EPA Superfund
Record of Decision:
PB97-964510
EPA/541/R-97/132
January 1998
Iron Mountain Mine
Redding, CA
9/30/1997
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RECORD OF DECISION
IRON MOUNTAIN MINE
SHASTA COUNTY, CALIFORNIA
THE DECLARATION
I, SITE NAME AND LOCATION
Iron Mountain Mine (IMM)
Shasta County, California (approximately 9 miles northwest of Redding, California)
II. STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected interim remedial action for control of releases
of hazardous substances from widespread area sources in the Slickrock Creek watershed at
the Iron Mountain Mine Site. The selected interim remedial action was chosen in accordance
with the Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA), as amended by the Superfund Amendments and Reauthorization Act (SARA),
and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). This
decision is based upon the Administrative Record for this Site.
The State of California concurs with the selected interim remedial action for the Slickrock
Creek area source acid mine drainage (AMD) discharges at the Iron Mountain Mine Super-
fund Site.
III. ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from this Site, if not addressed by
implementing the response action selected in this Record of Decision (ROD), may present an
imminent and substantial endangerment to public health, welfare, or the environment.
The Slickrock Creek area sources of AMD include the numerous waste piles on the mine
property, disturbed areas related to mining activity, contaminated groundwater and interflow
seepage, underground mine workings, and underground mineralization exposed through
mining-induced hydrologic and physical changes. The general disturbances in this area of
Slickrock Creek are shown in Photo Exhibit 1. The releases from these sources consist of
highly acidic, heavy metal-bearing waters, termed acid mine drainage, or AMD. The heavy
metals contained in the AMD from Slickrock Creek area sources include, among others, cop-
per, cadmium, and zinc. The AMD contains acidity and concentrations of copper, cadmium,
and zinc that are toxic to aquatic life and harmful to humans. The response action will also
address the hematite mine waste piles, which contain high levels of arsenic and are actively
eroding into Slickrock Creek and thence to downstream areas.
The principal threat posed by these releases is the creation of conditions toxic to aquatic life
in the receiving waters downstream of the Site. Surface water is the primary exposure path-
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way for discharges from the Slickrock Creek sources. The surface waters in the Spring Creek
drainage affected by the Slickrock Creek area sources (Slickrock Creek, Spring Creek, and
the Spring Creek Reservoir [SCR]) are essentially devoid of aquatic life as a result of releases
of hazardous substances from the Site.
The SCR meters contaminated IMM AMD into the Sacramento River at Keswick Reservoir.
The SCR, coupled with the prior CERCLA response actions implemented pursuant to the
1986 (ROD1), 1992 (ROD2), and 1993 Records of Decision (ROD3), provides some degree
of protection to aquatic resources and public health below the SCR, but IMM AMD
discharges continue to harm and pose risks to aquatic resources in Keswick Reservoir and the
Sacramento River (particularly during certain storm events when discharges from the Site are
greatest), and to a significantly lesser degree, to public health. These discharges also fail to
comply with CERCLA requirements. Even taking into account the response actions imple-
mented to date (which have reduced sitewide releases by approximately 80 to 90 percent on
average over the past several years), IMM AMD is expected to cause regular annual exceed-
ances of protective water quality standards in Keswick Reservoir, continued exceedances in
the Sacramento River under certain storm conditions, and the continued release of 25,000 to
70,000 pounds per year of copper and 40,000 to 90,000 pounds of zinc to Keswick Reservoir
and the main stem of the Sacramento River in normal to wet water years. These discharges
are approximately one to three times the metal load of all industrial discharges in the
Sacramento River, Bay, and Delta combined.
Just below the point at which IMM AMD enters the Sacramento River, the Sacramento River
supports a valuable fishery that includes four species of chinook salmon, steelhead, and resi-
dent trout. The winter-run chinook salmon has been designated as an endangered species
under the federal Endangered Species Act, and at least one other species (the Sacramento
River steelhead) is currently being considered for listing as endangered under that statute.
The spring-run chinook salmon is currently a candidate species under the State Endangered
Species Act. These species are particularly sensitive to toxic metals such as copper,
cadmium, and zinc. The National Oceanic and Atmospheric Administration (NOAA) has
identified the affected area as the most important salmon habitat in California.
Releases of hazardous substances from the site also pose a potential threat to human health.
Concentrated AMD is harmful to humans. There is also a human health risk associated with
consumption of fish contaminated by heavy metals from the site. The Sacramento River
which receives releases of hazardous substances from the site serves as a source of drinking
water for the City of Redding, although exceedances of drinking water criteria for metals and
acidity due to site releases is expected to be rare. In addition, releases of arsenic from mine
waste piles poses a potential threat to humans.
Through the performance of continuing remedial investigations and feasibility studies, the
U.S. Environmental Protection Agency (EPA) has identified the control of the IMM area
source AMD discharges from the Slickrock Creek and Boulder Creek watersheds as being
necessary to meet remedial action objectives for the Site. Actual or threatened releases of
AMD from both of these watersheds, if not addressed by implementing appropriate response
actions, may present an imminent and substantial endangerment to human health or the
environment. The response action selected in this Record of Decision (ROD4), however,
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only addresses the Slickrock Creek area source AMD discharges (which are estimated to
account for approximately 60 to 70 percent of the copper load and 40 to 50 percent of the
zinc and cadmium load associated with the currently uncontrolled Site discharges). The
selected response action for the Slickrock Creek area source AMD discharges is expected to
make significant progress toward abating the imminent and substantial endangerment to
human health and the environment caused by the continuing AMD discharges from the IMM
area sources. The EPA has determined that further study is warranted to support continued
development and evaluation of remedial alternatives for the Boulder Creek area source AMD
discharges. The EPA anticipates that an additional remedial investigation and feasibility
study will be conducted to develop and evaluate control strategies for the area sources in
Boulder Creek. The EPA also anticipates investigating the need to respond to other sources
of mining-related hazardous substance releases from IMM, including but not limited to
sediments deposited by past and current AMD releases.
IV. DESCRIPTION OF PRIOR REMEDIAL ACTIONS
The first ROD for the IMM Site (ROD1), signed in October 1986, provided for implementa-
tion of limited source control actions to begin lessening the IMM AMD discharges and also
provided water management capability to manage the ongoing IMM AMD releases to surface
waters. Specific activities authorized by ROD1 include a diversion of Slickrock Creek
around contaminant-bearing landslide debris, diversion of Upper Spring Creek to the Flat
Creek drainage, and a partial cap of Brick Flat Pit and seven subsidence areas. All of these
projects have been completed. ROD1 also authorized the enlargement of the Spring Creek
Debris Dam (SCDD) and the diversion of the South Fork of Spring Creek (SFSC). These
two water management projects were deferred by EPA to allow for additional evaluation.
Pursuant to Records of Decision signed by EPA in 1992 (ROD2) and 1993 (RODS), essen-
tially all AMD releases from the three largest sources of IMM AMD (the Richmond portal,
the Lawson portal, and the Old/No. 8 Mine Seep) are treated at the IMM treatment plant.
The EPA selected the high density sludge (HDS) treatment process to ensure the long-term
reliability, effectiveness, and cost-effectiveness of IMM treatment and sludge disposal opera-
tions. The treatment residuals are disposed of onsite in the inactive open pit mine, Brick Flat
Pit. The response actions implemented pursuant to these two RODs have significantly
reduced the release of hazardous substances from the Site. For example, during the period
from January 1995 through March 1995, treatment of the IMM AMD from these three under-
ground mine workings reduced sitewide discharges of copper, zinc, and cadmium by
approximately 80 to 90 percent.
V. ERA'S JUNE 1994 PROPOSED PLAN
In a Proposed Plan issued in June 1994, EPA proposed to enlarge the SCDD to establish a
15,000-acre-foot reservoir and to defer implementation of the SFSC diversion. Enlargement
of the SCDD and construction of the SFSC were both components of the 1986 ROD. The
1986 ROD had deferred sizing of the reservoir. At the of the June 1994 Proposed Plan, it
was EPA's assessment that source control and treatment alternatives were not available that
could provide sufficient control of the IMM area source AMD discharges to meet remedial
action objectives for the Site. The EPA had determined that the proposed enlargement of the
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SCDD would provide sufficient water management capability to meet certain remedial action
objectives for the Site, considering the extent of technical practicability limitations. The EPA
received comments during the public comment period that identified additional source con-
trol and treatment alternatives for the IMM area source AMD discharges. The comments
supported the technical feasibility of the source control and treatment approaches. Com-
menters also stated a preference for source control and treatment approaches over water
management remedial alternatives. Taking into account these comments, the EPA deferred
remedy selection and performed further studies of the suggested source control and treatment
alternatives.
VI. DESCRIPTION OF THE SELECTED REMEDY
The selected interim remedial action is the fourth ROD for the IMM Superfund cleanup
action. It focuses on the Slickrock Creek area source AMD discharges. The selected remedy,
which is the same remedy EPA proposed in its May 1996 Proposed Plan, was largely derived
from an alternative developed by a potentially responsible party and submitted to EPA during
the public comment period on the 1994 Proposed Plan. The selected remedy addresses the
principal threat posed by contaminant releases from area sources within the Slickrock Creek
watershed at the IMM Site through collection, conveyance, and treatment of all of the flows
in the most contaminated reach of Slickrock Creek, located directly downstream of the most
heavily disturbed mining area in the basin. The selected remedy will involve constructing a
dam to establish a small reservoir in Slickrock Creek to collect and contain the contaminated
runoff for controlled conveyance to an expanded IMM HDS treatment plant. The selected
remedy also involves constructing a surface water diversion to keep relatively
uncontaminated surface water from flowing into the reservoir. The diversion will minimize
the amount of water that requires treatment and the size of the dam required to ensure
adequate storage capacity of the containment reservoir. New and modified pipelines will
convey the contaminated water from the reservoir to the treatment plant Necessary
modifications to the IMM HDS treatment plant will be constructed. A conceptual depiction
of the remedy is shown in Photo Exhibit 2.
The major components of the selected remedy include:
Construct a retention dam and necessary surface water diversion facilities to ensure the
collection and storage of contaminated surface runoff, interflow, and groundwater in the
Slickrock Creek watershed at IMM.
Construct facilities to provide controlled release of contaminated waters from the
retention dam to the AMD conveyance pipeline to the IMM HDS/ASM b'me
neutralization treatment plant
Construct facilities to divert relatively uncontaminated surface water from the area
upstream from the highly disturbed mining area of the Slickrock Creek basin and divert
that water around the Slickrock Creek retention reservoir. The diversion shall also divert
around the retention reservoir the water from the unmined side of the Slickrock Creek
watershed.
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Take appropriate steps (including consideration of emergency failure scenarios) to
integrate into the operation of the reservoir the collection and conveyance of the Old/No.
8 Mine Seep AMD to the IMM HDS/ASM lime neutralization treatment plant.
Construct a hematite erosion control structure consistent with California mining waste
requirements.
Construct one or more sedimentation basin(s) or other EPA approved control structures in
the Slickrock Creek watershed to minimize sedimentation of the Slickrock Creek
retention reservoir and to ensure proper functioning of the controlled release facilities.
Upgrade the hydraulic capacity of the existing pipeline (or if necessary construct a new
pipeline) from Slickrock Creek to the Boulder Creek crossing as required to ensure
adequate reliable capacity to convey Slickrock Creek and Old/No. 8 Mine Seep AMD.
Construct an additional pipeline to reliably convey Slickrock Creek and Old/No. 8 Mine
Seep AMD from the Boulder Creek Crossing to the IMM HDS/ASM lime neutralization
treatment plant.
Modify the IMM HDS/ASM lime neutralization treatment plant to ensure proper
treatment, using the HDS/ASM treatment process, of the Slickrock Creek area source
AMD discharges in conjunction with AMD flows collected pursuant to other Records of
Decision.
Construct a tunnel to provide for gravity discharge of the high volumes of effluent from
the IMM HDS/ASM treatment plant to Spring Creek below the Upper Spring Creek
diversion to Flat Creek.
Construct facilities to assure collection of significant identified sources (including but not
limited to seeps from Brick Rat Pit and the hematite piles) and convey those releases to
the Slickrock Creek Retention Reservoir.
Perform long-term operations and maintenance (O&M) of all components.
VII. STATUTORY DETERMINATIONS
Protective of Human Health and the Environment
With respect to the releases of hazardous substances that will be addressed by this interim
action, this selected interim remedy is-protective of human health and the environment. The
selected interim remedy essentially eliminates the potential exposure and the resultant threats
to human health and the environment from the Slickrock Creek area sources and the AMD
discharge pathways addressed in this interim remedy. While the interim remedy is expected
to essentially eliminate the risk posed by certain releases of hazardous substances from the
facility, the interim remedy responds to only a subset of the currently uncontrolled releases of
hazardous substances being released from the facility. The EPA therefore anticipates that the
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remedy will not fully protect human health and the environment and that additional remedial
action will be required to respond to releases of hazardous substances from the facility.
Compliance with ARARs
Except for those applicable or relevant and appropriate requirements (ARARs) that EPA is
waiving for this interim remedy, the interim remedy will comply with all Federal and State
ARARs.
The EPA is waiving compliance with certain ARARs on the basis that this proposed action is
an interim action that will not respond to all releases of hazardous substances from the
facility. This interim action is not expected to provide for compliance with all ARARs at all
times because the dam and treat interim remedial action for the Slickrock Creek area source
AMD discharges does not address releases other than area sources in the Slickrock Creek
watershed above the containment structure to be constructed on Slickrock Creek, such as
releases from area sources in the Boulder Creek watershed, the existing sediments in SCR
and Keswick Reservoir, and the streambeds in the Spring Creek watershed.
Since the action selected in this ROD is an interim action that leaves some releases of haz-
ardous substances unabated, EPA is relying on the ARARs waiver for "interim measures"
(CERCLA § 121(d)(4)(A); 40 CFR § 300.430(f)(l)(ii)(C)(l)) for this remedial action. In
particular, EPA anticipates that the remedy will improve water quality in Spring Creek, SCR,
Keswick Reservoir, and the Sacramento River, but EPA does not anticipate that this remedy,
in conjunction the other remedies implemented to date, will be sufficient to ensure compli-
ance with (1) the numeric, chemical-specific standards contained in the State Basin Plan
Standards (SBPS) for copper, cadmium, or zinc, and (2) California Fish and Game Code
§ 5650 (which prohibits discharge of contaminants "deleterious to fish, plant life, or bird
life"). The EPA is therefore waiving compliance with those standards for the interim action
to the extent those standards cannot be achieved by the remedy selected in this ROD in
conjunction with the remedies implemented under prior RODs. The EPA anticipates that
completion of additional remedial actions will address compliance with these ARARs.
Cost-Effectiveness
The EPA has determined that the selected remedy is cost-effective pursuant to evaluations in
accordance with § 300.430(0(1 )(ii)(D) of the NCP.
Permanent Solutions and Treatment Technologies
The EPA has determined that the selected remedy represents the maximum extent to which
permanent solutions and treatment technologies can be utilized for the remedial action for the
Slickrock Creek area source AMD discharges. This proposed remedy involves as its prin-
cipal element the treatment of hazardous substance releases from the Slickrock Creek area
sources upstream of the retention dam.
The remedy will not reduce the generation of hazardous substances in the same manner that a
remedy that reduces or eliminates AMD-forming reactions (and thereby reduce the need for
ongoing treatment operations). The EPA has concluded that source-specific control actions
may be available for at least some of the Slickrock Creek area source AMD discharges.
However, those control actions are not currently implementable, effective, or cost-effective in
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comparison to the selected dam and treat remedial action. While current technology and
knowledge are not sufficient to permit implementation of reliable source-specific controls for
the Slickrock Creek area sources, EPA encourages the continued development of those alter-
natives that could reduce or eliminate the AMD-forming reactions. The EPA will continue to
consider subsequent action for the IMM Site that could supplant the need to perform long-
term treatment of the area source AMD discharges.
Consistency with Final Remedy
This action of selecting a remedial alternative that addresses Slickrock Creek without first
requiring completion of the studies for Boulder Creek is consistent with 40 CFR § 300.430
(a)(ii)(A), which identifies as a program management principle that "[s]ites should generally
be remediated in operable units when necessary or appropriate to achieve significant risk
reduction quickly, when phased analysis and response is necessary or appropriate given the
size and complexity of the Site, or to expedite the completion of total Site cleanup." The
investigations conducted by the EPA to date, including an intensive peer review of control
options, indicate that technically practicable and cost-effective remedies are available to
remediate releases of hazardous substances from Boulder Creek area sources and from
sediments in and below SCR.
This action does not constitute the final remedy for the IMM Site. Additional response
actions will further address the statutory preference for remedies employing treatment that
reduces toxicity, mobility, or volume as a principal element Subsequent actions are planned
to fully address the threats posed by the conditions at the facility. This remedy will result in
hazardous substances remaining onsite above health-based levels, so within 5 years after
commencement of the remedial action, EPA will conduct a review to ensure that the remedy
continues to provide adequate protection of human health and the environment. This is an
interim action ROD, so review of this facility and of this remedy will be ongoing as EPA
continues to develop final remedial alternatives for the Site.
Keith A. Takata, Director Date
Superfund Division
U.S. Environmental Protection Agency
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RECORD OF DECISION
IRON MOUNTAIN MINE
SHASTA COUNTY, CALIFORNIA
THE DECISION SUMMARY
I. SITE NAME, LOCATION, AND DESCRIPTION
1.1 Site Name
Iron Mountain is located in Shasta County, California, approximately 9 miles northwest of
the City of Redding (Figure 1). The collection of mines on Iron Mountain is known as Iron
Mountain Mines. The Iron Mountain Mines are the southernmost mines in the West Shasta
Mining District The District encompasses more than a dozen sulfide mines that have been
worked for silver, gold, copper, zinc, and pyrite.
\2 Site Location
The Iron Mountain Mine (IMM) Superfund Site is defined pursuant to CERCLA to include
the inactive mines on Iron Mountain and areas where hazardous substances released from the
mines are now located. The IMM Site contains approximately 4,400 acres of land that
includes the mining property on Iron Mountain; the several inactive underground and open
pit mines; numerous waste piles; abandoned mining facilities; mine drainage treatment
facilities; the downstream reaches of Boulder Creek, Slickrock Creek, Flat Creek, and Spring
Creek; Spring Creek Reservoir (SCR); Keswick Reservoir (which includes both the Spring
Creek arm of the Keswick Reservoir and the main body of Keswick Reservoir); and the
Sacramento River affected by drainage from IMM.
1.3 Site Description
The summit of Iron Mountain is 3,583 feet above mean sea level and is approximately
3,000 feet above the Sacramento River, 3 miles to the east. The terrain is very steep, with
slopes dropping 1 to 2 feet for every 2 feet horizontally, or steeper. The mountain is pre-
dominantly forested with areas of brush, and there are numerous unpaved roads leading to the
various work locations.
Several, and possibly all, of the mines and the waste rock piles are discharging acidic waters,
typically with a high content of heavy metals. These discharges are herein referred to collec-
tively as acid mine drainage, or AMD,. The largest sources of AMD are located within the
IMM property. The largest source of AMD is the Richmond Mine, and the second largest is
the Hornet Mine. Both of these sources drain into Boulder Creek. The third largest source,
Old/No. 8 Mine Seep, drains into Slickrock Creek. From 1988 to 1994 a portion of these
sources were treated at an emergency treatment plant. Starting in 1994, essentially all of
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IRON
MOUNTAIN
XL* "* V
'*'%, \T- SPRING CREEK
V A RESERVOIR
KESWICK
RESERVOIR
WHISKEYTOWN
LAKE
SITE LOCATION
FIGURE 1
LOCATION OF
IRON MOUNTAIN SITE
IRON MOUNTAIN MINE
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these sources have been treated at the IMM treatment plant constructed onsite at Minnesota
Flats. From 1994 to 1996 the AMD was treated using the simple mix treatment method.
Since January 1997, the HDS treatment system has provided an improved means of treating
these discharges.
These remedies have been highly effective in reducing the release of metals from the site.
Over the past several years, the treatment of selected AMD flows from IMM has reduced the
release of copper, cadmium, and zinc by approximately 80 to 90 percent
The remaining discharges derive from widely dispersed area sources associated with past
mining activities. The IMM area sources include waste piles; sidecast spoils; ground dis-
turbed by mining-related activities; mineralization exposed by mining-induced water table
depressions and other hydraulic changes induced by mining; discharges from buried workings
or partially accessible workings; contaminated soil and debris; mining-caused seeps;
contaminated interflow and groundwater; and contaminated sediments in the Slickrock
Creek, Boulder Creek, and Spring Creek watersheds at IMM. This ROD addresses area
sources in the Slickrock Creek watershed, which account for approximately 60 to 70 percent
of the uncontrolled copper loads, and 40 to 50 percent of the uncontrolled zinc and cadmium
loads currently being generated at IMM. The discharges from these sources are closely
associated with heavy rainfall and high runoff storm events.
The fishery resources and other sensitive aquatic species in Keswick Reservoir and in the
Sacramento River below Keswick Dam are the primary natural resources at risk to the con-
tinuing uncontrolled IMM heavy metal discharges from the Site. The exceedance of water
quality standards and the accumulation of toxic sediments downstream of IMM contribute to
the risks to species in the areas impacted by IMM releases. As a result of past mining
activities and current IMM AMD releases, the affected water bodies upstream of the Spring
Creek Debris Dam (SCDD) are essentially devoid of aquatic life and amphibians, which are
dependent upon that aquatic life. The releases also pose a potential threat to human health.
1.4 Adjacent Land Uses
The adjacent land is largely undeveloped wilderness property that is currently infrequently
visited because of the rugged topography and scarcity of roads. Off-road vehicles have been
known to visit these areas, and the U.S. Bureau of Land Management (BLM) has notified
EPA with regard to potential acquisition of adjacent lands for preservation as wilderness and
enhancement for recreational use.
