TECHNICAL SUPPORT FOR ROCKY MOUNTAIN ARSENAL

Offpost Operable Unit

Endangerment Assessment/Feasibility Study

Final Report

Volume I of VIII

(Introduction)

November 24, 1992

Contract Number DAAA15-88-0021

Task RIFS1 (Delivery Order 0001)

PREPARED BY

Harding Lawson Associates

Environmental Science and Engineering, Inc.

PREPARED FOR

PROGRAM MANAGER FOR ROCKY MOUNTAIN ARSENAL

THIS DOCUMENT IS INTENDED TO COMPLY WITH THE NATIONAL

ENVIRONMENTAL POLICY ACT OF 1969.

THE INFORMATION AND CONCLUSIONS PRESENTED IN THIS REPORT REPRESENT

THE OFFICIAL POSITION OF THE DEPARTMENT OF THE ARMY UNLESS EXPRESSLY MODIFIED BY A SUBSEQUENT DOCUMENT. THIS REPORT CONSTITUTES THE RELEVANT PORTION OF THE ADMINISTRATION RECORD FOR THIS CERCLA OPERABLE UNIT.

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Page

VOLUME I - INTRODUCTION

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

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

PR E FA C E ........................................................... P-1

EXECUTIVE SUMM ARY .............................................. ES- I

IN TRODU CTIO N ..................................................... 1-1

G LO SSA R Y .......................................................... G -i

VOLUME II - ENDANGERMENT ASSESSMENT

PR E FA C E ........................................................... II - P-1

1.0 IDENTIFICATION OF CHEMICALS OF POTENTIAL CONCERN ........... 11- 1-1

1.1 GENERAL SITE DATA EVALUATION CONSIDERATIONS .......... 11-1-4

1.2 STATISTICAL PROCEDURES FOR COMPARISON WITH

BACKGROUND ............................................. 11 - 1-g

1.3 SELECTION OF CHEMICALS OF CONCERN ...................... II - 1-15

1.3.1 G roundwater ......................................... II - 1-15

1.3.2 Surface Water/Sediment ................................. 11- 1-17

1.3.3 Surficial Soil .......................................... 11 - 1-21

1.3.4 B iota ................................................ II - 1-22

1.4 SU M M A RY ................................................ II - 1-24

1.5 U NCERTAINTIES ........................................... II - 1-26

2.0 EXPOSURE ASSESSMENT ......................................... II - 2-1

2.1 PROPERTIES AND PROBABLE ENVIRONMENTAL FATES

OF CHEMICALS OF CONCERN ................................ 11- 2-1

2.1.1 Equilibrium Partitioning Properties of Chemicals of Concern ..... II - 2-2

2.1.1.1 Information Sources ............................. II - 2-3

2.1.1.2 Data Evaluation ................................ I I - 2- 5

2.1.1.3 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 .................. II - 2-19

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2.1.2.4 Compounds Containing Sulfur ...................... II - 2-23

2.1.2.5 Compounds Containing Phosphorus .................. Il - 2-24

2.1.2.6 Ionic Chem icals ................................. Il - 2-26

2.1.2.7 Miscellaneous Compounds ......................... Il - 2-30

2.1.3 U ncertainties ......................................... II - 2-31

2.2 CHARACTERIZATION OF EXPOSURE SETTING .................. II - 2-32

2.2.1 Site Characteristics Affecting Contaminant Migration ........... II - 2-32

2.2.1.1 Site Description and History ....................... 11- 2-32

2.2.1.2 Environmental Setting ............................ Il - 2-33

2.2.1.3 Sampling Locations and Media ..................... II - 2-34

2.2.1.4 Summary of Offpost Operable Unit Contamination ...... II - 2-36

2.2.2 Potentially Exposed Populations ........................... 11- 2-37

2.2.2.1 Residential Land Use ............................ 11- 2-38

2.2.2.1.1 Procedures ........................... Il - 2-38

2.2.2.1.2 Results .............................. Il - 2-41

2.2.2.2 Commercial/ Industrial Land Uses ................... II - 2-42

2.2.2.3 Qualitative Assessment 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 ..................................... Il - 2-45

2.2.2.4.1 Existing Groundwater Use ............... 11 - 2-45

2.2.2.4.2 Projected Future Use of Groundwater ....... II - 2-49

2.2.2.4.3 Surface-Water Use ..................... 11 - 2-50

2.3 EXPOSURE PATHWAYS ...................................... 11 - 2-51

2.3.1 Potential Sources, Release Mechanisms, and Transport Media ..... 11 - 2-51

2.3.1.1 G roundwater ................................... Il - 2-51

2.3.1.2 Surface Water and Sediment ....................... 11- 2-54

2.3.1.3 A tm ospheric ................................... Il - 2-55

2.3.1.4 B iotic ........................................ 11 - 2-55

2.3.2 Potential Exposure Points ................................ II - 2-56

2.3.3 Potential Exposure Pathways and Routes ..................... II - 2-57

2.3.3.1 Inhalation Route ................................ II - 2-57

2.3.3.2 Dermal Route .................................. 11 - 2-60

2.3.3.3 Ingestion Route ................................. 11 - 2-61

2.3.4 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 ....................................... 11 - 2-66

2.4.2 Exposure Assessment Procedures and Exposure Point

Concentrations ........................................ II - 2-71

2.4.2.1 Statistical Procedures Used to Evaluate Monitoring

D ata ......................................... II - 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 ...................................... 11 - 2-74

2.4.2.3.1 Chicken Eggs ......................... II - 2-75

2.4.2.3.2 Vegetables ............................ II - 2-75

2.4.2.3.3 Beef ................................ II - 2-81

2.4.2.3.4 Dairy ............................... II - 2-82

2.4.2.4 Summary of Nonche mical -specific Parameters ......... II - 2-83

2.4.2.4.1 Groundwater Fraction Used for

Irrigation (GWF) ....................... 11- 2-83

2.4.2.4.2 Fraction Exposed (f.) ................... Il - 2-83

2.4.2.4.3 Partition Coefficient Deposited from

Spray (K d.p)) .......................... II - 2-83

2.4.2.4.4 Cattle Water/Feed Intakes (IPWM and Ipwd) .... Il - 2-84

2.4.2.4.5 Cattle Feed/Soil Intake (1p.) ............... Il- 2-84

2.4.2.5 Sample Calculations and Comparison With the Available

M onitoring Data ................................ II - 2-84

2.4.2.6 R esults ....................................... II - 2-86

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

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

2.4.3.2 Exposure Factors ................................ II - 2-95

2.4.3.3 R esults ....................................... 11 - 2-98

2.4.4 Estimation of Chemical Intakes for Commercial/ Industrial

Scenario ............... II - 2-99

2.4.4.1 Estimation of Chemical Intakes ..................... II - 2-100

2.4.5 Uncertainty Analysis (Residential) ......................... II - 2-100

2.4.5.1 Preliminary Sensitivity Analysis .................... Il - 2-101

2.4.5.2 Additional Scoping Considerations .................. Il - 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 II - 2-106

2.4.5.5.1 Input Parameters ....................... 11 - 2-106

2.4.5.5.2 Example Results ....................... Il - 2-108

2.4.5.5.3 Summary of Results .................... Il - 2-110

2.5 SUMMARY OF EXPOSURE ASSESSMENT ........................ II - 2-112

2.5.1 Residential Scenario ...... 11-2-113

2.5.2 Commercial/ Industrial Scenario ........................... II - 2-116

2.6 UNCERTAINTIES ........................................... II - 2-116

3.0 TOXICITY ASSESSMENT .......................................... 11- 3-1

3.1 HUMAN REFERENCE DOSES ................................. II - 3-1

3.2 POTENTIAL CARCINOGENICITY OF CHEMICALS OF CONCERN .... 11- 3-5

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

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

3.3 NONHUMAN RECEPTOR TOXICITY REFERENCE VALUES ........ 11- 3-7

3.3.1 V egetation ........................................... 11 - 3-8

3.3.2 Aquatic Organism s ..................................... 11- 3-8

3.3.3 Terrestrial Organisms ................................... II - 3-9

3.3.3.1 Derivation of a No-Observed- Adverse- Effect Level ..... 11 - 3-10

33.3.2 Phylogenetic Differences .......................... 11 - 3-13

3.3.3.2.1 Intraspecies Differences ................. 11 - 3-16

3.3.3.2.2 Genus and Species Differences ............ 11 - 3-16

3.3.3.2.3 Family/Order Differences ................ II - 3-18

3.3.3.2.4 Threatened or Endangered Species .......... 11 - 3-19

3.4 MAXIMUM ACCEPTABLE TISSUE CONCENTRATIONS ............ 11 - 3-19

3.5 UNCERTAINTIES IN TOXICITY ASSESSMENT .................... Il - 3-20

3.5.1 Human Toxicity Assessment .............................. II - 3-20

3.5.2 Toxicity Reference Values ............................... 11- 3-21

VOLUME III - ENDANGERMENT ASSESSMENT

4.0 HUMAN RISK CHARACTERIZATION ............................... III - 4-1

4.1 RESIDENTIAL SCENARIO .................................... III - 4-2

4.1.1 Hypothetical Future Exposures ............................ 111- 4-3

4.1.1.1 Hypothetical Carcinogenic Risks Related to Background . . III - 4-4

4.1.1.2 Child Chronic Hypothetical Future Hazard Indices ...... III - 4-5

4.1.1.3 Adult Chronic Hypothetical Future Hazard Indices ...... III - 4-6

4.1.1.4 Hypothetical Future Carcinogenic Risk ............... III - 4-6

4.1.1.5 Zone-specific Risks ............................. III - 4-6

4.1.1.6 Acute/Subchronic Effects ......................... 111- 4-10

4.1.2 Hypothetic Current Risks Versus Hypothetical Future Risks ...... 111- 4-12

4.1.3 Health Risk at* Most Likely Exposure Intakes ................. III - 4-12

4.1.4 Alternative Risk Estimate Based on Predicted Decline in

Groundwater Concentrations .............................. III - 4-14

4.2 COMMERCIAL/INDUSTRIAL SCENARIO ........................ 111-4-14

4.2.1 Adult Chronic Hypothetical Future Hazard Indices ............. III - 4-15

4.2.2 Hypothetical Future Carcinogenic Risks III - 4-15

4.2.3 Carcinogenic 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 Systems .............................. III - 5-2

5.1.1.2 Aquatic Systems ...................... : , * * * * * , * * III - 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 ............................. III - 5-8

5.2.1.2 Aquatic Receptors ............................... III - 5-10

5.2.2 Potential Exposure Pathways .............................. 111- 5-11

5.2.3 Exposure Point Concentrations ............................ III - 5-14

5.2.4 Ecological Assessment Endpoints .......................... III - 5-15

5.2.4.1 Terrestrial ..................................... III - 5-15

5.2.4.2 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 ................ III - 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 ...................... III - 5-24

5.2.6.5 Dietary and Soil Ingestion Pathways for Livestock ....... III - 5-24

5.3 RISK CHARACTERIZATION .................................. III - 5-26

5.3.1 Terrestrial Food Web Ecological Risk ....................... III - 5-26

5.3.2 Aquatic Food Web Ecological Risk ......................... III - 5-29

5.3.3 Underwater Aquatic Life ................................ III - 5-30

5.3.4 Agricultural Life ...................................... III - 5-30

5.3.5 Ecological Risk Assessment Uncertainty ..................... III - 5-31

5.3.5.1 Site Characterization ............................. III - 5-31

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

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

5.4 SU M M A R Y ................................................ III - 5-34

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6.0 CONCLUSIONS .................................................. 111-6-1

7.0 REFERENCES ................................................... 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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VOLUME 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 II - 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 N o A ction ............................................ V - 2-23

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

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

2.7.4 R em oval ............................................. V - 2-24

2.7.5 Treatm ent ............................................ V - 2-24

2.7.6 D isposal ............................................. V - 2-24

2.8 IDENTIFICATION AND SCREENING OF TECHNOLOGY TYPES AND

PROCESS OPTIONS .......................................... V - 2-25

2.8.1 U niversal 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

2.8.4.4.1 Water Flushing ........................ V - 2-46

2.8.4.4.2 Enhanced Biological Treatment ............ V - 2-47

2.8.4.5 Containment ................................... V - 2-48

2.8.4.5.1 Subsurface Barriers ..................... V - 2-48

2.9 SUMMARY OF PROCESS OPTION SCREENING ................... V - 2-50

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

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

VOLUME VI - FEASIBILITY STUDY

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

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

3.1.1 U.S. Environmental Protection Agency Guidance for

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

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

3.2.1 A pproach ............................................ V I - 3-3

3.2.1.1 Groundwater Model Input Into Alternatives

Developm ent ................................... 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 ........................... VI - 3-12

3.4.1.2 Groundwater Pretreatment Process Options ............ VI - 3-13

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3.4.1.3 Continued Operation of the Boundary Systems and

Compliance With Off'post Operable Unit Preliminary

Remediation Goals .............................. VI - 3-13

3.5 GROUNDWATER REMEDIAL ALTERNATIVES IDENTIFICATION ... VI - 3-13

3.5.1 Identification of Groundwater Alternatives: North Plume Group ............. - 3-14 ....: ...................... V I

3.5.1.1 Alternative No. N- I o 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

Plum e G roup .................................. VI - 3-25

4.0 SCREENING OF ALTERNATIVES ................................... VI - 4-1

4.1 M ETHODOLOGY ............................................ VI - 4-1

4.1.1 Effectiveness Evaluation ................................. VI - 4-1

4.1.2 Implementability Evaluation .............................. VI - 4-2

4.1.3 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

Necessary ..................................... VI - 4-6

4.2.1.2.1 Effectiveness .......................... VI - 4-7

4.2.1.2.2 Implementability ....................... VI - 4-8

4.2.1.2.3 Cost ................................ VI - 4-8

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

Restrictions .................................... 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 ................... : , , , , * * * , * , I * 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 ................................ V I - 4-17

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

4.2.2 Screening of Groundwater Alternatives - Northwest Plume

G roup ............................................... V I - 4-18

4.2.2.1 Alternative No. NW-1: No Action .................. VI - 4-18

4.2.2.1.1 Ef fectiveness .......................... VI - 4-19

4.2.2.1.2 Implementability ....................... VI - 4-20

4.2.2.1.3 Cost ........................ * , , * , * * * V I - 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 ................................ V I - 4-22

4.2.2.3 Alternative No. NW-3: Land Acquisition and Deed

R estrictions .................................... 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 ................................ V I - 4-27

4.2.2.5 Alternative Screening Summary and Recommendation .... VI - 4-27

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

5.1 CR ITER IA ................................................. 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: No Action ................... VI - 5-17

5.4.2.1.1 Chemical -specific Applicable or

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

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Pa_p&

5.4.2.1.2 Action-specific Applicable or Relevant

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

5.4.2.1.3 Location -specific Applicable 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 Chemical- specific Applicable or

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

5.4.2.2.2 Action-specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-18

5.4.2.2.3 Location -specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-18

5.4.2.3 Alternative No. N-4: Interim Response Action A ....... VI - 5-18

5.4.2.3.1 Chemical-specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-18

5.4.2.3.2 Action-specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-18

5.4.2.3.3 Location -specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-18

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

Response Action A ..................... VI - 5-18

5.4.2.4.1 Chemical _ specific Applicable or Relevant

and Appropriate Requirements ............ VI - 5-18

5.4.2.4.2 Action-specific Applicable or Relevant

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

5.4.2.4.3 Location -specific Applicable or Relevant

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

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

5.4.2.5.1 Chemical-specific Applicable or Relevant

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

5.4.2.5.2 Action-specific Applicable or Relevant

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

5.4.2.5.3 Location-specific Applicable 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

N ecessary ..................................... V I - 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 ................ Vl- 5-26

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

5.4.5.2.2 Adverse Environmental Impacts ........... V1- 5-26

5.4.5.2.3 Implementation Period .................. Vl- 5-26

5.4.5.3 Alternative No. N-4: Interim Response Action A ........ VI- 5-27

5.4.5.3.1 Protection 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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5.4.6 Implementability ....................................... VI - 5-29

5.4.6.1 Alternative No. N-1: No Action .................... VI - 5-29

5.4.6.2 Alternative No. N-2: Continued Operation 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 Cost ................... ' * * * * ' :****'- *- **- - ** VI - 5-31

