PB96-964402
EPA/ROD/R08-96/112
March 1996
EPA Superfund
Record of Decision:
Silver Bow/Butte Creek,
Streamside Tailings O.U., MT
11/29/1995
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RECORD OF DECISION
STREAMSIDE TAILINGS OPERABLE UNIT
SILVER BOW CREEK/BUTTE AREA
(original portion)
NATIONAL PRIORITIES LIST SITE
SILVER BOW AND DEER LODGE
COUNTIES, MONTANA
Montana Department of Environmental Quality
Environmental Remediation Division
2209 Phoenbc Ave
Helena, Montana 59620-0901
(Lead Agency)
United States
Environmental Protection Agency
Region VIE - Montana Office
Federal Building, 301 S. Park, Drawer 10096
Helena, MT 59626-0096
(Support Agency)
November 1995
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RECORD OF DECISION
STREAMSIDE TAILINGS OPERABLE UNIT OF THE SILVER BOW
CREEK/BUTTE AREA (original portion) NATIONAL PRIORITY LIST SITE
INTRODUCTION
The Montana Department of Environmental Quality (MDEQ)1 and the U.S. Environmental
Protection Agency (EPA) present the record of decision for the Streamside Tailings Operable
Unit (the SST OU) of the Silver Bow Creek/Butte Area (original portion) National Priorities
List (NPL) Site, Butte, Montana. The record of decision is based on the administrative
record, remedial investigation/feasibility study, the proposed plan (MDEQ, 1995a), the
public comments received, including those from the potentially responsible party, EPA
comments, and other pertinent information. The record of decision presents a brief outline
of the remedial investigation/feasibility study, actual and potential risks to human health and
the environment, and the selected remedy. MDEQ followed the Comprehensive
Environmental, Response, Compensation and Liability Act (CERCLA), the National
Contingency Plan (NCP), and EPA guidance in preparation of the record of decision. The
record of decision has the following three purposes:
1. To certify that the remedy selection process was carried out in accordance with the
requirements of the CERCLA, 42 U.S.C. 9601 et seq., as amended by the Superfund
Amendments and Reauthorization Act (SARA), and, to the extent practicable, the
National Contingency Plan (NCP);
2. To outline the remedial components and goals of the selected remedy; and
3. To provide the public with a consolidated source of information about the history,
characteristics, and risks posed by the conditions at the OU, as well as a summary of
the cleanup alternatives considered, their evaluation, the rationale behind the selected
remedy, and the agencies' consideration of and responses to the comments received.
The record of decision is organized into three distinct sections:
o The Declaration functions as an abstract for the key information contained in
the record of decision and is the section of the record of decision signed by the
Director of the Montana Department of Environmental Quality and the
Assistant Regional Administrator for Ecosystems Protection and Remediation,
' The Montana Department of Environmental Quality was created on July 1, 1995, by consolidating
environmental programs from the Departments of Health and Environmental Sciences, Natural Resources and
Conservation, and State Lands. The majority of the SST OU investigation was conducted under the authorities of
the predecessor Montana Department of Health and Environmental Sciences (MDHES).
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EPA Region VIE;
o The Decision Summary provides an overview of the OU characteristics, the
. alternatives evaluated, and the analysis of those options. The Decision
Summary also identifies the selected remedy and explains how the remedy
fulfills statutory requirements; and
o The Responsiveness Summary addresses public comments received on the
proposed plan (MDEQ, 1995a), the remedial investigation/feasibility study and
other information in the administrative record.
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DECLARATION
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECLARATION
OPERABLE UNIT NAME AND LOCATION
Streamside Tailings OU of the Silver Bow Creek/Butte Area (original portion) National
Priority List Site in Silver Bow and Deer Lodge Counties, Montana.
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected remedy for the Streamside Tailings Operable
Unit (the SST OU) of the Silver Bow Creek/Butte Area National Priorities List (NPL) Site.
The Montana Department of Environmental Quality (MDEQ), in consultation with the United
States Environmental Protection Agency (EPA), selected the remedy in accordance with
CERCLA, as amended by SARA, and, to the extent practicable, the NCP. The EPA
concurs in and adopts the selected remedy. The attached index identifies categories of
documents or records that comprise the administrative record upon which the selection of the
remedial action is based (Appendix B).
ASSESSMENT OF THE OU
Actual or threatened releases of hazardous substances from this OU, if not addressed by
implementing the response action selected in this record of decision, may present an
imminent and substantial endangerment to public health, welfare, or the environment.
DESCRIPTION OF THE SELECTED REMEDY
This is the final remedial action for the SST OU. This remedial action addresses the
principal threats and provides for treatment and appropriate disposal of contaminated
tailings/impacted soils, instream sediments, and railroad materials. Much of the treated
materials will remain in the OU. Consequently, the OU will require long-term management
and monitoring.
The principal contaminants of concern at the SST OU are arsenic, cadmium, copper, lead,
mercury, and zinc. This remedial action is generally described as Alternative 5 in the
Feasibility Study (ARCO, 1995b) and the proposed plan (MDEQ, 1995a). Some refinements
to Alternative 5 have been made to clarify the criteria used to require excavation of
tailings/impacted soils, to more precisely identify excavation of contaminated railroad bed
materials, and to specify an institutional controls/maintenance program that will be used to
manage the Silver Bow Creek corridor in the future. This record of decision establishes
cleanup levels or physical criteria for these and all other contaminants of concern at the SST
OU. The major components of the selected remedy include:
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECLARATION
Tailings/Impacted Soils
1. Excavation of contaminated tailings/impacted soils from most areas within the
present 100-year floodplain as delineated in the CH2M Hill (1989) Flood
Modeling Study ("floodplain"). The removed volume will include all
tailings/impacted soils continuously or seasonally saturated by groundwater
together with the tailings/impacted soils overlying these saturated tailings
(collectively, "saturated tailings"), tailings/impacted soils located where in-situ
Streambank Tailings and Revegetation Study (STARS) treatment cannot
reliably immobilize the contaminants, and tailings/impacted soils subject to
erosion and re-entrainment into the stream. These criteria, together with the
other details on the selected remedy, are more fully described in the Decision
Summary below. The total volume of saturated and overlying
tailings/impacted soils to be removed is presently estimated at approximately
700,000 cy. The total volume of tailings/impacted soils subject to erosion and
therefore to be excavated is estimated at approximately 850,000 cy (1,550,000
cy collectively). Specific locations and volumes of excavated materials will be
determined by the agencies during remedial design/remedial action.
2. To meet the established OU remedial objectives, tailings/impacted soils will be
removed from the floodplain where: (1) tailings/impacted soils are saturated by
groundwater during any part of the year, (2) in-situ Streambank Tailings and
Revegetation Study (STARS) treatment cannot reliably immobilize the
contaminants, for example, due to the thickness of the tailings/impacted soils,
proximity of the tailings/impacted soils to groundwater, or lack of appropriate
buffer materials between the treated tailings/impacted soils and the
groundwater, or (3) the treated tailings/impacted soils could be eroded back
into the stream by natural lateral stream migration, channel avulsion, overbank
flow, or flood events. A detailed discussion of this topic is presented in
Section IX (Selected Remedy) of the Decision Summary.
3. All remaining tailings/impacted soils (approximately 950,000 cy) within the
OU will be treated in-situ with the STARS technology and appropriately
protected from washout or erosion from lateral stream migration and flood
flows. In-situ and adjacent repository STARS treated areas will not be placed
or left where they can be eroded back into Silver Bow Creek.
4. Excavated tailings/impacted soils will be relocated to safe, local repositories
clearly outside of the present 100-year floodplain as defined by CH2M Hill
(1989) provided that appropriate locations can be identified and delineated for
repository use and that an appropriate institutional controls/maintenance
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECLARATION
program can be implemented. Tailings/impacted soils placed in the relocation
repositories will be fully treated with lime amendments in 2-foot lifts and will
be revegetated in accordance with the STARS technology. If appropriate
locations and an appropriate institutional control/monitoring and maintenance
program cannot be implemented, excavated tailings/impacted soils and other
wastes would be removed to centralized dry repositories and appropriately
handled and disposed of there.
5. Replacement fill will be required in most locations where tailings/impacted
soils are removed. Replacement fill and streambank reconstruction with
suitable growth media having an appropriate texture and particle size
distribution will be required. A key to long-term streambank stabilization will
be establishment of mature riparian vegetation. Grass, forb, willow, and tree
species will be specified based on local climatic conditions, proximity to
stream channel, and ability to produce dense root systems at maturity. The
overall topography of the replacement fill material will be appropriately sloped
toward the stream channel, with the goal of creating geomorphic stability.
6. Because numerous repositories, which will be treated with the STARS
technology, will be located near the floodplain in several areas along the
length of the stream, and because in Subareas 2 and 4 a substantial amount of
tailings will be treated with the STARS technology on the edges or just outside
of the floodplain, a permanent monitoring, management, and maintenance
program is an integral part of the remedy. Monitoring, management and
maintenance will address vegetative performance on both STARS treatment
areas and remediated streambanks, streambank stability and channel meander.
This remedy will also ensure that the metals are immobilized at all in-situ
remediated areas and removal repositories through vadose zone, saturated
zone, and overland flow monitoring.
Instream Sediments
7. Fine-grained instream sediments (less than or equal to one millimeter in size
[< 1mm]) located in every depositional areas will be removed and placed in
repositories with the excavated tailings/impacted soils and railroad materials.
This size fraction was identified because it corresponds with the size of the
tailings/impacted soils and contains the bulk of instream contamination.
Specific volumes and locations to be excavated will be determined by the
agencies during remedial design/remedial action. This sediment volume is
presently estimated at 73,000 cy as presented in the RI report (ARCO, 1995a).
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECLARATION
8. After removal of contaminated sediments, the channel bed and streambank will
be reconstructed to an appropriate slope and other critical dimensions with
materials of appropriate size, shape and composition. This reconfigured bed
will contain suitable bedform morphology (riffles, bars, pools, etc.) for aquatic
habitat. Streambanks will require adequate growth media to allow for
immediate establishment of a healthy riparian vegetative system to protect the
remedy from high flows.
9. Instream sediment monitoring will be performed during and after the response
action to ensure that contaminated instream sediments have been adequately
remediated. Monitoring will include sampling of instream sediment for
sediment contaminant concentrations as well as macroinvertibrate abundance
and diversity. Maintenance to deal with continuing sediment contamination
over time may be necessary, depending on the results of long-term monitoring.
Railroad Materials
10. The remedy will excavate, treat and/or cover all contaminated railroad bed
materials that pose a risk to human health or the environment. All concentrate
spills, which are the primary human health concern for the railroad beds, will
be removed and disposed in an appropriate and secure disposal facility in
accordance with any applicable RCRA requirements. Railroad materials which
directly impact the stream either at bridge abutments or along the streambank
will be excavated and disposed in repositories along with the tailings/impacted
soils and instream sediments. The actual amount and methods of excavation
and/or treatment will be determined during remedial design. The estimated
volume of excavated materials is presently 71,000 cy. The in-situ STARS
technology or soil capping is expected to be appropriate for all other areas of
the inactive grade presenting environmental risk.
11. Monitoring and maintenance of the remediated railroad materials will be
required to ensure that contaminant sources are not exposed as a result of
erosion and do not cause future contaminant loading to the stream.
Ground and Surface Water
12. While Silver Bow Creek ground and surface water are primary receptors of
SST OU contamination, no separate remedial action is being prescribed for
these media. Remedial activities for other SST OU media under this record of
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECLARATION
decision and for sources of contaminants upstream/offsite under other cleanup
actions will limit further releases to ground and surface water with the goal of
ultimately attaining ground and surface water standards within the OU.
Removing the source of groundwater contamination by addressing the
tailings/impacted soils and railroad materials, will allow contaminants in
groundwater to attenuate over time through dilution, adsorption, precipitation.
and dispersion.
13. Removal of the tailings/impacted soils, fine-grained instream sediments, and
railroad materials will allow for the attainment of instream sediment and
surface water objectives, over tune. Removing the sources and interrupting
the pathways for surface water contamination by addressing all the
contaminated materials should permit eventual attainment of the surface water
objectives.
14. Long-term monitoring of ground and surface water is a critical element of the
remedy. Surface water will be monitored for compliance at a number of
points in the OU to ascertain possible surface water contaminant loading from
onsite/nearsite contaminant sources. Groundwater will be monitored at
locations of documented or suspected groundwater contamination, all
relocation areas, and other locations where STARS treatment has been applied.
Coordination and Schedule
15. An institutional controls program, which must be funded on a permanent basis
as part of the remedy, will be coordinated through a joint effort of the Butte-
Silver Bow and Anaconda-Deer Lodge local governments. Institutional
controls, monitoring, and maintenance will be integrated into a Silver Bow
Creek corridor management program. The program will be established and
maintained in a manner that will ensure that all aspects of the OU remedial
action, both within and outside of the floodplain, are maintained for the long-
term, and ensure that the future land use in the area is consistent with the
scenarios upon which cleanup decisions for this action have been based.
16. Construction of the proposed remedy will be coordinated with other cleanup
activities along Silver Bow Creek. Releases of Contaminated instream
sediments and surface waters prior to, during, and following remedial action,
which might re-contaminate Silver Bow Creek, will be suitably controlled and
treated. The design and schedule of the OU remedy will be coordinated with
the design and installation of upstream sediment control basins. If adequate
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECLARATION
upstream control facilities are not in service at the time of initiation of
construction of this remedy, then additional sediment control and treatment
facilities will be provided as a part of this remedy or other scheduling
adjustments will be made. The implementation of the remedy will also be
coordinated to the maximum extent possible with the possible implementation
of the State's natural resource damage restoration plan in order to avoid
duplication of effort and unnecessary costs and to maximize the benefits to the
area.
17. Butte-Silver Bow County and ARCO are initiating research on constructed
wetlands as a potential treatment technology for waste water nutrient discharge
and storm water metals contamination. To coordinate with this research, the
end land use in Subarea 1 has been delineated as wetlands. After removal of
all the above mentioned contaminant sources, reconstruction of the Subarea
will be designed to incorporate use of the area as wetlands. Constructed
wetlands in this area may be used as a treatment system for nutrients and/or
metals from upstream, if such treatment is ultimately determined to be
appropriate in this area.
STATUTORY DETERMINATIONS
The selected remedy is protective of human health and the environment, complies with
federal and state requirements that are legally applicable or relevant and appropriate to the
remedial action except where a waiver of such requirements has been determined to be
appropriate, and is cost-effective. This remedy uses permanent solutions and alternative
treatment technologies to the maximum extent practicable and satisfies the preference for
remedies that employ treatment that reduces toxicity, mobility, or volume as a principal
element. Because this remedy will result in hazardous substances remaining in the OU above
health or environmental based risk levels, periodic five-year reviews of the remedial action
shall be conducted, beginning within five years after initiation of remedial action, to ensure
that the remedy continues to provide adequate protection to human health and the
environment.
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Mr. Mfirk A. Simonich Date
Dirfirtor
Montana Department of Environmental Quality
Mr. William Yellbwtail Date7 7
Regional Administrator / '
Environmental Protection Agency, Region Vffi
DECLARATION - 'I
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DECISION SUMMARY
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TABLE OF CONTENTS
LIST OF TABLES iv
LIST OF FIGURES v
LIST OF APPENDICES vi
ACRONYMS vii
GLOSSARY ix
I. OPERABLE UNIT NAME, LOCATION AND DESCRIPTION 1
H. OU HISTORY 1
Waste Transport 6
Railroad History 6
Enforcement Actions 7
m. HIGHLIGHTS OF COMMUNITY PARTICIPATION 9
IV. SCOPE AND ROLE OF RESPONSE ACTION 11
V. SUMMARY OF OU CHARACTERISTICS 12
General Description of Subareas 13
Conceptual Model of Contaminant Transport 15
Estimated Volumes of Contaminated Materials By Subarea 29
Terrestrial Resources 36
Benthic Macroinvertebrate Resources 37
VI. SUMMARY OF OU RISKS 39
Human Health Conclusions 39
Ecological Conclusions 40
VH. DESCRIPTION OF ALTERNATIVES 59
Alternative No. 1 - No Action 61
Alternative No. 2 - STARS Treatment of Tailings/Impacted Soils, No Action
for Instream Sediments, and In-situ Treatment of Railroad Materials .... 61
Alternative No. 3 - Partial Relocation and Partial STARS Treatment for
Tailings/Impacted Soils, Limited Removal for Instream Sediments, and
In-situ Treatment of Railroad Materials 62
Alternative No. 4 - Partial Removal and Partial STARS Treatment of
Tailings/Impacted Soils, Limited Removal of Instream Sediments, and
Limited Removal of Railroad Materials 63
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Alternative No. 5 - Total Relocation of Tailings/Impacted Soils in Subareas 1
and 3, Partial Relocation and Partial STARS Treatment in Subareas 2
and 4, Limited Instream Sediment Removal, and Limited Removal of
Railroad Materials 63
Alternative No. 6 - Total Removal of Tailings/Impacted Soils in Subareas 1
and 3, Partial Removal and Partial STARS Treatment in Subareas 2 and
4, Limited Instream Sediment Removal, and Limited Removal of
Railroad Materials 64
Alternative No. 7 - Total Removal of Tailings/Impacted Soils, Total Removal
of Instream Sediments, and Limited Removal of Railroad Materials 64
VIE. SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES . 66
Evaluation and Comparison Criteria 66
Overall Protection of Human Health and the Environment 67
Compliance with ARARs 68
Long-term Effectiveness and Permanence 68
Reduction of Toxicity, Mobility or Volume Through Treatment 69
Short-term Effectiveness 69
Implementability 70
Cost 70
State Agency Acceptance 70
Community Acceptance 71
IX. SELECTED REMEDY 73
Components of Selected Remedy 73
Description and Limitations of the Streambank Tailings and Revegetation
Studies (STARS) Technology 89
Criteria For Application of the Streambank Tailings and Revegetation Study
(STARS) Technology 93
Estimated Costs of the Remedy 96
Final Remediation Goals, Cleanup\Performance Standards, and Points of
Compliance 101
Compliance Monitoring Program 110
Engineering and Institutional Controls 110
Remedial Design/Remedial Action Process 112
Contingency Measures 114
X. STATUTORY DETERMINATIONS 116
Protection of Human Health and the Environment 116
Compliance with Applicable or Relevant and Appropriate Requirements 118
Cost-Effectiveness . . . 120
Utilization of Permanent Solutions and Alternative Treatment Technologies to
the Maximum Extent Practicable 121
Preference for Treatment as a Principal Element 122
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XI. DOCUMENTATION OF SIGNIFICANT CHANGES 123
XH. REFERENCES 127
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LIST OF TABLES
Table 1 Streamside Tailings OU Median Concentrations -
Tailings/Impacted Soil 12
Table 2 • Silver Bow Creek Surface Water Quality Geometric Mean Low
Flow Concentrations 17
Table 3 SST OU WQB-7 Human Health Groundwater Exceedances 23
Table 4 Silver Bow Creek Mean Instream Sediment Concentrations 28
Table 5 Streamside Tailings OU Volumes of Saturated Tailings and
Relevant Groundwater Information 31
Table 6 Carcinogenic Risks for the Residential Scenario 41
Table 7 Noncarcenogenic Hazard Quotients and Hazard Indices for the
Residential Scenario 42
Table 8 Carcinogenic Risks for the Occupational Scenario 43
Table 9 Noncarcenogenic Hazard Quotients and Hazard Indices for the
Occupational Scenario 44
Table 10 Carcinogenic Risks for the Recreational Scenario 45
Table 11 Noncarcenogenic Hazard Quotients and Hazard Indices for the
Recreational Scenario 46
Table 12 Simplified Summary of Ecological Risks from Chemical
Stressors 47
Table 13 Total Volumes of Contaminated Materials Removed or
Relocated and Cost 71
Table 14 Summary of Estimated Media Specific Removal Volumes for
SST Remedial Action 85
Table 15 Remedial Alternative Cost Summary - Tailings/Impacted Soils 98
Table 16 Remedial Alternative Cost Summary - Instream Sediments 99
IV
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LIST OF TABLES (cont.)
Table 17 Remedial Alternative Cost Summary - Railroad Materials 100
Table 18 Minimum Post-Remedy Monitoring Requirements Ill
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LIST OF FIGURES
Figure 1 Site Location-Map 3
Figure 2 Streamside Tailings Vicinity Map 4
Figure 3 • Conceptual Model of Subarea 1 19
Figure 4 Conceptual Model of Subarea 2 20
Figure 5 Conceptual Model of Subarea 3 21
Figure 6 Conceptual Model of Subarea 4 22
Figure 7 Dissolved Copper - SST Surface Water . . . 50
Figure 8 Dissolved Zinc - SST Surface Water 51
Figure 9 Total Arsenic - SST Sediment 52
Figure 10 Total Cadmium - SST Sediment 53
Figure 11 Total Copper - SST Sediment 54
Figure 12 Total Lead - SST Sediment 55
Figure 13 Total Mercury - SST Sediment 56
Figure 14 Total Zinc - SST Sediment 57
Figure 15 Location and Extent of Unsaturated and Saturated Tailings/Impacted
Soils and Conceptual Repository Locations 75
Figure 16 Conceptual Removal and STARS Locations . . . 83
VI
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LIST OF APPENDICES
Appendix A Applicable or Relevant and Appropriate Requirements (ARARS)
Appendix B Administrative Record Index of Document Categories
Appendix C Baseline Risk Assessment Executive Summary
Appendix D Responsiveness Summary
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ACRONYMS
ADL Anaconda-Deer Lodge County
AMC Anaconda Copper Mining Company
AOC Administrative Order of Consent
ARARs Applicable or Relevant and Appropriate Requirements
ARCO • Atlantic Richfield Company
AWQC Ambient Water Quality Criteria
ARM Administrative Rules of Montana
BA&P Butte, Anaconda and Pacific Railroad
bgs below ground surface
BRA Baseline Risk Assessment
BSB Butte-Silver Bow County
CERCLA Comprehensive Environmental Response, Compensation and Liability Act
CFR Code of Federal Regulations
cfs cubic feet per second
CMSP Chicago, Milwaukee, St. Paul and Pacific Railroad
COC contaminants of concern
cy cubic yards
DNRC Department of Natural Resources and Conservation
DPS Development Permit System
EPA U.S. Environmental Protection Agency
FS Feasibility Study
ft/ft foot per foot
ICPD Institutional Controls Planning Document
ICs Institutional Controls
ICMM Institutional Controls, Monitoring, and Maintenance
LAO Lower Area One
MCLs Maximum Contaminant Levels
MCLGs Maximum Contaminant Level Goals
MCA Montana Code Annotated
MDEQ Montana Department of Environmental Quality
mg/kg milligram per kilogram
mm millimeter
MU Montana Union
NCP National Oil and Hazardous Substances Pollution Contingency Plan
NP Northern Pacific
NPL National Priorities List
OU Operable Unit
O&M Operation and Maintenance
PAH Polycyclic Aromatic Hydrocarbons
PCP Pentachlorophenol
PRAOs Preliminary Remedial Action Objectives
PRAOR Remedial Action Objectives Report
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PRGs Preliminary Remediation Goals
PRP Potential Responsible Party
RAOs . Remedial Action Objectives
RI Remedial Investigation
Rocker Rocker Timber Framing and Treating Plant
ROD Record of Decision
SARA Superfund Amendments and Reauthorization Act
SBC Silver Bow Creek
SPAOD Superfund Planning Area Overlay District
SST Streamside Tailings
STARS Streambank Tailings and Revegetation Studies
su Standard Units
TES Threatened, Endangered and Sensitive (Species)
TTSD Treatment Technology Screening Document
fjig/l micrograms per liter
UP Union Pacific
WSP Warm Springs Ponds
WQB-7 Montana Water Quality Circular 7
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GLOSSARY
Administrative record: The files containing all documents relied upon by the agencies in
selecting a remedy at a Superfund site.
Applicable or Relevant and Appropriate Requirements (ARARs): Legal requirements,
criteria, or'limitations which are set forth in federal and state environmental and facility
siting laws and regulations.
Backfill: Clean soil used to replace contaminated material which was removed.
Baseline human health and ecological risk assessments: Studies conducted as part of the
remedial investigation describing the risks posed to public health and the environment at a
Superfund site.
Ground water: The water contained in interconnected pores located below the water table.
Impacted soils: Soils mixed with tailings or which tailings have leached inorganics into.
In-situ: Activity occurring in-place or without removing the contaminated material.
Institutional controls (ICs): Laws, regulations, or covenants that restrict certain activities or
uses to ensure the effectiveness of remedy, such as zoning restrictions, deed restrictions, well
bans, etc.
Maximum Contaminant Levels (MCLs): Federal drinking water standards which represent
the maximum permissible level of a contaminant in a public water system.
Maximum Contaminant Level Goals (MCLGs): Non-enforceable drinking water standards
that represent the levels of contaminants that are fully protective of human health and allow
an adequate margin of safety.
National Contingency Plan (NCP): The federal regulations implementing Superfund, found
at 40 CFR Part 300.
Operable Unit (OU): A term used to describe a designated portion of a Superfund site. An
operable unit may be established based on a particular type of contamination, contaminated
media (e.g., soils, water), source of contamination, and/or geographical location.
Operation and maintenance costs: The costs of activities conducted to maintain the
effectiveness of the remedy, after physical construction and initial implementation of the
remedy.
Potentially responsible party (PRP): Individual, organization or business who may be liable
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to implement or pay for a cleanup under Superfund law.
Remedy: The response action that addresses potential or actual threats to public health,
welfare and/or the environment at a Superfund site.
Record of decision (ROD): A public document that selects and describes the remedy that
will be used at a Superfund site. The record of decision includes the explanation of the
agency's rationale for choosing a remedy.
Relocation: Excavation of tailings/impacted soils from the 100-year floodplain, placement of
those wastes in a nearby, local repository, and treatment of those wastes using STARS
treatment.
Remedial investigation/feasibility study (RI/FS): During the remedial investigation, the
types, amounts and locations of contamination at a site are identified. In the feasibility
study, alternatives for site remedy are identified, screened and evaluated.
Removal: Excavation of tailings/impacted soils located in the floodplain and placement in a
regional dry repository. The two potential repository locations identified in the SST OU
Feasibility Study were Browns Gulch and the Opportunity Ponds.
Streambank Tailings and Revegetation Studies (STARS): Chemically amending floodplain
tailings in-situ. Lab, greenhouse, and field studies, commonly referred to as STARS,
developed a technology specifically for consideration at the Streamside Tailings OU.
Tailings: A sand to silt sized by-product of ore milling operations.
Vadose Zone: The zone between land surface and the water table. Pore spaces in this zone
contain disconnected water.
WQB-7: A promulgated list of State water quality standards specifying concentrations of
contaminants which, if not exceeded, should be protective of human health and should
support a healthy ecosystem. Concentrations of contaminants which are toxic to aquatic life
are usually expressed in terms of acute (short term) or chronic (long-term) effects. Acute
toxicity is usually expressed as a lethal concentration while chronic toxicity refers to effects
over an extended time period.
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
I. OPERABLE UNIT NAME. LOCATION AND DESCRIPTION
Streamside Tailings (SST) Operable Unit (OU) of the
Silver Bow Creek/Butte Area (original portion)
National Priority List (NPL) Site
Butte, Montana
The SST OU is located along Silver Bow Creek in Butte-Silver Bow and Anaconda-Deer
Lodge Counties, Montana. Figure 1 displays the general location of the OU. Figure 2
illustrates the SST OU. Silver Bow Creek is the main drainage within the SST OU and is
the headwaters of the Clark Fork River. Silver Bow Creek originates in Butte at the
confluence of the Metro Storm Drain and Blacktail Creek.
The OU boundary has been defined in the Administrative Order on Consent (AOC)
(MDHES, 1991) as the extent of fluvially deposited tailings along Silver Bow Creek,
including adjacent railroad beds. The upstream boundary of SST OU is the Lower Area One
(LAO) portion of the Priority Soils OU, and the downstream boundary is the Warm Springs
Pond (WSP) OU. For the purposes of the remedial action, the operable unit boundary will
also include any additional areas in close proximity to the contamination that are necessary
for implementation of the remedial action.
The area containing and surrounding the previous location of the Rocker Timber Framing
and Treating Plant (Rocker OU) adjacent to Silver Bow Creek in Rocker, Montana, is a
separate and distinct OU. The Rocker OU is being investigated and evaluated separately
with regard to contaminants associated with historical wood treating activities and mining
wastes mixed with such wastes at the Rocker operation. Remediation of the streamside
tailings and railroad materials containing contaminants of concern within the Rocker OU will
be coordinated with the SST OU.
II. OU HISTORY
The first recorded disturbance of the Silver Bow Creek channel occurred in 1864 when
placer mining techniques were used to extract gold along the stream and its tributaries
(Freeman, 1900 and Smith, 1952). The gold recovered by placer mining was relatively pure,
in the form of dust, flakes, or nuggets. Mercury was sometimes used to "attract" small
pieces of gold. This phase of mining activity was short-lived; most placer operations in the
area had ceased by 1869, although minor activity continued on a few local streams
(Reclamation Research Unit and Schafer and Associates [RRU and Schafer], 1993).
Some evidence of early placer mining along upper portions of Silver Bow Creek is still
evident in the form of waterways required to convey water for hydraulic mining and spoils
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
piles (Historical Research Associates [HRA], 1983). The waterways are in disrepair and no
longer convey water. As Butte's placer deposits played out during the 1870s, miners turned
their attention to the area of hardrock mining. There is no clear record of the amount of
mining wastes produced and disposed of by placer miner operations.
Concomitant with placer mining along Silver Bow Creek, hard rock mining started on
mineralized vein outcroppings on Butte Hill, north of Silver Bow Creek (Smith, 1952).
Some mining claims on the Butte Hill were re-staked hi the 1870s because of favorable
assays of silver ore found in the area (Smith, 1952). Silver mill construction during the mid-
1870s ushered in the era of industrial mining in Butte. This rejuvenated mining activity in
Butte and, by 1878, several small mills were operating in the area. A combination of factors
contributed to a boom in Butte's silver production during the early 1880s. Completion of
railroads to Butte hi 1881 along with favorable silver prices led to a drastic increase in mine
production. Most existing mills increased their production.
Between 1879 and 1885, at least six major mills were built along Silver Bow Creek from
Meaderville to Williamsburg. These mills were operated more or less continuously until
1910 (Freeman, 1900; Smith, 1952; HRA, 1983). The early mills were steam-powered
stamp mills (5-10 stamps) designed to crush, concentrate, and amalgamate silver ore. Mills
constructed during this tune were the: Centennial, Dexter, Davis, Young and Roudebush,
Walker Brothers, Clipper, Silver Bow, Grove Gulch, and Thornton (Gagnon)(HRA, 1983).
By 1886 five new mills appeared in the vicinity of Butte's Missoula Gulch and along Silver
Bow Creek: the Alice, the Moulton, the Lexington, the Marget Ann, and the Blue Bird
(HRA, 1983). The Blue Bird mill was located on Silver Bow Creek east of the town of
Rocker (Figure 2) and contained 90 stamps which was unusually large at the time.
Production capacities from these new mills were many orders of magnitude greater than
previous mills. Butte's silver era ended with the repeal of the Sherman Silver Act in 1893.
These mills produced tailings and other mining wastes, which were disposed of near the
mills. Some of that waste material was disposed directly into or washed into Silver Bow
Creek.
By the late 1880s copper mining had become more important, and Butte became one of the
nation's prominent copper mining centers. Many of the previously described mills and
smelters were used for copper production, and- more mills and smelters were added. Five
such facilities located along Silver Bow Creek were especially significant. They are the
Colorado Smelter, the Butte Reduction Works facility, the Parrott Smelter, the Montana Ore
and Purchasing Company Smelter, and the Butte and Boston Smelter. All of the described
facilities along Silver Bow Creek discharged wastes alongside or directly into Silver Bow
Creek.
-------
Montana
Streamside Tailings Operable Unit
Montana State Library
Natural Resource Information System
Map #96epaa4c - 9/14/95
Figure 1
PWHC
Scale of Milan
20 40 60 80
100
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
These facilities operated large concentrators and smelters and disposed of very large volumes
of waste directly into or near Silver Bow Creek.
A copper smelter (Old Works) was constructed near the mouth of Warm Springs Creek at the
new town of Anaconda, 27 miles west of Butte, in 1884 (Smith, 1952; RRU and Schafer,
1993). The new Washoe Smelter was constructed and began operations on Smelter Hill,
directly east of Anaconda, in 1903. The major smelters erected along Silver Bow Creek in
the Butte vicinity continued to operate until approximately 1910 (HRA, 1983). The
Amalgamated Copper Company and the Anaconda Copper Mining Company took possession
and control of almost all other companies and facilities in the Butte area. These companies
ultimately combined into the Anaconda Copper Mining Company. After 1910, most of the
ore mined in Butte was then shipped via the Butte, Anaconda and Pacific Railway (BA&P) to
the Anaconda Copper Mining Company's (AMC) Washoe Smelter for processing (RRU and
Schafer, 1993).
By 1917, approximately 150 mines were located in and near Butte. These mines, which
were controlled by AMC or its predecessors, produced a total of approximately 934 million
pounds of copper (Techlaw, 1985). This corresponds to a maximum of approximately 4.2
million cubic yards of ore assuming a 5 percent copper content and an ore density of 163
pounds per cubic foot (Techlaw, 1985). Water pumped from these mines contributed to the
contamination of Silver Bow Creek.
AMC constructed three treatment ponds, the Warm Springs Ponds (WSP), at the headwaters
of the Clark Fork River near Warm Springs, Montana, in 1911, 1916, and between 1954 and
1959, respectively. The purposes of the ponds were to settle out mining wastes from Silver
Bow Creek and to improve the quality of water released to the Clark Fork River (RRU and
Schafer, 1993). The inlet to the WSP represents the downstream extent of the SST OU
(Figure 2).
AMC commenced surface mining of low-grade copper ore with the opening of the Berkley
Pit in 1955 and built the Weed Concentrator in 1963 to process this ore. These operations
contributed contamination to Silver Bow Creek.
In 1977, the assets of AMC were purchased by the Atlantic Richfield Company (ARCO)
which expressly assumed liability for AMC. ARCO closed all underground mines in 1980
and continued active mining only in the Berkley Pit. ARCO closed the Berkley Pit in 1982
and the East Berkley Pit in 1983. The Washoe Smelter in Anaconda, the last active smelting
facility in the area, was closed in 1980 and subsequently dismantled (RRU and Schafer,
1993).
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Waste Transport
Although floods and storm events contributed to the transport of waste into and within the
SST OU, they were not the exclusive cause of contamination. As noted, upstream facilities
discharged waste directly into or along Silver Bow Creek, and did not exercise due care in
anticipating flood events or storm events and taking precautions to avoid waste movement.
Waste was transported from these operations downstream via overland flow and surface
water transport.
In June of 1908, the largest flood in recorded history in the Silver Bow Creek basin
occurred, contributing to the extent of fluvially-deposited tailings found today. Heavy rains
(8.12 inches) fell in late May and early June, melting the snow pack and causing extensive
flooding (CH2M Hill, 1989a). Flood waters transported tailings from smelting facilities in
Butte and along Silver Bow Creek and deposited them downstream as flood waters waned.
Flood flows and fluvial deposits were physically constrained by railroad grades constructed
parallel to Silver Bow Creek, limiting the areal extent of flood deposited tailings.
Other recorded significant storm events occurred in 1892, 1894, 1938, 1948, 1975 and 1980
(CH2M Hill, 1989a). All of these events occurred during the spring and early summer when
precipitation and melting snow combined to produce large runoffs. These events also
contributed to the movement of mine wastes from their sources into the Silver Bow Creek
floodplain.
Railroad History
The Utah & Northern, a subsidiary of the Union Pacific Railroad (UP) and the first railroad
in Montana, reached Butte in December of 1881. It linked the towns of Anaconda and Butte
to the UP line from Utah in 1884 when it completed a narrow gage rail line between the
mines in Butte and the smelter in Anaconda (GCM, 1991). This was the first railroad
constructed within the SST OU.
Immediately following the Utah & Northern advancement into Montana, track laying crews
of the Northern Pacific (NP), a predecessor to Burlington Northern Railroad, entered eastern
and western Montana to complete a northern transcontinental rail line. By September 1883,
construction was complete. The UP and NP then pooled their resources and formed the
Montana Union Railroad which ran from Butte to Garrison (GCM, 1991).
Marcus Daly, owner and founder of the AMC, after disagreement with the Montana Union
(MU) Railroad over freight rates charged to ship ore from mines in Butte to smelting
facilities, suspended mining and smelting operations and announced that the AMC would
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
construct its own railroad. On September 30, 1892, Daly and a group of investors
incorporated the BA&P, with close subsidiary links to Anaconda, to construct and operate a
separate rail line to transport ore from Butte to the smelter in Anaconda. This was the
second rail line construction adjacent to Silver Bow Creek. Additionally, AMC used the
BA&P to transport copper concentrate from Butte to Anaconda after construction of the
Weed Concentrator in 1964. Today the BA&P track is occupied and operated by the Rarus
rail line (Butte Archives, 1994; GCM, 1991).
In 1905, the Chicago, Milwaukee, St. Paul and Pacific Railroad (CMSP) began construction
of another railroad line (the third) to run along Silver Bow Creek. Until 1913, the CMSP
used the BA&P rails along Silver Bow Creek from Butte to Finlen. At that time, the CMSP
constructed its own grade (popularly known as the Milwaukee Road) along Silver Bow Creek
(GCM, 1991). In 1980, the CMSP abandoned its rail line. The tracks were removed shortly
afterward (GCM, 1991).
In the early twentieth century, the Union Pacific Railroad leased the track near the
Fairmont/Gregson area east into Butte under a long-term lease to the Great Northern
Railroad. The Great Northern Railroad eventually became the Burlington Northern Railroad.
The lease was subsequently transferred to the Montana Western Railroad in 1986, which
operates on this line today (GCM, 1991).
Presently, there are three rail lines adjacent to the SST OU area: 1) Rarus (BA&P) from
Anaconda to Butte, 2) Montana Western Railroad (leased from UP), and 3) the UP Railroad.
Rarus (BA&P) and Montana Western have existing tracks adjacent to Silver Bow Creek.
The UP line terminates at its northern extent at the switching yards of Port of Montana near
Silver Bow, Montana. The abandoned CMSP grade parallels Silver Bow Creek within the
SST OU although the rails and ballast have been removed.
Parts of all three rail lines were constructed with waste materials. The lines which
transported concentrate materials for the smelter in Anaconda were additionally contaminated
by spillage from this concentrate transportation.
Enforcement Actions
Environmental investigations in the vicinity of the SST OU were initiated by the EPA in
1982 to address mining impacts along Silver Bow Creek. The Silver Bow Creek/Butte Area
Site (original portion) was listed on the NPL in 1983 by EPA under the CERCLA and site
investigations began in 1984 with the Phase I Remedial Investigation (RI) prepared by
MultiTech Services under contract to the MDEQ. A supplemental RI report was prepared by
CH2M Hill (1987). The Phase H RI described in the Draft RI Report (ARCO, 1995a) was
7
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
conducted by ARCO and describes investigation activities, characterizations and
interpretations performed since 1991. All pre-1991 studies or data that were determined by
ARCO and the MDEQ to be applicable or pertinent to current OU conditions were
incorporated in the OU characterization in the Draft RI Report (Phase n). The Draft RI
Report complied with Superfund law, defined the nature and extent of the contamination to
the extent necessary to determine remedial action and provided information to complete the
baseline human health and ecological risk assessments (ARCO, 1995a). The baseline risk
assessment was released by MDEQ in December of 1994 (MDEQ, 1994a). The feasibility
study, released by ARCO in June 1995, included the development, screening and evaluation
of potential OU remedies (ARCO, 1995b). The proposed plan was also released in June
1995 and delineated the preferred alternative (MDEQ, 1995).
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
m. HIGHLIGHTS OF COMMUNITY PARTICIPATION
CERCLA sections 113 and 117 provide for public participation in the development of the
administrative record upon which the remedy selection is based. These sections require that,
before adoption of any plan for remedial action, the lead agency shall:
1. Publish a notice and brief analysis of the proposed plan and make such plan available
to the public; and
2. Provide a reasonable opportunity for submission of written and oral comments and an
opportunity for a public meeting at or near the OU regarding the proposed plan and
any proposed findings relating to cleanup standards. The lead agency shall keep a
transcript of the meeting and make such transcript available to the public. The notice
and analysis published under item #1 shall include sufficient information to provide a
reasonable explanation of the proposed plan and alternative proposals considered.
Additionally, notice of the final remedial action plan (record of decision) adopted shall be
published and the plan shall be made available to the public before commencing any remedial
action. Such a final plan shall be accompanied by a discussion of any significant changes to
the preferred remedy presented in the proposed plan along with the reasons for the changes
and a response (Responsiveness Summary) to each of the significant comments, criticisms,
and new data submitted in written or oral presentations during the public comment period.
MDEQ has conducted extensive community participation activities beyond what is required
under the National contingency Plan. Public participation began prior to initiation of the site
investigation with the issuance of the draft RI/FS Administrative Order on Consent and draft
RI/FS Work Plan. Three public informational meetings (in Missoula, Anaconda, and Butte)
and a formal public hearing (in Ramsay) were held in 1991 to gather public input on the
proposed study. Comments were incorporated into the final RI/FS AOC and Work Plan, and
a responsiveness summary addressing those comments was published. Additional public
meetings were held to provide progress updates on the investigation and to gather public
comments on the SST OU demonstration projects, as well as the work plan for the draft
Baseline Risk Assessment. In addition, ARCO and MDEQ held a series of meetings,
moderated by the Headwaters Resource Conservation and Development District, with SST
OU landowners during 1992 and 1993 to provide information about alternatives under
consideration and to gather input from local landowners. During late 1994 and 1995, as the
SST OU investigation was concluding and the major RI/FS reports were prepared and
published, community participation activities included the following: nine (9) public
"roundtable" meetings, numerous OU tours, two meetings to discuss the Remedial
Investigation, three informational meetings on the Baseline Risk Assessment, three Proposed
Plan informational meetings, a 60 day public comment period, a public hearing, and
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
presentation of the selected remedy in the Record of Decision. The Record of Decision
documents changes to the preferred remedy as a result of public comments.
The proposed plan (MDEQ, 1995a) for the OU was released for public comment on June 9,
1995, and mailed to over 1,300 citizens on various Montana Superfund mailing lists. The
proposed plan was made available to the public at the Environmental Protection Agency
(EPA) offices in Helena, MT, and information repositories maintained at: MDEQ Superfund
office, State Library, EPA Office, and the Montana Historical Society in Helena; Hearst Free
Library in Anaconda; Montana State University in Bozeman; Silver Bow Library, Montana
Tech Library, Butte Public Library, EPA Office and the Citizens Technical Environmental
Committee Office in Butte; Missoula Public Library, University of Montana Mansfield
Library, and the Clark Fork Pend-Oreille Coalition Office in Missoula. The notice of
availability of the proposed plan (MDEQ, 1995a) was published in the Butte-Montana
Standard, the Missoulian, and the Anaconda Leader newspapers on June 9, 1995. The full
administrative record is maintained by EPA in Helena. Microfilm copies of the
administrative record are also made available to the public at several of the information
repositories listed above.
During the 60-day public comment period (June 9 through August 7, 1995) public
informational meetings were held at: Fairmont Hot Springs on June 20; Butte Community
Center on June 21; and, Missoula Courthouse Annex on June 22, 1995. At these meetings,
representatives from MDEQ answered questions about contamination issues, the remedial
alternatives under consideration, and the preferred remedy. A public meeting/hearing was
held on July 10, 1995, at Fairmont Hot Springs at which MDEQ accepted formal oral
comments from the public. A court reporter transcribed the entire meeting/hearing and
MDEQ made the transcript available by placing it in the administrative record. A response
to the comments received during the public comment period is included in the
Responsiveness Summary (Appendix D). Also, community acceptance of the selected
remedy is discussed in Section VHI of the Decision Summary, Summary of Comparative
Analysis of Alternatives.
MDEQ considered public comments and revised the selected alternative as a result (see
Section XI).
10
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
IV. SCOPE AND ROLE OF RESPONSE ACTION
The primary focus of the SST OU RI/FS was to evaluate findings of previous investigations,
to collect additional data to assist in characterizing current and future risks, and to develop
and evaluate remedial action alternatives. The RI/FS was performed in accordance with the
National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40 CFR Part
300, and CERCLA Section 104, 42 U.S.C. § 9604.
The overall objectives of the RI/FS were:
o To collect data on the types, concentrations, extent and movement of
contaminants present in tailings, subsurface soils, railroad materials, surface
water, groundwater, and instream sediment at the OU;
o To provide information for estimating volume, location, transport and fate of
contaminated media and materials;
o To provide information on OU physical characteristics and contaminants for
use in the risk assessment and the feasibility study;
o To assess the present and potential future risks to human health and the
environment at the OU;
o To identify applicable or relevant and appropriate legal requirements (ARARs)
for the remedial action; and
o To identify and evaluate remedial alternatives to address human health and
environmental risks.
Based on these evaluations, findings of previous investigations and the results of the RI field
investigation, the sources and the areas of environmental contamination at the Streamside
Tailings Operable Unit have been delineated sufficiently to allow the agencies to evaluate and
select an appropriate remedy for the OU contamination.
The remedy outlined in this record of decision represents the final remedial action at the OU
and will address the principal threats to human health and the environment which are posed
by the contaminated media and materials.
11
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
V. SUMMARY OF OU CHARACTERISTICS
This section presents a summary of RI conclusions for each of the four OU geographic
subareas and for OU-wide aquatic and terrestrial resources (ARCO, 1995a). Detailed
information is presented in Sections 4.3 through 4.8 of the Draft RI Report (ARCO, 1995a).
Contamination was found in all media (soil, groundwater, surface water, railroad beds and
instream sediments) throughout most of the SST OU. Table 1 enumerates contaminant
concentrations found in tailings/impacted soils.
The OU has been divided into four subareas based upon geologic and topographic features
that control the soil, hydrogeologic, geomorphic, surface water, ecologic, demographic and
land use characteristics of the OU (Figure 2). Additionally, Silver Bow Creek was further
divided into stream reaches for more detailed evaluation and characterization of OU
information. A total of 12 reaches were defined with one to several reaches located in each
subarea.
Table 1
Streamside Tailings OU
Median Concentrations - Tailings/Impacted Sol!
(iag/kg)
Analyte
PH(SU)
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Reference1
5.6
39
3.2
99
55
0.13
126
Subarea 1
4.3
278
7.8
739
540
2.1
2,400
Snbarea 2
4.3
563
16.2
2,710
1,510
11.0
5,400
Subarea 3
4.0
215
5.5
1,290
316
1.2
1,445
Subarea 4
4.5
249
6.3
1,315
638
2.7
1,805
R£F: SST OU RI (ARCO, 199 a), mg/kg = milligrams per kilogram, su = standard units. l-"Reference" soils are considered to be outside
the influence of flood deposited tailings but could be impacted by other contaminant sources.
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
General Description of Subareas
As shown on Figure 2, the SST OU consists of Silver Bow Creek and areas in and near its
floodplain from the downstream extent of LAO west of Butte to the 1-90 bridge directly
upstream of the WSP OU northeast of Opportunity.
Subarea 1 - Rocker
The Rocker Subarea extends from the west end of LAO to approximately 1,000 feet
upstream of the confluence of Sand Creek and Silver Bow Creek (Figure 2). Sand Creek is
approximately 400 feet west of the bridge adjacent to the community of Silver Bow. During
the development of the initial stages of the current RI, Subarea 1 was originally defined at
the downstream end by the Rocker Fault, located near the town of Rocker. Subarea 1 was
extended to its current boundary because of the nature of the stream and the tailings rather
than the bedrock and alluvial geology.
Intermittent tributaries within this subarea include Whiskey Gulch and Gimlet Gulch. The
subarea encompasses approximately 5.2 miles of Silver Bow Creek and loses approximately
88 feet in elevation over the subarea. Tailings/impacted soils within the subarea are
continuous and confined to a narrow floodplain.
The communities of Rocker, Fredricksburg, and Nissler are adjacent to the SST OU within
this subarea. The Rocker OU, ARCO's Demonstration Project I, and the Rocker
Streambank Tailings and Revegetation Study (STARS) plots are also located within this
subarea.
Subarea 2 - Ramsay
The Ramsay Subarea extends from 1,000 feet upstream of the confluence of Sand Creek and
Silver Bow Creek to approximately 700 feet west of Miles Crossing (Figure 2). The
communities of Silver Bow, Ramsay, Dawson and Miles Crossing are adjacent to the OU
within this subarea. Industries adjacent to the OU include the Rhone-Poulenc Basic
Chemicals Plant, the Port of Montana and the Union Pacific switching yards.
The subarea encompasses the Ramsay Flats, a tailings deposit of approximately 160 acres.
Tailings/impacted soils within the subarea are continuous along a floodplain wider than that
of Subarea 1. Tributaries within the subarea include the intermittent Sand Creek and
perennial Browns Gulch. Average flow in Browns Gulch is approximately 0.5 to 5 cubic
feet per second (cfs). Other inflows within the subarea include the Silver Lake Pipeline
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
discharge, with an approximate flow of 5 to 20 cfs, and a seep near Rhone-Poulenc, with an
approximate flow of 0 to 0.25 cfs. The subarea encompasses approximately 5.6 miles of
Silver Bow Creek losing approximately 68 feet in elevation over the length of the subarea.
Subarea 3 - Canyon
The Canyon Subarea extends the length of Durant Canyon from slightly above the mouth of
the canyon near Miles Crossing to Fairmont Bridge over Silver Bow Creek near the Fairmont
Resort (Figure 2). The small community of Finlen is adjacent to the OU within this subarea.
German Gulch is the main tributary within the subarea with an average flow of 5 to 20 cfs.
During summer months, most of German Gulch's flow is diverted just above its mouth for
irrigation purposes and does not enter Silver Bow Creek. The subarea encompasses
approximately 5.0 miles of Silver Bow Creek losing approximately 174 feet in elevation over
the length of the subarea. Tailings/impacted soils within the subarea are discontinuous along
the narrow canyon. A limited number of abandoned meander scars and sloughs containing
tailings deposits exist on the opposite side of the railroad embankments from Silver Bow
Creek.
Subarea 4 - Upper Deer Lodge Valley
The Upper Deer Lodge Valley Subarea extends from the Gregson Bridge to the 1-90 bridge
just south of the WSP (Figure 2). The communities of Fairmont, Crackerville and
Opportunity are adjacent to the SST OU within this subarea.
Gregson Creek is the only notable intermittent tributary within the subarea. Perennial Mill
and Willow Creeks are separated from Silver Bow Creek by a diversion dike and diverted
away from Silver Bow Creek. The subarea encompasses approximately 6.8 miles of Silver
Bow Creek losing approximately 194 feet in elevation over the length of the subarea.
Tailings deposits within the subarea are continuous along at wide floodplain, interspersed with
some vegetation. Tailings within the subarea were initially deposited along a system of
overflow channels. More recently, the stream has been channelized with dikes along the
upper portions of this subarea which somewhat limit overbank flow and flow to the overflow
channels.
Railroad Materials and Instream Sediments
Two other media are also present throughout the OU but are not necessarily related to the
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
subarea divisions. These media include the railroads and instream sediments. Four types of
railroad materials, including bed and ballast construction materials and spilled materials, all
contain contaminants of concern. The four material types include waste rock or low grade
ore, concentrate spills, impacted material consisting of non-vegetated soil, and slag. Native
alluvium, native rock and imported crushed rock were also used to construct the railroad bed
and as ballast.
