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 Number DAAA15-88-0021

Task RIFS1 (Delivery Order 0001)

PREPARED BY

Harding Lawson Associates

PREPARED FOR

PROGRAM MANAGER FOR ROCKY MOUNTAIN ARSENAL

THIS DOCUMENT IS INTENDED TO COMPLY WITH THE NATIONAL

ENVIRONMENTAL POLICY ACT OF 1969.

THE INFORMATION AND CONCLUSIONS PRESENTED IN THIS REPORT REPRESENT

THE OFFICIAL POSITION OF THE DEPARTMENT OF THE ARMY UNLESS EXPRESSLY

MbDIFIED BY A SUBSEQUENT DOCUMENT. THIS REPORT CONSTITUTES THE

RELEVANT PORTION OF THE ADMINISTRATION RECORD FOR THIS CERCLA

OPERABLE UNIT.

M9200038
TABLE OF CONTENTS

PM

VOLUME I - INTRODUCTION

LIST OF TA BLES ..................................................... xix

LIST OF FIG U RES .................................................... xxv

PR EFA C E ........................................................... P-1

EXECUTIVE SUM M ARY .............................................. ES- I

IN TR OD U CTIO N .....................................................

G LO SSA R Y .......................................................... G -1

VOLUME II - ENDANGERMENT ASSESSMENT

PR E F A C E ........................................................... 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 G roundwater ......................................... 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 SU M M A RY ................................................ 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 of Chemicals of Concern ..... 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 R esults ....................................... 11 - 2-7

2.1.2 Offpost Environmental Fate of Chemicals of Concern ........... 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

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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 Chem icals ................................. II - 2-26

2.1.2.7 Miscellaneous Compounds ......................... II - 2-30

2.1.3 U ncertainties ......................................... 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 of Offpost 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 R esults .............................. 11- 2-41

2.21.".2 Commercial/Industrial Land Uses ................... Il - 2-42

2.213 Qualitative Assessment of the Likelihood of Occurence

of the Selection of Future Land Use for the Offpost

Endangerment Assessment/Feasibility Study ........... II - 2-44

2.2.2.4 W ater U se ..................................... II - 2-45

2.2.2.4.1 Existing Groundwater Use ............... II - 2-45

2.2.2.4.2 Projected Future Use of Groundwater ....... 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 G roundwater ................................... II - 2-51

2.3.1.2 Surface Water and Sediment ....................... II - 2-54

2.3.1.3 A tm ospheric ................................... 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 U ncertainties ......................................... 11- 2-64

2.4 QUANTIFICATION OF EXPOSURE ............................. 11 -2-64

2.4.1 Identification of Zones 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

D ata ......................................... 11 - 2-72

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2.4.2.2 Model Used to Estimate 30-Year Groundwater Exposure

Point Concentration ............................. II - 2-73

2.4.2.3 Models Used to Estimate Concentrations in Agricultural

Products . '6 'i ..... *-'*-*-*-**- *** - ** 11-2-74

2.4.2.3.1 h cken Eggs ......................... 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 of Nonchemical-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

M onitoring Data ................................ 11- 2-84

2.4.2.6 R esults ....................................... Il- 2-86

2.4.3 Estimation of Chemical Intakes ............................ 11-2-90

2.4.3.1 Chemical- specific Parameters ...................... 11-2-94

2.4.3.2 Exposure Factors ................................ Il- 2-95

2.4.3.3 R esults ....................................... Il - 2-98

2.4.4 Estimation of Chemical Intakes for Commercial/Industrial

Scenario ............ 11-2-99

2.4.4.1 Estimation of Cheýi*c a'l' int a*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 of Input 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 of Results .................... 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

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3.2.1 W eight of Evidence ...................................... 11- 3-5

3.2.2 Slope Factor .......................................... II - 3-6

3.3 NONHUMAN RECEPTOR TOXICITY REFERENCE VALUES ........ Il - 3-7

3.3.1 V egetation ........................................... II - 3-8

3.3.2 Aquatic Organism s ..................................... II - 3-8

3.3.3 Terrestrial Organism s ................................... II - 3-9

3.33.1 Derivation of a 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 or Endangered 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 Health Risk at Most 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

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4.4 UNCERTAINTIES IN THE HUMAN HEALTH ASSESSMENT ......... 111-4-18

5.0 ECOLOGICAL ASSESSMENT ....................................... III - 5-1

5.1 SITE CHARACTERIZATION ................................... III - 5-1

5.1.1 Study Area Definition ................................... III - 5-1

5.1.1.1 Terrestrial System s .............................. III - 5-2

5.1.1.2 Aquatic System s ................................ 111- 5-3

5.1.2 Ecological Characterization of the Offpost Operable Unit ........ III - 5-4

5.1.3 Contamination Pertaining to Offpost Biota ................... III - 5-5

5.1.4 Selection of Chemicals of Concern for Biota .................. III - 5-6

5.2 EXPOSURE ASSESSMENT ..................................... III - 5-7

5.2.1 Potential Biological Receptors and Sensitive Subpopulations ...... III - 5-7

5.2.1.1 Terrestrial Receptors ............................. 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 A quatic ....................................... 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 Direct Exposure to Chemicals of Concern .................... III - 5-21

5.2.6.1 Surface-Water Ingestion Pathway ................... III - 5-21

5.2.6.2 Direct Contact with Surface Water or Sediment ......... III - 5-23

5.2.6.3 Soil Ingestion .................................. III - 5-23

5.2.6.4 Dietary Ingestion for Wildlife ...................... 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 Site Characterization ............................. III - 5-31

5.3.5.2 Exposure Assessment ............................ III - 5-32

5.3.5.3 Risk Characterization ............................ III - 5-34

5.4 SU M M A RY ................................................ III - 5-34

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6.0 CONCLU SIONS .................................................. 111-6-1

7.0 REFEREN CES ................................................... III - 7-1

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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 OF POSSIBLE OCCURRENCE IN RMA OFFPOST AREA

H2 - BIOACCUMULATION FACTORS, BIOMAGNIFICATION FACTORS, AND

PREDICTED TISSUE CONCENTRATIONS

- TERRESTRIAL FOOD WEB

- AQUATIC FOOD WEB

H3 - EXPOSURE POINT CONCENTRATIONS OF CHEMICALS IN SURFACE

WATER AND PREDICTED CHEMICAL INTAKE FOR AVIAN SPECIES

H4 - HAZARD QUOTIENT SUMMARY TABLES FOR CATTLE

H5 - MAXIMUM ALLOWABLE TISSUE CONCENTRATION VALUES

H6 - SPATIAL WEIGHING ADJUSTMENT FACTORS

H7 - ONPOST HHRC SOFTWARE BLUE VERSION 1.0 PREPARED FOR THE

PROGRAM MANAGER RMA EBASCO SERVICES, INC., MARCH 1992

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OLUME V - FEASIBILITY STUDY

PR EFA C E ........................................................... 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 STEP IV - SELECTION OF THE PREFERRED SITEWIDE

ALTERNATIVE ............................................. V - 1-3

2.0 DEVELOPMENT OF REMEDIAL ACTION OBJECTIVES AND SCREENING

OF TECHNOLOGIES .............................................. V - 2-1

2.1 OVERVIEW OF REMEDIAL ACTION OBJECTIVES DEVELOPMENT .. V - 2-1

2.2 NATIONAL CONTINGENCY PLAN AND ACCEPTABLE RISK RANGE

CONSIDERATIONS .......................................... V - 2-2

2.2.1 Comparison of Cumulative Risk With the Acceptable Risk Range . . V - 2-2

2.2.2 Identification of Media Requiring Remedial Action Objectives .... V - 2-4

2.2.3 Site-specific Factors Considered for Groundwater

Remedial Action Objectives Development .................... V - 2-6

2.3 DEVELOPMENT OF GROUNDWATER REMEDIAL ACTION

OBJECTIVES ............................................... V - 2-6

2.3.1 Development of Remedial Action Objectives, Step 1: Identification

of Chemicals of Concern ......................... * * ' * * ' ' ' V - 2-7

2.3.2 Development of Groundwater Remedial Action Objectives Step 2:

Identification of Potential 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 of Future Land Use on the Development of

Preliminary Remediation Goals ........................... V - 2-11

2.5.2 National Contingency Plan and Point of Departure Considerations

for Development of Preliminary Remediation Goals ............ V - 2-12

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2.5.3 Types of Groundwater Preliminary Remediation Goals .......... V - 2-15

2.5.3.1 Identification of Applicable or

Relevant and Appropriate Requirements ............. V - 2-15

2.5.3.1.1 Chemical- specific Applicable or

Relevant and Appropriate Requirements .... V - 2-17

2.5.3.1.2 Location -specific Applicable or Relevant

and Appropriate Requirements ............ V - 2-18

2.5.3.1.3 Action-specific Applicable or

Relevant and Appropriate Requirements .... V - 2-18

2.5.3.2 Health-based Criteria ............................ V - 2-18

2.5.3.3 Background Concentrations ........................ V - 2-20

2.5.3.4 Ecological Criteria .............................. V - 2-20

2.5.4 Development and Identification of Preliminary 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 of Groundwater 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 A ction ............................................ V - 2-23

2.7.2 Institutional Controls ................................... V - 2-23

2.7.3 Containm ent .......................................... V - 2-23

2.7.4 Rem oval ............................................. V - 2-24

2.7.5 Treatm ent ............................................ 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 of Selected 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 M onitoring ........................... V - 2-29

2.8.4 Groundwater Process Options ............................. V - 2-30

2.8.4.1 Rem oval ...................................... 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 of Groundwater ................. V - 2-37

2.8.4.3.1 Solids Removal ........................ V - 2-37

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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 SELECTION OF REPRESENTATIVE PROCESS OPTIONS ............ V - 2-50

2.10.1 Representative Process Options for Groundwater Remediation .... V - 2-51

VOLUME VI - FEASIBILITY STUDY

3.0 DEVELOPMENT OF REMEDIAL ALTERNATIVES ..................... VI - 3-1

3.1 FEASIBILITY STUDY OVERVIEW .............................. VI - 3-1

3.1.1 U.S. Environmental Protection Agency Guidance for

Alternatives Development and Evaluation .................... VI - 3-1

3.2 ALTERNATIVES IDENTIFICATION ............................. VI - 3-3

3.2.1 Approach ............... *- ****- - . : .............. VI - 3-3

3.2.1.1 Groundwater Model Input Into Alternatives

Development ................................... VI - 3-4

3.2.1.1.1 Chemicals of Concern .................. VI - 3-4

3.2.1.1.2 Use of the Model in Alternatives

Development .......................... VI - 3-5

3.2.1.2 Groundwater Alternative Types .................... VI - 3-9

3.3 LAND OWNERSHIP IMPLICATIONS FOR IMPLEMENTING REMEDIAL

ALTERNATIVES ............................................ VI - 3-10

3.4 COMMONALITIES OF ALTERNATIVES ......................... VI - 3-10

3.4.1 Commonalities of Groundwater Remedial Alternatives .......... VI - 3-11

3.4.1.1 Groundwater Alternatives Institutional Controls ........ VI - 3-11

3.4.1.1.1 Provision of an 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

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3.4.1.3 Continued Operation of the 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 of Groundwater Alternatives: North

Plum e G roup ......................................... 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 of the North

Boundary Containment System With Improvements as

Necessary ..................................... VI - 3-14

3.5.1.3 Alternative No. N-3: Land Acquisition and Use

Restrictions .................................... V I - 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

A ction A ..................................... V I - 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 of Alternatives Identified for the North Plume

G roup .......................... ............. V I - 3-21

3.5.2 Identification of Groundwater Alternatives: Northwest Plume

G roup ......... ..................................... V I - 3-22

3.5.2.1 Alternative NW-1: No Action ...................... VI - 3-22

3.5.2.2 Alternative NW-2: Continued Operation of the Northwest

Boundary Containment System ..................... VI - 3-22

3.5.2.3 Alternative No. NW-3: Land Acquisition With Use

Restrictions .................................... VI - 3-23

3.5.2.4 Alternative No. NW-4: Northwest Plume Group

Extraction/Recharge System ....................... VI - 3-24

3.5.2.5 Summary of Alternatives 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 Cost Evaluation ........................................ VI - 4-3

4.2 SCREENING OF ALTERNATIVES .............................. VI - 4-4

4.2.1 Screening of Alternatives - 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 ................................ V I - 4-6

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Page

4.2.1.2 Alternative No. N-2: Continued Operation of the North

Boundary Containment System With Improvements as

N ecessary ..................................... V I - 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 ............ ::*.'*****'*'' * * * *** , V I - 4-8

4.2.1.3 Alternative No. N-3: Land Acquisition and Deed

R estrictions .................................... V I - 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 ................................ V I - 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 ................................ V I - 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 ....... ........................ V I - 4-15

4.2.1.6 Alternative No. N-6: Expansion 2 to Interim

Response Action A .............................. VI - 4-15

4.2.1.6.1 Effectiveness .......................... VI - 4-15

4.2.1.6.2 Implementability ....................... VI - 4-16

4.2.1.6.3 Cost ................................ VI - 4-17

4.2.1.7 Alternative Screening Summary and Recommendation .... VI - 4-17

4.2.2 Screening of Groundwater Alternatives - Northwest Plume

Group .................. VI - 4-18

4.2.2.1 Alternative No. NW-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 of the

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 .................................... V I - 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

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Page

5.0 DETAILED ANALYSIS OF ALTERNATIVES ........................... VI - 5-1

5.1 CR ITERIA ................................................. VI - 5-2

5.1.1 Overall Protection of Human 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 of Toxicity, Mobility, or Volume .................. VI - 5-3

5.1.5 Short-term Effectiveness ................................ VI - 5-3

5.1.6 Im plem entability ....................................... VI - 5-4

5.1.7 C ost ................................................ V I - 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 of the North

Boundary Containment System With Improvements as Necessary ... VI - 5-8

5.3.3 Alternative No. N-4: Interim Response Action A .............. VI - 5-8

5.3.4 Alternative No. N-5: Expansion I to Interim Response

A ction A ............................................ V I - 5-10

5.3.5 Alternative No. NW-1: No Action ........................ VI - 5-11

5.3.6 Alternative No. NW-2: Continued Operation of the 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 of Human Health and the Environment ...... VI - 5-12

5.4.1.1 Alternative No. N-1: No Action ................... VI - 5-12

5.4.1.2 Alternative No. N-2: Continued Operation of

the North Boundary Containment System With

Improvements as Necessary ....................... VI - 5-13

5.4.1.3 Alternative No. N-4: Interim Response Action A ...... VI - 5-14

5.4.1.4 Alternative No. N-5: Expansion I to Interim

Response Action A ............................. VI - 5-15

5.4.1.5 Alternative No. NW- 1: No Action ................. VI - 5-15

5.4.1.6 Alternative No. NW-2: Continued Operation of the

Northwest Boundary Containment System With

Improvements as Necessary ....................... VI - 5-16

5.4.2 Compliance With Applicable or Relevant 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

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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 or Relevant

and Appropriate Requirements ............ VI - 5-17

5.4.2.2 Alternative No. N-2: Continued Operation of the North

Boundary Containment System With Improvements

as Necessary ................................... VI - 5-17

5.4.2.2.1 Chem ical- 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 -spec if 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 or Relevant

and Appropriate Requirements ............ VI - 5-19

5.4.2.5 Alternative No. NW-1: No Action ................. VI - 5-19

5.4.2.5.1 Chemical -specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-19

5.4.2.5.2 Action-specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-19

5.4.2.5.3 Location -specific Applicable or Relevant

and Appropriate Requirements .... , , , , * , , * VI - 5-19

5.4.2.6 Alternative No. NW-2: Continued Operation of the

Northwest Boundary Containment System With

Improvements as Necessary ........................ VI - 5-19

5.4.2.6.1 Chemical -specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-19

5.4.2.6.2 Action-specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-20

5.4.2.6.3 Location-specific Applicable 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 of North

Boundary Containment System With Improvements as

Necessary ..................................... VI - 5-20

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5.4.3.3 Alternative No. N-4: Interim Response Action A ....... VI - 5-21