1.5 Natural Resources Uses
The natural resources on the mining property and in the surface waters which flow on or
adjacent to the mining property atone time included mature stands of timber, fish, other
aquatic populations, and sulfide minerals. The IMM Site contains one very large mass of
nearly pure sulfide, several small sulfide deposits, several zones of disseminated sulfides, and
a large gossan. The mineral deposits are contained in a rhyolite bedrock. The gossan is a
rock zone from which sulfides have been almost completely removed by natural solution,
leaving a residue of iron and other metals. The gossan has been mined by open pit for resid-
ual metals. The sulfide deposits have been mined in open pit and underground openings for
copper, cadmium, zinc, and pyrite. Commercial mining at the IMM Site started in 1879 and
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continued with few interruptions until .1963. In the early twentieth century, the Site was one
of the largest copper mines in the United States. At that time, mineral extraction objectives
and methods varied widely at the Site. In recent years metal recovery activity at the Site has
been limited to extracting copper from the AMD using copper cementation.
The valuable natural resources in the downgradient Sacramento River include the Sacramento
River fishery, recreational use of the river and the Keswick Reservoir, and the water resource
itself, which is a major component of the U.S. Bureau of Reclamation's (USSR's) water
distribution system in California.
The portions of Boulder Creek, Slickrock Creek, and Spring Creek impacted by IMM AMD
are essentially lifeless. Spring Creek Reservoir was constructed in part as a mitigation
measure for the AMD discharges and does not support aquatic life, nor is it currently used for
any recreational purpose. The portion of Keswick Reservoir affected by IMM AMD has
reduced recreational value. The resident trout fishery in Keswick Reservoir and the main
body of the Sacramento River is impacted by both the heavy metal contaminants in the water
column of the mixing zones and the heavy sediment loading caused by the precipitation of
iron and other heavy metals discharged from IMM over the past century.
The upper Sacramento River salmon fishery is the most important fishery in the State of
California. The salmon fishery has experienced large population declines because of a
number of factors, including the IMM AMD impacts. The Sacramento River also supports a
major steelhead trout and resident trout fishery.
The IMM AMD discharges impact the beneficial uses of the Central Valley Project (CVP)
water resources. The CVP is a central component of the California water distribution system.
Shasta Lake, which is above the influence of IMM, plays an important role in California's
water distribution system for California's municipal and agricultural interests. The high metal
loads from IMM require large volumes of dilution water to dilute the pollution to levels that
are safe for the affected resources. The large pollution loads generated at IMM have required
emergency releases of clean water from Shasta Lake to dilute the IMM AMD. For example,
in 1992 the USER released more than 92,000 acre-feet of water during the sixth year of a
drought to dilute a spill of IMM-contaminated waters. This amount of water is sufficient to
supply the water demand for 360,000 people for one full year.
Currently, the SCR is relied on to meter the Spring Creek watershed surface waters,
contaminated by the continuing uncontrolled IMM AMD area source discharges, into the
Sacramento River at Keswick Reservoir. The SCR, coupled with the prior CERCLA
response actions implemented pursuant to ROD1, ROD2, and ROD3, provides some degree
of protection to aquatic resources and public health below the SCR, but IMM AMD dis-
charges continue to harm and pose risks to aquatic resources and human health in Keswick
Reservoir and the Sacramento River (particularly during certain storm events when dis-
charges from the Site are greatest). Under certain conditions, the intense hydrology of the
Spring Creek watershed and the highly polluted IMM AMD overwhelm the ability of the
SCR to contain releases until they can be safely diluted. When the SCR is full, IMM AMD
spills uncontrollably into Keswick Reservoir and the Sacramento River.
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The SCR is currently operated to target certain interim metal levels below Keswick Dam.
These operational targets approximate but do not equal the SBPS. If the SCR were operated
to target compliance with a more stringent standard such as the SBPS or the Proposed
California Toxics Rule (PCTR), water would be metered at a slower rate from the SCR,
which in turn would cause the reservoir to fill and spill more frequently. Under current
conditions, uncontrolled SCDD spills are expected to occur on average every 3 to 4 years if
the SCDD is operated to achieve the SBPS below Keswick Dam. Operating the SCDD to
meet the recently proposed PCTR (below Keswick Dam) would cause the spills to occur ever
2 to 3 years on average. Spills would occur even more frequently if the SCR were operated
to target compliance with these standards in Keswick Reservoir rather than downstream of
Keswick Dam. Even during non-spill periods, metal levels in the part of Keswick Reservoir
closest to the SCDD are toxic to aquatic life for much of the year and many miles of creek
above the SCDD are completely devoid of life as a result releases from the site. The
frequency of SCDD spills can be reduced by reducing metal loads to SCR (by controlling
pollution at Iron Mountain). The lower metal loads to SCR will permit the IMM AMD to be
evacuated from the SCDD at a faster rate, which in turn would decrease the frequency of
SCDD spills and exceedances of water quality criteria.
A major portion of the sulfide minerals remains in the mines and in undeveloped areas. The
market for sulfide minerals has not been attractive in recent years, and there is no verified
proposal to mine these deposits in the near future.
The timber that remains at IMM is not a valuable resource. The timber has either been
removed for the mine operations or sale or it was extensively damaged by smelter operations
in the early 1900s.
1.6 Location of and Distance from Human Populations
Iron Mountain Mine is relatively remote from human populations because of the rugged ter-
rain and the single-access roadway. The City of Redding has a population of approximately
70,000 people and is located approximately 9 miles from the Site. The closest community is
Keswick, located just east of the Site. There are several isolated residences between Keswick
and the mine property. The EPA has provided metal gates, which are locked at most times,
to discourage casual entry to the Site. Currently, human contact with surface waters impacted
by IMM contaminant discharges is mainly limited to areas downstream of the SCDD, which
include Keswick Reservoir and the Sacramento River below Keswick Dam.
1.7 General Surface-Water and Groundwater Resources
Iron Mountain Mine surface drainage includes Boulder Creek, located northeast of the
mountain, and Slickrock Creek, located to the southwest. Boulder Creek and Slickrock
Creek flow into Spring Creek, which flows south and east to the SCR. The USER releases
flow into the Sacramento River from the SCR. Flat Creek drains an area to the east of Iron
Mountain and enters the Sacramento River approximately 0.8 mile north of Spring Creek. As
a result of a water diversion project constructed in 1990 as part of the CERCLA response at
Iron Mountain, Flat Creek also receives water from Upper Spring Creek.
Slickrock Creek drains the south side of Iron Mountain and flows generally from the north-
west to the southeast. The headwaters of Slickrock Creek are at about Elevation 3200 feet.
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The creek flows about 3 miles to its confluence with Spring Creek at Elevation 1350. The
stream carries water from several small ephemeral tributaries as well as discharges from
Old/No. 8 Mine Seep and Big Seep, 200 to 300 feet upstream. Slickrock Creek also receives
drainage from Brick Flat Pit. The average daily flow of Slickrock Creek at its confluence
with Spring Creek is 9.4 cubic feet per second (cfs) (4,200 gallons per minute [gpm]).
The rainfall-runoff varies significantly between and during storm events. The amount of run-
off is dependent on antecedent moisture conditions, storm intensity, the vegetative cover,
ground slope, length of distributing area, and geology. Major storm events produce a rapid
rise in water levels in the creeks.
The rhyolite rock that makes up IMM is very dense, with two to three sets of joints and a
number of faults. The rock mass lacks significant porosity because of joint/fault discontinui-
ties. The sulfide mass deposits were largely isolated from the groundwater before mining
because the joints generally do not extend from the rhyolitic rock into the mineralized zone.
Groundwater was present in the disseminated sulfide zones. Mine openings and fracturing
caused by ground movements induced by mining have created access routes for the ground-
water to the large volumes of massive sulfide deposits and have increased groundwater
access to the disseminated sulfide mineralization. The additional groundwater movement and
increased circulation of air within the mountain has greatly accelerated the process of sulfide
dissolution and the formation of metal-rich acid mine drainage.
Surface water and groundwater at Iron Mountain were previously used for mining operations
and to provide water supply to the mine staff and their families. These resources are essen-
tially unused today because the mines are inactive and surface waters are being contaminated
by AMD.
1.8 Surface and Subsurface Features
The largest sulfide ore mines on Iron Mountain include an open pit mine at Brick Flat,
underground workings at Old Mine, No. 8 Mine, the Confidence-Complex Mine on the
southern flank of the mountain, and the Richmond and Hornet Mines on the northern flank.
The Slickrock Creek drainage mines include the Old Mine, No. 8 Mine, Confidence Mine,
and the Okosh Mine. The Old Mine and No. 8 Mine have had more significant mining
operations and are considered more significant sources of AMD. The Okosh and Confidence
Mines are considered to be less significant sources than the Old Mine and No. 8 mine but do
discharge AMD during certain periods.
Old Mine was developed to mine portions of a gossan deposit which could not be reached by
quarrying. The mine is under the north slope of Slickrock Creek Valley with the mine work-
ings ranging from the elevation of the lower slope to well below the elevation of the adjacent
reach of Slickrock Creek. Mining in the Old Mine relied upon a method of underground
mining called slice sloping. The ore was removed in 7-foot-high layers working from the
bottom toward the top of the deposit. A working surface was maintained by progressively
backfilling the mined opening with rock rubble returned to the mine through dropholes from
the ground surface. The extent of the backfilling is not clear from the records available, but
the volume of remaining voids at the time of closure appears to have been small compared to
adjacent mines. The backfilling operation was performed to support the working surface,
ROD4.DOC 14
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was highly porous, and did not re-establish the pre-mining, undisturbed hydrologic conditions
that would serve to reduce the rate of pyrite oxidation. In fact, the temperature of sulfides in
the backfilled areas of the mine was so high, resulting from the ongoing oxidation reactions,
that the sulfide minerals regularly caught on fire, presenting a severe safety hazard to miners.
The ore deposit of the No. 8 Mine is at the level of the middle of the north slope of Slickrock
Creek Valley. The intervening 300 feet of rock has little or no sulfide mineralization. The
ore is a mass of rock with disseminated chalcopyrite mineralization in veins. In contrast, the
other mines on the IMM Site consist of massive sulfide or massive disseminated ore bodies.
The No. 8 Mine consists of three levels of tunnels and small- to moderate-size openings
which follow the veins. The mine is as high as Elevation 2400, but portions are below the
elevation of Slickrock Creek. Mining started in 1907 and ended after World War H Portions
of the mine are reported to have been backfilled with waste rock or tailings slime. In order to
support this effort to backfill the mine openings, the No. 8 Adit was plugged. Although the
attempt to backfill the No. 8 Mine with gossan slimes was essentially unsuccessful, plugging
the mine opening has resulted in the flooding of the underground workings to a level approxi-
mately 100 feet above elevation of the No. 8 Adit This discharge emerges from the massive
Slickrock Creek debris slide as the Old/No. 8 Mine Seep. An estimated 1.7 million tons of
ore was extracted from the Old and No. 8 Mines.
The Brick Flat open pit mine was operated between 1929 and 1942 for gossan and from 1955
to 1962 for pyrite. Approximately 500,000 tons of ore were extracted. Millions of tons of
overburden containing low grade, disseminated mineralization were dumped into Slickrock
Creek in the effort to expose the ore in Brick Flat Pit. Most of the overburden and waste rock
was placed in a large waste pile south of the pit and above the north slope of Slickrock Creek
Valley. In 1955, a large landslide of these materials moved into the Slickrock Creek Valley,
covered the Old Mine and No. 8 Mine portals, and filled the valley bottom to a depth of 80
feet. A comparison of old and recent topographic maps indicates that the present bed of
Slickrock Creek is about 40 feet south of the bed prior to the large, mining-induced slide.
The slide surface is presently almost devoid of vegetation, suggesting continued sliding.
Significant portions of the gossan cap on Iron Mountain were mined to recover gold and sil-
ver in a heap leaching operation. Approximately 2.7 million tons of gossan were extracted,
crushed, and processed for recovery of precious metals. The extraction of gossan ore
required the excavation and wasting of significant amounts of overburden and low grade
gossan, which were dumped on steep slopes of the Slickrock Creek watershed or in the creek
itself behind tailings dams. The finely crushed wastes from the heap leaching operations
were dumped into Hogtown Gulch, forming the enormous waste piles that today are called
the hematite piles.
II. SITE HISTORY AND ENFORCEMENT ACTIVITIES
11.1 History of Site Activities that Led to Current Problem
Iron Mountain Mine was first secured for mining purposes in 1865, and various individuals
held the property and conducted limited mining for the recovery of silver from the gossan
areas in the late 1800s. The waste-generating activities that created the surface sources of
AMD likely began in the 1880s when the gossan was first mined on a large scale, and waste
ROD4.DOC 15
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rock that was removed to reach the ore was apparently dumped into ravines and eventually
washed into the creeks.
Beginning in late 1894, Mountain Mining Co., Ltd. (Mountain Copper), began operation of
the mine. In approximately 1896, Mountain Copper assumed ownership of the mine. Under
Mountain Copper, IMM became the largest producer of copper in California and the sixth
largest producer in the country during the first quarter of the twentieth century. High-grade
copper ore was mined in Old Mine until 1907, No. 8 mine from 1907 until as late as 1923,
Hornet Mine from 1907 to 1926, the Richmond Mine from 1926 through 1956, and Brick
Flat Pit from 1929 to 1942 and 1955 to 1962.
In 1967, Stauffer Chemical Co. (SCC) acquired Mountain Copper. In 1968, SCC obtained
legal title to the properties comprising IMM from its wholly owned subsidiary, Mountain
Copper Company, Ltd. SCC originally to'ok steps to reopen the mine, but the price of sulfur
dropped to a pbint that caused the option to be uneconomical. SCC operated the copper
cementation plant on Boulder Creek during its ownership of the Site and continued to inves-
tigate the commercial mining potential of the property. In November 1976, the Central
Valley Regional Water Quality Control Board (CVRWQCB) issued an order to SCC
requiring the abatement of the continuing pollution from the mountain.
In December 1976, SCC transferred ownership of 31 parcels on Iron Mountain to Iron
Mountain Mines, Inc. (IMMI), and in December 1980, SCC transferred five additional
parcels to IMMI. IMMI, a California corporation, is the current owner of Iron Mountain, but
SCC retained ownership of certain property interests at the Site. IMMI constructed a copper
cementation plant on Slickrock Creek in 1977. IMMI has intermittently operated this plant
and the copper cementation plant on Boulder Creek to recover copper from the AMD.
11.2 Impacts of Mining Activity at Iron Mountain
Mining activities have fundamentally altered the geochemical and hydrologic conditions at
Iron Mountain. In an undisturbed condition, a series of geologic and geochemical factors
combined to permit the several large masses of sulfide mineralization to remain in place
below the water table over geologic time. Now that mining has altered those conditions,
however, the massive mineralization is no longer protected by the water table from oxidation,
which in turn has exposed the mineralization to conditions that permit the rapid (on a
geologic time scale) oxidation and release of acidity and metals from that deposit Although
the mineral deposit was formed about 400 million years ago, mining has accelerated the rate
of oxidation such that it will now take only about 3,000 years to deplete the entire deposit.
These mining-induced changes are the source of the severe pollution problem at IMM.
When pyrite is exposed to moisture and an oxidant (such as free oxygen or an aqueous ferric
iron), the pyrite oxidizes and releases acidity. This acidity mobilizes metals, such as copper,
cadmium, and zinc, into solution. The overall driving force for this reaction is the
accessibility of an oxidant, either in the form of free oxygen or some other oxidant such as
aqueous ferric iron. The rate at which pyrite oxidizes is limited by the access of the pyrite to
oxidants. The oxidation of pyrite produces an iron oxide material or gossan.
ROD4.DOC 16
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Prior to mining, a gossan cap and relatively impervious bedrock protected the fresh
mineralization (i.e., unoxidized pyrite) from extensive oxidation. Although relatively small
amounts of pyrite and metal exist within the weathered gossan on the surface, those materials
did not generate appreciable amounts of heavy metals and acidity relative to current
conditions. The undisturbed gossan provided a protective shell that limited the access of
water and oxygen to the residual unoxidized pyrite and metals locked within the gossan.
The undisturbed gossan contained preferential flow paths that conveyed rainfall as runoff to
the creeks. These flow paths would typically be highly weathered by exposure over geologic
time. Since they were highly weathered, the flow paths would permit rainfall to move
quickly through the gossan without becoming highly acidic. These preferential flow paths
also channeled water along the surface so rainfall tended to not penetrate to deeper areas
where unoxidized mineralization was present Water traveling through highly weathered
gossan therefore contains essentially no dissolved metals or acidity.
In the undisturbed condition, the fresh (i.e., unoxidized) mineralization at IMM was largely
below the water table and therefore isolated from conditions (namely, both free oxygen and
water) that permit the formation of highly acidic and metal-laden AMD. While limited
oxidation occurred near the contact between the iron oxides of the gossan and the fresh
massive sulfide, numerous factors combine to severely limit the flow through the area of
oxidation as well as the rate of oxidation. In an undisturbed mineralized environment, the
hydrology typically permits only a small fraction of the groundwater to contact the min-
eralization deep below the surface because, with depth, the ground tends to become less
permeable and less fractured. When fractures do occur at depth in undisturbed mineraliza-
tion, the fractures tend to be highly localized, which in turn restricts the flow of water and
oxygen into and out of the fracture. Buildup of oxidation products (i.e. clays) within the area
of oxidation would also act to limit the infiltration of fresh water to the zone, which would
act to further restrict the flow in the area of oxidation. The steep topography at Iron Moun-
tain further limits the introduction of groundwater because a greater portion of rainfall would
be expected to run off rather than infiltrate the mountain. Furthermore, the water that does
infiltrate will be subject to very high hydraulic gradients promoting groundwater flow to the
creeks rather than to the relatively deep oxidation zone under natural conditions.
As groundwater infiltrates below the groundwater table and the zone of active oxidation,
oxygen is depleted and the groundwater becomes reduced. In this reducing environment,
soluble copper from the oxidized zone is immobilized as secondary copper sulfides. Since
secondary sulfides retain at least some of the metals, metals are not entirely released from the
massive sulfide to the groundwater entering Boulder and Slickrock Creeks.
Mining activities at Iron Mountain changed these conditions in profound ways. Mountain
Copper employed sloping, block caving, and room-and-pillar mining techniques in the
underground mines; side-hill and open-pit techniques were used at the ground surface. The
extensive mine disturbance in the Slickrock Creek basin is shown in Photo Exhibit 1, located
at the back of this Record of Decision. These mining activities and subsequent collapse of
some of the underground mine workings have fractured the bedrock overlying the mines.
The sulfides in the fractured bedrock above the mines and the sulfides remaining in the mines
are, in the post-mining period, more exposed to water, air, and bacterial action. The potential
ROD4.DOC 17
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for acid drainage and metals contamination is greater than prior to mining and, since the
mining ceased, this potential may have increased in response to deterioration of the ground
over the abandoned mines.
The engineered mine openings and the partially collapsed mineralized zones affected by
mining activity now function as effective groundwater drains drawing groundwater and
unsaturated percolation to and through the sulfide mineralization. Prior to mining, ground-
water movement through this area would have been quite limited relative to current condi-
tions. The increased flows through these unoxidized areas altered the rate of oxidation in
these areas. Increased flows resulted in releases of acidity and metals above the levels that
existed before the mining disturbance.
Mining also altered the release of metals and acidity by exposing sulfides that were once
largely below the water table (and therefore not exposed to free oxygen or another oxidant) to
conditions that permit the rapid oxidation and release of metals and acidity. Mining activities
lowered the groundwater table through channeling groundwater through engineering mine
workings, mine fractures, and other mine disturbances. The lowering of the groundwater
table exposes fresh sulfides to free oxygen and water (where prior to mining these sulfides
were not exposed to free oxygen because they were under water). The lowering of the
groundwater table therefore increases the rate of oxidation and release of acidity and metals.
The increased oxidation of the sulfide elevates the overall temperature in the sulfide min-
eralized zone because the reaction is exothermic. The increased heat associated with these
higher reaction rates induces convective airflow, and likely induces evaporation of some
subsurface mine waters. These processes contribute to the intensity and pattern of acidic
discharges.
Mining also increased the oxidation rate of gossan by fracturing, crushing, pulverizing and
otherwise breaking the gossan, which in turn exposes the residual metals and pyrite within
the gossan to greater flows of water and oxidants.
These mining-related characteristics, in combination with the occurrence of the highly
concentrated massive sulfide deposits surrounded by bedrock with very little neutralizing
capacity, result in a unique hydrogeochemical reactor that is nearly optimal for maximum
production of acid mine waters. Iron Mountain produces runoff that is among the most acidic
in the world, containing extremely elevated concentrations of copper, cadmium, zinc, and
other metals known to be toxic to aquatic life and humans.
Mining has changed not only the pH and the concentration of heavy metals in the receiving
waters, but also the pattern of release of hazardous substances. Prior to mining, the metal and
acidity releases that-did occur would have been diluted releases associated with surface
runoff from the highly weathered surfaces of Iron Mountain and groundwater that would have
not been exposed to highly reactive mineralization (because the elevated water table would
submerge unreacted sulfides, excluding oxygen and inhibiting the oxidation reaction). In
contrast, the post-mining discharges include surface runoff that percolates through enormous
highly porous waste piles, disturbed soils, and surface mining areas; groundwater that
percolates through fractured geologic systems in contact with highly reactive mineralization
ROD4.DOC 18
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exposed by the depressed water table; and significant discharges of highly concentrated AMD
issuing from the mine workings that results from inflow of near-surface waters deep into the
fractured mineralized zones through conduits of collapsed and caved ground. These
disturbances therefore create the intense peak metal discharges associated with high-flow
events, in addition to the high metal loads associated with low-flow conditions.
