge treated water. From 1975 tothe present, numerous groundwater monitoring programs have been conducted at RMA. The Armydesigned and implemented the 360 Degree Monitoring Program tomonitor regional groundwater and surface water. The Armydesigned and implemented boundary system monitoring program to support the operation ofthe boundary control systems. Studies conducted at RMA to assess groundwater and surface-water conditions are discussed below. The RMA Offpost Contamination Assessment Report (CAR) (ESE, 1987a) incorporated data from several studies todepict the distribution and concentrations ofoffpost contamination north and northwest ofRMA. The scope ofthis investigation was intended toaddress critical data gaps required toevaluate acomprehensive set ofmultimedia exposure pathways. In the mid- 1980s, the potential for contamination ofprivate wells was investigated. These were referred toas Consumptive Use (CU) Studies, Phases 1, 11, and III.The CU Phase Iand 11 studies (ESE, 1985; ESE

20000,317.10
- I-intro 0306111192 1-81986) addressed the RMA offpost area bounded tothe south by East 80th Avenue, to the northwest by the South Platte River, and to thenorth and east by Second Creek. In the CU Phase III study (ESE, 1987b), theArmy conducted an inventory ofprivately owned drinking water wells inan area bound by East 80th Avenue on the south, East 96th Avenue
on the north, the South Platte River on the west, and RMA on the east. The objectives ofthe study were as follows:

- Locate allshallow domestic wells (less than 100 feet)in the study area.

- Sample arepresentative number ofthe located wells.

- Assess the groundwater quality ofthe shallow alluvial aquifer.
U.S. Environmental Protection Aqency Study Area In 1981, arandom national survey ofdrinking water systems was conducted by EPA. Several organic chemicals were detected in South Adams County Water and Sanitation District (SACWSD) wells. Additional sampling in 1982 and 1985 confirmed these results. As a result of these findings, EPA began an RI/FS ofan area located west ofRMA and south ofthe Offpost OU. RMA was suspected asone ofthe potential sources ofcontaminants in the EPA study area because ofthe history ofwaste disposal practices on that site. Inresponse, the Army and EPA builta water supply system for SACWSD. Further investigation by EPA's FieldInvestigation Team indicated that source areas other than RMA may have been contributing to groundwater contamination detected within the study area. Groundwater monitoring wells installed on the Chemical Sales Company (CSC) property have since confirmed that CSCis a possible source of groundwater contamination west ofRMA and south ofthe Offpost OU.
Commehensive Monitorinp,Projaram In the mid-1980's, the Program Manager for RMA (PMRMA) developed the Comprehensive Monitoring Program (CMP), along-term multimedia monitoring program designed to provide data

20000,317.10
- I-intro 0306111192 1-9to facilitate evaluation of response actions. Sample collection under the CMP commenced in 1987, and data from the CMP were used in performing this EA/FS. Scope ofthe Remedial Investipations Based on known areas of onpost and offpost contamination and the predominant groundwater and surface-water flow patterns, the Offpost OU for theOffpost RI/FS is the area between north and northwest boundaries of RMA and the South Platte River. The specific boundaries of the unit are the same as for theOffpost CAR, as shown in Figure 2 and described below:

- Southeast boundary north and northwest boundaries ofRMA

- Southwest boundary 80th Avenue

- West and northwest boundary - South Platte River

- Northeast boundary - Second Creek
The Offpost OU was originally selected on the basis ofa conservative estimate ofthe area with which RMA chemicals may now ormay eventually exist. However, based on current knowledge (HLA, 1991a), most ofthe Offpost OU is not contaminated by chemicals originating from RMA. The surface waters of Barr Lake havealso been included in the Offpost OU because ofthe potential forcontaminant migration through surface-water features. Several sources oftrichloroethene have been documented south ofthe Offpost OU in or near Commerce City. Also, recent investigations by EPA and the Army along the western sections of RMA have detected the presence of atrichloroethene plume entering Township 35, Range 67W, Section 9 along the southern boundary ofRMA. Although trichloroethene has been detected in selected dewatering wells ofthe Irondale system, no trichloroethene has been detected in the influent or effluent sumps ofthe system. Because ofthe potential for multiple trichloroethene
sources upgradient oftheOffpost OU, trichloroethene detected in the area between 80th and 88th Avenues falls under thejurisdiction ofEPA. The primary objectives of the Offpost RI were to:

- Collect additional data to refine the current understanding ofgroundwater flow and surface-water patterns, and the nature and extent ofcontaminants offpost ofRMA.

20000,317.10 - I-intro 0306111892 1-10M

- Evaluate the potential for chemical migration tothe Offpost OU in various media, such as groundwater, surface water, sediment, air, andbiota.

- Provide additional data necessary, tocomplete the EA/FS.
The review ofpast studies provided the data to evaluate wells thathave been sampled inthe past, useresults from previous aquifer tests, toanalyze historical onpost and offpost contaminant plumes, and toexamine and develop an overall geologic and hydrologic understanding ofthe Offpost OU. Additionally, biota and air quality information for the Offpost OU were reviewed and used to assess the human and environmental receptors thatmay be at risk andto define airborne pollutant pathways. As aresult ofthe review ofthe past programs and theoriginal Offpost RI program, limitations tothe groundwater, soil, surface water, sediment, and biota databases were identified, and appropriate sampling and analysis were completed in the RI Addendum (HLA, 1991g) program. Data collection consisted ofcompiling newhydrogeologic and chemical data relevant to the Offpost OU. Data were obtained by drilling new wells and borings, collecting groundwater and surface-water samplers for analysis, measuring groundwater levels and surface-water flows, conducting aquifer tests, and obtaining sediment samples for analysis. Surface-water and sediment samples were collected in the Offpost OU todefine chemicals in the media. Samples were collected from streams, creeks, impoundments, and lakesthat were suspected pathways for migration ofonpost contamination tothe Offpost OU. The data were used to evaluate contamination insurface water and sediment as well as to evaluate surface water and groundwater interaction. Biota and air-quality condition were evaluated using onpost andoffpost information collected during past and current studies. Input from the Offpost CAR was used to assess transport ofchemicals and impacts on biota inthe Offpost OU from onpost conditions. Data from the AirRI Report (ESE, 1988b) were used to assess the potential for migration ofairborne chemicals to the Offpost OU.

20000,317.10 - 1-intro 0306111192The water, sediment, biota, and air quality information was organized so thata comprehensive evaluation ofRMA chemicals in all media could be made in the Offpost OU. The information collected during the Offpost RI and RI Addendum was integrated with historical data
as well as data being collected during other ongoing RMA investigations. In general, the RI Addendum summarizes new information primarily pertaining to further assessment ofthe extent ofcontamination in various media (groundwater, soil, surface water, sediment, and blota) within specific geographic areas. Activities performed in preparation ofthe RI Addendum include a review of existing data and collection and interpretation ofadditional field data to address identified data needs. NATURE AND EXTENT OF CONTAMINATION This section discusses the nature and extent ofcontaminants in the groundwater, soil, surface water, sediment, and air media in the Offpost OU ascurrently understood. The Offpost RI and RI Addendum reports were the primary sources of information for the groundwater, soil, surface water, sediment, and biota media. Another source ofinformation for the groundwater medium was CMP annual groundwater data. The primary source of information on the air medium was the CMP Air Quality Data Assessment Report for 1989 (RLSA, 1990). In determining COCs and exposure point concentrations, the EA used environmental data for the period 1985 to 1991 including these reports. Groundwater - Sernivolatile Orpanic Comvounds This section provides a summary ofthe nature and extent ofcontamination in groundwater in theOffpost OU on the basis ofgroundwater occurrence in both the UFS and CFS. Diisopropy1methylphosphonate (DIMP), dicyclopentadiene, dieldrin, and endrin are the most widespread and consistently detected sernivolatile organic compounds (SVOCs) in groundwater in the Offpost OU ofthese chemicals. The most widespread contaminant detected in groundwater in the Offpost OU is DIMP. As Figure 3illustrates, DIMP is distributed in acontinuous plume extending from the RMA north