5.4.7.1 Alternative No. N-1: No Action .................... VI - 5-31

5.4.7.2 Alternative No. N-2: Continued Operation 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

Environm ent ................................... VI - 5-33

5.5.1.2 Compliance With Applicable or Relevant and

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

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

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

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

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

5.5.1.7 Cost ......................................... V I- 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

Environment ................................... VI- 5-37

5.5.2.2 Compliance With Applicable or Relevant and

Appropriate Requirements ........................ Vl- 5-37

5.5.2.3 Long-term Effectiveness and Permanence ............. VI- 5-37

5.5.2.4 Reduction in Toxicity, Mobility, and Volume .......... VI- 5-37

5.5.2.5 Short-term Effectiveness .......................... VI- 5-38

5.5.2.6 Implementability ................................ VI- 5-38

5.5.2.7 C ost ......................................... 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

A lternative .................................... V I - 6-7

6.2.2 Consistency 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 SU M M ARY ................................................ VI - 6-9

7.0 REFER EN CES ................................................... 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 II - ENDANGERMENT ASSESSMENT

1.0-1 Data Needs in Each Medium

1.3.1-1 Statistical Comparison With Background - Groundwater

1.3.1-2 Chemicals 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 - Surf icial 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 KOW)

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

2.1-6 Uptake to Roots, Kwr (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, K., (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, KPM1 for All Chemicals of Concern

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

2.1-12 Fish Bioaccumulation Coefficients, KWf (1/kg), for Surface-Water Chemicals of

Concern

2.2.2.1.2-1 Population by Land-Use Area

2.2.2.1.2-2 Land Use by Land-Use Area (in acres)

2.2.2.1.2-3 Potentially Sensitive Subpopulations

2.2.2.4.1-1 Well-Use Data From Colorado State Master Extract Register

2.2.2.4.1-2 Well-Use Data From Consumptive Use Phase 1, 11, and III Studies

2.2.2.4.1-3 Preliminary Estimate of the Number of Wells by Well Use in the Offpost Operable Unit

2.2.2.4.1-4 Well Use Data From the Tri-County 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 I

2.4.2.6-2 Exposure Concentrations, Groundwater, Zone 2 (Northern Paleochannel)

2.4.2.6-3 Exposure Concentrations, Groundwater, Zone 3 (96th Avenue and Peoria Street)

2.4.2.6-4 Exposure Concentrations, Groundwater, Zone 4 (First Creek Paleochannel)

2.4.2.6-5 Exposure Concentrations, Groundwater, Zone 5 (Northwest Boundary)

2.4.2.6-6 Exposure Concentrations, Groundwater, Zone 6

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(Continued)

2.4.2.6-7 Estimated Future Exposure Concentrations for Aldrin and Dieldrin, Groundwater, Zones 3 and 4

2.4.2.6-8 Exposure Concentrations in Surface Water

2.4.2.6-9 Exposure Concentrations in Surficial Soil and Sediments (mg/kg)

2.4.2.6-10 Reasonable Maximum Exposure Concentrations in Vegetables: Maximum

Concentrations Estimated in Any Zone

2.4.2.6-11 Reasonable Maximum Exposure Concentrations in 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 - I Dermal Absorption from Soil/Sediment

2.4.3.2-1 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 Summary

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

4

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 Summary 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 - FEASIBILITY 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 - 1-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 Summary 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 xxiv
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

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0306111892 xxv
LIST OF FIGURES

(Continued)

Volume II - ENDANGERMENT ASSESSMENT

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

Operable Unit

1.2-1 Offpost Operable Unit Background Surficial Soil Sampling Locations

1.2-2 Offpost Operable Unit Designated Surficial Soil Data Sets for Comparison With

Background

1.2-3 Off'post Operable Unit First Creek Surface-Water Sampling Locations

1.2-4 Offpost Operable Unit First Creek Sediment Sampling Locations

1.2-5 Off post Operable Unit Surface-Water Sampling Locations

1.2-6 Offpost Operable Unit Sediment Sampling Locations

2.2.2.1.1-1 Off post Operable Unit Land Use Areas and Consumptive Use Phase 11 Study

Area

2.2.2.1.2-1 Offpost Operable Unit - Future Land Use

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

2.3.1-1 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 - i 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

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0306111992 xxvi
LIST OF FIGURES

(Continued)

2.4.5-2 Offpost 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 Offpost 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)

2.4.5.5.2-4 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 Offpost 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

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0306111992 xxvii
M

LIST OF FIGURES

(Continued)

4.1.1-4 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway -

Zone ]A, Lifetime Rural Resident, RME

4.1.1-5 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway -

Zone IB, Lifetime Rural Resident, RME

4.1.1-6 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway -

Zone IC, Lifetime Rural Resident, RME

4.1.1-7 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway -

Zone 2, Lifetime Rural Resident, RME

4.1.1-8 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway -

Zone 3, Lifetime Urban Resident, RME

4.1.1-9 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway -

Zone 4, Lifetime Urban Resident, RME

4.1.1-10 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway - Zone 5, Commercial/Industrial, RME

4.1.1-11 Carcinogenic Risks Described by Chemical, Medium, and Exposure Pathway -

Zone 6, Lifetime Rural Resident, RME

4.1.1-12 Child Acute Liver Hazard Indices

4.1.1-13 Subchronic Child Liver Hazard Indices, Maximum and Minimum 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

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0306111892 xxviii
LIST OF FIGURES

(Continued)

Volume V - FEASIBILITY STUDY

2.5.1-1 Offpost 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

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0306111892 xxix
PREFACE TO THE FINAL ENDANGERMENT ASSESSMENT/FEASIBILITY STUDY

The Rocky Mountain Arsenal Offpost Operable Unit (OU) Endangerment Assessment/Feasibility Study (EA/FS) is presented in eight volumes. The contents of each volume are

outlined below. To assist the reader, the complete Table of Contents is included at the beginning

of each text volume; appendix volumes include a list of appendixes in the front. Tables and

figures for each volume are included at the end of that volume for the sections included in the

same volume. The Introduction, EA, FS, and each appendix have separate reference lists.

VOLUMEI

- Table of Contents EA/FS - complete Table of Contents for all volumes, followed by List

of Tables and List of Figures

- Preface EA/FS - explanation of the organization of the EA/FS report

- Executive Summary - summary of information presented in the EA/FS

- Introduction to the EA/FS - introductory material common to both the EA and the FS,

including site history and nature and extent of contamination at the Offpost OU

- Glossary EA/FS - list of acronyms and abbreviations used in the EA/FS

VOLUME II

- Table of Contents EA/FS - complete Table of Contents is included in each volume

- Preface EA - outline of the organization of the EA

- Section 1.0 EA - Identification of Chemicals of Potential Concern

- Section 2.0 EA - Exposure Assessment

- Section 3.0 EA - Toxicity Assessment

- Volume II Tables EA - tables for Sections 1.0, 2.0, and 3.0 of the EA

- Volume 11 Figures EA - figures for Sections 1.0, 2.0, and 3.0 of the EA

VOLUME III

- Table of Contents EA/FS - complete Table of Contents is included in each volume

- Section 4.0 EA - Human Risk Characterization

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0306111892 P-1
- Section 5.0 EA - Ecological Assessment

- Section 6.0 EA - Conclusions

- Section 7.0 EA - References

- Volume III Tables EA - tables for Sections 4.0, 5.0, and 6.0 of the EA

- Volume III Figures EA - figures for Sections 4.0, 5.0, and 6.0 of the EA

VOLUME IV

- List of EA Appendixes

- EA Appendixes (A through H) - All Appendixes for the EA

VOLUME V

- Table of Contents EA/FS, - complete Table of Contents is included in each volume

- Preface FS - outline of the organization of the FS

- Section 1.0 FS - Feasibility Study Purpose and Organization

- Section 2.0 FS - Development of Remedial Action Objectives and Screening of

Technologies

- Volume V Tables FS - tables for Sections 1.0 and 2.0 of the FS

- Volume V Figures FS - figures for Sections 1.0 and 2.0 of the FS

VOLUME VI

- Table of Contents EA/FS - complete Table of Contents is included in each volume

- Section 3.0 FS - Development of Remedial Alternatives

- Section 4.0 FS - Screening of Alternatives

- Section 5.0 FS - Detailed Analysis of Alternatives

- Section 6.0 FS - Selection of the Preferred Sitewide Alternative

- Section 7.0 FS - References

- Volume VI Tables FS - tables for Sections 3.0, 4.0, 5.0, and 6.0 of the FS

- Volume VI Figures FS - figures for Sections 3.0, 4.0, 5.0, and 6.0 of the FS

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0306111892 P-2
VOLUME VII

- List of FS Appendixes

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

VOLUME VIII

- Response to Comments

- Glossary - list of acronyms used in the responses

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0306111892 P-3
EXECUTIVE SUMMARY

This Final Endangerment Assessment/Feasibility Study (EA/FS) is consistent with the

National Contingency Plan (NCP), the Comprehensive Environmental Response, Compensation,

and Liability Act (CERCLA), the regulations implementing the National Environmental Policy

Act of 1969 (NEPA), and Federal Facility Agreement (FFA).

ENDANGERMENT ASSESSMENT

An Endangerment Assessment was performed for the Offpost Operable Unit (OU) of Rocky

Mountain Arsenal (RMA). The offpost area consists of 27 square miles located to the north and

northwest of RMA. The Offpost OU is defined by the Federal Facility Agreement as that portion

of the offpost area where the hazardous substances, pollutants, or contaminants from RMA are

found, and which is subject to remedial action. On the basis of information existing at the

conclusion of the offpost remedial investigation (RI) and the beginning of the EA/FS, the Offpost

OU is assumed to be coincident with the offpost area. It is currently characterized by rural

agricultural and residential land uses, with some industrial land use. In the future, land use is

projected to change to more commercial, industrial, and recreational land use in areas adjacent to

RMA, with some areas zoned for residential development (Adams County Planning Commission,

1990). For these reasons, a rural residential scenario (including agriculture), an urban residential

scenario (excluding farm animals), and a commercial/industrial scenario were evaluated. An

ecological assessment was also performed, due in part to the bald eagle habitat and other sensitive

environments in the Offpost OU. The major steps performed in the EA included data evaluation,

identification of chemicals of potential concern, exposure assessment, toxicity assessment, human

risk characterization, and ecological assessment.

Identification of Chemicals of Potential Concern

Chemicals of potential concern (COCs) were identified by medium. The primary criterion

for identification of COCs was a statistically significant increase in concentration in samples

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0306111892 ES- I
collected f rom the Of f post OU when compared with samples f rom locations believed to be

unaffected by RMA contamination (i.e., background).

The statistical procedures used in this assessment to determine whether chemical concentrations were elevated above background levels contained several conservative elements when

compared with procedures recommended by published guidance. These conservative elements

were included to compensate for small sample size and low frequency of detection above certified

reporting limits in some of the data sets. The conservative features built into the statistical

procedure exceeded published guidance and resulted in the inclusion of four groundwater COCs,

two surface-water COCs, and one surface soil COC that would normally have been excluded.

Thirty-four COCs were identified for groundwater, including nine pesticides, five inorganic

compounds, and 20 volatile or sernivolatile organic compounds. Ten COCs were identified for

surface water, including four pesticides, two organic compounds, and four inorganic compounds.

Each is also a COC for groundwater, the primary source of offpost surface-water contamination.

The six COCs identified in sediments are all pesticides. These COCs are associated with

groundwater and/or surface water that interacts with the sediments in First Creek. Six pesticides

were identified as COCs in surface soils.

All of the thirty-four COCs were evaluated for biota; however, only those COCs for which a

complete pathway of exposure existed for a specific receptor organism were evaluated in the

ecological assessment.

Exr)osure Assessment

The major elements of the exposure assessment included fate and transport of COCs,

characterization of the exposure setting and exposure pathways, quantification of exposure, and

an uncertaintv analysis of calculated exposure intakes.

Chemicals migr ated to the Offpost OU as a result of past operations at RMA, primarily by

shallow groundwater and airborne pathways . Contaminant transport by both pathways has been

controlled by onpost interim remedial actions. Offpost OU surface water was contaminated

primarily by the natural interaction with offpost groundwater. Offpost OU surface soil was

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0306111892 ES-2
contaminated by the deposition of airborne contaminants, non-RMA-related intentional

agricultural application of pesticides, and irrigation practices. Air monitoring data indicate that

the air pathway does not contribute to human exposure.

The COCs exhibit great variability in their mobility and persistence in environmental media.

Organochlorine pesticides are relatively immobile and persistent, tending to associate with soils

and sediments and tending to bioaccumulate in the food chain; the organochlorine pesticides are

the only COCs elevated above background levels in soils and sediments. Most of the remaining

COCs are mobile in groundwater, and the aromatics and aliphatics are volatile in surface waters.

The fate properties of the COCs tend to determine their distribution in the Offpost OU.

Groundwater containing elevated levels of COCs exists north and northwest of RMA in

three distinct plumes with characteristically different groundwater quality conditions. These flow

paths are referred to as the northern paleochannel, due north of the RMA north.boundary; the

First Creek paleochannel, paralleling First Creek to the northwest from the RMA north boundary;

and the northwest paleochannel, west of the RMA northwest boundary. The northern and First

Creek paleochannels comprise the North Plume Group, and the northwest paleochannel is referred

to as the Northwest Plume Group. The alluvial flow system transports most of the contamination

in paleochannels characterized by coarser sediments. Groundwater traveling through the First

Creek paleochannel discharges to First Creek, probably seasonally, resulting in elevated levels of

several COCs in First Creek. First Creek discharges to O'Brian Canal. Concentrations of COCs

are reduced substantially upon discharge to O'Brian Canal; only two COCs (diisopropyl

methylphosphonate [DIMP] and fluoride) are elevated in the Canal.

Land use in the Offpost OU has been predominantly agricultural and rural residential, with

localized commercial/ industrial land uses and open space. The portion of the Offpost OU north

of O'Brian Canal, where irrigation water is available from Burlington Ditch, contains many

vegetable and turf farms. A recent change in land use affecting exposure to COCs was the

purchase of former residential properties near the intersection of 96th Avenue and Peoria Street

by Shell Oil Company. Based on local planning documents, it is expected that development

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0306111892 ES-3
resulting from encroachment of the Denver suburban fringe from the southwest and the new

regional airport to the east will supplant agricultural land uses with residential and commercial/industrial land uses over the next 20 years.

The predominant traditional agricultural land use of the area supports the evaluation of

exposure pathways involving consumption of foods produced in the Offpost OU. A complete

pathway must have a source, a mechanism of release, a transport medium, an exposure point, a

receptor (e.g., humans must be present to be exposed), and an exposure route (e.g., ingestion).

The most important pathways considered under the residential reasonable maximum exposure

(RME) scenario, including hypothetical future exposure pathways that may not be complete at this

time, are direct ingestion of groundwater, inhalation of volatile COCs released from groundwater

used for domestic purposes (e.g., showering, cooking), and consumption of vegetables, meat, eggs,

and dairy products produced in the Offpost OU. Exposure concentrations in foods were estimated

using equilibrium partition models. Predictions by the models were compared to limited sitespecific sampling and analytical data, and the model results approximated the limited number of

observed concentrations in meat and eggs. Data for milk and vegetables were insufficient to

verify the models.

Current and projected future com merc ial/ industrial land uses in zone 5 suggested that

exposure pathways consistent with this land use should be evaluated. The most important

pathways considered in the RME commercial/industrial scenario are direct ingestion of groundwater and inhalation of volatile COCs from other uses (e.g., showering).

For purposes of the EA, the Offpost OU was subdivided into six geographic zones, each

with distinct exposure conditions. Variations in medium-specific exposure concentrations and

land and water use were considered in defining these zones, which are shown in Figure ESI. A

separate exposure assessment was performed for each zone. Hypothetical future intakes under the

RME scenario are greatest in zones 2, 3, and 4, directly north of the RMA north boundary.

Exposure factors used in this EA conformed to U.S. Environmental Protection Agency

(EPA) RME guidance wherever applicable factors existed. Where EPA guidance was not

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available, RME exposure factors were derived for the 90th percentile of the range of the exposure

factor. COC intakes were estimated for lifetime, chronic, and acute exposure durations. The

lifetime scenario begins at age 0 and extends for 30 years, considering age-dependent body

weight, milk consumption, and direct ingestion of soil. Intakes were estimated for children and

adult women to address potentially sensitive subpopulations. The child chronic scenario assumes

an exposure duration from ages I to 9. Children tend to be exposed at greater rates than adults, so

the child chronic scenario represents the RME for chronic noncarcinogenic risk assessment.

Commercial/industrial intakes were estimated for adult workers with a 25-year duration.