The sources addressed by the action selected in this Record of Decision include the area
sources in the Slickrock Creek watershed. These sources include waste piles, sidecast spoils,
ground disturbed by mining-related activities, discharges from buried workings or partially
accessible workings, mine-contaminated soil and debris, mining-related seeps, mining-
contaminated interflow and groundwater, and mining-contaminated sediments in the
Slickrock Creek watershed at IMM. These sources have clearly been altered by mining
Photo Exhibits 1 and 2 (located at the back of this Record of Decision) illustrate both the
extent of mining disturbance in the area being remediated and the degree to which the
response action is focused upon the most heavily disturbed portion of the Slickrock Creek
basin. Among the sources being remediated, EPA is aware of no identifiable release or threat
of release of a naturally occurring substance in its unaltered form, or altered solely through
naturally occurring processes or phenomena, from a location where it is naturally found.
11.3 Central Valley Project-Related Impacts
The Sacramento River is a primary water resource for much of the State of California. As
growth increased the demand for water, the importance of the Sacramento River has grown as
well. The increasing demand for scarce water resources, coupled with a growing under-
standing of the sensitivity of aquatic resources to trace levels of toxic metals present in the
Sacramento River as a result of past mining activities, has increased the significance of IMM
AMD impacts in the Sacramento River.
In response to the growing demand for water and the need to control flood waters, the USER
constructed the Shasta Dam to control Sacramento River flows. USER completed the Shasta
Dam in 1943 and the Keswick Dam, located downstream of Shasta Dam, in 1950. Construc-
tion of the dams changed the conditions in the Sacramento River. Once USER completed the
Shasta and Keswick Dams in 1950, the salmon and steelhead were restricted to spawning
grounds in areas downstream of Keswick Dam, which is one of the areas of the Sacramento
River with the greatest exposure to AMD discharges from Iron Mountain (the other area
being Keswick Reservoir). The dam also reduced the availability of dilution flows at certain
times, which would tend to increase the metal concentrations in the river. While the Shasta
and Keswick Dams changed the river system, toxicity problems are documented both before
and after the completion of Shasta Dam in 1943. Only limited water quality information is
available from the pre-Shasta period, but water quality modeling and the limited available
data indicate that, prior to the construction of the Shasta Dam, the IMM mine discharges
caused metal levels in the Sacramento River to exceed levels that are safe for aquatic life for
more than 330 days each year on average, even after the releases become fully mixed with
Sacramento River waters downriver of the confluence of Spring Creek and the Sacramento
River. Prior to full mixing, the waters would have been even more toxic to exposed
resources.
ROD4.DOC 19
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In 1963, USBR constructed the SCDD to help control the toxic releases from Spring Creek
and to prevent sediment from forming a delta in the vicinity of the Spring Creek Ppwerplant
tailrace. The SCDD allows for the storage and controlled release of water from the Spring
Creek basin. Optimally, releases from SCR are timed to coincide with releases from Shasta
Lake to meet interim water quality criteria in the Sacramento River. However, because the
capacity of SCR is not sufficiently large to contain peak discharges from the Spring Creek
watershed, large flows can cause the highly polluted SCR waters to spill over the reservoir in
an uncontrolled manner. The SCDD has reduced but not eliminated the incidence and
severity of major fish kills in the Sacramento River below Keswick Dam and in Keswick
Reservoir. As a result of discharges from IMM, soluble metal levels below Keswick Dam can
be just below the State Basin Plan Standards (SBPS) for much of the wet season, and metal
levels in the Spring Creek arm of Keswick Reservoir (SCAKR) exceed those standards on a
regular basis. (See EPA's 1996 Water Management Feasibility Study Addendum (FSA),
Volume n, Appendix G.) As would be expected from these large metal loads, fish tissue
samples from Keswick Reservoir trout have some of the highest levels of cadmium and
copper in the state.
The most significant IMM sources of metals are currently being controlled, but the IMM
releases are still too large to prevent toxic levels of metals in Keswick Reservoir and, under
certain conditions, in the main stem of the Sacramento River below Keswick Dam. During
storms in 1995 and 1996, SCR waters, with full treatment of the three major mine discharges
(which EPA estimates controlled approximately 80 to 90 percent of the metal load from the
Site), exhibited levels of contamination of 400 to 800 parts per billion (ppb) dissolved copper
(compared to the existing SBPS of 5.6 ppb copper) and 600 to 1,200 ppb dissolved zinc
(compared to the existing SBPS of 16 ppb zinc). Storm inflows into the SCR can exceed
1,000 cfs. Sacramento River flows are frequently near minimum legal flows during the first
storm of the season, or not more than 10,000 cfs. Under these conditions, the Sacramento
River flows cannot provide sufficient dilution of the IMM AMD-contaminated Spring Creek
watershed surface waters at current levels of contamination to prevent the IMM discharges
from causing exceedances of water quality standards in the Sacramento River. At the current
status of the IMM Superfund cleanup action, with full-scale treatment of the three major
IMM sources, IMM discharges will continue to cause exceedances of water quality standards
below Keswick Dam even under best-case assumptions regarding SCDD operations.
The two most important factors which currently make it impossible for the SCDD to permit
dilution of IMM AMD in a manner that maintains water quality conditions in the Sacramento
River within safe bounds for ecosystem protection are: (1) the storm inflows to the SCR are
highly contaminated from IMM, and (2) storms that cause these contaminated waters to fill
the reservoir within just a few days will likely occur every 5 to 10 years. Significant further
remediation of the IMM area source AMD discharges is required to ensure that the existing
SCDD will be able to provide sufficient capacity to avoid exceedances of water quality
standards below the SCDD.
11.4 History of Federal and State Site Investigations
Remedial investigation (RI) activities at Iron Mountain began in September 1983, when Iron
Mountain was placed on the National Priorities List of the nation's most contaminated sites.
ROD4.DOC 20
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In conjunction with EPA's Record of Decision (ROD1) for the first operable unit at Iron
Mountain, EPA issued a remedial investigation/feasibility study (RI/FS) report in 1985 and
an FS Addendum in 1986. The 1985 RI report characterized the entire IMM Site with respect
to the nature and extent of contamination. The EPA's Public Health Risk Assessment was
updated in 1991. Site characterization studies continued for the Boulder Creek watershed,
and EPA prepared a second RI/FS report for that area in 1992. An Endangerment
Assessment (EA) was prepared in 1992 to characterize and evaluate the current and potential
threats to the environment that may be posed by IMM contaminants migrating to the ground-
water, surface water, and air. Site characterization studies continued for the Slickrock Creek
watershed, and EPA prepared an RI/FS report for that area in 1993. The EPA issued its
Water Management FS in 1994, the Boulder Creek Remedial Alternatives Study in 1995, and
the Water Management FS Addendum in 1996.
The EPA signed the first Record of Decision for the IMM Site in October 1986. ROD1
selected an interim remedy at the Site, identifying a number of specific projects. These proj-
ects included the construction of a partial cap over the Richmond mineralized zone, including
a cap of Brick Flat Pit; construction of a diversion in Slickrock Creek to avoid an AMD-
generating slide; construction of a diversion of the Upper Spring Creek to avoid polluting its
cleaner water and filling SCR; construction of a diversion of the South Fork of Spring Creek
for a similar purpose; a study of the feasibility of filling mine passages with low-density cel-
lular concrete; and an enlargement of SCDD, the exact size of which would be selected after
a determination of the effectiveness of the other remedies. EPA tentatively selected a 9,000-
acre-foot reservoir size in ROD1 although the underlying studies indicated that a 15,000-
acre-foot reservoir would be required for a protective remedy. In its tentative selection of a
smaller reservoir size, EPA relied on a fund-balancing waiver, which permits EPA to waive
compliance with protective standards for cleanups that are being paid for by the Superfund.
The Boulder Creek Operable Unit (OU) ROD, signed in September 1992, addressed remedial
actions for (1) AMD from the Richmond and Lawson portals, the two largest sources of
acidity and metals contamination at Iron Mountain; and (2) the numerous waste rock piles,
tailing piles, seeps, and contaminated sediments that also affect contaminant levels in Boul-
der Creek. .The Old/No. 8 Mine Seep OU ROD, signed in September 1993, addressed the
third largest source of contaminant discharges at IMM.
On the basis of the results of its ongoing monitoring program, EPA concluded that the area
source discharges of heavy metals, especially copper, zinc, and cadmium, were closely
associated with the intense storm-related high runoff events that characterize the hydrology of
the Spring Creek watershed at IMM.
Through a formal action in 1991 known as an explanation of significant difference (ESD),
EPA revoked the fund balancing waiver upon which EPA relied for ROD1. This formal
action removed the legal basis for EPA's tentative selection of a 9,000-acre-foot reservoir in
ROD2 in lieu of a larger, more protective dam. Consistent with the SCDD enlargement
component of ROD1 and the ESD, EPA conducted engineering and other studies regarding
enlarging the SCDD. These studies indicated that a reservoir of at least 15,000 acre-feet
would be required. Due to the projected increased costs of the SCDD enlargement and the
availability of other new information, EPA decided to expand its studies, re-evaluate other
ROD4.DOC 21
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remedial technologies, and publish for public review and comment a new feasibility study
and proposed plan.
In June 1994, EPA published a Water Management FS, which examined potential remedial
alternatives that could control, treat, or manage the safe release of continued uncontrolled
contaminant discharges from the numerous and widely dispersed area sources in the Boulder
Creek and Slickrock Creek watersheds at IMM. In the 1994 Water Management FS, EPA
developed five alternatives for detailed evaluation. These alternatives included a range of
approaches that relied on source control, collection and treatment, and water management
technologies. Although some area sources could be readily identified and remediated (such
as waste piles), a large proportion of the area source discharge was, in general, difficult to
identify and characterize. Proven cost-effective, source-specific remedial approaches for
these sources are often either unavailable or difficult to identify. Generally, the expected
effectiveness of-identified source control approaches for these sources is highly uncertain. As
a result, the approaches used in the remedial alternatives developed and evaluated in the
Water Management FS relied more heavily on collection and treatment and water manage-
ment rather than on source control..
In June 1994, EPA issued a Proposed Plan with a set of remedial actions for the IMM area
source AMD discharges. The Proposed Plan largely relied on a water management approach,
with some additional treatment of IMM AMD discharges, consisting of the following three
components:
1. Collect and treat the contaminated base flows of Slickrock Creek;
2. Enlarge the SCR to 15,000 acre-feet to enhance water management capabilities for the
Site; and
3. Study the technical and administrative feasibility of purchasing dilution water to mitigate
the rare contaminant spills that would be expected to occur under this approach.
The EPA invited public comment on EPA's analyses, the alternatives that EPA developed and
evaluated, and EPA's preferred alternative.
During the public comment period for the 1994 Proposed Plan, a potentially responsible party
(PRP), Rhone-Poulenc, Inc. (Rhone-Poulenc) (through its representative, Stauffer Man-
agement Company [SMC]) submitted a Focused Feasibility Study (FFS). Like the EPA
feasibility study, the FFS identified a range of general collect and treat alternatives for the
area source releases from the Slickrock Creek watershed. Rhone-Poulenc urged EPA to
delay selecting a remedy so that an additional season of data could be collected.
The EPA reviewed and analyzed the alternatives developed in Rhone-Poulenc "s 1994 FFS, as
well as other comments submitted during the comment period. The EPA determined that
delay in remedy selection was justified because the information submitted by Rhone-Poulenc
suggested that it was technically feasible (and also more cost-effective) to control the IMM
pollution on the mountain rather than simply diluting pollution by enlarging the SCDD.
ROD4.DOC 22
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This delay permitted Rhone-Poulenc and EPA an opportunity to collect additional data. Over
the 1994-95 wet season, Rhone-Poulenc implemented a substantial data-gathering program to
characterize the IMM area source AMD discharges. This data acquisition program included
activities intended to identify and characterize Boulder Creek area sources to support an
effort to develop and evaluate source-specific remedial approaches. Rhone-Poulenc did not
investigate source-specific controls for the Slickrock Creek area sources, but rather directed
its efforts toward general collect and treat approaches such as the Slickrock Creek dam and
treat approach. Rhone-Poulenc performed engineering studies intended to further character-
ize and define key hydrologic and engineering factors for the development and evaluation of
the Slickrock Creek "dam and treat" approach. Rhone-Poulenc also developed remedial
design concepts for proposed Slickrock Creek and Boulder Creek remedies. The data col-
lected by Rhone-Poulenc confirmed EPA's earlier determination that additional response
actions were needed to control the releases from IMM (as well as EPA's estimates of the
effectiveness of-the remedial steps implemented to date).
The EPA also performed independent engineering, laboratory, and field studies and reviewed
and prepared analyses of the data generated by the Rhone-Poulenc sampling effort. The EPA
participated in technical meetings with Rhone-Poulenc to develop remedial design concepts
for a Slickrock Creek "dam and treat" remedy.
To ensure that technically implementable remedies were available for the Boulder Creek
watershed, EPA conducted a Boulder Creek Remedial Alternatives Study in 1995, which
evaluated the technical feasibility of remediating Boulder Creek area sources to various target
cleanup levels. Rhone-Poulenc also studied the feasibility of remediating Boulder Creek area
sources. Both EPA's and Rhone-Poulenc's studies concluded that the Boulder Creek area
sources could be remediated to within the range of potential target cleanup levels presented
by EPA as part of the 1995 Boulder Creek Remedial Alternatives Study.
In August 1995, EPA and Rhone-Poulenc presented their respective analyses and conclusions
with regard to the ongoing Boulder Creek studies to a panel of senior technical specialists for
review and technical comment. The EPA requested that the panel evaluate the feasibility of
remediating the Boulder Creek area sources to achieve a range of potential cleanup criteria.
The Boulder Creek Peer Review panel members concurred that the range of potential cleanup
targets for Boulder Creek could be met through a program of Boulder Creek remedial actions.
The independent peer review panel members' comments presented a range of opinions on the
preferred technical approach for remediating the Boulder Creek metal discharge sources.
Consistent with the panel comments, EPA concluded that adequate control of the Boulder
Creek area sources was feasible, but deferred action on developing and evaluating proposed
remedial approaches for these sources to allow time for additional study.
The EPA incorporated these and other investigations into a Water Management Feasibility
Study Addendum (FSA) in May 1996. The FSA evaluated an additional remedial alternative
as a supplement to the June 1994 Water Management Feasibility Study. EPA's May 1996
Public Comment Water Management FSA updated the public record to include an evaluation
of an alternative that addressed only the remediation of Slickrock Creek, Alternative SRI.
The 1994 FS evaluated remedial options that would respond to all AMD releases from the
Site. In particular, the alternatives would have addressed both the Slickrock and Boulder
ROD4.DOC 23
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Creek sources through source control, treatment, or water management remedial approaches.
In May 1996, EPA formally announced that it proposed to select Alternative SRI as its
"Preferred Alternative" for the contaminated Slickrock Creek flows. The EPA proposed to
perform additional studies regarding the Boulder Creek area source AMD discharges to
support further development and evaluation of alternatives for decision making.
11.5 History of CERCLA Enforcement Activities and Remedial Actions
The EPA's Superfund program became involved with the Iron Mountain pollution problem
shortly after the enactment of the Superfund law in December 1980. On April 5,1982, EPA
issued general notices of liability to SCC and IMMI for the past and continuing releases of
hazardous substances from Iron Mountain and the resulting damage to and destruction of
natural resources.
The IMM Site was listed on the National Priorities List in 1983. From 1983 through 1985,
EPA conducted an RJ/FS of the Site and published its report in 1985. After public comment
and publication of a Feasibility Study Addendum, EPA signed ROD1 in October 1986. That
ROD selected an interim remedy at the Site, which included a number of specific projects.
These projects included the construction of a partial cap over the Richmond mineralized
zone, including a cap of Brick Flat Pit; construction of a diversion in Slickrock Creek to
avoid an AMD-generating slide; construction of a diversion of the Upper Spring Creek to
avoid polluting its cleaner water and filling SCR; construction of a diversion of the South
Fork of Spring Creek for a similar purpose; a study of the feasibility of filling mine passages
with low-density cellular concrete; and an enlargement of SCDD, the exact size of which
would be selected after a determination of the effectiveness of the other remedies.
During 1987 and 1988, EPA sought a court order to ensure access to the Site for the purpose
of constructing the first of these actions. The court granted EPA access and ordered the
property owner not to interfere with the remedial actions. On July 19, 1988, EPA initiated
construction of the partial cap over the Richmond mineralized zone. As part of that con-
struction, EPA remediated tailings materials from the Minnesota Flat area and other selected
areas, by placing the materials into Brick Flat Pit below an impermeable membrane or "cap."
The EPA completed construction of the partial cap in July 1989. The EPA, through the
USER, began construction of the Slickrock Creek diversion in July 1989 and completed
construction in January 1990. Under EPA Administrative Order 90-08, Rhone-Poulenc, the
successor to Stauffer Chemical Company (through its indemnitor, ICI Americas, Inc.
[ICIA]), began construction of the Upper Spring Creek (USC) diversion in July 1990. The
USC diversion became operational in January 1991.
In addition to the activities implemented pursuant to ROD1, EPA recognized the need for
additional actions. During the-4 988-89-wet season* EPA operated an emergency treatment
plant at the Site to reduce the toxicity of the AMD releases.
In August 1989, EPA issued Administrative Order 89-18, which required the PRPs to operate
an emergency treatment plant at the Site to reduce the toxicity of the AMD discharges for the
upcoming 1989-90 winter wet season and to provide for metals removal for future years until
remedial actions could be selected and implemented. This plant was to be comparable in
scope and operation to the plant operated by EPA the previous winter. Pursuant to that order,
ROD4.DOC 24
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ICI A, on behalf of Rhone-Poulenc, constructed the treatment plant and operated this treat-
ment plant during the 1989-90,1990-91, and 1991-92 wet seasons. Because of the continu-
ing drought in California and the critical fishery conditions, EPA issued Administrative Order
92-26 on September 2, 1992, for the 1992-93 wet season, requiring that additional emergency
measures be implemented, including increasing the capacity of the treatment plant. The EPA
also issued Administrative Order 91-07, requiring the PRPs to operate and maintain EPA-
constructed remedial actions and the remedial projects undertaken by the PRPs under other
orders.
As part of its ongoing efforts to control the AMD from IMM, EPA conducted an operable
unit feasibility study (OUFS) to develop and evaluate remedial alternatives for the AMD
discharges in the Boulder Creek watershed. The EPA's 1992 RI report summarizes the data
which show the concentration, volume, and historic patterns of releases of AMD from the
Boulder Creek watershed at IMM. On September 30,1992, EPA signed ROD2, a Record of
Decision that selected treatment of the AMD discharges from the Richmond and Lawson
portals, the two largest AMD discharges at IMM, on an interim basis in a lime neutralization
HDS treatment plant. That Record of Decision also selected the consolidation and capping of
seven waste piles onsite. Under ROD2, treatment plant sludges are to be disposed of onsite
in the inactive open pit mine, Brick Flat Pit, which was modified to comply with applicable
disposal standards.
On November 3,1992, EPA issued Administrative Order 93-01, requiring the PRPs to design
and construct all necessary facilities to collect, convey, and treat the discharges of AMD from
the Richmond and Lawson portals (including facilities for disposal of treatment sludges).
Administrative Order 93-01 also required the PRPs to excavate, consolidate, and cap seven
waste piles. Pursuant to that order, ICIA, on behalf of Rhone-Poulenc, agreed to design and
construct the treatment plant and to excavate, consolidate, and cap the seven waste piles.
However, ICIA opposed EPA's selection of the HDS process technology and performed
studies to support its position that the HDS components to the treatment plant should not be
constructed. Instead of requiring Rhone-Poulenc to build the HDS component of the treat-
ment plant selected in ROD2, EPA built that component, reserving its rights to recover the
costs of doing so.
The EPA continued to conduct studies to control the AMD discharges from IMM and per-
formed an OUFS to develop and evaluate remedial alternatives for the AMD discharges in
the Slickrock Creek watershed. In February 1993, EPA published an RI/FS report sum-
marizing data regarding AMD discharges in the Slickrock Creek watershed. The February
1993 RI/FS developed and evaluated remedial alternatives for the Old/No. 8 Mine Seep
AMD discharges. On September 24, 1993, EPA signed ROD3, a Record of Decision that
selected treatment of the AMD discharges from the Old/No. 8 Mine Seep on an interim basis
at the IMM lime neutralization HDS treatment plant, as appropriately modified.
On April 19, 1994, EPA issued Administrative Order 94-12, requiring the PRPs to design and
construct all necessary facilities to collect, convey, and treat the discharges of AMD from the
Old/No. 8 Mine Seep. Administrative Order 94-12 also required the PRPs to operate the
IMM treatment plant. SMC, on behalf of Rhone-Poulenc, agreed to design and construct the
collection and conveyance facilities and the necessary modifications to the IMM treatment
ROD4.DOC 25
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plant to assure treatment of the Old/No. 8 Mine Seep AMD discharges. Rhone-Poulenc aJso
agreed to operate the aerated simple mix components of the IMM treatment plant.
The aerated simple mix treatment plant became fully operational in October 1994. For the
past 3 years, the EMM treatment plant has treated essentially all of the AMD discharges from
the Richmond and Lawson portals and the Old/No. 8 Mine Seep. EPA constructed the HDS
components of the treatment plant, which became operational in January 1997. The EPA has
amended Administrative Order 94-12 to clarify requirements pertaining to HDS plant
operations.
The EPA and the State of California have brought a civil suit under CERCLA § 107 against
the PRPs to obtain reimbursement for government funds spent in responding to the EMM
AMD discharges. The cost recovery case is ongoing.
The EPA has identified the following persons as PRPs: the former owner and operator,
Rhone-Poulenc, Inc. (the successor to Mountain Copper, Ltd. and its subsidiaries, and
Stauffer Chemical Company), and the current owner and operator, Iron Mountain Mines, Inc.,
and its president and primary owner, T. W. Arman.
