EPA 542-R-14-007
Office of Solid Waste and Emergency Response
United States Office of Superfund Remediation
Environmental Protection and Technology Innovation
Agency
Optimization Review
Carson River Mercury Superfund Site
Carson City, Nevada
www.clu-in.org/optimization | www.epa.gov/superfund/cleanup/postconstruction/optimization
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Optimization Review
Carson River Mercury Superfund Site
Carson City, Nevada
Report of the Optimization Review
Site Visit Conducted at Carson River Mercury Superfund Site on
December 11 -12,2013
FINAL TECHNICAL MEMORANDUM
August 6, 2014
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NOTICE AND DISCLAIMER
Work described herein, including preparation of this report, was performed by Tetra Tech Inc. for the
U.S. Environmental Protection Agency under Work Assignment 2-58 of EPA contract EP-W-07-078 with
Tetra Tech EM Inc., Chicago, Illinois. 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 the EPA that focuses on protectiveness, cost-
effectiveness, site completion, technical improvements and green remediation. 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.
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 site remediation strategy. 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
recommendations are not meant to supersede other, more comprehensive planning documents such as
work plans, sampling plans and quality assurance project plans (QAPP), nor are they intended to override
applicable or relevant and appropriate requirements (ARARs). Further analysis of recommendations,
including review of EPA policy, may be needed prior to implementation.
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PREFACE
This report was prepared as part of a national strategy to expand Superfund optimization from remedial
investigation to site completion implemented by the EPA Office of Superfund Remediation and
Technology Innovation (OSRTI)1. The project contacts are as follows:
Organization
Key Contact
Contact Information
EPA OSRTI
Tom Kady
EPA OSRTI
Technology Innovation and Field Services Division (TIFSD)
2777 Crystal Drive
Arlington, VA 22202
kady.thomas (giepa.gov
phone: 732-735-5822
Tetra Tech
(Contractor to EPA)
Jody Edwards, P.G.
Tetra Tech
45610 Woodland Road, Suite 400
Sterling, VA 20166
iody.edwards@tetratech.com
phone: 802-288-9485
Peter Rich, P.E.
Tetra Tech
51 Franklin St.
Annapolis, MD 21401
peter.rich(g),tetratech.com
Phone: 410-990-4607
Mark Shupe P.G.
Tetra Tech
45610 Woodland Road, Suite 400
Sterling, VA 20166
mark. shupe (gitetratech. com
Phone: 703-885-5516
U.S. Environmental Protection Agency. 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 28,2012.
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ACRONYMS AND ABBREVIATIONS
(ig/L Micrograms per liter
ATSDR Agency for Toxic Substances and Disease Registry
cfs Cubic feet per second
COPC Constituent of Potential Concern
CRMS Carson River Mercury Site
CRS Carson River System
CSM Conceptual Site Model
EC Environmental Covenant
EPA U.S. Environmental Protection Agency
ESD Explanation of Significant Differences
FDA Food and Drug Administration
FYR Five-Year Review
GIS Geographic Information System
FIHRA Human Health Risk Assessment
1C Institutional Control
LTM Long-Term Monitoring
LTSRP Long-Term Sampling and Response Plan
mg/kg Milligrams per kilogram
Mcf Million cubic feet
NDEP Nevada Division of Environmental Protection
NDOW Nevada Department of Wildlife
ng/L Nanograms per liter
NOAA National Oceanic and Atmospheric Administration
OSRTI Office of Superfund Remediation and Technology Innovation
OSWER Office of Solid Waste and Emergency Response
OU Operable Unit
PRG Preliminary Remediation Goal
P&T Pump and treat
QAPP Quality Assurance Project Plan
RCRA Resource Conservation and Recovery Act
RfD Reference dose
RI/FS Remedial Investigation/Feasibility Study
ROD Record of decision
RSE Remediation System Evaluations
RSL Regional Screening Level
SPP Systematic Project Planning
SQuiRT Screening Quick Reference Tables
TCLP Toxicity Characteristic Leaching Procedure
TIFSD Technology Innovation and Field Services Division
USFWS U.S. Fish and Wildlife Service
USGS U.S. Geological Survey
in
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CONTENTS
NOTICE AND DISCLAIMER
PREFACE
ACRONYMS AND ABBREVIATIONS
1 0
? 0
3 0
4.0
5 o
60
INTRODUCTION
1 . 1 Optimization Study Background
1 2 Optimization Review Objectives
1 3 Optimization Review Team
1 .4 Site Visit Participants
1.5 Documents Reviewed
1 6 Quality Assurance
PROJECT STATUS
CONCEPTUAL SITE MODEL
FINDINGS AND CONCLUSIONS
RECOMMENDATIONS
5 1 Improving Effectiveness
5 2 Reducing Cost
5.3 Technical Improvement
5.4 Site Completion
5 5 Green Remediation
REFERENCES
i
ii
iii
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1
2
2
3
3
3
4
9
13
14
15
15
16
16
16
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IV
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FIGURES
Figure 1. Carson River Mercury Superfund Site, Risk Area Boundary Map Showing OU 1 and OU 2
Figure 2. Comparison of Total Mercury and Methylmercury in Surface Water
Figure 3. Total Mercury Concentration Range in Sediments
Figure 4. Median Mercury (Hg) Concentrations for Fish in Lahontan Reservoir
Figure 5a. Carson River CSM Schematic Profile, Pre-1859 Conditions
Figure 5b. Carson River CSM Schematic Profile, Post Mining and Pre-Reservoir (1859-1915)
Figure 5c. Carson River CSM Schematic Profile, Post Reservoir (1915 to present)
Figure 6. Stratigraphic Section of Upper Carson River Floodplain Sediments with Total Mercury
Concentrations Posted Indicating the Extreme Variability in Concentrations over Short
Distances
TABLES
Table 1. Optimization Review Team
Table 2. Site Visit Participants
Table 3. Background and Biological Effect Screening Level Concentrations
Table 4. Summary of Mercury Mass Balance Estimate
APPENDICES
Appendix A. Review Documents Matrix
Appendix B. Mass Balance Calculation
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1.0 INTRODUCTION
The Carson River Mercury Site (CRMS) (Figure 1) is located in northwest Nevada and was designated a
Superfund site in 1990 because of elevated mercury concentrations observed in surface water, sediments
and biota inhabiting the site. The CRMS encompasses the 80-mile Carson River System (CRS)
downstream of Carson City, numerous historical mill tailings sites along the Carson River and foothill
tributaries, the Lahontan Reservoir constructed approximately 30 miles downstream from Carson City,
and the lake, wetland and canal complex downstream from the reservoir. The mill sites used mercury to
extract gold and silver from the ore obtained by Comstock Lode mining operations. As part of ore
refining operations, mill sites imported a large quantity of mercury (estimated to be 7,500 tons [Bailey
and Phoenix 1944]), much of which was released to the environment. Beginning in the 1970s,
characterization studies and research projects were performed by various parties to understand the
distribution, fate and transport, and risks posed by mercury contamination in the Carson River watershed.
This technical memorandum provides background on the U.S. Environmental Protection Agency's
optimization program, identifies review team members and site visit participants, discusses current site
status, summarizes the conceptual site model (CSM) and presents findings, conclusions and
recommendations.
1.1 OPTIMIZATION STUDY BACKGROUND
During fiscal years 2000 and 2001, independent site optimization reviews called Remediation System
Evaluations (RSEs) were conducted at 20 operating Fund-lead pump and treat (P&T) sites (that is, those
sites with P&T systems funded and managed by Superfund and the states). In light of the opportunities
for system optimization that arose from those RSEs, the U.S. Environmental Protection Agency Office of
Superfund Remediation and Technology Innovation (OSRTI) has incorporated RSEs into a larger post-
construction completion strategy for Fund-lead remedies as documented in Office of Solid Waste and
Emergency Response (OSWER) Directive No. 9283.1-25, Action Plan for Ground Water Remedy
Optimization. Concurrently, the EPA developed and applied the Triad Approach to optimize site
characterization and development of a CSM. The EPA has since expanded the definition of optimization
to encompass investigation stage optimization using Triad Approach best management practices,
optimization during design and RSEs. The 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 other
approaches to identify opportunities for greater efficiency and effectiveness. "2
As stated in the definition, optimization refers to a "systematic site review," indicating that the site as a
whole is often considered in the review. Optimization can be applied to a specific aspect of the remedy
(for example, a focus on long-term monitoring [LTM] optimization or focus on one particular operable
unit [OU]), but other components of the site or remedy are still considered to the degree that they affect
the focus of the optimization. An optimization review considers the goals of the remedy, available site
data, CSM, remedy performance, protectiveness, cost-effectiveness and closure strategy. A strong interest
U.S. Environmental Protection Agency. 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), OSWER 9200.3-75.
September 28, 2012.
1
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in sustainability has also been developed in the private sector and within federal, state and municipal
governments. Consistent with this interest, OSRTI has developed a Green Remediation Primer
(www.cluin.org/greenremediation) and now routinely considers green remediation and environmental
footprint reduction during optimization reviews.
This optimization review includes reviewing site documents, visiting the site and compiling this report,
which includes recommendations in the following categories:
Protectiveness
Cost-effectiveness
Technical improvement
Site completion
Environmental footprint reduction.
The recommendations are intended to help the site technical team identify opportunities for improvements
in these areas. In many cases, further analysis of a recommendation, beyond that provided in this report,
may be needed before the recommendation can be implemented. Note that the recommendations are
based on an independent evaluation and represent the opinions of the optimization review team. These
recommendations do not constitute requirements for future action, but rather are provided for
consideration by the Region and other site stakeholders. Also note that while the recommendations may
provide some details to consider during implementation, the recommendations are not meant to replace
other, more comprehensive, planning documents such as work plans, sampling plans and quality
assurance project plans (QAPP).
