TECHNICAL SUPPORT FOR ROCKY MOUNTAIN ARSENAL

Offpost Operable Unit Endangerment Assessment/Feasibility Study Final Report Volume V of VIII (FS Sections 1.0, 2.0)

November 24, 1992 Contract NumberDAAA15-88-0021

TaskRIFS1 (Delivery Order 0001)

PREPARED BY Harding Lawson Associates

PREPARED FOR PROGRAM MANAGER FOR ROCKY MOUNTAIN ARSENAL

THIS DOCUMENT IS INTENDED TOCOMPLY WITH THE NATIONAL ENVIRONMENTAL POLICY ACT OF 1969. THE INFORMATION AND CONCLUSIONS PRESENTED IN THISREPORT REPRESENT THE OFFICIAL POSITION OF THE DEPARTMENT OFTHE ARMY UNLESS EXPRESSLY MbDIFIED BYA SUBSEQUENT DOCUMENT. THISREPORT CONSTITUTES THE RELEVANT PORTION OF THE ADMINISTRATION RECORD FOR THISCERCLA OPERABLE UNIT. 

# M9200038TABLE OF CONTENTS
PM VOLUME I- INTRODUCTION LIST OFTABLES ..................................................... xix LIST OFFIG URES .................................................... xxv PREFACE ........................................................... P-1 EXECUTIVE SUMMARY .............................................. ES- I INTRODUCTION ..................................................... GLOSSARY .......................................................... G-1
VOLUME II - ENDANGERMENT ASSESSMENT PREFACE ........................................................... 11 - P-1 1.0 IDENTIFICATION OF CHEMICALS OF POTENTIAL CONCERN ........... 11- 1-1 1.1 GENERAL SITE DATA EVALUATION CONSIDERATIONS .......... II - 1-4 1.2 STATISTICAL PROCEDURES FOR COMPARISON WITH BACKGROUND ............................................. II - 1-8 1.3 SELECTION OF CHEMICALS OF CONCERN ...................... II - 1-15 1.3.1 Groundwater ......................................... 11- 1-15 1.3.2 Surface Water/Sediment ................................. II - 1-17 1.3.3 Surficial Soil .......................................... 11- 1-21 1.3.4 Biota ................................................ 11

- 1-22 1.4 SUMMARY ................................................ 11- 1-24 1.5 UNCERTAINTIES ........................................... 11- 1-26 2.0 EXPOSURE ASSESSMENT ......................................... 11-2-1 2.1 PROPERTIES AND PROBABLE ENVIRONMENTAL FATES OF CHEMICALS OF CONCERN ................................ 11-2-1 2.1.1 Equilibrium Partitioning Properties ofChemicalsofConcern ..... 11-2-2 2.1.1.1 Information Sources ............................. 11 -2-3 2.1.1.2 Data Evaluation ................................ 11- 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 .................. Il- 2-19 20000,317.10 - I-toc 0306111892 iTABLE OF CONTENTS (Continued) Page 2.1.2.4 Compounds Containing Sulfur ............. II - 2-23 2.1.2.5 Compounds Containing Phosphorus .................. II - 2-24 2.1.2.6 Ionic Chemicals ................................. II - 2-26 2.1.2.7 Miscellaneous Compounds ......................... II - 2-30 2.1.3 Uncertainties ......................................... II - 2-31 2.2 CHARACTERIZATION OF EXPOSURE SETTING .................. 11- 2-32 2.21. 1 Site Characteristics Affecting Contaminant Migration ........... 11 - 2-32 .C..2.1.1 Site Description and History ....................... II - 2-32 2.2.1.2 Environmental Setting ............................ 11- 2-33 2.2.1.3 Sampling Locations and Media ..................... 11- 2-34 2.2.1.4 Summary ofOffpost Operable Unit Contamination ...... 11 - 2-36 2.2.2 Potentially Exposed Populations ........................... Il - 2-37 2.2.2.1 Residential Land Use ............................ Il - 2-38 Procedures ........................... 11- 2-38 2.".1.2 Results .............................. 11- 2-41 2.21.".2 Commercial/Industrial Land Uses ................... Il - 2-42 2.213 Qualitative Assessment ofthe Likelihood of Occurence oftheSelection ofFuture Land Use for the Offpost Endangerment Assessment/Feasibility Study ........... II - 2-44 2.2.2.4 Water Use ..................................... II - 2-45 2.2.2.4.1 Existing Groundwater Use ............... II - 2-45 2.2.2.4.2 Projected Future Use ofGroundwater ....... Il-- 2-49 2.2.2.4.3 Surface-Water Use ..................... Il - 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 ................................... II - 2-51 2.3.1.2 Surface Water and Sediment ....................... II - 2-54 2.3.1.3 Atmospheric ................................... II - 2-55 2.3.1.4 Biotic ........................................ 11 - 2-55 2.3.2 Potential Exposure Points ................................ 11 - 2-56 2.3.3 Potential Exposure Pathways and Routes ..................... 11 - 2-57 2.3.3.1 Inhalation Route ................................ Il - 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 OFEXPOSURE ............................. 11 -2-64 2.4.1 Identification ofZones Having Distinct Exposure Concentrations and/or Pathways ....................................... Il- 2-66 2.4.2 Exposure Assessment Procedures and Exposure Point Concentrations ........................................ 11- 2-71 2.4.21. 1 Statistical Procedures Used to Evaluate Monitoring Data ......................................... 11 - 2-72 20000,317.10 -I-toc 0306111992TABLE OF CONTENTS (Continued) Page 2.4.2.2 Model Usedto Estimate 30-Year Groundwater Exposure Point Concentration ............................. II - 2-73 2.4.2.3 Models Used toEstimate Concentrations inAgricultural Products . '6 'i..... *-'*-*-*-**- ***- ** 11-2-74 2.4.2.3.1 h ckenEggs ......................... 11- 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 ............................... 11- 2-82 2.4.2.4 Summary ofNonchemical-specific Parameters ......... II - 2-83 2.4.2.4.1 Groundwater Fraction Used for Irrigation (GWF) ....................... II - 2-83 .(-.4.2.4.2 Fraction Exposed (fe) ................... II - 2-83

.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) .... 11 - 2-84 2.4.2.4.5 Cattle Feed/Soil Intake (1p.) ................ II - 2-84 .,..4.2.5 Sample Calculations and Comparison With the Available Monitoring Data ................................ 11- 2-84 2.4.2.6 Results ....................................... Il- 2-86 2.4.3 Estimation ofChemical Intakes ............................ 11-2-90 2.4.3.1 Chemical- specific Parameters ...................... 11-2-94 2.4.3.2 Exposure Factors ................................ Il- 2-95 2.4.3.3 Results ....................................... Il - 2-98 2.4.4 Estimation ofChemical Intakes forCommercial/Industrial Scenario ............ 11-2-99 2.4.4.1 Estimation ofCheýi*ca'l'inta*k* e's* 11-2-100 2.4.5 Uncertainty Analysis (Residential) ......................... 11-2-100 2.4.5.1 Preliminary Sensitivity Analysis .................... 11-2-101 2.4.5.2 Additional Scoping Considerations .................. 11-2-102 2.4.5.3 Procedures .................................... 11-2-103 2.4.5.4 Determination ofInput Parameter Distributions ........ II - 2-104 2.4.5.5 Results ....................................... 11- 2-106 2.4.5.5.1 Input Parameters ....................... 11-2-106 2.4.5.5.2 Example Results ....................... 11- 2-108 2.4.5.5.3 Summary ofResults .................... 11-2-110 2.5 SUMMARY OF EXPOSURE ASSESSMENT ........................ 11-2-112 2.5.1 Residential Scenario ...... 11- 2-113 2.5.2 Commercial/Industrial Scenario ........................... Il- 2-116 2.6 UNCERTAINTIES ........................................... 11-2-116 3.0 TOXICITY ASSESSMENT .......................................... II - 3-1 3.1 HUMAN REFERENCE DOSES ................................. II - 3-1 3.2 POTENTIAL CARCINOGENICITY OF CHEMICALS OF CONCERN .... II - 3-5

20000,317.10 - 1-toc 0306111892TABLE OF CONTENTS (Continued)
Pan 3.2.1 Weight ofEvidence ...................................... 11- 3-5 3.2.2 Slope Factor .......................................... II - 3-6 3.3 NONHUMAN RECEPTOR TOXICITY REFERENCE VALUES ........ Il - 3-7 3.3.1 Vegetation ........................................... II - 3-8 3.3.2 Aquatic Organisms ..................................... II - 3-8 3.3.3 Terrestrial Organisms ................................... II - 3-9 3.33.1 Derivation ofa No-Observed-Adverse- Effect Level ..... II - 3-10 3.3.3.12 Phylogenetic Differences .......................... II - 3-13 3.3.3.2.1 Intraspecies Differences ................. II - 3-16 3.3.3.2.2 Genus and Species Differences ............ II - 3-16 3.3.3.2.3 Family/Order Differences ................ Il - 3-18 3.3.3.2.4 Threatened orEndangered Species .......... II - 3-19 3.4 MAXIMUM ACCEPTABLE TISSUE CONCENTRATIONS ............ Il - 3-19 3.5 UNCERTAINTIES IN TOXICITY ASSESSMENT .................... II - 3-20 3.5.1 Human Toxicity Assessment .............................. II - 3-20 3.5.2 Toxicity Reference Values ............................... Il - 3-21
VOLUME III - ENDANGERMENT ASSESSMENT 4.0 HUMAN RISK CHARACTERIZATION ............................... 111-4-1 4.1 RESIDENTIAL SCENARIO .................................... 111- 4-2 4.1.1 Hypothetical Future Exposures ............................ III - 4-3 4.1.1.1 Hypothetical Carcinogenic Risks Related to Background . . III - 4-4 4.1.1.2 Child Chronic Hypothetical Future Hazard Indices ...... III - 4-5 4.1.1.3 Adult Chronic Hypothetical Future Hazard Indices ...... 111-4-6 4.1.1.4 Hypothetical Future Carcinogenic Risk ............... 111-4-6 4.1.1.5 Zone-specific Risks ............................. 111-4-6 4.1.1.6 Acute/Subchronic Effects ..... *. , ***I,,*ki**s',,**,* 111-4-10 4.1.2 Hypothetic Current Risks Versus Hypothetical Future sk ...... 111-4-12 4.1.3 HealthRisk atMost Likely Exposure Intakes ................. 111-4-12 4.1.4 Alternative Risk Estimate Based on Predicted Decline in Groundwater Concentrations .............................. 111-4-14 4.2 COMMERCIAL/INDUSTRIAL SCENARIO ........................ 111-4-14 4.2.1 Adult Chronic Hypothetical Future Hazard Indices ............. III- 4-15 4.2.21 Hypothetical Future Carcinogenic Risks ..................... 111- 4-15 4.2.3 Carcinogenic Risk at Most Likely Exposure Intakes ............. III - 4-15 4.3 RISK CHARACTERIZATION SUMMARY ........................ III - 4-15
20000,317.10 - 1-toc 0306111992 ivTABLE OF CONTENTS (Continued) Page 4.4 UNCERTAINTIES IN THE HUMAN HEALTH ASSESSMENT ......... 111-4-18 5.0 ECOLOGICALASSESSMENT ....................................... 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 ................................ 111- 5-3 5.1.2 Ecological Characterization ofthe Offpost Operable Unit ........ III - 5-4 5.1.3 Contamination Pertaining to Offpost Biota ................... III - 5-5 5.1.4 Selection ofChemicals ofConcern forBiota .................. 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 ............................. 111- 5-8 5.2.1.2 Aquatic Receptors ............................... III- 5-10 5.2.2 Potential Exposure Pathways .............................. III - 5-11 5.2.3 Exposure Point Concentrations ............................ III - 5-14 5.2.4 Ecological Assessment Endpoints .......................... III - 5-15 5.2.4.1 Terrestrial ..................................... III - 5-15 5.2.4.2 Aquatic ....................................... 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 ................ 111- 5-20 5.2.5.4 Aquatic Food Web Predicted Tissue Concentrations ...... III - 5-21 5.2.6 DirectExposure toChemicals ofConcern .................... III - 5-21 5.2.6.1 Surface-Water Ingestion Pathway ................... III - 5-21 5.2.6.2 Direct Contact with Surface Water orSediment ......... III - 5-23 5.2.6.3 Soil Ingestion .................................. III - 5-23 5.2.6.4 Dietary Ingestion for Wildlife ...................... 111- 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 ....................... 111- 5-26 5.3.2 Aquatic Food Web Ecological Risk ......................... 111-5-29 5.3.3 Underwater Aquatic Life ................................ III - 5-30 5.3.4 Agricultural Life ...................................... 111- 5-30 5.3.5 Ecological Risk Assessment Uncertainty ..................... III - 5-31 5.3.5.1 SiteCharacterization ............................. III- 5-31 5.3.5.2 Exposure Assessment ............................ III- 5-32 5.3.5.3 Risk Characterization ............................ 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 OF APPENDIXES A RELEASE OF VOLATILE CONTAMINANTS FROM GROUNDWATER WITH SUBSEQUENT EXPOSURE IN BASEMENTS: SCREENING LEVEL ANALYSIS B ESTIMATE OF AMBIENT 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 SPECIES OFPOSSIBLE OCCURRENCE IN RMA OFFPOST AREA H2 - BIOACCUMULATION FACTORS, BIOMAGNIFICATION FACTORS, AND PREDICTED TISSUE CONCENTRATIONS

- TERRESTRIAL FOODWEB

- AQUATIC FOOD WEB H3 - EXPOSURE POINT CONCENTRATIONS OF CHEMICALS INSURFACE 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

200W,317.10 - 1-toc 0306111892 viiTABLE OF CONTENTS (Continued) Page OLUME 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 11 - DEVELOPMENT AND SCREENING OF ALTERNATIVES .... V - 1-2 1.3 STEP III - DETAILED ANALYSIS OF ALTERNATIVES ............. V - 1-2 1.4 STEPIV - SELECTION OF THE PREFERRED SITEWIDE ALTERNATIVE ............................................. V - 1-3 2.0 DEVELOPMENT OF REMEDIAL ACTION OBJECTIVES AND SCREENING OFTECHNOLOGIES .............................................. 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 of Cumulative Risk Withthe Acceptable Risk Range . . V - 2-2 2.2.2 Identification ofMedia Requiring Remedial Action Objectives .... V - 2-4 2.2.3 Site-specific Factors Considered for Groundwater Remedial ActionObjectives 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 the Development of Preliminary Remediation Goals ........................... V - 2-11 2.5.2 National Contingency Plan and Point ofDeparture Considerations for Development ofPreliminary 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 andAppropriate Requirements .... V - 2-17 2.5.3.1.2 Location-specific Applicable orRelevant 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 or Relevant 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 ixTABLE OF CONTENTS (Continued) Page 2.8.4.3.2 Phase Transfer ........................ V - 2-39 2.8.4.3.3 Sorption ............................. V - 2-40 2.8.4.3.4 Oxidation ............................ V - 2-42 2.8.4.3.5 Radiation ............................ V - 2-44 2.8.4.3.6 Biological Treatment .................... V - 2-45 2.8.4.4 In Situ Treatment ............................... V - 2-46 ,(-.8.4.4.1 Water Flushing ........................ V - 2-46 2.8.4.4.21 Enhanced Biological Treatment ............ V - 2-47 Z-8.4.5 Containment ................................... V - 2-48 2.8.4.5.1 Subsurface Barriers ..................... V - 2-48 2.9 SUMMARY OF PROCESS OPTION SCREENING ................... V - 2-50 /-.10 SELECTIONOF 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 Input Into Alternatives Development ................................... VI - 3-4 3.2.1.1.1 Chemicals ofConcern .................. VI - 3-4 3.2.1.1.2 Use ofthe Model in Alternatives Development .......................... VI - 3-5 3.2.1.2 Groundwater Alternative Types .................... VI - 3-9 3.3 LAND OWNERSHIP IMPLICATIONS FOR IMPLEMENTING REMEDIAL ALTERNATIVES ............................................ VI - 3-10 3.4 COMMONALITIES OFALTERNATIVES ......................... VI - 3-10 3.4.1 Commonalities ofGroundwater Remedial Alternatives .......... VI - 3-11 3.4.1.1 Groundwater Alternatives Institutional Controls ........ VI - 3-11 3.4.1.1.1 Provision ofan Alternative Water Supply (Exposure Control) ..................... VI - 3-11 3.4.1.1.2 Monitoring Networks ................... VI - 3-12 3.4.1.1.3 Site Review .........

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

20000,317.10 - 1-toc 0306111892 XTABLE OF CONTENTS (Continued) Page 3.4.1.3 Continued Operation ofthe Boundary Systems ýnd Compliance With Offpost Operable Unit Preliminary Remediation Goals .............................. VI - 3-13 3.5 GROUNDWATER REMEDIAL ALTERNATIVES IDENTIFICATION ... VI - 3-13 3.5.1 Identification ofGroundwater Alternatives: North Plume Group ......................................... VI - 3-14 3.5.4.1 Alternative No. N-1: No 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: LandAcquisition 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 METHODOLOGY ............................................ 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 xiM

TABLE 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 ................................ 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 ofGroundwater Alternatives - Northwest Plume Group .................. VI - 4-18 4.2.2.1 Alternative No. NW-I: No Action .................. VI - 4-18 4.2.2.1.1 Effectiveness .......................... VI - 4-19 4.2.2.1.2 Implementability ....................... VI - 4-20 4.2.2.1.3 Cost ......... VI - 4-20 4.2.2.2 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements As Necessary ....................... VI - 4-20 4.2.2.2.1 Effectiveness .......................... VI - 4-21 4.2.2.2.2 Implementability ....................... VI - 4-22 4.2.2.2.3 Cost ............... VI - 4-22 4.2.2.3 Alternative No. NW-3: Land Acquisition an 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 - 1-toc 0306111892 xiiTABLE OF CONTENTS (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, or Volume .................. VI - 5-3 5.1.5 Short-term Effectiveness ................................ VI - 5-3 5.1.6 Implementability ....................................... VI - 5-4 5.1.7 Cost ................................................ VI - 5-4 5.1.8 State Acceptance ....................................... VI - 5-4 5.1.9 Community Acceptance ................................. VI - 5-5 5.2 MODELING RESULTS SUMMARY ............................. VI - 5-5 5.3 FURTHER DEFINITION OF ALTERNATIVES ..................... VI - 5-7 5.3.1 Alternative No. N-1: No Action ........................... VI - 5-7 5.3.2 Alternative No. N-2: Continued Operation ofthe North Boundary Containment System With Improvements asNecessary ... 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 Ito Interim Response Action A ............................................ VI - 5-10 5.3.5 Alternative No. NW-1: No Action ........................ VI - 5-11 5.3.6 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements as Necessary VI- 5-11 5.4 DETAILED ANALYSIS 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 BoundaryContainment System With Improvements asNecessary ....................... 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 asNecessary ....................... VI - 5-16 5.4.2 Compliance With Applicable orRelevant and Appropriate Requirements ........ : ....-- *-***-- VI-5-16 5.4.2.1 Alternative No. N-1: NoAction ................... VI - 5-17 5.4.2.1.1 Chemical-specific Applicable or Relevant and Appropriate Requirements ... VI - 5-17

20000,317.10 - 1-toc 0306111892 xiiiTABLE OF CONTENTS (Continued) Page 5.4.2.1.2 Action-specific Applicable 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 or Relevant and Appropriate Requirements ............ VI - 5-18 5.4.2.3 Alternative No. N-4: Interim Response Action A ....... VI - 5-18 5.4.2.3.1 Chemical-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-18 5.4.2.3.2 Action-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-18 5.4.2.3.3 Location-specif ic 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 orRelevant and Appropriate Requirements ............ VI - 5-19 5.4.2.5 Alternative No. NW-1: No Action ................. VI - 5-19 5.4.2.5.1 Chemical-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-19 5.4.2.5.2 Action-specific Applicable orRelevant andAppropriate 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 SystemWith Improvements as Necessary ........................ VI - 5-19 5.4.2.6.1 Chemical-specific Applicable orRelevant and Appropriate Requirements ............ VI - 5-19 5.4.2.6.2 Action-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-20 5.4.2.6.3 Location-specific Applicable or Relevant and Appropriate Requirements ............ VI - 5-20 5.4.3 Long-term Effectiveness and Permanence ................... VI - 5-20 5.4.3.1 Alternative No. N-1: No Action .................... VI - 5-20 5.4.3.2 Alternative No. N-2: Continued Operation ofNorth Boundary Containment System With Improvements as Necessary ..................................... VI - 5-20 20000,317.10 - I-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 toInterim 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 to Interim 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 as Necessary ........................ 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 andWorkers ...... VI - 5-26 5.4.5.1.2 Adverse Environmental Impacts ........... VI - 5-26 5.4.5.1.3 Implementation Period .................. VI - 5-26 5.4.5.2 Alternative No. N-2: Continued Operation of North Boundary Containment System ................ VI - 5-26 5.4.5.2.1 Protection ofCommunity and Workers ...... VI - 5-26 5.4.5.2.2 Adverse Environmental Impacts ........... VI- 5-26 5.4.5.2.3 Implementation Period .................. VI - 5-26 5.4.5.3 Alternative No. N-4: Interim Response Action A ........ VI - 5-27 5.4.5.3.1 Protection ofCommunity and Workers ...... VI - 5-27 5.4.5.3.2 Adverse Environmental Impacts ........... 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 andWorkers ...... VI- 5-28 5.4.5.5.2 Adverse Environmental Impacts ........... VI- 5-28 5.4.5.5.3 Implementation Period .................. VI - 5-28 5.4.5.6 Alternative No. NW-2: Continued Operation of Northwest Boundary Containment System With Improvements as Necessary ........................ VI - 5-28 5.4.5.6.1 Protection ofCommunity andWorkers ...... 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 - 1-toc 0306111892 xvTABLE OF CONTENTS (Continued) Page 5.4.6 Implementability ................ : ...................... VI - 5-29 5.4.6.1 Alternative No. N-1: No Action .................... VI - 5-29 5.4.6.2 Alternative No. N-2: Continued Operation ofNorth Boundary Containment System With Improvements as Necessary ..................................... VI - 5-29 5.4.6.3 Alternative No. N-4: Interim Response Action A ....... VI - 5-30 5.4.6.4 Alternative No. N-5: Expansion I to Interim Response Action A .............................. VI - 5-30 5.4.6.5 Alternative No. NW-1: No Further Action ............ VI - 5-30 5.4.6.6 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements as Necessary ........................ VI - 5-31 5.4.7 Cost ................................................ VI - 5-31 5.4.7.1 Alternative No. N-1: No Action .................... 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 to Interim Response Action A .............................. VI - 5-32 5.4.7.5 Alternative No. NW-1: No Action .......... **'' **' ' VI - 5-32 5.4.7.6 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Containment System With Improvements as Necessary ........................ VI - 5-32 5.5 COMPARATIVE ANALYSIS OF REMEDIAL ALTERNATIVES ........ VI - 5-33 5.5.1 Comparison of Alternatives - 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 WithApplicable orRelevant and Appropriate Requirements ........................ VI - 5-34 5.5.1.3 Long-term Effectiveness and Permanence ............. VI - 5-34 5.5.1.4 Reduction inToxicity, Mobility, and Volume .......... VI - 5-34 5.5.1.5 Short-term Effectiveness .......................... VI - 5-35 5.5.1.6 Implementability ................................ VI - 5-35 5.5.1.7 Cost ................... 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 ........................ VI - 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 - I-toc 0306111892 xviTABLE OF CONTENTS (Continued) Page 6.0 SELECTION OFTHE PREFERRED SITEWIDE ALTERNATIVE ........... VI - 6-1 6.1 IDENTIFICATION OF THE PREFERRED SITEWIDE ALTERNATIVE .. VI - 6-1 6.1.1 Preferred Sitewide Alternative Description ........ .**''***** VI - 6-3 6.1.1.1 Alternative No. N-4: Interim Response Action A ....... VI - 6-3 6.1.1.2 Alternative No. NW-2: Continued Operation ofthe Northwest Boundary Control System With Improvements as Necessary ........................ VI - 6-6 6.2 CONSISTENCY WITH THE REQUIREMENTS OF CERCLA AND THE NATIONAL CONTINGENCY PLAN .................... VI - 6-7 6.2.1 Principal Threats Addressed by the Preferred Sitewide Alternative VI - 6-7 6.2.2 Consistencv With the Statutory Requirements ofCERCLA in Section 121 ........................................... VI - 6-7 6.2.2.1 Protection of Human Health and the Environment ....... VI - 6-7 6.2.2.2 Compliance With Applicable or Relevant and Appropriate Requirements ........................ VI - 6-8 6.2.2.3 Cost-effectiveness ............................... VI - 6-8 6.2.2.4 Utilization ofPermanent Solutions tothe Maximum Extent Practicable .................................... VI - 6-8 6.2.3 Consistency With the National Contingency Plan ............... VI - 6-8 6.3 SUMMARY ................................................ VI - 6-9 7.0 REFERENCES ................................................... VI - 7-1

