PB95-964504
EPA/ROD/R09-95/134
June 1995
EPA Superfund
Record of Decision:
Carson River Mercury Site
(OU 1), Lyon/Churchill County, NV
3/30/1995
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION IX
75 Hawthorne Street
San Francisco, CA 94105-3901
RECORD OF DECISION
CARSON RIVER MERCURY SITE,
WEST CENTRAL NEVADA
OPERABLE UNIT 1: SURFACE SOIL
March 30, 1995
Printed on Recycled I'apcr
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TABLE OF CONTENTS
~
PART I. DECLARATION. 1
PART II. DECISION SUMMARY. 4
Section 1. Site Description. 4
Section 2. Site History. . 9
Section 3. Enforcement Actions. 10
Section 4. Community Relations Activities. 11
Section 5. Scope and Role of the Response Action. 12
Section 6. Summary of Site Characteristics. 13
Section 7. Summary of Remedial Investigation. 15
Section 8. Summary of Site Risks. 18
Section 9. Comparative Analysis of Alternatives. 30
Section 10. The Selected Remedy. 48
Section 11. Statutory Determinations. . 50
Section 12. Documentation of Significant Differences. 50
References. . 51
PART III. RESPONSIVENESS SUMMARY. 53
Section 1. Written Comments. . 53
Section 2. Comments from January 18, 1995 Public Meeting. 56
Section 3. Comments from January 19, 1995 Public Meeting. 58
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
LIST OF TABLES
Exposure Pathways of Potential Concern.
Hazard Indices for Individuals Living on or Adjacent
to Impacted Areas. .
Hazard Indices for Recreational Land Use In and Around
I mpacted Areas.
Hazard Indices for Consumption of Fish and Waterfowl.
Cancer Risks for Individuals Living on or Adjacent
to Impacted Areas. .
Cancer Risks for Recreational Land Use In and Around
Impacted Areas.
Summary of Risk Assessment Uncertainties. .
Cost Estimates.
22
25
25
26
27
27
28
47
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Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
LIST OF FIGURES
~
Study Area. .
Hydrographic Valleys.
Location 01 Historic Millsites.
Actionable Areas in Dayton.
Actionable Areas in Silver City. .
5
6
19
20
21
CRMS Record of Decision, March 30, 1995
ii
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PART 1. DECLARATION
SITE NAME AND LOCATION
Carson River Mercury Site
Lyon, Storey and Churchill County, Nevada
STATEMENT AND PURPOSE
- This Record of Decision (URODU) presents the selected remedial action for
Operable Unit 1 (UOU-1U) of the Carson River Mercury Site (UCRMSU) which is located
in Lyon, Storey and Churchill Counties, Nevada. This document was developed in
accordance with Comprehensive Environmental Response, Compensation, and
Liability Act of 1980 (UCERCLAU) as amended by the Superfund Amendments and
Reauthorization Act of 1986 rSARA U), 42 U.S.C. Section 9601 et seq., and in
accordance with the National Oil and Hazardous Substances Pollution Contingency
Plan, 40 C.F.R. Section 300 et seq., (UNCpU). This decision is based on the
administrative record for this operable unit.
In a letter to EPA dated March 29, 1995, the State of Nevada, through the
Nevada Division of Environmental Protection (NDEP) concurred with the selected
remedy for this operable unit of the CRMS.
ASSESSMENT OF THE SITE
Actual or threatened release of hazardous substances from this site, if not
addressed by implementing the response action selected in this ROD, may present an
imminent and substantial endangerment to public health, welfare, or the environment.
DESCRIPTION OF THE REMEDY
. The remedial action objective for OU-1 of the CRMS is to reduce human health
risks by reducing direct exposure to surface soils containing mercury at concentrations
equal to or greater than 80 milligrams per kilogram (mg/kg) in residential areas. There
are six areas which are considered actionable based on this cleanup objective: five
residential yards and one ditch rDayton Ditch.).
The selected remedy for the five residential yards is to excavate contaminated
surface soil (estimated to go to a depth of approximately 2 feet below ground surface),
dispose of the soil at a RCRA municipal landfill if the soils do not exceed the TCLP
standards, and restore the excavated areas. Approximately 5000 cubic yards of soil
will be excavated and disposed of as part of this response action. If it is determined
that all or part of the excavated soil exceeds the TCLP standards, then the excavated
soil will either be treated and disposed of at a RCRA municipal landfill or disposed of
CRMS Record 01 Decision, 3/30/95
1
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. at a RCRA hazardous waste landfill. Which of these sub-alternatives that will be used
will depend on which sub-alternative is found to be more cost effective and the
logistics of implementing each sub-alternative.
The selected remedy for the Dayton Ditch is no action. EP A selected no action
for the Dayton Ditch because the health risks for this area are not great enough to
warrant response actions such as capping or excavation and the State of Nevada and
the community expressed opposition to institutional controls (Le., restricting access
with a fence). Although EPA has selected no action for the Dayton Ditch, additional
samples will be collected from the ditch during the remedial design to further evaluate
the level of impact. In the event that EP A determines that some form of remediation is
warranted, then EPA will document this remedy selection in an -Explanation of
Significant Differences (ESD)- or ROD amendment, or the area will be addressed as
part of OU-2.
The response actions for the residential yards address the incidental soil
ingestion exposure pathway which was found to be of potential concern for.
populations near impacted areas. Also found to be an exposure pathway of potential
concern is consumption of fish or waterfowl from the Carson River system. However,
this remedial action is not attempting to address this pathway. Operable unit 2 of the
remedial investigation and feasibility study (-RlfFS-) will evaluate methods to reduce
mercury concentrations in fish and waterfowl.
The major components of the selected remedy include:
.
Excavation of approximately 5000 cubic yards of contaminated soils, disposal at
a RCRA municipal and/or hazardous waste landfill, and restoration of
properties. In the event that subsurface soil (greater than or equal to 2 feet
below ground surface) is impacted and is not addressed, then this alternative
may also include institutional controls; and
Implementation of institutional controls to ensure that any residential
development in present open land use areas known or suspected to be
impacted by mercury includes characterizing mercury levels in surface soils
and, if necessary, addressing impacted soils. These institutional controls will be
referred to as the -Long-term Sampling and Response Plan.-
.
This remedial action addresses a principal risk at the CRMS by removing
contaminants from surface soil, thereby significantly reducing the toxicity, mobility or
volume of hazardous substances in surface soil. This remedial action will reduce the
possibility of human contact with mercury and thereby reduce the human health risks.
CRMS Record of Decision, 3/30/95
2
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STATUTORY DECLARATION
The selected remedy is protective of human health and the environment,
complies with federal State requirements that are legally applicable or relevant and
appropriate to the remedial action, and is cost-effective. This remedy utilizes.
permanent solutions and alternative treatment (or resource recovery) technologies to
the maximum extent practicable. However, because treatment of soils may not occur,
this remedy may not satisfy the statutory preference for treatment as a principal
element of the remedy. Because this remedy will result in hazardous substances
remaining on-site above health-based levels, a five-year review, pursuant to CERCLA
Section 121, 42 U.S.C. Section 9621, will be conducted at least once every five years
after initiation of the remedial action to ensure that the remedy continues to provide
adequate protection of human health and the environment.
~ar ~ -nU~-
Keith Takata
Deputy Director,
Hazardous Waste Management Division
3-~~
Date.
CRMS Record of Decision, 3/30/95
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PART 2. DECISION SUMMARY
This Decision Summary provides an overview of the problems posed by the
Carson River Mercury Site (aCRMsa or the aSitea), the alternatives considered for
addressing those problems which are within the scope of operable unit (aOU-1 a), and
presents the analysis of the remediation alternatives. This Decision Summary also
provides the rationale for the remedy selection and describes how the selected
remedy satisfies the statutory requirements.
1.0
SITE DESCRIPTION
SITE DEFINITION
1.1
The Carson River Mercury Site (CRMS) consists of the portions of the Carson
drainage and Washoe Valley in Northw~stern Nevada which are affected by mercury
released from milling operations during the Comstock Lode. The exact boundaries of
the affected area were not defined as part of this remedial investigation because
knowledge of these boundaries were considered to have little or no influence on the
findings of the risk assessment.
The current definition of the CRMS study area is as follows: sediments in an
approximately 70-mile stretch of the Carson River beginning near Carson City, Nevada
and extending downstream through the Lahontan Reservoir to the terminal wetlands in
the Carson Desert (Stillwater National Wildlife Refuge and Carson Lake); tailing piles,
sediments and soil in Gold Canyon, Sixmile Canyon, and Sevenmile Canyon; and
sediments and soil in Washoe Valley (Figure 1).
This Record of Decision (aRODa) calls for remedial action in Dayton and Silver
City, Nevada. Both Dayton and Silver City are located in Lyon County.
1.2
SITE PHYSIOGRAPHY
The Carson River drainage basin drains approximately 3,980 square miles in
east-central California and west-central Nevada. The Carson River heads in the
eastern Sierra Nevada mountains south of Lake Tahoe and generally flows
northeastward and eastward to the Carson Sink ( Figure 1). The Carson River flows
through a series of generally separate alluvial valleys from the headwaters area to the
Carson Sink. In downstream order, the alluvial valleys passed by the river include
Carson Valley, Eagle Valley, Dayton Plains, Stagecoach Valley, Churchill Valley, and
Carson Desert (Figure 2). Between New Empire and Dayton the river flows through a
narrow, high-gradient stretch along which large ore-processing mills were situated
during the late 1800s. The flow of the river is interrupted west of Fallon by Lahontan
Reservoir, which was constructed in 1915 as part of the Newlands Irrigation Project.
Below Lahontan Dam, flow is routed through a complex network of ditches, drains,
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CARSON RIVER MERCURY SITE
STUDY AREA
WEST CENTRAL NEVADA
LYON
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and canals of the Newlands Irrigation Project. Irrigation return flow eventually
discharges to Carson Lake, the Stillwater Wildlife Refuge, and/or the Carson Sink.
Stream flow in the Carson River above Lahontan Reservoir is highly seasonal.
The major source of water for the Carson River is the winter snowpack in the Sierra
Nevada mountains. Base flow is reached in late summer (August, September, and
October) and flow then increases slightly through the fall and winter (November
through March), until the snowmelt season starts in early spring. Maximum annual
flow typically occurs in April, May and June.
The areal extent of water bodies and wetlands in the Carson Basin is highly
variable, both seasonally and from year to year. This is especially true in the Carson
Desert. For example, between July 1984 and February 1985, following three
unusually wet years, the water surface area of the Carson Sink was approximately
200,000 acres (Rowe and Hoffman, in press), yet by April 1988 (during a second
consecutive drought year) the sink was dry (Hoffman, 1988).
Washoe Valley lies between the Carson Mountain Range and the Virginia
Mountain Range which separates Washoe Valley from the Carson Basin (see Figure
1). There are two water bodies in Washoe Valley, Washoe Lake and Little Washoe
Lake. Most runoff in Washoe Valley drains the eastern slope of the Carson Range.
Franktown and Ophir Creeks provide the bulk of the surface runoff that reaches
Washoe and Little Washoe Lakes. Steamboat Creek, flowing from Washoe Valley,
and Brown's Creek and Galena Creek, comprise the bulk of the surface water
resources for Pleasant Valley.
1.3
CLiMA TE
The climate of the region is dry due to the Drain shadow effectD created by the
Sierra Nevada Mountains which form the western boundary of the region. Average
annual precipitation throughout the Carson River drainage basin ranges from between
25 to 50 inches in the headwaters area in the Sierra Nevada Mountains to between 4
and 5 inches near Lahontan Reservoir and Carson Desert (Twiss et. aI., 1971).
1.4
DEMOGRAPHICS
The Carson River Mercury Site intersects Lyon County, Storey County,
Churchill County, and Washoe County. According to the 1990 census taken by the
Department of Commerce, U.S. Bureau of the Census, the population of the counties
which are intersected by CRMS are as follows: Lyon County (population 20,001),
Storey County (population 2,52~), Churchill County (population 17,938), and the South
Valley of Washoe County (population 4,596). Additional demographic information is
provided in Section 5.0.
CRMS Record of Decision, 3/30/95
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1.5
LAND USE
Historical land use in the Carson River basin was mostly agriculture and mining
in the 1840s and '50s. The mining industry and population in the basin fell rapidly in
the 1880s; however, railroad access to other markets helped promote ranching and
farming. Another change in land use was an increase in irrigated acreage in the
Carson Desert prompted by the impoundment of Lahontan Reservoir in 1915 and the
creation of the Newlands Irrigation Project. Alfalfa is the principal irrigated crop, in
terms of acreage and revenue, in the Newlands Irrigation Project. The estimated
irrigated acreage ranged from 61,000 to 67,000 acres for the Newlands Project during
1980-87 (U.S. Bureau of Reclamation, 1980). Dayton and Churchill Valleys, which
have the smallest populations in the Nevada portion of the Carson basin, are primarily
rangeland, with agricultural areas along the Carson River. Land use and population
remained relatively unchanged in the Carson River basin from 1890 until 1950, with
the advent of suburban development. Since 1950, Carson City, Fallon, and rural
populations have grown considerably with most of the urban and suburban
development occurring on land that was previously used for agriculture (either irrigated
cropland or rangeland). Presently, the local economy and urban land use are
dominated by the retail trade and service sectors, primarily casinos and adjunct
businesses such as hotels, motels, and restaurants that cater to tourists (Nevada
Commission on Economic Development, 1985).
1.6
WATER USE
Major water bodies in the Carson basin include the Carson River, Lahontan
Reservoir, Carson Lake, the Stillwater National Wildlife Refuge, and temporary lakes,
reservoirs, and alkali flats in the Carson Desert. Lahontan Reservoir is the main
storage reservoir for the Truckee Carson Irrigation District (TCID). Uses of surface
water include: (1) agriculture irrigation; (2) maintenance of waterfowl and fishery
habitats; (3) recreational use by the public such as hunting, fishing, birdwatching,
. swimming, and camping; and (4) to a limited extent, municipal and light-industrial
purposes. Public drinking water systems are only supplied by aquifers and not by the
Carson River.
