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EPA Superfund Record of Decision: EASTERN MICHAUD FLATS

0,28

CONTAMINATION

172

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5944

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

2003

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TABLE OF CONTENTS

PREFACE . i

LIST OF FIGURES .vii

LIST OF TABLES ix

LIST OF ACRONYMS USED IN THIS DOCUMENT x

DECLARATION FOR THE RECORD OF DECISION 1

1.0 SITE NAME, LOCATION, AND DESCRIPTION . 5

1.1 Site Name and Location 5

1.2 General Site Description 5

1.2.1 Land Use 5

1.2.2 Geology and Hydrogeology 8

1.2.3 Hydrology (Surface Water) . 8

1.2.4 Climate . 10

1.2.5 Ecology . 10

1.3 Site Subareas . 10

1.3.1 FMC Plant Area 12

1.3.2 Simplot Plant Area 12

1.3.3 Off-Plant Area 15

2.0 SITE HISTORY AND ENFORCEMENT ACTIVITIES 16

2.1 Historical Land Use 16

2.1.1 FMC Plant . 16

2.1.2 Simplot Plant . 16

2.2 Previous Studies . 17

2.3 Listing on the National Priorities List 17

2.4 Company Actions to Date 17

2.4.1 Simplot . 18

2.4.2 FMC . 19

2.5 History of EPA Enforcement Activity 20

2.5.1 FMC Plant . 20

2.5.2 Simplot Plant . 21

2.5.3 Off-Plant Area 21

3.0 HIGHLIGHTS OF COMMUNITY PARTICIPATION 21

4.0 SCOPE AND ROLE OF RESPONSE ACTION 23

4.1 Air 23

4.2 RCRA . 24

5.0 SUMMARY OF SITE CHARACTERISTICS 25

5.1 Geologic Setting . 26

5.2 Hydrogeology . 26

5.3 Surface Water Hydrology 27

5.4 Climate 27

5.5 Ecosystems and Species of Concern 28

5.6 Key Remedial Investigation Findings 29

5.6.1 Soils and Solids 29

5.6.2 Ground water 30

5.6.3 Surface Water/Sediments . 31

5.6.4 Air . 33

5.6.5 Terrestrial and Aquatic Investigations 34

6.0 SUMMARY OF SITE RISKS 35

6.1 Human Health Risks . 35

6.1.1 Approach to Human Health Risks 35

6.1.2 Conceptual Site Model . 35

6.1.3 Background Concentrations . 36

6.1.4 Contaminants of Potential Concern . 36

6.1.5 Toxicity Assessment . 38

6.1.5.1 Quantitative Indices of Toxicity . 38

6.1.5.2 Combining Radionuclide and Chemical Cancer Risks . 40

6.1.6 Exposure Assessment . 40

6.1.6.1 Alternate Future Uses of the FMC and Simplot Plants 41

6.1.7 Risk Characterization . 41

6.1.7.1 Residential Areas 42

6.1.7.1.1 Near Plant Areas . 42

6.1.7.1.2 Existing Residential Areas . 42

6.1.7.2 Plant Workers 43

6.1.7.2.1 Noncarcinogenic Risks 44

6.1.7.3 Assessment of Potential Health Effects from Inhalation of Airborne Particulate Matter (PM

10) 44

6.2 Ecological Risk Assessment . 45

6.3 Uncertainty 47

6.3.1 Uncertainty in the Human Health Risk Assessment . 48

6.3.1.1 Air Pathway Uncertainty 48

6.3.1.2 Summary of the Exposure Assessment Uncertainties . 49

6.3.1.3 Summary of Toxicity Assessment Uncertainties . 50

6.3.2 Ecological Risk Assessment Uncertainties 50

6.4 Need for Action 50

7.0 REMEDIAL ACTION OBJECTIVES . 50

7.1 FMC and Simplot Plant 51

7.2 Off-Plant Area . 51

8.0 DESCRIPTION OF ALTERNATIVES 53

8.1 Off-Plant area 53

8.1.1 Alternative 01: No Action . 53

8.1.2 Alternative 02: Vegetation/Bio Monitoring . 53

8.1.3 Alternative 03: Institutional Controls 54

8.1.4 Alternative 04: Removal and Replacement of Soil Cover . 54

8.2 FMC Subarea (FMC) 54

8.2.1 Alternative F2: No Further Action . 54

8.2.2 Alternative F3: Institutional Controls and Ground water Monitoring 55