5.4.3.4 Alternative No. N-5: Expansion I to Interim

Response Action A .............................. VI - 5-21

5.4.3.5 Alternative No. NW-1: No Action ................. VI - 5-22

5.4.3.6 Alternative No. NW-2: Continued Operation of the

Northwest Boundary Containment System With

Improvements as Necessary ........................ VI - 5-22

5.4.4 Reduction of Toxicity, Mobility, or Volume .................. 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 of the

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 of Community and Workers ...... VI - 5-26

5.4.5.1.2 Adverse Environmental Impacts ........... VI - 5-26

5.4.5.1.3 Implementation Period .................. VI - 5-26

5.4.5.2 Alternative No. N-2: Continued Operation of

North Boundary Containment System ................ VI - 5-26

5.4.5.2.1 Protection of Community 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 of Community 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 I to Interim

Response Actoin A ........... VI - 5-27

5.4.5.4.1 Protection of Community 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 of Community and Workers ...... VI- 5-28

5.4.5.5.2 Adverse Environmental Impacts ........... VI- 5-28

5.4.5.5.3 Implementation Period .................. VI - 5-28

5.4.5.6 Alternative No. NW-2: Continued Operation of

Northwest Boundary Containment System With

Improvements as Necessary ........................ VI - 5-28

5.4.5.6.1 Protection of Community and Workers ...... VI - 5-28

5.4.5.6.2 Adverse Environmental Impacts ........... VI - 5-29

5.4.5.6.3 Implementation Period .................. VI - 5-29

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Page

5.4.6 Im plem entability ................ : ...................... 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 of North

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 of the

Northwest Boundary Containment System With

Improvements as Necessary ........................ VI - 5-31

5.4.7 C ost ................................................ V I - 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 of the North

Boundary Containment System With Improvements as

N ecessary ..................................... V I - 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 of the

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 of Human Health and the

Environment ................................... VI - 5-33

5.5.1.2 Compliance With Applicable or Relevant and

Appropriate Requirements ........................ VI - 5-34

5.5.1.3 Long-term Effectiveness and Permanence ............. VI - 5-34

5.5.1.4 Reduction in Toxicity, Mobility, and Volume .......... VI - 5-34

5.5.1.5 Short-term Effectiveness .......................... VI - 5-35

5.5.1.6 Implementability ................................ VI - 5-35

5.5.1.7 Cost ................... VI - 5-36

5.5.2 Comparison of Alternatives - Northwest Plume Group .......... VI - 5-36

5.5.2.1 Overall Protection of Human Health and the

Environm ent ................................... 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 ......................................... V I - 5-38

5.5.3 Ranking of Alternatives - North Plume Group and

Northwest Plume Group ................................. VI - 5-39

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6.0 SELECTION OF THE PREFERRED SITEWIDE ALTERNATIVE ........... VI - 6-1

6.1 IDENTIFICATION OF THE PREFERRED SITEWIDE ALTERNATIVE .. VI - 6-1

6.1.1 Preferred Sitewide Alternative Description ........ .**''***** VI - 6-3

6.1.1.1 Alternative No. N-4: Interim Response Action A ....... VI - 6-3

6.1.1.2 Alternative No. NW-2: Continued Operation of the

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 of CERCLA in

Section 121 ........................................... V I - 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 of Permanent Solutions to the Maximum Extent

Practicable .................................... V I - 6-8

6.2.3 Consistency With the National Contingency Plan ............... VI - 6-8

6.3 SUM M ARY ................................................ VI - 6-9

7.0 REFERENCES ................................................... VI - 7-1

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VOLUME VII - FEASIBILITY STUDY

LIST OF APPENDIXES

A APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARs)

ANALYSIS

B WETLAND DELINEATION AND ASSESSMENT

C DERIVATION OF HEALTH-BASED CRITERIA AND ECOLOGICAL CRITERIA

D SECOND LEVEL PROCESS OPTION SCREENING

E GROUNDWATER MODELING RESULTS SUMMARY

F COST ESTIMATES

VOLUME VIII - RESPONSES TO COMMENTS

U.S. ENVIRONMENTAL PROTECTION AGENCY

U.S. FISH AND WILDLIFE SERVICE

COLORADO DEPARTMENT OF HEALTH

SHELL OIL COMPANY

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LIST OF TABLES

Table No.

Volume 11 - ENDANGERMENT ASSESSMENT

1.0-1 Data Needs in Each Medium

1.3.1-1 Statistical Comparison With Background - Groundwater

1.3.1-2 Chemicals of Concern - Groundwater

1.3.1-3 Summary of Available Information on Toxicity and Essentiality of Calcium, Iron,

Potassium, Magnesium, and Sodium

1.3.2-1 Statistical Comparison With Background - Surface Water (First Creek)

1.3.2-2 Chemicals of Concern - 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

of Concern

2.1-4 Octanol/Water Partition Coefficients (log K0,.)

2.1-5 Adsorption Coefficient (1/kg) for Chemicals Elevated in Soil or Sediment

2.1-6 Uptake to Roots, K,,, (1/kg), for Organic Groundwater Chemicals of Concern

2.1-7 Uptake to Plants, Kwp (1/kg), for Organic Groundwater Chemicals of Concern

2.1-8 Plant Uptake Coefficients, Kr (Dimensionless), for Chemicals of Concern in

Offpost Surficial Soil

2.1-9 Plant Uptake Coefficients, K,P1 for Chemicals of Concern in Offpost Surficial

Soil

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(Continued)

2.1-10 Beef Bioaccumulation Coefficients, KPM9 for All Chemicals of Concern

2.1-11 Milk Bioaccumulation Coefficients, Kpd, for All Chemicals of Concern

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 of the Number of Wells 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 Combined Estimate of the Number of Wells by Well Use in the Offpost Operable

Unit

2.3.3.1-1 Exposure Pathways: Inhalation Route

2.3.3.2-1 Exposure Pathways: Dermal Route

2.3.3.3-1 Exposure Pathways: Ingestion Route

2.4.2.4-1 Nonchemical-specific Parameters Used in Bioaccumulation Models

2.4.2.5-1 Concentration of Aldrin Plus Dieldrin in Zone 3

2.4.2.5-2 Chemical -specific Properties of Aldrin 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

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(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 - I I Reasonable Maximum Exposure Concentrations in Dairy and Meat Products:

Maximum Concentration Estimated in Any Zone

2.4.2.6-12 Reasonable Maximum Exposure Concentration in Eggs (Zones 1, 2, and 6)

2.4.3-1 Summary of Land 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 - I a Parameters Used in Time-weighted Average Intakes Calculation (Milk and Soil

Ingestion)

2.4.3.2-2 Exposure Factors: Exposure Frequency and Duration

2.4.3.2-3 Exposure Factors: Physiology

2.4.4-1 Exposure Factors: Commercial/Industrial (Reasonable Maximum Exposure)

2.4.4-2 Exposure Factors: Commercial/Industrial (Most Likely Exposure)

2.4.5.1-1 Sensitivity Analysis Summaiy

2.4.5.5.3-1 Uncertainty Analysis Results

3.1-1 Hierarchy of Documents Referenced Regarding Toxicity Data

3.1-2 Toxicity Data for Rocky Mountain Arsenal Offpost Chemicals of Concern

3.1-3 Noncarcinogenic Reference Doses and Potential Noncarcinogenic Effects

3.1-4 Cancer Slope Factors and Potential Carcinogenic Effects of Carcinogenic

Operable Unit Offpost Chemicals of Concern

3.1-5 Regulatory Criteria for Rocky Mountain Arsenal Offpost Operable Unit,

Chemicals of Concern

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(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 in Table 3.3.3-1

3.3.3.2.1-1 Nonprimate Mammalian Oral LD50 Data

Volume III

4.0-1 Target Organ- or System-specific Chemicals of Concern

4.1.1-1 Summary of Residential 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 of Dieldrin and Other Chemicals to the Child Acute Hepatic Hazard

Index

4.1.1-4 Summary of Residential Hypothetical Future Reasonable Maximum Exposure

Subchronic Hazard Indices: Children

4.1.1-5 Summary of Residential Hypothetical Future Reasonable Maximum Exposure

Subchronic Hazard Indices: Adult Females

4.1.1-6 Comparison of Residential Reasonable Maximum Exposure and Most Likely

Exposure Hypothetical Future Carcinogenic Risks by Zone

5.1.2-1 Wildlife Species Observed in Offpost Operable Unit: Winter 1989-90

5.1.4-1 Chemicals of Concern and Tissue Chemicals of Concern for the Offpost

Ecological Risk Assessment

5.2.1-1 Terrestrial Species Selected as Indicators of Ecological Impacts

5.2.1-2 Aquatic/Wetland Species in Relation to Indicator Species Selection Criteria

5.2.2-1 Potential Exposure Pathways for Biota

5.2.3-1 Exposure Point Concentrations for Soil, Surface Water, and Sediment Used for

the Offpost Ecological Assessment

5.2.5.1-1 Dietary Fractions for Each of the Species in the Terrestrial Food Web

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(Continued)

5.2.5.2-1 Predicted Tissue Concentrations (mg/kg) for the Terrestial Food Web Ecological

Receptors

5.2.5.4-1 Predicted Tissue Concentrations (mg/kg) for the Aquatic Food Web Ecological

Receptors on the Basis of Surface-Water Concentrations

5.2.5.4-2 Predicted Tissue Concentrations (mg/kg) for the Aquatic Food Web Ecological

Receptors on the Basis of Sediment Concentrations

5.3.1-1 Summary of Intakes from Zone 3 Soil, Surface Water, and Diet for the Bald Eagle

5.3.1-2 Summary of Intakes From Zone 3 Soil, Surface Water, and Diet for the American

Kestrel

5.3.1-3 Summary of Intakes From Zone 3 Soil, Surface Water, and Diet for the Great

Horned Owl

5.3.1-4 Summarv of Intakes From Zone 3 Soil, Surface Water, and Diet for the Deer

Mouse

5.3.1-5 Summary of Intakes From Zone 3 Soil, Surface Water, and Diet for the Prairie

Dog

5.3.2-1 Summary of Intakes From Zone 3 Sediment, Surface Water, and Diet for the

Great Blue Heron

5.3.2-2 Summary of Intakes From Zone 3 Sediment, Surface Water, and Diet for the

Mallard Duck

5.3.4-1 Summary of Chicken Hazard Quotient by Zone, Offpost Operable Unit

Volume V - FEASIBIL TY STUDY

2.2.1-1 Offpost Operable Unit Carcinogenic Risks for Each Medium

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 of Concern Without Applicable

or Relevant and Appropriate Requirements

2.5.2-3 Preliminary Remediation Goals for Offpost Operable Unit Groundwater

2.8.1-1 Screening of Process Options for Groundwater

2.10.1-1 Selection of Representative Process Options for Groundwater

20000,317.10 - I-toc

0306111992 xxiii
LIST 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 of Groundwater Alternatives; North Plume Group

4.2.2.5-1 Summary of Screening of Groundwater Alternatives; Northwest Plume Group

5.5.3-1 Summary of the Detailed Analysis and Ranking of Groundwater Alternatives for

the North Plume Group

5.5.3-2 Summary of the Detailed Analysis and Ranking of Groundwater Alternatives for

the Northwest Plume Group

20000,317.10 - 1-toc

0306111892 xx1v
LIST OF FIGURES

Figure No.

Volume I - INTRODUCTION

I Location Map of Onpost Operable Unit, Rocky Mountain Arsenal

2 Offpost Area, Rocky Mountain Arsenal

3 Distribution of Diisopropylmethyl Phosphonate (DIMP) in the Offpost

Unconfined Flow System

4 Distribution of Dicyclopentadiene in the Offpost Unconfined Flow System

5 Distribution of Dieldrin in the Offpost Unconfined Flow System

6 Distribution of Endrin in the Offpost 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 of Dibromochloropropane in the Offpost Unconfined Flow System

10 Distribution of Trichloroethene (TRCLE) in the Offpost Unconfined Flow

System

I I Distribution of Tetrachloroethene in the Offpost Unconfined Flow System

12 Distribution of Arsenic in the Offpost Unconfined Flow System

13 Distribution of Chloride in the Offpost Unconfined Flow System

14 Distribution of Fluoride in the Offpost Unconfined Flow System

15 Offpost Operable Unit Confined Denver Formation Monitoring Well Network

16 Distribution of Organochlorine Pesticides Detected in Offpost Soil

17 Distribution of Organochlorine Pesticides Detected in 96th Avenue Area Offpost

Soil

18 Distribution of Organic Compounds Detected in Offpost Operable Unit Surface

Water

19 Distribution of Organic Compounds Detected in Offpost Operable Unit StreamBottom Sediment

20000,317.10 - 1-toc

0306111892 xxv
LIST OF FIGURES

(Continued)

Volume 11 - ENDANGERMENT ASSESSMENT

1.0-1 Preliminary Site Conceptual Model, Pre-Remedial Investigation, Offpost

Operable Unit

1.2-1 Offpost Operable 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 Off post Operable Unit Surface-Water Sampling Locations

1.2-6 Offpost Operable Unit Sediment Sampling Locations

2. 2.21. 1. 1 - I Off post Operable Unit Land Use Areas and Consumptive Use Phase II Study

Area

2.2.2.1.2-1 Offpost Operable Unit - Future Land Use

2.2.2.1.2-2 Offpost Operable Unit Study Area Selected Current Zoning Map, 1991

2.3.1-1 Site Conceptual Model Offpost Operable Unit

2.4.1-1 Offpost Operable Unit Zones Major Pathways of Groundwater 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 of Chloroform 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 of Ingestion Rate

of Locally Produced Milk (IRd, kg/day) for the Child Chronic and Lifetime

Scenarios - Residential

20000,317.10 - 1-toc

0306111992 xxvi
LIST OF FIGURES

(Continued)

2.4.5-2 Off'post Operable Unit Histograms Describing the Distribution of ingestion Rate

of Locally Produced Vegetables (IRv, kg/day) for the Child Chronic and Lifetime

Scenarios - Residential

2.4.5-3 Offpost Operable Unit Histograms Describing the Distribution of Ingestion Rate

of Locally 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 of Lifetime Oral Intake of Dieldrin in Zone 3

(mg/kg/day) - Residential

2.4.5.5.2-2 Offpost Operable Unit Uncertainty in the Mean Concentration of Dieldrin in

Groundwater (mg/1) in Zone 3

2.4.5.5.2-3 Offpost Operable Unit Uncertainty in the Mean Concentration of Dieldrin in

First Creek Surface Water (mg/1)

_4.5.5.2-4 Offpost Operable Unit Uncertainty in the Mean Concentration of Aldrin and

Dieldrin in Surface Soil of Zone 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 of Child Chronic Oral Intake of DIMP in

Zone 4 (mg/kg/day) - Residential

2.4.5.5.2-7 Off'post Operable Unit Distribution of Lifetime Oral Intake of Chloroform in

Zone 2 (mg/kg/day) - Residential

2.4.5.5.2-8 Offpost Operable Unit Distribution of Lifetime Inhalation of Chloroform in

Zone 2 (mg/kg/day) - Residential

3.3.1-1 Methodology for Determining Water and Soil Reference Media Concentrations

for Vegetation and Aquatic Organisms

3.3.3-1 Methodology to Derive Toxicity Reference Values (TRVs) From Class-specific

Toxicity Data

Volume III

4.1.1-1 Offpost Operable Unit Combined Carcinogenic Risks (All Pathways) by

Groundwater Zone - Residual Scenarios

4.1.1-2 Offpost Operable Unit Child Resident Hazard Indices Described 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 xxvii
LIST 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 Risks Described 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 of Range

4.2.1-1 Noncarcinogenic Hazard Indices Zone 5; Adult Commercial/Industrial; Chronic

RME

5.1.1-1 Offpost Operable Unit Biota Sampling Locations

5.1.1-2 Habitat Map for First Creek Portion of Offpost 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 xxviii
LIST OF FIGURES

(Continued)

Volume V - FEASIBILITY STUDY

2.5.1-1 Off'post Operable Unit Feasibility Study Contaminant Distribution Zones

2.6.1 Areas of Exceedances of Groundwater PRGs in the Offpost Unconfined Flow

System

2.8-1 Groundwater Process Options

2.8.1-1 Results of Universal Screening of Groundwater Process Options

2.9-1 Results of the Second Level Screening of Groundwater Process Options

2.10.1-1 Selected Representative Process Options for Development of Groundwater

Remedial Alternatives

Volume VI

3.2.1-1 Offpost Operable Unit Groundwater Plume Groups

3.5.1.4-1 Alternative No. N-4: Interim Response Action A

3.5.1.5-1 Alternative No. N-5: Expansion I to 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 xxix
PREFACE

The Feasibility Study (FS) is an element of a combined Endangerment Assessment/

Feasibility Study (EA/FS) for the Offpost Operable Unit (OU) and is consistent with the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), the Superfund

Amendments and Reauthorization Act (SARA), the revised National Contingency Plan (NCP), and

the regulations implementing the National Environmental Policy Act of 1969. Volume I of the

EA/FS contains an introduction that includes site history and a summary of the nature and extent

of contamination in the Offpost OU. Volume I also provides an Executive Summary that presents

an overview of the findings from each section and summarizes the selection of the preferred

sitewide alternative for the Offpost OU.