The RME COC intake estimates include hypothetical exposure pathways that have not been

complete for several years (i.e., exposure has not occurred by these pathways). For example,

previous residents in zones 3 and 4 and current residents in zone 5 have water supplies other than

shallow wells. There are no current residents in zones 5 and 4. Therefore, residential intake

estimates in these zones are conservative because the pathways do not represent existing exposures.

A limited quantitative uncertainty analysis was performed to. evaluate the possible exposure

variation among the potentially exposed population. The uncertainty analysis implies that up to

99 percent of a future exposed population would experience intakes less than the RME. Although

there are uncertainties in exposure estimates, the EA generally used conservative approaches to

limit the potential for underestimating exposures. Thus, it is reasonable to conclude that the RME

falls above the 95th percentile of possible exposures and is thus in the range of exposures

consistent with the definition of RME. The uncertainty analysis combines uncertainty in defining

exposure concentrations (from monitoring data and models) and variability in hypothetical

exposures. The uncertainty analysis process demonstrates that most of the variance in intake

estimates can be attributed to variability across the population rather than uncertainty in defining

the exposure concentrations.

Toxicity Assessment

Available information on the toxic effects of the COCs, emphasizing information pertinent

to the evaluation of subchronic and chronic exposures at relatively low intakes, is summarized in

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the toxicity assessment section of the report. Available reference doses and cancer slope factors

published by EPA were used in this EA. When chronic reference doses were unavailable from

EPA, they were estimated or identified from other sources, particularly the RMA onpost toxicity

assessment contained in the Final Human Health Exposure Assessment (Ebasco, 1990).

Two of the COCs, arsenic and benzene, are known human carcinogens (EPA category A).

Ten COCs are probable human carcinogens (EPA category B2). Category B2 chemicals have

sufficient evidence that the chemical causes cancer in laboratory animals, but insufficient

evidence for cancer in humans. Most of the COCs have the potential for noricarcinogenic effects

on the liver (hepatic system), and these chemicals were grouped to evaluate the probability of

adverse effects on the liver.

The potential effects of the contaminants on terrestrial wildlife, livestock, terrestrial

vegetation. and aquatic organisms were also summarized in the toxicity assessment section of this

report. Toxicity reference values for biota were developed, which are intended to represent

exposure levels that would result in a low probability of adverse effects on a population of

nonhuman receptors, rather than to protect every individual animal. The potential for ecological

effects was also evaluated by comparing observed tissue concentrations of COCs in biota samples

to maximum allowable tissue concentrations, which are summarized in the toxicity assessment and

ecological assessment.

Human Risk Characterization

Additive carcinogenic risks for residential hypothetical future exposures at RME intake

levels by zone are highest in zones 2, 3, and 4. These zones are south of O'Brian Canal and within

approximately one mile of the RMA north boundary. Based on the uncertainty analysis, the

hypothetical risks may be overstated by threefold from intake considerations alone. Future

hypothetical cancer risks (assuming pathways are complete and without considering additional

remediation) in these zones are estimated to be less than 3 x 10-4. More than 60 percent of the

Psk in each of these zones is attributable to category B2 and C human carcinogens. Thus, the risk

estimate is critically dependent on the extrapolation of toxicological data from animals to humans.

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The largest contributor to total carcinogenic risk is dieldrin. Two toxicological profiles discussing

both animal and human data are in Appendix F of the EA (page F- I and F- 1 12).

In addition to RMA-related sources, dieldrin in surface soils north of O'Brian Canal appears

to be associated with agricultural practices in the Offpost OU. The hypothetical carcinogenic risk

associated with dieldrin in soil resulting from agricultural practices in zones other than zone 3 and

4 is 4 x 10-5. In addition, naturally occurring arsenic in groundwater contributes approximately

4.4 x 10-5 risk. Summing these two risks yields a 8 x 10-5 risk that is not attributable to RMA.

More than 95 percent of the residential hypothetical carcinogenic risk in each zone is

attributable to the following pathways. listed in order of their contribution to risk:

1. Ingestion of shallow groundwater

Consumption of homegrown vegetables

3. Ingestion of locally produced milk

4. Inhalation of volatiles via domestic use of shallow groundwater (e.g., showering, cooking)

5. Ingestion of locallv produced eggs

6. Ingestion of locally produced meat

Dermal exposures for all media do not contribute significantly to carcinogenic risk for the

residential exposure, nor does incidental ingestion of soil and sediments. The oral exposure route

for all media accounts for more than 70 percent of total carcinogenic risk, with the remainder

predominantly by inhalation.

Groundwater is the dominant source medium contributing to total carcinogenic risk in

zones 4.. 3, and 4 accounting for 60 to 80 percent of total risk, depending on the zone. In the

remaining zones where groundwater concentrations are lower, soil contributes relatively more to

total risk (40 to 50 percent), and soil alone contributes a risk from agricultural practices of

approximately 4 x 10-5 In all zones. Groundwater, surface water, and soil may contribute to

estimated risks via multiple pathways, specifically those involving food production within the

Offpost OU. Groundwater and surface water are assumed to be used for irrigation of vegetable

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crops and watering of livestock. Each of the food pathways may also accumulate COCs from soil,

and these relationships are quantified via the equilibrium partition models.

Hypothetical risks from all carcinogens are added to determine total carcinogenic risk

regardless of target organ/systern or weight-of -evidence category. The dominant contribution to

total carcinogenic risk in all zones is from category B2 and C carcinogens, as previously presented.

Carcinogenic risks are also posed by arsenic, a category A human carcinogen.

Hypothetical future noncarcinogenic effects were evaluated for all COCs by calculating a

hazard index (1-11), which is the estimated intake divided by a reference dose. An HI of greater

than 1.0 warrants further evaluation. Children are a potentially sensitive subpopulation in the

residential scenario with the largest potential for adverse noncarcinogenic effects, due to higher

intakes. Considering the target organ/system potentially affected by each of the COCs, the most

probable noncarcinogenic effect would be to the central nervous system (CNS). The maximum

hypothetical future additive child chronic HI for CNS toxicants is 4 in zone 4. Hepatic (liver)

effects are also a potential, although smaller, risk, with additive chronic Hl of 2 in zones 2 and 3.

RME estimates of hypothetical current carcinogenic risks for residential land use are

substantially less than future hypothetical risks. No one resides in zones 3 and 4; hence, there is

no hypothetical current risk for these zones. Residents in zones IB and 2 do not use water from

the shallow aquifer. Consequently, the domestic use groundwater pathway is not and has not been

complete in these zones for several years. Hypothetical current risks in zones I B and 2 are at least

3 to 4 times lower than the hypothetical future RME estimates.

For the commercial/ industrial RME scenario, hypothetical future carcinogenic risks in

zone 5 is approximately 3 x 10-5, with 83 percent of the risk in zone 5 from aldrin, dieldrin, and

arsenic. The estimated chronic His (liver toxicants) for the commerc tat/ industrial scenario in

zone 5 are less than one.

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Ecological Assessment

The objective of the ecological assessment was to determine hypothetical adverse affects of

COCs on the environment and nonhuman receptors. Two major natural ecosystem types occur in

the Offpost OU: terrestrial and aquatic. There is also extensive agricultural use of the area.

Potential hazards to.the different ecological components of the Offpost OU were addressed

by considering the hazards to terrestrial, aquatic, and agricultural biota separately. Bioaccumulation and direct toxicity endpoints were evaluated for terrestrial and aquatic life. Maximum

allowable tissue concentrations (MATCs) were developed to assess risk from tissue residues as a

function of bioaccumulation. The predicted tissue concentrations for endrin for the owl and

kestrel exceeded the MATC; however, these predicted tissue concentrations are not supported by

actual data from lower trophic levels. In addition, exposure concentrations or intakes were

compared to acceptable intakes, such as toxicity reference values or reference media

concentrations, resulting in a hazard quotient (HQ). The estimated intake of DDE, DDT, aldrin,

dieldrin, and endrin for the ecological receptors did not exceed the toxicity reference values.

However, an HQ equal to I was calculated for the American kestrel for endrin.

The results of the ecological risk characterization indicate that a minimal potential for

adverse effects to receptor species in the aquatic and terrestrial foodwebs exist. Species in the

agricultural food web are not expected to be at risk because of exposure to the COCs. Plant life,

cattle, and chickens will be relatively unaffected based on the results of the risk characterization.

Endangerment Assessment Conclusion

The objectives of the EA were to provide an analysis of risks in the absence of additional

remediation (baseline risks) and to provide a basis for determining the need for remedial action at

the Offpost OU. The EA for the Offpost OU has identified hypothetical carcinogenic risks that

are within the acceptable carcinogenic risks as defined by the revised NCP (EPA, 1990) and the

Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions (EPA, 1991).

Hazard indices only exceeded 1.0 in some noncarcinogenic exposure scenarios.

20000,317.10 - I-es

0306111892 ES-9
Although these findings indicate that the Offpost OU remedial action is not warranted on a

risk basis, site-specific factors suggest that remedial alternatives for the groundwater medium

should be considered. Accordingly, a Feasibility Study has been prepared as a companion

document to the EA for the Offpost OU.

FEASIBILITY STUDY

Based on the results of the EA, the FS concurrently developed and evaluated a range of

remedial alternatives consistent with the NCP. Based on the evaluation presented in this FS, the

Army selected a preferred sitewide alternative, which is consistent with CERCLA and the NCP.

The FS shows that the preferred sitewide alternative meets the statutory requirements of CERCLA

and the NCP. The major steps performed in the FS include development of remedial action

objectives (RAOs), development and screening of remedial alternatives, detailed analysis of

remaining alternatives, and selection of the preferred sitewide alternative.

Develot)ment of Remedial Action Obiectives

The development of RAOs consisted of three steps:

- Identification of COCs by medium

- Identification of media of concern

- Identification of exposure pathways.

Six media were evaluated in the remedial investigation (RI) for the Offpost OU: groundwater, soil, surface water, sediment, air, and biota. Each medium was evaluated in the

Offpost EA with respect to (1) the nature and extent of contamination and (2) potential exposure

pathways and associated risk characterization.

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).

Since the Offpost OU cumulative risk is within the acceptable cancer risk range specified by EPA,

Offpost OU remedial action is not warranted. The Army, nevertheless, recognizes that there are

site-specific factors that suggest remediation of groundwater is preferable to no-action in the

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0306120392 ES-10
Offpost OU. Groundwater contributes approximately 75 percent of the total hypothetical risk,

and the data available showed exceedances of some MCLs in groundwater. Additionally,

substantial progress has been made toward the construction and startup of an offpost groundwater

treatment system. Since the remaining media contribute a minor amount of risk to the total, the

Army concludes that these media do not require development of remedial action objectives

(RAOs). On this basis, groundwater was identified as a medium of concern. Soil, surface water,

and sediment were identified as not requiring remediation due to the low risk attributable to these

media. Air was not identified as a medium of concern because air monitoring data have indicated

air quality within the Offpost OU is not affected by contaminants related to RMA. Biota were

not identified as a medium of concern. Direct remediation of biota was not included on the basis

that it is not effective except by methods that temporarily eliminate receptor species from the

contaminated area. However, protection of biota was addressed through the development of

ecological criteria for the protection of species potentially at risk.

Groundwater RAOs specify the attainment of preliminary remediation goals (PRGs) for the

identified COCs and exposure pathways. In accordance with the NCP, PRGs were developed

considering applicable or relevant and appropriate requirements (ARARs), health-based criteria,

factors related to technical limitations (e.g., analytical detection limits), land use, and ecological

criteria. Final remediation goals will be determined when the remedy is selected and the Record

of Decision is issued.

Groundwater exceedances of PRGs were identified in two plume groups, the North Plume

Group and the Northwest Plume Group, an area encompassing approximately 590 acres in the

Offpost OU. Groundwater alternatives were developed to address the areas of PRG exceedances.

Develot)ment and Screenina of Remedial Alternatives

Remedial alternatives for the Offpost OU were developed by (1) identifying the media in

which COCs were detected at levels exceeding PRGs, (2) calculating the areas and volumes of

media exceeding PRGs, and (3) assembling combinations of representative process options into

alternatives representing a range of treatment and containment combinations that address the

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0306120392 ES-11
RAOs. Consistent with the NCP, a range of alternatives for groundwater was developed from no

action to complete removal or destruction of contaminants exceeding PRGs.

Use of Groundwater Modeling in Alternatives Development

To aid in the analysis of groundwater alternatives, two numerical models (North Plume

Group and Northwest Plume Group) were prepared to simulate the groundwater flow and

dissolved chemical transport in the Offpost OU. Due to the approximate nature of the models,

and the considerable Uncertainty in the conceptual model and hydrogeologic parameters, none of

the modeling results should be construed as accurate predictions of future contaminant

distribution. Rather, the models and modeling results should be viewed as tools for assessing the

relative merits of remedial alternatives. Although there are inherent uncertainties in the

groundwater model, this is a tool being used by the FS and predicted differences in remediation

timeframes are considered with respect to evaluating alternative effectiveness. Simulations of

contaminant transport were made corresponding to the No Action alternative and other configurations for both the North and Northwest Plume Groups. Initial conditions were chosen to reflect

the contaminant plumes and to reflect contaminant removal at the North Boundary Containment

System (NBCS) and Northwest Boundary Containment System (NWBCS) consistent with attainment of Offpost OU PRGs at the boundary systems.

North Plume Group Alternatives

After screening several extraction/ recharge configurations, the following groundwater

alternatives were developed for the North Plume Group. The major components of each

alternative are also listed.

Alternative No. N-1: No Action

The components are as follows:

- Long-term groundwater monitoring

- Five-year site reviews

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0306111892 ES- 12
This alternative was retained for the detailed analysis step as required by the NCP.

Common to the following alternatives are long-term groundwater monitoring and five-year

site reviews, as well as the Army's commitment to provide alternative water (i.e., exposure

control) to any identified future users of groundwater exceeding PRGs.

Alternative No. N-2: Continued Ogeration of the North Boundary Containment System With

lmi)rovements as Necessary

The major components are as follows:

- Continued operation of the NBCS

- Improvements to the NBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control

This alternative was retained for the detailed analysis step.

Alternative No. N-3: Land Acouisition and Use Restrictions

The major components are as follows:

- Land acquisition

- Access and deed restrictions

- Continued operation of the NBCS

- Improvements to the NBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control

This alternative was not retained for the detailed analysis step.

Alternative No. N-4: Interim ReSDonse Action A

The major components are as follows:

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0306111892 ES- 13
- Removal of contaminated unconfined groundwater north of the RMA boundary in the

First Creek and northern paleochannels, using Interim Response Action (IRA) A groundwater extraction wells

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

- Recharge of treated groundwater to the unconfined flow system (UFS), using IRA A wells

and trenches

- Continued operation of the NBCS

- Improvements to the NBCS and IRA A as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control

This alternative was retained for the detailed analysis step.

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

The major components are as follows:

- Removal of contaminated UFS groundwater north of the RMA boundary in the First

Creek and northern paleochannels, using IRA A groundwater extraction wells

- Expansion I of IRA A (additional wells and trenches)

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

- Recharge of treated groundwater to the UFS, using wells and trenches

- Continued operation of the NBCS

- Improvements to the NBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control

This alternative was retained for the detailed analysis step.

Alternative No. N-6: Expansion 2 to Interim Response Action A

The major components are as follows:

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0306111892 ES- 14
- Removal of contaminated UFS groundwater north of the RMA boundary in the First

Creek and northern paleochannels, using IRA A groundwater extraction wells

- Expansion 2 of IRA A (additional wells and trenches)

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

- Recharge of treated groundwater to the UFS, using wells and trenches

- Continued operation of the NBCS

- Improvements to the NBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure co'ntrol

This alternative was not retained for the detailed analysis step.

Northwest Plume GroUD Alternatives

After screening several extraction/ recharge configurations, the following groundwater

alternatives were developed for the Northwest Plume Group. The major components for each

alternative are also listed.

Alternative NW- 1: No Action

The major components are as follows:

- Long-term monitoring

- Five-year site review

This alternative was retained for the detailed analysis step as required by the NCP.

Common to the following alternatives are long-term groundwater monitoring and five-year

site reviews, as well as the Army's commitment to provide alternative water (i.e., exposure

control) to ariv identified future users of groundwater exceeding PRGs.

Alternative NW-2: Continued Operation of the Northwest Boundary Containment System With

Improvements as Necessary

The major components are as follows:

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0306111892 ES- 15
- Continued operation of the NWBCS

- Improvements to the NWBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control

This alternative was retained for the detailed analysis step.

