DERR-2024-008593

Optimization Review Report
Remedial Process Optimization Study

Murray Smelter Superfund Site
Superfund Site
Murray, Utah
EPA Region 8

www.clu-in.org/optimization | www.epa.gov/superfund/remedytech | www.epa.gov/superfund/cleanup-optimization-superfund-sites

OPTIMIZATION REVIEW

MURRAY SMELTER SUPERFUND SITE

MURRAY, UTAH
EPA REGION 8

DRAFT FINAL REPORT
June 2024
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EXECUTIVE SUMMARY

NATIONAL OPTIMIZATION STRATEGY BACKGROUND

The U.S. Environmental Protection Agency’s (EPA’s) definition of optimization is as follows:

“Efforts at any phase of the removal or remedial response to identify and implement
specific actions that improve the effectiveness and cost-efficiency of that phase. Such
actions may also improve the remedy’s protectiveness and long-term implementation,
which may facilitate progress towards site completion. To identify these opportunities,
Regions may use a systematic site review by a team of independent technical experts,
apply techniques or principles from Green Remediation or Triad, or apply some other
approaches to identify opportunities for greater efficiency and effectiveness.”1

An optimization review considers the goals of the remedy, available site data, conceptual site model
(CSM), remedy performance, protectiveness, cost-effectiveness, and closure strategy. A strong interest in
sustainability has also developed in the private sector and within federal, state, and municipal
governments. Consistent with this interest, principles of green remediation and environmental footprint
reduction are now routinely considered during optimization reviews when applicable.

This optimization review includes reviewing site documents, interviewing site stakeholders, and
compiling a report that includes recommendations intended to address the following:
• Remedy effectiveness
• Technical improvement
• Cost reduction
• Progress to site closure
• Reuse/revitalization
• Energy and material efficiency
• Climate resilience

The recommendations are intended to help the site team identify opportunities for improvements in these
areas. Analysis of recommendations, beyond that provided in this report, may be needed prior to
implementation. All recommendations are based on an independent review and represent the opinions of
the optimization review team. The recommendations are not requirements; they are provided for
consideration by the EPA Region and other site stakeholders. While the recommendations provide some
details, they do not replace other more comprehensive planning documents such as work plans, sampling
plans, and Quality Assurance Project Plans (QAPPs).

The national optimization strategy includes a system for tracking the outcome of the recommendations
and includes a provision for follow-up technical assistance from the optimization review team as mutually
agreed upon by the site management team and EPA Office of Land and Emergency Management

1 EPA, 2012. Memorandum: Transmittal of the National Strategy to Expand Superfund Optimization Practices
from Site Assessment to Site Completion. From: James. E. Woolford, Director Office of Superfund Remediation
and Technology Innovation. To: Superfund National Policy Managers (Regions 1 – 10). Office of Solid Waste and
Emergency Response (OSWER) 9200.3-75. September 28.
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(OLEM) and the Office of Superfund Remediation and Technology Innovation (OSRTI).

SITE-SPECIFIC BACKGROUND
The Site is located in Murray, Salt Lake County, Utah and includes the former operational areas of the
Murray Smelter and Germania Smelter as well as surrounding residential and commercial areas. The 142
acres of former smelter operational areas are collectively referred to as the on-facility area. The on-facility
area is bounded to the north by Little Cottonwood Creek, to the east by State Street, to the south by 5300
South Street, and to the west by the westernmost set of the Denver & Rio Grande Western railroad tracks.
The off-facility area is based on where air dispersion modeling suggested the greatest amount of
contaminant deposition and consists of 30 acres to the west and 106 acres to the south and southeast of
the on-facility and a small area between 5200 South Street and Little Cottonwood Creek (EPA, 1998).
The Germania Smelter was built in 1872 in the northwest corner of the present day on-facility area and
operated until 1902 (EPA, 1998). The Murray smelter operated from 1902 to 1949. Both smelters
processed silver and lead ores. Products included arsenic (as sulfates/oxides in flue dust or as arsenic
trioxide), matte (an iron sulfide matrix with high lead and copper content), arsenical speiss (an iron-
arsenic-sulfide matrix), and slag (a vitrified iron silicate) (EPA, 1998). In addition to lead, several
byproducts were also generated including gold, silver, copper, antimony, bismuth, arsenic, and cadmium.
The smelter layout included an extensive rail network, two stacks, eight blast furnaces, roasters, arsenic
kitchens, sinter plants, mills, power houses, and a bag house for emission control (EPA, 1998). Lead ore,
blast furnace products/byproducts (i.e., matte/speiss, slag), flue dust, arsenic trioxide, and stack emissions
resulted in elevated arsenic and lead concentrations at the Site (EPA, 1998).
The majority of the smelter was demolished in 1949, and slag was used as cover to support
redevelopment. A land use plan was adopted in 1997. Subsequent development was largely completed by
2009 and includes a Costco Wholesale store, the Intermountain Medical Center, and a railway station.

SUMMARY OF CONCEPTUAL SITE MODEL / KEY FINDINGS

The Record of Decision (ROD) characterized materials from smelter operations into the following
categories:

• Category I: These materials were large volumes of undiluted arsenic trioxide, and EPA
considered these materials to be principal threat wastes. These materials were associated with
arsenic concentrations in shallow groundwater of 15 milligrams per liter (mg/L) or more and were
generally located where arsenic trioxide was produced or stored, such as the arsenic kitchens,
western compartment of the baghouse, and the arsenic storage bins. These materials would also
be considered a principal threat if brought to the surface.

• Category II: These materials generally consist of large volumes of diluted arsenic trioxide or flue
dust mixed with soil, fill, or debris. EPA considers these materials to be a potentially significant
source of groundwater contamination and were generally associated with arsenic concentrations
in groundwater above the Alternate Cleanup Level (ACL) of 5 mg/L.

• Category III: These materials are contaminated surface soils within specific exposure units (areas
of the Site) that were predicted to pose an unacceptable risk to non-contact intensive workers but
were not expected to be a source of groundwater contamination. These materials were
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characterized as soils in which the arithmetic mean in the exposure unit exceeded 5,600
milligrams per kilogram (mg/kg) for lead or the 95 percent upper confidence limit of the
arithmetic mean in the exposure unit exceeded 1,200 mg/kg for arsenic.

• Category IV: This category is slag, which is not expected to be a risk due to direct contact or
groundwater.

The only Contaminants of Concern (COC) for groundwater is arsenic, and the ROD established the
Maximum Contaminant Level (MCL) at the time of the ROD (0.05 mg/L) as the cleanup level for the
intermediate aquifer and the shallow aquifer east and west of the on-facility area. For the on-facility area,
the ROD established an ACL of 5 mg/L for dissolved arsenic with a compliance point for this ACL where
groundwater discharges to Little Cottonwood Creek (EPA, 1998).

The ACL was developed with the intent of protecting Little Cottonwood Creek by maintaining surface
water concentrations of trivalent arsenic below 190 micrograms per liter (μg/L) as a 4-day average and
360 μg/L as a 1-hour average as well as meet the Utah Standard of Water Quality for Waters of the State
for dissolved arsenic of 100 μg/L. The most rigorous of these three standards is the 100 μg/L (0.1 mg/L)
standard, and it is this standard that was used to develop the ACL (EPA, 1998).

The groundwater aquifers of interest at the Site are referred to as the shallow aquifer and the intermediate
aquifer (EPA, 1998):
• The shallow aquifer is unconfined and consists of interbedded sandy clays and clayey sands
occurring above the 30-foot (ft) thick Bonneville Blue Clay.
• The intermediate aquifer is confined and consists of approximately 10 to 20 ft of coarse-grained
deposits.
A deeper aquifer is also present several hundred feet below the intermediate aquifer but is not impacted
by Site-related contamination or considered further in this report.
Arsenic concentrations in off-facility monitoring wells are below the MCL and only one on-facility
monitoring well exceeds the ACL of 5 mg/L (MW-10 at 21.5 mg/L). Prior to 2008, the arsenic
concentration at MW-2D historically exceeded the ACL with concentrations as high as 14 mg/L. Arsenic
concentrations appear to generally decrease over time with the exception of MW-5D, located in the on-
facility area.

The increasing concentrations at MW-5D are concerning because MW-5D is not in the immediate
proximity of a former smelter feature that was expected to be a source of arsenic. It is unclear how much
higher the concentrations at MW-5D will continue to increase. This area was largely covered with slag
and was not otherwise used as an operational area and the Remedial Investigation and Feasibility Study
(FS) concluded that slag was not a threat to groundwater because the arsenic in slag is not mobile (MFG,
1997 and EPA, 1998). As a result, the increasing concentration of arsenic at MW-5D may be the result of
migration in shallow groundwater. If the arsenic concentration trend at MW-5D continues to increase, this
would likely correspond to increased arsenic loading to Little Cottonwood Creek.

The FS, ROD, and Remedial Design also stated that the principal source of arsenic to Little Cottonwood
Creek was identified as discharge from a storm sewer that runs along State Street (MFG, 1997; EPA,
1998; MFG, 1998). As part of this optimization review, the optimization team was unable to identify any
definitive information about this source or if it had been addressed. The optimization team believes that
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this source was at least partially addressed, but it may still be possible for some impacted groundwater to
migrate toward the storm sewer and either migrate in the bedding or infiltrate into the sewer and
subsequently discharge to the creek.

Surface water sampling confirms that arsenic is discharging into Little Cottonwood Creek in the vicinity
of the Site. Arsenic discharge to the stream between SW-13 and SW-15 would be consistent with
discharge from the storm sewer along State Street or discharge from groundwater along the eastern half of
the northern Site boundary with Little Cottonwood Creek. Arsenic and stream flow data from a nearby
U.S. Geological Survey (USGS) gauging station (approximately co-located with surface water sampling
location SW-5) provides additional information about remedy performance. The data show the following:
• Arsenic concentrations in Little Cottonwood Creek exceeded the Utah Standard of Water Quality
for Waters of the State of 0.1 mg/L around 1997 to 1999 when routine sampling began and again
in one instance around 2012.
• Arsenic concentrations are highest when stream flow is lowest.
• Arsenic concentrations have reached approximately 0.05 mg/L on multiple occasions since 2012
during low flow conditions.
• The arsenic concentrations in Little Cottonwood Creek are too variable to be reasonably
characterized using the historical Site sampling frequencies (quarterly, semi-annually, annually,
or once every five years).
• The Remedial Action (RA) appears to have resulted in a significant improvement in arsenic
discharge to Little Cottonwood Creek within a few years.
Based on these findings, the optimization team is encouraged that the remedy has been effective at
meeting standards since 2012. Given the relatively rapid response in surface water arsenic concentrations
following the RA activities in 2001, the optimization team hypothesizes that the decreases in the arsenic
concentration in surface water is due to the removal or containment of arsenic sources that were
discharging to the State Street sewer and subsequently discharging to the river. Installation of
impermeable surfaces associated with redevelopment may have also reduced infiltration through
contaminated soil.