20000,317.10 - 1-intro 0306111892and northwest boundaries tothe South Platte River. Samples from 89 monitoring wells were analyzed for DIMP, which DIMP was above the CRL in 71 ofthesesamples. In general, the highest concentrations ofDIMP offpost occur between the RMA northern boundary and the O'Brian Canal. The highest observed concentrations were 5800 micrograms per liter(,ug/1) in the FirstCreek paleochannel, 860jug/l inthe northern paleochannel, and80 Ug/l inthe northwest paleochannel. Current dataindicate the distribution ofdicyclopentadiene, as shown in Figure 4, is generally limited to the FirstCreek paleochannel. Themaximum concentrations ofdicyclopentadiene reported in the Offpost RI Addendum was 600 ug/1. The distribution ofdieldrin isshown in Figure 5. Dieldrin occurs inthe Offpost OU north ofthe northern and northwestern RMA boundaries. The highest concentrations ofdieldrin are found inwells located in the First Creek paleochannel, ranging from0.6 to 0.9jug/l. Dieldrin plumes arealso interpreted in limited areas in the northern paleochannel and in twoareas north of the northwestern RMA boundary. Detectable concentrations ofdieldrin inthe northern paleochannel andnorthwestern paleochannel ranged from 0.05 to0.14 ug/l. Thedistribution ofendrin is shown in Figure 6. The highest concentrations ofendrin ranged from approximately 0.25 to0.75 Mg/l for wells immediately north ofthe northern RMA boundary. The maximum concentration ofendrin was 0.748 jug/l from well 37309, located approximately 1500 feet north ofRMA. Endrin was also detected in groundwater samples collected from wells in the central portionofthe northern paleochannel. Other SVOCs were detected in groundwater samples from the Offpost OU. The other SVOCs detected include the pesticides atrazine, malathion, and parathion; theorgansulfur compounds 4-chlorophenylmethyl sulfone (CPMS02) and4-chlorophenylmethyl sulfoxide (CPMSO); and the organchlorine pesticides aldrin, isodrin, chlordane, 2,2-bis (para-chlorophenyl)- 1,1-dichloroethene (DDE), and 2,2-bis (para-chlorophenyl)- 1,1,1-trichloroethane (DDT). The distribution ofatrazine inthe Offpost OU is similarto that ofthe organochlorine pesticides (OCPs). Atrazine was detected in 21 Offpost OU wells, with the maximum
20000,317.10 - I-intro 0306111192 1-13concentrations occurring in the First Creek (46.0 ug/1) and northern (72.9 Ag1l) paleochannels. Atrazine was generally not detected ingroundwater samples collected from the Offpost OU off the northwestern RMA boundary, except fortwo isolated occurrences. Although CPMSO and CPMS02 are both organosulfur compounds, their distributions in offpost groundwater differ. CPMSOwas generally only found in samples collected fromwells installed inthe northern paleochannel, whereas CPMS02 was generally only found in samples collected from wells located inthe First Creek paleochannel. CPMSO was generally found at levels higher than those reported for CPMS02- CPMSOwas detected at concentrations up to 82.2 ;Ag/l in the northern paleochannel. CPMS02 was also detected inthe First Creek paleochannel at concentrations up to21.0jug/l. The distribution ofthe additional OCPs (aldrin, isodrin, chlordane, DDE, and DDT) is similar to the previously discussed distribution oftheOCPs dieldrin and endrin. The maximum concentrations ofthese compounds generally occur in the First Creek paleochannel, usually in the
area 500 to 1000 feet north ofthe NBCS. Generally, only sporadic, isolated occurrences ofthese compounds were observed inthe Offpost OU north ofthe RMA northwestern boundary. Groundwater - Volatile Organic Comvounds The volatile organic compounds (VOC) most frequently detected in the OffpostOU include chloroform, chlorobenzene, dibromochloropropane, tetrachloroethene, trichloroethene, 1,2-dichloroethene, carbon tetrachloride, and benzene. Chloroform occurs primarily downgradient ofthe NWBCS and inthe northern paleochannel, as shown inFigure 7. Chloroform was generally not found inthe First Creek paleochannel. Concentrations ofchloroform emanating from the northern RMA boundary are higher than concentrations in the Offpost OU north ofthe northwestern RMA boundary. Thehighest concentrations ofchloroform occur atthe north end ofthe northern paleochanneI (200 to 400Ag1l). The highest concentration ofchloroform was 19.8 tig/l in the northwestern paleochannel.

20000,317.10 - I-intro 0306111092 1-14The distribution ofchlorobenzene is presented in Figure 8. The plumes are confined to localized portions ofthe First Creek and northern paleochannels. The maximum concentration of chlorobenzene was 38.2 ug/I in a groundwater sample collected from a welllocated in the northern paleochannel approximately one mile north ofRMA. The maximum reported concentration in the First Creek paleochannel is less than 2 ug/l. The distribution ofdibromochloropropane isshown inFigure 9. Asshown in Figure 9, dibromochloropropane wasgenerally onlyfound in samples from wells inthe northern paleochannel. A few isolated occurrences ofdibromochloropropane were observed in the First Creek paleochannel and immediately downgradient ofthe O'Brian Canal near the northern end ofthe northern paleochannel. The maximum concentrations ofdibromochloropropane ranged from approximately 2 to 7jug/l ina few wells located inthe northern paleochannel. All other detectable levels ofdibromochloropropane were less than I ug/l. The distribution oftrichloroethene and tetrachloroethene is presented in Figures 10 and 11, respectively. These VOCs are found in the First Creek and northern paleochannels. The highest concentrations ofthese compounds were detected insamples collected from wells located at the northern end ofthe northern paleochannel. The concentrations oftetrachloroethene are higher than those reported for trichloroethene. The maximum concentrations oftetrachloroethene were approximately 100 pg/I intwo wells located in thenorthern paleochannel, approximately one-mile north ofthe RMA boundary. The highest concentrations oftrichloroethene in the Offpost OU north ofRMA ranged from approximately 5 to 7 ug/l. Other volatile organic compounds (VOCs) detected inthe Offpost OU includebenzene, carbon tetrachloride, 1,1,1-trichloroethane, 1,1-dichloroethane, 1,2-dichloroethene, toluene, and xylenes. These compounds were generally found inonly afew groundwater samples collected from wells installed in the UFS.
Groundwater - Inorganic Compounds This section describes the distribution ofselected inorganic constituents in groundwater. The inorganics presented below include arsenic, chloride, fluoride, and mercury.
20000,317.10 - I-intro 0306111092 1-15The distribution ofarsenic based on data collected in support oftheOffpost RI Addendum and for the CMP, isshown inFigure 12. As shown in Figure 12, thedistribution ofarsenic is sporadic, with detectable levels ofarsenic occurring in anumber ofareas. Arsenic occurs in a plume along the FirstCreek paleochannel. The maximum concentrations ofarsenic in the Offpost OU are 4 to 5 ug/l. The distribution ofchloride is shown in Figure 13. Chloride occurs in plumes inthe Offpost OU north ofthe northern and northwestern RMA boundaries. Chloride concentrations in the First Creek and northern paleochannels generally exceed 250,000 Ug/l. The maximum concentrations ofchloride occur inthe First Creek paleochannel. Offpost ofthe northwestern RNIA boundary, chloride concentrations exceeding 250,000 AgIl occur immediately downgradient ofthe RMA boundary. Concentrations ofchloride below 50,000 Ug/l occur only in limited areas (Figure 13). The distribution offluoride is presented inFigure 14. Fluoride concentrations generally exceed 3000 tzg/l in the First Creek paleochannel and 2200 ug/l in the northern paleochannel. Concentrations average approximately 2000kig/l in the northwestern paleochannel. The Final Offpost RI reported mercury inonly one offpost groundwater sample. The sample, which was collected from well 37342 located inthe First Creek paleochannel, had a mercury concentration of0.36 ug/l. Data generated during Offpost RI Addendum activities showed detectable levelsofmercury in four samples collected fromwells located 2000 to7000 feet offpost ofthe northwestern RMA boundary. Mercury concentrations inthese wellsranged from 0.210 Mg/l to 1.64jug/l. The distribution ofthese sampling locations does not suggest amercury plume in the OffpostOU, and detections are considered sporadic. Additionally, data collected under the Fall 1989 CMP show a higherfrequency ofdetection for mercury than reported in the Final Offpost RI. The FY90 CMP reported that field orlaboratory contamination existed for those mercury results. Thus, data for mercury are considered questionable and not representative of actual groundwater conditions.