The national optimization strategy includes a system for tracking consideration and implementation of
optimization review recommendations and includes a provision for follow-up technical assistance from
the optimization review team as mutually agreed on by the site management team and EPA OSRTI.
1.2 OPTIMIZATION REVIEW OBJECTIVES
The objectives of this optimization review are to recommend (1) an appropriate remedial strategy for the
CRMS, (2) approaches for improving remedy implementation, and (3) any additional characterization
efforts. The findings and conclusions and recommendations presented in Sections 4.0 and 5.0 result from
review of site documentation and data in conjunction with a site visit and systematic project planning
(SPP) meeting.
1.3 OPTIMIZATION REVIEW TEAM
The optimization review team consisted of the following individuals:
Table 1. Optimization Review Team
Name
Tom Kady
Lili Wang
Peter Rich, P.E.
Mark Shupe, P.G.
Affiliation
EPA OSRTI
EPA OSRTI
Tetra Tech
Tetra Tech
Phone
732-735-5822
614-206-9733
410-990-4607
703-885-5516
Email
kady .thomas@epa. gov
wang.lili@epa.gov
peter.rich@tetratech.com
mark.shupe(a),tetratech.com
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1.4 SITE VISIT PARTICIPANTS
The optimization review team and the site technical team including representatives from U.S.
Environmental Protection Agency Region 9 and the Nevada Division of Environmental Protection
(NDEP) participated in a site visit and preliminary SPP meeting on December 11 and 12, 2013.
Table 2. Site Visit Participants
Name
Andrew Bain
Jeff Collins
David Friedman
Alex Lanza, P.E.
Lili Wang
Thomas Kady
Peter Rich, P.E.
Mark Shupe, P.G.
Affiliation
EPA Region 9
Nevada Division of
Environmental
Protection
EPA OSRTI
Tetra Tech
Phone
(415)972-3167
(775)687-9381
(775) 687-9385
(775) 687-9547
(202)564-9156
(732) 735-5822
(410)990-4607
(703) 390-0653
Email
bain.andrew@epa.gov
jrcollins@ndep.nv.gov
dfriedman@ndep.nv.gov
alanza@ndep.nv.gov
wang.lili@epa.gov
kady .thomas@epa. gov
peter.rich@tetratech.com
mark . shupe @tetratech . com
1.5 DOCUMENTS REVIEWED
Section 6 lists the references that were included in this optimization review. The documents were
prepared by a range of organizations, principally EPA Region 9, the U.S. Geological Survey (USGS), the
NDEP, the U.S. Fish and Wildlife Service (USFWS) and the Nevada Department of Wildlife (NDOW).
In addition, the optimization review team also reviewed a number of reports by researchers from various
academic institutions.
This optimization review included creation of a Microsoft Excel spreadsheet containing a listing of site
documents for sorting and cataloging (the review documents matrix) (see Appendix A). The documents
matrix classifies each of the 167 documents provided by EPA Region 9 according to geographic area
(OU), environmental medium, depositional environment (river, reservoir or agricultural area), and key
investigation elements such as analytical data reporting, data gap analysis and CSM discussion. Given the
size of the CRMS and the volume of existing information, the review documents matrix was an important
and useful tool for efficient review and evaluation of the previous investigations conducted at the site.
1.6 QUALITY ASSURANCE
This optimization review uses existing environmental data to interpret the CSM. The available data from
the document database were compiled to support an evaluation of the general mass distribution of
mercury in the various component subareas of the CRMS. The objective of this evaluation is to identify
general trends in the mass distribution of mercury. Based on a review of the available documents, the
review team and site technical team concluded the data would be of acceptable quality for this purpose.
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2.0 PROJECT STATUS
This section discusses the current status of the CRMS, including a description of the site OUs, site
remediation efforts completed to date and mercury concentration data in affected media. Table 3 shows
available background concentration data and applicable mercury screening levels for comparison to the
concentration data discussed in this section for the environmental media of concern.
Table 3. Background and Biological Effect Screening Level Concentrations
Surface Water
Source
National Primary
Drinking Water
Standard
(EPA 2002)
EPA National
Recommended Water
Quality Criteria
(Criteria Maximum
Concentration)1
Nevada Water Quality
Criteria
(State of Nevada 1994)
Uncontaminated
Background
(Gustinetal. 1994)
Truckee Basin Alpine
Creeks
(Wayne etal. 1996)
Truckee Canal at
Lahontan Dam
(Wayne etal. 1996)
Unfiltered Total
Mercury (ug/L)
2
1.4
0.0 12 (aquatic life)
2 (drinking water)
10 (livestock water)
0.001-0.003
0.0013-0.0016
0.004 - 0.0044
Sediment/Soil
Source
EPA Region 9 RSL
(Industrial Soil)
EPA Region 9 RSL
(Residential Soil)
NOAA SQuiRT
(Probable Effects Level)
NOAA SQuiRT
(Threshold Effects
Level)
Uncontaminated
Background
(Gustinetal., 1994)
Regional Bedrock
(Gustinetal., 1994)
Total Mercury (mg/kg)
350
23
0.486
0.174
10-50
10-50
1.Source: water.epa.gov/scitech/swguidance/standards/criteria/current/upload/nrwqc-2009.pdf
Modified from Craft, etal. (2005).
Notes: ^g/L = micrograms/liter; mg/kg = milligram/kilogram; RSL = Regional Screening Level; NOAA
= National Oceanic and Atmospheric Administration; SQuiRT = Screening Quick Reference Tables.
The CRMS includes the former ore mill sites located in the Comstock region of northern Nevada and
mercury-contaminated sediment, surface water and biota in the 80-mile stretch of the Carson River from
New Empire, just east of Carson City, to its termination points at Carson Lake, Stillwater Wildlife Refuge
and the Carson Sink (Figure 1). The terms "site" and "CRMS" refer to both the Carson River Mercury
Site and multiple former ore processing "mill sites" that collectively constitute the OU1 portion of the
"site" (that is, CRMS). The EPA partitioned the site into two OUs as follows:
OU1 consists of the portions of the Carson drainage and Washoe Valley in northwestern Nevada
that are affected by mercury released from milling operations during the Comstock Lode mining
event (EPA 1995). OU1 includes upland mercury-contaminated tailings associated with 236
known former ore processing mills (EPA 2011) located along the Carson River from New Empire
(eastern Carson City area) to Dayton (Figure 1) and in the tributary canyons including Daney,
Gold and Six Mile Canyon (and also Seven Mile Canyon, a tributary to Six Mile Canyon). OU1
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also includes the six former mill sites located adjacent to Washoe Lake and Steamboat Creek and
the tailings-contaminated sediments contained in these two water bodies. Washoe Lake and
Steamboat Creek are located west and northwest of Carson City in the adjacent Truckee River
watershed (Figure 1).
OU2 consists of the mercury-contaminated sediments in the Carson River, Lahontan Reservoir,
Carson Lake and the Stillwater National Wildlife Refuge. (Figure 1).
The EPA finalized a Record of Decision (ROD) for OU1 in 1995; the remedial investigation/feasibility
study (RI/FS) for OU2 is ongoing (as of January 2014). The status of OU1 and OU2 is discussed in more
detail below.
OU1. EPA Region 9 collected tailings samples from 42 OU1 mill sites, with an average of 10 samples
collected per mill location. The average area for the 42 locations investigated was 1.5 acres (EPA 1994).
The average across all locations was 298 milligrams per kilogram (mg/kg) and maximum mercury
concentrations were 1,007 mg/kg (EPA 1994). Based on the results of a site human health risk assessment
(HHRA, EPA 1994), the EPA developed a ROD for OU1, which included a soil cleanup goal of 80 mg/kg
for total mercury and a selected remedy of surface soil removal or capping. The cleanup goal for mercury
in soil (80 mg/kg) is based on the child exposure equivalent to EPA's oral reference dose (RfD) for
inorganic mercury. In addition to mercury, the ROD also identifies arsenic and lead as constituents of
potential concern (COPC). The ROD requires the implementation of institutional controls (ICs) consisting
of characterization of COPC concentrations in surface soils suspected to be contaminated with mercury,
arsenic or lead above the ROD-defmed cleanup goals in areas where residential development is planned.
If necessary, any soil determined to be contaminated above the cleanup levels will then be remediated by
removal or capping.
The EPA applied the selected remedy within two communities where soils exceeded the 80 mg/kg
cleanup goal for mercury. The selected remedy included excavating contaminated surface soil to the
approximate depth of 2 feet and disposing of the excavated soils in a municipal landfill. Soils that
exceeded hazardous waste standards using toxicity characteristic leaching procedure (TCLP) analysis
(which considers leaching) were to be disposed of at an appropriate Resource Conservation and Recovery
Act (RCRA) hazardous waste disposal facility (EPA 1995). Three OU1 areas in Dayton and one OU1
area in Silver City located approximately 3 miles up-canyon from the Carson River were remediated.
Between August 1998 and December 1999, a combined area of approximately 3 acres was remediated
through excavation and appropriate disposal of 9,087 cubic yards of contaminated soil (EPA 2003). EPA
Region 9 has completed three Five-year reviews (FYRs) (EPA 2003, 2008 and 2013) since the remedy
was completed. As documented in the FYRs, actions taken since the signing of the ROD include:
Development of a plan governing the pre-development characterization of land proposed for
residential development (the Carson River Mercury Superfund Site Draft Long-Term Sampling
and Response Plan [LTSRP] [NDEP 2011]) and extension of the requirements of the LTSRP to
any construction or renovation that disturbs more than 3 cubic yards of soil,
Adoption of a 2013 Explanation of Significant Differences (ESD) that instituted a better site
boundary definition (supported through the use of geographic information system [GIS]-based
tools) and more stringent screening levels for arsenic and lead, and
Establishment of measures to make ICs information more readily accessible to the public.
In general, the reviews conclude that the remedy is protective given that the planned ICs are fully
implemented.