Instream sediments (i.e. sediment within the present active channel of Silver Bow Creek)
contain contaminants of concern extending throughout the entire length of the SST OU
stream channel. Instream sediments consist of tailings, soil and rock particles that have been
deposited instream or are carried through the OU as a result of surface water transport.
Conceptual Model of Contaminant Transport
Data collected during the remedial investigation revealed five primary sources of
contamination to Silver Bow Creek:
1) upstream;
2) tailings/impacted soils;
3) groundwater;
4) instream sediments; and
5) railroad embankments
Contaminants move through the area and between environmental media in response to a
variety of processes. Some of the primary means by which contaminants move within the
SST OU are listed below.
1) Upstream
Upstream sources include, but are not limited to, mine wastes in and near the City of Butte,
mine/mill tailings in the Colorado Tailings and Butte Reduction Works areas, and the Butte
storm and waste water systems and Butte Operations areas. Contaminants from these source
areas enter the SST OU primarily in Silver Bow Creek surface water and instream sediments.
Off-OU contaminants also enter via groundwater from the Colorado Tailings area and the
Rocker Timber Framing and Treating Plant OU.
Surface water entering (inflow) the SST OU from upstream areas is highly contaminated
(Table 2). Water quality data indicate that contaminants are added to Silver Bow Creek in
the upper portion of the OU during most flow conditions (Table 2). However, control of
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
upstream contamination is outside of the scope of this operable unit, but will be addressed in
other operable unit or site cleanups, or permit activities under other environmental laws.
2) Tailings/Impacted Soils
Persistent and widespread expanses of tailings/impacted soils are present along nearly the
entire 24-mile reach of Silver Bow Creek. Impacted soils are defined here as soils which
have been mixed with the tailings or where the tailings have leached inorganics into the soils.
Tailings/impacted soils are the primary source of contamination for the SST OU. Some
tailings/impacted soils are mixed with native soils, which makes visual identification of
contaminated materials difficult. The lateral and vertical extent of tailings/impacted soils was
determined by analysis of 764 samples. The volume of these materials was estimated at 2.4
to 2.8 million cubic yards lying within 1,270 acres of the historic Silver Bow Creek
floodplain with measured thickness ranging from a few inches to greater than seven feet.
Most of these tailings/impacted soils contain elevated concentrations of arsenic, cadmium,
copper, lead, mercury, and zinc.
Erosion and runoff are the most obvious and damaging contaminant transport mechanisms for
the SST OU. Erosion, as it is discussed here, encompasses three major processes: channel
migration or avulsion, bank/mass wasting, and surface or overland flow. The channel has
and is expected to continue to migrate through many parts of the Silver Bow Creek
floodplain (Schumm, 1995). This constant and sometimes dramatic migration re-entrains
substantial volumes of tailings/impacted soils back into the Silver Bow Creek ecosystem
(CH2M Hill, 1989a). Surface water elevation changes in Silver Bow Creek itself can cause
bank storage which causes mechanical failure, high flows which cause tractive force failure,
and undercutting of banks, all of which cause direct erosion of metals-laden streambank
tailings/impacted soils into the stream. In addition, ice buildup in the stream during winter
and spring months can cause streambank erosion and stream avulsion. Precipitation or
snowmelt runoff moves metals-bearing materials through erosion and carries the
contaminants to Silver Bow Creek. Metallic salts are sometimes wicked to the surface of
tailings through capillary action, and are encrusted on the tailings surface as the water
evaporates, and are subsequently dissolved or directly eroded by water into the stream during
precipitation or runoff events. People and animals can also cause streamside tailings to
directly enter the stream by disturbing the tailings/impacted materials on the bank (Figures 3,
4, 5 and 6).
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Table 2
Silver Bow Creek Surface Water Quality
Geometric Mean Low Flow Concentrations
Analyte
pH(5U,
Arsenic
Cadmium
Copper
Lead
Zinc
WQB - 7*
Chronic
,NA
IPO
I.I
12
3.2
110
••••••••
Acute
NA
360
33
18
82
120
•••MMi
SS-07
inflow
7.3
8.7
1.6
178
5.3
662
SS-10
Saver
Bow
8.0
14.5
2.5
322
15.2
860
SS44
Mile
Crossing
7.9
11.7
1.1
163
5.4
532
: ss-16
I Fairmont
8.2
15.4
1.1
140
4.6
455
SS47
Opportunity1
9.6
18
0.7
140
1.9
366
NA = not applicable; su = standard units; SS-7 monitoring station on SBC; values in "total recoverable" concentrations, (/ig/1).
1 - WQB-7 generally corresponds to "Gold Book" aquatic standards at a total hardness of 100 mg/I CaCO3.
2 - Parameters for station SS-17 represent July 1985 event only. A geometric mean for this station was not calculated.
Contaminants not carried into Silver Bow Creek may also be adsorbed to the soil. These
metals will remain in this semi-stable form until geochemical conditions alter the chemical
stability of the soil system to re-release the metals. Contaminant transport by the many
erosive processes described previously is the most significant method of metals introduction
into the Silver Bow Creek aquatic and riparian system.
3) Groundwater
The main objectives of the groundwater investigation were to determine if groundwater was
contaminated and to define where the contaminated groundwater was located (ARCO,
1991a). A third objective was to quantify the interaction between groundwater and Silver
Bow Creek surface water and instream sediments.
A total of 30 wells were installed in the OU and monitored. Because of the limited number
of wells and their spatial distribution throughout the OU's 24-mile length, groundwater
characterization is discussed in terms of general OU conditions and does not fully
characterize the range of contaminant concentrations or contaminant locations within the OU.
17
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
The 30 wells installed in the alluvium were screened at two different depths, within 20 feet
of the ground surface (upper alluvial) and greater than 20 feet below the ground surface
(lower alluvial). The designation between these two units (upper and lower alluvial) was
intended only for SST RI data analysis. Both of these units are hydrogeologicly
interconnected and should be considered as a single alluvial aquifer.
Generally, groundwater flows toward and into the stream except in several reaches (the most
significant being the outlet of Durant Canyon) where surface water flows into groundwater.
Elevated concentrations of copper and zinc and exceedances of drinking water standards
(Maximum Contaminant Levels [MCLs], or Montana Water Quality Standards (WQB-7),
Table 3) for arsenic and cadmium were found in many of the shallow monitoring wells.
In many areas, groundwater is in direct contact with tailings/impacted soils for at least part
of a typical year (Figure 3). In the RI/FS documents and in the ROD these materials are
designated the term "saturated tailings". The seasonal groundwater level fluctuation averages
two feet (Table 4). This direct contact with metals enriched tailings/impacted soil mobilizes
metals which in turn contaminate groundwater. The volume of tailings/impacted soils
saturated with groundwater for a portion of the year and tailings which overlie them are
listed in Table 4. This is a principal mechanism for groundwater contamination at the OU
(ARCO, 1995a and Benner et al., 1995).
Movement of water from the tailings on the surface through the unsaturated (vadose) zone
and into the saturated (groundwater) zone also causes transport of contaminants into
underlying soils and groundwater. This is most likely to happen during longer precipitation
or snowmelt events. Metals weakly held to tailings are leached by the infiltrating water and
eventually can be carried into the underlying native soils and groundwater. Profiles of many
soils in the SST OU show evidence of metals migration from the tailings into underlying
native materials.
Contaminated groundwater flows into Silver Bow Creek along the majority of stream
reaches. This is most likely to happen in areas where the stream gains flow from the
groundwater and results in the greatest site related impact to Silver Bow Creek water quality
during low-flow conditions. This mechanism is the likely cause for increases in most surface
water contaminant concentrations in Subareas 1 and 2 during low or base-flow conditions
because many of the other possible pathways, except for instream sediments potential for
contaminate release, for contaminant movement are inactive during low-flow (e.g., runoff
and infiltration) (Table 2). The opposite of this is true during high-flow conditions in portions
of the stream when surface water may flow into and contaminate groundwater.
Silver Bow Creek surface water and instream sediments are the primary recipients of
contaminants from the streamside tailings as well as from off-OU sources.
18
-------
Pathway;
Overland runoff eroda*
telling* and salt* Into
Silver Bow Creek
Sour;*:
water, groundweler and aedlmanla
and enter OU
Oxidation of aulfldea and
dl*aolullon mobllUe* metal*
Source;
Railroad b«d«, eon»lrucl«d
of mln* wail* *r« • sourc*
of m*lal* to runoff
Sourc*:
Talllngi. g«n*r*Hy coara* allly
• and* wllh ralallvaly high
Infiltration rait*
Pathway:
Runoff and ponded waUr
parcolalaa through tailing*
recharging groundwaUr ayatam
Souraa;
Placer working* »r* potential
•ourca of mercury
Pathway;
Bank erosion eauaaa lalllnga
to directly entar atream
Oeochemlcat M«ehenlam;
Preclpllallon, copreclpltatlon,
•d*orpllon and compilation
Inhibit migration of melala
Zone of water
lab!* fluctuation
Pathway;
Rlalng water table raleaaaa
m*lala to groundwal*r
Dow Creak, upper portion
contain* moat metala
CONCEPTUAL MODEL
OF SUBAREA 1
FIGURE 3
-------
Palhwayj
Overland runoff erode •
tailings and dissolve* salt*
transporting metals to Silver
Bow Creak
Soy ree:
Tailings, predominantly fine
sandy sills with relatively
low Infiltration rales
Pathway: •
Surface water, groundwaler
and atraem sediment* from
Subarea 1
Source;
Railroad beds, constructed
of mine waste are a source
of metals to runoff
urge:
Placer workings are
potential source of i
Zone of weler
table fluctuation
Pathway;
High metric potential
wlcke pore water rich
In metal sells to surface
Pathway;
Geochemlcaj Mechanism:
Oxidation of eulfldee and
dissolution of metals mobilize
metals from tailings
percolates through tellings
recherglng groundwatar aystem
Organic layer buffers acidity tn pore wolcr
causing metals to adsorb, precipitate end
copreclpltale resulting In decrease In vadosa
xone metals concentration wllh depth
Pathwa
Tailings tn contact wllh groundwater
release melets to groundwater
CONCEPTUAL MODEL
OF SUBAREA 2
Pathway:
Rlalng water table ralea
metal* to groundwaler
of upper Flameey Flats, Silver flow
Cr*«K o*'"" How from groumlwatcr.
FIGURE 4
-------
Pathway;
Overland runoff arodaa
latlln
aalta transporting malata
to Sllvar Bow Craak
Sourca;
Railroad b«ds, conatruclad
of mlna waala ara • aourca
of malaU to runoff
Sourca;
Talllnga, predominantly
allly aanda
Pathwa
Bank aroilon, lalllnga
anlar era ad dlraclly
during high flow
ourc a
Contamln«tad aurfaca walar
groundwatar and atraam
• •dlmanta antar
from Subaraa 2
Sourca;
Plaoar working* ara potantlal
aouroa of rnarcury
fntlllratlon through
lalllnga earrlaa
malala Into
Talllnga In contact with groundwalar
ithw
High malrlc potential
wlcka pora wal*r
rich In matal aalta
to aurlaca
Gaochamlcal Machanjmm;
Oxidation of autfldaa
and dlaaolullon moblllza*
malaU
CONCEPTUAL MODEL
OF SUBAREA 3
/
Caochamlcal Machanlam:
Praclpllatlon. copraclpllallon
ad>orpllon and complvxatlon
Inhibit m«tal> migration
Pathway;
Sllvar Bow Craak galna
How from groundwalar
FIGURE 5
-------
Source;
T«ltlng», predominantly
(In* grained allt/eanda.
aome tailing depoelled by flood
Irrigation outalda of flood plain
Pathway;
to directly enter atraam
Pathway;
Overland runoff «rod«a
tailing* and dlaeolve*
• alia transporting metal*
to Silver Dow Creek
Goechemleal MechinUrn:
Precipitation, copreclpltallo
Zone of water
Uble fluctuation
Source:
Contaminated aurlace walar,
groundwater and alream aedlment*
enter from Subarea 3
Burled eolt horizon
Pathweyj
Rl»lng water table retei
melala to groundwaler
Geochemlcal Meehenjem:
Oxidation of aulllde*
and dlsiolutlon
mobilize* metal*
Overflow channel
CONCEPTUAL MODEL
OF SUBAREA 4
Inhibit metala migration
High metric potential
Wick* pore water
rich In metal aall*
to auftece
Pathway:
Infiltration through tailing* carrle
metal* Into groundwater
FIGURE 6
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Table 3
SST OH WQB-7 Human Health Gjwradwater Esmdauees &
Well No,*
C-1
C-14
C-16
C-18
C-21
C-22
C-23
C-24
C-25
C-26
C-3
Sample Interval
19-24
15-20
2.8-7.1
3-7
5-9.7
4.5-8.9
4.5-8.9
4-8.7
4.5-8.9
11.4-16.1
13-18
Date
08/19/93 '
08/19193
10127192
10127192
03110/93
06/07/93
08/19/93
10/27/92
03/10/93
06107/93
08119193
10127/92
03/10193
06/07/93
08/19/93
10/27/92
03/10/93
06/07/93
08119/93
03/10/93
06/07/93
03/10/93
06/07/93
08/19/93
11/23/91
10/27/92
03/10/93
06/07/93
; BTW®
; (feet)
3.55
8.46
2.56
3.25
3.34
3.80
3.70
5.28
4.88
4.69
4.54
5.15
4.64
4.71
4.87
4.40
4.82
4.88
5.06
4.22
3.60
4.94
4.95
5.53
6.81
6.72
5.30
5.36
Arsenic
W-)
3.2
6.0
11.5
13.0
5.5
5.8
11.8
76J-
48.3
41.7
53.?
123,
2S.fr
20J
tB£
27£
25.4.
24$
3U
1.9
4.1
3.5
2.3
6.2
1.6 U
1.9
4.4
1.0
Cadmium
fctg/L)
0.0
0.04 U
S.2
12.1
8.8
R
8.1
0.6
0.1
0.2
0.2
0.8
0.3
0.2
0.2
0.5
0.2
0.2
0.2
S,S
'3.8
29.®
9.6
0.63 U
1Q.4
9.2
10,0
8.8
Mercury
Gtg/L)
0.19
0.15
0.16 U
0.16 U
0.12
0.29
0.30
•
*
*
*
+
*
•
*
•
-
*
0.12
0.10 U
0.13
0.10 U
0.10
0.23
0.2 U
0.16 U
0.10 U
0.14
(1) WQB-7 - Montana Water Quality Bureau Standards Numeric Water Quality Standards (Arsenic 18 fjgll; Cadmium 5 /sg/L; Mercury 0.14 /yg/U; Shading
indicates an exceedance; U - Below method detection limit; R - Rejected data.
(2) RH-/DP- - Well and drive points installed in the Rocker Operable Unit; wells represent ground water concentrations at shallow, intermediate, and deep
depths; not inclusive of all wells with exceedances. DW - Domestic wells - 200 series wells are located in Rocker, Nissler, and Miles Crossing areas; 300
series wells are located in the upper Deer Lodge Valley.
(3) DTW - Depth to water below ground surface ! - Unknown * - Not analyzed + - Data not available
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Table 3
SST OU WQB-7 Human H&Uth Groimdwater Exceedanm (t)
Well No,®
C-4
C-4
C-4S
C-5
C-6
C-7
DP-2
DP-3
DP-4
DP-5
DW-203
DW-206
DW-207
DW-212
Sample interval
{feet}
7.5-13
7.5-13
7.5-9.5
24-29
13-18
6.8-8.8
+
+
•+•
5-8.1
93-98
< 30
38-43
30-?
Bate
08/19/93
11/25/91
10/27/92
03/10/93
06/07/93
08/19/93
03/10/93
06/07/93
08/19193
08/19193
08119/93
03110/93
08119/93
09/22/92
09/22/92
09129/92
09130/92
01/07/85
01107/85
04/24/85
12/13185
01/07/85
02/28/85
04/24/85
J01/07/85
04/24/85
12/12/85
BTW3'
(feet)
5.75
4.86
4.34
3.09
3.41
3.70
3.21
3.54
3.87
7.97
4.40
7.62
7.97
4-
+
•f
2.56
+
!
1
!
+
+
+
i
!
!
Arsenic
Otg/L>
1.2 U
6.1
8.3
5.8
4.1
3.6
11.9
9.1
12.0
3.9
5.2
8.8
3.5
83,7
1830.0
18000,0
131J&
2CL&
3S.&
26J3
29.0
21J
24.U
184J
zla
22£
me
Cadmium
(flgflt
S.S
25.7
291
*U
ttJ
4*2
0.6
0.3
0.5
R
0.16 U
W
5.8
*
*
*
*
0.70 U
0.70 U
0.50 U
1.1
0.70 U
1.1 U
0.50 U
0.70 U
0.50 U
1.0
M«r«nry
: Wto
.
4
0.16 U
0.10 U
: 0,19
Q.4?
; 0,W
i Q^fff
i' d.23:
\ 0.1S
55ff
*
*
-
*
*
*
*
*
«
•
-
•»
*
»
.
•»
(1) WQB-7 - Montana Water Quality Bureau Standards Numeric Water Quality Standards (Arsenic 18 fjgll; Cadmium 5 fjgll; Mercury 0.14 /ygIL); Shading
indicates an exceedance; U - Below method detection limit; R - Rejected data.
(21 RH-/DP- - Well and drive points installed in the Rocker Operable Unit; wells represent ground water concentrations at shallow, intermediate, and deep
depths; not inclusive of all wells with exceedances. DW - Domestic wells - 200 series wells are located in Rocker, Nissler, and Miles Crossing areas; 300
series wells are located in the upper Deer Lodge Valley.
(3) DTW - Depth to water below ground surface ! - Unknown * - Not analyzed + - Data not available
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Table 3
SST OU WQB-7 Human Health GrooiKtoater Exceedaoces °*
Well No.p!
DW-215
OW-230
DW-230
OW-313
GS-04
GS-06
RH-1
RH-10
RH-14
RH-14
Sample Interval
i
< 40
< 40
< 25
3-8
19-29
3-13
7-17
29-39
29-39
Bate
01/08/85
03/10/93
01/08/85
04/24/85
07/25/85
12/12/85
03/10/93
03/10/93
01/16/85
02/28/85
03/28/85
06/11/85
03/10/93
06/07/93
08/19/93
12/12/85
08/19183
08/20/87
09/14/88
11/12/91
09/23/92
08/21/87
09/13/88
11/07/91
09/29/92
09/13/88
11/08/91
09/28/92
DTW^
(fee®
11.50
I
j
I
!
i
j
•»•
+
+
•4-
-f
+
+
•f
8.20
+
8.42
9.58
+
+
NO
10.47
+
+
10.25
+
+
Ajsenie
&g/L}
22,&
22.1
S8.&
734*
36.fr
35J-
38J
gg.a
41J1
29J*
2BJ?
zm
21^
26.7
R
17.0
13.0
10.0
16.0
2 U
3.0 U
amo
5020,0
• }21ftQ
3D88.0
494«.a
1358.0
8060.Q
Cadmium
w&
0.60 U
0.2
0.60 U
0.50 U
0.20 U
1.0
0.1
0.2
6.9
7.4
8,1
5.0
1.1
0.7
R
IIS
&.9
88.8
30.0
24>e
3?,1
90JI
.
6.2
ftS
5.00 U
2 U
2.0 U
Mercury
O^g/L)
-
•
*
•
*
*
•
•
.
*
»
•
0.10 U
0.19
0.13
.
-
•
*
•
*
*
•
*
»
*
*
•
(II WQB-7 - Montana Water Quality Bureau Standards Numeric Water Quality Standards (Arsenic 18 /;g/L; Cadmium 5 /jg/L; Mercury 0.14 /yg/L); Shading
indicates an exceedance; U - Below method detection limit; R - Rejected data.
(2) RH-/DP- - Well and drive points installed in the Rocker Operable Unit; wells represent ground water concentrations at shallow, intermediate, and deep
depths; not inclusive of all wells with exceedances. DW - Domestic wells - 200 series wells are located in Rocker, Nissler, and Miles Crossing areas; 300
series wells are located in the upper Deer Lodge Valley.
(3) DTW - Depth to water below ground surface ! - Unknown * - Not analyzed * - Data not available
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Table 3
SST OU WQB-7 Human Hsaltb Graim^water Exceedauces (t)
Well Nfc®
RH-15
RH-15
RH-18
RH-3
RH-33
RH-4
RH-47
RH-5
RH-6
RH-8
RH-9
Sample Interval
fleet)
+
+
+
5-15
+
5-15
+
8-18
29-39
30-40
6-16
Date
11/07/91
09/24/92
11/07/91
11/12/91
11/07/91
09/28/92
08/21/87
09/14/88
11/12/91
09124/92
09/23/92
08/20/87
06/03/88
09/13/88
11/07/91
09/28/92
08/20/87
06/03/88
09/13/88
11/07/91
09/28/92
09/14/88
09/23/92
08/20187
DTWP>
(f«*>
+
+
+
•»•
+
+
5.10
5.08
+
+
-f
10.81
10.79
11.23
+
+.
11.69
10.94
12.33
•f
+
9.28
•1-
8.81
Arsenic
WU*
360.0
, as5.&
35.JU
2.1
14?E&0.
' 2S70&.0
23,a
34,?
38.4
S3.*
9.2
489.9
706.*
J27&Q
1688,8
221S,fl
t608.fl
?8ftfl
180.9
875JJ
S5S.O
rw
18.2
21 .a
Cadmium
wu
2.4
2.0 U
2U
5.8
46.1
2.0 U
S.OO U
*
2U
2.0 U
ata
78.0
gfi.o
azo
42J
' ' 465
}?£
14J8
5.00 U
2 U
' 2.0 U
5.00 U
2.0 U
5.00 U
i Mercury
; 6«ft.)
•
»
*
-
.
-
*
*
*
*
*
.
.
*
«•
-
•
*
.
•»
*
»
*
-
(1) WQB-7 - Montana Water Quality Bureau Standards Numeric Water Quality Standards (Arsenic 18 //g/L; Cadmium 5 //g/1; Mercury 0.14 //g/L); Shading
indicates an exceedance; U - Below method detection limit; R - Rejected data.
(2) RH-/DP- - Well and drive points installed in the Rocker Operable Unit; wells represent ground water concentrations at shallow, intermediate, and deep
depths; not inclusive of all wells with exceedances. DW - Domestic wells - 200 series wells are located in Rocker, Nissler, and Miles Crossing areas; 300
series wells are located in the upper Deer Lodge Valley.
(3) DTW - Depth to water below ground surface ! - Unknown * - Not analyzed + - Data not available
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Because the majority of inorganic compounds are typically most soluble at low (acidic) pH,
metals carried with acidic groundwater entering the relatively higher pH water of Silver Bow
Creek precipitate out of the water and adsorb onto instream sediments. Researchers working
on Silver Bow Creek have documented that instream sediments accumulate the majority of
contaminant load from groundwater (Benner et al., 1995; Smart, 1995). Under conditions of
extremely acidic (pH = 1.0 to 4.5), low dissolved oxygen (less than 1,000 jig/1), and metal-
rich groundwater (avg. Cu = 20,000 jug/1 and Zn = 60,000 /*g/l) discharging to a neutral to
basic (pH = 7.9 to 9.1), oxidized (8,000 /xg/1) stream with relatively lower contaminant
concentrations (avg. Cu = 100 /zg/1 and Zn = 1,000 /ig/1), the vast bulk of contaminant
loading from groundwater to surface water is attenuated in the instream sediments (Benner et
al., 1995 and Smart, 1995). The attenuation mechanisms are most likely adsorption and/or
precipitation. Contaminated groundwater is doubtless a source of additional contamination to
instream sediments and surface water of Silver Bow Creek.
4) Instream Sediments
Instream sediments (i.e. sediment within the active channel of Silver Bow Creek) are
severely contaminated with metals arsenic, cadmium, copper, lead, mercury and zinc
extending throughout the entire length of the SST OU stream channel (Table 4). Instream
sediment concentrations of Silver Bow Creek are similar to the concentrations found in the
tailings/impacted soils, so, for conceptual purposes, they can be considered "tailings in the
stream". The SST OU risk assessment determined that arsenic, cadmium, copper, lead,
mercury and zinc are, individually, major contributors to the impairment of the aquatic
community of Silver Bow Creek (MDEQ, 1994a).
Essig and Moore (1992) described concentrations of Silver Bow Creek instream sediments as
between 10 and 65 times higher for arsenic, cadmium, lead, and zinc, and 400 tunes higher
for copper than are found in other area streams which drain highly mineralized geologic
areas. Like tailings themselves, the majority of contaminated sediments vary in size from a
coarse sand (1 mm) to a very fine silt or clay (Table 4).
While in the stream, these sediments are presently toxic to most macroinvertibrates (Besser et
al., 1995a,b), serve as a potential future source of metals contamination to the surface water
system, and could potentially impact future fish populations by biologic up-take from
contaminated benthic invertebrates (Woodward et al., 1994).
Besser et al., (1995a,b) and Kubitz et al. (1995) tested instream sediments in the fall of 1993
from analogous locations to samples tested in the fall of 1991 by Kembel et al. (1994) and
Ingersoll et al. (1994).
27
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Table 4
Silver Bow Creek
Mean Instream Sediment Concentrations
(mg/kg)
Analyte
Arsenic
Cadmium
Copper
Lead
Mercury3
Zinc
Background1
(<6Jjua)
7
0.2
20
15
NA
57
Saml Fraction2
at«ffl-62jsa)
92
3.8
694
225
0.8
1,357
Clay/Silt Fraction2
«62 ftm)
378
76
10,459
6,702
—
12,782
NA = not analyzed. 1 - Clark Fork Damage Assessment Bed Sediment Sampling And Chemical Analysis Report, University of
Montana - Oct. 1992. 2 - sediment contaminant concentration analysis, data used PTI, ARCO, Essig & Moore, and CH2M Hill -
Oct. 1995. 3 - As reported in Titan Oct. 12, 1994 submittal, not analyzed by size fraction, ^m = micrometers, mg/kg = milligrams
per kilogram.
Kubitz et al. (1995) tested the amphipod Hyalella azteca and Besser et al. (1995a,b) tested
the midge Chrionomus tentans. These studies were conducted in accordance to both USEPA
and ASTM standard sediment toxicity and bioaccumulation test methods with the standard
test organisms (Ingersoll 1991, Ingersoll et al., 1995a, USEPA 1994, ASTM 1995a,b).
Instream sediment chemistry, toxicity, and bioaccumulation was similar between the 1991
and 1993 sampling dates. The sediments from Silver Bow Creek were consistently the most
toxic of the samples collected in the Clark Fork basin and resulted in the highest
bioaccumulation of metals by both amphipods and midges (Ingersoll per com. September 27,
1995). Moreover, concentrations of metals in these sediment samples consistently exceeded
a variety of sediment quality guideline concentrations (Ingersoll et al. 1995b,c; MacDonald et
al. 1995; Smith et al. 1995).
5) Railroad Materials
Certain portions of several historic and existing railroad embankments along Silver Bow
Creek were constructed or contaminated with mine waste rock and/or mine and mill tailings.
28
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
This material represents a source of metals to groundwater or to Silver Bow Creek via
runoff.
Estimated Volumes of Contaminated Materials By Subarea
Contaminated tailings/impacted soils volume estimates are presented in Table 4. These
volumes were originally presented in the Draft RI as generated by the Natural Resource
Information System (NRIS) Geographic Information System (GIS) database. A more detailed
description of the various methods and measures used to calculate these quantities is
presented in the Draft RI (ARCO, 1995a).
Subarea 1
There are approximately 285,000 cubic yards (cy) of tailings/impacted soils impacting
approximately 154 acres within Subarea 1 (Table 4). Tailings/impacted soils are generally
coarse textured, comprised primarily of sand and silt size materials. The coarse nature of
these tailings increases the potential for movement of water through the tailings and transport
of contaminants into the ground and surface water. Tailings deposits are primarily fluvial
bar type deposits. The maximum lateral width of tailings/impacted soils is approximately
1,200 feet and the measured thickness of tailings/impacted soils ranges up to approximately
four feet. These deposits are generally narrow and lie close to the stream.
Metals-elevated railroad bed and ballast materials identified in Subarea 1 include
approximately 203,000 cy of waste rock, 74,500 cy of slag, and a single small (1.3 cy)
concentrate spill. Approximately 95,000 cy (47%) of this total quantity of waste rock are
present along the CMSP rail line outside the floodplain, relatively far away from the stream.
The only significant means of migration of railroad materials is erosion and transport by
runoff from near-stream areas and infiltration through contaminated materials. There are
several locations within Subarea 1 where railroad materials are likely to be eroded and
transported directly to the stream: at two railroad bridges above and below the Rocker
siding; and, near Whiskey Gulch and Nissler where the railroad bed forms one of the
streambanks of Silver Bow Creek. Approximately 55,000 cy of waste rock are present in
locations proximal to the streambanks or bridge abutments at two stream crossings. About
24,000 cy of this total are located in areas proximal to the stream along the northern and
eastern sides of the Rocker Siding, a large multi-track siding used by both the Montana
Western and Rams railroad companies. The volume of slag used as ballast material in these
same locations proximal to the stream is approximately 15,000 cy.
Surface water flows into the OU from the LAO OU containing concentrations of cadmium,
copper, lead and zinc above chronic and acute aquatic surface water quality standards (Table
29
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
2). Generally, Silver Bow Creek gains flow from groundwater inflow throughout Subarea 1
(groundwater recharges the stream), indicating that this is a pathway for contaminated
groundwater to move into the stream. Evidence that this pathway exists is the presence of
some contaminants measured in groundwater in Subarea 1 at concentrations much greater
than those measured in Silver Bow Creek during low flow conditions and the notable increase
in all dissolved contaminants in the surface water between Subareas 1 & 2 (Table 2).
Runoff from areas of overbank tailings to Silver Bow Creek is considerable in Subarea 1
based on high flow water quality data. The confined nature of the floodplain which slopes
toward the stream results in transport of both particulate and metal salts to the stream during
runoff events.
The alluvial aquifer system is generally close to the ground surface within Subarea 1, ranging
between zero to eight feet below ground surface (bgs) in the floodplain. Groundwater levels
within the floodplain were found to have a maximum seasonal fluctuation of up to two feet in
monitoring wells further from the stream but within the floodplain during the three year
monitoring period. Because of groundwater fluctuation in combination with the near-surface
groundwater levels, Subarea 1 contains the second largest quantity of tailings/impacted soils
considered to be saturated tailings (Table 5).
Infiltration of water through the vadose zone in tailings deposits and into the saturated zone
is another method by which contaminants move into groundwater. This is most likely to
occur during longer duration precipitation or snowmelt events or in those locations where
groundwater is located close to the ground surface and tailings/impacted soils are of a coarse
texture.
MCL exceedances for arsenic in groundwater were measured in wells located proximal to
and within the Rocker OU. These exceedances may be partially attributed to sources within
the Rocker OU. Exceedances of cadmium MCLs in groundwater appear to be related to the
presence of fluvially-deposited streamside failings and/or railroad materials composed of
mining wastes or other industrial sources. Such exceedances appear to be confined to
samples obtained from monitoring wells completed in the upper portion of the alluvial aquifer
in source areas within the floodplain.
The volume of metals-impacted stream sediment in Subarea 1 is 15,000 cy, as defined in the
RI. A recent stream survey identified that 20 percent of the stream channel is classified as
riffles, 70 percent is runs, and 9 percent is pools. Runs and riffles contain the bulk of
contaminated instream sediments (Maxim, 1995).
30
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Table 5
Streamside Tailings OtJ
Volumes of Saturated Tailings and Relevant Groundwater
Information
Subarea
1
2
3
4
Total
Max. Observed
G,W. fluctuation
{ft}
1.98
2.09
1.68
3.06
Total Volume
Tailings
fey)
285,000
808,000
160,400
1,292,000
2,545,400
Volume: Saturated
aa
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Creek. Tailings are predominantly composed of fine sandy silts with some tailings underlain
by a buried organic layer and a clay-silt laminated layer. Tailings/impacted soils generally
range in measured thickness from one to four feet although tailings/impacted soils up to five
feet thick were measured hi several areas.
Tailings/impacted soil samples from Subarea 2 contain most of the highest median
concentrations of contaminants of concern for the SST OU (Table 1). The tailings/impacted
soils in this reach reflect relatively low-energy overbank deposition of medium to fine
grained tailings. A buried soil horizon was penetrated in many of the borings in this
subarea, especially in the vicinity of Ramsay Flats. This buried soil horizon provides some
protection to groundwater where it is present, since the organic material present in the soil
geochemically binds the metals in contaminated pore water moving through the vadose zone.
Railroad materials containing arsenic and metals that were identified in Subarea 2 include
approximately 187,000 cy of waste rock, 48,000 cy of slag, and approximately 1,000 cy of
impacted material. There are several railroad bridges within Subarea 2 where railroad
materials are likely to be eroded and transported directly to Silver Bow Creek or a tributary:
at the Silver Bow and Miles Crossing bridges and where the stream crosses Browns Gulch.
At these locations, there are about 60,000 cy of waste rock and 5,000 cy of slag out of the
total volumes presented above.
Surface water flows into the subarea containing concentrations of cadmium, copper, lead,
and zinc above acute and chronic aquatic water quality standards (Table 2). During low flow
periods, metals levels in surface water are generally higher at the upstream end of the
subarea compared to the downstream end of the subarea. Contaminants of concern in runoff
impact Silver Bow Creek substantially during high flows as evidenced by trends of increasing
total and dissolved zinc and total copper. Silver Bow Creek appears to slightly gain flow
from groundwater inflow in Subarea 2 in the reach of stream adjacent to Ramsay Flats where
there is evidence of groundwater impacts to surface water. Silver Bow Creek is less armored
within Subarea 2 than any other portion of the OU. Therefore, considerable streambank
erosion in many areas is evident. The degree to which surface water is impacted by the
groundwater pathway could not be quantified with the data ARCO collected for RI purposes.
Data collected on SBC by other researchers quantified the effects of saturated tailings on
groundwater and the subsequent impact of contaminated groundwater on instream sediments
and surface water (Benner et al., 1995; Smart, 1995).
The alluvial aquifer in Subarea 2 is generally near the surface as in Subarea 1, ranging from
approximately zero to eleven feet bgs in the floodplain. In Ramsay Flats, depth to water is
approximately five feet below ground surface. Groundwater levels within the floodplain
exhibited an observed fluctuation of over two feet in wells further from the streambank. In
the larger areas of tailings such as Ramsay Rats, the groundwater elevation is far enough
32
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
below the surface that a relatively small percentage of tailings are considered saturated.
Because of this and the finer grained texture of the tailings/impacted soils deposits,
precipitation and adsorption mechanisms may, to a greater extent than in Subarea 1.
potentially retard contaminants of concern in the soil. Vadose zone transport of contaminants
of concern are limited and less significant within Subarea 2 than anywhere else in the OU.
For instance, on Ramsay Flats, the largest single area of tailings with limited data points
(monitoring wells), no drinking water MCL exceedances were observed over the Phase n RI
monitoring period.
Groundwater MCL exceedances have been detected in several other locations within Subarea
2, primarily where groundwater is close to the surface. Exceedances of the cadmium MCL
have been measured in wells in the Silver Bow Siding area. Groundwater samples collected
from wells located near the mouth of Browns Gulch and near Miles Crossing have
periodically exceeded the arsenic MCL.
The volume of metals-impacted stream sediment in Subarea 2 is 22,700 cy, as defined in the
RI. A recent stream survey identified that 21 percent of the stream channel is classified as
riffles, 65 percent is runs, and 14 percent is pools. As with Subarea 1 runs and riffles
contain the bulk of contaminated instream sediments (Maxim, 1995).
Subarea 3
Subarea 3 is almost wholly contained within Durant Canyon, the canyon setting constituting
the main difference between this subarea and the other three subareas. There are no
improved roads in the subarea although access can be gained along an unimproved inactive
railroad bed which parallels the stream. Within the narrow canyon, the stream channel is
generally confined to a narrow floodplain between the railroad embankments.
There are approximately 160,400 cy of tailings and impacted soils covering over
approximately 92 acres within Subarea 3 (Table 5). Of this quantity, approximately 78,400
cy of tailings/impacted soils are considered saturated and above. The texture of tailings in
this subarea is primarily very fine grained silty sands. Tailing deposits in Subarea 3 are
primarily channel bar and impoundment deposits, with minor overbank and channel fill. The
maximum lateral width of tailings/impacted soils is approximately 620 feet; tailings deposits
are discontinuous through the narrow canyon. Tailings/impacted soils are generally less than
two feet thick, averaging 0.5 feet thick. The maximum measured thickness of this material
is approximately 4 feet.
Railroad materials containing contaminants of concern identified in Subarea 1 include
approximately 60,000 cy of waste rock and approximately 35,000 cy of slag with about
33
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
24,000 cy present in areas proximal to the stream. These materials were present in the bed
and ballast at five locations within Subarea 3 where railroads cross Silver Bow Creek or
where the railroad bed makes up one of the streambanks. Additionally, the confined nature
of the canyon and location of the railroads adjacent to Silver Bow Creek increase the area
where materials containing contaminants of concern are likely to be eroded and transported
directly to Silver Bow Creek. Erosion and transport of these railroad materials is potentially
more significant in Subarea 3 than elsewhere in the SST OU.
As in Subarea 2, surface water flows into the subarea at levels above chronic and acute
aquatic water quality standards for most metal parameters (Table 2, SS-14). At low flow,
contaminant levels hi surface water are generally higher at the upstream end of the subarea
than at the downstream end of the subarea. This decrease probably occurs primarily from
dilution of the input of relatively higher quality German Gulch water to the system. Silver
Bow Creek is armored in Subarea 3, more than any other portion of the OU.
Runoff from areas of overbank tailings to Silver Bow Creek is potentially significant. The
confined nature and relatively steep slopes of the floodplain near the stream within the
canyon may result in transport of both paniculate and dissolved salts to the stream during
precipitation runoff events.
Based on data from the five monitoring wells located in Subarea 3, the alluvial aquifer is
relatively near-surface, ranging from approximately zero to nine feet bgs. Groundwater
levels were found to fluctuate between approximately 0 and 1.7 feet. Vadose zone transport
of contaminants of concern may be considerable as a result of the fine grained sandy texture,
the shallow depth to groundwater and the fluctuation of the water table.
Groundwater MCL exceedances measured in Subarea 3 were from a near-stream well
completed in coarse tailings. Samples from this well have exceeded the cadmium MCL three
out of five tunes that it has been sampled. Stream stage and groundwater level data indicate
that the surface water is gaining with varying stream stage in the upper end of the subarea
near Miles Crossing.
The volume of metals-impacted stream sediment in Subarea 3 is 5,600 cy, as defined in the
RI. A recent stream survey identified that 49 percent of the stream channel is classified as
riffles, 40 percent is runs, and 11 percent is pools. Runs contain the bulk of contaminated
instream sediments for this subarea (Maxim, 1995).
Subarea 4
The character of Subarea 4 is quite different from the other three upstream subareas in that
34
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
the floodplain is wide and contains numerous overflow channels. These overflow channels
are active during various high flow events and contain some of the thicker deposits of
tailings/impacted soils and generally contain the majority of off-stream saturated tailings. In
the upper half of Subarea 4, Silver Bow Creek flows through a relatively straight man-made
channel which limits to some extent potential overbank flows which would normally enter the
overflow channels. Below the town of Stuart, the channel is characterized as meandering.
Subarea 4 contains the largest quantity of tailings and impacted soil of all four subareas.
approximately 1,300,000 cy over approximately 700 acres (Table 4)(ARCO, 1995a). 50,000
cy has been removed from Demonstration Project EL Of the 1,250,000 cy, approximately
321,400 cy are considered saturated or overlying saturated tailings. Subarea 4 contains about
52 % of the volume of tailings/impacted soils within the SST OU. The texture of tailings
materials in Subarea 4 is primarily very fine, silty sands. Tailings deposits are discontinuous
along a wide floodplain and are sparsely vegetated. Measured tailings/impacted soils
thicknesses range from a few inches to over 4.5 feet.
Subarea 4 contains the smallest quantity of railroad materials containing metals and arsenic,
including only approximately 8,300 cy of waste rock and approximately 23,000 cy of
impacted material. Railroad materials are proximal to Silver Bow Creek at a single location
on an abandoned railroad grade at Stuart, which contains approximately 5,000 cy of waste
rock. Because the limited quantity of railroad materials containing contaminants of concern
is located in the floodplain in a single location in Subarea 4, erosion and transport of railroad
materials to Silver Bow Creek is not significant.
Surface water flows into Subarea 4 at levels above chronic and acute aquatic water quality
standards for most metal parameters (Table 2, SS-16). With the exception of arsenic, metals
levels in surface water are generally higher at the upstream end of the subarea than at the
downstream end during low flow with most of the decrease occurring below the Stewart
Street Bridge. Conversely, during high flow events, concentrations of both total and
dissolved fractions of most contaminants of concern increase by up to an order of magnitude
between the upper and lower ends of the subarea.
As Silver Bow Creek flows through the subarea, the upper (southern) part of the subarea
loses flow to groundwater and the lower (northern) portion of the OU gains flow from
groundwater during low flow. Surface water does not appear to impact groundwater quality
in the losing reaches of the subarea.
Runoff of precipitation and snowmelt from the overbank tailings occurs along portions of
Subarea 4, primarily through the various overflow channels that meander through the
floodplain. Because runoff quality and quantity were not directly measured during the RI,
the magnitude of runoff inflow in Subarea 4 could not be quantified.
35
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
The alluvial aquifer system is relatively near-surface within Subarea 4, ranging from zero to
seven feet bgs in areas away from the active channel. Groundwater levels within the
floodplain were found to fluctuate between approximately 0.5 to 3.0 feet. Drinking water
MCL exceedances of cadmium in groundwater were detected in two areas, near Crackerville
and Stuart. Copper and zinc concentrations where found to be many orders of magnitude
greater than surface water standards in near stream wells. This groundwater would be
expected to discharge into the creek in gaining sections. These cadmium exceedances were
measured along with relatively high concentrations of other metals in the same wells. One of
the wells in Subarea 4 that exhibited relatively high metals concentrations was installed in
saturated tailings, indicating that the exceedances may be related to the presence of
tailings/impacted soils in the saturated interval.
The volume of metals-impacted stream sediment hi Subarea 4 is 30,000 cy, as defined in the
RI. A recent stream survey identified that 37 percent of the stream channel is classified as
riffles, 45 percent is runs, 10 percent is pools, and 8% is dewatered. In this subarea, runs
contain the bulk of contaminated instream sediments (Maxim, 1995).
Terrestrial and Aquatic Resources
The Terrestrial and Aquatic Resources Investigations characterized the representative plant
communities and the benthic macroinvertebrate community within the SST OU. The
Terrestrial Investigation focused on vegetation mapping and vegetation uptake of
contaminants of concern. The aquatic investigation focused on benthic macroinvertebrate
communities and density of species.
Terrestrial Resources
The general objectives of the Terrestrial Investigation were to characterize representative
plant communities within the operable unit in relation to soil conditions and to determine the
existence and extent of bioaccumulation of contaminants of concern in tissues of selected
plant species. Riparian plant communities were surveyed at stations representing a gradient
of contaminant concentrations in soil. The results provide information for assessing potential
effects of elevated concentrations of contaminants of concern on plant communities and
wildlife that depend on vegetation for habitat and food.
The following conclusions were made on the bases of the limited data collected for the RI:
• Riparian meadow communities within the SST OU consist mainly of stands
dominated by tufted hairgrass or redtop, with species of forbs and other
36
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STREAMS1DE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
grasses occurring in less abundance.
Concentrations of contaminants of concern in soil and pH levels are the
significant variables that affect riparian meadow community characteristics. In
some areas of tailings with elevated contaminant concentrations, plant biomass
and cover can reach levels characteristic of unimpacted reference areas because
soil pH is relatively high (>6.0).
Willows displayed leaf tip burn, general chlorosis, curling of leaves, and
brown margins and brown necrotic spots on leaves that could be attributable to
trace metal toxicity. However, it is possible that some of the effects observed
are attributable to nutrient deficiency due to localized soil conditions.
Benthic Macroinvertebrate Resources
Since 1986, benthic macroinvertebrate assemblages have been studied at four sampling
stations in Silver Bow Creek by the MDEQ (McGuire, 1995). The macroinvertebrate data
are analyzed using a series of 10 community metrics that are combined into a single index of
biological integrity. Such a measure indicates the severity of mining impacts to Silver Bow
Creek. Selected metrics are also combined to develop separate indices of biological integrity
for metals and organic effects at each station. The interpretation of the macroinvertebrate
data is dependent upon many subjective factors associated with the validity of individual
metrics, the combination of metrics used for cumulative assessments, and the impact
categorizations based on index scores. Notwithstanding these limitations, the data provide an
indication of the current status of macroinvertebrate communities, the degree of recovery
over past conditions, and some insight into potential causative agents.
Four macroinvertebrate sampling stations were located along Silver Bow Creek. Two of
these stations were located upstream of the SST OU boundary, one below the waste water
treatment plant and one below the Colorado Tailings. The other two stations were located at
Miles Crossing and at the lower end of the operable unit above the Warm Springs Ponds.
The results and conclusions for this reach of stream indicated that biological integrity was
severely impaired by metals and organic pollution and that metals remained the primary
cause of impacts to macroinvertebrates above the Warm Springs Ponds (McGuire, 1995).
Metals toxicity depressed biological integrity and restricted the benthic fauna to a few
tolerant species. Biological responses to nutrient and organic inputs were limited in the
metals-dominated environment.
Results from these stations also indicated that there was a slight improvement in biological
37
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
integrity from below the Colorado Tailings to the Warm Springs Ponds. This condition was
hypothesized to reflect the buffering effect of organics from the waste water treatment plant
effluent and/or the distance from potential sources of contamination.
Algae are useful biomonitors of water quality because they have known environmental
requirements and pollution tolerances. The results of this study for the Miles Crossing
station and the station upstream of the Warm Springs Ponds indicated that the biological
integrity at both stations was poor and the overall impairment at both stations was severe.
For comparison, just below the ponds at a station on the Clark Fork River below the mouth
of Warm Springs Creek, biological integrity was good and the overall impairment was
minor.
38
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
VI. SUMMARY OF OU RISKS
The Draft Baseline Risk Assessment for the SST OU was issued by MDEQ for public
comment in January 1995 (MDHES, 1994a). The U.S. EPA and MDEQ have defined
carcinogenic potential risk in excess of 1 in 10,000 and hazard indices in excess of 1.0 as
unacceptable. This definition of unacceptable risk to human health has been incorporated
into the Draft Baseline Risk Assessment for the SST OU and the SST OU Preliminary
Remediation Goals (PRGs). The BRA Executive Summary is located in Appendix C.
Human Health Conclusions
The Streamside Tailings Baseline Human Health Risk Assessment evaluated three exposure
scenarios to determine the health risks related to OU use by residents, workers
(occupational), and recreationists. Both existing and reasonably anticipated future exposure
scenarios were evaluated. Risks were divided into those which may cause cancer and those
which cause adverse health effects other than cancer (non-carcinogenic risks).
Residents
To evaluate potential residential exposure to floodplain contaminants, MDEQ considered a
house located outside, but adjacent to, the floodplain with a yard leading down to Silver Bow
Creek. Under this scenario, children and adults could be exposed to contaminated soils
located outside and inside the floodplain and within the residential yard. Exposure to stream
water and instream sediments was evaluated under the recreational scenario. The vast
majority of residents in Rocker, Silver Bow, Ramsay, and Opportunity live outside the area
of greatest impact from tailings and their exposure to contaminants is expected to be limited.
The primary carcinogenic risk to people living in or near the OU comes entirely from
potential exposure to arsenic in soil and groundwater (Table 6). Elevated concentrations of
arsenic can be found in tailings areas such as the Ramsay Flats and in upper alluvial (less
than 20-feet below ground surface), near-stream groundwater.
Noncarcinogenic risks exceeded acceptable levels for arsenic in soils under the residential
scenario (Table 7). As with the carcinogenic risks, the noncarcinogenic risks vary depending
on the amount of contamination a person contacts. Noncarcinogenic risks related to arsenic,
cadmium, copper and zinc in groundwater were found only in upper alluvial, near-stream
groundwater within and directly adjacent to the floodplain. The risks posed by lead
contamination in soil are generally within the acceptable range based on the risk model used
in Butte.
39
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Limited grqundwater data demonstrate that the upper alluvial groundwater exceeds drinking
water standards in some areas and also suggest that lower alluvial groundwater does not
presently exceed drinking water standards except in Subarea 4. Most, if not all, water
supply wells are located in lower alluvial groundwater but could potentially draw water from
the upper alluvial system.
Occupational
The occupational scenario evaluates the risk to workers within the OU and focuses on
agricultural workers in areas outside the floodplain. The risk assessment indicates that
carcinogenic risk falls within an acceptable range (Table 8). Noncarcinogenic risks to
agricultural workers are mostly related to arsenic and are also generally acceptable (Table 9).
If workers were to equally divide their work time between areas inside and outside the
floodplain their risks might be higher by a factor of three and could exceed acceptable levels.
Recreationists
Both carcinogenic and noncarcinogenic risks to OU visitors are posed by future use of the
railroad beds which exceed the acceptable EPA risk range (Tables 10 and 11). This could
become a concern if present plans for use of railroad beds as a trail system are developed.
Elevated levels of arsenic where past ore concentrate spills occurred on the railroad beds
create a hazard to recreational users and would therefore require cleanup. As in the
residential scenario, using the Butte model, the risks posed by lead are within the acceptable
range.
Ecological Conclusions
The Ecological Risk Assessment was conducted in a manner similar to, although less
quantitative than, the human health risk assessment. The conclusions generally focus on
whether the environment (plant and animal life) is or may be adversely impacted. A
summation of the risks is presented in Table 12.
In Silver Bow Creek, which is devoid of fish and most other aquatic life forms, the presence
of mine waste contamination is the primary factor limiting the health of the aquatic
environment. These contaminants affect both the water quality and instream sediments in
Silver Bow Creek and create a toxic environment for fish and most benthic
macroinvertebrates. Other physical conditions which may adversely affect the health of
Silver Bow Creek include siltation of the stream bottom, channelization, and disturbance of
adjacent land and stream side (riparian) habitat.
40
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TABLE 6
Carcinogenic Risks for the Residential Scenario3
Pathway
Ingestion of Soil/Sediment
Ingestion of Groundwater
Dermal Contact with Groundwater
.Inhalation'of Dust
Total Carcinogenic Risk
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Arsenic
RME Risk
2.5 x10'4
NC
NC
NC
NC
NC
3.11 x1(T
NC
NC
NC
NC
NC
2.99 x10'3
3.17 x10'5
5.6X10-4
Average Risk
4.4x10'-
NC
NC
NC
NC
NC
6.7 x1CT3
NC
NC .
NC
NC
NC
NA
9.51 x1CT
1.1 x1Q-4
8 Total carcinogenic risks have been rounded to the nearest tenth.
NC = Not calculated, chemicals are not carcinogens for this exposure pathway, or carcinogenic slope
factors are not available.
NA = Only RME exposure is assessed for this pathway.