Alternative No. NW-3: Land Acouisition With Use Restrictions

The major components are as follows:

- Land acquisition

- Access and deed restrictions

- Continued operation of the NWBCS

- Improvements to the NWBCS as necessary

- Long-term groundwater monitoring

- Five-year site reviews

- Exposure control

This alternative was not retained for the detailed analysis step.

Alternative No. NW-4: Northwest Plume Groundwater Extraction /Recharge System

The major components are as follows:

- Removal of contaminated UFS groundwater northwest of the RMA boundary, using three

groundwater extraction wells

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

- Recharge of treated groundwater to the UFS, using five wells

- Continued operation of the NWBCS

- Improvements to the NWBCS as necessary

- Long-term groundwater monitoring

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0306111892 ES- 16
- Five-year. site reviews

- Exposure control

This alternative was not retained for the detailed analysis step.

Detailed Analysis of Alternatives

The remaining alternatives (Alternative Nos. N-1, N-2, N-4, N-5, NW-1, and NW-2) were

evaluated with respect to the threshold and primary balancing criteria required by the NCP. The

criteria are listed below

Threshold Criteria

- Overall protection of human health and the environment

- Compliance with ARARs

Primary Balancing Criteria

- Long-term effectiveness and permanence

- Reduction of toxicity, mobility, or volume

- Short-term effectiveness

- Implementability

- Cost

Evaluation of the modifying criteria (i.e., the state and community acceptance) is deferred

until completion of the state and public comment periods.

A comparative analysis of the remedial alternatives identifying the relative advantages and

disadvantages of each alternative was performed. Based on the analysis, a preferred sitewide

alternative was selected.

Selection of the Preferred Sitewide Alternative

Using the evaluation of the alternatives with respect to the criteria required by CERCLA

and the NCP, the preferred alternative was selected. The preferred sitewide alternative consists of

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0306111892 ES-17
Alternative No. N-4 (Interim Response Action A) for remediation of groundwater in the North

Plume Group and Alternative No. NW-2 (Continued Operation of the NWBCS with Improvements

as Necessary) for remediation of groundwater in the Northwest Plume Group.

Redefinition of the Offyost Or)erable Unit

On the basis of the FS analysis of and selection of the preferred alternative and the Federal

Facility Agreement definition of the Offpost OU, the offpost area is not coincident with the

Offpost OU. Consistent with the Federal Facility Agreement definition limiting the Offpost OU

to that portion of the off'post area where hazardous substances, pollutants, or contaminants from

RMA are found at levels subject to remedial action, the Offpost OU is defined as only zones 2, 3,

and 4 in the offpost area.

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0306111892 ES- 18
INTRODUCTION TO THE ENDANGERMENT ASSESSMENT/FEASIBILITY STUDY

OFFPOST OPERABLE UNIT

The Final EA/FS report complies with guidelines prepared under the provisions of the

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (Title 42,

United States Code [USC], Sections 9601-9675), the Superfund Amendments and Reauthorization

Act of 1986 (SARA), the revised National Contingency Plan (NCP) (Title 40, United States Code

(USC) of Federal Regulations [CFR] Part 300), the regulations implementing the National

Environmental Policy Act of 1969 (NEPA), and associated U.S. Environmental Protection Agency

(EPA) guidance documents.

This introduction provides background information for the Offpost OU including setting,

site history and land use, previous investigations, nature and extent of contaminants, and response

actions for the Offpost OU.

SETTING

This section describes the site location, environmental setting, geology, and hydrogeology of

the Offpost OU.

Site Location

The RMA National Priorities List (NPL) site is comprised of two OUs: Onpost and Offpost.

As shown in Figure 1, the offpost area occupies 27 square miles in southern Adams County,

Colorado, and lies north of the Denver metropolitan area and east of Commerce City, Colorado.

The offpost area is defined as the area southeast of the South Platte River, north of 80th Avenue,

southwest of Second Creek, and north of the north and northwest boundaries of RMA, as depicted

in Figure 2. The Offpost OU is defined by the Federal Facility Agreement as that portion of the

offpost area where hazardous substances, pollutants, or contaminants from RMA are found, and

which is subject to remedial action. Additionally, the Offpost OU includes the surface waters of

O'Brian Canal and Burlington Ditch as they extend northeast of Second Creek and the surface

20000,317.10 - I-intro

0306111192 1-]

t
water of Barr Lake. The Offpost OU encompasses rural residential, agricultural, and

commercial/industrial areas located north and northwest of RMA.

Environmental Settinp

The topography of the Offpost OU is similar to the topography onpost and consists of

stream-valley lowlands separated by gently rolling uplands. The maximum local topographic

relief in the area is about 300 feet. The elevation above mean sea level (MSL) ranges from

approximately 5330 feet at the southern boundary of RMA to about 5030 at the South

Platte River.

Cropland and rangeland provide habitat for numerous animal species, including game species

such as cottontails, ring-necked pheasants, and mourning doves. Lake and wetland areas at Barr

Lake provide feeding, breeding, and roosting areas for waterfowl and endangered species,

including the bald eagle.

The climate of the offpost area is characterized by sunny, semiarid conditions. Approximately 37 percent of the total annual precipitation (16 inches) occurs in the spring, with much of

this moisture falling as snow in the early spring. Summer is the hottest season and is characterized

by scattered local thunderstorms during afternoons and evenings. Approximately 31 percent of

the total annual precipitation occurs during the summer season. Winter is the coldest season,

during which time approximately 13 percent of the total annual precipitation occurs.

The regional surface drainage is to the northeast toward the South Platte River. Surface

water originating south of RMA, on RMA, or in the Offpost OU flows toward the South Platte

River. Two major canals, O'Brian Canal and Burlington Ditch, and several smaller ditches flow

from southwest to northeast between RMA and the South Platte River. O'Brian Canal receives

some drainage from the Offpost OU and RMA where the canal intercepts First Creek. Burlington

Ditch may receive surface water infrequently from First Creek.

20000,317.10 - I-intro

0306111192 1-2
Geology

Sediments at the land surface in the Offpost OU consist of unconsolidated alluvial and eolian

deposits of Pleistocene and Holocene age. The composition of the unconsolidated sediments varies

from clays to coarse gravels, and the thickness varies from less than 10 feet to approximately

100 feet. The thickest deposits of unconsolidated sediments occur in paleochannels eroded into

the underlying Denver Formation.

The Denver Formation is of late Cretaceous to early Tertiary age, and consists of 250 to

300 feet of interbedded shale, claystone, siltstone, and sandstone, with a regional dip of one-half

to one degree to the southeast. The uppermost bedrock unit was subjected to erosion before

deposition of the overlying unconsolidated units. Paleochannels incised into the bedrock surface

are present in many areas in the Offpost OU.

The presence of paleochannels in the Denver Formation surface has an impact on groundwater flow in the unconfined flow system (UFS). Two such paleochannels, the First Creek and

northern paleochannels, are present north of the RMA North Boundary Containment System

(NBCS). An additional paleochannel, the northwest paleochannel, is present west of the RMA

Northwest Boundary Containment System (NWBCS). Coarse, unconsolidated materials commonly

found within these paleochannels provide for preferential groundwater movement in the UFS.

Groundwater contaminant plumes that have historically migrated across the RMA boundaries to

the Offpost OU are generally confined to these paleochannels.

The Arapahoe Formation lies beneath the Denver Formation at depths of 230 to 300 feet at

the RMA north boundary and has a regional dip of one-half to one degree to the southeast. The

formation consists of 400 to 700 feet of interbedded conglomerate, sandstone, siltstone, and shale.

The upper portion consists predominantly of 200 to 300 feet blue to gray shale with some

conglomerate and sandstone beds. The lower portion consists largely of sandstone and conglomerate with less prevalent beds of shale. The lower portion is a source zone for many water supply

wells in the area. The Arapahoe Formation is the oldest geologic unit present beneath the site that

was investigated in the Offpost Remedial Investigation (RI) and Offpost RI Addendum programs.

20000,317.10 - 1-intro

0306111192 1-3
Alluvial and eolian Pleistocene and Holocene deposits form much of the ground surface in

the Offpost OU. At some locations, Denver Formation units crop out at the ground surface. The

Arapahoe Formation is not present at the ground surface anywhere in the Offpost OU.

Hydrogeology

The two principal water-bearing units in the Offpost OU that have been impacted by

chemicals originating from RMA are the unconsolidated alluvial deposits and the underlying

Denver Formation. The hydraulic properties of these two units, including hydraulic conductivity,

porosity, and associated, groundwater flow velocities, are distinctly different. Hydraulically, these

two units generally behave as distinct hydrostratigraphic units.

Groundwater flow in the Offpost OU area occurs within an UFS that overlies a confined

flow system (CFS). The UFS includes groundwater present in the unconsolidated materials

overlying the Denver Formation, the weathered upper portion of the Denver Formation, and, near

the South Platte River, the weathered upper portion of the Arapahoe Formation.

The CFS includes the deeper portions of the Denver Formation and the underlying Arapahoe

Formation. The Final Water RI (Ebasco, 1989), the Final Offpost RI (ESE, 1988a), and the Draft

Final Offpost RI Addendum (Harding Lawson Associates [HLA], 1991a) reports provide further

information concerning the conceptual model of groundwater flow in the unconfined and

confined flow systems (UFS and CFS). On the basis of an evaluation of the distribution of

contaminant plumes in the Offpost OU area, the UFS is considered the principal migration route

for groundwater contaminants from onpost to the Offpost OU, although some contaminants are

present in the CFS in the Denver Formation and isolated occurrences of a few contaminants have

been detected in some domestic Arapahoe Formation wells.

Water-level data for the UFS were collected from all Offpost OU monitoring wells during

several monitoring events and programs. The UFS potentiometric surface slopes predominantly

toward the northwest, indicating groundwater flow in that direction. This information is

consistent with the interpretation that the South Platte River is a regional discharge point for the

groundwater system in the Offpost OU. Hydraulic gradients in the Offpost OU range from

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0306111192 1-4
0.003 to 0.02 ft/ft and average approximately 0.004 to 0.005 ft/ft. The hydraulic gradients are

highest in the area immediately downgradient of the NBCS and in the vicinity of O'Brian Canal

and Burlington Ditch.

The hydraulic gradient of the UFS near the canals is consistent with that reported in the

Final Offpost RI. However, the hydraulic gradient near the NBCS has increased as a result of the

installation and operation of recharge trenches in late 1988. Operation of these trenches has

increased groundwater recharge in northern portions of Sections 23 and 24, near the northern

RMA boundary.

The confined Denver Formation is heterogeneous and consists of interbedded claystones,

siltstones, sandstones, and organic-rich (lignitic) intervals. Water-bearing layers of sandstone and

siltstone occur in irregular beds dispersed within thick sequences of relatively impermeable

material. Individual sandstone layers commonly are lens-shaped and range in thickness from a

few inches to as much as 50 feet. Confined aquifer conditions are observed in sandstone layers

within the deeper portions of the Denver Formation.

Water-level data collected from three Arapahoe Formation wells installed under the RI

Addendum program indicate that the Arapahoe Formation is a confined aquifer. Data generally

indicate that the Arapahoe Formation has a northerly to northwesterly regional groundwater flow

direction, as presented in the Final Offpost RI.

SITE HISTORY AND LAND USE

This section presents a discussion of former RMA and Offpost OU activities and land uses.

Former Disi)osal Practices

RMA began operation in 1942. RMA was a site for the manufacture and demilitarization of

chemical and incendiary munitions and the manufacture of industrial chemicals, primarily

pesticides and herbicides, until 1984. A detailed account of disposal practices associated with

these operations is presented in the Onpost Study Area Reports and RI Media Reports for each

potential site.

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0306111192 1-5
M

From 1945 to 1950, RMA distilled available stocks of Levinstein mustard, demilitarized

several million rounds of mustard-filled shells, and test-fired mortar rounds filled with smoke and

high explosives. Also, many different types of obsolete World War (WW) 11 ordnance were

destroyed by detonation or burning.

Colorado Fuel and Iron (CF&I) leased facilities at RMA in 1946. Julius Hyman & Company

first leased facilities in 1947, and succeeded to the CF&I leasehold interest, with some modifications and additions in 1949. Shell Oil Company acquired a majority interest in Hyman in 1952,

and operated the plant as the Julius Hyman Company until 1954, when the operation became the

Shell Chemical Company - Denver Plant.

RMA was selected as the site for construction of a facility to produce Sarin, a nerve agent.

The facility was completed in 1953, with the manufacturing operation continuing until 1957 and

the munitions- filling operations continuing until late 1969. From 1970 until 1984, RMA was

involved primarily with the disposal of chemical warfare material. This disposal included the

incineration of TX anticrop agent and mustard agent explosive components, and the destruction of

Sarin and related munitions casings by caustic neutralization.

Chemicals were introduced to the RMA environment primarily by the burial or surface

disposal of solid wastes, discharge of wastewater to basins, and leakage of wastewater and

industrial fluids from chemical and sanitary sewer systems. Munitions were destroyed and

disposed of in trenches. Wastewater generated by the Army and private industry in the South

Plants and North Plants areas was discharged to a series of unlined evaporation and holding basins

(Basins A, B, C, D, and E) and to asphalt-lined Basin F at various times throughout the history of

RMA operations.

The primary areas that have contributed to groundwater contamination at RMA include

(1) former manufacturing facilities, (2) former waste storage basins, (3) solid waste disposal areas,

(4) the chemical sewer system, and (5) locations with in the rail classification yard, and (6) the

motor pool area.

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0306111192 1-6
Land Use

The current land use within the Offpost OU is predominantly agricultural and rural

residential with localized com merc ial/ industrial land uses and open spaces. Areas within the

Offpost OU are largely used for rangeland and dryland farming, with some rural residential areas

and, scattered areas of intensive agricultural use. Certain areas within the Offpost OU are

currently zoned and developed for commerci.al/ industrial activities. Commerce City, which is

located west of RMA, is the only urban area in the immediate vicinity of RMA and has recently

annexed lands within the Offpost OU. Another geographic feature in the Offpost OU is Barr

Lake, a state recreation area.

Farming in the Offpost OU ranges from large grain operations covering square miles to

small subsistence farms to vegetable gardens. A number of these farms also maintain livestock.

Subsistence and hobbv farmers often consume a large part of their diet from locally produced

vegetables and livestock produced in the Offpost OU.

Intentional application of pesticides for pest control purposes likely accounts for the

presence of some concentrations of pesticides in Offpost OU soil. Many of the pesticides detected

in Offpost OU soil are or have been commercially available and may have been applied agriculturallv or residentially. These pesticides include cyclodiene compounds and chlorinated hydrocarbon insecticides.

The cyclodiene compounds aldrin, endrin, dieldrin, and isodrin detected in Offpost OU soil

have been used as insecticides in areas similar to the Offpost OU from the 1940s to the mid- 1970s.

Aldrin was used in the early 1950s to protect cotton against boll weevils and in the 1970s for soil

application in grain crops and termite control. In Colorado, dieldrin was used to control insects in

field vegetable, grain, and fruit crops (Mullins, 1971) and against termites and locusts. Endrin

was also used to control a wide range of pests. These insecticides were banned for general uses in

1974 by the EPA. Aldrin and dieldrin may still be used for certain restricted uses such as

subsurface insertion for termite control and dipping of nonfood roots.

20000,317.10 - I-intro

0306111892 1-7
Evaluation of projected future land use at the Offpost OU indicates that areas of commercial/industrial land use will increase (Adams County Planning Commission, 1987). Rural

residential (including agricultural) land use is expected to decrease in the Offpost OU.

PREVIOUS INVESTIGATIONS

As a result of the detection of chemicals in the Offpost OU, the Army initiated a regional

sampling of hydrogeologic surveillance program requiring the quarterly collection and analysis of

samples from more than 100 onpost and offpost wells and surface-water stations. This program

was carried out under the direction of the RMA Contamination Control Program, established in

1974 to ensure compliance with federal and state environmental laws. The objectives of this

program were to evaluate the nature and extent of contamination and to develop response actions

to control chemical migration. Potential and actual chemical sources were assessed, and chemical

migration pathways were evaluated. To minimize offpost discharge of RMA chemicals via

groundwater, three boundary containment systems were constructed, one each at the northern,

western, and northwestern boundaries of RMA. All three systems are currently in operation to

intercept and treat contaminated groundwater and to recharge treated water.

From 1975 to the present, numerous groundwater monitoring programs have been conducted

at RMA. The Army designed and implemented the 360 Degree Monitoring Program to monitor

regional groundwater and surface water. The Army designed and implemented boundary system

monitoring program to support the operation of the boundary control systems. Studies conducted

at RMA to assess groundwater and surface-water conditions are discussed below.