8.2.3 Alternative F4: Institutional Controls, Surface Controls and Soil Cover, and Groundwater

Monitoring . 55

8.2.4 Alternative F4A: Institutional Controls, Surface Controls and Capillary Barrier Cap, and

Ground water Monitoring . 55

8.2.5 Alternative F5A: Institutional Controls, Source Containment and Native Soil Cap, and Ground

water Monitoring . 56

8.2.6 Alternative F5B: Institutional Controls, Source Containment and Asphaltic Concrete Cap, and

Ground water Monitoring 56

8.2.7 Alternative F5C: Institutional Controls, Surface Controls and Multi-Layer Cap, Source

Goontainment, and Ground water Monitoring . 56

8.2.8 Alternative F6A- Institutional Controls, Source Containment and Asphaltic Concrete Cap,

Excavation and Disposal, and Ground water Monitoring 56

8.2.9 Alternative F6B: Institutional Controls, Surface Controls and Soil Cover, Excavation and

Stabilization, and Ground water Monitoring 57

8.2.10 Alternative F7-Institutional Controls, Surface Controls and Multi-Layer Cap, and Ground

water Monitoring, Extraction and Recycling: . 57

8.2.11 Alternative F8B- Institutional Controls, Surface Controls and Asphaltic Concrete Cap,

Excavation and Stabilization, and Ground water Monitoring, Extraction, Treatment and Recycling 57

8.3 Simplot Plant 58

8.3.1 Alternative S2: No Further Action . 58

8.3.2 Alternative S3: Institutional Controls & Ground water Monitoring 58

8.3.3 Alternative S4A: Institutional Controls, Removal/Disposal, Source Control #1 . 58

8.3.4 Alternative S4B: Institutional Controls, Removal/Disposal, Ground water Containment, Source

Control #1 . 59

8.3.5 Alternative S5: Institutional Controls, Removal/Disposal, Source Control #2 . 59

9.0 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES 59

9.1 Threshold Criteria . 59

9.1.1 Overall protection of human health and the environment 59

9.1.2.Compliance with Applicable or Relevant and Appropriate Requirements (ARARs) . 60

9.2 Primary Balancing Criteria . 61

9.2.1. Long-term effectiveness and permanence . 61

9.2.2. Reduction of toxicity, mobility, or volume through treatment or recycling 61

9.2.3 Short-term effectiveness 62

9.2.4 Implementability 62

9.2.5 Estimated Cost 63

9.3 Modifying Criteria . 63

9.3.1 State acceptance 63

9.3.2.Community acceptance 63

10.0 THE SELECTED REMEDY 63

10.1 Simplot Operable Unit (OU) 64

10.1.1 Ground water . 64

10. 1. 1. 1 Ground water Extraction (Alternative S4B) 64

10.1.1.1.2 Ground water Extraction System Evaluation 64

10.1.1.2 Improvement to Gypsum Decant System (Alternative S4B) . 65

10.1.1.3 Groundwater Monitoring and Evaluations (Alternative S4B) 65

10.1.2 Air (Alternative S4B) 65

10.1.3 Soils and Solids (Alternative S4B) . 66

10.1.3.1 Worker Safety Programs (Alternative S4B) 66

10.1.3.2 Personnel Monitoring (Alternative S4B) 66

10.1.4 Land Use Controls (Alternative S4B) 66

10.1.4.1 Construction of Radon-Resistant Buildings (Alternative S4B) 66

10.1.5 Off-Plant Area . 66

10.1.5.1 Fluoride Monitoring (Alternative 03) 67

10.1.5.2 Soils (Alternative 03) 67

10.1.5.3 Ground water Monitoring . 68

10.1.6 Estimated costs for the Simplot OU 68

10.2 FMC Operable Unit . 68

10.2.1 Contaminated Ground water (Alternative F4/F4A) 68

10.2.1.1 Ground water Monitoring and Evaluation 68