Washoe Lake and Steamboat Creek. As indicated previously, Washoe Lake and Steamboat Creek
(Figure 1) are included in OU1 but are not tributaries to the Carson River. As these water bodies are
located in different watersheds and sediments within each are affected by significantly different
depositional processes, the optimization review team recommends that Washoe Lake and Steamboat
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Creek be designated as a separate OU or OUs, distinct from OUs 1 and 2. Conditions in these two water
bodies are discussed below.
Washoe Lake is located between Reno and Carson City and discharges to Steamboat Creek, a tributary to
the Truckee River. Historical milling of Comstock ore has resulted in mercury contamination in Washoe
Lake and Steamboat Creek surface water, sediment and biota. Blum et al. (2001) indicate that total
mercury concentrations in Steamboat Creek ranged from 82 to 419 nanograms per liter (ng/L) and that 90
percent of this total is associated with suspended solids (above 0.45 microns). The maximum total
mercury concentrations in surface water measured by Blum et al. (2001) were observed at the headwaters
of Steamboat Creek, at the outfall from Washoe Lake. In addition, Blum et al. (2001) observed that
methylmercury concentrations in samples from Steamboat Creek and Washoe Lake wetlands generally
exceeded methylmercury concentrations in Steamboat Creek stream bank and stream channel samples.
NDEP noted during the site visit that the Galena Creek Ditch Company (a local irrigation water purveyor)
periodically spot-excavates accumulated overbank sediments where water discharges from Washoe Lake
to Steamboat Creek. Lower concentrations occur in downstream channel and stream bank sediments.
Rubik Environmental Consultants, Inc. (2013), measured sediment floodplain concentrations for lower
Steamboat Creek that ranged from less than 1 to a maximum of 570 mg/kg and averaged 34 mg/kg in
sampling to support construction of a new roadway in Reno.
Concentrations of mercury in some fish species (carp, Sacramento perch and white bass) collected from
Washoe Lake have exceeded the EPA advisory level of 0.6 mg/kg and the Food and Drug Administration
(FDA) level of 1.0 mg/kg. The NDOW recommends against consumption of these species from Washoe
Lake and advises limited human consumption of various species from Steamboat Creek
(www.ndow.org/Fish/Fish Safetv/Mercury/Health Advisory Status of Western Nevada Waters).
Washoe Lake and Steamboat Creek differ in several key respects from the other water bodies that make
up the CRMS OUs and, as noted above, should be designated as a separate OU or OUs. In addition to
their locations in different watersheds, the historical mill sites in the vicinity of Washoe Lake were
generally located on the floodplain of the lake rather than along steep tributary canyons, as was the typical
setting for the historical mill sites in the Carson River watershed. Sediments in the Washoe Lake mill site
source areas, therefore, are subjected to sedimentary processes more typical of a low-energy lacustrine
environment, whereas sediments in the Carson River watershed mill sites are subjected to sedimentary
processes typical of a high-energy, fluvial environment.
OU2. OU2 encompasses the sediment (below the high water mark) portion of the CRMS from New
Empire downstream to the terminal wetland areas below Lahontan Reservoir. As noted, this portion of the
site is currently undergoing an RI/FS. Elevated mercury concentrations, sourced to the OU1 historical
mill sites, exist in surface water, sediments and biota of the Carson River, Lahontan Reservoir and
terminal wetlands.
The Carson River originates south of Lake Tahoe in the Sierra Nevada Mountains and flows 160 miles to
the northeast to terminal wetlands in the Carson Sink. CRMS OU2 begins in the Carson River valley,
where the large historical quantities of mercury-contaminated tailings entered the river at the OU1 former
mill sites located along the river near Carson City (New Empire to Dayton [Figure 1]), and in the adjacent
tributary canyons. The influx of contaminated tailings to the Carson River is believed to have begun with
the beginning of Comstock mining operations in 1859 (with the most significant quantities entering the
river from the beginning of mining through the early 1900s) (Miller et al. 1996); tailings influx rates
varied over time. The tailings influx has dispersed tailings-contaminated sediments within the Carson
River floodplain from the New Empire - Dayton vicinity downstream to the terminal wetlands. The
mercury present in the floodplain sediments serves as a secondary source to surface water and biota in
OU2. The Lahontan Reservoir, completed in 1915 as part of the Newlands Project for land reclamation, is
located approximately 30 miles downstream from Dayton. A delta exists where the Carson River enters
the Lahontan Reservoir. The delta formed through the deposition of floodplain sediments eroded by the
river upstream from the reservoir. The Newlands Project also included construction of an extensive canal
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system to drain and irrigate the area downstream from the Lahontan Reservoir (Craft et al. 2005). A large
agricultural area and system of wildlife refuges currently exist in this area. Elevated mercury
concentrations exist in the soils, sediments and biota present in the Carson River basin downstream from
Lahontan Reservoir as a result of pre-dam historical sediment migration and ongoing discharges from the
reservoir during both normal flow and flood events.
The most significant mercury contamination in the agricultural and wetland areas downstream of the
reservoir occurred during floods that predated construction of the reservoir (Turtle et al. 2001). Most of
the mercury in OU2 is inorganic mercury associated with the suspended solids in the river water and
secondarily as coarse-grained channel sediments (Craft et al. 2005). Since its construction, the reservoir
has functioned as a depositional sink for suspended and channel sediments from the river (Hoffman and
Taylor 1998). Although mercury-contaminated surface water and sediment continue to discharge from the
reservoir, the rate of downstream mercury loading has been significantly reduced since the reservoir was
built (Turtle etal. 2001).
Craft et al. (2005) compiled a summary of the available mercury and methylmercury data for surface
water, sediments and biota in the Carson River System. The data were obtained from USGS databases and
previous studies conducted by universities and various state and federal agencies. Figure 2, based on data
obtained from Craft et al. (2005), compares total mercury and total methylmercury concentrations in
Carson River headwaters with results for samples collected from the river between Dayton and the
Lahontan Reservoir (Upper Carson River), the Lahontan Reservoir itself, and the wetlands and canals
downstream from Lahontan Dam (Below Dam). Figure 3 compares the ranges of total mercury and
methylmercury concentrations in sediment for Carson River headwaters, Upper Carson River, Lahontan
Reservoir and the wetlands and canals below the dam.
Upstream from OU2, total mercury levels in surface water and sediment of Carson River are slightly
above uncontaminated background concentrations, which reflects the native volcanic geology of the
region and, to some extent, minor anthropogenic sourcing (Craft et al. 2005). Mercury inputs to the
Carson River headwaters have been documented from the Leviathan Superfund Site, an abandoned open-
pit sulfur mine located near the East Fork of the Carson River in Alpine County, California (Craft et al.
2005).
Large historical influxes of mercury-contaminated tailings from OU1 have affected the Carson River
downstream from OU1. Mercury-contaminated tailings continue to enter the Carson River from OU1, but
at a very low rate relative to historical levels. As a result of the influx of tailings-contaminated sediments
from OU1, concentrations of total mercury in water and sediment downstream increase exponentially, as
shown by a comparison of the upstream Carson River mercury concentrations in surface water and
sediment to those measured in the Upper Carson River downstream from OU1 (Figures 2 and 3). Erosion
of the contaminated floodplain sediments occurs annually during high flow spring runoff events. The total
methylmercury concentrations in sediment and surface water exhibit a more gradual increase downstream
from the OU1 source areas and reflect lower flow conditions, which are more favorable for methylation
processes. Although elevated, methylmercury concentrations in the surface water discharging from the
reservoir show a nearly fivefold concentration decrease from the inflow concentrations. Craft et al. (2005)
note that some studies report that higher exit concentrations can occur. Overall, as noted above, the
reservoir acts as a sink for incoming mercury in sediment and surface water. Hoffman and Taylor (1998)
estimate that the reservoir retains up to 90 percent of the mercury entering from the Carson River.
Downstream from Lahontan Reservoir, total mercury concentrations in surface water are comparable to
the reservoir, while methylated mercury exhibits an increase to levels comparable to the Carson River
above the reservoir. These results indicate that mercury methylation is occurring in the below-reservoir
canals and wetlands.
With regard to mercury concentrations in biota, data compiled by Craft et al. (2005) indicate that some
mercury bioaccumulation is occurring in the Carson River upstream from the OU1 source areas, but the
observed concentrations are within background levels. Downstream from OU1, mercury concentrations in
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natural vegetation and in fish and waterfowl tissue increase as the Carson River approaches Lahontan
Reservoir. Tissue from fish inhabiting the reservoir exhibit extremely elevated mercury concentrations
(Figure 4). The NDOW routinely stocks surface water bodies in the state with game fish
(www.ndow.org/Fish/Stocking_Updates/). The Lahontan Reservoir is included in the fish stocking
program, provided that reservoir water levels are sufficiently high to support the additional fish
population. As a result of prolonged drought conditions in the southwestern U.S., the water level in the
Lahontan Reservoir during the current year (2014) is too low to support stocking.
Elevated mercury concentrations in all biota persist in the canals and terminal wetlands below the
reservoir. With only one exception, NDOW recommends against consumption offish caught in the
Carson River downstream from OU1, Lahontan Reservoir or the terminal canals and wetlands because
fish tissue concentrations in nearly all species exceed EPA and FDA levels. The exception is the
Sacramento blackfish, a forage fish harvested commercially; the NDOW approves this fish for
consumption on a limited basis, as indicated on the current NDOW website
www.ndow.org/Fish/Fish Safety/Mercury/Health Advisory Status of Western Nevada Waters/.