However, the optimization team is concerned about the increasing concentrations at MW-5D. These
increasing concentrations may lead to future increased arsenic loading to Little Cottonwood Creek via
groundwater discharge along the norther boundary of the Site.

Arsenic concentrations are generally below the cleanup criteria of 0.05 mg/L in the five intermediate
aquifer wells. However, there have been sporadic increases above 0.05 mg/L in IPM-1 and IPM-2. The
optimization team did not have all sampling records to review but was able to review the sampling logs
for the arsenic spikes in IPM-2 in March 2010 and March 2011 and confirmed that both of these samples
were highly turbid. Arsenic is known to naturally occur in Site soils and the clay between the shallow and
intermediate aquifers, and the optimization team believes that all exceedances of the 0.05 mg/L in the
sampling record at IPM-1 and IMP-2 are due to turbidity and are not representative of actual arsenic
concentrations in groundwater.

In accordance with the ROD, Murray City created a Smelter Site Overlay District (SSOD) through city
ordinance in April 1998. The SSOD requires development permits to be obtained that include grading,
drainage plans, and monitoring and maintenance plans for caps and barriers while also prohibiting the use
of existing wells or constructing new wells except for the remedy monitoring wells.
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KEY DATA GAPS AND UNCERTAINTIES

The optimization review team has identified the following key data gaps and uncertainties:
• The Site data suggest that the remedy is performing as expected given the existing groundwater
cleanup levels (MCL of 0.05 mg/L referenced in the ROD and the ACL). However, there is
insufficient data at present to confirm monitored natural attenuation will be effective over the
long term.
• The conceptual model for the arsenic concentration increases at MW-5D is uncertain. The
optimization team believes the increases may be due to faster arsenic transport in groundwater
than was estimated during the FS, but there is insufficient information to confirm this or other
potential conceptual models.
• The current arsenic discharges from the State Street storm sewer are uncertain. In addition, if
there is continued arsenic discharge from the sewer, the remaining sources of that arsenic are
uncertain.
• It is uncertain if the current ACLs are protective of Little Cottonwood Creek. Arsenic
concentrations near the creek are currently well below the ACL, and the remedy is currently
protective of the creek; however, if concentrations continue to increase at MW-5D (or other
locations near the river), this may not be the case over the long term.

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RECOMMENDATIONS

The optimization team developed the following recommendations:

• The optimization team recommends incorporating the USGS surface water sampling data from
Little Cottonwood Creek into annual reports and the evaluation of remedy effectiveness. The
optimization team believes that implementing this recommendation would add approximately
$500 in cost per year.
• The optimization team recommends sampling the State Street storm sewer discharge to determine
the arsenic loading to the creek from the sewer. This sampling could be done in the near term or
could be postponed to some point in the future if the arsenic concentration trends in MW-5D or
the USGS surface water sampling continue to increase causing concern that arsenic
concentrations in surface water quality might exceed the criteria of 0.1 mg/L. The optimization
team estimates that the cost for this sampling would be less than $1,500.
• The optimization team recommends continuing with the current monitoring program and paying
particular attention to the trend at MW-5D and the arsenic concentrations from the USGS surface
water sampling. Implementing this recommendation would not increase costs.
• Due to the turbid samples and accompanying arsenic concentration spikes at IPM-1 and IPM-2,
the optimization team recommends paying particular attention to collecting non-turbid samples
during groundwater sampling. If turbidity continues to be an issue in particular wells, then focus
can be placed on the dissolved arsenic sampling results rather than the total arsenic sampling
results. Implementing this recommendation may lead to a slight increase in field sampling time
perhaps amounting to an extra $1,000 per year.
• The optimization team reviewed the ACL calculations from the ROD and revisited those
calculations based on data collected before and after the ROD. The optimization team concluded
that an average groundwater concentration at SPM-3b, SPM-4b, SPM-5, and MW-5D should not
exceed 0.74 mg/L to 1.1 mg/L to be protective of Little Cottonwood Creek. However, this
conclusion is highly sensitive to the amount of arsenic that may be discharging from the sewer.
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CONTENTS
EXECUTIVE SUMMARY ........................................................................................................................... i
CONTENTS ................................................................................................................................................ vii
NOTICE AND DISCLAIMER .................................................................................................................... ix
PREFACE ..................................................................................................................................................... x
LIST OF ACRONYMS AND ABBREVIATIONS ..................................................................................... xi
1.0 OBJECTIVES OF THE OPTIMIZATION REVIEW ...................................................................... 1
2.0 OPTIMIZATION REVIEW TEAM ................................................................................................. 2
3.0 SITE BACKGROUND ..................................................................................................................... 3
3.1 Site Description and Brief History ................................................................................................ 3
3.2 Remedial Action Objectives (RAOs) ............................................................................................ 4
3.3 Overview of Remedy Implementation .......................................................................................... 5
4.0 FINDINGS ........................................................................................................................................ 6
4.1 Working Conceptual Site Model ................................................................................................... 6
4.1.1 Primary and Secondary Sources of Contamination .............................................................. 6
4.1.2 Contaminants of concern (COCs) and Cleanup Levels ........................................................ 6
4.1.3 Geology and Hydrogeology .................................................................................................. 7
4.1.4 COC Distribution, Fate, and Transport ................................................................................. 8
4.1.5 Remedy Performance .......................................................................................................... 11
4.1.6 ICs ....................................................................................................................................... 11
4.2 Approximate Costs ...................................................................................................................... 11
4.3 Remedy Climate Resilience ........................................................................................................ 11
4.4 Summary of Key Data Gaps and Uncertainties .......................................................................... 13
5.0 RECOMMENDATIONS ................................................................................................................ 15
5.1 Incorporate the USGS Surface Water Sampling Results into the Annual Evaluation of the
Remedy ................................................................................................................................................... 15
5.2 Sample the Storm Sewer for Arsenic during Low Flow Conditions ........................................... 15
5.3 Continue Current Monitoring Practices and Track the Arsenic Concentration Trend at MW-5D .
.................................................................................................................................................... 15
5.4 Improve Sample Collection Technique to Reduce Turbidity...................................................... 16
5.5 Evaluate the Provided ACL Calculations Provided by the Optimization Team ......................... 16

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TABLES

Table 1 Optimization Review Team
Table 2 Other Optimization Review Contributors
Table 3 Brief Site Chronology
Table 4. Summary of Reviewed Surface Water Sampling Results
Table 5 Recommendations and Cost Summary

FIGURES FROM EXISTING SITE DOCUMENTS (presented in Appendix B)

• Site Location Map
• Shallow Aquifer Groundwater Investigation Sampling Locations
• Intermediate Aquifer Groundwater Investigation Sampling Locations
• Annual 2021 Shallow Aquifer Potentiometric Surface Map (August 30, 2021)
• Annual 2021 Intermediate Aquifer Potentiometric Surface Map (August 30, 2021)
• Surface Water Investigation Sampling Locations

FIGURES CREATED BY OPTIMIZATION REVIEW TEAM (presented in Appendix C)

Figure C-1 Current Site Layout with Historical Smelter Features and Excavation Areas
Figure C-2 Current Site Layout with Historical Smelter Features, Excavation Areas, and Historical
Areas of Soil and Groundwater Contamination
Figure C-3 Little Cottonwood Creek Flow (cfs) from February 2023 to February 2024
Figure C-4 2021 Arsenic Concentrations in Groundwater and Arsenic Concentration Trend Charts
for Key Monitoring Wells
Figure C-5 USGS Surface Water Monitoring Data for Little Cottonwood Creek Flow (cfs) and
Filtered Arsenic Concentrations (μg/L)
Figure C-6 Location and Arsenic Concentration Trends for the Five Intermediate Aquifer Wells

APPENDICES

Appendix A References
Appendix B Figures from Existing Site Documents
Appendix C Figures Prepared by the Optimization Team
Appendix D Transport Calculations
Appendix E ACL Calculations

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NOTICE AND DISCLAIMER

Work described herein, including preparation of this report, was performed by HydroGeoLogic, Inc.
(HGL) and ICF Incorporated, LLC (ICF) for the U.S. Environmental Protection Agency (EPA) under
Prime Contract EP-W-14-001 between the ICF and the EPA Office of Superfund Remediation and
Technology Innovation (OSRTI). The report was approved for release as an EPA document, following the
Agency’s administrative and expert review process.
This optimization review is an independent study funded by EPA that evaluates existing data, discusses
the conceptual site model (CSM), analyzes remedy performance, and provides suggestions for improving
remedy efficacy, reducing cost, and making progress toward Site reuse and closure at the Murray Smelter
Superfund Site (Site). Detailed consideration of EPA policy was not part of the scope of work for this
review. This report does not impose legally binding requirements, confer legal rights, impose legal
obligations, implement any statutory or regulatory provisions, or change or substitute for any statutory or
regulatory provisions. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use by EPA.
Recommendations are based on an independent evaluation of existing Site information, represent the
technical views of the optimization review team, and are intended to help the Site team identify
opportunities for improvements in the current remediation strategy and operation and maintenance plan.
These recommendations do not constitute requirements for future action; rather, they are provided for
consideration by the EPA Region and other Site stakeholders.
While certain recommendations may provide specific details to consider during implementation, these are
not meant to supersede other, more comprehensive planning documents such as work plans, sampling
plans and Quality Assurance Project Plans (QAPPs), nor are they intended to override Applicable or
Relevant and Appropriate Requirements (ARARs) established in the Record of Decision. Further analysis
of recommendations, including review of EPA policy, may be needed before implementation.