In Washoe Valley there are two water bodies, Little Washoe Lake and Washoe
Lake. Little Washoe Lake is used primarily for recreation. Big Washoe Lake is an
intermittent lake which provides waterfowl and fishery habitats when it contains water,
and provides recreational use for the public. Public drinking water systems are only
supplied by aquifers and not directly by the lakes in Washoe Valley.
CRMS Record 01 Decision, 3/30/95
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2.0
SITE HISTORY
2.1
SITE BACKGROUND
Mining in the Carson River drainage basin commenced in 1850 when placer
gold deposits were discovered near Dayton at the mouth of Gold Canyon. Throughout
the 1850s, mining consisted of working placer deposits for gold in Gold Canyon and
Sixmile Canyon. These ore deposits became known as the Comstock Lode.
The initial ore discovered was extremely rich in gold and silver; gold was more
abundant in Gold Canyon while silver was more abundant in Sixmile Canyon (Smith,
1943). The early mining methods concentrated on exposing as much of the lode as
was possible in wide trenches. Throughout 1859, ore was shipped to San Francisco
for processing. After local ore processing began in 1860, most major mines operated
their own mills, but there were also a large number of private mills. Initial ore
processing techniques were slow and inefficient and a fair amount of trial and error
experimenting went into the development of an effective ore-processing technique.
Refinements were aimed primarily at increasing the speed of gold and silver recovery,
increasing the percentage of gold and silver recovered, and decreasing the amount of
gold and silver discarded in tailings piles. The general milling process employed
before 1900 involved pulverizing ore with stamp mills, creating a slurry, and adding
mercury to the mixture. The mercury forms an amalgam with the precious metals
which is then separated from the solution and retorted. After 1900, cyanide leaching
and flotation processes replaced amalgamation.
Gold and silver production from the Comstock Lode increased slowly during the
early years and 1863 was the first year of large production. Throughout the remainder
of the 1860s and most of the 1870s, production remained high as rich ore bodies
continued to be discovered at progressively deeper depths. The bottom of the lode
was abruptly reached in 1877 at a depth of about 1,650 feet, and 1878 was the first
year of dramatically reduced production. Between 1877 and 1878, ore production.
dropped from 562,519 tons to 272,909
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2.2
HISTORY OF SITE INVESTIGATIONS
Elevated mercury levels in the Carson River drainage basin were discovered in
the early 1970s when sampling conducted by the U.S. Geological Survey (USGS)
revealed elevated levels in river sediment and unfiltered surface water from the Carson
River downstream from pre-1900 ore milling sites (Van Denburgh, 1973). Subsequent
studies by a number of investigators (Richins, 1973; Richins and Risser, 1975;
Cooper, 1983; Cooper et. aI., 1985; Hoffman et. aI., 1990) have further delineated the
extent of mercury in river and lake sediment and water. Based largely on the
information presented in these studies, the Carson River below New Empire was
added to the National Priorities List (NPL) in August, 1990 due to the widespread
occurrence of mercury.
3.0
ENFORCEMENT ACTIONS
Enforcement activities at the CRMS have included issuing orders for the
removal of mercury contaminated tailing piles which were found to pose imminent and
substantial health risks and conducting a comprehensive investigation of potentially
responsible parties (PRPs).
In November, 1990, mercury laden tailings located five miles east of Dayton
and adjacent to U.S. Highway 50 were .excavated and'treated in response to an order
issued by EPA. The Respondents addressed the contamination by excavating
ostensible tailings and taking the material to the Flowery Mine heap leaching facility for
treatment by cyanidation.
In August, 1992, mercury laden tailings located in Dayton, Nevada were
excavated and treated in response to an order issued by EPA. For the area bounded
by U.S. Highway 50 on the east, Douglas Street to the north, and River Road to the
west, the Respondents were ordered to prevent exposure to soil with mercury
concentrations greater that 25 ppm. The Respondents addressed the contamination
by excavating contaminated soil, backfilling withc;elean soil, and taking the
contaminated soil to the Flowery Mine heap leaching facility for treatment by
cyanidation.
As part of the RifFS, EPA conducted a comprehensive investigation of
potentially responsible parties (UPRPsU) for the CRMS. This PRP search included
historical research to determine the locations of Comstock mills, to develop chain-of-
titles for the mills, and to develop general information regarding the operation of the
mills. This information was then used to identify PRPs for the CRMS as well as to
direct OU-1 field investigations. The findings of the PRP search included maps which
describe the locations of 143 historic millsites, identification of 213 entities who had
significant involvement with the Comstock Lode, identification of possible corporate
successors of historic milling companies, and identification of 300 current land owners.
CRMS Record of Decision, 3/30/95
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The identification of corporate successors of historic milling companies is a complex
process and EPA's investigation is not yet complete. Accordingly to date, EPA has
not yet determined whether any existing entities are actual corporate successors who
would be PRPs at the CRMS.
4.0
COMMUNITY RELATIONS ACTIVITIES
There have been extensive community relations activities throughout the course
of this project. Community relations activities for the CRMS have included: setting up
information repositories, issuing fact sheets to the affected communities (Dayton, Silver
City, Virginia City, and Fallon), organizing a technical advisory committee (-TAC-)
made up of local representatives from various State and federal agencies, making
contacts with editors of local newspapers, meeting with county officials, making
presentations at county hearings, making presentations for professional organizations,
conducting public meetings at the outset of the project and at the proposed plan stage,
and speaking with local residents by phone or in person to request property access
and to present sampling results. These community relations activities have provided
for effective dissemination of information throughout the affected communities as well
as for good feedback from the affected communities.
Information repositories were set up to provide public access to the reports
used by EP A for developing a strategy for the RifFS and to access reports produced
by EPA (Le., RifFS). The locations of ttiese information repositories are as follows: .
.
Nevada State Library and Archives
401 N. Carson Street
Carson City, Nevada 89710
.
Dayton Valley Library
Dayton, Nevada 89403
.
Churchill County Library
553 South Maine Street
Fallon, Nevada 89406
Fact sheets were distributed to the members of the affected communities
throughout the course of the project to provide the status of the project and to report
important findings. The fact sheets issued to date are as follows:
.
March 1991, EPA Begins Cleanup of Mercury Contamination;
.
August 1991, EPA Update on the Carson River Mercury Site;
.
September 1992, Carson River Mercury Investigation Continues: Surveying and
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Mapping of Millsites;
.
March 1993, EPA to Begin Field Sampling;
.
November 1994, EPA Announces Sampling Results; and
December 1994, EPA Announces Proposed Plan for Soil.
To date, EPA has conducted two series of public meetings for the CRMS
project. The purpose for the first series of public meetings was to explain why the
region was declared a Superfund site, to describe the Superfund process, and to
present EPA's strategy for conducting the RI/FS. This presentation was made in
Carson City, Dayton, and Fallon, Nevada on March 24, 25, and 26, 1992, respectively.
The purpose for the second series of public meetings was to present the proposed
plan for OU-1. This presentation was made in Dayton and Silver City, Nevada on
January 18 and 19, 1995, respectively.
.
5.0
SCOPE AND ROLE OF THE RESPONSE ACTION
SCOPE OF THE RESPONSE ACTION
5.1
The remedy selected for OU-1 of the CRMS addresses human health risks
associated with direct exposure to surface soil with elevated mercury levels. It is not
within the scope of this response action to address human health and ecological risks
associated with mercury in the Carson River system. Although the human health risks
associated with consumption of fish and waterfowl from the Carson River system were
assessed in the risk assessment for OU-1, response actions to reduce mercury
concentrations in fish, waterfowl and other biota will be evaluated in the RifFS for OU-
2. Thus, the ~,emedy selected for OU-1 is only intended to reduce direct exposure to
mercury contaminated surface soils and not to protect surface water.
The remedial action objective for OU-1 is to address residential areas where
mercury in surface soils is equal to or greater than 80 milligrams per kilogram (mgfkg).
There are five areas in Dayton and one area in Silver City, Nevada where mercury
levels in surface soil exceed this level. These six areas include five residential yards
and one ditch (DDayton Ditch.).
The selected remedy for the five residential yards is to excavate surface soil
(estimated to go to a depth of approximately 2 feet below ground surface), dispose of
the soil at a RCRA municipal landfill if the soils do not exceed TCl? standards, and
restore the excavated areas. If, it is determined that all or part of the excavated soil
exceed TClP standards, then the excavated soil will either be treated and disposed of
at a RCRA municipal landfill or disposed of at a RCRA hazardous waste landfill.
Which of these sub-alternatives to be used will depend on which sub-alternative is
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," ~, ~ ..~ .
..
found to be more cost effective and the logistics of implementing each sub-alternative.
Approximately 5000 cubic yards of soil will be excavated and disposed of as part of
this response action. .
The selected remedy for the Dayton Ditch is no action. EPA selected no action
for the Dayton Ditch because the ~ealth risks for this area are not great enough to
warrant response actions such as excavation or capping and the State of Nevada and
the community do not support addressing the area with institutional controls (Le.,
restricting access with a fence). Although EPA has selected no action for the Dayton
Ditch, additional samples will be collected from the ditch during the remedial design to
further evaluate the level of impact. In the event that EPA determines that some form
of remediation is warranted, then EP A will document this remedy selection in an
"Explanation of Significant Differences (ESD)" for this ROD or the area will be
addressed as part of OU-2.
5.2
ROLE OF THE RESPONSE ACTION
The human health risks assessment established that the exposure pathways of
potential concern for the CRMS are: (1) consumption of fish or waterfowl from the
Carson River system and (2) incidental ingestion of contaminated soil. The role of the
selected remedy is to reduce human health risks by reducing exposure via incidental
ingestion of contaminated surface soil. Based on the human health risk assessment,
this pathway is found to be of potential concern where surface soils contain mercury at
levels equal to or greater than 80 mg/kg.
6.0
SUMMARY OF SITE CHARACTERISTICS
6.1
SOURCES
. Sources of mercury in the Carson drainage basin and Washoe Valley include
mercury imported during the Comstock era and, possibly, naturally occurring mercury.
There is insufficient information to characterize the full extent and significance of
naturally occurring mercury in the Carson drainage basin and Washoe Valley.
However, according to reports which characterize the geology of the Carson River
drainage basin (Thompson, 1956; Bonham, 1969; and Moore, 1969), naturally
occurring deposits of mercury of economic importance do not exist in the basin. Less
significant natural occurrences of mercury can be associated with mineralized zones
and hot springs deposits. Although it is possible that there are such natural
occurrences of mercury in the region, such sources are not considered important
relative to the large amount of mercury imported to the region during the Comstock
era.
Mercury imported to the region during the Comstock era was purchased by
mills for processing gold and. silver ore. These mills employed various processes to
CRMS Record of Decision. 3/30/95
13
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amalgamate gold and silver. All of these processes included pulverizing the ore with
stamps; creating an amalgam by mixing the crushed ore, salt, and elemental mercury
into a slurry; separating the impregnated amalgam; and, finally, separating the gold
and silver from the mercury with a retort. It is estimated that 186 such mills operated
during the Comstock era (Ansari, 1989).
6.2
RELEASE MECHANISMS FROM SOURCES
The most widely used ore-processing method during the Comstock era was the
.Washoe Process. (Smith, 1943). With this process, the raw ore is wet crushed with
stamps, the crushed ore is separated from the slurry in a settling tank and then the
crushed ore is charged with mercury (approximately 10 percent of the weight of the
ore) (Smith, 1943)) in the amalgamation pan. The amalgam is separated from the
slurry and the silver and gold is separated from the amalgam with a retort. It is
thought that the majority of the mercury released to the environment was associated
with tailings which were separated from the amalgam slurry and discharged into the
drainage. Other possible release mechanisms would have included air emissions from
the retort, fugitive air emissions throughout the process, and spilling throughout the
process where mercury was handled. It is estimated that the loss of mercury
exceeded 1 pound for each ton of ore milled which translates to approximately.
14,000,000 pounds of mercury (Smith, 1943).
6.3
TRANSPORT MECHANISMS
Potential migration pathways for mercury through the CRMS include surface
water, groundwater, soil, and air. . Transport mechanisms are as follows:
.
fluvial transport of mercury laden sediment and soil,
fluvial transport of dissolved mercury,
air transport of particulate mercury,
air transport of volatile mercury, and
percolation of elemental mercury and/or amalgam.
.
.
.
.
Fluvial transport is considered the most important mechanism for distributing
mercury throughout the Carson Drainage and Washoe Valley. This is because mill
tailings are considered the most significant release mechanism and this material is
easily transported by fluvial processes. Eolian transport mechanisms may also
account for the widespread dispersion of mercury in the region. The fate and transport
of gaseous mercury emissions to the atmosphere is not well defined, however, it is
believed that gaseous mercury was released to the environment from mills while
operating and that mercury evasion is presently occurring. Also included as a
transport mechanism is percolation which refers to the vertical movement of mercury
through the subsurface. This transport mechanism would account for the vertical
movement of elemental mercury or amalgam that was released to the environment.
CRMS Record of Decision, 3/30/95
14
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~-----
." . . " \ ~/'. - ., '::- ,- .
. .i'
6.4
AREAS OF DEPOSITION AND ACCUMULATION
Areas of deposition and accumulation refers to areas where mercury imported
to the region is presently deposited and potentially accumulating as a result of the fate
and transport mechanisms discussed in the preceding section. For the purpose of
characterizing and assessing human exposure at the CRMS, areas of deposition and
accumulation were broken out and assessed separately. These areas and how they
were defined for the remedial investigation are as follows:
Millsitesrrailing Piles: refers to the locations of the historic millsites and all associated
features (Le., tailing piles, tailing ponds, flumes, etc.) which are recognized as the
original point sources of mercury in the drainage;
Tributaries: refers to the tributaries which drain the Virginia Mountain Range into the
Carson basin and Washoe Valley (Le., Six Mile Canyon, Gold Canyon, etc.,);
Alluvial Fan: refers to the alluvial fan below the mouth of Sixmile Canyon;
Flood Plain: refers to the Carson River floodplain beginning above New Empire and
extending to the terminal wetlands;
Carson River: refers to the main channel of the Carson River beginning above New
Empire and extending to the terminal wetlands;
Lahontan Reservoir: refers to Lahontan Reservoir which has a surface area of
approximately 4,856 acres (EPA, 1977);
Carson Lake: refers to Carson Lake which occupies approximately 5,600 acres
(Hoffman et. aI., 1990);
Stillwater Wildlife Management Area: refers to the Stillwater Wildlife management area
which occupies approximately 9,600 acres during an average water year (Hoffman et.
aI., 1990);
Indian Lakes: refers to the Indian lakes recreation area which have a total surface
area of approximately 549 acres during an average water year (Tuttle, 1992); and
Washoe Lake: refers to the combined area of Little and Big Washoe Lake which have
a combined area of approximately 5,100 acres during a normal water year (Washoe
County, 1992).