20000,317.10 - I-intro 0306111092 1-16Nature and Extent ofConfined DenverFormation Contamination The nature and extent ofthe confined Arapahoe formation was evaluated through a sampling program ofdomestic and monitoring wells. Thedata and interpretations presented in this section are for groundwater samples collected from 14 offpost confined DenverFormation wells inthe Offpost OU. Figure 15 presents the locations ofthese wells. Additional information concerning the confined DenverFormation groundwater is presented in Section 3.3.2 ofthe Final Offpost RI report. Data were examined fromthe Fall 1989 and Spring 1991 CMP sampling rounds, which represent the two most recent sampling rounds. The data reported detections ofthe following organic compounds: benzene, chlorobenzene, chloroform, DIMP, dibromochloropropane, phenol, and 1,1,1-trichloroethane. Themost frequently detected compounds were DIMP, chloroform, and chlorobenzene. In general, the detections were notconsistent from one sampling event to the next forthe same well. DIMPwas detected most frequently; however, detections occurred in only II sampling events outof42 sampling events. Theconcentrations ofDIMPranged from 0.443 ILg/l to 46.0 Ag1l. Chloroform and chlorobenzene detection frequencies were below 10 percent. Chloroform concentrations ranged from 0.631 Ag1l to 1.30jug/l. Chlorobenzene detections ranged from 1.10 ug/l to 51.5 ug/l. The observed detections indicate sporadic, isolated low-level occurrences ofthese compounds in the Offpost OU inthe confined Denver Formation. The data are not consistent temporally for the same well and do notindicate aspatial or areal trend indicative ofa contaminant plume.
Nature and Extent ofConfined Araoahoe Formation Contamination The nature and extent oftheconfined Arapahoe formation was evaluated through a sampling program ofdomestic and monitoring wells. Two isolated detections ofDIMP and one of chloroform were observed in approximately 30 Arapahoe Formation wells sampled by the Army. The detections do not appear to be representative ofoverall aquifer conditions. For example, the majority ofsamples collected from Arapahoe Formation wellsdid not contain detectable 20000,317.10

- I-intro 0306111092 1-17concentrations oforganic compounds. In addition, DIMPand chloroform were notdetected consistently from one sampling event tothe next. Surface Soil This section presents the concentrations and distributions ofcompounds detected insoil in the Offpost OU. Surface soil includesthe upper 2 inches ofthe soil profile. As shown in Figure 16, the organochlorine pesticides (OCPs) DDT, DDE, aldrin, chlordane, dieldrin, endrin, hexachlorocyclopentadiene, and isodrin were detected above Certified Reporting Limits (CRLs) in surficial soil collected in the Offpost OU. The most widespread and frequently detected OCPwas dieldrin. Concentrations ofdieldrin detected in samples in the Offpost OU ranged from 2.05 to 250 micrograms per kilogram (,ug/kg). DDT, aldrin, endrin, and DDE were also frequently detected, generally in samples where dieldrin was also detected. Offpost OU suface soil wascontaminated by the deposition ofairborne contaminants and non-RMA-related intentional agricultural application ofpesticides and irrigation practices. The greatest number ofcompounds and highest concentrations were observed north of RMA, with afew occurrences to theeast and west ofRMA. Several reasons may, in part, explain the presence ofthese compounds north and west ofthecanals: (1) several ofthe compounds detected in the surficial soil are orhave been available commercially and may have been applied agriculturally orresidentially and (2) some areas where samples were collected may have been previously irrigated with surface water and/or groundwater originating from RMA. Arsenic wasdetected inapproximately 20 percent ofthe samples at concentrations ranging from 2.61 to4.62 micrograms per gram (,ug/g). The distribution ofarsenic was limited to the following detection areas:

- East ofRMA

- Immediately northofRMA

- Westofthe northwest boundary

- Along Burlington Ditch

20000,317.10 - 1-intro 0306111092 1-18No identifiable pattern tothe distribution is evident. Mercury was detected inapproximately 10 percent ofthe samples at concentrations ranging from 0.0719 ug/g to0.325 ug/g. A discernable pattern to the distribution ofmercury is not evident. The concentrations ofarsenic and mercury in soil werenot statistically evaluated above background as presented in the Offpost EA (Volume 11, Section 1.0).
Subsurface Soil Six subsurface soil samples were collected in the96th Avenue residential area and analyzed for OCPs, arsenic, and mercury. Subsurface soil samples were collected from approximately I-foot and 5-foot depths. Only one detection ofOCPs was reported in subsurface soil samples. Dieldrin was detected at a concentration of7.0 pg/kg in a sample collected between 0 and Ifoot. Arsenic was detected above the CRL in one subsurface soil sample at a concentration of3.59 Ag/g in asample collected between 0 and Ifoot. Mercury was notdetected above the CRL in any subsurface soil samples.
Surface Water Figure 17presents the distribution oforganic contaminants detected inOffpost OU surface water as presented inthe Offpost RI Addendum. The concentrations oforganic compounds detected inoffpost surface-water samples typically have been highest inFirst Creek near the O'Brian Canal. DIMP was the organic compound mostfrequently detected in surface water in the Offpost OU. DIMP was also the most widely distributed compound and was detected in surfacewater samples collected from First Creek, O'Brian Canal, and Burlington Ditch at concentrations ranging from 0.532 ug/l to59.0 pg/l. The greatest number and highest concentrations ofdetected OCPs occur in the reach ofFirst Creek between the northern RMA boundary and the confluence with O'Brian Canal.

20000,317.10 - I-intro 0306111092 1-19The maximum detections ofarsenic and several other inorganic constituents including chloride and sulfate were found in samples collected from First Creek along the reach between the RMA boundary and the FirstCreek confluence with O'Brian Canal. Arsenic wasdetected at concentrations ranging from2.78 to 280jug/l inOffpost RI Addendum samples. Theconcentrationof 280jug/l is considered anomalous and notrepresentative ofsurface-water quality inthe Offpost OU. The maximum concentrations ofarsenic arecommonly found in surface-water samples collected from FirstCreek immediately downstream ofthe onpost sewage treatment plant. Arsenic concentrations ofapproximately 70 pg/l have been detected at thislocation (RSLA, 1990). Groundwater and surface-water interaction isknown to occur in the reach ofFirst Creek between the northern RMA boundary and the confluence ofFirst Creek with O'Brian Canal. This interaction has been discussed and documented in the Final Offpost RI and FY90 Surface Water CMP. Comparison ofthe concentrations oforganic compounds detected in surface-water samples with those detected ingroundwater samples collected in the vicinity ofthisreach ofFirstCreek supports the conclusion thatcontaminated groundwater discharging into First Creek may be the
source oforganic contamination in surface water. The decrease in number and concentrations of organic compounds in Burlington Ditch and the O'Brian Canal indicates that dilution ofsurface water by the ditch and canal is occurring. The distribution ofarsenic in offpost surface water suggests a source other than groundwater. A potential source appears tobe onpost Sewage Treatment Plant discharge to First Creek.
Sediment Figure 18 presents the distribution oforganic contaminants detected in sediment as presented in the Offpost RI Addendum. The following organic compounds had the highest frequency ofdetection insediment samples in theOffpost OU: aldrin, chlordane, dieldrin, and dibromochloropropane. The detections were predominantly in samples collected from in First Creek and were generally low concentrations.