III. HIGHLIGHTS OF COMMUNITY PARTICIPATION
The EPA has regularly provided information to the public regarding the Superfund cleanup
activities at Iron Mountain. The community has maintained interest in the progress of
cleanup at the Site. Prior to the winter wet seasons of 1991 and 1992, community involve-
ment was moderate. Community interest and involvement increased in 1992 as a result of the
special release of 92,000 acre-feet of valuable water resources from Shasta Lake to dilute
pollution from EMM (during serious drought conditions). Since that time, community and
other State and Federal agency interest in the progress of the EPA Superfund cleanup of the
IMM AMD discharges has remained significant. Throughout the cleanup activities, EPA has
regularly provided information to the local television news and the press regarding the ongo-
ing study and cleanup actions, and this has resulted in significant media coverage. The EPA
has provided regular updates on the progress of cleanup actions through the release and
distribution of factsheets and through presentations to local community groups.
111.1 Public Participation for Previous RODs
The EPA issued its first Record of Decision for the IMM Site in October 1986. The EPA has
issued factsheets regarding that decision and commencement of remedial design (July 1987),
commencement of remedial action (July 1988), implementation of emergency response
treatment actions (February 1989), and the performance of a demonstration program under
EPA's Superfund Innovative Technology Evaluation (SITE) program (August 1991). The
EPA also updated its-Community Relations Plan, which was finalized in May 1990.
In May 1992, EPA issued a Proposed Plan for the Boulder Creek OU at IMM. The Proposed
Plan provided an update on the status of remedial and emergency response activities at the
Site. The May 1992 Proposed Plan summarized EPA's development and evaluation of
remedial alternatives for the AMD discharges from the Richmond and Lawson portals and
invited public comment on EPA's proposed cleanup approach. The EPA held a public meet-
ing in June 1992 to present its Proposed Plan, to answer questions, and to receive public
R004.DOC 26
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comments. In September 1992, EPA issued its second Record of Decision for the Site. The
second Record of Decision selected the interim treatment remedy described above.
In February 1993, EPA issued a Proposed Plan for the Old/No. 8 Mine Seep OU to address
the AMD discharges from this source at IMM. The Proposed Plan provided an update on the
status of remedial and emergency response activities at the Site. The February 1993 Pro-
posed Plan summarized EPA's development and evaluation of remedial alternatives for the
AMD discharges from the Old/No. 8 Mine Seep and invited public comment on EPA's
proposed cleanup approach. The EPA held a public meeting in February 1993 to present its
Proposed Plan, to answer questions, and to receive public comments. The EPA issued its
third Record of Decision for the Site in September 1993, selecting the interim treatment
remedy for these AMD discharges.
In October 1993, EPA issued a Technical Assistance Grant (TAG) to the Shasta Natural
Science Association. The grant has provided funding to support the development and dis-
semination of information to the community regarding EPA's IMM cleanup activities. The
TAG was annually extended through March 1997 and has now expired.
\\\2 Public Participation for the 1994 Proposed Plan
In June 1994, EPA issued a Proposed Plan to enlarge the SCDD and conduct baseflow
treatment of Slickrock Creek area sources (the term baseflow refers to the flow in the creek
before, after, and between peak discharge flows related to storm runoff; baseflow treatment
was one component of the preferred alternatives from the 1994 Proposed Plan) as the
"preferred alternative." During the 60-day public comment period, EPA held a public meeting
in Redding, California (July 7,1994). The proposed action attracted significant community
interest and the public meeting was well attended (approximately 50 to 70 private citizens).
At the meeting, EPA received oral comments, and several members of the public submitted
written comments. The EPA received detailed technical comments from representatives of
Rhone-Poulenc. The EPA also received comments from interested State and Federal
agencies. In general, the comments from private citizens were supportive of EPA's Proposed
Plan. The comments indicated general agreement with EPA's intention to ensure protection
of the Sacramento River fishery and water supply. They also indicated agreement with EPA's
portrayal of the proposed remedy selection criteria which recognize that cost and technical
impracticability factors might limit the extent to which the EMM metals discharge could be
controlled and the restoration of the Spring Creek watershed could be implemented.
Other comments included:
• Action should be taken to protect the Sacramento River as soon as possible.
• Action should be deferred until the effectiveness of the IMM treatment plant and the need
for additional action could be evaluated further.
• A preference exists for a remedy that would eliminate the metals discharges through
controls.
HOD4.DOC 27
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• Continued investigation of such approaches was recommended in conjunction with the
water management remedy.
The comments from State and Federal agencies generally supported EPA's preferred alter-
native. Several agencies indicated a preference for additional source control or treatment
remedies, but indicated their willingness to rely on a water management remedy if it could
clearly be demonstrated that the other approaches were technically impracticable. Several
agencies suggested that additional data should be collected over another wet season. The
State requested that EPA re-evaluate the "two-dam" alternative, and indicated an interest in a
full evaluation of Rhone-Poulenc's clean water diversion / "dam and treat" approach for
Slickrock Creek.
Rhone-Poulenc commented that no further action was necessary at the Site to provide a pro-
tective remedy, and that EPA should take ho action at this time. Nonetheless, Rhone-Poulenc
proposed to implement treatment of contaminated Slickrock Creek base flows. Rhone-
Poulenc also submitted comments criticizing specific aspects of the modeling work
conducted by EPA in the Water Management FS, EPA's characterization of the IMM area
sources and their potential for remediation, EPA's analysis of ancillary environmental impacts
associated with an enlargement of SCDD, and EPA's 1994 Fisheries Benefit Analysis.
Rhone-Poulenc indicated that it believed there were more cost-effective approaches to
reducing the toxic discharges from Slickrock and Boulder Creeks than the ones EPA had
identified in its Water Management FS.
In conjunction with its other comments, Rhone-Poulenc submitted an FFS that evaluated sev-
eral new remedial alternatives. The FFS developed a No Action Alternative, four new alter-
natives, and presented Rhone-Poulenc's evaluation of EPA's preferred alternative. Although
Rhone-Poulenc indicated a belief that no further action was warranted, Rhone-Poulenc pro-
posed to implement treatment of the contaminated Slickrock Creek base flows with addi-
tional treatment of identified Boulder Creek sources. Rhone-Poulenc suggested that this
alternative should be implemented and evaluated prior to any subsequent actions at the Site.
Rhone-Poulenc also developed two alternatives that relied on clean water diversions, and a
"dam and treat" approach to control the contaminated discharges from Slickrock Creek, but
concluded that these alternatives were not needed at this time and could be implemented later
if subsequent monitoring demonstrated their need.
The EPA considered and analyzed in detail comments received from Rhone-Poulenc and
other members of the public. The EPA conducted further investigatory and sampling work to
develop additional data on the issues identified by Rhone-Poulenc. The EPA's review
concluded that there are additional alternatives that may provide for a cost-effective source
control and treatment approach for. remediation of Ihe. Slickrock Creek area sources. On the
basis of this review and the technical merit of some of the alternatives developed by Rhone-
Poulenc, EPA deferred action on remedy selection from 1994 to 1997 to perform additional
studies of these potential source control and treatment alternatives. Detailed responses to the
public comments on the 1994 Proposed Plan are included in the Response to Comments
document. In addition, the 1996 Water Management FSA includes a discussion of the major
comments raised in connection with the 1994 Proposed Plan.
ROD4.DOC 28
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111.3 Public Participation for the 1996 Proposed Plan
In May 1996, EPA issued a revised Proposed Plan to implement a "dam and treat" remedy
largely derived from the most effective alternative identified by Rhone-Poulenc in the FFS.
The remedy involved diverting upper Slickrock Creek flows (and flows from the unmined
side of Slickrock Creek Valley) around the most heavily mining-impacted reach of Slickrock
Creek and collecting and treating the reach of Slickrock Creek that is most heavily impacted
by past mining activities. The EPA proposed to perform further study of the Boulder Creek
area source AMD discharges to support the additional development and evaluation of
remedial alternatives for these sources. The public comment period was held for 60 days
(EPA extended the public comment period in response to a request from Rhone-Poulenc).
On May 23,1996, EPA held a public meeting in Redding, California, to present EPA's
Proposed Plan, to answer questions, and to receive public comments. The EPA also par-
ticipated in a June 12,1996, community workshop that was organized by the Shasta Natural
Science Association (the IMM TAG grantee) to present the Proposed Plan, answer questions,
and invite community participation in the decision making process.
The EPA received detailed written technical comments on the May 1996 Proposed Plan from
Rhone-Poulenc and its representatives (EPA considers the comments submitted on behalf of
Rhone-Poulenc collectively as the comments of Rhone-Poulenc). The EPA also received
written comments from interested State and Federal agencies, but no comments from the
general public. Rhone-Poulenc continued to submit comments and information after the
close of the public comment period, and EPA continued to accept and consider the infor-
mation submitted by Rhone-Poulenc.
The EPA carefully reviewed, analyzed, and considered the comments that were received.
The EPA has provided detailed responses to the comments on the 1996 Proposed Plan (as
well as EPA's 1994 Proposed Plan and other technical studies that were performed during the
period from 1994 to 1996, including the 1995 Boulder Creek Remedial Alternatives Study) in
the Response to Comments document produced in conjunction with this Record of Decision.
The Administrative Record includes a transcript of the public meetings held in connection
with the 1994 and 1996 Proposed Plans. The balance of this section contains a brief review
of principal comments received in connection with the 1996 Proposed Plan.
111.3.1 Summary of State and Federal Agency Comments on 1996 Proposed Plan
In general, the-comments ftpm State and Federal agencies were supportive of EPA's 1996
Proposed Plan for the Slickrock Creek area source AMD discharges. All of the agencies
agreed that the proposed Slickrock Creek "dam and treat" alternative was preferable to water
management approaches, such as EPA's previous 1994 proposal to enlarge the SCDD. Most
agencies agreed with EPA's proposal to perform additional study regarding the Boulder Creek
area source AMD discharges. However, Mr. Joel Medlin, on behalf of the U.S. Fish and
Wildlife Service (USFWS), commented that he believed that sufficient information is
currently available to support the selection of a "dam and treat" remedy for the Boulder Creek
area source AMD discharges, and he urged EPA to select such a remedy for these sources
now. Mr. Roger Patterson, on behalf of the USER, also stated a strong preference for the
implementation of a "dam and treat" remedy for the Boulder Creek area source AMD dis-
charges, but commented that further study may be warranted.
ROD4.DOC 29
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111.3.2 Summary of Rhone-Poulenc Comments on 1996 Proposed Plan
Rhone-Poulenc agrees with EPA that constructing a dam on Slickrock Creek is more
appropriate than enlarging the SCDD. Rhone-Poulenc also agrees that the remedy is techni-
cally feasible and that the remedy would effectively control the Slickrock Creek area sources.
However, Rhone-Poulenc does not concur with EPA that further remedial action is required,
and Rhone-Poulenc urged EPA to conduct further studies before proceeding to take any
additional actions at the Site.
Weed for Further Action
Rhone-Poulenc commented that no further action is appropriate at this time. Rhone-Poulenc
bases its position in large pan upon its assumption that a response action is not needed to
protect the Sacramento River fishery below Keswick Dam. In particular, Rhone-Poulenc
commented that despite the intensity of the storm and resulting spill in January 1995 (and the
exceedances of the SBPS that occurred during that spill), no toxicity occurred during the
January 1995 spill. This position appears to be based largely on the lack of "observed"
toxicity in the Sacramento River and a fish toxicity test conducted by a Rhone-Poulenc
consultant with water collected during the January 1995 spill.
The EPA agrees that protecting the fishery and other aquatic resources below Keswick Dam
is an important goal of the IMM response action, but EPA does not agree that the current
level of response is sufficient to protect the fishery or the other resources below Keswick
Dam. The metal concentrations that occurred during the January 1995 storm clearly
exceeded levels that are acutely toxic to fish and other exposed resources. The lack of
"observed" toxicity is not surprising in light of the general size of the Sacramento River
downstream of Keswick Reservoir, the difficulty of visually observing dying or dead fish
during periods when the water is turbid, and the life stages of fish most likely to have been
acutely affected by the toxic conditions, namely eggs, juveniles, and fry, which are also the
most difficult to observe. Similarly, the Rhone-Poulenc toxicity tests do not provide a
reliable indicator of whether toxicity occurred below Keswick Dam. Although the toxicity
test used water collected during the January 1995 spill, the test water was not representative
of conditions observed in the river. For example, the water samples closely approximated the
SBPS while much higher concentrations existed throughout much of the spill. Although
EPA requested the information, the Rhone-Poulenc consultant did not provide quality assur-
ance test results such as positive control (reference toxicant tests) to validate the health and
responsiveness of the trout tested during the studies. These tests are standard protocol for the
type of experiments conducted by Rhone-Poulenc. Because of the lack of detailed supporting
information on testing procedures, it was not possible to perform a full independent review of
the testing or for EPA to rely on the test results. The other available evidence strongly indi-
cates that toxicity occurred during the spill.. RhonerPoulenc's comment also does not take
into account the continued release of mass loads of heavy metals to the Sacramento River
system, which exposes species to long-term sub-lethal levels of metals.
In addition, EPA disagrees with Rhone-Poulenc's assumption that the fishery below Keswick
Dam is the only resource at risk from releases from IMM. Significant environmental degra-
dation continues to exist above Keswick Dam as a result of the continuing releases of sig-
nificant loads of heavy metals and acidity from IMM. The most obvious degradation exists
ROD4.DOC 30
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upstream of the SCDD, where practically all beneficial uses are impaired, arid the creeks are
essentially devoid of aquatic life. IMM releases also severely impair conditions in the Spring
Creek arm of the Keswick Reservoir. In sum, EPA believes that the available data clearly
establish that current releases of hazardous substances from the Site warrant additional
response action. More details regarding the risks posed by releases from IMM and the
manner in which this response action will address those risks are discussed extensively in
other parts of this document and in other parts of the Administrative Record.
Request for Further Delay
Rhone-Poulenc urges EPA to continue to defer selecting a response action based upon the
lack of need for immediate action, the need to collect additional data, the possibility that the
Sacramento River flows could change due to new legislation, and the possibility that the
SBPS will be made less stringent The EP,A does not believe that a further period of evalua-
tion is warranted. Releases from the Site continue to pose a significant threat to the environ-
ment. The available evidence clearly demonstrates the technical feasibility, effectiveness,
and cost-effectiveness of the proposed Slickrock Creek "dam and treat" remedy. Additional
data acquisition is not expected to substantially alter EPA's understanding of the significance
of the Slickrock Creek area source AMD discharges or lead to the identification of cost-
effective alternate control strategies. A further delay is also unlikely, to lead to changes in
Sacramento River flows that would cause the response action to be unnecessary. Information
available since 1994 in fact indicates that less water could be available in the future due to
other important water needs. Finally, a further delay is not likely to lead to a change in the
SBPS that would affect the scope of the response action. As explained below, the available
science, which is substantial, supports the reasonableness of the existing SBPS, and the EPA
is not aware of any planned changes to the SBPS.
Comments on the EPA Water Quality Model
Rhone-Poulenc also submitted extensive comments on the EPA water quality model. The
EPA has relied upon the model as one tool to predict the effectiveness of various remedial
alternatives with respect to limiting the frequency of SCDD spills and exceedances of the
SBPS below Keswick Reservoir. Rhone-Poulenc states that the model relies upon inappro-
priate assumptions and that the model lacks predictive ability. The EPA has reviewed the
Rhone-Poulenc comments regarding the model. The EPA review revealed that Rhone-
Poulenc input improper data to the EPA model which, in turn, caused the model to not func-
tion properly. When the model is run correctly, the model predicts, with reasonable accuracy,
the types of conditions that would cause SCDD spills and exceedances of the SBPS and the
types of conditions that would exist in the main stem of the Sacramento River below
Keswick Dam during those spills.
In response to Rhone-Poulenc comments regarding specific model assumptions (and other
information obtained since May 1996), EPA conducted additional modeling analyses.
Among other things, EPA conducted new model runs using water quality and flow data
obtained since the 1996 modeling effort, new flow projections from the USER, recently
proposed water quality criteria (the Proposed California Toxics Rule fPCTR]), and additional
information regarding the operational efficiency of the SCDD. This additional analysis,
which is set forth in the Response to Comments document, confirms the reliability and
ROD4.DOC 31
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reasonableness of the 1996 IMM water quality model (WQM). The model consistently
indicates that in the absence of further response actions, exceedances of the SBPS (and the
PCTR) will continue to occur on a regular and frequent basis below Keswick Dam.
The EPA also conducted additional analysis of several parameters used in the model. For
example, Rhone-Poulenc commented that the EPA model should have relied upon a Spring
Creek Reservoir capacity of 5,400 acre-feet rather than 5,016 acre-feet. A review of the
Rhone-Poulenc analysis, however, reveals that Rhone-Poulenc did not consider operational
constraints that limit the usable capacity of the reservoir to approximately 5,000 acre-feet.
Rhone-Poulenc also submitted extensive comments on the precipitation values used in the
1996 model (the precipitation value reflects the extent to which dissolved metals precipitate
from solution to form heavy metal particulates as the pH increases due to mixing AMD with
less polluted water in Keswick Reservoir). The additional EPA review confirmed the
appropriateness of the precipitation values used in the EPA model.
Reliance on SBPS
Rhone-Poulenc commented that the SBPS do not provide a reliable indicator of the need for
further remediation because the standards are, according to Rhone-Poulenc, overly conserva-
tive and not based on sound science. The EPA does not agree with Rhone-Poulenc that the
standards are overly conservative or scientifically unsound. The available information, which
is quite substantial, strongly supports the reasonableness of the existing SBPS. Site-specific
toxicity tests conducted by the State of California in 1995 and Hagler-Bailly in 1996 indicate
that the existing SBPS are appropriate and not overly protective. Those tests are consistent
with previous site-specific toxicity tests. To further evaluate the comments submitted by
Rhone-Poulenc on the SBPS, EPA sought comment from several other agencies with
expertise on this issue, including the CVRWQCB, the National Marine Fisheries Service
(NMFS), the NOAA, the USFWS, and the California Department of Fish and Game (CDFG).
The comments of these other agencies support EPA's conclusion that the existing standards
are a reliable indicator of the need for further response action and that the standards are not
overly conservative.
In addition, EPA's Water Management Division recently proposed new statewide water
quality criteria for the State of California, the PCTR. The EPA developed these criteria using
EPA's most current guidance for developing water quality criteria. Because the new criteria
are not yet finalized, the proposed criteria qualify as 'To Be Considered Standards" rather
than potential ARARs. The PCTR are more stringent than the SBPS with respect to the need
for further response action at IMM. These criteria therefore indicate that the SBPS are a
reasonable indicator of risk to aquatic resources in the Sacramento River.
Rhone-Poulenc comments that EPA should.waive the SBPS on the basis of technical imprac-
ticability for areas of Slickrock Creek. The EPA is adopting an interim waiver for compli-
ance with those standards for this interim remedy. The EPA is still evaluating whether a
permanent partial waiver of the SBPS is appropriate.
Rhone-Poulenc submitted several legal arguments to support its position that EPA should not
adopt the SBPS as ARARs (among others, (1) the standards were adopted specifically to
serve as cleanup objectives at the Iron Mountain Site, (2) the SBPS are not of general appli-
ROD4.DOC 32
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cability and have not been consistently applied, and (3) the standards do not properly apply to
the tributaries of the Sacramento River such as Spring Creek and Slickrock Creek). As
explained more fully in the Response to Comments document, EPA does not agree with
Rhone-Poulenc's comments on this issue.
Need for Slickrock Creek Retention Pond
Rhone-Poulenc also objects to the proposed Slickrock Creek remedy on the basis that the
retention pond is not necessary to meet the Basin Plan Objectives in the Sacramento River
and that, if EPA selected additional response action at the Site, EPA should select baseflow
treatment of Slickrock Creek AMD flows. However, baseflow treatment would not meet the
requirements of CERCLA. Baseflow treatment is significantly less effective than Alternative
SRI with respect to metal removal. For example, implementing Alternative SRI in lieu of
baseflow treatment would eliminate an additional discharge load of copper of 8,000 to 27,000
pounds per year. -This additional copper reduction associated with Alternative SRI compared
to baseflow treatment is roughly equal to 33 percent to 100 percent of the load discharged
from all of the regulated dischargers of copper to the Sacramento River system, including the
San Francisco Bay and Delta.
Baseflow treatment is also less effective with respect to reducing the frequency and duration
of exceedances of the protective SBPS in Keswick Reservoir. While exceedances in
Keswick Reservoir are expected to continue under either alternative, Alternative SRI would
be expected to reduce the frequency, duration and degree of the exceedances.
Baseflow treatment is also less effective than Alternative SRI with respect to protecting the
Sacramento River below Keswick Dam. Even after baseflow treatment is implemented,
SCDD spills are expected to occur every 4 to 8 years, which is approximately twice the spill
frequency expected after implementation of Alternative SRI (which is expected to reduce
spill frequency to once every 8 to 10 years). SCDD spills typically cause SBPS and PCTR
exceedances below Keswick Dam lasting from one day to several weeks. If the SCDD were
operated to meet the PCTR chronic criteria for copper, the frequency of exceedance would be
greater under each approach, but the duration of the exceedances would be significantly
longer for the baseflow treatment approach than under Alternative SRI.
Baseflow treatment would also be less effective than Alternative SRI with respect to
restoring the beneficial uses of waterbodies and habitat values in the Spring Creek watershed.
»
A remedial action that does not address these risks when other technically practicable and
implementable alternatives are available to establish more protective conditions, does not
meet the requirements of CERCLA for remedy selection (40 C.F.R. § 300.430(f)(l)(i)(A) and
(ii)(A) and (B)).