7.0
SUMMARY OF REMEDIAL INVESTIGATION
The objectives of this phase of the remedial investigation are as follows:
CRMS Record of Decision, 3/30/95
15
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.
identify the contaminants of potential concern (COPC),
develop data for the human health risk assessment (i.e., estimate exposure
point concentrations for potentially complete exposure pathways), and
characterize mercury levels at and around historic millsites.
.
.
The remedial investigation activities associated with each of these objectives are
described herein.
7.1
IDENTIFY CONTAMINANTS OF POTENTIAL CONCERN
In order to determine if other trace metals occur at levels of concern,
approximately 10% of the soil samples (119 samples) were analyzed for all of the
trace metals included in EPA's -Target Analyte List (TAL)" Contaminants of potential
concern were identified by a two step process. The first step compared the maximum
detected concentration in surface soils with EPA's preliminary remediation goal (PRG).
Those trace metals exceeding their respective PRG were retained for the second step
which compared the arithmetic mean of the concentrations detected at historic millsites
. and extant tailing piles with the estimated background level for the trace metal. If this
mean concentration exceeded the background level, then the trace metal was
identified as a COPC. In addition to mercury, arsenic and lead were identified as
COPCs by this process.
In assessing the hazards from mercury in a particular environment, it is not
enough to know the form in which mercury entered that environment because various
transformations can take place. The major forms of mercury which have been
identified to date are methyl-mercury, elemental mercury, and mercuric mercury. As
part of the effort to identify contaminants of potential concern, soil samples were
analyzed to determine the species of mercury generally occurring in soil. These
results determined that less than 10% of the total mercury in soils is mercuric chloride
or soluble mercury and approximately 90% of the mercury is either mercuric sulfide or
elemental mercury. Mercury occurring in fish and waterfowl was assumed to be 100%
methyl mercury.
7.2
DEVELOP DATA FOR THE HUMAN HEALTH RISK ASSESSMENT
In order to assess human health risks, exposure point concentrations are
determined for the potentially complete exposure pathways. The exposure point
concentration is an estimate of the concentration of the CO PC that is contacted via an
exposure pathway (i.e., ingestion of soil) over a given period of time. In order to
estimate exposure point concentrations, samples were collected from media potentially
affected by mercury (i.e., soil, air and water) in areas where mercury contamination
was suspected to occur. The majority of this environmental sampling was conducted
in Dayton where it was assumed that there are the highest levels of mercury occurring
in a populated area. This assumption was primarily based on the fact that there were
CRMS Record of Decision. 3/30/95
16
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several historic millsites located in and around Dayton. Also, because Dayton is
located at the mouth of Gold Canyon and on the flood plain of the Carson River,
tailings could be deposited in and around Dayton from other upgradient source areas.
Samples were collected from soil, ground water, air, and domestic produce; and
exposure point concentrations were derived from the arithmetic mean and the
associated 95 percent upper confidence limit (95 UCL). If the data set was insufficient
to calculate the 95 UCL, the maximum detected value was used as the exposure point
concentration. In addition to the Dayton area, soil samples were also collected from
Sixmile Canyon, Gold Canyon, the alluvial fan below Sixmile Canyon, the Carson
River flood plain, the beach areas of Lahontan Reservoir, Washoe Lake, and Indian
Lakes; and exposure pOint concentrations were derived to represent the level of
contamination in these areas. Exposure point concentrations were also derived for
muscle tissue from fish and waterfowl using data from Nevada Department of Wildlife,
Nevada Division of Environmental Protection, and United States Fish and Wildlife
Service.
The results of this sampling were used to assess the human health risks for the
entire study area and establish a mercury action level for surface soil. The human
health risk assessment is discussed in Section 8, Summary of Site Risks. The site
specific action level born out of this risk assessment is 80 mg/kg. This action level
identies a soil level that would create a dose for a child (age 1 - 6) equivalent to the
oral reference dose (RfD) for inorganic mercury. This action Jevel takes into account
the species of mercury generally found in the soil matrix (see Section 7.1 ) and the
bioavailability of those species. The bioavailability factor which was used to derive the
site specific action level for mercury is presented in Section 8.1, Exposure
Assessment.
7.3
CHARACTERIZE AND ASSESS HISTORIC MILLSITES
Among the areas where mercury was thought to occur, it was assumed that the
highest levels of mercury would occur at and around historic mil/sites and extant tailing
piles. The basis for this assumption is that there would be minimal dilution caused by
transport. Thus, the remedial investigation included an exhaustive research effort to
identify the Comstock mills and map the millsites. Out of this research, the location of
131 mills were identified and the area of these millsites were mapped (Figure 3). At
each of the millsites, 5 to 25 surface soil samples were collected to evaluate if levels
of mercury, arsenic, and lead were significant. Although subsurface soil was also
sampled at millsites, the main objective was to evaluate whether incidental ingestion of
surface soil was an exposure pathway of concern at the millsites. Surface soil
samples were collected at locations where mercury was thought likely to occur (Le.,
tailing piles, tailing ponds, ruins, etc.,).
The significance of mercury contamination was evaluated by comparing
mercury levels with EPA's site specific Preliminary Remediation Goal (PRG) for soil
CRMS Record of Decision, 3/30/95
17
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which is 25 mg/kg. Sampling areas where there were no sample results greater than
or equal to 25 ppm were screened out of further evaluation. Sampling areas where
there were more than two sampling locations equal to or greater than 25 ppm were
evaluated by defining a subarea with the sampling results equal to or greater than 25
ppm and determine the arithmetic mean using the data included in this subarea.
Subareas were not defined for sampling areas where there was only one or two
samples equal to or greater than 25 ppm, unless the sample(s) could be grouped with
an adjacent subarea. Also, if two adjacent samples were equal to or greater than 25
ppm, a line between the two points was buffered to create a subarea. Using the site
specific action level of 80 mg/kg, these areas were assessed. Through this process, 6
subareas of potential concern were identified and are described in Figures 5 and 6.
8.0
SUMMARY OF SITE RISKS
The data from the remedial investigation was used to assess human health risk
following the procedures described in the Risk Assessment Guidance for Superfund,
Volume I, Human Health Evaluation Manual (Part A), Interim Final, EPA/540/1-89/002,
December 1989 (BRAGS.).
8.1
EXPOSURE ASSESSMENT
The purpose for the exposure assessment is to characterize and evaluate the
significance of potentially complete exposure pathways. A complete exposure
pathway includes the following four elements: "1 ) a source and mechanism of chemical
release, 2) retention or transport medium, 3) a point of human contact or exposure
point, and 4) an exposure route (Le., ingestion, inhalation, or dermal contact) at the
contact point. Exposure pathways that were evaluated for the COPCs are described
in Table.1.
CRMS Record of Decision, 3/30/95
18
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HISTORIC COMSTOCK MILL LOCATIONS
STOREY - LYON COUNTY, NEVADA
~
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. Dayton
. Silver City
. Gold Canyon
. Carson River
. Virginia City
. Gold Hill
. American Flat
. Sixmile Canyon
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FIGURE 3
-------
ACTIONABLE AREAS
DAYTON
o
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FIGURE 6
-------
TABLE 1: Exposure Pathways Evaluated for the Contaminants of Potential
Concern
Contaminant 01 Potential Concern
Exposure Pathway Mercury Arsenic Lead
Incidental soil ingestion yes yes yes
Incidental sediment ingestion yes yes no
Incidental surface water yes yes no
ingestion
Ground water ingestion yes yes yes
Fish consumption yes no no
Waterfowl consumption yes no no
Air inhalation yes yes yes
Ingestion of ground water, surface water and sediment were screened out of
the exposure assessment because the COPCs were detected at relatively low levels in
these media. The other exposure pathways were evaluated by estimating the chronic
daily intake (CDI) of the COPCs for each pathway. The CDI is determined by
multiplying the exposure point concentration by the intake factor for that medium.
The estimated CDI of mercury and arsenic via incidental soil ingestion was
adjusted to reflect the degree to which metal species are available for absorption
following ingestion. The estimated CDI of mercury via incidental soil. ingestion was
multiplied by 0.28 to reflect the degree to which mercury species are available for
absorption following ingestion. Based on mercury species data developed for the
CRMS, it was assumed that approximately 90% of the mercury in soil is mercuric
sulfide (HgS) and 10% is mercuric chloride (HgCI2). This was considered a
conservative assumption given that the mercuric chloride component was generally
less than 10%. Using 15% as the oral absorption value for mercuric chloride and 3%
for mercuric sulfide, an oral absorption factor of 0.28 was derived «3/15 x 0.90) +
(15/15 x 0.10) = 0.28). The estimated CDI of arsenic via incidental soil ingestion was
multiplied by 0.80 to reflect the degree to which arsenic is assumed to be available for
absorption.
8.2
TOXICITY ASSESSMENT
The toxicity assessment weighs available evidence regarding the potential for
CRMS Record of Decision, 3/30/95
22
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particular chemicals to cause adverse effects in exposed individuals (weight-of-
evidence), and quantitatively characterizes the relationship between the extent of
exposure to an agent and the increase likelihood and/or severity of adverse effects
(dose-response assessment).
The toxicity assessment evaluates noncancer effects using reference doses
(RfD) as numeric indicators of toxicity. The RfD is an estimate (with uncertainty
spanning perhaps an order of magnitude or greater) of a daily exposure level for the
human population, including sensitive subpopulations, that is likely to be without an
appreciable risk of deleterious effects during a lifetime. The oral RfD which was used
to evaluate exposure via ingestion to both inorganic and organic mercury is 0.3 ug/kg-
day. Because there is an ongoing debate as to whether the RfD for methyl mercury is
sufficiently health protective for unborn or young children in critical stages of
development, this RfD was not used to evaluate exposure via fish consumption for
children and pregnant or nursing mothers. The reference concentration (RfC) used to
evaluate exposure to mercury via inhalation is 0.3 ug/m3. The oral RfD which was
used to evaluate exposure to arsenic via ingestion is 0.3 ug/kg-day. The RfDs and
RfC were obtained from the Integrated Risk Information System (IRIS) updated
through June 1993 and the Health Effects Assessment Summary Tables (HEAST)
updated through March 1993.
EP A withdrew the established RfD for lead in 1989. This was done because 1)
there is not a discernible threshold for health effects related to lead exposure and 2)
there are numerous environmental sources of lead which have to be considered in
estimating lead exposure. In lieu of the RfD, it was determined that blood levels,
which can be correlated with toxic effects, provide the best index for evaluating lead
exposure. The blood lead Alevel of concernA is 10 ug/dL.
The toxicity assessment evaluates cancer effects based on the assumption that
cancer can occur at any exposure level (Ano-threshold-). EPA use the linear
multistage model for extrapolating cancer risks from high dose levels, where cancer
responses can be measured, to relatively low dose levels, which are of concern in the
environment. This dose-response extrapolation is known as a cancer slope factor
(CSF) which is used to estimate lifetime cancer risks associated with chronic low-level
exposures to contaminants. The CSFs were also obtained from the Integrated Risk
Information System (IRIS) updated through June 1993 and the Health Effects
Assessment Summary Tables (HEAST) updated through March 1993.
8.3
RISK CHARACTERIZATION
Risk characterization combines the exposure and toxicity assessments to
produce quantitative estimates of risk from the chemicals of potential concern. EPA
evaluated the noncancer and cancer health risks associated with each of the complete
exposure pathways.
CRMS Record of Decision, 3/30/95
23
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Estimates of noncancer health risks are calculated by dividing the estimated
chemical-specific CDI (ug/kg-day) by the respective RfD (uglkg-day). This ratio is
referred to as a uHazard Quotient (HQ = CDIIRfD). U The sum of HQs for multiple
chemicals and pathways is the UHazard Index (HI).u EPA suggests that a HI greater
than one indicates that the associated exposure scenario has a potential to result in
adverse noncancer health effects and additional evaluation may be necessary.
Although the potential for adverse health effects increases as the HI value increases,
the level of concern does not increase linearly. This is because RfDs do not have
equal accuracy or precision and are not based on the same severity of toxic effects.
Noncancer health risks associated with lead are quantitatively characterized
with the EPA Lead Uptake/Siokinetic Model, Version 0.5 (.USK ModeID). The USK
model was designed to estimate the blood lead levels in children ° to 6 years of age,
based on multi-media lead exposures. The model accounts for the potential
environmental and maternal sources of lead (air, diet, drinking water, dust, soil, and
the lead concentration in the mother's blood during gestation) for which numerous
fundamental assumptions are used.
Cancer risks which are described as the incremental probability that an
individual will develop cancer in their lifetime are estimated by multiplying the
estimated chemical-specific CDI by the respective cancer slope factor (CSF). The
cancer risk range of 10-4 to 10-6 is established as generally acceptable by EPA. In
other words, the probability that one additional person out of 10,000 to 1,000,000
could develop cancer as a result of their exposure isconsidered an acceptable risk.
The estimated His and probability of cancer risks are summarized in Tables 2
through 6.
8.4
UNCERTAINTY ASSESSMENT
It must be recognized that the assessment of cancer risks and noncancer
hazards by available (generally indirect) methods can provide only crude estimates of
risk and this should be borne in mind in making regulatory decisions about permissible
exposure concentrations in environmental media.
EPA evaluated the uncertainty of the risk assessment and identified elements of
the risk assessment that would tend to overestimate or underestimate potential
exposure and risk to individuals within the study area. Risk uncertainties specific to
this HHRA are summarized in Table 7.