20000,317.10 - I-intro 0306111092 1-20Arsenic and mercury were detected at low concentration levels in sediment samples in the Offpost OU. Mercury was detected only inthe Burlington Ditch, O'Brian Canal, and Barr Lake samples. Arsenic wasdetected in sediment samples in theOffpost OU from all waterbodies sampled.
Air Results from onpost RMA air monitoring during 1988 andreported inthe CMPAir Quality Data Assessment Report (R.L. Stollar &Associates, 1990) (FY88 Air CMP) indicated thattotal suspended particulate (TSP) levels at RMA boundaries werebelow the levels ofmetropolitan Denver. Asbestos was monitored but notdetected. VOCsmeasured at RMA boundaries appear to present toxic risks similar tothose encountered inthe urban environment ofmetropolitan Denver. Levels ofSVOCs were detected at negligible and/or regional baseline levels at RMA boundaries. Metal levels were proportional to TSPconcentrations and were notelevated.
GROUNDWATER TREATMENT SYSTEMS THAT AFFECT THE OFFPOST OPERABLE UNITThree major containment/treatment systems, the Irondale Containment System (ICS), the NBCS, and the NWBCS, have been installed at the RMA boundaries to control the migration of contaminants to offpost areas. All three ofthe systems are currently in operation to intercept and treat contaminated groundwater and to recharge the treated water. In addition to the boundary control systems, a groundwater intercept and treatment system north ofRMA (Groundwater Intercept and Treatment System North ofRMA Interim Response Action A [IRA A]) is currently being constructed toprovide remediation ofalluvial groundwater in the Offpost OU.
Irondale Containment System The ICSis located atthe southern end ofthe RMA northwest boundary within Section 33 and consists ofahydraulic control system and acarbon treatment system. The ICSbecame operational in 1981. The majority ofthe area downgradient ofthe ICS is contained within the EPA offpost study area, although portions ofthedowngradient area are within the confines ofthe

20000,317.10 - 1-intro 0306111092 1-21OffpostOU. A review ofmonitoring data downgradient ofthe ICS shows contaminant concentrations to below and probably attributable to the source ofcontamination within the EPA offpost study area rather than RMA. Therefore, the configuration, operation, and performance of the ICS are notrelevant to this study and will not bediscussed further.
North Boundary Containment System The NBCS islocated just south ofthe RMA north boundary inSections 23 and 24. The NBCS consists ofasystem of dewatering wells with contaminated groundwater from the unconfined flow system, asoil-bentonite barrier to separate contaminated and treated groundwater and toimpede offpost migration ofcontaminated groundwater, a carbon-adsorption treatment system toremove organic contaminants, and a system ofrecharge wells and trenches to return treated groundwater to the UFS. TheNBCS was constructed intwo phases during 1978 and 1981. Initially a pilot system was installed andbecame operational in 1978. The pilotsystem was expanded approximately 1400 feet to the west and 3840 feet tothe east in 1981. Recharge trenches were added tothe west end of the system in 1988. Additional recharge trenches were added tothe east end ofthe system in 1990. Currently, the soil-bentonite barrier is 6740 feet long and approximately 3 feet wide, with
a designed hydraulic conductivity of I X 10-7 centimeters per second (cm/sec) or less. The barrier depth varies from 20feet at the western endto over 40feet alongthe eastern extension. The barrier isanchored in the Denver Formation. Currently, the average flow through the NBCS treatment system is approximately 240 to 250 gallons per minute (gpm) according to the Final Implementation Documentfor IRA A (HLA, 1991b). All water is treated and recharged to the alluvial portion ofthe UFS. Examination ofgroundwater contaminant distribution patterns indicates that the NBCS is having a significant effect on thedistribution oforganic compounds in the Offpost OU. The NBCS treatment plant iseffectively removing the organic contaminants for which itwas designed. Concentrations oforganic contaminants above CRLs have not generally been detected in the system effluent. Inorganic contaminants such aschloride and fluoride arenot being treated.
20000,317.10 - I-intro 0306111092 1-22Northwest Boundary Containment System The NWBCS islocated alongthe northwest boundary ofRMA in the southeast quarter of Section 22. Construction ofthe NWBCS began in 1983, and the systembecame operational in 1984. The purpose ofthis system was tointercept and remove dibromochloropropane and other organic compounds from aplume ofcontaminated groundwater originating onpost. Contaminant bypass was observed at the northeast end ofthe system in 1988. Recharge was increased at the northeast end in December 1988 toprevent continued contaminant bypass. The system consists ofa lineof 15 upgradient dewatering wells, a soil bentonite barrier extending approximately two-thirds ofthe length ofthe dewatering system, 21 downgradient recharge wells, and a carbon-adsorption treatment facility. Groundwater ispumped from the dewatering wellson the upgradient side ofthe barrier, treated by carbon adsorption, and returned to theaquifer through recharge wells near the RMA boundary. An IRA to improve the NWBCS was initiated in 1989. In April 1990, the NWBCS Improvements IRA B(ii) was divided into two phases: NWBCS Short-Term Improvements IRA and NWBCS Long-Term Improvements IRA. The long-term improvements involve amore thorough assessment ofthe NWBCS and the short-term improvements. Under the NWBCS Short-Term Improvements IRA, the existing groundwater intercept system was extended both tothe southwest and northeast. The soil-bentonite wall wasextended
across the alluvial channel found northeast ofthe system to prevent contaminant bypass. Additional extraction wells were added to theexisting system to intercept and treat the waterin this channel. The northeast extension was completed inJuly 1990, and recharge rates at the northeast end ofthe system were reduced. Higher recharge rates resumed inJuly 1991 atthe northeast end ofthe system. New extraction wellsand recharge wellswere added tothe southwest end ofthe system and became operational in August 1991.
Interim Rest)onse Action A IRA A addresses contaminant migration north of RMA along two primary contaminant pathways, defined by the First Creek and northern paleochannels. 20000,317.10 - I-intro 0306111092 1-23In the area north ofthe RMA north boundary, IRA A is being implemented for remediation ofcontamination in alluvial groundwater in theFirst Creek and northern paleochannels. The system has been designed tointercept and extract contaminated groundwater from the UFS in each paleochannel, treat the organic fraction ofthe groundwater, and recharge treated water to the UFS. Groundwater extraction will be achieved by installing and operating well systems. Water will be treated using a granular activated carbon adsorption system and will be recharged to the UFS using a combination ofwells and trenches. The IRA was designed to be flexible to be compatible with the final remedy. Compatibility with the final remedy could be achieved by modifying the system toinclude the addition ofnew wells, treatment processes, or additional treatment capacity ifnecessary. Construction ofIRA A began inNovember 1991. The groundwater treatment system forIRA A isdesigned totreat a maximum flow of 720 gpm and an average initial flow of480 gpm; however, the facilities will be able to accommodate flows less than the average, with aminimum flow of 200 gpm.

20000,317.10 - 1-intro 0306111092 1-24REFERENCES
Adams County Planning Commission. 1987. Adams County Future Land Use Plan, Brighton, CO. Ebasco Services, Inc. 1989. Technical Support for Rocky Mountain Arsenal Draft Final Water Remedial Investigation Report. Contract Nos. DAAKI1-84-DOO16 and DAAAI5-88-DO024. Denver, CO. Environmental Science and Engineering, Inc. 1985. Rocky Mountain Arsenal Offpost Assessment: Ground Water Quality Report (Consumptive Use - Phase 1)for Sampling PeriodDecember 1984 through January 1985. Prepared for U.S. Army Toxic and Hazardous Materials Agency. Denver, CO. Environmental Science and Engineering, Inc. 1986. Rocky Mountain Arsenal Offpost Assessment: Ground Water Quality Report (Consumptive Use - Phase 11) for Sampling Period September through October 1985. Contract No. DAAK- II-D-007, Task Order0006. Denver, CO. Environmental Science and Engineering, Inc. 1987a. Rocky Mountain Arsenal Off'post Assessment, Contamination Assessment Report: Draft Final, Denver prepares for office ofthe Program Manager, Rocky Mountain Arsenal. Environmental Science and Engineering, Inc. 1987b. Rocky Mountain Arsenal Off'post Assessment: Ground Water Quality Report (Domestic Use - Phase III) forSampling Period September through October 1986 and February 1987. Contract No. DAAK- I1-83-D-007, Task Order 0006. Environmental Science and Engineering, Inc. 1988a. Offpost Operable Unit Remedial Investigation and Chemical Specific Applicable or Relevant and Appropriate Requirements, Final Report. Prepared by Environmental Science and Engineering, Inc., Harding Lawson Associates; and Applied Environmental, Inc., Rocky Mountain Arsenal, Commerce City, CO. Environmental Science and Engineering, Inc. 1988b. Air Remedial Investigation Report, Final. Prepared for Office ofthe Program Manager. Denver, CO. Environmental Science and Engineering, Inc. 1989a. Draft Final Endangerment Assessment/ Feasibility Study and Applicable orRelevant and Appropriate Requirements. Prepared for Office ofthe Program Manager. Denver, CO. Harding Lawson Associates. 1991a. Draft Final Offpost Operable Unit Remedial Investigation Addendum. Prepared for the Program Manager for Rocky Mountain Arsenal. Harding Lawson Associates. 1991b. Final Implementation Document for the Groundwater Intercept and Treatment System North of Rocky Mountain Arsenal Interim Response Action. Mullins, D.E., Johnsen, R.E., and Starr, R.I. 1971. Persistence ofOrganoclorine Insecticide Residues in Agricultural Soils ofColorado. Pest. Monit.J. 5: 268-275. R.L. Stollar &Associates, Inc. 1990. Comprehensive Monitoring Program; Air Quality Data Assessment Report for 1989. Contract Number DAAA15-87-0095. Prepared for U.S. Army Program Manager for Rocky Mountain Arsenal. Commerce City,CO. U.S. Environmental Protection Agency. 1988a. CERCLA Compliance with Other Laws Manual Draft, OSWER Directive 9234.1-0 1,August.