8469-1 !5\lNihrc\ES-4.Tbl 12-29-94 vc
-------
TABLE 7
Noncarcinogenic Hazard Quotients and Hazard Indices for the Residential Scenario3
Pathway
Ingestion of Soil/Sediment
Pathway HI
Ingestion of Groundwater
Pathway HI
Dermal Contact with Groundwater
Inhalation of Dust
Total HI
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Arsenic
RME.HQ
1.05x10'
8.97 x10'2
5.26x10''
NC
NC
7.11 x10'2
1.1 x101
3.10x10°
1.6x10°
2.73x10°
NC
NC
4.00x10°
1.2X101
2.23 x10'5
NC
2.3 X101
Average Risk
3.03 x10:
2.44x10':
1.5x10'!
NC
NC
2.28 x10'2
3.2x10°
2.22 x10:
7.30x10''
1.69 x10:
NC
NC
4.75x10';
5.1 X10°
NA
NC
8.4x10°
" Pathway His and total His have been rounded to the nearest tenth.
NC = Not calculated, data are insufficient for quantitative analysis.
NA = Only RME exposure is assessed for this pathway.
HQ= Hazard Quotient
HI = Hazard Index
8469-115Whhrc\ES-5.Tbl 12-29-94 vc
-------
TABLE 8
Carcinogenic Risks for the Occupational Scenario3
Pathway
Ingestion of Soil/Sediment
Inhalation of Dust
Total Carcinogenic Risk
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
RMERisk
5.4x 10'5
NC
NC
NC
NC
NC
8.5x1fJ6
6.2 xlfJ5
Average Risk
3.4 x 1CT6
NC
NC
NC
NC
NC
5.1 x 10'5
8.5x10^
a Total carcinogenic risks have been rounded to the nearest tenth.
NC = Not calculated, chemicals are not carcinogens for this exposure pathway, or carcinogenic slope
factors are not available.
8469-115\lf\hhrc\ES-6.Ttl 12-29-9-1 vc
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TABLE 9
Noncarcinogenic Hazard Quotients and Hazard Indices for the Occupational Scenario3
Pathway
Ingestion of Soil/Sediment
Pathway HI
Inhalation of Dust
Total HI
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
RME Risk
8.05x10°
8.0 x10'3
3.29 x10-2
NC
NC
3.64 x10'3
8.5 x1CT1
NC
8.5 xtO'1
Average Risk
4.99 x 10'2
6.07X10"1
2.39 x10'3
NC
NC
2.90 X10'1
5.3 X10'2
NC
5.3 x10-2
a Pathway His and Total His have been rounded to the nearest tenth.
NC = Not calculated, data are insufficient for quantitative analysis.
8469-115\tt\hhrc\ES-7.Tbl 12-29094 vc
-------
TABLE 10
Carcinogenic Risks for the Recreational Scenario3
Pathway
Ingestion of Soil/Sediment
Pathway Risk
Ingestion of Surface Water
Pathway Risk
Dermal Contact with Surface Water
Ingestion of Rail Road Bed Materials
Pathway Risk
Inhalation of Rail Road Bed Materials
Pathway Risk
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
RME Risk
6.2 x10'5
NC
NC
NC
NC
NC
6.2 x10'5
3.4 xirj8
NC
NC
NC
NC
NC
3.4 xirj8
3.2 x10'9
1.2 x10'3
NC
NC
NC
NC
NC
1.2 x10'3
1.8x10'5
NC
NC
NC
NC
NC
1.8 xirj5
Average Risk
9.0 xirj6
NC
NC
NC
NC
NC
9.0 x1(T
7.8x1(T
NC
NC
NC
NC
NC
7.8xlfJ9
7.3x10"'°
1.4X10"'
NC
NC
NC
NC
NC
1.4X10"1
9.2x1Q-s
NC
NC
NC
NC
NC
9.2 x10'6
a Total carcinogenic risks have been rounded to the nearest tenth.
NC = Not calculated, chemicals are not carcinogens for this exposure pathway, or carcinogenic slope
factors are not available.
8469-115\IIWirc\ES-8.Tbl 12-29-94 vc
-------
TABLE 11
Noncarcinogenic Hazard Quotients and Hazard Indices for the Recreational Scenario3
Pathway
Ingestion of Soil/Sediment
Pathway HI
Ingestion of Surface Water
Pathway HI
Dermal Contact with Surface Water
Ingestion of Rail Road Bed Materials
Pathway HI
Inhalation of Rail Road Bed Materials
Pathway HI
Total HI
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
4-1 2 Year Old Child
RMEHQ
8.95 x10"'
6.34 x 10°
3.97 x10"2
NC
NC
6.28 xlfj3
9.5 x10''
3.89 x10"4
2.25 x10"5
3.26 x10'6
NC
NC
1.35x1fJ5
4.6 X10"1
1.96x10"5
1.65x10'
7.42 x10"2
1.91 x10°
NC
NC
1.56x10-'
1.9 X101
NC
NC
NC
NC
NC
NC
NC
2.0 x101
Average HQ
1.03x10-'
8.14 x10"4
5.15x10°
NC
NC
8.89 X10"4
1.1 x10-1
9.0 x10"5
5.22 x10'6
6.94 x10"6
. NC
NC
2.23 x10"6
1.0 X10"4
4.57 x10'6
2.02x10°
1.08X10'2
1.8x10''
NC
NC
8.07 x10"3
2.2x10°
NC
NC
NC
NC
NC
NC
NC
2.4x10°
1-3 Year Old Child
RMEHQ
4.17x10°
3.47 x10"2
2.18x10"'
NC
NC
3.02 X10'2
4.5x10°
8.75 X10"1
5.05 x10"5
7.33 x10"5
NC
NC
3.04 x10'5
1.3 x10"3
3.06 x10'5
7.44x10'
3.34x10"'
8.58x10°
NC
NC
7.02 x10"'
8.4 X101
NC
NC
NC .
NC
NC
NC
NC
9.0x10'
Average HQ
2.91 x10': .
2.05x10°
1.52x10"
NC
NC
2.31 x10":
3.1 X10"1
2.02 X1Q-1
1.17x10"
1.56x10'£
NC
NC
5.02x10"
2.3x10~
7.12 x 10"
4.55 x 10:
2.43 x 10'2
4.06x10':
NC
NC
1.82X10"2
5.0x10°
NC
NC
NC
NC
NC
NC
NC
5.4x10°
' Pathway His and Total His have been rounded to the nearest tenth.
NC = Not calculated, data are insufficient for quantitative analysis.
HQ = Hazard Quotient
HI = Hazard Index
8469-11S\tl\hhrc\ES-9.Tabl
12/29/94 vc
-------
TABLE 12
Simplified Summary of Ecological Risks from Chemical Stressors
Media (units)
Chemical
Arith. Mean Cone/
U95 Cone
Effects
Cone 1
Risk
Potential
Surface Water
mg/L
M9/L
M9/L
ug/L
mg/L
M9/L
ug/L
mg/L
M9/L
ug/L
Mg/L
Ammonia
Arsenic (D)
Cadmium (D)
Copper (D)
Dissolved
Oxygen
Lead (D)
Mercury (D)
Nitrogen
(total soluble)
PAHs (individual)
PCP
Zinc (D)
3.11 /NC
15.56/24.1
1.66/2.26
50.74/59.56
-9.5 /NC
3.0/6.57
0.16/0.16 •
1.75-9.19/NC
0.02 / NC
8.01/NC
336.19/585.99
0.53-2.7
48-850
0.47-5.0
3.9-54
4.0
0.8-500 '
0.012-4.0
0.03-1.0
0.1-5.0
3.5-14.5
40-277 -
Mod to High
(location/liming
dependent)
Low
Mod
High
Low to High
(location/timing
dependent)
Mod'
Low to Mod
Mod to high
(location/timing
dependent)
Low
Mod
High
Sediment
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
Arsenic
Cadmium
Copper
Lead
Mercury
PAHs (individual)
PCP
Zinc
75.16/113.11
4.66/7.01
828/1,579.89
250.5/318.66
3.49/6.7
0.054-1 .563 / NC
0.367/0.634
1,380.13/2,120.27
23.8-24.8
3.9
325-354
62:4
0.2-2.0
4-100
4.2-21
1,064
High
High
High
High
High
Low
Low
High
8469-115Wihrc\ES-10.Tbl 12-29-94 vc
-------
TABLE 12 (continued)
Simplified Summary of Ecological Risks from Chemical Stressors
Media (units)
Chemical
Arith. Mean Cone/
U95 Cone
Effects
Cone1
Risk
Potential
Surface Soil
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
Arsenic
Cadmium
Copper
Lead
Mercury
PAHs (individual)
PCP
Zinc
303.1/514.9
6.45/11.95
1 ,470.4 / 2,484.9
723.63/1,241.4
1 .82 / 5.7
Not Analyzed
Not Analyzed
1,835.6/2,920.7
25-100
4-50
60-100
250-1 ,000
2-10
1-10
0.5-5.0
200-500
High
Mod
High
High
Low to mod
Unknown/
Probably low
Unknown/
Probably low
High
1 Description and source listed in Table 5-17
NC: not Calculated
D: dissolved
8469-115\lMihrc\ES-10.Tbl 12-29-94 vc
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
In addition to the metals associated with mining waste, the risk assessment also evaluated the
risk to the environment from pentachlorophenol (PCP) and polycyclic aromatic hydrocarbons
(PAH), both of which originated from the Montana Pole Superfund site, as well as from
dissolved ammonia and nitrogen related to the Butte public treatment works.PCP and PAH
were not considered significant for instream sediment. Ammonia, nitrogen, and low
dissolved oxygen content are important to water quality in some areas of Silver Bow Creek
which are affected by these parameters. These contaminants are expected ultimately to be
addressed in connection with the sewage treatment operations.
Soil
Many near-stream surface soil areas are critically impacted by tailings deposits and devoid of
vegetation. Surface soil risk is evaluated in terms of the toxicity of contaminants to plants
(phytotoxicity). The contaminants posing the greatest threat in surface soils include arsenic,
copper, lead, and zinc. Moderate threats are posed by cadmium and mercury because of
uptake into plants.
Surface Water
Surface water has been severely impacted throughout the length of Silver Bow Creek and
serves as a contaminant pathway to the aquatic environment. In Silver Bow Creek,
populations of trout and other fish have been eliminated entirely. Risks from surface water
relate to how the contaminants may adversely affect aquatic plants, fish and other stream life.
Surface water contaminants which pose the greatest risk to the health of the stream include
copper and zinc (Figures 7 and 8). Copper is a significant risk throughout the OU. Zinc is
a significant threat in upstream sections of Silver Bow Creek but its concentration and
potential risk decrease somewhat downstream of Miles Crossing. Cadmium, lead, mercury,
and pentachlorophenol are considered moderate threats. Ammonia, nitrogen, and to a lesser
extent, low dissolved oxygen are other significant limiting factors in certain reaches of Silver
Bow Creek.
Sediment
The contaminated instream sediments of Silver Bow Creek are a critical contaminant pathway
to impacted surface water and aquatic biota, particularly benthic macroinvertebrates.
Contaminants in sediment posing a high risk to the environment are arsenic, cadmium,
copper, lead, mercury, and zinc (Figures 9 - 14). Mercury is a contaminant which
bioaccumulates and can potentially biomagnify. Mercury poses a small current threat
because there are no fish in the stream. However, fish and other biota exposed to the levels
of mercury currently in the stream sediment could be at risk.
49
-------
Concentration (mg/L)
CO P
H w
g
en
O
<
CD
CL
0
o
-a
CD
— t
rl
^
— ^
5
CD
o'
^
CD
Q)
^3
,
(J)
i
CD
01
C
O
|—
2
(D
-i
n
—I
O
3
c
•a
-^
3
O
03
O
c
a.
j
3 0 0 •-»
3 '° ^ 2
J -* O Q
•» o O a
-f
i
-L
1 j i
IM
i mi
i nil
•HI
II- "I \*
TT > I i IK
T i I C 12
i i ii in i
T I il in
•S-H
K + -E- +
f j
' /
//
i ^"-rri©
f +-Sr -r
1 IKM i
•
II
II
II
n
ii
m. _t!_
TS^ BI
\\
rn x\n f I
Ul^/iit" T
1
1
1
1
1 17^1 1 l_
1 L££u ^~T
(1
/I
rfii | i i
rr ' '
11! ill
\
/Tf 1 1 1 1
«,"! T1 T
'
I
$T+
|
2). T
T T
~r
X '„ ' •''' -1 '^' '•_ '
2 2 2
S o g w °°
S
-------
, T^tf^^^'" ^ > '
\Effecferf^n\^f^ ^
_.• "•>•*,&** ^w/vSV'
ConccntraUpn 5 \
l($&$?8&i$$&i
3.9
5.0
10.3
12
18
54
;Bas(s\for;EfJFecte^ConcentrationS;; '-\ ']'-"- \ * " \^"^r: *;<;; -
," < vV' - t>W"" v*-v< s- ^ ''" *v<^ ^i^^*^ ^ >x' '-<\ ' ' /- - ' ss ;- -
-- -;\ $£&•&£<&*'*«'?? -•• --< --/ «?'$%J^-<* , <.--.-x -.•-.•
S4 ^^'^wi^^e^ t ^ : v" v ;=;^>v*^HrH 's. **x ^ - - ^-$ > x -^ ?, ^ -,<• i ,
LOAEC (growth & reproduction), freshwater invertebrates
and salmonids (EPA 1985c)
LOAEC (growtli), freshwater plants (EPA 1985c)
Chronic AWQC (dissolved), hardness = 100 nig CaCO3/L
(EPA 1985c)
Chronic AWQC, hardness = 100 mg Ca CO3/L (EPA
1985c)
Acute AWQC, haithicss = 100 mg Ca CO3/L (EPA 1985c)
Mean 96 hr LC50, Rainbow trout, CFR — similar water
quality (USFWS & VW 1992)
Copper Effects Concentrations
in Surface Water
-------
10.00
1.00 -
Concentration (mg
i
4- -I-
Els-
tt -K -,- £ - *
4= I(= ^ 1= 15 -"===::-.-. sft -4- -tfcl.-G 3.277
•qr-H-
_1_ _1_ U}iriii|v_ i_/, y
.150
.120
o in -T- r^^— -(-_ —TTTTTTT 7.—:: : \ KT.—=7=—r=i-
. - -y ..- .1[0
-I' =1= H--I- J.0935
^ _fc 1 :o4o
-I-
0.01 -I , : , : , : ,_
0 5 10 15 20 25
River Miles From Upstream OU Boundary
Dissolved Zinc -HSI— Arithmetic Mean --©-- 95% UCL
FIGURE 8
Dissolved Zinc
SST Surface Water
-------
Eff«&;>VT:'-
,5, > ,-»,',\ -\- % •*» o
Concentration,
(«g^)I"x^'i>%
40
93.5
110
120
150
277
Basis - ' - \^t^<\, ** " , ••'" ;ov - ;
/ , st« >" - 'C'''^" ,'> •. • < - •>> ->v <^V ^ v, ' - '' ^- " ~ - ,, ; s
/ , • "/'»'^ •."'"'' >.: "-",- --,-*- z V,y;""- ' -% < ' V
LOAEC (growth), freshwater plants (EPA 1987)
Chronic AWQC (dissolved), hardness = 100 mg CaCO3/L
(EPA 1987)
Chronic AWQC, hanlncss = 100 mg CaCO3/L (EPA 1987)
Acute AWQC, hardness = 100 mg Ca CO3/L (EPA 1987)
Mean 96 hr LC50, Rainbow trout, CFR — similar water
quality (USFWS & VW 1992)
LOAEC (growth & reproduction), freshwater invertebrates
and salmonids
Zinc Effects Concentrations
in Surface Water
-------
O
w c
re 3
m
2. o'
UJ .a. 2
— oo cc
-------
Effects >
Concentration
(mg71«?V*V" '' " -
4.2 '
6.0
22.1
23.8
24.8
33
50
54
85
Basis for Effects Concentration' v ;
< !' -'„ * ? >vr - / :- >- - -, ' - ~ ; ' - '?" /
.. j - ^j. - <
Background conccuhntions, unconfaminatcd sediment,
Great Lakes precolonial hoiizou (Pcreaud . 1993)
Lowest Effect Level, benthic organisms, Ontario (Persaud
et al 1993)
Low range of bioassay effects concentrations, co-
occurrence analyses (COA), multiple species (Long &
Morgan 1990)
No Effect Concentration (NEC), length, Hyalella azteca
(FWS & UW 1992)
NEC, maturation, Hyalella azteca,. (FWS & UW 1992)
Severe Effect Level, benthic organisms, Ontario (Persaud
et OA1993)
Concentration at which adverse effects are always observed
(Long & Morgan 1990)
Low range of apparent effects concentrations (AET),
multiple species (Long & Morgan 1990)
Effects Range - Median (ER-M) (Long & Morgan 1990)
Arsenic Effects Concentrations
in Sediment
-------
cn
05 O
CD B>
a a
•n
D
fiS
CD C.
S3
m
H
CD
CO
03
T)
H
CO
CD
I
o
o
cb"
CD
CD
D
w'
r-t-
D)
rs
o
CD
CD
CO
o -
Concentration (mg/kg)
I
S
0
\
\
\
\D W SN 00 O ° O
-------
Effects
Concentration
(mg/kg) V;;: %. •
1.1
3.9
4.3
5.6
5.8
6.0
9.0
10.0
Basis for Effects Concentration ^ ; , - -"- , <:
5 <• % * ''•.•.
''- '**•* - , -,, '..,- > ,v">xS-,- <--"• "- %* :- ~
% ' Si \'\yjj .. '' s
Background concentrations, uncontaminated sediment, .
Great Lakes pnccolonial horizon (Pcrsaud . 1993)
No Effect Concentration (NEC), length and maturation,
Hyalella azteca (FWS & UW 1992)
Low range of bioassay effects concentrations, co-
occurrence analyses (COA), multiple species (Long &
Morgan 1990)
Low range of spiked sediment bioassay (SSB), multiple
species (Long & Morgan 1990)
Low range of apparent effects concentrations (AET),
multiple species (Long & Morgan 1990)
Lowest Effect Level, beuthic organisms, Ontario (Persaud
et al 1993)
Effects Range — Median (ER-M) and concentration always
associated with adverse effects (Long & Morgan 1990)
Severe Effect Level, benthic organisms, Ontario (Persaud
etaL1993)
Cadmium Effects Concentrations
in Sediment
-------
Concentration (mg/Kg)
CO
GO ~i
Q. O O
— • o c
3 T3 3D
ra -o m
13 re -
F-f -t -i
1
1
-a
_i
CO
f~f\
CO
,
A
T
1
tj
H
CO
CD
i
f
0
£1)
0
CD'
_ x
CD
CD
ro
'S
o
Ol -
.
q°-
U)
(—+•
—1
o
0
IE
CD"
^^ ' 01 —
ro
o -
K)
1. C
I g
k
5
J
i_ft i
b c
A <
> 00
8
8
1
K>
<^
b
•,
LJ
O """
8 g
. 8 S
1
P
'
N./
A t
U
§ i)
/ 4
/ /:
/
/ /!
§ Of
/ \ i
/ l \
1 \ *
i \
\ \
/T\ 1
Y/ 1
; 1
i •
; i
i
/ i
/ i
/ !
' i
/ !
1 0 f
;
I
1
•
i
i
i
i
•9 i
//
/ i
i i
i
10
*J W
ss
)
)
5
.
-------
Effects
Concentration
(mg/kg); ;:;
15.0
16.0
17.8
25.0
110
325
354
390
Basis for Effects Concentration
••' \4 * - ' * ^ ' ' - ^ '•""'•... % *
it s •."•'' ' f' ' f '• *• ' \ '
Low range of bioassay effects concentrations, co-
occurrence analyses (COA), multiple species (Long &
Morgan 1990)
Lowest Effect Level, bcuthic organisms, Ontario (Persaud
et al. 1993)
Low range of spiked sediment bioassay (SSB), multiple
species (Long & Morgan 1990)
Background concentrations, uncoudiniiuntcd sediment,
Great Lakes prccolonial horizon (Persaud . 1993)
Low range of apparent effects concentrations (AET),
multiple species (Long & Morgan 1990) and Severe
Effect Level, bcnthic organisms, Ontario (Persaud et
a/11993)
No Effect Concentration (NEC), length, Hyalella azteca
(FWS & UW 1992)
No Effect Concentration (NEC), maturation, Hyalella
azteca (FWS & UW 1992)
Effects Range — Median (ER-M) and concentration
always associated with adverse effects (Long & Morgan
1990)
Copper Effects Concentrations
in Sediment
-------
CO
~D
H
CD
00
CD
~D
H
CD
CD
o
o>
3
o
g
CD'
CD
ro
Concentration (mg/kg)
o
o
o
o
o
•p
b
o
o
o
p
'o
o
o
o
o
p
o
o
O o -
13
O
CD
CD
01 ~
o -
ro
Oi
S. Q. ro
-------
Effects ;
Concentration
(rag/leg?
23
26.6
31
62.4
110
120
250
Basis for Effects Concentration .
< ' *• •-
Background conccntnitious, uncoutamiuatcd sediment,
Great Lakes precolouial horizon (Persaud . 1993)
Low range of bioassay effects concentrations, co-
occurrence analyses (COA), multiple species (Long &
Morgan 1990)
Lowest Effect Level, bcntllic organisms, Ontario (Persaud
et al. 1993)
No Effect Concentration (NEC), length and maturation,
Hyalella azteca (FWS & UW 1992)
Effects Range-Median (ER-M)
Low range of apparent effects concentrations (AET),
multiple species (Long & Morgan 1990)
Severe Effect Level, bcnthic organisms, Ontario (Persaud
et o£1993)
Lead Effects Concentration
in Sediment
-------
Concentration (mg/kg)
O3 -J
O3 O
sis
II S
E.-< w
-------
: Effects Concentration;:
(mg/Kg) .
0.02
0.08
0.1
0.2
0.41
1.3
2.0
2.15
Basis for Effects Concentration (EPA 1985e)
Background concentrations, uncontaminated sediments,
South Dakota (Eisler 1987a)
Range of bioassay effects concentrations , co-occurrence
analyses (COA), multiple species (Long & Morgan 1990)
Background concentration, uncontaminated sediments,
Great Lakes pre-colonial horizon (Persaud ct. al 1993)
Lowest Ettect Level, benthic organisms, Ontario
(Persaud et. al 1993)
Range of apparent effects concentrations(AET), multiple
species (Long & Morgan 1990)
Effects Range-Median (ER-M) (Long & Morgan 1990)
Severe Effect Level, benthic organisms, Ontario (Persaud
et. al 1993)
Range of spiked sediment bioassay (SSB), multiple spe-
cies (Long & Morgan 1990)
Mercury Effects Concentrations
in Sediment
-------
CONCENTRATION (mg/KG)
cn
C/)
3 -^
S- n
Q
,
[T]
_g
H
_i
CD
CO
CO
(j)
1
Tl
H
CO
CO
\
j_
j
O
03
o
n>'
CD
CO
ro
UI -
o -
D
0)
2
Z
O
m
"?
^»
cb"
i/>
^^-^
en —
ro _
rm»"»
[
_...-•••'*'
,-'
,•'
-•'"
jj^l
1
\
E
[T
r~
L;
1
^r
i-
\
;
;
T
\
\
~iX
\
^
-,y
J y
1
1
, 1
1
(1)
t
J
t
1
!
\ j
'i j
VI
'.)
(•
®]
y.
I/
1
.1
/I
• 1
; 1
1
1
J
*
t
t
1
1
1
1
1
6
i — i
WOO— — "KJ So
issll II II
o
*¥^
i
1
I
-
\
\
V
i
i
!
__
1
•
-------
Effects , >
•• •. , ; x1* *' ' * < * - •• "
Concentration
(mgykg)^;^w\
51
65
98
120
130
260
270
820
1064
> Basis 'for Effects Concentration , ,\-v , " ;; SM '
"'''•• *s * % * '%~ \ •• '*«' '^V
x > - - \ ->s -.<"-x- f< -- - ;-' -* :^' - " --'
s /-, -'-'"•7^-^ >*i - '-"-- " - "^'"tt* **' c- c-,s><.+'\ * -Uv- , >: ° ;
Low range of spiked sediment bioassay (SSB), multiple
species (Long & Morgan 1990)
Background concentrations, uncontaminatcd sediment,
Great Lakes pnecolonial horizon (Persaud . 1993)
Low range of bioassay effects concentrations, co-
occurrence analyses (COA), multiple species (Long &
Morgan 1990)
Lowest Effect Level, bcuthic organisms, Ontario (Persaud
et al, 1993)
Low range of apparent effects concentrations (AET),
multiple species (Long & Morgan 1990)
Concentration at which adverse effects arc always observed
(Long & Morgan 1990)
Effects Range ~ Median (ER-M) (Long & Morgan 1990)
Severe Effect Level, benthic organisms, Ontario (Persaud
ef a£1993)
No Effect Concentration (NEC), length and maturation,
Hyalella azteca (FTPS & UW 1992)
Zinc Effects Concentrations
in Sediment
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VH. DESCRIPTION OF ALTERNATIVES
A brief description of the OU cleanup alternatives the agencies considered in the Feasibility
Study (FS) report follows. The estimated present worth cost of each alternative includes
capital cost and annual operation and maintenance cost. In calculating costs, remedial action
time frames are limited to 30 years, even for those alternatives requiring perpetual operation
and maintenance.
The development and evaluation of remediation alternatives under consideration for the SST
OU is more fully documented in the FS (ARCO, 1995b). Initial screening was reported in
the Preliminary Remedial Action Objectives Report/Treatment Technology Scoping Document
(ARCO, 1993d). Subsequent development and refinement of the alternatives was
documented in the FS. A full range of alternatives from no action through total removal of
all contaminants was carried through the detailed analysis of the FS. Alternatives were
considered for each of the four contaminated media and were evaluated, utilizing the NCP's
remedy selection criteria, on a subarea basis in the FS. Those alternatives which were
significantly deficient in meeting remedial action objectives in certain subareas for specified
media were dropped from further consideration after the detailed analysis. Alternatives
carried forward were then subjected to"comparative analysis in the FS, again on a media-
specific and subarea basis. Finally, representative groupings of the media-specific and
subarea alternatives were assembled into comprehensive OU-wide alternative packages to
enable MDEQ to evaluate the interaction of alternatives for the different media and to
conduct a reasonable comparison of the costs of various alternatives.
The detailed and comparative analyses of the separate media alternatives formed the basis for
the assembly of the OU-wide alternatives. The media-specific and subarea-specific analyses
identified several alternatives that were not capable of providing adequate levels of
performance, either for the OU as a whole, for some subareas, or for certain conditions
within a subarea. Those alternatives were eliminated from consideration for use where they
were deemed inappropriate.
Of the seven tailings/impacted soils alternatives, Surface Water Controls and Near-stream
STARS were determined to be wholly inadequate in meeting OU remediation objectives and
were eliminated from consideration for use anywhere in the operable unit. The remaining
five site-wide alternatives were used in the OU-wide combinations.
The tailings/impacted soils elements of the four site-wide alternatives include four possible
components: STARS, partial relocation, partial removal, total relocation or total removal.
STARS is the application of lime amendments to the tailings/impacted soils and revegetation
to treat and stabilize the tailings in place. Relocation and removal differ only in the location
of the repository for excavated materials (numerous local repositories vs. one or two regional
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repositories, respectively). The difference between partial relocation/removal and total
relocation/removal is how much tailings/impacted soils are excavated. Total
relocation/removal of materials for the entire OU would excavate all 2.5 million cy of
tailings/impacted soils. Partial relocation/removal alternatives would excavate only portions
of the tailings/impacted soils, as described in each alternative.
Of the railroad alternatives, two active alternatives, Limited Removal and In-situ
Amendment, were used in addition to no action.
In addition to no action, two groundwater remediation alternatives, Source Control and Pump
and Treat, were considered in the FS. The pump and treat alternative was eliminated from
further consideration because the cost of active treatment was not commensurate with benefits
gained in actively treating the potentially widespread, but relatively low level, of
groundwater contamination found at the OU. Therefore, except for the No Action combined
alternative, only Source Control was included in the OU-wide alternatives.
Three alternatives for remediating instream sediments were considered: No Action, Limited
Removal, and Total Removal. For either removal option, both on-OU and regional
repository locations were evaluated.
The OU-wide alternatives were assembled by building on the No Action alternative, which
was used to provide a baseline for comparing the other alternatives. As was the case for the
comparative analysis, subarea characteristics pertinent to a specific alternative were
considered during the assembly process so that, generally, alternatives that were determined
not to be applicable to certain subareas were not used in an OU-wide alternative. One
exception to this condition is the STARS alternative which, although determined to have
limited applicability in Subareas 1 and 3 and not carried forward through the comparative
analysis for these subareas, was used as an OU-wide alternative to provide an option lying
between total in-situ treatment and total removal for the entire OU.
Although there were many different combinations possible for OU-wide alternatives due to
both the number of alternatives considered and the number of subareas in the SST OU, the
progression from simpler and less costly alternatives to more complex and more costly
alternatives could be accomplished using only a relatively few combinations. This was done
by combining media alternatives that added a clear benefit toward achieving maximum
attainment of the evaluation criteria, thereby noticeably improving each progressive
combination. Consequently, only a limited number of OU-wide alternatives were assembled
for further consideration.
During the process of developing the OU-wide alternatives, MDEQ recognized that overall
protection of human health and the environment and long-term effectiveness and permanence
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could be enhanced in certain subareas by modifying the quantity of material that would be
excavated under the partial removal/STARS or partial relocation/STARS alternatives. The
partial removal/STARS and partial relocation/STARS options evaluated in the detailed and
comparative analyses removed only saturated tailings/impacted soils and overlying tailings,
leaving substantial areas of tailings that were to be STARS treated in floodplain. The
STARS treated areas would be subject to erosion and re-entrainment of tailings into the
stream during stream meander and high-flow events. The considerable residual risk and the
need for waiver of the floodplain and solid waste disposal ARARs associated with those
alternatives led MDEQ to develop and consider modified partial removal/STARS and partial
relocation/STARS alternatives as potential OU-wide alternatives that could provide better
protectiveness and better compliance with ARARs. Details of the modified partial
removal/STARS and modified partial relocation/STARS alternatives are provided in the FS
(ARCO, 1995b) and the proposed plan (MDEQ, 1995).
Alternative No. 1 - No Action
Estimated present worth cost: $700,000 to $1,400,000
Implementation time: 3-5 years
This alternative includes the No Action Alternative for tailings/impacted soils, railroad
materials, groundwater and instream sediments. The No Action Alternative is included
primarily to satisfy NCP requirements and provide a baseline by which to compare other
site-wide alternatives.
Under Alternative No. 1, no further action would be taken. Contaminated tailings/impacted
soils, instream sediments, railroad materials, and groundwater would remain in the OU and
would continue to migrate and impact groundwater, Silver Bow Creek, and instream
sediments. The costs for the no-action alternative are those associated with continued
administration of monitoring and institutional controls for a period of 30 years. Actual costs
and efforts associated with the no action alternative would be incurred indefinitely beyond the
30-year period.
Alternative No. 2 - STARS Treatment of Tailings/Impacted Soils, No Action for
Instream Sediments, and In-situ Treatment of Railroad Materials
Estimated present worth cost: $13,000,000 to $24,000,000
Implementation tune: 3-5 years
The primary component of this alternative is STARS, which was developed as a potential
low-cost alternative to the removal and controlled disposal of the tailings/impacted soils that
comprise the primary source of contamination at the OU. Although STARS treatment of
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tailings/impacted soils was not evaluated in the comparative analysis for Subareas 1 and 3
because of potential effects of erosion of STARS treated areas due to stream meander and
overbank flows, this alternative was included in the OU-wide analysis so that total in-situ
treatment could be compared with the other OU-wide removal alternatives.
Under this alternative, approximately 1,950,000 cy of tailings/impacted soils would be
treated in-situ with the STARS technology. An estimated 550,000 cy of tailings underlying
the treated materials would remain untreated. This treatment would enable establishment of
vegetation thereby reducing overland flow and wind erosion. Instream sediments and
groundwater would receive no action and a limited amount of impacted railroad materials
posing a risk to human health and the environment would be treated in-situ with lime
amendments. In areas of expected residential development (i.e. outside the floodplain) this
alternative would use a soil cover where the contaminants pose significant human health risk.
Considerable long-term maintenance and monitoring would be required. Restrictions on OU
access and use would be necessary.
Alternative No. 3 - Partial Relocation and Partial STARS Treatment for
Tailings/Impacted Soils, Limited Removal for Instream Sediments, and In-situ
Treatment of Railroad Materials
Estimated present worth cost: $21,000,000 to $40,000,000
Implementation tune: 3-5 years
This alternative was developed to address one of the primary sources of contaminated
groundwater, saturated tailings. Under this alternative, a total of approximately 480,000 cy
of tailings/impacted soils and an additional 220,000 cy of tailings/impacted soils which
overlie the saturated tailings/impacted soils would be excavated, relocated outside the
floodplain, and treated with STARS amendments. Fill material would be brought in to
replace a portion of the excavated soils. The remaining approximately 1,800,000 cy of
tailings/impacted soils not considered to be saturated would be treated in place with STARS
amendments and revegetated.
Instream sediments would be removed and relocated out of the floodplain with the relocated
tailings. The volume of instream sediments defined for limited removal represents all fine-
grained (< 1mm) instream sediments, which account for the majority of highly contaminated
instream sediments. Only limited data exist to estimate the volumes of instream sediments
by size fraction. Based on quantities of instream sediments estimated during the RI, about
73,000 cy of fine-grained instream sediments would be removed.
Railroad materials would receive in-situ treatment under this alternative by applying STARS
amendments to the impacted railroad grade materials. As part of the STARS treatment,
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limited soil c'over is also considered where recreational users might come into contact with
hish concentrations of contaminated railroad material.
Alternative No. 4 - Partial Removal and Partial STARS Treatment of Tailings/Impacted
Soils, Limited Removal of Instream Sediments, and Limited Removal of Railroad
Materials
Estimated present worth cost: $27,000,000 to $47,000,000
Implementation time: 3-5 years
This alternative is nearly the same as Alternative No. 3 except that the saturated
tailings/impacted soils and instream sediments would be transported to a regional repository
at Opportunity Ponds or a location along Browns Gulch. In addition, railroad materials
containing contaminants that pose a risk to human health or the environment would be
removed and disposed along with the tailings/impacted soils and instream sediments.
Alternative No. 5 - Total Relocation of Tailings/Impacted Soils in Subareas 1 and 3,
Partial Relocation and Partial STARS Treatment in Subareas 2 and 4, Limited Instream
Sediment Removal, and Limited Removal of Railroad Materials
Estimated present worth cost: $32,000,000 to $55,000,000
Implementation time: 4-6 years
This alternative has been developed to address the limitations of STARS in effectively
meeting the SST OU's threshold protectiveness standards and ARARs. Under this
alternative, an estimated total of 1.76 million cy of tailings/impacted soils which are
saturated by groundwater, potentially eroded by natural stream migration and/or flood events
would be relocated to dry closure areas located adjacent to the OU but outside of the
floodplain. Total excavation of all tailings/impacted soils within the floodplain would be
required in Subareas 1 and 3 because those in-situ treatment areas could not be adequately
protected from erosion. This alternative modifies partial relocation to include excavation and
relocation of all tailings/impacted soils within the floodplain in Subarea 2 and excavation and
relocation of additional near-stream tailings in Subarea 4. In Subarea 2, about 280,000 cy of
tailings/impacted soils in the Ramsay Flats area located outside of the floodplain would be
consolidated and treated with STARS, with a portion covered with top soil if residentially
used. In Subarea 4, approximately 540,000 cy out of the 1,300,000 cy identified in the
subarea would be relocated and the remainder treated with STARS. Excavated
tailings/impacted soils would be fully treated with lime amendments prior to placement in the
relocation areas.
As in Alternative No. 3, fine-grained (< 1mm) instream sediments would be excavated and
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placed in the relocation areas with the relocated tailings. The volume of instream sediments
defined for limited removal includes all fine-grained instream sediments, which represent
those posing the most significant risk to health and the environment. As in OU-wide
Alternative. No. 4, selected contaminated railroad materials would be excavated and placed
into local relocation repositories.
Alternative No. 6 - Total Removal of Tailings/Impacted Soils in Subareas 1 and 3,
Partial Removal and Partial STARS Treatment in Subareas 2 and 4, Limited Instream
Sediment Removal, and Limited Removal of Railroad Materials
Estimated present worth cost: $39,000,000 to $66,000,000
Implementation time: 4-6 years
Alternative No. 6 was the alternative proposed by the agencies in the proposed plan. This .
alternative is similar to Alternative No. 5, with the exception that tailings/impacted soils,
instream sediments, and railroad materials removed would be transported and deposited in a
regional dry closure repository instead of adjacent relocation areas. Under this alternative,
an estimated total of 1.76 million cubic yards of tailings/impacted soils would be removed to
regional repositories located in Browns Gulch and/or at Opportunity Ponds. Total removal
of all tailings/impacted soils within the floodplain would be required under this alternative in
Subareas 1 and 3. In Subarea 2, about 280,000 cy of tailings/impacted soils in the Ramsay
Flats area located outside of the floodplain would be consolidated and treated with STARS
and a portion covered with top soil. In Subarea 4, approximately 540,000 cy out of the
approximately 1,300,000 cy identified in the subarea would be removed and the remainder
treated with STARS.
The same amounts of instream sediments and railroad materials would be removed as under
Alternative No. 5, but they also would be hauled to the regional repository.
Alternative No. 7 - Total Removal of Tailings/Impacted Soils, Total Removal of
Instream Sediments, and Limited Removal of Railroad Materials
Estimated present worth cost: $48,000,000 to $79,000,000
Implementation time: 4-7 years
This OU-wide alternative requires the most rigorous action and essentially removes all
identified materials containing contaminants in tailings/soils and instream sediments.
Removal of railroad materials would be limited to those areas where they pose a potential
risk to human health and the environment. This alternative differs from Alternatives 5 and 6
in that it includes removal of all waste sources in and out of the floodplain to a regional dry
repository. A total of approximately 2.55 million cy of tailings/impacted soils would be
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
removed from the OU. In addition, instream sediment removal would address all instream
sediments, not just the fine-grained fraction. Sediment volumes for total removal would be
approximately 236,000 cy, which would include instream sediments to a depth of about 2.5
feet below the present stream bed. There would be a minor level of long-term maintenance
and monitoring associated with this alternative.
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
SUMMARY OF COMIV
Section 300.430(e)(9) of the NCP requires that the agencies evaluate and compare the
remedial cleanup alternatives based on the nine criteria listed below. The first two criteria -
overall protection of human health and the environment and compliance with ARARs, are
threshold criteria and must be met. The selected remedy must represent the best balance of
the selection criteria.
Evaluation and Comparison Criteria
Threshold Criteria
1. Overall protection of human health and environment addresses whether or not a
remedy provides adequate protection and describes how potential risks posed through
each pathway are eliminated, reduced or controlled through treatment, engineering
controls or institutional controls.
2. Compliance with applicable or relevant and appropriate requirements (ARARS')
addresses whether or not a remedy will comply with federal and state environmental
laws or provides grounds for invoking a waiver.
Primary Balancing Criteria
3. Long-term effectiveness and permanence refers to the ability of a remedy to maintain
reliable protection of human health and the environment over time once cleanup goals
have been met.
4. Reduction of toxicity. mobility and volume through treatment refers to the degree that
the remedy reduces toxicity, mobility and volume of the contamination.
5. Short-term effectiveness addresses the period of time needed to complete the remedy,
and any adverse impact on human health and the environment that may be posed
during the construction and implementation period until cleanup goals are achieved.
6. Implementability refers to the technical and administrative feasibility of a remedy,
including the availability of materials and services needed to carry out a particular
option.
7. Cost evaluates the estimated capital costs and operation and maintenance costs,
calculated at present value, for each alternative.
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Modifying Criteria
8. State agency acceptance indicates whether, based on its review of the information, the
state (MDEQ) concurs with, opposes or has no comment on the preferred alternative.
However, for this OU, MDEQ is the lead management agency and EPA is the
support agency. As such, the State has identified the selected remedy and EPA has
concurred with and adopted that identification.
9. Community acceptance is based on whether community concerns are addressed by the
selected remedy and whether or not the community has a preference for a remedy.
Although public comment is an important part of the final decision, MDEQ and EPA
are compelled by law to balance community concerns with all of the other criteria.
In assessing cleanup options, MDEQ and EPA evaluated a wide range of media-specific
alternatives for each of the four subareas of the SST OU. After detailed analysis and
comparative evaluation of the media-specific alternatives, seven comprehensive alternatives
addressing all media in the entire OU were developed and evaluated. The seven alternatives
were described and key elements of the evaluation were presented in the preceding section.
Following is a brief summary of the agencies' comparative evaluation of the seven
alternatives. Additional detail regarding the entire development and evaluation of the SST
remediation alternatives is presented in the Feasibility Study (ARCO, 1995b), and additional
analysis is presented in the Responsiveness Summary (Appendix D) in response to specific
comments regarding the evaluation of alternatives.
1) Overall Protection of Human Health and the Environment: OU-wide Alternatives 1
(No Action) and 2 (STARS) were determined to not meet the threshold criterion of overall
protection of human health and the environment. Alternatives 3 (Limited Relocation/STARS)
and 4 (Limited Removal/STARS) provided significant improvements in overall
protectiveness, but were found deficient in demonstrating long-term protectiveness because of
reliance on STARS technology at extensive locations within the floodplain that would be
subject to erosion and failure during natural stream meander and high-flow events.
Alternatives 5 (Modified Relocation/STARS) and 6 (Modified Removal/STARS) were
evaluated to provide acceptable overall protectiveness in the short and long-term.
Alternatives 3 through 6 all included limited removal of instream sediments. Limited
removal of instream sediments was determined to be adequately protective of human health
and the environment, assuming that successful tailings/impacted soils remediation was also
completed. Alternative 7 (Total Removal) would provide the greatest overall protection of
human health and the environment.
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2) Compliance with ARARs: OU-wide Alternative 1 would comply with very few of the
ARARs established for the OU. Alternative 2 would not comply with major surface water,
groundwater, floodplain, or solid waste disposal ARARs. Alternatives 3 and 4 would be
expected to improve surface water quality in the near term, but would likely be a factor in
the inability of Silver Bow Creek to meet surface water ARARs in the long-term. This is
because MDEQ reasonably expects that STARS applied on a large scale in the floodplain will
fail to some degree over time, causing future contaminant loading to the stream. In addition,
the application of STARS within the floodplain does not meet the floodplain and solid waste
ARARs. Alternatives 5 and 6 comply with all ARARs with the exception of the floodplain
and solid waste management ARARs for the areas in which STARS would be applied in the
floodplain under these alternatives. As discussed in Section X below, the agencies have
determined that, under certain conditions, an ARAR waiver may be invoked for the limited
use of in-situ STARS treatment, leaving treated wastes in certain areas of the floodplain, as
contemplated under Alternatives 5 and 6. The more extensive use of STARS in the
floodplain under Alternatives 3 and 4 would not meet the criteria for invoking the ARAR
waiver, which are detailed in Sections IX and X below. Alternative 7 would meet all
ARARs without waiver.
3) Long-term Effectiveness and Permanence: OU-wide Alternative 1 provides no long-
term effectiveness. Alternative 2 would provide no improvement in groundwater quality
where tailings and groundwater are in contact and would have severe limitations in
effectiveness and permanence where STARS is applied to near-stream and floodplain
locations. Alternatives 3 and 4 are roughly equivalent in terms of long-term effectiveness.
Both offer major improvements over Alternative 2 by removing many of the tailings causing
groundwater contamination and much of the overland flow sediment loading to the stream.
Also, these alternatives remove contaminated fine-grained instream sediments. However, the
over-reliance on STARS technology in the floodplain reduces substantially any expectation of
long-term effectiveness and permanence of the remedy and the remedy would be expected to
unravel over time. Alternative 3 is somewhat downgraded in long-term effectiveness to the
extent it would rely on in-situ treatment of impacted railroad materials, which is considered
less effective than limited removal. Alternatives 5 and 6 greatly increase the expected long-
term effectiveness and permanence by removing most contaminant sources from the
floodplain so that any chance of re-entrainment of contaminated materials into the stream is
effectively eliminated. Contaminants would be left in the floodplain only in those locations
where they could be determined to be safe from future erosion and re-entrainment.
Contaminated fine-grained instream sediments would be removed under Alternatives 5 and 6,
providing adequate long-term effectiveness for that media. Alternative 7 provides the
greatest level of long-term effectiveness and permanence.
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4) Reduction of Toxicity, Mobility or Volume Through Treatment: OU-wide Alternative
1 provides no reduction of toxicity, mobility, or volume. Alternative 2 provides for in-situ
lime treatment of nearly 2 million cubic yards of tailings/impacted soils that would reduce
mobility and therefore phytotoxicity of certain metals in the soil. However, the preference
established in CERCLA is for treatment which "permanently and significantly reduces"
volume, toxicity or mobility of the contaminants. 42 U.S.C. § 9621(b)(l). The treatment
involved here could not be expected to be permanent if the lime amendments are physically
separated from the contaminants through erosion or other processes. Alternative 3 provides
reduced levels of in-situ treatment in comparison with Alternative 2, but provides more
permanent reduction in mobility by placing some treated contaminants into dry repositories
not subject to erosion by stream forces. Alternative 3 would treat contaminated railroad
materials by lime amendment and therefore further reduce the mobility and toxicity of those
contaminants. However, erosion of the amended materials, which would reverse the
treatment, is considered possible and even likely in certain locations. Alternative 4 has
considerably reduced use of treatment, but would achieve a reduction in mobility by placing
the materials in a dry repository. Alternative 5 has the maximum permanent reduction in
mobility through treatment because all materials would be treated, either in protected in-situ
locations or in the relocation areas. Alternative 6 would provide reduced levels of treatment,
but substantial permanent reduction in mobility by removing most contaminants from the
floodplain environment. The degree of reduction in toxicity, mobility, or volume through
treatment of contaminated instream sediments would depend entirely on whether excavated
instream sediments were treated during disposal. This would be possible under Alternatives
3 and 5. However, Alternatives 4 and 6 would attain permanent reduction of mobility by
placing the materials in secure repositories. Alternative 7 would provide no treatment, but
would accomplish permanent reduction in mobility by placing all materials in a secure
repository.
5) Short-term Effectiveness: Alternative 1 has no risks associated with implementation
since no action is taken, although future actions would be required because no remedial
action objectives would be met. Alternative 2 requires the least construction of any action
alternative and therefore provides greater short-term effectiveness, although this again would
be offset by the probability that a future action would be required. Alternatives 3 and 4
would have greater short-term impact on both nearby residents and the environment because
substantial excavation, haulage, and disposal would be required. Of the two, impact on the
local communities would be greater with Alternative 4 because considerably more truck
traffic would be necessary to transport e'xcavated materials to regional disposal areas.
Alternatives 5 and 6, by requiring excavation of about twice as much tailings/impacted soils
as Alternatives 3 and 4, would exhibit even greater short-term impacts during construction of
the remedy. Alternatives 3 through 6 are all considered relatively equal with respect to
short-term impact on the environment during construction. Alternative 7 would have the
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greatest risk to local communities and the environment during construction.
6) Implementability: All alternatives are considered implementable using standard
construction technologies. Alternative 2 is the most easily implemented action alternative
since it involves lime application and revegetation using standard construction and
agricultural equipment with very little work in areas of shallow groundwater. Alternatives 3
and 4 present greater difficulties because excavation of saturated tailings is required, although
standard construction dewatering techniques are expected to be adequate to facilitate
excavation. Alternatives 5 and 6 require more substantial excavation, although generally no
greater excavation under saturated conditions than for Alternatives 3 and 4. Alternatives 3
through 6 would all require some removal of instream sediments, which presents construction
difficulties but should not be substantially different than removal of near-stream tailings
saturated in the groundwater. In fact, excavation of saturated tailings and re-routing of the
stream into the excavated area will be the likely approach for dewatering the stream so that
excavation of instream sediments can proceed. Alternative 7 would require total removal of
instream sediments, which would present significantly greater difficulties than any of the
alternatives requiring limited removal of fine-grained instream sediments only. Alternatives
that require limited removal of railroad material would present implementation difficulties in
terms of coordinating construction during use of the active rail lines. Alternatives requiring
in-situ treatment of railroad beds could be more easily implemented. If rail haul of
excavated materials were used under Alternatives 6 or 7, difficulties in terms of coordinating
loading and haul operations with active railroad use would be encountered.
7) Cost: The combination of the media-alternatives into OU-wide alternatives presents the
range of total costs that could be expected if all four media (tailings/soils, groundwater,
railroad materials, and instream sediments) were remediated concurrently. The presentation
of costs in this manner eliminates duplicative cost elements, such as road building,
monitoring, and operation and maintenance (O&M), between the media.
Total costs include anticipated capital costs to construct the remedy and anticipated operation,
maintenance, and monitoring costs over a 30-year period (Table 13). The annual operation,
maintenance and monitoring costs have been discounted at a 7 percent annual capitalization
rate to obtain a present worth for those costs.
8) State Agency Acceptance: The State of Montana has been the lead agency for the
development of this record of decision and has selected an amended Alternative 5 as the
remedy contained herein. EPA has participated in the remedy selection process as the
support agency and has concurred with and adopted the remedy selection.
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Table 13
Total Volumes of Contaminated Materials Removed or
Relocated and Cost
Site- Wide
Alternative
Number
1
2
3
4
5
6
7
Volume Relocated to
Near Site Repository
(cy)
0
0
773,000
0
1,716,940
0
0
Volume Removed to
Regional Repository
(cy)
0
0
0
943,800
0
1,936,940
2740,300
Estimated
Cost
(millions)
$0.7-51.4
$13 - $24
$21 - $40
$27 - $47
$32 - $55
$39 - $66
$48 - $79
NOTE: Cost of the remedy described in this ROD are different from those listed in the FS. The
main reasons are (1) 50,000 cy has already been removed from ARCO's Demonstration Project II in
Subarea 4, (2) in Subarea 4 an additional 170,000 cy of additional tailings/impacted soils would be
treated in-situ, (3) use of a soils cover to protect human health in impacted areas outside the
floodplain, (4) the volumes of railroad materials to be removed or treated was better delineated, and
(5) Ramsay Flats has an additional 40,000 cy outside of the 100-year floodplain.
9) Community Acceptance: Public comment on the Remedial Investigation, Risk
Assessment, Feasibility Study, proposed plan (MDEQ, 1995a) and all other pertinent
documents was solicited during the formal public comment period extending from June 9,
1995, to August 7, 1995. An analysis of and responses to community comments are found
in the Responsiveness Summary (Appendix D).
During the public comment period, MDEQ and EPA received extensive comments from
ARCO, the potentially responsible party which conducted the RI/FS under an Administrative
Order on Consent issued by MDEQ. Comments received from ARCO indicate its opposition
to the preferred alternative No. 6 in the proposed plan (MDEQ, 1995a) and the selected
remedy, Alternative 5. In its initial comments, ARCO preferred the approach of a
combination of site-wide Alternatives 2 and 3; ARCO's proposed action consists primarily of
in-situ STARS treatment with removal of approximately 50% of the saturated tailings.
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ARCO comments with MDEQ and EPA responses are also found in the Responsiveness
Summary. •
As is clear, in the summary text and tables of Appendix D - Responsiveness Summary, the
majority of people and entities who commented on the proposed plan (MDEQ, 1995a)
supported the proposed alternative, Alternative 6, or preferred a more protective cleanup
(Alternative 7). Many people who commented believed that the 100-year floodplain was an
unsafe place to store tailings and that STARS technology long-term effectiveness was
extremely questionable.