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

VOLUME VII - FEASIBILITY STUDY LIST OFAPPENDIXES A APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARs) ANALYSIS B WETLAND DELINEATION AND ASSESSMENT C DERIVATION OF HEALTH-BASED CRITERIA AND ECOLOGICAL CRITERIA D SECOND LEVEL PROCESS OPTION SCREENING E GROUNDWATER MODELING RESULTS SUMMARY F COSTESTIMATES
VOLUME VIII - RESPONSES TO COMMENTS U.S. ENVIRONMENTAL PROTECTION AGENCY U.S. FISH AND WILDLIFE SERVICE COLORADO DEPARTMENT OF HEALTH SHELL OIL COMPANY

20000,317.10 - I-toc 0306111892 xviiiLISTOF TABLES
Table No. Volume 11 - ENDANGERMENT ASSESSMENT 1.0-1 DataNeeds in Each Medium 1.3.1-1 Statistical Comparison With Background - Groundwater 1.3.1-2 Chemicals ofConcern - Groundwater 1.3.1-3 Summary of Available 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) for Organic Groundwater Chemicals ofConcern 2.1-4 Octanol/Water Partition Coefficients (log K0,.) 2.1-5 Adsorption Coefficient (1/kg) for Chemicals Elevated in Soilor Sediment 2.1-6 Uptake toRoots, K,,, (1/kg), for Organic Groundwater Chemicals ofConcern 2.1-7 Uptake toPlants, Kwp (1/kg), forOrganic Groundwater Chemicals ofConcern 2.1-8 Plant Uptake Coefficients, Kr (Dimensionless), forChemicals ofConcern in Offpost Surficial Soil 2.1-9 Plant Uptake Coefficients, K,P1 for Chemicals ofConcern in Offpost Surficial Soil

20000,317.10 - I-toc 0306111892 xiXLISTOF TABLES (Continued)

2.1-10 BeefBioaccumulation Coefficients, KPM9 for All Chemicals ofConcern 2.1-11 Milk Bioaccumulation Coefficients, Kpd, for All Chemicals ofConcern 2.1-12 Fish Bioaccumulation Coefficients, K.,f (1/kg), for Surface-Water Chemicals of Concern 2.2.2.1.2-1 Population by Land-Use Area .1.2-2 Land,Use bv Land-Use Area (in acres) 2.2.2.1.2-3 Potentially Sensitive Subpopulations 2.2.2.4.1-1 Well-Use Data From Colorado State Master Extract Register 2.2.2.4.1-2 Well-Use Data From Consumptive Use Phase 1,11, and III Studies ._..ý.2.4.1-3 Preliminarv Estimate ofthe Number ofWells bv Well Use the Offpost Operable Onit 2.2.2.4.1-4 Well Use Data From the Tri-Countv Health Department Survey 2.2.2.4.1-5 CombinedEstimate ofthe Number ofWells by WellUse in theOffpost 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 1 2.4.2.6-2 Exposure Concentrations, Groundwater, Zone 2 (Northern Paleochannel) 2.4.2.6-3 Exposure Concentrations, Groundwater, Zone 3 (96th Avenue and Peoria Street) 2.4.2.6-4 Exposure Concentrations, Groundwater, Zone 4(First Creek Paleochannel) 2.4.2.6-5 Exposure Concentrations, Groundwater, Zone 5 (Northwest Boundary) 2.4.2.6-6 Exposure Concentrations, Groundwater, Zone 6

20000,317.10 - 1-toc 0306111992 xxLISTOF TABLES (Continued)

2.4.2.6-7 Estimated Future Exposure Concentrations for Aldrin and Diel. drin, 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) /-.4.2.6-10 Reasonable Maximum Exposure Concentrations in Vegetables: Maximum Concentrations Estimated in Any Zone 4.2.6-II Reasonable Maximum Exposure Concentrations inDairy and Meat Products: Maximum Concentration Estimated in Any Zone 2.4.2.6-12 Reasonable Maximum Exposure Concentration in Eggs (Zones 1,2, and 6) 2.4.3-1 Summary ofLand Use Scenarios Used to Estimate Reasonable Maximum Exposure Intakes by Zone .2.4.3.1-1 Dermal Absorption from Soil/Sediment .:..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 Summaiy 2.4.5.5.3-1 Uncertainty Analysis Results
3.1-1 Hierarchy ofDocuments Referenced Regarding Toxicity Data 3.1-2 Toxicity Data for Rocky Mountain Arsenal Offpost Chemicals ofConcern 3.1-3 Noncarcinogenic Reference Doses and Potential Noncarcinogenic Effects 3.1-4 Cancer Slope Factors and Potential Carcinogenic Effects of Carcinogenic Operable Unit OffpostChemicals ofConcern 3.1-5 Regulatory Criteria for Rocky Mountain Arsenal Offpost Operable Unit, Chemicals of Concern
20000,317.10 - 1-toc 0306111992 xxiLISTOF TABLES (Continued)

3.3.1-1 Reference Media Concentrations for Vegetation and Aquatic Organisms 3.3.3-1 Toxicity Reference Values for Avian and Terrestrial Vertebrate Species of Concern Identified at Rocky Mountain Arsenal 3.3.3-2 References for Critical Toxicity Studies Used to Derive Terrestrial Toxicity Reference Values Listed inTable 3.3.3-1 3.3.3.2.1-1 Nonprimate Mammalian Oral LD50 Data
Volume III 4.0-1 Target Organ- or System-specific Chemicals ofConcern 4.1.1-1 Summary ofResidential Hypothetical Future Carcinogenic Risks: Reasonable Maximum Exposure 4.1.1-2 Summary of Residential Child Chronic Combined Noncarcinogenic Hazard Indices (HIs >1) 4.1.1-3 Contribution ofDieldrin and Other Chemicals tothe Child Acute Hepatic Hazard Index 4.1.1-4 Summary ofResidential Hypothetical Future Reasonable Maximum Exposure Subchronic Hazard Indices: Children 4.1.1-5 Summary ofResidential Hypothetical Future Reasonable Maximum Exposure Subchronic Hazard Indices: AdultFemales 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 inOffpost 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 in Relation to Indicator Species Selection Criteria 5.2.2-1 Potential Exposure Pathways for Biota 5.2.3-1 Exposure Point Concentrations forSoil, 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 - I-toc 0306111892 xxiiLIST OFTABLES (Continued)

5.2.5.2-1 Predicted Tissue Concentrations (mg/kg) forthe Terrestial Food Web Ecological Receptors 5.2.5.4-1 PredictedTissue 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 Basisof Sediment 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 3Soil, Surface Water, and Dietfor the Great Horned Owl 5.3.1-4 Summarv of Intakes From Zone 3 Soil, Surface Water, and Diet for the Deer Mouse 5.3.1-5 Summary of Intakes From Zone 3Soil, Surface Water, and Dietfor 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 ofIntakes From Zone 3 Sediment, Surface Water, and Diet for the Mallard Duck 5.3.4-1 Summary ofChicken Hazard Quotient by Zone, Offpost Operable Unit

Volume V - FEASIBIL TY STUDY 2.2.1-1 Offpost Operable Unit Carcinogenic Risks for EachMedium 2.3.1-1 Offpost Operable Unit Groundwater Chemicals of Concern 2.5.2-1 Preliminary Chemical-specific Applicable or Relevant and Appropriate Requirements for Groundwater 2.5.2-2 Health-based Criteria for Groundwater Chemicals ofConcern Without Applicable orRelevant and Appropriate Requirements 2.5.2-3 Preliminary Remediation Goals forOffpost Operable Unit Groundwater 2.8.1-1 Screening ofProcess Options for Groundwater 2.10.1-1 Selection of Representative Process Options for Groundwater

20000,317.10 - I-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 of Preliminary North Plume Group Groundwater Alternatives 3.5.2-1 Groundwater Alternatives for the Northwest Plume Group 3.5.2.5-1 Summarv of Preliminary Northwest Plume Group Groundwater Alternatives

4.2.1.7-1 Summary of Screening 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 ofGroundwater Alternatives for the North Plume Group 5.5.3-2 Summary ofthe Detailed Analysis and Ranking ofGroundwater Alternatives for the Northwest Plume Group

20000,317.10 - 1-toc 0306111892 xx1vLIST OF FIGURES Figure No. Volume I - INTRODUCTION I Location Map ofOnpost Operable Unit, Rocky Mountain Arsenal 2 Offpost Area, Rocky Mountain Arsenal 3 Distribution ofDiisopropylmethyl Phosphonate (DIMP) in the Offpost Unconfined Flow System 4 Distribution ofDicyclopentadiene inthe Offpost Unconfined Flow System 5 Distribution ofDieldrin in theOffpost Unconfined Flow System 6 Distribution ofEndrin in theOffpost Unconfined Flow System 7 Distribution of Chloroform in the Offpost Unconfined Flow System 8 Distribution of Chlorobenzene in the Offpost Unconfined Flow System 9 Distribution ofDibromochloropropane in the Offpost Unconfined Flow System 10 Distribution ofTrichloroethene (TRCLE) in the Offpost Unconfined Flow System II Distribution of Tetrachloroethene in the Offpost Unconfined Flow System 12 Distribution ofArsenic in theOffpost Unconfined Flow System 13 Distribution ofChloride inthe Offpost Unconfined Flow System 14 Distribution ofFluoride inthe Offpost Unconfined FlowSystem 15 Offpost Operable Unit Confined Denver Formation Monitoring Well Network 16 Distribution ofOrganochlorine Pesticides Detected inOffpost 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 inOffpost Operable Unit StreamBottom Sediment

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

Volume 11 - ENDANGERMENT ASSESSMENT 1.0-1 Preliminary Site Conceptual Model, Pre-Remedial Investigation, Offpost Operable Unit 1.2-1 OffpostOperable Unit Background Surficial Soil Sampling Locations 1.2-2 Offpost Operable Unit Designated Surficial Soil Data Sets for Comparison With Background 1.2-3 Offpost Operable Unit First Creek Surface-Water Sampling Locations 1.2-4 Offpost Operable Unit First Creek Sediment Sampling Locations 1.2-5 Offpost Operable Unit Surface-Water Sampling Locations 1.2-6 Offpost Operable Unit Sediment Sampling Locations
2.2.21.1.1- I Offpost Operable Unit Land Use Areas and Consumptive Use Phase IIStudy 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 Site Conceptual Model OffpostOperable 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 2.4.3.3-1 Offpost Operable Unit Chronic Intake ofChloroform by Pathway and Groundwater Zone - Residential Scenarios 2.4.3.3-2 Offpost Operable Unit Intake of Dieldrin by Zone and Pathway - Residential Scenario 2.4.5-1 Offpost Operable Unit Histograms Describing the Distribution ofIngestion Rate ofLocally Produced Milk (IRd, kg/day) for the Child Chronic and Lifetime Scenarios - Residential

20000,317.10 - 1-toc 0306111992 xxviLIST OF FIGURES (Continued)

2.4.5-2 Off'post Operable Unit Histograms Describing the Distribution of ingestion Rate ofLocally Produced Vegetables (IRv, kg/day) for the ChildChronic and Lifetime Scenarios - Residential 2.4.5-3 Offpost Operable Unit Histograms Describing the Distribution ofIngestionRate ofLocally Produced Meat (IRm, kg/day Fresh Weight) for the Child Chronic and Lifetime Scenarios - Residential 2.4.5.5.2-1 Off'post Operable Unit Distribution ofLifetime Oral Intake of Dieldrin inZone 3 (mg/kg/day) - Residential 2.4.5.5.2-2 Offpost Operable Unit Uncertainty in the Mean Concentration ofDieldrin in Groundwater (mg/1) inZone 3 2.4.5.5.2-3 Offpost Operable Unit Uncertainty inthe Mean Concentration ofDieldrin in First Creek Surface Water (mg/1) _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 of Dieldrin 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 Off'post Operable UnitDistribution ofLifetime Oral Intake ofChloroform in Zone 2 (mg/kg/day) - Residential 2.4.5.5.2-8 Offpost Operable Unit Distribution ofLifetime Inhalation ofChloroform in Zone 2 (mg/kg/day) - Residential
3.3.1-1 Methodology for Determining Water and Soil Reference Media Concentrations for Vegetation and Aquatic Organisms 3.3.3-1 Methodology to Derive Toxicity Reference Values (TRVs) From Class-specific Toxicity Data
Volume III 4.1.1-1 Offpost Operable Unit Combined Carcinogenic Risks (All Pathways) by Groundwater Zone - Residual Scenarios 4.1.1-2 Offpost Operable Unit ChildResident Hazard Indices Described for Toxic Chemicals and Exposure Pathways - Residential Scenarios 4.1.1-3 Offpost Operable Unit Contributors to Carcinogenic Risks - Residential Scenario

20OW,317.10 - 1-toc 0306111992 xxviiLIST OF FIGURES (Continued)

4.1.1-4 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone IA. Lifetime Rural Resident, RME 4.1.1-5 Carcinogenic RisksDescribed by Chemical, Medium, and Exposure Pathway - Zone III, 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; AdultCommercial/Industrial; Chronic RME
5.1.1-1 Offpost Operable Unit BiotaSampling Locations 5.1.1-2 Habitat Map for First CreekPortion ofOffpost Operable Unit 5.2.2-1 Ecological Site Conceptual Model Offpost Operable Unit 5.2.5.1-1 Offpost Operable Unit Terrestrial Food Web 5.2.5.3-1 Offpost Operable Unit Aquatic Food Web 5.2.6.5-1 Offpost Operable Unit Agricultural Food Web

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

Volume V - FEASIBILITY STUDY 2.5.1-1 Off'post Operable Unit Feasibility Study Contaminant Distribution Zones 2.6.1 Areas ofExceedances ofGroundwater PRGs in the Offpost Unconfined Flow System 2.8-1 Groundwater Process Options 2.8.1-1 Results of Universal 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
The Feasibility Study (FS) isan element ofa combined Endangerment Assessment/ Feasibility Study (EA/FS) forthe Offpost Operable Unit (OU) and isconsistent withthe Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), the Superfund Amendments andReauthorization Act (SARA), the revised National Contingency Plan (NCP), and the regulations implementing the National Environmental Policy Actof 1969. Volume Iofthe EA/FS contains an introduction that includes site history and a summary ofthe nature and extent of contamination inthe Offpost OU. Volume I alsoprovides an Executive Summary that presents

an overview ofthe findings from each section and summarizesthe selection ofthe preferred sitewide alternative for the Offpost OU.
PURPOSE AND ORGANIZATION The primary objectives ofthe FSare:

- Develop and evaluate a range ofremedial alternatives that protecthuman health and theenvironment

- Provide ananalysis ofthe range ofremedial alternatives that will support the selection ofthe finalremedy
The FSis organized into seven sections and associated appendixes. Section 1.0 describes the
purpose and the organization ofthe report. Section 2.0presents the development ofremedial action objectives (RAOs), the development ofpreliminary remediation goals (PRGs), andthe identification and screening oftechnologies. Section 3.0 presents thedevelopment ofalternatives. The screening of alternatives with respect toeffectiveness, implementability, andcost is presented in Section 4.0. The detailed analysis ofalternatives, considering the criteria mandated by the NCP, is presented in Section 5.0. Selection ofthe preferred sitewide alternative is contained in Section 6.0. Section7.0 presents the references for the FS.

20000,317.10 - FS 1127111092 V - P-11.0 FEASIBILITY STUDY PURPOSE AND ORGANIZATION
The primary objective ofthe Feasibility Study (FS) for the Offpost OU is toevaluate remedial alternatives in accordance with CERCLA, asamended by SARA, and the NCP so that relevant information concerning the remedial alternatives canbe presented to adecision maker and an appropriate remedy canbe selected. The following subtasks further describe the purpose ofthe FS evaluation: I. Develop and screen a rangeofremedial alternatives that provide for protection of human health and the environment and thatconsider effectiveness, implementability, and cost criteria. 2. Integrate this FSwith allapplicable Offpost Remedial Investigation (RI), Offpost RI Addendum, comprehensive monitoring program (CMP), OffpostEndangerment Assessment (EA), Onpost RI/FS, and interim response action (IRA) activities to ensure that allremedial alternatives aredeveloped, screened, and evaluated ina systematic and objective manner. 3. Provide an analysis ofthe range ofremedial alternatives developed thatwill support the selection ofaremedial alternative(s) that is technically feasible andprovides the necessary protection ofhuman health and the environment ina cost-effective manner.
The FS was conducted in foursteps:

- Step I - Development ofRemedial Action Objectives

- Step 11 - Development and Screening of Alternatives

- Step III - Detailed Analysis ofAlternatives

- Step IV - Selection ofthe Preferred Sitewide Alternative
1.1 STEP I- DEVELOPMENT OF REMEDIAL ACTION OBJECTIVES Step Iofthe FS included the following activities:

I. To set the context ofthe FS, a summary ofbackground information regarding the site and aconcise statement ofthe problem were made. 2. RAOs weredeveloped specifying the chemicals and media ofconcern, exposure pathways asdocumented in the OffpostEA (Volume II, Section 1.0), and PRGs that provide the guidelines for the development ofa range ofremedial alternatives. The PRGs were developed on the basisofchemical-specific applicable orrelevant and appropriate requirements (ARARs), health-based criteria (HBC), exposure factors, and the statutory requirements stated in Section 121 ofCERCLA.

20000,317 - FS 1109111092 V - 1-13. General response actions thatmay be takento satisfy RAOs were developed foreach medium of concern, defining individual controls, such ascontainment, treatment, excavation, pumping, orother actions, singly orcombined. 4. Volumes or areas ofmedia to which general response actions might be applied were identified considering the requirements forprotectiveness as identified in the RAOs and the chemical and physical characterization ofeach medium. 5. The technology types (e.g., containment, chemical treatment, thermal treatment) and corresponding process options (e.g., carbon adsorption, air stripping) were identified and screened on the basis oftechnical implementability. Technology typesand process options not applicable to the media orcontaminants in the Offpost OU were eliminated. Technically implementable technology types and process options, including innovative technologies,,were retained for further evaluation. 6. Process options were screened on the basis ofeffectiveness, implementability, and cost to select a representative process option (RPO) foreach technology type retained for consideration.
1.2 STEP11 - DEVELOPMENT AND SCREENING OFALTERNATIVES Step 11 ofthe FSincluded the following activities:

I. The selected RPOs from Step IoftheFS were assembled intoa range ofremedial alternatives addressing containment, source control, treatment, and satisfying the statutory requirements and preferences stated in Section 121 ofCERCLA as amended by SARA. 2. The remedial alternatives were further refined and screened on a general basis to assess their effectiveness, implementability, and cost. 3. On the basis ofthis screening, a set ofremedial alternatives was retained forfurther analysis in Step 111.
1.3 STEP III- DETAILED ANALYSIS OFALTERNATIVES Step III ofthe FSincluded the following activities:

1. Retained alternatives werethen further developed to provide the basis for adetailed analysis in accordance with the NCP and with U.S. Environmental Protection Agency (EPA) guidance. 2. ARARs and other pertinent advisories, criteria, orguidance were identified regarding specific actions proposed foreach remedial alternative. 3. The alternatives were assessed and compared onthe basis ofrelative performance with respect tothe following evaluation criteria (categorized into three groups) specified in the NCP:

- Threshold criteria
o Overall protection ofhuman health andthe environment

20000,317 - FS 1109111092 V - 1-2o Compliance with ARARs

- Primary balancing criteria " Long-term effectiveness and permanence " Reduction ofmobility, toxicity, orvolume through treatment " Short-term effectiveness " Implementability " Cost

- Modifying criteria " State acceptance " Community acceptance 4. Based on the comparative analysis ofremedial alternatives and risk management decisions, a preferred alternative was selected.
1.4 STEP IV - SELECTION OFTHE PREFERRED SITEWIDE ALTERNATIVE StepIV ofthe FS selects the U.S. Department ofthe Army's (Army's) preferred alternative, based on the detailed analysis ofalternatives.