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PREFACE

This report was prepared as part of a national strategy to expand Superfund optimization practices from
site assessment to site completion implemented by the U.S. Environmental Protection Agency Office
of Land and Emergency Management (OLEM) (formerly Office of Solid Waste and Emergency
Response [OSWER])2. The project contacts are as follows:

ORGANIZATION CONTACT CONTACT INFORMATION
EPA OLEM Kirby Biggs
EPA OSRTI
Technology Innovation and Field Services Division
2777 Crystal Drive
Arlington, VA 22202
[e-mail]
Telephone: [phone]
ICF
(Contractor to EPA)
Patti Sinski

ICF
9300 Lee Highway
Fairfax, VA 22031
[e-mail]

HydroGeoLogic, Inc.
(Contractor to EPA)
Doug Sutton

HydroGeoLogic, Inc.
[e-mail]

2 EPA, 2012. Memorandum: Transmittal of the National Strategy to Expand Superfund Optimization Practices from
Site Assessment to Site Completion. From: James. E. Woolford, Director Office of Superfund Remediation and
Technology Innovation. To: Superfund National Policy Managers (Regions 1 – 10). Office of Solid Waste and
Emergency Response (OSWER) 9200.3-75. September 28.
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LIST OF ACRONYMS AND ABBREVIATIONS

μg/L micrograms per liter
mg/kg milligrams per kilogram
mg/L milligrams per liter

ACL Alternate Concentration Limits
AOC Administrative Order on Consent
ARAR Applicable or Relevant and Appropriate Requirements

bgs below ground surface

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
cfs cubic feet per second
COC contaminant of concern
CPCMB Construction and Post-Construction Management Branch
CSM conceptual site model

EE/CA Engineering Evaluation/Cost Analysis
EPA U.S. Environmental Protection Agency

FEMA Federal Emergency Management Agency
FS Feasibility Study
ft feet
FYR Five-Year Review

HGL HydroGeoLogic, Inc.
HQ EPA Headquarters

IC institutional control
ICF ICF Incorporated, LLC

MCL Maximum Contaminant Level
MNA monitored natural attenuation
MOU Memorandum of Understanding

NCI Non-contact intensive
NPL National Priorities List

O&M operations and maintenance
OLEM Office of Land and Emergency Management
OSRTI Office of Superfund Remediation and Technology Innovation
OSWER Office of Solid Waste and Emergency Response

QAPP Quality Assurance Project Plan

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RA Remedial Action
RAO Remedial Action Objective
RD Remedial Design
RI Remedial Investigation
ROD Record of Decision
RPM Remedial Project Manager

Site Murray Smelter Superfund Site
SSOD Smelter Site Overlay District

UDEQ/DERR Utah Department of Environmental Quality, Division of Environmental Response
and Remediation
USGS U.S. Geological Survey

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1.0 OBJECTIVES OF THE OPTIMIZATION REVIEW

For more than a decade, the Office of Land and Emergency Management (OLEM) has provided technical
support to the U.S. Environmental Protection Agency (EPA) regional offices by using independent (third
party) optimization reviews at Superfund sites. The Murray Smelter Superfund Site (EPA ID
UTD980951420) (the Site) was nominated for an optimization review by the EPA Region 8 Site
Remedial Project Manager (RPM) and optimization coordinators.
The focus of this optimization review is to evaluate historical data and provide recommendations to
optimize the current remedial response and associated Site characterization and monitoring. The specific
objectives identified for this optimization review were to evaluate: 1) performance of the monitored
natural attenuation (MNA) remedy and 2) use Site-specific information to evaluate the current ACLs.
This optimization review used existing environmental data to interpret the conceptual site model (CSM),
identify potential data gaps, and recommend improvements to the remedy. The optimization review team
evaluated the quality of the existing data before using the data for these purposes. The evaluation for data
quality included a brief review of data collection and management methods (where practical, the Site
Quality Assurance Project Plan [QAPP] is considered), the consistency of the data with other Site data,
and the potential use of the data in the optimization review. Data that were of suspect quality were either
not used as part of the optimization review or were used with the quality concerns noted. Where
appropriate, this report provides recommendations made to improve data quality.

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2.0 OPTIMIZATION REVIEW TEAM

The optimization review team, which collaborated with representatives of EPA Headquarters
(HQ), EPA Region 8, and Utah Department of Environmental Quality, Division of Environmental
Response and Remediation (UDEQ/DERR) consists of the independent, third-party participants
listed in Table 1.
TABLE 1. Optimization Review Team
NAME ORGANIZATION TELEPHONE EMAIL
Rob Greenwald HGL 732-239-6407 [e-mail]
Doug Sutton HGL 732-233-1161 [e-mail]
HGL = HydroGeoLogic, Inc.

Individuals that contributed to the optimization review process—including participation in the
scoping call on 13 October 2023, kickoff call on 18 December 2023, and/or at a virtual Site visit on
25 January 2025—are listed in Table 2.
TABLE 2. Other Optimization Review Contributors
NAME ORGANIZATION TITLE/ROLE
Kirby Biggs1,2 EPA OSRTI Optimization Program Lead
Vanessa Van Note1,2 EPA OSRTI Optimization Support
Amanda Van Epps1,2 EPA OSRTI CPCMB Lead
Ian Bowen1 EPA OSRTI Optimization Project Lead and EPA Region 8
Optimization Coordinator
Sydney Chan1,2 EPA Region 8 RPM
Fran Costanzi1 EPA Region 8 Senior RPM
Angela Frandsen1,2 EPA Region 8 Hydrogeologist, technical support
Missy Haniewicz1 EPA Region 8 Community Involvement Coordinator
Maureen Petit1,2 UDEQ/DERR Project Manager
Trae Stokes1,2 City of Murray City Engineer
Phil Markham1,2 City of Murray Community and Economic Development Director
Russ Kakala1,2 City of Murray Public Works Director
Patti Sinski1,2 ICF Optimization Task Order Lead
Jim Morrison1,2 ICF Optimization Support
1 = attended scoping and/or kickoff call; 2 = attended Site visit in person or virtually.
CPCMB = Construction and Post-Construction Management Branch; ICF = ICF Incorporated, LLC;
OSRTI = Office of Superfund Remediation and Technology Innovation; RPM = Regional Project Manager.

Documents reviewed for the optimization effort are listed in Appendix A.

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3.0 SITE BACKGROUND
3.1 SITE DESCRIPTION AND BRIEF HISTORY
The Site is located in Murray, Salt Lake County, Utah and includes the former operational areas of the
Murray Smelter and Germania Smelter as well as surrounding residential and commercial areas. A Site
location map is provided in Appendix B (EPA, 1998). The 142 acres of former smelter operational areas
are collectively referred to as the on-facility area. The on-facility area is bounded to the north by Little
Cottonwood Creek, to the east by State Street, to the south by 5300 South Street, and to the west by the
westernmost set of the Denver & Rio Grande Western railroad tracks (see Appendix B). The off-facility
area is based on where air dispersion modeling suggested the greatest amount of contaminant deposition
and consists of 30 acres to the west and 106 acres to the south and southeast of the on-facility and a small
area between 5200 South Street and Little Cottonwood Creek (EPA, 1998).
The Germania Smelter was built in 1872 in the northwest corner of the present day on-facility area and
operated until 1902 (EPA, 1998). The Murray smelter operated from 1902 to 1949. Both smelters
processed silver and lead ores. Products included arsenic (as sulfates/oxides in flue dust or as arsenic
trioxide), matte (an iron sulfide matrix with high lead and copper content), arsenical speiss (an iron-
arsenic-sulfide matrix), and slag (a vitrified iron silicate) (EPA, 1998). At the time of construction, the
Murray Smelter was reportedly the largest primary lead smelter in the world. In addition to lead, several
byproducts were also generated including gold, silver, copper, antimony, bismuth, arsenic, and cadmium.
The smelter layout (Appendix B) included an extensive rail network, two stacks, eight blast furnaces,
roasters, arsenic kitchens, sinter plants, mills, power houses, and a bag house (for emission control) (EPA,
1998). Lead ore, blast furnace products/byproducts (i.e., matte/speiss, slag), flue dust, arsenic trioxide,
and stack emissions resulted in elevated arsenic and lead concentrations at the Site (EPA, 1998).
The majority of the smelter was demolished in 1949, and slag was used as cover to support
redevelopment. Some structures remained until 1980, and some, including the stacks, were still present at
the time of the Record of Decision (ROD) in 1998 but later removed (EPA, 1998). A land use plan was
adopted in 1997. Subsequent development was largely completed by 2009 and includes a Costco
Wholesale store, the Intermountain Medical Center, and a railway station.
A brief Site chronology is listed in Table 3.
TABLE 3. Brief Site Chronology
DATE ACTION
1872 Germania Smelter was built and began operating.
1902 Murray Smelter was built and began operating. Operations at the Germania Smelter stopped.
1949 Operations at the Murray Smelter stopped, and the majority of the smelter structures were
demolished.
1994 EPA proposed listing the site on the National Priorities List (NPL) and issued a notice letter to
Asarco.
1995
EPA and Asarco entered into an Administrative Order on Consent (AOC) for performing an
Engineering Evaluation/Cost Analysis (EE/CA) for the Site. EPA and Asarco also entered into an
AOC for a time-critical removal to excavate contaminated soils within and adjacent to a
playground. Asarco completed the work in 1995.
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DATE ACTION
1996
EPA and Murray City entered into a Memorandum of Understanding (MOU), which established
that Murray City would assist EPA with respect to identifying land use and implementing
institutional controls (ICs) at the Site.
1997
The Murray City Council adopted a land use plan for future development of the on-facility portion
of the Site. The 1995 EE/CA was changed to a Feasibility Study (FS) and the baseline human
health and ecological risk assessments were completed. The proposed plan was issued.
1998 EPA issued the Record of Decision (ROD) and Remedial Action (RA) activities began.
2000 A removal action was conducted to demolish and remove the smelter stacks.
2001 RA activities were completed.
2003 Asarco developed an operations and maintenance (O&M) plan for the repository system and
groundwater and surface water monitoring.
2005 The Costco Wholesale store was constructed.
2009 The large majority of redevelopment had been completed. The settling defendants began
implementing the O&M plan.
2003 The First Five-Year Review (FYR) was completed.
2009 The Second FYR was completed.
2014 The Third FYR was completed.
2019 The Fourth FYR was completed.
3.2 REMEDIAL ACTION OBJECTIVES (RAOS)
According to the ROD, the overarching RAO for the Site is to “develop a comprehensive remedy that
protects human health and the environment, is consistent with the current and reasonably anticipated
future land use, and removes obstacles to Site development associated with real or perceived
environmental contamination” (EPA, 1998). Media-specific RAOs were developed based on the
assumption that future land use would be commercial/industrial in the on-facility portion of the Site and
residential in the off-facility areas where homes are currently located. More specifically, the following
media-specific RAOs were developed (with cleanup levels discussed further in Section 4.1.2):
On-Facility Soils/Smelter Materials:
• Prevent unacceptable risks to current and future workers or to ecological receptors due to the
ingestion of soil/smelter materials containing arsenic or lead.
• Reduce the uncertainties in the predicted risks to ecological receptors.
On-Facility Groundwater
• Minimize future transport of arsenic from source materials to the shallow aquifer.
• Prevent exposure of human and ecological receptors to ground water with arsenic concentrations
that represent an unacceptable risk.
• Prevent unacceptable increases in the arsenic concentrations of the intermediate aquifer resulting
from arsenic migration from the shallow aquifer.
Little Cottonwood Creek Surface Water
• Protect Little Cottonwood Creek water quality by preventing unacceptable increases of arsenic
concentrations in surface water resulting from ground water discharges or surface water run-off
from the Site.
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Off-Facility Soils
• Prevent unacceptable risks to current and future residents due to the ingestion of soil containing
lead.
• Prevent unacceptable risks to current and future non-contact intensive (NCI) workers due to the
ingestion of soil containing lead.
On-Facility Ecological Study Areas
• Reduce uncertainties in predicted risks to ecological receptors.