CRMS Record of Decision, 3/30/95
24
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TABLE 2: Estimated Hazard Indices for Individuals Living On or Adjacent to
Impacted Areas
Exposure Contaminant Typical Estimate1 High-end
Pathway Estimate2
Soil Ingestion3 Mercury 0.09 2.80
Arsenic 0.05 1.23
Dust and/or Vapor Mercury 0.10 0.38
Inhalation Arsenic 0.002 0.007
Consumption of Mercury 0.40 0.80
Domestic Produce
Hazard Index 0.64 5.22
1. Typical estimate is for an adult.
2. High-end estimate is for a young child «6 years).
3. Chronic daily intake (CDI) was estimated based on mercury levels measured in
surface soil at the MS004 sample area in Dayton.
TABLE 3: Estimated Hazard Indices for Recreational Land Use In and
Around Impacted Areas
Exposure Contaminant Typical Estimate 1 High-end
Pathway Estimate
Soillngestion2 Mercury 0.01 0.24
Arsenic 0.002 0.10
Dust and/or Vapor Mercury 0.002 0.016
Inhalation Arsenic 0.00003 0.0003
Hazard Index 0.01 0.36
1. Both the typical and high-end estimates are for a school age child (7 - 18 years
of age).
2. Chronic daily intake (CDI) was estimated based on mercury levels measured in
surface soil
at the TP007 sample area in Sixmile, Canyon.
-------
TABLE 4: Estimated Hazard Indices for Consumption of Fish and Waterfowl
Indicator SpecieslLocation Contaminant Typical High-end
Estimate1 Estimate
White Bass/Carson River Above Mercury 3.5 6.5
Lahontan
Walleye/Lahontan Reservoir Mercury 2.6 4.9
White Bass/Carson River Below Mercury 1.1 2.1
Lahontan
White Bass/Indian Lakes Mercury 2.2 4.1
White BasslWashoe Lake Mercury 0.6 1.2
Shovelers/Carson Lake Mercury 1.4 2.0
Shovelers/Stillwater Mercury 0.5 0.8
Mallards/Carson Lake Mercury 0.3 0.6
Mallards/Stillwater Mercury 0.2 0.5
1. Both typical and high-end estimates are for an adult.
CRMS Record of Decision, 3/30/95
26
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TABLE 5: Potential Cancer Risks for Individuals Living On or Adjacent to
Impacted Area
Exposure Contaminant Typical Estimate1 High-end
Pathway Estimate
Soil Ingestion2 Arsenic 3 E-6 4 E-5
Dust and/or Vapor Arsenic 1 E-6 4 E-6
Inhalation
Cancer Risk 4 E-6 4 E-5
1. Both the typical and high-end estimates are for an adult (life-time resident).
2. Chronic daily intake (CDI) was estimated based on arsenic levels measured in
surface soil
in Dayton.
TABLE 6: Potential Cancer Risks for Recreational Landuse in Impacted
Areas
Exposure Contaminant Typical Estimate High-end
Pathway Estimate
Soil Ingestion2 Arsenic 4 E-8 1 E-5
Dust and/or Vapor Arsenic 2 E-8 2 E-7
Inhalation
Cancer Risk 6 E-8 1 E-5
1. Both the typical and high-end estimates are for a school-age child (7 - 1 8
years).
2. Chronic daily intake (CDI) was estimated based on arsenic levels measured in
surface soil
in Sixmile Canyon.
CRMS Record of Decision, 3/30/95
27
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TABLE.7: Summary of Site Specific Uncertainties Associated with Risk Estimates
Uncertainty Factor Effect of Uncertainty Comment
Exposure point concentrations used for May over- or underestimate risk Exposure point concentrations used for volatile mercury were derived from the
volatile mercury. method detection limit and were not actually measured. Therefore, levels of volatile
mercury In Indoor and ambient air may actually be more or less than the exposure
point concentration.
Exposure point concentrations for mercury May overestimate risk Exposure point concentrations used to evaluate Incidental ingestion 01 soil on the
levels in surface soil on the alluvial fan. alluvial fan were derived from a data set which Included samples from the area of
transport where tailings from Slxmile Canyon are deposited. Current residential
areas on the alluvial fan are north of the area of transport. Mercury levels
measured in samples collected from current residential areas did not exceed 25
mg/kg.
Exposure point concentrations for mercury May overestimate risk Exposure point concentrations used to evaluate Incidental Ingestion of soil on the
levels in surface soil on the flood plain. flood plain were derived from the highest concentrations detected on the flood
plain. The 95 UCL for all of the samples collected from the flood plain (18.20
mg/kg) is a factor of 20 less than the value used to estimate the high-end risks for
this scenario.
Use of an indicator species to estimate May overestimate risk To the extent that the actual diets include lesser contaminated fish and waterfowl,
mercury exposure associated with the Indicator species approach used In this HHRA is likely to overestimate
consumption of fish and waterfowl. exposures.
Arsenic which was identified in tailings and May underestimate risk Arsenic can also be taken up by plants.
at historic millsltes was not measured In
fruit and vegetables.
Cancer slope factors for arsenic May overestimate risks Slope factors are based on a 95th percent UCL derived from a linearized model.
Considered unlikely to underestimate risks.
Cancer risk estimates assume there is no May overestimate risks Possibility that some threshold exists.
threshold.
Reference doses (RfDs) for mercuric May over- or underestimate risks Extrapolation from an animal to human may induce error because of dillerences in
mercury are derived from animal studies. absorption, pharmacokinetics, target organs, enzymes, and population variability.
CRMS Record of Decision, 3/30/95
28
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~. .... .
8.5
ECOLOGICAL RISK ASSESSMENT
The ecological assessment for the CRMS is presently ongoing and the results
of this study will be presented in the remedial investigation report for OU-2. The focus
of this study is to assess the severity of ecological risks and impacts associated with
mercury in the Carson River system. Mercury is unique among metals in its tendency
to bioaccumulate and biomagnify in higher trophic levels. Bioaccumulation most
readily occurs in aquatic environments where mercury is methylated and then either
ingested or absorbed by aquatic organisms. This ecological assessment is most
concerned with the diversity of wildlife which are supported by the Carson River
watershed and are part of the aquatic food chain. In particular, the Lahontan
Reservoir and wetland areas below Lahontan Dam provide significant habitat for large
populations of migrating and resident water birds.
The outcome of this ecological assessment will be an understanding of how
severely wildlife are impacted or threatened by the present levels of mercury in the
Carson River system as well as an understanding of what factors regulate mercury
cycling in the Carson River system. This information will provide the basis for
evaluating methods to reduce mercury concentrations in fish, waterfowl, and other
biota. If there is any evidence that current loading from point and diffuse sources will
achieve this end, then further soil remediation may occur to reduce loading. At this
time, the only remedial action objective is to reduce direct human exposure to mercury
contaminated surface soil.
8.6
RISK ASSESSMENT CONCLUSIONS
The conclusions of the HHRA for the CRMS are as follows:
.
The contaminants of potential concern (COPCs) for the CRMS are mercury,
arsenic and lead. Mercury was imported to the region during the Comstock era
(1859 - 1900) to process ore. Although mercury is also naturally occurring in
the region, such sources are not considered important relative to the large
amount of mercury imported to the region during the Comstock era. Arsenic
and lead are naturally occurring trace metals in the region which were
concentrated in the environment by natural and anthropogenic processes.
.
The highest concentrations of the COPCs are found at and around historic
millsites and extant tailing piles. The COPCs also occur in areas where
discharged tailings and other eroded material from historic millsites have come
to be deposited. These areas include: the alluvial fan below Sixmile Canyon,
the flood plain of the Carson River below New Empire, the active channel of the
Carson River below New Empire, Lahontan Reservoir, Carson Lake, Stillwater,
Indian Lakes and Washoe Lake.
CRMS Record of Decision, 3/30/95
29
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.
Although the soil ingestion pathway is important for all of the COPCs, the
significance of this pathway varies according to the land use (Le., residential,
occupational and recreational) and according to the concentration of the COPC
in surface soil. For residential land use, mercury was detected in surface soil
at levels which translate into a HI>1 for a young child « 6 years of age). For
recreational or open land use areas (Le., Brunswick, Sixmile Canyon, Gold
Canyon, Lahontan Reservoir, Indian Lakes, and Washoe Lake beach areas),
none of the COPCs were found to occur in surface soil at levels which are
considered significant for this exposure pathway.
.
Inhalation of airborne contaminants does not appear to be an exposure pathway
of concern for any of the COPCs irrespective of the land use scenario (HI<1).
.
Ingestion of ground water does not appear to be an exposure pathway of
concern for any of the COPCs.
.
Incidental ingestion of surface water and sediment while swimming does not
appear to be an exposure pathway of concern for any of the COPCs.
.
Consumption of produce grown in contaminated soil was found to be a
complete exposure pathway for mercury. However, this pathway does not
appear to be of concern (HI<1). .
.
Individuals who consume fish or waterfowl from the Carson River system should
be cautioned that the risks are proportional to the amount and type of fish and
waterfowl consumed. Using an indicator species approach, typical HI estimates
for selected indicator species were found to exceed 1 for the consumption of
white bass from the Carson River above and below Lahontan Reservoir and
Indian Lakes; and for consumption of walleye from Lahontan Reservoir. Also
using an indicator species approach, typical HI estimates were found to exceed
1 for the consumption of shovelers from the Carson Lake area. Because fish
and waterfowl from the Carson River system are contaminated with mercury, it
is recommended that pregnant or nursing mothers and young children « 6
years) not consume fish or waterfowl from this drainage.
9.0
COMPARATIVE ANALYSIS OF ALTERNATIVES
This section presents the comparative analysis of the remediation alternatives
considered to prevent incidental ingestion of surface soils where mercury levels in
surface soil exceed 80 mg/kg in existing residential areas. This comparative analysis
is a summary of the Feasibility Study Report for the Carson River Mercury Site
prepared by Ecology and Environment, Inc., and dated December 20, 1994 ("FS").
The purpose for the FS was to identify, screen and evaluate remedial alternatives to
achieve the remedial action objective for OU-1 .
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. ~":"?'\~I~~"':: .~'.,':)::;:'
!'~. ~i" j'J" 'j .. .. '.: :" . .
9.1
DESCRIPTION OF REMEDIATION ALTERNATIVES
The basic remediation alternatives which were considered in the FS are as
follows:
.
No Action
Institutional Controls
Capping
Ex-situ stabilization
In-situ stabilization
Ex-situ treatment/Land Disposal
.
.
.
.
.
With exception for Alternative 1, the FS identified numerous methods and technologies
for each of these alternatives. For example, as part of Alternative 5, eight different
remediation technologies were identified for treating mercury contaminated soil.
Different methods and technologies were also identified for institutional controls,
capping, excavation, disposal, restoration, and containment. All of these technologies
and methods were screened according to effectiveness, implementability, and cost in
order to limit the number of alternatives which were further evaluated in the detailed
analysis.
The alternatives that were retained through this screening process and were
evaluated in the detailed analysis are as follows:
Alternative 1- No Action
The uNo Actionu alternative serves as a baseline for comparing other remedial
alternatives. Under the this alternative, the areas of concern are neither addressed by
engineering measures nor institutional controls. Thus, there are no costs associated
with this alternative.
Alternative 2 - Institutional Controls
Institutional controls are measures to protect public health by controlling access
to the areas of concern but not by physically addressing the impacted surface soils.
The types of institutional controls that were considered for the current areas of concern
include deed restrictions, posting signs, and erecting fences.
Alternative 3 - Capping
This alternative consist$ of paving over the surface soil to prevent exposure to
the soil. As necessary, soil would be excavated to make space for paving, but as
much soil as possible would be left in place. The excavated soil would be transported
to an off-site landfill for disposal. Equipment required for excavation would include
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backhoes, loaders and hand tools.
Paving would consist of covering exposed soil with asphalt or concrete. In
order to ensure the integrity of the cap, annual inspection of the paved areas would be
required so that cracks and other breaks could be repaved. Site restoration would
consist of replacing fences and other structures to the extent possible. However, trees
and vegetation would not be replaced in the capped areas.
As part of this alternative, deed or construction restrictions might also be
required to prevent disturbance of subsurface mercury remaining onsite, and/or to
require health and safety measures for the protection of onsite workers and residents
during any future subsurface construction. If such restrictions are necessary, then the
specifics of the restrictions would be determined as part of the remedial design.
Alternative 4 - Excavation and Off-Site Land Disposal with or without Treatment
This alternative, which is the remedial alternative that EP A is selecting in the
ROD, includes options for disposing of some or all of the contaminated soil at a
municipal landfill, and ex-situ treatment if warranted by the total mercury levels at
specific locations. Whether excavated soil will require treatment before disposal
depends on whether these soils exceed the mercury standards for the toxicity
characteristic leachate procedure (TCLP) set forth in 40 C.F.R. ~ 261.241. If TCLP
tests determine that certain portions of the excavated soils exceed the TCLP
standards ( 0.2 mg/I), then those excavated soils which exceed the TCLP standard will
receive ex-situ treatment before disposal at a RCRA municipal landfill or, alternatively,
will be taken to a RCRA hazardous waste landfill. However, if the excavated soils do
not exceed the TCLP standard, then excavated soils will be disposed of at a RCRA
municipal landfill without treatment. Based on data developed as part of the remedial
investigation, excavated soils are not expected to exceed the TCLP standard.
In the event that treatment is required before disposal at a municipal landfill,
then this alternative sets forth. performance standards for treatment in lieu of a specific
treatment alternative. Thus, if treatment is found to be necessary, then any technology
that meets the prescribed performance standards can be employed. The performance
standards that would be applied to a treatment technology are set forth in the Nevada
Bureau of Mining Regulation and Reclamation Guidance Document for Alternate Use
of Mine Waste Solids-Disposal Outside of Containment, dated May 3, 1994. This
1 As discussed further in Section 8.2.2 below, EPA has determined that the wastes being
remediated at the CAMS are exempt from the definition of hazardous waste under Section
3001(b)(3)(A)(ii), and 40 C.F.R. ~261,4(b)(7), (the "Bevill amendment" provision). Nevertheless, EPA
has determined that, based on certain guidance from the Nevada Bureau of Mining and on public
health considerations, contaminated soils that exceed TCLP standards should not be disposed of in a
municipal landfill without treatment.