PURPOSE AND ORGANIZATION

The primary objectives of the FS are:

- Develop and evaluate a range of remedial alternatives that protect human health and

the environment

- Provide an analysis of the range of remedial alternatives that will support the selection

of the final remedy

The FS is organized into seven sections and associated appendixes. Section 1.0 describes the

purpose and the organization of the report. Section 2.0 presents the development of remedial

action objectives (RAOs), the development of preliminary remediation goals (PRGs), and the

identification and screening of technologies. Section 3.0 presents the development of alternatives.

The screening of alternatives with respect to effectiveness, implementability, and cost is presented

in Section 4.0. The detailed analysis of alternatives, considering the criteria mandated by the

NCP, is presented in Section 5.0. Selection of the preferred sitewide alternative is contained in

Section 6.0. Section 7.0 presents the references for the FS.

20000,317.10 - FS

1127111092 V - P-1
1.0 FEASIBILITY STUDY PURPOSE AND ORGANIZATION

The primary objective of the Feasibility Study (FS) for the Offpost OU is to evaluate

remedial alternatives in accordance with CERCLA, as amended by SARA, and the NCP so that

relevant information concerning the remedial alternatives can be presented to a decision maker

and an appropriate remedy can be selected. The following subtasks further describe the purpose

of the FS evaluation:

I . Develop and screen a range of remedial alternatives that provide for protection of

human health and the environment and that consider effectiveness, implementability,

and cost criteria.

2. Integrate this FS with all applicable Offpost Remedial Investigation (RI), Offpost RI

Addendum, comprehensive monitoring program (CMP), Offpost Endangerment

Assessment (EA), Onpost RI/FS, and interim response action (IRA) activities to ensure

that all remedial alternatives are developed, screened, and evaluated in a systematic and

objective manner.

3. Provide an analysis of the range of remedial alternatives developed that will support the

selection of a remedial alternative(s) that is technically feasible and provides the

necessary protection of human health and the environment in a cost-effective manner.

The FS was conducted in four steps:

- Step I - Development of Remedial Action Objectives

- Step 11 - Development and Screening of Alternatives

- Step III - Detailed Analysis of Alternatives

- Step IV - Selection of the Preferred Sitewide Alternative

1. 1 STEP I - DEVELOPMENT OF REMEDIAL ACTION OBJECTIVES

Step I of the FS included the following activities:

I . To set the context of the FS, a summary of background information regarding the site

and a concise statement of the problem were made.

2. RAOs were developed specifying the chemicals and media of concern, exposure

pathways as documented in the Offpost EA (Volume II, Section 1.0), and PRGs that

provide the guidelines for the development of a range of remedial alternatives. The

PRGs were developed on the basis of chemical -specific applicable or relevant and

appropriate requirements (ARARs), health-based criteria (HBC), exposure factors, and

the statutory requirements stated in Section 121 of CERCLA.

20000,317 - FS

1109111092 V - 1-1
3. General response actions that may be taken to satisfy RAOs were developed for each

medium of concern, defining individual controls, such as containment, treatment,

excavation, pumping, or other actions, singly or combined.

4. Volumes or areas of media to which general response actions might be applied were

identified considering the requirements for protectiveness as identified in the RAOs and

the chemical and physical characterization of each 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 of technical implementability. Technology types and process

options not applicable to the media or contaminants in the Offpost OU were eliminated.

Technically implementable technology types and process options, including innovative

tech nolog i es,, were retained for further evaluation.

6. Process options were screened on the basis of effectiveness, implementability, and cost

to select a representative process option (RPO) for each technology type retained for

consideration.

1.2 STEP 11 - DEVELOPMENT AND SCREENING OF ALTERNATIVES

Step 11 of the FS included the following activities:

I . The selected RPOs from Step I of the FS were assembled into a range of remedial

alternatives addressing containment, source control, treatment, and satisfying the

statutory requirements and preferences stated in Section 121 of CERCLA 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 of this screening, a set of remedial alternatives was retained for further

analysis in Step 111.

1.3 STEP III - DETAILED ANALYSIS OF ALTERNATIVES

Step III of the FS included the following activities:

1. Retained alternatives were then further developed to provide the basis for a detailed

analysis in accordance with the NCP and with U.S. Environmental Protection Agency

(EPA) guidance.

2. ARARs and other pertinent advisories, criteria, or guidance were identified regarding

specific actions proposed for each remedial alternative.

3. The alternatives were assessed and compared on the basis of relative performance with

respect to the following evaluation criteria (categorized into three groups) specified in

the NCP:

- Threshold criteria

o Overall protection of human health and the environment

20000,317 - FS

1109111092 V - 1-2
o Compliance with ARARs

- Primary balancing criteria

" Long-term effectiveness and permanence

" Reduction of mobility, toxicity, or volume through treatment

" Short-term effectiveness

" Implementability

" Cost

- Modifying criteria

" State acceptance

" Community acceptance

4. Based on the comparative analysis of remedial alternatives and risk management

decisions, a preferred alternative was selected.

1.4 STEP IV - SELECTION OF THE PREFERRED SITEWIDE ALTERNATIVE

Step IV of the FS selects the U.S. Department of the Army's (Army's) preferred alternative,

based on the detailed analysis of alternatives.

20000,317 - FS

1109111092 V - 1-3
2.0 DEVELOPMENT OF REMEDIAL ACTION OBJECTIVES

AND SCREENING OF TECHNOLOGIES

RAOs and general response actions that address the RAOs were developed. Technologies

accomplishing a given response action were then identified and screened, and RPOs were selected

to be carried forward into the development and screening of alternatives.

Section 2.0 presents an overview of development of RAOs, 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 goals designed to protect human health and the environment.

RAOs address chemicals of concern (COCs), media of concern, exposure pathways, and PRGs.

RAOs and PRGs were used to guide the evaluation of technologies and the development of

remedial alternatives. PRGs are established considering chemical -specific ARARs, site-specific

HBC, factors related to technical 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 to provide protection of human health and the environment. The

RAOs guided the selection of response actions, technology types, process options, and remedial

alternatives.

General response actions are defined as remedial 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 of evaluating

technologies.

After the definition of general response actions, broad technology groups (i.e., technology

types) and specific processes within a technology type (i.e., process options) were identified on the

basis of chemicals present and the media in which they were detected at the site. Technology

types and process options were screened in a first step, solely on the basis of technical

implementability. The technical implementability criterion eliminated technology types and

20000,317.10(g) - FS

1014111892 V - 2-1
process options that could not be effectively implemented because of site conditions in the

Offpost OU.

During the second level of screening, process options within each technology type were

evaluated and screened on the basis of three criteria: effectiveness, implementability, and cost.

Subsequently, one or more RPO was selected for each technology type retained during this second

level of screening. RPOs were carried forward to the development and screening of alternatives.

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 of the cumulative risk for the Offpost OU as

presented in the EA and compares the cumulative risk to the acceptable risk range. The Army's

approach for evaluating cumulative risk and development of PRGs presented in the following

sections is consistent with the NCP and EPA interpretive guidance. The Army has followed EPA

guidance regarding (1) use of the acceptable cancer risk range in assessing whether remediation is

required and (2) development of PRGs for sites exceeding the 10-4 acceptable risk level.

2.2.1 Comparison of Cumulative Risk With the Accemable Risk Range

The cumulative Offpost OU hypothetical cancer risk is a maximum of 3 x 10-4 on the basis

of the RME risks presented in the EA (Volume 111, Section 4.0 and Volume IV, Appendix G).

This value is a summation of the 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 of zones 2,3 and 4, where the HIs slightly exceed 1.0. The RME risks calculated in

the EA are a conservative estimate of Offpost OU hypothetical risk. The conservatism of the

RME risks presented in the EA is discussed in detail in Volume III, Section 4.0. The quantitative

uncertainty analysis presented in Volume 111, Section 4.0 can be used to assess the level of

conservatism of the RME estimates. The results of the 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 in the EA, Volume 11,

20000,317.10(g) - FS

1014111892 V - 2-2
Section 2.0, is highly conservative. The rural residential scenario used in zones 1, 2, and 6

includes all pathways contributing substantially to hypothetical risk, even though the majority of

the total population is not exposed to the majority of the agricultural exposure pathways. The

urban residential exposure scenario in zones 3 and 4 is very conservative because the probable

future use of that land is commercial/ industrial rather than residential for reasons listed in

Volume V, Section 2.5.1.

The Offpost OU cumulative risk is within the acceptable cancer risk range specified by

EPA. Risks attributable to the 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 of the 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 less than 10-4 , action is generally not

warranted... (Risk Assessment Memorandum, page 4)

- The upper boundary of the 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 if justified based on site-specific conditions (Risk

Assessment Memorandum, page 1).

EPA Region VIII provided the following position to the Army with regard to use of the 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 of a risk in excess of 5 x 1 0-4 to exceed the

intent of the 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 - 2-3
2.2.2 Identification of Media Reauirinp, Remedial Action Obiectives

Offpost OU remedial action is not warranted because Offpost OU cumulative risk is 3 x 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 to no action in the Offpost OU.

Groundwater contributes a maximum risk of 2 x 10-4, or approximately 73 percent of the

total, to the cumulative hypothetical risk in zones 2, 3, and 4. The following potential human

exposure pathways were identified in the EA for groundwater: direct ingestion, inhalation during

showering, consumption of crops irrigated with contaminated groundwater, and consumption of

dairy products and beef produced 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 to the cumulative hypothetical risk

through a combination of the following potential human exposure pathways: direct ingestion,

dermal contact, consumption of crops cultivated in contaminated soil, consumption of dairy

products and beef from livestock inhabiting areas of contaminated soil, and consumption of eggs

from poultry inhabiting areas of 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 of the 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 for soil.

Surface water and sediment contribute a maximum risk of 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 of the acceptable risk range; hence, no remediation is appropriate for these media.

Therefore, RAOs and PRGs were not developed.

20000,317.10(g) - FS

1014111892 V - 2-4
Air and biota media in the Offpost OU do not require remediation for the following reasons.

Air quality at RMA and within the Offpost 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 of concern, and therefore, RAOs were not

developed for the air medium. The biota medium consists of all plants and animals potentially

exposed to Offpost OU contaminants in water, soil, and sediment. The source of biotic

contamination originates from abiotic materials, such as water, soil, and sediment. Direct

remediation of biota is not effective except by methods that temporarily eliminate receptor species

from the area of contamination during remediation of the 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 of RAOs.

Specifically, information presented in the ecological risk assessment (Volume III, Section 5.0) and

ecological- based criteria presented in Volume VII, Appendix C were evaluated during the

development of RAOs.

Additional support for eliminating media that contribute minor levels of risk 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 of PRGs may not be appropriate (Risk Assessment Guidance for

Superfund [RAGS]: Volume I - Human Health Evaluation Manual, Part B - Development of

Risk-based Preliminary Remediation Goals, Office of Solid Waste and Emergency Response

[OSWER] Directive 9285.7-0113, December 1991) (RAGS-B).

20000,317.10(g) - FS

1014111892 V - 2-5
2.2.3 Site-sr)ecific Factors Considered for Groundwater Remedial Action Obiectives

Development

The Army considers the following factors to be important in assessing whether groundwater

RAOs should be developed even though the cumulative risk in the Offpost OU is within the

acceptable risk range

- Groundwater is the major contributor to total risk.

- Groundwater is a potential source of drinking 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 a number of exposure

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 of a

groundwater collection and treatment system.

His for children slightly exceed 1.0 in zones 2,3, and 4, with groundwater contributing

approximately 74 percent of the total risk.

For the reasons stated above, the Army considers groundwater PRG development to be appropriate even though cumulative Offpost OU cancer risk is within the acceptable 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 of departure. Thus, groundwater PRGs were developed using the 10-r, point

of departure.

2.3 DEVELOPMENT OF GROUNDWATER REMEDIAL ACTION OBJECTIVES

RAOs are medium-specific goals for protecting human health and the environment. The

NCP states that RAOs should specify the following: (1) contaminants of concern, (2) media of

concern, (3) exposure pathways, and (4) remediation goals. The development of groundwater

RAOs was performed in a step-wise fashion:

Step 1: Identification of COCs

Step 2: Identification of exposure 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 of PRGs, which are developed in Section 2.5.

2.3.1 Development of Remedial Action Obiectives. Ster) 1: Identification of Chemicals

of Concern

COCs were identified in the Offpost EA (Volume 11, Section 1.0), primarily on the basis of

the following four criteria:

1. The primary criterion for identifying COCs was a statistically significant increase in

concentration in samples collected from the Offpost OU when compared with samples

from locations believed to be unaffected by RMA contamination (background).

2. Although certain chemicals may have not fully satisfied the statistical criterion stated

above, if the), were degradation products of COCs, they were selected as COCs.

3. Several COCs are essential human nutrients and have low toxicity at observed concentrations. These potential COCs include calcium, magnesium, potassium, and sodium,

and were eliminated from consideration.

Background concentrations include naturally occurring chemicals and chemicals from anthropogenic sources, such as the agricultural application of pesticides.

Groundwater COCs are presented in Table 2.3.1-1. Groundwater PRGs are presented in

Section 2.5.

2.3.2 Develogment of Groundwater Remedial Action Obiectives SteL) 2: Identification of

Potential Exposure Pathways

The primary potential pathways of exposure were identified in the Offpost EA (Volume 11,

Section 2.0). RAOs consider the protection of human health and the environment. Therefore,

exposure pathways for both human and ecological receptors were considered in the development

of RAOs.