Rhone-Poulenc recently proposed to study the feasibility and effectiveness of installing
french drains in the Slickrock Creek Basin and a surface water collector in the Big Seep area
in Slickrock Creek to control area sources. EPA had previously considered the appropriate-
ness of alternative groundwater and surface water collection approaches in its technology
R004.DOC 33
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screening process for the 1994 and 1996 feasibility studies. Groundwater interception
approaches are considered to be inappropriate technologies for addressing Slickrock Creek
area sources generally. The groundwater flows are only a minor component of the Slickrock
Creek area sources, so a groundwater collection system would not provide a sufficient degree
of protection or comply with other CERCLA requirements. EPA's review of data developed
since 1996 confirmed the earlier conclusion regarding this issue. Rhone-Poulenc also pro-
posed to study the collection and treatment of a limited amount of surface water, but the
approach proposed by Rhone-Poulenc is not technically feasible. The proposed location of
the surface-water collection system, the Big Seep area, is highly unstable and in the midst of
a massive waste disposal area. Massive amounts of sediments are expected to come down
from the debris slide and impact efforts to collect surface runoff without extensive sediment
controls. The peak nature of the runoff would be expected to adversely impact efforts to
assure treatment of the discharges without adequate flow equalization. The EPA has con-
cluded that the proposed Rhone-Poulenc alternative would not be effective in capturing the
majority of the Slickrock Creek area source metal discharges. The EPA also believes that
Rhone-Poulenc underestimates the cost of this proposed approach: The surface-water
collection system would cost substantially more than Rhone-Poulenc estimates because
additional flow equalization facilities and sediment controls are necessary to allow surface-
water collection and treatment efforts.
Rhone-Poulenc also commented that EPA did not adequately justify several particular design
components of the proposed alternative, including the hematite containment structure, the
5-acre sedimentation pond, a microtunnel between the HDS plant thickener and Spring
Creek, and restoration of montane hardwood-conifer habitat As explained more fully in the
Response to Comments document, each of these components is an important part of the
selected remedy.
Naturally Occurring Substances
Rhone-Poulenc objects to the remedy on the ground that installation of the Slickrock Creek
retention pond will clean up Slickrock Creek to below "natural background levels." In sup-
port of its position, Rhone-Poulenc submitted numerous technical reports that purport to
estimate metal loads attributable to "natural sources" at Iron Mountain. Rhone Poulenc relies
on these reports to conclude that a significant portion of metals loading to Slickrock Creek is
attributable to "natural sources."
Rhone-Poulenc's comments on this issue concern the limitation contained in CERCLA Sec-
tion 104(a)(3)(A). That section provides that "[t]he President shall not provide for a removal
or remedial action under [Section 104] in response to a release or threat of release-(A) of a
naturally occurring substance in its unaltered form, or altered solely through naturally
occurring processes or phenomena, from a location where it is naturally found."
The Slickrock Creek remedy is consistent with EPA's authority under CERCLA. The reme-
dial response is directed at responding to releases altered by mining. As shown in Photo
Exhibits 1 and 2, the selected remedy focuses on collecting the releases from the portion of
the Slickrock Creek basin that is most heavily disturbed by mining. The area sources of these
metals include buried mine portals, mine seeps, waste piles, tailing piles, and buried minerali-
zation exposed by mining through fracturing, lowering of the water table, and removal of
ROD4.DOC 34
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surface materials. Water from upstream of the heavily disturbed mining area and from the
unmined side of the valley will be diverted around the disturbed mining area. These diverted
flows will not be collected or treated at the IMM treatment plant as part of this remedy.
Despite detailed study of Site conditions and review of the extensive data and analysis sub-
mitted by Rhone-Poulenc, EPA has been unable to identify any release of hazardous sub-
stances from the Slickrock Creek area sources being addressed in this response action that are
unaltered by mining. To the extent that such releases may exist, the releases would be
commingled with and indistinguishable from the mining-related sources (and therefore
"altered" by those releases). Even if such releases could be identified, EPA is aware of no
cost-effective, protective, and reliable alternative that would be capable of isolating the
mining-related releases from the "release of a naturally occurring substance in its unaltered
form, or altered solely through naturally occurring processes or phenomena, from a location
where it is naturally found." The EPA is also not aware of any alternative that would restore
the hydrology and geology to its pre-mining condition, which essentially isolated the fresh
mineralization from conditions that permit the rapid and extreme release of large loads of
highly acidic and metal-laden waters.
The EPA has also reviewed and analyzed the reports submitted by Rhone-Poulenc on this
issue. Several of the reports attempt to estimate the pre-mining baseline metal loads. The
focus on pre-mining metal concentrations, however, does not address the central issue:
whether or not a remedial action is taken in response to a release or threat of release "of a
naturally occurring substance in its unaltered form, or altered solely through naturally
occurring processes or phenomena, from a location where it is naturally found." Even if it
were appropriate to evaluate pre-mining metal loads, the studies submitted by Rhone-Poulenc
do not provide an accurate estimate of pre-mining metal discharges. For example, the
Rhone-Poulenc reports rely heavily upon water samples collected in the highly disturbed
mining area. The reports incorrectly assume that these samples are "undisturbed" by mining
and represent "natural background conditions." The reports also rely on other analyses that
fail to account for changes induced by mining. As a result, the reports greatly overstate the
pre-mining metal levels.
A few of the Rhone-Poulenc reports do try to distinguish between current releases associated
with mining versus current "natural" releases, but those reports fail to accurately distinguish
between these two categories. For example, the reports assume that all weathering of miner-
alization is natural. Although weathering of mineralization is a natural process that occurred
prior to the time when mining commenced, mining has significantly altered the weathering of
mineralization by exposing fresh sulfides to oxygen and water through a host of actions.
These changes have greatly increased the rate of oxidation, acidification of water, and release
of metals. Such releases are therefore altered by mining and not within the limitation con-
tained in CERCLA Section 104(a)(3)(A).
The EPA also evaluated actual field conditions to assess the validity of the natural
background estimates presented by Rhone-Poulenc. These methods include application of
the Rhone-Poulenc natural background model to an unmined mineralized area at IMM,
evaluation of geologic data regarding the time the mineralization has been exposed to atmos-
ROD4.DOC 35
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pheric conditions, and biologic and genetic studies of areas upstream of the mine-impacted
area.
The EPA applied the Rhone-Poulenc natural background model to an unmined mineralized
area at IMM. The model predicted copper concentrations ranging from 2,420 to 4,120 ppb
and zinc concentrations ranging from 850 to 1450 ppb. When the actual values are measured,
however, the concentrations range from 3.7 to 9.4 ppb for copper and 17.3 to 33.8 ppb for
zinc. This large degree of error indicates that the Rhone-Poulenc model is not a reliable
indicator of pre-mining metal loads.
The EPA also evaluated the Rhone-Poulenc pre-mining metal estimates by examining the
available geologic evidence to determine if those rates are geologically possible in light of the
time needed to create the gossan deposit at IMM. The pre-mining metal release rates sug-
gested by Rhone-Poulenc indicate that the-mineralization has been exposed for less than
50,000 years (based on the current volume of gossan and numerous conservative assumptions
that would tend to overstate the period of exposure). Recent paleomagnetic investigations
reveal that the gossan has been exposed at least since the last reversal in the earth's magnetic
field, which occurred more than 780,000 years ago. This evidence also indicates that the pre-
mining release rates predicted by Rhone-Poulenc are gross overstatements.
The Rhone-Poulenc hypothesis regarding pre-mining metal concentrations is also inconsis-
tent with biologic and genetic studies conducted by EPA that indicate that, in the pre-mining
period, metal concentrations in Spring Creek, Boulder Creek, and Slickrock Creek were at
sufficiently low levels such that each of these surface waters supported a healthy aquatic
ecosystem.
In sum, each of the independent methods used by EPA to evaluate pre-mining metal loads
indicates that pre-mining metal loads were at most a very small fraction of the current loads
being released from IMM.
Cost-Benefit Analysis
Rhone-Poulenc commented that EPA should have conducted and considered a cost-benefit
analysis that weighs the costs of the proposed remedial action with any benefits that may
derive from the remedial action to the fishery below Keswick Reservoir. The manner in
which EPA is to consider costs (and benefits) is set forth in the NCP, and those provisions do
not require the type of analysis suggested by Rhone-Poulenc. The NCP is carefully structured
so that "protection of human health and the environment" will not be compromised by other
selection factors, such as cost. See 55 Fed. Reg. 8726 (1990). Although EPA balances nine
selection criteria (including cost) in selecting a remedy, all of the criteria are not given equal
weight Instead, they are divided into three classifications: threshold criteria, balancing
criteria, and modifying criteria. Only remedies meeting the threshold criteria (overall
protection of human health and the environment and compliance with ARARs) are eligible
for consideration in the balancing process by which the remedy is selected. Rhone-Poulenc
also incorrectly assumes that protecting the fishery below Keswick Dam is the only benefit of
the response action.
ROD4.DOC 36
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The EPA considered cost and cost-effectiveness in conducting its scoping analysis, analyzing
alternatives, identifying a preferred alternative, and selecting this response action. Through
the FS scoping process, EPA identified technologies and remedial alternatives that could
potentially meet the threshold requirements. In the Water Management FS and Water Man-
agement FSA, EPA evaluated and considered the cost (including all capital costs and the
present worth of all operating and maintenance costs) of those alternatives as one of several
balancing criteria. As discussed above, alternatives that do not meet the threshold require-
ments (such as Slickrock Creek baseflow treatment in the absence of enlarging the Spring
Creek Debris Dam) are not eligible for consideration in the balancing process.
In selecting the remedy, EPA considered the cost-effectiveness of the selected remedy, as
required by the NCP, by evaluating the overall effectiveness of the proposed Slickrock Creek
alternative in proportion to its cost. 40 CFR § 300.430(f)(l)(ii)(D). The EPA determined the
overall effectiveness by evaluating the alternative's long-term effectiveness and permanence;
reduction of toxicity, mobility, or volume through treatment; and short-term effectiveness.
Id. The overall effectiveness was then compared to cost to evaluate whether the alternative
was cost-effective. As set forth below, this analysis indicates that the selected remedy is
cost-effective. The EPA also considered cost in evaluating the statutory preference for
treatment as a principal element of the response action.
Consistency with Final Remedy
Rhone-Poulenc commented that EPA had failed to ensure consistency of the proposed action
with a final remedy for the Site. As set forth elsewhere in this ROD, the Slickrock Creek
remedy makes significant progress toward meeting the remedial action objectives of the IMM
CERCLA response action. While the response action is likely to continue for some time and
other response actions might be developed in the future (such as resource recovery), the
interim action is not inconsistent with those types of final remedies. The manner in which
this response action fits within the overall Site response action is set forth more fully in the
following section.
IV. SCOPE AND ROLE OF THE OPERABLE UNIT WITHIN SITE STRATEGY
IV.1' Role of the IMM Remedial Action
The overall objective of EPA's IMM Superfund cleanup program is to eliminate IMM AMD
discharges that are harmful to human health and the environment. Due to the complexity and
magnitude of the pollution problem, EPA divided the IMM response action into separate
operable units. This approach enabled EPA to address the most serious problems quickly and
to achieve a rapid reduction in hazardous substance releases. Remedial steps already imple-
mented at the Site have reduced the heavy metal load release by approximately 80 to 90 per-
cent. Despite the effectiveness of the remedies already-implemented, releases from the Site
still cause the receiving waters in the Spring Creek watershed to be essentially devoid of
aquatic life, the release of significant heavy metal loads to Spring Creek Reservoir, Keswick
Reservoir, and the Sacramento River, and exceedances of protective standards in the
Sacramento River and Keswick Reservoir on a regular basis. Additional response actions are
needed to address these remaining problems. The most significant remaining areas in need of
a response action include (1) the area sources in the Slickrock Creek basin (constituting
ROD4.DOC 37
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approximately 60 to 70 percent of the copper and 40 to 50 percent of the zinc and cadmium
releases that are currently uncontrolled), (2) the area sources in the Boulder Creek basin
(constituting approximately 30 to 40 percent of the copper and 50 to 60 percent of the zinc
and cadmium releases that are currently uncontrolled), and (3) the heavy metal sediments
associated with past and current releases of IMM AMD (including sediments in Spring Creek
and its tributaries, SCR, Keswick Reservoir, the Sacramento River, Flat Creek, and other
areas). Studies of these problems are currently underway. These additional studies will also
assess the feasibility of further source control and the appropriateness and feasibility of
relying on water management options as a component of a final Site remedy, and the need for
other response actions. Proceeding in this phased manner enhances the ability of EPA to
evaluate the feasibility of restoring portions of the receiving waters in the Spring Creek
watershed and other affected water bodies.
IV.2 Scope of the Problem Addressed by the Selected Remedial Action
The specific problem addressed in this remedial action is the release of metals and acidity in
the AMD from the area sources in the Slickrock Creek watershed at IMM. The response
action is expected to essentially eliminate the discharges from the sources being addressed .in
this interim action. The collected flows, which will account for approximately 60 to 70 per-
cent of the copper and 40 to 50 percent of the zinc and cadmium releases that are currently
uncontrolled, will be treated to remove more than 99 percent of the metals and to neutralize
the acidity of the water. The releases addressed by this response action contribute a signifi-
cant metal load and acidity to the receiving waters. The releases cause or contribute to
exceedances of the protective water quality standards, including the SB PS and the proposed
California Toxics Rule (PCTR), in Slickrock Creek, Spring Creek, SCR, Keswick Reservoir,
and in the Sacramento River below Keswick Dam.
The State of California set the SBPS to assure protective conditions for the Sacramento River
fishery and the ecosystem in the upper Sacramento River and its tributaries. The SBPS were
reviewed and approved by EPA as a Federal standard under the Clean Water Act The PCTR
are proposed numeric statewide water quality criteria for the State of California. The
proposed water quality criteria for aquatic life and human health are designed to establish
pollutant levels that would protect aquatic life and human health, respectively. The proposed
aquatic life criteria include criteria based on both short-term and 96-hour exposure durations.
These two exposure values are intended to represent average pollutant concentrations which
will produce water quality generally suited to maintenance of aquatic life. Exceedance of the
SBPS (or the PCTR) indicates that aquatic resources are not being adequately protected. The
Slickrock Creek area source AMD discharges also result in the formation of toxic sediments
in SCAKR and in the main body of Keswick Reservoir and the release of significant volumes
of heavy metals in paniculate form into the water column of the Sacramento River.
Since this interim remedy is not intended to address all remaining uncontrolled AMD
releases, the interim remedy continues to rely on continuing operations of the SCDD to
provide for the safe release of the continuing IMM contaminant discharges from the SCR (to
the extent technically feasible in light of the current state of the response action at IMM).
The interim water management actions are necessary to reduce the likelihood of uncontrolled
SCDD spills, reduce the reliance on special releases of CVP waters to dilute IMM AMD-
ROD4.DOC 38
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contaminated surface waters, and meet the SBPS for water quality to the extent feasible.
Consistent with the analysis in the Water Management FS, EPA anticipates that the
operational targets of the SCDD can be revised to reflect the reduced metal loads from IMM
once this remedial action has been implemented. Based upon the current operational
procedures used by USER, these changed operational targets would likely be able to attain
the SBPS (and potentially the PCTR) below Keswick Dam under most circumstances,
although regular exceedances in areas of Keswick Reservoir and in the Spring Creek
watershed are likely to continue without further response action at the Site.
This Record of Decision represents an interim remedy for a portion of the Site, so EPA has
considered the need of this remedy to be consistent with future remedial action and the need
to reduce significant risks as soon as possible. This interim action addresses the most
significant source of currently uncontrolled IMM AMD-the Slickrock Creek area sources
entering the reach of Slickrock Creek directly below the most heavily disturbed mining area.
The selected remedy is consistent with other potential response actions for the remaining
IMM discharges. The remedy is consistent with remediation of existing sediments because
the remedy significantly reduces the release of new precipitates into the waters of the state.
The remedy is consistent with a response action on Boulder Creek because this remedy does
not affect a response action for those sources and takes into account a range of possible
actions on Boulder Creek. The remedy is also consistent with reliance on resource recovery
once that technology is developed, since the collection systems could potentially be utilized
to implement such a system.
V. SITE CHARACTERISTICS
V.1 Contamination
Analytical data collected over several decades indicate that IMM is releasing large volumes
of hazardous substances to the environment via AMD discharges. The IMM AMD
originating in the Slickrock Creek basin is characterized by its extremely low pH (resulting in
a pH of approximately 3 in Slickrock Creek) and very high concentrations of heavy metals
(causing current copper concentrations in Slickrock Creek to range from 1,200 to 5,800 ppb
during the 1995-96 water year, which is several orders of magnitude more concentrated than
the SBPS for copper).
The water quality parameters of concern from a public health exposure perspective are pH,
cadmium, copper, and zinc. These parameters are selected because of potential dermal con-
tact effects caused by low pH and potential consumption of AMD (with these three metals
being of greatest concern from a water consumption perspective).
The contaminants of concern from the perspective of fisheries (salmon, steelhead trout and
other aquatic resources) exposure are pH, cadmium, zinc, copper, and aluminum. These
parameters are selected because of their toxicity in the receiving waters to aquatic resources
such as salmonids. Those species are sensitive to low pH waters and waters containing metal
concentrations ranging from 1 ug/L for cadmium to 100 ug/L for aluminum (copper toxicity
levels are in the range of 10 ug/L, and zinc toxicity levels are in the range of 50 ug/L).
Recently conducted studies reinforce the sensitivity of aquatic resources (including fish and
ROD4.DOC 39
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algae) to even lower levels of these metals. For comparison, 1 pg/L equals approximately
0.001 mg/L or 1 part per billion (1 ppb).
The contaminants of concern with respect to terrestrial wildlife include arsenic as well as
those listed above for aquatic species.
Since October 1994, essentially all AMD discharges from the three largest point sources at
IMM have been treated at the IMM treatment plant Over this period, the IMM treatment
plant operations have reduced the uncontrolled IMM discharges of copper, zinc, and
cadmium by approximately 80 to 90 percent.
The remaining IMM AMD discharges .derive from the widely dispersed area sources. The
IMM area sources include waste piles, sidecast spoils, ground disturbed by mining-related
activities, discharges from buried workings or partially accessible workings, contaminated
soil and debris, seeps, contaminated groundwater, and contaminated sediments in the Slick-
rock Creek, Boulder Creek, and Spring Creek watersheds at IMM.
The area sources tend to have very complex characteristics that cause the relative significance
of the source to vary depending on a host of factors, including storm duration, storm inten-
sity, and antecedent moisture condition. Significant portions of the sources are buried and
difficult to locate without an expensive investigation. Some of these buried mine-impacted
sources discharge below large landslide areas. Other sources are located on the surface but
might discharge metals to groundwater and interflow. Many source discharges can form
salts, which in turn become sources of intense metal loading when re-exposed to moisture.
Numerous field investigations have been conducted to characterize these IMM area source
discharges and to define the sources related to the discharges. Some specific sources of the
AMD discharges have been identified. However, although extensive efforts have been
undertaken over the past several years, the majority of the sources of the area source dis-
charges have not been identified. It has been possible to identify an approximate ISO-acre
area, disturbed by extensive mining efforts, as the area source of essentially all of the Slick-
rock Creek heavy metal and acidity discharges. See Photo Exhibit 1. Similarly, it has been
possible to define an approximate 1,000-foot reach of Boulder Creek adjacent to an area used
for extensive mining activities as the area in which 50 to 70 percent of the Boulder Creek
area source discharges enter the creek.
Slickrock Creek and Boulder Creek serve as collection points for contaminated groundwater,
interflow, and surface water for area sources in the respective watersheds.
The discharges from the area sources are closely associated with heavy rainfall and high run-
off storm events. Remedies that are effective at low flow (such as treating baseflows of
Slickrock Creek) become significantly less effective as flows increase, which are the time
periods when the Site produces the largest releases of hazardous substances.
Releases of arsenic from the several hematite mine processing piles also pose a potential
threat to public health and the environment. The piles are actively eroding into state waters
and result in arsenic being released into the environment. For example, the arsenic-laden
sediments deposited in Spring Creek Reservoir result in exposure of maintenance workers to
R004.DOC 40
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levels of arsenic in ambient air that exceed safe levels for workers under OSHA
requirements.
Contamination at the Watersheds above SCDD
The receiving waters upstream of the SCDD impacted by releases from IMM are essentially
devoid of aquatic life as a result of releases of hazardous substances from the Site (and in the
case of Spring Creek, in small part due to the release of metals from the Stowell Mine). The
sources of the ongoing contamination include the current AMD releases, contaminated sedi-
ments, eroded mine tailings and wastes from past mining activities, and current releases of
tailings and mine wastes into surface waters. In contrast, the reaches of these streams
upstream of past mining activities support abundant aquatic life.
Contamination Downstream of SCDD
The fishery resources and other sensitive aquatic species in Keswick Reservoir and in the
Sacramento River (below Keswick Dam) are the primary natural resources currently at risk
because of the continuing uncontrolled IMM heavy metal discharges. The IMM releases
contribute to the risks to species in this area by causing the acute exceedance of water quality
standards, by exposing aquatic resources to long-term sub-lethal metal levels, and by
exposing aquatic resources and benthic organisms to toxic precipitates and heavy metal-laden
sediments.
The SCR controls the rate at which IMM AMD is released into Keswick Reservoir and the
Sacramento River. The USBR meters the highly polluted IMM AMD into the Sacramento
River to permit dilution of the IMM AMD using large volumes of CVP waters. The USBR
operates the SCDD in accordance with a 1980 Memorandum of Understanding (MOU),
which contains interim operational targets for heavy metals below Keswick Dam. These
interim operational targets are intended to provide safe releases of IMM AMD to the extent
possible in light of the intense hydrology of the Spring Creek watershed and the very large
metal loads released by EMM.