However, comments submitted by ARCO, as well as representatives of local government and
various business entities in the area, vehemently objected to certain cost elements of the
proposed Alternative 6. Since cost is a primary concern and was a clear focus of certain of
the public comments received, the agencies have modified their proposal to substantially
reduce the costs of implementing the remedy, still allowing for the design and
implementation of a remedy that will protect human health and the environment and attain
ARARs, except as appropriately waived.
72
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
IX. SELECTED REMEDY
MDEQ and the EPA have selected a remedy that is intended to be the final remedial action
for the SST OU. This action addresses the principal threats and provides for treatment and
appropriate long-term management of contaminated tailings/impacted soils, instream
sediments, and railroad materials. Much of the treated materials will remain in the OU.
Consequently, the OU will require long-term management and monitoring.
Based upon consideration of CERCLA requirements, the detailed analysis of alternatives, and
public comments, MDEQ and EPA have determined that OU-wide Alternative 5, as generally
described in the Feasibility Study (ARCO, 1995b) and the proposed plan (MDEQ, 1995a),
with certain clarifications, represents the best balance of considerations using the selection
criteria and is the appropriate remedy for the OU. As presented here, this alternative will
protect human health and the environment by removing or treating sources of contamination
to soils, surface water, groundwater, and instream sediments. The long-term effectiveness
and degree of permanence of the selected remedy are high. MDEQ does not expect any
unmanageable short-term risks associated with this alternative. This remedy will comply
with all applicable or relevant and appropriate requirements, except where a waiver of such
requirements has been determined to be appropriate. This remedy is cost-effective because
the estimated costs are proportional to its overall effectiveness. This remedy uses permanent
solutions and treatment technologies to the maximum extent practicable. All contaminated
OU materials will be treated, therefore the selected remedy will also satisfy the preferences
for treatment as a principal element of the remedy and for on-site remedies established in
CERCLA. While certain other alternatives may better satisfy certain individual selection
criteria, the selected remedy best meets the entire range of the selection criteria and achieves,
in the determination of both EPA and MDEQ, the appropriate balance, considering OU
specific conditions and the criteria identified in CERCLA and the NCP. The criteria
described above are discussed in more detail in Section X, Statutory Determinations.
Components of Selected Remedy
Some refinements to OU-wide Alternative 5 have been made to clarify the criteria used to
require excavation of tailings/impacted soils, to more precisely identify excavation of
contaminated railroad bed materials, to delineate an end land use for Subarea 1, and to
specify institutional controls, monitoring, and maintenance requirements that will be used to
manage the Silver Bow Creek corridor in the future. This record of decision establishes
cleanup levels or physical criteria for the contaminants of concern. The principal
contaminants of concern at the SST OU are arsenic, cadmium, copper, lead, mercury, and
zinc.
73
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Tailings/Impacted Soils
Tailings/impacted soils are the primary contaminant source for the SST OU (Figure 15).
There are three predominant ways in which tailings/impacted soils contaminate other Silver
Bow Creek media: tailings in direct contact with groundwater; infiltration of precipitation
through tailings; and erosion of tailings into Silver Bow Creek (Figures 3-6).
To meet the established OU remedial action objectives, tailings/impacted soils will be
removed from the 100-year floodplain, as defined in the CH2M Hill (1989a) report, where:
(1) tailings/impacted soils are saturated by groundwater during any part of the year, (2) in-
situ Streambank Tailings and Revegetation Study (STARS) treatment cannot reliably
immobilize the contaminants, for example, due to the thickness of the tailings/impacted soils,
proximity of the tailings/impacted soils to groundwater, or lack of appropriate buffer
materials between the treated tailings/impacted soils and the groundwater, or (3) the treated
tailings/impacted soils could be eroded back into the stream by natural lateral stream
migration, avulsion, overbank flow or flood events and subsequent erosion.
Excavation of contaminated tailings/impacted soils from most areas within the floodplain is
required. The specific depth of excavation and the amount of excavated materials will be
determined by the agencies during remedial design/remedial action. The removed volume
will include all tailings/impacted soils continuously or seasonally saturated by groundwater
together with the tailings/impacted soils overlying these saturated tailings (collectively,
"saturated tailings"), as well as tailings/impacted soils subject to erosion and reentrainment
into the stream over time as determined by the agencies. These two criteria relate primarily
to the location of the particular tailings deposit; the agencies having determined that it is not
appropriate to leave treated tailings in place in such locations. In addition, in determining
whether other tailings must be removed, the agencies are to consider, for the particular
tailings deposit, such factors as the depth and thickness of the tailings deposit, the proximity
of the tailings to groundwater and the nature of any buffer materials/native soils between the
tailings and the groundwater. The basis for and the manner in which all of these criteria are
to be applied is further explained later in this section. Tailings that are not in a saturated or
threatened location and that are situated so that STARS treatment can reliably immobilize the
contaminants will be treated in-situ.
The total volume of saturated and overlying tailings/impacted soils to be removed is presently
estimated at approximately 700,000 cy. The total volume of tailings/impacted soils subject to
erosion and therefore to be excavated is estimated at approximately 850,000 cy. All
remaining tailings/impacted soils (approximately 950,000 cy) within the OU will be treated
in-situ with the STARS technology and will include appropriate monitoring, maintenance and
protection from washout or erosion from lateral stream migration and flood flows.
74
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Streamside Tailings
Operable Unit
Extent of Saturated
and Unsaturated
Tailings/Impacted Soil
and Conceptual
Repository Locations
Township 3N, Range 8W
Ko.kJ
Railroad
Ah.indonod Railroad
StrfM-m
IntPimittrnt
Si-clion 1 in
M,iirh t ine
Ivlf-nt of
Imparted Soil
phutus of 19fl-> a>
. In... nf Rapid Ci!\, SI
'v 1^4,000 sralp f)
Scale in Peel
0 500 1000 1500 2001
PW1 ' Ha^iil ' ' I
nm St»t» Ubrary
NRIS Natural Resource Information Syjte
Map t96«paa4i-l, S«ptefnbef 20,
-------
Township 3N, Range 9W
Township 3N, Range 8W
Streamside Tailings
Operable Unit
Extent of Saturated
and Unsaturated
Tailings/Impacted Soils
and Conceptual
Repository Locations
Road
Railroad
Abandoned Railroad
Stream
Intermittent Stream
Section I inn
Match 11 HP
Surface Water
Lxtent of lailinBi/
Imparted Soil
Tailings/Imparted Soil
saturate*) by ground water
Conceptual Repository
location
t
North
Stale ir- le«
500 InflO 1500 ?IK10
Figure 15b
Montana StBt(^JJbraiy__
Natural Resource Information System
Map tS6i>pu4a-2, September 20, 1995
-------
Township 3N, Range 9W
Streamside Tailings
Operable Unit
Extent of Saturated
and Unsaturated
Tailings/Impacted Soils
and Conceptual
Repository Locations
Road
Railroad
Abandoned Railroad
Stream
Intermittent Stream
Section I ine
Match tine
Surface Water
Ixtcnt of I.tilings/
Imparted Soil
Tailingv'lmrvuted Soil
(.stUMied hy ground water
("onrpptu.il Repository
location
t
North
Sral<- In I eel
| n sno i (xin I son ?oon
Figure 15c
Mont«n«_Stat»_ Library
NRIS Natural Rcsouree hfomadon System
Map *9f.r-paa*a-3, S-'pU'Tiln-t 20, 1995
-------
Township 3N, Range 9W
Streamside Tailings
Operable Unit
Extent of Saturated
and Unsaturated
Tailings/Impacted Soils
and Conceptual
Repository Locations
Koad
1 ' Abandoned R.iilrond
Slrcam
Intnrmitlfnt Slrcam
Match line
| Surfncf W'ntnr
p&'IPJ fcxtcnt of failings/
«^^ lm,wrted Soil
^^^H Iailings/lmp,irtcd Soil
^^^™ •v.itumled hy ground w
B^H G>nreptu/i1 Rpfxisitorv
je- and Himindwatcr infortnatum ptovidcd by
)a^> map i". from aerial pli.itin of 1984 and
giiirpd by Hoh7cxis, Inr., of Rapid Cih', SO,
i (.: S. C*'»'oniial Survry 1:24,000 wale DiRit
t
North
Scale in Heet
0 500 1000 1500 2000
Figure 15d
Montana 8t«t» Ubrarv
NRlS N>lural tomnM Infonmlion SyHen
Mip t9fef»a4*-4, S«pt«nb«f 20, 1995
-------
19
Township 3N, Range 9W
Streamside Tailings
Operable Unit
Extent of Saturated
and Unsaturated
Tailings/Impacted Soils
and Conceptual
Repository Locations
CZD
Surface Water
Extent of Tailings/
Imparted Soil
Tailings/Impacted Soil
saturated by ground water
Conceptual Repository
location
t
20
North
Montana State library
Map *
Figure 15e
S
21
-------
Streamside Tailings
Operable Unit
Extent of Saturated
and Unsaturated
Tailings/Impacted Soils
and Conceptual
Repository Locations
-— Road
!->-<'- Railroad
11 ' ' Abandoned Railroad
—;— Stream
Intermittent Stream
Section line
Match Line
Surface Water
Extent of Tailings/
Imparted SoJl
lalllngs/lmnafted Soil
saturated by ground water
Conceptual Repository
location
, MI. Sal
lilaii.
1991
r,,p»al">'i pp"i'id,-ri by
I phr»nn, of 1984 and
ii , df Rapirf City, SO,
,-v 1-74000 "-alt- Digital
North
0 500 1000 15no ?000
Figure 15f
Montana State Library
Map f96cpaj4i-6, Swlembet 20, 1995
-------
Streamside Tailings
Operable Unit
Extent of Saturated
and Unsaturated
Tailings/Impacted Soils
and Conceptual
Repository Locations
Tailings/Imparted Soil
saturated by ground water
-------
Streamside Tailings
Operable Unit
Extent of Saturated
and Unsaturated
Tailings/Impacted Soils
and Conceptual
Repository Locations
I | Surface Walcr
E3&.U&.S3 Imparted Soil
j^HI lai lings/Imparted Soil
^^^^™ saturated hy ground water
^^^^B Conceptual Repository
^^^™ location
-------
Township 3N, Range 9W
Sireamside Tailings
Operable Unit
Conceptual Removal
and STARS locations
Railroad
Abandoned Kaitro.id
Stream
Intormittrnt Stream
Srt-tlon line.
SurfiU e. Watpr
IvTrnr of Tailings/
to be Rpmovrti
to he lr(
hv SI ARS
I'l^t'".-' .V,iS [ir,,v,,;,-|) |,v :hi" Mi.rl.U.8 |Vtlt
Ml I >ivi'..rT>n-f»Al Qiidlily, Snpclfimd S^lmn.
$*•*• rn.ip K friun a.-,-,A\ pholos nf 19fl4 and
199' HiKirifr^ hv HdH/ims. Inc., of Rapid Gty,
.ITU! lri.ni I. S. Oo'riRifill Si'rvCV I:?4,000 Jtalf
'
t
North
Srale In reel
0 500 1000 1500 2000
Figure 16a
Mpnt«r>«_St.t» JJlMry
^.NRIS NiMnl Raom-c hftraulioii Sysnn
Map #96epu4b-1, September 20, 1995
-------
Streamside Tailings
Operable Unit
Conceptual Removal
and STARS locations
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Table 14 presents the estimated volumes to be removed by subarea. Figure 15 portrays
examples of possible relocation repositories and saturated tailings, while Figure 16 illustrates
potential removal and in-situ STARS treatment locations.
Table 14
Sammary of Estimated Media Specific Removal Volumes
for SST Remedial Action
(cy)
Subarea
1
2
3
4
Total
failings/Impacted Soil
{total volume of
tailings/impacted soil)
285,000
(285,000)
529,000
(808,000)
160,000
(160,000)
576,000
(1,300,000)
1,550,000
(2^50,000)1
Instream
Sediments
15,000
27,000
5,600
29,700
73,000
Railroad
Materials
17,000
25,000
30,000
0
72,000
1 The site contains approximately 2.5 mcy of tailings/impacted soils of which 2,220,000 cy are in the current 100-year
floodplain. 280,000 are located within Ramsay Flats and out of the present 100-year floodplain. Approximately 50,000
cy was removed from ARCO's Demonstration Project n in Subarea 4. All volumes are in cubic yards (cy).
Excavated tailings/impacted soils will be relocated to safe, local repositories clearly outside
of the 100-year floodplain as defined by CH2M Hill (1989a), provided that appropriate
locations can be obtained and an appropriate institutional controls/maintenance program can
be implemented (see Contingency Measures at the end of this section). Tailings/impacted
soils placed in the relocation repositories will be fully treated with lime amendments in lifts
and will be revegetated in accordance with the STARS technology.
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Instream Sediments
A portion of the tailings/impacted soil eventually becomes incorporated with instream
sediments at the bottom of Silver Bow Creek. These sediments are highly contaminated.
Concentrations are between 10 and 65 times higher for arsenic, cadmium, lead, zinc, and
400 times higher for copper than are found in other area streams which drain highly
mineralized geologic areas (Essig and Moore, 1992). Numerous researchers have
demonstrated that while in the stream, these sediments severely limit the number and types of
benthic macroinvertebrates which live in the stream sediments, and these sediments could act
as a source of contamination to future cleaner surface water (Ingersoll et al., 1995b,c;
MacDonald et al., 1995; Smith et al., 1995; Woodward et al., 1995). Like tailings
themselves, the majority of contaminated sediments vary in size from a coarse sand to a very
fine silt or clay (PTI, 1989).
To meet the remedial objectives for the SST OU, MDEQ and EPA have determined that all
contaminated fine-grained sediments will be removed. Fine-grained (defined here as all
instream sediments equal to or less than one millimeter) instream sediments located in all
depositional areas will be removed and placed in repositories outside the floodplain with the
tailings/impacted soils and railroad materials. This size fraction was identified because it
corresponds with the size of the tailings/impacted soils and contains the bulk of instream
contamination. Specific volumes and locations to be excavated will be determined by the
agencies during remedial design. This sediment volume is presently estimated at 73,000 cy
(Table 14), although recent mapping performed by ARCO (Maxim, 1995) has indicated that
a lesser volume may be present (approximately 25,000 cy).
After removal of contaminated instream sediments, the channel bed and streambank will be
reconstructed to an appropriate slope and other critical dimensions with materials of
appropriate size, shape and composition. This reconfigured streambed will contain suitable
bedform morphology (riffles, bars, pools, etc.) for aquatic habitat.
Instream sediment monitoring will be performed during and after the response action to
verify the locations and concentrations of contaminated instream sediments, and
macroinvertebrate abundance and diversity, as well as appropriate geomorphic bed
configuration. Maintenance to address continuing sediment contamination over time may be
necessary, depending on the results of long-term monitoring. Streambanks will require
adequate growth media to allow for immediate establishment of a healthy riparian vegetative
system to protect the remedy from high flows.
86
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Railroad Materials
Certain portions of one abandoned historic railroad embankment and two operating railroads
along Silver Bow Creek were constructed with mine and mill wastes from the Anaconda
Company operations such as waste rock and slag. This material represents a source of
contaminants to Silver Bow Creek via runoff, to groundwater via infiltration, and to
recreationists who might use the abandoned embankment as a trail for walking or biking.
The remedy will excavate, treat and/or cover all contaminated railroad bed materials that
pose a risk to human health or the environment. All concentrate spills, which are the
primary human health concern, will be removed and disposed in an appropriate and secure
disposal facility in accordance with any applicable RCRA requirements. The in-situ STARS
technology or soil capping is expected to be appropriate for all other areas of the inactive
grade presenting human health risk and not likely to be eroded by the stream. Railroad
materials that directly impact the stream either at bridge abutments or where these materials
form a streambank will be excavated and disposed in repositories outside the floodplain along
with the tailings/impacted soils and instream sediments. The actual amount and methods of
excavation and/or treatment will be determined during remedial design. The estimated
volumes designated for removal have been refined since the release of the proposed plan
(MDEQ, 1995a). The estimated volume of excavated railroad materials is 72,000 cy (Table
14).
Monitoring and maintenance of the remediated railroad areas and materials will be required
to ensure that contaminant sources are not exposed from erosion and do not cause
contaminant loading to the stream.
Ground and Surface Water
Generally, groundwater within the OU flows towards and into Silver Bow Creek. Elevated
concentrations of copper and zinc and exceedances of drinking water standards for arsenic
and cadmium are present in groundwater (ARCO, 1995a). Surface water and instream
sediment quality is impacted by discharging contaminated groundwater (Benner et al., 1995).
While Silver Bow Creek ground and surface water are primary receptors of SST OU
contamination, no separate remedial action is being prescribed for these media. Remedial
activities for other SST OU media under this record of decision and for sources of
contaminants upstream/offsite under other cleanup actions will limit further releases to
ground and surface water with the goal of ultimately attaining ground and surface water
standards within the OU. The prescribed removal of tailings/impacted soils, fine-grained
instream sediments, and railroad materials will allow for the attainment of instream sediment
and surface water objectives and standards, over time. Removing the source of groundwater
contamination by addressing the tailings/impacted soils and railroad materials, will allow
87
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
contaminants in groundwater to attenuate over time through dilution, adsorption,
precipitation, dispersion, and should allow eventual attainment of groundwater standards.
Long-term monitoring of surface water and groundwater is a critical element of the remedy.
Surface water will be monitored for compliance at numerous points in the OU to ascertain
possible contaminant loading from onsite/nearsite contaminant sources. Groundwater will be
monitored at locations of documented or reasonably suspected groundwater contamination, all
relocation areas, and other locations where STARS treatment has been applied.
Monitoring, Coordination, and Schedule
An institutional controls program, which must be funded on a permanent basis as part of the
remedy, will be coordinated through a joint effort of the Butte-Silver Bow and Anaconda-
Deer Lodge local governments. Institutional controls, monitoring, and maintenance will be
integrated into a Silver Bow Creek corridor management program. The program will be
established and maintained in a manner to be approved by the agencies that will ensure that
all aspects of the OU remedial action, both within and outside of the floodplain, are
maintained for the long term, that future land uses in the area are consistent with the
scenarios upon which cleanup level decisions for this action have been based (recreational),
and that institutional control, monitoring and maintenance mechanisms will be adequate to
ensure protectiveness over the long term.
Butte-Silver Bow County and ARCO are initiating research on constructed wetlands as a
potential treatment technology for waste water nutrient discharge and stormwater metals
contamination. To coordinate with this research, the end land use in Subarea 1 has been
delineated as wetlands. After removal of all identified contaminant sources (tailings/impacted
soils, instream sediments, railroad materials, etc.), in Subarea 1, reconstruction of the
Subarea will be designed to incorporate use of the area as wetlands. Constructed wetlands
may be used as a treatment system for nutrient and/or metals treatment, if use of such
wetlands treatment in this area is ultimately determined to be appropriate.
Construction of the proposed remedy will be coordinated with other cleanup activities along
Silver Bow Creek. Releases of contaminated sediments and surface waters prior to, during,
and following remedial action, which might re-contaminate Silver Bow Creek, will be
suitably controlled and treated. The design and schedule of the OU remedy will be
coordinated with the design and installation of upstream sediment control basins and other
cleanup activities. If adequate upstream control facilities are not in service at the time of
initiation of construction of this remedy, then additional sediment control and treatment
facilities will be provided as a part of this remedy.
-------
STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
The State of "Montana and ARCO are engaged in litigation, brought under CERCLA,
involving natural resource damages in the Upper Clark Fork River Basin (State of Montana
v. Atlantic Richfield Company. U.S.D.C. Case No. CV-83-317-H). That litigation includes
claims for damages for injuries to natural resources within the SST OU. As a result of that
litigation, the State has developed a restoration plan which would provide for certain actions
to restore the injured resources in the OU. (See "Restoration Determination Plan, Upper
Clark Fork River Basin," October 1995). As provided by CERCLA and applicable
regulations, the restoration plan seeks to accomplish more extensive goals than the remedial
action, and would do so by addressing the same contaminated areas. The implementation of
the final remedial action plan for the SST OU will be coordinated to the maximum extent
possible with any implementation of the State's restoration plan for Silver Bow Creek, in
order to maximize the benefits of both efforts and to avoid duplication of effort. Such
coordination could include, for example, adjustment of schedules for specific portions of the
actions, the combination or coordination of specific actions under the two plans, or allowing
a more extensive restoration action to be implemented in certain areas, as long as the
restoration action would accomplish all of the goals of the remedial action in those areas.
Description and Limitations of the Streambank Tailings and Revegetation Studies (STARS)
Technology
In 1986, the Montana Department of Health and Environmental Sciences (now MDEQ)
initiated the Streambank Tailings and Revegetation Studies (STARS) to determine the
feasibility of chemically amending tailings materials in-situ adjacent to Silver Bow Creek.
The purpose was to attempt to develop an effective alternative less costly than removal.
The purpose of the study was three-fold:
1) Buffer the acid produced by metal sulfides present in the tailings materials.
2) Reduce the mobility of metals that leach through the tailings.
3) Provide a suitable growth medium that will support a vegetative cover
consisting of grasses and forbs. Woody species such as willows were not
investigated in the STARS study. The vegetative cover would act to reduce
the amount of moisture that could percolate through the amended tailings,
reduce erosion from surface runoff, and reduce wind blown dust.
The study was conducted by Montana State University's Reclamation Research Unit and
Schafer and Associates in three phases. Phase I was designed to test a variety of chemical
amendments on tailings in the laboratory and to determine the combination of amendments
that best reduced the concentration of metals measured in water leached through the amended
89
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
tailings. In conjunction with the chemical testing, greenhouse studies were undertaken to
determine the mixture of plant species that would grow best in amended tailings. Phase n
consisted of field trials to test the most effective chemical amendments determined in Phase
I. Several different amendment mixing techniques were tested during this phase to maximize
the depth to which the amendments could be incorporated. Several different seed mixtures
were also tested based on the results of the greenhouse trials. Phase HI consisted of
collecting various types of soil, water, and vegetative data over the course of three years and
evaluating each of the treatments applied.
The agencies determined that the application of STARS amendments were effective: in
reducing runoff production from treated tailings; for reducing (but not eliminating) the acid
produced by metal sulfides present in the tailings materials, reducing the toxicity or mobility
of most metals that leach through the tailings; providing a favorable growth medium that will
support a vegetative cover; reducing the amount of moisture that could percolate through the
amended tailings through vegetative management of the annual soil water budget; and
reducing wind blown dust.
The agencies discuss below specific concerns which limit the implementation of the STARS
technology in the SST OU. The STARS treatability study itself was a scientific, quantitative
study which was limited in its scope. However, in evaluating the use of the technology as
part of this remedy, the agencies have to consider the full range of issues involving
implementation of STARS in the floodplain.
1. STARS amendments do not appear to completely eliminate
contaminant movement in porewater.
Data collected during the study demonstrated that soil pore water quality was highly variable
from treatment to treatment and year to year. General trends in soil pore water chemistry
indicated that amended plots generally showed an increase in pore water pH and a decrease
in the concentrations of most metals. Due to funding limitations, porewater data was limited
to three sampling events without the benefit of replicated instrumentation. Because of this,
as well as difficulties in appropriately mixing amendments deeper in the profile, only the 40
cm depth increment (the shallowest depth monitored) conclusively demonstrated effective
reductions in porewater metals concentrations. Arsenic concentrations were observed to
increase at depth in the amended plots at some of the monitored sites, which may be
attributed to the greater solubility of arsenic with increasing pH. The metals aluminum,
iron, and copper were substantially less soluble in soil pore water as pH increased while
manganese, cadmium, and zinc concentrations did not have a clear correlation with
increasing pH until pore water pH could be raised to levels greater than 7.0. Much higher
amendment rates may be needed to substantially reduce concentrations of cadmium,
manganese and.zinc. Because of these findings, there is some uncertainty in the
90
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
effectiveness "of STARS to prevent the movement of some contaminants through the vadose
zone.
2. STARS amendments do not mitigate the migration of metals
from tailings/impacted soils saturated by groundwater.
Two principal hydrologic processes govern the migration of metals from tailings to
groundwater: first, downward movement of precipitation (infiltration) through tailings to the
saturated zone; and second, the inundation of tailings by groundwater.
The STARS technology was never intended to remediate groundwater. The STARS study
was developed to reduce the mobility of metals in the amended tailings and enhance water
use within the rootzone, with the intent of limiting vertical movement of vadose zone water
and contaminants. There is still much debate as to the ability of the STARS technology to
effectively manage the soil water budget resulting in a substantial reduction in infiltration to
groundwater. One associated condition of considerable concern is implementing STARS in
riparian areas of shallow groundwater (12 to 18 inches below ground surface) because plant
roots may tap the groundwater table, rather than use vadose zone moisture. Reestablishment
of a vegetative cover, even if it successfully eliminates infiltration to groundwater, is not
capable of addressing metals mobilized by the saturation of tailings/impacted soils by
groundwater. OU groundwater was found to fluctuate approximately two feet. In many
areas a large volume of tailings/impacted soils are permanently saturated by groundwater or
within this two foot fluctuation and are therefore seasonally saturated by groundwater.
Saturation of tailings/impacted soils by groundwater releases metals weakly bound to these
materials as well as metals associated with acidic vadose zone water.
In addition, it has never been determined if lime amendments can be successfully
incorporated into saturated soils. Neither STARS nor any other demonstration studies in the
Clark Fork basin investigated this issue or the types of plant species that might be used in
saturated conditions. The STARS test plot at the Manganese Stockpile site failed, at least
partly because of the saturated conditions at the site during long periods. Also, in MDEQ's
analysis of the STARS treatment in saturated tailings conditions, two critical factors
concerning STARS implementation indicate that STARS will not be effective: 1) The
equipment designed to mix lime amendments into tailings is not likely to be able to
adequately mix below the water table; and, 2) Because the highly soluble calcium oxide or
calcium hydroxide is used to make up 40% of the STARS amendment, it is likely to be
removed from the amended profile in ground water in those amended tailings that are
seasonally saturated, primarily during the first year after amendment.
To expand on the first critical factor, mixing STARS amendments below the water table was
not demonstrated at any of the ARCO demonstration projects (Demonstration Projects I, n,
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
and HI), nor was lime mixed below the water table during Phase n of the STARS
investigation at the Manganese Stockpile. MDEQ believes that adequate mixing of lime
amendments in ground water would not occur due to the inherent problems of plowing
saturated materials and the physical process used to deliver the lime to the tailings to be
mixed. Whether saturated tailings were amended during implementation of the Governor's
Project could not be confirmed in the published documentation of the project.
The second critical factor is based on the solubility of calcium oxide or calcium hydroxide
amendment. When mixed with soil, the pH generally rapidly rises to 9 to 10 standard units
after mixing and tends to elevate soil pH for several months. As ground water rises into
recently amended tailings, some quantity of the soluble calcium amendments are likely to be
solubilized and removed from the soil as the water table lowers, even where ground water
has a near neutral pH and is slightly alkaline. While no data is available to quantify the
amount of amendment that could be removed, MDEQ believes that the uncertainty associated
with this issue, at the very least, limits the application of STARS to tailings located greater
than two feet above the 1992 low water table elevation.
Contaminated groundwater results in continuing, long-term contamination of Silver Bow
Creek's surface water and instream sediments. Where contaminated groundwater has the
potential to discharge to the stream, metals have been shown to precipitate/adsorb on the
stream substrate (instream sediments) and potentially remain a source of contamination to
surface water. The STARS study was never designed to investigate this contaminant
migration pathway.
3. Contaminants could continue to be transported to Silver Bow
Creek from a treated floodplain by various hydrologic
processes.
Overbank flows and channel migration could be expected to re-entrain amended tailings into
the stream and instream sediments, thereby subjecting the tailings to oxidation. This is
especially true in the areas immediately adjacent to the active stream channel where channel
migration and streambank erosion processes are most prevalent. In addition, under flood
conditions, the stream channel is at the greatest risk of making major changes in channel
location by avulsion or "jumping" into abandoned channels or migrating into areas
susceptible to erosion. Once a STARS treated area is eroded, the amendment is likely to
separate from the treated tailings and basic geochemistry suggests that, over-time, these
tailings would produce acid and re-mobilize the metals which would be expected to become
bioavailable. The impacts of these bioavailable metals would severely limit the ability for
remedial actions to meet specified ecologic and possibly surface water quality objectives.
4. Long-term effectiveness
92
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
There is substantial debate regarding the long-term effectiveness and permanence of STARS
treatment. The STARS study was designed to compare treatments against untreated tailings
conditions and to measure relative differences between treatments. Data collected during the
three year monitoring period reasonably represents the short-term effects of the treatments.
However, it is conceivable that actual long-term effects may be different than trends evident
in the three years of data presented in the STARS reports (MDOJ, 1995).
In any event, no single treatment proved to ameliorate metals contamination for all
environmental matrices or for the range of environmental conditions represented in the study.
Consequently, it is apparent that the STARS treatment is not suited for all the conditions
present at the SST OU. The agencies believe that STARS is best suited and has the fewest
limitations in tailings locations well away from the active stream channel and well above the
seasonal high ground water elevation.
Criteria For Application of the Streambank Tailings and Revegetation Study (STARS)
Technology
i
A critical element of the remedy selection is the determination of which tailings may be left
in place and treated with the STARS technology and which tailings must be removed from
the floodplain before being treated with STARS. After evaluating STARS fully and
considering the limitations inherent in such treatment, MDEQ and EPA have identified
certain criteria which define where within the floodplain STARS may effectively and reliably
be implemented.
The STARS study was designed to compare treatments against untreated tailings conditions
and to measure relative differences between treatments. Data collected during the three year
monitoring period reasonably represents the short term effects of the treatments. Because of
the extreme heterogeneity encountered at the study sites, however, many statistical
comparisons between treatments can not be supported at this time. It is possible that actual
long-term effects may be different than trends evident in the three years of data presented in
this report. Also, no one single treatment proved to ameliorate metals contamination for all
environmental matrices or for the range of environmental conditions represented hi the study.
The criteria for determining that specific tailings/impacted soils may be STARS treated in-
situ in the floodplain are:
1) The tailings/impacted soils involved cannot be saturated in groundwater during
any part of the year. The SST OU Remedial Investigation delineated the
location and volumes of saturated tailings/impacted soils (ARCO, 1995a).
Generally, groundwater seasonally fluctuates slightly over two feet hi the OU.
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STREAMSIDE TAILINGS OPERABLE UNIT ROD • DECISION SUMMARY
Groundwater movement into and out of tailings, even in STARS treated
tailings, will cause continued contaminant migration to groundwater.
2) STARS treatment must effectively immobilize the contaminants in the
tailings/impacted soils. The STARS study identified the ability of the
technology to successfully immobilize most contaminants of concern in the
short term where the amendments can be adequately mixed into the tailings
and soils. The depth to which the necessary soil amendments have been
demonstrated to be effectively incorporated is limited to two feet. Future
techniques may prove capable of effectively incorporating amendments to a
greater depth. Moreover, because the STARS technology may not completely
immobilize cadmium and zinc and may potentially increase the mobility of
arsenic, a minimum thickness of native soils material between STARS treated
tailings and groundwater is needed to act as a protective buffer. The nature
and chemistry of the buffer materials must be considered in determining how
much of a buffer constitutes adequate separation to prevent migration of
contaminants into the groundwater. Tailings deposits that are thin enough that
underlying native soils can also be tilled into the tailings is a positive
consideration under this criterion.
3) The tailings/impacted soils cannot be located where they may be eroded and
re-entrained into the stream system through normal stream processes or major
flood events. STARS treated tailings could be transported into the stream
system if eroded during natural stream channel migration, avulsion or as a
result of overbank flows. Erosion and inundation from bank-full and flood
events can be estimated based on a number of sources including CH2M Hill's
Silver Bow Creek - Flood Modeling Study, which analyzes the lateral extent
and water velocity of various flood events from regular bank-full to greater
flood events. Another uncomplicated method of determining where the stream
might meander to is to examine where the stream has been in the recent past.
Where the STARS technology is applied, regression or failure of a well-established
vegetation could occur in the future. Failure could be due to one or more of the following:
(1) weathering of pyritic wastes producing acidity, which in turn alters the availability of
plant nutrients and toxic metals; (2) depletion of nutrients required for growth; (3) extreme
weather or surface water flow conditions; and, (4) upward migration of acidity, metals, or
salts into the amended zone (MDOJ, 1995). Because numerous repositories, which will be
treated with the STARS technology, will be located near the floodplain in several areas along
the length of the stream, and because in Subareas 2 and 4 large areas of tailings will be
treated in-situ with the STARS technology at the edges of or outside of the floodplain, a
permanent monitoring, management, and maintenance program will be an integral part of this
94
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
remedy. Monitoring, management and maintenance will address vegetative performance on
both STARS treatment areas and remediated streambanks, streambank stability and channel
meander, and ensure that metals are immobilized at in-situ remediated areas. Each
repository will be monitored through vegetative performance, vadose zone, saturated zone,
and overland flow monitoring. The ultimate number and locations of relocation repositories
will be determined and approved by the agencies during remedial design.
Replacement fill will be required in most locations where tailings/impacted soils are
removed. Replacement fill and streambank reconstruction with suitable growth media having
an appropriate texture and particle size distribution will be required. To the extent
practicable, clean material excavated from nearby repositories will be used for replacement
fill. A key to long-term streambank stabilization will be establishment of mature riparian
vegetation. Grass, forb, willow, and tree species will be specified based on local climatic
conditions, proximity to stream channel, and ability to produce dense root systems at
maturity. The overall topography of the replacement fill material will be appropriately
sloped toward the stream channel, with the goal of creating geomorphic stability.
While the exact delineation of STARS-treated areas will be established during remedial
design/action, these three criteria were used in analyzing each subarea to preliminarily
determine where STARS can be expected to effectively achieve protection of human health
and the environment.
In Subarea 1, 67% of tailings/impacted soils are saturated by groundwater. The confined
nature of the floodplain and the steeper stream gradient in Subarea 1 increase the probability
of adverse flood impacts on STARS treated areas. The negative effects from saturated
tailings, streambank erosion, and likely future overbank deposition of sediment on treated
areas precludes implementing STARS in this subarea. Reconstruction of excavated areas in
Subarea 1 will be designated to accommodate wetlands. These constructed wetlands will be
designed in such a manner that they will have the potential for use as organic or inorganic
contaminant treatment, if appropriate.
The evaluation of overall protection for Subarea 2 is the same as for Subarea 1 except for a
considerable quantity of tailings/impacted soils which lie outside the floodplain. In the
Ramsay Flats area, an estimated 280,000 cubic yards of tailings/impacted soils lie outside
this demarcation. Because these tailings/impacted soils are located outside the floodplain. are
generally unsaturated by groundwater, are finer grained in size, and are located, hi areas,
above a rich organic soil horizon which helps attenuate metals movement, the application of
STARS treatment in this defined area should meet remedial action objectives (RAOs).
However, the STARS treatment technology is presently only effective in tailings 2 feet thick
and less. With present technology tailings thicker than 24-inches will need to be removed or
relocated. These in-situ STARS treated areas will by required to be completely protected
95
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
from erosion. An estimated 529,000 cy of tailings/impacted soils will be removed from this
subarea (Table 14).
Because of-the confined nature of the floodplain in Subarea 3 (a relatively steep, narrow
canyon), the analysis of these criteria is much the same as for Subarea 1. Overall
protectiveness would be compromised by saturated tailings, streambank erosion, and likely
future overbank deposition of sediment on treated areas, precluding implementation of
STARS in this subarea. An estimated 160,400 cy of tailings/impacted soils will be removed
from this subarea (Table 14).
In Subarea 4, the potential for flood impacts to STARS treated tailings at the edge of the
floodplain is smaller as a result of the wide floodplain, which allows dispersion of stream
energy to a much greater degree than in the upper three subareas. In the near-stream areas
there is ample evidence of stream migration in the recent past. Some of the channels are
activated during spring snowmelt on an annual basis (MDOJ, 1995). The presence of buried
soils and, in many places, the separation of tailings from groundwater is adequate to
minimize the movement of metals through the vadose zone. Thus the potential effectiveness
of STARS treatment appears to be greater in this subarea than the other three subareas. In
Subarea 4 an estimated 724,000 will be treated in-situ with the STARS technology while
576,000 will be removed to a relocation repository (Table 14).
Estimated Costs of the Remedy
The total present worth cost of Alternative 5 was estimated in the feasibility study in the
range of $32 million to $55 million (ARCO, 1995b). The estimated cost of the agencies'
selected remedy, a modified Alternative 5, is estimated to be $24 to $46 million. These
costs are.substantially less than originally estimated because of the near stream repositories,
the estimated removal volumes of tailings/impacted soils are somewhat lower due to better
defined removal criteria, a more accurate quantification of railroad materials that will be
treated or removed, and the determination that soil cover materials will not be needed for
potential residential areas outside the floodplain. The cost uncertainties that are associated
with this revised estimate are listed in Tables 15, 16, amd 17.
Cost Uncertainties
The agencies believe that the estimate of costs for this alternative as presented by ARCO in
the Draft FS report are accurate for decision making purposes. Although the agencies
believe that several important line item costs are significantly over-stated in the FS,
considering the magnitude of this remedial action and the complexity of OU conditions, the
96
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
cost for this remedial action has been reasonably delineated (Table 14).
The operation and maintenance costs beyond the thirty year time frame used in the FS, and
the discount rate used to evaluate the present worth of operation and maintenance costs are
important considerations. MDEQ recognizes that the 7 percent annual discount rate used in
the FS and calculation of present worth costs without inclusion of inflation, as required by
the NCP, tends to underestimate future costs. Discounting makes the costs of remedies that
rely more heavily on future actions such as operations and maintenance, appear less costly
than capital intensive remedies.
Some elements of the remedy will be further refined during remedial design. Listed below
are cost elements on which ARCO and MDEQ differed when developing the SST OU
Feasibility Study. The cost range estimated in Tables 15 - 17 is based on MDEQ's
determinations regarding these issues.
• Quantities of Tailings/Impacted Soils - Quantities of tailings/impacted soils as
calculated by NRIS were used to develop the cost estimates for removal. The
quantities of saturated tailings include both the saturated tailings and the tailings that
overlie the saturated tailings. This quantity was also calculated by NRIS. The
accuracy of locations and amounts of tailings/impacted soils is restricted by limited
data points (Table 15).
97
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Table 15
Remedial Alternative Cost Summary - Tailings/Impacted Soils
Streamslde Tailings Operable Unit
Activity
Roadbulldlng (Intcnul)
Roddbuildtaj (external)
Clear/Grub (>lle)
G radios (.IK)
Clear/Grub (relocation Area)
Grading (relocation area)
Soil Cover (relocation area)
Dozer/Loader/Trackhoe
Haul (on-alte, excavated T/S)
STARS
dean Fin Streambank Replacement
Clean Fin Streambank Placement (Dozer)
Riprap (include* placement)
Reveg (relocation area)
Revegetation (lite)
Engineering De*ign/Con*tnjction Oventte
Mob/Demobilization
Conatruction Overhead
tnttitutional Control*
Operation and Maintenance
Roadbuilding (internal)
RoadbuUdlng (eirtemal)
aear/Grub(iite)
Grading (lite)
dear/Grub (relocation area*)
Grading (relocation area*)
Soil Cover (relocation area)
Dozer/Loader/Trackhoe
Haul Unit Co*t (on-.l»)
STARS
Clean Fffl Streambank Replacement
Clean Fttl Streambank Placement (Dozer)
Riprap (Include* placement)
Reveg (Ute)
Revegetation (relocation area*)
Engineering De*ign/Conatructlon Ovenlte
Mob/Demobilization
Cofutruction Overhead
Institutional Control*
Operation and Maintenance
Mtiinui Maxlmun Mudjamm Maidamm
Co*t Coil Coat Coil
U«it U*lt Exleaded Extended
Quality Umll Price Price Price Price
Subarea 1: Partial Relocation, Partial STARS Treatment and ICs
U mUe $23,100 $31200 $123,760 $162,240
SJ mtte $1,200 $20,200 $42,640 $105,040
153,6 acre $600 $1300 $92,160 $199,610
153.6 acre $350 $750 $53,760 $115,200
69 acre $600 » 1,300 $41,419 $(9,740
69 acre $350 $750 $24,161 $51.773
0.0 cy $630 $127 $0 $0
215,000 cy $2.90 J4.20 $126,500 $1,197,000
285,000 cy $0.13 $1.11 $236,550 $316.350
0.0 acre $4,000 $7,100 $0 SO
15,500 cy $0.13 11.11 $70.965 $94,905
85,500 cy $2.90 M.20 $247,950 $359,100
395 cy $25 $30 $9,975 $11,150
69 acre $4,000 $7,100 $276.125 $490.121
153.6 acre $500 $1,000 $76,100 $153,600
Subtotal $2,122,4*4 $},M6,6M
1 b 13* 18* $275,946 $602399
1 1* 1% 6* $2X227 $200,796
1 1* 8* 15* $169,113 $501,990
1 1* 138,500 $82.500 $31,500 $12.500
11* 1* 2,110,796 2,110,796 $232,188 $232.111
StttoOl $717,67* SMlMtt
Tot*l S2JM,1M S4.966.M1
Subarea 2: Partial Relocation, Partial STARS Treatment and ICa
5.6 mUe 523,800 $31,200 $133.210 $174,720
5.6 mUe $1,200 520,200 $45,920 $113,120
320 acre • $600 $1300 $192.000 $416,000
320 acre $350 $750 $112.000 $240.000
128.1 acre $600 $1300 $76,179 $166.571
121.1 acre $350 $750 $44,846 $96,099
0.0 cy 56.30 $127 $0 $0
529.000 cy $2.90 $4.20 $1,534.100 $2,221,800
529,000 cy 50.83 $1.11 $439,070 5587,190
ITS acre $4,000 $7,100 $700,000 $1,7(5.269
158,700 cy 50.83 $1.11 $131.721 $176,157
151,700 cy $2.90 $4.20 $460,230 $666,540
0.0 cy $25 $30 $0 $0
320 acre $500 $1,000 $160,000 $320,000
128.1 acre $4,000 $7,100 5512,526 $909,734
SMfcroMl S4.5U372 $7J75,1»
1 I* 13* 18* $590,534 51,417,176
1 b 1* 6* $45,426 $472392
1 1* 1* IS* $363,406 51,180,980
1 1* $112,000 $240,000 $112,000 $240,000
32* U 2,110,796 2,110.796 $675,455 $675.455
SvMotef $1,71*421 S3.*M,002
Totll M.329,391 $11,«51,101
Minimum Muuuua Minimum Maxuaun
Co*l Co*t Coal Coal
Uall Unit Exteaded Extended
Quality U>lt Price Price Prke Price
Subarea 3: Partial Relocation, Partial STARS Treatment and ICa
5 mUe $23,800 531,200 .$119,000 $156,000
5 mtte 58,200 $20400 $41,000 $101,000
92 acre $600 $1300 $55,200 $119,600
92 acre $350 $750 $32,200 569,000
38.8 acre $600 $1,300 $23,253 $50,381
38.8 acre $350 $750 $13,564 $29,066
0.0 cy $6-30 $1.27 $0 $0
160,000 cy 52.90 54.20 $464,000 $672,000
160,000 cy $0.13 $1.11 $132.100 $177.600
0.0 acre $4,000 $7,100 $0 $0
41,000 cy 50.83 $1.11 539,840 $53,280
41.000 cy $2.90 $4.20 $139,200 $201.600
1.971 cy $25 $30 $49,450 $59340
92 acre $500 $1,000 $46,000 $92,000
31.1 acre $4,000 $7,100 $155.017 $275,156
Subtotal $1,>U,S24 S2,*56,I22
1 1* 13* IS* $170361 5370,084
1 b 1* 6* $13.105 $123361
1 b I* 15* $104.142 $301,403
1 b $21.000 $45,000 $21,000 $45,000
6* b 2,110,796 2,110.796 $126,641 $126,641
S*ttoM $t»,Ml S97I.4M
Tottl $1.744,487 U,619,5U
Subarea 4: Partial Relocation, Partial STARS Treatment and ICa
6.8 mUe 523,800 $31,200 $161,840 $211160
6.1 mtte $8,200 $20,200 $55,760 $137360
700 acre $600 $1300 $420,000 $910,000
700 acre $350 $750 $245,000 $525,000
139.5 acre $600 .$1300 583,709 $1«1370
139.5 acre $350 $750 548,830 $104,637
0.0 cy $630 $8.27 $0 $0
576,000 cy $2.90 $4.20 $1,670,400 $2,419,200
576,000 cy 50.83 $1.11 $471,010 $639360
450 acre $4.000 $7,100 $1,900,000 $3.549.591
172,100 cy $0.13 $1.11 $143.424 $191,101
172,100 cy $2.90 $4.20 $501,120 $725,760
791 cy $25 $30 $19,775 $23,730
700 acre $500 $1,000 $350,000 $700,000
139.5 acra $4,000 $7.100 $551,062 $990,561
Subtotal M3M.M1 $11,31.^14
1 b 13* 11* $949,610 $2,035,195
1 b 1* 6* $65360 $671,632
1 b 1* 15* $522,990 $1,696,579
1 b $171,500 $312.500 $171.500 $312.500
51* b 2,110,796 2,110,796 $1,071,403 $1,071.403
Sebtelfl tt,U7,*21 J5.M5.0M
Tot*/ M,I2J,»24 S17.1753M
OPERABLE UNIT TOTAL -TAILINGS AND SOILS: $19,422,367 $35,410,854
Kevifal Nevtmber 15,1995
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Table 16
Remedial Alternative Cost Summary - In-Stream Sediments
Streamside Tailings Operable Unit
Activity
Trackhoe (wet excavation)
Sediment Pond (coiutruction)
Sediment Pond (loader excavate)
Truck Haul (on site)
Silt Fence
Streambank Replacement
Final Grading
STARS
Revegetation
Mob/Demobilization
Construction Overhead
Engineering Design/Construction Overall
Operation and Maintenance (30 yean)
Trackhoe (wet excavation)
Sediment Pond (construction)
Sediment Pond (loader excavate)
Truck Haul (on site)
Silt Fence
Streambank Replacement
Final Grading
STARS
Revegetation
Mob/Demobilization
Construction Overhead
Engineering Design/Construction Oversil
Operation and Maintenance (30 years)
Minimum Maximum
Minimum Maximum Cost Cost
Minimum Maximum Cost Cost Extended Extended
Quantity Quantity Unit Unit Price Unit Price Price Price
Subarea 1: Limited Removal, On-Slte STARS Treatment
15,000 15,000 bey $435 $630 $65,250 $94500
1,144 3,661 bey $2.90 $4,20 $3,318 $15375
15,000 15,000 bey $2.90 $4.20 $43,500 $63,000
15,000 15,000 bey $0.83 $1.11 $12,450 $16,650
03 03 mile $52,800 $73,920 $13,728 $19,219
5.2 5.2 mile $84500 $211,000 $439/400 $1,097,200
1.4 4.5 acre $350 $750 $496 $3,404
1.4 4.5 acre $4,000 $7,100 $5,673 $32,221
1.7 5.4 acre $500 $1,000 $851 $5/446
Subtotal $5*4,666 $1,347,015
1 Is 1* 6% $5,847 $80,821
1 la 8% 15% $46,773 $202,052
1 Is 8X 13* $46,773 $175,112
21 X X $478,358 $478358 $100/455 $100,455
Subtotal $199,848 $558,440
Total $784^14 $1,905,455
Subarea 2: Limited Removal, On-Slte STARS Treatment
22,700 22,700 bey $435 $6.30 $98,745 $143,010
1,711 5/476 bey $190 $4.20 $4,962 $22,997
22,700 22,700 bey $190 $4.20 $65,830 $95340
22,700 22,700 bey $0.83 $1.11 $18,841 $25,197
03 03 mile $52,800 $73,920 $14,784 $20,698
5.6 5.6 mil. $84500 $211,000 $473,200 $1,181,600
2.1 6.8 acre $350 $750 $742 $5,091
2.1 6.8 acre $4000 $7,100 $g/485 $48,194
2.5 8.1 acr* $500 $1,000 $1,273 $8,145
Subtotal $686,862 $1.550,272
1 Is IX 6% $6,869 $93,016
1 Is 8X 15X $54949 $232,541
1 Is 8* 13X $54949 $201,535
31 X X $478358 $478358 $148,291 $148,291
Subtotal $265,05» $675,384
Total $951,920 $£225,656
(
Minimum Maximum
Minimum Maximum Cost Cost
Minimum Maximum Cost Cost Extended Extended
Quantity Quantity Unit Unit Price Unit Price Price Price
Subarea 3: Limited Removal, On-Slte STARS Treatment
5,000 5,000 bey $435 $630 $21,750 $31,500
1,000 3,000 bey $Z90 $4.20 $2,900 $12,600
5,000 5,000 bey $2.90 $420 $14500 $21,000
5,000 5,000 bey $0.83 $1.11 $4150 $5350
03 03 mile $52,800 $73,920 $15,840 $22,176
5.0 5.0 mile $84500 $211,000 $422300 $1,055,000
0 0 acre $350 $750 $0 $0
0 0 acre $4000 $7,100 $0 $0
0 0 acre $500 $1,000 $0 $0
Subtotal $481,640 $1,147,826
1 la IX 6X $4816 $68370
1 Is 8X 15X $38331 $172,174
1 Is 8X 13X $38331 $149,217
7X X $478358 $478358 $33,485 $33,485
Subtotal $115,364 $423,746
Total $597,004 $1371372
Subarea 4: Limited Removal, On-Site STARS Treatment
29,700 29,700 bey $435 $630 $129,195 $187,110
997 3,191 bey $2.90 $420 $2392 $13,404
29,700 29,700 bey $2.90 $420 $86,130 $124740
29,700 29,700 bey $0.83 $1.11 $24651 $32,967
0.1 0.1 mile $52,800 $73,920 $7,181 $10,053
6.8 6.8 mile $84300 $211,000 $574600 $1/134800
1.2 40 acre $350 $750 $433 $2,967
1.2 40 acre $4000 $7,100 $4945 $28,090
13 47 acre $500 $1,000 $742 $4748
Subtotal $830,769 $1,8M,»79
1 Is IX 6X $8308 $110333
1 Is 8X 15X $66/462 $275332
1 Is 8X 13X $66/462 $239,054
41 X X $478358 $478358 $196,127 $196,127
Subtotal $337358 $821,346
Total $1,168,127 $2,660,225
3PERABLE UNIT TOTAL -IN-STREAM SEDIMENTS: $3,501,564 $8,362,904
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Table 17
Remedial Alternative Cost Summary - Railroad Materials
Streantside Tailings Operable Unit
Adl.lly
Excavation of Matoriab (dotar/loadar/trackhoa)
Haul Coat
Land AconMtton
Oaar/Grub (dry damn ana)
Grado (Arj donm ana)
Scrapor (diyclooun ana)
Dozar/Uador/Trackhoo (dry cloaun ma)
RoO«r(oU)
Excavata/Raraovo on concaatrata ipiU
Rova|ataUoit (nplacod malarUla)
Mob/DoraobUliatlon
ConatrucUoo Ovaihaad
EnjlnMitai Daalp/ConatnictionOyonlta
OixraUon and Malntananca (30 yr>
Excavation of Matoiiab (ootar/loadW/tracUioa)
Haul Coat
Land Acoulamon
Claac/Grub (dry doMn ana)
Gnda (dry cloaun ana)
Scraper (dry down ana)
Doiar/Loadar/Tnckfcoa (dry cloaun ana)
Hollar (dry doaun ana)
Low PamujabUity Covar
R«vn«UMoi> (npoaitory)
Haul Unit Colt (S A 1, Import loll)
IUv*f atatton (nplacad nutarlab)
Mob/DanobiUiatton
ConatructtonOvarhaad
Eafhunriiuj Dadfn/Conabuctlon Ovanito
OparaUon anil n.i-»— .-~ (90 yr)
Mla»«»a» Maximum NU«l»ra» Madam
Coal C««l Call Coal
MhJmam Maximum LWt Uml bla«4a4 Exla>o»J
Qu^lty Quaollly UaJI Prica Prka Prica Prin
Subareal: Replacement at Railroad Materlab
ItOlO 16,515 cj $2.90 14.20 S31,92» $M^«3
IL010 1*^15 c; S2.U S3.H $29,177 J4J.41I
155 0.17 acn (1000.00 57,000 00 $351 54,000
0.55 0.57 ocn 5*00.00 5UOOOO $330 $743
1.55 0.37 acn $350.00 $75000 Sl« MM
3,101 3427 cr UM 55.04 SR4JJ SH2»3
1L010 H,!l! cy 5125 $170 513,743 $445*1
11,010 16,515 cr 50.75 $1.25 51451 $10>44
23.NI !4,t«3 (f»2 $0.60 5160 $ll3tt $32<
Total tOMfl ftlUU
Subareafc RepUccment of Railroad MatertaU
16>51 24,977 cr $2.90 $4.20 Utjtt S104.M1
16>51 24,977 cy 52.63 55 M $44,125 $95,910
0.13 0.16 acn $1,000.00 57,00000 $13$ 56\050
0.0 O.U acn $60000 5WOO.OO $500 $1124
0.0 Ott ocn $350.00 $750.00 $291 $>4I
4701 4,»0 cjr $4.M $5.04 S2U13 524,5%
UvtSl 16JS51 c, $125 $2.70 $20^14 $44.951
Uvo51 16>51 cr $0.75 $1.25 S12.4M $20414
Mja5.lt 37,64624 tt"2 U.60 5160 $21,760 5WJ34
0.0 0.«6 acn $500.00 51JXXI.OO 5416 $IM
lt>51 U>31 cj $5.50 $7.41 $91511 $124,549
1.0 2.0 acn $500.00 $1000.00 $500 $2400
SrttoUI: $H3,4tt $416.647
1 b l.OOX 6.00X $2>34 $29,199
1 b IOOX 15 OCX $21473 $72,997
1 b I.OOX 1J.OOX $21473 563,264
33.0X 33.0X b $124490 $124490 $40,930 $40,950
SuMoUl; 115,729 $2H4U
Tout SH9.117 5JM).W7
Minimum M«d«^i Mlnlduoi M*dm*m
Coal Coal Coal Cart
f-- Maxlnam V*U Vmlt EidaalaJ Bd.«IU
Quantity QuaiUily U«II Ptlca Ptin Plica Pflco
SubareaS: Replacement of Railroad Material*
19,704 29,551 CJ $2.90 $4.20 $57,142 $124,135
19,704 29,556 cj 5165 $3.4 552J16 $113.495
0.99 1.02 acn $1400.00 $7,000.00 $9t5 $7,159
0.99 1.02 acn $600.09 $1.300.00 $591 SUM
0.99 1.02 acn $350.00 $730.00 $345 $767
5,563 3,775 cy $4.64 $5.04 $25413 i $29,105
19,704 29,556 CJ 51.25 52.70 $24430 $79401
19,704 29,556 cy 50.75 $1.25 514,771 $36,945
42,915 44,549 ff2 $0.60 $1.60 525,749 $7X271
0.99 1.02 acn $500.00 $1.000.00 $493 $1,02}
19.704 19^04 cy 56.30 51.27 $124,135 $162.952
II 0 hi $0 $0 $0 $0
0.7 0.7 acn $500.00 $1,000.00 $350 $700
Subtotal 5327,226 5621,690
1 b l.OOX 6.00X $3472 $37721
1 b IOOX 15.00X 526,171 $94403
1 b 1.00X 13.00X $26,171 $11730
34.0X 34 OX b $124490 5124,090 $42,191 $42,191
SfbUUt 5)97419 $25*945
Tout 5J43S449 9U4,U3
Subaru 4: Replacement of Railroad Material*
0 0 cr S2.W $440 $0 $0
0 0 cr $2.65 $7.40 $0 $0
0.00 0.00 acn 51,000.00 $0.00 $0 $0
0,00 000 acn $600.00 $0.00 $0 $0
0-00 0.00 acn $350.00 $0.00 $0 $0
0 0 cy $4.64 $3.04 $0 $0
0 1 qr $2.90 $440 $0 $0
0 0 cy $0.75 $145 $0 $0
0 0 ftA2 $0.60 $1.60 $0 $0
0.00 0.00 acn $500.00 51,000.00 $0 $0
1 0 cr $630 $147 $0 $0
00 0.0 acn $500.00 51,000.00 $0 $0
SutloUl: It $4
1 b tOOX 4.00X $0 $0
1 b IOOX 15.00X 50 $0
1 b IOOX 13.00% $0 $0
0.0% 0.0% b $124,090 $124.090 $0 $0
Soolout- 91 M
Tout S* M
OPERABLE UNITTOTAL- RAILROAD MATERIALS: J1.029.S23 S2.093.S56
KmkW Nou<»tw 15, IMS
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Truck Haul - Truck haul costs were not altered from those presented in the original
cost estimate (ARCO, 1995b). While MDEQ believes that the bulking factor used in
ARCO's unit cost calculation is high and the travel speeds used are low, the
combination of these two factors provide some conservatism to the quantity estimates
and allow for overage that might be expected during tailings removal (Table 15).