3.3 OVERVIEW OF REMEDY IMPLEMENTATION
Groundwater in the surficial aquifer is addressed by source removal, source control, and MNA. Source
removal and source control consisted of excavation and off-Site disposal of principal threat waste,
excavation and consolidation of low-level wastes in an on-Site repository that serves as the base of a road
(Cottonwood Street), and redevelopment of the area that isolates the waste from human contact.
Institutional controls (ICs) in the form of a city ordinance establish a Superfund overlay district and
restrictive easements that run with the land that prohibit construction of new wells or the use of existing
wells within the on-facility area and the east and west off-facility areas except for EPA-approved
monitoring wells (EPA, 1998).
On-facility surface soils above cleanup levels, including slag, are covered in place with barriers sufficient
to prevent direct contact. ICs, in the form of the overlay district, prevent residential and contact intensive
industrial uses within the former smelter operational areas and require barriers and controls in this same
area. Off-facility surface soils above cleanup levels have been removed to a depth of 18 inches and
replaced with clean fill. The removed soil was used on-facility as subgrade material in the construction of
the repository system.
The surface water of Little Cottonwood Creek is monitored to confirm protection from impacted
groundwater. The ecological study area is monitored to reduce uncertainties in the final risk assessment
for the Site.
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4.0 FINDINGS
4.1 WORKING CONCEPTUAL SITE MODEL
The Optimization Review Team’s working CSM based on efforts to date is presented below.
4.1.1 Primary and Secondary Sources of Contamination

The ROD characterized materials from smelter operations into the following categories:

• Category I: These materials were large volumes of undiluted arsenic trioxide, and EPA
considered these materials to be principal threat wastes. These materials were associated with
arsenic concentrations in shallow groundwater of 15 milligrams per liter (mg/L) or more and were
generally located where arsenic trioxide was produced or stored, such as the arsenic kitchens,
western compartment of the baghouse, and the arsenic storage bins. These materials would also
be considered a principal threat if brought to the surface.

• Category II: These materials generally consist of large volumes of diluted arsenic trioxide or flue
dust mixed with soil, fill, or debris. EPA considers these materials to be a potentially significant
source of groundwater contamination and were generally associated with arsenic concentrations
in groundwater above the Alternate Cleanup Level (ACL) of 5 mg/L.

• Category III: These materials are contaminated surface soils within specific exposure units (areas
of the Site) that were predicted to pose an unacceptable risk to non-contact intensive workers but
were not expected to be a source of groundwater contamination. These materials were
characterized as soils in which the arithmetic mean in the exposure unit exceeded 5,600
milligrams per kilogram (mg/kg) for lead or the 95 percent upper confidence limit of the
arithmetic mean in the exposure unit exceeded 1,200 mg/kg for arsenic.

• Category IV: This category is slag, which is not expected to be a risk due to direct contact or
groundwater.

Figure C-1 in Appendix C provides a present-day base map to reference current landmarks and illustrates
the locations of key historical smelter operations or structures and areas identified in the Remedial Design
(RD) for excavation of Category I and Category II materials. Figure C-2 in Appendix C retains the
features from Figure C-1 and adds areas identified in the Remedial Investigation (RI) that had elevated
arsenic concentrations in surface soil, subsurface soil, and groundwater. Together, these two figures
generally illustrate where sources of arsenic contamination were present at the time of the RI and RD.
These figures also indicate the repositories where Category II materials were consolidated.
4.1.2 Contaminants of concern (COCs) and Cleanup Levels

The only Contaminant of Concern (COC) for groundwater is arsenic, and the ROD established the
Maximum Contaminant Level (MCL) at the time of the ROD (0.05 mg/L) as the cleanup level for the
intermediate aquifer and the shallow aquifer east and west of the on-facility area. The MCL has changed
from 0.05 mg/L to 0.01 mg/L, and during the past two Five-Year Reviews (FYRs), the Site team
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determined that no immediate change to the cleanup criteria was needed but that a potential change to
0.01 mg/L would be evaluated in future FYRs. For the on-facility area, the ROD establishes an ACL of 5
mg/L for dissolved arsenic with a compliance point for this ACL where groundwater discharges to Little
Cottonwood Creek (EPA, 1998).

The ACL was developed with the intent of protecting Little Cottonwood Creek by maintaining surface
water concentrations of trivalent arsenic below 190 micrograms per liter (μg/L) as a 4-day average and
360 μg/L as a 1-hour average as well as meet the Utah Standard of Water Quality for Waters of the State
for dissolved arsenic of 100 μg/L. The most rigorous of these three standards is the 100 μg/L (0.1 mg/L)
standard, and it is this standard that was used to develop the ACL (EPA, 1998).

The ROD established soil cleanup levels for lead and arsenic based on direct exposure. On-facility soils
shall not exceed 1,200 mg/kg of arsenic as the 95 percent upper confidence limit on the arithmetic mean
within any given exposure unit and shall not exceed 5,600 mg/kg of lead as the arithmetic mean within
any given exposure unit. For off-facility soils, cleanup standards for lead are 5,600 mg/kg for commercial
areas (arithmetic mean) and 1,200 mg/kg for residential areas (arithmetic mean). No off-facility surface
soil cleanup levels were set for arsenic (EPA, 1998).
4.1.3 Geology and Hydrogeology

The ROD states that the geologic units at the Site consist primarily of clays, silts, sand, and gravel lake
sediments from Pleistocene Lake Bonneville with more recent alluvial floodplain deposits located near
Little Cottonwood Creek (EPA, 1998). Shallow soils have been disturbed by historical use and
construction and slag were present at the surface.

The groundwater aquifers of interest at the Site are referred to as the shallow aquifer and the intermediate
aquifer (EPA, 1998):
• The shallow aquifer is unconfined and consists of interbedded sandy clays and clayey sands
occurring above the 30-foot (ft) thick Bonneville Blue Clay.
• The intermediate aquifer is confined and consists of approximately 10 to 20 ft of coarse-grained
deposits.
A deeper aquifer is also present several hundred feet below the intermediate aquifer, but it is not impacted
by Site-related contamination or considered further in this report.
The hydraulic conductivity of the shallow zone ranges from approximately 1 to 112 ft per day with a
geometric mean of 5 ft per day; the Feasibility Study (FS) assumed 5 ft per day to 15 ft per day (MFG,
1997). Groundwater in the shallow zone flows from south to north across the Site and discharges to Little
Cottonwood Creek. Flow in the intermediate zone is to the northwest and there are downward gradients
between the shallow and intermediate aquifers in the middle of the on-facility area.
Flow in Little Cottonwood Creek ranges from less than 1 cubic foot per second (cfs) to several hundred
cfs during flood conditions. In addition to short term responses to individual rain events, there is also a
seasonal component to flow in the creek. Figure C-3 illustrates river flow between February 2023 and
February 2024 and shows that individual precipitation events can result in discharges of over 100 cfs.
Discharges are consistently several hundred cfs during the wet season from late spring to late summer.
Low-flow conditions are approximately 1 cfs.

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4.1.4 COC Distribution, Fate, and Transport

Shallow Aquifer and Surface Water

The Remedial Action (RA) intended to remove Category I materials from the Site and consolidate
Category II materials in an on-Site repository to protect shallow groundwater and allow arsenic
concentrations in groundwater to decrease below the cleanup goals. Figure C-4 depicts the present-day
Site layout and includes 2021 arsenic groundwater sampling results and trend charts of arsenic
concentrations at key monitoring wells. It is apparent from Figure C-4 that 2021 arsenic concentrations in
off-facility monitoring wells are below the MCL referenced in the ROD (0.5 mg/L) and that only one on-
facility monitoring well exceeds the ACL of 5 mg/L (MW-10 at 21.5 mg/L). The arsenic concentration at
MW-2D historically exceeded the ACL (prior to 2008) with concentrations as high as 14 mg/L. Arsenic
concentrations appear to generally decrease over time with the exception of MW-5D.

The increasing concentration at MW-5D is concerning because a comparison of Figures C-2 and C-4
shows that the increasing concentration at MW-5D is not immediately near a former smelter feature that
was expected to be a source of arsenic. It is unclear how much higher the concentrations at MW-5D will
continue to increase. This area was largely covered with slag and was not otherwise used as an
operational area. Furthermore, the RI and FS concluded that slag was not a threat to groundwater because
the arsenic in slag is not mobile (MFG, 1997 and EPA, 1998). As a result, the increasing concentration of
arsenic at MW-5D may be the result of migration in shallow groundwater. The results from the
monitoring network along the current repository and between MW-2D and MW-5D suggest that the
contamination is not likely to be migrating from the MW-2D area or the current repository. However, the
flow path from MW-10 to MW-5D is not well characterized, and the area of historical groundwater
impacts shown in Figure C-2 shows elevated arsenic groundwater contamination present in areas
downgradient of the known sources (immediately east of MW-4UR and MW-4D). If the arsenic
concentration trend at MW-5D continues to increase, this would likely correspond to increased arsenic
loading to Little Cottonwood Creek.