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document prescribes criteria for evaluating if material is acceptable for alternate uses.
Based on the FS, the technologies that would most likely be used for treating
contaminated soil are either gravity separation or a conventional mining technology
(i.e., cyanidation). .
In the event that the excavated soil does not exceed the TClP standard, then
this alternative involves excavation of surface soil, disposal at a municipal landfill, and
restoration of excavated areas. Both alternatives involve excavation of contaminated
surface soil (estimated to go to depth of approximately 2 feet below ground surface),
and site restoration. Site restoration would involve returning the affected area to pre-
excavation conditions which may include replacing fences, structures, and vegetation.
Potential institutional controls would be the same as described for Alternative 3.
Long-term Sampling and Response Plan
With exception for Alternative 1, certain institutional controls were considered to
be an additional part of each of the described alternatives. These institution controls,
which will be known as the 'long-term Sampling and Response Plan,. are to manage
impacted areas that will not be remediated as part of this operable unit. The FS did
not evaluate remediation alternatives for impacted areas in Sixmile Canyon and
adjacent to the Carson River between New Empire and Dayton because these areas
do not pose health risks with the current land use (non-residential). In the event that
residential development is proposed in these areas or other areas where mercury
levels may exceed 80 mg/kg, then certain procedures described in the long-term
Sampling and Response Plan will be followed.
The long-term Sampling and Response Plan will set forth specific sampling
guidelines for characterizing mercury levels in surface soils and for addressing
impacted areas. The areas where any residential development will be subject to the
guidelines prescribed in this plan are generally described as follows:
Sixmile Canyon - Refers to the tributary of the Carson River that begins near Virginia
City in the Virginia mountain range and meets the Carson River approximately five
miles east of Dayton. The segment of concern is the canyon which begins just below
Virginia City and extends to the mouth of the canyon just above the alluvial fan.
Alluvial Fan - Refers to the alluvial fan below the mouth of Sixmile Canyon. The fluvial
channels extending across the fan from the mouth of Sixmile Canyon to the Carson
River confluence are the areas of concern.
Brunswick Canyon - Refers to the Carson River flood plain between New Empire (the
Mexican Mill) and Dayton.
Carson River Flood Plain Above Lahontan Dam - Refers to the Carson River flood
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I-
I
plain extending between Dayton and Lahontan Reservoir.
Carson River Flood Plain Below Lahontan Dam - Refers to the flood plain of the South
Branch of the Carson River beginning below Lahontan Dam and extending to Carson
Lake.
In instances where residential development is proposed within these defined
areas, Nevada Division of Environmental Protection (NDEP) will provide the interested
parties with the Long-term Sampling and Response Plan Guidelines. The guidelines
will provide specific instructions for sampling an area to assess mercury levels in
surface soils, instructions for interpreting and reporting results, instructions for follow-
up sampling, and instructions for addressing impacted areas.
The Long-term Sampling and Response Plan Guidelines will be developed by
EP A as part of the remedial design for this operable unit. The guidelines will be
administered through NDEP's Bureau of Corrective Actions. However, development
within the boundaries of the specified areas will be monitored through NDEP's Bureau
of Water Pollution Control which reviews sewerage facility plans for new developments
made up of five or more subdivisions. For smaller developments, the county planning
offices will notify NDEP of proposed developments and NDEP will contact the
developer. The Long-term Sampling and Response Plan does not provide for NDEP
to enforce the implementation of the guidelines. Rather, NDEP will notify EPA of any
recalcitrant parties and EPA will have the discretion of using the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA), Sections 104
and 106 authorities to enforce compliance with the guidelines..
9.2
DETAILED ANALYSIS OF ALTERNATIVES
This section provides an explanation of the criteria used to select the remedy,
and the analyses of the remedial action alternatives in light of those criteria,
highlighting the advantages and disadvantages of each of the alternatives.
9.2.1 CRITERIA
The alternatives were evaluated using nine criteria. These criteria, which are
listed below, are derived from requirements contained in the National Contingency
Plan (NCP), 40 C.F.R. ~ 300 et seq. and CERCLA Section 121(b) and 121 (c).
Overall Protection 0' Human Health and the Environment - The assessment against
this criterion describes how the alternative, as a whole, achieves and maintains
protection of human health and the environment.
Compliance with ARARs - The assessment against this criterion describes how the
alternative complies with ARARs as well as any advisories, criteria, and guidance that
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the lead and support agencies have agreed are Uto be considered..
Long-term Effectiveness and Permanence - The assessment of alternatives against
this criterion evaluates the long-term effectiveness of alternatives in maintaining
protection of human health and the environment after response objectives have been
met.
Reduction of Toxicity, Mobility, and Volume Through Treatment - The assessment
against this criterion evaluates the anticipated performance of the specific treatment
technologies an alternative may employ.
Short-term Effectiveness - The assessment against this criterion examines the
effectiveness of alternatives in protecting human health and the environment during
the construction and implementation of a remedy until response objectives are
attained.
Implementability - This assessment evaluates the technical and administrative
feasibility of alternatives and the availability of required goods and services.
Cost - This assessment evaluates the capital and operation and maintenance (O&M)
costs of each alternative.
State Acceptance - This assessment reflects the State's (or support agency's)
apparent preferences among or concerns about alternatives.
Community Acceptance - This assessment reflects the community's apparent
preferences among or concerns about alternatives.
9.2.2 APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS
(ARARS)
Section 121 (d) of the Comprehensive Environmental Response, Compensation
and Liability Act (CERCLA), 42 U.S.C. Section 121 (d) requires that remedial actions at
Superfund sites comply with all the requirements of Federal or State environmental or
facility siting laws, which are known in the Superfund program as Applicable or
Relevant and Appropriate Requirements (ARARs).
This section summarizes the Federal and State statutes and regulations which
EPA has determined are the ARARs for the selected remedial alternative for OU 1 of
the CRMS.
Definition of ARARs
ARARs are defined as standards or requirements that are found to be either
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Napplicablea or arelevant and appropriate a to the conditions and circumstances found at
the site. Guidance for identifying ARARs may be found in the National Contingency
Plan (55 Fed. Reg. 8741 et. seQ. March 8 1990) and CERCLA Compliance With Other
Laws Manual. Part I. Overview of RCRA Clean Water Act and Safe Drinking Water
Act, OSWER Directive 9234.1-01 (August 1988) and CERCLA Compliance with Other
Laws Manual Part II Clean Air Act. State Requirements and Other Environmental
Statutes. OSWER Directive 9234.1-02 (August 1989). .
"Applicable. requirements are defined as those cleanup standards of control, and other
substantive environmental protection requirements, criteria or limitations promulgated
under Federal or State law that specifically address or regulate a hazardous
substance, pollutant, contaminant, remedial action, location or other circumstance at a
Superfund site. . a Applicability. implies that the remedial action or the circumstances at
the site satisfy all of the jurisdictional prerequisites of a requirement.
"Relevant and Appropriate" requirements are defined as those standards of control,
and other substantive environmental protection requirements, criteria or limitations
promulgated under Federal or State law, that, while not .applicablea to a hazardous
substance, pollutant, contaminant, remedial action, location or other circumstance at a
CERCLA site, address problems or situations sufficiently similar to those encountered
at the CERCLA site that their use is well suited to the particular site or to the remedial
action alternatives. For example, requirements may be relevant and appropriate if
they would be "applicable" but for jurisdictional restrictions associated with the
requirement.
In addition to legally binding laws and regulations, EPA or the State may
identify other non-promulgated advisories, criteria or guidance as aTo Be Considered~
requirements (TBCs). If no ARARs address a particular situation, or if existing ARARs
do not ensure protectiveness, then advisories, criteria or guidelines are to be
considered (TBCs) to set cleanup goals. If such an advisory, criterion or guideline is
selected in the ROD, then it becomes a requirement that the remedial action must
meet.
Section 121 (e) implicitly states that no Federal, State, or local permits
(administrative requirements) are required for remedial actions conducted entirely on
site. However, these on-site remedial actions must meet the substantive requirements
of ARARs. Any action which takes place off-site, however, is subject to the full
requirements of Federal, State, and local regulations. Requirements which are
applicable to offsite actions are not ARARs and are not -frozena at the time the ROD
is signed. Rather, all requirements--whether substantive or administrative--which exist
at the time of the offsite action. must be met.
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._~--~. -.------- .~-;-.-
',-- "
- -; .-..-.
State Requirements as ARARS
Under CERCLA, all Federal requirements may be ARARs for a particular site;
State requirements may be considered ARARs provided that they are:
- Promulgated standards, with full weight of law;
- More stringent than Federal requirements;
- Identified to EPA in a timely manner;
- Found not to result in a statewide prohibition on land disposal; and
- Consistently applied statewide.
ARAR Categories
ARARs have been divided into three categories: (1) chemical-specific. (2)
location-specific, and (3) action-specific requirements. Not all requirements fall neatly
into these categories; some requirements may overlap and encompass more than one
category. The three categories are defined as follows:
Chemical-specific requirements are usually health or risk-based numerical values or
methodologies that set limits on concentrations of specific hazardous substances,
pollutants and contaminants that may be found in, or allowed to discharge into, the
environment.
Action-specific ARARs are technology or activity-based requirements which set
limitations on actions taken with respect to removal, treatment or disposal of
hazardous substances.
Location-specific requirements set restrictions on concentrations of contaminants or
conduct of activities solely because they occur in a special location. These ARARs
relate to the geographic or physical location of the site, such as in a wetland,
floodplain, wildlife reserve or historic site.
The legal requirements determined to be ARARs for the remedial action
selected in this ROD are as follows:
Chemical-specific requirements
Nevada Contaminated Soil and Ground Water Remediation Policy, June 25, 1992.
There are no promulgated Federal or Nevada. regulations which govern soil
cleanup levels for the type of remedial action selected in this ROD. However, the
Nevada Contaminated Soil and Ground Water Remediation Policy, although not
promulgated, contains soil cleanup standards that have previously been identified as
"to be considered. II After further review, and in the absence of other promulgated
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standards, EP A has determined that the cleanup standards in this policy should apply
to the remedial action selected in the ROD.
The intent of this policy is to provide a rational and concise process for
determining remediation standards for soil and ground water. Section A.S of the policy
recommends particular cleanup levels in cases where ingestion or dermal exposure is
of primary concern and groundwater has not been impacted nor is expected to be.
For the COPCs at the CRMS, the cleanup levels are as follows:
mercury
arsenic
lead
20 mg/kg
80 mglkg
no standard
Section C of the policy states that site specific cleanup levels may be used in
place of those set forth in the policy if the site specific levels are developed according
to a scientifically valid risk assessment. For the CRMS, EPA performed a human
health risk assessment and developed a surface soil standard for mercury of 80 mg/kg
based on this risk assessment. Thus, this standard will be used in lieu of the cleanup
level recommended in the policy. EPA did not develop a site specific standard for
arsenic; therefore, the cleanup level recommended in the policy is pertinent and will
be followed.
Nevada Bureau of Mining Regulation and Reclamation Guidance Document for
Alternate Use of Mine Waste Solids-Disposal Outside of Containment dated May
3, 1994.
This guidance document describes the types of tests (Le., Toxicity
Characteristic Leaching Procedure, EPA Method 1311) and the respective criteria
which should be used to determine if mine waste solids are acceptable for alternate'
uses. Under the selected remedy, if any excavated soils exceed TCLP levels, then
the soils will undergo treatment. The purpose for this guidance is to ensure that mine
wastes, particulary spent heap leach material, is not placed in unmanaged disposal
facility (Le., without a liner, monitoring system, etc.,) unless certain prescribed tests,
including TCLP, demonstrate that metals are not mobile or leachable and that the'
material will not generate acid drainage. Although not promulgated, EP A has
previously identified this guidance document as ato be considered. a After further
review, and in the absence of other promulgated standards, EPA has determined that,
in the event any of the wastes are treated, the test procedures and criteria set forth in
this policy should apply. Also according to this guidance, EPA has determined that if
any portion of the excavated material does not meet TCLP standards, then the
material must be treated before disposal at a RCRA municipal landfill or the material
must be disposed of at a RCRA hazardous waste landfill.
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Action-specific Requirements
Discussion of the Resource Conservation and Recovery Act.
EPA has determined that requirements relating to hazardous waste under the
Resource Conservation and Recovery Act (RCRA), Subtitle C, 42 U.S.C. 96921 et
seq., and the regulations promulgated thereunder, are not ARARs for the selected
remedial action. The basis for this determination is that the wastes to be remediated
under this ROD are mining wastes that are exempt from the definition of hazardous
waste under RCRA Section 3001 (b)(3)(A)(ii), 42 U.S.C. 96921 (b)(3)(A)(ii), and 40
C.F.R. Section 261.4(b)(7) (also known as the aBevili amendmentU).
Pursuant to 40 C.F.R. 9261.4(b)(7), the Bevill exclusion provides that .solid
waste from the extraction, beneficiation and processing of ores and minerals (including
coal), including phosphate rock and overburden from the mining of uranium ore [are
not hazardous wastes]. For purposes of 9261.4(b)(7), beneficiation of ores and
minerals is restricted to the following activities: crushing, grinding, washing, dissolution,
crystallization, filtration, sorting, sizing, drying, sintering, pelletizing, briquetting,
calcining to remove water and/or carbon dioxide, roasting in preparation for
leaching...gravity concentration, magnetic separation, electrostatic separation,
floatation, ion exchange, solvent extraction electrotwinning, precipitation,
amalgamation, and heap, dump, vat, tank, and insitu leaching..
40 C.F.R. 9261.4(b)(7) also provides that solid waste from the processing of
ores and minerals includes only twenty specific wastes that are set forth in that
subsection. .
Since the wastes at the CRMS stem from gold and silver ore mining and milling
activity that occurred in the middle of the nineteenth century, it is difficult to say with
certainty whether or not the waste involved at the CRMS fall within the Bevill
exclusion. However, based upon available information, the wastes stem from
beneficiation and extraction of minerals; such wastes are exempt from the definition of
hazardous waste under RCRA. Accordingly, EPA has concluded that RCRA
regulations are not ARARs for the CRMS.