The RMA Offpost Contamination Assessment Report (CAR) (ESE, 1987a) incorporated data

from several studies to depict the distribution and concentrations of offpost contamination north

and northwest of RMA. The scope of this investigation was intended to address critical data gaps

required to evaluate a comprehensive set of multimedia exposure pathways. In the mid- 1980s, the

potential for contamination of private wells was investigated. These were referred to as Consumptive Use (CU) Studies, Phases 1, 11, and III. The CU Phase I and 11 studies (ESE, 1985; ESE

20000,317.10 - I-intro

0306111192 1-8
1986) addressed the RMA offpost area bounded to the south by East 80th Avenue, to the

northwest by the South Platte River, and to the north and east by Second Creek.

In the CU Phase III study (ESE, 1987b), the Army conducted an inventory of privately

owned drinking water wells in an area bound by East 80th Avenue on the south, East 96th Avenue

on the north, the South Platte River on the west, and RMA on the east. The objectives of the

study were as follows:

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

- Sample a representative number of the located wells.

- Assess the groundwater quality of the shallow alluvial aquifer.

U.S. Environmental Protection Aqency Study Area

In 1981, a random national survey of drinking water systems was conducted by EPA.

Several organic chemicals were detected in South Adams County Water and Sanitation District

(SACWSD) wells. Additional sampling in 1982 and 1985 confirmed these results. As a result of

these findings, EPA began an RI/FS of an area located west of RMA and south of the

Offpost OU.

RMA was suspected as one of the potential sources of contaminants in the EPA study area

because of the history of waste disposal practices on that site. In response, the Army and EPA

built a water supply system for SACWSD. Further investigation by EPA's Field Investigation

Team indicated that source areas other than RMA may have been contributing to groundwater

contamination detected within the study area. Groundwater monitoring wells installed on the

Chemical Sales Company (CSC) property have since confirmed that CSC is a possible source of

groundwater contamination west of RMA and south of the Offpost OU.

Commehensive Monitorinp, Projaram

In the mid-1980's, the Program Manager for RMA (PMRMA) developed the Comprehensive

Monitoring Program (CMP), a long-term multimedia monitoring program designed to provide data

20000,317.10 - I-intro

0306111192 1-9
to facilitate evaluation of response actions. Sample collection under the CMP commenced in 1987,

and data from the CMP were used in performing this EA/FS.

Scope of the Remedial Investipations

Based on known areas of onpost and offpost contamination and the predominant groundwater and surface-water flow patterns, the Offpost OU for the Offpost RI/FS is the area between

north and northwest boundaries of RMA and the South Platte River. The specific boundaries of

the unit are the same as for the Offpost CAR, as shown in Figure 2 and described below:

- Southeast boundary north and northwest boundaries of RMA

- Southwest boundary 80th Avenue

- West and northwest boundary - South Platte River

- Northeast boundary - Second Creek

The Offpost OU was originally selected on the basis of a conservative estimate of the area

with which RMA chemicals may now or may eventually exist. However, based on current

knowledge (HLA, 1991a), most of the Offpost OU is not contaminated by chemicals originating

from RMA. The surface waters of Barr Lake have also been included in the Offpost OU because

of the potential for contaminant migration through surface-water features.

Several sources of trichloroethene have been documented south of the Offpost OU in or near

Commerce City. Also, recent investigations by EPA and the Army along the western sections of

RMA have detected the presence of a trichloroethene plume entering Township 35, Range 67W,

Section 9 along the southern boundary of RMA. Although trichloroethene has been detected in

selected dewatering wells of the Irondale system, no trichloroethene has been detected in the

influent or effluent sumps of the system. Because of the potential for multiple trichloroethene

sources upgradient of the Offpost OU, trichloroethene detected in the area between 80th and

88th Avenues falls under the jurisdiction of EPA.

The primary objectives of the Offpost RI were to:

- Collect additional data to refine the current understanding of groundwater flow and

surface-water patterns, and the nature and extent of contaminants offpost of RMA.

20000,317.10 - I-intro

0306111892 1-10
M

- Evaluate the potential for chemical migration to the Offpost OU in various media, such as

groundwater, surface water, sediment, air, and biota.

- Provide additional data necessary, to complete the EA/FS.

The review of past studies provided the data to evaluate wells that have been sampled in the

past, use results from previous aquifer tests, to analyze historical onpost and offpost contaminant

plumes, and to examine and develop an overall geologic and hydrologic understanding of the

Offpost OU. Additionally, biota and air quality information for the Offpost OU were reviewed

and used to assess the human and environmental receptors that may be at risk and to define

airborne pollutant pathways.

As a result of the review of the past programs and the original Offpost RI program,

limitations to the groundwater, soil, surface water, sediment, and biota databases were identified,

and appropriate sampling and analysis were completed in the RI Addendum (HLA, 1991g)

program. Data collection consisted of compiling new hydrogeologic and chemical data relevant to

the Offpost OU. Data were obtained by drilling new wells and borings, collecting groundwater

and surface-water samplers for analysis, measuring groundwater levels and surface-water flows,

conducting aquifer tests, and obtaining sediment samples for analysis.

Surface-water and sediment samples were collected in the Offpost OU to define chemicals in

the media. Samples were collected from streams, creeks, impoundments, and lakes that were

suspected pathways for migration of onpost contamination to the Offpost OU. The data were used

to evaluate contamination in surface water and sediment as well as to evaluate surface water and

groundwater interaction.

Biota and air-quality condition were evaluated using onpost and offpost information

collected during past and current studies. Input from the Offpost CAR was used to assess

transport of chemicals and impacts on biota in the Offpost OU from onpost conditions. Data from

the Air RI Report (ESE, 1988b) were used to assess the potential for migration of airborne

chemicals to the Offpost OU.

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0306111192
The water, sediment, biota, and air quality information was organized so that a

comprehensive evaluation of RMA chemicals in all media could be made in the Offpost OU. The

information collected during the Offpost RI and RI Addendum was integrated with historical data

as well as data being collected during other ongoing RMA investigations.

In general, the RI Addendum summarizes new information primarily pertaining to further

assessment of the extent of contamination in various media (groundwater, soil, surface water,

sediment, and blota) within specific geographic areas. Activities performed in preparation of the

RI Addendum include a review of existing data and collection and interpretation of additional

field data to address identified data needs.

NATURE AND EXTENT OF CONTAMINATION

This section discusses the nature and extent of contaminants in the groundwater, soil,

surface water, sediment, and air media in the Offpost OU as currently understood. The Offpost

RI and RI Addendum reports were the primary sources of information for the groundwater, soil,

surface water, sediment, and biota media. Another source of information for the groundwater

medium was CMP annual groundwater data. The primary source of information on the air

medium was the CMP Air Quality Data Assessment Report for 1989 (RLSA, 1990). In determining COCs and exposure point concentrations, the EA used environmental data for the period

1985 to 1991 including these reports.

Groundwater - Sernivolatile Orpanic Comvounds

This section provides a summary of the nature and extent of contamination in groundwater

in the Offpost OU on the basis of groundwater occurrence in both the UFS and CFS. Diisopropy1methylphosphonate (DIMP), dicyclopentadiene, dieldrin, and endrin are the most widespread

and consistently detected sernivolatile organic compounds (SVOCs) in groundwater in the

Offpost OU of these chemicals.

The most widespread contaminant detected in groundwater in the Offpost OU is DIMP. As

Figure 3 illustrates, DIMP is distributed in a continuous plume extending from the RMA north

20000,317.10 - 1-intro

0306111892
and northwest boundaries to the South Platte River. Samples from 89 monitoring wells were

analyzed for DIMP, which DIMP was above the CRL in 71 of these samples. In general, the

highest concentrations of DIMP offpost occur between the RMA northern boundary and the

O'Brian Canal. The highest observed concentrations were 5800 micrograms per liter (,ug/1) in the

First Creek paleochannel, 860 jug/l in the northern paleochannel, and 80 Ug/l in the northwest

paleochannel.

Current data indicate the distribution of dicyclopentadiene, as shown in Figure 4, is

generally limited to the First Creek paleochannel. The maximum concentrations of dicyclopentadiene reported in the Offpost RI Addendum was 600 ug/1.

The distribution of dieldrin is shown in Figure 5. Dieldrin occurs in the Offpost OU north

of the northern and northwestern RMA boundaries. The highest concentrations of dieldrin are

found in wells located in the First Creek paleochannel, ranging from 0.6 to 0.9 jug/l. Dieldrin

plumes are also interpreted in limited areas in the northern paleochannel and in two areas north of

the northwestern RMA boundary. Detectable concentrations of dieldrin in the northern paleochannel and northwestern paleochannel ranged from 0.05 to 0.14 ug/l.

The distribution of endrin is shown in Figure 6. The highest concentrations of endrin

ranged from approximately 0.25 to 0.75 Mg/l for wells immediately north of the northern RMA

boundary. The maximum concentration of endrin was 0.748 jug/l from well 37309, located

approximately 1500 feet north of RMA. Endrin was also detected in groundwater samples

collected from wells in the central portion of the northern paleochannel.

Other SVOCs were detected in groundwater samples from the Offpost OU. The other

SVOCs detected include the pesticides atrazine, malathion, and parathion; the organsulfur

compounds 4-chlorophenylmethyl sulfone (CPMS02) and 4-chlorophenylmethyl sulfoxide

(CPMSO); and the organchlorine pesticides aldrin, isodrin, chlordane, 2,2-bis (para-chlorophenyl)- 1, 1 -dichloroethene (DDE), and 2,2-bis (para-chlorophenyl)- 1, 1, 1 -trichloroethane (DDT).

The distribution of atrazine in the Offpost OU is similar to that of the organochlorine

pesticides (OCPs). Atrazine was detected in 21 Offpost OU wells, with the maximum

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0306111192 1-13
concentrations occurring in the First Creek (46.0 ug/1) and northern (72.9 Ag1l) paleochannels.

Atrazine was generally not detected in groundwater samples collected from the Offpost OU off

the northwestern RMA boundary, except for two isolated occurrences.

Although CPMSO and CPMS02 are both organosulfur compounds, their distributions in

offpost groundwater differ. CPMSO was generally only found in samples collected from wells

installed in the northern paleochannel, whereas CPMS02 was generally only found in samples

collected from wells located in the First Creek paleochannel. CPMSO was generally found at

levels higher than those reported for CPMS02- CPMSO was detected at concentrations up to

82.2 ;Ag/l in the northern paleochannel. CPMS02 was also detected in the First Creek paleochannel at concentrations up to 21.0 jug/l.

The distribution of the additional OCPs (aldrin, isodrin, chlordane, DDE, and DDT) is

similar to the previously discussed distribution of the OCPs dieldrin and endrin. The maximum

concentrations of these compounds generally occur in the First Creek paleochannel, usually in the

area 500 to 1000 feet north of the NBCS. Generally, only sporadic, isolated occurrences of these

compounds were observed in the Offpost OU north of the RMA northwestern boundary.

Groundwater - Volatile Organic Comvounds

The volatile organic compounds (VOC) most frequently detected in the Offpost OU include

chloroform, chlorobenzene, dibromochloropropane, tetrachloroethene, trichloroethene,

1,2-dichloroethene, carbon tetrachloride, and benzene.

Chloroform occurs primarily downgradient of the NWBCS and in the northern paleochannel,

as shown in Figure 7. Chloroform was generally not found in the First Creek paleochannel.

Concentrations of chloroform emanating from the northern RMA boundary are higher than

concentrations in the Offpost OU north of the northwestern RMA boundary. The highest

concentrations of chloroform occur at the north end of the northern paleochanneI (200 to

400 Ag1l). The highest concentration of chloroform was 19.8 tig/l in the northwestern

paleochannel.

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0306111092 1-14
The distribution of chlorobenzene is presented in Figure 8. The plumes are confined to

localized portions of the First Creek and northern paleochannels. The maximum concentration of

chlorobenzene was 38.2 ug/I in a groundwater sample collected from a well located in the northern

paleochannel approximately one mile north of RMA. The maximum reported concentration in the

First Creek paleochannel is less than 2 ug/l.

The distribution of dibromochloropropane is shown in Figure 9. As shown in Figure 9,

dibromochloropropane was generally only found in samples from wells in the northern paleochannel. A few isolated occurrences of dibromochloropropane were observed in the First Creek

paleochannel and immediately downgradient of the O'Brian Canal near the northern end of the

northern paleochannel. The maximum concentrations of dibromochloropropane ranged from

approximately 2 to 7 jug/l in a few wells located in the northern paleochannel. All other detectable levels of dibromochloropropane were less than I ug/l.

The distribution of trichloroethene and tetrachloroethene is presented in Figures 10 and 11,

respectively. These VOCs are found in the First Creek and northern paleochannels. The highest

concentrations of these compounds were detected in samples collected from wells located at the

northern end of the northern paleochannel. The concentrations of tetrachloroethene are higher

than those reported for trichloroethene. The maximum concentrations of tetrachloroethene were

approximately 100 pg/I in two wells located in the northern paleochannel, approximately one-mile

north of the RMA boundary. The highest concentrations of trichloroethene in the Offpost OU

north of RMA ranged from approximately 5 to 7 ug/l.

Other volatile organic compounds (VOCs) detected in the Offpost OU include benzene,

carbon tetrachloride, 1,1,1-trichloroethane, 1,1-dichloroethane, 1,2-dichloroethene, toluene, and

xylenes. These compounds were generally found in only a few groundwater samples collected

from wells installed in the UFS.

Groundwater - Inorganic Compounds

This section describes the distribution of selected inorganic constituents in groundwater.

The inorganics presented below include arsenic, chloride, fluoride, and mercury.

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0306111092 1-15
The distribution of arsenic based on data collected in support of the Offpost RI Addendum

and for the CMP, is shown in Figure 12. As shown in Figure 12, the distribution of arsenic is

sporadic, with detectable levels of arsenic occurring in a number of areas. Arsenic occurs in a

plume along the First Creek paleochannel. The maximum concentrations of arsenic in the

Offpost OU are 4 to 5 ug/l.

The distribution of chloride is shown in Figure 13. Chloride occurs in plumes in the

Offpost OU north of the northern and northwestern RMA boundaries. Chloride concentrations in

the First Creek and northern paleochannels generally exceed 250,000 Ug/l. The maximum

concentrations of chloride occur in the First Creek paleochannel. Offpost of the northwestern

RNIA boundary, chloride concentrations exceeding 250,000 AgIl occur immediately downgradient

of the RMA boundary. Concentrations of chloride below 50,000 Ug/l occur only in limited areas

(Figure 13).

The distribution of fluoride is presented in Figure 14. Fluoride concentrations generally

exceed 3000 tzg/l in the First Creek paleochannel and 2200 ug/l in the northern paleochannel.

Concentrations average approximately 2000 kig/l in the northwestern paleochannel.

The Final Offpost RI reported mercury in only one offpost groundwater sample. The

sample, which was collected from well 37342 located in the First Creek paleochannel, had a

mercury concentration of 0.36 ug/l. Data generated during Offpost RI Addendum activities

showed detectable levels of mercury in four samples collected from wells located 2000 to 7000 feet

offpost of the northwestern RMA boundary. Mercury concentrations in these wells ranged from

0.210 Mg/l to 1.64 jug/l. The distribution of these sampling locations does not suggest a mercury

plume in the Offpost OU, and detections are considered sporadic. Additionally, data collected

under the Fall 1989 CMP show a higher frequency of detection for mercury than reported in the

Final Offpost RI. The FY90 CMP reported that field or laboratory contamination existed for

those mercury results. Thus, data for mercury are considered questionable and not representative

of actual groundwater conditions.

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0306111092 1-16
Nature and Extent of Confined Denver Formation Contamination

The nature and extent of the confined Arapahoe formation was evaluated through a

sampling program of domestic and monitoring wells. The data and interpretations presented in

this section are for groundwater samples collected from 14 offpost confined Denver Formation

wells in the Offpost OU. Figure 15 presents the locations of these wells. Additional information

concerning the confined Denver Formation groundwater is presented in Section 3.3.2 of the Final

Offpost RI report.

Data were examined from the Fall 1989 and Spring 1991 CMP sampling rounds, which

represent the two most recent sampling rounds. The data reported detections of the following

organic compounds: benzene, chlorobenzene, chloroform, DIMP, dibromochloropropane, phenol,

and 1, 1, 1 -trichloroethane. The most frequently detected compounds were DIMP, chloroform, and

chlorobenzene. In general, the detections were not consistent from one sampling event to the next

for the same well. DIMP was detected most frequently; however, detections occurred in only

I I sampling events out of 42 sampling events. The concentrations of DIMP ranged from

0.443 ILg/l to 46.0 Ag1l. Chloroform and chlorobenzene detection frequencies were below

10 percent. Chloroform concentrations ranged from 0.631 Ag1l to 1.30 jug/l. Chlorobenzene

detections ranged from 1.10 ug/l to 51.5 ug/l.