The FS developed parameters for estimating the groundwater velocity and the arsenic transport velocity.
The hydraulic gradient was estimated to be 0.014 ft/ft, the effective porosity was estimated to be 0.2, and
the average hydraulic conductivity was estimated to range from 5 to 15 ft per day (MFG, 1997). Using
these parameters, the groundwater velocity is expected to range from approximately 130 ft per year to 550
ft per year. The arsenic transport velocity was assumed to be much slower (approximately 1 ft per year to
9 ft per year) because of high partitioning to soil resulting in retardation coefficients ranging from 62 to
141. Please refer to Appendix D for the associated transport velocity calculations. Migration of arsenic
from MW-10 to MW-5D would involve arsenic transport of 2,000 ft. Migration over this distance would
be impractical with the retardation coefficients used during the FS but would be consistent with
substantially lower retardation coefficients.

The FS, ROD, and RD also stated that the principal source of arsenic to Little Cottonwood Creek has
been identified as discharge from a storm sewer that runs along State Street (MFG, 1997; EPA, 1998;
MFG, 1998). The FS and RD suggested that the source of the arsenic was probably related to 1) indirect
discharge from a pipe originating in the Category I and II material areas in the main portion of the former
smelter to the vicinity of the sewer, 2) leaching from high arsenic fill material in the vicinity of the pipe,
or 3) an off-Site source, possibly associated with a former smelter site east of the Murray Smelter (MFG,
1997 and MFG, 1998). The ROD stated that a Site-related source near a storm drain was the primary
source of the contamination in the sewer, that the RA would address this source, and that arsenic
concentrations in the river would decrease to below 0.1 mg/L within three years (EPA, 1998). A
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supplemental design investigation, identified contaminated groundwater in the vicinity of the sewer and a
hydraulic gradient suggesting that contaminated groundwater was originating from the southwest
(generally from the roasting plant or baghouse area) (Hydrometrics, 1998). As part of this optimization
review, the optimization team was unable to identify any definitive information about this source or if it
had been addressed. The optimization team believes that this source was at least partially addressed, but
that it may still be possible for some impacted groundwater to migrate toward the storm sewer and either
migrate in the bedding or infiltrate into the sewer and subsequently discharge to the creek.

Surface water sampling confirms that arsenic is discharging into Little Cottonwood Creek in the vicinity
of the Site. Table 4 presents a summary of surface water sampling reviewed by the optimization team.
The results confirm discharge of arsenic to the stream between the upstream sample location (SW-13) and
the sample location located midway between the upstream and downstream boundaries of the Site (SW-
15). The arsenic concentrations between SW-15 and the downstream sample (SW-5) suggest minimal
change in arsenic concentrations in surface water. Arsenic discharge to the stream between SW-13 and
SW-15 would be consistent with discharge from the storm sewer along State Street or discharge from
groundwater along the eastern half of the northern Site boundary with Little Cottonwood Creek.

Arsenic and stream flow data from a nearby U.S. Geological Survey (USGS) gauging station
(approximately co-located with surface water sampling location SW-5) provides additional information
about remedy performance. Figure C-5 presents a map identifying the USGS gauging station, plots of
discharge, and arsenic concentrations across three different time scales. The data show the following:
• Arsenic concentrations in Little Cottonwood Creek exceeded the Utah Standard of Water Quality
for Waters of the State of 0.1 mg/L around 1997 to 1999 when routine sampling began and again
in one instance around 2012.
• Arsenic concentrations are highest when stream flow is lowest.
• Arsenic concentrations have reached approximately 0.05 mg/L on multiple occasions since 2012
during low flow conditions.
• The arsenic concentrations in Little Cottonwood Creek are too variable to be reasonably
characterized using the historical Site sampling frequencies (quarterly, semi-annually, annually,
or once every five years).
• The RA appears to have resulted in a significant improvement in arsenic discharge to Little
Cottonwood Creek within a few years.
Based on these findings, the optimization team is encouraged that the remedy has been effective at
meeting standards since 2012. Given the relatively rapid response in surface water arsenic concentrations
following the RA activities in 2001, the optimization team hypothesizes that the decreases in the arsenic
concentration in surface water are due to the removal or containment of arsenic sources that were
discharging to the State Street sewer and subsequently discharging to the river. Installation of
impermeable surfaces associated with redevelopment may have also reduced infiltration through
contaminated soil.
However, the optimization team is concerned about the increasing concentrations at MW-5D. These
increasing concentrations may lead to future increased arsenic loading to Little Cottonwood Creek via
groundwater discharge along the northern boundary of the Site. Arsenic concentrations in surface water
routinely reach approximately 0.05 mg/L during low flow conditions, so a future increase in arsenic
loading could cause arsenic concentrations in Little Cottonwood Creek to exceed the standard of 0.1
mg/L. Furthermore, the optimization team is concerned about the appropriateness of the current ACL to
protect surface water. The ACL was calculated using various assumptions during the FS, and the
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optimization team believes that groundwater velocity and arsenic transport may be faster than estimated
during the FS. If this is the case, then arsenic discharges to the creek may be higher than assumed during
ACL development.

TABLE 4. Summary of Reviewed Surface Water Sampling Results
River Flow
(cfs)
SW-13
(mg/L, upstream)
SW-15
(mg/L, midstream)
SW-5
(mg/L, downstream)
2010 Q2 > 800 <0.005 <0.005 <0.005
2010 Q4 1.3 to 3 <0.005 0.091 0.057
2011 Q2 Flood <0.005 <0.005 <0.005
2011 Q4 ~ 3 <0.005 0.049 0.051
2012 Q2 22 to 24 0.0064 0.0089 0.012
2012 Q4 0.76 to 1.1 <0.005 0.079 0.045
2013 Q2 38 to 63 <0.005 0.0063 0.0062
2013 Q4 0.24 to 0.63 <0.005 0.033 0.026
2015 Q2 1.1 to 1.7 0.0054 0.0051 0.0084
2021 10 to 12 0.0163 0.0189 0.0215
Cells for the 6 highest concentrations are highlighted.
Utah Standard of Water Quality for Waters of the State dissolved arsenic = 0.1 mg/L.

Intermediate Aquifer

Arsenic concentrations are generally below the cleanup criteria of 0.05 mg/L in the five intermediate
aquifer wells. However, there have been sporadic increases above 0.05 mg/L in IPM-1 and IPM-2. Figure
C-6 illustrates the locations of the intermediate aquifer wells and the arsenic concentration trends for the
five intermediate aquifer wells. The optimization team did not have all sampling records to review but
was able to review the sampling logs for the arsenic spikes in IPM-2 in March 2010 and March 2011 and
confirmed that both of these samples were highly turbid. Arsenic is known to naturally occur in Site soils
and the clay between the shallow and intermediate aquifers. The optimization team believes that all
exceedances of the 0.05 mg/L in the sampling record at IPM-1 and IMP-2 are due to turbidity and are not
representative of actual arsenic concentrations in groundwater.

The optimization team notes that arsenic concentrations in several of the intermediate aquifer wells
exceed the current MCL of 0.01 mg/L. Given the stable arsenic trends in these wells, the optimization
team finds it unlikely that the arsenic concentrations at IPM-5 will decrease below 0.01 mg/L. The
optimization team also believes it is possible that the arsenic detected in these wells is, at least in part, due
to natural background. The optimization defers to the Site team on the appropriateness of changing the
arsenic cleanup standard for the intermediate aquifer and encourages the Site team to consider potential
background conditions before adopting a new arsenic standard.

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4.1.5 Remedy Performance

The Site data, combined with surface water data from the USGS, generally demonstrate that the remedy is
performing as expected. The primary concern regarding future effectiveness at protecting human health
and the environment is the increasing arsenic concentration trend at MW-5D. If this increasing trend is
indicative of arsenic contamination migrating closer to the river, then it may indicate a future increase in
the discharge of arsenic from groundwater to Little Cottonwood Creek along the northern Site boundary.

4.1.6 ICs
In accordance with the ROD, Murray City created a Smelter Site Overlay District (SSOD) through city
ordinance in April 1998. The SSOD requires development permits to be obtained that include grading,
drainage plans, and monitoring and maintenance plans for caps and barriers while also prohibiting the use
of existing wells or constructing new wells except for the remedy monitoring wells.

4.2 APPROXIMATE COSTS
The optimization team did not discuss costs, but it is recognized that funding for this Site is particularly
constrained because the Site is not on the National Priorities List (NPL).

4.3 REMEDY CLIMATE RESILIENCE
The EPA factsheet What Climate Change Means for Utah summarizes how climate is expected to change
across the state. Most of Utah has warmed about 2°F in the past century, and temperatures will continue
increasing over the coming decades. Rising temperatures have the potential to contribute to more frequent
heat waves and drought. In addition, rising temperatures are expected to significantly impact snowpack
across Utah. Warming means less precipitation will fall as snow and a larger amount of snow will melt
during the winter. The decline in snowpack could further limit the supply of water for some purposes.
Mountain snowpacks are natural reservoirs collecting the snow that falls during winter and releasing
water when the snow melts during spring and summer. Over the past 50 years, snowpack has been
melting earlier in the year. Dams capture most meltwater and retain it for use later in the year. However,
less water is available upstream of these reservoirs during droughts for ecosystems, fish, water-based
recreation, and landowners who draw water directly from a flowing river (EPA, 2016). Overall, if climate
changes result in less stream flow in the vicinity of the Site, then arsenic concentrations in Little
Cottonwood Creek may increase.

The Utah Division of Emergency Management released the 2019 Utah State Hazard Mitigation Plan to
address the impact of climate change on natural hazard risk throughout the state. The report notes higher
temperatures will increase the incidence of drought, lengthen the fire season, result in dry soils, increase
the dryness of dead wood, and increase transpiration from plants. These factors lead to an increased risk
of wildfire. The report also notes that climate change will cause an increase in extreme weather patterns
related to both drought and floods. Extreme precipitation and warming temperatures will likely cause a
greater incidence of floods. Warmer temperatures will likely cause a greater incidence of rain-on-snow
events that cause mid-winter flooding (Utah Division of Emergency Management, 2019).