20000,317 - FS 1109111092 V - 1-32.0 DEVELOPMENT OF REMEDIAL ACTION OBJECTIVES AND SCREENING OFTECHNOLOGIES
RAOs and general response actions thataddress the RAOs were developed. Technologies accomplishing agiven response action werethen identified and screened, and RPOs were selected to be carried forward into the development and screening ofalternatives. Section 2.0presents an overview ofdevelopment ofRAOs, identification and screening of technology types and process options, and selection of RPOs.
2.1 OVERVIEW OF REMEDIAL ACTION OBJECTIVES DEVELOPMENT RAOs are medium-specific goalsdesigned toprotect human health and theenvironment. RAOs address chemicals of concern (COCs), media ofconcern, exposure pathways, and PRGs. RAOs and PRGs were used to guide theevaluation oftechnologies and the development of remedial alternatives. PRGs are established considering chemical-specific ARARs, site-specific HBC, factors related totechnical considerations (e.g., analytical detection limits), background concentrations, and ecological criteria. The PRGs were established using information developed in the Offpost EA and considering expected exposures, associated risks for each alternative, and land use. RAOs were developed toprovide protection ofhuman health and the environment. The RAOs guided the selection ofresponse actions, technology types, process options, and remedial alternatives. General response actions are defined asremedial measures that will satisfy RAOs. General response actions include no action, institutional controls, containment, removal, disposal, and treatment options. General response actions were identified to guide the process ofevaluating technologies. After the definition ofgeneral response actions, broad technology groups (i.e., technology types) and specific processes within a technology type (i.e., process options) were identified on the basisofchemicals present and the media in which theywere detected at the site. Technology types and process options were screened in a first step, solely on the basis oftechnical implementability. The technical implementability criterion eliminated technology types and

20000,317.10(g) - FS 1014111892 V - 2-1process options thatcould notbe effectively implemented because ofsite conditions in the Offpost OU. During the second level ofscreening, process options within each technology type were evaluated and screened on the basis ofthree criteria: effectiveness, implementability, and cost. Subsequently, one or more RPO was selected for each technology type retained during this second level ofscreening. RPOs were carried forward tothe development and screening ofalternatives.
2.2 NATIONAL CONTINGENCY PLAN AND ACCEPTABLE RISK RANGE CONSIDERATIONS

This section describes NCP considerations for developing RAOs and PRGs for the Offpost OU. The section begins with a discussion ofthe cumulative risk for the Offpost OU as presented in the EA and compares the cumulative risk to theacceptable risk range. The Army's approach forevaluating cumulative risk and development of PRGs presented inthe following sections isconsistent with the NCP and EPA interpretive guidance. The Army has followed EPA guidance regarding (1) use oftheacceptable cancer risk range in assessing whether remediation is required and (2) development ofPRGs for sitesexceeding the 10-4 acceptable risk level.
2.2.1 Comparison ofCumulative Risk With the Accemable Risk Range The cumulative Offpost OU hypothetical cancer risk isa maximum of3x 10-4on the basis ofthe RME risks presented in the EA (Volume 111, Section 4.0 and Volume IV, Appendix G). This value isa summation ofthe highest calculated risk in each medium regardless of zone. The calculated hazard indices (Hls) presented in the EA (Volume III, Section 4.0) are below 1.0, with the exception ofzones 2,3 and 4, where the HIs slightly exceed 1.0. The RME risks calculated in the EA are aconservative estimate ofOffpost OU hypothetical risk. The conservatism ofthe RME risks presented inthe EA isdiscussed in detail in Volume III, Section 4.0. The quantitative uncertainty analysis presented in Volume 111, Section 4.0can be used to assess the level of conservatism ofthe RME estimates. The results ofthe uncertainty analysis suggest that RME estimates may be two to six times more conservative than the 95th percentile, the lower boundary for an RME estimate. Additionally, the future land-use scenario presented inthe EA, Volume 11,
20000,317.10(g) - FS 1014111892 V - 2-2Section 2.0, is highly conservative. The ruralresidential scenario used in zones 1,2, and 6 includes all pathways contributing substantially tohypothetical risk, even though the majority of the total population isnot exposed to the majority oftheagricultural exposure pathways. The urban residential exposure scenario in zones 3and 4 is very conservative because the probable future use ofthat land is commercial/ industrial rather than residential forreasons listed in Volume V, Section 2.5.1. The Offpost OU cumulative risk is within theacceptable cancer risk range specified by EPA. Risks attributable tothe individual media are presented in Volume V, Table 2.2.1-1. The Army used the NCP and relevant EPA guidance to establish the acceptable risk range for the Offpost OU. For example, an EPA memorandum entitled "Role ofthe Baseline Risk Assessment in Superfund Remedy Decisions" (OSWER Directive 9355.0-30, April 22, 1991) (Risk Assessment Memorandum) provides guidance on interpreting the NCP mandate that remedial actions attain a
10-4 (one in 10,000) to 10-6 (one in 1,000,000) cancer risk. The Risk Assessment Memorandum makes the following conclusions:

- For sites where the cumulative risk to an individual based on reasonable maximum exposure for both current and future land use is lessthan 10-4,action is generally not warranted... (Risk Assessment Memorandum, page 4)

- The upper boundary ofthe risk range is not a discrete line at I X 10-4,but EPA generall. uses I X 10-4 in making risk-management decisions. A specific risk estimate around 10-1 may be considered acceptable ifjustified based on site-specific conditions (Risk Assessment Memorandum, page 1).
EPA Region VIII provided the following position to the Army with regard touse ofthe 10-4 risk level at the Offpost OU: Although EPA guidance states that the 10-4 is not an absolute trigger point, under proper site-specific circumstances, we consider use ofa risk in excess of5 x 1 0-4 to exceed the intent ofthe guidance's latitude (Letter to the Army dated February 21, 1992). Relying on both EPA Headquarters and Region VIII guidance addressing the upper boundary of the acceptable cancer risk range, the Army interpreted that boundary to be 5 x 10-4.

20000,317.10(g) - FS 1014111892 V - 2-32.2.2 Identification ofMedia Reauirinp,Remedial Action Obiectives Offpost OU remedial action isnot warranted because Offpost OU cumulative risk is 3x 10-4
at a maximum and below the previously mentioned acceptable risk range. Nevertheless, the Army recognizes that there are several site-specific factors, when considered in totality, that suggest remediation of groundwater is preferable tono action inthe Offpost OU. Groundwater contributes a maximum risk of 2 x 10-4, or approximately 73 percent ofthe total, tothe cumulative hypothetical risk in zones 2, 3, and 4. The following potential human exposure pathways were identified in the EA forgroundwater: direct ingestion, inhalation during showering, consumption ofcrops irrigated with contaminated groundwater, and consumption of dairy products and beefproduced from livestock watered with contaminated groundwater and/or fed grain irrigated with contaminated groundwater. Moreover, HIs for children slightly exceed 1.0 in zones 2,3, and 4. Soil contributes a maximum risk of 8 x 10-5 in zone 3 tothe cumulative hypothetical risk through a combination ofthe following potential human exposure pathways: direct ingestion, dermal contact, consumption ofcrops cultivated in contaminated soil, consumption ofdairy products and beef from livestock inhabiting areas ofcontaminated soil, and consumption ofeggs from poultry inhabiting areasof contaminated soil. That is, the maximum risk would only be realized for a population exposed at the RME levels for all pathways. Because this seems unlikely and because maximum cancer risks are within the EPA risk range, the Army concludes that soil requires no further action. Additionally, comparison ofthe geometric mean soil contaminant exposure point concentrations with the soil ecological criteria presented in Volume VII, Table C2, indicate no action is warranted. Therefore, RAOs and PRGs were not developed forsoil. Surface water and sediment contribute a maximum riskof 5 x 10-7 and 8 x 10-7, respectively, to the cumulative hypothetical risk in zones 3 and 4. Both risks are below the lower limit ofthe acceptable risk range; hence, noremediation is appropriate for these media. Therefore, RAOs and PRGs were not developed.

20000,317.10(g) - FS 1014111892 V - 2-4Air and biota media in theOffpost OU do notrequire remediation for the following reasons. Air quality at RMA and within theOffpost OU has been monitored for particulates, asbestos, organic contaminants, and metals. Based on data collected through the air CMP (R.L. Stoller and Associates, Inc. [RLSA], 1990c) and presented in Volume I(Introduction - Nature and Extent of Contamination), air in the Offpost OU is not a medium ofconcern, and therefore, RAOs werenot developed for theair medium. The biota medium consists ofall plants and animals potentially exposed to Offpost OU contaminants in water, soil, and sediment. The source ofbiotic contamination originates from abiotic materials, such as water, soil, and sediment. Direct remediation ofbiota isnot effective except by methods that temporarily eliminate receptor species from the area ofcontamination during remediation ofthe abiotic media. Therefore, biota is not a medium of concern. However, ecological criteria developed for the protection of species potentially at risk were considered as remediation goals during the development ofRAOs. Specifically, information presented in theecological risk assessment (Volume III, Section 5.0) and ecological- based criteria presented in Volume VII, Appendix C were evaluated during the development ofRAOs. Additional support for eliminating media that contribute minor levels ofrisk to the Offpost OU cumulative risk is presented in the EA through consideration of (1) multiple contaminants, (2) multiple exposure pathways, (3) sensitive subpopulations, (4) cross-media impacts, and (5) impacts on environmental receptors. Further, EPA also implies that for media with risks less than 10-4,development ofPRGs may not beappropriate (Risk Assessment Guidance for Superfund [RAGS]: Volume I - Human Health Evaluation Manual, Part B - Development of Risk-based Preliminary Remediation Goals, Office of SolidWaste and Emergency Response [OSWER] Directive 9285.7-0113, December 1991) (RAGS-B).

20000,317.10(g) - FS 1014111892 V - 2-52.2.3 Site-sr)ecific Factors Considered forGroundwater Remedial Action Obiectives Development The Army considers the following factors tobe important inassessing whether groundwater RAOs should be developed even though thecumulative risk in the Offpost OU is within the acceptable risk range

- Groundwater is the majorcontributor tototal risk.

- Groundwater is apotential source ofdrinking water within the Offpost OU and Maximum Contaminant Levels (MCLs) and Maximum Contaminant Level Goals (MCLGs) are exceeded. ,

- Groundwater can potentially impact human receptors through anumber ofexposure pathways, as described in Section 2.2.2.

- Significant reductions in groundwater contaminant concentrations and corresponding cumulative site risk can be attained by implementing groundwater remedial actions.

- Significant progress has already been made towards construction and implementation ofa groundwater collection and treatment system. His for children slightly exceed 1.0 in zones 2,3, and 4, with groundwater contributing approximately 74 percent ofthe total risk.
Forthe reasons stated above, the Army considers groundwater PRG development to be appropriate even though cumulative Offpost OU cancer risk is within theacceptable risk range of 10-4 to 10-6 as specified in the NCP. Generally, EPA guidance suggests that PRGs be developed with 10-r'risk as the point ofdeparture. Thus, groundwater PRGs were developed using the 10-r,point ofdeparture.
2.3 DEVELOPMENT OF GROUNDWATER REMEDIAL ACTION OBJECTIVES RAOs are medium-specific goals forprotecting human health and theenvironment. The NCP states that RAOs should specify the following: (1) contaminants ofconcern, (2) media of
concern, (3) exposure pathways, and (4) remediation goals. The development ofgroundwater RAOs was performed in a step-wise fashion: Step 1: Identification ofCOCs Step 2: Identification ofexposure pathways Step 3: Identification of PRGs

20000,317.10(g) - FS 1014111892 V - 2-6

### COCs were identified in the Offpost EA and are also discussed in the following section. Primary exposure pathways were identified in the Offpost EA and are presented in Section 2.3.2. Groundwater RAOs are identified in Section 2.4. The RAOs address the primary exposure pathways and the achievement ofPRGs, which aredeveloped in Section 2.5. 

### 2.3.1 Development ofRemedial Action Obiectives. Ster)1: Identification ofChemicals ofConcern COCs were identified inthe Offpost EA(Volume 11, Section 1.0), primarily onthebasisof the following fourcriteria: 1. The primary criterion foridentifying COCswas astatistically significant increase in concentration insamples collected fromthe Offpost OU whencompared withsamples from locations believed to beunaffected byRMA contamination (background). 2. Although certain chemicals may 

### havenotfully satisfied thestatistical criterion stated above, ifthe),weredegradation productsofCOCs, theywere selected as COCs. 3. Several COCs are essential human nutrients andhave lowtoxicityatobserved concentrations. These potential COCs includecalcium, magnesium, potassium, and sodium, and were eliminated from consideration. Background concentrations include naturally occurringchemicals and chemicals from anthropogenic sources, suchas the agricultural application ofpesticides. Groundwater COCsarepresented in Table 2.3.1-1. Groundwater PRGsarepresented in Section 2.5. 2.3.2 Develogment ofGroundwater Remedial Action Obiectives SteL)2: Identification of Potential Exposure Pathways Theprimarypotential pathways ofexposure were identified in the Offpost EA (Volume 11, Section 2.0). RAOs consider theprotection ofhumanhealth andtheenvironment. Therefore, exposurepathways for bothhuman and ecological receptors were considered inthedevelopment ofRAOs. The following primary exposurepathways were identified forgroundwater: Human receptors oDirect ingestion ofcontaminated groundwater 20000,317.10(9) -FS 1014111892 V - 

### 2-7" Showering with contaminated groundwater " Consumption ofcrops irrigated with contaminated groundwater " Consumption ofdairy products orbeefproduced from livestock watered with contaminated groundwater and/or fed crops irrigated with contaminated groundwater Environmental receptors " Watering of livestock withcontaminated groundwater " Feeding of livestock with crops irrigated with contaminated groundwater
The Offpost EA considered three potential.groundwater exposure pathways that were eliminated from further consideration on the basis that the pathways did not contribute significant potential health risks to humans. The following potential groundwater exposure pathways were eliminated:

- Inhalation ofvapors in residences

- Dermal contact with groundwater for domestic uses

- Consumption ofgame harvested from the Offpost OU
All remaining groundwater exposure pathways were considered in thedevelopment ofgroundwater RAOs.
2.4 GROUNDWATER REMEDIAL ACTION OBJECTIVES Groundwater RAOs forthe Offpost OU were developed toprovide protection ofhuman health and the environment from potential exposure tocontaminants detected in groundwater. RAOs were developed to meet the intentof CERCLA and include the general provision to reduce potential health risks associated with affected media tothe NCP-prescribed cumulative 10-4 to 10-6 risk range forcarcinogens and a hazard index < 1.0 for noncarcinogens by achieving PRGs. All remedial actions will be consistent with CERCLA, the NCP, and the Federal Facility Agreement (FFA) (EPA and others, 1989a). EPA Guidance forConducting Remedial Investigations and Feasibility Studies Under CERCLA, Interim Final, October 1988 (EPA, 1988b) provides that:
20000,317.10(g) -FS 1014111892 V - 2-8Remedial action objectives consist of

### medium-specific oroperable unit specific goals for protecting human health and theenvironment ... Remedial action objectives aimed at protecting human health and the environment should specify:

- The contaminant(s) ofconcern

- Exposure route(s) and receptor(s)

- An acceptable contaminant level orrange of levels for each exposure route (i.e., a

preliminary remediation goal) Remedial action objectives forprotecting human receptors should express both a contaminant level and an exposure route, rather than contaminant levels alone, because protectiveness may be achieved byreducing exposure (such as capping area, limiting access, orproviding an alternate water supply) as well as by reducing contaminant levels.
2.4.1 Groundwater Remedial Action Obiectives Groundwater RAOs consist ofgoals for groundwater quality that are protective ofhuman health and the environment.
2.4.1.1 Human Health' 1. Reduce the COCbconcentrations in groundwater and/or prevent exposure associated with groundwater within the Offpost OU tomeet groundwater remediation goals' and to attain the NCP-prescribed cumulative risk range. 2. Prevent domestic use of, ingestion ofcrops irrigated with, and ingestion oflivestock watered with groundwater containing COCsbat concentration levels in excess of groundwater remediation goals'.
2.4.1.2 Environmental Protection 1. Prevent acute or chronic toxicity to biota from groundwater within the Offpost OU at COCbconcentrations in excess ofgroundwater remediation goals'.

Several potential groundwater exposure pathways including inhalation ofvapors in residences, direct contact with groundwater fordomestic uses, and consumption ofgame (i.e., pheasants) harvested from the Offpost OU, were evaluated in the Offpost EA process and were eliminated from further consideration. b Groundwater COCs were identified in the Offpost EA (Volume II, Section 1.0) and are listed in Table 2.3.1-1 ofthis report. The development ofpreliminary and final remediation goals, in accordance with the NCP and the FFA, is an ongoing process requiring continual evaluation ofsite-specific conditions and evolving health-based and regulatory standards to attain the NCP-prescribed cumulative risk range of 10-4 to 10-6 forcarcinogens and a hazard index < 1.0 for noncarcinogens. These preliminary goals may change asthe FS progresses. Final remediation goals may be based on but are not limited to HBC, ARARs, biota criteria, background concentrations, and CRLs. 20000,317.10(9) - FS 1014111892 V - 2-92.5 DEVELOPMENT OF GROUNDWATER PRELIMINARY REMEDIATION GOALS PRGs arechemical-specific remediation criteria that identify media requiring remediation and treatment goals. A set ofremediation criteria may be composed of different typesofPRGs. For example, groundwater PRGs may include ARARs (such asMaximum Contaminant Levels [MCLs]), HBC, background concentrations, ecological criteria, and certified reporting limits (CRLs). More than one type of cleanup criteria may be identified as being potentially suitable for evaluating remediation,requirements. The development of PRGs is an ongoing process requiring continual evaluation ofsitespecific conditions and evolving health-based and regulatory standards. In accordance with the NCP, Section 300.430(e)(i), PRGs were developed considering ARARs, HBC, factors related to technical limitations (e.g., detection limits), background concentrations, land use, and ecological criteria. Final remediation goals will be determined when the remedy isselected and the Record of Decision (ROD) is issued. Section 121(d) ofCERCLA establishes aprocess fordeveloping and selecting remedial actions that are protective ofhuman health and the environment. Remedial actions that limit an excess lifetime cancer risk to an individual to a level between 10-4and 10-6 on the basis ofmethodologies and evaluations developed and presented in the Offpost EA (Volume 111, Section 4.0) are protective (NCP, Section 300.430(e)(2)). EPA guidance specifies that where action is warranted, the 10-6 risk level should be used as the point of departure for identifying PRGs foralternatives when ARARs are not available or are not sufficiently protective because ofthe presence of multiple contaminants or multiple pathways ofexposure. Additionally, the EPA guidance document, Role ofthe Baseline Risk Assessment in Superfund Remedy Selection Decisions (EPA, 1991), states that: (1) For groundwater actions, MCLs, and non-zero MCLGs will generally be used to gauge whether remedial action is warranted, (2) For sites where thecumulative site risk to an individual is less than 10-4,action generally is not warranted, but may be warranted ifachemical specific standard thatdefines acceptable risk is violated or unless there are noncarcinogenic effects or an adverse environmental impact that warrants action, (3) Furthermore, the upper boundary ofthe risk range is not a discrete line at I X 10-4, although EPA generally uses I x 10-4 in
20000,317.10(g) - FS 1014111892 V - 2-10making risk management decisions, and (4) A specific riskestimate around 10-4 may be considered acceptable ifjustified based on site-specific conditions including any uncertainties on thenature and extent ofcontamination and associated risks.
2.5.1 Effects ofFuture Land Use on the Development of Preliminary Remediation Goals The Offpost OU is subdivided into six geographic zones (zones I through 6 in Figure 2.5.1 -1) used in the Offpost EA (Volume II, Section 2.0) for assessing differences in expected exposures. The EA (Volume 11, Sections 2.2.2.1 and 2.2.2.2) provides the background discussion on current and future land use for the Offpost OU. Thepurpose ofthis section isto evaluate the information within the context ofEPA guidance, and to select the most probable land use scenarios for the EA/FS. Evaluation of land use for the Offpost OU considered the following sources for guidance and pertinent information: 1. The NCP 2. Risk Assessment Guidance for Superfund (RAGs) 3. Local City and County Planning Documents, including the Airport Environs Plan (Adams County Planning Commission, 1990) and the 96th Avenue/Quebec Street Area Transportation Study (CH2M Hill, 1988) 4. Discussions with local officials
The NCP states: The analysis forpotential exposures under future land use conditions is used to provide decision-makers with an understanding ofexposures that maypotentially occur inthe future. This analysis should include a qualitative assessment ofthe likelihood that the assumed future land use will occur. The reasonable maximum exposure estimate estimates for future uses ofthe site will provide the basis for the development of protective exposure levels. In general, a baseline risk assessment will look at a future land use that is both reasonable, from land use development patterns, and may be associated with the highest (most significant) risk, in order to be protective. The assumption of residential land use is not a requirement ofthe program but rather is an assurnption that may be made, based on conservative butrealistic exposures. An assumption offuture residential land use may not bejustifiable ifthe probability that the site will support residential use inthe future is small, (NCP preamble [55 FR 8710] Remedial Investigation-baseline risk assessment).

20000,317.10(9) - FS 1014111892 V - 2-11M

The discussion above indicates that it iswithin the guidance to select afuture land use other than residential before filing a ROD. Based on the data presented in the EA (Volume 11, Sections 2.2.2.2 and 2.2.2.3), the most likely future land uses for the Offpost OU are asfollows:

- Rural residential forzones 1,2, and 6

- Urban residential for zone 3and 4

- Commercial/industrial for zone 5
A summary ofthe qualitative assessment ofthe likelihood ofoccurrence ofthese future land

uses includes thefollowing findings:

- The completion ofthe new Denver Airport and its proximity tothe Offpost OU will stimulate growth, particularly along the East96th Avenue Corridor, and said growth is most likely to include commercial and industrial development.

- Transportation agencies have mapped an enlargement and realignment ofEast 96th Avenue to handle increased traffic tothe new Denver Airport, and said realignment ispositioned within zones 2, 3, and 4 ofthe subject land parcels.

- Floodplains and wetlands occur primarily in zones 3 and 5 inthe subject parcels and would tend to prevent buildings in these areas but may promote recreational uses.