Because of the high pollution loads generated by IMM, water must often be released from
SCR at a slow rate to ensure appropriate dilution. This slow release rate can cause the SCR
to become full in relatively short periods of time (i.e., several days). Once the capacity of
SCR is exceeded, SCR water spills into Keswick Reservoir in an uncontrolled manner (or
just prior to a spill, SCR water is otherwise released using emergency release procedures) for
periods lasting from a few hours to, more commonly, several days or weeks. Spills from the
SCR (and to a slightly lesser extent SCR releases during emergency release procedures) cause
exceedances of the SBPS and PCTR in areas of Keswick Reservoir and, in almost all cases,
exceedances below Keswick Dam. If the USBR were to operate the SCDD in a manner to
achieve more stringent standards below Keswick Dam, the SCR would need to release water
more slowly, which in turn would cause the SCR to fill and spill more often. For these
reasons, the 1980 MOU recognizes that without extensive controls in place at Iron Mountain,
the USBR cannot operate the SCDD in a manner that will be able to ensure compliance with
fully protective standards. EPA modeling indicates that in the absence of further
remediation, SCDD spills and corresponding exceedances of the SBPS below Keswick
Reservoir are expected to occur on average every 3 to 4 years if the SCDD is operated to
ROD4.DOC 41
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achieve the SBPS below Keswick Dam. Operating the SCDD to meet the recently proposed
PCTR (below Keswick Dam) would cause the spills to occur every 2 to 3 years on average.
Spills would occur even more frequently if the SCR were operated to target compliance with
these standards in Keswick Reservoir rather than downstream of Keswick Dam.
The flows in the Sacramento River available at the onset of major early season storm events
cannot generally provide adequate dilution of the IMM contaminants at current levels of
metals discharges. The EPA has performed an analysis of the hydrologic and water quality
factors and has calculated the Sacramento River flow required to ensure the dilution of IMM-
contaminated SCR waters to meet water quality standards. During storms in 1995 and 1996,
SCR waters, with full treatment of the three major mine discharges, exhibited levels of con-
tamination of 400 to 800 ppb dissolved copper (compared to the SBPS of 5.6 ppb copper at
hardness of 40 ppm). The SCR water contains similarly high levels of cadmium and zinc.
Storm inflows into the SCR are frequently observed at several hundred to 1,000 cfs.
Sacramento River flows are frequently near minimum legal flows during the first storm of the
season, or are not generally more than 10,000 cfs.
Events in 1995 provide a good illustration of the types of conditions that present acute risks
to the aquatic organisms downstream of the Site. During the January 1995 storms, IMM
metal discharges were the source of greater than 90 percent of the Keswick Reservoir metal
loads. During that period, a large volume of untreated AMD was released from the Site into
the Sacramento River for a period of several weeks. This continuous release of untreated
AMD from the Site caused the SBPS to be exceeded in the main stem of the Sacramento
River continuously from January 9,1995, through January 27,1995. At times during the
storm event, copper concentrations were more than twice the levels considered safe under the
SBPS and the PCTR. For more information on this issue, see Section 2.3.2.3 of the Water
Management Feasibility Study Addendum and reports referenced therein.
During the January 1995 storm event, metal concentrations in the Sacramento River were
elevated to levels that are clearly toxic to fish and other aquatic organisms. For example,
based on the loxicity testing recently completed by Hagler-Bailly (Hagler-Bailly, 1996), the
copper concentrations in the Sacramento River were measured at or near the 96-hour LC50
for rainbow trout fry in the low pH and low alkalinity waters observed during the January
1995 spill. (The LC50 is the concentration of a toxic constituent [in this case, copper] that
would result in the mortality of fifty percent of the test organisms [in this case, rainbow trout
fry] within a specified time period [in this case, 96 hours]). The LC50 established for
rainbow trout in the Hagler-Bailly testing is also applicable with respect to establishing the
toxic effects of the elevated January 1995 metal concentrations on the valuable Sacramento
River salmon fishery. Additional California RWQCB toxicity testing (RWQCB, 1997) has
shown that copper concentrations much lower than the observed conditions of the 1995 spill
are toxic to algae, an important element of the Sacramento River ecosystem. For example,
RWQCB tests indicate that copper concentrations at or near the current SBPS (5.6 ppb
copper at a hardness of 40 mg/1 as CaCC^) can be toxic to algae, while concentrations during
the January 1995 storm were well above those levels.
EPA's modeling analyses indicate the following:
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• Under current conditions, with treatment of the three major IMM sources, SCDD spills of
contaminated waters would be expected to occur regularly, even assuming that USER
would always be able to perfectly define the appropriate releases during highly variable
storm conditions. Using a more realistic estimate of SCR operations would increase the
frequency of the predicted exceedances. Site releases also continue to affect natural
resources below the SCDD by discharging large loads of heavy metals which form
precipitates that contaminate downstream sediments.
• The two most important factors which currently make it impossible for SCDD to permit
dilution of IMM AMD in a manner that maintains the SBPS below Kes wick Dam in the
Sacramento River are: (1) the storm inflows to the SCR are highly contaminated, and (2)
storms that cause these contaminated waters to fill the reservoir within a few days will
likely occur every 5 to 10 years. More frequent SCDD spills (on the order of one spill
every 3 to 4 years) will occur as a result of other factors such as preceding drought
conditions that will limit the flow in the Sacramento River. Spills would occur more
frequently if the SCR were operated to target compliance with a more stringent standard
or at a point in Keswick Reservoir closer to the SCDD.
• Significant further remediation of the IMM area source discharges, such as reducing dis-
solved copper concentrations in SCR to 100 ppb or less, is required to ensure that
continued operations of SCDD would be able to safely release any continuing
uncontrolled IMM discharges to protect the Sacramento River below Keswick Dam.
Additional controls would be needed to fully restore the Keswick Reservoir aquatic
ecosystem.
V.2 Location of Contamination and Known or Potential Migration Routes
The major mechanism for onsite and offsite transport of contaminants is surface water. The
AMD enters Boulder and Slickrock Creeks, and these two creeks discharge into Spring
Creek, which flows to the Sacramento River at Keswick Reservoir.
The contaminants of concern can be biologically transported through the aquatic food chain.
For example, the initial uptake of contaminants would be by phytoplankton, periphyton, and
other aquatic vegetation. These food sources would be ingested by benthic invertebrates
and/or zooplankton. The plankton and benthos would be ingested by fish at subsequently
higher trophic levels and ultimately consumed by birds, animals, and humans.
The major processes that affect the fate and transport of copper, cadmium, and zinc are
coprecipitation with iron hydroxides and precipitation as carbonates. As Spring Creek dis-
charges into the main body of Keswick Reservoir, IMM AMD mixes with water from
Keswick Reservoir, which dilutes the SCR waters and increases the pH of those waters.
These processes reduce the concentration of dissolved metals but also generate significant
volumes of metal precipitates, some of which become river sediment while another portion
continues to remain suspended in the water column as the water moves down river. Under
current conditions, IMM AMD causes approximately 5 to 15 tons of copper to precipitate
into State waters in normal and wet years. In addition, the acidic releases from Iron
Mountain introduce cadmium, zinc, and iron precipitants into state waters.
ROD4.DOC . 43
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Above the SCDD
The IMM AMD drains to Boulder Creek and Slickrock Creek, which in turn flow into Spring
Creek and the SCR. For combined distance of several miles, these receiving waters are
essentially devoid of aquatic life as a result of hazardous substance releases from the Site.
Releases from the Site also continue to severely impair the habitat of non-aquatic species,
particularly amphibians and other species heavily dependent on aquatic resources. Mining-
related contaminated sediments also exist in these water bodies, although their current impact
is overshadowed by the extreme acidity and metal loads in the surface water.
Below the SCDD
The IMM AMD releases pass through the SCR and Keswick Reservoir and into the main
body of the Sacramento River. The USER operates the SCR in a manner that reduces the
concentration of IMM AMD by metering 'in the SCR water into the Sacramento River flows
in Keswick Reservoir. However, even with implementation of the highly effective interim
IMM treatment remedial action, the SCR operations continue to be unable to meet either the
MOU release schedule for total metals or the SBPS for soluble metals. The inability to
maintain the appropriate release schedule and SBPS compliance arises from the large metal
loads generated by IMM AMD and the intense hydrology of the Spring Creek watershed. If
the SCDD were operated to comply with the PCTR, the frequency and duration of SCDD
spills would increase even further because the SCR would have to be released a slower rate to
permit the dilution needed to comply with the more stringent criteria. This slower release
rate would cause the SCR to fill and spill more often during storm periods.
Other factors also exacerbate the toxicity posed by uncontrolled AMD discharges below the
SCDD. The types of storm events that tend to cause uncontrolled spills from the SCDD also
tend to create the most difficult periods of SCDD operations and a depression of the hardness
in the Sacramento River. As water hardness decreases, metals become more toxic to aquatic
resources. Factoring the more difficult operations and the influence of hardness on water
quality criteria would therefore tend to compound the difference between the modeled and
current SCDD operations. These factors seriously impede USBR's efforts to operate the
SCDD in a manner that would be necessary to comply with the SBPS and otherwise maintain
fully protective conditions below the SCDD.
The most significant hydrologic conditions related to operating the SCDD in a manner that
controls the continuing IMM AMD discharges (or spills) are the combination of low releases
from Shasta Lake and high inflows of highly contaminated waters into the SCR. The low
releases from Shasta Lake typically occur when Shasta Lake storage is low after one or more
years of dry conditions. In such conditions, USSR operations criteria specify that water
should be stored for beneficial uses rather than released above certain minimum flows.
Shasta Lake storage capacity is approximately 4.55 million acre-feet, with non-usable storage
of about 116,000 acre-feet.
When the Sacramento River flow is low, it is very difficult to safely discharge highly
contaminated waters from the SCR because, due to the highly contaminated IMM AMD dis-
charges, significant dilution is necessary to meet the water quality criteria below Keswick
Dam. The inability to release significant amounts of contaminated water from the SCR is a
ROD4.DOC 44
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critical factor with respect to the problem of high inflows to SCR during storm events. The
SCR can fill in a few days during high runoff events. Large storm events with several thou-
sand acre-feet of inflow can cause an uncontrolled spill of contaminated waters within a few
days. Prolonged storm events combined with antecedent drought conditions can cause the
SCDD to spill for extended periods of time. For example, the SCDD spill in 1992 and 1993
lasted for several weeks and resulted in prolonged exposure of aquatic resources to toxic
levels of heavy metals.
All of the six largest storm events since 1955 have occurred in December or January.
Historically, most releases from Shasta Lake and Whiskeytown Reservoir in these months
total less than 10,000 cfs. Relatively low winter flows particularly at the beginning of the wet
season are expected in future years due to current and future water demand and other CVP
operational constraints.
The competing demands for fresh water in California for domestic, environmental,
agriculture and industrial use are expected to constrain these flows further in future years.
Although water availability from one to the next is uncertain, particularly considering the
time-period that IMM is expected to continue generated large volumes of hazardous
substances, recently acquired information indicates that less Sacramento River water could be
available in future water years. For example, the United States Department of Interior, the
agency responsible for CVP operations, is currently considering whether to hold more water
during the winter months to permit greater flows at other times of the year to protect
endangered species. These storage requirements would reduce the available storage capacity
of Shasta Lake and the available dilution water for IMM pollution. Other CVP operations
being considered by the U.S. Department of Interior would reduce the release of water during
high flow periods, which in turn would reduce the water available to dilute IMM AMD.
Other statutes and programs could also affect the flows in the Sacramento River. The
available information regarding two such programs, the Central Valley Project Improvement
Act (CVPIA) and the Bay-Delta Accord, indicates that those programs are unlikely to have a
significant impact on releases from Shasta Lake in December or January, the two months
during which the six major storm events since 1955 occurred. Higher release requirements
might occur in the spring months through June, but these releases would typically not benefit
the IMM response action because SCDD spills typically occur in the early winter months.
Additionally, the future diversion of Trinity River flows to the Sacramento River via the
Spring Creek Power House is likely to be significantly reduced as the result of efforts to
restore the Trinity River ecosystem. The reduced availability of these waters, that have in the
past been relied on to dilute the IMM heavy metal releases, would necessitate further
remedial action and control of the IMM discharges.
VI. SUMMARY OF SITE RISKS
VI.1 General
The IMM Superfund Site was placed on the National Priorities List on September 8,1983.
The Site was listed because of the impacts of metals-laden AMD discharges on the
Sacramento River, which supports a major fishery and which also serves as a source of
drinking water and other domestic water supplies for the City of Redding. Throughout much
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of its history, the Iron Mountain Site has been associated with water quality degradation and
impacts on aquatic resources in nearby drainages. Impacts include numerous fish kills in the
upper Sacramento River (at least 39 documented fish kills since 1940), the primary salmon-
producing river in California (CDWR, 1985; CDFG, 1990). For more detailed information
regarding these risks, see the Public Comment Environmental Endangerment Assessment
(May 1992) and the Human Health Risk Assessment (May 1991), as well as other documents
in the Administrative Record.
Although EPA Superfund response activities currently control 80 to 90 percent of the IMM
AMD releases, hazardous substance releases from the Site continue to pose serious environ-
mental risks. The portions of Boulder Creek, Slickrock Creek, and Spring Creek that receive
AMD from Iron Mountain continue to be essentially devoid of aquatic life. During storm
periods, the continuing IMM AMD releases constitute the vast majority (more than 90 per-
cent in the January 1995 storm) of metal loading to Keswick Reservoir. Even if the SBPS are
met, IMM AMD releases continue to impair water quality through the discharge of large
heavy metal loads, a portion of which form precipitates as heavy metal-laden sediments that
contaminate the streambed in Keswick Reservoir on an almost continuous basis. In the main
stem of the Sacramento River, current IMM AMD releases are expected to cause exceedances
of the SBPS and the PCTR on a regular basis. The IMM AMD continues to cause an average
of 5 to 15 tons per year of copper precipitates in Keswick Reservoir and the Sacramento
River in normal to wet years. For comparison, Iron Mountain currently discharges to State
waters an annual average of 80 to 240 pounds of copper per day, which is roughly one to
three times the average daily copper discharge of all of the regulated industrial discharges to
the entire Sacramento River, San Francisco Bay and Delta.
VI.2 Human Health Risks
Persons who might come into direct contact with or consume concentrated AMD at Iron
Mountain could be at risk. Such persons include people working, living, or hiking at the Site.
Individuals who enter the Iron Mountain Site are at risk if they have direct contact with or
ingest the AMD. The risk of such exposure is currently limited by controlled access to the
minesite. The property owner has posted the property to discourage trespassers. The prop-
erty is located between two heavily used national forests, so direct exposure is clearly
possible.
Persons who might come into direct contact with surface water downstream from Iron
Mountain include people working, living, hiking, or swimming near the Site. Individuals
who come in direct contact with water from the main body of Keswick Reservoir or
Sacramento River are not currently at risk.
Persons who might consume surface water downstream from Iron Mountain include people
working, living, or hiking near the Site.
Persons who might consume fish taken from the Sacramento River downstream from Iron
Mountain include the general population in the upper Sacramento River Valley. Tissue
samples from fish inhabiting this area have some of the highest metal levels of anywhere in
the State. Individuals who consume fish from the main body of Keswick Reservoir or
Sacramento River may currently be at some risk, but the risk has not been quantified.
ROD4.DOC 46
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Children are at somewhat greater risk than adults when considering noncancer toxicity
resulting from incidental ingestion of affected creek water downstream from Iron Mountain.
Although an arsenic pathway has not been studied extensively, USER workers measured
arsenic levels in excess of safe worker exposure levels while conducting maintenance on the
SCDD. The most likely source of this arsenic is the arsenic-laden hematite piles in the Slick-
rock Creek watershed, which have been actively eroding into Slickrock Creek for several
decades.
VI.3 Environmental Risks
The principal risks posed by the runoff of metals-bearing AMD from Iron Mountain are the
associated impacts on aquatic life in the Spring Creek drainage, Keswick Reservoir, and the
Sacramento River downstream of Keswick Dam. Among these natural resources, the most
important are the fishery resources in the Sacramento River downstream of Keswick Dam.
Migratory populations of chinook salmon, steelhead trout, resident trout, and numerous other
aquatic and terrestrial species, can be or are affected by AMD from Iron Mountain.
Fishery Resources below SCDD
The salmon and steelhead trout populations have high commercial and/or recreational value
to the region. The susceptibility of these populations to contaminants originating from Iron
Mountain has been well documented (Wilson, 1982; Finlayson, 1989 and 1995; Hagler-
Bailly 1996). One of the chinook salmon runs, the winter-run, is a species listed by the Fed-
eral and State Governments as endangered. The steelhead in this region are currently being
considered for listing as an endangered species under the federal Endangered Species Act.
The spring-run salmon is a candidate species under the State Endangered Species Act.
Pollution from Iron Mountain is considered to be a major factor causing the decline in
Sacramento River fishery resources and impeding fishery resource restoration goals. Other
major factors contributing to the fishery decline include loss of spawning habitat, predation,
habitat degradation, mortality at dams and diversions, overfishing, and natural disasters (such
as drought) (Vogel, 1989). Fish migrating into the uppermost reach of the Sacramento River
risk being killed by AMD from Iron Mountain; offspring of adult fish spawning in that reach
have reduced chances of survival because of the Iron Mountain AMD (Finlayson and Wilson,
1979). There is an indication that AMD from Iron Mountain has reduced the suitability of
available spawning grounds for salmon in the uppermost reaches of the Sacramento River
and that fish population reductions have occurred following uncontrolled spillage of Iron
Mountain AMD (Finlayson, 1979). The greatest decline in salmon-spawning populations has
occurred within the uppermost river reach from Balls Ferry upstream to Redding, a distance
of approximately 26 river miles (NOAA, 1989). Sub-lethal exposure to toxic metals can also
adversely affect exposed species.
Fish counts were initiated at Red Bluff Diversion Dam in the late 1960s. The fish counts
document major declines in each of the anadromous salmonid runs. A more extensive data
base is available specifically for fall-run salmon. This data base demonstrates that recent
levels of spawning escapement to the upper Sacramento River are only about 50 percent of
levels observed during the late 1950s. The greatest decline among the salmon runs has
occurred for the winter-run, which has been reduced to less than 5 percent of run sizes during
ROD4.DOC 47
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the late 1960s. This serious decline prompted the 1989 listing of this fish as a threatened spe-
cies by the Federal Government (NMFS, 1989) and an endangered species by the State of
California (CDFG, 1989). The Federal Government subsequently reclassified the winter-run
as an endangered species.
Currently, the fisheries populations with the greatest potential exposure include the salmonids
and steelhead trout present in the Sacramento River below Keswick Dam. The upper
Sacramento River chinook salmon runs, steelhead trout run, and resident populations of
rainbow trout have life history characteristics that make them vulnerable to potentially
adverse effects from AMD originating from IMM. The probability and magnitude of
potential exposure depends on the releases of contaminated water from SCDD, the releases
of water from Shasta Lake and Whiskeytown Reservoir, and the life stages offish present
within the zone of impact.
For spring- and fall-run chinook salmon, in a worst-case scenario, approximately half of an
entire year's spawning production could be at risk from contaminants released from Iron
Mountain. The impact of the release depends in large part on the pattern of releases from
Shasta Lake and Whiskeytown Reservoir relative to when releases occur from IMM. For
example, flood control releases from Shasta Lake could cause most of the year's production
to migrate downstream of the affected water quality zone, thereby reducing the AMD's
impact.
Under certain circumstances, the endangered winter-run chinook salmon could be at higher
risk compared to other runs. That run is most likely to seek cooler water in areas closest to
Keswick Dam because of potentially lethal water temperatures in lower reaches of the
Sacramento River. Under drought-type conditions, these fish are the most important to future
runs because eggs laid further downstream arc more likely to be adversely affected by lethal
warm water temperatures. However, these same drought conditions are more likely to create
conditions (low water flows in the Sacramento River) where AMD from IMM could pose a
high risk to juvenile rearing in the uppermost reach of the river. While winter run salmon do
not spawn during the period that is most likely to experience an SCDD spill, a spill during the
winter run spawning period is not impossible. More importantly, juvenile salmon are gener-
ally present in the Sacramento River below Keswick Dam during December and January,
when a spill is most likely. Although juvenile salmon are more tolerant of copper and zinc
concentrations than eggs and fry, the juvenile salmon could be impacted by IMM contami-
nant spills during the December and January time period.
The steelhead trout and resident rainbow trout populations that are potentially at risk are not
well-defined or understood. However, both the adult and yearling life stages are potentially
at risk because both are present in the river when fish kills have historically occurred.
At present, the USER operates the SCDD pursuant to an MOU. Pursuant to that MOU,
USER operates the SCDD in a manner that (when considering releases of waters from CVP
facilities, including Shasta Lake, Whiskeytown Reservoir, and Keswick Dam) will meet
operation criteria for control of metal concentrations in the Sacramento River intended to
protect aquatic life in the Sacramento River downstream of Keswick Dam, taking into
consideration the extreme releases from the Site and provided such operations would not (1)
ROD4.00C 48
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cause flood control parameters on the Sacramento River to be exceeded, or (2) interfere
unreasonably with other project requirements.
The USBR must also operate Shasta Dam to provide electric power, irrigation water, and
flood control. The USBR estimated that it would incur significant losses of revenues,
depending on the level of protection required in the Sacramento River, if special releases of
CVP waters continue to be relied on for purposes of diluting IMM contaminant discharges.
There is the potential that USBR's ability to supply adequate dilution water will be further
reduced because of conflicting priorities for water use, thereby increasing the potential risk to
the aquatic community. It is also important to note that the operational parameters of the
1980 MOU approximate the SBPS below Keswick Dam but do not assure compliance at that
location under all circumstances. For example, the 1980 MOU is based on an assumption
that 50 percent of the dissolved metals will form precipitates in Keswick Reservoir. More
recent and detailed studies by EPA indicate that the precipitation rate is more appropriately
estimated at 35 percent under most conditions. Operation of the SCDD in conformance with
the 1980 MOU will therefore still result in exceedances of the SBPS (even without taking
into account hydrologic events requiring emergency SCDD releases or causing uncontrolled
spills).