The following primary exposure pathways were identified for groundwater:

Human receptors

o Direct ingestion of contaminated groundwater

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" Showering with contaminated groundwater

" Consumption of crops irrigated with contaminated groundwater

" Consumption of dairy products or beef produced from livestock watered with contaminated groundwater and/or fed crops irrigated with contaminated groundwater

Environmental receptors

" Watering of livestock with contaminated groundwater

" Feeding of livestock with crops irrigated with contaminated groundwater

The Offpost EA considered three potential.ground water 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 of vapors in residences

- Dermal contact with groundwater for domestic uses

- Consumption of game harvested from the Offpost OU

All remaining groundwater exposure pathways were considered in the development of groundwater RAOs.

2.4 GROUNDWATER REMEDIAL ACTION OBJECTIVES

Groundwater RAOs for the Offpost OU were developed to provide protection of human

health and the environment from potential exposure to contaminants detected in groundwater.

RAOs were developed to meet the intent of CERCLA and include the general provision to reduce

potential health risks associated with affected media to the NCP-prescribed cumulative 10-4 to

10-6 risk range for carcinogens 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 for Conducting Remedial Investigations and Feasibility Studies Under

CERCLA, Interim Final, October 1988 (EPA, 1988b) provides that:

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Remedial action objectives consist of medium-specific or operable unit specific

goals for protecting human health and the environment ... Remedial action objectives aimed at protecting human health and the environment should specify:

- The contaminant(s) of concern

- Exposure route(s) and receptor(s)

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

preliminary remediation goal)

Remedial action objectives for protecting human receptors should express both a

contaminant level and an exposure route, rather than contaminant levels alone,

because protectiveness may be achieved by reducing exposure (such as capping

area, limiting access, or providing an alternate water supply) as well as by

reducing contaminant levels.

2.4.1 Groundwater Remedial Action Obiectives

Groundwater RAOs consist of goals for groundwater quality that are protective of human

health and the environment.

2.4.1.1 Human Health'

1. Reduce the COCb concentrations in groundwater and/or prevent exposure associated

with groundwater within the Offpost OU to meet groundwater remediation goals' and

to attain the NCP-prescribed cumulative risk range.

2. Prevent domestic use of, ingestion of crops irrigated with, and ingestion of livestock

watered with groundwater containing COCs b at 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

COCb concentrations in excess of groundwater remediation goals'.

Several potential groundwater exposure pathways including inhalation of vapors in residences,

direct contact with groundwater for domestic uses, and consumption of game (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 of this report.

The development of preliminary and final remediation goals, in accordance with the NCP and

the FFA, is an ongoing process requiring continual evaluation of site-specific conditions and

evolving health-based and regulatory standards to attain the NCP-prescribed cumulative risk

range of 10-4 to 10-6 for carcinogens and a hazard index < 1.0 for noncarcinogens. These

preliminary goals may change as the FS progresses. Final remediation goals may be based on

but are not limited to HBC, ARARs, biota criteria, background concentrations, and CRLs.

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2.5 DEVELOPMENT OF GROUNDWATER PRELIMINARY REMEDIATION GOALS

PRGs are chemical-specific remediation criteria that identify media requiring remediation

and treatment goals. A set of remediation criteria may be composed of different types of PRGs.

For example, groundwater PRGs may include ARARs (such as Maximum 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 of sitespecific 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 is selected and the Record

of Decision (ROD) is issued.

Section 121(d) of CERCLA establishes a process for developing and selecting remedial actions

that are protective of human health and the environment. Remedial actions that limit an excess

lifetime cancer risk to an individual to a level between 10-4 and 10-6 on the basis of methodologies

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 for alternatives

when ARARs are not available or are not sufficiently protective because of the presence of

multiple contaminants or multiple pathways of exposure. Additionally, the EPA guidance

document, Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions (EPA,

199 1 ), 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 the cumulative

site risk to an individual is less than 10-4 , action generally is not warranted, but

may be warranted if a chemical specific standard that defines acceptable risk is

violated or unless there are noncarcinogenic effects or an adverse environmental

impact that warrants action, (3) Furthermore, the upper boundary of the risk

range is not a discrete line at I X 10-4, although EPA generally uses I x 10-4 in

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making risk management decisions, and (4) A specific risk estimate around 10-4

may be considered acceptable if justified based on site-specific conditions

including any uncertainties on the nature and extent of contamination and

associated risks.

2.5.1 Effects of Future 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 Off post 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. The purpose of this section is to evaluate the

information within the context of EPA 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 for potential exposures under future land use conditions is used to provide

decision-makers with an understanding of exposures that may potentially occur in the

future. This analysis should include a qualitative assessment of the likelihood that the

assumed future land use will occur. The reasonable maximum exposure estimate

estimates for future uses of the 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 of the program but rather is an assurnption that may be made, based on conservative but realistic exposures. An

assumption of future residential land use may not be justifiable if the probability

that the site will support residential use in the future is small, (NCP preamble

[55 FR 8710] Remedial Investigation-baseline risk assessment).

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M

The discussion above indicates that it is within the guidance to select a future 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 as follows:

- Rural residential for zones 1, 2, and 6

- Urban residential for zone 3 and 4

- Commercial/industrial for zone 5

A summary of the qualitative assessment of the likelihood of occurrence of these future land

uses includes the following findings:

- The completion of the new Denver Airport and its proximity to the Offpost OU will

stimulate growth, particularly along the East 96th Avenue Corridor, and said growth is

most likely to include commercial and industrial development.

- Transportation agencies have mapped an enlargement and realignment of East

96th Avenue to handle increased traffic to the new Denver Airport, and said realignment

is positioned within zones 2, 3, and 4 of the subject land parcels.

- Floodplains and wetlands occur primarily in zones 3 and 5 in the 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 of Departure 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 as chemical -specific ARARs or other reliable information. Preliminary remediation goals should be modified, as necessary, as more information becomes

available during the RI/FS. Final remediation goals will be determined when the

remedy is selected. Remediation goals shall establish acceptable exposure levels that

are protective of human health and the environment 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 of a lifetime, incorporating an adequate margin of safety;

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(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 of between 10-4 and 10-6 using information on the relationship

between dose and response. The 10-6 risk level shall be used as the point of

departure for determining remediation goals for alternatives when ARARs are

not available or are not sufficiently protective because of multiple contaminants at a site or multiple pathways of exposure...

Section 2.5.4.1 and Table 2.5.2-1 of the 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, of the FS presents the methodology used in the calculation of

HBC and PRGs. The NCP states that PRGs may be revised on the basis of consideration 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 to the 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 to meet these

requirements. These calculations were verified with the Automated Risk Evaluation System

(ARES) software developed for the EA. HBC and risk development considered each of the

reasonable maximum exposure (RME) factors described above, including multiple pathways,

multiple contaminants, sensitive subpopulations (child chronic), and cross-media impacts. In

addition, the development of PRGs considered environmental impacts on ecological receptors by

using maximum allowable tissue concentrations (MATCs), I iterature -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 of the alternatives, the weight of scientific evidence

concerning exposures and cumulative health effects, and the reliability of exposure data. The

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M

effectiveness of the alternatives is evaluated in Volume VI, Sections 4.0 and 5.0. The uncertainty

associated with the performance of the selected groundwater treatment alternative is low because

of the Army's experience with similar designs of the boundary containment systems (BCSs) for

treating the COCs. Uncertainties associated with the weight of scientific evidence on exposure

and health risks were investigated both qualitatively in each major section of the EA and

quantitatively for the exposure assessment, which goes beyond the requirements of applicable

EPA guidance. These uncertainties indicate the assumptions in the EA are predominantly

conservative, and therefore, exposures may exceed by three-fold the 95th percentile of the

potential exposure distributions (Volume 11, Section 2.4.5). In this manner, the reliability of the

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 of a combination of RME and average exposure assumptions when the

net result is still "reasonable maximum exposure" (EPA, 1989b).

The NCP also requires evaluation of technical factors in the selection of PRGs, such as

detection/quantitation limits, technical limits to remediation, the ability to monitor and control

movement of contaminants, and background levels of contaminants. 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 to lower the risk

corresponding to PRGs. As a result, although the Army initially considered ARARs as PRGs, it

was necessary to reduce many of the 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 for groundwater (Volume 111, Section 4.1.1.1).

These technical and exposure factors were also considered in the evaluation. The FS also

evaluated technical limitations to remediation (e.g., treatability) in the selection of representative

process options and development of alternatives, 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).

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1014111892 V - 2-14
In 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 as the most health protective goal that is technically achievable, meets or exceeds ARARs,

has low uncertainty and large conservatism, and complies with applicable guidance (EPA, 1990).

Table 2.5.2-3 in Volume V presents the groundwater PRGs for the Offpost OU and the

media-specific risk. The summary risk for all chemicals, pathways, and media is in Volume VII,

Appendix C.

2.5.3 Tvves of Groundwater Preliminary Remediation Goals

A brief description of the types of PRGs evaluated for the Offpost OU is presented in the

following subsections. The types of PRGs evaluated include ARARs, HBC, background

concentrations, and ecological criteria.

2.5.3.1 Identification of Agglicable or Relevant and Apt)rooriate ReGuirements

EPA guidance (1988a), which is reflected in this section, describes the identification and

application of ARARs for the RI/FS process. Under Section 121(d)(1) of CERCLA, remedial

actions must attain a degree of remediation considered protective of human health and the

environment. In addition, CERCLA remedial actions must attain a level or standard of control

that at least meets standards, requirements, limitations, or criteria that are "applicable or relevant

and appropriate" upon completion of the action. These requirements, known as ARARs, may be

waived only in certain cases specified in Section 121(d)(4) of CERCLA.

ARARs are derived from both federal and state laws. The definitions of "applicable" or

"relevant and appropriate" requirements are found in the NCP, 40 CFR 300.5.

Applicable requirements refer to those cleanup standards, standards of control, and other

substantive requirements, criteria, or limitations promulgated under federal environmental or state

environmental or facility setting laws that specifically address a hazardous substance, pollutant,

chemical, remedial action, location, or other circumstance found at a CERCLA site.

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1014111992 V - 2-15
Relevant and appropriate requirements refer to those cleanup standards, standards of

control, and other substantive requirements, criteria, or limitations promulgated under federal

environmental or state environmental or facility setting laws that, although not applicable to a

hazardous substance, pollutant, contaminant, remedial action, location, or other circumstance at a

CERCLA site, address problems or situations sufficiently similar to those encountered at the

CERCLA site that their use is well suited to the particular site.

The analysis of requirements with respect to their relevance and appropriateness is somewhat

flexible. Relevant statutes require comparison of the types of remedial actions contemplated to

hazardous substances present, characteristics of the waste, physical characteristics of the site, and

other appropriate factors to establish relevant and appropriate requirements. It is possible to

consider only part of a requirement relevant and appropriate. Those state standards that are

identified in a timely manner and are more stringent than federal requirements may be applicable

or relevant and appropriate.

Within the confines of existing regulations and policy, the U.S. Department of the Army, as

the lead agency, assesses the applicability or relevance and appropriateness of requirements.

Other criteria and advisories that are not promulgated regulations can be used as guidelines

to ensure protection of human health and the environment. These "to be considered" (TBC)

criteria may include EPA health advisories (HAs), proposed MCLs, and other similar advisories.

Three different classifications of ARARs exist. The first type includes chemical -specific

requirements. Examples of potential 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 for Surface

Water.

The second type of ARAR includes location -specific requirements that restrict activities on

the basis of site characteristics and immediate site environment. These requirements may affect

the type of remedial action that can be implemented. A limit on activities within flood plains is

an example of a location -specific ARAR.

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1014111992 V - 2-16
The third type of ARAR includes action-specific requirements. Such ARARs are

technology based and are associated with the type of remedial alternative under consideration. An

example of an action-specific ARAR is the Resource Conservation and Recovery Act's (RCRA)

hazardous waste labeling requirements.

Chemical -specific ARARs were considered during the development of PRGs. Locationand action-specific ARARs were considered during the detailed analysis of specific remedial

alternatives (Section 5.0) and are not related to the development of PRGs. An evaluation of

ARARs with respect to the Offpost OU is in Appendix A.

2.5.3.1.1 Chemical -specific Agolicable or Relevant and At)t)rot)riate ReQuirements

A chemical -specific ARAR is a health-based or risk-based numerical value or methodology

that, when applied to site-specific conditions, results in the establishment of numerical values.

These values establish the acceptable amount or concentration of a chemical that is required to

meet protectiveness criteria established for the site.

Identification of chemical-specific ARARs was performed in several steps. The first step

was to identify chemicals for which an ARAR determination was warranted based on

42 USC 9621(d), which provides that ARARs are to be selected only for hazardous substances,

pollutants, or contaminants. The second step was to determine whether specific standards existed

for the designated hazardous substances, pollutants, or contaminants identified as COCs in the EA.

The third step was to determine which ARARs were to be attained for purposes of remedial

action for the Offpost OU. Chemical -specific ARARs are discussed in Appendix A and are

addressed for each medium during the development and selection of PRGs.

Potential chemical -specific ARARs for the Offpost OU have been identified and are

presented in the ARARs subsections for each medium of concern. For contaminants without

potential ARARs, health-based levels, based on the risks identified in the EA (Volume 111,

Section 4.0), were developed and are presented in the HBC subsections for each medium of

concern. Chemical -specific ARARs are identified and discussed in Appendix A.

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2.5.3.1.2 Location -specific Applicable or Relevant and AnDropriate ReQuirements

Location-specific ARARs generally are requirements placed upon the contaminated areas or

upon the conduct of activities solely because they are in special locations, such as flood plains,

wetlands, historic places, and sensitive ecosystems or habitats. Location -specific ARARs are

identified and discussed in Appendix A. An evaluation of wetlands ecosystems within the Offpost

OU is presented in Appendix B.

2.5.3.1.3 Action -sr)ecific Applicable or Relevant and Apprwriate Reauirements

Action-specific ARARs are usually technology- based or activity-based requirements or

limitations on actions taken with respect to hazardous wastes or requirements to conduct certain

actions to address particular circumstances at a site. Action-specific ARARs are identified and

discussed in Appendix A.

2.5.3.2 Health-based Criteria

HBC presented in subsequent subsections for carcinogens correspond to the point of

departure of 10-6 excess cancer risk in accordance with the NCP. Further, the NCP requires that

acceptable exposure levels for noncarcinogens with an adequate margin of safety must not cause

any adverse effect during all or part of a lifetime, including sensitive population groups. EPA's

Risk Assessment Guidance for Superfund (EPA, 1989b) requires that individual calculated

chemical intakes divided by the reference doses be summed into a hazard index (HI) for noncarcinogens. Further, the guidance specifies segregation of HIs by toxic effect and mechanism. This

approach was used in establishing health-based PRGs for the noncarcinogens.

Expected future land use had an impact on the development of HBC in the Offpost OU.

Three different exposure scenarios were developed in the Offpost EA. A rural residential

(including agriculture) scenario was developed for zones 1, 2, and 6, an urban residential scenario

was developed for zones 3 and 4, and a commercial/industrial scenario was developed for zone 5.

The Offpost EA (Volume 11, Section 2.0) also developed exposure parameters consistent with

both RME and Most Likely Exposure (MLE) estimates.

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A summary of the approach used for the 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 of each

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 of concern.

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 of the 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 of carcinogens 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

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indeed conservative and can be used with confidence in the development of preliminary remediation goals.

2.5.3.3 Backaround Concentrations

Background concentrations were one of several types of criteria evaluated for selection of

PRGs when there were contaminant sources in or contributing to a medium other than sources

related to RMA. Background levels may also be considered as PRGs when remediation of a

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 for protection of predators at the top of the food chain

including bald eagles, owls, herons, and kestrels. Ecological criteria address the requirement

stated in the NCP for protection of the 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 of Preliminary Remediation Goals - Groundwater

The evaluation of PRGs for groundwater in the Offpost 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 or relevant and appropriate for remediation of groundwater in the Offpost OU.

Consistent with EPA guidance, the Army selected the chemical -specific ARARs listed in

Table 2.5.2- 1.