The selected remedial action will involve disposal of the wastes offsite. Laws
and regulations that are pertinent to off-site activity are not ARARs per se, and thus
are not frozen at the time the ROD is signed. Rather, the pertinent requirements
which exist at the time of the offsite action must be met. In light of the Bevill
exemption, the wastes disposed of off-site would not be subject to RCRA regulation.
However, in order to ensure that public health is protected and given the
recommended procedures in the Nevada Bureau of Mining Regulation and
Reclamation Guidance of May 3, 1994, EP A has determined that excavated wastes
that exceed the mercury standards for the TCLP test (Le., TCLP exceeds 0.2 mg/l) will
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either be treated and disposed of at a municipal landfill or, alternatively, will be
disposed of at a hazardous waste landfill. As noted previously, Based on the data
EPA has reviewed to date, EPA believes that little if any of the contaminated soils will
exceed the TCLP standard for mercury. .
Nevada Bureau of Mining Regulation and Reclamation Guidance Document for
Alternate Use of Mine Waste Solids-Disposal Outside of Containment dated May
3, 1994.
As discussed above in reference to chemical-specific requirements, EP A has
determined that the test procedures and criteria set forth in this criteria should be
followed in the event any of the wastes are subject to treatment.
Nevada Administrative Code 1445.734 (Fugitive Dust Emissions).
Nevada Administrative Code ~445.734 requires that the handling, transporting
or storing of any material be performed in a manner which does not allow controllable
particulate matter to become airborne. The excavation of contaminated soils will need
to comply with this requirement.
Location-Specific ARARs
Executive Order No. 11988; 40 C.F.R.16.302(b); 40 C.F.R. Part (Appendix A).
These requirements provide that within areas subject to a one percent or
greater chance of flooding in any given year, actions shall be taken to reduce the risk
of flood loss, minimize the impact of floods on human safety, health and welfare, and
restore and preserve the natural and beneficial values of flood plains. Since certain of
the areas where remedial action will be taken are within a 100 year flood plain, these
requirements are applicable to the extent that the remedial action should be performed
in such a manner that it does not increase the risk of flood loss.
Executive Order on Protection of Wetlands Exec. Order No. 11990.
This Executive Order requires Federal agencies to avoid, to the extent possible,
the adverse impacts associated with the destruction or loss. of wetlands, as defined in
Executive Order 11990, ~7{c), and 40 C.F.R. Part 6, Appendix A, ~4{j). Since certain
of the areas where remedial action will occur are adjacent to the Carson River, this
requirement is applicable to the extent that the selected remedial action should be
performed in such a manner that it avoids any adverse impact on wetlands.
Clean Water Act 1404; 40 C.F.R. Part 230; 33 C.F.R. Part 320-330.
These requirements protect wetlands, as defined in 40 C.F.R. ~230.3{t) and 33
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C.F.R. ~328.3(b), by prohibiting the discharge of dredged or fill material without a
permit, and taking actions to avoid adverse effects, minimize potential harm, and
preserve and enhance wetlands to the extent possible. Since certain areas where
remedial action will occur are adjacent to the Carson River, these requirements are
applicable. .
Archaeological and Historic Preservation Act, 16 U.S.C. g469, 40 C.F.R. i6.301(b)
and (c).
This Federal law and the pertinent regulation establishes procedures to
preserve historical and archaeological data which might be destroyed through
alteration of terrain as a result of Federal activity. Given the limited scope and area of
the selected remedial action, EPAbelieves that it is unlikely that any historical property
or archaeological remains will be encountered. However, in the event any such
property or data are encountered, EPA will comply the required procedures to ensure
that such property or data are preserved.
9.2.3 COMPARATIVE ANALYSIS
This section evaluates the relative performance of the alternatives described in
Section 8.1 with respect to the nine criteria so that the advantages and disadvantages
associated with each cleanup option are clearly presented. This analysis is described
herein according to each 01 the nine criteria.
Overall Protection of Human Health and the Environment
The scope of this OU-1 is to only address human health risks associated with
direct exposure to surface soils bearing mercury in excess of 80 mg/kg and is not
attempting to address environmental risks. Methods to address environmental risks
will be evaluated as part 01 OU-2.
For the residential yards, Alternatives 3 and 4 satisfy this criterion. With
Alternative 1, the impacted yards would not be addressed in any manner and the risks
described in Section 7.4 would not be reduced. Alternative 2 is also not considered to
adequately reduce human health risks because the residential yards remain impacted
and it is difficult to control access to residential yards, especially by young children.
Both Alternatives 3 and 4 provide protection of human health by eliminating the
exposure pathway of concern and thereby reducing the human health risks.
Alternative 3 eliminates the exposure pathway by capping the impacted areas and
Alternative 4 eliminates the exposure pathway by removing the impacted soil from the
residential yards.
For the Dayton Ditch, Alternatives 2, 3, and 4 satisfy this criterion. Again,
Alternative 1 would not address the defined risks in any manner. It is noted that the
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Dayton Ditch may pose less of a health risk than the other areas because (1) mercury
levels measured in the Dayton Ditch are relatively low (maximum = 109 mg/kg,
minimum = 9 mg/kg, and n = 4); and (2) the action level assumes that a young child is
exposed to contaminated soil 350 days per year which is considered a conservative
estimate for the ditch. Alternative 2 would satisfy this criteria if access to the ditch is
effectively controlled. Unlike the residential yards, the Dayton Ditch is not private
property and thus it is feasible to use fencing to control access. With a fence erected
along the stretch of the Dayton Ditch that extends through Dayton, access would be
minimized and the health risks would thereby be reduced. Alternative 3 would entail
lining the ditch channel with either rip-rap, cement, grass, or with a combination of
these. This would effectively reduce exposure to mercury contaminated soils
presently deposited in this reach of the Dayon Ditch. However, this would not ensure
that additional contaminated soils are not deposited in this reach of the ditch in the
future. Thus, it is not known whether this alternative would satisfy this criterion in the
future. Alternative 4 would entail excavating the contaminated soils from the Dayton
Ditch which would effectively reduce exposure to mercury contaminated soils presently
deposited in this reach of the Dayon Ditch and would satisfy this criterion. However,
as with Alternative 3, it is unknown whether this alternative would satisfy this criterion
in the future. .
Compliance with ARARs
As discussed in greater detail in Section 8.2.2, EPA has determined that the
contaminated soils being addressed in this ROD are probably exempt from regulation
under RCRA by virtue of the Bevill Amendment. Thus RCRA requirements are not
ARARs for this OU. The only other directly applicable or relevant and appropriate
requirements (as distinguished from guidance and advisories 8to be consideredU) are
certain action-specific and location specific requirements which would only be pertinent
to alternatives 3 or 4 and which alternatives 3 or 4 would meet. Thus it would appear
that any of the remedial alternatives would comply with directly applicable or relevant
and appropriate requirements.
In addition, however, EPA has identified two Nevada guidance documents that
are pertinent to the remedial alternatives for this OU and has determined that the
recommended procedures should be followed. The two Nevada guidance documents
are: the Nevada Contaminated Soil and Groundwater Remediation Policy, dated June
25, 1992, which provides cleanup standards for soil; and the Nevada Bureau of Mining
regulation and Reclamation Guidance Document for Alternate Use of Mine Waste
Solids/Disposal Outside of Containment, dated May 3, 1994, which provides that in
appropriate circumstances (such as where the use or displacement of the wastes may
degrade surface water or ground water) mining wastes should be evaluated under the
TCLP procedures.
EPA has determined that the standards and procedures provided in these
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c:. .~ 'I >',""';'~T"
~. .:,I.':J-",/,.:i',i:( .
guidance documents are pertinent to the risk-reduction objectives of this OU and that
the selected remedial alternative should comply with them. Both remedial alternatives
3 and 4 would meet the criteria of the two Nevada guidance documents. Alternative 4
would unequivocally meet the criteria and Alternative 3 would meet the criteria
assuming that Nevada considered the capping to be sufficiently protective.
Long-term Effectiveness and Permanence
For the residential yards, Alternatives 3 and 4 would satisfy this criterion. Since
Alternatives 1 and 2 are not considered protective of human health for the reasons
previously described, these alternatives would not provide long-term effectiveness and
permanence.
Alternative 3 mitigates human exposure by placing a cap over the impacted
areas. Given that this alternative does not attempt to address the full depth of the
surface soil horizon and thereby may leave behind soils with concentrations exceeding
80 mg/kg, it is possible that periodic monitoring may be required to ensure the integrity
of the cap (Le., 5 year reviews). However, even if cracks were to form on the cap,
any contamination exposed by cracks would not pose significant health risks. This is
because the average mercury concentration over the impacted area would still be
much less than 80 mg/kg. On the other hand, if portions of the cap were purposely
removed for excavation (Le., utility repairs or installations), then the excavated soil and
the exposed area might be of concern. Thus, the long-term effectiveness would
depend on the residual levels of mercury contamination and the effectiveness of the
institutional controls. Because such long-term institutional controls are difficult to
enforce, this is considered a disadvantage for Alternative 3.
Alternative 4 mitigates exposure by removing the contaminated surface soil
from the impacted area and replacing it with clean fill. As with Alternative 3, there is a
potential for leaving behind mercury concentrations exceeding 80 mg/kg. However,
the advantages with this alternative are that: (1) a larger amount of the contaminated
soil is removed from the impacted areas than is the case with Alternative 3, by
excavating to a maximum depth of 2 feet below ground surface, and thus less
impacted soil is left behind, and (2) it is less likely that institutional controls will be
required with Alternative 4 because it is less likely that impacted soil will be left behind
and the mercury concentrations at 2 feet below ground surface and greater will be
better defined as a result of confirmation sampling. In light of this criterion, Alternative
4 is considered the better alternative for addressing impacted yards.
For the Dayton Ditch, Alternative 1 would provide no added risk reduction and
thus this criterion is not applicable. Alternative 2 does not attempt to remove mercury
contaminated soil from the Dayton Ditch and thus, the long-term effectiveness and
permanence depends on the long-term effectiveness of the institutional controls. It is
not possible to predict how effectively the fence will reduce access nor is it possible to
CRMS Record of Decision, 3/30/95
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predict how long the fence will be properly maintained. Therefore, these uncertainties
are disadvantages for Alternative 2. Both Alternatives 3 and 4 would effectively
address the contaminated soil and sediments presently deposited in the Dayton Ditch
but it is unknown whether future runoff will deposit significant levels of contamination in
the ditch. Alternatives 2, 3, and 4 compare about the same against this criterion.
Reduction of Toxicity. Mobility. or Volume Through Treatment
For both the residential yards and the Dayton Ditch, only Alternative 4 may
include treatment and thereby may be evaluate,d according to this criterion. Treatment
will become part of Alternative 4 if a significant portion of the impacted soil does not
attain TCLP standards for mercury and thereby is a characteristic hazardous waste
(see Section 8.1). In the event that excavated soils are found to be characteristic
hazardous waste, then treatment will be required before disposal at a municipal
landfill. In lieu of specifying a treatment technology, this alternative sets forth
performance standards for a treatment technology. Thus, if treatment is found to be
necessary, then any technology that meets the prescribed performance standards can
be employed. The performance standards that would be applied to a treatment
technology are set forth in the Nevada Bureau of Mining Regulation and Reclamation
Guidance Document for Alternate Use of Mine Waste Solids-Disposal Outside of
Containment, dated May 3, 1994. Based on the FS, the technologies that would most
likely be used for treating contaminated soil are either gravity separation or a
conventional mining technology (i.e., cyanidation). .
Any technology for treating mercury contaminated soil is, at best, only capable
of separating mercury from the soil matrix. Mercury, which is an element of the Earth,
cannot be broken down or reduced in mass. Thus, despite what technology is used to
treat soil, the treatment products will always include concentrated mercury and clean
soil. Given that there are several technologies that are equally capable of recovering
mercury from soil, this alternative could include anyone of the technologies which are
capable of achieving the specified performance standards. The performance
standards which are specified in the referenced guidance document satisfy this
criterion by reducing the toxicity of the soil and reducing the mobility of the mercury.
Short-term Effectiveness
In protecting human health and the environment during the construction and
implementation phase, Alternatives 1 and 2 pose little to no hazards to human health
and environment while Alternatives 3 and 4 do include implementation activities which
might create hazards for nearby residents and for workers. Both Alternatives 3 and 4
include excavation. The principal hazards for both residents and workers associated
with excavation are: (1) generation of suspended dust; (2) operation of heavy
equipment; and (3) the traffic of haul trucks in residential areas. These hazards will be
thoughtfully considered in the remedial design and effective measures will be
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employed to minimize these hazards. These measures may include: performing the
work when the winds are least strong, using dust suppressants to control emissions,
properly covering staged material and material in the haul trucks to control dust
emissions, using traffic controllers to monitor and regulate traffic, and relocating
residents. The only environmental hazard is surface erosion of excavation areas and
staging piles. This hazard will be minimized by performing the work during the dry
season and maintaining covers over staged soil and excavated areas. Both
Alternatives 3 and 4 will require approximately four weeks per area to achieve the
remedial action objective. In summary, Alternatives 1 and 2 pose little to no hazards
to human health and environment while Alternatives 3 and 4 each pose the same
hazards and require about the same amount of time to implement.
I mplementability
Technical implementability does not apply to Alternative 1.
There are no foreseen technical obstacles for erecting a fence around the
boundaries of the Dayton Ditch, Alternative 2. However, accessing the ditch during
peak flow events is a special consideration. During peak flow events, the culverts
which pass beneath Highway 50 and Pike Street can become obstructed by debris. In
such events, access to the culverts is necessary to remove debris and prevent
flooding. Thus, if a fence is erected along the ditch, a gate or some other means of
access will be required at the culverts. A potential administrative factor for this
alternative is ensuring that the fence is properly maintained in perpetuity. If necessary,
long-term maintenance of the fence would have to become part of the State Superfund
Contract for this operable unit.
The excavation component of Alternatives 3 and 4 is technically straight forward
with only minor considerations. Technically, the excavation should be easy to carry
out using standard equipment that is readily available. The only foreseen technical
issues are: (1) excavating material near the banks of the Carson River (see MS001-
SA on Figure 4), and (2) excavating material near unstable slopes and structures
(MS004-SA on Figure 4). At MS001-SA, it is possible that excavation and backfilling
activities will require reshaping the river bank in order to fill in a ditch and create an
evenly graded area. In order to ensure that any buried material and the disturbed top
soil resists erosion, erosion control measures will have to implemented. Although
there is a large variety of erosion control measures, it will be a challenge to find the
best measure for this area. At MS004-SA, the impacted area is near the toe of
hillside. Based on a cursory examination of this hillside, it appears that it is not stable.