20000,317.10 - I-intro 0306111092 1-25U.S. Environmental Protection Agency. 1988b. Guidance on Remedial Actions for Contaminated Groundwater at Superfund Sites, OSWER Directive 9283.1-2, August. U.S. Environmental Protection Agency. 1988c. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA, Interim Final, EPA/540/G-89004, October. U.S. Environmental Protection Agency. 1989a. The Risk Assessment Guidance for Superfund (RAGS). Office ofEmergency and Remedial Response, Washington, DC. EPA/540/1-89/002. U.S. Environmental Protection Agency. 1989b. Exposure Factors Handbook, Final Report, Office ofHealth and Environmental Assessment, Washington, DC. EPA/600/8-89/043.

20000,317.10 - 1-intro 0306111092 1-26RMA1 1104



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

EXPLANATION Isoconcentration Line, Dashed where Inferred 2.65 Isolated Detection inggA. Two Values Shown ifSampled Twice. LT- Indicates

0 Analyte was notDetectedAbove the Certified Reporting I-imit. LT 0 1500 3000 A, Monitoring WellSampled Under Offpost RIAddendum Program (1989-1990) 0 Monitoring WellSampled Under CMP (Fall 1989) Scale in Feet N Domestic Well Sampled Under Offpost RI Addendum Program (1989-1990)--- ----- ----

------- . ....

RIVIA1 1147

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

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

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

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

0
A

.................. 9 ............... 0 ........................ A ............. .............. * 1ý1-'.." ........................... ............ A .................... .................................................................................. ................. ........... ..... ............... ........... z ........................................ ...........

A A' A

--400500 A -0-0. 0.0616 U0 A 00*1 -'...0.0621 0.0706

.............. ........... A

A V'.

A

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

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

...

..........

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

EXPLANATION Isoconcentration Line, Dashed where Inferred 2,65 Isolated Detection, ingg/l

0
0 1500 3000 A Monitoring Well Sampled UnderOffpost RIAddendum Program (1989-1990) 9 Monitoring Well Sampled UnderCMP (Fall 1989) Scalein Feet 1AW1 C- 1-A 11-4., nff-f Q1 AAA-A- P-r- NORG-10Q01RMAI 1134

'A

1.04

LT 2.32M

A > 0 Aý &0 A\ 1.92 -. 11-1-1-.- . ,-.--.-.,-,-.-..,..,.....-,.,.....,...,-,.."",-....I ........... A.. .. ................ hA

A A A 'A 1.52 A SOO 0so(r1.23 . ......... 1.17 X. A
0:

0

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



### EXPLANATION
Concentrations inmicrograms perliter(ggA) Isoconcentration Line, Dashedwhere Inferred 2-65 Isolated Detection, ingg/l. Two Values Shown ifSampled Twice. LT - IndicatesAnalyte wasnotDetected Above the

* Certified Reporting Limit. LT A Monitoring Well Sampled Under Offpost RI Addendum Program (1989-1990). 0 1500 3000 February 1991 CMP Data for theseWells were Considered during Construction ofPlume Contours. CZZZl11_MWGM= 0 Monitoring Well Sampled Under CMP (Fall 1989) Scalein Feet I-A- r)ff - - - 1,D1 AAA-4,.- D-- t10QQ_iQQnNRMA1 1149

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

1.34

4.99

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

4.89

....... ..

.
2.86

0.942

1.48

0 0 1.93 r4N W 7 1.89 vj. 325 8.39 0 10.0
............................................. ............... ............... ........... .............. ................................... ........... ...................................... ............................................. .................. 6 ...................... ............ ...................... .....................

A 0.ýio
Alk 969:: 9.56 0 2.25 4.53

............. ............. & .......... ...........................

A

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

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

Z.-

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

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

EXPLANATION Isoconcentration Line, Dashed where Inferred 2.65 Isolated Detection, inpg/I Monitoring Well Sampled Under Offpost RIAddendum Program (1989-1990).

February 1991 CMP Data forthese Wellswere Considered during Construction of Plume Contours. Monitoring Well Sampled Under CMP (Fall 1989) 0 1500 3000 Domestic Well Sampled Under Offpost RIAddendum Program (1989-1990) %ZZZr--1= Scale inFeet Isoconcentration Value (;.ig/1)RMA1 1150

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

............... .................... .............................. ......................................... ........................ ......................... ý11

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

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

:0.522

J. I

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

LI.............. .. .................. ................................

0.3T7

A A

0

0

.. . . .....

Isoconcentration Line, Dashed where Inferred It PN

C

EXPLANATION

2.65 Isolated Detection, in gg/I

A Monitoring Well Sampled Under Otfpost RIAddendum Program (1989-1990). 0 1500 3000 during Construction of PlumeContours. February 1991 CMPData for theseWells wereConsidered
Scale in Feet Monitoring Well Sampled Under CMP (Fall 1989)
m Domestic Well Sampled Under OffpostRlAddendum Program (1989-1990)RMAI 1151

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

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

...........

A 7.04 *A)t

.......... ................... 0 :: ........................................ ................... 0 ........... 0 .............................................. .............. I...... .............................. ..... ....

..

. .. .... ..

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

C3 A I 0560 N Aýl 0 A
A

............ -- .0 ...... ............ ....... .......... ............ A ........... ........................ ........... ............ 22

A

0 4i A A

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

7.85 02.73

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

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

EXPLANATION Isoconcentration Line, Dashed where Inferred 2.65 Isolated Detection, in ýtg/l

0'k Monitoring Well Sampled Under RIAddendum Cffpost Program (1989-1990). February 1991 CMP Data fortheseWellswere Considered 0 1500 3000 during Construction ofplume Contours. 10- Scale in Feet e Monitoring Well Sampled Under CMP (Fall 1989)- -- - ---------

- ------

-----

RMAI 1152

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

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

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

15.5

A Aý 100 7.74 10 0' A

.......... ........................................................... ...... ...... .......
.............................................................. 9 ............... .................. .... ..................................... ........... ........... ............. ............ ............... .................................

10.0) ff 0 VA C2 Alk 3

........... .......................... .................................. ............ A .......... ..............................

................. 40.

A

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

3.74

....................... ............................................................... .............................................. ......... - .................. ----------------------------- ............................... ................................................... .............

EXPLANATION Isoconcentration Line, Dashed where Inferred 2.65 Isolated Detection, in ggA Monitoring Well Sampled Under Offpost RIAddendum Program (1989-1990).

February 1991 CMP Datafor these Wellswere Considered during Construction ofPlume Contours. 0 1500 3000 0 Monitoring Well Sampled Under CMP (Fall 1989) =ZP=n'C= Scale inFeet M Domestic Well Sampled Under Offpost RIAddendum Program (1989-1990) Isoconcentration Value (gqA)I j I j I I I I 

### -T ---- - -- --------

-

RMA1 1153

3.48 31

................................................................................. .............. ............................... ......... ....... ........ ....... ......................... ......................... ...................................... ................................. ........................ ... ... ... 7

A 2.73

Aý' 4.26 LT A 4.00 5.23 j 2.51 2.46

A& LT 2.65 LT A, 2.65 419 ?

............
4.90

A A

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

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

................................. N ...........