- For the remaining Offpost OU, residential and agriculture are the most likely future land uses. 2.5.2 National ContinpencN, Plan and Point ofDeparture Considerations for Development of Preliminary Remediation Goals The FS followed EPA guidance in establishing groundwater PRGs. The NCP states: Initially, preliminary remediation goals are developed based on readily available information, such aschemical-specific ARARs orother reliable information. Preliminary remediation goals should be modified, as necessary, as more information becomes available during the RI/FS. Final remediation goals willbe determined when the remedy is selected. Remediation goals shall establish acceptable exposure levels that are protective ofhuman health and theenvironment and shall be developed by considering the following: (A) Applicable or relevant and appropriate requirements.... and the following factors: (1) For systemic toxicants, acceptable exposure levels shall represent concentration levels to which the human population, including sensitive subgroups, may be exposed without adverse effect during a lifetime or part ofa lifetime, incorporating an adequate margin ofsafety; 20000,317.10(9) - FS 1014111892 V - 2-12(2) For known or suspected carcinogens, acceptable exposure levels are generally concentration levels that represent an excess upper-bound lifetime cancer risk to an individual ofbetween 10-4and 10-6 using information on the relationship between dose and response. The 10-6risk level shall be used as the point of departure fordetermining remediation goals foralternatives when ARARs are not available or are not sufficiently protective because ofmultiple contaminants at a site or multiple pathways ofexposure...
Section 2.5.4.1 and Table 2.5.2-1 ofthe FS present groundwater chemical-specific ARARs for the Offpost OU. Section 2.5.4.2 and Table 2.5.2-2 present HBC(acceptable exposure levels) for COCs without ARARs that are systemic toxicants. The preliminary HBC are presented at an HI of<1.0 for noncarcinogens. Volume V11, Appendix C, ofthe FS presents the methodology used in the calculation of HBC and PRGs. The NCP states that PRGs may be revised on the basis ofconsideration of appropriate factors, including, but not limited to exposure factors, uncertainty factors, and technical factors (EPA, 1990). This section describes how these factors were evaluated to select final PRGs. According tothe NCP and EPA guidance (EPA, 1990, 1989b), the exposure assessment considers the cumulative effect of multiple contaminants, multiple pathways, population sensitivities, potential impacts on environmental receptors, and cross-media impacts. Appendix C describes in detail how the Army calculated HBC and risk associated with PRGs tomeet these requirements. These calculations were verified with the Automated Risk Evaluation System (ARES) software developed for the EA. HBC and risk development considered each ofthe reasonable maximum exposure (RME) factors described above, including multiple pathways, multiple contaminants, sensitive subpopulations (child chronic), and cross-media impacts. In addition, the development ofPRGs considered environmental impacts on ecological receptors by using maximum allowable tissue concentrations (MATCs), Iiterature-based biornagnification factor (BMF) values, as well as toxicity reference values (TRVs), and soil and dietary ingestion. The Army also evaluated uncertainty factors in selecting HBC and PRGs. Uncertainty factors evaluated include the effectiveness ofthe alternatives, the weight ofscientific evidence concerning exposures and cumulative health effects, and the reliability ofexposure data. The

20000,317.10(9) - FS 1014111892 V - 2-13M

effectiveness ofthe alternatives isevaluated in Volume VI, Sections 4.0 and 5.0. The uncertainty associated with the performance ofthe selected groundwater treatment alternative is low because ofthe Army's experience with similar designs ofthe boundary containment systems (BCSs) for treating the COCs. Uncertainties associated with the weightof scientific evidence on exposure and health risks were investigated both qualitatively in each major section ofthe EA and quantitatively for the exposure assessment, which goes beyond the requirements ofapplicable EPA guidance. These uncertainties indicate the assumptions in the EA are predominantly conservative, and therefore, exposures may exceed by three-fold the 95th percentile ofthe potential exposure distributions (Volume 11, Section 2.4.5). In this manner, the reliability ofthe exposure data was bounded and conservatively estimated as exceeding the 95th percentile targeted by the RME. In addition, all exposure assumptions were maintained at the RME level although EPA guidance allows use ofa combination of RME and average exposure assumptions when the
net result is still "reasonable maximum exposure"(EPA, 1989b). The NCP also requires evaluation oftechnical factors in the selection of PRGs, such as detection/quantitation limits, technical limits to remediation, the ability to monitor and control movement ofcontaminants, and background levels ofcontaminants. The risk corresponding to MCLs and non-zero MCLGs exceeds 10-6. Thus the Army evaluated detection limits, called certified reporting limits (CRLs) by the Army, for use as PRGs, attempting tolower the risk corresponding toPRGs. As a result, although the Army initially considered ARARs asPRGs, it

was necessary to reduce many ofthe PRGs to CRLs to achieve the targeted carcinogenic risk range of 10-4 to 10-6. In addition, naturally occurring arsenic in groundwater contributes significantly to the hypothetical risk attributable forgroundwater (Volume 111, Section 4.1.1.1). These technical and exposure factors were also considered in the evaluation. The FS also evaluated technical limitations toremediation (e.g., treatability) in the selection ofrepresentative process options and development ofalternatives, in Volumes V and VI, Sections 2.0 and 3.0, and ability to monitor (Volume VI, Section 3.0) and control contaminant migration (Volume VII, Appendix E, Groundwater Modeling).

20000,317.10(g) - FS 1014111892 V - 2-14In summary, the EA/FS contains discussion and description necessary to evaluate exposure, uncertainty, and technical factors and criteria that support the selection of 10-4 risk for groundwater asthe mosthealth protective goal thatis technically achievable, meets orexceeds ARARs, has low uncertainty and large conservatism, andcomplies with applicable guidance (EPA, 1990). Table 2.5.2-3 in Volume V presents the groundwater PRGs for the Offpost OU andthe media-specific risk. The summary risk for allchemicals, pathways, and media is in Volume VII, Appendix C.
2.5.3 Tvves ofGroundwater Preliminary Remediation Goals A brief description ofthe typesofPRGs evaluated for the Offpost OU is presented in the following subsections. The types ofPRGs evaluated include ARARs, HBC, background concentrations, and ecological criteria.
2.5.3.1 Identification ofAgglicable orRelevant and Apt)rooriate ReGuirements EPA guidance (1988a), which is reflected in this section, describes the identification and application ofARARs for the RI/FS process. Under Section 121(d)(1) ofCERCLA, remedial actions must attain a degree ofremediation considered protective ofhuman health and the environment. In addition, CERCLA remedial actions must attain a level or standard ofcontrol that atleast meets standards, requirements, limitations, orcriteria that are "applicable or relevant and appropriate" upon completion ofthe action. Theserequirements, known asARARs, may be waived only in certain cases specified in Section 121(d)(4) ofCERCLA. ARARs are derived from both federal and state laws. Thedefinitions of"applicable" or "relevantand appropriate" requirements are found in the NCP, 40 CFR 300.5. Applicable requirements refer to those cleanup standards, standards ofcontrol, and other substantive requirements, criteria, or limitations promulgated under federal environmental or state environmental orfacility setting laws that specifically address ahazardous substance, pollutant, chemical, remedial action, location, or other circumstance found at aCERCLA site.

20000,317.10(9) - FS 1014111992 V - 2-15Relevant and appropriate requirements refer to those cleanup standards, standards of control, andother substantive requirements, criteria, orlimitations promulgated under federal environmental or state environmental or facility setting laws that, although notapplicable toa hazardous substance, pollutant, contaminant, remedial action, location, orother circumstance at a CERCLA site, address problems or situations sufficiently similar to those encountered at the CERCLA sitethat their use iswell suited to the particular site. The analysis ofrequirements with respect to theirrelevance and appropriateness is somewhat flexible. Relevant statutes require comparison ofthe types ofremedial actions contemplated to hazardous substances present, characteristics ofthe waste, physical characteristics ofthe site, and other appropriate factors to establish relevant and appropriate requirements. It ispossible to consider only part ofarequirement relevant and appropriate. Those state standards thatare identified in atimely manner and are more stringent than federal requirements may be applicable

orrelevant and appropriate. Within the confines ofexisting regulations and policy, the U.S. Department ofthe Army, as the lead agency, assesses the applicability orrelevance and appropriateness ofrequirements. Other criteria and advisories thatare not promulgated regulations can be used as guidelines to ensure protection ofhuman health and the environment. These "tobe considered" (TBC) criteria may include EPA health advisories (HAs), proposed MCLs, and other similar advisories. Three different classifications ofARARs exist. The firsttype includes chemical-specific requirements. Examples ofpotential ARARs include: (1) MCLs established under the Safe Drinking Water Act (SDWA), (2) National Ambient Air Quality Standards (NAAQS), (3) Ambient Water Quality Criteria (AWQC), and (4) The Basic Standards and Methodologies forSurface Water. Thesecond type ofARAR includes location-specific requirements that restrict activities on the basis of site characteristics and immediate site environment. These requirements may affect the typeofremedial action thatcan be implemented. A limiton activities within flood plains is

an example ofa location-specific ARAR.
20000,317.10(g) -FS 1014111992 V - 2-16The third type ofARAR includes action-specific requirements. Such ARARs are technology based and areassociated with the type ofremedial alternative under consideration. An example ofan action-specific ARAR isthe Resource Conservation and Recovery Act's (RCRA) hazardous waste labeling requirements. Chemical-specific ARARs were considered during the development ofPRGs. Locationand action-specific ARARs wereconsidered during the detailed analysis ofspecific remedial alternatives (Section 5.0) and are not related to thedevelopment ofPRGs. Anevaluation of ARARs with respect to the Offpost OU is in Appendix A.
2.5.3.1.1 Chemical-specific Agolicable orRelevant and At)t)rot)riate ReQuirements A chemical-specific ARAR is a health-based orrisk-based numerical value or methodology that, when applied to site-specific conditions, results in the establishment ofnumerical values. These values establish the acceptable amount or concentration ofachemical that isrequired to meet protectiveness criteria established for the site. Identification ofchemical-specific ARARs was performed in several steps. The first step was toidentify chemicals for which an ARAR determination was warranted based on 42 USC 9621(d), which provides that ARARs are tobe selected only for hazardous substances, pollutants, orcontaminants. The second step was todetermine whether specific standards existed for the designated hazardous substances, pollutants, orcontaminants identified as COCs in the EA. The third step wasto determine which ARARs were to be attained for purposes ofremedial action for the OffpostOU. Chemical-specific ARARs arediscussed in Appendix A and are addressed foreach medium during the development and selection ofPRGs. Potential chemical-specific ARARs forthe Offpost OU have been identified and are presented in the ARARs subsections for each medium ofconcern. For contaminants without potential ARARs, health-based levels, based on the risks identified in the EA (Volume 111, Section4.0), were developed and are presented in the HBC subsections for each medium of
concern. Chemical-specific ARARs are identified and discussed in Appendix A.

20000,317.10(9) - FS 1014111992 V - 2-17M



### 2.5.3.1.2 Location-specific Applicable orRelevant andAnDropriate ReQuirements Location-specific ARARs generally arerequirements placedupon the contaminated areasor uponthe conduct ofactivities solelybecause they are inspecial locations, such asflood plains, wetlands, historic places, and sensitive ecosystems orhabitats. Location-specific ARARs are identified anddiscussed inAppendix A. An evaluation ofwetlands ecosystems withinthe Offpost OU ispresented in AppendixB. 2.5.3.1.3 Action-sr)ecific Applicable orRelevant andApprwriate Reauirements Action-specific ARARs areusually technology-based or activity-based requirements or limitations on actions taken with respectto hazardous wastes orrequirements toconduct certain actions to address particular circumstances ata site. Action-specific ARARs are identifiedand discussed in Appendix A. 2.5.3.2 Health-based Criteria HBCpresented insubsequent subsections forcarcinogens correspond tothe point of departure of 10-6 

### excess cancer risk in accordance withthe NCP. Further, the NCPrequires that acceptable exposure levelsfor noncarcinogens with an adequate margin ofsafety mustnotcause any adverse effect during allor partofa lifetime, including sensitive population groups. EPA's RiskAssessment Guidance for Superfund (EPA, 1989b) requires that individual calculated chemical intakes divided by the reference dosesbe summed into ahazard index (HI) fornoncarcinogens. Further, the guidance specifies segregation ofHIs by toxiceffect and mechanism. This approach wasused in establishing health-based PRGsfor the noncarcinogens. Expected future land usehad animpact onthe development ofHBCin the Offpost OU. Three different exposure scenarios were developed in the OffpostEA. Arural residential (including agriculture) scenario was developed forzones 1,2, 

### and 6, 

### an urban residential scenario wasdeveloped for zones 3and 4, and a commercial/industrial scenario was developed for zone5. The Offpost EA (Volume 11, Section 2.0) alsodeveloped exposure parameters consistentwith both RME andMost LikelyExposure (MLE) estimates.

20000,317.10(g) - FS 1014111992 

### V - 2-18A summary of the approach used forthe development of HBC is presented here. HBC for COCs are developed in the FS using the exposure parameters selected in the EA. The risk assessment software, ARES, was used to develop HBC at 10-6 risk for carcinogens and hazard indices of I for noncarcinogens. HBC were estimated by proportional analyses using the EA ARES risks presented in Volume IV, Appendix G. HBC risks were then calculated using HBC as input exposure concentrations in the ARES model. By using ARES, the individual risk ofeach HBC is determined, as well as the cumulative risk of multiple chemicals and media. The EA calculated risks use an intake equation in Section 2.4 of the EA and in Appendix C of the FS. To develop HBC, the intake equation is rearranged, an acceptable intake is calculated (see Appendix C), and the equation is rearranged and solved for concentration. This calculation is performed for each COC, exposure pathway, and medium ofconcern. Groundwater HBC were calculated using an equation that normalizes the importance of individual exposure pathways by taking the inverse of each individual exposure pathway HBC, summing these, and taking the inverse ofthe calculated sum (see Appendix C). The resultant groundwater HBC were then adjusted for the contributions of multiple carcinogens or noncarcinogens by dividing by the number ofcarcinogens that were contributors to risk. The resultant HBC corresponds to the target risk level (i.e., 10-4 to 10-6) and to the risks calculated in the EA. Quantitative uncertainty analysis was used to help assess the conservativeness of the RME estimates (Volume 11, Section 2.4). For the several pathways studied, RME estimates were in reasonable agreement with the 95th percentile values from the exposure distributions, but the RME estimates were often higher. Differences ranged between factors of I and 6, and in general, the RME estimates exceeded the 95th percentile values by a factor of 3. Considering the uncertainty in knowledge of potential exposures, these differences are relatively small. However, the fact that the RME estimates were consistently higher suggests that the results of the quantitative uncertainty analysis can be used to support the conclusion that the RME estimates are

20000,317.10(g) - FS 1014111892 V - 2- 19indeed conservative and can be used with confidence in thedevelopment ofpreliminary remediation goals.
2.5.3.3 Backaround Concentrations Background concentrations were one ofseveral types ofcriteria evaluated forselection of PRGs when there were contaminant sources in orcontributing to a medium other than sources related to RMA. Background levels may also be considered as PRGs when remediation ofa medium to below background levels is not technically feasible because of naturally occurring
sources of COCs in the environment.
2.5.3.4 Ecolopical Criteria Ecological criteria were developed forprotection ofpredators at the top ofthe food chain including bald eagles, owls, herons, and kestrels. Ecological criteria address the requirement stated in the NCP for protection ofthe environment and therefore are included as PRGs. The methods used in developing ecological criteria are presented in Appendix C.
2.5.4 Develoment and Identification ofPreliminary Remediation Goals - Groundwater The evaluation of PRGs forgroundwater in theOffpost OU includes an assessment of ARARs and HBC.
2.5.4.1 Groundwater Chemical-specific Agglicable or Relevant and AL)r)ropriate Reauirements The chernical-specific ARARs pertaining to Offpost OU groundwater COCs are listed in Table 2.5.2- 1. Consistent with EPA guidance, MCLGs set at zero are not considered potential ARARs. MCLs from the National Primary Drinking Water Standards (NPDWS) and CBSG can be applicable orrelevant and appropriate for remediation ofgroundwater in the Offpost OU. Consistent with EPA guidance, the Army selected thechemical-specific ARARs listed in Table 2.5.2- 1.

20000,317.10(9) - FS 1014111892 V - 2-20DIMP is the subject ofan EPA Health Advisory used to set the TBC at 600 micrograms per liter (jug/l). The TBC has been reviewed and found protective by the National Academy of Sciences. Therefore, theTBC will be adopted asan ARAR. No ARAR determinations are final until the Offpost ROD is final. The levels listed as proposed are not ARARs but may be evaluated asARARs iffinalized before issuance ofthe ROD for the Offpost OU.
2.5.4.2 Groundwater Health-based Criteria Groundwater HBC forcarcinogens are risk-based values that correspond to the range of allowable risks ( 10-4 to 10-6) prescribed in the NCP. HBCfor noncarcinogens correspond to concentrations such that thecalculated HI isbelow 1.0. HBC were developed fora residential (including agriculture), commercial/industrial exposure scenario. The methodology for calculating the HBC is presented in Appendix C. Table 2.5.2-2 presents the HBC forgroundwater COCs without ARARs. Several groundwater COCs have only HBC asgroundwater PRGs (because there
are no ARARs for theseCOCs). These COCs include CPMS, CPMSO, CPMS02, dicyclopentadiene, dithiane, isodrin, malathion, and oxathiane. CRLs have been included in Table 2.5.2-2. For those cases where HBC are less than CRLs, the CRLs would be adopted as the performance standard because values below CRLs cannot be reliably quantified.
2.5.4.3 Selection ofGroundwater Preliminary Remediation Goals Groundwater PRGs were developed on the basis ofARARs and HBC. PRGs developed for consideration in assessing groundwater and developing remedial alternatives are presented in Table 2.5.2-3. Groundwater PRGs used ARARs forcontaminants with promulgated standards, residential 10-r'RME HBC forcarcinogens without ARARs, and residential RMEs for noncarcinogens without ARARs. CRLs are adopted as PRGs in cases where the ARARs or HBCs
are below the CRL. Groundwater PRGs are consistent with the NCP. Additionally, the EPA Office ofSolid Waste and Emergency Response (OSWER) Directive 9355.0-30, Role ofthe

20000,317.10(9) - FS 1014111892 V - 2-21Baseline Risk Assessment in Superfund Remedy Selection Decisions (EPA, 1991) allows for the
use ofeither ARARs or HBC as remediation goals.
2.6 QUANTITIES OF GROUNDWATER REQUIRING REMEDIATION The area ofgroundwater requiring remediation in the Offpost OU was calculated. This area
was used in thedevelopment and screening ofalternatives to evaluate the effectiveness, implementability, and cost of groundwater remedial alternatives. The quantity of groundwater requiring remediation in theOffpost OU was calculated on the basis ofPRGs and the extent of contamination asdefined by data collected duringthe Offpost RI, the Offpost Rl Addendum, and the CMP (RLSA, 1989; 1990a; 1990b; 1991a; 1991b). PRGs were compared with concentrations for each groundwater COC, taking into account overlapping volumes and areas for COCs. The plumes ofunconfined groundwater contamination exceeding PRGs are shown in Figure 2.6- 1. Although not all PRGs for all contaminants are exceeded throughout theareas shown, the plumes shown in the figures represent the areaover which at least one contaminant PRG is exceeded for groundwater. Within the areas shown on Figure 2.6-1 PRGs are exceeded forthe carcinogens arsenic, chloroform, dibromochloropropane, tetrachloroethylene, trichloroethylene, and dieldrin. PRGs are also exceeded for the noncarcinogens chlorobenzene, dicylcopentadiene, DIMP. The total area ofgroundwater exceeding PRGs encompasses approximately 590 acres ofthe Offpost OU.
2.7 GENERAL RESPONSE ACTIONS General response actions are defined as those actions that will satisfy the RAOs and PRGS described herein. General response actions were developed foreach medium and include no act-ion, institutional controls, containment, removal, disposal, and treatment. These response actions may be combined to produce appropriate remedial alternatives.

20000,317.10(g) -FS 1014111892 V - 2-222.7.1 No Action The No Action general response action recognizes, although does not incorporate, the substantial interim response actions already implemented. Under the No Action alternative, the current status ofthe site would not change except by natural attenuation and degradation processes. There would be no further effort toreduce risk to human health and the environment by physical restriction ofaccess to affected areas or by other remedial actions. Operations at the boundary containment systems would cease, and IRA A would not continue. Groundwater monitoring would be used to monitor concentrations ofcontaminants, theareal extent ofcontamination, and its migration. A risk assessment would be performed every 5years, as required by CERCLA Section 121(c).
2.7.2 Institutional Controls Institutional controls are nonengineering methods by which federal, state, and local governments or private parties can prevent or limit access to affected environmental media. Institutional controls are commonly in the form ofdeed or access restrictions, but may include actions such as land acquisition, warning signs, zoning controls, well restrictions, property condemnation, provision for alternative water supplies, relocation ofpotentially affected populations, and biota management. 2.7.3 Containment Containment response actions provide a means by which contaminant migration and risk associated with exposure pathways are minimized oreliminated by the use ofphysical and/or hydraulic barriers. Containment reduces ordisrupts the mobility oftheaffected media, consequently reducing the migration ofchemicals within the media and the risk associated with exposure pathways. Containment response actions can be implemented both in subsurface (e.g., slurry wall) and aboveground (e.g., soil cover).