Clean Fill for Streambank Replacement - The quantity of clean fill used for
streambank replacement was increased from ARCO's draft FS submittal to account
for a 4-inch lift of coversoil placed over these areas. This material is expected to be
used where necessary to provide an adequate seedbed for germination. Costs
associated with truck haulage were used to estimate costs to transport this material
from local sources (Table 16).
Roadbuilding - Roadbuilding was broken into two categories, internal and external,
along with the minimum and maximum costs developed from the demonstration
projects for each category. For each of the alternatives except TS3, one times (IX)
the stream length was used for internal roads and one times (IX) the stream length
was used for external roads (Table 15).
Revegetation (relocation area) - The costs associated with STARS treatment in the
relocation areas were increased to reflect the cost of applying STARS to multiple lifts
of relocated tailings. ARCO's original estimate provided only for treating one 12-
inch lift without treatment of the remaining 14 lifts of tailings placed in the relocation
areas. Unit costs for this item were changed to the STARS unit costs and the acreage
of the relocation areas adjusted to reflect applying STARS in seven, 2-foot lifts (Table
15).
Operations and Maintenance - These costs were recalculated to reflect a percent
failure expected for each alternative rather than the man hour and equipment hour
method used in ARCO's original cost estimate. These costs were also discounted to
net present value at an annual discount rate of 7% in accordance with EPA guidance
(EPA, 1993) (Table 15).
Instream Sediments - Costs were included to replace the streambank in addition to the
backfill placed for the tailings/soils alternatives. Replacement costs were based on the
lineal foot of streambank replaced using a minimum and maximum range of $16 to
$40, respectively (Table 16).
Final Remediation Goals. Cleanup\Peiformance Standards, and Points of Compliance
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Preliminary remedial action objectives and preliminary remediation goals were identified in
the Preliminary Remedial Action Objectives Report/Treatment Technology Scoping
Document (PRAOR/TTSD) (ARCO, 1993d). This section clarifies the final remediation
objectives, .goals, levels, specific cleanup standards, and points of compliance for each of the
media addressed under the SST OU record of decision. Not all of the preliminary
remediation goals identified in the PRAOR/TTSD are carried forward into the final
remediation standards. Where separate preliminary goals are addressed by the same final
standard, only a single goal has been identified, and although preliminary goals were
established for organic parameters, final standards for organics have not been established
because site characterization has determined that separate remedial action under this operable
unit is not necessary to address organics.
Surface Water and Instream Sediments
The final remedial action objectives and final remediation standards for surface water are:
1. Meet the more restrictive of the aquatic life or human health standards for surface
water identified in MDEQ Circular WQB-7, through application of I-classification
requirements.
2. Prevent exposure of humans and aquatic species to instream sediments having
concentrations of inorganic contamination in excess of risk-based standards. A
physical criterion is used to define those sediments posing the greatest risk to receptor
species. A contingency is established to develop metal-specific concentrations which
would be risk-based, and allow sediment cleanup standards if the physical criterion
standard cannot be employed appropriately.
3. Provided that upstream sources of Silver Bow Creek contaminants are eliminated,
meeting the two remediation standards identified above should attain the remedial
action objective to improve the quality of Silver Bow Creek's surface water and
instream sediments to the point that Silver Bow Creek could support the growth and
propagation of fishes and associated aquatic life, one of the designated goals for an I-
class stream, including a self-sustaining population of trout species.
Within a reasonable time frame after implementation of the selected remedy, and contingent
upon adequate cleanup of upstream sources, ambient surface water quality standards,
ultimately including the WQB-7 standards described above, must be attained at all points in
Silver Bow Creek within the OU. I-classification procedures allow for a gradual attainment
of the standards by permitting point source discharges at the higher concentration of (1) the
applicable Circular WQB-7 standard, (2) an adopted site-specific standard, or (3) one-half of
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
the mean monthly instream concentration immediately upstream of the discharge. Since no
site-specific standards have been developed as of the issuance of this record of decision, any
point source discharges under this remedial action must meet one-half the mean monthly
concentration in the stream immediately upstream of the discharge point, eventually reducing,
as upstream water quality improves, down to the WQB-7 levels.
As effective ambient water quality standards for the stream, the WQB-7 levels also set the
contaminant specific goal for the remediation of non-point sources. The remediation is to be
designed and implemented to ensure that non-point sources, specifically those contaminant
sources identified in this record of decision, do not contribute a contaminant loading to the
stream that causes an exceedance of these standards. While upstream water quality continues
to exceed these standards, the applicable I-class limitation for these non-point sources is that
no discharge from such sources may commence or continue which lowers or is likely to
lower the overall quality of the stream waters. Thus discharges from the non-point sources
in excess of WQB-7 levels will not actually be in violation of the standards until the water
coming into the stream from upstream sources is of a better quality. Therefore the
implementation of the remedy and initial monitoring of non-point sources should serve to
identify any continuing contaminant loadings from non-point sources, so that these sources
can be effectively remediated prior to the improvement of upstream water quality.
Accordingly, monitoring should be designed to identify and locate any continuing
contaminant source. For this purpose the stream may be divided into reaches, which could
be modified or narrowed, as appropriate, to identify and locate contaminant sources.
Potential stream reaches for which performance could be initially measured are the
following:
• LAO to the Silver Lake Pipeline discharge point
• Silver Lake Pipeline discharge point to Browns Gulch
• Browns Gulch to head of Durant Canyon
• Head of Durant Canyon to German Gulch
• German Gulch to Fairmont Road bridge
• Fairmont Road bridge to Highway 1 bridge
• Highway 1 bridge to Warm Springs Pond inlet
Where perennial tributaries enter the SST OU (Silver Lake Pipeline, Browns Gulch, and
German Gulch), the downstream sampling point for the upper reach will be immediately
upstream of the tributary and the upstream sampling point for the downstream reach will be
sufficiently downstream of the tributary to allow for mixing of the SBC and tributary flows.
Specific stream reaches for monitoring will be delineated during the remedial design and
adjusted as necessary to identify continuing contaminant sources.
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
The intent of the surface water performance standard is to allow determination of whether
remedial actions taken at the OU are successful in providing for the improvement of Silver
Bow Creek water quality over time in accordance with the I-classification requirements. As
remedial action performance data is collected, revisions may be made to the stream reaches
used for compliance and monitoring requirements as appropriate. Additional details of the
performance standards may be included in any implementing order.
No metals concentration cleanup goal is established for instream sediments by this action.
Cleanup performance standards are based on physical size criteria applied to all depositional
areas. Specific standards may be identified in any implementing order, and the specific
locations requiring instream sediment excavation will be determined prior to or during
remedial design, based on more precise sampling and mapping of instream sediment grain
size and depositional areas.
The compliance requirements for instream sediments, including locations of compliance, will
be specified during remedial design but will entail, at a minimum, multiple locations along
Silver Bow Creek. During implementation of the remedial action, compliance will require
that sediments mapped for excavation are removed in accordance with design requirements.
Instream sediment sampling will be performed during the response action to verify the
locations and concentrations of contaminated instream sediments.
The specific performance standards for instream sediments will be removal of the sand sized
fraction and less (
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
The final remedial action objectives and final remediation standards for tailings/impacted
soils are:
1. Prevent human exposure to tailings/impacted soils from residential or occupational
activity within the SST OU. This will be accomplished, in part, through institutional
controls that will require the entire OU to be developed into a recreational corridor.
2. Prevent erosion or migration of inorganic contaminants of concern in
tailings/impacted soils into Silver Bow Creek or into groundwater that would prevent
attainment of groundwater, surface water, and sediment remediation levels.
3. Protect all solid waste within the SST OU from flood displacement, washout, or
erosion in accordance with ARARs.
4. Prevent the saturation of tailings/impacted soils by groundwater during any period of
the hydrologic year or by bank storage of high-flow stream discharge.
5. Prevent migration of contaminants of concern in tailings/impacted soils that would
cause phytotoxicity in terrestrial vegetation.
Because the remediation of tailings/impacted soils is based primarily upon the need to reduce
risks to environmental receptors at the SST OU and because adopted soil cleanup levels to
address the contaminants of concern are not available, no chemical action level is defined for
tailings/impacted soils. Instead, an "order of magnitude definition" as defined in the Draft
RI report (ARCO, 1994a) of contaminated tailings/impacted soils is utilized to identify those
soils requiring remediation. This methodology is expected to provide for an easily defined
performance standard for field implementation, while also yielding a degree of cleanup of
tailings/impacted soils that will provide adequate protectiveness for receptor species without
setting specific chemical action levels. Specific locations and depths of excavation or in-situ
treatment of tailings/impacted soils to be required will be defined during remedial design.
Numerous (possibly hundreds) additional borings will be required to ascertain the base of
tailings for the purposes of: (1) the concentration with depth, (2) determining if the
tailings/impacted soils are saturated by groundwater, and (3) how much and what tailings
will be removed or treated in-situ.
Performance will be monitored by agency oversight during construction to ensure that
excavation, backfill, and in-situ treatment and revegetation are conducted in accordance with
specifications developed during remedial design. Compliance with remedial design will be
required at all locations of remedial action for tailings/impacted soils. During long-term
maintenance of the remedy, vegetation and soil monitoring will be required at a
105
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
representative number of locations within the SST OU. Vegetation will be monitored for
cover and density, as well as for signs of chemical stress from contaminants of concern.
Soils will be measured for pH while soil pore-water will be monitored for pH and all
appropriate, analytes, which will include all major cations and anions. The specific locations
and requirements for the long-term monitoring program will be developed as part of the
remedial design and remedial action at the OU.
An important element of the selected remedy is the establishment of several local repositories
for treated, excavated tailings/impacted soils. Although it is expected that these repositories
will be designed and constructed to prevent any migration of contaminants to underlying
groundwater, it will be important to monitor the vadose zone water of each individual
repository to confirm that the technology is performing as designed. Vadose zone pore-water
will be monitored for pH and all appropriate analytes which will include all major cations
and anions. Vegetation will also be monitored for cover and density, as well as for signs of
chemical stress from contaminants of concern. The specific locations of lysimeters and
sampling regimen will be determined during remedial design and remedial action (Table 18).
Methodology to Determine the Base of Tailings/Impacted Soil
Soil samples were collected within and adjacent to the SST OU to determine both the nature
of tailings/impacted soils ("tailings") and native soil and to provide a frame of reference
against which to assess the impact of tailings on the environment. The method used for
delineating tailings/impacted soil from "nonimpacted" soils within the SST OU is described
below.
To some extent, contaminants of concern mobilized by the chemical reactions have moved
out of the tailings and into the underlying soils. This results in a gradual decrease in
concentration of contaminants of concern with depth, with no distinct base. In addition,
although several of the contaminants of concern behave in a similar manner, the exact
mobility of each is unique. These conditions combine to make the determination of the base
of the tailings/impacted soils somewhat problematic.
Graphs of data for distinct boreholes showing lithologic, chemical and physical parameters
versus depth in the soil reveal that often the point at which the change in each of these
parameters is greatest is approximately the same for several parameters. At some depth most
metals concentrations decreased an approximate "order of magnitude," or factor of ten, from
concentrations measured in the surface to near-surface depth intervals. This order of
magnitude decrease in metals concentrations generally coincided with an increase in soil pH
and a decrease in electrical conductivity. In other words, although there is no unique base of
tailings with an abrupt, step-like change in chemical and physical parameters, the point that
most closely approaches that distinct change can be quantitatively chosen by examination of
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
multiple parameters. While this decrease in metals concentrations was not equal to a specific
value for any metal, this observation provided a good "rule of thumb" to semi-quantitatively
determine the base of tailings impacts for volume determinations.
Using this method, the data for each borehole was examined and the base of tailings was
determined. The term "tailings/impacted soils" is used to describe those soils that lie above
the order of magnitude change in chemical and physical parameters and the term
"nonimpacted" soil is used to describe those soils that lie below the order of magnitude
decrease. This definition is used to calculate volumes of tailings/impacted soils and to draw
isopach maps of tailings/impacted soils. The phrase "non-impacted soils" is a working
phrase, used here to indicate that the soils, as a whole, have lower concentrations of
contaminants of concern than tailings/impacted soils.
To determine if this, semi-quantitative manner of determining the base of tailings/impacted
soils was applied consistently and if there was a real and distinct difference between the
materials that were above and below the point chosen as the base of tailings/impacted soils, a
statistical analysis of the two groups was done. Details of this statistical analysis are
provided in Appendix C of the Draft Remedial Investigation Report (ARCO, 1995a). This
statistical analysis showed there was a distinct difference between the materials in the two
categories, "tailings/impacted materials" and "nonimpacted materials." This performance
standard will be applied in determination of tailings/impacted soils and nonimpacted soils.
Sampling will be performed during the response action to verify that all tailings/impacted
soils contaminated above the order of magnitude cleanup criteria are appropriately addressed.
The sampling program shall be developed by the agencies during remedial design.
Railroad Materials
The final remedial action objectives and final remediation levels for railroad materials are:
1. Prevent exposure by recreational users of the railroad beds in excess of acceptable
cancer and noncancer risks from arsenic. Risks will be adequately reduced by
removal of ore concentrate spills and other impacted railroad materials exhibiting
arsenic concentrations in excess of 2,000 mg/kg (MDEQ, 1995b).
2. Prevent erosion of contaminated railroad bed materials into Silver Bow Creek to the
degree that surface water standards would be exceeded, or instream sediments would
be contaminated, or vegetation on adjacent relocation or STARS treated areas would
be adversely impacted.
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
The SST OU Baseline Risk Assessment determined that the OU posed unacceptable health
risk to recreational users of the railroad beds, but that those risks were primarily related to
the existence of a limited number of highly contaminated spills of ore concentrate or fine-
grained slag material. The selected remedy for the site requires removal and appropriate
disposal of those materials. Specific procedures for sampling and designation of materials to
be removed will be developed during remedial design. Compliance will be determined by
confirmation sampling of locations where highly-contaminated materials were removed.
The selected remedy requires excavation of contaminated railroad bed materials that form the
streambank of Silver Bow Creek. These materials are found primarily at bridge abutments
and along certain stream reaches. During implementation of the remedial action, compliance
with the construction specifications will be required. During long-term maintenance, repair
of eroded materials will be required to ensure structural integrity of the railroad bed.
All concentrate spills will be removed and disposed in an appropriate secure repository in
compliance with applicable RCRA requirements. Concentrate spill material will not be
placed in relocation repositories. The STARS technology or soil capping is expected for all
other areas of the inactive grade. Railroad materials which directly impact the stream either
at bridge abutments or along the streambank will be excavated and disposed in the adjacent
relocation repositories. The actual amount and methods of excavation and/or treatment will
be determined during remedial design.
Groundwater
The final remedial action objectives and final remediation standards for groundwater are:
1. Attain compliance with applicable MDEQ Circular WQB-7 standards, federal MCL's,
and federal nonzero maximum contaminant level goals (MCLGs) for all OU
groundwater.
2. Prevent discharge of groundwater that would prevent attainment of Silver Bow Creek
ambient Circular WQB-7 standards or instream sediment remediation goals.
A primary element of the selected remedy is to excavate and relocate tailings/impacted soils
that act as sources of groundwater contamination at the SST OU because the tailings are in
contact with groundwater either continually or seasonally. The purpose of these source
removals is two fold. First, removal of the sources will allow natural attenuation to restore
groundwater to compliance with Circular WQB-7 standards in a reasonable time frame.
Second, as groundwater quality improves, contaminant loading to Silver Bow Creek in areas
where near-stream groundwater discharges to the stream will be dramatically reduced. Over
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
time, groundwater should not adversely impact water quality or instream sediment quality of
the stream. To delineate the potentiometric surface to the degree necessary for saturated
tailings quantification, numerous piezometers (possibly hundreds) will need to be installed
with accurate horizontal/vertical survey control and monthly groundwater level
measurements.
After construction of the remedy, at areas of suspected or known historic exceedances of
groundwater standards, monitoring wells will be installed. These wells will be constructed
so that the well screen is located in the appropriate hydrostratigraphic zone and monitored at
proper time intervals to confirm that the source removals and natural attenuation are working
to improve groundwater quality. The specific locations and number of wells required and the
necessary sampling regimen will be determined during remedial design and remedial action.
Another element of the selected remedy is the establishment of several local repositories for
treated, excavated tailings/impacted soils. Although it is expected that these repositories will
be designed and constructed to prevent any migration of contaminants to underlying
groundwater, it will be important to monitor the groundwater beneath each individual
repository to confirm that they are performing as designed. The specific locations of
monitoring wells and sampling regimen will be determined during remedial design and
remedial action.
The groundwater levels to be attained consist of the more stringent of the MCL, any non-
zero MCLG, or the WQB-7 human health standard for each parameter. More detail on the
legal requirements that establish these levels is set forth in Appendix A, which identifies and
discusses the ARARs for this remedial action.
Groundwater sampling will be performed during the response action to verify the locations of
contaminated groundwater (Table 18). It is anticipated that the treatment prescribed for
sources of contamination at the OU will effectively reduce the locations and levels of
contamination and shrink the contaminant plumes within a reasonable period of time.
Air Resources
The final remediation standard for air resources is:
1. Compliance with air ARARs within and adjacent to the SST OU during
implementation of the remedial action.
During construction of the remedy, dust-suppression measures will be required. In addition,
provisions will be specified during remedial design to limit wind-borne dispersion of lime
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
amendments used as part of the in-situ treatment of tailings/impacted soils. Monitoring of
paniculate matter will be required initially and on an as-needed basis for the duration of
construction activities at the OU. The intensity of the monitoring may be reduced over time
depending on the results of the initial sampling.
Compliance Monitoring Program
A sampling program for monitoring the remedial action and determining compliance with the
performance standards shall be implemented during the remedial action. Table 18 lists
minimum monitoring requirements. In addition, to ensure that performance standards are
maintained, it is expected that there will be monitoring at least quarterly for a period of at
least ten years following completion of remediation construction. Continued monitoring after
that period may be conducted less frequently if MDEQ and EPA determine that a reduced
frequency is appropriate. These monitoring programs will be developed during remedial
design and shall include, at a minimum, the following parameters to evaluate success of the
remedial action. Physical parameters of geomorphologic stability, macroinvertebrates
(diversity and abundance) and aquatic health, riparian vegetation and analytical parameters
(focusing on the contaminants of concern including mercury, but analyzing other
contaminants, if any, that are not contaminants of concern and are determined to be
occurring at levels exceeding performance standards), sampling points, sampling frequency
and duration, and statistical methods for evaluating data. Specific performance monitoring
points shall be specified and approved by EPA and MDEQ during remedial design and
remedial action.
Because residual hazardous substances will be left in the OU and the cleanup is expected to
take several years, the selected remedy will require five year reviews under Section 121(c) of
CERCLA, Section 300.430(f)(4)(ii) of the NCP, and applicable guidance to ensure the long-
term protectiveness of the remedy.
Engineering and Institutional Controls
These controls are required to maintain the protectiveness of the remedy. Since attainment
of RAOs for all media are not likely to be met in less than 10 years, measures must be
instituted to control risks during implementation of the remedy.
Because all OU contamination will remain on-site, a creative and secure institutional
controls, monitoring, and maintenance (ICMM) program will be required. This ICMM
program must: (1) ensure adequate land use/access restrictions to safeguard the waste
materials treated in-situ and/or relocated to adjacent repositories, (2) be managed,
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
maintained, and monitored in perpetuity, and (3) ensure that shallow contaminated
groundwater use is controlled.
Table 18
Minimum Post-Remedy Monitoring Requirements1
Media
Surface Water
Instream Sediments,
Geomorphology ,
Aquatic Biologic
Resources
Groundwater
Soil
Vegetation
Vadose Zone
Locatious/Hiysieal
Parameters
SS-07, SS-10, SS-13, SS-14, SS-15, SS-16,
SS-17, SS-19
Surface water locations and at each
depositional areas. Physical stream
parameters such as geomorphologic stability
(erosion rates and locations) and bedform
morphologic features. Macroinvertebrate
diversity, abundance and aquatic health.
Upstream end near Colorado Tailings,
Rocker, Silver Bow, Nissler, Ramsay Flats,
Miles Crossing, Fairmont, Crackerville,
Stuart, Opportunity, STARS in-situ treatment
areas and every repository location
Minimum one (1) sample per 10 acres and
three (3) sample per repository
In conjunction with soil sample locations
In conjunction with groundwater sampling
locations; three (3) per repository location
Analytical Parameters
Metals: Total recoverable and dissolved: As,
Cd, Cu, Pb, Hg, Zn
Commons:Ca, Mg, Na, K, Cl", SO42'
Nutrients: Nitrate + Nitrite Nitrogen, Phosphorous
Physical: Temperature, pH, Eh, conductance, dissolved O2
Metals: Total As, Cd, Cu, Pb, Hg, Zn. To be analyzed
by three size fractions: 1mm and greater,
between 1mm and 63 ftm, and less then 63 fim.
Metals: Dissolved As, Cd, Cu, Pb, Hg, Zn
Commons: Ca, Mg, Na, K, CK, SO42'
Phvsical: Temperature, pH, Eh, conductance, dissolved O2
Neutralization potential, sulfur fractionation, conductance,
pH
Percent cover (total and by species), production (total and
by species)
Metals: Dissolved As, Cd, Cu, Pb, Hg, Zn
Commons: Ca, Mg. Na, K, Cl", SO42'
Physical: Temperature, pH, Eh, conductance
' - Monitoring will focus on principal contaminants of concern As, Cd, Cu, Pb, and Zn including mercury (Hg), but analyzing other
contaminants, if any, that are not principal contaminants of concern and are determined to be occurring at levels exceeding
performance standards. The level of monitoring effort described in this table should be considered as minimal requirements. The
necessity to meet remediation goals, cleanup/performance standards, and points of compliance might dictate a more substantial effort.
The agencies will determine the final level of monitoring which includes sampling locations, frequency and duration, as well as
statistical methods for evaluating the data, as needed, during remedial design.
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
An important component will be provisions to physically protect areas of in-situ STARS
treatment from stream erosion and to provide for any necessary re-treatment of in-situ or
repository STARS treated areas. If necessary, additional work, including engineering
controls (e.g., riprap or removal of STARS treated areas) to prevent erosion of STARS
treated areas, will be required. A critical component to this ICMM program will be
provisions, to be approved by the agencies, which will ensure sufficient arrangements for
financial resources to support the entities who will manage, operate, and maintain the
institutional controls program.
Stream erosion would be significantly reduced from its present condition by establishment of
woody vegetation (i.e., willows and cottonwoods) and backfill to maintain channel
geomorphic stability.
The remedial action plan will incorporate the removal of tailings/impacted soils,
contaminated instream sediments and certain railroad bed materials from the floodplain,
except in those specific locations where such materials can be adequately protected in place
and treated with the STARS technology to prevent further migration of the contaminants.
The agencies believe that the selected remedy can be implemented in a manner that provides
protection of the public health, safety, welfare and the environment and attains legally
applicable or relevant and appropriate requirements.
Remedial Design/Remedial Action Process
The evaluation, selection, and description of the remedy identified in the record of decision
were conducted at a feasibility study level of detail. The effectiveness and cost evaluations
relied on a relatively limited amount of information collected during the remedial
investigation. Although the RI/FS information is sufficient to support the setting of cleanup
criteria and standards and the selection and conceptual design of the remedy, additional data
will be necessary to complete the detailed design and implementation of the remedy.
The conceptual design of the remedy presented in this record of decision provides MDEQ's
current best estimates of (1) the volumes and locations of contaminated media to be
excavated or STARS-treated in place, (2) potential locations of the repositories for excavated
materials, and (3) construction techniques to be employed. These estimates are based on the
existing remedial investigation and feasibility study information. Remedy design details and
construction specifications will be finalized during the remedial design phase of the cleanup.
The actual volumes of excavated materials and in-situ treated materials, lime application
rates, stream stabilization features, construction techniques, monitoring and maintenance
requirements, etc. ultimately required under the remedy will be determined by the agencies
during design, based on the criteria identified in this record of decision. Actual volumes to
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be excavated x>r treated in-situ may be either higher or lower than the current estimate.
Likewise, the actual locations of excavated areas, in-situ treated areas, and relocation areas
may vary from what is presently assumed in the record of decision. The final remedy
design, however, must be approved by the agencies and must be able to attain the final
remediation goals and compliance and performance standards specified in this record of
decision in order to ensure protection of human health and the environment and attainment of
ARARs, except where appropriately waived.
Remedial design typically involves primarily the potentially responsible parties and the
overseeing agencies, along with their respective technical contractors. Consistent with recent
EPA Superfund Administrative Reforms, MDEQ and EPA intend to conduct an open
remedial design process that will include, in a consultative role, other parties that have an
interest in the Streamside Tailings OU. These parties include Butte-Silver Bow, Anaconda-
Deer Lodge, and Missoula county governments, interested state and local environmental
permitting agencies, local environmental groups, the Silver Bow Creek/Butte area technical
assistance grantee, natural resource trustees, and other interested individuals. As provided
by CERCLA and the NCP, the agencies are ultimately responsible for making final
determinations regarding remedial design.
Given the disparity of opinions regarding the ability of engineered stream stabilization
features to control the hydraulic forces of Silver Bow Creek and offer long-term effectiveness
in preventing erosion of STARS-treated areas over time and therefor compliance with
performance standards, MDEQ and EPA will make earnest efforts to procure supplemental
technical expertise in stream mechanics and stream geomorphology to assist in the design
process. The focus of the remedial design process will be to identify and develop detailed
specifications of the most cost-effective selected remedy design that will attain the cleanup
criteria and performance standards set forth in this record of decision.
Provided that the final design of the SST OU remedy can attain the SST OU cleanup criteria
and performance standards, it should to the degree possible incorporate components
consistent with the following environmental and community improvement actions in the
project area:
• A Silver Bow Creek recreational corridor land uses as designated and adopted
by Butte-Silver Bow and Anaconda-Deer Lodge county governments;
• The use of wetlands treatment for Butte wastewater nutrient loadings and/or
Butte area storm water runoff metals loadings, if appropriate;
• Preservation and enhancement of significant historical and prehistorical
resources in accordance with the Regional Historic Preservation Plan; and
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• Coordination with pertinent restoration actions implemented as part of the
Upper Clark Fork River Basin natural resource damage restoration plan.
EPA and MDEQ will make conceited efforts to assist Butte-Silver Bow and Anaconda-Deer
Lodge counties in obtaining EPA Brownfields redevelopment grants and Montana Resource
Development Grants to enhance reclamation projects within the Silver Bow Creek corridor.
Contingency Measures
The decisions to invoke any or all of these contingency measures may be made by the
agencies at any time during remedial design or implementation of the remedial action, as
appropriate.
Repository Locations
As noted in the description of the selected remedy, the use of numerous near-stream
repositories for the treated tailings/impacted soils and other materials is contingent upon
obtaining adequate space at suitable locations for such repositories, securing adequate control
over land use, access, and management of those sites, and the successful establishment of an
adequately funded institutional controls/maintenance program as part of this remedy. In the
event these requirements are not met, the remedial action shall incorporate instead the use of
centralized repositories as determined appropriate by the agencies.
The use of centralized repositories would substantially reduce the need for land acquisition
within the Silver Bow Creek corridor and the need for institutional controls and continued
land use restrictions within the stream corridor, as well as the amount of maintenance
required for such repositories. In such event, the agencies may also need to determine that a
greater amount of tailings/impacted soils needs to be removed from the OU in order to
ensure protection of the stream from reentrainment of tailings/impacted soils from STARS
treated areas in the absence of a permanent management, monitoring, and maintenance
program.
The locations of the centralized repositories would be determined by the agencies based upon
the availability of appropriate locations at that time. For some tailings/impacted soils and
other contaminated materials, the Opportunity Ponds could still be considered an appropriate
location. Although there was some concern expressed during the public comment period
regarding the use of the Opportunity Ponds as a disposal area, primarily by local government
representatives from Deer Lodge County, the majority of comments addressing this issue
recognized the Opportunity Ponds as an appropriate repository for such wastes. Possibly
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limiting the wastes disposed in this area to those wastes from the lower portion of the OU
would address some of the concerns raised by those who objected to the use of the
Opportunity Ponds.
By the time that this decision would be made, there may be additional information from
studies for other operable units within the site that would assist in identifying additional
appropriate repositories. The agencies recognize that there was also substantial opposition
during the public comment period to the siting of a repository in the Browns Gulch area.
That location could also be avoided, if possible.
Instream Sediments
The use of the < 1mm grain size standard is intended as an indicator that will allow for ease
of field implementation, enabling reasonably reliable visual identification of the material to
be removed in the field without the need for continued sampling and expensive, slow
analytical analysis of instream sediments. MDEQ and EPA believe that this particle size
fraction will reasonably identify the tailings/impacted soils located in the active streambed of
Silver Bow Creek, particularly that fraction of the instream sediments that poses the greatest
threat as a contaminant source, and therefore will serve as a reliable indicator for
implementation in the field.
However, if it is demonstrated from design studies or initial field work that this size fraction
standard is not a reliable indicator of the contaminated sediments that must be removed in
order to eliminate the threat to aquatic life in the stream, sampling and chemical analysis
may be used to identify the materials that must be excavated or another appropriate indicator
may be selected. In any event, sampling and analysis may be used in coordination with the
use of this indicator to establish that a specific deposit of sediments within this particle size
are in fact natural, uncontaminated sand or silt size instream sediment and not
tailings/impacted soils or contaminated instream sediments that require removal. For
example, demonstration that specific materials contain concentrations similar to instream
sediment concentrations found in like Montana streams that are located in similar
geologic/hydrologic environments, that are relatively unimpacted by mining activity, and that
contain a reproducing trout fishery would establish that such instream sediments need not be
removed.
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X. STATUTORY DETERMINATIONS
While the large majority of the comments received from the community supported the
selection of Alternative 6, the alternative initially proposed by the agencies, comments
submitted by the primary PRP, with support from both Butte/Silver Bow and Anaconda/Deer
Lodge local governments, as well as numerous local business interests promoted
implementation of a less extensive and less expensive remedy. After considering all the
comments fully, as detailed in the Responsiveness Summary, the agencies have determined
that certain changes to the proposed plan (MDEQ, 1995a) can accomplish substantial cost
savings and still satisfy the statutory requirements for remedies under CERCLA. MDEQ and
EPA have determined that, considering all appropriate factors, including OU specific
conditions and the remedy selection criteria specified in CERCLA and the NCP, the remedy
presented in this record of decision is the proper remedy for the OU and meets the statutory
requirements for remedies under CERCLA, as described below.
Under CERCLA Section 121, MDEQ and EPA must select, a remedy that is protective of
human health and the environment, complies with applicable or relevant and appropriate
requirements (unless a statutory waiver is justified), is cost-effective, and utilizes permanent
solutions and alternative treatment technologies or resource recovery technologies to the
maximum extent practicable. In addition, CERCLA provides a preference for remedies that
include treatment which permanently and significantly reduces the volume, toxicity, or
mobility of hazardous wastes as a principal element. The following sections discuss how the
selected remedy meets these statutory requirements.
Protection of Human Health and the Environment
The selected remedy will protect human health and the environment through actions designed
to address all identified sources of contamination in the OU, including tailings/impacted soil,
instream sediments, and railroad materials, together with permanent monitoring and
maintenance (including retreatment or replacement, if necessary) of the remediated areas
through a comprehensive institutional controls, monitoring, and maintenance program.
This remedial action will reduce much of the potential risk to human health and terrestrial
and aquatic flora/fauna by establishing vegetation throughout the entire OU and relocating
much of the contaminated materials outside of the 100-year floodplain. Contaminated
materials to be relocated will include all tailings deposits that are saturated or within the
observed groundwater fluctuation of two feet and all near stream tailings which may
reasonably be expected to be eroded through natural stream processes.
Groundwater quality will improve significantly in many areas after the removal of source
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tailings. Tailings/impacted soils close to or saturated by groundwater and tailings in those
areas that may be subject to erosion into the stream will be relocated safely outside of the
100-year floodplain and treated, significantly reducing the potential for impacts to
groundwater or re-entrainment of tailings/impacted soils into the stream. Runoff and
transport of total and dissolved metals and arsenic to the stream will be significantly reduced
or eliminated. In those areas to be treated in-situ with STARS, the treatment will somewhat
reduce pore water acidity and mobility of certain contaminants. An institutional controls
program will monitor and maintain the integrity of all STARS treated areas, and, if
necessary, additional work, including engineering controls to protect STARS treated areas
from erosion or retreatment or removal of the STARS treated areas, will be required.
Stream erosion would be significantly reduced from its present condition by establishment of
woody vegetation (i.e., willows and cottonwoods) and backfill to maintain channel
geomorphic stability.
All railroad materials which affect human health or the environment will be removed or
treated in-situ. All concentrate spills will be removed and disposed in an appropriate, secure
landfill. The STARS technology or soil capping is expected for all other areas of the
inactive grade. Railroad materials which directly impact the stream either at bridge
abutments or along the streambank will be excavated and disposed in the local relocation
repositories.
Instream sediment quality and recovery time will improve dramatically through removal of
all depositional areas of fine (< 1mm) grained instream sediments.
After the sources of continuing contamination are addressed, groundwater quality will
improve slowly by attenuation and dilution in areas where it is currently impacted.
Institutional controls restricting use of and exposure to contaminated groundwater will be
necessary until the standards are attained.
After the sources of contamination are addressed as provided for in the selected remedy, (and
after upstream sources are addressed by actions in other operable units) protection of affected
surface waters will be achieved. Once source control is achieved, flushing and dilution will
restore the stream to acceptable and protective levels for contaminants of concern for this
OU.
There are no short term threats associated with the selected remedy that cannot be readily
controlled. A variety of institutional controls and access restrictions will be implemented
with the remedy to ensure protectiveness while the remedy is being implemented.
Accordingly, the agencies have determined that the combination of actions, controls, and
contingencies designated in this record of decision for the remedial action at this OU will
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provide protection of human health and the environment.
Compliance with Applicable or Relevant and Appropriate Requirements
The final determination of ARARs by MDEQ and EPA is set forth in Appendix A attached
to this record of decision. The selected remedy will attain most applicable or relevant and
appropriate requirements (ARARs). A waiver of certain solid waste and floodplain
management ARARs is necessary where the STARS technology will be implemented in the
100-year floodplain. Some significant ARARs compliance issues are discussed below.
Contaminant-specific ARARs
Contaminant-specific ARARs typically set levels or concentrations of chemicals that may be
allowed in or discharged to the environment. For groundwater, the contaminant-specific
ARARs for this remedial action include the maximum contaminant levels (MCLs) and non-
zero maximum contaminant level goals (MCLGs) established under the federal Safe Drinking
Water Act, and the human health standards specified in MDEQ Circular WQB-7. The
selected remedy is to be designed to address source areas of contamination to groundwater
sufficiently to allow natural attenuation and dilution of groundwater to eventually attain these
standards in the groundwater throughout the OU.
In addition the remedy will attain the surface water quality standards for OU contaminants in
Silver Bow Creek, as designated under Montana law. ARM 16.20.623 specifies the
standards for the "I" classification applicable to Silver Bow Creek and, for each contaminant,
requires eventual attainment of the more restrictive of the aquatic life standard or the human
health standard set forth hi MDEQ Circular WQB-7.
Location-specific ARARs
Location-specific ARARs establish requirements or limitations based on the physical or
geographic setting of the OU or the existence of protected resources in the OU.
The SST OU lies almost entirely within the 100-year floodplain of Silver Bow Creek.
Several different ARARs limit or prohibit storing or disposing the SST mine tailings in the
floodplain. The Montana Solid Waste Regulations prohibit placing any facility for the
treatment, storage, or disposal of solid wastes in a 100-year floodplain. The Montana
Floodplain Management Regulations prohibit solid and hazardous waste disposal or storage of
toxic or hazardous materials within the 100-year floodplain.
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The remedial" action plan provides for the use of STARS treatment of tailings in place in the
floodplain in a portion of Subarea 4. Because this will constitute disposal of solid waste in
the floodplain, this action will not comply with these location-specific ARARs, and an ARAR
waiver is necessary.
MDEQ and EPA have determined that, in those locations satisfying the technical criteria
identified in this ROD for where STARS treatment may appropriately be implemented within
the floodplain (Section IX), and when consistently and permanently monitored and
maintained by an appropriate institutional controls, monitoring, and maintenance program to
be established and funded as part of this remedy, the use of STARS treatment, together with
any necessary maintenance or replacement actions, will attain a standard of performance that
is equivalent to that required by these floodplain and solid waste regulations through use of
another method or approach. Accordingly, the agencies invoke the ARAR waiver provided
by CERCLA Section 121(d)(4)(D), 42 U.S.C. § 9621(d)(4)(D). In determining that this
ARAR waiver may properly be invoked in this limited context, MDEQ and EPA have
considered that the purpose behind the solid waste and floodplain regulations is to ensure that
such wastes do not contaminate the stream or adjacent groundwater and to prevent the
washout of solid waste disposal areas by the stream or floodwaters. The criteria used by the
agencies to determine where tailings may be left in place within the floodplain, together with
an institutional controls program to monitor the effectiveness of STARS and ensure the
integrity of STARS treated areas (including the additional use of engineering controls, such
as riprap, or re-treatment or removal of STARS treated areas, if necessary) can attain these
specific goals at an equivalent level of performance.
Design of the remedy will have to ensure that treated tailings/impacted soils are protected by
their location, placement or sufficient engineering controls to ensure that such materials will
not be subject to any level of washout or erosion. Appropriately ensuring against any level
of washout or erosion is a required condition for the application of this ARAR waiver. All
other ARARs identified in Appendix A, including those specifically requiring the protection
of solid wastes or toxic or hazardous materials in the floodplain from washout or erosion,
remain applicable or relevant and appropriate and must be met by appropriate design and
implementation of the remedy.
During design and implementation of the remedy, several other location-specific ARARs
must continue to be observed. Several of these, including the Fish and Wildlife Coordination
Act, the Endangered Species Act, the Migratory Bird Treaty Act and the Bald Eagle
Protection Act, require continued consultation with the U.S. Fish and Wildlife Service.
Other location-specific ARARs require consideration of historical resources and continued
consultation with the State Historic Preservation Officer. ARCO, EPA, MDEQ, the State
Historic Preservation Officer, the National Council on Historic Preservation, and both local
governments in the area have entered into a Programmatic Agreement to ensure the
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appropriate consideration of cultural and historic resources in the Clark Fork Basin, including
those within the SST OU.
Action-specific ARARs
Action-specific ARARs generally provide guidelines for the manner in which specific
activities must be implemented. Thus, compliance with many action-specific requirements
must be ensured through appropriate design and implementation of the remedy.
The remedy is to be designed and implemented in accordance with dust suppression and air
quality regulations, certain reclamation requirements which have been determined to be
relevant and appropriate to this action, and other action-specific ARARs identified in
Appendix A.
Cost-Effectiveness
MDEQ and EPA have determined that the selected remedy is cost-effective in mitigating the
principal risks posed by the tailings/impacted soils, instream sediments, railroad materials
and contaminated groundwater. Section 300.430(f)(ii)(D) of the NCP requires evaluation of
cost-effectiveness. The remedy must provide overall effectiveness proportional to its costs.
Overall effectiveness is determined by the following three balancing criteria: long-term
effectiveness and permanence; reduction of toxicity, mobility or volume through treatment;
and short-term effectiveness.
The estimated costs of the selected remedy, as well as the costs of the other alternatives
considered, are described in Tables 15, 16, and 17 of this record of decision. To the extent
that the estimated cost of the selected remedy exceeds the costs of other alternatives, the
additional cost is reasonably related to the additional benefits in long-term effectiveness and
permanence and reduction of toxicity and mobility of the contaminants through the relocation
and treatment to be used.
With respect to the short-term effectiveness of the remedy, including consideration of the
risks involved to workers and the community as the remedy is being implemented, the
agencies have revised the remedy from the preferred alternative identified hi the proposed
plan (MDEQ, 1995a). The change from Alternative 6, using one or two centralized
repositories, to Alternative 5, using numerous local relocation repositories, will reduce
concerns regarding the short-term effectiveness of the remedy. The use of numerous local
repositories will dramatically reduce the length of trips travelled by trucks hauling the
contaminated materials, and consequently will reduce the risk of traffic accidents and the
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risks/inconvenience to local communities that would be affected by such construction traffic.
The remaining risks posed during implementation can be adequately addressed by proper
safety precautions in the implementation of the remedy.
The selected remedy, fully addressing the sources of contamination, and provides the best
overall effectiveness of all alternatives proportional to its cost. The tailings/impacted soils
and railroad remediation are believed necessary in order to adequately protect Silver Bow
Creek and the alluvial aquifers, in addition to providing a realistic opportunity to fully
stabilize and achieve cleanup goals at the OU in the future. The agencies have determined
that, if the tailings/impacted soils designated for relocation were not removed from the
floodplain prior to treatment, the reduction in toxicity and mobility resulting from such
treatment could well be only temporary. Thus the agencies have determined that such
relocation is appropriate and cost-effective. The tailings that will remain in the floodplain
are those that the agencies believe can be adequately protected by long-term maintenance
activities or the addition of engineering controls, if necessary. In addition, the actions
prescribed for sediments are necessary and cost-effective to address threats to and adverse
impacts on the environment, including toxicity to aquatic organisms, ranging from
macroinvertebrates to fish, as well as to prevent recontamination of the water in the stream.
As detailed above, the agencies have determined that the costs of this remedy are
proportional to the overall effectiveness that will be achieved by the selected remedy.
Utilization of Permanent Solutions and Alternative Treatment Technologies to the Maximum
Extent Practicable
MDEQ and EPA have determined that the selected remedy represents the maximum extent to
which an alternative treatment technology, STARS, can be used within the OU consistent
with the need to provide a permanent solution. The specific nature of the STARS treatment
technology must be considered in evaluating the appropriate use of STARS. STARS was
developed by the State as a low cost, in-situ, alternative treatment technology. Considering
the limitations on the effectiveness of the technology, it has been included in the remedy to
the maximum extent practicable. Removal of the material from the floodplain prior to using
STARS effects a permanent solution, as well as utilizes an alternative treatment technology,
since outside the floodplain, the STARS treated areas can be expected to remain intact. Thus
by this combination of removal of certain vulnerable tailings/impacted soils from the
floodplain along with STARS treatment of all tailings/impacted soils both within and outside
the floodplain, the selected remedy attempts to maximize the use of both permanent solutions
and alternative treatment technologies.
Of those alternatives that are protective of human health and the environment and comply
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with ARARs or have an adequate bases for an ARAR waiver, MDEQ and EPA have
determined that this selected remedy provides the best balance of trade-offs in terms of long-
term effectiveness and permanence, reduction in toxicity, mobility, or volume achieved
through treatment, short-term effectiveness, implementability and cost, while also considering
the statutory preference for treatment as a principal element and considering state and
community acceptance. The detailed evaluation of the balance of these criteria among the
alternatives considered is set forth in the FS Report and is summarized in Section VHI,
Summary of Comparative Analysis of Alternatives, of this record of decision.
The selected remedy includes removal and treatment of contaminated media which will
permanently and significantly reduce the principal threats posed by the tailings/impacted
soils, instream sediments and railroad materials. The other alternative considered which
could achieve similar or more substantial reductions, Alternative #6, would do so at
significant additional expense, although there was, overall, widespread support for OU-wide
Alternative 6 from communities in the basin. Other alternatives considered, including
containment, capping and partial excavation, did not offer similar prospects for
protectiveness, effectiveness or permanence.
Preference for Treatment as a Principal Element
As discussed in the section on utilization of alternative treatment technologies above, the
selected remedy incorporates the use of STARS treatment of practically all contaminated
materials. Such treatment will be used for all the tailings left in the floodplain and will be
used extensively in construction of the tailings repositories located outside the floodplain.
Thus, by utilizing treatment as a significant portion of the remedy, the statutory preference
for remedies that employ treatment as a principal element is satisfied.
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XL DOCUMENTATION OF SIGNIFICANT CHANGES
In the proposed plan (MDEQ, 1995a), MDEQ and EPA submitted as the preferred remedy
for the OU the combination of actions set out as OU-wide Alternative 6 in Draft Feasibility
Study Report (ARCO, 1995b). This remedy was detailed in a proposed plan which was
submitted for public comment for 60 days from June 9 through August 7, 1995. Over 580
comments were received from local government entities, a potentially responsible party,
environmental groups, business organizations, and numerous individual citizens. Comments
were received from the Butte area, the Anaconda area, the Missoula area, and several other
areas of Montana, as well as out of state.
The vast majority of the comments supported the preferred remedy as delineated hi the
proposed plan (MDEQ, 1995a), and most strongly supported full and effective cleanup of the
Silver Bow Creek corridor. One distinct group of comments, which included support from
local government entities in both the Butte and Anaconda areas, promoted a remedy which
would incorporate a "greenway" or recreational corridor conceptual land use proposal. In
addition, some comments, including government representatives in the Butte and Anaconda
area, strongly objected to use of the two proposed repositories.
After considering the public comments received, especially the concerns expressed by local
government representatives, MDEQ and EPA have included certain modifications to the
proposed remedy. This record of decision will achieve substantial cost savings by avoiding
transport of the excavated materials to a single repository, and by instead allowing the use of
several local repositories which would be maintained over the long-term by an institutional
controls plan such as a recreational corridor or similar designated recreational use plan.