The Agency for Toxic Substances and Disease Registry (ATSDR) evaluated environmental risk factors
that might be linked to leukemia cases in the Fallen area, a municipality located in the agricultural area
downstream from the Lahontan Reservoir (ATSDR 2003). This evaluation concluded that human
consumption of mercury-contaminated waterfowl and fish is the most significant human exposure
pathway to mercury and that infrequent exposure to soil, sediment and surface water was unlikely to
result in adverse human health effects. ATSDR (2003), however, noted that data were limited regarding
mercury bioaccumulation in local crops and livestock. Terrestrial mercury bioaccumulation has been
documented in waterfowl in the Carson River terminal wetlands area (Hoffman 1996). Turtle et al. (1998)
note that livestock (cattle) in the terminal wetlands grazed on vegetation near ponds characterized by
elevated trace metal concentrations that may potentially bioaccumulate in livestock. Understanding the
conditions under which livestock bioaccumulate mercury is an ongoing area of research. Chilbunda and
Janssen (2013) observed that livestock grazing in mercury-contaminated areas in a gold mining area in
Tanzania exhibited elevated mercury concentrations in liver samples. Mercury concentrations in the
muscle tissue of these animals, however, were generally within acceptable limits. Additional agricultural
product sampling is, therefore, likely needed to assess what, if any, hazards exist regarding human
consumption of livestock and produce from the Carson River floodplain area.
Existing Institutional Controls. The primary exposure pathways of concern regarding human health and
ecological receptors are contact with and incidental ingestion of mercury-contaminated sediment and soil
and consumption of mercury-contaminated biota. As noted above, NDOW has issued consumption
advisories for fish caught in site surface waters. With regard to site soil and sediment, NDEP, in
conjunction with EPA Region 9, developed the draft LTSRP (NDEP 2011), as previously discussed. The
LTSRP is a regional risk assessment and soil management plan developed to address site-specific
mercury contamination in OU1 and OU2. The plan sets forth sampling requirements to assess the mercury
hazard at any location within the CRMS where site development is planned and would disturb surface
soils. Below the Lahontan Dam, OU2 includes only a narrow portion of the floodplain adjacent to the
Carson River and main distributary channels for the Carson River (Figure 1); the agricultural and canal
areas away from the flood plain and distributary channels, therefore, are not covered by the LTSRP. As an
example of implementation of the LTSRP, the optimization review team visited a subdivision (Onda
Verde Subdivision in Fallen, Nevada). The required sampling after the development process had already
been initiated did not identify mercury above 80 mg/kg within the top 2 feet of the subdivision soil. A
number of parcels within the subdivision had been purchased by private citizens; therefore, NDEP sent
letters to the property owners requesting that they record Environmental Covenants (ECs) for the
properties. An EC is a durable voluntary agreement between NDEP and a property owner and is
associated with a given land parcel in perpetuity (remains in effect after changes in ownership). As
applied to the CRMS, an EC would provide notice to the public that a given parcel is subject to the
conditions specified in the LTSRP.
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3.0 CONCEPTUAL SITE MODEL
A CSM is a comprehensive description of a site and its environmental setting including contaminant
sources, migration pathways and potential ecologic and human health receptors. A significant amount of
data and associated analyses exist for the CRMS to understand the sources, fate and transport, and
receptors of site-related mercury contamination. This section provides a brief review of mercury
occurrence, toxicity and methylation processes, a summary of the CSM and associated data gaps.
Mercury Occurrence and Toxicity. Most mercury in the environment occurs in its elemental form or as
inorganic mercury compounds. Mercury in liquid form readily volatilizes to the atmosphere. Elemental
mercury readily combines with other metals such as gold and silver to form amalgams, the basis for the
milling process used for the Comstock ore processed in the OU1 tailings source areas. A first step in
generation of bioavailable mercury is methylation of inorganic mercury by microorganisms (Hsu-Kim
2013). Mercury, in both organic and inorganic forms, is a potent neurotoxin in humans. Exposure can
result from direct contact and oral exposure. Neurological effects have been observed from acute to long-
term chronic exposures involving relatively low concentrations (ATSDR 1999). The ecological impacts
of mercury include reproductive and behavioral impairment offish and waterfowl (Hoffman et al. 1990).
A mercury amalgamation process was used to extract gold and silver from the Comstock ores. Bailey and
Phoenix (1944) estimate that approximately 7,500 tons of mercury were imported for ore processing in
the Carson River watershed over the period from initial discovery of the Comstock Lode in 1859 through
approximately 1900. The vast majority of mercury in the Carson River system is held within the tightly
bound mercury amalgam produced by ore processing (Gandhi et al. 2007). Modeling studies suggest that
slow dissolution of the amalgam may increase the fraction of dissolved inorganic mercury in the system
over time (Gandhi et al. 2003). The erosion of floodplain sediments and the associated generation of fine
sediment particles (suspended solids) with large concentrations of sorbed mercury, however, is a much
more significant source of mercury to the system.
Microorganisms, including iron- and sulfate-reducing bacteria, can convert inorganic mercury into
methylmercury. Methylmercury bioaccumulates in fish and other aquatic species. The largest predatory
fish within an ecosystem typically accumulate the highest methylmercury concentrations. Human
consumption of mercury-contaminated fish is a key route of exposure to human receptors at the CRMS.
Mercury methylation occurs predominantly in anoxic environments and results from processes mediated
by anaerobic microorganisms. These processes involve a variety of microorganisms and can both produce
(methylate) and destroy (demethylate) methylmercury. Hsu-Kim et al. (2013) review the current
understanding of microbial mercury methylation. They note that fundamental questions currently remain
regarding mercury methylation, including the geochemical forms of inorganic mercury that persist in
anoxic settings, the mode of uptake by methylating bacteria, and the biochemical pathway by which these
microorganisms produce and degrade methylmercury. Additional scientific research on mercury
methylation processes, therefore, is needed to improve remedy evaluations for mercury sites as large and
complex as the CRMS.
Mercury Mass Balance. The optimization review team evaluated available sediment characterization
data to support development of the CSM. The objective of the review was to compile a mass balance of
total mercury for each component of the CRMS. The mass balance calculations are included in Appendix
B. The review focused on Carson River watershed portions of OU1 and OU2 because data were not
readily available to extend this analysis to Washoe Lake and Steamboat Creek. In general, the size of the
CRMS, the comparative sparseness of mercury concentration measurements and the variability of the
concentration data limited the quantitative results of this assessment. However, the available data were
used to assess the relative distribution of mercury among the site components and identify where
uncertainties exist. As noted above, an estimated 7,500 tons of mercury were imported to the OU1 area
for use in processing Comstock Lode ore (Bailey and Phoenix 1944). Even without accounting for
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mercury released to Washoe Lake and Steamboat Creek, the existing data appear to account for only 10
percent of this total, as shown in Table 4.
Table 4. Summary of Mercury Mass Balance Estimate
Site Area
Upper Carson River
Delta Area and
Lahontan Reservoir
Terminal canals,
lakes and wetlands
Total Estimated Mass
Estimated
Mercury Mass
(Tons)
115
450
100
665
Volume
(Mcf)
127
292
300
719
Assumptions/Comments
Assumes average mercury
concentration of 15 mg/kg
increasing downstream from the
OU1 source areas
Assumes average mercury
concentration of 20 mg/kg for the
delta and 24 mg/kg for the reservoir
Assumes average mercury
concentration of 1 mg/kg for an
area of approximately 100 square
miles (1 foot average depth)
Assuming that the 7,500-ton
estimate (Baily and Phoenix
[1944]) is accurate, 6,835 tons
cannot be accounted for in OU2
sediments
Note: See Appendix A for calculation details.
Mcf: million cubic feet
mg/kg: Milligrams per kilogram
As shown in Table 4, these mass balance calculations suggest that a large amount of mercury (6,835 tons)
remains at the OU1 mill sites, a significant amount of mercury was lost via unaccounted processes (for
example, volatilization and bioaccumulation) or the amount of mercury believed to have been imported
was overestimated.
CSM. The dynamics of Carson River discharge are an important consideration in the CSM. The discharge
flow of the Carson River at the Fort Churchill stream gage is measured near the river's discharge point to
the Lahontan Reservoir. Flow is very low (on average 1 to 4 cubic feet per second [cfs]) during August
and September. During the spring, however, snowmelt in the Sierra Mountains causes an increase in
median monthly flow rates to 1,100 cfs in May and 865 cfs in June (Craft et al. 2005). Extreme flood
events can also occur. For example, as a result of a rain-on-snow event in the Sierra Nevada headwaters
of the Carson River, a peak discharge of 22,300 cfs was measured at Fort Churchill in January 1997. In
addition, temporal changes in the flux of tailings-sourced sediments contaminated with mercury are
evaluated in Figures 5a through 5c. These figures were prepared to understand the evolution of the current
distribution of mercury contamination and the applicable fate and transport processes that have operated
and continue to operate at the site.
Figure 5a shows conditions in the watershed that predate mining and milling operations (pre-1859). The
Carson River and the streams occupying the canyons in OU1 are in general equilibrium with runoff and
sediment inputs. The profile of the Upper Carson River downstream from OU1 consists of a steeper,
upstream canyon-bound reach and a flatter, downstream reach occupying a wide valley (Carroll et al.
2000).
Figure 5b shows conditions in the watershed after the start of mining and milling but before construction
of the Lahontan Reservoir Dam, the period from 1859 to the early 1900s. With the discovery of the
Comstock Lode in 1859 and the associated beginning of mining and milling operations, large quantities
of mill tailings consisting of byproducts from the mercury amalgamation process were dumped into the
steep canyons that serve as tributaries to the Carson River. A number of other mills that also discharged
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tailings are located on the Carson River between New Empire and Dayton. At the height of operations,
approximately 544 metric tons of mill tailings were produced each day (Smith 1943). Based on an
analysis of depositional patterns in the Six Mile Canyon alluvial fan, Miller et al. (1996) conclude that
tailings were mostly transported during storm events. The massive influx of tailings to Carson River
resulted in inundation of the pre-mining stream deposits.
Mining operations ceased in the early 1900s. From that time on, erosion primarily associated with storm
events continued to release mercury-contaminated tailings into the Carson River. Before the Lahontan
Reservoir was built, high spring runoff and flood events transported tailings-contaminated sediments
downstream as coarser-grained channel bed deposits and a finer suspended silt and clay size fraction.