20000,317.10(9) - FS 1014111892 V - 2-232.7.4 Removal Removal technologies are operations that remove thecontaminated media and/or waste from its location onsite. They include extraction and transportation either offsite or toanother location onsite for treatment or disposal. Removal may be accomplished by pumping, draining, and excavation.
2.7.5 Treatment Treatment response actions for liquids or solids reduce or eliminate toxicity, mobility, or volume ofa chemical bydirectly affecting the chemical through an external force thateither would alter the structure ofthechemical or would bond with, isolate, or completely destroy the chemical. Treatment response actions can be implemented onsite oroffsite. Some treatment response actions can be implemented in-situ. SARA recommends that a range oftreatment
measures be developed and evaluated. The NCP requires that for source control actions, a range of alternatives be developed in which treatment that reduces the toxicity, mobility, or volume of the hazardous substances, pollutants, orcontaminants isa principal element. Further, the NCP requires that for groundwater response actions, a limited number ofremedial alternatives be developed that achieve site-specific remediation goals within different restoration timeframes utilizing one or more different technologies.
2.7.6 Disposal When a remedial alternative includes removal orextraction and treatment, a contaminated medium or treatment residuals requiring proper management and disposal are usually produced. Depending on the treatment residuals, several disposal options may be considered. Representative disposal options for solids thatrequire management include onsite land disposal complying with the intent ofRCRA, and offsite disposal in a RCRA-approved landfill. Treated solids that no longer exhibit hazardous waste characteristics may be delisted and disposed as nonhazardous solids. Disposal options for treated liquid end products include discharge to surface water,

20000,317.10(g) - FS 1014111892 V - 2-24discharge to publicly owned treatment works (POTW), reinjection/recharge to groundwater, and land application.
2.8 IDENTIFICATION AND SCREENING OF TECHNOLOGY TYPES AND PROCESS OPTIONS

During the process ofdeveloping alternatives for remediation for the RMA Offpost OU, it
was necessary toidentify, evaluate, and screen the universe ofpotentially applicable technology types and process options. The screening determined which technology types and process options
were unable to treat the contaminants present or were incompatible with the site conditions ofthe Offpost OU, thus eliminating them from further consideration. The screening also determined which technology types were appropriate, thus retaining them for further consideration. Technology types were defined in accordance with EPA guidelines asgeneral categories of technologies (EPA, 1988b). Examples oftechnology types include thermal treatment, solidification/stabiI ization, and chemical treatment. Process options are defined as specific processes, systems, or actions within each technology type. Forexample, the chemical treatment technology type includes such process options asprecipitation, oxidation/reduction, and solvent extraction. Process options are usually combined to generate remedial alternatives. In some instances, a process option may be considered as a remedial alternative by itselfifit meets specified RAOs for the affected media. Technology types and process options were evaluated with respect to remediation of groundwater. Technology types and process options suitable for remediation of soil, surface water, sediment, air, and biota were not identified forthe reasons presented in Volume V, Section 2.2.2. The screening oftechnology types and process options is atwo-step process. Universal screening is the first step and involves the identification oftechnology types and process options that are technically implementable. A universal list oftechnology types and process options developed for groundwater ispresented in Figure 2.8-la through e. The second screening step

20000,317.10(g) - FS 1014111892 V - 2-25involves the evaluation and screening ofselected or representative process options utilizing three criteria: effectiveness, implementability, and cost.
2.8.1 Universal Screening A screening ofknown process options for the technology types discussed in this section is summarized for groundwater in Table 2.8.1 - 1. Universal screening eliminated process options and technology types that were not technically implementable. The evaluation oftechnical implementability was based on two criteria. The first criterion isthe ability ofa process option tobe implementable under conditions at the site. This includes conditions such as type ofmedia contaminated, area and volume ofcontaminated media, depth to bedrock, subsurface geology, and subsurface hydraulic characteristics. The second criterion is the ability ofthe process option tobe effective for reducing the mobility, toxicity, or volume ofthe specific contaminants present inthe affected medium. These two criteria use information obtained during the OffpostRI, Offpost RI Addendum, and CMP on contaminant types, concentrations, and sitecharacteristics. A summary ofthe process options remaining after the universal screening forgroundwater is presented in Figure 2.7.1 -1a through e. 2.8.2 Evaluation and Screening ofSelected Process Options In Sections 2.8.3 and 2.8.4, each applicable process option retained for further consideration from the universal screening isdescribed and isfurther screened. The purpose ofthis screening is to select one RPO from each technology type (Section 2.10). The RPO will then be used inthe assembly, development, and screening ofremedial alternatives. In somecases, twoor more RPOs within the same technology type may be different enough with respect toperformance or effect that more than one option may be selected within a technology type to ensure proper representativeness. In other cases, an entire technology type may be eliminated after further examination. The basis for screening ofthe process options consists ofthe following three criteria: 1. Effectiveness

- The potential effectiveness ofprocess options in treating the estimated areas or volumes of media and meeting thecleanup goals defined in the RAOs 20000,317.10(9) -FS 1014111892 V - 2-26- The effectiveness ofthe process option in protecting human health and the environment during the construction and implementation phase

- The reliability ofthe process with respect to the contaminants and siteconditions
2. Implementability

- The ability to obtain permits for offsite actions

- The availability oftreatment, storage, and disposal services

- The availability of skilled workers and equipment
3. Cost

- Relative capital costs within technology types (high, medium, or low)

- Relative operation and maintenance (O&M) costs within technology types (high, medium, or low) Also, treatment process options are only retained ifthey areeffective as a primary treatment process. Process options that may act only as a pretreatment process are notretained for further consideration but may be used in the final remedy.
2.8.3 Nonmedia-specific Process Owions 2.8.3.1 No Action The No Action option will be carried through the FS primarily asa baseline for comparison. Under this option, no additional remedial action would be performed within the Offpost OU to reduce the toxicity, mobility, or volume ofcontaminants. It is assumed that the NBCS and NWBCS containment and treatment systems would cease operation and IRA A would not continue. Natural attenuation would occur, resulting in areduction in measurable contaminant levels over time. Defining thedegree ofnatural attenuation and the length oftime required toachieve the cleanup goals with certainty is not possible because there are no data corresponding to the nonoperation ofthe boundary containment systems. However, contaminant concentrations would be monitored by continuation of groundwater and surface-water monitoring.

20000,317.10(9) - FS 1014111892 V - 2-272.8.3.2 Institutional Controls With respect to the protectiveness and risk-reduction considerations ofthe three identified evaluation criteria, institutional control options do not directly reduce the toxicity, mobility, or volume ofthe affected media. Institutional controls serve, in effect, asa barrier orexposure pathway interruption tominimize oreliminate direct human contact with groundwater at the site. Thus, they are effective in mitigating the risks from potential exposures associated with futureuse scenarios. Although institutional controls by themselves may not be completely effective in addressing the intent ofCERCLA as amended by SARA, they can be instrumental in maintaining the integrity ofany "action"alternative selected and will, therefore, be retained in combination with other process options for further evaluation during the development ofalternatives.
2.8.3.2.1 Access Restrictions Access restrictions provide a means to minimize or eliminate direct human contact with affected media and include land use/deed restrictions, fencing and warning signs, and land acquisition.
Land Use/Deed Restrictions A deed restriction is a written and recorded document, usually kept on file in the county recorder's office. A deed restriction may contain a number ofrestrictions primarily related to activity on a particular property, including surface and subsurface activities, such as prohibiting subsurface foundation construction and domestic well installations. Fencinp,and Warning SiPns Fencing and warning signs are self-explanatory. When fences are constructed properly and
are adequately maintained, they act as an effective deterrent to public access to a contaminated
area. Fences may also limit exposure ofcertain wildlife to a contaminated area. Implementation of fencing may require acquisition ofproperty on portions ofthe Offpost OU. Warning signs,

20000,317.10(g) -FS 1014111892 V - 2-28alone and combined with fencing, can reduce the likelihood ofhumanexposure to contaminated media.
Land Acouisition Acquisition ofproperty in the Offpost OU may be necessary to implement remedial actions. Land may be acquired for construction oftreatment plants, providing pipeline right-of-way for pump-back,to treatment facilities, orto reduce risk by implementing access/deed restrictions and exposure control options. Property would be purchased from land owners at a rate dependent on thecurrent market value.
2.8.3.2.2 Alternative Water Supplies Providing alternative water supplies toresidents whose potable water supply hasbeen affected by offpost contamination isa means ofeliminating risk associated with use ofthe contaminated water. A short-term alternate water supply would include bottled water, and longterm alternate water supply options would entail either connection to South Adams County Water District's (SACWD's) municipal potable water distribution system, formation ofwater districts using groundwater from an uncontaminated aquifer, or provision ofa private well completed in
an uncontaminated aquifer. The Army has committed toproviding an alternate water supply to future identified users whose wells exceed PRGs.
2.8.3.2.3 Monitorinp, Monitoring consists of a specified data-collection activity designed to provide information concerning ongoing siteconditions in specified media for use in decision making. A monitoring program is an effective measure to track contaminant migration and evaluate remediation effects. Monitoring was implemented during the CMP and the Offpost RI and RI Addendum programs.

20000,317.10(g) - FS 1014111892 V - 2-292.8.4 Groundwater Process Ovtions 2.8.4.1 Removal Removal refers tothe extraction ofcontaminated and uncontaminated media. Removal may serve the purpose of mass removal ofcontaminants or be incorporated as part ofa containment system. Removal process options forgroundwater include pumping ofwell points, extraction wells, and/or subsurface drains, and may include water-flushing technologies for the enhancement of contaminant removal.
2.8.4.1.1 Groundwater Extraction Groundwater extraction can consist ofwell points, extraction wells, and subsurface drains. Descriptions ofthese process options follow.
Well Points Well-point systems are typically used forextraction ofshallow groundwater in unstratified soil. Well-point systems are constructed by manifolding a group ofclosely spaced wells toa header pipe. Groundwater is removed using a suction pump. The primary disadvantages to wellpoint systems are the limited depth from which they can effectively extract groundwater and the limited flow rates achievable. The practical limit for the use ofsuction lift well points isabout 22 feet (EPA, 1985). Most ofthe Offpost OU requiring groundwater remediation would require pumping at heads in excess of 22 feet. Because well points are not effective for groundwater removal over most ofthe Offpost OU, well points are eliminated from further consideration.
Extraction Wells Extraction wells may be used to remove affected groundwater (and hence chemical mass) from the groundwater flow system. The purposes ofextraction wells include removal ofwater for treatment, gradient control for the purpose ofplume containment, and increasing groundwater flux rates through the subsurface to enhance the rate ofchemical mass removal. Extraction well arrays are often combined with subsurface injection to enhance cleanup byflushing clean water 20000,317.10(g) - FS 1014111892 V - 2-30through the aquifer. In relatively high-permeability materials, the areas ofextraction and recharge can be laterally separated. Ifproperly designed, such a system will achieve both containment and mass removal. In materials with lower permeability, extraction and injection wells may have tobe interspersed in a grid pattern to reduce thedistances between points of extraction and injection. Extraction wells are more flexible than well-point systems because they can remove water from any depth. Extraction wells were chosen asa process option for removal ofcontaminated groundwater on the Offpost OU at Offpost IRA and are used onpost in association with the NWBCS, NBCS, and ICScontainment and treatment systems. Extraction wells will be retained for further consideration for thefollowing reasons: (I) their utility in mass removal, pump and treat, and containment alternatives, (2) the conventional nature oftheir installation and ease ofoperation, and (3) their proven effectiveness at many hazardous waste sites, including RMA.
Subsurface Drains Subsurface drains consist of linear structures having enhanced permeability that are designed to increase the efficiency of groundwater collection. They may be used for both containment and mass removal activities. For example, slurry wall containment systems often incorporate a subsurface drain to aid in containing migrating contaminants in shallow groundwater while providing mass removal before treatment. Drains can be constructed by excavating atrench below the water table and then backfilling theexcavation with permeable granular material, which acts as a filter. In indurated materials, a drain may also be constructed with controlled blasting, which creates alinear rubble zone ofenhanced permeability. In any case, groundwater is extracted from the drain by a limited number ofsumps, which may be constructed as the drain is built or may consist of wells drilled into the drain. Subsurface drains are often the most efficient extraction system in low hydraulic conductivity soil. Three types ofsubsurface drains include French/tile drains, dual-media drains, and trench/gallery drains. French/tile drains incorporate a section ofperforated pipe placed in the 20000,317.10(9) -FS 1014111892 V - 2-31trench and surrounded by permeable fill. Dual-media drains are identical to French/tile drains except that a geotextile material is added to reduce clogging ofthe drain byfine particles. Trench
or gallery drains are similar to French/tile drains, but are configured as a radial group oftrenches that discharge into a common sump orgallery. Because oftheeffectiveness ofsubsurface drains in extraction and containment systems and because they are a conventional readily implementable process option, subsurface drains are retained for further consideration.
Water Flushinp, Water flushing can potentially enhance removal ofcontaminants by increasing the number of pore volumes of water flowing through acontaminated aquifer per unit time. Water flushing process options include injection and flooding/infiltration. Description ofthese process options follows: In Injection is a process option thatflushes uncontaminated water into the subsurface using either recharge wells ortrenches. Theprocess stimulates groundwater flow by increasing the hydraulic gradient in the vicinity ofthe injection system and aids the removal of adsorbed contaminants by increasing the number ofpore volumes ofclean water flushed through the aquifer and/or the vadose zone in a given time interval. Water typically is extracted downgradient and treated before reinjection. Injection serves the dual purpose asa means ofeffectively enhancing contaminant removal and a method ofdisposing oftreated water. Injection wells and trenches were implemented aspart ofthe onpost boundary containment and treatment systems and will be used for the implementation ofOffpost IRA. The injection systems onpost were used for disposal oftreated groundwater; they were notused in flushing operations. Onpost injection systems have proved to be readily implementable. The effectiveness offlushing operations for organic contaminants similar to many ofthe contaminants in Offpost OU groundwater hasbeen demonstrated at hazardous waste sites; therefore, injection is retained for further consideration. Floodinp/Infiltration Flooding and infiltration are process options that use uncontaminated water applied at the ground surface by ponding or flooding to flush the vadose zone and the aquifer. This stimulates groundwater flow by increasing the hydraulic gradient in the vicinity ofthe injection and facilitates the removal ofadsorbed contaminants by increasing the number ofpore volumes ofclean water flushed through the contaminated media in a given time interval. Water typically is extracted downgradient and treated before surface application.

20000,317.10(g) - FS 1014111892 V - 2-32Flooding and infiltration serve the same purpose as injection but have thedisadvantages ofrequiring larger surface areas and losing water to evaporation. Also, during winter, freezing may be a problem. The advantage ofusing flooding or infiltration over injection is thatpercolating water through large areas ofthe vadose zone effectively remediates the vadose zone soil. However, the vadose zone in the Offpost OU isnot a source ofgroundwater contamination and is not contaminated. Therefore, because ofthe large area requirements forflooding/infiltration and the lack of any additional benefits over injection, flooding and infiltration areeliminated from further consideration.
2.8.4.2 DisL)osal Disposal ofgroundwater involves technologies that represent the final disposition ofeither contaminated or treated water. Disposal isdivided into subsurface disposal and aboveground discharge technology types. 2.8.4.2.1 Subsurface Disposal The subsurface disposal process options, including pump-back toboundary containment systems, deep well injection, and shallow aquifer recharge, are discussed in the following paragraphs. Pump-back to Boundary Containment Systems Pumping groundwater to the onpost boundary containment and treatment systems is an effective disposal process option. Contaminated groundwater would be extracted and pumped to either the NWBCS or NBCS facilities. The water would be treated by the facility along with extracted onpost water. Implementation ofthis process would require coordination with the facility operations and may require treatment facility expansion and additional recharge systems. Land acquisition may also be required to provide pipeline right-of-way. Water rights implications also require consideration. Thepump-back process option iseffective and potentially implementable; therefore, this process is retained for further consideration. Deep-Well In*ection The deep-well injection process option includes both onsite deep injection and transport to
an offsite permitted deep-well injection facility. Deep-well injection involves pumping the 20000,317.10(9) - FS 1014111892 V - 2-33contaminated water into adeep hydraulically isolated formation under sufficient pressure to displace native fluids while avoiding excessive migration ofthe waste and fracturing ofthe formation. The formation should not have value as aresource. Deep-well injection oftreated water isnot appropriate because risks associated with exposure to treated water are acceptable for unrestricted use. Therefore, treated water should be disposed in a manner that allows for future use (which isnot the case for deep-well injection). Under appropriate geologic conditions, deep-well injection isan effective process for disposing contaminated groundwater. However, both offsite and onsite injection are not implementable forthe following reasons:

- Onsite deep-well injection " Pastonpost deep-well injection activities may have induced earthquake activity. " Agency approval is difficult to obtain.

- Offsite deep-well injection at a permitted treatment, storage, and disposal (TSD) facility " It is not practical to transport large volumes ofcontaminated groundwater. " Water rights may require replacement ofextracted groundwater.
Shallow-Aouifer Recharge Recharge wells and trenches are process options for shallow aquifer disposal oftreated or contaminated water. Recharge wells and trenches may provide forcontainment ofcontaminated groundwater and water flushing ofcontaminants. Recharge wells are constructed in essentially the same manner as extraction wells with the exception that treated groundwater is recharged into the aquifer. Treated groundwater is recharged by a gravity-induced head. Spacing ofrecharge wells is dependent on the hydraulic properties ofthe aquifer and the specific application such as gradient control. Recharge trenches vary in width depending on the construction method. Recharge trenches are commonly constructed using either oftwomethods:

- A one-pass trenching machine that installs pipe and installs fill in one operation

- Conventional trenching using abiopolymer slurry below the water table to stabilize the walls 20000,317.10(9) - FS 1014111892 V - 2-34Trenches are backfilled with drain rock up to a depth of 18 inches below ground surface. A slotted pipe is installed within the drain rock throughout the length ofthe trench. Treated groundwater is pumped into the trench via the perforated pipe and recharges through the drain rock into the aquifer. Shallow-aquifer recharge ofcontaminated groundwater is noteffective in reducing the mobility, toxicity, or volume ofcontamination and may increase the mobility and volume of contaminated media. Therefore, shallow-aquifer recharge ofcontaminated water iseliminated from further consideration. Shallow-aquifer recharge provides an effective means ofreturning treated groundwater to the aquifer. Recharge oftreated groundwater into the UFS was implemented at the NBCS, NWBCS, and ICS. Also, recharge oftreated water was selected as the method ofdisposal for Offpost IRA (HLA, 1989). Recharge oftreated water into the shallow aquifer is readily implementable and effective. Replacing the extracted contaminated water with treated water aids in the reclamation ofthe site. Because ofits effectiveness and ease ofimplementation, recharge oftreated groundwater into the shallow aquifer is retained for further consideration.
2.8.4.2.2 Aboveground Discharpe Three process options representing aboveground discharge, including discharge to POTW, discharge to surface water, and infiltration basins, are discussed in the following paragraphs. Discharpe toPublicly Owned Treatment Works Discharge to a POTW is an effective process for disposing contaminated groundwater or treated groundwater. The implementability ofdischarging to aPOTW is governed by numerous factors that include the proximity to a sanitary sewer line, the capacity ofthe sewer line and the treatment facility and pretreatment requirements.

20000,317.10(g) -FS 1014111892 V - 2-35Discharge ofcontaminated water to aPOTW iseliminated from further consideration for the following reasons: (1) the water would not meet pretreatment requirements, and nonregulated compounds may interfere with operations at the treatment facility and (2) water rights may require replacement ofextracted groundwater. Discharge oftreated water to a POTW is retained
as a potential means of disposal, recognizing that POTW capacity limitations are yet tobe determined. Discharge to Surface Water Discharge ofcontaminated groundwater to a surface-water body is not implementable or effective for the following reasons: (1) the process is not implementable because contaminated water would not meet the requirements specified by theClean Water Act; (2) the process is ineffective because it does not significantly reduce the mobility, toxicity, orvolume ofcontamination; (3) discharge to surface water would likely contaminate the water body, the biota that use the water body, and the sediments within the water body; (4) there is a possibility ofa fugitive emissions problem from volatile organic compounds; and (5) public and agency acceptance are unlikely. Therefore, discharge ofcontaminated groundwater to a surface-water body is eliminated from further consideration. Discharge oftreated groundwater to a surface-water body is an effective means ofdisposal. However, difficulties in implementing surface-water discharge oftreated water arise from the impactsof increased water flow on the receiving water body. It has not yet been determined whether this difficult), would affect the implementation ofdischarging to surface water. The discharge oftreated groundwater to surface water iseliminated from further consideration.
Infiltration Basins Disposal to infiltration basins involves the discharge ofcontaminated or treated groundwater into a man-made basin or natural surface depression.

20000,317.10(9) - FS 1014111892 V - 2-36Discharge ofcontaminated groundwater into an infiltration basin is not only a disposal option but can act as a form ofland treatment. Contaminated groundwater may undergo limited remediation/treatment via three mechanisms when itisdischarged into an infiltration basin: volatilization, adsorption, and biodegradation. Discharging contaminated water into an infiltration basin is difficult to implement for the following reasons: (1) there may be fugitive emissions from the volatilization oforganic compounds, (2) although the infiltrating water may be treated, the effectiveness in reducing theconcentration ofCOCs islimited, and (3) because ofthe limited effectiveness ofthe process option there may be an associated increase the volume of contaminated media to include the subsurface soil and groundwater adjacent to the infiltration basin. Therefore, disposal ofcontaminated groundwater via discharge into infiltration basins is eliminated from further consideration. Discharge oftreated groundwater into infiltration basins has the following implementation problems: (I) surface area required, (2) freezing during the winter, and (3) losses to evaporation during summer. Because ofdifficulties in implementation and effectiveness considerations, discharge oftreated groundwater into infiltration basins is eliminated from further consideration.
2.8.4.3 In-vessel Treatment ofGroundwater In-vessel treatment refers to those technology types and process options thatare implemented in constructed facilities after removal ofthe contaminated groundwater. Groundwater extracted by wells or drains would require treatment to specific cleanup levels before discharge to surface streams or reinjection tothe aquifer.
2.8.4.3.1 Solids Removal Removal ofsolids from a waste stream is a necessary pretreatment step for many downstream process options. Also, solidscan cause accelerated wear on pumps and can form excessive heavy deposits in pipelines. Solids can cause premature fouling ofmembrane systems and rapid head loss in carbon adsorption columns and can reduce the efficiency ofion exchange units.