The agencies' initial proposal for one or two central repositories was founded upon certain
advantages including: (1) the wastes would be removed from the stream corridor where the
relocation repositories might be incompatible with future residential or other land uses; (2)
significantly less restriction on residential, agricultural (grazing, irrigating, etc.) land uses;
(3) the amount of presently undisturbed land used for waste repositories would be
significantly reduced or eliminated; (4) substantially reduced long-term monitoring and
maintenance requirements; and (5) reduced lime requirements for the remedy. The agencies
acknowledge the comments by ARCO and other supporters of a designated recreational use
plan that a recreational corridor concept allows an implementable means of ensuring long-
term monitoring and maintenance of numerous local repositories, thus addressing many of
those concerns which led the agencies to propose a central repository. In light of the cost
savings that can be achieved if the appropriate maintenance program can be established, as
well as reduced short-term risk impacts on local communities during construction, the
agencies believe use of numerous local repositories will be more cost effective.
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Consequently, the agencies are including in the f, :al remedial action plan the use of local
relocation repositories rather than a central repos: .>ry, if it can be demonstrated that adequate
space for such repositories is available outside of ;ie CH2M Hill (1989a) floodplain and that
the long-term maintenance and monitoring of sue! repositories can be ensured through a
properly designed and adequately funded institutional controls program.
The cost savings which could be obtained by the changes from the proposed plan (MDEQ,
1995a) remedy is estimated at $15,000,000 - $20,000,000. The savings achieved by this
remedial action plan, will allow full funding of the institutional controls/management and
monitoring plan, through establishment of a designated recreational use plan, and still
provide substantial cost savings in the implementation of the remedy.
The remedial action plan will still incorporate the removal of tailings/impacted soils,
contaminated instream sediments and certain railroad bed materials from the floodplain,
except in those specific locations where such materials can be adequately protected in place
and treated with the STARS technology to prevent further migration of the contaminants.
The agencies believe that the final remedial action plan, as described, including the
utilization of several local repositories, if appropriate, can be implemented in a manner that
provides protection of the public health, safety, welfare and the environment and attains
legally applicable or relevant and appropriate requirements. This change also takes into
account the Butte-Silver Bow and Anaconda-Deer Lodge Counties' desire for a recreational
land use plan for the Silver Bow Creek corridor.
Based on these concerns the agencies have revised the preferred remedy to a modified
Alternative 5 as delineated in the Feasibility Study and proposed plan (MDEQ, 1995a).
This change in repository locations does not substantially reduce the protectiveness of the
remedy. When implemented correctly, the modified Alternative 5 will be protective of
human health and the environment. The differences between the final remedial action plan
and the proposed plan are as follows:
All removed materials will be placed in local relocation
repositories and fully treated by the STARS technology in two
foot lifts. These repositories will be located safely outside of
the 100-year floodplain as delineated by CH2M Hill (1989a),
and will be monitored and maintained as part of an institutional
controls, monitoring and maintenance program for the Silver
Bow Creek corridor.
Although the specific volumes of tailings/impacted soils to meet
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the protectiveness criteria will be determined by the agencies
during remedial design re-evaluation of the site data have
indicated that less excavation than that proposed will be
necessary. The approximate volumes have been slightly
adjusted to take into account the 50,000 cy removed at the
Demonstration Projects in Subarea 4 and to allow for
implementation of in-situ STARS treatment for an additional
170,000 cy in Subarea 4.
Constructed wetlands are designated as the end land use for
Subarea 1. After removal of all identified contaminant sources,
reconstruction of the Subarea will be designed to incorporate use
of the area as wetlands. Constructed wetlands in this area may
be used as a treatment system for nutrients and/or metals from
upstream, if such treatment is ultimately determined to be
appropriate in this area.
The requirements for removal of instream sediments has been
specified that fine-grained (< 1mm) sediments in all depositional
areas (regardless of size) will be removed.
The volume of railroad bed materials to be excavated or treated
has been estimated more precisely to include only those
materials directly impacting Silver Bow Creek at bridge
abutments or along the stream bank.
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. REFERENCES
Atlantic Richfield Company (ARCO), 1991a. Silver Bow Creek/Butte Area
National Priorities List Site (NPL). Streamside Tailing Operable Unit
Remedial Investigation/Feasibility Study (RI/FS). Final Work Plan. October
1991.
1993, Silver Bow Creek/Butte Area NPL Site, Streamside Tailings Operable
Unit RI/FS, Remedial Action Objectives Report/Treatment Technology
Scoping Document, June.
1994. SST OU Sediment Survey Summary. Submittal Letter. June 7, 1994
1995a. Streamside Tailings Operable Unit, Draft Remedial Investigation
Report. January 1995.
1995b. Streamside Tailings Operable Unit, Draft Feasibility Study Report.
June 1995.
ASTM, 1995a. Standard test methods for measuring the toxicity of sediment-
associated contaminants with freshwater invertebrates. ASTM E1706-905a.
ASTM 1995 Annual Book of Standards Volume 11.05, Philadelphia, PA.
1995b. Standard guide for determining the bioaccumulation of sediment-
associated contaminants by benthic invertebrates. ASTM El 688-95. ASTM
1995 Annual Book of Standards Volume 11.05, Philadelphia, PA.
Axtmann, E.V. and Luoma, S.N., 1991. Large-Scale Distribution of Metal Contamination
in the Fine-Grained Sediments of the Clark Fork River, Montana, U.S.A., Applied
Geochemistry, vol. 6, pp. 75 - 88.
Ayres Associates, 1995. Channel Change - Silver Bow Creek and the Clark Fork
River. Prepaired for the Montana Department of Justice, October.
Beck, S., D. Melfi, and K. Yalamanchili, 1993. Lateral Migration of the Genesse
River, New York. River Meandering, Proceedings of the Conference Rivers
'83, ASCE, New Orleans, October.
Benner, G.B., Smart, E.W., and Moore, J.N., 1995. Metal Behavior During
Surface - Groundwater Interaction, Silver Bow Creek, Montana.
Environmental Science and Technology, Vol. 29, No. 7.
127
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Besser, J.M., J.A. Kubitz, C.G. IngersoII, E. Braselton, and J.P. Giesy, 1995a.
Influences on copper bioaccumulation, growth, and survival of the midge
Chironomus tentans in metal-contaminated sediments. J. Aquatic Ecosystem
Health: In press.
Besser, J.M., C.G. IngersoII, and J.P. Giesy. 1995b. Spatial and temporal
variability of acid volatile sulflde on the bioavailability of copper and zinc in
freshwater sediments. Environ. Toxicol. Chem.: In press.
Butte Archives. 1995. Personal communication. August 10, 1995.
CH2M Hill, 1987. Data Summary Report Addendum; Supplemental Remedial
Investigation, Silver Bow Creek Site, Butte, Montana. Helena, Montana.
1989a. Silver Bow Creek Flood Modeling Study. Prepared for Montana
Department of Health and Environmental Sciences. Helena, Montana.
November 1989.
1989b. Silver Bow Creek CERCLA Phase H Remedial Investigation Data
Summary. Warm Springs Ponds Operable Unit.
Essig, D.A. and Moore J.N., 1992. Clark Fork Damage Assessment Bed Sediment
Sampling And Chemical Analysis Report, University of Montana.
Freeman, H.C., 1900. A Brief History of Butte, Montana, The World's Greatest
Mining Company. Henry O. Shepard Company. Chicago, Illinois.
GCM Services Inc., 1991. Silver Bow Creek Streamside Tailings RI/FS. Cultural
Resources Inventory. Prepared for ARCO. August 1991.
Historical Research Associates (HRA), 1983. Title Search and Historical Survey,
Site Narrative Reports. Butte/Silver Bow Creek, Silver Bow County,
Montana.
IngersoII, C.G., 1991. Sediment toxicity and bioaccumulation testing methods.
ASTM Standardization News 19:28-33.
IngersoII, C.G., W.G. Brumbaugh, FJ. Dwyer, and N.E. Kemble. 1994.
Bioaccumulation of metals by Hyalella azteca exposed to contaminated
sediments from the upper Clark Fork River, Montana. Environ. Toxicol.
Chem. 13:2013-2020.
128
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Ingersoll, C.G., G.T. Ankley, D.A. Benoit, G.A. Burton, F.J. Dwyer, I.E.
Greer, T.J. Norberg-King, and P.V. Winger. 1995a. Toxicity and
bioaccumulation of sediment-associated contaminants with freshwater
invertebrates: A review of methods and applications. Environ. Toxicol.
Chem.: In press.
Ingersoll, C.G., Haverland P.S., Brunson, EX., Canfield, T.J, Dwyer, F.J.,
Henke, C.E., and Kembel, N.E.. 1995b. Calculation and evaluation of
sediment effect concentrations for the amphipod Hyalella aztecz and the midge
Chironomus riparius. J. Great Lakes Res.: In review.
Ingersoll, C.G., Haverland P.S., Brunson, E.L., Canfield, T.J, Dwyer, F.J.,
Henke, C.E., and Kembel, N.E.. 1995c. Calculation and evaluation of
sediment effect concentrations. National Biologic Service final report for the
USEPA GLNPO assessment and remediation of contaminated sediments
project. EPA series number pending, Chicago, IL.
Ingersoll, C.G., G.A. Burton, G.T. Ankley, R. Baudo, D.D. MacDonald, S.
Luoma, T. Reynoldson, R.C. Swartz, K. Solomon, W. Warren-Hicks.
1995d. Critical issues in methodological uncertainty for sediment risk
assessments. Biddinger, G., and T. Dillon (eds.). Sediment Ecological Risk
Assessment. SETAC Press, Pensacola, FL: In press.
Kemble, N.E., W.G. Brumbaugh, E.L. Brunson, F.J. Dwyer, C.G. Ingersoll,
D.P. Monda, and D.F. Woodward. 1994. Toxicity of metal-contaminated
sediments from the upper Clark Fork River, Montana to aquatic invertebrates
and fish in laboratory exposures. Environ. Toxicol. Chem. 13:1985-1997.
Kubitz, J.A., J.M. Besser, E. Breselton, and J.P. Giesy. 1995. An optimal
experimental design for a small-volume, static-renewal sediment toxicity test
using Hyatella azteca. Environ. Toxicol. Chem.: In review.
Long, E.R. and Morgan, L.G., 1990. The Potential for Biologic Effects of Sediment-
Sorbed Contaminants Tested in the National Status and Trends program. National
Oceanic and Atmospheric Administration. Seattle, WA.
MacDonald, D.D., R.S. Carr, F.D. Calder, E.R. Long, and C.G. Ingersoll.
1995. Development and evaluation of sediment quality guidelines for Florida
coastal waters. J. of Environmental Health: In press.
Maxim, 1995. Streamside Tailings Operable Unit - Addendum to Sediment Survey
129
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Summary, Report prepared for MDEQ, September 21.
McGuire, D.L., 1995. Clark Fork River Macroinvertebrate Community Biointegrity: 1986
through 1994. McGuire Consulting. In press.
Meast, A.S., 1995. Rebuttal of ARCO's Reports on STARS. Prepaired for the State
of Montana, Natural Resource Damage Litigation Program, October.
Montana Department of Health and Environmental Sciences (MDHES, now
MDEQ)., 1983. An intensive survey of Silver Bow Creek and the Upper
Clark Fork River. Montana Department of Health and Environmental
Sciences, Water Quality Bureau. Helena, Montana.
1991. Administrative Order on Consent.
1993a. An Assessment of Biological Integrity and Impairment of Aquatic Life
in the Clark Fork River and its Major Tributaries Based on Structure and
Composition of Algae Associations in the Periphyton Community, August
1991 and 1992. July 1993.
1993b. Clark Fork River Macroinvertebrate Community Biointegrity, 1986
through 1992. August 1993.
1994a. Draft Baseline Risk Assessment, Streamside Tailings Operable Unit,
Silver Bow Creek/Butte Area NPL Site," prepared by Camp, Dresser and
McKee, Inc., December.
1994b. Screening and Description of Potential Applicable or Relevant and
Appropriate Requirements for the Feasibility Study Analysis of Alternatives, "
December.
1995a. Streamside Tailings Operable Unit - Proposed Plan, June.
1995b. Streamside Tailings Operable Unit - Risk Associated with Ore
Concentrate Spills, November.
1995c. Erosion and Instream Sediment Toxicity letter from MDEQ to ARCO,
November.
Montana Department of Justice (MDOJ)., 1995. Evaluation on Critique of the
Streambank Tailings and Revegetation Studies (STARS) Remediation
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Technology. Montana Department of Justice, Natural Resource Damage
Litigation Program. Helena, Montana.
MultiTech., 1987. Silver Bow Creek Remedial Investigation Draft Final Report.
Prepared for Montana Department of Health and Environmental Sciences,
Solid and Hazardous Waste Bureau. Helena, Montana. May 1987.
Nanson, G. C. and E. J. Hie kin, 1986. A Statistical Analysis of Bank Erosion and
Channel Migration in Western Canada. Geological Society of America Bulletin, V.
97, p. 497-504.
PTI, 1989. Silver Bow Creek Water Quality and Sediment Sampling Data, for
Parcel, Mauro, Hultan & Spaanstra, Denver, Colorado, September.
Reclamation Research Unit of Montana State University (RRU), Schafer &
Associates and CH2M Hill, Inc. 1989a. Silver Bow Creek RI/FS.
Streambank Tailings and Revegetation Studies Phase I Final Summary Report,
Volume I.
1989b. Silver Bow Creek RI/FS. Streambank Tailings and Revegetation
Studies Phase n Final Summary Report, Volume I.
1993. Streambank Tailings and Revegetation Studies, STARS Phase m Final
Report. Montana Department of Health and Environmental Sciences. Helena
Montana.
R2 Resource Consultants, 1995. Silver Bow Creek Long-Term Concentrations of
Metals in Stream Sediments Resulting from Lateral Channel Migration. Report
prepaired for ARCO.
Schumm, S.A., 1995. Channel Change - Silver Bow Creek and the Clark Fork
River, Ayres and Associates, Fort Collins, CO, October.
Simons, D.B., 1995. Analysis of Silver Bow Creek. Report prepaired for ARCO,
August.
Smart, E.W., 1995. Surface Water and Groundwater in a Shallow Unconfined
Alluvial Aquifer and Small Mountain Stream, Silver Bow Creek, Montana.
Master of Science Thesis, University of Montana, Missoula, Montana.
131
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STREAMSIDE TAILINGS OPERABLE UNIT ROD - DECISION SUMMARY
Smith, S.L., D.D. MacDonald, K.A. Kennleyside, C.G. Ingersoll, and J. Field.
1995. A preliminary evaluation of sediment quality assessment values for
freshwater ecosystems. J. Great Lakes Research: In review.
Smith, R.j. 1952. History of Early Reduction Plants of Butte, Montana. Reprint
from De Re Metallica. Vol. 18. Nos. 2 and 3.
Spindler, J.C. 1976. The clean-up of Silver Bow Creek. Prepared for the
Anaconda Mining Company. Butte, Montana.
Techlaw, Inc. 1985. Final Report, Silver Bow Creek, Montana. U.S. EPA Region
Vffl.
Titan Environmental, 1995. Natural Recovery of Sediments with Bank Erosion
Tailings Input. Memorandum to ARCO, March.
U.S. Environmental Protection Agency. 1977. Interim report: geohydrological
evaluation of Silver Bow Creek and its floodplain, Butte, Montana area. U.S.
Environmental Protection Agency National Enforcement Investigations Center.
Denver, Colorado.
1988. Guidance for Conducting Remedial Investigations and Feasibility
Studies Under CERCLA. Interim Final. EPA/540/G-89-004. U.S.
Environmental Protection Agency, Office of Emergency and Remedial
Response. Washington D.C.
1989. Methods for Evaluating the Attainment of Cleanup Standards. Volume
1: Soils and Solid Media. EPA 230/02-89-042.
1993. OSWER Directive No. 9355.3-20, Revisions to OMB Circular A-94
on Guidelines and Discount Rates for Benefit-Cost Analysis.
1994. Methods for measuring the toxicity and bioaccumulation of sediment-
associated contaminants with freshwater invertebrates. EPA 600/R-024,
Duluth, MN.
Woodward, D.F., Brumbaugh, W.G., DeLonay, A.J., Little, E.E., and Smith,
C.E., 1994. Effects on Rainbow Trout Fry of a Metals-Contaminated Diet of
Benthic Invertebrates from the Clark Fork River, Montana, American
Fisheries Society, 123:52-62.
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APPENDIX A
IDENTIFICATION AND DESCRIPTION OF
APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS
STREAMSIDE TAILINGS OPERABLE UNIT
SILVER BOW CREEK/BUTTE ADDITION NPL SITE
November 1995
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TABLE OF CONTENTS
Pa 2e
I. FEDERAL CONTAMINANT SPECIFIC REQUIREMENTS 3
A. Groundwater Standards - Safe Drinking Water Act (Relevant and
Appropriate) 3
B. Surface Water - Ambient Standards and Point Source Discharges 4
C. Air Standards - Clean Air Act (Applicable) 5
H. FEDERAL LOCATION SPECIFIC REQUIREMENTS 5
A. Fish and Wildlife Coordination Act (Applicable) 5
B. Floodplain Management Order (Applicable) 5
C. Protection of Wetlands Order (Applicable) . 6
D. The Endangered Species Act (Applicable) 6
E. The National Historic Preservation Act (Applicable) 6
F. Archaeological and Historic Preservation Act (Applicable) 7
G. Historic Sites, Buildings, and Antiquities Act (Applicable) 7
H. Migratory Bird Treaty Act (Applicable) 7
I. Bald Eagle Protection Act (Applicable) 7
J. Resource Conservation and Recovery Act (Relevant and Appropriate) ... 7
m. FEDERAL ACTION SPECIFIC REQUIREMENTS 8
A. Solid Waste (Applicable), Surface Mining Control and Reclamation
(Relevant and Appropriate), and RCRA (Relevant and Appropriate)
Requirements 8
B. Air Standards - Clean Air Act (Applicable) 8
C. Point Source Controls - Clean Water Act (Applicable) 9
D. Dredge and Fill Requirements (Applicable) 10
E. Underground Injection Control (Applicable) 10
F. Transportation of Hazardous or Contaminated Waste (Relevant and
Appropriate) 10
IV. MONTANA CONTAMINANT SPECIFIC REQUIREMENTS 11
A. Water Quality 11
1. Surface Water Quality Standards (Applicable) 11
2. Groundwater Pollution Control System (Applicable) 14
B. Air Quality 15
V. MONTANA LOCATION SPECIFIC REQUIREMENTS 16
A. Floodplain and Floodway Management Act and Regulations
(Applicable) .16
B. Solid Waste Management Regulations (Applicable) 19
C. Natural Streambed and Land Preservation Standards (Applicable) 22
VI. MONTANA ACTION SPECIFIC REQUIREMENTS 22
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A. Water Quality 22
1. Groundwater Act (Applicable) 22
2. - Public Water Supply Regulations (Applicable) 23
B. Air Quality 23
1. Air Quality Regulations (Applicable) 23
C. Solid Waste Regulation 24
D. Reclamation Requirements 25
1. Reclamation Activities - Hydrology Regulations (Relevant and
Appropriate) 26
2. Reclamation and Revegetation Requirements (Relevant and
Appropriate) • 27
TO BE CONSIDERED DOCUMENTS (TBCS) 28
Vm. OTHER LAWS (NON-EXCLUSIVE LIST) 28
A. Other Federal Laws 29
1. Occupational Safety and Health Regulations 29
B. Other Montana Laws 29
1. Groundwater Act 29
2. Water Rights 29
3. Controlled Ground Water Areas 30
4. Occupational Health Act 31
5. Montana Safety Act . • 31
6. Employee and Community Hazardous Chemical Information Act . . 31
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LIST OF ACRONYMS
ARAR Applicable or Relevant and Appropriate Requirements
ATSDR Agency of Toxic Substances and Disease Registry
BAT Best Available Technology Economically Achievable
BCT Best Conventional Pollutant Control Technology
BPCTCA Best Practicable Control Technology Currently Available
BPJ Best Professional Judgment
BTCA Best Technology Currently Available
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act of
1980
DNRC Department of Natural Resources and Conservation (Montana)
DSL Department of State Lands (Montana)
EPA U.S. Environmental Protection Agency
FIFRA Federal Insecticide, Fungicide, and Rodenticide Act
HWM Hazardous Waste Management
LNAPL Light Non-aqueous Phase Liquid
MCL Maximum Contaminant Level
MCLG Maximum Contaminant Level Goal
MDEQ Montana Department of Environmental Quality
MGWPCS Montana Groundwater Pollution Control System
MPDES Montana Pollutant Discharge Elimination System
NCP National Contingency Plan
NESHAPS National Emissions Standards for Hazardous Air Pollutants
NPL National Priorities List
NPDES National Pollutant Discharge Elimination System
PAH Polynuclear Aromatic Hydrocarbon
PCP Pentachlorophenol
POHC Principal Organic Hazardous Constituents
POTW Public Owned Treatment Works
PSD Prevention of Significant Deterioration
RCRA Resource Conservation and Recovery Act
RI/FS Remedial Investigation/Feasibility Study
ROD Record of Decision
SHPO State Historic Preservation Officer (Montana)
SIP State Implementation Plan
TBC To Be Considered
TU Turbidity Unit
UIC Underground Injection Control
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INTRODUCTION
Section 121(d) of CERCLA, 42 U.S.C. § 962l(d), certain provisions of the current National
Contingency Plan (the NCP), 40 CFR Part 300 (1990), and guidance and policy issued by
the Environmental Protection Agency (EPA) require that remedial actions taken pursuant to
Superfund authority shall require or achieve compliance with substantive provisions of
applicable or relevant and appropriate standards, requirements, criteria, or limitations from
state environmental and facility siting laws, and from federal environmental laws at the
completion of the remedial action, and/or during the implementation of the remedial action,
unless a waiver is granted. These requirements are threshold standards that any selected
remedy must meet. See Section 121(d)(4) of CERCLA, 42 U.S.C. § 9621(d)(4); 40 CFR §
300.430(f)(l). EPA calls standards, requirements, criteria, or limitations identified pursuant
to section 121(d) "ARARs," or applicable or relevant and appropriate requirements.
ARARs are either applicable or relevant and appropriate. Applicable requirements are those
standards, requirements, criteria, or limitations promulgated under federal or state
environmental or facility siting laws that specifically address a hazardous substance,
pollutant, or contaminant, remedial action, location, or other circumstance found at a
CERCLA site. Relevant and appropriate requirements are those standards, requirements,
criteria, or limitations promulgated under federal environmental or state environmental or
facility siting laws that, while not "applicable" to hazardous substances, pollutants,
contaminants, remedial actions, locations, or other circumstances found at a CERCLA site,
address problems or situations sufficiently similar to those encountered at the CERCLA site
such that their use is well suited to the particular site. Factors which may be considered in
making this determination are presented in 40 CFR § 300.400(g)(2). Compliance with both
applicable and relevant and appropriate requirements is mandatory.1
Each ARAR or group of related ARARs is identified by a specific statutory or regulatory
citation, a classification describing whether the ARAR is applicable or relevant and
appropriate, and a description which summarizes the requirements, and addresses how and
when compliance with the ARAR will be measured (some ARARs will govern the conduct of
the remedial action, some will define the measure of success of the remedial action, and
some will do both).2 The descriptions given here are provided to allow the reader a
reasonable understanding of each requirement without having to refer constantly to the statute
or regulation itself and to provide an explanation of how the requirement is to be applied in
the specific circumstances involved at this operable unit.
See CERCLA Section 121(d)(2)(A), 42 U.S.C. Section 9621(d)(2)(A).
40 CFR Section 300.435(b)(2); Preamble to the Proposed NCP, 53 Fed.. Reg. 51440 (December 21, 1988);
Preamble to the Final NCP, 55 Fed. Reg. 8755-8757 (March 8, 1990). The Atlantic Richfield Company (ARCO),
an identified potentially responsible party for this operable unit, argues that the NCP's application of ARARs
during the remedial action is not consistent with the CERCLA statute. However, ARCO did not challenge the
NCP in the District of Columbia Court of Appeals in a timely manner, and therefore has waived the right to assert
this argument. See Section 113(a) of CERCLA, 42 U.S.C. Section 9613(a).
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Also contained in this list are policies, guidance and other sources of information which are
"to be considered" in the selection of the remedy and implementation of the record of
decision (ROD). Although not enforceable requirements, these documents are important
sources of information which EPA and the State of Montana Department of Environmental
Quality (MDEQ) may consider during selection of the remedy, especially in regard to the
evaluation of public health and environmental risks; or which will be referred to, as
appropriate, in selecting and developing cleanup actions.3
Finally, this list contains a non-exhaustive list of other legal provisions or requirements
which should be complied with during the implementation of the ROD.
ARARs are divided into contaminant specific, location specific, and action specific
requirements, as described in the NCP and EPA guidance. Contaminant specific ARARs are
listed according to specific media and govern the release to the environment of specific
chemical compounds or materials possessing certain chemical or physical characteristics.
Contaminant specific ARARs generally set health or risk based numerical values or
methodologies which, when applied to site-specific conditions, result in the establishment of
numerical values. These values establish the acceptable amount or concentration of a
chemical that may be found in, or discharged to, the ambient environment.
Location specific ARARs are restrictions placed on the concentration of hazardous substances
or the conduct of cleanup activities because they are in specific locations. Location specific
ARARs generally relate to the geographic location or physical characteristics or setting of the
site, rather than to the nature of the site contaminants.
Action specific ARARs are usually technology or activity based requirements or limitations
on actions taken with respect to hazardous substances.
Only the substantive portions of the requirements are ARARs.4 Administrative requirements
are not ARARs and thus do not apply to actions conducted entirely on-site. Administrative
requirements are those which involve consultation, issuance of permits, documentation,
reporting, recordkeeping, and enforcement. The CERCLA program has its own set of
administrative procedures which assure proper implementation of CERCLA. The application
of additional or conflicting administrative requirements could result in delay or confusion.5
Provisions of statutes or regulations which contain general goals that merely express
legislative intent about desired outcomes or conditions but are non-binding are not ARARs.6
40 CFR Section 300.400(g)(3); 40 CFR Section 300.415(i); Preamble to the Final NCP, 55 Fed. Reg. 8744-8746
(March 8, 1990).
40 CFR Section 300.5. See also Preamble to the Final NCP, 55 Fed. Reg. 8756-8757 (March 8, 1990).
Preamble to the Final NCP, 55 Fed. Reg. 8756-8757 (March 8, 1990); Compliance with Other Laws Manual,
Vol. I, pp. 1-11 through 1-12.
Preamble to the Final NCP, 55 Fed. Reg. 8746 (March 8, 1990).
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Many requirements listed here are promulgated as identical or nearly identical requirements
in both federal and state law, usually pursuant to delegated environmental programs
administered by EPA and the states, such as the requirements of the federal Clean Water Act
and the Montana Water Quality Act. The preamble to the new NCP states that such a
situation results in citation to the state provision as the appropriate standard, but treatment of
the provision as a federal requirement. ARARs and other laws which are unique to state law
are -identified separately by the State of Montana.
This document constitutes MDEQ's and EPA's formal identification and detailed description
of ARARs for remedial action at the Streamside Tailings Operable Unit. This ARARs
analysis is based on section 121 (d) of CERCLA, 42 U.S.C. § 962l(d); CERCLA
Compliance with Other Laws Manual, Volumes I and E, OSWER Dirs. 9234.1-01 and-02
(August 1988 and August 1989 respectively); various CERCLA ARARs Fact Sheets issued as
OSWER Directives; the Preamble to the Proposed NCP, 53 Fed. Reg. 51394 et seq.
(December 21, 1988); the Preamble to the Final NCP, 55 Fed. Reg. 8666-8813 (March 8,
1990); the Final NCP, 40 CFR Part 300 (55 Fed. Reg. 8813-8865, March 8, 1990), and the
substantive provisions of law discussed in this document.
FEDERAL ARARS
I. FEDERAL CONTAMINANT SPECIFIC REQUIREMENTS
A. Groundwater Standards - Safe Drinking Water Act (Relevant and Appropriate)7
The National Primary Drinking Water Standards (40 CFR Part 141), better known as
maximum contaminant levels and maximum contaminant level goals (MCLs and MCLGs),
are not applicable to the Streamside Tailings Operable Unit area because the aquifer
underlying the area is not a current public water system, as defined in the Safe Drinking
Water Act, 42 U.S.C. § 300f(4). These standards are relevant and appropriate standards,
however, because the groundwater in the area is a potential source of drinking water.
Groundwater use through private wells occurs in the area, and some of the groundwater in
the area is a current source of drinking water. In addition, the aquifer discharges to Silver
Bow Creek, which is designated as a potential drinking water source. Since Silver Bow
Creek is also a potential source of drinking water, these standards are relevant and
appropriate for that surface water as well.
Use of these standards for this action is fully supported by EPA regulations and guidance.
The Preamble to the NCP clearly states that MCLs are relevant and appropriate for
groundwater that is a current or potential source of drinking water (55 Fed. Reg. 8750,
March 8, 1990), and this determination is further supported by requirements in the
regulations governing conduct of RI/FS studies found at 40 CFR § 300.430(e)(2)(i)(B).
EPA's guidance on Remedial Action for Contaminated Groundwater at Superfund Sites states
that "MCLs developed under the Safe Drinking Water Act generally are ARARs for current
42 U.S.C. Sections 300f et seq.
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or potential drinking water sources." MCLGs which are above zero are relevant and
appropriate under the same conditions (55 Fed. Reg. 8750-8752, March 8, 1990). See also,
State of Ohio v. EPA. 997 F.2d 1520 (D.C. Cir. 1993), which upholds EPA's application of
MCLs and non-zero MCLGs as ARAR standards for groundwater which is a potential
drinking water source.
As noted above, standards such as the MCL and MCLG standards are promulgated pursuant
to both federal and state law. Currently, none of the State MCL's is more stringent than the
corresponding federal MCL.
Chemical MCLG MCL
Arsenic N.A.8 0.05 milligrams per liter (mg/1)9
Cadmium 0.005 mg/110 0.005 mg/111
Copper 1.3 mg/112 1.3 mg/113
Lead N.A.14 0.015 mg/115
Mercury 0.002 mg/116 0.002 mg/117
These standards incorporate applicable Resource Conversation and Recovery Act (RCRA)
standards for groundwater found at 40 CFR Part 264, Subpart F, which is incorporated
pursuant to state law at ARM 16.44.702. The RCRA standards are the same or less
stringent than the MCLs or MCLGs identified above.
B. Surface Water - Ambient Standards and Point Source Discharges.
CERCLA and the NCP provide that federal water pollution criteria that match designated 01
anticipated surface water uses are the usual surface water standards to be used at Superfund
cleanups, as relevant and appropriate standards, unless the state has promulgated surface
water quality standards pursuant to the delegated state water quality act. The State of
8 The MCLG for arsenic is zero, which is not considered appropriate for Superfund site cleanups.
9 40 CFR § 141.11, 60 Fed. Reg. 33926 (June 29, 1995).
10 40 CFR §141.51
" 40 CFR § 141.62.
12 40 CFR § 141.51
13 40 CFR § 141.80(c). The requirement is an action level rather than a simple numerical standard.
14 The MCLG for lead is zero, which is not considered appropriate for Superfund site cleanups.
15 40 CFR § 141.80(c), which establishes an action level rather than a pure numerical standard.
16 40 CFR § 141.51.
17 40 CFR § 141.62.
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Montana has designated uses for Silver Bow Creek and the Clark Fork River, and has
promulgated specific standards accordingly. Those standards and their application to the
Streamside Tailings-Operable Unit, as well as other surface water standards, are included in
the state ARARs identified below. These standards will be applied to all contaminants of
concern identified in the Streamside Tailings Operable Unit remedial investigation, both to
point sources retained or created by the Streamside Tailings cleanup and to ambient water in
the-Streamside Tailings Operable Unit.
C. Air Standards - Clean Air Act (Applicable)
Limitations on air emissions resulting from cleanup activities or emissions resulting from
wind erosion of exposed hazardous substances are set forth in the action specific
requirements, below.
E. FEDERAL LOCATION SPECIFIC REQUIREMENTS
A. Fish and Wildlife Coordination Act (Applicable)
These standards are found at 16 U.S.C. §§ 661 et seq. and 40 CFR § 6.302(g). They
require that federally funded or authorized projects ensure that any modification of any
stream or other water body affected by a funded or authorized action provide for adequate
protection of fish and wildlife resources. Compliance with this ARAR necessitates
consultation with the U.S. Fish and Wildlife Service (USFWS) and the State of Montana
Department of Fish, Wildlife, and Parks. Further consultation with these agencies will occur
during cleanup selection and implementation, and specific mitigative or other measures may
be identified to achieve compliance with this ARAR.
B. Floodplain Management Order (Applicable)
This requirement (40 CFR Part 6, Appendix A, Executive Order No. 11,988) mandates that
federally funded or authorized actions within the 100 year flood plain avoid, to the maximum
extent possible, adverse impacts associated with development of a floodplain. Compliance
with this requirement is detailed in EPA's August 6, 1985 "Policy on Floodplains and
Wetlands Assessments for CERCLA Actions." Specific measures to minimize adverse
impacts may be identified following consultation with the appropriate agencies.
If the remedial action selected for the Streamside Tailings Operable Unit is found to
potentially affect the floodplain, the following information will be produced: a Statement of
Findings which will set forth the reasons why the proposed action must be located in or
affect the floodplain; a description of significant facts considered in making the decisions to
locate in or affect the floodplain or wetlands including alternative sites or actions; a statement
indicating whether the selected action conforms to applicable state or local floodplain
protection standards; a description of the steps to be taken to design or modify the proposed
action to minimize the potential harm to or within the floodplain; and a statement indicating
how the proposed action affects the natural or beneficial values of the floodplain.
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C. Protection of Wetlands Order (Applicable)
This requirement (40 CFR Part 6, Appendix A, Executive Order No. 11,990) mandates that
federal agencies and potentially responsible parties (PRPs) avoid, to the extent possible, the
adverse impacts associated with the destruction or loss of wetlands and to avoid support of
new construction in wetlands if a practicable alternative exists. Section 404(b)(l), 33 U.S.C.
§ 1344(b)(l), also prohibits the discharge of dredged or fill material into waters of the United
States. (See also section IH.D below.) Together, these requirements create a "no net loss"
of wetlands standard.
Compliance with this ARAR will be achieved through consultation with the U.S. Fish and
Wildlife Service and the U.S. Corp of Engineers, to determine the existence and category of
wetlands present at the site, and any avoidance or mitigation and replacement which may be
necessary. ARCO, USFWS, and EPA have established a protocol for addressing these issues
during the RI/FS process.
D. The Endangered Species Act (Applicable)
This statute and implementing regulations (16 U.S.C. §§ 1531 - 1543, 50 CFR Part 402, and
40 CFR § 6.302(h)) require that any federal activity or federally authorized activity may not
jeopardize the continued existence of any threatened or endangered species or destroy or
adversely modify a critical habitat.
Compliance with this requirement involves consultation with USFWS, and a determination of
whether there are listed or proposed species or critical habitats present in the Streamside
Tailings Operable Unit, and, if so, whether any proposed activities will impact such wildlife
or habitat.
E. The National Historic Preservation Act (Applicable)
This statute and implementing regulations (16 U.S.C. § 470, 40 CFR § 6.310(b), 36 CFR
Part 800) require federal agencies or federal projects to take into account the effect of any
federally assisted undertaking or licensing on any district, site building, structure, or object
that is included in, or eligible for, the Register of Historic Places. If effects cannot be
avoided reasonably, measures should be implemented to minimize or mitigate the potential
effect. In addition, Indian cultural and historical resources must be evaluated, and effects
avoided, minimized, or mitigated.
In order to comply with this ARAR, EPA, MDEQ, and the PRP may consult with the State
Historic Preservation Officer (SHPO), who can assist in identifying listed or eligible
resources, and in assessing whether proposed cleanup actions will impact the resources and
any appropriate mitigative measures. Additionally, in April 1992, ARCO, EPA, MDEQ,
SHPO, the National Council on Historic Preservation, and local governments entered into a
Programmatic Agreement to ensure the appropriate consideration of cultural and historical
resources in a systematic and comprehensive manner throughout the Clark Fork Basin, in
connection with response actions at the four Clark Fork Basin Superfund sites. A Second
Programmatic Agreement was agreed upon in September 1994. The results of the
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Programmatic Agreements may provide additional consideration of the factors to be
addressed under this ARAR, and the two historical ARARs described below.
F. Archaeological and Historic Preservation Act (Applicable)
The statute and implementing regulations (16 U.S.C. § 469, 40 CFR § 6.30l(c)) establish
requirements for evaluation and preservation of historical and archaeological data, including
Indian cultural and historical resources, which may be destroyed through alteration of terrain
as a result of federal construction projects or a federally licensed activity or program. If
eligible scientific, prehistorical, or archaeological data are discovered during site activities,
they must be preserved in accordance with these requirements.
G. Historic Sites, Buildings, and Antiquities Act (Applicable)
Th; iuirement states that "in conducting an environmental review of a proposed EPA
act, .he responsible official shall consider the existence and location of natural landmarks
using information provided by the National Park Service pursuant to 36 CFR § 62.6(d) to
avoid undesirable impacts upon such landmarks. The Programmatic Agreement activities
described above should aid all parties in compliance with this ARAR.
H. Migratory Bird Treaty Act (Applicable)
This requirement (16 U.S.C. §§ 703 et seq.) establishes a federal responsibility for the
protection of the international migratory bird resource and requires continued consultation
with the USFWS during remedial design and remedial construction to ensure that the cleanup
of the site does not unnecessarily impact migratory birds. Specific mitigative measures may
be identified for compliance with this requirement.
I. Bald Eagle Protection Act (Applicable)
This requirement (16 U.S.C. §§ 668 et seq.) establishes a federal responsibility for
protection of bald and golden eagles, and requires continued consultation with the USFWS
during remedial design and remedial construction to ensure that any cleanup of the site does
not unnecessarily adversely affect the bald and golden eagle. Specific mitigative measures
may be identified for compliance with this requirement.
J. Resource Conservation and Recovery Act (Relevant and Appropriate)
Any discrete waste units created or retained by the Streamside Tailings site cleanup must
comply with the siting restrictions and conditions found at 40 CFR § 264.18(a) and (b).
These sections require management units to be designed, constructed, operated, and
maintained to avoid washout, because they are within or near the 100 year flood plain.
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m. FEDERAL ACTION SPECIFIC REQUIREMENTS
A. Solid Waste (Applicable), Surface Mining Control and Reclamation (Relevant and
Appropriate), and RCRA (Relevant and Appropriate) Requirements
The contamination at the Streamside Tailings Operable Unit is primarily mining waste from
various man-made sources. For the purposes of this record of decision, EPA and the State
have determined that these wastes are not RCRA hazardous waste, in accordance with 40
CFR § 261.4(b)(7) (the Bevill exemption), although certain RCRA hazardous waste
requirements have been determined to be relevant and appropriate in the handling of these
wastes. For any management (i.e., treatment, storage, or disposal) or removal or retention
of that contamination, the following requirements are ARARs.
1. Requirements described at 40 CFR §§ 257.3-l(a), 257.3-3, and 257.3-4,
governing waste handling, storage, and disposal, including retention of the waste, in general,
and 40 CFR §§ 257.3-5, relating to precautions necessary to ensure that cadmium is not
taken up into crops, including pasture grasses, that may enter the food chain.18
2. For any discrete waste units which are addressed by the Streamside Tailings
cleanup, reclamation and closure regulations found at 30 CFR Parts 816 and 784, governing
coal and to a lesser extent, non-coal mining, are relevant and appropriate requirements.19
3. RCRA regulations found at 40 CFR §§ 264.116 and .119 (governing notice and
deed restrictions), 264.228(a)(2)(i) (addressing de-watering of wastes prior to disposal), and
264.228(a)(2)(iii)(B), (C), and (D) and .251(c), (d), and (f) (regarding run-on and run-off
controls), are relevant and appropriate requirements for the waste management units created
or retained at the Streamside Tailings Operable Unit.20
B. Air Standards - Clean Air Act (Applicable)
These standards, promulgated pursuant to section 109 of the Clean Air Act,21 are applicable
to releases into the air from any Streamside Tailings Operable Unit cleanup activities.
Solid Waste regulations are promulgated pursuant to the federal Solid Waste Disposal Act, as amended by the
Resource Conversation and Recovery Act, 42 U.S.C. 6901 et seq. They are applicable regulations, although the
State of Montana has the lead role in regulating solid waste disposal in the State of Montana.
The Surface Mining Control and Reclamation Act is promulgated at 30 U.S.C. Sections 1201 - 1326.
As noted earlier, federal RCRA regulations are incorporated by reference into applicable State Hazardous Waste
Management Act regulations. See ARM 17.54.702. Use of select RCRA regulations to mining waste is
appropriate when discrete units are addressed by a cleanup and site conditions are distinguishable from EPA's
generic determination of low toxicity/high volume status for mining waste. See Preamble to the Final NCP, 55
Fed. Reg. 8763 - 8764 (March 8, 1990), CERCLA Compliance with Other Laws Manual, Volume II (August
1989 OSWER Dir. 9234.1-02) p. 6-4; Preamble to Proposed NCP, 53 Fed. Reg. 51447 (Dec. 21, 1988), and
guidance entitled "Consideration of RCRA Requirements in Performing CERCLA Responses at Mining Wastes
Sites," August 19, 1986 (OSWER).
42 U.S.C. §§ 7401 et seq.
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1. Lead: No person shall cause or contribute to concentrations of lead in the ambient air
which exceed 1.5 micrograms per cubic meter (jug/m3) of air, measured over a
90-day average.
These standards are promulgated at ARM 16.8.815 as part of a federally approved State
Implementation Plan (SIP), pursuant to the Clean Air Act of Montana, §§ 75-2-101 et seq..
MCA. Corresponding federal regulations are found at 40 CFR § 50.12.22
2. Particulate matter that is 10 microns in diameter or smaller (PM-10):
No person shall cause or contribute to concentrations of PM-10 in the ambient air
which exceed:
- 150 jug/m3 of air, 24 hour average, no more than one expected exceedence per
calendar year;
- 50 /xg/m3 of air, annual average.
These regulations are promulgated at ARM 16.8.821 as part of a federally approved SIP,
pursuant to the Clean Air Act of Montana, §§ 75-2-101 et seq.. MCA. Corresponding
federal regulations are found at 40 CFR § 50.6.
Ambient air standards under section 109 of the Clean Air Act are also promulgated for
carbon monoxide, hydrogen sulfide, nitrogen dioxide, sulfur dioxide, and ozone. If
emissions of these compounds were to occur at the site in connection with any cleanup
action, these standards would also be applicable. See ARM 16.8.811 and 40 CFR Part 50.
C. Point Source Controls - Clean Water Act (Applicable)
If point sources of water contamination are retained or created by any Streamside Tailings
Operable Unit remediation activity, applicable Clean Water Act standards would apply to
those discharges. The regulations are discussed hi the contaminant specific ARAR section,
above, and in the State of Montana identification of ARARs. These regulations would
include storm water runoff regulations found at 40 CFR Parts 121, 122, and 125 (general
conditions and industrial activity conditions). These would also include requirements for best
management practices and monitoring found at 40 CFR §§ 122.44(i) and 440.148, for point
source discharges.
The ambient air standards established as part of Montana's approved State Implementation Plan in many cases
provide more stringent or additional standards. The federal standards by themselves apply only to "major
sources", while the State standards are fully applicable throughout the state and are not limited to "major sources"
See ARM 16.8.808 and 16.8.811-.821. As part of an EPA-approved State Implementation Plan, the state
standards are also federally enforceable. Thus, the state standards which are equivalent to the federal standards
are identified in this section together. A more detailed list of State standards, which include standards which are
not duplicated in federal regulations, is contained in the State ARAR identification section.
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D. Dredge and Fill Requirements (Applicable)
Regulations found at 40 CFR Part 230 address conditions or prohibitions against depositing
dredge and fill material into water of the United States. If remediation activities would result
in an activity subject to these regulations, they would be applicable.
E. Underground Injection Control (Applicable)
Requirements found at 40 CFR Part 144, promulgated pursuant to the Safe Drinking Water
Act, allow the re-injection of treated groundwater into the same formation from which it was
withdrawn for aquifers such as the aquifer beneath the Streamside Tailings Operable Unit,
and addresses injection well construction, operation, maintenance, and capping/closure.
These regulations would be applicable to any reinjection of treated groundwater.
F. Transportation of Hazardous or Contaminated Waste (Relevant and Appropriate)
40 CFR Part 263 establishes regulations for the transportation of hazardous waste. These
regulations would govern any on-site transportation pf material. Any off-site transportation
would be subject to applicable regulations.
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STATE OF MONTANA ARARS
As provided by Section 121 of CERCLA, 42 U.S.C. § 9621, only those state standards that
are more stringent than any federal standard and that have been identified by the state in a
timely manner are appropriately included as ARARs. To be an ARAR, a state standard must
be "promulgated," which means that the standards are of general applicability and are legally
enforceable.
IV. MONTANA CONTAMINANT SPECIFIC REQUIREMENTS
A. Water Quality
1. Surface Water Quality Standards (Applicable)
Under the state Water Quality Act, §§ 75-5-101 et seq.. MCA, the state has promulgated
regulations to protect, maintain, and improve the quality of surface waters in the state. The
requirements listed below are applicable water quality standards with which any remedial
action must comply.
ARM 16.20.604(1 )(b)(Applicable) provides that Silver Bow Creek (mainstem) from the
confluence of Blacktail Deer Creek to Warm Springs Creek is classified "I" for water use.
The "I" classification standards are contained in ARM 16.20.623 (Applicable) of the
Montana water quality regulations. This section states:
[T]he goal of the state of Montana is to have these waters fully support the
following uses: drinking, culinary, and food processing purposes after
conventional treatment; bathing, swimming, and recreation; growth and
propagation of fishes and associated aquatic life, waterfowl, and furbearers;
and agricultural and industrial water supply.
These beneficial uses are considered supported when the concentrations of toxic,
carcinogenic, or harmful parameters in these waters do not exceed the applicable standards
specified in department Circular WQB-7 when stream flows equal or exceed the stream flows
specified in ARM 16.20.631(4)(10-year 7-day low flow, i.e., minimum consecutive 7-day
average flow which may be expected to occur on the average of once in 10 years).
Alternatively, site-specific criteria may be developed using the procedures given in the Water
Quality Standards Handbook (US EPA, Dec. 1983), provided that other routes of exposure to
toxic parameters by aquatic life are addressed.23 These standards set the contaminant
specific requirement for ambient water quality in the stream.
To allow a gradual attainment of these requirements in already impacted streams, the I
classification allows point source discharges to be permitted at the higher concentration of (1)
Such other routes of exposure in this operable unit would include, for example, contaminated sediment/food chain routes of
exposure. In any event, no site specific standards have been developed for Silver Bow Creek, as of the issuance of the record
of decision, and consequently the applicable numeric standards are those set forth in WQB-7.
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the applicable standards specified in department Circular WQB-7, (2) the site-specific
standards, or (3) one-half of the mean instream concentrations24 immediately upstream of
the discharge point. .This effectively requires eventual attainment of the Circular WQB-7
levels in the stream, while allowing consideration of the current, impacted stream quality (a
graduated reduction of point source discharge concentrations based on the mean instream
concentration where the stream is substantially degraded). As the quality of the stream
improves due to control of other sources, including cleanup of non-point source areas, point
source dischargers must improve the quality of their discharges down to the instream
standards (either WQB-7 or, for aquatic life only, site specific standards).
With respect to the remediation of non-point sources, the WQB-7 standards effectively set the
ambient water quality standards that are to be attained by the remedial action. As an ambient
standard, the point of compliance for these standards would be throughout the stream, and
compliance should be measured by monitoring at several different points within the stream.
as determined by any significant point sources or significant reaches of non-point sources.
For the primary contaminants of concern, the WQB-7 levels are listed below. WQB-7
provides that "whenever both Aquatic Life Standards and Human Health Standards exist for
the same analyte, the more restrictive of these values will be used as the numeric Surface
Water Quality Standard. "
Chemical WOB-7 Standard
Arsenic 18 /ig/125
Cadmium 1.1 /*g/l26
Copper 12
Lead 3.2
Mercury 0.012
I classification standards also include the following criteria:
24 Mean instream concentration is the monthly mean instream concentration, as defined by the MDHES Water
Quality Bureau.
25 Human Health Standard. The acute and chronic Aquatic Life Standards are 360 ^g/1 and 190 jtg/1, respectively.
26 Chronic Aquatic Life Standard based on 100 mg/1 hardness (CaCO3). The method for adjusting the standard for
water hardness is provided in WQB-7. See Detailed Note of Explanation 12 in Circular WQB-7. In no event can
the level for cadmium exceed the human health standard of 5 /Jg/1.
27 Chronic Aquatic Life Standard based on 100 mg/1 hardness. See Detailed Note of Explanation 12 in Circular
WQB-7.
28 Chronic Aquatic Life Standard based on 100 mg/1 hardness. See Detailed Note of Explanation 12 in Circular
WQB-7. In no event can the level for lead exceed the human health standard at 15 fjg/1.
29 Chronic Aquatic Life Standard. The human health standard for mercury is 0.14 ^g/1.
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1. Dissolved oxygen concentration must not be reduced below 3.0 milligrams per
liter.
2. Hydrogen ion concentration (Ph) must be maintained within the range of 6.5 to
9.5.
3. No increase in naturally occurring turbidity, temperature, concentrations of
sediment and settleable solids, oils, floating solids, or true color is allowed
which will or is likely to create a nuisance or render the waters harmful,
detrimental, or injurious to public health, recreation, safety, welfare, livestock,
wild animals, birds, fish or other wildlife.
4. No discharges of toxic, carcinogenic, or harmful parameters may commence
or continue which lower or are likely to lower the overall water quality of
these waters.
Additional restrictions on any discharge to surface waters are included in:
ARM 16.20.633 (Applicable), which prohibits discharges containing substances that
will:
(a) settle to form objectionable sludge deposits or emulsions beneath the
surface of the water or upon adjoining shorelines;
(b) create floating debris, scum, a visible oil film (or be present in
concentrations at or in excess of 10 milligrams per liter) or globules of grease
or other floating materials;
(c) produce odors, colors or other conditions which create a nuisance or
render undesirable tastes to fish flesh or make fish inedible;
(d) create concentrations or combinations of materials which are toxic or
harmful to human, animal, plant or aquatic life;
(e) create conditions which produce undesirable aquatic life.
ARM 16.20.925 (Applicable), which adopts and incorporates the provisions of 40
C.F.R. Part 125 for criteria and standards for the imposition of technology-based
treatment requirements in MPDES permits. Although the permit requirement would
not apply to on-site discharges, the substantive requirements of Part 125 are
applicable, i.e., for toxic and nonconventional pollutants treatment must apply the best
available technology economically achievable (BAT); for conventional pollutants,
application of the best conventional pollutant control technology (BCT) is required.
Where effluent limitations are not specified for the particular industry or industrial
category at issue, BCT/BAT technology-based treatment requirements are determined
on a case by case basis using best professional judgment (BPJ). See CERCLA
Compliance with Other Laws Manual, Vol. I, August 1988, p. 3-4 and 3-7.
Applicable for both surface water and ground water, § 75-5-605, MCA, provides that it is
unlawful to cause pollution as defined in 75-5-103 of any state waters or to place or cause to
be placed any wastes where they will cause pollution of any state waters.
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Section 75-5-308, MCA, allows DEQ to grant short-term exemptions from the water quality
standards or short-term use that exceeds the water quality standards for the purpose of
allowing certain construction or emergency environmental remediation activities. Such
exemptions typically extend for a period of 30-60 days. However, any exemption must
include conditions that minimize to the extent possible the magnitude of the violation and the
length of time the violation occurs. In addition, the conditions must maximize the protection
of state waters by ensuring the maintenance of beneficial uses immediately after termination
of the exemption. Water quality and quantity monitoring and reporting may also be included
as conditions.