It is extremely difficult to quantify fish mortality in the Sacramento River as a result of con-
tamination from IMM. This is due to a variety of factors, including the general size of the
Sacramento River downstream of Keswick Reservoir and the difficulty of visually observing
dying or dead fish during periods when the water is turbid. However, there have been
39 documented fish kills near Redding since 1940, and since the installation of the SCDD in
1963, there have been observations of adult steelhead mortalities near Redding attributable to
metal contamination from IMM.
The current mass loading of metals from IMM also exposes aquatic resources to sub-lethal
metal levels. For example, metal concentrations in Keswick Reservoir and below Keswick
Dam regularly exceed the recently proposed chronic water quality criteria for copper, indi-
cating species in those waters are at risk with respect to chronic exposure to copper. Fish in
the area contain some of the highest levels of metals of any fish in the State. In addition,
because the SBPS are stated in terms of dissolved and not total metal concentrations, the
standards do not protect fish from the effects of exposure to the non-dissolved fraction of
total metal concentrations. While the non-dissolved fraction is less toxic than the dissolved
fraction, long-term exposure to total metal concentrations is also known to pose risks to
exposed organisms.
Environmental Impacts above the SCDD
The environmental effects are even more severe upstream of the SCDD. The waters receiv-
ing IMM AMD upstream of the SCDD (Boulder Creek, Slickrock Creek, and Spring Creek)
are currently devoid of fish and aquatic invertebrates. These creeks may remain sterile fol-
lowing current remediation activities at Iron Mountain. Whether reaches of those creeks
could be restored to a degree that would support aquatic life or other beneficial uses is
currently unknown. Implementation of this interim action and the ongoing study of further
ROD4.DOC 49
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action from Boulder Creek area sources will enhance EPA's understanding of the feasibility
and appropriateness of taking additional response actions to further address those impacts.
Water Column and Benthic Organisms
Past and current IMM AMD releases also pose a risk to water column and benthic aquatic
populations in Keswick Reservoir downstream of Spring Creek. IMM AMD releases have
caused and continue to cause the contamination of the water column and stream or reservoir
sediments. Below Keswick Dam, contaminant concentrations in the water column occa-
sionally exceed toxic concentrations for sensitive life stages and frequently exceed both EPA
and State of California criteria to protect aquatic life, indicating that benthic and water
column populations are at risk. The formation of heavy metal precipitates as the AMD
releases are diluted poses threats to benthic organisms through smothering as the precipitates
settle and through chemical toxicity. Benthic survey information indicates that benthic
populations are severely reduced or absent from areas where extensive heavy metal-laden
sediments are present in the Spring Creek arm of Keswick Reservoir and in the main body of
Keswick Reservoir. The streams above SCDD influenced by IMM are currently essentially
devoid of aquatic life.
Terrestrial Wildlife
IMM AMD releases also have the potential to adversely affect onsite terrestrial wildlife.
More than 300 species of amphibians, reptiles, birds, and mammals can be expected to occur
in the Boulder Creek and Slickrock Creek basins and downstream areas. These species can
be directly exposed to AMD. For example, deer can drink from contaminated creeks, lick
metals-laden salts along the flume system, or consume contaminated plants or other organ-
isms. AMD has severely impacted the habitat and food sources for species heavily dependent
on aquatic resources, such as amphibians. In the absence of hazardous substance
contamination, the area could provide habitat for a host of special-status and other species.
VII. DESCRIPTION OF ALTERNATIVES
VII.1 General
Consistent with the NCP, EPA has developed remedial action objectives to assist the Agency
in studying remedial alternatives. 40 CFR § 300.430(e)(2)(i). The overall remedial action
objective at the Site is to eliminate IMM Site discharges that are harmful to the environment.
The EPA has also identified three primary goals for the IMM Superfund remedial action:
1. Comply with the water quality criteria established under the Clean Water ACL
2. Reduce the mass discharge of toxic heavy metals through application of appropriate con-
trol technologies.
3. Minimize the need to rely on special releases of California's valuable water resources to
ensure compliance with water quality standards in the Sacramento River through special
releases of waters to dilute toxic spills of IMM contaminants.
The contaminants of concern identified in the 1986 ROD are acidity and toxic metals, which
include copper, cadmium, and zinc. All of these are present in AMD from Slickrock Creek
ROD4.DOC SO
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area sources. Arsenic is an additional contaminant of concern that has been identified with
respect to the large hematite pile that is actively eroding into Slickrock Creek and down-
stream areas. The arsenic in the hematite pile exceeds the total threshold limit criteria
(TTLC) established by the State of California. The high arsenic concentrations that are
present in this waste pile pose a threat to human health and the environment.
VIL2 Technology Screening Evaluation
The technology screening phase of the feasibility study consists of a two-step process. The
first step involves identifying general response actions that could potentially meet the reme-
dial action objectives for the sources being addressed. The second step involves analyzing
and comparing technologies and process options that EPA has determined are appropriate for
consideration.
The EPA determined that the Site conditions restrict the number of alternatives to four gen-
eral types of response actions:
1. No-Action—No further actions would be implemented as part of the EPA Superfund
cleanup action at the Site.
2. Source Control Response Actions—Prevent AMD formation through isolation of water
and/or air from the sulfide rock.
3. Treatment Response Actions—Collect and treat the AMD, dispose of the treatment
residuals (sludge), and discharge the treated water.
4. Water Management Response Actions—These options include surface-water diversions
of clean water flows and construction of dams to contain the contaminated flows until
they can be treated or safely released.
The EPA then refined the range of alternatives within each category by first evaluating
whether the alternative was technically implementable at this Site. If an option was not tech-
nically implementable, the option was eliminated from further consideration. The EPA then
evaluated the remaining options more closely to determine the options and technologies to be
developed into remedial alternatives. This selection is made by comparing the options on the
basis of implementability and effectiveness, with implementability being the more important
criterion during the screening process.
Following is a brief summary of the screening evaluation.
Vll.2.1 No Further Action
In accordance with the NCP, EPA evaluated the No Further Action alternative in detail.
Vll.22 Source Control Response Actions
Source control response actions involve source-specific responses for individual AMD
sources. Potential source control response actions include ground water control, capping,
surface controls, removal of waste piles and sediments, and resource recovery. For purposes
of clarity, this document refers separately to source controls that prevent AMD formation and
ROD4.DOC 51
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general collect and treat technologies. Certain other documents refer to these non-water
management technologies as "source control" remedies.
An EPA review of the types of sources being addressed in Slickrock Creek indicated that a
source-specific approach would be difficult to implement, and even if feasible, would likely
be less cost-effective than a general collect and treat approach. In general, the Slickrock
Creek area sources are difficult to identify and characterize. The sources are spread through-
out the Slickrock Creek basin in the vicinity of areas affected by intense mining activity.
Many of the sources, such as the mine workings and mineralization exposed through changes
in hydrology, are belowground and/or buried below the large debris slide. Despite Rhone-
Poulenc's best efforts to locate buried mine portals during the past 2 or 3 years, it has not
been able to locate buried mine workings with AMD. The presence of millions of cubic
yards of mine overburden and other materials over the mine workings severely impedes the
identification of these sources. Even if the workings are identified; one would need to
develop a reliable strategy for responding to releases associated with that source.
With respect to some of the more significant area sources that are readily identifiable, the
most effective remedial strategy appears to involve a general collect and treat approach. For
example, the large debris slide is a source of mining-related hazardous substance releases.
The debris slide contains millions of cubic yards of materials so that excavation and consoli-
dation would be very difficult and prohibitively costly to implement. In addition, removal or
consolidation of the debris slide would likely increase the exposure of the underlying sulfides
to oxygen and water, thereby increasing the release of AMD. Source control of disturbed
mineralization would likely be even more difficult because the areas are widespread and not
easily accessible. These factors suggest that general collect and treat approaches would be
more effective and cost-effective than source-specific type approaches.
Source Control by Groundwater Control
Source control by groundwater control involves reducing or eliminating groundwater contact
with sulfide rock by blocking lateral groundwater flow with a barrier or intercepting the flow
with an active well-dewatering system. Since this technique is not effective in broken ground
located above and around mine workings and around waste piles prevalent in the target area,
the approach cannot be used as a primary response action for these sources. The EPA also
reviewed and rejected as not practical or effective the use of pressure grouting to control seep
flow.
Source Control by Capping
Capping involves placing a cap in a manner that reduces the inflow of fresh water to the acid-
forming zones. The feasibility of this approach depends on the feasibility of placing an
impervious cover above the source, the practicality of maintaining the cover during the life of
the project, and the proportion of water actually diverted from the sites of reaction. While
this strategy is implementable and could potentially be used with respect to a few sources, the
approach is not a practical means to control Slickrock Creek area sources generally due to the
very large area over which AMD-forming reactions appear to be occurring, the steep terrain
in those areas, and the potential for landslides and the continued movement of the waste
materials and debris to be capped.
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Source Control by Surface Controls
Source control by surface drainage controls involves routing surface water away from waste
piles and disturbed areas through the use of grading and diversions. While this strategy is
implementable and could potentially be used with respect to a few sources, the approach is
not a practical means to control Slickrock Creek area sources generally. The Slickrock Creek
area sources cover an area of approximately 150 acres. Extensive surface water diversions
would be required to prevent surface water from entering this source area. However, these
surface controls would not prevent rainfall from falling directly onto these area sources
resulting in AMD formation and discharge. The approach is unlikely to obviate the need for
a general collection approach. Surface water controls may be useful in controlling specific
areas in future actions at IMM.
Source Control by Removal of Waste Piles
Excavation and consolidation of waste piles, contaminated soils, debris, and/or sediments, is
considered to be impracticable for the Slickrock Creek area sources in general. The amount
of material present in the debris slide and other contaminated areas is too extensive to make
this approach feasible for general remediation of the Slickrock Creek area sources. The steep
and difficult terrain would also make this approach difficult to implement throughout the
basin. In addition, removal of the debris slide might increase the exposure of sulfides and
therefore exacerbate the release of hazardous substances. The approach is also unlikely to be
cost-effective relative to a general collect and treat approach. However, removal of specific
waste piles may be appropriate in a final remedy for the Site. Also, removal of contaminated
sediments, although very difficult, may be necessary as part of the Site remedy to achieve
ARARs compliance.
Source Control by Resource Recovery for Waste Piles
EPA also evaluated several resource recovery treatment options that could be used to recover
certain metals from some of the waste piles. These options include flotation (a historic treat-
ment method for ore) or soil washing (such as acid leaching, which has been also used to
treat ore). The removal efficiencies of these processes are expected to be low because the in
situ metals concentration in piles is relatively low, and the metals are likely to be present
primarily as insoluble sulfides. The implementability and effectiveness of these treatment
options cannot be currently evaluated, but the available information does not establish that
this current technology would permit this approach to be cost-effective or implementable at
this time. Laboratory or bench-scale testing is required to provide sufficient information to
conduct more detailed assessments. Because of the lack of demonstrated effectiveness, EPA
dropped these alternatives from further consideration in the analysis.
VII2.3 Collection of Seeps and Surface Water
The EPA also considered the feasibility of collecting and treating seeps using groundwater
extraction systems, such as wells or drains. This approach could be implemented in combi-
nation with treatment of portal discharges at the IMM HDS treatment plant currently in
operation. There are technical and cost limitations concerning the treatment of seeps because
of the expected small flow rates and metals loads from these sources and because access to
some of the seeps will be difficult. The EPA eliminated this approach from further consid-
ROD4.DOC 53
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eration in the FSA because of its limited effectiveness for the dispersed Slickrock Creek
AMD discharges.
The EPA considered the feasibility of collecting and treating contaminated tributary flows
and treating those flows at the existing IMM HDS treatment plant. There are technical and
cost limitations concerning the collection and treatment of contaminated surface waters
because of the large volumes of contaminated runoff associated with storm events that may
require treatment and because of the dilute nature of these flows. The presence of the exist-
ing HDS neutralization treatment plant and its ongoing operations significantly enhances the
implementability and cost-effectiveness of this approach. Collection systems for surface-
water collection and treatment approaches would include surface-water diversions to ensure
collection of contaminated surface waters from remote contaminated areas and retention
basins and to regulate their discharge to a treatment plant. The surface-water collection
technologies were retained for further study in the FSA.
VII3.4 Treatment Response Actions
Treatment was considered both as a stand-alone response action and in combination with
other technologies to form combined alternatives. The HDS neutralization/precipitation of
AMD is considered the primary treatment option on the basis of past studies. The HDS
treatment process was selected in ROD2 and RODS for IMM. The reliance on the HDS
process is expected to provide significant benefit for the treatment of the dilute Slickrock
Creek area source AMD discharges. The full-scale IMM HDS treatment plant became
operational at IMM in January 1997.
In-stream treatment, cementation, membrane processes, ion exchange, and passive treatment
were dropped because of their expected limited effectiveness or because they were not
implementable. Mechanical evaporation, liquid-liquid extraction, and biological treatment
were retained for further consideration as secondary treatment options.
Disposal options were studied because all primary treatment options generate a sludge that
requires disposal. RCRA landfills were not considered because past IMM RODs concluded
that a non-RCRA sludge disposal option is the preferred technology. A non-RCRA landfill is
currently in operation at IMM at Brick Flat Pit. Treatment of the Slickrock Creek area source
AMD discharges is not expected to change the nature of the treatment sludges or disposal
requirements. The EPA has concluded that the non-RCRA sludge disposal technology would
be effective, implementable, and cost-effective. Sequential modifications could be made to
the Brick Flat Pit sludge disposal facility to enable sufficient storage capacity for sludge
disposal for 50,100, or several hundred years, depending on the volume of AMD treated and
the characteristics of the sludge produced. The Brick Flat Pit non-RCRA sludge disposal
option was retained for further consideration.
The additional treatment plant effluent resulting from treatment of the Slickrock Creek area
source discharges could be discharged either onsite to Spring Creek, Boulder Creek, or Slick-
rock Creek, or offsite to the Sacramento River. The IMM treatment plant currently dis-
charges to Spring Creek by a pipeline. The larger volumes of effluent will require the con-
struction of additional facilities such as a gravity tunnel or an additional pipeline. The EPA
dropped from consideration an alternative involving piping the discharge to the Sacramento
ROD4.DOC 54
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River because the option would be more costly to implement but did not provide any addi-
tional benefit over the Spring Creek discharge option. The EPA retained discharge of the
treatment plant effluent to Spring Creek.
Vll.2.5 Water Management Response Actions
Water management response actions include surface-water diversions of clean water flows
and construction of dams to contain the contaminated flows until they can be treated or safely
released. These response actions could be implemented to meet several distinct project
objectives: (1) divert clean waters away from contaminated areas to reduce AMD-forming
reactions; (2) increase the effectiveness of treatment approaches by diverting clean flows
away from the collection basin; and (3) provide capability to manage releases of contami-
nants to surface waters that cannot be feasibly controlled to ensure protection of human
health and the environment.
Surface Diversion
The intent of surface-water diversions for water management remedial approaches is to divert
less contaminated surface-water flows around AMD containment basins. The diversion of
less contaminated waters can be accomplished by a variety of methods. Clean-water
diversions were retained for further consideration as they can be designed to perform
effectively in combination with other technologies, and offer the opportunity to develop more
cost-effective remedial approaches.
Containment Dams
Containment dams create reservoirs (basins) for storage of contaminated waters until the
water can be safely released or treated.
The SCDD could be enlarged to provide additional storage capacity for the contaminated
Spring Creek watershed inflows. The existing SCDD establishes a 5,016-acre-foot reservoir
to contain IMM-contaminated waters. Although the existing SCR provides some protection
to the environment, it is undersized to allow for full protection in the absence of additional
remedial alternatives beyond the No-Action Alternative. An enlarged reservoir would be
needed for storage of the IMM-contaminated waters to permit the water to be released in
accordance with protective water quality criteria.
Under an alternate approach, new dams could be built in Boulder Creek, Slickrock Creek,
and/or Spring Creek above SCR to establish new reservoirs. These alternate reservoirs could
be relied on as storage reservoirs in conjunction with the existing SCR.
Under a third approach, potential onsite containment basins would be relied on in combina-
tion with treatment remedial action components to ensure treatment of the contaminated
waters contained by the dams. Studies indicate that control and treatment of the Slickrock
Creek area source AMD discharges are consistent with viable remedial strategies for the Site
that could be effective and cost-effective.
Containment dams were retained for further consideration as they can be designed to perform
effectively in combination with other technologies, and offer the opportunity to develop more
cost-effective remedial approaches.
ROD4.DOC 55
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Reliance on CVP Dilution Water
The current interim remedy relies upon water management options because the SCR is used
to contain IMM AMD releases until they can be safely discharged, taking into account the
dilution available in the Sacramento River flows and the limitations imposed by intense
hydrologic conditions as well as the intense pollution loading from IMM. Additional source
control programs at IMM will reduce, but may not eliminate, the heavy metal discharges.
Special releases of Sacramento River waters may be required in the future to ensure adequate
dilution of the IMM discharges. The manner in which dilution water may be acquired and
provided to ensure protection of the Sacramento River fishery and aquatic ecosystem is
described in EPA's June 1994 Water Management FS. Potential IMM remedial strategies
that rely on special releases of dilution water as part of a final IMM remedy were taken into
consideration in evaluating the appropriateness of the water management actions considered.
The purchase of dilution water was retained for further consideration as a component of
future remedial actions. Purchase of dilution water may provide an effective and cost-
effective approach to providing a fully protective remedy for human health and the
environment below Keswick Reservoir.
V 112.6 Summary of Screening Analysis
Through this screening process, EPA determined that the following technologies and options
are potentially suitable for assembly into alternatives for the Slickrock Creek area source
AMD discharges:
• No further action
• Collection of surface water for treatment
• Physical-chemical treatment using the lime/HDS neutralization/precipitation process as a
primary treatment process
• Physical-chemical treatment using the mechanical evaporation/crystallization process as a
secondary treatment process following the lime/HDS process
• Landfill disposal of treatment sludge in a non-RCRA landfill
• Discharge of treated water to surface waters using an outfall
• Surface water diversions of less contaminated water using pipelines, open channels,
dams, drop inlets, or ditches
• Containment basins in Slickrock Creek to temporarily store contaminated waters until
water can be safely released or treated
VII.3 Alternatives
In June 1994, EPA published a Water Management FS, which examined potential remedial
alternatives that could control, treat, or manage the safe release of continued uncontrolled
contaminant discharges from the numerous and widely dispersed area sources in the Boulder
Creek and Slickrock Creek watersheds at IMM. In the Water Management FS, EPA devel-
ROD4.DOC 56
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oped five alternatives for detailed evaluation that included a range of approaches relying on
source control, collection and treatment, and water management technologies. Although
some area sources could be readily identified and remediated (such as waste piles), a large
proportion of the area source discharge was, in general, difficult to identify and characterize.
As a result, the remedial alternatives that were developed and evaluated in the Water Man-
agement FS relied more heavily on collection and treatment approaches and water manage-
ment approaches rather than on source control approaches. The five original detailed
remedial alternatives for a sitewide remedy for the IMM area source AMD discharges were
labeled WMO, WM1, WM2, WM3, and WM4. The EPA relied on the Water Management
FS to develop its 1994 Proposed Plan, which identified a variation of Alternative WM3 as the
preferred alternative. The EPA published this Proposed Plan in June 1994 and requested
public comment on the proposed plan and related documents.
As a result of comments from the public and further study by EPA, EPA prepared the 1996
Water Management FSA, which presented a revised analysis of the No-Action Alternative,
WMO, and developed and evaluated a new remedial alternative, SRI, which focused on a
Slickrock Creek source control and treatment remedy.
Each of the alternatives is summarized below.
Alternative WMO
The No Further Action Alternative was evaluated as required by the NCP at 40 CFR
§ 300.430(e)(6) to determine the risks that would be posed to human health and the environ-
ment if no further actions were taken at IMM to address the continuing AMD discharges.
The No Further Action Alternative is relied on as a baseline alternative against which other
alternatives are judged. The No Further Action Alternative would include provisions for
continued limited monitoring, operation and maintenance of the IMM treatment plant
facilities, operation and maintenance of the ancillary facilities and other projects constructed
pursuant to ROD1, ROD2, and RODS for the IMM Site, and continued operation of SCDD in
accordance with the existing 1980 Memorandum of Understanding.
The EPA has determined that this alternative would not meet remedial action objectives.
Alternative WM1
Alternative WM1 relies on the increased water management capability provided by the
enlargement of the SCR to 15,000 acre-feet. This approach would involve the construction
of a 75-foot raise to the SCDD. The USBR would coordinate operations of the SCR with its
CVP operations. Dilution water would not be purchased during the expected infrequent spill
events.
The EPA's analysis concluded that the increased storage capacity for the contaminated IMM
discharges and Spring Creek watershed runoff would reduce SCDD contaminant spills to one
to three per century and provide significantly increased protection to the Sacramento River.
The cost of this alternative is estimated to be $75.2 million.
ROD4.DOC 57
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Alternative WM2
Alternative WM2 relies on the increased water management capability provided by the
enlargement of the SCR to 15,000 acre-feet Additionally, under this alternative, the con-
taminated base flow of Slickrock Creek would be collected and treated at the existing IMM
treatment plant In addition to the 75-foot raise to SCDD, this approach involves the con-
struction of a small dam in Slickrock Creek, a pipeline, and only limited modifications to the
IMM treatment plant.
The EPA's analysis concluded that the increased storage capacity, coupled with treatment of
the contaminated Slickrock Creek base flows, would reduce SCDD contaminant spills to
once per century, reduce the currently uncontrolled site discharges by 30 to 35 percent
(copper) and 20 to 25 percent (zinc and cadmium) by treating up to 50 percent of the
Slickrock Creek area source AMD, and provide significantly increased protection to the
Sacramento River. The cost of this alternative is estimated to be $79.4 million.