Downstream from OU1, this transport occurred throughout the entire river valley, including the terminal
lake and wetland area. The finer-grained suspended load was deposited as overbank sediments in the
lower-gradient portion of the Upper Carson River Valley and in the terminal lake and wetland area. As
the river eroded its banks, it continuously changed course, resulting in the formation of numerous (up to
100) meanders that were later cut and abandoned. Extreme flood events result in significant rerouting and
channel modification (Hoffman et al. 1998). The resulting deposits range from overbank sediments of
variable thickness to a complex of cross-cutting paleochannels (Miller et al. 1998). The cross-section
shown in Figure 6 illustrates the complexity of the floodplain sediments and the extreme variability of
total mercury concentrations that typically exists in these deposits. Miller et al. (1998) conclude that this
extreme variability and the extent of the area of impact would complicate any efforts to adequately
characterize the distribution of mercury in these sediments.
During periods of reduced river flow, mercury present in the stream bank sediments undergoes
methylation and contributes to the total mercury load in the river. Carroll et al. (2000) estimate that
conditions in the river banks are conducive for mercury methylation during river flows below the high
end of the typical spring runoff range (1,000 cfs). Before the reservoir was constructed in 1915,
methylation likely also occurred in the Carson Sink terminal lakes and wetlands.
Figure 5c shows conditions in the watershed after mining ceased and the Lahontan Reservoir was built in
1915. Tailings continue to be eroded from the former OU1 mill sites during storm events, but at a much
reduced rate compared with pre-1900 levels. For example, Miller et al. (1996) indicate that, although
erosion processes will continue to act on the Six Mile Canyon fan and an unquantified amount of
mercury-contaminated sediment will be discharged to the Carson River, the current and future rates these
sediments will move to the river is expected to be very slow. With the disappearance of the dams
supporting the mills on Carson River between New Empire and Dayton, the accumulated tailings were
washed downstream from the steeper portion of the Upper Carson River to the low-gradient reach
upstream from Lahontan Reservoir. During the spring flooding season, a large flux of total mercury
continues to be transported downstream through bank erosion in the lower-gradient reaches of the Carson
River. With completion of Lahontan Dam and Reservoir, however, approximately 90 percent of
sediments transported by fluvial processes are retained in the reservoir.
Both methylation and demethylation occur in sediments in the reservoir (Kuwabara 2002), resulting in
decreased, but still elevated, methylmercury concentration in the reservoir outflow. Seasonally, the
reservoir water level is typically drawn down to accommodate irrigation needs. This seasonal water level
rising and lowering may enhance the bioavailability of mercury in the reservoir (Craft et al. 2005).
Bioaccumulation of methylmercury in the reservoir ecological system may also be a significant sink for
methylmercury (Gandhi 2007). As noted previously, an extensive network of canals was constructed
below the reservoir when the reservoir was developed. Methylation of mercury in the Upper Carson River
stream bank deposits and in the canals and wetlands below the dam is ongoing during low flow periods.
Figures 5a, b and c focus on temporal changes in mercury fate and transport in the CRMS. With respect to
Washoe Lake and Steamboat Creek, historical milling sites also operated along these water bodies and
resulted in discharge of large quantities of mercury-contaminated tailings. Historically, contaminated
sediments have been flushed down Steamboat Creek to the Truckee River floodplain during periods of
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high runoff. The discharge of these tailings into Washoe Lake and Steamboat Creek has resulted in
mercury-contaminated sediments, generation of methylmercury, and bioaccumulation of methylmercury
in the ecological systems of these water bodies. Although a comprehensive document base describing
Washoe Lake and Steamboat Creek was unavailable for this optimization review, it is likely that elevated
mercury concentrations associated with these water bodies are present and exhibit significant variability.
In addition, the area of impact is much smaller compared with the area of impact associated with Carson
River because there are only six known historical ore processing mills in the Washoe Lake area.
CSM Data Gaps. The existing level of characterization provides a working understanding of the
processes that resulted in the current distribution of mercury contamination observed at CRMS.
Significant data gaps remain that should be considered during development of characterization and
remediation strategies for the site:
OU1 source area storm flow data for sediment and surface water are needed to verify current low-
level total mercury loading rates to Carson River and lower Steamboat Creek.
The order of magnitude discrepancy between the initial estimate of mercury mass imported to the
OU1 source area (Baily and Phoenix 1944) and the mercury mass that can be accounted for based
on available sampling results from Carson River floodplain, Lahontan Reservoir and terminal
wetlands sediments should be investigated.
Any residual tailings concentrations in the Carson River Valley portion of OU1 that may be
especially vulnerable to erosion by the river during extreme flood events should be inventoried.
An inventory of residual zones of source area tailings that are especially vulnerable to erosion in
the OU1 tributary valleys in the vicinity of the former mill sites should be developed.
A more complete understanding of the environmental conditions that influence methylation and
demethylation rates in Lahontan Reservoir is needed.
A more complete understanding of the distribution of mercury-contaminated sediments in the
Upper Carson River floodplain and in the canals, soils and sediments in the area downstream
from the Lahontan Reservoir is needed.
Data regarding mercury bioaccumulation in livestock and produce from the agricultural area are
needed to assess the potential for human exposure to mercury from ingestion of contaminated
agricultural products.
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4.0 FINDINGS AND CONCLUSIONS
The following are the primary findings and conclusions resulting from this optimization review.
Elevated mercury concentrations exist in OU1 tailings piles and in sediments derived from the
erosion, transport and deposition of tailings-contaminated sediments in OU2. Contaminated
sediments are present throughout CRMS OU2 downstream from OU1.
Elevated mercury concentrations are present in Washoe Lake sediments and the sediments
contained in the Steamboat Creek floodplain downstream from Washoe Lake.
During storm events, there is a potential for low-level releases of total mercury from the
remaining mercury-contaminated tailings in the OU1 source areas. Releases of these tailings have
most likely diminished substantially as the drainages have readjusted to more normal sediment
loads in recent decades. As a result, current mercury release rates from OU1 are likely low.
Using approximate averages for mercury concentrations in sediment and order-of-magnitude
estimates for sediment volume for the flood plain, reservoir and terminal wetlands, the estimated
total mass of mercury present in OU2 sediments is an order of magnitude less than the estimated
initial mercury mass imported to the OU1 source area.
Given the size of the area involved (80 miles of floodplain) and the random occurrence of zones
of elevated mercury concentration in the OU2 area, both above and below the Lahontan
Reservoir, comprehensive sampling to identify mercury hotspots would be extremely challenging
logistically and scientifically and would be cost-prohibitive.
Areas at the site where conditions are most conducive for mercury methylation include the
Carson River stream bank deposits and the wetlands below the Lahontan Reservoir.
Most of the mercury loading (sediment and surface water) to Lahontan Reservoir consists of
inorganic mercury associated with suspended particles, and 90 percent of suspended particle load
is retained in the reservoir as deposited sediment.
Methylmercury concentrations are greater in the inflow to the Lahontan Reservoir from the
Carson River than are concentrations in the water exiting the reservoir. Some of the reduction is
the result of demethylation processes and some is the result offish uptake. Modeling suggests that
fish may be an important sink for methylmercury in the reservoir.
Fish tissue levels exceed the EPA mercury advisory level and the FDA action level; fish
advisories recommend not consuming fish from the river, with one exception: the Sacramento
blackfish is a forage fish that inhabits the lake and is commercially harvested for human
consumption, with advisories warning to limit consumption (one 8-ounce serving per month for
an adult).
Based on the HHRA completed with the CRMS RI (EPA 1994), the human health exposure
pathways of concern are ingestion of residential soils and consumption of mercury-contaminated
wildlife, especially fish and waterfowl.
Other hypothetical exposure pathways that may pose a concern include ingestion of products
from the agricultural area downstream from Lahontan Dam and incidental ingestion of surface
water.
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5.0 RECOMMENDATIONS
The remedy components that are recommended to be the focus of CRMS remedy evaluations are
presented in this section. Recommendations for improving these components are then discussed in
Sections 5.1 through 5.5.
Consistent with EPA Region 9 and NDEP consensus, the results of more than 20 years of characterization
investigations, and the impracticality of meaningfully addressing data gaps in sediment characterization,
this optimization review recommends that the most reasonable approach to ensure protectiveness for the
CRMS should emphasize ICs. Given the scale of the site (80 miles of floodplain) and the random and
temporal distribution of zones with elevated mercury concentrations, extensive soil and sediment
characterization efforts are not recommended, except to support remedy implementation, as necessary.
Similarly, other active remedial options such as excavation or stabilization should be considered only for
limited implementation and within the context of enhancing the 1C strategy. Elements of the 1C remedy
for sediment and soil and for tissue are discussed below.
The following recommendations are based on the primary optimization review and do not consider the
application and results from the potential use of these technologies.
Sediment and Soil. The anticipated remedial alternatives analysis will emphasize ICs. This remedy
approach provides controls that help to prevent exposure while allowing natural processes that are already
at work transporting the contaminated sediment downstream to continue. Over time, contaminated
sediments will be buried by more recent clean sediments that are generated naturally within the
watershed.
The ICs would consist of the soil management protocols defined in the LTRSP specifically, soil
sampling conducted on an "as-needed" basis. As the term is used here, "soil" refers to both surface soils
affected by current and historical overbank deposition of mercury-contaminated sediment and to
subsurface soil consisting of buried, mercury-contaminated floodplain deposits. Mercury concentrations
would be characterized at a specific location where development is contemplated and the threat of
mercury exposure requires direct assessment. Site-specific spot excavations or capping remedies should
then be implemented, as needed, based on site-specific analytical findings. ICs should include the
establishment of ECs for CRMS properties subjected to development.