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DIMP is the subject of an 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, the TBC will be adopted as an ARAR.

No ARAR determinations are final until the Offpost ROD is final. The levels listed as

proposed are not ARARs but may be evaluated as ARARs if finalized before issuance of the ROD

for the Offpost OU.

2.5.4.2 Groundwater Health-based Criteria

Groundwater HBC for carcinogens are risk-based values that correspond to the range of

allowable risks ( 10-4 to 10-6) prescribed in the NCP. HBC for noncarcinogens correspond to

concentrations such that the calculated HI is below 1.0. HBC were developed for a 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 for groundwater COCs

without ARARs. Several groundwater COCs have only HBC as groundwater PRGs (because there

are no ARARs for these COCs). 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 of Groundwater Preliminary Remediation Goals

Groundwater PRGs were developed on the basis of ARARs 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 for contaminants with promulgated standards,

residential 10-r' RME HBC for carcinogens 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 of Solid Waste and Emergency Response (OSWER) Directive 9355.0-30, Role of the

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Baseline Risk Assessment in Superfund Remedy Selection Decisions (EPA, 1991) allows for the

use of either ARARs or HBC as remediation goals.

2.6 QUANTITIES OF GROUNDWATER REQUIRING REMEDIATION

The area of groundwater requiring remediation in the Offpost OU was calculated. This area

was used in the development and screening of alternatives to evaluate the effectiveness,

implementability, and cost of groundwater remedial alternatives.

The quantity of groundwater requiring remediation in the Offpost OU was calculated on the

basis of PRGs and the extent of contamination as defined by data collected during the 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 of unconfined groundwater contamination exceeding PRGs are shown in

Figure 2.6- 1. Although not all PRGs for all contaminants are exceeded throughout the areas

shown, the plumes shown in the figures represent the area over which at least one contaminant

PRG is exceeded for groundwater. Within the areas shown on Figure 2.6-1 PRGs are exceeded

for the carcinogens arsenic, chloroform, dibromochloropropane, tetrachloroethylene, trichloroethylene, and dieldrin. PRGs are also exceeded for the noncarcinogens chlorobenzene, dicylcopentadiene, DIMP. The total area of groundwater exceeding PRGs encompasses approximately

590 acres of the 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 for each medium and include no

act-ion, institutional controls, containment, removal, disposal, and treatment. These response

actions may be combined to produce appropriate remedial alternatives.

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2.7.1 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 of the site would not change except by natural attenuation and degradation

processes. There would be no further effort to reduce risk to human health and the environment

by physical restriction of access 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 of contaminants, the areal extent of contamination, and its migration. A risk assessment would be performed every 5 years, 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 of deed 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 of potentially 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 or eliminated by the use of physical and/or

hydraulic barriers. Containment reduces or disrupts the mobility of the affected media,

consequently reducing the migration of chemicals 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).

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2.7.4 Removal

Removal technologies are operations that remove the contaminated media and/or waste from

its location onsite. They include extraction and transportation either offsite or to another 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 of a chemical by directly affecting the chemical through an external force that either

would alter the structure of the chemical or would bond with, isolate, or completely destroy the

chemical. Treatment response actions can be implemented onsite or offsite. Some treatment

response actions can be implemented in-situ. SARA recommends that a range of treatment

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, or contaminants is a principal element. Further, the NCP

requires that for groundwater response actions, a limited number of remedial 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 or extraction 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 that require management include onsite land disposal complying with

the intent of RCRA, 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,

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discharge 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 of developing alternatives for remediation for the RMA Offpost OU, it

was necessary to identify, evaluate, and screen the universe of potentially 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 of the

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 as general categories of

technologies (EPA, 1988b). Examples of technology types include thermal treatment, solidification /stab i I ization, and chemical treatment. Process options are defined as specific processes,

systems, or actions within each technology type. For example, the chemical treatment technology

type includes such process options as precipitation, 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 itself if it 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 for the reasons presented in Volume V,

Section 2.2.2.

The screening of technology types and process options is a two-step process. Universal

screening is the first step and involves the identification of technology types and process options

that are technically implementable. A universal list of technology types and process options

developed for groundwater is presented in Figure 2.8-la through e. The second screening step

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involves the evaluation and screening of selected or representative process options utilizing three

criteria: effectiveness, implementability, and cost.

2.8.1 Universal Screening

A screening of known 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 of technical implementability was based on two criteria. The first criterion is the ability of a process option to be

implementable under conditions at the site. This includes conditions such as type of media

contaminated, area and volume of contaminated media, depth to bedrock, subsurface geology, and

subsurface hydraulic characteristics. The second criterion is the ability of the process option to be

effective for reducing the mobility, toxicity, or volume of the specific contaminants present in the

affected medium. These two criteria use information obtained during the Offpost RI, Offpost RI

Addendum, and CMP on contaminant types, concentrations, and site characteristics. A summary

of the process options remaining after the universal screening for groundwater is presented in

Figure 2.7. 1 -1 a through e.

2.8.2 Evaluation and Screening of Selected Process Options

In Sections 2.8.3 and 2.8.4, each applicable process option retained for further consideration

from the universal screening is described and is further screened. The purpose of this screening is

to select one RPO from each technology type (Section 2.10). The RPO will then be used in the

assembly, development, and screening of remedial alternatives. In some cases, two or more RPOs

within the same technology type may be different enough with respect to performance 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 of the process options consists of the following three criteria:

1. Effectiveness

- The potential effectiveness of process options in treating the estimated areas or

volumes of media and meeting the cleanup goals defined in the RAOs

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- The effectiveness of the process option in protecting human health and the environment during the construction and implementation phase

- The reliability of the process with respect to the contaminants and site conditions

2. Implementability

- The ability to obtain permits for offsite actions

- The availability of treatment, 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 if they are effective as a primary treatment

process. Process options that may act only as a pretreatment process are not retained 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 as a baseline for comparison.

Under this option, no additional remedial action would be performed within the Offpost OU to

reduce the toxicity, mobility, or volume of contaminants. 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 a reduction in measurable contaminant levels over

time. Defining the degree of natural attenuation and the length of time required to achieve the

cleanup goals with certainty is not possible because there are no data corresponding to the nonoperation of the boundary containment systems. However, contaminant concentrations would be

monitored by continuation of groundwater and surface-water monitoring.

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2.8.3.2 Institutional Controls

With respect to the protectiveness and risk-reduction considerations of the three identified

evaluation criteria, institutional control options do not directly reduce the toxicity, mobility, or

volume of the affected media. Institutional controls serve, in effect, as a barrier or exposure

pathway interruption to minimize or eliminate 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 of CERCLA as amended by SARA, they can be instrumental in maintaining the

integrity of any "action" alternative selected and will, therefore, be retained in combination with

other process options for further evaluation during the development of alternatives.

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 of restrictions 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 of certain wildlife to a contaminated area. Implementation

of fencing may require acquisition of property on portions of the Offpost OU. Warning signs,

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alone and combined with fencing, can reduce the likelihood of human exposure to contaminated

media.

Land Acouisition

Acquisition of property in the Offpost OU may be necessary to implement remedial actions.

Land may be acquired for construction of treatment plants, providing pipeline right-of-way for

pump-back, to treatment facilities, or to reduce risk by implementing access/deed restrictions and

exposure control options. Property would be purchased from land owners at a rate dependent on

the current market value.

2.8.3.2.2 Alternative Water Supplies

Providing alternative water supplies to residents whose potable water supply has been

affected by offpost contamination is a means of eliminating risk associated with use of the

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 of water districts

using groundwater from an uncontaminated aquifer, or provision of a private well completed in

an uncontaminated aquifer. The Army has committed to providing 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 site conditions 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.

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2.8.4 Groundwater Process Ovtions

2.8.4.1 Removal

Removal refers to the extraction of contaminated and uncontaminated media. Removal may

serve the purpose of mass removal of contaminants or be incorporated as part of a containment

system. Removal process options for groundwater include pumping of well 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 of well points, extraction wells, and subsurface drains.

Descriptions of these process options follow.

Well Points

Well-point systems are typically used for extraction of shallow groundwater in unstratified

soil. Well-point systems are constructed by manifolding a group of closely spaced wells to a

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 of suction lift well points is about

22 feet (EPA, 1985). Most of the 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 of the 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 of extraction wells include removal of water for

treatment, gradient control for the purpose of plume containment, and increasing groundwater

flux rates through the subsurface to enhance the rate of chemical mass removal. Extraction well

arrays are often combined with subsurface injection to enhance cleanup by flushing clean water

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through the aquifer. In relatively high -permeability materials, the areas of extraction and

recharge can be laterally separated. If properly designed, such a system will achieve both

containment and mass removal. In materials with lower permeability, extraction and injection

wells may have to be interspersed in a grid pattern to reduce the distances 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 as a process option for removal of contaminated

groundwater on the Offpost OU at Offpost IRA and are used onpost in association with the

NWBCS, NBCS, and ICS containment and treatment systems.

Extraction wells will be retained for further consideration for the following reasons:

(I) their utility in mass removal, pump and treat, and containment alternatives, (2) the

conventional nature of their installation and ease of operation, 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 a trench

below the water table and then backfilling the excavation with permeable granular material, which

acts as a filter. In indurated materials, a drain may also be constructed with controlled blasting,

which creates a linear rubble zone of enhanced permeability. In any case, groundwater is

extracted from the drain by a limited number of sumps, 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 of subsurface drains include French/tile drains, dual-media drains, and

trench/gallery drains. French/tile drains incorporate a section of perforated pipe placed in the

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trench and surrounded by permeable fill. Dual-media drains are identical to French/tile drains

except that a geotextile material is added to reduce clogging of the drain by fine particles. Trench

or gallery drains are similar to French/tile drains, but are configured as a radial group of trenches

that discharge into a common sump or gallery.

Because of the effectiveness of subsurface 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 of contaminants by increasing the number of

pore volumes of water flowing through a contaminated aquifer per unit time. Water flushing

process options include injection and flooding/infiltration. Description of these process options

follows:

In

Injection is a process option that flushes uncontaminated water into the subsurface using

either recharge wells or trenches. The process stimulates groundwater flow by increasing

the hydraulic gradient in the vicinity of the injection system and aids the removal of

adsorbed contaminants by increasing the number of pore volumes of clean 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 as a means of effectively enhancing contaminant

removal and a method of disposing of treated water. Injection wells and trenches were

implemented as part of the onpost boundary containment and treatment systems and will

be used for the implementation of Offpost IRA. The injection systems onpost were used

for disposal of treated groundwater; they were not used in flushing operations. Onpost

injection systems have proved to be readily implementable. The effectiveness of flushing

operations for organic contaminants similar to many of the contaminants in Offpost OU

groundwater has been demonstrated at hazardous waste sites; therefore, injection is

retained for further consideration.

Flood inp / 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 of the

injection and facilitates the removal of adsorbed contaminants by increasing the number

of pore volumes of clean water flushed through the contaminated media in a given time

interval. Water typically is extracted downgradient and treated before surface application.

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Flooding and infiltration serve the same purpose as injection but have the disadvantages

of requiring larger surface areas and losing water to evaporation. Also, during winter, freezing may be a problem. The advantage of using flooding or infiltration over injection

is that percolating water through large areas of the vadose zone effectively remediates the

vadose zone soil. However, the vadose zone in the Offpost OU is not a source of groundwater contamination and is not contaminated. Therefore, because of the large area

requirements for flooding/infiltration and the lack of any additional benefits over

injection, flooding and infiltration are eliminated from further consideration.

2.8.4.2 DisL)osal

Disposal of groundwater involves technologies that represent the final disposition of either

contaminated or treated water. Disposal is divided into subsurface disposal and aboveground

discharge technology types.

2.8.4.2.1 Subsurface Disposal

The subsurface disposal process options, including pump-back to boundary 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 of this 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.

The pump-back process option is effective 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

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contaminated water into a deep hydraulically isolated formation under sufficient pressure to

displace native fluids while avoiding excessive migration of the waste and fracturing of the

formation. The formation should not have value as a resource.

Deep-well injection of treated water is not 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 is not the case for deep-well injection).

Under appropriate geologic conditions, deep-well injection is an effective process for

disposing contaminated groundwater. However, both offsite and onsite injection are not

implementable for the following reasons:

- Onsite deep-well injection

" Past onpost 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 of contaminated groundwater.

" Water rights may require replacement of extracted groundwater.

Shallow- Aouifer Recharge

Recharge wells and trenches are process options for shallow aquifer disposal of treated or

contaminated water. Recharge wells and trenches may provide for containment of contaminated

groundwater and water flushing of contaminants. 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 of recharge

wells is dependent on the hydraulic properties of the 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 of two methods:

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

- Conventional trenching using a biopolymer slurry below the water table to stabilize the

walls

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Trenches 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 of the trench. Treated

groundwater is pumped into the trench via the perforated pipe and recharges through the drain

rock into the aquifer.

Shallow-aquifer recharge of contaminated groundwater is not effective in reducing the

mobility, toxicity, or volume of contamination and may increase the mobility and volume of

contaminated media. Therefore, shallow-aquifer recharge of contaminated water is eliminated

from further consideration.

Shallow-aquifer recharge provides an effective means of returning treated groundwater to

the aquifer.

Recharge of treated groundwater into the UFS was implemented at the NBCS, NWBCS, and

ICS. Also, recharge of treated water was selected as the method of disposal for Offpost IRA

(HLA, 1989). Recharge of treated water into the shallow aquifer is readily implementable and

effective. Replacing the extracted contaminated water with treated water aids in the reclamation

of the site.

Because of its effectiveness and ease of implementation, recharge of treated 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 to Publicly Owned Treatment Works

Discharge to a POTW is an effective process for disposing contaminated groundwater or

treated groundwater. The implementability of discharging to a POTW is governed by numerous

factors that include the proximity to a sanitary sewer line, the capacity of the sewer line and the

treatment facility and pretreatment requirements.

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Discharge of contaminated water to a POTW is eliminated 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 of extracted groundwater. Discharge of treated water to a POTW is retained

as a potential means of disposal, recognizing that POTW capacity limitations are yet to be

determined.

Discharge to Surface Water

Discharge of contaminated 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 the Clean Water Act; (2) the process is

ineffective because it does not significantly reduce the mobility, toxicity, or volume of contamination; (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 of a fugitive

emissions problem from volatile organic compounds; and (5) public and agency acceptance are

unlikely. Therefore, discharge of contaminated groundwater to a surface-water body is

eliminated from further consideration.

Discharge of treated groundwater to a surface-water body is an effective means of disposal.

However, difficulties in implementing surface-water discharge of treated water arise from the

impacts of increased water flow on the receiving water body. It has not yet been determined

whether this difficult), would affect the implementation of discharging to surface water.

The discharge of treated groundwater to surface water is eliminated from further

consideration.

Infiltration Basins

Disposal to infiltration basins involves the discharge of contaminated or treated groundwater

into a man-made basin or natural surface depression.

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Discharge of contaminated groundwater into an infiltration basin is not only a disposal

option but can act as a form of land treatment. Contaminated groundwater may undergo limited

remediation/treatment via three mechanisms when it is discharged 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 of organic compounds, (2) although the infiltrating water may be

treated, the effectiveness in reducing the concentration of COCs is limited, and (3) because of the

limited effectiveness of the 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 of contaminated groundwater via discharge into infiltration basins is

eliminated from further consideration.

Discharge of treated 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 of difficulties in implementation and effectiveness considerations,

discharge of treated groundwater into infiltration basins is eliminated from further consideration.

2.8.4.3 In-vessel Treatment of Groundwater

In-vessel treatment refers to those technology types and process options that are

implemented in constructed facilities after removal of the contaminated groundwater. Groundwater extracted by wells or drains would require treatment to specific cleanup levels before

discharge to surface streams or reinjection to the aquifer.