The observed detections indicate sporadic, isolated low-level occurrences of these

compounds in the Offpost OU in the confined Denver Formation. The data are not consistent

temporally for the same well and do not indicate a spatial or areal trend indicative of a

contaminant plume.

Nature and Extent of Confined Araoahoe Formation Contamination

The nature and extent of the confined Arapahoe formation was evaluated through a

sampling program of domestic and monitoring wells. Two isolated detections of DIMP and one of

chloroform were observed in approximately 30 Arapahoe Formation wells sampled by the Army.

The detections do not appear to be representative of overall aquifer conditions. For example, the

majority of samples collected from Arapahoe Formation wells did not contain detectable

20000,317.10 - I-intro

0306111092 1-17
concentrations of organic compounds. In addition, DIMP and chloroform were not detected

consistently from one sampling event to the next.

Surface Soil

This section presents the concentrations and distributions of compounds detected in soil in

the Offpost OU. Surface soil includes the upper 2 inches of the soil profile. As shown in

Figure 16, the organochlorine pesticides (OCPs) DDT, DDE, aldrin, chlordane, dieldrin, endrin,

hexachlorocyclopentadiene, and isodrin were detected above Certified Reporting Limits (CRLs) in

surficial soil collected in the Offpost OU. The most widespread and frequently detected OCP was

dieldrin. Concentrations of dieldrin detected in samples in the Offpost OU ranged from 2.05 to

250 micrograms per kilogram (,ug/kg). DDT, aldrin, endrin, and DDE were also frequently

detected, generally in samples where dieldrin was also detected.

Offpost OU suface soil was contaminated by the deposition of airborne contaminants and

non-RMA-related intentional agricultural application of pesticides and irrigation practices.

The greatest number of compounds and highest concentrations were observed north of

RMA, with a few occurrences to the east and west of RMA. Several reasons may, in part, explain

the presence of these compounds north and west of the canals: (1) several of the compounds

detected in the surficial soil are or have been available commercially and may have been applied

agriculturally or residentially and (2) some areas where samples were collected may have been

previously irrigated with surface water and/or groundwater originating from RMA.

Arsenic was detected in approximately 20 percent of the samples at concentrations ranging

from 2.61 to 4.62 micrograms per gram (,ug/g). The distribution of arsenic was limited to the

following detection areas:

- East of RMA

- Immediately north of RMA

- West of the northwest boundary

- Along Burlington Ditch

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0306111092 1-18
No identifiable pattern to the distribution is evident.

Mercury was detected in approximately 10 percent of the samples at concentrations ranging

from 0.0719 ug/g to 0.325 ug/g. A discernable pattern to the distribution of mercury is not

evident.

The concentrations of arsenic and mercury in soil were not statistically evaluated above

background as presented in the Offpost EA (Volume 11, Section 1.0).

Subsurface Soil

Six subsurface soil samples were collected in the 96th Avenue residential area and analyzed

for OCPs, arsenic, and mercury. Subsurface soil samples were collected from approximately

I -foot and 5-foot depths. Only one detection of OCPs was reported in subsurface soil samples.

Dieldrin was detected at a concentration of 7.0 pg/kg in a sample collected between 0 and I foot.

Arsenic was detected above the CRL in one subsurface soil sample at a concentration of 3.59 Ag/g

in a sample collected between 0 and I foot. Mercury was not detected above the CRL in any

subsurface soil samples.

Surface Water

Figure 17 presents the distribution of organic contaminants detected in Offpost OU surface

water as presented in the Offpost RI Addendum. The concentrations of organic compounds

detected in offpost surface-water samples typically have been highest in First Creek near the

O'Brian Canal.

DIMP was the organic compound most frequently detected in surface water in the

Offpost OU. DIMP was also the most widely distributed compound and was detected in surfacewater samples collected from First Creek, O'Brian Canal, and Burlington Ditch at concentrations

ranging from 0.532 ug/l to 59.0 pg/l.

The greatest number and highest concentrations of detected OCPs occur in the reach of First

Creek between the northern RMA boundary and the confluence with O'Brian Canal.

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The maximum detections of arsenic and several other inorganic constituents including

chloride and sulfate were found in samples collected from First Creek along the reach between the

RMA boundary and the First Creek confluence with O'Brian Canal. Arsenic was detected at

concentrations ranging from 2.78 to 280 jug/l in Offpost RI Addendum samples. The concentration of 280 jug/l is considered anomalous and not representative of surface-water quality in the

Offpost OU. The maximum concentrations of arsenic are commonly found in surface-water

samples collected from First Creek immediately downstream of the onpost sewage treatment

plant. Arsenic concentrations of approximately 70 pg/l have been detected at this location

(RSLA, 1990).

Groundwater and surface-water interaction is known to occur in the reach of First Creek

between the northern RMA boundary and the confluence of First Creek with O'Brian Canal. This

interaction has been discussed and documented in the Final Offpost RI and FY90 Surface Water

CMP. Comparison of the concentrations of organic compounds detected in surface-water samples

with those detected in groundwater samples collected in the vicinity of this reach of First Creek

supports the conclusion that contaminated groundwater discharging into First Creek may be the

source of organic contamination in surface water. The decrease in number and concentrations of

organic compounds in Burlington Ditch and the O'Brian Canal indicates that dilution of surface

water by the ditch and canal is occurring. The distribution of arsenic in offpost surface water

suggests a source other than groundwater. A potential source appears to be onpost Sewage

Treatment Plant discharge to First Creek.

Sediment

Figure 18 presents the distribution of organic contaminants detected in sediment as

presented in the Offpost RI Addendum. The following organic compounds had the highest

frequency of detection in sediment samples in the Offpost OU: aldrin, chlordane, dieldrin, and

dibromochloropropane. The detections were predominantly in samples collected from in First

Creek and were generally low concentrations.

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Arsenic and mercury were detected at low concentration levels in sediment samples in the

Offpost OU. Mercury was detected only in the Burlington Ditch, O'Brian Canal, and Barr Lake

samples. Arsenic was detected in sediment samples in the Offpost OU from all water bodies

sampled.

Air

Results from onpost RMA air monitoring during 1988 and reported in the CMP Air Quality

Data Assessment Report (R.L. Stollar & Associates, 1990) (FY88 Air CMP) indicated that total

suspended particulate (TSP) levels at RMA boundaries were below the levels of metropolitan

Denver. Asbestos was monitored but not detected. VOCs measured at RMA boundaries appear to

present toxic risks similar to those encountered in the urban environment of metropolitan Denver.

Levels of SVOCs were detected at negligible and/or regional baseline levels at RMA boundaries.

Metal levels were proportional to TSP concentrations and were not elevated.

GROUNDWATER TREATMENT SYSTEMS THAT AFFECT THE OFFPOST OPERABLE

UNIT

Three major containment/treatment systems, the Irondale Containment System (ICS), the

NBCS, and the NWBCS, have been installed at the RMA boundaries to control the migration of

contaminants to offpost areas. All three of the systems are currently in operation to intercept and

treat contaminated groundwater and to recharge the treated water. In addition to the boundary

control systems, a groundwater intercept and treatment system north of RMA (Groundwater

Intercept and Treatment System North of RMA Interim Response Action A [IRA A]) is currently

being constructed to provide remediation of alluvial groundwater in the Offpost OU.

Irondale Containment System

The ICS is located at the southern end of the RMA northwest boundary within Section 33

and consists of a hydraulic control system and a carbon treatment system. The ICS became

operational in 1981. The majority of the area downgradient of the ICS is contained within the

EPA offpost study area, although portions of the downgradient area are within the confines of the

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0306111092 1-21
Off post OU. A review of monitoring data downgradient of the ICS shows contaminant

concentrations to be low and probably attributable to the source of contamination within the EPA

offpost study area rather than RMA. Therefore, the configuration, operation, and performance of

the ICS are not relevant to this study and will not be discussed further.

North Boundary Containment System

The NBCS is located just south of the RMA north boundary in Sections 23 and 24. The

NBCS consists of a system of dewatering wells with contaminated groundwater from the

unconfined flow system, a soil-bentonite barrier to separate contaminated and treated

groundwater and to impede offpost migration of contaminated groundwater, a carbon -adsorption

treatment system to remove organic contaminants, and a system of recharge wells and trenches to

return treated groundwater to the UFS.

The NBCS was constructed in two phases during 1978 and 1981. Initially a pilot system was

installed and became operational in 1978. The pilot system was expanded approximately 1400 feet

to the west and 3840 feet to the east in 1981. Recharge trenches were added to the west end of

the system in 1988. Additional recharge trenches were added to the east end of the system in

1990. Currently, the soil-bentonite barrier is 6740 feet long and approximately 3 feet wide, with

a designed hydraulic conductivity of I X 10-7 centimeters per second (cm/sec) or less. The barrier

depth varies from 20 feet at the western end to over 40 feet along the eastern extension. The

barrier is anchored in the Denver Formation.

Currently, the average flow through the NBCS treatment system is approximately 240 to

250 gallons per minute (gpm) according to the Final Implementation Document for IRA A (HLA,

1991b). All water is treated and recharged to the alluvial portion of the UFS.

Examination of groundwater contaminant distribution patterns indicates that the NBCS is

having a significant effect on the distribution of organic compounds in the Offpost OU. The

NBCS treatment plant is effectively removing the organic contaminants for which it was designed.

Concentrations of organic contaminants above CRLs have not generally been detected in the

system effluent. Inorganic contaminants such as chloride and fluoride are not being treated.

20000,317.10 - I-intro

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Northwest Boundary Containment System

The NWBCS is located along the northwest boundary of RMA in the southeast quarter of

Section 22. Construction of the NWBCS began in 1983, and the system became operational in

1984. The purpose of this system was to intercept and remove dibromochloropropane and other

organic compounds from a plume of contaminated groundwater originating onpost.

Contaminant bypass was observed at the northeast end of the system in 1988. Recharge was

increased at the northeast end in December 1988 to prevent continued contaminant bypass. The

system consists of a line of 15 upgradient dewatering wells, a soil bentonite barrier extending

approximately two-thirds of the length of the dewatering system, 21 downgradient recharge wells,

and a carbon -adsorption treatment facility. Groundwater is pumped from the dewatering wells on

the upgradient side of the barrier, treated by carbon adsorption, and returned to the aquifer

through recharge wells near the RMA boundary.

An IRA to improve the NWBCS was initiated in 1989. In April 1990, the NWBCS Improvements IRA B(ii) was divided into two phases: NWBCS Short-Term Improvements IRA and

NWBCS Long-Term Improvements IRA. The long-term improvements involve a more thorough

assessment of the NWBCS and the short-term improvements.

Under the NWBCS Short-Term Improvements IRA, the existing groundwater intercept

system was extended both to the southwest and northeast. The soil-bentonite wall was extended

across the alluvial channel found northeast of the system to prevent contaminant bypass.

Additional extraction wells were added to the existing system to intercept and treat the water in

this channel. The northeast extension was completed in July 1990, and recharge rates at the

northeast end of the system were reduced. Higher recharge rates resumed in July 1991 at the

northeast end of the system. New extraction wells and recharge wells were added to the southwest

end of the system and became operational in August 1991.

Interim Rest)onse Action A

IRA A addresses contaminant migration north of RMA along two primary contaminant

pathways, defined by the First Creek and northern paleochannels.

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In the area north of the RMA north boundary, IRA A is being implemented for remediation

of contamination in alluvial groundwater in the First Creek and northern paleochannels. The

system has been designed to intercept and extract contaminated groundwater from the UFS in

each paleochannel, treat the organic fraction of the groundwater, and recharge treated water to

the UFS. Groundwater extraction will be achieved by installing and operating well systems.

Water will be treated using a granular activated carbon adsorption system and will be recharged to

the UFS using a combination of wells and trenches.

The IRA was designed to be flexible to be compatible with the final remedy. Compatibility

with the final remedy could be achieved by modifying the system to include the addition of new

wells, treatment processes, or additional treatment capacity if necessary. Construction of IRA A

began in November 1991.

The groundwater treatment system for IRA A is designed to treat a maximum flow of

720 gpm and an average initial flow of 480 gpm; however, the facilities will be able to accommodate flows less than the average, with a minimum flow of 200 gpm.

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REFERENCES

Adams County Planning Commission. 1987. Adams County Future Land Use Plan, Brighton, CO.

Ebasco Services, Inc. 1989. Technical Support for Rocky Mountain Arsenal Draft Final Water

Remedial Investigation Report. Contract Nos. DAAK I 1-84-DOO 16 and DAAA I 5-88-DO024.

Denver, CO.

Environmental Science and Engineering, Inc. 1985. Rocky Mountain Arsenal Offpost Assessment: Ground Water Quality Report (Consumptive Use - Phase 1) for Sampling Period December

1984 through January 1985. Prepared for U.S. Army Toxic and Hazardous Materials Agency.

Denver, CO.

Environmental Science and Engineering, Inc. 1986. Rocky Mountain Arsenal Offpost Assessment: Ground Water Quality Report (Consumptive Use - Phase 11) for Sampling Period September

through October 1985. Contract No. DAAK- I I -D-007, Task Order 0006. Denver, CO.

Environmental Science and Engineering, Inc. 1987a. Rocky Mountain Arsenal Off'post Assessment, Contamination Assessment Report: Draft Final, Denver prepares for office of the Program

Manager, Rocky Mountain Arsenal.

Environmental Science and Engineering, Inc. 1987b. Rocky Mountain Arsenal Off'post Assessment: Ground Water Quality Report (Domestic Use - Phase III) for Sampling Period September

through October 1986 and February 1987. Contract No. DAAK- I 1-83-D-007, Task Order 0006.

Environmental Science and Engineering, Inc. 1988a. Offpost Operable Unit Remedial

Investigation and Chemical Specific Applicable or Relevant and Appropriate Requirements, Final

Report. Prepared by Environmental Science and Engineering, Inc., Harding Lawson Associates;

and Applied Environmental, Inc., Rocky Mountain Arsenal, Commerce City, CO.

Environmental Science and Engineering, Inc. 1988b. Air Remedial Investigation Report, Final.

Prepared for Office of the Program Manager. Denver, CO.

Environmental Science and Engineering, Inc. 1989a. Draft Final Endangerment Assessment/

Feasibility Study and Applicable or Relevant and Appropriate Requirements. Prepared for Office

of the Program Manager. Denver, CO.

Harding Lawson Associates. 1991a. Draft Final Offpost Operable Unit Remedial Investigation

Addendum. Prepared for the Program Manager for Rocky Mountain Arsenal.

Harding Lawson Associates. 1991b. Final Implementation Document for the Groundwater

Intercept and Treatment System North of Rocky Mountain Arsenal Interim Response Action.

Mullins, D.E., Johnsen, R.E., and Starr, R.I. 1971. Persistence of Organoclorine Insecticide

Residues in Agricultural Soils of Colorado. Pest. Monit. J. 5: 268-275.

R.L. Stollar & Associates, Inc. 1990. Comprehensive Monitoring Program; Air Quality Data

Assessment Report for 1989. Contract Number DAAA15-87-0095. Prepared for U.S. Army

Program Manager for Rocky Mountain Arsenal. Commerce City, CO.

U.S. Environmental Protection Agency. 1988a. CERCLA Compliance with Other Laws Manual

Draft, OSWER Directive 9234.1 -0 1, August.

20000,317.10 - I-intro

0306111092 1-25
U.S. Environmental Protection Agency. 1988b. Guidance on Remedial Actions for Contaminated

Groundwater at Superfund Sites, OSWER Directive 9283.1-2, August.

U.S. Environmental Protection Agency. 1988c. Guidance for Conducting Remedial Investigations

and Feasibility Studies Under CERCLA, Interim Final, EPA/540/G-89004, October.

U.S. Environmental Protection Agency. 1989a. The Risk Assessment Guidance for Superfund

(RAGS). Office of Emergency and Remedial Response, Washington, DC. EPA/540/1-89/002.

U.S. Environmental Protection Agency. 1989b. Exposure Factors Handbook, Final Report,

Office of Health and Environmental Assessment, Washington, DC. EPA/600/8-89/043.