.. ........ K

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

EXPLANATION Isoconcentration Line, Dashed where Inferred 2.65 Isolated Detection, in4g/l. Two Values Shown if Sampled Twice. LT- IndicatesAnalyte was not

LT DetectedAbove theCertified Reporting Limit. 10
0 1500 3000 Monitoring Weil Sampled UnderOffpost RIAddendum Program (1989-1990) T6-=ý ý 9 Monitoring Well Sampled Under CMP (Fall 1989) Scale in Feet Domestic Well Sampled Under Cffpost RI Addendum Program (1989-1990) Isoconcentration Value (jagA)RMA1 1140

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

A. A.

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

-

0 '00

75,000 75,000 Aý5oo,ood 150,000 150,000

......................................... ........................... .............. ................................. ..... . ............ 4 .0............ .............. ... ............... ......

- ........................................ ............

1000000 150,000 A

00
'Po 150000

............ *""'*'*..... ...... ......... 1. -00-'

..500,000 1,000,000/

-Aý....

-0

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

EXPLANATION isoconcentration Line, Dashed where Inferred MonitoringWell Sampled Under Offpost RlAddendum Program

(1989-1990) Monitoring Well Sampled Under CMP (Fall 1989) Domestic WellSampled Under Offpost RIAddendum Program (1989-1990) Isoconcentration Value (4g/1) 0 1500 3000 75,000 150,000 Scale in Feet 500,000 1,000,000RMA1 1141

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

.......................................................... - ................. .................................................................................................. ................ ..................................................... .................................................................. ................................

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

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

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

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

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

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

......... A&

...................................................... ............... ................. ............... ..... .............. ............ ............... 0 . ...................... ....... ........... .........

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

A r

00

........................... .......................... .......................... ................... ............ A ....................... .............................

('ý200o..

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

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

EXPLANATION Isoconcentration Line, Dashed where Inferred 2-65 Isolated Detection orConcentration Less Than Lowest Isoconcentration Value, in ggA Monitoring Well Sampled Under OffpostRIAddendum Program 0 1500 3000 (1 RA-Aand RIAddendum, 1989-1990) Scale In Feet Monitoring Well Sampled Under CMP (Fall 1989) Domestic Well Sampled Under RIAddendum Program (1989-1990) lsoconcentration Value (lAg/1)RMA1 1139

32 33 34 35 36 31

C:)

5 4 3 2 1 6 /Ver

C;h leoo

8 12 7

. It Cýj 17 6 15 14 13 0 37322 8 37321

ý,3!365 I 37317 37316 37318 37380 37319

379 37388 10 0 / 1 3T jq 37387# 37372f ' 37390 cp k37376 RIVIA BOYNDARY 20/-(- (,e 21 22 23 24 19

NORTH BOUNDARY CONTAINMENT SYSTEM

-----4 29 28 /27 1 26 25 30 100 NORTHWEST BOUNDARY CONTAINMENT SYSTEM r NORTH PLANTS

EXPLANATION Confined DenverFormation monitoringwell location

0 1500 3000 Scalein FeetRMA1 1154

rr zis 1 2t-' 2ý4 2!8 27 L 2_8

.......... ....................................... ......................................... ............ ............................. .................. .......... w ......................... . ............... ............ ..... .. ..................... ................ ..................... ............. .... ...............

......................................
DDT 14.4 33 3 DOE 24.7 36 Dieldrin 23,6 Endrin 9.19 DDT 58.9 DDT 41.9 DOE 64.0 DOE 22.6 39k.5 (ýiJ5ý011 Dieldrin 22.7 Dield 0

1 DDT rin 4.5 180

.................................................. ........ drin3.99 (7.43 DO E 260 Endrin 14.7 ..... ............. . ......... ...................................... I ..................... ........ .................................................... .......................... I...... Is rin 2.20 Endrin 6.21 (ND Dieldrin 3.58 1 Endrin 9.80 DDT 790 DDT 4.18 DOE 170 DDT 9.86 Dieldrin 130 Dieldrin 2.05 (DDT 408)

DID 69.5 DDT 860 DOE Dieldrin 4 DI 3.5 40 Idin 1 CL6CP 20.3

.................................................. n .... ....

71'ý ... ............................. ............ ................ .............. .............. .............. ........... ....... .................................................... ................................................. e r drin 40.2 

# ý"E DDT 3.80 DDT Dieldri 10.8 Dieldrin 4%571 5.8 DDT 5.47 D0 2.

T]d

rin 25.00 Dieldrin 2.15 Endrin 13.5 Dieldrin 2.60 DDT 3.50 1 Dieldri 0 n 8.0 DDT 6.50 DOE 113 DDT 7.90 7'go DDE 630 Is.d"n 260 Diefdrin 22.5 Dieldrin 15.5 FDieldnn 290 DOE 6.30 DDT 5.10 Dieldrin 4.00 D Idnn 400 E drin Dieldrin 7.70 5.64 Isodrin 2.60 (ND)

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

. . ................. ................................................... - .............................. ............................................... ... . ... ...... 0 ..................................... .................. ..................... ........ ...... DDT 7.40 DD 58 DDT Diefdrin 11.1 T -9 -D-OTT-75-1 07L 19. DOE 32.0 DOE 56.1 Dieldrin 10.7 Dieldrin5.50 CýIordane 52 DDT 10.3)

ieldrin 93. Dieldrin 5.30) 38.8 D ieldrin4.40) 85.7 ndrin 39 I drin 4.31 Dieidrin 7.44 Endrin 6.67 DDT 22-1 -8.77 DDT 7.00 Dieldrin2.20 1 3.1 Dieldrin rin DOE 4.80 DDT 26.0 .1drin 4.70 Aldrin 5.30 DOE 6.70 Dieldrin 16.0 Diefdrin 18.4 DDT 44.3 Endrin 6.60 Endrin 5.10 FINDj___ 

### MA
.............. ...................... ............ DO E 8.40 .................... .............. .......... Dieldrin 18.7 DDT 5.60 Endrin 39.4 Dieldrin 16.7 Isodrin 3.40 DDT 10.6 8.25 Diel Aldrin 5.70 Dieldrin 10.9 Dieldrin 14.8 DDT 4.70 : Endrin 11.1 21" Dieldrin 12.8 CL6CP 2.70 bieldrin 3.20 Di.IdnT6.3 Isodrin 3.50 Dieldrin 7.10 DDT 6.60 /'(Di6ldrin 6.30) DDT 3.60 Aldrin 4.80 Dieldrin 46.1 Dieldrin 33.2 Endrin 99.3 1 DT 7.00 Idhn 4.07 ieiddn 58.2 DDT6.30 ndrin 9.46 DDT ýDieldrin 99.00ý DDT 2.80 DOE 4.50 

## NTýý Dieldrin 12.426. 25 2V Endrin 5.10 Aldrin 5.30 (ND) Wý,R.T' Dieldrin 5.40 t

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

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

....... ............ 7 ............. ....... ........................... ............
.......... svs: - I Dieldrin2.20

V F Aldr,7590 Dieldrin 99.2 Aldrin 6.20 Dieldrin 24.5

4
L Aldrin 4.10 Pod Dieldrin 10.6 YARD
DDT 10.3 Dieldrin 3.60

> 

### EXPLANATION :RMABowndarv 0 Surficial Soil Sampling Location, June-July 1990 Surficial Soil SampingLocation, May 1991 Duplicate Sample Results 0 2000 4000 Concentrations inmicrograms per kilogramRIVIA1 1194 EXPLANATION 0 SurficialSoil Sampling Location,Februai Duplicate Sample CDH Surficial SoilSampling Location, Ff 

## 13 Section Number CDH Colorado Department ofHealth HLA Harding LawsonAssociates Indicates CDH Resultsfor Samples Colk DDT -Bis (parachlorophenyl) - 1,1,1 -Tric 2,2 DDE 2,2-Bis (parachlorophenyl) -1.1 -Dichk

...

... Concentrations inmicrograms per kilogr,

...

....

.. Not Detected at orabove the Certified Ri

...

.

.........
12

= Aldrin 7.00 500 E r, loo Dieldrin 55.0 ')o ndrini0.0 DDT 5.00

Dieldrin 10

............
NBCS 23 24 NWBPS

....

....