Thus, if any excavation is necessary at the toe of this hillside, it will be a challenge to
control sloughing. Finally, there are two small sheds within the impacted area which
appear to be unstable structures. If it is necessary to excavate material from around
these structures, it may be necessary to destroy these sheds and replace the
structures.
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The excavation component for Alternatives 3 and 4 may pose some
administrative and logistical challenges. At MS003-SA, it appears that the impacted
soil extends beneath several mobile homes. Rather than attempting to excavate
between the trailers which are very restrictive spaces, it may be more efficient to move
the mobile homes before excavating the areas. If relocation is necessary, between 10
and 15 households will have to be relocated during the period of excavation. It is
estimated that the period of excavation will be approximately 4 weeks, which includes
disconnecting utilities as well as inventorying, moving, and storing all of the property
and structures associated with each mobile home. The principal challenges
associated with relocation include: coordinating with residents, accommodating all of
the needs of the residents during the excavation period, and providing temporary .
residency in Dayton where there are no motels or hotels. A possible way to manage
the relocation with the least disruption to residents is to relocate trailers to a nearby
trailer park. It is believe that this would minimize the effort associated with moving
personal items and would minimize disruption to daily lives. This and other options
will be further evaluated as part of the remedial design.
Finally, Alternative 4 may include soil treatment. Although there are various
technologies for recovering mercury from soil, the best technology for treating soil will
depend on the species of mercury in the soil matrix. Mercury speciation was
performed as part of the remedial investigation but the results were inconclusive. The
results clearly demonstrated what fraction of the mercury is mercuric chloride
(information required for the risk assessment) but did not conclusively determine the
relative fractions of elemental mercury and mercuric sulfide. If treatment is required,
further speciation analyses or bench scale testing may be necessary for identifying the
best treatment technology. .
Cost
The cost estimates for residential yards are described in Table 8. Cost
estimates for Alternatives 3 and 4 were not developed for the Dayton Ditch because it
was recognized that the costs for these alternatives would be significantly greater than
institutional controls and because the risks associated with this area do not warrant.
these alternatives.
State and Public Acceptance
The Feasibility Study and the Proposed Plan fact sheet were reviewed by
Nevada Division of Environmental Protection (NDEP) and they expressed support for
Alternative 4 for the residential yards and opposed Alternative 2 for the Dayton Ditch.
In a letter dated March 29, 19~5, the State of Nevada (NDEP) concurred with EPA's
selected remedy for OU-1 of the CRMS.
The Proposed Plan fact sheet was provided to the communities of Dayton and
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Silver City and public hearings were conducted in Dayton and Silver City on January
18 and 19, 1995, respectively. The Proposed Plan fact sheet solicited written
comments from the communities and comments were also recorded at the public
hearings. The majority of the comments EPA received from the public expressed
skepticism regarding the health risks associated with mercury in surface soil and the
TABLE 8: Cost Estimates for Residential Yards
Alternative Capital Cost Operation & 30 Year Present
Maintenance Cost Worth
1 $0 $0 $0
2 NAB NA NA
3 $543,OOOb $0 $543,000
4a $2,090,OOOc $0 $2,090,000
4b $4,792,095d $0 $4,792,095
4c $829,8348 $0 $829,834
a. Not applicable because institutional controls were not considered a viable alternative for residential
yards.
b. Assumes excavation and replacement of 1005 cubic yards of soil, disposal without treatment at a
municipal landfill, paving over 67,500 square feet, and installation of 400 feet of fence around the
Dayton Ditch.
c. Assumes excavation and replacement of 6000 cubic yards of soil, disposal without treatment at a
hazardous waste landfill ($150/ton), and installation of 400 feet of fence around the Dayton Ditch.
d. Assumes excavation and replacement of 6000 cubic yards of soil, treatment at $500/ton, and
disposal at a municipal landfill ($10/ton), and installation of 400 feet of fence around the Dayton
Ditch.
e. Assumes excavation and replacement of 6000 cubic yards of soil, disposal without treatment at a
municipal landfill ($10/ton), and installation of 400 feet of fence around the Dayton Ditch..
value of any type of remediation. However, the owners of impacted parcels did not
object to Alternative 4. The communities also expressed some concern with
Alternative 2 for the Dayton Ditch. Residents are mainly concerned with the aesthetics
of a fence and that a fence would cause problems during peak flow events when
access to the culverts can be essential to remove large debris and avoid flooding.
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10.0 SELECTED REMEDY
Based upon consideration of the requirements of CERCLA, the detailed
analysis of the alternatives, and comments from the State and the public, EP A has
selected Alternative 4 for the residential yards and Alternative 1 for the Dayton Ditch.
The selected remedy for the five residential yards is to excavate contaminated
surface soil (estimated to go to a depth of approximately 2 feet below ground surface),
dispose of the soil at a RCRA municipal landfill if the soils do not exceed TCLP
standards, and restore the excavated areas. Approximately 5000 cubic yards of soil
will be excavated and disposed of as part of this response action. If it is determined
that all or part of the excavated soil exceed TCLP standards, then the excavated soil
will either be treated and disposed of at a RCRA municipal landfill or disposed of at a
RCRA hazardous waste landfill. Which of these sub-alternatives that will be used will
depend on which sub-alternative is found to be more cost effective and the 'logistics of
implementing each sub-alternative. In the event that subsurface soil is impacted and
is not addressed, then this remedy may also include institutional controls which would
prescribe handling and disposal requirements for any future excavations within the
impacted area.
Both Alternatives 3 and 4 were considered to be viable alternatives for
residential yards, however, Alternative 4 was selected over Alternative 3 based on
along-term effectiveness and permanence. a Both Alternatives 3 and 4 are considered
to be protective of human health and both of the alternatives achieve all of the ARARs
for this operable unit. Issues regardi!1g implementability and short-term effectiveness
are very similar for Alternatives 3 and 4 because both alternatives include excavation.
In the unlikely event that Alternative 4 includes treatment or disposal at a RCRA
Subtitle C disposal facility, then there may be more implementability issues and factors.
than there are for Alternative 3. The capital cost for Alternative 3 is estimated to be
less than for any of the scenarios presented for Alternative 4. Among the three
scenarios presented for Alternative 4, it is most likely that this alternative will not.
require either treatment or disposal at a hazardous waste landfill. Thus, the cost
comparison was based primarily on the estimated cost for Alternative 4c in Table 8.1.
Although the estimated capital cost for Alternative 3 is less than for Alternative 4c,
Alternative 4 was selected based on along-term effectiveness and permanence. a
Alternative 4 requires that soil is excavated to a maximum depth of 2 feet below
ground surface or to the depth of contamination. Alternative 3 would require minimal
excavation to prepare the surface for the cap and it is likely that institutional controls
would be required to address future exposure to subsurface contamination or to
address the uncertainty. Because a larger amount of contaminated soil is removed
with Alternative 4 and because this alternative will require more rigorous confirmation
sampling to define the depth of excavation, it is less likely that institutional controls
would be required to manage residual contamination or to address any uncertainty
regarding subsurface contamination. Although it is not possible to project costs for
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institutional controls at this time, EPA believes that the cost for Alternative 3 would be
augmented by institutional control costs. In light of this criterion, Alternative 4 is
considered the better alternative.
The selected remedy for the Dayton Ditch is no action. EPA selected no action
for the Dayton Ditch because the health risks for this area are not great enough to
warrant response actions such as excavation or lining the ditch and the State of
Nevada and the community do not support addressing the area with institutional
controls (Le., restricting access with a fence). Although EPA has selected no action
for the Dayton Ditch, additional samples will be collected from the ditch during the
remedial design to further evaluate the level of impact. In the event that EPA
determines that some form of remediation is warranted, then EP A will document this
remedy selection in an .Explanation of Significant Differences (ESD). or ROD
amendment, or the area will be addressed as part of OU-2.
Alternative 2 was originally proposed by EPA for the Dayton Ditch which would
have entailed fencing the ditch to restrict access and thereby reducing exposure. EPA
selected this alternative over capping and excavation based on human health risks
and cost. Although the Dayton Ditch is an actionable area based on the 80 mg/kg
action level, the health risks are considered less significant than for the residential
yards. The basis for this judgement is (1) the relatively low mercury levels measured
in the Dayton Ditch (maximum = 109 mg/kg, minimum = 9 mg/kg, and n = 4); and (2)
the action level assumes that a young child is exposed to contaminated soil 350 days
per year which is considered a conservative estimate for the ditch. Given the relatively
low risks, EPA could not justify the costs associated with either excavating or lining the
ditch. Thus, EPA proposed restricting access with a fence. Although this alternative
would provide some risk reduction, it is not considered to be significant enough to
override the opposition expressed by the State of Nevada and the community of
Dayton. Therefore, EPA is selecting Alternative 1 for the Dayton Ditch. EPA will
collect additional samples from the ditch during the remedial design to further evaluate
the level of impact. In the event that EPA determines that some form of remediation is
warranted, then EPA will document this remedy selection in an Explanation of
Significant Differences (ESD) or ROD amendment, or the area will be addressed as
part of OU-2.
In summary, the selected remedy for OU-1 of the CRMS is as follows:
.
Excavation of approximately 5000 cubic yards of contaminated soils, disposal at
a RCRA municipal and/or hazardous waste landfill, and restoration of
properties. In the event that there is residual contamination in the subsurface
soil and it is not addressed, then this alternative may also include institutional
controls; and .
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.
Implementation of institutional controls to ensure that any residential
development in present open land use areas known or suspected to be
impacted by mercury includes characterizing mercury levels in surface soils
and, if necessary, addressing impacted soils. These institutional controls will be
referred to as the Dlong-term Sampling and Response Plan..
11.0 STATUTORY DETERMINATIONS
As required under Section 121 of CERCLA, the selected remedial action is
protective of human health, complies with Federal and State requirements that are
legally applicable or relevant and appropriate to the remedial action, and is cost
effective. The selected remedy utilizes permanent solutions and alternative treatment
technologies to the maximum extent practicable. However, because treatment of
soils may not occur, this remedy may not satisfy the statutory preference for treatment
as a principal element of the remedy.
The selected remedy is protective of human health in that it mitigates exposure
to mercury which is equal to or exceeds 80 mg/kg in surface soil. The selected
remedy is technically feasible and meets all of the ARARs which are pertinent to this
operable unit.
Because this remedy will result in hazardous substances remaining on-site
above health-based levels, a five-year review, pursuant to CERClA Section 121, 42
U.S.C. Section 9621, will be conducted at least once every five years after initiation of
the remedial action to ensure that the remedy continues to provide adequate
protection 01 human health and the environment. ..
12.0 DOCUMENTATION OF SIGNIFICANT CHANGES
The remedy selected in this ROD is different from the remedy originally
proposed by EPA. In the Proposed Plan fact sheet, EPA proposed fencing the Dayton
Ditch in order to restrict access and thereby reduce exposure. Based on opposition
expressed by the State of Nevada and the community of Dayton, the selected remedy
for the Dayton Ditch is Alternative 1, No Action. The basis for this change is
discussed in Section 10.
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REFERENCES
Agency for Toxic Substances and Disease Registry. 1992. Draft Toxicological Profile for
Mercury.October
Ansari, M.B., 1989, Mines and mills 01 the Comstock region western Nevada. Camp
Nevada Monograph No.8.
Bonham, Harold F. and Keith G. Papke, 1969, Geology and Mineral Deposits 01 Washoe
and Storey Counties, Nevada: Nevada Bureau of Mines & Geology Bulletin 70.
Churchill County, 1990, Churchill County 1990 Master Plan.
Cooper, J.J., S. Vigg, A. W. Bryce, and A.L. Jacobson, 1983, Limnology 01 Lahontan
Reservoir, Nevada, 1980-1981, Bioresources and Water Resources Centers,
Desert Research Institute, University of Nevada, Reno; Publication 50021,
September 1983.
Cooper, J.J., A.O. Thomas, and S.M. Reed, 1985, Total Mercury in Sediment, Water, and
Fishes in the Carson River Drainage, West Central Nevada. Nevada Division of
Environmental Protection.
Environmental Protection Agency, 1977, Report on Lahontan Reservoir Churchill and
. Lyon Counties Nevada, EPA Region 9 Working Paper No. 807.
Environmental Protection Agency, 1989a. Risk Assessment Guidance for Superfund.
Volume 1. Human Health Evaluation Manual (Part A). Interim Final. Washington,
D.C. December.
Environmental Protection Agency, 1989b. Risk Assessment Guidance for Superfund
Human Health Risk Assessment: U.S. EPA Region IX Recommendations. Interim
Final. San Francisco, CA. December.
Environmental Protection Agency, 1993b. Integrated Risk Information System (IRIS).
Health Criteria and Assessment Office, Cincinnati, OH, for the Office of Solid
Waste and Emergency Response, Office of Emergency and Remedial Response,
Washington, D.C. FY-1991.
Hoffman, R.J., R.J. Hallock, T.G. Rowe, M.S. Lico, H.L. Burge, and S.P. Thompson,
1990, Reconnaissance Investigation of Water Quality, Bottom Sediment, and Biota
Associated with IrrigatiQn Drainage in and near Stillwater Wildlife Management
Area, Churchill County, Nevada, 1986-87: U.S. Geological Survey Water
Resources Investigation Report 89-4105.
CRMS Record of Decision 3/30/95
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Lyon County, 1990, Lyon County Master Plan
Nevada Commission on Economic Development, 1985, Nevada industrial directory 1985-
86: Nevada Commission on Economic Development.
Richins, R.T., and A.C. Risser, Jr., 1975, Total mercury in water, sediment and selected
aquatic organisms, Carson River, Nevada, 1972. Pesticide Monitoring Journal,
Volume 9, No.1.