2.8.4.3.1 Solids Removal

Removal of solids from a waste stream is a necessary pretreatment step for many downstream process options. Also, solids can cause accelerated wear on pumps and can form excessive

heavy deposits in pipelines. Solids can cause premature fouling of membrane systems and rapid

head loss in carbon adsorption columns and can reduce the efficiency of ion exchange units.

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M

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 of suspended solids. Filtration is often

appropriate as a pretreatment process for carbon adsorption and membrane processes to prevent

plugging or overloading problems. Also, filtration can be used for the removal of flocs formed

during precipitation and coagulation/flocculation. Two common types of filters are granular

media and bag filters.

Granular media filters usually contain the filter 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 of filter bags supported by perforated steel baskets and are sealed in a

metal housing. The bag material acts as the 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 as a primary treatment process and is not retained

for consideration during the development of alternatives, but may be implemented as a pretreatment process option.

Sedimentation

Sedimentation is a process option that uses gravity to settle suspended solids out of an

aqueous waste Stream. Sedimentation may be implemented in the form of settling ponds, sedimentation basins, and clarifiers. Sedimentation is often used as a pretreatment step for carbon

adsorption, stripping, membrane processes, and filtration. Suspended solids removal is not

expected to be required as a primary treatment process for extracted groundwater. Therefore,

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M

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 of contaminants 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 of these process options follows.

Air StriLvinp,

Air stripping is an effective and reliable method for removing volatile organic compounds

(VOCs) from aqueous waste streams. Of the 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 of air with

contaminated water in a packed-tower arrangement to promote transfer of the VOCs from 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 small droplets,

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 air phase. Depending

on the compound stripped and its concentration, the contaminated air stream may require

treatment.

Air stripping is retained for further evaluation during the development of alternatives

because air stripping is a proven technology demonstrated to be effective for the removal of VOCs

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

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compounds with smaller Henry's Law constants than conventional air stripping, but requires a

greater capital cost and higher O&M costs including construction of a steam -generating plant.

Although steam stripping has the additional benefit over air stripping of removing 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 of the required construction

of a 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 of evaporation followed by

condensation. The process effectively concentrates inorganic compounds into the blowdown waste

stream, thereby reducing the volume of heavy metals and other inorganic -containing liquids in the

treated stream. VOCs and SVOCs are vaporized with the water and are recovered during

condensation. If the 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, a condenser,

and a product cooler 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 of the high cost of operating and maintaining a distillation unit and the

availability of other processes with equal effectiveness for removal of organics, 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 - 2-40
M

absorption. Sorption process options retained in the universal screening were granular activated

carbon adsorption and resin adsorption. These process options are discussed in the following

paragraphs.

Granulated Activated Carbon (GAC) Adsorption

Activated carbon is a well-developed technology widely used in removal of organic

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 'adsorbed onto the internal pores of the carbon 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 is most effective for

nonpolar, high molecular weight, slightly soluble compounds.

Carbon adsorption is readily implementable. Carbon adsorption is a demonstrated, 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 of offpost contaminated groundwater at Offpost IRA. Because of its

proven effectiveness for removing RMA contaminants and its ease of implementation, 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 as the adsorbing medium instead of carbon. Adsorption resins are

20000,317.10(9) - FS

1014111892 V - 2-41
more selective in removal of contaminants than carbon. Thus, specific resins must be chose.n for

effective removal of target compounds.

Resin adsorption is usually accomplished in a downflow, 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

of the 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), of the contaminants.

Resin adsorption is a relatively 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 as chlorine, ozone, hydrogen peroxide) for detoxification of waste 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 for disinfection, purification, odor control, and

micro-flocculation in the treatment of drinking water. Ozone has also been shown to oxidize

organics in hazardous waste streams, but generally requires large doses and long reaction times to

be effective for complete oxidation of chlorinated organics.

Ozone treatment systems typically consist of an ozone generator, a reactor where the gas is

bubbled through the contaminated water in a contact chamber, and an offgas collection and

20000,317.10(9) - FS

1014111892 V - 2-42
treatment 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 is eliminated 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 consist of a rapid-mix oxidizing solution addition

system followed by a reaction vessel. Batch or continuous flow reactors can be used. Hydrogen

peroxide dose and reactor retention time vary depending on the nature of the waste stream and the

target compound's resistance to oxidation. Because of the nonspecific nature of hydrogen

peroxide as an oxidizing agent, other contaminants (organic and inorganic) can reduce the

effectiveness of removing the target compounds.

Hydrogen peroxide can be effective in the oxidation of hazardous 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 light acts as a

catalyst in the oxidation process and promotes the formation of the hydroxyl radical, which is a

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 - 2-43
efficiency and kinetics may be pH-dependent, and may require pH adjustment to achieve

optimum destruction efficiency.

The UV-peroxide treatment process is a combination of hydrogen peroxide and UV light

that induces rapid photochemical oxidation of organic compounds. A UV-peroxide system

includes a hydrogen 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 of hydrogen peroxide, and some systems may include

acid and catalyst addition to maximize destruction efficiency. In general, catalysis dramatically

increases the destruction efficiency of both 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 sites to be effective for removal of some

chlorinated organics (EPA, 1989c). The organic constituents in the offpost groundwater that may

be effectively treated by AOP include OCPs and DIMP. Therefore, AOP are retained for further

consideration.

2.8.4.3.5 Radiation

Radiation treatment process options use electromagnetic energy for the 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 of hazardous waste constituents. The process can treat both aqueous waste streams and

sludges. Electron beam irradiation has been used for full-scale treatment of municipal 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 is directed. The electrons enter the waste stream

20000,317.10(g) - FS

1014111892 V - 2-44
and ionize the water, producing aqueous electrons and hydrogen and hydroxyl radicals. These

species react with the organics in the waste stream. This process has been shown to remove

significant amounts of organic compounds in water; chloroform, benzene, and trichloroethylene

have shown reductions ranging from 50 to near 100 percent where initial concentrations ranged

from 400 to 1500 micrograms per liter.

Although the electron beam irradiation process has been demonstrated to be effective for

removal of compounds contained in Offpost OU groundwater, the process is very difficult to

implement. The electron accelerator has very high capital costs and requires specially trained

personnel for operation. Also, the process has not been demonstrated at full scale for hazardous

waste treatment. Therefore, the electron beam irradiation process is eliminated 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 of much 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 of similar implementation difficulties in comparison with the electron

beam process, gamma irradiation is eliminated from further consideration.

2.8.4.3.6 -Biolopical Treatment

Biological degradation of hazardous 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, or genetically altered microorganisms.

Biological degradation occurs when microbes use (i.e., metabolize) organ ic'compounds

(substrates) as a source of carbon and energy. Organic compounds are metabolized in the presence

of enzymes produced by the microorganisms that act as catalysts. Production of enzymes can be

induced by the presence of a primary substrate (i.e., can act as sole source of carbon) or by

20000,317.10(g) - FS

1014111892 V - 2-45
conditions within the cell (e.g., low concentrations of adenosine triphosphate [ATP]). Hazardous

waste organics can be degraded as a primary substrate or by cometabolism when enzymes are

produced because of the presence of another 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 to be treated.

Biological treatment is eliminated from further consideration for the following reasons:

- The concentration of organic 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 of incubation

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 to remediate 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 as a removal process option in Section 2.8.4.1.1.

20000,317.10(9) - FS

1014111892 V - 2-46
Water flushing acts as a treatment process because it reduces contamination in groundwater

by enhancing the removal of contaminants. In some cases, chemicals can be added to the flushing

solution to enhance the removal of contaminants. These chemicals include organic solvents,

chelating agents, and surfactants.

Water flushing solutions can be actively injected into the subsurface in wells and 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 is retained for further consideration.

2.8.4.4.2 Enhanced Biological Treatment

Biological treatment is a technology used to remediate the zone 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 of aerobic bioreclarnation depends on numerous factors, which include

biodegradability of the 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 of an oxygen source such as air

or hydrogen peroxide. Contaminants of interest can act as the 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 is eliminated from further consideration.

20000,317.10 - III-02TS

1109111892 V - 2-47
2.8.4.5 Containment

Affected groundwater may be remediated by the processes of groundwater containment.

Containment is achieved by minimizing the rate of chemical 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 or reduce the migration of

contaminants either by emplacement of a 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 of these process options follows.

Slurrv Wall

Slurry walls are physical subsurface barriers typically constructed of a mixture of water 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 of a trench. The

water- ben tonite-sol I slurry 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 of lower 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 of documented effectiveness onpost and ease of implementation, 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 of one of a variety

of fluids 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 of a predetermined amount of grouting

fluid into the strata to be sealed. Injection points are usually arranged in a triple line of primary

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 of the material into which the grout is being injected.

Various types of grout are available including cement, clay (e.g., kaolinite, illite), claycement mixtures, bentonite, alkali silicates, and organic polymer grouts. Selection of grout 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 or reversed 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 of a source area. Wells (rather than drains) are preferred for gradient control

because extraction/recharge pumping rates can be individually controlled at each well location.

Although gradient control by groundwater extraction may involve some removal of chemical mass,

the primary purpose of the system is to contain, rather than remove, mass.

20000,317.10 - III-02.FS

1109111892 V - 2-49
Hydraulic gradient control was chosen as the appropriate process option for groundwater

extraction and containment of contaminants for IRA A (HLA, 1991 b). In addition, hydraulic

controls were implemented onpost as part of the 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 of the most effective barriers to groundwater flow, but

are difficult to implement. Difficulties arise from site conditions 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 to install than

slurry walls. Therefore, because of difficulties in implementation and cost considerations,

subsurface dams are eliminated from further consideration.

2.9 SUMMARY OF PROCESS OPTION SCREENING

A summary of the process option screening for groundwater is presented in Figure 2.9-la

through c. Process options that were eliminated were screened out on the basis of uncertainties

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 of the evaluation and screening of process options (Section 2.8) a representative process option (RPO) was selected for each technology type retained for consideration. One

RPO was selected, if possible, for each technology type to simplify the subsequent development

and evaluation of alternatives without limiting flexibility during remedial design. The process

20000,317.10 - III-02.FS

1109111892 V - 2-50
option determined to be the most effective and most implementable within a technology type was

selected as the RPO. A process option that was effective for all of the contaminants present was

selected as the RPO. Process options that have been demonstrated at pilot- or full-scale were

generally selected instead of emerging processes with little or no performance or cost data

available. Innovative technology process options were selected if evaluation indicated that they

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 of two or more process options were equivalent. Selected RPOs were used to

develop, screen, and perform a detailed analysis of remedial alternatives.

In some cases, varying conditions across the site make selection of a single RPO for a

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. For example, effective

implementation of access restrictions may incorporate land acquisition, use restrictions, and fences

and warning signs to achieve effective protection of human 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 if it is determined that the new process option is more effective

or implementable than the original 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 is presented 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 of selection for the groundwater

medium. Figures 2. 10. 1 - la and b summarize the selection of groundwater RPOs. In a few

instances, all process options within a technology type were screened out during the first and

20000,317.10 - III-02.FS

1109111892 V - 2-51
second levels of screening presented in Section 2.8. These technology types are not represented by

any process option and will not be used to develop remedial alternatives.

20000,317.10 - 111-02.FS

1109111892 V - 2-52
Table 2.2.1-1: Offpost Operable Unit Carcinogenic Risks for Each Medium

Cumulative

Zone Groundwater Soil Surface Water Sediment- Risk

lAa 7 x 10-1 4 x 10-5 - - I X 10-4

IBa 9 x 10-5 4 x 10-1 - - I X 10-4

Ica 7 x 10-1 4 x 10-1 - - I X 10-4

2a 2 x 10-4 4 x 10-1 - - 2 x 10-4

3a 2 X, 10-4 8 x IQ-5 5 x 10-7 8 X 10-7 3 x 10-4

4b 2 x 10-4 1 x 10-5 5 x 10-7 8 X 10-7 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

a Urban residential exposure scenario.

b Commercial/industrial exposure scenario.

- = pathway not included in exposure scenario

2000,317.10(11) - FS

1108111092
Table 2.3.1 - 1: Offpost Operable Unit Groundwater Chemicals of Concern

Groundwater Chemicals

of Concern

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

0309111092
Table 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 per liter (,ug/1).

a total trihalomethanes

b DIMP is the subject of an EPA Health Advisory that has been 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

0309111992
Table 2.5.2-2: Health-based Criteria for Groundwater Chemicals of Concern Without

Applicable or Relevant and Appropriate Requirements

Certified

Chemical Adjusted Rural Reporting

of Concern 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 of contaminants 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

0309111892
Table 2.5.2-3: Preliminary Remediation Goals for Offpost Operable Unit Groundwater

Groundwater Rural

Preliminary Residential

Chemicals Remediation Hypothetical

of Concern Goals' Cancer Risk

Aldrin 0.05 (CRIý) I X 10-1

Arsenic 2.35 (CRL-) 6 x 10-'

Atrazine 4.03 (CRk) NA

Benzene 3 (HBC 2 x10-6

Carbon tetrachloride 0.99 (CRL 3 x 10-6

Chlordane 0.095 (CRL b 10-6

Chlorobenzene 25 (HBCO) NA

Chloroform 15 (HBCb) 2 x 10-'

CPMS 30 (HBC) NA

CPMSO 36 (HBC) NA

CPMS02 36 (HBý) NA 10-6 Dibromochloropropane 0.195 (CRL ) 4 x

Dicyclopentadiene 46 (HBC) NA

DDE 0.054 (CRL) 5 X 10-7

DDT 0.049 (CRIý) 2 x 10-7

1,3-Dichlorobenzene 6.5 (HBC-) NA

1,2-Dichloroethane 1.1 (CRL b) 3 x 10-6

Dieldrin 0.05 (CRL) 3 x 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) 4 x Toluene 1000 (MCk) NA

Trichloroethene 3 (HBC I X 10-6

Xylene 1000 (HBC b NA

Total I X 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 that the

b calculated hazard index (HI) is below 1.0.

Chemicals of concern with ARARs that were adjusted to reduce overall risk.

ARAR = applicable or relevant 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 = not applicable, either noncarcinogenic or EPA Category C carcinogen (insufficient human

evidence)

OU = operable unit

20000,317.10 - FS

0309111892
Table 2.8.1 - 1: Screening of Process Options for Groundwater

(Page I of 13)

Further

General Response Action Technology Type Process Option Consideration Comment

No Further Action No Action None Yes National Contingency Plan requires No Action to be carried through

the detailed analysis of alternatives.

Institutional Controls Access Restrictions Land use/deed restrictions Yes Effective means of reducing exposure to contaminated water.

Fencing and warning signs Yes Effective means of limiting access to contaminated areas.

Land acquisition Yes May be required to allow for implementation of remedial alternatives.

Alternative Water Supplies Alternative water supplies Yes Already implemented for residents whose potable water supply has

been affected; alternative water supply has included wells completed

in the Arapahoe Formation.

Monitoring Groundwater monitoring Yes Groundwater monitoring has already been implemented during site

characterization and the Comprehensive Monitoring Program and will

continue as specified in the Final Technical Plan, Groundwater Element, Comprehensive Monitoring Program (R.L. Stollar & Associates,

1989).

Removal Groundwater Extraction Well points Yes (3) Effective technology for shallow groundwater extraction in

unstratified soils.

Extraction wells Yes (3) Will be implemented in conjunction with Interim Response Action A;

extracted water is subsequently treated onsite; it is likely that extraction wells will be used in conjunction with any future onsite treatment

technologies.

Subsurface drains Yes (3) Effective technology for removal of shallow groundwater; efficient

removal in areas with low hydraulic conductivity.