Local Climate Change Projections

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Site to county-level modeled climate projections were used to assess impacts due to climate change for
the following climate hazards:

• Temperature and Precipitation: Climate Explorer temperature and precipitation projections
produced by the U.S. Climate Resilience Toolkit (U.S. Federal Government, 2021)

• Flooding: National Flood Hazard Layer produced by Federal Emergency Management Agency
(FEMA) (FEMA, 2021)

• Wildfire: Climate Mapper fire danger projections produced by the University of California,
Merced (Abatzoglou and Brown, 2012) and Wildfire Hazard Potential dataset produced by the
United States Department of Agriculture Forest Service, Fire Modeling Institute (Dillon and
Gilbertson-Day, 2020)

Temperature

The observed average daily maximum temperature in the Murray and Salt Lake City area between 1961
and 1990 was 59.4°F. The median projected average daily maximum temperature in the 2080s is 65.9 and
69.9°F (an increase of 6.5 and 10.5°F above the historical average) for the lower emissions and higher
emissions scenarios, respectively. The range projected in the higher emissions scenario is 65.3 to 77°F.
The median projected average daily maximum temperature in the 2050s is 64.9 and 66°F (an increase of
5.5 and 6.6°F above the historical average) for the lower emissions and higher emissions scenarios,
respectively. The range projected in the higher emissions scenario is 61.9 to 70.9°F.

The historic average (1961-1990) of the annual number of days with a maximum temperature above 95°F
was 7.2 days for the Murray and Salt Lake City area. The mean projections for the lower emissions and
higher emissions scenarios indicate that the number of days with a maximum temperature above 95°F will
increase to 35.4 and 58.7 days by the 2080s, respectively.

Other temperature variables, including average daily minimum temperature and days with a minimum
below 32°F, suggest a similar warming trend.

Precipitation

In the 2080s, median total annual precipitation is projected to be 0.15 inches above (lower emissions
scenario) or 1.1 inches above (higher emissions scenario) the 1961-1990 observed baseline of 22.2 inches;
in the 2050s, the median projections are 0.32 to 0.51 inches above the observed baseline. The 1990s
historic range is 13.4 to 31 inches; the 2080s projected range is 13.9 to 37.6 inches (higher emissions
scenario). Overall, the projections suggest a slight increase in total annual precipitation in the coming
decades.

The number of days receiving greater than 1 inch of precipitation is expected to remain similar to the
historic average throughout the coming decades. In the 2080s, the median number of days with greater
than 1 inch of precipitation is projected to be 1.4 days in the low emissions scenario and 1.7 days in the
high emissions scenario; the historic average (1961-1990) of days per year with more than 1 inch of
precipitation is 1.3 days.

Compared to the observed baseline (1961-1990) of 227.6 days, the annual number of dry days in the
Murray and Salt Lake City area is projected to increase by 6.9 days under the low emissions scenario and
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8.3 days under the high emissions scenario by the 2080s. The range in dry days in the 2080s is projected
to be 162.8 to 278.7 days per year (higher emissions scenario), compared to the 1990s range of 193.6 to
267.5 days per year.

Flooding

According to the FEMA flood hazard map, no part of the site lies within the 100-year floodplain except
the immediate area surrounding Little Cottonwood Creek.

Wildfires

Fire danger days in Murray and Salt Lake City area are expected to increase by mid-century. The number
of high fire danger days from June to August is projected to reach 61.7 days under the high emissions
scenario by mid-century compared to the observed baseline of 57.4 days. In addition, the number of very
high fire danger days from June to August is projected to reach 42.2 days (compared to the observed
baseline of 33 days) and the number of extreme fire danger days is projected to reach 20.6 days
(compared to the observed baseline of 10.7 days) under the high emissions scenario by mid-century. High
fire danger days are calculated as days with 100-hour fuel moisture below the 20th percentile from
historical years, very high fire danger days correspond to days with 100-hour fuel moisture below the
10th percentile, and extreme fire danger days correspond to days with 100-hour fuel moisture below the
3rd percentile.

Wildfire hazard potential is low at the Murray Site since the Site is in a highly urban area with non-
burnable surfaces. However, a forested, mountainous area 7 miles east of the site has a high to very high
wildfire hazard potential. Areas with high wildfire hazard potential indicate fuels with a higher
probability of experiencing torching, crowning, and other forms of extreme fire behavior under conducive
weather conditions.

Interpretation

Of all of the potential changes in climate, increased rainfall is the most likely to affect the remedy if the
increased rainfall results in a higher water table that may come into contact with potential residual arsenic
sources. However, based on the forecast of a slight potential increase in precipitation, the optimization
team does not expect climate change to meaningfully impact remedy effectiveness.

4.4 SUMMARY OF KEY DATA GAPS AND UNCERTAINTIES
The optimization review team has identified the following key data gaps and uncertainties:
• The Site data suggest that the remedy is performing as expected given the existing groundwater
cleanup levels (MCL of 0.05 mg/L referenced in the ROD and the ACL). However, there is
insufficient data at present to confirm MNA will be effective over the long term.
• The conceptual model for the arsenic concentration increases at MW-5D is uncertain. The
optimization team believes the increases may be due to faster arsenic transport in groundwater
than was estimated during the FS, but there is insufficient information to confirm this or other
potential conceptual models.
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• The current arsenic discharges from the State Street storm sewer are uncertain. In addition, if
there is continued arsenic discharge from the sewer, the remaining sources of that arsenic are
uncertain.
• It is uncertain if the current ACLs are protective of Little Cottonwood Creek. Arsenic
concentrations near the creek are currently well below the ACL, and the remedy is currently
protective of the creek. However, if concentrations continue to increase at MW-5D (or other
locations near the river), this may not be the case over the long term.

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5.0 RECOMMENDATIONS

Site-specific recommendations are provided for the six major areas associated with optimization: remedy
effectiveness, cost reduction, technical improvement, progress toward Site closure, property reuse or
revitalization, and energy and materials efficiency. Table 5 provides a summary of the recommendations
and estimated costs (or savings) for implementing each recommendation. The levels of certainty for the
cost estimates provided are comparable to those typically prepared for CERCLA FS reports (-30 to +50
percent) and are considered rough estimates for planning purposes.

5.1 INCORPORATE THE USGS SURFACE WATER SAMPLING RESULTS INTO THE
ANNUAL EVALUATION OF THE REMEDY
The monitoring of Little Cottonwood Creek conducted by the USGS provides sufficient data to evaluate
conditions in the creek throughout the year under various flow conditions. These results can be used to
evaluate remedy effectiveness at protecting Little Cottonwood Creek. The annual reports and FYRs
should incorporate these sampling results in the form of graphs similar to one or more graphs provided in
Figure C-5. For the optimization review, the USGS data was obtained from the link below using the
parameter codes 00061 for instantaneous discharge (cfs) and 01000 for filtered arsenic concentrations.
Please note that unfiltered samples were not available. Note that the website data repository is in the
process of moving as of February 2024. Therefore, the process to obtain the data in the future is likely
different than the process the optimization team used.

USGS Data for Little Cottonwood Creek at Jordan River

The optimization team believes that implementing this recommendation would add approximately $500 in
cost per year.

5.2 SAMPLE THE STORM SEWER FOR ARSENIC DURING LOW FLOW CONDITIONS
It would be helpful to know if the storm sewer continues to discharge arsenic to Little Cottonwood Creek
and if the arsenic in the sewer discharge originates from Site groundwater. The optimization team
therefore recommends that during a low flow period the State Street storm sewer discharge be sampled
for arsenic. This sampling could be done in the near term or could be postponed to some point in the
future if the arsenic concentration trends in MW-5D or the USGS surface water sampling continue to
increase causing concern that arsenic concentrations in surface water quality might exceed the criteria of
0.1 mg/L. The optimization team estimates that the cost for this sampling should be less than $1,500.

5.3 CONTINUE CURRENT MONITORING PRACTICES AND TRACK THE ARSENIC
CONCENTRATION TREND AT MW-5D
The current monitoring program provides useful information for tracking decreasing, stable, or increasing
concentrations. The optimization team recommends continuing the current groundwater monitoring
program on an annual basis for the foreseeable future and paying close attention to the trend at MW-5D
Optimization Review Murray Smelter Superfund Site

June 2024 FINAL 16

and the concentrations of arsenic in the USGS surface water sampling. Implementing this
recommendation should not increase costs.

5.4 IMPROVE SAMPLE COLLECTION TECHNIQUE TO REDUCE TURBIDITY
Occasional spikes in arsenic concentrations, particularly in IPM-1 and IPM-2 can be explained by turbid
samples. The optimization team recommends using extra care when sampling (especially off-facility and
intermediate aquifer wells) to allow field parameters to stabilize, to avoid drawdown in the well, and
hopefully avoid turbid samples. If turbidity continues to be an issue in particular wells, then focus can be
placed on the dissolved arsenic sampling results rather than the total arsenic sampling results.
Implementing this recommendation may lead to a slight increase in field sampling time perhaps
amounting to an extra $1,000 per year.

5.5 EVALUATE THE PROVIDED ACL CALCULATIONS PROVIDED BY THE
OPTIMIZATION TEAM
The optimization team reviewed the ACL calculations from the ROD and revisited those calculations
based on data collected before and after the ROD. Using the same methodology with an updated data set,
the optimization team calculated an ACL of 1.2 mg/L to 3.3 mg/L (see Appendix D). The optimization
team notes that these lower values are consistent with the range of values calculated in the appendix to the
ROD but that the ROD appeared to select a value of 5 mg/L from a range of calculated values. Both the
optimization team’s calculations and the ROD appendix calculations result in average groundwater
concentrations that are assumed to discharge uniformly to the Little Cottonwood Creek, and these average
groundwater concentrations are adopted as ACLs. In reality, the groundwater and arsenic discharge to the
creek is likely to vary significantly both in time and location along the length of the creek that borders the
Site. For example, a narrow plume that has an arsenic concentration as high as 10 mg/L might still be
protective of Little Cottonwood Creek if the discharging groundwater on either side of the plume has a
very low arsenic concentration. Therefore, comparing calculated average values of 1.2 mg/L, 3.3 mg/L,
and 5 mg/L may be misleading if these values are going to be compared to individual monitoring points.