Rowe, T.G., and Hoffman, R.J., 1990, Wildlife kills in the Carson Sink, western Nevada,
winter of 1986-87, in Carr, J.E., Chase, E.B., and Paulson, R.W. and Moody, D.W.,
comps., National water summary 1987-Hydrologic events and water supply and
use: U.S. Geological Survey Water-Supply Paper 2350.
Thompson, G.A., 1956, Geology of the Virginia City quadrangle Nevada. U.S. Geological
Survey Bulletin 1042-C.
Tuttle, Peter, 1992, Mercury in Fish Collected from the Indian Lakes System Stillwater
Wildlife Management Ares, Churchill County, Nevada. U.S. Fish and Wildlife
Service Report.
Twiss, R.H., Elford, C.R., James, J.W., Mueller, P.K., Smith, K.C., Warburton, Joseph,
and Wong Woo, Harmon, 1971, Climate and air quality of the Lake Tahoe Region:
South Lake Tahoe, Calif., Tahoe Regional Planning Agency and U.S. Forest
Service.
U.S. Bureau of Reclamation, 1980, Watasheamu Division Washoe Project, Nevada-
California, Ground-water geology and resources definite plan appendix, Carson
Valley, Nevada: Sacarmento, Calif., U.S. Water and Power Resources Service
report.
Washoe County Department of Comprehensive Planning, 1992, Comprehensive Plan
South Valleys Area Plan
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PART III. RESPONSIVENESS SUMMARY
This section summarizes and responds to all significant comments received
during the public comment period (32 days) on EPA's proposed plan for Operable Unit
1 (OU-1) of the Carson River Mercury Site (CRMS) in Storey, Lyon, and Churchill
Counties, Nevada. This summary is divided into three sections. Section 1 provides a
summary of the major issues raised as written comments. Sections 2 and 3
summarize the questions and comments made at the public meetings held in Dayton
and Silver City on January 18 and 19, 1995, respectively. Copies of all of the written
comments received by EPA are included in the CRMS Administrative Record, which
are available for review at the information repositories. The transcript of the public
meeting, including all of the questions and comments, is also available at the
information repositories.
1.0
WRITTEN COMMENTS
1. Nevada Division of Environmental Protection
Comment: As part of the proposed plan for OU-1 of the CRMS, EPA is proposing
institutional controls referred to as the -Long-term Sampling and Response Plan
(L TSRP)- for non-residential areas that are impacted and, possibly, deed restrictions
for any subsurface contamination that is not addressed. How will EPA ensure that
these institutional controls are implemented and does EPA have the legal authority to
enforce these institutional controls.
Response: The concern expressed by NDEP is also shared by EPA, especially for
the L TSRP. First, EPA does have the legal authority to enforce compliance with
institutional controls under CERCLA, Section 104 and 106. However, EPA believes
that the L TSRP will be effectively implemented through public awareness. By now, it
is commonly known that part of the Carson drainage is a Superfund site due to .
mercury and that there are liability risks related to purchasing property that is impacted
by mercury. Given that EPA is unable to clearly delineate the exact boundaries of the
Superfund site, prospective buyers, realtors, lending institutions, and environmental
consultants should recognize the value of using prescribed guidelines for evaluating
properties of interest. With regard to institutional controls at the impacted residential
properties, EPA has selected Alternative 4, Excavation, in hope of minimizing the need
for such institutional controls. However, if necessary, institutional controls will be
utilized at those impacted properties if there is residual contamination in the
subsurface soil and it is not addressed.
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. 2. Nevada Division of Environmental Protection
Comment: In the Proposed Plan fact sheet, EPA indicates that there are no capital or
future costs associated with Altemative 1, No Action, when this alternative should
include future costs for long-term monitoring. Please explain.
Response: Based on the definition of -no action- EPA used in the Feasibility Study
and the Proposed Plan fact sheet, no action does not include any future monitoring.
Rather, long-term monitoring is considered a form of institutional controls. Thus there
are no long-term monitoring costs associated with this alternative.
3. Sharon D. Hunt
Comment: The commenter believes that mercury contamination in Dayton is not a
public health hazard based on the apparent well being of many of the residents who
have spent their entire lives in the Dayton area. The commenter then suggests that
Altemative 1, No Action, is the better alternative.
Response: EPA is addressing areas where mercury contamination in surface soil is
equal to or greater than 80 mg/kg. This action level is based on the potential health
risks for a young child (less than 6 years of age) who may ingest an average of 200
mg of soil per day. This action level, 80 mg/kg, translates to a level of exposure for a
young child that is below the level at which adverse effects are expected to occur.
These adverse effects are to the kidney progressing from swelling and redness to
more serious effects such as proteinurea (proteins in the urine). By selecting an
action level which is below the threshold for adverse effects, EPA is being protective
of human health.
4. Sharon D. Hunt
Comment: First, the commentor would like to know what are the implications if her
property, which presently appears to be impacted, is not addressed. Secondly, the
commentor is concerned that the value of her property is already reduced due to the
presence of mercury and she would like to know if her property will regain the full
market value after cleanup. Finally, the commentor would like to know if the property
. will have limited landuse after the cleanup.
Response: As a result of the human health risk assessment, EPA has set forth an
action level (80 mglkg) which the Agency is using to determine if properties are
impacted by mercury. In the event that a property owner objects to cleanup activities
on his or her property, EPA may attempt to negotiate an agreement with the property
owner, or EPA may issue an unilateral order to that property owner. Should EPA not
address an impacted property, the property owner will be subject to some risks. First,
there are the health risks which are discussed under Comment 3. Secondly, there are
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liability risks if an incident of mercury poisoning is attributed to the property. Finally,
there are risks that the value of the property will be reduced and that the property
owner will be unable to sell the property or borrow money against the property. If EPA
addresses contamination on the property, the specifics of the cleanup will be
documented in an appropriate manner. After cleanup, if no residual contamination
remains on the property, there will be no land use limitations for the property.
However, as discussed in the .Selected Remedy. section of the ROD, some
institutional controls may be utilized in the event that residual contamination remains
on the property.
5. Mickey Lawler. 21 st Century Environmental Management. Inc.
Comment: The commenter requests the results from soil analyses, wildlife analyses,
and TCLP analyses. The commentor also requests any maps which describe the
distribution of mercury in surface soil.
Response; The Human Health Risk Assessment and Remedial Investigation Report
. for the Carson River Mercury Site, December 1994, which is available at the
information repositories, contains results from all of the soil sampling and provides
maps which describe where EP A collected samples and provides the respective
levels. As part of this phase of the remedial investigation, seven soil samples which
contained elevated mercury were analyzed using TCLP. These analyses were
performed as preliminary test to determine if excavated soil would exceed TCLP.
These results are discussed in this ROD and are included in the administrative record.
Wildlife sampling is part of Operable Unit 2 (OU-2) of the remedial investigation and
feasibility study, and thus there are no results to provide at this time. The final report
for OU-2, which will contain the results from all wildlife sampling, is scheduled to be
completed in October, 1995.
Comment: The commenter refers to 40 C.F.R. Part 268.42 and poses the following
questions: (1) what is the sampling plan for determining the total mercury content of
excavated soil, and (2) will the total mercury content affect how the soil is regulated
and thereby addressed (i.e., if soils exceed 260 mg/kg and are thereby defined as
DHigh MercuryD in the Land Disposal Restrictions)?
Response: The sampling plan for determining the total mercury content of excavated
soil will be developed as part of the remedial design which is scheduled to be
completed in the Fall, 1995. However, as is discussed in this ROD, mercury
contaminated soil from the CRMS is exempt from Land Disposal Restrictions by virtue
of the Bevill Amendment. Thus, even if the soils are found to exceed 260 mg/kg, the
soils will not be addressed differently. However, if soils are found to exceed TCLP
standards, the soils will have to be treated before disposal at a RCRA municipal
landfill or disposed of at a RCRA hazardous landfill. If the soil is sent to a RCRA
hazardous waste landfill, the soil will be subject to the regulations which govern the
CRMS Record of Decision 3/30/95
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)
I
landfill.
Comment: The commentor requests additional information regarding the cost analysis
for Alternative 4.
Response: A description of the cost analysis is provided in the Feasibility Study for
the Carson River Mercury Site dated December 20, 1994. This study is available for
review at the information repositories.
2.0
COMMENTS FROM DAYTON PUBLIC MEETING ON JANUARY 18, 1995
6. Harold Tracey
Comment: The commenter owns property in Dayton and believes that property values
have dropped signficantly since the local media started releasing information regarding
the Carson River Mercury Site. The commenter would like to receive compensation
for the depreciation of real estate prices.
Response: This comment is concerning property values as they relate to the
boundaries of the Carson River Superfund site and the public perception of the
problem. For this site, EPA has not attempted to define the perimeter of the site
because the extent of mercury contamination is too widespread. Thus, there has been
an ongoing uncertainty about what areas are impacted and what areas are clean.
Although EP A is unaware of any actual depreciation in real estate values, it is possible
that this uncertainty might have some effect on real estate values in Dayton and other
areas. Now that EPA has identified the historic millsites, established an action level,
and has identified the impacted areas based on this action level, there should be less
uncertainty as to whether a property is impacted. Also, by providing the State with
prescribed sampling guidelines, EP A believes that property values will be less affected
by uncertainty. With regards to what the local media reports, EPA only releases
factual information to the media. Unfortunately, EPA has little control over how the
information is relayed to the public through newspapers, radio, and television.
7. Victoria Predere
Comment: The commenter has been a resident of Dayton for over 60 years and she
finds it difficult to believe that health risks that EPA is attempting to reduce are actually
real.
Response: See Comment 3.
8. Don Dallas
Comment: The commenter does not understand why the Carson River is a Superfund
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Site. The commenter is also concerned that EPA will not select Alternative 1, No .
Action, even if the community unanimously supports this alternative.
Response: The CRMS was added to the National Priorities List (NPL) in August, 1990
due to the widespread occurence of mercury. As with all Superfund sites, the site
was evaluated and scored according to EPA's Hazard Ranking System (HRS) model.
With the HRS model, a site is scored based on the contaminants of concern, the
affected media, exposure pathways, the size and proximity of potentially exposed
human populations, and the proximity of wildlife habitat. In order to be proposed for
the NPL, a site must score above 28.5. The HRS score for the CRMS was 39. In the
circumstance where a state does not have any Superfund sites, that state can propose
a site for the NPL if that site is eligible according to the HRS. The CRMS was
nominated by the State of Nevada as the State's first Superfund site.
The purpose for the proposed plan comment period is to provide the public an
opportunity to comment on the response actions proposed by EPA. In the event that
the public provides valid reasons for modifying the proposed remedy or selecting a
different remedy, EPA will strongly consider those comments and EPA might change
the remedy selection based on the comments. Although the prevailing opinion among
the communities is that the health risks are not real and that Alternative 1 is the best
alternative, EPA feels that remediation is warranted based on the reasons presented
under Comment 3. Also, the owners of the impacted properties recognized the
practical value of addressing the impacted areas and they support the proposed
remedy.
9. Gloria Marsh
Comment: The commenter would like to know how EPA will formally document that a
property is .cleana after remediation is complete.
Response: See Comment 4.
10. Harold Tracy
Comment: The commenter is concerned with the Long-term Sampling Response
Plan. In particular, he is concerned th~t the L TSRP will impose regulations on
privately owned property and will reduce the value of the land and reduce the chances
for people to develop their land.
Response: The areas that will be managed with the.L TSRP are areas that were found
to be impacted or areas that are potentially impacted by mercury. Given that these
areas are identified in the remedial investigation report, it is likely that if a landowner
elects to develop in one of these impacted areas, mercury contamination will be an
issue that the landowner will have to address. The purpose for the L TSRP is to
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,)
provide the landowner with clear guidelines for assessing if mercury is a problem and,
if necessary, guidelines for addressing the problem. By providing these guidelines,
EP A feels that the inevitable costs associated with developing or transferring land that
is impacted or is potentially impacted by mercury will be greatly reduced.
3.0
COMMENTS FROM SILVER CITY PUBLIC MEETING ON JANUARY 19, 1995
11. Tom Card
Comment: First, the commenter asks if EPA determined the species of mercury in
surface soil and then he asks if elemental mercury is really a health hazard.
Response: As part of soil investigations EPA attempted to characterize the species of
mercury in surface soil, but due to conflicting results from two different labs using two
different procedures, EPA was unable to establish whether mercuric sulfide 'or
elemental mercury is the predominant species. However, EP A was able to conclude
that less than 10 percent of the total mercury is mercuric chloride, which is the most
soluble form of inorganic mercury. It is true that elemental mercury is the least soluble
form of mercury and, as a result, poses the least risk when ingested. Since EP A
could not establish what is the predominant form of mercury in surface soil, the action
level assumed that 90 percent is mercuric sulfide and 10 percent is mercuric chloride.
Comment: Based on the assumption that elemental mercury is the predominant form
of mercury in the soil matrix, the commenter expresses skepticism about the health
risks associated with exposure to soil and recommends Alternative 1, No Action, as
the best alternative.
Response: See Comment 3.
Comment: The commenter is concerned that EPA will use outside contractors to
perform all of the work associated with the remedial action and would like to see I.ocal
contractors used to perform the work.
Response: To the maximum extent possible, EPA will attempt to use local contractors
to perform the remediation work. It is important to note that before a contractor can be
considered to perform the soil excavation work, the contractor will have to meet certain
requirements for handling hazardous substances. Assuming that local contractors
possess the required qualifications, EPA will attempt to employ them.
12. Mr. Laughlin
Comment: The commenter believes that the CRMS was added to the NPL for political
reasons. The commentor also refers to the open hearths of the steel mills in
Pittsburgh as more significant problems.
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, "
Response: See Comment 8.
13. Harold Tracy
Comment: The commenter questions whether EP A had access approval to perform
sampling on the Ricci Ranch. Secondly, the commenter questions whether EPA used
prison crews to perform sampling. '
Response: Access was requested prior to accessing private property to perform
sampling. There were a handful of properties where EPA was unable to contact the
land owner prior to conducting sampling. In those instances, EPA proceeded with the
sampling when there were no fences or signs that denied access. but sampling was
carried out anyway because there were no fences or signs to prevent access. In
response to the second comment, EP A only used professionals to perform field
investigations and EP A never used a prison team. '
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