Water Flushing Injection/flooding- Yes (3) Potentially effective technology for enhancing groundwater flow and

infiltration contaminant removal; water is typically extracted downgradient and

subsequently treated.

20000,317.10 - FS

0309111092
Table 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 of extracted 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 is pumped

into an appropriate geologic formation which prevents migration of

the waste.

Shallow aquifer recharge Yes (3)

Potential technology for replacement of treated water but not effective for reduction of mobility, toxicity or volume of contaminants

when disposing of contaminated groundwater.

Aboveground Discharge Discharge to publically -owned Yes Potential technology for disposal of treated water, implementability

treatment works depends on proximity 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 of treated water; not implementable

for contaminated water due to lack of effectiveness in contaminant

removal and associated risk to human health and the environment.

Infiltration basin Yes (8) Potential technology for the disposal of treated water and as a component of water flushing operations; difficult to implement for disposal of contaminated water.

In-Vessel Treatment: Solidification/ Solid ific ation/st abili zat ion No (1, 3. 5,) Rarely implemented for immobilization of dilute liquid wastes; not Physical/Chemical Stabilization implementable for high volume low concentration waste stream due to

the production of large volumes of waste which must be disposed of.

Chemical Inorganics Magnetic separation No (27) Process may be utilized for removal of paramagnetic metals; these

Treatment metals are not present above preliminary remediation goal concentrations in groundwater at the Offpost Operable Unit; not effective for

removal of organic contaminants.

20000,317.10 - FS

0309111092
Table 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 be utilized for removal of inorganic 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 for removal of organic contaminants.

Complexation No (3)

Process generally ineffective for removal of inorganic and organic

contaminants; complexing agents typically increase the solubility of

constituents.

Solids Removal Filtration Yes (3) Effective conventional technology for removal of suspended solids

from liquid waste streams.

Sedimentation Yes (3) Effective conventional technology for separation of suspended solids

from waste stream utilizing sedimentation and gravitational

techniques.

Liquid Phase Separation Liquid phase separation No (4, 9 Processes utilized for separation of nonaqueous phase liquids (e.g.,

oils, greases, insoluble organics) from aqueous portion of a 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 of inorganic contaminants; inorganic contaminants are not present above preliminary remediation

goal concentrations in groundwater at the Offpost Operable Unit; not

effective for removal of organic contaminants.

Ultrafiltration No (1, 6) Not effective for removal of molecules with a molecular weight less

than 500 atomic mass units.

Dialysis No (12) Not effective for removal of dilute contaminant waste streams; process

driven by concentration gradients across a membrane requiring high

concentrations of individual contaminants.

Electrodialysis No (5, 17) Process may be utilized for removal of inorganic contaminants; inorganic contaminants are not present above preliminary remediation

goal concentrations in groundwater at the Offpost Operable Unit; not

effective for removal of organic contaminants.

20000,317.10 - FS

0309111092
Table 2.8.1 - 1: Screening of Process Options for Groundwater

(Page 4 of 13)

Further

General Response Action Technoloxy Type Process Option Consideration Comment

In-Vessel Treatment: Phase Transfer Air stripping Yes (1, 3, 5) Well-developed technology effective in the removal of volatile Physical/Chemical organics compounds from aqueous waste streams; resulting air

(continued) emissions may require further treatment.

Steam stripping Yes (1, 5) Well-developed technology effective in the removal of volatile and

selected sernivolatile organics from aqueous waste streams; more

effective than air stripping for removal of less volatile, higher boiling

point, and more soluble organics; can handle broader concentration

ranges than air stripping; requires steam source.

Steam distillation Yes (1, 5, 12) Well-developed technology effective in removal of volatile and

sernivolatile organics. Distillate and still bottoma require further

treatment and disposal.

Sorption Granular activated carbon Yes (3) Well-developed technology effective in the removal of mixed organics (GAC) adsorption from waste streams; already implemented onpost for treatment of

groundwater extracted containment systems (i.e., Northern Boundary

Containment System and Nnorthwest Boundary Containment

System); will be implemented offpost during treatment of Interim

Remedial Action A extracted water; carbon must be disposed of or

regenerated.

Resin adsorption Yes (1) Potentially effective process for removal of organic contaminants from

aqueous waste streams; effectiveness depends on specific type of resin

used; typically used as a polishing step; resin regenerants require

further treatment.

Ion exchange No (1, 3, 17, Process may be utilized for removal of inorganic contan-dnants; inor18) ganic contaminants are not present above preliminary remedistion

goal concentrations in groundwater at the Offpost Operable Unit; not

effective for removal of organic contaminants.

20000,317.10 - FS

0309111092
Table 2.8. 1 - 1: Screening of Process Options for Groundwater

(Page 5 of 13)

Further

General Response Action Technology Type Process Option Consideration Comment

In-Vessel Treatment: Sorption (continued) Activated alumina No (18, 19) Process may be utilized for removal of inorganic contaminants;

Physical/Chemical inorganic contaminants are not present above preliminary remediation

(continued) goal concentrations in groundwater at the Offpost Operable Unit; not

effective for removal of organic contaminants.

Chemical Organics Hydrolysis No (5) Primarily used as a pretreatment process for organic compounds that

Treatment are otherwise refractory to treatment; none of the organics present in

water on the Offpost Operable Unit require hydrolysis in order to

implement treatment.

Solvent extraction No (1, 5) Not implementable for the following reasons: large volume of dilute

groundwater to be treated and the corresponding large volume of

required solvent; numerous solvents may be required to achieve

efficient extraction of each organic contaminant; generally both the

raffinate and the extract require further treatment.

Dechlorination No (5) Not implementable for aqueous media.

Oxidation Chlorination No (3, 5) Implementable but is likely to form chlorinated organics such as

chloroform; not effective for oxidation of low molecular weight

chlorinated organics.

Ozone oxidation Yes (5) Effective oxidizing agent for many organic compounds; by-product

analyses should be conducted; additional treatment may be required.

Hydrogen peroxide oxidation Yes (5) Utilized for oxidation of organics; common industrial process; often

requires addition of catalysts which include ferrous iron and ultraviolet light radiation (see ozone/hydrogen peroxide).

Ultraviolet light /ozone/- Yes (6) Effective in oxidation of halogenated organics, including halogenated

hydrogen peroxide solvents, chlorophenols, pesticides and polychlorinated biphenyls;

utilizes ultraviolet light radiation hydrogen peroxide, and/or ozone;

has been demonstrated on contaminated groundwater and leachate.

20000,317.10 - FS

0309111092
Table 2.8.1 - 1: Screening of Process Options for 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; used primarily for reduction of chromium (VI), Physical/Chemical mercury, lead; heavy metals are not contaminants of concern in

(continued) groundwater at the Offpost Operable Unit; not effective for removal

of organics.

Electrochemical reduction No (3) Reduction not applicable (see Chemical reduction).

Radiation Ultraviolet photollysis No (5) Generally not effective for complete destruction of organic compounds; by-products formed would require subsequent treatment.

Electron beam/gamma Yes (13, 14) Process has not been demonstrated for full-scale hazardous waste

irradiation treatment, but has been demonstrated at pilot/bench scale to be

effective for destruction of chloroform and other halogenated organics.

In-Vessel Treatment: Biological Rotating biological contactor Yes (1, 5, 10) Potentially effective for degradation of some organic compounds in

Biological Offpost Operable Unit groundwater (literature indicates that DIMP

and dieldrin are very resistant to biodegradation); organic substrate

concentrations in groundwater may be too low and require supplemental substrate addition; additional treatment may be required due to

biorefractory nature of chloroform, and DIMP.

Stabilization pond/lagoon No (7) Odor and offgas problems creating a fugitive emission and exposure

pathway problems; not effective for halogenated organics removal;

affected by temperature fluctuations.

Activated sludge Yes (1, 3, Effective conventional process for removal of many organic com5, 10) pounds (DIMP and dieldrin are resistant to biodegradation); heavy

metals and some organics can be harmful to organisms; potentially

effective for halogenated organics; additional treatment may be

required; treatment of generated offgases may be required.

Powder activated carbon Yes (1, 6) Utilizes activated sludge technology with the addition of powder

treatment (PACTO) activated carbon; advantages over conventional activated sludge

treatment include ability to deal with shock loading of toxic organics,

improved removal of chlorinated organics, and reduced offgas production of volatile organic compounds.

20000,317.10 - FS

0309111092
Table 2.8 .1 - 1: Screening of Process Options for 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 for degradation of some organic compounds Biological detected in Offpost Operable Unit groundwater (DIMP and dieldrin

(continued) are very resistant to biodegradation); additional organic substrate may

be required to sustain microbial population; additional treatment may

be required due to biorefractory nature of chloroform, dieldrin, and

DIMP.

Trickling filter Yes (1, 5, 10) Potentially effective for degradation of some organic compounds

detected in Offpost Operable Unit water (DIMP and dieldrin are very

resistant to biodegradation); organic substrate concentrations may be

too low and require supplemental substrate addition; additional

treatment may be required due to biorefractory nature of chloroform,

dieldrin, and DIMP.

Publicly owned treatment works No Difficult to implement for ilhe following reasons: publicly owned

treatment works unlikely to accept water containing RMA

contaminants; water rights may require replacement of groundwater.

Potentially effective for degradation of some organic compounds in

Offpost Operable Unit groundwater; water may require supplemental

organic substrate addition; not as well demonstrated as aerobic treatment processes for hazardous waste treatment; does not degrade as

broad a range of organic compounds but is more effective for degradation of some halogenated organics; additional treatment may be

required.

Submerged fixed film reactor Yes (2, 10) Potentially effective for degradation of some organic compounds

detected in Offpost Operable Unit groundwater (DIMP and dieldrin

are very resistant to biodegradation); organic substrate concentrations

may be too low and require supplemental substrate addition; additional treatment may be required due to biorefractory nature of

chloroform, dieldrin, and DIMP.

20000,317.10 - FS

0309111092
Table 2.8.1-1: Screening of Process Options for Groundwater

(Page 8 of 13)

Further

General Response Action Technoloxy Type Process Option Consideration Comment

In-Vessel Treatment: Evaporation Solar evaporation No (1, 11, 12) Not implementable due to the large area that would be required to Thermal treat the volumes of contaminated groundwater and fugitive emissions problems associated with the volatilization of contaminants.

Enhanced evaporation No (1, 11, 12) Not implementable due to area requirements and fugitive emissions

control of volatile contaminants.

Thermal oxidation/ Rotary hearth incineration No (15) Effective but difficult to implement due to large volumes of water to incineration be treated and the low concentrations of contaminants.

Multiple hearth incineration No (3) Effective but difficult to implement due to large volumes of groundwater to be treated and the low concentrations of contaminants.

Fluidized bed incineration No (3, 5) Effective but difficult to implement due to large volumes of groundwater to be treated and the low concentration of contaminants.

Circulating bed combustion No (3, 5, 6) Effective modified fluidized bed technology but difficult to implement

for large volumes of groundwater to be treated and the low concentration of contaminants.

Rotary kiln incineration No (3, 5) Effective but difficult to implement due to large volumes of groundwater to be treated and the low concentration of contaminants.

Submerged quench liquid No (20) Effective but difficult to implement due to large volumes of ground- incineration water to be treated and the low concentration of contaminants.

High temperature fluid wall No (3, 5) Effective but difficult to implement due to large volumes of groundreactor water to be treated and the low concentration of contaminants.

Molten salt destruction/sodium No (6) Not implementable for liquid wastes; low water content waste is

fluxing required.

Plasma arc No (3, 5) Effective for contaminants present but difficult to implement due to

large volumes of groundwater and the dilute concentrations of waste

to be treated.

20000,317.10 - FS

0309111092
Table 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 for contaminants present but difficult to implement for large Thermal incineration volumes of dilute groundwater requiring treatment.

(continued) (continued)

Wet air oxidation 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 difficult to implement due to

the large volumes of dilute groundwater to be treated.

In Situ Treatment Physical/Chemical Permeable treatment bed No (3) Potentially effective but not implementable for large volumes and

areas of contaminated 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 due to extensive area

requiring treatment. Complete oxidation of contan-dnants would be

difficult to achieve and there is potential for the formation of toxic

oxidation by-products.

Reduction No (3) Not applicable; used primarily for reduction of chromium (VI),

mercury, and lead to less soluble forms; not effective for treatment of

organics.

Water flushing Yes (3, 5) Potentially effective method for removing contaminants; potential for

(saturated zone) inadvertent mobilization of wastes and further plume development;

process increases the rate of contaminant removal and is typically a

component of pump and treat alternatives.

20000,317.10 - FS

0309111092
Table 2.8.1 - 1: Screening of Process Options for Groundwater

(Page 10 of 13)

Further

General Response Action Technology Type Process Option Consideration Comment

In-situ Treatment Enhanced Biological Aerobic degradation Yes (1, 3, 5, 6) Potentially effective for degradation of some of the organic (continued) contaminants detected in Offpost Operable Unit groundwater (DIMP

is resistant to biological treatment); may require organic substrate and

nutrient supplements.

Anaerobic degradation Yes (3,5) Potentially effective for degradation of organics (DIMP is resistant to

biodegradation); difficult to implement due to difficulties in maintaining an anaerobic environment in the aquifer.

Containment Subsurface Barriers Slurry wall Yes (3) Effective method of controlling groundwater and contaminant

migration when associated with groundwater extraction; already

implemented for RMA onpost contamination (i.e., Northern Boundary

Containment System and Northwest Boundary Containment System)-

Grout curtain Yes (3) Implementable for system of limited size; effectiveness depends on

ability to achieve a continuous barrier; typically grout curtains are less

effective than slurry walls.

Sheet piling No (3) Difficult to achieve effective seals at joints in sandy soils; difficult to

penetrate weathered bedrock; piling can be damaged by rocky soil;

implement ability depends on size of system required and depth to

bedrock.

Bottom sealing No (3) Not implementable due to the depth of contaminated groundwater,

the geologic conditions, and the broad areal extent of the plume;

effectiveness depends on achieving complete bottom seal which is

difficult to ensure.

Pneumatic seal No Difficult to implement over large areas of contamination, effectiveness

depends on complete pneumatic seal which is difficult to achieve.

Synthetic membrane cutoff wall No Difficult to implement due to depth to bedrock; ineffective if not

keyed into impermeable bedrock.

20000,317.10 FS

0309111092
Table 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 the prevention of groundwater migration.

Hydraulic controls Yes (3) Effective means of controlling groundwater migration by extraction

and injection of water which is used to modify hydraulic gradients;

selected as a part of the system for Interim 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 of closely 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. Cape and covers are utilized to prevent

infiltration of precipitation and runoff. Caps and covers may be

utilized as technologies for the remediation of groundwater if they act

to reduce plume development by significantly reducing groundwater

flow or if they eliminate a source of groundwater contamination by

preventing the contact of infiltrating water with soluble contaminants

in the vadose zone. Neither of theme applications applies to conditions

on the Offpost Operable Unit. Infiltration from precipitation has been

evaluated to be a very minor contribution to groundwater flow on the

offpost. No potential sources for groundwater contamination exist in

the offpost soil and vadose zone, except for low 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 source of groundwater

contamination.

20000,317.10 - FS

0309111092
Table 2.8.1 - 1: Screening of Process Options for Groundwater

(Page 12 of 13)

Further

General Response Action Technoloizy Type Process Option Consideration Comment

Storage Surface impoundment No Difficult to implement due to fugitive emission problem and risk

associated with volatile contaminants.

Containers No Not effective for large volumes of contaminated groundwater.

REFERENCES

(1) Metcalf & Eddy, Inc., 1985, Briefing: Technologies Applicable to Hazardous Waste, Prepared for U.S. Environmental Protection Agency Office of Research and Development, Hazardous Waste Enginering Research Laboratory, Cincinnati, Ohio, May.