The optimization team notes that during low flow conditions, the arsenic concentration in Little
Cottonwood Creek is typically between 0.025 mg/L and 0.05 mg/L. The highest detected arsenic
concentration in groundwater near the river is approximately 1 mg/L at MW-5D, but the average
concentration discharging to the river might be closer to 0.37 mg/L (the average of the concentrations at
SPM-3b, SPM-4b, SPM-5, and MW-5D). Using this average groundwater concentration (and the other
parameters the optimization team used in Appendix D), the calculated low flow arsenic concentration in
the river would be approximately 0.016 to 0.038 mg/L. An additional contribution from the sewer may
explain the difference between the calculated surface water concentrations (0.016 to 0.038 mg/L) and the
observed concentrations (0.025 mg/L to 0.05 mg/L). The upper ends of these ranges (0.038 mg/L and
0.05 mg/L) are approximately a factor of 2 to 3 lower than the criteria of 0.1 mg/L. As such, it would
follow that the average groundwater concentration at SPM-3b, SPM-4b, SPM-5, and MW-5D should not
exceed 2 to 3 times the current average concentration of 0.37 mg/L (0.74 mg/L to 1.1 mg/L). These values
are comparable to the lower end of the calculated ACL values the optimization obtained. However, the
optimization team notes that this calculation is sensitive to the arsenic discharge that may be occurring
from the sewer.

The analysis performed here by the optimization team underscores 1) the importance of considering
average concentrations discharging to the river, 2) determining the contribution from the sewer, 3) the
Optimization Review Murray Smelter Superfund Site

June 2024 FINAL 17

concern regarding the increasing concentration at MW-5D, and 4) the potential value in considering a
lower ACL.
Optimization Review Murray Smelter Superfund Site
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June 2024 FINAL 18
TABLE 5. Recommendations and Cost Summary
RECOMMENDATION
EF
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N
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SI
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C
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RE
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RE
V
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A
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A
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N

EN
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G
Y

A
N
D

MA
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I
A
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EF
F
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N
C
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ES
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A
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E
D

CA
P
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A
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C
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CH
A
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I
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AN
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COS
T

5.1 INCORPORATE THE USGS SURFACE
WATER SAMPLING RESULTS INTO THE
ANNUAL EVALUATION OF THE REMEDY
X X $0 $500
5.2 SAMPLE THE STORM SEWER FOR
ARSENIC DURING LOW FLOW
CONDITIONS
X X $1,500 $0
5.3 CONTINUE CURRENT MONITORING
PRACTICES AND TRACK THE ARSENIC
CONCENTRATION TREND AT MW-5D
X $0 $0
5.4 IMPROVE SAMPLE COLLECTION
TECHNIQUE TO REDUCE TURBIDITY X $0 $1,000
5.5 EVALUATE THE PROVIDED ACL
CALCULATIONS PROVIDED BY THE
OPTIMIZATION TEAM
X X $0 $0
“X” Indicates that the recommendation pertains to the indicated optimization category
Values in parentheses “()” indicate estimated annual cost savings
Optimization Review Murray Smelter Superfund Site
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June 2024 FINAL

APPENDIX A:

REFERENCES

Optimization Review Murray Smelter Superfund Site
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June 2024 FINAL

Abatzoglou, J.T., Brown, T.J. 2012. A Comparison of Statistical Downscaling Methods Suited for
Wildfire Applications. International Journal of Climatology. https://doi.org/10.1002/joc.2312
Dillon, G., Gilbertson-Day, J. 2020. Wildfire Hazard Potential for the United States (270-m), version
2020. 3rd Edition. Fort Collins, CO: Forest Service Research Data Archive.
https://doi.org/10.2737/RDS-2015-0047-3
ENVIRON, 2010. Quarterly Monitoring Report, Second Quarter 2010, Former Murray Smelter Site,
Murray, Utah. August.
ENVIRON, 2011a. Quarterly Monitoring Report, First Quarter 2011, Former Murray Smelter Site,
Murray, Utah. August.
ENVIRON, 2011b. Quarterly Monitoring Report, Third Quarter 2011, Former Murray Smelter Site,
Murray, Utah. December.
ENVIRON, 2012. Quarterly Monitoring Report, Fourth Quarter 2011, Former Murray Smelter Site,
Murray, Utah. March.
ENVIRON, 2012. Quarterly Monitoring Report, First Quarter 2012, Former Murray Smelter Site,
Murray, Utah. May.
ENVIRON, 2012. Quarterly Monitoring Report, Second Quarter 2012, Former Murray Smelter Site,
Murray, Utah. August.
ENVIRON, 2012. Quarterly Monitoring Report, Third Quarter 2012, Former Murray Smelter Site,
Murray, Utah. November.
ENVIRON, 2013. Quarterly Monitoring Report, Fourth Quarter 2012, Former Murray Smelter Site,
Murray, Utah. March.
ENVIRON, 2014. Quarterly Monitoring Report, Fourth Quarter 2013, Former Murray Smelter Site,
Murray, Utah. July.
EPA, 1998. Record of Decision, Murray Smelter Proposed National Priorities List Site, Murray, Utah.
April 1.
EPA, 2003. First Five-Year Review Report, Former Murray Smelter Superfund Site, Murray, Utah.
September 22.
EPA, 2009. Second Five-Year Review Report, Former Murray Smelter Superfund Site, Murray, Utah.
March 18.
EPA, 2014. Third Five-Year Review Report, Former Murray Smelter Superfund Site, Murray, Utah.
September 14.
EPA, 2016. What Climate Change Means for Utah. Publication Number EPA 430-F-16-046. August.
Available at: https://www.epa.gov/sites/default/files/2016-09/documents/climate-change-ut.pdf
EPA, 2019. Fourth Five-Year Review Report, Murray Smelter Superfund Site, Murray, Utah. August 14.
FEMA, 2021. National Flood Hazard Layer Viewer. [Online] https://msc.fema.gov/nfhl. Accessed
8/7/2023.
Hydrometrics, Inc., 1998. Supplemental Remedial Design Investigation Report, Former Murray Smelter
Site, Murray, Utah, May 22.
Optimization Review Murray Smelter Superfund Site
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McCulley, Frick & Gilman, Inc. (MFG), 1997. Feasibility Study for The Former Murray Smelter Site,
Murray, Utah, August 28.
McCulley, Frick & Gilman, Inc., 1998. Former Murray Smelter Site, Murray, Utah, Remedial Design
Report Former Smelter Complex Area Category I and II Materials, April 13.
Ramboll, 2015. Monitoring Report, Second Quarter 2015, Former Murray Smelter Site, Murray, Utah.
September.
Ramboll, 2015. Monitoring Report, Second Quarter 2015, Former Murray Smelter Site, Murray, Utah.
September.
Ramboll, 2022. 2021 Annual Monitoring Report, Former Murray Smelter Site, Murray, Utah. June.
Ramboll, 2023. 2022 Annual Monitoring Report, Former Murray Smelter Site, Murray, Utah. December.
U.S. Federal Government, 2021. U.S. Climate Resilience Toolkit Climate Explorer. [Online] https://crt-
climate-explorer.nemac.org/. Accessed 8/7/2023.
Utah Division of Emergency Management, 2019. Utah State Hazard Mitigation Plan. February. Available
at: https://hazards.utah.gov/state-of-utah-hazard-mitigation-plan/

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June 2024 FINAL

APPENDIX B:

FIGURES
(From Existing Site Documents)

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SITE LOCATION MAP FIGURE 1
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Source: 2020 USGS 7.5 Minute Series Salt Lake City South and Sugar House, Utah Topographic Quadrangles; Contour Interval 5 Feet.
KEY MAP
UTAH
Map Scale: 1:24,000
Map Center: 40°39'34.6206", -111°53'33.3175"
N
FORMER MURRAY SMELTER SITE
TRUST OWNED PROPERTY
APPROXIMATE SUPERFUND
SITE BOUNDARY
PZ-3b
SPM-4b
SPM-2b
SPM-5 PZ-2
MW-1D
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PARKING REPOSITORY OWNED BY THE TRUST
ROADWAY REPOSITORY OWNED BY MURRAY CITY
PIEZOMETER (SHALLOW AQUIFER)
NATURAL ATTENUATION MONITORING
REPOSITORY DETECTION MONITORING
REPOSITORY DETECTION MONITORING &
NATURAL ATTENUATION MONITORING
PERFORMANCE MONITORING
LITTLE COTTONWOOD CREEK
SHALLOW AQUIFER
GROUNDWATER
INVESTIGATION
SAMPLING LOCATIONS
FORMER MURRAY SMELTER SITE
Aerial Imagery Source: Google EarthTM, dated 10/10/2019.
NOTE:
IN THE EVENT THAT THE REPOSITORY DETECTION MONITORING PROGRAM
IDENTIFIES A POTENTIAL RELEASE FROM THE REPOSITORY, WELL MW-5D
WILL BECOME THE REPOSITORY COMPLIANCE MONITORING POINT.
IPM-1
IPM-2
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PARKING REPOSITORY OWNED BY THE TRUST
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INTERMEDIATE AQUIFER PERFORMANCE MONITORING
LITTLE COTTONWOOD CREEK
INTERMEDIATE AQUIFER
GROUNDWATER
INVESTIGATION
SAMPLING LOCATIONS
FORMER MURRAY SMELTER SITE
Aerial Imagery Source: Google EarthTM, dated 10/10/2019.
PZ-3b
SPM-4b
SPM-2b
SPM-5 PZ-2
MW-1D
MW-2U
MW-1U
4,304.86
4,304.60
4,303.51
4,298.04
4,305.16
4,300.824,297.68
4,270.69
4,265.40
MW-3U
Dry
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4,263.28
MW-3D
4,287.21
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FIGURE 4
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APPROXIMATE SUPERFUND SITE BOUNDARY
PARKING REPOSITORY OWNED BY THE TRUST
ROADWAY REPOSITORY OWNED BY MURRAY CITY
PIEZOMETER (SHALLOW AQUIFER)
NATURAL ATTENUATION MONITORING
REPOSITORY DETECTION MONITORING
REPOSITORY DETECTION MONITORING & NATURAL ATTENUATION MONITORING
PERFORMANCE MONITORING
GROUNDWATER CONTOUR (5 FT INTERVAL)
GROUNDWATER ELEVATION (FT AMSL)
GROUNDWATER FLOW DIRECTION
LITTLE COTTONWOOD CREEK
ANNUAL 2021
SHALLOW AQUIFER
POTENTIOMETRIC
SURFACE MAP
(AUGUST 30, 2021)
FORMER MURRAY SMELTER SITE
Aerial Imagery Source: Google EarthTM, dated 10/10/2019.
4300
IPM-1
4,279.18
4,271.65
4,253.77
4,255.63
IPM-2
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FIGURE 5
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APPROXIMATE SUPERFUND SITE BOUNDARY
PARKING REPOSITORY OWNED BY THE TRUST
ROADWAY REPOSITORY OWNED BY MURRAY CITY
INTERMEDIATE AQUIFER PERFORMANCE MONITORING
GROUNDWATER CONTOUR (5 FT INTERVAL)
GROUNDWATER ELEVATION (FT AMSL)
GROUNDWATER FLOW DIRECTION
LITTLE COTTONWOOD CREEK
ANNUAL 2021
INTERMEDIATE AQUIFER
POTENTIOMETRIC
SURFACE MAP
(AUGUST 30, 2021)
FORMER MURRAY SMELTER SITE
Aerial Imagery Source: Google EarthTM, dated 10/10/2019.
4280
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A RAMBOLL COMPANY
RAMBOLL US CONSULTING, INC.
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FIGURE 6
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Feet
600
N
APPROXIMATE SUPERFUND SITE BOUNDARY
PARKING REPOSITORY OWNED BY THE TRUST
ROADWAY REPOSITORY OWNED BY MURRAY CITY
SURFACE WATER
LITTLE COTTONWOOD CREEK
SURFACE WATER
INVESTIGATION
SAMPLING LOCATIONS
FORMER MURRAY SMELTER SITE
Aerial Imagery Source: Google EarthTM, dated 10/10/2019.
1/97 D:\5324\5324-43.DWG BY:SCG
LEGEND:
ISZ
ON-FACILITY AREA
OFF-FACILITY AREA
INITIAL STUDY ZONE
SCALE
600 600 FEET
FORMER MURRAY SMELTER SITE
FIGURE 1-1FORMER MURRAYSMELTER SITE
PROJECT: 3324,1REV;DATE JANUARY, 1997BY: SCO I CHECKED: AKMcCULLEY, FR1CK & GILMAN, INC.
1/97 D:\5324\5324-42.DWG BY-.SCG
ExposedSlog .EGEND:
FORMER SMELTER FACILITY COMPONENTS
EXISTING SURFACE FEATURES
ON-FACILITY BOUNDARY
5JOO SOUTH ST
SCALE
200 200 FEET
FORMER MURRAY SMELTER SITE
FIGURE 1-2LOCATION OF HISTORICALSMELTER OPERATIONS
PROJECT: 5324,1REV.:DATE JANUARY, 1997BY: SCO | CHECKS): AKMcCULLEY, FRICK & OILMAN, INC.' MKF
Optimization Review Murray Smelter Superfund Site
_____________________________________________________________________________________
June 2024 FINAL

