DERR-2024-008228

RECORD OF DECISION

KENNECOTT SOUTH ZONE, OPERABLE UNIT 2

SOUTHWEST JORDAN RIVER VALLEY GROUND WATER PLUMES

U. S. Environmental Protection Agency, Region VIII
Utah Department of Environmental Quality

December 13, 2000

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TABLE OF CONTENTS

Page
LIST OF FIGURES iv
LIST OF TABLES v
PART 1: DECLARATION 1
PART 2: DECISION SUMMARY 6
A. Site Name, Location, and Brief Description 6
B. Site History and Enforcement Activities 8
C. Community Participation 12
D. Scope of Role of Operable Unit or Response Action 13
E. Site Characteristics 19
F. Current and Potential Future Site and Resource Uses 39
G. Summary of Site Risks 44
H. Remedial Action Objectives 54
I. Description of Alternatives 56
J. Summary of Comparative Analysis of Alternatives 73
K. Principal Threat Waste 80
L. Selected Remedy 80
M. Statutory Determinations 90
N. Documentation of Significant Changes 93
PART 3: RESPONSIVENESS SUMMARY
E-Mails 94
iii
Letters 95
Phone Messages 108
Public Hearing Testimony 110
Technical Issues 115
APPENDIX A A-1
iv
LIST OF FIGURES

Page
Figure 1: Regional Location Map 7
Figure 2: Sulfate Concentrations 29
Figure 3: Model Prediction, Reduced Pumping, Layer 4, Year 2022 30
Figure 4: Model Prediction, Reduced Pumping, La yer 4, Year 2047 31
Figure 5: Model Prediction, Reduced Pumping, Layer 4, Year 2147 32
Figure 6: Geologic Cross Section 37
Figure 7: Well Inventory Map 38
Figure 8: Land Use Map 43
v
LIST OF TABLES
Page
Summary of OU2 Enforcement Activities 10
Kennecott Operable Units 13
Kennecott South Zone Environmental Cleanups 16
Volume of Contaminated Ground Water 25
Concentrations of Chemicals of Concern 26
Water Suppliers and Sources of Water 40
Types of Water Uses 41
Concentrations of Chemicals of Concern 44
Health Effects of Elevated Inorganic Components in Drinking Water 47
Risk of Chemicals of Concern in Acid Plume 48
Comparison of Water Quality in Wells with Jordan River Water Quality 50
Standards
Potential Concentrations of Contaminants in Jordan River if Acid Plume 52
is not Contained
Estimated Costs for Alternative 1 57
Estimated Costs for Alternative 2 59
Estimated Costs for Alternative 3 61
Estimated Costs for Alternative 4 64
Estimated Costs for Alternative 5 67
Estimated Costs for Alternative 6 70
Summary Table of Alternatives 78
vi
Project Cost Estimate, Capital Costs 83
Estimated Annual Project Costs, Operations and Maintenance 85
Summary of Total Costs, Capital and Net Present Value 87
Final Cleanup Levels for the Selected Remedy 88
Appendix A, Federal and State ARARs A-1
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RECORD OF DECISION
KENNECOTT SOUTH ZONE OPERABLE UNIT 2
SOUTHWEST JORDAN RIVER VALLEY GROUND WATER PLUMES

PART 1: DECLARATION

A. Site Name and Location

This Record of Decision covers Operable Unit 2 (Southwest Jordan River Valley
Ground Water Plumes) of the Kennecott South Zone Site, proposed for the NPL in
1994. Operable Unit 2 is located in Salt Lake County, Utah, and encompasses the
groundwater beneath all or portions of the municipalities of West Jordan, South
Jordan, Riverton, Herriman, and portions of unincorporated Salt Lake County.
The CERCLIS ID is UTD000826404.

B. Statement of Basis and Purpose

This decision document presents the Selected Remedy for the Kennecott South Zone
Operable Unit 2 Site in Salt Lake County, Utah, which was chosen in accordance with
the Comprehensive Environmental Response, Compensation and Liability Act
(CERCLA), as amended by the Superfund Amendments and Reauthorization Act
(SARA), 42 U.S.C. §§ 9601 et. seq, and, to the extent practicable, the National
Contingency Plan (NCP), 40 C.F.R. Part 300. This decision is based on the
Administrative Record file for this site.

The State of Utah concurs with the Selected Remedy. Their concurrence is based upon
the belief that the remedy will benefit the public within the affected area and begin to
protect public health and the environment.

C. Assessment of Site

The response action selected in this Record of Decision is necessary to protect the
public health or welfare or the environment from actual or threatened releases of
hazardous substances and pollutants or contaminants into the environment.

D. Description of Selected Remedy

The selected remedy for Operable Unit 2 (Southwest Jordan River Valley Ground
Water Plumes) addresses the ground water contamination for this Kennecott South
Zone Site. The surface contamination which originally constituted the principal
threat at the site has already been addressed in other removal and remedial actions
at OU1 (Bingham Creek), OU3 (Butterfield Creek), OU4 (Large Bingham
Reservoir), OU5 (ARCO Tails), OU6 (Lark Tailings and Waste Rock), OU7
(South Jordan Evaporation Ponds), OU10 (Copperton Soils), and OU17 (Bastian
Area).