(2) U.S. Environmental Protection Agency, 1989, Bioremediation of Hazardous Waste Sites Workshop, Speaker Slide Copies and Supporting Information: CERI-89-11, Office of Research and Development, Washington, D.C., Center for Environmental 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 of Emergency and Remedial Response, Washington, D.C., Office of Research and Development, Hazardous Waste Engineering Research Laboratory, Cincinnati, Ohio, October.

(4) The RCRA Land Disposal Restrictions - A Guide to Compliance, 1988 Edition, McCoy and Associates, Inc.

(5) U.S. Environmental Protection Agency, 1987, A Compendium of Technologies Used in the Treatment of Hazardous Wastes: EPA/625/8-87/014, Center for 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., New York, New York.

(8) Metcalf & Eddy Inc., Ehobanolous, G., 1979, Wastewater Engineering Treatment, Disposal, and Resuse, 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 Protection Agency, Washington, D.C., January.

(11) Ausum, S.R., 1985, Wastewater Treatment Plants Planning, Designing, and Operation, CBS College Publishing, New York, New York.

20000,317.10 - FS

0309111092
Table 2.8.1-1: Screening of Process Options for Groundwater

(Page 13 of 13)

REFERENCES (Continued)

(12) Kernmer, F.N., McCallion, J., 1979, The NALCO Water Handbook, McGraw Hill, New York, New York.

(13) Lichtenstrin, E.P., Schultz, K.R., and Fuhreman, T.W., Long-Term Effects of Carbon in Reducing Uptake of Insecticidal Soil Residues by Crops, Journal of Economic 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 of Miami.

(16) McCoy & Associates, 1983, Guide to Incinerator Manufacturers, The Hazardous Waste Consultant, Vol. I, No. 2, October.

(17) Forest, S., D., and Aly O.M., 1983, Chemistry of Water Treatment, Butterworth Publishers, Woburn, MA.

(18) Bennefield, L.D., Judkins, J.F., Weand, B.L., 1982, Process chemistry for Water and Wastewater Treatment, Prentice-Hall, Inc., Englewood Cliffs, N.J.

(19) Patterson, J.W., 1985, Industrial Wastewater Treatment Technology, 2 edition, Butterworth Publishers, Stoneham, MA.

(20) Brunner, C.R; 1987, Chemical Engineering; Vol. 94, No. 14, October 12.

20000,317.10 - FS

0309111092
Table 2.10.1-1: Selection of Representative Process Options for Groundwater

(Page I of 2)

Process Options Retained

From Second Level Selected Representative Technology Type - of Screeninj[ Process Option Criteria for Selection

No Further Action None No Further Action Retained as required by the National Contingency Plan.

Access Restrictions Land Use/Deed Restrictions Land Use/Deed Restrictions Effective in minimizing human contact with groundwater and

restricting use of groundwater for crop irrigation and watering offivestock.

Fencing and Warning Signs Fencing and Warning Signs Effective in reducing human exposure to contaminated media.

Land Acquisition Land Acquisition May be required to implement remedial action on privately

owned land.

Alternative Water Supplies Alternative Water Supplies Alternative Water Supplies Effective in preventing human contact with groundwater for

residents who rely on wells for domestic use.

Monitoring Groundwater Monitoring Groundwater Monitoring Effective in tracking plume development, natural attenuation,

and rernediation effects.

Groundwater Extraction Extraction Wells Extraction Wells Demonstrated effective at the boundary containment systems

for removal of groundwater; readily implementable at depths

which make for difficult installation of subsurface drains.

Subsurface Drains

Water Flushing Injection Injection Demonstrated effective at the boundary containment systems;

minimizes losses to evaporation in summer months, no difficulties associated with freezing in winter months.

Subsurface Injection Pump Back to Boundary Pump Back to Boundary Injection and treatment facilities already constructed and Containment System Containment System operational; cost-effective disposal and treatment option for

limited quantities of groundwater dependent on facility

(North Boundary Containment System, Northwest

Boundary Containment System) capacity.

Shallow Aquifer Injection Shallow Aquifer Injection Shallow aquifer injection demonstrated effective at the

boundary containment systems, minimizes losses to evaporation, allows for control of groundwater gradient; Shallow

aquifer injection includes both injection wells and trenches.

20000,317.10 - FS

0529111092
a

Table 2.10.1-1: Selection of Representative Process Options for Groundwater

(Page 2 of 2)

Process Options Retained

From Second Level Selected Representative

Technology Type of Screening Process Option Criteria for Selection

Chemical Inorganics Treatment Chemical Precipitation Chemical Precipitation Conventional process option, readily implementable, welldemonstrated, effective for removal of inorganics.

Phase Transfer Air Stripping Air Stripping Readily implemented; reliable and effective process option for

removing volatile organic compounds, easily operated.

Sorption Granular Activated Carbon Granular Activated Carbon Demonstrated effective for removal of organics at the boun- Adsorption Adsorption dary containment systems.

Oxidation Ultraviolet Ultraviolet Light/ Ozone/ Hydrogen Effective for destruction of a broad range of organic com- Light /Ozone/Hydrogen Peroxide Peroxide pounds.

In Situ Physical/Chemical Water Flushing (Saturated Zone) Water Flushing (Saturated Zone) Potentially effective for enhancing removal of contaminants

as a component of pump and treat alternatives.

Subsurface Barriers Slurry Wall Slurry Wall Demonstrated effective at the boundary containment systems.

Hydraulic Controls Hydraulic Controls Demonstrated effective at the boundary containment systems.

20000,317.10 - FS

0529111092
RMA1 1170

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Prepared for: Figure 2.5.1 -1

Program Manager for OFFPOST OPERABLE UNIT FEASIBILITY

Rocky Mountain Arsenal STUDY CONTAMINANT DISTRIBUTION ZONES

Commerce City, Colorado
RMAI 1122.1

32 33 34 35 315, 31

C>

4 6

L

9 12 7

7 16 15 14

OR BOWUNDA

22 24 19

0ý

NORTH BOUNDARY

CONTAINMENT

SYSTEM

30

01 -27 NORTýWEST 26 25 J

BOUNDARY

CONTAJNMENT C,

0 /10001" SYSTEM

NORTH

PLANTS

EXPLANATION

0 Well location

Areas where groundwater plumes of selected chemicals

tetrachloroethene, trichloroethene, dibromochloropropane, chloroform,

0 )o 3000 dieldrin (state std.05), DIMP (>600 ppb), exceed groundwater PRGs

Sea* In F"

Prepared for: Figure 2,6-1

Program Manager for

Rocky Mountain Arsenal AREAS OF EXCEEDANCES OF

GROUNDWATER PRGs IN THE OFFPOST

Commerce City, Colorado -UNCONFINED FLOW SYSTEM
RMA1 1034A.1

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

No Further Action -- 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

Shallow Aquff7-r ln7ject7ion]

Disposal

Discharge To POTW

Aboveground Surface Water Discharge

Discharge

Infiltration 13--In7]

Prepared for: Figure 2.8-1 a

Program Manager for

Rocky Mountain Arsenal GROUNDWATER PROCESS OPTIONS

Commerce City, Colorado
RMA1 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

Prepared for: Figure 2.8-1 b

Program Manager for

Rocky Mountain Arsenal GROUNDWATER PROCESS OPTIONS

Commerce City, Colorado
RMA1 1034C.1

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

Chlorination

Ozone Oxidation

Oxidation Hydrogon Peroxide

Oxidation

In-Vessel Treatment: Reduction -Chemical Reduction

Physical/Chemical Electra, 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, Colorado
RMA1 1034D.1

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

Submerged auench

Liquid Incineration

High Temperature

Fluid Wall Reactor

Molten Salt Destruction/

Sodium FIL

In-Vessel Treatment:

Thermal (Cont) Incineration (6-1,;

Supercritica

Oxidation

Wot Air

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

cutoff Wall

Dynamic Deep

Compaction__

Hydraulic Controls

Subsurlaceý-ým

Freezing 7771

Prepared for: Figure 2.8-1d

Program Manager for

ROCKY Mountain Arsenal GROUNDWATER PROCESS OPTIONS

Commerce City, Colorado
RMA1 1034E

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

Containment (cont)

Surface Imp-7u-dm

Storage 

Containers

Prepared for: Figure 2.8-1 e

Program Manager for

Rocky Mountain Arsenal GROUNDWATER PROCESS OPTIONS

Commerce City, Colorado
RMA1 103M

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

No Further Action No Further Action None

Land Use/Deed

Restrictions

r-Fencing and

Access Restrictions I Warning Signs

Alternative Vifililliti Alternative Water

Institutional Controls Supplies I Supplies

Monitoring -fGýr-undwater llwlionitorlnýg

Well Points

Groundwater Extraction

Surface Drains

Removal

Injection

Water Flushing

Flooding/Inf 117trstioýný:]

Pump Back to Boundary

Containment System

Subsurface Injection

Shallow Aquifer

Disposal Injection

Discha go To POTW

Aboveground

Dischargrdý

L-J Infiltration Basin

EXPLANATION

Technology Type/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

Commerce City, Colorado
RMAI 10388.1

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

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

S NO

-----------

Filtration

Solids Removal 

Sedimentation

In-Vessel Tr i i i i n

Physical/Ch en. ZT,

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

.... ......

9

Phase Transfer -Fsteam Stripping

steam Distil7lation7]

GAC Adsorption

Sorption 

Resin Adsor7pt7ion77 ]

ii .........ggg

.. .... .... ...... .......... .. WW . ........... ...

EXPLANATION

Technology Type/Process Option

Eliminated During Universal Screening

Prepared for: Figure 2.8.1 -1 b

Program Manager for

Rocky Mountain Arsenal RESULTS OF UNIVERSAL SCREENING OF

GROUNDWATER PROCESS OPTIONS

Commerce City, Colorado
RMA1 1038C.1

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

yw

ozone Oxidation

Oxidation i

r-Hydrogen Peroxide

Oxidation

IV---Vessel Treatment: I

Physical Chemical (co .... ýc 6ft

V-M

-- FR-di-tion Electron Beam/

Gamma Irradiation

Rotating B1

Contactor

=*ý"= NO

Activated S17udg-77]

Powdered Activated

Carbon Treatment (PACTO)l

Sequencing Batch In-Vessel Treatment: Reactor Biological _j 71

Trickling F117te7l'7771

... .

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

-FAn-eroble Digester

Submerged Fixed

Film Reactor

.... :j.6... ......

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

N 77M w

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

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

... .....

EXPLANATION

Technology Type/Process Option

Eliminated During Universal Screening

Prepared for: Figure 2.8.1-1c

Program Manager for

Rocky Mountain Arsenal RESULTS OF UNIVERSAL SCREENING OF

GROUNDWATER PROCESS OPTIONS

Commerce City, Colorado
M

RMA1 iO38D.1

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

............ ---- I'M

'M og, om

YX

m

Physical/Chemical

Water Flushing In-Situ Treatment (Saturated Zone)

Enhanced Biological 

Aerobic Degradation

Anaerobic ýe7gr-dýation

Slurry Wall

Grout Curtain

8 . . .

Containment Subsurface Barriers

..........

Hydraulic Control

_7u r 7f- c 7-D -FSub- ýmEXPLANATION

Technology Type/Pr9cess Option

Eliminated During Universal Screening

Prepared for: Figure 2.8.1-1d

Program Manager for

Rocky Mountain Arsenal RESULTS OF UNIVERSAL SCREENING OF

GROUNDWATER PROCESS OPTIONS

Commerce City, Colorado
a

RMA1 103SE

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

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

Containment (cont)

...........

.......... "I", QIQ..... *7 ..... =711

EXPLANATION

Technology Type/Process Option

Eliminated During Universal Screening

Prepared for: Figure 2.8.1-le

Program Manager for

Rocky Mountain Arsenal RESULTS OF UNIVERSAL SCREENING OF

GROUNDWATER PROCESS OPTIONS

Commerce City, Colorado
RMAI 1040A.1

RESPONSE ACTION TECHNOLOGY TYPE 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

Pump Back To Bound ry

Containment System

Subsurface Injection

Shallow Aqu

Injection

Disposal

........ 

..... ......... ............... w fftao VO W

In-Vessel Treatment: .............. Physical/Chemical .......... * ......

EXPLANATION

Technology Type/Process Option

Eliminated During the Second Level Screening

Prepared for: Figure 2.9-1a

Program Manager for

Rocky Mountain Arsenal RESULTS OF THE SECOND LEVEL

SCREENING OF GROUNDWATER

Commerce City, Colorado PROCESS OPTIONS
RMA1 1040B.1

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

Air Stripping

Phase Transfer

In-vessel Treatment: Sorption GAC Adsorption

Physical/Chemical (cond

Oxidation

...

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

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

Water Flushing Physical/C hemical (Saturated ZI one)

In-Situ Treatment

EXPLANATION

Techno' I e/process Option

Elimin.t%gyDuyrP.ng the Second Level Screening

Prepared for: Figure 2.9-1 b

Program Manager for RESULTS OF THE SECOND LEVEL Rocky Mountain Arsenal SCREENING OF GROUNDWATER

Commerce City, Colorado PROCESS OPTIONS
RMA1 1040C.1

RESPONSE ACTION TECHNOLOGY TYPE PROCESS OPTION

Slurry Wall

t I * oe'. * o I'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 OF THE SECOND LEVEL Rocky Mountain Arsenal SCREENING OF GROUNDWATER

Commerce City, Colorado PROCESS OPTIONS
RMA1 1063A.1

REPRESENTATIVE

RESPONSE ACTION TECHNOLOGYTYPE PROCESS OPTION PROCESS OPTION

No Further A ............... ,_FNo_ne "`

Land Use/Deed Land Use/Deed

Restrictions Restrictions

Fencing and Fencing and

Access Res rl Warning Slijilirilill Warning Signs

-4 ýýnd Agul-I L-nd Aq-i7,,1tl-_n

Institutional Entrols - _ Eitpo-rnatIve __ % __ ! I'll Alternative Water -Alternative Alternative .. ............... Su Plies Supplies Supplies Supplies

__[Groundwater- Groundwater -F ; ,onItorInq ............................................. M onitoring M onitoring

Extraction We Is

Groundwater Extraction -Týýxtra-tlon

rface

Subsurface D 8

Removal

Pump Back to Boundary Pump Back to Bounder

Disposal ... ......... Subsurface injection Containment System Containment System

................. ................... Shallow Aq% 11: 1 Shallow Aq Injection Injection

P hase Traniiii I'lilit, A ir Strippirill;ii ................

In-Vessel Treatment: ýPhysical/Chemical

Idation UV/Ozone/ UV/Ozone/

-Fox- - """"" ...... Hydrogen P111.1i iý, ill ill! I ililill! Hydrogen Peroxide

In-Situ Treat i'l a I' A VII'll'i I :illit I Water Flushirill[l Water Flushing

....................... D _ _ý (Saturated Zo iil Ill (Saturated Zone)

Prepared for: Figure 2.10.1-1a

Program Manager for SELECTED REPRESENTATIVE PROCESS

Rocky Mountain Arsenal OPTIONS FOR DEVELOPMENT OF

Commerce City, Colorado GROUNDWATER REMEDIAL ALTERNATIVES
RMAI 1063B.1

REPRESENTATIVE

RESPONSE ACTION TECHNOLOGYTYPE PROCESS OPTION PROCESS OPTION

slurry wall -sýlu-rrywýa,,ýý

Containmen, ......

-- fHydr-ulic C ydraulle controls

Prepared for: Figure 2.10.1 -1 b

Program Manager for SELECTED REPRESENTATIVE PROCESS

Rocky Mountain Arsenal OPTIONS FOR DEVELOPMENT OF

Commerce City, Colorado GROUNDWATER REMEDIAL ALTERNATIVES