Fish and Waterfowl Tissue. Exposure to contaminated fish and waterfowl tissue is a significant human
health and ecologic issue at the CRMS. Elevated mercury levels in tissue are a direct result of the
introduction of mercury-contaminated sediments to the river and the reservoir. No reductions in tissue
concentrations can likely be achieved until the sediment contamination is addressed. Active sediment
remediation would be impractical for CRMS because of the large scale of the site, the relatively random
distribution of elevated mercury and the ability to control most potential exposure pathways using ICs.
ICs in the form of signage warning of the mercury contamination present in fish and waterfowl and
vigorous public awareness efforts are, therefore, key elements of the anticipated approach to limiting
human exposure from consumption of contaminated fish tissue. In addition to ICs, routine monitoring of
fish tissue would continue. The EPA would also encourage additional research to improve the
understanding of the processes that control the bioavailability of mercury at the site.
As stated in Section 1.2, the objectives of this review are to recommend an appropriate remedial strategy
for the CRMS and to recommend approaches for improving remedial and additional characterization
efforts. The following sections discuss recommendations to optimize the implementation of ICs at the
CRMS. As indicated in the following sections, suggestions for additional characterization sampling are
also offered, but only within the context of implementing the 1C strategy.
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5.1 IMPROVING EFFECTIVENESS
Recommendations to improve remedy effectiveness include the following. The applicability of each
recommendation to OU1, OU2 or both OUs is noted for each recommendation.
To increase awareness of the LTRSP and the hazards of consuming contaminated fish, ensure that
the existing community involvement plan effectively defines specific approaches for outreach to
city and county officials, developers and the public (both OUs).
To understand the extent of potential remaining source areas, inventory remaining large
concentrations of tailings that could erode directly into the Carson River and classify them
regarding their susceptibility to erosion. Consider stabilization or removal to reduce the potential
for a direct influx of additional contaminated tailings releases during major flood events (OU1)
for any tailings that appear especially vulnerable to erosion.
To better characterize the potential for human exposure through consumption of locally produced
agricultural products, consider sampling livestock and produce from the agricultural area to
assess the potential for human exposure from this pathway (OU2).
Conduct alternatives analysis to identify potential engineering controls to cost-effectively reduce
or eliminate the need to spot-excavate sediments at the discharge point of Washoe Lake at the
headwaters of Steamboat Creek (OU1).
To reduce human exposure through consumption of contaminated fish tissue, post effective
signage warning against fish consumption from the OU2 area at all public access points (docks,
boat ramps and similar locations) to the Lahontan Reservoir, Carson River, and the lakes and
wetlands downstream from Lahontan Reservoir (OU2).
To reduce human and waterfowl exposure to contaminated fish tissue, the practice of stocking the
Lahontan Reservoir with game fish should end. This measure would also reinforce the health
advisory against the consumption offish caught in the reservoir (OU2).
End the commercial harvesting of the Sacramento black fish from Lahontan Reservoir to
eliminate this human exposure pathway (OU2).
Research reservoir water level management as a potential approach to reduce mercury
methylation (OU2).
To more effectively manage site restoration efforts, Washoe Lake and Steamboat Creek should be
assigned to a separate OU, distinct from OUs 1 and 2. This recommendation is put forth because
Washoe Lake and Steamboat Creek are in a separate watershed and depositional processes
operating to disperse contaminated sediments may differ from those that dominate sediment
transport in the Carson River watershed, (OU1).
5.2 REDUCING COST
Recommendations to reduce cost include:
The anticipated strategy emphasizing ICs will more cost-effectively manage the mercury issues at
CRMS compared with other strategies that involve source control or removal measures. However,
to be effective, special attention must be focused on 1C implementation and monitoring to ensure
protectiveness (both OUs).
Consider ways to expedite the LTRSP process by streamlining, to extent possible, the application
process. Tools such as standardized application checklists and procedures can minimize
administrative application review costs (both OUs).
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5.3 TECHNICAL IMPROVEMENT
Recommendations for technical improvement include:
With respect to LTRSP implementation, expand the use of GIS tools and the use of risk boundary
polygons developed by NDEP (NDEP undated). The designation of high, moderate, and low risk
areas and associated LTRSP requirements tailored to each area will improve implementation of
the LTRSP (both OUs).
With regard to mercury bioavailability, encourage research organizations such as the USGS and
universities to continue investigating mercury methylation and demethylation processes in the
Carson River and Washoe Lake and Steamboat Creek watersheds (OU2).
In coordination with the recommended research regarding mercury methylation, research should
be encouraged to identify and evaluate potential measures to prevent or inhibit methylation
processes in site water bodies (OU2).
To help address uncertainties in the mercury mass balance, review and verify the calculations
performed by Bailey and Phoenix (1944) regarding the amount of mercury imported to OUlto
support ore processing operations (OU1).
5.4 SITE COMPLETION
Recommendations for site completion include:
Conduct continued, routine monitoring of surface water and sediment quality both in the Carson
River and in the OU1 tributaries so that any significant reductions in mercury concentrations can
be established to assess progress toward site completion and to evaluate the effectiveness of ICs.
This monitoring can also support ongoing studies regarding the factors controlling mercury
bioavailability (both OUs).
Consider a site-wide, hyperspectral aerial imaging survey to attempt to map mercury distribution.
The imaging sensor system should be flown over the area during the annual period of lowest
water (typically August/September). The survey will require soil and sediment sampling,
combined with laboratory-based analytical and spectral signature determination, to ground-truth
the mercury identified through aerial imagery. If successful, the survey could indicate areas of
relatively higher mercury concentrations in soils and sediments that could be considered for more
targeted institutional controls or containment or removal actions. As the survey is anticipated
would be performed by EPA's Office of Research and Development, no costs for the effort are
provided.
5.5 GREEN REMEDIATION
Recommendations for green remediation:
Consider developing and maintaining a CRMS soils database to facilitate leveraging sampling
results across neighboring project sites, thus potentially minimizing the extent of characterization
needed for the CRMS and conserving project resources (both OUs).
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6.0 REFERENCES
Agency for Toxic Substances and Disease Registry (ATSDR). 1999. Toxicological Profile for Mercury.
March.
ATSDR. 2003. Health Consultation, Fallen Leukemia Project, Fallen, Churchill County, Nevada,
February.
Bailey E.H. and Phoenix D.A. 1944. Quicksilver Deposits in Nevada. University of Nevada Bulletin
38:12-46.
Blum M., Gustin M.S., Swanson S. and Donaldson S.G. 2001. Mercury in Water and Sediment of
Steamboat Creek, Nevada: Implications for Stream Restoration. Journal of the American Water
Resources Association 37(4). August.
Carroll R.W.H., Warwick J.J., Heim K.J., Bonzongo J.C., Miller J.R and Lyons W.B. 2000. Simulation
of Mercury Transport and Fate in the Carson River, Nevada. Ecological Modelling 125 (2000)
255-278.
Chibunda, R.T. and Janssen C.R., 2013. Mercury Residues in Free-Grazing Cattle and Domestic Fowl
from the Artisanal Gold Mining Area of Geita District, Tanzania. Food Additives &
Contaminants: Part A: Chemistry, Analysis, Control, Exposure & Risk Assessment 26.11 (2009):
1482-1487.
Craft D., Fields J. and Yoder N. 2005. Mercury in the Carson River Basin. U.S. Geological Survey
Technical Memorandum TSC-2005-8290-001.
Gandhi N. and Diamond M. 2003. Development of Mercury Speciation, Fate and Bioaccumulation
Model: Application to Lahontan Reservoir, Nevada. Prepared on the behalf of CH2M Hill for
U.S. EPA Region 9. March.
Gandhi N., Bhavsar S.P., Diamond M.L. and Kuwabara J.S. 2007. Development of a Mercury Speciation,
Fate, and Biotic Uptake (Biotranspec) Model: Application to Lahontan Reservoir (Nevada, USA).
Environmental Toxicology and Chemistry, Vol. 26, No. 11, pp. 2260-2273.
Gustin M.S., Taylor G.E. Jr. and Leonard T.L. 1994. High Levels of Mercury Contamination in Multiple
Media of the Carson River Drainage Basin of Nevada: Implications for Risk Assessment.
Environmental Health Perspectives, Vol. 102, pp. 772-777'.
Hoffman R.J. 1996. Mercury Contamination in the Carson River Basin, West-Central Nevada, U.S.
Geological Survey Workshop on Mercury Cycling in the Environment, Golden, Colorado, July
7-9.
Hoffman R.J., Hallock R.J., Rowe T.G., Lico M.S., Burge H.L. and Thompson S.P. 1990.
Reconnaissance Investigation of Water Quality, Bottom Sediment, and Biota Associated with
Irrigation Drainage in and near Stillwater Wildlife Management Area, Churchill County, Nevada,
1986-87. U.S. Geological Survey Water Resources Investigation Report 89-4105.
Hoffman R.J. and Taylor R.L. 1998. Mercury and Suspended Sediment, Carson River Basin Nevada,
Loads to and from Lahontan Reservoir in Flood Year 1997 and Deposition in Reservoir Prior to
1983. U.S. Geological Survey Fact Sheet FS-001-98. January.
17
-------
Hsu-Kim H., Kucharzyk K.H., Zang T., Deshusses M.A. 2013. Mechanisms Regulating Mercury
Bioavailability for Methylating Microorganisms in the Aquatic Environment - A Critical Review,
Environmental Science and Technology, 47, 2441-2456.
Kuwabara J.S., Marvin-Dipsasquale M., Praskins W., Bryon E., Topping B.R., Carter J.C., Fend S.V.,
Parchaso F., Krabbenhoft D.P. and Gustin M.S. 2002. Flux of Dissolved Forms of Mercury
across the Sediment-water Interface in Lahontan Reservoir, Nevada. U.S. Geological Survey
Water Resources Report 02-4138.