20000,317.10(g) - FS 1014111892 V - 2-37M

Solids removal process options that were retained from the universal screening process are discussed in the following paragraphs.
Filtration Filtration is typically used for the removal ofsuspended solids. Filtration is often appropriate asa pretreatment process for carbon adsorption and membrane processes to prevent plugging or overloading problems. Also, filtration can be used for the removal offlocs formed during precipitation and coagulation/flocculation. Two common types offilters are granular media and bag filters. Granular media filters usually contain thefilter media within a vessel supported by an underdrain system. Commonly used filter media include sand and anthracite coal. Single or multimedia filters can be used, depending on the specific application. Filters are backwashed based on two criteria: breakthrough of suspended solids and/or significant head loss caused by excessive pore clogging. Bag filters consist offilter bags supported by perforated steel baskets and are sealed in a metal housing. The bag material acts asthe filtration medium. Standard bag materials include nylon, polyester, and polypropylene. Bags can be removed and replaced when pressure drop
across the bags exceeds design limitations. Filtration is not expected to be required asa primary treatment process and is notretained forconsideration during the development ofalternatives, but may be implemented as apretreatment process option.
Sedimentation Sedimentation is aprocess option that uses gravity to settle suspended solidsout ofan aqueous waste Stream. Sedimentation maybe implemented in the form of settling ponds, sedimentation basins, and clarifiers. Sedimentation isoften used asa pretreatment step for carbon adsorption, stripping, membrane processes, and filtration. Suspended solids removal isnot expected to be required as aprimary treatment process for extracted groundwater. Therefore,
20000,317.10(g) - FS 1014111892 V - 2-38M

sedimentation is eliminated from further consideration but may be implemented as a pretreatment process option.
2.8.4.3.2 Phase Transfer Phase transfer process options remediate contaminated aqueous media by enhancing mass transfer ofcontaminants from the liquid to the gaseous phase. Phase transfer process options retained in the universal screening include air stripping, steam stripping, and steam distillation. A discussion ofthese process options follows.
Air StriLvinp, Air stripping is an effective and reliable method for removing volatile organic compounds (VOCs) from aqueous waste streams. Ofthe COCs detected in the Offpost OU groundwater samples, chloroform is the most likely candidate for air stripping. The most common air stripping method involves mixing large volumes ofair with contaminated water in a packed-tower arrangement topromote transfer ofthe VOCsfrom the liquid phase to the gas phase. In packed-tower aeration, loosely packed material is placed within
a vertical cylindrical tower. Water cascading through the packing breaks into smalldroplets, providing a large surface area to enhance mass transfer. Air forced upward through the packing from the tower base promotes the transfer of VOCs from the water phase to airphase. Depending
on the compound stripped and its concentration, the contaminated air stream may require treatment. Air stripping is retained for further evaluation during thedevelopment ofalternatives because air stripping is aproven technology demonstrated to be effective forthe removal ofVOCs at hazardous waste sites.
Steam Strippinp, Steam stripping removes VOCs and semi-volatile organic compounds (SVOCs) using the
same principles as air stripping, except steam is used to raise the water temperature and, thereby, enhance organic contaminant volatilization. This process is more effective in removing organic 20000,317.10(g) - FS 1014111892 V - 2-39compounds with smaller Henry's Law constants than conventional air stripping, but requires a greater capital cost and higher O&M costs including construction ofa steam-generating plant. Although steam stripping has the additional benefit over air stripping ofremoving SVOCs, carbon adsorption should also be effective in removing these compounds. Also, stream stripping is much
more difficult to implement and is costlier than air stripping because ofthe required construction ofa stream-generation facility. Steam stripping is eliminated from further consideration because of difficulties of implementation and increased cost as compared to technologies with similar effectiveness.
Steam Distillation Steam distillation is a separation and recovery process consisting ofevaporation followed by condensation. The process effectively concentrates inorganic compounds into the blowdown waste stream, thereby reducing the volume ofheavy metals and other inorganic-containing liquids in the treated stream. VOCs and SVOCs are vaporized with the water and are recovered during condensation. Ifthe system is designed appropriately, organic contaminants can be separated from the treated stream and recovered. Components of a distillation system include a steam-production unit, a still, acondenser, and a productcooler and receiver. Blowdown water and still-bottom residues are recovered and treated. Distillation units have low to moderate capital costs but have high O&M costs. The primary potential application for distillation at the site would be to separate organics from the waste stream. Because ofthe high costofoperating and maintaining a distillation unit and the availability ofother processes with equal effectiveness for removal oforganics, distillation is eliminated from further consideration.
2.8.4.3.3 Sormion Sorption is a treatment technology type that includes process options that remove contaminants from the liquid phase by concentration onto a solid phase by adsorption and/or

20000,317.10(g) - FS 1014111892 V - 2-40M

absorption. Sorption process options retained in the universal screening were granular activated carbon adsorption and resin adsorption. Theseprocess options are discussed in the following paragraphs.
Granulated Activated Carbon (GAC) Adsorption Activated carbon is a well-developed technology widely used in removal oforganic contaminants from liquid hazardous waste streams and offgas airstreams. The waste stream comes in contact with GAC by flowing through one or more packed-bed reactors. Organics and, to some degree, inorganics are 'adsorbedonto the internal pores ofthecarbon granules by surfaceattractive phenomena. Activated carbon is generally used in granular form either in fixed-bed batch, pressure, or gravity vessels, or in fluidized-bed operations. Fixed-bed columns are the most common treatment configuration. Occasionally, activated carbon is used in powdered form. Primary design considerations for activated carbon include column configuration and loading rate, column size, carbon usage rate, and a spent-carbon handling program (i.e., regeneration or disposal). Activated carbon removes many nondegradable organic compounds and ismost effective for nonpolar, high molecular weight, slightly soluble compounds. Carbon adsorption is readily implementable. Carbon adsorption is ademonstrated, proven technology documented to be effective at the NWBCS, NBCS, and ICS systems onpost for removing DIMP, dieldrin, and dibromochloropropane. Carbon adsorption was chosen as the process option for treatment ofoffpost contaminated groundwater at Offpost IRA. Because ofits proven effectiveness for removing RMA contaminants and its ease ofimplementation, carbon treatment is retained for further consideration.
Resin Adsorotion Resin adsorption is a process option that removes organic compounds from aqueous waste streams by adsorption onto a synthetic resin. Resin adsorption is similar to GAC adsorption except that resin beads act asthe adsorbing medium instead ofcarbon. Adsorption resins are
20000,317.10(9) - FS 1014111892 V - 2-41more selective in removal ofcontaminants than carbon. Thus, specific resins must be chose.n for effective removal oftarget compounds. Resin adsorption is usually accomplished in adownflow, fixed-bed, stainless-steel or rubber-lined column. Resin performance is sensitive to suspended solids load and pH and may be damaged by oxidizing agents. Therefore, resin adsorption columns typically require pretreatment ofthe waste stream. After the resin adsorption capacity is exhausted, the bed is regenerated with
an appropriate solvent. The regenerant solution requires subsequent treatment with potential for recover), ofthe contaminants. Resin adsorption is arelatively new process primarily used in industrial applications for single-component waste streams and has limited demonstration in treatment at hazardous waste sites. Difficulties in implementation arise from limited experience and the fact that numerous resins may be required to remove all target organic compounds. Therefore, resin adsorption is eliminated from further consideration.
2.8.4.3.4 Oxidation Oxidation is a chemical treatment technology type that uses chemical reagents (i.e., oxidizing agents such aschlorine, ozone, hydrogen peroxide) fordetoxification ofwaste streams. Oxidation process options retained in the universal screening process include ozone oxidation, hydrogen peroxide oxidation, and ultraviolet (UV) light/ozone/hydrogen peroxide oxidation. These process options are discussed below.
Ozone Oxidation Ozone is a strong oxidizing agent used fordisinfection, purification, odorcontrol, and micro-flocculation in the treatment ofdrinking water. Ozone has also been shown tooxidize organics in hazardous waste streams, but generally requires large doses and long reaction times to be effective forcomplete oxidation ofchlorinated organics. Ozone treatment systems typically consist ofan ozone generator, a reactor where the gas is bubbled through the contaminated water in acontact chamber, and an offgas collection and

20000,317.10(9) - FS 1014111892 V - 2-42treatment system for handling unreacted residual ozone and VOC emissions. Incomplete oxidation byproducts produced during the reaction must be monitored and may require subsequent treatment. Based on its limited effectiveness in treating hazardous organics and implementation difficulties (e.g., offgas treatment requirements), ozone oxidation iseliminated from further consideration. Hydrogen Peroxide Oxidation Hydrogen peroxide is a moderately strong oxidizing agent commonly used in industrial applications. Hydrogen peroxide has been used to degrade many organic pollutants, but often generates toxic, incomplete oxidation byproducts. Hydrogen peroxide treatment systems consistofa rapid-mix oxidizing solution addition system followed by a reaction vessel. Batch orcontinuous flow reactors can be used. Hydrogen peroxide dose and reactor retention time varydepending on the nature ofthe waste stream and the target compound's resistance to oxidation. Because ofthe nonspecific nature ofhydrogen peroxide as an oxidizing agent, other contaminants (organic and inorganic) can reduce the effectiveness ofremoving the target compounds. Hydrogen peroxide can be effective in the oxidation ofhazardous waste streams but typically requires very large doses and long contact times to achieve high removal efficiencies. Oxidation byproducts may be toxic and the waste stream may require further treatment. For these reasons, hydrogen peroxide oxidation is eliminated from further consideration.
Ultraviolet Light/Ozone/HN,drogen Peroxide (Advanced Oxidation Processes) Chemical oxidation using oxidizing agents with UV light and/or catalysts to increase process effectiveness are referred to as advanced oxidation processes (AOP). Oxidizing agents used in AOP include ozone and hydrogen peroxide. UV lightacts as a catalyst in the oxidation process and promotes the formation ofthe hydroxyl radical, which isa strong oxidizing agent. Also, UV light destroys organic compounds via photolysis. Other potential catalysts used are ferrous iron, platinum, copper, tungsten, and nickel. Oxidation

20000,317.10(g) - FS 1014111892 V - 2-43efficiency and kinetics may be pH-dependent, and may require pH adjustment to achieve optimum destruction efficiency. The UV-peroxide treatment process is acombination ofhydrogen peroxide and UV light that induces rapid photochemical oxidation of organic compounds. A UV-peroxide system includes ahydrogen peroxide feed system and a UV-peroxide reactor. Some systems combine
ozone and hydrogen peroxide in the UV-oxidant reactor to increase organic destruction efficiency. Other systems use ozone in place ofhydrogen peroxide, and some systems may include acid and catalyst addition tomaximize destruction efficiency. In general, catalysis dramatically increases the destruction efficiency ofboth hydrogen peroxide and ozone. This increased efficiency leads to shorter retention time requirements, generally more complete oxidation, and fewer problems with oxidation byproducts. AOP have been demonstrated at hazardous waste sitesto be effective for removal of some chlorinated organics (EPA, 1989c). The organic constituents in theoffpost groundwater that may beeffectively treated by AOP include OCPs and DIMP. Therefore, AOP are retained forfurther consideration.
2.8.4.3.5 Radiation Radiation treatment process options use electromagnetic energy forthe destruction of contaminants in waste streams. Process options retained in the universal screening process include electron beam and gamma irradiation. These process options are discussed below. Electron Beam The electron beam irradiation process uses high-energy beta particles (electrons) for the destruction ofhazardous waste constituents. The process can treat both aqueous waste streams and sludges. Electron beam irradiation has been used for full-scale treatment ofmunicipal wastewater and sludges but has had limited use in hazardous waste treatment. Process equipment required for an electron beam irradiation system includes an electron accelerator and a reactor into which the beam isdirected. The electrons enter the waste stream

20000,317.10(g) - FS 1014111892 V - 2-44and ionize the water, producing aqueous electrons and hydrogen and hydroxyl radicals. These species react with theorganics in the waste stream. Thisprocess has been shown toremove significant amounts oforganic compounds in water; chloroform, benzene, and trichloroethylene have shown reductions ranging from 50 to near 100percent where initial concentrations ranged from 400 to 1500 micrograms per liter. Although the electron beam irradiation process has been demonstrated tobe effective for removal ofcompounds contained in Offpost OU groundwater, theprocess is very difficult to implement. Theelectron accelerator has very high capital costs and requires specially trained personnel foroperation. Also, the process has notbeen demonstrated at full scale for hazardous waste treatment. Therefore, the electron beam irradiation process iseliminated from further consideration.
Gamma Irradiation Gamma irradiation is similar to electron beam irradiation with the exception that gamma particles are directed at the waste stream. Gamma particles have the advantage ofmuch greater penetration depths than beta particles; however, this also requires more shielding for the reactor. This process has been used for sewage treatment but has less demonstration history than electron beam irradiation. Because ofsimilar implementation difficulties in comparison with the electron beam process, gamma irradiation is eliminated from further consideration.
2.8.4.3.6 -BiolopicalTreatment Biological degradation ofhazardous organic substances can be accomplished by using aerobic bacteria or anaerobic bacteria. Cultures used in biological degradation processes can be indigenous microbes, selectively adapted microbes, orgenetically altered microorganisms. Biological degradation occurs when microbes use (i.e., metabolize) organic'compounds (substrates) as a source ofcarbon and energy. Organic compounds are metabolized in the presence of enzymes produced by the microorganisms that act ascatalysts. Production ofenzymes can be induced by the presence ofa primary substrate (i.e., can act as sole source of carbon) or by
20000,317.10(g) - FS 1014111892 V - 2-45conditions within thecell (e.g., low concentrations ofadenosine triphosphate [ATP]). Hazardous waste organics can be degraded as a primary substrate or by cometabolism when enzymes are produced because ofthe presence ofanother primary substrate. Complete mineralization degrades the organic compounds to carbon dioxide and water. However, hazardous waste organic compounds may be only partially degraded. Partial degradation products may be toxic and require further treatment or mav be used and further degraded by other microbial species present. Biological hazardous waste treatment may occur in batch or continuous flow systems. The microbial population can be suspended or attached. Aerobic and anaerobic environment treatment technologies exist. The appropriate reactor configuration and environment depend on the waste stream tobe treated. Biological treatment is eliminated from further consideration for the following reasons:

- The concentration oforganic compounds in Offpost OU groundwater is too low to sustain a significant microbial population and would require substrate addition to implement invessel biological treatment.

- Studies have shown that DIMP is not measurably degraded after 12 weeks ofincubation even when conditions favoring cometabolism are promoted (EPA, 1989c)

- Dieldrin is very recalcitrant to biodegradation.
This eliminates the following process options: rotating biologic contractors (RBCs), activated sludge, PACTO, sequencing batch reactors, trickling filters, anaerobic digesters, and submerged fixed film reactors.
2.8.4.4 In Situ Treatment In-situ treatment refers to technology types and process options designed toremediate the contaminated medium while it remains in place.
2.8.4.4.1 Water Flushinp, The water flushing process option is an extraction process that uses liquid as a solvent to increase the rate of contaminant removal in the subsurface. Treated water is a commonly used flushing solution and was discussed asa removal process option in Section 2.8.4.1.1.

20000,317.10(9) - FS 1014111892 V - 2-46Water flushing acts asa treatment process because it reduces contamination in groundwater by enhancing the removal ofcontaminants. In some cases, chemicals can be added tothe flushing solution to enhance the removal ofcontaminants. These chemicals include organic solvents, chelating agents, and surfactants. Water flushing solutionscan be actively injected into the subsurface in wellsand trenches or
can passively infiltrate through infiltration basins. Water flushing is an effective, readily implementable process that may be incorporated in addition to other process options. Therefore, water flushing isretained for furtherconsideration.
2.8.4.4.2 Enhanced Biological Treatment Biological treatment is a technology used to remediate thezone of contamination by microbial degradation. Microbial degradation can be either aerobic or anaerobic. In general, most compounds are more rapidly and completely degraded aerobically. In-situ anaerobic biological treatment is not a well-developed process option. Anaerobic environments are difficult to maintain in large in-situ applications. Therefore, anaerobic biological treatment is eliminated from further consideration. The feasibility ofaerobic bioreclarnation depends on numerous factors, which include biodegradability ofthe organic contaminants and environmental factors such as pH, temperature, redox conditions, and site hydrology. Bioreclamation may be enhanced by the addition of nutrients (e.g., nitrogen, phosphorus, and sulphur) and/or addition ofan oxygen source such asair
or hydrogen peroxide. Contaminants of interest can act asthe sole carbon source/substrate, or an appropriate substrate can be added to stimulate cometabolic degradation. Appropriate microorganisms can also be injected into the contaminated media to enhance degradation. Evidence indicates that both DIMP and dieldrin are very resistant to degradation by biological processes (Khanna, 1989). Therefore, in-situ biological treatment iseliminated from further consideration.

20000,317.10 - III-02TS 1109111892 V - 2-472.8.4.5 Containment Affected groundwater maybe remediated by the processes ofgroundwater containment. Containment is achieved by minimizing the rate ofchemical migration away from source areas. Depending on site conditions, containment may be achieved by the use of subsurface barriers, which include physical barriers and/or hydraulic barriers/gradient control (i.e., groundwater pumping).
2.8.4.5.1 Subsurface Barriers Subsurface barriers include process options that prevent orreduce the migration of contaminants either by emplacement ofa physical barrier in the subsurface or by controlling the hydraulic gradient. Process options retained in the universal screening include slurry walls, grout curtains, hydraulic controls, and subsurface dams. Discussion ofthese process options follows. Slurrv Wall Slurry walls are physical subsurface barriers typically constructed ofa mixture ofwater and soil, bentonite, and/or cement. Upgradient extraction systems are commonly used with slurry walls to prevent contaminant bypass. Slurry walls are constructed by excavation ofa trench. The water-bentonite-solIslurry is mixed onsite and continuously added to the trench during excavation. Appropriate mixing ratios are determined by compatibility and permeability testing with groundwater at the site. Target slurry wall permeability is typically less than 1 0-7 cm/sec. Commonly used equipment includes backhoes, clam shells, loaders, and haul trucks. The trench may be excavated into bedrock in order to "key"the slurry wall into a layer oflower permeability. Slurry walls not keyed into bedrock are known as hanging slurry walls. Slurry walls have already been implemented onpost in association with the NBCS and NWBCS. Because ofdocumented effectiveness onpost and ease ofimplementation, slurry walls are retained for further consideration.

20000,317.10 - 111-02.FS 1109111892 V - 2-48

### Grout Curtains Grout curtains are subsurface barriers constructed by pressure injection ofone ofa variety offluids into unconsolidated material. The grout sets after injection and forms a lowpermeability barrier to groundwater flow and contaminant migration. Grout curtains are constructed by pressure injection ofa predetermined amount of grouting fluid into the strata tobe sealed. Injection points are usually arranged in a triple lineofprimary and secondary grout holes. After primary holes have been injected and the grout has had time to solidify, the secondarN holes are injected to fill any gaps left by the primary holes. Hole spacing is primarily dependent on the nature ofthe material into which the grout is being injected. Various types ofgrout are available including cement, clay (e.g., kaolinite, illite), claycement mixtures, bentonite, alkali silicates, and organic polymer grouts. Selection ofgrout type is based on soil grain size and compatibility with contaminants present. Grout curtains can have setting and durability problems in contaminated groundwater. Compatibility testing between the contaminants and the grouting fluid is often required. Grout curtains are typically more costly and more permeable than slurry walls. Therefore, grout curtains
are eliminated from further consideration. Hydraulic Gradient Control Containment of affected groundwater may be achieved by modifying the hydraulic gradients driving groundwater flow, thus achieving a hydraulic barrier to contaminant migration via groundwater. Hydraulic gradients may be reduced orreversed by controlled groundwater extraction and/or injection. Extraction is typically achieved using extraction wells within or near a chemical source area. Recharge systems using groundwater injection wells are typically installed downgradient ofa source area. Wells (rather than drains)are preferred forgradient control because extraction/recharge pumping rates can be individually controlled at each well location. Although gradient control by groundwater extraction may involve some removal ofchemical mass, the primary purpose ofthe system is to contain, rather than remove, mass.

20000,317.10 - III-02.FS 1109111892 V - 2-49Hydraulic gradient control was chosen as the appropriate process option for groundwater extraction and containment ofcontaminants for IRA A (HLA, 1991b). In addition, hydraulic controls were implemented onpost aspart ofthe NBCS, NWBCS, and ICS. Therefore, because of demonstrated effectiveness and ease of implementation, hydraulic gradient control is retained as a process option.
Subsurface Dam The subsurface dam process option is a subsurface barrier technology constructed by backfilling an excavated trench with compacted clay. Subsurface dams are potentially one ofthe most effective barriers to groundwater flow, but
are difficult to implement. Difficulties arise from siteconditions that include deep excavation in unconsolidated material, sidewall instability in unconsolidated materials, and large groundwater inflows during excavation and construction. Subsurface dams are much more costly toinstall than slurry walls. Therefore, because ofdifficulties in implementation and cost considerations, subsurface dams are eliminated from further consideration. 2.9 SUMMARY OF PROCESS OPTIONSCREENING A summary ofthe process option screening forgroundwater ispresented in Figure 2.9-la through c. Process options that were eliminated were screened outon the basis ofuncertainties with respect to effectiveness, difficulties associated with implementation, and excessive cost with respect to other effective and implementable process options. Figure 2.9- 1 a through c indicates those technologies that were retained and those that were eliminated (i.e., shaded process options
were eliminated) for groundwater.
2.10 SELECTION OF REPRESENTATIVE PROCESS OPTIONS Upon completion ofthe evaluation and screening ofprocess options (Section 2.8) a representative process option (RPO) was selected foreach technology type retained for consideration. One RPO was selected, ifpossible, for each technology type to simplify the subsequent development and evaluation ofalternatives without limiting flexibility during remedial design. The process
20000,317.10 - III-02.FS 1109111892 V - 2-50option determined to be the most effective and most implementable within atechnology type was selected as the RPO. A process option that was effective forall ofthecontaminants present was selected as the RPO. Process options that have been demonstrated at pilot- or full-scale were generally selected instead ofemerging processes with little or no performance orcost data available. Innovative technology process options were selected ifevaluation indicated thatthey may provide better treatment, fewer or less adverse effects, or lower costs than other process options. Cost was used as the criterion to select an RPO in cases where the effectiveness and implementability oftwo or more process options were equivalent. Selected RPOs were used to develop, screen, and perform a detailed analysis ofremedial alternatives. In some cases, varying conditions across the site make selection ofa single RPO fora technology type inappropriate. For example, one process option may be readily implementable and effective under conditions present at one location, while different conditions elsewhere make selection of a different process option more appropriate. In addition, more than one process option within a technology type may be required to achieve PRGs. Forexample, effective implementation ofaccess restrictions may incorporate land acquisition, use restrictions, and fences and warning signs to achieve effective protection ofhuman health and the environment. For these reasons, more than one RPO was selected for some technology types. The RPO that was chosen to develop, screen, and perform a detailed analysis of alternatives may be substituted with another process option from the same technology type at any time in the FS process or in remedial design ifit is determined that the new process option ismore effective
or implementable than theoriginal one. The specific process option used to implement the remedial action may not be selected until the remedial design phase. The selection of RPOs for the groundwater medium ispresented in Section 2.10.1.
2. 10.1 Representative Process Options for Groundwater Remediation Table 2. 10.1 -1 presents the selected RPOs and the criteria ofselection for the groundwater medium. Figures 2. 10.1- la and b summarize the selection ofgroundwater RPOs. Ina few instances, all process options within a technology type were screened out during the first and 20000,317.10 - III-02.FS 1109111892 V - 2-51second levels of screening presented in Section 2.8. These technology types are notrepresented by any process option and will not be used to develop remedial alternatives.