2. Groundwater Pollution Control System (Applicable')
In addition to the standards set forth below, relevant and appropriate MCLs and MCLGs are
included in the federal ARARs identified above.
ARM 16.20.1002 (Applicable) classifies groundwater into Classes I through IV based on the
present and future most beneficial uses of the groundwater, and states that groundwater is to
be classified according to actual quality or actual use, whichever places the groundwater in a
higher class. Class I is the highest quality class; class IV the lowest. Based upon its specific
conductance, the great majority of the groundwater in the Streamside Tailings Operable Unit
should be considered Class I groundwater, with the remainder of the groundwater Class
n.30
ARM 16.20.1003 (Applicable) establishes the groundwater quality standards applicable with
respect to each groundwater classification. Concentrations of dissolved substances in Class I
or n groundwater (or Class HI groundwater which is used as a drinking water source) may
not exceed the human health standards Listed in department Circular WQB-7. For the
primary contaminants of concern these levels are listed below. Levels that are more
stringent than the MCL or MCLG identified in the federal portion of the ARARs are set out
in boldface type.
ARM 16.20.1002 provides that Class I groundwaters have a specific conductance of less than 1000 micromhos per
centimeter at 25° C; Class II groundwaters: 1000 to 2500; Class III groundwaters: 2500 to 15,000; and Class IV
groundwaters: over 15,000. The groundwater in the operable unit generally ranges from 298 to 3245
micromhos/cm, with the majority of the wells testing well below 1000. See 1991 Remedial Investigation Activities
Data Summary Report, Table 11 (ARCO, August 1993); Final 1992 Data Summary Report, Table 15 (ARCO,
September 1994)(showing a range of 331-2092 ^mhos/cm).
At the uppermost level of the aquifer, in those locations where the groundwater is in contact with a contaminant
source, there are areas that have specific conductance greater than 2500 /imhos/cm. However, the groundwater in
this aquifer generally is of Class I quality, with the areas of greater specific conductance constituting discrete areas
of contamination. For purposes of applying these standards in this action, the classification of the groundwater in
the area should be based on the quality of the groundwater generally, rather than the specific areas of
contamination.
In addition, classification of the groundwater is based on actual quality or actual use as of October 29, 1982. See
ARM 16.20.1002(3). Considering the history of contamination at the site, there is no reason to assume that the
quality of this ground water in 1982 would have been other than Class I or II.
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Chemical WOB-7 Human Health Standard
Arsenic " 18 /ig/1
Cadmium 5 jug/I
Copper 1000 ng/l
Lead 15 ,ug/l
Mercury 0.14 jig/1
Concentrations of other dissolved or suspended substances must not exceed levels that render
the waters harmful, detrimental or injurious to public health. Maximum allowable
concentration of these substances also must not exceed acute or chronic problem levels that
would adversely affect existing or designated beneficial uses of groundwater of that
classification. ARM 16.20.1003 specifies certain references that may be used as a guide in
determining problem levels unless local conditions make these values inappropriate.
An additional concern with respect to ARARs for groundwater is the impact of groundwater
upon the surface water. If significant loadings of contaminants from groundwater sources to
Silver Bow Creek contribute to the inability of the stream to meet the I class standards (i.e.,
the WQB-7 levels described in the Surface Water section above), then alternatives to alleviate
such groundwater loading must be evaluated and, if appropriate, implemented. Groundwater
in certain areas may need to be remediated to levels more stringent than the groundwater
classification standards for certain parameters in order to achieve the standards for affected
surface water. See Compliance with Federal Water Quality Criteria, OSWER Publication
9234.2-09/FS (June 1990)("Where the ground water flows naturally into the surface water,
the ground-water remediation should be designed so that the receiving surface-water body
will be able to meet any ambient water-quality standards (such as State WQSs or FWQC)
that may be ARARs for the surface water.")
The 1995 Montana Legislature enacted several revisions to the Montana Water Quality
Statutes. Except as reflected in the analysis above, none of these changes has altered the
application of these water quality requirements to the Streamside Tailings Operable Unit.
One bill exempted from the permit requirements certain discharges from a water conveyance
structure or certain groundwater discharged to surface water, but these exemptions do not
apply if the discharged water contains "industrial waste." See § 75-5-401, MCA, as
amended. "Industrial waste" means a waste substance from the process of business or
industry or from the development of any natural resource..." § 75-5-103(10), MCA. Since
the contamination found in the water in this operable unit is industrial waste, these new
exemptions would not apply here.
B. Air Quality
In addition to the standards identified in the federal action specific ARARs above, the State
of Montana has identified certain air quality standards in the action specific section of the
State ARARs below.
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V. MONTANA LOCATION SPECIFIC REQUIREMENTS
A. Floodplain and Floodway Management Act and Regulations (Applicable)
The Floodplain and Floodway Management Act and regulations specify types of uses and
structures that are allowed or prohibited in the designated 100-year floodway31 and
floodplain.32 Since the SST Operable Unit lies primarily within the 100-year floodplain of
Silver Bow Creek, these standards are applicable to all actions contemplated for this operable
unit.
1. Allowed uses
The law recognizes certain uses as allowable in the floodway and a broader range of uses as
allowed in the floodplain. Residential use is among the possible allowed uses expressly
recognized in both the floodway and floodplain. "Residential uses such as lawns, gardens,
parking areas, and play areas," as well as certain agricultural, industrial-commercial,
recreational and other uses are permissible within the designated floodway, provided they do
not require structures other than portable structures, fill or permanent storage of materials or
equipment. § 76-5-401, MCA; ARM 36.15.601 (Applicable). In addition, in the flood
fringe (i.e., within the floodplain but outside the floodway), residential, commercial,
industrial, and other structures may be permitted subject to certain conditions relating to
placement of fill, roads, floodproofing, etc. § 76-5-402, MCA; ARM 36.15.701
(Applicable). Domestic water supply wells may be permitted, even within the floodway,
provided the well casing is watertight to a depth of 25 feet and the well meets certain
conditions for floodproofing, sealing, and positive drainage away from the well head. ARM
36.15.602(6).
2. Prohibited uses
Uses prohibited anywhere in either the floodway or the floodplain are:
1. solid and hazardous waste disposal; and
2. storage of toxic, flammable, hazardous, or explosive materials.
The "floodway" is the channel of a watercourse or drainway and those portions of the floodplain adjoining the
channel which are reasonably required to carry and discharge the floodwater of the watercourse or drainway.
ARM 36.15.101(13).
The "floodplain" is the area adjoining the watercourse or drainway which would be covered by the floodwater of a
base (100-year) flood except for sheetflood areas that receive less than one foot of water per occurrence. The
floodplain consists of the floodway and flood fringe.
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ARM 36.15.605(2) and 36.15.703 (Applicable33); see also ARM 36.15.602(5)(b)
(Applicable).
In the floodway, additional prohibitions apply, including prohibition of:
1. a building for living purposes or place of assembly or permanent use by
human beings;
2. any structure or excavation that will cause water to be diverted from the
established floodway, cause erosion, obstruct the natural flow of water, or
reduce the carrying capacity of the floodway; and
3. the construction or permanent storage of an object subject to flotation or
movement during flood level periods.
§ 76-5-402, MCA (Applicable).
One commenter asserted that these regulations are not applicable to the SST OU. MDEQ has evaluated these
arguments and has still determined that these are applicable requirements. Under the NCP, 40 CFR § 300.400(g)(l),
MDEQ must make an "objective determination of whether the requirement specifically addresses a hazardous
substance, pollutant, contaminant, remedial action, location, or other circumstance found" at the site. MDEQ has
made the determination here that these requirements specifically address the hazardous substances and location involved
and are applicable legal requirements. While these prohibitions are applicable requirements, exactly how these
prohibitions apply to specific mining wastes being addressed in this operable unit and the manner in which these
prohibitions apply to specific actions requires some analysis. The floodplain management regulations include a version
of this prohibition in three different provisions. ARM 36.15.605(2) and 36.15.703, applicable to the floodway and
the flood fringe, respectively, state this prohibition generally as noted above. ARM 36.15.602(5)(b), applicable to
the floodway, allows storage of materials and equipment under certain conditions, but provides "Storage of flammable,
toxic, or explosive materials shall not be permitted."
Neither the regulations nor the Floodplain Management Act defines the terms disposal, storage, solid waste, hazardous
waste, toxic materials or hazardous materials. In most contexts, the regulations are clear enough, by their plain
meaning, to be easily implementable. As applied to the specific circumstances at this operable unit, however, these
terms require some interpretation. This interpretation is further complicated by the fact that at least a substantial part
of the tailings deposited along Silver Bow Creek can be assumed to have been deposited before the effective date of
the regulations here. Thus the initial disposal of these materials does not constitute a violation of the regulations.
However, as discussed in footnote 36, below, actions taken to actively manage these materials as part of the remedial
action effectively trigger applicability of such requirements in certain circumstances.
These issues are discussed more fully in the responsiveness summary portion of the record of decision, in response
to comments submitted by the Atlantic Richfield Company regarding ARARs issues. Summarized here, the
department's analysis has determined that the tailings and mining wastes in the SST OU are included in the term solid
wastes, as well as the terms toxic materials or hazardous materials, and that the prohibition on the disposal or storage
of those wastes/materials within the floodplain applies to actions which constitute the active management/disposal of
those wastes as part of the remedial action. The agencies further note that, if there were some jurisdictional
prerequisite which were technically not met for applicability, the requirements identified here would be relevant and
appropriate requirements as described for this remedial action. In such case, the agencies would apply these
requirements as relevant and appropriate considering the factors set forth at 40 CFR § 300.400(g)(2)(i) through (viii).
Finally, in the record of decision, MDEQ and EPA invoke a waiver of this requirement under section 121(d)(4)(D)
of CERCLA, 42 USC § 9621(d)(4)(D), to allow the remedial action, under certain conditions, to incorporate certain
actions that will attain a standard of performance that is equivalent to that required under the prohibitions described
above. The analysis of the ARAR waiver and the conditions on which the agencies have determined that equivalent
standard of performance can be attained are set out in the Decision Summary portion of the record of decision.
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3. Applicable considerations in use of floodplain or floodway
Applicable regulations also specify factors that must be considered in allowing diversions of
the stream, changes in place of diversion of the stream, flood control works, new
construction or alteration of artificial obstructions, or any other nonconforming use within the
floodplain or floodway. Many of these requirements are set forth as factors that must be
considered in determining whether a permit can be issued for certain obstructions or uses.
While permit requirements are not directly applicable to remedial actions conducted entirely
on site, the substantive criteria used to determine whether a proposed obstruction or use is
permissible within the floodway or floodplain are applicable standards. Factors which must
be considered in addressing any obstruction or use within the floodway or floodplain include:
1. the danger to life and property from backwater or diverted flow caused by the
obstruction or use;
2. the danger that the obstruction or use will be swept downstream to the injury
of others;
3. the availability of alternate locations;
4. the construction or alteration of the obstruction or use in such a manner as to
lessen the danger;
5. the permanence of the obstruction or use; and
6. the anticipated development in the foreseeable future of the area which may be
affected by the obstruction or use.
See § 76-5-406, MCA; ARM 36.15.216 (Applicable, substantive provisions only).
Conditions or restrictions that generally apply to specific activities within the floodway or
floodplain are:
1. the proposed activity, construction, or use cannot increase the upstream
elevation of the 100-year flood a significant amount (1A foot or as otherwise
determined by the permit issuing authority) or significantly increase flood
velocities, ARM 36.15.604 (Applicable, substantive provisions only); and
2. the proposed activity, construction, or use must be designed and constructed to
minimize potential erosion.
For the substantive conditions and restrictions applicable to specific obstructions or uses, see
the following applicable regulations:
Excavation of material from pits or pools - ARM 36.15.602(1).
Water diversions or changes in place of diversion - ARM 36.15.603.
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Flood control works (levees, floodwalls, and riprap must comply with specified safety
standards) - ARM 36.15.606.
Roads, streets, highways and rail lines (must be designed to minimize increases in
flood heights) - ARM 36.15.701(3)(c).
Structures and facilities for liquid or solid waste treatment and disposal (must be
floodproofed to ensure that no pollutants enter flood waters and may be allowed and
approved only in accordance with MDEQ regulations, which include certain additional
prohibitions on such disposal) - ARM 36.15.701 (3)(d).
Residential structures - ARM 36.15.702(1).
Commercial or industrial structures - ARM 36.15.702(2).
B. Solid Waste Management Regulations (Applicable)
Regulations promulgated under the Solid Waste Management Act, §§ 75-10-201 et seq..
MCA, specify requirements that apply to the location of any solid waste management
facility.34 Under ARM 17.50.505 (formerly 16.14.505)(Applicable), a facility for the
treatment, storage or disposal of solid wastes:35
These requirements apply, inter alia, to the treatment, storage, or disposal of solid waste. See ARM
16.14.502(17).
The solid waste regulations are applicable to the wastes at issue in this operable unit, which consist of mining wastes,
primarily tailings, which have been washed downstream and deposited along Silver Bow Creek for many years.
Section 75-10-203(11) provides:
(a) "Solid waste" means all putrescible and nonputrescible wastes, including but not limited to
garbage; rubbish; refuse; ...
(b) Solid waste does not mean municipal sewage, industrial wastewater effluents, mining wastes
regulated under the mining and reclamation laws administered by the department of environmental
quality, slash and forest debris regulated under laws administered by the department of natural
resources and conservation, or marketable byproducts."
As noted, "solid waste" does not include "mining wastes regulated under the mining and reclamation laws administered
by the Department of Environmental Quality," see § 75-10-203(11), MCA, as amended by Chapter 418, Laws of
Montana 1995. However, the mining wastes found in the Streamside Tailings Operable Unit are not regulated under
the mining and reclamation laws administered by the Department of Environmental Quality, because they are not part
of any current mining permit or mine reclamation plan.
One commenter argued that "mining wastes are specifically excluded from the definition of 'solid waste.'" This
argument may be read as an assertion that the exemption of "mining wastes regulated under the mining and reclamation
laws" is broad enough to cover all mining wastes. However, both the plain meaning of the language and other
principles of statutory construction weigh against such an interpretation. The words "regulated under the mining and
reclamation laws" suggest actual regulation rather than a categorical exclusion of all mining wastes whether specific
wastes are actually regulated or not. Where this statute provides a categorical exclusion, it does so in clear categorical
language, without the qualification "regulated under ..." For example, the statute categorically exempts "municipal
sewage" and "industrial wastewater effluents" without any such qualification.
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(a) must be located where a sufficient acreage of suitable land is available for solid
waste management;
(b) may not be located in a 100-year floodplain;
.36
The commenter's interpretation of the statute would render the words "regulated under ..." superfluous, in
contravention of accepted principles of statutory construction. Moreover, an apparent purpose for the exemption is
to avoid duplicative or conflicting regulation of the wastes, which would occur only in the event the wastes were
actually subject to both sets of regulations. The language of the statute is not ambiguous, and under the plain meaning
of the provision the exemption of mining wastes should be viewed as limited to those wastes which are actually
regulated under the mining and reclamation laws. The mining wastes being addressed in this operable unit are not
so regulated, and thus are not within this exemption from solid waste regulations.
36 The application of this requirement to certain alternatives considered in the SST OU remedy selection requires some
clarification. This regulation was promulgated in the 1970's, and for purposes of this determination, the initial
"disposal" of these wastes in the SSTOU can be assumed to have occurred before promulgation of the regulation. Thus
as these wastes lie in the ground, no one would be required to remove them in order to comply with the solid waste
regulations. However, compliance with such regulations is required if any action taken with respect to such wastes
constitutes "active management" of those wastes. EPA has interpreted "active management" as "physically disturbing
accumulated wastes within a management unit ..." See, e.g., 57 Fed. Reg. 37298 (August 18, 1992), 54 Fed. Reg.
36597 (September 1, 1989).
Effectively, any "active management" is to be regarded as constituting a new "disposal" of these solid wastes,
triggering applicability of the state solid waste regulations, including the prohibition on disposing solid wastes in the
floodplain. As applied to the alternatives being considered for the SSTOU, either excavating and placing the wastes
in a repository or applying STARS treatment in situ, which consists of tilling lime-based amendments into the tailings
in place, would constitute "active management" of the wastes. Thus treating floodplain wastes in place in mis manner
would not comply with the prohibition on storage or disposal of these wastes within the floodplain, and an ARAR
waiver would be required for this alternative.
One commenter has asserted that disposal does not occur where waste is consolidated within a unit, waste is capped
in place, including grading prior to capping, or waste is treated in situ. This argument derives from discussion in the
CERCLA Compliance with Other Laws Manual: Interim Final (August 1988), p. 2-16. However, this discussion in
the manual relates to "land disposal" or "placement" of wastes under RCRA Subtitle C (hazardous waste) and land
ban rules, referred to in the manual as "placement/disposal."
A distinction must be made between RCRA's broad jurisdictional definition of "disposal," which is virtually identical
to the state's broad definition of disposal, and the specific type of disposal triggering certain RCRA Subtitle C and land
ban requirements, referred to as "land disposal." The term "disposal" is often used as shorthand in discussing RCRA's
Subtitle C hazardous waste requirements, when technically referring to "land disposal." Thus in some instances the
language in the manual and other sources seems to address the definition of disposal generally, rather than
placement/disposal for land ban purposes.
However, an analysis of other sources makes clear that the activities addressed in this section of the manual relate only
to RCRA's definition of land ban placement or "land disposal," and not to the broader definition of "disposal" under
RCRA. The preamble to the final NCP notes the "Congressional choice to define 'land disposal' more narrowly ...
than the already existing term 'disposal,'" which has a much broader meaning under RCRA. The Preamble continues:
Under RCRA section 1004(3), the term "disposal" is very broadly defined and includes any
"discharge, deposit, injection, dumping, spilling, leaking, or placing" of waste into or on any land
or water. Thus "disposal" [in a statutory, rather than the regulatory subtitle C meaning of the
term] would include virtually any movement of waste, whether within a unit or across a unit
boundary.... However, Congress did not use the term "disposal" as its trigger for the RCRA land
disposal restrictions, but instead specifically defined the new, and more narrow, term "land
disposal" in section 3004(k). The broader "disposal" language continues to be applicable to
RCRA provisions other than those in subtitle C, such as section 7003. (Emphasis added.)
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(c) may be located only in areas which will prevent the pollution of ground and
surface waters and public and private water supply systems;
(d) must be located to allow for reclamation and reuse of the land;
(e) drainage structures must be installed where necessary to prevent surface runoff
from entering waste management areas; and
(f) where underlying geological formations contain rock fractures or fissures which
may lead to pollution of the ground water or areas in which springs exist that are
hydraulically connected to a proposed disposal facility, only Class HI disposal facilities may
be approved.37
55 Fed. Reg. 8759 (March 8, 1990). The state's definition of "disposal" in the Montana Solid Waste Management
Act is identical to the broader definition of disposal under RCRA. See § 75-10-203(3), MCA. Thus what constitutes
a new disposal triggering applicability of the solid waste requirements should be based on the broader "disposal" test,
rather than the narrower "land disposal" test proffered by the commenter.
Such an interpretation of "disposal" is also supported by judicial interpretations of the definition of "disposal" under
CERCLA, which also is identical to the definition appearing in the state's Solid Waste Management Act and
regulations. See, e.g., Kaiser Aluminum & Chemical Corporation v. Catellus Development Corporation. 976 F.2d
1338 (9th Cir. 1992)("the term 'disposal' should not be limited solely to the initial introduction of hazardous substances
onto property. Rather, consistent with the overall remedial purpose of CERCLA, "disposal" should be read broadly
to include the subsequent [movement, dispersal, or release] of such substances during landfill excavations and
fillings.") (quoting Tanglewood East Homeowners v. Charles-Thomas, Inc., 849 F.2d 1568 (5th Cir. 1988)).
Finally, § 75-10-214(l)(b), MCA, provides that the Solid Waste Management Act does not apply to the operation of
a mine, mill, or smelter. This provision exempts any disposal of wastes as part of the operation of a mine, mill, or
smelter from the requirements of the Solid Waste Management Act and corresponding regulations. The agencies must
still determine, however, whether these requirements are applicable to actions taken as part of a remedial action under
CERCLA rather than as part of the operation of a mine, mill, or smelter or whether these requirements should be
considered relevant and appropriate requirements for this remedial action.
The agencies have determined that for certain actions that are to be conducted as part of the remedial action for the
operable unit, the regulations should be considered applicable legal requirements. As noted above, those actions that
constitute "active management," or anew disposal, of the wastes trigger applicability of the regulations to such actions.
The exemption for the operation of a mine, mill or smelter does not exempt such an action since the new disposal
cannot be regarded as part of the operation of a mine, mill or smelter.
Moreover, if any of the exemptions noted above or any jurisdictional basis for exempting these wastes from the Solid
Waste Management Act were justified, the agencies would find, using the criteria specified in the NCP, 40 CFR §
300.400(g)(2)(i) through (viii), that the solid waste management regulations specifically identified in this ARARs
analysis are relevant and appropriate requirements for this remedial action. The identified requirements address
problems or situations sufficiently similar and are well-suited to the circumstances involved here so that they should
be considered relevant and appropriate requirements for this action. Specifically, the identified requirements are
intended to address the type and location of wastes and the remedial actions contemplated here. They were developed
for the purpose of preventing future problems resulting from the inappropriate storage or disposal of solid wastes,
particularly those wastes containing hazardous substances that pose a threat to human health or the environment, such
as the tailings and other materials involved here, and particularly those problems that result from inappropriate
selection of a disposal site or location, such as areas that are in contact with groundwater or streams.
-7 Group III wastes consist of primarily inert wastes, including "industrial mineral wastes which are essentially inert
and non-water soluble and do not contain hazardous waste constituents." ARM 16.14.503(l)(b). The tailings and
similar wastes found in the SSTOU do not fall within this category and are at least Group II wastes.
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C. Natural Streambed and Land Preservation Standards (Applicable)
Sections 87-5-502 arid 504, MCA, (Applicable — substantive provisions only) provide that a
state agency or subdivision shall not construct, modify, operate, maintain or fail to maintain
any construction project or hydraulic project which may or will obstruct, damage, diminish.
destroy, change, modify, or vary the natural existing shape and form of any stream or its
banks or tributaries in a manner that will adversely affect any fish or game habitat. The
requirement that any such project must eliminate or diminish any adverse effect on fish or
game habitat is applicable to the state in approving remedial actions to be conducted. The
Natural Streambed and Land Preservation Act of 1975, §§ 75-7-101 et seq.. MCA,
(Applicable - substantive provisions only) includes similar requirements and is applicable to
private parties as well as government agencies.
ARM 36.2.404 (Applicable) establishes minimum standards which would be applicable if a
remedial action alters or affects a Streambed, including any channel change, new diversion,
riprap or other streambank protection project, jetty, new dam or reservoir or other
commercial, industrial or residential development. No such project may be approved unless
reasonable efforts will be made consistent with the purpose of the project to minimize the
amount of stream channel alteration, insure that the project will be as permanent a solution as
possible and will create a reasonably permanent and stable situation, insure that the project
will pass anticipated water flows without creating harmful erosion upstream or downstream,
minimize turbidity, effects on fish and aquatic habitat, and adverse effects on the natural
beauty of the area and insure that Streambed gravels will not be used in the project unless
there is no reasonable alternative. Soils erosion and sedimentation must be kept to a
minimum. Such projects must also protect the use of water for any useful or beneficial
purpose. See § 75-7-102, MCA.
While the administrative/procedural requirements, including the consent and approval
requirements, set forth in these statutes and regulations are not ARARs, the party designing
and implementing the remedial action for the Streamside Tailings Operable Unit is
encouraged to continue to consult with the Montana Department of Fish, Wildlife and Parks.
and any conservation district or board of county commissioners (or consolidated city/county
government) as provided in the referenced statutes, to assist in the evaluation of factors
discussed above.
VI. MONTANA ACTION SPECIFIC REQUIREMFJ^TS
In the following action-specific ARARs, the nature of the action triggering applicability of
the requirement is stated in parentheses as part of the heading for each requirement.
A. Water Quality
1. Groundwater Act (Applicable1) (Construction and maintenance of groundwater wells)
Section 85-2-505, MCA, (Applicable) precludes the wasting of groundwater. Any well
producing waters that contaminate other waters must be plugged or capped, and wells must
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be constructed and maintained so as to prevent waste, contamination, or pollution of
groundwater.
2. Public Water Supply Regulations (Applicable) (Reconstruction or modification of
public water or sewer lines on the site)
If remedial action at the site requires any reconstruction or modification of any public water
supply line or sewer line, the construction standards specified in ARM 16.20.401(3)
(Applicable) must be observed.
B. Air Quality
1. Air Quality Regulations (Applicable) (Excavation/earth-moving; transportation)
Dust suppression and control of certain substances likely to be released into the air as a result
of earth moving, transportation and similar actions may be necessary to meet air quality
requirements. Certain ambient air standards for specific contaminants and particulates are set
forth in the federal action specific section above. Additional air quality regulations under the
state Clean Air Act, §§ 75-2-101 et seq., MCA, are discussed below.
ARM 16.8.1302 (Applicable) lists certain wastes that may not be disposed of by open
burning38, including oil or petroleum products, RCRA hazardous wastes, chemicals, and
treated lumber and timbers. Any waste which is moved from the premises where it was
generated and any trade waste (material resulting from construction or operation of any
business, trade, industry or demolition project) may be open burned only in accordance with
the substantive requirements of 16.8.1307 or 1308.
ARM 16.8.1401(1) and (2) (Applicable) provides that no person shall cause or authorize the
production, handling, transportation or storage of any material; or cause or authorize the use
of any street, road, or parking lot; or operate a construction site or demolition project, unless
reasonable precautions to control emissions of airborne particulate matter are taken.
Emissions of airborne particulate matter must be controlled so that they do not "exhibit an
opacity of twenty percent (20%) or greater averaged over six consecutive minutes." ARM
16.8.1401(1) and (2) (Applicable) and ARM 16.8.1404 (Applicable).
In addition, state law provides an ambient air quality standard for settled particulate matter.
Particulate matter concentrations in the ambient air shall not exceed the following 30-day
average: 10 grams per square meter. ARM § 16.8.818 (Applicable).
The Butte area has been designated by EPA as non-attainment for total suspended
particulates, as well as PM-10. 40 CFR § 81.327. ARM 16.8.1401(4) (Applicable) requires
that any new source of airborne particulate matter that has the potential to emit less than 100
tons per year of particulates shall apply best available control technology (BACT); any new
"'Open burning' means combustion of any material directly in the open air without a receptacle, or in a receptacle
other than a furnace, multiple chambered incinerator or wood waste burner ..." ARM 16.8.1301(5).
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source of airborne particulate matter that has the potential to emit more than 100 tons per
year of particulates shall apply lowest achievable emission rate (LAER). The BACT and
LAER standards are" defined in ARM 16.8.1430. A significant source of the non-attainment
for particulates and PM-10 in the Butte area is road dust. Accordingly, special precautions
should be taken in this area to limit dust emissions from remedial activities.
ARM 26.4.761 (Relevant and Appropriate) specifies a range of measures for controlling
fugitive dust emissions during mining and reclamation activities. Some of these measures
could be considered relevant and appropriate to control fugitive dust emissions in connection
with excavation, earth moving and transportation activities conducted as part of the remedy at
the site. Such measures include, for example, paving, watering, chemically stabilizing, or
frequently compacting and scraping roads, promptly removing rock, soil or other dust-
forming debris from roads, restricting vehicle speeds, revegetating, mulching, or otherwise
stabilizing the surface of areas adjoining roads, restricting unauthorized vehicle travel,
minimizing the area of disturbed land, and promptly revegetating regraded lands.
C. Solid Waste Regulations
As noted in Section V.B above, the state Solid Waste Management Regulations are applicable
to the disposal/active management of the tailings and similar wastes within this operable unit.
Certain location specific requirements are identified in Section V.B above. Action specific
solid waste regulations are discussed below.
ARM 17.50.505(2) (formerly 16.14.505(2))(Applicable) specifies standards for solid waste
management facilities, including the requirements that:
1. if there is the potential for leachate migration, it must be demonstrated that
leachate will only migrate to underlying formations which have no hydraulic
continuity with any state waters;
2. adequate separation of such wastes from underlying or adjacent water must be
provided, considering terrain, type of underlying soil formations, and facility
design (the Waste Management Division of MDEQ has generally construed
this to require a minimum separation of 10-20 feet); and
3. no new disposal units or lateral expansions may be located in wetlands.
ARM 17.50.523 (formerly 16.14.523)(Relevant and Appropriate) requires that such waste
must be transported in such a manner as to prevent its discharge, dumping, spilling, or
leaking from the transport vehicle.
Section 75-10-206, MCA, allows variances to be granted from solid waste regulations if
failure to comply with the rules does not result in a danger to public health or safety or
compliance with specific rules would produce hardship without producing benefits to the
health and safety of the public that outweigh the hardship. In light of the nature of the
wastes at issue and the likelihood that any repository would contain only a single type of
waste, i.e. tailings and related materials, considering the volume of wastes involved (1.5 to
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2.5 million cubic yards) and the cost of full compliance with all solid waste requirements,
and considering available Superfund procedures for the maintenance of remedies and the
ability of the agencies, within the Superfund process, to consider the characteristics of the
particular wastes at issue in appropriately determining and designing repositories, certain of
the Solid Waste Regulations regarding design of landfills, ARM 17.50.506, operational and
maintenance requirements, ARM 17.50.520-521, and landfill closure requirements and post-
closure care, ARM 17.50.530-531, may appropriately be subject to variance in implementing
the remedy at this operable unit. The scope and manner of applying the variance can be
determined in finalizing and approving of the remedial design by the agencies. For example,
the barrier layer (liner) and leachate collection and removal system requirements of ARM
17.50.506 (Design Criteria for Landfills) may be subject to variance as long as the design
approved by MDEQ ensures that the concentration values listed in Table 1, ARM 17.50.506,
will not be exceeded in the uppermost aquifer. Similarly, the groundwater monitoring
requirements of ARM 17.50.701 et seq. can be considered and coordinated with any other
monitoring requirements under CERCLA.
D: Reclamation Requirements
The Strip and Underground Mine Reclamation Act, §§ 82-4-201 et seq.. MCA, technically
applies to coal and uranium mining, but that statute and the regulations promulgated under
that statute and discussed in this section, set out the standards that mine reclamation should
attain. Those requirements identified here have been determined to be relevant and
appropriate requirements for this action. Section 82-4-231 (Relevant and Appropriate)
requires the reclamation and revegetation of the land as rapidly, completely, and effectively
as the most modern technology and the most advanced state of the art will allow. In
developing a method of operation and plans of backfilling, water control, grading, topsoiling
and reclamation, all measures shall be taken to eliminate damages to landowners and
members of the public, their real and personal property, public roads, streams, and all other
public property from soil erosion, subsidence, landslides, water pollution, and hazards
dangerous to life and property. Sections 82-4-231(10)(j) and (i) and ARM 26.4.751
(Relevant and Appropriate) provide that reclamation of mine waste materials shall, to the
extent possible using the best technology currently available, minimize disturbances and
adverse impacts of the operation on fish, wildlife, and related environmental values and
achieve enhancement of such resources where practicable, and shall avoid acid or other toxic
mine drainage by such measures as preventing or removing water from contact with toxic-
producing deposits. ARM 26.4.641 (Relevant and Appropriate) also provides that drainage
from acid-forming or toxic-forming spoil into ground and surface water must be avoided by
preventing water from coming into contact with such spoil. ARM 26.4.505 (Relevant and
Appropriate) similarly provides that acid, acid-forming, toxic, toxic-forming or other
deleterious materials must not be buried or stored in proximity to a drainage course so as to
cause or pose a threat of water pollution.
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1. Reclamation Activities - Hydrology Regulations (Relevant and Appropriate)
(Excavation, earth moving, altering drainage patterns)
The hydrology regulations provide detailed guidelines for addressing the hydrologic impacts
of mine reclamation activities and earth moving projects and are relevant and appropriate for
addressing these impacts in the Streamside Tailings Operable Unit.
ARM 26.4.631 (Relevant and Appropriate) provides that long-term adverse changes in the
hydrologic balance from mining and reclamation activities, such as changes in water quality
and quantity, and location of surface water drainage channels shall be minimized. Water
pollution must be minimized and, where necessary, treatment methods utilized. Diversions
of drainages to avoid contamination must be used in preference to the use of water treatment
facilities. Other pollution minimization devices must be used if appropriate, including
stabilizing disturbed areas through land shaping, diverting runoff, planting quickly
germinating and growing stands of temporary vegetation, regulating channel velocity of
water, lining drainage channels with rock or vegetation, mulching, and control of acid-
forming, and toxic-forming waste materials.
ARM 26.4.633 (Relevant and Appropriate) provides water quality performance standards that
may be invoked in the event that runoff from the treated areas threatens the water quality or
sediments in the stream, including the requirement that all surface drainage from a disturbed
area must be treated by the best technology currently available (ETCA). Treatment must
continue until the area is stabilized.
ARM 26.4.634 (Relevant and Appropriate) provides that, in reclamation of drainages,
drainage design must emphasize channel and floodplain dimensions that approximate the
premining configuration and that will blend with the undisturbed drainage above and below
the area to be reclaimed. The average stream gradient must be maintained with a concave
longitudinal profile, and the channel and floodplain must be designed and constructed to:
1. establish or restore the drainage channel to its natural habit or characteristic
pattern with a geomorphically acceptable gradient. The habits or
characteristics of individual streams include their particular reactions to general
laws related to stream work, whether or not the stream has attained the
conditions of equilibrium, and the stream channel morphology and stability;
2. remain in dynamic equilibrium with the system;
3. improve unstable premining conditions;
4. provide for floods; and
5. establish a premining diversity of aquatic habitats and riparian vegetation.
ARM 26.4.635 through 26.4.637 (Relevant and Appropriate) set forth requirements for
temporary and permanent diversions.
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ARM 26.4.638 (Relevant and Appropriate) specifies sediment control measures to be
implemented during operations.
ARM 26.4.640 (Relevant and Appropriate) provides that discharge from sedimentation
ponds, permanent and temporary impoundments, and diversions shall be controlled by energy
dissipaters, riprap channels, and other devices, where necessary, to reduce erosion, prevent
deepening or enlargement of stream channels, and to minimize disturbance of the hydro logic
balance.
2. Reclamation and Revegetation Requirements (Relevant and Appropriate) (Excavation)
ARM 26.4.501 and 501A (Relevant and Appropriate) give general backfilling and final
grading requirements.
ARM 26.4.514 (Relevant and Appropriate) sets out contouring requirements.
ARM 26.4.519 (Relevant and Appropriate) provides that an operator may be required to
monitor settling of regraded areas.
ARM 26.4.702 (Relevant and Appropriate) requires that during the redistributing and
stockpiling of soil (for reclamation):
1. regraded areas must be prepared to eliminate any possible slippage potential,
to relieve compaction, and to promote root penetration and permeability of the
underlying layer; this preparation must be done on the contour whenever
possible and to a minimum depth of 12 inches;
2. redistribution must be done in a manner that achieves approximate uniform
thicknesses consistent with soil resource availability and appropriate for the
postmining vegetation, land uses, contours, and surface water drainage
systems; and
3. redistributed soil must be reconditioned by subsoiling or other appropriate
methods.
ARM 26.4.703 (Relevant and Appropriate) When using materials other than, or along with,
soil for final surfacing in reclamation, the operator must demonstrate that the material (1) is
at least as capable as the soil of supporting the approved vegetation and subsequent land use,
and (2) the medium must be the best available in the area to support vegetation. Such
substitutes must be used in a manner consistent with the requirements for redistribution of
soil in ARM 26.4.701 and 702.
ARM 26.4.711 (Relevant and Appropriate) requires that a diverse, effective, and permanent
vegetative cover of the same seasonal variety and utility as the vegetation native to the area
of land to be affected shall be established except on road surfaces and below the low-water
line of permanent impoundments. The vegetative cover must also be capable of meeting the
criteria set forth in § 82-4-233, MCA. Vegetative cover is considered of the same seasonal
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variety if it consists of a mixture of species of equal or superior utility when compared with
the natural vegetation during each season of the year. (See also ARM 26.4.716 below
regarding substitution of introduced species for native species.)
ARM 26.4.713 (Relevant and Appropriate) provides that seeding and planting of disturbed
areas must be conducted during the first appropriate period for favorable planting after final
seedbed preparation but may not be more than 90 days after soil has been replaced.
ARM 26.4.714 (Relevant and Appropriate) requires use of a mulch or cover crop or both
until an adequate permanent cover can be established. Use of mulching and temporary cover
may be suspended under certain conditions.
ARM 26.4.716 (Relevant and Appropriate) establishes the required method of revegetation,
and provides that introduced species may be substituted for native species as part of an
approved plan.
ARM 26.4.717 (Relevant and Appropriate) relates to the planting of trees and other woody
species if necessary, as provided in § 82-4-233, MCA, to establish a diverse, effective, and
permanent vegetative cover of the same seasonal variety native to the affected area and
capable of serf-regeneration and plant succession at least equal in extent of cover to the
natural vegetation of the area, except that introduced species may be used in the revegetation
process were desirable and necessary to achieve the approved intended land use plan.
ARM 26.4.718 (Relevant and Appropriate) requires the use of soil amendments and other
means such as irrigation, management, fencing, or other measures, if necessary to establish a
diverse and permanent vegetative cover.
ARM 26.4.728 (Relevant and Appropriate) sets forth requirements for the composition of
vegetation on reclaimed areas.
VH. TO BE CONSIDERED DOCUMENTS (TBCS)
The use of documents identified as TBCs is addressed on page 2 of the Introduction, above.
A list of TBC documents is included in the Preamble to the NCP, 55 Fed. Reg. 8765 (March
8, 1990). Those documents, plus any additional similar or related documents issued since
that time, will be considered by EPA and MDEQ in implementation of the remedy.
Vm. OTHER LAWS (NON-EXCLUSIVE LIST)
CERCLA defines as ARARs only federal environmental and state environmental and facility
siting laws. Remedial design, implementation, and operation and maintenance must
nevertheless comply with all other applicable laws, both state and federal, if the remediation
work is done by parties other than the federal government or its contractors.
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The following "other laws" are included here to provide a reminder of other legally
applicable requirements for actions being conducted at the Streamside Tailings Operable
Unit. They do not purport to be an exhaustive list of such legal requirements, but are
included because they set out related concerns that must be addressed and, in some cases,
may require some advance planning. They are not included as ARARs because they are not
"environmental or facility siting laws." As applicable laws other than ARARs, they are not
subject to ARAR waiver provisions.
Section 121(e) of CERCLA exempts removal or remedial actions conducted entirely on-site
from federal, state, or local permits. This exemption is not limited to environmental or
facility siting laws, but applies to other permit requirements as well.
A. Other Federal Laws
1. Occupational Safety and Health Regulations
The federal Occupational Safety and Health Act regulations found at 29 CFR § 1910 are
applicable to worker protection during conduct of RI/FS or remedial activities.
B. Other Montana Laws
1. Groundwater Act
Section 85-2-516, MCA, states that within 60 days after any well is completed a well log
report must be filed by the driller with the DNRC and the appropriate county clerk and
recorder.
2. Water Rights
Section 85-2-101,' MCA, declares that all waters within the state are the state's property, and
may be appropriated for beneficial uses. The wise use of water resources is encouraged for
the maximum benefit to the people and with minimum degradation of natural aquatic
ecosystems.
Parts 3 and 4 of Title 85, MCA, set out requirements for obtaining water rights and
appropriating and utilizing water. All requirements of these parts are laws which must be
complied with in any action using or affecting waters of the state. Some of the specific
requirements are set forth below.
Section 85-2-301, MCA, of Montana law provides that a person may only appropriate water
for a beneficial use.
Section 85-2-302, MCA, specifies that a person may not appropriate water or commence
construction of diversion, impoundment, withdrawal or distribution works therefor except by
applying for and receiving a permit from the Montana Department of Natural Resources and
Conservation. While CERCLA exempts the portion of a remedial action conducted entirely
on site from permit requirements, appropriate notification and submission of an application
A-29
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should be performed and a permit should be obtained for all appropriations of water in order
to establish a priority date in the prior appropriation system.
Section 85-2-306, MCA, specifies the conditions on which groundwater may be appropriated,
and, at a minimum, requires notice of completion and appropriation within 60 days of well
completion.
Section 85-2-311, MCA, specifies the criteria which must be met in order to appropriate
water and includes requirements that:
1. there are unappropriated waters in the source of supply;
2. the proposed use of water is a beneficial use; and
3. the proposed use will not interfere unreasonably with other planned uses or
developments.
Section 85-2-336, MCA, closes the Upper Clark Fork River Basin to further appropriations
of surface water, with certain exceptions, including under certain conditions, appropriations
for water to conduct CERCLA response actions.
Section 85-2-402, MCA, specifies that an appropriator may not change an appropriated right
except as provided in this section with the approval of the DNRC.
Section 85-2-412, MCA, provides that, where a person has diverted all of the water of a
stream by virtue of prior appropriation and there is a surplus of water, over and above what
is actually and necessarily used, such surplus must be returned to the stream.
3. Controlled Ground Water Areas
Pursuant to § 85-2-507, MCA, the Montana Department of Natural Resources and
Conservation may grant either a permanent or a temporary controlled ground water area.
The maximum allowable time for a temporary area is four years.39.
Pursuant to § 85-2-506, MCA, designation of a controlled groundwater area may be
proposed if: (i) excessive groundwater withdrawals would cause contaminant migration; (ii)
groundwater withdrawals adversely affecting groundwater quality within the groundwater
area are occurring or are likely to occur; or (iii) groundwater quality within the groundwater
area is not suited for a specific beneficial use.
If a temporary controlled ground water area is granted, the statute requires DNRC to commence studies to determine
the designation or modification of a permanent controlled ground water area.
A-30
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4. Occupational Health Act. §§ 50-70-101 et seg., MCA.
ARM § 16.42.101 addresses occupational noise. In accordance with this section, no
worker shall be exposed to noise levels in excess of the levels specified in this regulation.
This regulation is applicable only to limited categories of workers and for most workers the
similar federal standard in 29 CFR § 1910.95 applies.
ARM § 16.42.102 addresses occupational air contaminants. The purpose of this rule
is to establish maximum threshold limit values for air contaminants under which it is believed
that nearly all workers may be repeatedly exposed day after day without adverse health
effects. In accordance with this rule, no worker shall be exposed to air contaminant levels in
excess of the threshold limit values listed in the regulation. This regulation is applicable
only to limited categories of workers and for most workers the similar federal standard in 29
CFR § 1910.1000 applies.
5. Montana Safety Act
Sections 50-71-201, 202 and 203, MCA, state that every employer must provide and
maintain a safe place of employment, provide and require use of safety devices and
safeguards, and ensure that operations and processes are reasonably adequate to render the
place of employment safe. The employer must also do every other thing reasonably
necessary to protect the life and safety of its employees. Employees are prohibited from
refusing to use or interfering with the use of safety devices.
6. Employee and Community Hazardous Chemical Information Act
Sections 50-78-201, 202, and 204, MCA, state that each employer must post notice of
employee rights, maintain at the work place a list of chemical names of each chemical in the
work place, and indicate the work area where the chemical is stored or used. Employees
must be informed of the chemicals at the work place and trained in the proper handling of
the chemicals.
A-31
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THE ADMINISTRATIVE RECORD FOR THE
SILVER BOW CREEK/BUTTE AREA (ORIGINAL PORTION) SITE
This index lists the documents which comprise the
administrative record for the Silver Bow Creek/Butte Area
(Original Portion) Superfund Site (abbreviated as SBCO Superfund
Site). Each record is identified by date, author, addressee, and
type (when known), and a short abstract of the document.
The Silver Bow Creek/Butte Area Superfund Site comprises one
of the largest Superfund Sites in the nation. Because of the
size and complexity of the Site, EPA has divided the site into a
Butte Portion and an Original Portion. The Butte Portion, or
SBCB, addresses the contamination in and around the city of Butte
away from the Silver Bow Creek streambed. The Original Portion,
or SBCO, addresses the stream contamination found from the
headwaters of Silver Bow Creek through the Warm Springs Ponds
area. As stated, this index contains record abstracts for the
SBCO Superfund Site.
The SBCO Superfund Site is divided into eight operable
units. The name and location of administrative record indexes or
locations for these operable units is as follows:
Lower Area One (once known as Area One) ERA operable unit - File
numbers 5.02.00.00 through 5.02.37.00
Rocker Timber Framing and Treating Plant operable unit - File
numbers 5.03.00.00 through 5.03.18.11
Streamside Tailings operable unit - File numbers 5.04.00.00
through 5.04.19.01
Warm Springs Ponds Active Area operable unit - File numbers
5.05.00.00 through 5.05.06.06 and 5.05.07.00 through
5.05.18.11
Mill Willow Bypass ERA operable unit - File number 5.05.06.07
Warm Springs Ponds Inactive Area operable unit - File number
5.05.06.08
Warm Springs Ponds Final Decision - File numbers 5.05.00.00
through 5.05.18.11
Manganese Stockpile Removal - Because this action was conducted
by EPA's Emergency Removal Branch, records are indexed and
maintained separately in EPA offices in Denver and Montana.
Some duplicated and related documents for this action are
found in file number 5.02.35.00.
The index also contains a section on site-wide material,
designated under the file numbers 5.01.01.00 through 5.01.29.06.
That section contains document or records which provide more
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general information about the SBCO Superfund Site. Each operable
unit specific administrative record listed above incorporates the
administrative- record documents identified for the "site-wide"
section of the SBCO record files.
In addition, each operable unit specific administrative
record incorporates the administrative record designated for the
Clark Fork Basin General system of records, which are listed in a
separate index. In other words, the administrative record for
each operable unit includes the administrative records for the
specific SBCO Superfund Site operable unit, the administrative
records for the SBCO site-wide component, and the administrative
records for the Clark Fork Basin General component.
Guidance documents referred to or relied upon by the
Environmental Protection Agency are also part of the
administrative record, and, although not specifically listed, are
incorporated into each operable unit specific administrative
record. Those documents are available through EPA's Montana
Superfund Records Center, located in Helena, Montana 59626, 301
South Park, Drawer 10096, Federal Building, (406) 449-5728.
Chain of custody documents and other supporting documents
for sample collection and data analysis pertaining to a
particular operable unit are incorporated into the administrative
record of each operable unit, or are specifically listed in the
index and contained in the physical files for the site. Those
documents are located in one of the following places:
EPA Helena offices, 301 South Park St., Drawer 10096, Helena,
Montana 59626
ARCO offices
State of Montana offices
Contractor offices for ARCO, EPA, or State of Montana contractors
Further review of those documents can be obtained by
contacting EPA's Montana Superfund Records Center at the above
address or telephone number.
A number of the documents contained in the administrative
record contain references to primary sources. Those sources are
incorporated by reference into each operable unit specific
administrative record in which the document which references the
material appears. Most of these references are publicly
available through libraries or other document repositories.
Those primary reference documents that are not publicly available
are specifically contained in this record index. Further review
of those documents can also be obtained by contacting EPA's
Montana Superfund Records Center at the above address or
telephone number.
The administrative record index contains some confidential
records. Those documents are listed separately, and are
abstracted in a manner similar to publicly available documents.
-------
A short summary of the contents of those documents is contained
in the abstract entry. Those documents are not available for
public review.-•
This administrative record index, including incorporated
documents, is established pursuant to section 113(k) of CERCLA,
42 U.S.C. Section 9613(k). These documents form the basis for
EPA's decision concerning response actions taken or to be taken
at the SBCO Superfund Site, and also indicate the involvement of
the potentially responsible parties and the public in the
decision making process. The index will be routinely updated, as
additional records or documents are obtained by EPA in relation
to each operable unit, unless that operable unit is closed.
Administrative record files for the following operable units are
closed, as response action was decided upon and taken by EPA for
those units.
Manganese Stockpile
Lower Area One ERA
Warm Springs Ponds'Active Area
Warm Springs Ponds Inactive Area
Mill Willow Bypass ERA
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5.04.00.00 STREAM SIDE TAILINGS OPERABLE UNIT
5.04.01.00 Operable Unit Overview
5.04.01.01 Summaries/Meetings
5.04.01.02 Briefing Materials
5.04.01.03 Operable Unit Management Plans
5.04.01.04 Background/Information
5.04.02.00 PRP Information
5.04.02.01 Financial Status
5.04.02.02 PRP Searches
5.04.02.03 AMC
5.04.03.00 Information Requests
5.04.03.01 FOIA's
5.04.03.02 Congressional Inquiries
5.04.03.03 Other
5.04.04.00 RI/FS Planning
5.04.04.01 Work Plans/Comments/Guidance
5.04.04.02 Quality Assurance Project Plan (QAPP)
5.04.04.03 Laboratory Analytical Protocol (LAP)
5.04.04.04 Sampling Analysis Plan (SAP)/Field
Operations Plan (FOP)
5.04.04.05 Standard Operating Procedures (SOP)
5.04.04.06 Remedial Action Master Plan (RAMP)
5.04.04.07 General
5.04.04.08 Health/Environmental
Assessment/Comments
5.04.04.09 AO/Consent
5.04.04.10 Special Notice Letters
5.04.04.11 Negotiations
5.04.05.00 ARAR's
5.04.06.00 RI/FS Reports
5.04.06.01 Sampling Data
5.04.06.02 Preliminary Reports
5.04.06.03 Final Reports
5.04.06.04 Screening Studies
5.04.06.05 Photos/Aerial
5.04.06.06 Comments/Responses/Summaries
5.04.06.07 Meetings/Agendas/Minutes
5.04.06.08 Risk Assessments
5.04.06.09 Historical
5.04.06.10 Proposed Plan
5.04.07.00 ROD
5.04.08.00 RD/RA
5.04.09.00 0/M
11
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5.04.10.00 Accounting and Cost Recovery
5.04.11V00 Community Relations
5.04.11.01 Mailing Lists
5.04.11.02 Press Releases
5.04.11.03 Press Clippings
5.04.11.04 Technical Assistance Grants
5.04.11.05 Repository Index
5.04.11.06 Fact Sheets
5.04.11.07 Public Comments
5.04.11.08 Administrative Record Index
5.04.11.09 Plans
5.04.11.10 Correspondence
5.04.12.00 SCAP
5.04.13.00 References
5.04.13.01 Miscellaneous Studies
5.04.13.02 Journal Articles
5.04.13.03 Other Operable Unit Information
5.04.14.00 State and Other Agency Coordination
5.04.14.01 Interagency Agreements (IAG's)
5.04.14.02 Fish and Wildlife Service (FWS)
5.04.14.03 U. S. Geological Survey (USGS)
5.04.14.04 Corp of Engineers (COE)
5.04.14.05 Bureau of Mines (BOM)
5.04.14.06 Office of Surface Mining (OSM)
5.04.14.07 Agency for Toxic Substances Disease
Registry (ATSDR)
5.04.14.08 Federal Emergency Management Agency
(FEMA)
5.04.14.09 Historical/Cultural Preservation
5.04.14.10 Bureau of Reclamation (BOR)
5.04.15.00 Natural Resource Damage Claims
5.04.16.00 Local Governments
5.04.16.01 General
5.04.16.02 Institutional Controls
5.04.17.00 Demonstration Projects
5.04.17.01 Demonstration Project I
5.04.17.02 Demonstration Project II
5.04.17.03 Demonstration Project III
5.04.18.00 Correspondence
5.04.18.01 Pre-1983/No Dates/Partial Dates
5.04.18.02 1983
5.04.18.03 1984
12
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5.04.18.04 1985
5.04.18.05 1986
5.04.18.06 1987
5.04.18.07 1988
5.04.18.08 1989
5.04.18.09 1990
5.04.18.10 1991
5.04.18.11 1992
5.04.18.12 1993
5.04.18.13 1994
5.04.19.00 Treatability Projects
5.04.19.01 Proposals
5.04.19.02 Correspondence
5.04.19.03 Studies
5.04.19.04 Comments
5.04.19.05 Reports
13
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Executive Summary
Introduction
The Streamside Tailings (SST) Operable Unit (OU) is one of seven operable units of the Silver Bow
Creek/Butte Area (original portion) NPL site. Silver Bow Cr.eek was listed as a Superfund site by
the EPA in 1982 pursuant to the Comprehensive Environmental Response, Compensation, and
Liability Act of 1980 (CERCLA). CERCLA, as amended by the Superfund Amendment and
Reauthorization Act, stipulates that remedial actions at Superfund sites must be protective of both
human and ecological receptors. To evaluate the degree to which remedial alternatives are
protective, it is necessary to assess both existing environmental and human health risks and
potential risks. The baseline Risk Assessment (RA) developed for the Streamside Tailings operable
unit of the Silver Bow Creek/Butte Area National Priorities List (NPL) site. The RA uses site-
related chemical concentrations, exposure potential, and toxicity information to characterize
potential human health and ecological risks which may exist at the site as a result of former mining
activities. The RA estimates current and potential future exposure and risk in the absence of future
remedial actions. The results of the baseline RA are used to help determine the need for
remediation of the site, to establish health-based remediation goals for contaminated media, and to
assist in the selection of remedial alternatives.