.. Ald inr 14.0 i" 1ý10 INDEX MAP Dieldrin 110 Er'dr,n 23.0 DDE 4.00 FAr.en,. 12L DDT 12.0 Aldrin 26.0 Dieldrin 110 Endrin 19.0 Aldrin 7.00 Isodrin 3.00 Chlordane 46.0 DDT 7.00 Dieldrin 110 Dieldrin 50 Aldrin 3.00 Endrin 19.0 Dieldrin 44.0 DDE 20.0 DDT 4.00 DDT 37.0 Dieldrin 10 DDE 20 r Dieldrin 20 0 DDT 140 ... Aldrin 10.0 Chlordane 151 0 41 0- Dieldrin 120 Endrin 15.0 Dieldrin 70 DDE 73.0 Scale inFeet

............... ...... D D

T 230 ... ............... Aldrin 3.00 .......... Dieldrin 40 ................ . FDieldrin 32.0 DDT 120 

## Prepared for: Aldrin 8.00 do Diell rin 20 Chlordane 100 ....... Dieldrin 89.0 

## Program Manager for Dieldrin 10:1 Endrin 16.0 

## Rocky Mountain Arsenal 4234ý00 DDE 11.0 Nrftý1 Bog ýnI ý!21 DDT 23.0 dane Dieldrin 2501 **Dieldrin 40 Endrin 29.0 Chlordane 6 DDT 18.0 2-1 Aldrin 16.0 Dieldrin 130 Allrin 2:" DDE 36.0 Commerce City,Colorado ChIl0"'I.n 520 DDT 53.0 Di ld,,n 210, 'in

19.0 ....... ....... Ed Dieldrin 90 DDE 4.00ý - IDDT 20.0 

## Figure 17 DISTRIBUTION OFORGANO PESTICIDESDETECTEDIN AREAOFFPOSTSOILRMAI 1143

rr Zý 2-9 

### ;t Lake

(ND)

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

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

..

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

32

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

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

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

FDIMP 111

DIMP0.840 Atrazine 4.13 DIMP 2.91 'Wrazine 4.50

................................................. ......... ................................................ ............... ........................ ................................. ...... ... . ....... I ................ .................. .......................... - ýrn 0.14 trazine 6.80 .96 j;, A." hlordane 0.338 DMMP 0.238 DIMP59.0 DGPD7.43 FCPMS02 19,41 DIMP 5.47 57 0MMP 0.209 Dithiane 44.2 Chloroform 0.599, V FND7 D(MP 13.1 DIMP4,92 DMMP4.92 DMMP 0.227 

### RNA.-A2-ounoary

......................................................... ................... ............................ CPMS02 170

MSO 0 Mort: "":0" 12 t Dieldrin 0.0760 DIMP4.76 J 2/* 2,;. DMMP0.251 2"'

4ý>N. X. 2ý- 2 29

z

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

............. ........... ...... ......... ....................... ...... . ...........
................................. ........... 01*

35 r

---------------- - ...... L P"*L YARD

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

.......... 

### RMABoundary EXPLANATION Concentrations inmicrograms perliter DDT= 2,2- Bis (parachlorophenyl) - 1,1,1 - Trichloroethane 0 2000 4000 DDE = 2,2- Bis (parachlorophenyl) - 1,1 - DichloroethaneRMAl 1142

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

27 J

DDT 11.8 DDE 6.70

............. .... . ..... ------- - ------- -- - ------ --------- -- - ------- Chlordane 64.5 Dieldrin 10.2
9 DDT5.20 ieldrin5.00 Endrin 6.00 DBCP19.0) '3al 

### J.f-sý

DDT21.5 DDE 6M Aldrin 10.2 Chlordans 37.6

...... Dieldrin 5.20

ND 12 rND (Dieldrin 5.00 CL6CP52.8)

............ .................. ............ I............................... ............................... ................ ......... ...................................... ......... ................... ...... DDT 14.8 ........... .............. d,,n 4f T 0 DDE 9.00 N0 I1Hýo 'FTDD 220 Chlordane 77.5 n 28.0 ................ --------------------- Dieldrin6.90 Enddn9.20 DBCP8.80 Aldrin 12.0 Dieldrin 26.0 EndHn 7.00 Adrin 14.00 Dieldrin25 ND DBCP240 ND Z.- O--N At MA60Sir
.......... ------- ............ 6L7 6.70 ,dan. 37.4

.2
A /.j

................................................................................. ................... 1............................ .................................................. .............. ......................... ............................................ ......................... ........................... .....

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

3 Ný F

.......... 10

2-1

2 3ý;

SACVVS C'

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

............................................ ............................................... Sf, UTH PLA. FS
4 5 N, !-3.

ýz

...................... - n. .................. ............................. ................... ............................ ................ ................................................ .............................................

. ..........

12

.................................................. ................................................ PmAis -Jarv

0 2000 4000 EXPLANATIONGLOSSARY Ag/g micrograms per gram pg/kg micrograms per kilogram lug/l micrograms per liter ABS chemical-specific absorption factor ACGIH American Conference ofGovernment Industrial Hygienists AChE acety1cholinesterase ACL Alternate Concentration Limit ADI acceptable daily intake AHPA Archeological and Historic Preservation Act ANOVA Analysis ofVariance AOP advanced oxidation process APEG alkali metal polyethane glycol AQCDs Air Quality CriteriaDocuments ARAR applicable or relevant and appropriate requirement ARES Automated Risk Evaluation System Armv U.S. Department ofthe Army AT averaging time ATP adenosine triphosphate ATSDR Agency forToxic Substances and Disease Registry AWQC ambient water quality criteria BAC Biotechnology Advisory Committee BAF bioaccumulation factor BCF bioconcentration factor BCRL below certified reporting level BCS Boundary Containment System BDAT best demonstrated technology

20000,317.10 - 1-glo 0306111092 G-iBDL below detection limit BEPA Bald Eagle Protection Act BEST basic extraction sludge treatment BF bioavailability factor BGEPA Bald and Golden Eagle Protection Act bgs below ground surface BHC benzene hexachloride BNIF biornagnification factor BOD Biological Oxygen Demand bw body weight C/l commercial/industrial CAA Compliance Assurance Agreement/Clean Air Act CAR Contamination Assessment Report CBSG Colorado Basic Standards for Groundwater CCP Composite Correction Plan (CWA) CCR Colorado Code ofRegulations CD Consent Decree CDH Colorado Department ofHealth CERCLA Comprehensive Environmental Response, Compensation, and Liability Act CF&I Colorado Fuel and Iron CFR Code ofFederal Regulations Cfs cubic feet per second/confined flow system cfs/mi cubic feet per second permile CHWMA Colorado Hazardous Waste Management Act CM centimeters cm/sec centimeters per second cm/hr centimeters per hour
20000,317.10 - I-glo 0306111092 G-2CM2 centimeters squared CMP comprehensive monitoring program CNS central nervous system COC chemical ofpotential concern COD Chemical Oxygen Demand COE U.S. Army CorpsofEngineers CPMS 4-chlorophenylmethyl sulfide CPMSO 4-chlorophenylmethyl sulfoxide
CPMS02 4-chlorophenylmethyl sulfone Cr concentration inplant roots/tubers CRL certified reporting limit CSC Chemical Sales Company CTM cattail marshes CU consumptive use Cv coefficient ofvariation C, chemical concentration inwater CWA Clean Water Act Da molecular diffusivities inair DAA detailed analysis ofalternatives days/yr days per year DBCP dibromochloropropane DDD 2,2-bis (para-chlorophenyl)-I,I-dichloroethane DDE 2,2-bis (para-chlorophenyl)-I,I-dichloroethene DDT 2,2-bis (para-chlorophenyl)-1,1,1-trichloroethane DDTR DDT and its metabolites DIMP diisopropyl methylphosphonate DNA deoxyribonucleic acid

20000,317.10 - I-glo 0306111092 G-3M

DOC dissolved organic carbon DQO data quality objective DRCOG Denver Regional Council ofGovernments DRE Destruction/ Removal Efficiency DSA development and screening ofalternatives DSMA disodium methanearsonate D,,, molecular diffusivities in water EA endangerment assessment Ebasco Ebasco Services, Inc. EC50 median effective concentration ED exposure duration EDB ethylene dibromide EF exposure frequency EFH Exposure Factors Handbook Eh redox potential EPA U.S. Environmental Protection Agency ERT Environmental Research and Technology ESA Endangered Species Act ESE Environmental Science and Engineering, Inc. ET exposure time FF fallow field FFA Federal Facility Agreement FI locally produced fraction FS feasibility study ft/day feetper day ft/ft feet perfoot ft/yr feet peryear