20000,317.10 - 111-02.FS 1109111892 V - 2-52Table 2.2.1-1: Offpost Operable Unit Carcinogenic Risks forEach Medium

Cumulative Zone Groundwater Soil Surface Water Sediment- Risk

lAa 7 x 10-1 4 x 10-5 - - IX 10-4 IBa 9x 10-5 4 x 10-1 - - I X10-4 Ica 7 x 10-1 4 x 10-1 - - I X10-4 2a 2 x 10-4 4 x 10-1 - - 2 x 10-4 3a 2 X,10-4 8x IQ-5 5 x 10-7 8 X10-7 3 x 10-4 4b 2 x 10-4 1x 10-5 5 x 10-7 8 X10-7 2 x 10-4 5b 3 x 10-1 5 x 10-r> - - 8 x 10-1 6a 3 x 10-' 4 x 10-1 - 7 x 10-1

aUrban residential exposure scenario. bCommercial/industrial exposure scenario.

- = pathway not included in exposure scenario 2000,317.10(11) - FS 1108111092Table 2.3.1-1: Offpost Operable Unit Groundwater Chemicals ofConcern

Groundwater Chemicals ofConcern Aldrin Arsenic Atrazine Benzene Carbon tetrachloride Chlordane Chloride Chlorobenzene Chloroform CPMS CPMSO CPMS02 Dibromochlopropane 1,3-Dichlorobenzene 1,2-Dichloroethene Dicyclopentadiene DDE DDT Dieldrin DIMP Dithiane Ethylbenzene Endrin Fluoride Hexachlorocyclopentadiene Isodrin Malathion Manganese Oxathiane Sulfate Tetrachloroethene Toluene Trichloroethene Xylene

20000,317.10 - FS 0309111092Table 2.5.2- 1: Preliminary Chemical-specific Applicable or Relevant and Appropriate Requirements for Groundwater Compound Level Source Arsenic 50 MCL Atrazine 3 MCL Benzene 5 MCL Chloroform 100a MCL Dibromochloropropane 0.2 MCL DDE/DDT 0.001 40 CFR 129.101 1,3-Dichlorobenzene 75 MCLG 1,2-Dichloroethane 5 Mck DIMP 600 HA Endrin 0.2 MCL Fluoride 4000 MCL Tetrachloroethene 5 MCL Toluene 1000 MCL Trichloroethene 5 MCL Xylene 10,000 MCL

All concentrations are micrograms perliter (,ug/1). a total trihalomethanes b DIMP is the subject ofan EPA Health Advisory that hasbeen reviewed and found protective by the National Academy of Sciences. EPA =U.S. Environmental Protection Agency HA =EPA Health Advisory MCL = maximum contaminant level MCLG = maximum contaminant level goal 20000,317.10 - FS 0309111992Table 2.5.2-2: Health-based Criteria forGroundwater Chemicals ofConcern Without Applicable or Relevant and Appropriate Requirements

Certified Chemical Adjusted Rural Reporting ofConcern Residential'- Limit RME Chloride VLT 278 Hexachlorocyclopentadiene 0.23 0.048 Chlorobenzene 25 0.82 CPMS 30 5.69 CPMSO 36 11.5 CPMS02 36 4.7 Dicyclopentadiene 46 5.00 Dithiane 18 0.114 Isodrin 0.06 0.051 Malathion 100 0.373 Oxathiane 160 2.38 Sulfate VLT 175

All concentrations are micrograms per liter (,ug/1). Values consider the number ofcontaminants in groundwater that affect the same target organ. Concentrations for noncarcinogens are reported at levels such that the calculated hazard index is below 1.0. See Appendix C. RME reasonable maximum exposure VLT verv low toxicity
20000,317.10 - FS 0309111892Table 2.5.2-3: Preliminary Remediation Goals for Offpost Operable Unit Groundwater Groundwater Rural Preliminary Residential Chemicals Remediation Hypothetical ofConcern Goals' Cancer Risk Aldrin 0.05 (CRIý) I X10-1 Arsenic 2.35 (CRL-) 6 x 10-' Atrazine 4.03 (CRk) NA Benzene 3 (HBC 2x10-6 Carbon tetrachloride 0.99 (CRL 3x 10-6 Chlordane 0.095 (CRLb 10-6 Chlorobenzene 25 (HBCO) NA Chloroform 15 (HBCb) 2x 10-' CPMS 30 (HBC) NA CPMSO 36 (HBC) NA CPMS02 36 (HBý) NA 10-6 Dibromochloropropane 0.195 (CRL ) 4x Dicyclopentadiene 46 (HBC) NA DDE 0.054 (CRL) 5 X 10-7 DDT 0.049 (CRIý) 2x 10-7 1,3-Dichlorobenzene 6.5 (HBC-) NA 1,2-Dichloroethane 1.1 (CRLb) 3x 10-6 Dieldrin 0.05 (CRL) 3x 10-' DIMP 600 (HA) NA Dithiane 18 (HBC) NA Ethylbenzene 200 (HBC) NA Endrin 0.2 (MCL) NA Fluoride 4000 (MCL) NA Hexachlorocyclopentadiene 0.23 (HBC) NA Isodrin 0.06 (HBC) NA Malathion 100 (HBC) NA Oxathiane 160 (HBC) NA 10-6 Tetrachloroethene 5 (MCL) 4x Toluene 1000 (MCk) NA Trichloroethene 3 (HBC IX 10-6 Xylene 1000 (HBCb NA Total IX 10-4

All concentrations are micrograms per liter (,ug/1). There are no preliminary remediation goals for manganese, chloride, and sulfate. ' Concentrations for noncarcinogens without ARARs are reported at levels such thatthe b calculated hazard index (HI) is below 1.0. Chemicals ofconcern with ARARs that were adjusted toreduce overall risk. ARAR = applicable orrelevant and appropriate requirement CRL = certified reporting limit HA = U.S. Environmental Protection Agency (EPA) Health Advisory HBC residential reasonable maximum exposure health-based criteria MCL maximum contaminant level NA = notapplicable, either noncarcinogenic orEPA Category C carcinogen (insufficient human evidence) OU = operable unit
20000,317.10 - FS 0309111892Table 2.8.1 -1: Screening ofProcessOptions for Groundwater (Page I of13)

Further General Response Action Technology Type Process Option Consideration Comment
NoFurtherAction No Action None Yes National Contingency Plan requires NoAction tobe carried through thedetailed analysis ofalternatives. Institutional Controls Access Restrictions Landuse/deed restrictions Yes Effective meansofreducing exposure tocontaminated water. Fencing and warning signs Yes Effective means oflimiting access tocontaminated areas. Land acquisition Yes May berequired toallow for implementation ofremedial alternatives. Alternative Water Supplies Alternative water supplies Yes Already implemented forresidents whosepotable watersupply has been affected; alternative water supply hasincluded wellscompleted in theArapahoe Formation. Monitoring Groundwater monitoring Yes Groundwater monitoring has already beenimplemented duringsite characterization and theComprehensive Monitoring Program and will continue asspecified in theFinal Technical Plan, Groundwater Element, Comprehensive Monitoring Program (R.L. Stollar&Associates, 1989). Removal Groundwater Extraction Wellpoints Yes (3) Effective technology forshallow groundwater extractionin unstratified soils. Extraction wells Yes (3) Will beimplemented in conjunction with Interim Response Action A; extracted wateris subsequently treated onsite; itis likelythat extraction wellswill beused in conjunction with any future onsite treatment technologies. Subsurfacedrains Yes (3) Effective technology forremoval ofshallow groundwater; efficient removal in areas withlow hydraulic conductivity. Water Flushing Injection/flooding- Yes (3) Potentially effective technology forenhancing groundwaterflow and infiltration contaminantremoval; water istypically extracted downgradient and subsequently treated.

20000,317.10 - FS 0309111092Table 2.8.1-1: Screening of Process Options for Groundwater (Page 2 of 13)

Further General Response Action Technology Type Process Option _ýjonsideraticon Comment Disposal Subsurface Injection Pump back to boundary Yes Effective for disposal ofextracted groundwater. Groundwater would containment systems be treated at either the Northwest Boundary Containment System or Northern Boundary Containment System. May require facility expansion. Deep well injection Yes (3) Technology utilized for contaminated water disposal; water ispumped into an appropriate geologic formation which prevents migration of the waste. Shallow aquifer recharge Yes (3) Potential technology forreplacement oftreated waterbut not effective forreduction ofmobility, toxicity or volume ofcontaminants when disposing ofcontaminated groundwater. Aboveground Discharge Discharge to publically-owned Yes Potential technology for disposal oftreated water, implementability treatment works depends onproximity to available sewer pipelines, publicly owned treatment works and collection system capacities, and pretreatment requirements; not implementable for untreated water. Surface water discharge Yes Potential technology for disposal oftreated water; notimplementable forcontaminated water due to lack ofeffectiveness in contaminant removal and associated risk to human health and the environment. Infiltration basin Yes (8) Potential technology forthe disposal of treated water and as a component ofwater flushing operations; difficult to implement fordisposal ofcontaminated water. In-Vessel Treatment: Solidification/ Solidification/stabilization No (1, 3. 5,) Rarely implemented for immobilization ofdilute liquid wastes; not Physical/Chemical Stabilization implementable for high volume low concentration waste stream due to the production oflarge volumes ofwaste which must be disposed of. Chemical Inorganics Magnetic separation No (27) Process may beutilized forremoval ofparamagnetic metals; these Treatment metals are not present above preliminary remediation goal concentrations in groundwater at the Offpost Operable Unit; not effective for removal oforganic contaminants.

20000,317.10 - FS 0309111092Table 2.8.1-1: Screening of Process Options for Groundwater (Page 3 of 13)

Further General Response Action Technology Type Process Option Consideration Comment
In-Vessel Treatment: Chemical Inorganics Chemical precipitation No (3, 5, 17, Process may beutilized for removal ofinorganic contaminants; inorPhysical/Chemical Treatment 18) ganic contaminants are not present above preliminary remediation (continued) (continued) goal concentrations in groundwater at the Offpoet Operable Unit; not effective forremoval oforganic contaminants. Complexation No (3) Process generally ineffective forremoval ofinorganic and organic contaminants; complexing agents typically increase the solubility of constituents. Solids Removal Filtration Yes (3) Effective conventional technology forremoval of suspended solids from liquid waste streams. Sedimentation Yes (3) Effective conventional technology for separation ofsuspended solids from waste stream utilizing sedimentation and gravitational techniques. Liquid Phase Separation Liquidphase separation No (4, 9 Processes utilized for separation ofnonaqueous phase liquids (e.g., oils, greases, insoluble organics) from aqueous portion ofa waste stream; not effective for dilute, organic, single-phase waste strearns. Membrane Separation Reverse osmosis No (1, 3, 17) Process may be utilized for removal ofinorganic contaminants; inorganic contaminants arenot present above preliminary remediation goal concentrations in groundwater at the Offpost Operable Unit; not effective forremoval oforganic contaminants. Ultrafiltration No (1, 6) Not effective forremoval ofmolecules with a molecular weight less than 500 atomicmass units. Dialysis No (12) Not effective forremoval ofdilute contaminant waste streams; process driven byconcentration gradients across a membrane requiring high concentrations ofindividual contaminants. Electrodialysis No (5, 17) Process may be utilized forremoval ofinorganic contaminants; inorganic contaminants are not present above preliminary remediation goal concentrations ingroundwater at the Offpost Operable Unit; not effective for removal oforganic contaminants. 20000,317.10 - FS 0309111092Table 2.8.1-1: Screening ofProcess Options for Groundwater (Page 4of 13)

Further General Response Action Technoloxy Type Process Option Consideration Comment In-Vessel Treatment: PhaseTransfer Air stripping Yes (1, 3, 5) Well-developed technology effective in the removalof volatile Physical/Chemical organics compounds from aqueous waste streams; resulting air (continued) emissions may requirefurthertreatment. Steam stripping Yes (1, 5) Well-developed technology effective in theremoval ofvolatile and selected sernivolatile organics fromaqueous waste streams;more effective than airstripping for removal oflessvolatile, higherboiling point, andmore soluble organics;can handlebroader concentration ranges than airstripping; requires steam source. Steam distillation Yes (1, 5, 12) Well-developed technology effective in removal ofvolatileand sernivolatile organics. Distillate andstill bottoma requirefurther treatment and disposal. Sorption Granular activated carbon Yes (3) Well-developed technology effective intheremoval ofmixed organics (GAC) adsorption fromwaste streams; already implemented onpost fortreatment of groundwater extracted containment systems (i.e., Northern Boundary Containment System and Nnorthwest Boundary Containment System); willbeimplemented offpostduringtreatment ofInterim RemedialAction A extracted water; carbon must be disposed ofor regenerated. Resin adsorption Yes (1) Potentially effective process forremoval oforganiccontaminants from aqueouswaste streams; effectiveness depends on specific type ofresin used; typically used asapolishing step;resinregenerants require further treatment. Ion exchange No (1, 3, 17, Process maybe utilized forremoval ofinorganic contan-dnants; inor18) ganic contaminants are not present above preliminary remedistion goalconcentrations in groundwater at theOffpost Operable Unit;not effectivefor removal oforganic contaminants.

20000,317.10 - FS 0309111092Table 2.8.1-1: Screening of Process Optionsfor Groundwater (Page 5of 13)

Further General Response Action Technology Type Process Option Consideration Comment
In-Vessel Treatment: Sorption (continued) Activated alumina No (18, 19) Process may beutilized for removal ofinorganic contaminants; Physical/Chemical inorganic contaminants are not present above preliminary remediation (continued) goal concentrations in groundwater atthe Offpost Operable Unit; not effective for removal oforganic contaminants. Chemical Organics Hydrolysis No (5) Primarily used as apretreatment process fororganic compounds that Treatment are otherwise refractory totreatment; none ofthe organicspresent in water on theOffpost Operable Unit requirehydrolysis in order to implement treatment. Solventextraction No (1, 5) Notimplementable for thefollowingreasons: largevolume ofdilute groundwater to be treated andthe corresponding large volumeof required solvent;numerous solventsmay berequired toachieve efficient extraction ofeach organic contaminant; generallyboth the raffinate and theextract requirefurthertreatment. Dechlorination No (5) Not implementable for aqueousmedia. Oxidation Chlorination No (3, 5) Implementable but islikely toform chlorinated organics such as chloroform; not effective foroxidation oflowmolecular weight chlorinated organics. Ozone oxidation Yes (5) Effective oxidizing agent formany organiccompounds; by-product analyses should beconducted; additional treatment may berequired. Hydrogenperoxide oxidation Yes (5) Utilized foroxidation oforganics; common industrial process; often requires addition ofcatalysts which include ferrous iron and ultraviolet light radiation (seeozone/hydrogen peroxide). Ultraviolet light /ozone/- Yes (6) Effective in oxidation ofhalogenated organics, including halogenated hydrogen peroxide solvents,chlorophenols, pesticides andpolychlorinated biphenyls; utilizes ultravioletlight radiation hydrogen peroxide, and/or ozone; has been demonstrated on contaminated groundwater and leachate.

20000,317.10 - FS 0309111092Table 2.8.1 -1: Screening ofProcess Optionsfor Groundwater (Page 6 of 13)

Further General Response Action Technology Type Process Option Consideration Comment
In-Vessel Treatment: Reduction Chemical reduction No (3) Not applicable; usedprimarilyfor reduction ofchromium (VI), Physical/Chemical mercury, lead;heavy metals arenot contaminants ofconcern in (continued) groundwater at the Offpost Operable Unit;not effective forremoval oforganics. Electrochemical reduction No (3) Reduction not applicable (seeChemical reduction). Radiation Ultraviolet photollysis No (5) Generally not effective forcomplete destruction oforganic compounds; by-products formed would require subsequent treatment. Electron beam/gamma Yes (13, 14) Process has not been demonstrated forfull-scale hazardous waste irradiation treatment, buthas been demonstrated atpilot/bench scale to be effective for destruction ofchloroform and otherhalogenated organics. In-Vessel Treatment: Biological Rotatingbiological contactor Yes (1, 5, 10) Potentially effective fordegradation ofsome organiccompounds in Biological Offpost Operable Unit groundwater (literature indicates thatDIMP and dieldrin arevery resistant tobiodegradation); organic substrate concentrations ingroundwater maybetoo low andrequire supplementalsubstrate addition; additional treatment may berequired due to biorefractory nature ofchloroform, and DIMP. Stabilization pond/lagoon No (7) Odor and offgas problemscreating a fugitive emission and exposure pathway problems; noteffective for halogenated organics removal; affected by temperature fluctuations. Activated sludge Yes (1, 3, Effective conventionalprocess forremoval ofmany organic com5, 10) pounds (DIMP and dieldrin are resistant tobiodegradation); heavy metals and someorganics can beharmful toorganisms; potentially effective forhalogenated organics; additionaltreatment may be required; treatment ofgenerated offgases maybe required. Powder activated carbon Yes (1, 6) Utilizes activated sludgetechnology with the addition ofpowder treatment (PACTO) activated carbon; advantagesover conventional activated sludge treatment include ability todeal with shock loadingoftoxic organics, improved removal ofchlorinated organics, and reducedoffgas production ofvolatileorganic compounds. 20000,317.10 - FS 0309111092Table 2.8.1-1: Screening of Process Optionsfor Groundwater (Page 7 of 13)

Further General Response Action Technology Type Process Option Consideration Comment
In-Vessel Treatment: Biological (continued) Sequencing batch reactor Yes (10) Potentially effective fordegradation ofsomeorganic compounds Biological detected in Offpost Operable Unit groundwater (DIMP and dieldrin (continued) are very resistanttobiodegradation); additional organicsubstrate may berequired to sustainmicrobial population; additional treatmentmay berequired due tobiorefractory nature ofchloroform, dieldrin, and DIMP. Trickling filter Yes (1, 5, 10) Potentially effective for degradation ofsome organiccompounds detected inOffpost Operable Unit water (DIMP and dieldrin are very resistant tobiodegradation); organic substrate concentrations maybe too low and require supplemental substrate addition; additional treatment mayberequired due tobiorefractory nature ofchloroform, dieldrin, and DIMP. Publicly owned treatment works No Difficult toimplement for ilhefollowingreasons: publicly owned treatment works unlikelyto accept watercontaining RMA contaminants; waterrights may requirereplacement ofgroundwater. Potentially effective fordegradation of someorganic compounds in Offpost Operable Unit groundwater; water may require supplemental organic substrate addition; not aswell demonstrated as aerobic treatmentprocesses forhazardous waste treatment; does not degrade as broad arange oforganic compounds but ismore effective fordegradationofsomehalogenated organics; additional treatment may be required. Submerged fixedfilm reactor Yes (2, 10) Potentially effective for degradation ofsomeorganic compounds detected inOffpost OperableUnit groundwater (DIMP and dieldrin are very resistant tobiodegradation); organic substrate concentrations may be toolow andrequire supplemental substrate addition; additional treatment may berequired due to biorefractory nature of chloroform, dieldrin, and DIMP.

20000,317.10 - FS 0309111092Table 2.8.1-1: Screening ofProcess Options for Groundwater (Page 8 of13)

Further General ResponseAction Technoloxy Type Process Option Consideration Comment In-Vessel Treatment: Evaporation Solarevaporation No (1, 11, 12) Not implementable due tothe largearea thatwould berequired to Thermal treat thevolumes ofcontaminated groundwater and fugitive emissionsproblems associated with the volatilizationofcontaminants. Enhanced evaporation No (1, 11, 12) Not implementabledue toarea requirements and fugitive emissions control ofvolatile contaminants. Thermal oxidation/ Rotary hearth incineration No (15) Effective but difficult to implement duetolarge volumes ofwaterto incineration be treated and thelow concentrations ofcontaminants. Multiple hearth incineration No (3) Effective butdifficult toimplement due tolarge volumesof groundwatertobe treated and thelow concentrationsof contaminants. Fluidized bed incineration No (3, 5) Effective butdifficult toimplement dueto largevolumes ofgroundwater tobe treated and thelow concentration ofcontaminants. Circulating bed combustion No (3, 5, 6) Effective modifiedfluidized bed technology butdifficult toimplement for largevolumes ofgroundwater tobe treated and the lowconcentration ofcontaminants. Rotary kiln incineration No (3, 5) Effective but difficult toimplement duetolarge volumesofgroundwater to betreated and the low concentration ofcontaminants. Submerged quench liquid No (20) Effective butdifficult toimplement due tolargevolumes ofground- incineration water tobe treated and thelow concentration ofcontaminants. High temperature fluid wall No (3, 5) Effective but difficult toimplement dueto largevolumes ofgroundreactor water tobetreated andthelow concentration ofcontaminants. Molten saltdestruction/sodium No (6) Not implementable forliquid wastes; lowwatercontent wasteis fluxing required. Plasma arc No (3, 5) Effective for contaminants present butdifficult toimplement due to largevolumes ofgroundwater and thedilute concentrations ofwaste tobetreated. 20000,317.10 - FS 0309111092Table 2.8.1-1: Screening of Process Options for Groundwater (Page 9 of 13)

Further General Response Action Technology Type Process Option Consideration Comment
In-Vessel Treatment: Thermal oxidation/ Supercritical water oxidation No (3, 5) Effective forcontaminants present but difficult toimplement for large Thermal incineration volumes ofdilute groundwater requiring treatment. (continued) (continued) Wet airoxidation No (5) Potentially effective for contaminants present but difficult to implement due to large volumes of dilute groundwater requiring treatment. Pyrolysis No (3, 5) Effective for contaminants present but difficultto implement due to the large volumes ofdilute groundwater to be treated.

In Situ Treatment Physical/Chemical Permeable treatment bed No (3) Potentially effective but notimplementable for largevolumes and areas ofcontaminated groundwater. Hydrolysis No (5) Controlling and predicting hydrolysis products which may be toxic is difficult; likely that hydrolysis would be ineffective in achieving remedial alternative objectives. Oxidation No (3) Potentially effective but difficult to implement dueto extensive area requiring treatment. Complete oxidation ofcontan-dnants wouldbe difficult to achieve and there is potential for the formation oftoxic oxidation by-products. Reduction No (3) Not applicable; used primarily for reduction ofchromium (VI), mercury, and lead to less soluble forms; not effective for treatment of organics. Water flushing Yes (3, 5) Potentially effective method forremoving contaminants; potential for (saturated zone) inadvertent mobilization ofwastes and further plume development; process increases the rate ofcontaminant removal and istypically a component ofpump and treat alternatives.