Site Description
The Streamside Tailings (SST) Operable Unit (OU) is located along Silver Bow Creek in Silver Bow
and Deer Lodge Counties, Montana. The SST OU includes approximately 25 miles of Silver Bow
Creek from below the Lower Area One portion of the Priority Soils Operable Unit in Butte,
Montana to the Warm Springs Ponds Active Area Operable Unit near Opportunity, Montana. The
site generally encompasses the 100-year floodplain and areas impacted by fluvially deposited mine,
mill, and smelter wastes within and adjacent to Silver Bow Creek. The OU also includes adjacent
railroad beds, because mine, mill, and/or smelter wastes were often used as base materials for
these beds. Since at least some of these beds may be converted to hiking, biking, and/or riding
trails, future human exposure is possible.
The site was divided into four subareas for the purposes of risk assessment, based upon geologic
and topographic features that control the soil, hydrogeologic, groundwater, surface water, ecologic,
demographic, and land use characteristics. Subarea 1, the Rocker subarea, extends from Colorado
Tailings to Nissler at the 1-15 bridge over Silver Bow Creek. Subarea 2, the Ramsay subarea,
extends from the 1-15 bridge to Miles Crossing. Subarea 3, the Canyon subarea, extends from Miles
Crossing to the 441 bridge. Subarea 4, the Opportunity subarea, extends from highway 441 to
Warm Springs Ponds.
The history of over 100 years of continuous mining and related activities greatly affected the
natural environment in and around Silver Bow Creek. Between 2.4 and 2.8 million cubic yards of
mill tailings and other mining wastes have been estimated to be present within the SST OU. These
mine wastes in and near the creek have contributed to substantial downstream contamination,
particularly by the potentially toxic elements arsenic, cadmium, copper, lead, mercury and zinc.
Organic pollution in Silver Bow Creek is contributed by municipalities via discharge from the Butte
sewage plant, and from other sources, such as wood treating operations, which were located close
to the creek. However, compared to the mining impacts such pollution appears to be a minor
factor.
CDM Camp Dresser & McKee
9469-115\tfthhrc\summary 12-30-94 ebk
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Executive Summary
There are no cities within the SST OU. Butte, with a population of approximately 30,000, is located
just east of the SST OU. Located within or near the SST OU are the small communities of Rocker,
Nissler, Silver Bow, "Ramsay, Miles Crossing, Finlen, Crackerville, and Opportunity, as well as
unnamed communities consisting of several houses scattered throughout the site. A detailed
overview of population, land use, economy, and related topics for Deer Lodge County is provided
in a 1990 Anaconda/Deer Lodge County comprehensive master plan.
Land use near and within the SST OU also includes industrial activities (railroad, Rhone-Poulenc),
mining (gravel), agriculture (grazing), and recreation (dirt biking, hiking, wading, etc.). Occasional
irrigated croplands are present on the alluvial plain next to Silver Bow Creek in some areas.
Human Health Risk Assessment
Chemicals of Potential Concerns (COPCs)
The principal contaminants of concern at the SST OU are metals associated with mining activities.
Those of particular concern for the HHRA are arsenic, cadmium, copper, lead, mercury, and zinc.
All of these materials, except for mercury, have been considered COPCs for OUs upstream and
downstream of SST. Mercury data for the site are very limited, but are consistent with elevated
levels in sediments and possibly in surface water within the OU. Mercury is therefore discussed
qualitatively in the assessment.
Organic chemicals (pentachlorophenol (PCP) and polycyclic aromatic hydrocarbons (PAH)) have
been released from wood treating sites upstream of and within the SST OU. The sources of these
contaminants are being addressed by actions at the Rocker Operable Unit and the Montana Pole
NPL site.
Exposure Point Concentrations
Two types of exposure estimates are required for Superfund human health RAs, a reasonable
maximum exposure (RME), and an average exposure. The RME is denned as an exposure well
above the average but still within the range of those that could reasonably be expected to occur for
a given exposure pathway at a site. The upper 95 percent confidence limit (UCL) on the arithmetic
mean of contaminant concentrations within an exposure area is used to evaluate potential RME
exposures. Arithmetic average exposure point concentrations are used to estimate potential
average exposures. UCL and average values are also useful for many comparisons made in the
ecological risk assessment. Exposure point concentrations for various media are provided in Table
ES-1.
Exposure Assessment
This assessment addresses potential pathways by which human receptors could be exposed to
contamination within the SST OU in accordance with EPA guidance. This guidance recommends
that exposure assumptions were selected so that estimates fall near the reasonable maximum
(RME) for that pathway. For most pathways evaluated in this assessment, an average exposure
was also calculated to provide a range of exposures and some semi-quantitative information on
uncertainties in the assessment. Inclusion of average exposures is intended to provide the risk
manager with a range of exposures which encompasses both the typical and upper-range of
exposures.
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Executive Summary
Combinations of exposure pathways and associated human receptors make up exposure scenarios.
There are three general exposure scenarios which are considered in this risk assessment, and these
are shown in schematic form in the site conceptual exposure model in Figure ES-1.
Residential Scenario
Residents might be exposed to contaminated soils and sediments while working or playing in their
yards, might inhale contaminated dust originating from soils in their yards and in neighboring
areas, might consume contaminated groundwater and be exposed dermally during bathing to
contaminated groundwater from a residential well, and might consume vegetables and/or animal
products grown/raised in/on contaminated soils and/or watered with contaminated surface water
or groundwater. Where residential properties might extend down to the stream bank, residents
might also be exposed to contaminated surface water, sediments and tailings on a regular basis
during activities such as wading. In addition, residential exposures might vary significantly over
the length of the OU, and residents in one area could potentially receive much higher or lower
exposures than their counterparts in other areas of the OU. Evaluation of the residential scenario,
then, considers both significant exposures by pathway and the distribution of exposures along the
OU.
Occupational Scenario
Workers might be exposed to contaminants while working outdoors within the OU. This could
occur, for example, in a lumber or brick yard, while moving cattle, or during planting, working and
harvesting crops on agricultural land impacted by the tailings. Likely exposure pathways are
incidental ingestion of contaminated soils/sediments, inhalation of contaminated dust suspended
in air by wind or other disturbances, and dermal contact with contaminated soils and sediments.
An agricultural worker is assumed to be representative for possible occupational exposures.
Recreational Scenario
People recreating in the SST OU may come into contact with contaminated surface water and
sediment from Silver Bow Creek and contaminated materials in railroad beds in the SST OU .
Recreational activities at the creek most likely include picnicking, swimming, wading, hunting, and
dirt-bike riding. During these activities, incidental ingestion of and dermal contact with
contaminants in surface water and sediments may occur. In addition, recreational visitors to the
site may also be exposed to contaminated materials in railroad beds. The county may consider
converting stretches of some railroad beds to recreational trails, and individuals and families who
use the trails for jogging, bicycling and hiking in the future may be exposed. Contaminants in
railroad bed materials may be incidentally ingested, and/or resuspended in air by wind or other
disturbances and inhaled.
Toxicity Assessment
The purpose of the toxicity assessment is to examine the potential for each contaminant of concern
(COC) to cause adverse effects in exposed individuals and to describe the relationship between the
extent of exposure to a particular contaminant and adverse effects. Adverse effects include both
noncarcinogenic (systemic) and carcinogenic health effects in humans.
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8469-115\tf\hhrc\summary 12-30-94 ebk
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Executive Summary
Toxicity Criteria
Toxicity criteria for carcinogens are slope factors in units of risk per milligram of chemical exposure
per kilogram body weight per day ((mg/kg-day)'1). These cancer slope factors (CSFs) are based on
the assumption that no threshold for carcinogenic effects exists and any dose, no matter how small,
is associated with a finite cancer risk. Toxicity values for noncarcinogens, or for significant
noncarcinogenic effects caused by carcinogens, are reference doses (RfDs) in units of milligrams of
chemical exposure per kilogram body weight per day (mg/kg-day). RfDs are estimates of
thresholds; exposures less than the RfD are not expected to cause adverse effects even in the most
sensitive populations. Toxicity criteria for COPCs are presented in Tables ES-2 and ES-3.
Risk Characterization
Residential Scenario
Carcinogenic risks associated with residential exposures (Table ES-4) to COPCs within the SST OU
are due entirely to potential exposures to arsenic in soil/sediment and in groundwater. Risks
based on average exposure assumptions are estimated at the upper edge of the EPA risk range of
10'4 to 10'6, and risks based on RME are greater by a factor of about 6. These risks could vary by a
factor of 50 percent based on the variability of arsenic soil concentrations found within the OU.
Higher concentrations of arsenic in soil occur in the Ramsay subarea of the site; this area is the most
likely location where residents might be exposed to generally higher arsenic concentrations.
Arsenic in groundwater is found in higher concentrations in both the Rocker and Ramsay areas.
However, all higher concentrations in these locations were found in shallow groundwater. Since
any future domestic drinking water well is likely to be installed much deeper than the near-surface
monitoring wells, potential for consumption of shallow groundwater is limited. It is, therefore,
unlikely that cancer risks are underestimated by a significant factor for exposure via ingestion of
groundwater.
Noncancer risks associated with the residential scenario (Table ES-5) exceed the target level (a
hazard index of one) for both average and RME. More importantly, individual target levels
(hazard quotients) are exceeded for arsenic, cadmium, copper and zinc estimates based on average
and/or RME. Noncancer health risk may be unacceptable for exposure to each of these COPCs.
Noncancer risks from exposure to arsenic may vary by as much as 50 percent based on variability
of arsenic soil concentrations found within the OU. It is unlikely that high concentrations of arsenic
in groundwater in subareas would have significant effect on risk estimates. Cadmium, copper and
zinc are of potential importance only through ingestion of contaminated groundwater.
Lead exposures within the OU are difficult to interpret. Based on bioavailability assumptions for
lead in soil used in nearby Butte, MT, lead risks may generally be in the acceptable range in the OU.
Based on the IEUBK model default for bioavailability, however, lead exposures may be excessive in
many areas of the OU. A clear determination of bioavailability may be necessary in order to fully
evaluate lead exposures. Moreover, in some areas of the site, lead concentrations reach very high
levels (up to 9000 mg/kg and greater). If some exposure situations were to be dominated by soils
with such high concentrations, lead risks could be significantly underestimated by use of site-wide
averages. Specific land-use evaluation on a much smaller scale than those considered in this
assessment may be necessary to determine if there are any small subareas of the OU which may
present a human exposure hazard above that presented in the risk assessment.
COM Camp Dresser & McKee
8469-115\t1\hhrc\summary 12-30-94 ebk
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Table ES-2
Carcinogenic Reference Concentrations for COCs
at the Streamside Tailings Site
C.OC
Pentachlorophenol
Benzo(a)pyrene
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Carcinogen
Classification
B2
B2
A
B1
D
B2
D
D
Oral
Slope Factor
(mg/kg-day)'1
1.2x10'1
7.3 X1CT0
1.75x1
-------
Table ES-3
Reference Doses for COCs at the Streamside Tailings Site
coc
Pentachlorophenol
Benzo(a)pyrene
Arsenic
Cadmium
Water
Food
Copper
Lead
Mercury
Inorganic
Methyl Hg
Zinc
Oral RfD
(mg/kg-day)
3x10'2
NA
3x10'4
5x10'4
1 x10'3
0.0356°
NA
3x10'4
3x1Q-4
3x10'1
Inhalation RfD
(mg/kg-day)
NA
NA
NA
NA
NA
NA
NA
3x10'4
NA
NA
Source
EPA 1 994a
—
EPA19943
EPA19943
EPA19943
EPA19946
—
EPA19943
EPA19943
EPA1994b
8 EPA (U.S. Environmental Protection Agency). 1994. Integrated Risk Information System (IRIS).
b EPA (U.S. Environmental Protection Agency). 1994. Health Effects Assessment Summary Tables
(HEAST).
0 As suggested in HEAST, the oral RfD was calculated from maximum Contaminant Level Goal
(MCLG).
NA = Not available.
8469-115\tl\hhrc\ES-3.Tbl 12-29-94 vc
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Table ES-4
Carcinogenic Risks for the Residential Scenario3
Pathway
Ingestion of Soil/Sediment
Ingestion of Groundwater
Dermal Contact with Groundwater
Inhalation of Dust
Total Carcinogenic Risk
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Arsenic
RME Risk
2.5 x10'4
NC
NC
NC
NC
NC
3.11 x10'4
NC
NC
NC
NC
NC
2.99 xlfJ9
3.17 x10'6
5.6 x10'4
Average Risk
4.4 xiry5
NC
NC
NC
NC
NC
6.7 x10'5
NC
NC
NC
NC
NC
NA
9.51 x10'7
1.1 x10'4
a Total carcinogenic risks have been rounded to the nearest tenth.
NC = Not calculated, chemicals are not carcinogens for this exposure pathway, or carcinogenic slope
factors are not available.
NA = Only RME exposure is assessed for this pathway.
8469-115\tf\hhrc\ES-4.Tbl 12-29-94 vc
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Table ES-5
Noncarcinogenic Hazard Quotients and Hazard Indices for the Residential Scenario3
Pathway
Ingestion of Soil/Sediment
»
Pathway HI
Ingestion of Groundwater
Pathway HI
Dermal Contact with Groundwater
Inhalation of Dust
Total HI
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper '
Lead
Mercury
Zinc
Arsenic
Arsenic
RME HQ
1.05X101
8.97 X10'2
5.26 x10-1
NC
NC
7.11 xlfj2
1.1 x101
3.10x10°
1.6x10°
2.73x10°
NC
NC
4.00x10°
1.2 X101
2.23 X10'5
NC
2.3 X101
Average Risk
3.03x10°
2.44 x10'2
1.5x1Q-1
NC
NC
2.28 x10'2
3.2x10°
2.22x10°
7.30 x10'1
1.69x10°
NC
NC
4.75 x10'1
5.1 X10°
NA
NC
8.4x10°
a Pathway His and total His have been rounded to the nearest tenth.
NC = Not calculated, data are insufficient for quantitative analysis.
NA = Only RME exposure is assessed for this pathway.
HQ = Hazard Quotient
HI = Hazard Index
8469-115Wihrc\ES-5.Tbl 12-29-94 vc
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Executive Summary
Occupational Scenario
Potential cancer risks for the occupational scenario (Table ES-6), based on potential exposure to
agricultural workers, fall within the EPA acceptable risk range. However, risks to agricultural
workers are estimated assuming exposures in areas outside the 100-year floodplain only. If
workers were to equally divided their work time between areas inside and outside the floodplain,
risks could be as much as three times higher than those calculated. This would place worker risks
at slightly more than 10"4.
Potential noncancer risks (Table ES-7) are due almost entirely to arsenic and fall near the target HI
of one, with arsenic risks based on RME essentially equal to the RfD, or "safe" dose. Upper-range
risk estimates are thus at, but do not exceed, an exposure generally recognized as safe, even for
lifetime exposure. In general, it does not appear that arsenic concentrations in the SST OU are
sufficiently high under the occupational scenario to represent human health risks that exceed
common EPA regulatory targets.
Recreational Scenario
Cancer risks for visitors (Table ES-8) to the SST OU are potentially large, with average and RME-
based risk estimates exceeding the upper edge of the EPA risk range. Little of this risk is, however,
contributed by exposures to visitors to the creek itself. Based on RME, it is future users of railroad
beds converted to trails that may suffer the highest risks calculated for the site (over
10'3). These risks are almost totally due to exposure to arsenic. Further, very high arsenic
concentrations appear to be associated with areas of past concentrate spills. The methods used in
this assessment essentially assume that future trail users will contact railroad bed materials with
relatively low concentrations of arsenic much of the time, but will occasionally encounter areas
where arsenic concentrations are greatly elevated ("hotspots").
Noncancer risks (Table ES-9) follow a pattern similar to noncancer risks. His based on both
average and RME exposures exceed unity, suggesting a potential for adverse noncancer effects.
Nearly all risk is contributed by arsenic, and, overall, noncancer risks in this scenario are the
highest encountered for the site. Arsenic in railroad bed materials again contributes the bulk of the
exposure.
Lead exposures within the OU are difficult to interpret. Based on bioavailability assumptions for
lead in soil used in nearby Butte, MT, lead risks may generally be in the acceptable range in the OU.
Based on the IEUBK model default for bioavailability, however, lead exposures may be excessive in
the OU, particularly for the rails-to-trails exposure scenario. A clear determination of
bioavailability may be necessary in order to fully evaluate lead exposures. Moreover, in some areas
of the site, lead concentrations reach very high levels (up to 11,500 mg/kg in one sample of railroad
bed materials). If some exposure situations were to be dominated by soils with such high
concentrations, lead risks could be significantly underestimated by use of site-wide averages.
Though very small scale variability is high, it is possible that some preferential recreational areas
within the site could have average exposure concentrations in excess of those used to estimate lead
exposures in this assessment.
In addition, the use of the IEUBK model for assessing lead exposures in non-residential settings is
very uncertain. Lead exposures based on occasional exposure in a recreational setting may not be
adequately estimated by the IEUBK model, and may, in fact be substantially, overestimated.
COM Camp Dresser & McKee 10
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ES-6
Carcinogenic Risks for the Occupational Scenario9
Pathway
Ingestion of Soil/Sediment
Inhalation of Dust
Total Carcinogenic Risk
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
RME Risk
5.4 xirj5
NC
NC
NC
NC
NC
8.5 x 10'6
6.2 xirj5
Average Risk
3.4 x1CT6
NC
NC
NC
NC
NC
5.1 X 10'6
8.5 x 10*
a Total carcinogenic risks have been rounded to the nearest tenth.
NC = Not calculated, chemicals are not carcinogens for this exposure pathway, or carcinogenic slope
factors are not available.
8469-115\tf\hhrc\ES-6.Tbl 12-29-94 vc
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Table ES-7
Noncarcinogenic Hazard Quotients and Hazard Indices for the Occupational Scenario3
Pathway
Ingestion of Soil/Sediment
Pathway HI
Inhalation of Dust
Total HI
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
RME Risk
8.05x10°
8.0 x10~3
3.29 x10'2
NC
NC
3.64 x10-3
8.5 x1CT1
NC
8.5 x1(T1
Average Risk
4.99 x10'2
6.07 x1Q-4
2.39 x10-3
NC
NC
2.90 x10'4
5.3 x10'2
NC
5.3 x10'2
a Pathway His and Total His have been rounded to the nearest tenth.
NC = Not calculated, data are insufficient for quantitative analysis.
8469-115\tf\hhrc\ES-7.Tbl 12-29094 vc
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Table ES-8
Carcinogenic Risks for the Recreational Scenario3
Pathway
Ingestion of Soil/Sediment
Pathway Risk
Ingestion of Surface Water
Pathway Risk
Dermal Contact with Surface Water
Ingestion of Rail Road Bed Materials
Pathway Risk
Inhalation of Rail Road Bed Materials
Pathway Risk
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
RME Risk
6.2 x1Cr5
NC
NC
NC
NC
NC
6.2 X10'5
3.4 x10'8
NC
NC
NC
NC
NC
3.4 x10'8
3.2 x10'9
1.2x10'3
NC
NC
NC
NC
NC
1.2 x10'3
1.8 xicr5
NC
NC
NC
NC
NC
1.8 x10'5
Average Risk
9.0 xicr6
NC
NC
NC
NC
NC
9.0 x10'5
7.8 x1CT9
NC
NC
NC
NC
NC
7.8 x10'9
7.3 x1Q-10
1.4 X10'4
NC
NC
NC
NC
NC
1.4 x10'4
9.2 x10'6
NC
NC
NC
NC
NC
9.2 X10'6
a Total carcinogenic risks have been rounded to the nearest tenth.
NC = Not calculated, chemicals are not carcinogens for this exposure pathway, or carcinogenic slope
factors are not available.
8469-115\lfthhrc\ES-8.Tbl 12-29-94 vc
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Table ES-9
Noncarcinogenic Hazard Quotients and Hazard Indices for the Recreational Scenario9
Pathway
Ingestion of Soil/Sediment
Pathway HI
Ingestion of Surface Water
Pathway HI
Dermal Contact with Surface Water
Ingestion of Rail Road Bed Materials
Pathway HI
Inhalation of Rail Road Bed Materials
Pathway HI
Total HI
Chemical
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
Arsenic
Cadmium
Copper
Lead
Mercury
Zinc
4-1 2 Year Old Child
RMEHQ
8.95x10-'
6.34 x10'3
3.97 x10'2
NC
NC
6.28x10°
9.5 x10'1
3.89 X1Q-4
2.25 x10'5
3.26 X10-6
NC
NC
1.35x10'5
4.6 xKT1
1.96x10-5
1.65x10'
7.42 x10'2
1.91 x10°
NC
NC
1.56x10''
1.9x101
NC
NC
NC
NC
NC
NC
NC
2.0 x101
Average HQ
1.03x10''
8.14 x10-4
5.15 x10'3
NC
NC
8.89 x10'4
1.1 x10'1
9.0 x10'5
5.22 x10'6
6.94 x10'6
NC
NC
2.23 X1Q-6
1.0x10-"
4.57 x10'6
2.02x10°
1.08x10-a
1.8x10''
NC
NC
8.07 x10'3
2.2x10°
NC
NC
NC
NC
NC
NC
NC
2.4x10°
1-3 Year Old Child
RMEHQ
4.17x10°
3.47 x10'2
2.18x10-1
NC
NC
3.02 x10'2
4.5x10°
8.75 x10'4
5.05 x10'5
7.33 x10'5
NC
NC
3.04 x1Q-5
1.3 x10'3
3.06 x1Q-5
7.44x10'
3.34x10''
8.58x10°
NC
NC
7.02x10''
8.4x10'
NC
NC
NC
NC
NC
NC
NC
9.0 x101
Average HQ
2.91 xlO'1
2.05 x10'3
1.52x10'2
NC
NC
2.31 x10'3
3.1 x10-1
2.02 x10'4
1.17x10'5
1.56x10'5
• NC
NC
5.02 x10'6
2.3 X10"1
7.12 x10'6
4.55x10°
2.43 x10'2
4.06 x 10'1
NC
NC
1.82X10'2
5.0x10°
NC
NC
NC
NC
NC
NC
NC
5.4x10°
a Pathway His and Total His have been rounded to the nearest tenth.
NC = Not calculated, data are insufficient for quantitative analysis.
HQ = Hazard Quotient
HI = Hazard Index
8469-115\tf\hhrc\ES-9.Tabl
12/29/94 vc
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Executive Summary
Results of IEUBK modeling for site visitors, and rails-to-trails users should be considered screening
level only. Such modeling would provide little scientific support for risk management decisions.
Once again, hotspots of lead dominate potential exposures and risks.
Uncertainties Associated with Risk Characterization
There is a degree of uncertainty associated with every step of the assessment process. Several
important uncertainties were identified in the SST OU risk assessment.
Some exposure parameters, especially those for recreational exposure scenarios are often poorly
characterized and may be based solely on professional judgement. Such exposure parameters
introduce potentially significant, but substantially unknown amounts of uncertainty, into the
assessment process. Generally, exposure parameters based on professional judgement are
conservative (i.e., they tend to err on the side of protection of human health). Thus, these exposure
parameters are generally more likely to cause overestimation of exposures than underestimation.
Land use in the SST OU is mixed and is likely to remain so in the future. However, it is difficult to
predict which areas might be developed for which land uses in the future. This risk assessment
does not make specific land use assumptions for specific areas. Instead, risk estimates are
developed on a site-wide basis and evaluated for representativeness for different subareas within
the OU. These risk estimates, with appropriate consideration given to subarea differences, can thus
be applied as needed to different specific areas within the OU.
The relative bioavailability of arsenic in all media is assumed to be high (80 or 100 percent).
Because arsenic in soil and sediments in the SST OU is largely derived from mining and milling
wastes, and the relative bioavailability of arsenic associated with such wastes may actually be
lower, potential risks from arsenic in soil and sediment may have been overestimated.
Several recent studies indicate current toxicity criteria for arsenic could overestimate risks.
Metabolic detoxification of arsenic at low doses may lessen the impact of arsenic exposure
predicted by linear extrapolation of results from higher exposures. In addition, new studies
indicate that background inorganic arsenic intake and skin cancer risks may have been
underestimated in the Taiwanese population on which current toxicity criteria are based. These
new studies have not been peer-reviewed, however, and current toxicity criteria are therefore not
modified for this RA.
The bioavailability of lead used in the RA is based in part on studies conducted for the Butte
Priority Soils OU, and on the assumption that mineral species present in Silver Bow Creek would
be similar to those found in Butte, since their source was Butte. There is some uncertainty
associated with this approach. For example, the geochemistry of tailings deposited as stream
sediments may not be identical to those from waste deposits not subject to constant or periodic
inundation. Such uncertainties may lead to either over or underestimation of risks associated with
lead depending on bioavailability assumptions made.
Quantitative assessment of exposures due to consumption of vegetables grown in contaminated
soils, or irrigated with contaminated water, was not carried out even though screening calculations
suggested that exposures via this pathway could be significant. It is possible, therefore, that
significant exposures and associated risks at the site were omitted from the final estimates.
COM Camp Dresser &. McKee 15
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Executive Summary
However, toxicity to plants is likely to restrict gardening within the SST OU to less contaminated
soils and/or to soils that have been extensively amended. Baker and Bower (1988) concluded, on
the basis of their study in Palmerton soils, that toxicity would limit cadmium exposure to a fraction
of current estimates of daily cadmium intake from diet and other "background" sources. It seems
likely that similar consideration might apply to gardens in the SST OU. It appears that any
underestimation of risk due to elimination of consumption of home-grown vegetables from the
quantitative risk assessment does not constitute a significant underestimation of total potential
risks in the OU.
The risk assessment assumed that exposures to metals and arsenic from consumption of animals
grazed on contaminated pastures and/or watered with contaminated surface or groundwater are
not significant contributors to overall exposures. Conservative, though generic, calculations
suggest that metal uptake into beef following ingestion of contaminated plants or soils will not be
significant in the SST OU. A possible exception is zinc. Uptake of zinc into plants in the more
heavily contaminated soils in the SST OU could raise concentrations of zinc in plants to a level that
could approach levels toxic to cattle that use the plants as forage. Zinc, however, is expected to be
toxic to the plants themselves at the higher concentrations found in the OU. Thus, the theoretical
potential for toxic effects to livestock is probably not actually realized at the site.
Arsenic appears to represent the major risk "driver" for the site when considering potential human
health impacts. However, arsenic background reference soil samples were collected very near
areas of contamination; the higher values could reflect some degree of contamination. Reference
concentrations for arsenic ranged from 5.7 to 142 mg/kg. RME and average exposure point
concentrations for arsenic are 511 and 296 mg/kg respectively (Table ES-1). Background may thus
contribute somewhat to total exposures and risks.
Thus, the high estimate for background contribution (based on comparison of maximum
background to the average exposure point concentration) may well overestimate actual
background contribution. The low background estimate is very unlikely to have received
significant contamination, but could be below the average background for the area. Actual
contributions from background for arsenic are likely to be greater than one percent, but may be
significantly less than 50 percent.
Ecological Risk Assessment
Introduction
Ecological Risk Assessments (ERAs) evaluate the likelihood that adverse ecological effects may
occur or are occurring at a site as a result of exposure to chemical or physical stressors. Risks result
from contact between ecological receptors and stressors that are of sufficiently long duration and of
sufficient intensity to elicit adverse effects. The primary purpose of this ERA is to identify and
describe actual or potential onsite conditions that can result in adverse effects to present or future
ecological receptors. These conditions are identified by comparing observed or likely effects with
actual or predicted exposures to physical and, primarily, chemical stressors. Another important
objective of this ERA is to provide information that can help establish remedial priorities and serve
as a scientific basis for regulatory and remedial actions for the Streamside Tailings Operable Unit
(SST OU).
COM Camp Dresser & McKee 16
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Executive Summary
The approach used to conduct this ERA is based on site-specific information and on recent EPA
guidance, primarily The Framework for Ecological Risk Assessment. The primary components of
this ERA are Problem Formulation, Analysis and Risk Characterization. Stressors identified for this
ERA are based on their potential to cause adverse ecological effects, especially effects due to
chemical contamination of surface water, sediment, and surface soil. This focus is based on the
potential for onsite contaminated media to currently preclude the existence of healthy and diverse
aquatic and riparian ecosystems in and adjacent to Silver Bow Creek. In addition, mining-related
and other activities have caused considerable physical damage to aquatic and terrestrial habitats
onsite.
The primary chemical Stressors identified for the site include the following:
Arsenic (surface water, sediment, surface soil)
Cadmium (surface water, sediment, surface soil)
Copper (surface water, sediment, surface soil)
Lead (surface water, sediment, surface soil)
Zinc (surface water, sediment, surface soil)
Mercury (surface water, sediment, surface soil)
The following chemicals, are also considered COPCs and are therefore evaluated in this ERA:
PCP (sediment, surface soil)
PAHs (surface water, sediment, surface soil)
Dissolved oxygen (surface water)
Ammonia (surface water)
Nitrogen (surface water)
In addition to chemical Stressors, ecological receptors that inhabit or use the SST OU may also be
exposed to physical or non-chemical Stressors. Important physical Stressors, related primarily to
past mining activities at this site, include the following:
• Degradation of instream substrates
• Channelization of Silver Bow Creek
• Degradation or disturbance of terrestrial and riparian habitats
The major habitats that have potential to be affected by chemical and physical Stressors include
aquatic habitats, riparian habitats, and terrestrial habitats. The types of organisms that may be
exposed to the chemical and physical Stressors identified at this site include aquatic and terrestrial
plants and animals (i.e., macroinvertebrates, fish, amphibians, reptiles, birds, and mammals) that
inhabit or use, or have the potential to inhabit or use, aquatic, streamside/wetland or terrestrial
habitats of the SST OU. No threatened, endangered, or sensitive species have been reported within
the SST OU.
The primary exposure pathway evaluated in this ERA is the direct contact of ecological receptors
with chemical and physical Stressors. Although of lesser importance for this ERA, effects due to
contaminant transfer through food chains are also evaluated.
COM Camp Dresser &. McKee 17
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Executive Summary
Risk Characterization
Potential risks to ecological receptors are evaluated by comparing current or predicted conditions
and chemical concentrations in exposure media (exposure assessment) with similar data correlated
with potential to cause adverse effects (effects assessment). The risk characterization phase of the
ERA integrates exposure assessment and effects assessment to estimate risk potential for ecological
receptors, and considers the ecological significance of predicted effects. A weight-of-evidence
approach, utilizing various measures of potential adverse effects instead of a single effects value, is
employed in this assessment.
A simplified summary of SST-OU wide potential risks to ecological receptors is presented on a
media-specific and chemical-specific basis in Table ES-10. Risk potentials (low, moderate, high) are
estimated by evaluating the difference or magnitude between average (arithmetic mean) and U95
values and relevant effects concentrations. Risk potential is estimated to be high where average or
U95 values greatly exceed relevant effects concentrations.
Surface Water
The assessment of potential risks to aquatic receptors is based on a comparison of dissolved COCs
in surface water to relevant effects concentrations. Measurements of total metals concentrations in
surface water may overestimate risks to aquatic receptors because only a portion of the total metals
measured is bioavailable and toxic.
Ammonia has potential to cause adverse effects on aquatic biota in Silver Bow Creek because of
elevated concentrations in some areas. Adverse effects are more likely, and probably more severe,
immediately below the Butte wastewater treatment plant (WWTP), which has been identified as the
only known point source of ammonia in Silver Bow Creek. Ammonia concentrations in the lower
reaches of Silver Bow Creek only rarely exceed site-adjusted (for pH and temperature) chronic
ambient water quality criteria (AWQC) for ammonia.
Recent measurements of dissolved arsenic in Silver Bow Creek have remained below important
effects concentrations. These effects concentrations range from 0.048 to 0.850 mg/L, and include
concentrations expected to protect freshwater plants and sensitive freshwater animals. Ambient
concentrations of dissolved arsenic in Silver Bow Creek range from approximately 0.01 to 0.04
mg/L, indicating low potential for risks to aquatic life from arsenic.
Unlike arsenic, dissolved cadmium concentrations in Silver Bow Creek commonly exceed critical
effects concentrations. Arithmetic mean values of dissolved cadmium for all sampled reaches of
Silver Bow Creek exceed the lowest effects concentrations but remain below the higher, less
protective effects concentrations but remain below the higher, less protective effects concentrations.
Cadmium appears to be an important and probably moderate contributor to overall toxicity of
Silver Bow Creek surface water. Dissolved copper in Silver Bow Creek is elevated throughout the
entire OU, with slightly lower concentrations measured in the most downstream reaches. All
recent samples of dissolved copper exceed the lowest effects concentrations for freshwater plants,
invertebrates, and fish. Site specific acute effects concentrations for rainbow trout are exceeded in
about half the samples measured. Dissolved copper is a major contributor to the toxicity of Silver
Bow Creek, and ambient concentrations commonly exceed safe levels for aquatic plants,
invertebrates, and fish.
COM Camp Dresser & McKee 18
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Table ES-10
Simplified Summary of Ecological Risks from Chemical Stressors
Media (units)
Chemical
Arith. Mean Cone/
U95 Cone
Effects
Cone 1
Risk
Potential
Surface Water
mg/L
M9/L
M9/L
ug/L
mg/L
M9/L
Mg/L
mg/L
ug/L
ug/L
M9/L
Ammonia
Arsenic (D)
Cadmium (D)
Copper (D)
Dissolved
Oxygen
Lead (D)
Mercury (D)
Nitrogen
(total soluble)
PAHs (individual)
PCP
Zinc (D)
3.11 /NC
15.56/24.1
1.66/2.26
50.74/59.56
-9.5 /NC
3.0/6.57
0.16/0.16
1. 75-9.1 9/NC
0.02 / NC
8.01/NC
336.19/585.99
0.53-2.7
48-850
0.47-5.0
3.9-54
4.0
0.8-500
0.012-4.0
0.03-1 .0
0.1-5.0
3.5-14.5
40-277
Mod to High
(locationAiming
dependent)
Low
Mod
High
Low to High
(location/timing
dependent)
Mod
Low to Mod
Mod to high
(location/timing
dependent)
Low
Mod
High
Sediment
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
Arsenic
Cadmium
Copper
Lead
Mercury
PAHs (individual)
PCP
Zinc
75.16/113.11
4.66 / 7.01
828 / 1 ,579.89
250.5/318.66
3.49 / 6.7
0.054-1. 563 /NC
0.367/0.634
1,380.13/2,120.27
23.8-24.8
3.9
325-354
62.4
0.2-2.0
4-100
4.2-21
1,064
High
High
High
High
High
Low
Low
High
8469-115\tf\hhrc\ES-10.Tbl 12-29-94 vc
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Table ES-10(Cont.)
Simplified Summary of Ecological Risks from Chemical Stressors
Media (units)
Chemical
Arith. Mean Cone/
U95 Cone
Effects
Cone1
Risk
Potential
Surface Soil
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
Arsenic
Cadmium
Copper
Lead
Mercury
PAHs (individual)
PCP
Zinc
303.1 / 51 4.9
6.45 / 1 1 .95
1 ,470.4 / 2,484.9
723.63 / 1 ,241 .4
1 .82 / 5.7
Not Analyzed
Not Analyzed
1, 835.6 /2,920'.7
25-100
4-50
60-100
250-1,000
2-10
1-10
0.5-5.0
200-500
High
Mod
High
High
Low to mod
Unknown/
Probably low
Unknown/
Probably low
High
1 Description and source listed in Table 5-17
NC: not Calculated
D: dissolved
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Executive Summary
Dissolved oxygen (D.O.) concentrations in Silver Bow Creek are below minimum national
coldwater criteria at some times and in some areas of Silver Bow Creek. For the most part,
however, D.O. concentrations remain above minimum criteria levels except in the reach
immediately below the Butte WWTP. Observed low D.O. concentrations in this and in other
reaches are probably the result of excess nutrient inputs and high biological oxygen demand (BOD)
discharges from the Butte WWTP. In the upper reaches, low D.O., along with elevated ammonia
and dissolved metals, contribute to the biological impairment of Silver Bow Creek.
Dissolved lead appears to be a minimal to moderate contributor to the toxicity of Silver Bow Creek
surface water. Although mean and U95 values generally exceed the lowest effects concentrations,
they never exceed the highest (least protective) effects concentrations. Dissolved lead in Silver Bow
Creek may add to the overall toxicity of the creek but is unlikely to be a major contributor,
especially compared to copper and zinc.
Dissolved mercury was only rarely detected in Silver Bow Creek surface water (one sample, 11
percent frequency of detection). Detection limits for mercury commonly exceed critical effects
concentrations or established criteria. Therefore, any detection of mercury in surface water can be
important. Because dissolved mercury was detected in only one sample, and because of increased
uncertainty associated with concentrations in the low ug/L range, dissolved mercury is not
expected to be critically important to environmental conditions in Silver Bow Creek.
Nitrogen compounds were detected in all surface water samples, as expected. Elevated nitrogen
compounds, measured as total soluble nitrogen or TSN can promote growth of nuisance algae.
Excessive algal growth can indirectly cause depletions in dissolved oxygen and can also impair
aquatic habitats. Excess nitrogen in Silver Bow Creek can be important and potentially serious
problem in some reaches (especially below the Butte WWTP and in areas of uncontrolled cattle
grazing).
PCP has moderate potential to cause adverse effects in surface water because it was detected in all
of the few surface water samples for which it was analyzed at concentrations similar to national
chronic ambient water criteria. The only known .Silver Bow Creek PCP source is currently being
addressed by remedial actions at the Montana Pole site.
Only one PAH, benzo(b)fluoranthene, was detected in Silver Bow Creek surface water, with all
detections (4 of 4 samples) 02 ug/L. Although only limited toxicity data are available for
individual PAHs in surface water, 0.02 ug/L is not expected to be acutely toxic to aquatic biota.
PAHs in surface water are not likely to be a significant contributor to the biological impairment of
Silver Bow Creek within the SST OU.
Elevated zinc concentrations are found throughout Silver Bow Creek, especially within the most
upstream 10 miles of the creek. The spatial distribution of dissolved zinc in Silver Bow Creek
indicates a general and consistent decrease in dissolved zinc as samples are taken further
downstream. However, even the most downstream samples are associated with exceedances of
critical effects concentrations. These data indicate that dissolved zinc is a major contributor to
toxicity in the upstream reaches of Silver Bow Creek. In the lower reaches, dissolved zinc is at least
a moderate contributor to Silver Bow Creek toxicity.
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Executive Summary
Sediment
There is less confidence (more uncertainty) in effects concentrations used to evaluate sediment
toxicity compared to concentrations used for surface water evaluation. For this reason, the list of
effects concentrations for assessing sediment toxicity include a greater variety of data, including
site specific toxicity data (lowest degree of uncertainty); non-site specific toxicity data (moderate
degree of uncertainty); background data; and other data based on co-occurrence of effects and
sediments contaminated with a mixture of chemicals (highest uncertainty). The greatest
uncertainty is with data that are statistically rather than lexicologically derived, such as Effects
Range-Median (ER-M) values of Long and Morgan. ER-M values represent the median value of
ranked concentrations associated with observed effects, and are based on sediments contaminated
with a mixture of chemicals. These values are therefore not entirely appropriate for comparison to
ambient sediments that are contaminated with a single or a few chemicals. ER-M values are
included in this risk characterization because they are commonly used by regulatory agencies and
others as a screening level tool in assessing potential sediment toxicity. For the most part, site
specific sediment toxicity data are preferred over all other effects data and, where available, these
serve as the primary effects data for comparison to recently collected sediment chemistry data.
The total arsenic concentrations of Silver Bow Creek sediments change little from upstream to
downstream stations. Both PTI and Canonic sampling events confirm the relative consistent
distribution of arsenic throughout the OU. The effects concentrations with the greatest confidence
and the least uncertainty (No Effect Concentration, sublethal effects, Hydlelo), are exceeded by the
concentrations of all sediment samples taken. Depending on the data source (PTI or Canonie),
ambient concentrations of total arsenic in Silver Bow Creek sediments exceed site-specific effects
concentrations by a factor of approximately 2 to 8. Total arsenic is a major contributor to the
potential toxicity of Silver Bow Creek sediments.
Unlike arsenic, the concentration of total cadmium in Silver Bow Creek sediments appears to vary
both spatially and temporally, and may be increasing over time. Based on the 1991 and 1992 data,
total cadmium in Silver Bow Creek sediments nearly always exceeds the site specific no adverse
effect concentration (NEC) for sensitive benthic invertebrates (3.9 mg/kg, Hyallela). Other effects
concentrations, including those based on spiked sediment bioassays (SSB) and apparent effects
concentrations (AET) are similar in magnitude to the site specific NEC. These data and others
indicate that total cadmium in Silver Bow Creek sediments have a high potential to adversely
impact sensitive benthic invertebrates and possibly salmonids.
Copper concentrations in Silver Bow Creek sediments remain consistently elevated from the most
upstream to the most downstream reaches of the creek.Copper concentrations in Silver Bow Creek
sediments remain consistently elevated from the most upstream to the most downstream reaches of
the creek. Studies from 1988,1991, and 1992 reveal increasingly higher concentrations over time.
Copper concentrations in Silver Bow Creek sediments are nearly always in excess of most of the
relevant effects concentrations used for comparison, even though the effects concentrations are
quite high. For example, all sediment samples collected in 1992 reveal copper concentrations in
excess of 1000 mg/kg, much higher than relevant effects concentrations of 325-350 mg/kg. Copper
in Silver Bow Creek sediments is a major contributor to the impairment of the aquatic community
of Silver Bow Creek.
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Executive Summary
Total lead in Silver Bow Creek sediments changes little with respect to location with the exception
of apparent increases approximately 1 and 8 miles downstream of the upstream border of the OU.
Lead concentrations measured in Silver Bow Creek sediments always exceed 100 mg/kg. All 1991
and 1992 samples reveal total lead in sediments in excess of 250 mg/kg. For comparison, the most
appropriate (i.e., those with the least uncertainty) effects concentrations are within the range of
about 30 to 120 mg/kg. Values in excess of 250 mg/kg are likely to result in severe, acute effects to
sensitive benthic biota, thereby potentially affecting organisms at several food chain levels,
especially upper level consumers of mercury-contaminated prey. This pathway is not a primary
concern at this time because it is incomplete in most cases due to limited numbers and types of
potential receptors. The toxicity of inorganic mercury can be increased by bacterial methylation in
aerobic and especially anaerobic sediments. Methylmercury concentrations in Silver Bow Creek
sediments are expected to remain quite low, however, because anaerobic conditions are not
expected to predominate.
PCP concentrations in Silver Bow Creek sediments within the SST OU ranged from 0.256 to 0.980
mg/kg. Relevant toxicity data for PCP in sediment are lacking. However, calculation of predicted
sediment pore water concentrations, based on the equilibrium partitioning approach, indicate that
Silver Bow Creek sediments within the SST OU have little potential to cause adverse ecological
effects. PCP is not considered to be a concern in Silver Bow Creek sediments.
Concentrations of individual PAHs in Silver Bow Creek sediments range from 0.0084 to 3.015
mg/kg within the SST OU. The most commonly detected PAHs include benzo(a)anthracene,
benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, dibenzanthracene, and pyrene. The
maximum mean value for any particular PAH (1.563 mg/kg, chrysene), only slightly exceeds the
low threshold value (1.0 mg/kg) that serves as a conservative guideline for evaluating surface soil
contamination. Based on available data, PAHs are not considered to be significant contributors of
biological impairment of Silver Bow Creek within the SST OU.
064 mg/kg is a No Effect Concentration (NEC), The probability and the severity of such adverse
effects increase with greater exceedances of the NEC. Therefore, while ambient concentrations
around 1,000 mg/kg may or may not cause adverse effects to resident species, depending on the
sensitivity of exposed organisms and on zinc bioavailabiliry, values greatly in excess of 1,000
mg/kg are likely to be harmful. Since so many recent measurements of zinc in Silver Bow Creek
sediments exceed 1,000 and even 2,000 mg/kg, sediment zinc is likely to adversely impact Silver
Bow Creek.
Surface Soil
The primary data source for evaluating surface soil phytotoxicity is CH2M Hill (1987), in which the
toxicities of arsenic, cadmium, lead, and zinc on soil, plants, and livestock in the Helena Valley of
Montana were assessed. Although not site specific, This document summarizes available
phytotoxicity data for most of the metals of concern and derives various threshold values for
evaluating phytotoxicity. These threshold values include Tolerable Level (maximum concentration
at which no phytotoxicity has been observed), Hazard Level (suggested hazard level based on
State, provincial, and national regulatory guidelines), and Phytotoxic Level (toxic level for various
crop species and soil parameters found in the Helena Valley). Of these, the Phytotoxic Level is
most useful because it provides a reasonable threshold (not to exceed) level based on sensitive crop
species found in the Helena Valley. Phytotoxic values are based on near-site (regional) data and
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Executive Summary
they therefore are the best available data for assessing potential phytotoxicity of As, Cd, Pb, and Zn
at the SST OU., Threshold Contamination, Contaminated, and Background Pollution are also used
for assessing the ecological risk potential for other chemicals of concern. Several of these values are
based on multiple soil uses and are not specifically intended to be used as surface soil criteria for
protecting ecological receptors. These values do, however, give a general indication of potential for
risks from surface soil contamination within the SST OU. The basis for and limitations of this
approach are discussed fully in the ERA.
Arsenic in SST surface soil is probably a major contributor to phytotoxicity within the SST OU
because all relevant phytotoxicity effects concentrations, including those based on regional (near-
site) studies, are greatly exceeded by site-wide mean, U95, and maximum concentrations measured
in SST surface soils.
Cadmium, although elevated in SST surface soils, appears to be less likely to result in phytotoxic
effects on local plants compared to arsenic. Site-wide mean, U95, and maximum concentrations of
cadmium in SST surface soils remain below phytotoxic concentrations derived for sensitive crop
species and regional soils. Site-wide mean, U95, and maximum values do, however, exceed
regional baseline, suggested hazard, non-regional phytotoxic, and tolerable levels. There is less
confidence in the ability of these values to predict or estimate potential phytotoxicity. Because
regional phytotoxicity values are not exceeded in any samples, along with the finding that non-
regional phytotoxic levels are exceeded in most samples, cadmium in surface soil is considered to
have moderate potential for risk.
Copper in SST surface soil is also expected to be a major contributor to phytotoxicity within the SST
OU because all relevant phytotoxicity effects concentrations are exceeded by site-wide mean, U95,
and maximum concentrations measured in SST surface soils. There is less certainty in using non-
regional or non-site specific effects data to estimate risk potential compared to using site specific
data. Selected non-site specific data presented in the ERA clearly reveal a high potential for
phytotoxicity. Although site- or regional-specific phytotoxicity data are lacking, it is unlikely that
the greatly elevated copper concentrations commonly measured in SST surface soil are conducive
to survival, growth, reproduction of sensitive native plant species.
Lead concentrations in SST surface soil are approximately half those of copper.. Comparisons of
site-wide mean, U95, and maximum exposure concentrations and regional phytotoxic levels reveal
a high potential for phytotoxicity. Site-wide mean (724 mg/kg) and U95 (1,241 mg/kg) values
approximate the regional phytotoxic level (1,000 mg/kg), while the maximum detected value (9,130
mg/kg) greatly exceeds the 1,000 mg/kg regional phytotoxic concentration. The risk potential for
lead in SST surface soil, based oh phytotoxicity, is high.
Recommended threshold concentrations (2.0 mg/kg) are exceeded by U95 and maximum SST
surface soil mercury concentrations. On the other hand, levels considered contaminated (10
mg/kg) are not exceeded by any surface soil sample. Because the effects concentrations used in
this evaluation are not specifically derived to protect ecological receptors, there is substantial
uncertainty in the conclusions reached. Mercury in surface soil is considered to have low to
moderate potential for ecological risk within the SST OU compared to other surface soil
contaminants (e.g., copper, lead, and zinc).
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Executive Summary
Site-wide exposure concentrations (average, U95, and maximum) of zinc in Silver Bow Creek
surface soil greatly exceed selected comparative data for regional baseline, non-regional phytotoxic
level, suggested hazard level, tolerable level, and regional phytotoxic level.
Non-chemical Stressors
The major non-chemical stressors contributing to biological impairment of Silver Bow Creek and
adjacent areas are disturbed aquatic and terrestrial habitats. Disturbances of aquatic habitat appear
to be primarily caused by sediment inputs from upstream sources and from streambank erosion.
Where such sedimentation includes deposition of fine grained materials, preferred habitat is lost
for most desirable benthic macroinvertebrates. Future spawning areas for salmonid fish would
also be similarly affected where deposition of fine grained sediments predominates. Adult
salmonids would also be affected by conditions that impair the colonization, survival, growth, and
reproduction of prey species, including benthic macroinvertebrates. Finally, fine grained
sediments are expected to be more toxic to aquatic life than large grained sediments because of
increased metals sorption on fine grained materials. Sedimentation in Silver Bow Creek is therefore
a source of both physical (habitat disturbance) and chemical (metals toxicity) stress on resident or
future resident biota.
Terrestrial habitats are disturbed by the physical presence of mine waste and the toxic conditions
associated with mine waste and surface soil that precludes the establishment of a diverse and
healthy plant community. This in turn adversely affects animals that require sufficient food
(herbivorous species) and cover (most all species) for survival and reproduction. Soil-dwelling
animals, along with sensitive plant species, are not present where mine waste overlies native soils.
This result is due to both physical (displacement or covering of native soil) and chemical (toxicity)
causes. Streambank tailings and other mine wastes also contribute to impairment of Silver Bow
Creek through erosion and runoff.
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