Miller J. R., Lechler P. J., Rowland J., Desilets M. and Hsu L. C. 1995. An integrated approach to the
determination of the quantity, distribution, and dispersal of mercury in Lahontan Reservoir,
Nevada, USA. Journal of Geochemical Exploration. 52 (1995) 45-55.
Miller J.R., Lechler P.J., Rowland J., Desilets M. and Hsu L.C. 1996. Dispersal of Mercury-Contaminated
Sediments by Geomorphic Processes, Sixmile Canyon, Nevada, USA: Implications to Site
Characterization and Remediation of Fluvial Environments, Water, Air, and Soil Pollution. 86,
373-388, 1996.
Miller J.R., Lechler P.J. and Desilets M. 1998. The Role of Geomorphic Processes in the Transport and
Fate of Mercury in the Carson River Basin, West-Central Nevada. Environmental Geology 33 (4)
March.
Nevada Division of Environmental Protection (NDEP). 2011. Draft Carson River Mercury Superfund Site
Long-term Sampling and Response Plan, prepared by the Nevada Department of Environmental
Protection in conjunction with EPA Region 9. December.
NDEP. Undated. Carson River Mercury Superfund Site, Site Boundary Evolution and Operable Units,
PowerPoint Presentation.
Rubik Environmental, Inc. 2013. Southeast Connector Phase 2 - Additional Soil Sampling and
Concentration Contour Modeling of Mercury in Soil, prepared on behalf of CH2M Hill for the
Regional Transportation Commission.
Smith G.H. 1943. The History of Comstock, 1850 - 1920. University of Nevada Bulletin No. 37.
State of Nevada. 1994. Nevada Administrative Code (NAC), Chapter 445 A, Water Controls, Nevada
Department of Conservation and Natural Resources, Division of Environmental Protection,
http://ndep.nv.gov/admin/nac445aO.htmtfstandard
Turtle, P.L. and Thodal, C.E. 1998. Field Screening of Water Quality, Bottom Sediment, and Biota
Associated With Irrigation in and near the Indian Lakes Area, Stillwater Wildlife Management
Area, Churchill County, West-Central Nevada, 1995, U.S. Geological Survey Water Resources
Investigation 97-4250.
Turtle. P.L. and Higgins O.K. 2001. Mercury Characterization in Lahontan Valley Wetlands Carson River
Mercury Site Lyon and Churchill Counties, Nevada, 1999. Prepared for EPA Region 9. February.
U.S. Environmental Protection Agency (EPA). 1994. Revised Draft Human Health Risk Assessment and
Remedial Investigation Report Carson River Mercury Site. Prepared by EPA Region 9.
December.
EPA. 1995. EPA Superfund Record of Decision: Carson River Mercury Site EPA ID: NVD980813646
OU1, Dayton, NV. March.
EPA. 2002. List of Contaminants and Their Maximum Concentration Limits, EPA 816-F-02-013,
Informational website, www.epa.gov/safewater/mcl.htmltfmcls
18
-------
U.S. Environmental Protection Agency. 2003. First Five Year Review Report for the Carson River
Mercury Site, Dayton and Silver City, Nevada. Prepared by EPA Region 9. September.
EPA. 2005. List of Contaminants and Their Maximum Concentration Limits, EPA 816-F-02-013,
Informational website, www.epa.gov/safewater/mcl.htmltfmcls
EPA. 2008. Five-Year Review Report, Second Five-Year Report for Carson River Mercury Site, Cities of
Dayton and Silver City, Lyon County, Nevada, September.
EPA. 2011. Carson River Mercury Superfund Site, Archaeological Studies of Flistorical Mill Sites.
Accessed at:
http://vosemite.epa.gov/r9/sfund/r9sfdocw.nsf/3dc283e6c5d6056f88257426007417a2/893b41cal
86989d08825788000604803/$FILE/CRMS4 11 436kb.pdf
EPA. 2013. Five-Year Review Report, Third Five-Year Report for Carson River Mercury Site, Cities of
Dayton and Silver City, Lyon County, Nevada, September.
Wayne D.M., Warwick J.J., Lechler P.J., Gill G.A. Lyons W.B. 1996. Mercury Contamination in the
Carson River, Nevada: Preliminary Study of the Impact of Mining Wastes, Water, Air, and Soil
Pollution. Vol. 92, pp. 391-408.
19
-------
FIGURES
-------
arson
terminal lakes and
wetlands
Stillwater
National Wildlife
Refuge
Agricultural and can
area, terminal lakes
and wetlands
Lanontan
Reservoir
Steamboat
Creek &
Upper
Carson River
FIGURE 1
CARSON RIVER MERCURY
SUPERFUND SITE
RISK AREA BOUNDARY MAP
SHOWING OPERABLE UNIT 1
AND OPERABLE UNIT 2
DECEMBER 1,2010
-------
100000
10000
1000
"5?
"?
s
oi
100
Upstream
Carson R.
Total Mercury
Upper
Carson R.
Lahontan
Reservoir
Below
Dam
0 Max
S Average
SMin
Total Methylmercury
0
^^ 7
^j '
"55
c fi
£
= c
1 5
E 4
£ ^?
a! J
to 2
II
I<
S § ^
^ ° g
^ _ ° 0
ssssssssssss
^ssssssss
QMax
m S Average
I-.
_. ^f
-------
Total Mercury and Methylmercury Concentration Ranges in Sediments
1000000
100000
10000
BO
Ji
BO
01
1000
100
10
THg, Upstream
Carson R.
THg, Upper
Carson R.
THg, Lahontan
Reservoir
THg, Below
Dam
MeHg, Upstream
Carson R.
MeHg, Upper
Carson R.
Figure 3. Total Mercury Concentration Range in Sediments
(THg: Total Mercury, MeHg: Methylmercury, ug/kg: microgram per kilogram)
-------
Overall Median = 1.90 mg/kg (n=385)
Number of
Samples
FDA 1.0 mg/kg
Action Level
EPA 0.6 rngftg
Advisory Level
Figure 4. Median Mercury (Hg) Concentrations for Fish in Lahontan Reservoir
Modified from Craft et al. (2005)
Mg/kg: milligrams per kilogram
-------
OU1 Tributary Canyons
(Daney, Gold, Sixmile, Seven
Mile)
Pre-mining (natural)
sediment surface
Higher gradient reach
-X-
Lower gradient reach
Carson River Headwaters
(Upstream from OU1
Background mercury
concentrtions in surface
water and sediment result
from erosion of regional
volcanic bedrock deposits.
Upper Carson River
(OU 1 to Lahontan Reservoir)
Terminal Lakes and
Wetlands
Figure 5A. Carson River CSM Schematic Profile, Pre-1859 Conditions (not to scale)
The OU1 tributaries and Carson River contain naturally-derived sediment. Stream channels are in general equilibrium with water flow and sediment input. Lahontan Reservoir has not yet
been constructed. From the OU1 area downstream, the Upper Carson River includes a high gradient reach followed by a lower gradient reach extemdomg to below the future location of the
-------
OU1 Tributary Canyons
(Daney, Gold, Sixmile, Seven
Mile): Large amounts of
mercury-contaminated
tailings are dumped into
canyons.
Surface of OU1 Mill
site tailings dumps
Pre-mining sediment
surface in equilibrium with
natural sediment influx
Post-mining, pre-reservoir
sediment surface (top of
mercury-contaminated
sediments
Higher gradient reach
Lower gradient reach
Carson River Headwaters
(Upstream from OU1
Low level mercury
concentrations as a result of
natural background and
minor anthropogenic inputs
tminor mining and milling
activity)
Upper Carson River
(OU 1 to Lahontan Reservoir
During high surface water fow events, floodplain sediments are
eroded resulting in the transport of mercury-contaminated sediment
downstream.
During low flow, mercury methylation occurs in streambank
deposits.
Terminal Lakes and Wetlands
During high surface water flow events,
mercury contaminated sediments are
deposited over the floodplain as overbank
deposits.
During non-flood conditions, mercury
methylation occurs in wetlands
Figure 5B. Carson River CSM Schematic Profile, Post Mining and Pre-Reservoir (1859 -1915, not to scale)
As a result of the generation of massive amounts of mercury-contaminated mill tailings in the OU1 tributary canyons, a large influx of tailings to the Carson River valley results. In the high-gradient,
bedrock-controlled canyon downstream from Carson City, large amounts of tailings accumulate behind dams constructed to support mil ling facilities on the river. In addition, large amounts of
mercury contaminated sediments are stored in the low gradient portion of the Upper Carson River and downstream in the terminal lakes and wetlands. Large amounts of total mercury are
transported downstream with high sediment load during spring floods; elevated levels of methylated mecury generated in stream bank deposits during low flow are discharged to the Carson River
and terminal wetlands and lakes.
-------
OU1 Tributary Canyons
(Daney, Gold, Sixmile, Seven
Mile): Although mercury-
contaminated tailings are no
longer being generated, a
significant amount remains.
Tailings continue to be
transported to Carson River,
but at much lower rate of
influx
Surface of OU1 Mill
site tailings dumps
Pre-mining sediment
surface in equilibrium with
natural sediment influx
Post-mining, pre-reservoir
sediment surface (top of
mercury-contaminated
sediments
Higher gradient reach
Lower gradient reach
Carson River Headwaters
(Upstream from OU1
Low level mercury
concentrations as a result of
natural background and
minor anthropogenic inputs
tminor mining and milling
activity)
Upper Carson River
(OU 1 to Lahontan Reservoir
During high surface water fow events, floodplain
sediments are eroded resulting in the transport of
mercury-contaminated sediment downstream.
During low flow, mercury methylation occurs in
streambank deposits.
90 percent of incoming sediment to Lahontan
Reservoir is retained.
Both methylation and demethylation of mercury
occurs in the reservoir with a net methylmercury
concentration reduction typically obsserved in
water exiting the reservoir
Terminal Lakes and Wetlands
Reduced but still elvated suspended sediment
associated total mercury concentrations are
discharged from the reservoir; during extreme
surface water flows, higher concentrations and
flux rates are likely.