20000,317.10 - 1-intro

0306111092 1-26
RMA1 1104

WELD CO. -------------- -------- -------------

76

BOULDER CO. 25 85

ff

Lake

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

JEFFERSON CO. ....... ...

ROCKY

MOUNTAIN.0

ARSENAL

2 .... ................ ....... ý- j

Stapleton ADAMS CO.

Airport

DENVER CO. ......... V""

225 ARAPAHOE CO.

L:

Cho"

Crook

ReservcWr

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

DOUGLAS CO.

EXPLANATION

Onpost operable unit

RMA boundary

0 2.5 5

§C=MwEC=

Scale in Miles

Prepared for: Figure 1

Program Manager for

Rocky Mountain Arsenal LOCATION MAP OF ONPOST OPERABLE UNIT,

Commerce City, Colorado ROCKY MOUNTAIN ARSENAL
RMAI 1101.1

EXPLANATION Brighton

Offpost area

RMA boundary

...........

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

.

'4114

Q*

0 1 2 .....

..........

Scale in miles .4

... ......

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

X X.

ANO . . ........... ......................

North Boundary

ContainmentlTrestrnent System

Northwest Boundary

Canto inmentfTrestrrent System .. .... .... ..

;iOn 

F ...............

X ..... a sin C

80th Avenue Rocky Mountain Irondslo Boundary

Containment/ Arsenal

Trestrrient System A

Upper

Derby Lake

L

Mary

L er y

Commerce City La r Lake

L -- -- -- -- -- -- -- -

Montbello

Prepared for: Figure 2

Program Manager for

Rocky Mountain Arsenal OFFPOST AREA,

ROCKY MOUNTAIN ARSENAL

Commerce City, Colorado
RMAII 1144

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

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

IN

'Q5

Ir

........................... ............ ................ . ...... ............. ... ......... ............. A ............ \ . ...... ...................................... ... ....... ...... . ............ .... ............

AL

0.4764\ '00

N

-xi

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

.0

loll

0

LT

2.15

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

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

EXPLANATION

r --,

--, _> Isoconcentration Une, Dashed where Inferred

2.65 Isolated Detection, in ggA. Two Values Shown if Sampled Twice. LT - Indicates Analyte was not

10LT Detected Above the Certified Reporting Limit.

A Monitoring Well Sampled Under Offpost RI Addendum Program (1989-1990)

Monitoring Well Sampled Under CMP (Fall 1989)

0 1500 3000 Domestic Well Sampled Under Off post RI Addendum Program (1989-1990) 1==PMWNt=

Scale In Feet Isoconcentration Value (gg/1)

0.392

A nn
RMA1 114S

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

A

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

AL

0

A6

A Aý S:00

A

Soo $ A

J N! A

-T,

i

N"D":RT"ý v3n-U'ýNDA- Y

A 41

A

ýz:

-Y

41

EXPLANATION

Isoconcentration Une, Dashed where Inferred

2.65 Isolated Detection, in I.Lg/I

: Monitoring Well Sampled Under Offpost RI Addendum Program (11989-1990)

0 1500 3000

iien%iiii-a * Monitoring Well Sampled Under CMP (Fail 1989)

Scale in Feet 0 Domestic Well Sampled Under Offpost RI Addendum Program (1989-1990)
RMA1 1146

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

................................................................ .................... ................................................... - : .......... ...............

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

........

0.230

.................................................................... ...................................... ................. .......... ...... ................. ...................................................... M . ........................... .................. - -.....................

A

A

00.0632

0.0530

3

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

0.0580

Ak

0.

NOO

O.D615

OP01 ............ .............................. & ..................... ....... ........... ............ ..... .................. ....... ..................

.......... 0

.0541

LT

sk

00.0

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

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

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

?

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

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

EXPLANATION

Isoconcentration Line, Dashed where Inferred

2.65 Isolated Detection in ggA. Two Values Shown if Sampled Twice. LT - Indicates 0 Analyte was not Detected Above the Certified Reporting I-imit. LT

0 1500 3000 A, Monitoring Well Sampled Under Offpost RI Addendum Program (1989-1990)

0 Monitoring Well Sampled Under CMP (Fall 1989)

Scale in Feet N Domestic Well Sampled Under Offpost RI Addendum Program (1989-1990)
RIVIA1 1147

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

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

0

A

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

A

A A' --400500

A

-0 -0.

0.0616 U0 A

00 *1 0.0706 -'...0.0621

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

V'. A

A

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

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

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

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

EXPLANATION

Isoconcentration Line, Dashed where Inferred

2,65 Isolated Detection, in gg/l 0

0 1500 3000 A Monitoring Well Sampled Under Offpost RI Addendum Program (1989-1990)

9 Monitoring Well Sampled Under CMP (Fall 1989)

Scale in Feet 1AW1 C- 1-A 1 1-4., nff-f Q1 AAA-A- P-r- NORG-10Q01
RMAI 1134

'A

1.04

LT

2.32 M

A

> 0

Aý &0

A\

1.92

-.11-1-1-.-.,-.--.-.,-,-.-..,..,.....-,.,.....,...,-,.."",-....I ........... A .. .. ................

hA

A A

A 'A

1.52

A

SOO 0 so(r1.23 . ......... 1.17

X.

A

0:

0

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

EXPLANATION

Concentrations in micrograms per liter (ggA)

Isoconcentration Line, Dashed where Inferred

2-65 Isolated Detection, in gg/l. Two Values Shown if Sampled Twice. LT - Indicates Analyte was not Detected Above the

* Certified Reporting Limit.

LT

A Monitoring Well Sampled Under Offpost RI Addendum Program (1989-1990).

0 1500 3000 February 1991 CMP Data for these Wells were Considered during Construction of Plume Contours.

CZZZl11_MWGM= 0 Monitoring Well Sampled Under CMP (Fall 1989)

Scale in Feet I-A- r)ff - - - 1, D1 AAA-4,.- D-- t10QQ_iQQnN
RMA1 1149

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

1.34

4.99

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

4.89

....... .. .

2.86

0.942

1.48

0

0

1.93 r W 4N7 1.89 vj. 325 8.39 0 10.0 ............................................. ............... ............... ........... ................................................. ........... ...................................... ............................................. .................. 6 ...................... .................................. ....................

A

0.ýio

Alk 9 69:: 9.56

0 2.25 4.53 ............. ............. & .......... ...........................

A

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

Z.-

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

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

EXPLANATION

Isoconcentration Line, Dashed where Inferred

2.65 Isolated Detection, in pg/I

Monitoring Well Sampled Under Offpost RI Addendum Program (1989-1990).

February 1991 CMP Data for these Wells were Considered

during Construction of Plume Contours.

Monitoring Well Sampled Under CMP (Fall 1989)

0 

%ZZZr--1=

1500 3000 Domestic Well Sampled Under Offpost RI Addendum Program (1989-1990)

Scale in Feet Isoconcentration Value (;.ig/1)
RMA1 1150

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

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

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

..........

:0.522

J. I

......... ................... ............................................ .................................... ............................. ................................................................... ............................................... ... L I .............. .. .................. ....................

0.3T7

A

A

0

0 .. . ......

Isoconcentration 

Line, 

Dashed 

where 

Inferred 

It 

PN

C

EXPLANATION

2.65 Isolated Detection, in gg/I

A Monitoring Well Sampled Under Otfpost RI Addendum Program (1989-1990).

0 1500 3000 during Construction of Plume Contours.

February 1991 CMP Data for these Wells were Considered

Scale in Feet Monitoring Well Sampled Under CMP (Fall 1989)

m Domestic Well Sampled Under Offpost Rl Addendum Program (1989-1990)
RMAI 1151

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

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

......

...........

A

7.04

*A)t

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

C3

A I

0560

N

Aýl 0

A

A

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

22

A

0

4i

A

A

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

7.85 02.73

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

EXPLANATION

Isoconcentration Line, Dashed where Inferred

2.65 Isolated Detection, in ýtg/l

0'k Monitoring Well Sampled Under RI Addendum Cffpost Program (1989-1990).

February 1991 CMP Data for these Wells were Considered

0 1500 3000 during Construction of plume Contours.

10-

Scale in Feet e Monitoring Well Sampled Under CMP (Fall 1989)
RMAI 1152

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

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

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

15.5

A

Aý

100 7.74 10

0' A

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

10.0)

ff 0

VA

C2

Alk

3 ........... .......................... .................................. ............ A .......... ..............................

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

40.

A

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

3.74

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

EXPLANATION

Isoconcentration Line, Dashed where Inferred

2.65 Isolated Detection, in ggA

Monitoring Well Sampled Under Offpost RI Addendum Program (1989-1990).

February 1991 CMP Data for these Wells were Considered

during Construction of Plume Contours.

0 1500 3000 0 Monitoring Well Sampled Under CMP (Fall 1989) =ZP=n'C=

Scale in Feet M Domestic Well Sampled Under Offpost RI Addendum Program (1989-1990)

Isoconcentration Value (gqA)
I j I j I I I I -T ---- ----------- -

RMA1 1153

3.48 31

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

... ... 7 ...

A 2.73

Aý'

4.26

LT

A

4.00 5.23

j

2.51

2.46

A&

LT

2.65

LT

A,

2.65

419

?

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

4.90

A

A

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

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

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

.. ........

K

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

EXPLANATION

Isoconcentration Line, Dashed where Inferred

2.65 Isolated Detection, in 4g/l. Two Values Shown if Sampled Twice. LT - Indicates Analyte was not

LT Detected Above the Certified Reporting Limit. 10

0 1500 3000 Monitoring Weil Sampled Under Offpost RI Addendum Program (1989-1990)

T6-=ý ý 9 Monitoring Well Sampled Under CMP (Fall 1989)

Scale in Feet

Domestic Well Sampled Under Cffpost RI Addendum Program (1989-1990)

Isoconcentration Value (jagA)
RMA1 1140

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

A.

A.

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

0

'00

75,000

75,000

Aý

5oo,ood

150,000 150,000

......................................... ........................... .............. ................................. ..... . ............ 4.0 ............ .............. ... ............... ...... - .................................

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

1 000000 150,000

A

00

'Po

............ 150000

*""'*'* ..... ...... ......... 1.

-00-'

.. 500,000 1,000,000/

-Aý....

-0

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

EXPLANATION

isoconcentration Line, Dashed where Inferred

Monitoring Well Sampled Under Offpost Rl Addendum Program

(1989-1990)

Monitoring Well Sampled Under CMP (Fall 1989)

Domestic Well Sampled Under Offpost RI Addendum Program (1989-1990)

Isoconcentration Value (4g/1)

0 1500 3000

75,000

150,000

Scale in Feet 500,000

1,000,000
RMA1 1141

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

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

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

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

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

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

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

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

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

......... A&

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

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

A

r

00 ........................... .......................... .......................... ................... ............ A ............. .......... .. ...........................

('ý200o..

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

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

EXPLANATION

Isoconcentration Line, Dashed where Inferred

2-65 Isolated Detection or Concentration Less Than Lowest Isoconcentration

Value, in ggA

Monitoring Well Sampled Under Offpost RI Addendum Program

0 1500 3000 (1 RA-A and RI Addendum, 1989-1990)

Scale In Feet Monitoring Well Sampled Under CMP (Fall 1989)

Domestic Well Sampled Under RI Addendum Program (1989-1990)

lsoconcentration Value (lAg/1)
RMA1 1139

32 33 34 3 5 36 31

C:)

5 4 3 2 1 6 / Ver

C;h

leoo

8 12 7

.It 

Cýj

17 6 15 14 13 0 37322 8 37321

ý,3!365

I

37317

37316 37318 37380 37319 379 37388 10 0 / 1 3T jq 37387# 37372f ' 37390

cp k37376

RIVIA BOYNDARY

20/-(- (,e 21 22 23 24 19

NORTH BOUNDARY

CONTAINMENT

SYSTEM

----- 4 29 28 /27 1 26 25 30

100 NORTHWEST

BOUNDARY

CONTAINMENT

SYSTEM r

NORTH

PLANTS

EXPLANATION

Confined Denver Formation monitoring well location

0 1500 3000

Scale in Feet
RMA1 1154

rr zis 1 2 t-'

2ý4 2!8 2 7 L

2 _8

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

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

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

DDT 14.4

33 3 DOE 24.7 3 6

Dieldrin 23,6

Endrin 9.19

DDT 58.9 DDT 41.9

39k.5 (ýiJ5ý011 DOE 64.0 DOE 22.6

1 DDT Dieldrin 22.7 Dield rin 4.5 0 180 .................................................. ........ drin 3.99 (7.43 D O E 260 Endrin Is rin 14.7 2.20 ..... ............. . ......... ...................................... I ..................... ........ ..................................................

.......................... I ...... Endrin 6.21 (ND Dieldrin 3.58 1

Endrin 9.80

DDT 790 DDT 4.18

DOE 170 DDT 9.86

Dieldrin 130 Dieldrin 2.05 (DDT 40 8)

DID 69.5 DDT 860

DOE Dieldrin 4

DI 3.5 

40

Id in 1 CL6CP 20.3 .................................................. n e r .... .... 71'ý ... ............................. ............ ................ .............. .............. .............. ........... ....... ..................................................

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

ý"E drin 40.2

DDT 3.80 DDT Dieldri 10.8 Dieldrin 4%571 5.8

DDT 5.47 D0 2. T]d rin 2 5. 00 Dieldrin 2.15

Endrin 13.5 Dieldrin 2.60 DDT 3.50 1 Dieldri 0 n 8.0

DDT 6.50 DOE 11 3 DDT 7.90

D D E 7 630'go

Is.d"n 2 60 Diefdrin 22.5 Dieldrin 15.5 FDieldnn 2 90 DOE 6.30

DDT 5.10 Dieldrin D Idnn 4.00 4 00

E drin Dieldrin 7.70 5.64 Isodrin 2.60

(ND) ................. ................................................... - .............................. ............................................... ... . ... ...... 0 ..................................... .................. ..................... ........ ......... .....................

.. ..

DDT 7.40

DD 58 DDT Diefdrin 11.1

T -9 -D-OTT-75-1 07L 19.DOE 32.0 DOE 56.1 Dieldrin 10.7 Dieldrin 5.50 CýIordane 52 DDT 10.3) 38.8 ieldrin 93. Dieldrin 5.30) D ieldrin 4.40) 85.7 ndrin 39

I drin 4.31 Dieidrin 7.44 Endrin 6.67 DDT 22-1 -8.77 DDT 7.00 Dieldrin 2.20

1 3.1 Dieldrin rin DOE 4.80 DDT 26.0 .1drin 4.70

Aldrin 5.30 DOE 6.70

Dieldrin 16.0 Diefdrin 18.4

DDT 44.3 Endrin 6.60 Endrin 5.10 FIN Dj___ MA .............. ...................... ............ D O E8.40 .................... .............. .......... Dieldrin 18.7 DDT 5.60

Endrin 39.4 Dieldrin 16.7

Isodrin 3.40 DDT 10.6

8.25 Diel Aldrin 5.70

Dieldrin 10.9 Dieldrin 14.8

DDT 4.70 : Endrin 11.1 21"

Dieldrin 12.8 CL6CP 2.70 bieldrin 3.20

Di.IdnT6.3 Isodrin 3.50

Dieldrin 7.10 DDT 6. 60

/'(Di6ldrin 6.30) DDT 3.60 Aldrin 4.80

Dieldrin 46.1 Dieldrin 33.2

Endrin 99.3 1

DT 7.00

Idhn 4.07

ieiddn 58.2

DDT 6.30 ndrin 9.46

DDT

ýDieldrin 99.00ý DDT 2.80

DOE 4.50 NTýý Dieldrin 12.426. 25 2 V

Endrin 5.10 Aldrin 5.30 (ND)

Dieldrin Wý,R.T' 5.40 t

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

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

........................................... ........ .......................................... ........... .... ....... ............ 7 ............. ....... ........................... ............ .......... svs: - I

Dieldrin 2.20

V

F Aldr,75 90

Dieldrin 99.2

Aldrin 6.20

Dieldrin 24.5

4

L Aldrin 4.10

Pod Dieldrin 10.6

YARD

DDT 10.3

Dieldrin 3.60

>

EXPLANATION

:RMA Bowndarv

0 Surficial Soil Sampling Location, June-July 1990

Surficial Soil Samping Location, May 1991

Duplicate Sample Results

0 2000 4000 Concentrations in micrograms per kilogram
RIVIA1 1194

EXPLANATION

0 Surficial Soil Sampling Location, Februai

Duplicate Sample

CDH Surficial Soil Sampling Location, Ff

13 Section Number

CDH Colorado Department of Health

HLA Harding Lawson Associates

Indicates CDH Results for Samples Colk

DDT 2,2 - Bis (parachlorophenyl) - 1,1,1 - Tric

DDE 2,2 - Bis (parachlorophenyl) - 1.1 - Dichk

...... Concentrations in micrograms per kilogr,

... .... .. Not Detected at or above the Certified Ri .... .........