20000,317.10 - FS 0309111092Table 2.8.1-1: Screening ofProcess Optionsfor Groundwater (Page 10of 13)

Further General ResponseAction Technology Type Process Option Consideration Comment In-situ Treatment Enhanced Biological Aerobic degradation Yes(1, 3, 5,6) Potentially effective for degradation ofsomeoftheorganic (continued) contaminants detected in Offpost Operable Unit groundwater (DIMP isresistant to biological treatment); may require organic substrate and nutrient supplements. Anaerobic degradation Yes (3,5) Potentially effective fordegradation oforganics (DIMP isresistant to biodegradation); difficult toimplement duetodifficulties in maintaining ananaerobic environment in theaquifer. Containment Subsurface Barriers Slurry wall Yes (3) Effective method ofcontrolling groundwater andcontaminant migration when associated with groundwater extraction; already implemented forRMAonpost contamination (i.e., Northern Boundary Containment System andNorthwest Boundary Containment System)- Groutcurtain Yes (3) Implementable forsystem oflimited size; effectiveness depends on ability toachieve acontinuous barrier; typically groutcurtains are less effective than slurry walls. Sheet piling No (3) Difficult toachieve effective sealsatjoints insandy soils; difficult to penetrate weathered bedrock; piling canbe damaged by rocky soil; implementabilitydepends on sizeofsystem required and depthto bedrock. Bottomsealing No (3) Not implementable duetothedepth ofcontaminated groundwater, thegeologic conditions, and thebroad areal extent oftheplume; effectiveness depends on achieving complete bottom seal which is difficult toensure. Pneumatic seal No Difficult to implement over large areasofcontamination, effectiveness depends oncomplete pneumatic seal which isdifficult toachieve. Synthetic membrane cutoffwall No Difficult toimplement duetodepth to bedrock; ineffective ifnot keyed intoimpermeable bedrock.

20000,317.10 FS 0309111092Table 2.8.1-1: Screening of Process Options for Groundwater (Page 11 of 13)

Further General Response Action Technology Type Process Option Consideration Comment
Containment Subsurface Barriers Dynamic deep compaction No Difficult to implement; usually used as a process to consolidate found- (continued) (continued) ation materials; generally not effective in theprevention ofgroundwater migration. Hydraulic controls Yes (3) Effective means ofcontrolling groundwater migration by extraction and injection ofwater which isused to modify hydraulic gradients; selected as a part ofthe system forInterim Response Action A, Northwest Boundary Containment System, Northern Boundary Containment System, and frondale Containment System groundwater intercept and treatment systems; readily implementable. Subsurface dam Yes Potentially effective means of controlling contaminant migration when combined with extraction; difficult implementation due to problems of construction in unconsolidated alluvium. Freezing No Difficult to implement due to the large number ofclosely spaced wells required; effective as temporary barrier to groundwater flow. Caps/Covers Caps/covers No (3) Although caps and covers are effective, readily implementable process options, they are not applicable to groundwater remediation on the Offpost Operable Unit. Capeand covers are utilized to prevent infiltration ofprecipitation and runoff. Caps and covers may be utilized as technologies for the remediation ofgroundwater if they act toreduce plume development by significantly reducing groundwater flow orif they eliminate a source ofgroundwater contamination by preventing the contact ofinfiltrating water with soluble contaminants in the vadose zone. Neither oftheme applications applies to conditions on the Offpost Operable Unit. Infiltration from precipitation has been evaluated tobe avery minor contribution to groundwater flow on the offpost. Nopotential sources for groundwater contamination exist in the offpost soil and vadose zone, except forlow concentrations of organochlorine pesticides in surficial soil. Organochlorine pesticides present in soil are immobile and sufficiently low in concentration such that they are not believed to be a sourceof groundwater contamination. 20000,317.10 - FS 0309111092Table 2.8.1-1: Screening ofProcess Options forGroundwater (Page 12 of13)

Further General Response Action Technoloizy Type Process Option Consideration Comment Storage Surface impoundment No Difficult toimplementdue tofugitive emission problem and risk associated withvolatile contaminants. Containers No Not effective forlarge volumes ofcontaminated groundwater.

REFERENCES (1) Metcalf &Eddy, Inc., 1985, Briefing: Technologies Applicable toHazardous Waste, Preparedfor U.S. Environmental ProtectionAgency OfficeofResearch andDevelopment, Hazardous Waste Enginering Research Laboratory, Cincinnati, Ohio, May. (2) U.S. Environmental Protection Agency, 1989,Bioremediation of Hazardous Waste Sites Workshop, SpeakerSlide Copies and SupportingInformation: CERI-89-11, Office of Research and Development, Washington, D.C., Center forEnvironmental Research Information, Cincinnati, Ohio, February. (3) U.S. Environmental Protection Agency, 1985, Remedial Action at Waste Disposal Sites, Revised Edition: EPA/6256-85/006, Office ofEmergency and Remedial Response, Washington, D.C., Office of Research and Development, Hazardous WasteEngineering Research Laboratory, Cincinnati, Ohio, October. (4) TheRCRA Land Disposal Restrictions - A Guide toCompliance, 1988Edition, McCoy andAssociates, Inc. (5) U.S. Environmental Protection Agency, 1987,A Compendium ofTechnologies Used in theTreatment ofHazardous Wastes: EPA/625/8-87/014, Centerfor Environmental Research Information, Cincinnati, Ohio, September. (6) U.S. Environmental Protection Agency, 1989, The Superfund Innovative Technology Evaluation Program: Technology Profiles: EPA/540/5-89/013, Office of Solid Waste and Emergency Response, Washington, D.C., Office of Research and Development, Washington, D.C., November. (7) Grady, C.R.L., Jr., and Lim, H.C., 1980,Biological Wastewater Treatment Theory and Applications, Marcel Decker, Inc., NewYork, NewYork. (8) Metcalf & EddyInc., Ehobanolous, G., 1979, Wastewater Engineering Treatment, Disposal, andResuse, McGraw Hill, New York, New York. (9) Echenfelder, W., 1989, Industrial Water Pollution Control, McGraw Hill,New York, New York. (10) Gordon, L., Hartley, W.R., 1989, Health Advisory on Diisopropyl Methylphosphate (DIMP), U.S. Environmental ProtectionAgency, Washington, D.C., January. (11) Ausum, S.R., 1985, Wastewater Treatment Plants Planning, Designing, and Operation, CBS College Publishing, NewYork, New York. 20000,317.10 - FS 0309111092Table 2.8.1-1: Screening of Process Optionsfor Groundwater (Page 13of 13)

REFERENCES (Continued) (12) Kernmer, F.N., McCallion, J., 1979, The NALCO WaterHandbook, McGraw Hill, New York, New York. (13) Lichtenstrin, E.P., Schultz, K.R., and Fuhreman, T.W., Long-Term EffectsofCarbon in Reducing Uptake ofInsecticidal Soil Residues by Crops, Journal ofEconomic Entomology, June, 1971. (14) Morse, D., Science/Technology, Electron Beam Could Treat Wastewater, Chemical & Engineering News, October, 1989. (15) Personal communication, Cooper, W.J., Director and Associate Professor, University ofMiami. (16) McCoy &Associates, 1983,Guide to IncineratorManufacturers, The Hazardous Waste Consultant, Vol. I, No. 2, October. (17) Forest, S., D., and Aly O.M., 1983, Chemistry ofWater Treatment, Butterworth Publishers, Woburn,MA. (18) Bennefield, L.D.,Judkins, J.F.,Weand, B.L., 1982, Process chemistry for Water andWastewater Treatment, Prentice-Hall, Inc., Englewood Cliffs, N.J. (19) Patterson,J.W., 1985, Industrial WastewaterTreatment Technology, 2 edition, Butterworth Publishers, Stoneham, MA. (20) Brunner, C.R; 1987, Chemical Engineering; Vol. 94, No. 14, October 12.

20000,317.10 - FS 0309111092Table 2.10.1-1: Selection ofRepresentative Process Options for Groundwater (Page Iof2)
Process Options Retained From Second Level Selected Representative Technology Type - ofScreeninj[ Process Option Criteriafor Selection No FurtherAction None No FurtherAction Retained asrequired by the National Contingency Plan. Access Restrictions Land Use/Deed Restrictions Land Use/Deed Restrictions Effective inminimizing human contact withgroundwater and restrictinguse ofgroundwater forcrop irrigation and wateringoffivestock. Fencing and Warning Signs Fencing and Warning Signs Effective in reducing human exposure tocontaminated media. LandAcquisition Land Acquisition May berequired to implement remedial action on privately owned land. Alternative WaterSupplies Alternative Water Supplies Alternative Water Supplies Effective in preventinghuman contact withgroundwater for residents who relyon wells fordomesticuse. Monitoring Groundwater Monitoring Groundwater Monitoring Effective intracking plumedevelopment, natural attenuation, andrernediation effects. Groundwater Extraction Extraction Wells Extraction Wells Demonstrated effective attheboundary containment systems for removalof groundwater; readily implementable atdepths which make for difficult installation ofsubsurface drains. Subsurface Drains Water Flushing Injection Injection Demonstrated effective atthe boundary containment systems; minimizes losses toevaporation in summermonths, nodifficulties associated with freezing in winter months. Subsurface Injection Pump BacktoBoundary Pump Back to Boundary Injection and treatmentfacilities already constructed and Containment System Containment System operational; cost-effective disposal andtreatment optionfor limited quantities ofgroundwater dependent onfacility (North Boundary Containment System,Northwest Boundary Containment System) capacity. Shallow Aquifer Injection ShallowAquifer Injection Shallow aquifer injection demonstrated effective atthe boundary containment systems, minimizes losses toevaporation,allowsfor control ofgroundwater gradient; Shallow aquiferinjection includes bothinjection wells and trenches.

20000,317.10 - FS 0529111092a

Table 2.10.1-1: Selection ofRepresentative Process Options for Groundwater (Page 2 of2)

Process Options Retained From Second Level Selected Representative Technology Type ofScreening Process Option Criteriafor Selection Chemical Inorganics Treatment Chemical Precipitation Chemical Precipitation Conventional process option, readilyimplementable, welldemonstrated, effective for removal of inorganics. Phase Transfer Air Stripping AirStripping Readily implemented; reliable and effectiveprocess optionfor removingvolatile organic compounds, easily operated. Sorption Granular Activated Carbon Granular Activated Carbon Demonstrated effective forremoval oforganics atthe boun- Adsorption Adsorption dary containment systems. Oxidation Ultraviolet Ultraviolet Light/Ozone/ Hydrogen Effectivefor destruction ofabroad range oforganic com- Light/Ozone/Hydrogen Peroxide Peroxide pounds. InSitu Physical/Chemical WaterFlushing (Saturated Zone) Water Flushing (Saturated Zone) Potentially effective forenhancing removal ofcontaminants as acomponent ofpump and treat alternatives. SubsurfaceBarriers Slurry Wall Slurry Wall Demonstrated effective atthe boundary containment systems. Hydraulic Controls Hydraulic Controls Demonstrated effective atthe boundary containment systems.

20000,317.10 - FS 0529111092RMA1 1170

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EXPLANATION 0 Welllocation Areaswheregroundwaterplumesofselectedchemicals tetrachloroethene, trichloroethene,dibromochloropropane, chloroform, 0 )o 3000 dieldrin (statestd.05),DIMP(>600ppb),exceedgroundwaterPRGs
Sea* InF" 

## Prepared for: Figure 2,6-1 Program Managerfor Rocky MountainArsenal AREAS OFEXCEEDANCES OF GROUNDWATER PRGsIN THEOFFPOST Commerce City,Colorado 

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### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

NoFurtherAction

-- fNoFurtýherActiýonýýýýýý Land Use/Deed Restrictions Fencing and Access Restrictions Warning Signs

Alternative Wate Alternative Water Institutional C*,=ntrols Supplies Supplies
Groundwater Monitoring Monitoring

Well Points -7 1 Groundwate7r7E,7t,7acti,ný]-

Removal

Water Flushing Injection Flooding/infiftration

Pump Back To Boundary Containment System Subsurface Injection Deep Well Injection
ShallowAquff7-r ln7ject7ion] Disposal Discharge To POTW Aboveground Surface Water Discharge Discharge Infiltration 13--In7]



## Prepared for: Figure 2.8-1a Program Managerfor Rocky MountainArsenal GROUNDWATER PROCESSOPTIONS Commerce City,ColoradoRMA1 1034B.1 

### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

Solidification/ Solidification/ Stabilization Stabilization - I
magnetic separation _____[-Chemical Inorganics Treatment

Filtration Solids Removal Sedimentation
Liquid Phase
_ F-Liquide Phase ]_Separation Separation

Reverse Osmosis
Ultrafiltration In-Vessel Treatme.ýntv embrane Sep-Tration Physical/Chemical Dialysis Electrodialysis

Air Stripping ýPhasee Transfer Steam Stripping
Steam Distillation

F_1__AC Adsorption

Resin Adsorption Sorption
L__FActIvatd Alumina Adsorptio Hydrolysis

__ 71 Chemical Organics Treatment
d Dechlorination


## Preparedfor: Figure 2.8-1b Program Managerfor RockyMountain Arsenal GROUNDWATER PROCESS OPTIONS Commerce City,ColoradoRMA1 1034C.1 

### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

Chlorination Ozone Oxidation Oxidation Hydrogon Peroxide Oxidation

In-Vessel Treatment: Reduction -Chemical Reduction Electra,Chemical Physical/Chemical (cont.) _o Reduction

Radiation UV Photolysi*77771 Electron Seem/ Gamma Irradiation
Rotating Bioiý`ýý Contactor Stabilization Pond/ Lagoon

___I_Po_-d_. r_ed_A_.t_1-a_te_d__ý Carbon Treatment (PACTS) In-Vessel Treatment: Biological Sequencing Batch Biological Reactor Trickling Filter

Anaerobic Digester Submerged Fixed Film Reactc

Evaporation Solar Evaporation Enhanced Evaporation

In-Vessel Treatment: Rotary Hearth Thermal Incineration _M_ul-ti p -19-H-. _.r

-thIncineration Themal Oxid tion/ Fluidized Bed Incineration Incineration/ Circulating Bed Combustion Rotary Kiln Incineration 

### Prepared for: Figure 2.8-1c Program Manager for Rocky Mountain Arsenal GROUNDWATER PROCESS OPTIONS Commerce City,ColoradoRMA1 1034D.1 

### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION Submerged auench LiquidIncineration High Temperature FluidWall Reactor Molten Salt Destruction/ Sodium FIL In-Vessel Treatment: Incineration (6-1,; Thermal (Cont) Supercritica Oxidation WotAir oxidation Pyrolysis

Permeable Treatment Bed Hydrolysis Physical/Chemical Oxidation Reduction Water Flushing In-Situ Treatment (Saturated Zone)

Aerobic Degradation Enhanced Biological Anaerobic Degradation
Slurry Wall Grout Curtain Sheet Pllin9777ý:] Bottom Sea7,1-97771 Pneumatic Containment Subsurface Barriers Synthetic M cutoffWall Dynamic Deep Compaction__ Hydraulic Controls Subsurlaceý-ým Freezing 

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Prepared for: Figure 2.8-1d Program Manager for ROCKY Mountain Arsenal GROUNDWATER PROCESS OPTIONS Commerce City,ColoradoRMA1 1034E 

### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

Containment (cont) Surface Imp-7u-dm Storage Containers



## Prepared for: Figure 2.8-1e Program Managerfor Rocky MountainArsenal GROUNDWATER PROCESSOPTIONS Commerce City,ColoradoRMA1 103M 

### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

No Further Action No FurtherAction None
Land Use/Deed Restrictions r-Fencing and Access Restrictions IWarning Signs

Alternative Vifililliti Alternative Water Institutional Controls Supplies ISupplies Monitoring -fGýr-undwater llwlionitorlnýg

Well Points Groundwater Extraction Surface Drains

Removal Injection Water Flushing Flooding/Inf117trstioýný:]
Pump Back toBoundary Containment System Subsurface Injection ShallowAquifer Disposal Injection Discha goToPOTW Aboveground Dischargrdý L-J Infiltration Basin

EXPLANATION TechnologyType/Process Option Eliminated During Universal Screening 

### Prepared for: Figure 2.8.1-1a Program Manager for Rocky Mountain Arsenal RESULTS OF UNIVERSAL SCREENING OF GROUNDWATER PROCESS OPTIONS CommerceCity,ColoradoRMAI 10388.1 

### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

..................
. ...... . . S NO

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Filtration Solids Removal Sedimentation

In-Vessel Tri i i i n Physical/Chen.

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steam Distil7lation7]

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Sorption Resin Adsor7pt7ion77]

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. . .......... ... EXPLANATION Technology Type/Process Option Eliminated During Universal Screening 

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### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION 

## yw
ozone Oxidation Oxidation ir-Hydrogen Peroxide Oxidation

IV---Vessel Treatment: I

Physical Chemical (co .. .. ýc 6ft V-M



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RotatingB1 Contactor =*ý"= NO Activated S17udg-77] PowderedActivated CarbonTreatment (PACTO)l

Sequencing Batch In-VesselTreatment: 

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. .. . .... EXPLANATION TechnologyType/Process Option Eliminated During Universal Screening 

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### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

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Water Flushing In-Situ Treatment (Saturated Zone)

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EXPLANATION Technology Type/Pr9cess Option Eliminated During Universal Screening 

### Prepared for: Figure 2.8.1-1d Program Managerfor Rocky MountainArsenal RESULTS OFUNIVERSAL SCREENING OF GROUNDWATER PROCESS OPTIONS Commerce City,Coloradoa RMA1 103SE 

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EXPLANATION Technology Type/Process Option Eliminated During Universal Screening 

### Prepared for: Figure 2.8.1-le Program Manager for Rocky Mountain Arsenal RESULTS OFUNIVERSAL SCREENING OF GROUNDWATER PROCESS OPTIONS Commerce City,ColoradoRMAI 1040A.1 

### RESPONSE ACTION TECHNOLOGYTYPE PROCESS OPTION No Further Action

Land Use/Deed Restrictions Access Restrictions Fencing and Warning Signs

Institutional Controls Alternative Water Alternative Water Supplies Supplies Groundwater Monit Monitoring

Kiý W

................... Groundwater Extraction Extraction Wells
Subsurface Drains Remo al Injection Water Flushing W-0
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.......... * ......

EXPLANATION Technology Type/Process Option Eliminated During the Second Level Screening 

### Prepared for: Figure 2.9-1a Program Manager for Rocky Mountain Arsenal RESULTS OFTHE SECOND LEVEL SCREENING OFGROUNDWATER Commerce City,Colorado PROCESS OPTIONSRMA1 1040B.1 

### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

Air Stripping PhaseTransfer

In-vessel Treatment: Sorption GAC Adsorption Physical/Chemical (cond

Oxidation



# . . .

............ -1 1 ........ . . ..

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

Water Flushing Physical/Chemical (SaturatedZI one) In-Situ Treatment

EXPLANATION Techno' I e/process Option Elimin.t%gyDuyrP.ng the Second Level Screening 

## Prepared for: Figure 2.9-1b Program Managerfor RESULTS OFTHESECOND LEVEL Rocky MountainArsenal SCREENING OFGROUNDWATER Commerce City,Colorado PROCESS OPTIONSRMA1 1040C.1 

### RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

SlurryWall

t I * oe'.

* oI'me., I., Containment -f Sub*urff7acý7e7B-rr1-7r-7jHydraulic Controls

EXPLANATION Technology Type/Process Option Eliminated During the Second Level Screening 

### Prepared for: Figure 2.9-1c Program Manager for RESULTS OFTHE SECOND LEVEL Rocky Mountain Arsenal SCREENING OF GROUNDWATER CommerceCity,Colorado PROCESS OPTIONSRMA1 1063A.1 REPRESENTATIVE RESPONSE ACTION TECHNOLOGYTYPE PROCESSOPTION PROCESS OPTION

No FurtherA ............... ,_FNo_ne "`

Land Use/Deed LandUse/Deed Restrictions Restrictions Fencing and Fencing and Access Res rl Warning Slijilirilill Warning Signs -4 ýýnd Agul-I L-ndAq-i7,,1tl-_n InstitutionalEntrols

-
__ __ ! I'll

_ Eitpo-rnatIve % Alternative Water -Alternative Alternative .. . .............. Su Plies Supplies Supplies Supplies __[Groundwater- Groundwater -F ; ,onItorInq ............................................. Monitoring Monitoring
Extraction We Is Groundwater Extraction -Týýxtra-tlon rface Subsurface D 8 Removal

Pump Backto Boundary Pump Back to Bounder Disposal ... ......... Subsurface injection Containment System ContainmentSystem

................. ................... ShallowAq%11 :

1 ShallowAq Injection Injection

PhaseTraniiiiI'lilit , AirStrippirill;ii ................

In-VesselTreatment: ýPhysical/Chemical

Idation UV/Ozone/ UV/Ozone/ -Fox- - """"" ......Hydrogen P111.1i iý,

ill ill!

Iililill! Hydrogen Peroxide

In-SituTreat i'l aI'

A VII'll'i I :illit

I WaterFlushirill[l Water Flushing

....................... D
__ý (SaturatedZoiil Ill (SaturatedZone)



## Prepared for: Figure 2.10.1-1a Program Managerfor SELECTEDREPRESENTATIVE PROCESS Rocky MountainArsenal OPTIONS FOR DEVELOPMENT OF CommerceCity,Colorado GROUNDWATER REMEDIALALTERNATIVESRMAI 1063B.1 REPRESENTATIVE RESPONSE ACTION TECHNOLOGYTYPE PROCESS OPTION PROCESS OPTION 

# slurrywall -sýlu-rrywýa,,ýý
Containmen, ......

-- fHydr-ulic C ydraulle controls



## Prepared for: Figure 2.10.1-1b Program Manager for SELECTEDREPRESENTATIVE PROCESS RockyMountainArsenal OPTIONS FORDEVELOPMENT OF CommerceCity,Colorado GROUNDWATER REMEDIALALTERNATIVES