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For purposes of clarifying agency authority over the cleanup operations of this
action, the agencies plan on using a joint CERCLA and State NRD approach.
The cleanup strategy presented within the text of this ROD is concerned primarily
with the acid plume in Zone A, under CERCLA authority. EPA maintains the
right to intervene in the cleanup of the sulfate plume in Zone B, if it is not
addressed sufficiently by the State NRD action. The State of Utah will maintain
authority of operations, in both Zones A and B, as they are intended to fulfill the
requirements of the NRD settlement. (Please refer to the footnote at the bottom of
page 28.)

The performance standards for the selected remedy include achieving the primary
drinking water standards in the aquifer of Zone A at the Kennecott property line (as
of the date of the signing of this document) for all hazardous substances (i.e.
metals). Active remediation (pump and treat) is required to achieve the health-
based goal of 1500 ppm for sulfate while monitored natural attenuation is used to
achieve the State of Utah primary drinking water standard for sulfate at 500
ppm. The water treated and delivered for municipal use must achieve all
drinking water standards of the State of Utah, as a requirement of both the
CERCLA action and the Natural Resource Damage (NRD) settlement between the
State of Utah and Kennecott Utah Copper Corporation. The performance standard
for treatment residuals as measured at or before the end of the tailings pipe is
demonstration that the tailings/treatment residuals combination meets the
characteristics of non-hazardous waste.

The selected remedy involves treatment and containment of contaminated ground
water plumes. The principal threats which caused the ground water contamination
have been addressed in previous actions or are contained under provisions of a Utah
Ground Water Protection Permit.

The selected remedy contains the following elements:

· Continuation of source control measures as administered through the State of
Utah Ground Water Protection Program.

· Prevent human exposure to unacceptably high concentrations of hazardous
substances and/or pollutants or contaminants by limiting access to the
contaminated ground water. Institutional controls include purchases of land,
purchases of water rights, limiting drilling of new wells and increased
pumping of nearby old wells as approved (on request) and administered
through the State of Utah State Engineer (Division of Water Rights).

· Prevent human exposure to unacceptably high concentrations of hazardous
substances and/or pollutants or contaminants through point-of-use
management which includes providing in-house treatment units to residents
with impacted wells, replacement of their water by hooking the properties
up to municipal drinking and/or secondary supplies, and/or modifying their
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wells to reach uncontaminated waters.

· Contain the acid plume in Zone A by installation of barrier wells at the
leading edge of the contamination (1500 ppm sulfate or less), pump and
treat the waters to provide a hydraulic barrier to further plume movement
while providing treated water for municipal use. The treatment technology
for the barrier well waters is reverse osmosis.

· Withdraw the heavily contaminated waters from the core of the acid plume
in Zone A and treat these contaminated waters using pretreatment with
nanofiltration or equivalent technology, followed by treatment with reverse
osmosis to provide drinking quality water for municipal use.

· Monitor the plume to follow the progress of natural attenuation for the
portions of the Zone A plume which contain sulfate in excess of the state
primary drinking water standard for sulfate (500 ppm sulfate).

· Disposal of treatment concentrates in existing pipeline used to slurry tailings to
a tailings impoundment prior to mine closure.

· Development of a post-mine closure plan to handle treatment residuals for
use when the mine and mill are no longer operating.

E. Statutory Determinations

The selected remedy is protective of human health and the environment, complies
with Federal and State requirements that are applicable or relevant and appropriate
to the remedial action, is cost-effective, and utilizes permanent solutions and
alternative treatment technologies to the maximum extent practicable.

This remedy also satisfies the statutory preference for treatment as a principal
element of the remedy (i.e., reduces the toxicity, mobility, or volume of hazardous
substances, pollutants, or contaminants as a principal element through treatment).

Because this remedy will result in hazardous substances, pollutants, or
contaminants remaining on-site above levels that allow for unlimited use and
unrestricted exposure, a statutory review will be conducted within five years after
initiation of remedial action to ensure the remedy is, or will be, protective of
human health and the environment.

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F. ROD Data Certification Checklist

The following information is included in the Decision Summary section of this
Record of Decision. Additional information can be found in the Administrative
Record file for this site.

· Chemicals of concern and their respective concentrations, pages 44-45.
· Baseline risk represented by the chemicals of concern, pages 48-49.
· Cleanup levels established for chemicals of concern and the basis for these
levels, pages 88-89.
· How source materials constituting principal threats are addressed, page 19.
· Current and reasonable anticipated future land use assumptions and
current and potential future beneficial uses of ground water used in the
baseline risk assessment and ROD, pages 40-42.
· Potential land and ground water use that will be available at the site as a
result of the Selected Remedy, page 42.
· Estimated capital, annual operation and maintenance (O&M), and total
present worth costs, discount rate, and the number of years over which the
remedy cost estimates are projected, pages 83-87.
· Key factor(s) that led to selecting the remedy (i.e., describe how the
Selected Remedy provides the best balance of tradeoffs with respect to the
balancing and modifying criteria, highlighting criteria key to the decision),
pages 73-79.
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G. Authorizing Signatures

The following authorized officials at EPA Region VIII and the State of Utah
approve the selected remedy as described in this Record of Decision:

Max H. Dodson Date
Assistant Regional Administrator
Office of Ecosystems Protection and Remediation
U. S. Environmental Protection Agency, Region VIII

Dianne R. Nielson, Ph.D. Date
Executive Director
Utah Department of Environmental Quality