APPENDIX C:

FIGURES PREPARED BY THE OPTIMIZATION TEAM

Former Roasting
Plant
Former Arsenic
Storage Area
Former Baghouse
Area
Former Southwest
Rail Line Area
Western Smelter
ARea
Outline of Former Slag Pile
(based on aerial photos)
Excavation area identified in the RD
Remediation
Repository
Figure C -1 Current Site Layout with Historical Smelter Features and Excavation Areas
Former Roasting
Plant
Former Arsenic
Storage Area
Former Baghouse
Area
Former Southwest
Rail Line Area
Western Smelter
ARea
Outline of Former Slag Pile
(based on aerial photos)
Excavation area identified in the RD
Remediation
Repository
Figure C -2 Current Site Layout with Historical Smelter Features, Excavation Areas, and
Historical Areas of Soil and Groundwater Contamination
High As in surface soil (0-2 ft) from FS
High As in deeper soil (5 ft) from FS
High As in GW from FS
Figure C -3 Little Cottonwood Creek Flow (cfs) from February 2023 to February 2024
SPM-1:
0.00514
SPM-2b:
0.00551
SPM-3b:
0.0407
SPM-5:
0.303
SPM-4b:
0.0609
MW-1D:
2.23
MW-2D:
1.47
MW-3D:
0.322
MW-10:
21.5
MW-11:
0.0951
MW-12R:
0.534
MW-4UR:
0.0439
MW-5D:
1.08
SMP-5 (GREEN)
MW-1U (RED) and MW-1D (BLUE)MW-2U (RED) AND MW-2D (BLUE)
MW-3U (RED) AND MW-3D (BLUE)
MW-5D (green)
SW-15:
0.0189
SW-13:
0.0163
SW-5:
0.0215
MW-4D:
0.0247
Figure C -4 2021 Arsenic Concentrations in Groundwater and Arsenic
Concentration Trend Charts for Key Monitoring Wells
SPM-2b:
0.00551
2021 Arsenic concentration (mg/L).
green < 0.05 mg/L
black > 0.5 mg/L and < 5 mg/L
red > 5 mg/L
MW-10
Figure C -5 USGS Surface Water Monitoring Data for Little Cottonwood Creek
Flow (cfs) and Filtered Arsenic Concentrations (μg/L)
Figure C -6 Location and Arsenic Concentration Trends for the Five Intermediate
Aquifer Wells
IPM-4, previously located
here, was abandoned in 2017.
Optimization Review Murray Smelter Superfund Site
_____________________________________________________________________________________
June 2024 FINAL

APPENDIX D:

TRANSPORT CALCULATIONS

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June 2024 FINAL

Appendix D: Transport Calculations

GW velocity ~ 130 ft/year to 550 ft/year
• i = 35 ft / 1800 ft = 0.02 ft/ft (2021) or 0.014 ft/ft (FS, MFG, 1997)
• K = 5 ft/day to 15 ft/day (FS, MFG, 1997)
• Effective porosity (n) = 0.20 (FS, MFG, 1997)
• v = Ki/n
• 5 ft/day * 0.014/0.2 * 365 days/year = 130 ft/year
• 15 ft/day * 0.02/0.2 * 365 days/year = 550 ft/year

Arsenic transport velocity ~ 1 ft/year to 9 ft/year
• GW velocity of ~ 130 ft/year to 550 ft/year
• Retardation coefficient of 62 to 141 (FS, MFG, 1997)
• varsenic = v/141 = 130/141 = ~ 1 ft/year
• varsenic = v/62 = 550/62 = ~ 9 ft/year

Various transport times to cover 2,000 ft
• varsenic = 1 ft/year = 2,000 years
• varsenic = 9 ft/year = 220 years
• varsenic = 130 ft/year = 15 years
• varsenic = 550 ft/year = 3.6 years

The concentration trends at MW-5D do not support such a high retardation coefficient especially if the
contamination is migrating from MW-10.
Optimization Review Murray Smelter Superfund Site
_____________________________________________________________________________________
June 2024 FINAL

APPENDIX E:

ACL CALCULATIONS

Optimization Review Murray Smelter Superfund Site
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June 2024 FINAL
Appendix E: ACL Calculations

Evaluation of ROD calculations
Fundamental equation is as follows: 𝐶𝐶𝑠𝑠=�𝐶𝐶𝑔𝑔𝑔𝑔∗ 𝑄𝑄𝑔𝑔𝑔𝑔+𝐶𝐶𝑟𝑟𝑟𝑟𝑟𝑟∗ 𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟��𝑄𝑄𝑔𝑔𝑔𝑔+𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟�
or (rearranged) 𝐶𝐶𝑔𝑔𝑔𝑔=𝐶𝐶𝑠𝑠∗�𝑄𝑄𝑔𝑔𝑔𝑔+ 𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟�−(𝐶𝐶𝑟𝑟𝑟𝑟𝑟𝑟∗ 𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟)𝑄𝑄𝑔𝑔𝑔𝑔
• Cs = State water quality standard for arsenic (0.1 mg/L)
• Cgw = arsenic concentration in groundwater (mg/L) or calculated ACL
• Qgw = groundwater flow rate (cubic ft per second)
• Criv = arsenic concentration in river upstream (mg/L)
• Qriv = river flow rate (cubic ft per second)

Two different data sets or scenarios were used to calculate ACLs in the ROD. Scenario 1 used the flow
and surface water discharges used in the groundwater flow and solute transport modeling. Scenario 2 used
information based on the scientist’s assessment of data from site characterization, the FS, and quarterly
reports.
Parameter Scenario 1 Value Scenario 2 Value
Criv 0.007 mg/L 0.007 mg/L
Qriv Low value is 3.0 cfs Low value is 2.5 cfs
Qgw 0.02 to 1.92 cfs 0.0075 cfs
Cgw To be calculated
Cs 0.1 mg/L for most stringent standard 0.1 mg/L for most stringent standard

Scenario 1
• Cgw = 0.245 to 14.05 mg/L
Scenario 2
• Cgw = 31.1 mg/L

An ACL of 5 mg/L was based on this range of values from 0.245 mg/L to 31.1 mg/L.
Optimization Review Murray Smelter Superfund Site
_____________________________________________________________________________________
June 2024 FINAL

ACL Calculation by the Optimization Team based on review of FS and sampling from 2010 to 2015

Fundamental equation is as follows: 𝐶𝐶𝑠𝑠=�𝐶𝐶𝑔𝑔𝑔𝑔∗ 𝑄𝑄𝑔𝑔𝑔𝑔+𝐶𝐶𝑟𝑟𝑟𝑟𝑟𝑟∗ 𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟��𝑄𝑄𝑔𝑔𝑔𝑔+𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟�
OR (rearranged) 𝐶𝐶𝑔𝑔𝑔𝑔=𝐶𝐶𝑠𝑠∗�𝑄𝑄𝑔𝑔𝑔𝑔+ 𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟�−(𝐶𝐶𝑟𝑟𝑟𝑟𝑟𝑟∗ 𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟)𝑄𝑄𝑔𝑔𝑔𝑔
• Cs = State water quality standard for arsenic (0.1 mg/L)
• Cgw = arsenic concentration in groundwater (mg/L) or calculated ACL
• Qgw = groundwater flow rate (cubic ft per second)
• Criv = arsenic concentration in river upstream (mg/L)
• Qriv = river flow rate (cubic ft per second)

The optimization team used information from the FS, sampling data from 2010 through 2015, and the
USGS surface water sampling data. Based on this review, a lower background concentration for the river
was assumed and a lower low flow rate for the river was assumed. The groundwater discharge rates were
generally similar to those from Scenario 1 provided in the ROD.
Parameter Scenario 1 Value
Criv 0.005 mg/L
Qriv Low value is 1 cfs
Qgw 0.03 cfs or 0.09 cfs*
Cgw To be calculated
C 0.1 mg/L for most stringent standard
*(K = 5 ft/day to 15 ft/day, dh/dl = 0.02 ft/ft, b = 10 ft, length of stream = 2600 ft)

Based on these values, an ACL of 1.2 mg/L to 3.3 mg/L was calculated. This value range is lower than
that adopted by the ROD, but it is consistent with the range of values calculated in the ROD appendix.