12

= Aldrin 

7.00 5 00

E r, 

Dieldrin loo 55.0 ')o ndrini 0.0

DDT 5.00

Dieldrin 10

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

NBCS

23 24

NWBPS .... .... .. Ald inr 14.0 i" 1ý10 INDEX MAP Dieldrin 110 Er'dr,n 23.0

DDE 4.00

FAr.en,. 12 L DDT 12.0 Aldrin 26.0

Dieldrin 110

Endrin 19.0

Aldrin 7.00 Isodrin 3.00

Chlordane 46.0 DDT 7.00

Aldrin 3.00 Dieldrin 110 Dieldrin 50 Endrin 19.0 Dieldrin 44.0 DDE 20.0 DDT 4.00 DDT 37.0 Dieldrin 10

DDE 20 r Dieldrin 20 0 DDT 140 ... Aldrin 10.0

Chlordane 151 0 41

0- Dieldrin 120

Endrin 15.0 Dieldrin 70 DDE 73.0 Scale in Feet ............... ...... D D T 230 ... ... ............

Aldrin 3.00 .......... Dieldrin 40 ................ . FDieldrin 32.0 DDT 120 Prepared for: Aldrin 8.00 do Diell rin 20 Chlordane 100 ....... Dieldrin 89.0 Program Manager for

Dieldrin 10:1 Endrin 16.0 Rocky Mountain Arsenal

4234ý00 DDE 11.0 Nrftý1 Bog ýnI ý! 21 DDT 23.0 dane

Dieldrin 2501 **Dieldrin 40 Endrin 29.0 Chlordane 6 DDT 18.0 2-1 Aldrin 16.0 Dieldrin 130 Allrin 2:" DDE 36.0 Commerce City, Colorado

ChIl 0"'I . n 520 DDT 53.0 Di ld,,n 210, ....... 'in 19.0 ....... E d Dieldrin 90 DDE 4.00ý - IDDT 20.0 Figure 17

DISTRIBUTION OF ORGANO

PESTICIDES DETECTED IN

AREA OFFPOST SOIL
RMAI 1143

rr

Zý 2-9 ;t Lake

(ND)

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

32

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

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

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

FDIMP 1 11

DIMP 0.840

Atrazine 4.13 DIMP 2.91

'Wrazine 4.50 ................................................. ......... ................................................ ............... ........................ ................................. ...... ... ........ I ................ .................. ...................

- ýr n 0. 14

trazine 6.80 

.96

j;, A." hlordane 0.338 DMMP 0.238

DIMP 59.0

DGPD 7.43 FCPMS02 19,41

DIMP 5.47

57 0MMP 0.209

Dithiane 44.2 Chloroform 0.599,

V FND7 D(MP 13.1 DIMP 4,92

DMMP 4.92 DMMP 0.227 RNA.-A 2-ounoary ......................................................... .................

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

Mort: "":0" CPMS02MSO 1700

12

t Dieldrin 0.0760

DIMP 4.76

J 2/* 2,;. DMMP 0.251 2"'

4ý>N.

X.

2ý- 2 2 9

z

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

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

35

r

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

L

P"*L YARD

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

..........

RMA Boundary EXPLANATION

Concentrations in micrograms per liter

DDT = 2,2 - Bis (parachlorophenyl) - 1,1,1 - Trichloroethane

0 2000 4000 DDE = 2,2 - Bis (parachlorophenyl) - 1,1 - Dichloroethane
RMAl 1142

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

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

27 J

DDT 11.8

DDE 6.70 ............. .... ...... ------- - ------- -- - ------ --------- -- - ------- Chlordane 64.5

Dieldrin 10.2

9 DDT 5.20 ieldrin 5.00

Endrin 6.00

'3al DBCP 19.0)

J. f-sý

DDT 21.5

DDE 6M

Aldrin 10.2

Chlordans 37.6

...... Dieldrin 5.20

N D

12

rND

(Dieldrin 5.00

CL6CP52.8)

......... ...................................... ......... ................... ...... DDT 14.8 ........... ............ .............. ........ .......... ............ I ............................... ...........................

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

d,,n 4f T 0

DDE 9.00 N 0 I 1H ýo

'FTDD 

Chlordane 77.5 22 n 028.0 ................ --------------------- Dieldrin 6.90

Enddn 9.20 DBCP 8.80

Aldrin 12.0

Dieldrin 26.0

EndHn 7.00 A drin 14.00

ND Dieldrin 25

Z.- 

DBCP 240 O--N ND At MA 60Sir .......... ------- .........

6L7 6.70

,dan. 37.4

.2

A /.j

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

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

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

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

3

Ný F

..........

10

2-1 2 3ý;

S A C VVS C'

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

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

Sf, UTH PLA. F S

4 5

N,

!-3. ýz

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

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

. ..........

12

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

PmAis -Ja rv

0 2000 4000 EXPLANATION
GLOSSARY

Ag/g micrograms per gram

pg/kg micrograms per kilogram

lug/l micrograms per liter

ABS chemical -specific absorption factor

ACGIH American Conference of Government Industrial Hygienists

AChE acety1cholinesterase

ACL Alternate Concentration Limit

ADI acceptable daily intake

AHPA Archeological and Historic Preservation Act

ANOVA Analysis of Variance

AOP advanced oxidation process

APEG alkali metal polyethane glycol

AQCDs Air Quality Criteria Documents

ARAR applicable or relevant and appropriate requirement

ARES Automated Risk Evaluation System

Armv U.S. Department of the Army

AT averaging time

ATP adenosine triphosphate

ATSDR Agency for Toxic Substances and Disease Registry

AWQC ambient water quality criteria

BAC Biotechnology Advisory Committee

BAF bioaccumulation factor

BCF bioconcentration factor

BCRL below certified reporting level

BCS Boundary Containment System

BDAT best demonstrated technology

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BDL below detection limit

BEPA Bald Eagle Protection Act

BEST basic extraction sludge treatment

BF bioavailability factor

BGEPA Bald and Golden Eagle Protection Act

bgs below ground surface

BHC benzene hexachloride

BNIF biornagnification factor

BOD Biological Oxygen Demand

bw body weight

C/l commercial/industrial

CAA Compliance Assurance Agreement/Clean Air Act

CAR Contamination Assessment Report

CBSG Colorado Basic Standards for Groundwater

CCP Composite Correction Plan (CWA)

CCR Colorado Code of Regulations

CD Consent Decree

CDH Colorado Department of Health

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CF&I Colorado Fuel and Iron

CFR Code of Federal Regulations

Cfs cubic feet per second/confined flow system

cfs/mi cubic feet per second per mile

CHWMA Colorado Hazardous Waste Management Act

CM centimeters

cm/sec centimeters per second

cm/hr centimeters per hour

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CM2 centimeters squared

CMP comprehensive monitoring program

CNS central nervous system

COC chemical of potential concern

COD Chemical Oxygen Demand

COE U.S. Army Corps of Engineers

CPMS 4-chlorophenylmethyl sulfide

CPMSO 4-chlorophenylmethyl sulfoxide

CPMS02 4-chlorophenylmethyl sulfone

Cr concentration in plant roots/tubers

CRL certified reporting limit

CSC Chemical Sales Company

CTM cattail marshes

CU consumptive use

Cv coefficient of variation

C, chemical concentration in water

CWA Clean Water Act

Da molecular diffusivities in air

DAA detailed analysis of alternatives

days/yr days per year

DBCP dibromochloropropane

DDD 2,2-bis (para-chlorophenyl)-I,I-dichloroethane

DDE 2,2-bis (para-chlorophenyl)-I,I-dichloroethene

DDT 2,2-bis (para-chlorophenyl)-1,1,1-trichloroethane

DDTR DDT and its metabolites

DIMP diisopropyl me thyl phos phonate

DNA deoxyribonucleic acid

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M

DOC dissolved organic carbon

DQO data quality objective

DRCOG Denver Regional Council of Governments

DRE Destruction/ Removal Efficiency

DSA development and screening of alternatives

DSMA disodium methanearsonate

D,,, molecular diffusivities in water

EA endangerment assessment

Ebasco Ebasco Services, Inc.

EC50 median effective concentration

ED exposure duration

EDB ethylene dibromide

EF exposure frequency

EFH Exposure Factors Handbook

Eh redox potential

EPA U.S. Environmental Protection Agency

ERT Environmental Research and Technology

ESA Endangered Species Act

ESE Environmental Science and Engineering, Inc.

ET exposure time

FF fallow field

FFA Federal Facility Agreement

FI locally produced fraction

FS feasibility study

ft/day feet per day

ft/ft feet per foot

ft/yr feet per year

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FWCA Fish and Wildlife Coordination Act

FWPCA Federal Water Pollution Control Act

FWRIR Final Water Remedial Investigation Report

FY Fiscal Year

FY88 fiscal year 1988

FY90 fiscal year 1990

g/cm 3 grams per cubic centimeter

g/1 grams per liter

g/day grams per day

GAC granulated activated carbon

GC/MS gas chromatography/mass spectroscopy

GN4P groundwater monitoring program

9pM gallons per minute

GPS Groundwater Protection Standards

GWF grasses and weedy forbs

HA health advisory

HADs Health Assessment Documents

HBC health-based criteria

HDPE High Density Polyethylene

HEA Health Effects Assessment

HEAST Health Effects Assessment Summary Tables

HEEDs Health and Environmental Effects Documents

HEEPs Health and Environmental Effects Profiles

HEW Health Education and Welfare

HI Hazard Index

HLA Harding Lawson Associates

HQ hazard quotient

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hr/day hours per day

HSBAA Historic Sites, Buildings, and Antiquities Act

HSDB Hazardous Substance Database

HSWA Hazardous and Solid Waste Amendments

1CP inductively coupled plasma

ICS Irondale Containment System

IRA Interim Response Action

IRA A Additional Interim Response Action

IRF In Situ Radio Frequency

IRIS Integrated Risk Information System

IRP Installation Restoration Program

ISV in-situ vitrification

Koc organic carbon coefficient

Kow octanol/water partition coefficient

1/day liters per day

1/kg liters per kilogram

I/CM3 liters per centimeter cubed

LAER Lowest Achievable Emission Rate

lb/acre pounds per acre

LC50 chemical concentration that is lethal to 50 percent of the exposed

population

LD50 chemical dose that is lethal to 50 percent of the exposed population

Ldn day-night average noise level

LDPE low-density polyethylene

LDR Land Disposal Restrictions

LOAEC lowest -observed -adverse -effect concentration

LOAEL lo west- observed -adverse -effect level

LOEC lowest -observed -effect concentration

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LOEL lowest -observed -effect level

M2/day square meters per day

MATC Maximum Allowable Tissue Concentration

MBTA Migratory Bird Treaty Act

MCL Maximum Contaminant Level

MCLG Maximum Contaminant Level Goal

MER Colorado Division of Water Resources Master Extract Register

N4 F modifying factor

MFO mixed function oxidose enzymes

mg/kg-bw-day milligrams per kilogram body weight per day

Mg milligrams

mg/CM2 milligrams per cubic centimeter

mg/kg/day milligrams per kilogram per day

mg/kg milligrams per kilogram

Mg/l milligrams per liter

mg/m2/day milligrams per meter squared per day

mg/m 3 milligrams per cubic meter

Mi2 square miles

MKC Morrison-Knudsen Corporation

NIKE Morrison-Knudsen Engineers, Inc.

N4KES MK -Environmental Services

MI/g milliliters per gram

MLE most likely exposure

MOP Method of Proportion

MP Malcolm-Pirnie, Inc.

MRL minimal risk level

NISL Mean Sea Level

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MSMA monosodium methanearsenate

MTV mobility, toxicity, and volume

N nitrogen

NAAQS National Ambient Air Quality Standards (CAA)

NAS National Academy of Sciences

NBCS North Boundary Containment System

NCI National Cancer Institute

NCP National Contingency Plan

NEPA National Environmental Policy Act (1969)

NESHAPS National Emissions Standards for Hazardous Air Pollutants (CAA)

NHPA National Historic Preservation act

NIOSH National Institute for Occupational Safety and Health

nm nanometers

NOAA National Oceanic and Atmospheric Administration

NOAEL no -observed -adverse -effect level

NOAEC no -observed -adverse -effect concentration

NOEC no -observed -effect concentration

NOEL no-observed-effect level

NPDES National Pollutant Discharge Elimination System (CWA)

NPDWS National Primary Drinking Water Standards

NPL National Priorities List (CERCLA)

NRC National Research Council

NRCC National Research Council of Canada

NRDAM/COE Natural Resource Damage Assessment Model for Coastal and Marine

Environments

NSPS New Source Performance Standards (CAA)

NTP National Toxicology Program

NWBCS Northwest Boundary Containment System

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O&M NBCS Operation and Maintenance North Boundary Control System

OCP organochlorine pesticide

OECD Organization for Economic Cooperation and Development

OHM/TADS Oil and Hazardous Material/Technical Assistance Data System

OSWER Office of Solid Waste and Emergency Response

OTSP organics in total suspended particulates

OU operable unit

PACT powder activated carbon treatment

PC permeability coefficient

PCNB pentachloronitrobenzene

PEG polyethylene glycol

PFF plowed fallow field

PM-10 respirable particulates less than 1.0 microns in diameter

PMO Program Managers Office

PMRMA Program Manager for Rocky Mountain Arsenal

POTW publicly owned treatment works

ppm parts per million

PQL Practical Quantitation Limit

PRG preliminary remediation goal

PSD Prevention of Significant Deterioration

PVC polyvinyl chloride

QA/QC quality assurance/quality control

R retardation factor

RA risk assessment

RACT Reasonably Available Control Technology

RAGS Risk Assessment Guidance for Superfund

RAO remedial action objective

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RBC rotating biological contractor

RCC Resource Conservation Corporation

RCRA Resource Conservation and Recovery Act

RD/RA Remedial Design/Remedial Action (CERCLA)

RD Remedial Design

RfD reference dose

RI remedial investigation

RI/FS remedial investigation /feasibility study

RIC Resource Information Center

RLSA R.L. Stollar & Associates, Inc.

RMA Rocky Mountain Arsenal

RME Reasonable Maximum Exposure

RNA ribonucleic acid

ROD Record of Decision

RPM Remedial Project Manager (CERCLA)

RPO representative process option

RRC regulatory risk criteria

RSA regional statistical area

RTECS Registry of Toxic Effects of Chemical Substances

SA skin surface area

SACWSD South Adams County Water and Sanitation District

SAF Spatial Adjustment Factor

SARA Superfund Amendments and Reauthorization Act (1986)

SAS Statistical Analysis System

SDWA Safe Drinking Water Act

SEP Standard Evaluation Procedure

SF slope factor

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SGOT serum glutarnate-oxymate aminotransferase

SIP State Implementation Plans

SUTRA Saturated -Unsaturated Transport

SVOC sernivolatile organic compound

TAC time for exchange of basement air

TBC to be considered

TCHD Tri-County Health Department

TCOC tissue chemicals of concern

TERIS Teratogen Information System

TG-W tall grass wetlands

TICs tentatively identified chemicals

TLV threshold limit value

TPP technical program plan

TRCLE trichloroethylene

TRV toxicity reference value

TSD Technical Support Document (or) Treatment, Storage, and Disposal

TSP total suspended particulates

TSS total suspended solids

TWA time-weighted average

UAFS unconfined alluvial flow system

UF uncertainty factor

UFS unconfined flow system

UIC Underground Injection Control

UL90 upper 90 percent confidence limit on the arithmetic mean

UL95 upper 95 percent confidence limit on the arithmetic mean

USABRDL U.S. Army Biomedical Research and Development Laboratory

USAF U.S. Air Force

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USC Unified Soil Classification (or) United States Code

USDA U.S. Department of Agriculture

USDHEW U.S. Department of Health Education and Welfare

USFWS U.S. Fish and Wildlife Service

USGS U.S. Geological Survey

UTM universal transverse mercator

USC United States Code

UV ultraviolet

VAR ratio of basement volume to surface air in contact with soil

VLT very low toxicity

VOC volatile organic compound

WES U.S. Army Engineer Waterways Experiment Station

WF weedy forbs

WHO World Health Organization

WQC water quality criteria

WQCA Water Quality Control Act

WWC Woodward-Clyde Consultants

0C degrees Celsius

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