20000,317.10 - 1-glo 0306111092 G-4FWCA Fish and Wildlife Coordination Act FWPCA Federal Water Pollution Control Act FWRIR Final Water Remedial Investigation Report FY Fiscal Year FY88 fiscal year 1988 FY90 fiscal year 1990 g/cm 3 grams percubic centimeter g/1 grams per liter g/day grams per day GAC granulated activated carbon GC/MS gas chromatography/mass spectroscopy GN4P groundwater monitoring program 9pM gallons perminute GPS Groundwater Protection Standards GWF grasses and weedy forbs HA health advisory HADs Health Assessment Documents HBC health-based criteria HDPE High Density Polyethylene HEA Health Effects Assessment HEAST Health Effects Assessment Summary Tables HEEDs Health and Environmental Effects Documents HEEPs Health and Environmental Effects Profiles HEW Health Education and Welfare HI Hazard Index HLA Harding Lawson Associates HQ hazard quotient

20000,317.10 - 1-glo 0306111092 G-5hr/day hours per day HSBAA Historic Sites, Buildings, and Antiquities Act HSDB Hazardous Substance Database HSWA Hazardous and Solid Waste Amendments 1CP inductively coupled plasma ICS Irondale Containment System IRA Interim Response Action IRA A Additional Interim Response Action IRF In Situ Radio Frequency IRIS Integrated Risk Information System IRP Installation Restoration Program ISV in-situ vitrification Koc organic carbon coefficient Kow octanol/water partition coefficient 1/day liters per day 1/kg liters perkilogram
I/CM3 liters percentimeter cubed LAER Lowest Achievable Emission Rate lb/acre pounds peracre LC50 chemical concentration thatis lethal to 50 percent ofthe exposed population LD50 chemical dose that is lethal to 50percent ofthe exposed population Ldn day-night average noise level LDPE low-density polyethylene LDR Land Disposal Restrictions LOAEC lowest-observed-adverse-effect concentration LOAEL lowest-observed-adverse-effect level LOEC lowest-observed-effect concentration

20000,317.10 - 1-glo 0306111092 G-6LOEL lowest-observed-effect level M2/day square meters per day MATC Maximum Allowable Tissue Concentration MBTA Migratory Bird Treaty Act MCL Maximum Contaminant Level MCLG Maximum Contaminant Level Goal MER Colorado Division ofWater Resources Master Extract Register N4F modifying factor MFO mixed function oxidose enzymes mg/kg-bw-day milligrams per kilogram body weight per day Mg milligrams mg/CM2 milligrams per cubic centimeter mg/kg/day milligrams per kilogram per day mg/kg milligrams per kilogram Mg/l milligrams perliter mg/m2/day milligrams permeter squared perday mg/m3 milligrams percubic meter Mi2 square miles MKC Morrison-Knudsen Corporation NIKE Morrison-Knudsen Engineers, Inc. N4KES MK-Environmental Services MI/g milliliters pergram MLE most likely exposure MOP Method ofProportion MP Malcolm-Pirnie, Inc. MRL minimal risk level NISL Mean Sea Level

20000,317.10 - I-glo 0306111092 G-7MSMA monosodium methanearsenate MTV mobility, toxicity, and volume N nitrogen NAAQS National Ambient Air Quality Standards (CAA) NAS National Academy ofSciences NBCS North Boundary Containment System NCI National Cancer Institute NCP National Contingency Plan NEPA National Environmental Policy Act (1969) NESHAPS National Emissions Standards for Hazardous Air Pollutants (CAA) NHPA National Historic Preservation act NIOSH National Institute forOccupational Safety and Health
nm nanometers NOAA National Oceanic and Atmospheric Administration NOAEL no-observed -adverse-effect level NOAEC no-observed -adverse-effect concentration NOEC no-observed -effect concentration NOEL no-observed-effect level NPDES National Pollutant Discharge Elimination System (CWA) NPDWS National Primary Drinking Water Standards NPL National Priorities List (CERCLA) NRC National Research Council NRCC National Research Council ofCanada NRDAM/COE Natural Resource Damage Assessment Model forCoastal and Marine Environments NSPS New Source Performance Standards (CAA) NTP National Toxicology Program NWBCS Northwest Boundary Containment System
20000,317.10 - 1-glo 0306111892 G-8O&M NBCS Operation and Maintenance North Boundary Control System OCP organochlorine pesticide OECD Organization for Economic Cooperation and Development OHM/TADS Oil and Hazardous Material/Technical Assistance DataSystem OSWER Office ofSolid Waste and Emergency Response OTSP organics intotal suspended particulates OU operable unit PACT powder activated carbon treatment PC permeability coefficient PCNB pentachloronitrobenzene PEG polyethylene glycol PFF plowed fallowfield PM-10 respirable particulates lessthan 1.0 microns in diameter PMO Program Managers Office PMRMA Program Manager for Rocky Mountain Arsenal POTW publicly owned treatment works ppm parts per million PQL Practical Quantitation Limit PRG preliminary remediation goal PSD Prevention ofSignificant Deterioration PVC polyvinyl chloride QA/QC quality assurance/quality control R retardation factor RA risk assessment RACT Reasonably Available Control Technology RAGS Risk Assessment Guidance for Superfund RAO remedial action objective
20000,317.10 - I-glo 0306111892 G-9RBC rotating biological contractor RCC Resource Conservation Corporation RCRA Resource Conservation and Recovery Act RD/RA Remedial Design/Remedial Action (CERCLA) RD Remedial Design RfD reference dose RI remedial investigation RI/FS remedial investigation/feasibility study RIC Resource Information Center RLSA R.L. Stollar &Associates, Inc. RMA Rocky Mountain Arsenal RME Reasonable Maximum Exposure RNA ribonucleic acid ROD Record ofDecision RPM Remedial Project Manager (CERCLA) RPO representative process option RRC regulatory risk criteria RSA regional statistical area RTECS Registry ofToxic Effects of Chemical Substances SA skin surface area SACWSD South Adams County Water and Sanitation District SAF Spatial Adjustment Factor SARA Superfund Amendments and Reauthorization Act (1986) SAS Statistical Analysis System SDWA Safe Drinking Water Act SEP Standard Evaluation Procedure SF slope factor

20000,317.10 - 1-glo 0306111892 G-10SGOT serum glutarnate-oxymate aminotransferase SIP State Implementation Plans SUTRA Saturated-Unsaturated Transport SVOC sernivolatile organic compound TAC time for exchange ofbasement air TBC to be considered TCHD Tri-County Health Department TCOC tissue chemicals ofconcern TERIS Teratogen Information System TG-W tall grass wetlands TICs tentatively identified chemicals TLV threshold limit value TPP technical program plan TRCLE trichloroethylene TRV toxicity reference value TSD Technical Support Document (or) Treatment, Storage, and Disposal TSP total suspended particulates TSS total suspended solids TWA time-weighted average UAFS unconfined alluvial flow system UF uncertainty factor UFS unconfined flow system UIC Underground Injection Control UL90 upper 90 percent confidence limit on the arithmetic mean UL95 upper 95 percent confidence limit on the arithmetic mean USABRDL U.S. Army Biomedical Research and Development Laboratory USAF U.S. Air Force
20000,317.10 -1-glo 0306111892 G-11USC Unified SoilClassification (or) United States Code USDA U.S. Department ofAgriculture USDHEW U.S. Department ofHealth Education and Welfare USFWS U.S. Fish and Wildlife Service USGS U.S. Geological Survey UTM universal transverse mercator USC United States Code UV ultraviolet VAR ratio ofbasement volume to surface air incontact with soil VLT very low toxicity VOC volatile organic compound WES U.S. ArmyEngineer Waterways Experiment Station WF weedy forbs WHO World Health Organization 

### WQC water quality criteria WQCA Water Quality Control Act WWC Woodward-Clyde Consultants 0C degrees Celsius

20000,317.10 - I-glo 0306111892 G-12