Mercury methylation occurs in terminal canals,
lakes, and wetlands
Figure 5C. Carson River CSM Schematic Profile, Post Reservoir (1915 to present, not to scale)
Large fluxes of total mercury continue to be transported downstream with high sediment load during spring floods. With the constuction of the Lahontan dam and reservoir, however, approximately 90
percent of these sediments are retained in the reservoir. Elevated levels of methylated mecury continue to be generated in stream bank deposits of the Upper Carson River. Mercury methylation and
demethylation (Kuwabara 2002) occurs in the reservoir with a net reduction in surface water concentrations of methylmercury typically observed.
-------
21.300 pg/g
112.000
6.020 jig/g
0.393 pg/g
\
10.200 Jig/g
Figure 6. Stratigraphic Section (length: approximately 246 ft) of Upper Carson River Floodplain Sediments with Total Mercury
Concentrations Posted Indicating the Extreme Variability in Concentrations over Short Distances (source: Miller et al., 1998)
-------
APPENDIX A
REVIEW DOCUMENTS MATRIX
-------
Appendix A-Review Documents Matrix
Carson River Mercury Superfund Site
Document Title
Date
Document
Filename
Background Documents / Side-Wide
Carson River Mercury Superfund Site Site
Boundary Evolution and Operable Units
Flux of Dissolved Forms of Mercury Across the
Sediment-water Interface in Lahontan Reservoir,
Nevada
First Five-Year Review Report for the Carson
River Mercury Site, Dayton and Silver City, Lyon
County, Nevada
Second Five-Year Review Report For Carson
River Mercury Site, Cities of Dayton and Silver
City, Lyon County, Nevada
Water Quality in the Las Vegas Valley Area and
the Caron and Truckee River Basins, Nevada and
California, 1992-96
Initial Site Visit to the Carson River Mercury Site
and Briefing by USGS on the Status of their Data.
Mills and Dams on the Carson in Words and
Pictures, The Quartz Mills, 1860
Atmospheric Mercury Concentrations Associated
with Geologically and Anthropogenically
Enriched Sites in Central Western Nevada
Carson River Chronology, A Chronological
History of the Carson River and Related Water
Issues
Ground-Water-Quality Assessment of the Carson
River Basin, Nevada and California: Analysis of
Available Water-Quality Data through!987
Hydrogeology of the Stillwater Geothermal Area,
Churchill County, Nevada. Plate
In Situ Bacterial Selenate Reduction in the
Agricultural Drainage Systems of Western
Nevada
Mercury in the Carson and Truckee River Basins
of Nevada
Mercury Results (Fish Tissue) 2005, 2006, 2007 &
2008
Methyl-Mercury Degradation Pathways: A
Comparison Among Three Mercury Impacted
Ecosystems
Methylmercury Formation and Degradation in
Sediments of the Carson River System
2003-09
9/30/2008
1998
5/1/2009
1897
1996
1997-04
1989
1982
1991-02
1973
3/8/2000
12/17/2001
Mini-Retreat
(2).ppt
07_15_2009_09_
47_00_57.pdf
carsn_003227.pdf
carsn_003226.pdf
07_15_2009_09_
47_51_4.pdf
05_28_2009_16_
06_10_16.pdf
carsn_003231.pdf
carsn_003511.pdf
carsn_003350.pdf
carsn_003234.pdf
carsn_003273.pdf
carsn_003523.pdf
carsn_003232.pdf
carsn_003359.pdf
carsn_003264.pdf
carsn_003245.pdf
CD
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Risk /
Community
!«
5 £
QJ O
2
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Analytical
Data
X
X
A-l
-------
Appendix A-Review Documents Matrix
Carson River Mercury Superfund Site
Document Title
Reconnaissance Survey of Ground-water Quality
in the Carson River Basin
Report on Lahontan Reservoir, Churchill and
Lyon Counties, Nevada
Draft Development of Remediation-Related
Hypotheses and Questions, Carson River
Mercury Site
Analytical Data for Soil and Well Core Samples
from the Carson River Basin, Lyon and Churchill
Counties, Nevada
Directory of Mining and Milling Operations
Chemical Analyses of Ground Water in the
Carson Desert near Stillwater, Churchill County,
Nevada, 2005
Revised Draft Ecological Assessment Field
Sampling Plan, Phase 1 Remedial
Investigation/Feasibility, Carson River Mercury
Site, Carson River, Nevada
Washoe Lake Data (Mercury in Fish Tissue)
Effects of Mercury on Fish-Eating Birds Nesting
along the Mid to Lower Carson River, Nevada
Preliminary Health Assessment, Carson River
Mercury Site, Lyon, Churchill, Storey Counties,
Nevada
Technical Memorandum, Updated (2007) Dafa
Gaps Identification - Carson River Mercury
Superfund Site
Nevada's Water Quality Standards and Low/High
Flow Statistics (7Q10)
Date
1988-01
1977-09
3/10/1997
1991
1989
2008
1994-04
1987
8/18/2000
1990
7/31/2007
2004-09
Document
Filename
carsn_003228.pdf
carsn_003230.pdf
carsn_003255.pdf
carsn_003389.pdf
carsn_003253.pdf
carsn_003265.pdf
carsn_003238.pdf
carsn_003371.pdf
carsn_003224.pdf
carsn_003246.pdf
carsn_003241.pdf
carsn_003361.pdf
Background Documents / OU1
Geologic Map and Geology of the Virginia City
Quadrangle, Washoe, Storey and Lyon Counties
and Carson City, Nevada
Technical Memorandum, Data Gaps
Identification and Remedial Alternatives
Screening - Carson River Site
Feasibility Study, Carson River Mercury Site
Revised Draft Human Health Risk Assessment
and Remedial Investigation Report, Carson River
Mercury Site
2009
10/27/1999
12/20/1994
1994-12
carsn_003354.pdf
carsn_003240.pdf
carsn_003247.pdf
carsn_003277.pdf
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X
X
X
X
X
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X
X
X
X
X
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X
X
Risk /
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X
X
!«
5 £
QJ O
2
X
X
X
X
X
X
Analytical
Data
X
X
X
X
A-2
-------
Appendix A-Review Documents Matrix
Carson River Mercury Superfund Site
Document Title
Revised Draft, Human Health Risk Assessment
and Remedial Investigation Report, Carson River
Mercury Site. Appendix: Data Validation Reports
Date
1994-12
Document
Filename
carsn_003270.pdf
Background Documents / OU2
Final Technical Memorandum - Conceptual Site
Model (CSM) for Carson River Mercury Site,
Operable Unit 2
Field Sampling Plan, Investigation of Mercury
Loading into Lahontan Reservoir (2000 - 2001),
Carson River Mercury Site, Lyon and Churchill
Counties, Nevada
Effects of the 1997 Flood on the Transport and
Storage of Sediment and Mercury within the
Carson River Valley, West-Central Nevada
Mercury Contamination of the Carson River,
Nevada Geology: Quarterly Newsletter of the
Nevada Bureau of Mines and Geology
Mercury Levels in Surface Waters of the Carson
River Lahontan Reservoir System, Nevada:
Influence of Historic Mining Activities
Modeling Erosion and Overbank Deposition
During Extreme Flood Conditions on the Carson
River, Nevada
Modeling Total and Methyl Mercury in the
Carson River, Nevada. Model Documentation:
Detailed Output
Simulating Sediment Transport in the Carson
River and Lahontan Reservoir, Nevada, USA
Simulating Sediment Transport in the Carson
River and Lahontan Reservoir, Nevada, USA
Simulation of Mercury Transport and Fate in the
Carson River, Nevada
The Role of Geomorphic Processes in the
Transport and Fate of Mercury in the Carson
River Basin, West-central Nevada
The Role of Geomorphic Processes in the
Transport and Fate of Mercury in the Carson
River Basin, West-Central Nevada
Understanding Mercury Mobility at the Carson
City Superfund Site, Western Nevada, USA:
Interpretation of Mercury Speciation Results
from Mill Tailings, Soils, and River and Reservoir
12/30/2011
4/19/2000
1999
1992
12/9/1997
2004
6/1/2000
1997-02
2000
1998
01_05_2012_13_
08_49_51.pdf
carsn_003262.pdf
carsn_003315.pdf
carsn_003357.pdf
carsn_003497.pdf
carsn_003327.pdf
carsn_003329.pdf
carsn_003272.pdf
carsn_003278.pdf
carsn_003334.pdf
carsn_003332.pdf
carsn_003492.pdf
carsn_003498.pdf
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X
X
X
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X
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X
X
X
X
Analytical
Data
X
X
A-3
-------
-------
-------
-------
-------
-------
-------
-------
-------
Appendix A-Review Documents Matrix
Carson River Mercury Superfund Site
Document Title
Dispersal of Mercury Contaminated Sediments
by Geomorphic Processes, Sixmile Canyon,
Nevada, USA: Implications to Site
Characterization and Remediation of Fluvial
Environments
Nutrient Assessment Protocols for Lakes and
Reservoirs in Nevada, Version 1
Strategic Plan for the Reduction of Mercury-
Related Risk in the Sacramento River Watershed
Date
1994
2008-12
Document
Filename
carsn_003254.pdf
carsn_003362.pdf
07 15 2009 09
48_24_57.pdf
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CD
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c
Abbreviations:
OU = Operable Unit
SW = Surface water
GW =Groundwater
Ag = Agricultural
CSM = Conceptual Site Model
Rl = Remedial Investigation
FS = Feasibility Study
A-12
-------
APPENDIX B
MASS BALANCE CALCULATION
-------
BY Peter Rich DATENov2013 PROJECT
"$ @kk'
SHEET NO._^ __ OF _1
C
4/5 ~
-Rr.t.
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Reference: Miller etal.
(1995)
HSIGEOTRANS
------- |