Alternative WM3
Alternative WM3 relies on the increased water management capability provided by the
enlargement of the SCR to 15,000 acre-feet, the collection and treatment of the contaminated
base flow of Slickrock Creek, and the purchase of dilution water during rare SCDD spill
events. In addition to the 75-foot raise to SCDD, this approach involves the construction of a
small dam in Slickrock Creek, a pipeline, and only limited modifications to the IMM treat-
ment plant.
The EPA's analysis concluded that this alternative would provide similar metals reductions to
Alternative WM2. The ability to purchase limited amounts of dilution water during spills
would allow for the mitigation of the expected rare SCDD spill event and provide for
increased protectiveness over Alternative WM2. The cost of this alternative is estimated to
be $89.1 million.
Alternative WM4
Alternative WM4 relies on the collection and treatment of all contaminated flows in Boulder
Creek and Slickrock Creek up to a 100-year storm event. This approach involves the con-
struction of two small dams, clean water diversions, pipelines, and an expanded treatment
plant. The alternative could potentially restore some of the beneficial uses upstream of the
SCDD.
The EPA's analysis concluded that this alternative would provide the most protection to the
Sacramento River and the resources upstream of the SCDD as well as the greatest reduction
in the Site metals discharges. The cost of this alternative is estimated to be $129.5 million.
Alternative SR1
Alternative SRI incorporates a retention dam within the Slickrock Creek drainage, a clean-
water diversion system, and upgrades to the pipeline and treatment plant Alternative SRI
relies on the collection and treatment of the AMD-contaminated surface-water discharges that
are from the area sources in the Slickrock Creek watershed at IMM. The remedy, as finally
designed and implemented, may rely to some extent on source control of specific sources and
ROD4.DOC 58
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on water management technologies (such as diverting nearby downstream sources into the
containment pond area) to ensure collection of the contaminated surface flows as well as to
minimize the amount of water that could become contaminated by the area source discharges
and require treatment.
The Slickrock Creek retention dam and pond would be located within the Slickrock Creek
drainage of Iron Mountain directly below the most heavily disturbed mining area in the
watershed. Inflows include surface-water runoff from the highly disturbed mining areas,
flows from the former open pit mine and current sludge disposal Site, flows from Slickrock
Creek, and flows from the Old/No. 8 Mine Seep, and flows from the hematite pile area. The
dam would be located approximately 200 feet upstream of the hematite pile (with the exact
location to be determined during design). A conceptual depiction of the remedy is shown in
Photo Exhibit 2. A dam at this location would collect drainage from an area of
approximately 546 acres; however, 387 acres of the drainage area would be intercepted by a
clean-water diversion (modified as necessary) and discharged into Slickrock Creek below the
proposed retention dam. An additional 44 acres of drainage above Brick Flat Pit is also
currently collected and diverted into Slickrock Creek below the proposed dam. The potential
AMD-generating area of the Slickrock Creek drainage is therefore approximately 115 acres.
The pond developed behind the dam will temporarily store AMD before it is conveyed by
pipeline to the HDS treatment plant onsite. The retention dam will be sized to contain 100-
year storms, which would require a reservoir capacity of at least 170 acre-feet The exact size
and capacity of the reservoir would be determined during the design phase, but preliminary
information indicates that the retention dam would be approximately 105 feet high (75 feet
above the existing streambed). This alternative also includes a retaining structure to prevent
erosion of the hematite pile, consistent with California mining waste requirements. The cost
of this alternative is estimated to be $ 21.2 million.
A bullet summary of the components of Alternative SRI is presented below:
Construct a retention dam and necessary surface water diversion facilities to ensure the
collection and storage of contaminated surface runoff, interflow, and groundwater in the
Slickrock Creek watershed at IMM.
Construct facilities to provide controlled release of contaminated waters from the
retention dam to the AMD conveyance pipeline to the IMM HDS/ASM lime
neutralization treatment plant.
Construct facilities to divert relatively uncontaminated surface water from the area
upstream from the highly disturbed mining area of the Slickrock Creek basin and divert
that water around the Slickrock Creek retention reservoir.' The diversion shall also divert
around the retention reservoir the water from the unmined side of the Slickrock Creek
watershed.
• Take appropriate steps (including consideration of emergency failure scenarios) to
integrate into the operation of the reservoir the collection and conveyance of the Old/No.
8 Mine Seep AMD to the IMM HDS/ASM lime neutralization treatment plant.
ROD4.00C 59
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Construct a hematite erosion control structure consistent with California mining waste
requirements.
Construct one or more sedimentation basin(s) or other EPA approved control structures in
the Slickrock Creek watershed to minimize sedimentation of the Slickrock Creek
retention reservoir and to ensure proper functioning of the controlled release facilities.
Upgrade the hydraulic capacity of the existing pipeline (or if necessary construct a new
pipeline) from Slickrock Creek to the Boulder Creek crossing as required to ensure
adequate reliable capacity to convey Slickrock Creek and Old/No. 8 Mine Seep AMD.
Construct an additional pipeline to reliably convey Slickrock Creek and Old/No. 8 Mine
Seep AMD-from the Boulder Creek Crossing to the IMM HDS/ASM lime neutralization
treatment plant.
Modify the IMM HDS/ASM lime neutralization treatment plant to ensure proper
treatment, using the HDS/ASM treatment process, of the Slickrock Creek area source
AMD discharges in conjunction with AMD flows collected pursuant to other Records of
Decision.
Construct a tunnel to provide for gravity discharge of the high volumes of effluent from
the IMM HDS/ASM treatment plant to Spring Creek below the Upper Spring Creek
diversion to Hat Creek.
Construct facilities to assure collection of significant identified sources (including but not
limited to seeps from Brick Flat Pit and the hematite piles) and convey those releases to
the Slickrock Creek Retention Reservoir.
Perform long-term operations and maintenance (O&M) of all components.
The alternatives are presented in tabular form below in Table 1.
TABLE 1
Summary of Descriptions
Record of Decision 1997, Iron Mountain Mine Superiund Site
Alternative Components
Alternative WMO-No Further Maintain partial cap, SlickrockOreek diversion, and Upper Spring
Action. Creek diversion.
Continue treatment of AMD discharge from Richmond and Lawson
portals and Old/No. 8 Mine Seep.
Assumes that USSR will continue to operate the SCR in accordance
with the 1980 MOD criteria.
Continue water monitoring.
ROD4.DOC 60
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TABLE 1
Summary of Descriptions
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Components
Alternative WM1 -Enlarge
SCR to 15,000 acre-feet and
dilute uncontrolled spill water,
if dilution water is available.
Contains same elements as Alternative WMO with the exception of
the SCR operations criteria.
Enlarge SCR to a capacity of 15,000 acre-feet.
Operate the SCR in compliance with the SBPS.
Provide special dilution releases for uncontrolled SCDD spills, only to
the extent they can be made available.
Contains same elements as Alternative WM1, including the
enlargement of the SCR to a capacity of 15,000 acre-feet.
Collect and treat 750-gpm base flow from Slickrock Creek in HOS
treatment facility.
Operate the SCR in compliance with the SBPS.
Provide special dilution releases for uncontrolled SCDD spills, only to
the extent they can be made available.
Contains same elements as Alternative WM2, including the
enlargement of the SCR to a capacity of 15,000 acre-feet, and the
collection and treatment of 750-gpm base flow from Slickrock Creek
in HDS treatment facility.
Operate the SCR in compliance with the SBPS.
Provide special dilution releases for uncontrolled SCDD spills with a
limited amount of purchased dilution water.
Contains same elements as Alternative WMO with the exception of
the SCR operations criteria.
Build two alternative dams on Slickrock Creek and Boulder Creek.
Build clean-water diversions.
Collect and treat all contaminated runoff.
Existing SCDD would be relied upon only as a backup in case of a
failure of the treatment system.
Alternative WM2-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water,
if dilution water is available.
Alternative WM3-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water
with purchased dilution water.
Alternative WM4-Rely on the
existing SCDD for backup for
plant failures, build two alter-
native dams (one in Slickrock
Creek and one in Boulder
Creek), build clean-water
diversions, and collect and
treat all contaminated water.
Alternative SR1 -Construct a
dam in Slickrock Creek and
clean-water diversions, collect
and treat all contaminated
Slickrock Creek runoff, and
build a retaining structure for
the hematite pile.
Contains same elements as Alternative WMO with the exception of
the SCR operations criteria.
Build clean-water diversions and a retention dam in Slickrock Creek.
Upgrade the capacity in conveyance pipelines and the IMM HDS
treatment plant. Build a tunnel to discharge treated AMD into Spring
Creek. Build a control structure to prevent hematite erosion into
Slickrock Creek.
Provide controlled release of Slickrock Creek AMD from retention
dam and treat at HDS plant.
Operate the SCR in compliance with the SBPS.
ROD4.DOC
61
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TABLE 1
Summary of Descriptions
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative Components
Provide special dilution releases for uncontrolled SCDD spills, only to
the extent they can be made available.
Alternative 8R1 can later be combined with an appropriate area
source remedial alternative for Boulder Creek (such as those
developed and evaluated in EPA's Boulder Creek Remedial Alter-
native Study).
VIII. ALTERNATIVE COMPARISONS
The detailed analysis of alternatives consists of an assessment of individual alternatives
against nine evaluation criteria identified in the NCP and a comparative analysis that focuses
on the relative performance of each alternative against those criteria. The resulting strengths
and weaknesses of the alternatives are weighed to identify the alternative providing the best
balance among the nine criteria. The nine evaluation criteria specified by the NCP in 40 CFR
§ 300.430(e)(9) are: (1) overall protection of human health and the environment; (2) compli-
ance with ARARs; (3) reduction of toxicity, mobility, or volume through treatment; (4) long-
term effectiveness and permanence; (5) short-term effectiveness; (6) implementability;
(7) cost; (8) State acceptance; and (9) community acceptance. Assessment of two of the nine
criteria, State acceptance and community acceptance, is not completed until after comments
on the Proposed Plan are received.
Other than Alternative SRI which addresses only remediation of area sources in the most
heavily impacted reach of Slickrock Creek and the No-Action Alternative, each alternative
addresses the remediation of AMD discharges from the entire IMM Site by addressing cap-
ture of both Slickrock and Boulder Creeks. Alternative SRI does not address Boulder Creek
area sources because further studies are underway to define the best way to remediate those
sources. As set forth in EPA's August 1995 Boulder Creek Remedial Alternatives Study,
EPA has determined that a range of alternatives is available for the Boulder Creek area
source AMD discharges so that Alternative SRI, in combination with an appropriate Boulder
Creek area source remedy, provides protection equivalent to Alternative WM4 and superior
to Alternatives WMO, WM1, WM2, and WM3.
The consideration of an alternative that addresses Slickrock Creek without requiring comple-
tion of the studies for Boulder Creek is consistent with 40 CFR § 300.430(a)(ii)(A), which
identifies as a program management principle that "[s]ites should generally be remediated in
operable units when necessary or appropriate to achieve significant risk reduction quickly,
when phased analysis and response is necessary or appropriate given the size and complexity
of the Site, or to expedite the completion of total Site cleanup."
ROD4.DOC 62
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VIII.1 Criterion 1—Overall Protection of Human Health and the Environment
Overall protection of human health and the environment addresses whether a remedy pro-
vides adequate protection and describes how risks posed through each pathway are elimi-
nated, reduced, or controlled through treatment, engineering controls, or institutional
controls.
Protection of Human Health
Concentrated acidic waters with high levels of heavy metals are harmful to humans. The
concentrated IMM AMD is mainly limited to remote and uninhabited areas, such as Spring
Creek and its tributaries. Controls are currently in place to restrict access to those areas, but
human consumption of these flows is not impossible. Alternatives WM4 and SRI provide
the potential for some improvement (compared to the other alternatives) in protection of
human health because in varying degrees these alternatives could reduce metal concentrations
in lower Spring Creek and its tributaries. Overall, however, this improvement is considered
marginal in light of the limited access to those water bodies.
The relative protection of human health associated with dilute AMD releases below the
SCDD is not a major issue for evaluating either the No-Action Alternative or the action
alternatives. Although the IMM AMD from the Slickrock Creek area sources discharges into
the Sacramento River, which is a source of drinking water, the nearest point of withdrawal
from the Sacramento River for domestic or municipal water use is downstream from Keswick
Dam. Even under the No-Action Alternative, EPA anticipates that the Safe Drinking Water
Standards will be met at that point. Further, the RWQCB coordinates with the City of
Redding during SCDD spill and emergency release periods so that groundwater can be used
if appropriate, thereby providing additional protection to human health. The remedies that
reduce metal loads to state waters would be expected to reduce human health risks associated
with consumption of fish contaminated with high levels of heavy metals from IMM, although
the risks associated with such consumption has not been quantified.
Remedy SRI would reduce exposure to arsenic associated with the hematite pile, so the
remedy would protect human health with respect to future releases from the hematite piles.
Exposures resulting from past releases from the hematite pile are not addressed by this
remedy.
Protection of the Environment
The level of environmental protection of the alternatives varies. The No-Action Alternative,
WMO, provides only a continuation of the controls now in place (the partial cap, the Spring
Creek and Slickrock Creek diversions, and treatment of the AMD discharges from the
Richmond/Lawson portals and Old Mine/No. 8 Mine Seep). The No-Action Alternative is
not considered to be protective. Present impacts to the environment would remain unchanged
or would become more severe over time. The current water quality degradation and associ-
ated impacts would continue in Slickrock Creek, Boulder Creek, Spring Creek, SCR, Kes-
wick Reservoir, and the Sacramento River. IMM AMD would continue to constitute the
dominant source of heavy metal loading to the upper Sacramento River during storms.
Uncontrolled SCDD spills are expected to occur on average every 3 to 4 years if the SCDD is
operated to achieve the SBPS below Keswick Dam. Operating the SCDD to meet the
ROD4.DOC 63
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recently proposed PCTR (below Keswick Dam) would cause the spills to occur ever 2 to 3
years on average. Spills would occur even more frequently if the SCR were operated to
target compliance with these standards in Keswick Reservoir rather than downstream of
Keswick Dam. If dilution water releases can be made available from Shasta Dam, then the
uncontrolled SCDD spill would be diluted, thereby minimizing its impact on the
environment This alternative, however, does not involve any action to ensure such flows
will be available, so reliance upon such flows would be speculative. IMM would continue to
discharge large volumes of heavy metal precipitates into the waters of the State. Some of
these precipitates would become toxic sediments, adversely affecting benthic organisms and
water column species and their habitat. High metal loads would continue to cause sub-lethal
effects on aquatic resources.
The alternatives which increase SCDD capacity (Alternatives WM1, WM2, and WM3)
reduce the frequency of an uncontrolled spill from the SCDD, which would decrease the
frequency of the exceedances of the SBPS and PCTR below the SCDD. Alternative WM1
would reduce SCDD spill frequency to approximately one to three spills per century.
Alternatives WM2 and WM3, which combine dam enlargement with treatment of the base
flow from Slickrock Creek, are estimated to reduce the amount of metals released into the
environment by about 30 to 35 percent (copper) and 20 to 25 percent (zinc and cadmium) on
average compared to Alternatives WMO or WM1. Alternatives WM2 and WM3 would
reduce spills to a frequency of one per century or less. Alternative WM3 attempts to mini-
mize the impact of the rare uncontrolled spills by arranging for purchase of some of the
required dilution water. The other two alternatives rely on current operations of Shasta Dam
to the extent special releases of dilution water could be made available and if downstream
conditions would allow for the releases. None of these alternatives would attain safe and
protective metal levels in the SCAKR. The severe impacts above the SCDD remain
unabated.
Alternative WM4 is expected to provide the most protection of the environment because the
remedy provides the greatest reduction in metals discharges. The remedy would be designed
to treat all contaminated flows up to a 100-year, 3-day storm, so Alternative WM4 would
reduce SCR contaminant spills to less than once per century. This remedy could generally
achieve safe and protective metal levels in the SCAKR. The alternative is also expected to
improve the water quality in the receiving waters in the Spring Creek watershed (including
Spring Creek, and possibly Boulder and Slickrock Creeks) because the remedy would remove
the large metal loads that would otherwise be discharged to those creeks. While EPA would
not anticipate that all beneficial uses would be restored, the conditions could potentially
improve to a point that many uses are partially restored. Additional response actions might
also be available to further enhance those water bodies, such as removal of the contaminated
stream sediments.
Alternative SRI involves treatment of the Slickrock Creek area sources discharging to the
most heavily impacted area of Slickrock Creek. The treatment of those sources is expected to
on average reduce the release of copper by 60 to 70 percent and zinc and cadmium by 40 to
50 percent compared to Alternatives WMO and WM1. The alternative is expected to reduce
the frequency of SCDD spills to once every 8 to 10 years (when the SCDD is operated to
ROD4.DOC 64
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target compliance with the SBPS below Keswick Dam). The duration and toxicity of spills
would be reduced from the spills that would occur under Alternatives WM1, WM2, and
WM3. Alternative SRI would also improve the water quality in the SCAKR and therefore
reduce the risk to species in that watershed. The alternative is also expected to improve the
water quality in the receiving waters in Spring Creek and Slickrock Creek because the rem-
edy would remove the large metal loads that would otherwise be discharged to those creeks.
While EPA would not anticipate that all beneficial uses would be restored to those creeks, the
conditions could potentially improve to a point that some uses are partially restored. This
remedy could potentially be more protective than Alternative WM4 with respect to lower
Slickrock Creek because Alternative SRI involves diverting relatively less contaminated
water to the lower reach of Slickrock Creek, which would provide dilution water and
additional flow to that reach. The alternative is less protective than Alternative WM4 with
respect to Spring Creek and Boulder Creek because Alternative SRI does not address the
metal being discharged to Boulder Creek. Alternative SRI would also reduce the risks posed
by the continuing release of arsenic from the hematite piles in the Slickrock Creek basin.
Alternative SRI, in combination with a subsequent remedy for the Boulder Creek area
sources, is expected to be able to reduce metal loads to practically the same degree as
Alternative WM4, if necessary. Alternative SRI, in combination with a Boulder Creek area
source remedy, is expected to be able to reduce SCDD spills to less than once per century, if
necessary, and to reduce mass metal loading to State waters to practically the same degree as
Alternative WM4. Alternative SRI, in combination with available alternatives for Boulder
Creek, could approach or equal Alternative WM4 with respect to protecting Keswick Reser-
voir and the water bodies upstream of the SCDD. Additional response actions might also be
available to further enhance those water bodies.
All of the remedies rely upon continuation of the existing treatment operations, and several of
the remedies involve treatment of additional flows. Although operational upsets of the treat-
ment plant are expected to be rare, occasional spills from the treatment plant related to opera-
tional problems are expected. The effect of treatment plant upsets is not expected to substan-
tially impact the overall protectiveness of the remedial approaches that rely on treatment.
The SCR would be relied on as a backup measure to store these contaminated plant spills
until they could be safely released into the Sacramento River.
Overall, the No-Action Alternative provides inadequate environmental protection. The
SCDD enlargement alternatives (WM1, WM2, and WM3) provide adequate to high levels of
protection of the environment below Keswick Dam and some additional protection to the
environment in Keswick Reservoir. Alternatives WM1, WM2 and WM3 do not appreciably
improve conditions upstream of the SCDD; Alternative WM4 provides the greatest
protection to the environment both above and below the SCDD. Alternative WM4 is also
most effective in terms of reducing the mass loading of heavy metals to the waters of the
State and provides the greatest potential for restoration of some beneficial uses above the
Spring Creek Debris Dam. Alternative SRI provides significant protection to resources
below the SCDD and the potential for some additional protection for reaches of Spring Creek
and Slickrock Creek. Alternative SRI coupled with an available response action in Boulder
ROD4.DOC 65
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Creek could provide protection equivalent to Alternative WM4 and superior to Alternatives
WMO, WM1, WM2, and WM3.
Table 2 presents a comparison of each alternative's ability to protect human health and the
environment.
TABLE 2
Summary of Overall Protection of Human Health and the Environment
Record of Decision 1997, Iron Mountain Mine Superftmd Site
Alternative
Component
Alternative WMO-No Further
Action.
Alternative WM1-Enlarge
SCR to 15,000 acre-feet and
dilute uncontrolled spill water,
if dilution water is available.
Human health risk is expected to be low.
If the SCDD is operated to achieve the SBPS below Keswick Dam,
uncontrolled SCDD spills are expected to occur on average every 3
to 4 years. Operating the SCDD to target the PCTR below Keswick
Dam would cause the spills to occur ever 2 to 3 years on average.
Spills would occur even more frequently if the SCR were operated to
target compliance with these standards in Keswick Reservoir rather
than downstream of Keswick Dam.
Repeated uncontrolled SCDD spills may increase severity of
environmental impacts.
Spring Creek arm of Keswick Reservoir continues to have regular
exceedances of the SBPS and PCTR.
IMM AMD would continue to discharge very large loads of heavy
metals to State waters and expose aquatic resources to sub-lethal
levels of dissolved and particulate heavy metals.
No environmental improvement above SCDD.
Human health risk is expected to be low.
Significant environmental impact reduction by reducing SCDD spill
frequency to two to three times in 100 years H SCDD targets
compliance with the SBPS below Keswick Dam; AMD spills
expected to occur more frequently if SCDD targets compliance with
the PCTR below Keswick Dam.
Spring Creek arm of Keswick Reservoir continues to have regular
exceedances of the SBPS and PCTR.
Release of mass metal loads from IMM to State waters continues
unabated; risk to benthic, water column, and other species because
of continuous exposure to large loads of dissolved and particulate
heavy metals.
No environmental improvement above SCDD.
HOD4.DOC
66
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TABLE 2
Summary of Overall Protection of Human Health and the Environment
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
Alternative WM2-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water,
if dilution water is available.
Alternative WM3-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water
with purchased dilution water.
Human health risk is expected to be low.
Provides significant environmental impact reduction by reducing
SCDD spill frequency to once in 100 years or better (assuming
SCDD targets compliance with the SBPS below Keswick Dam) and
by reducing toxicity of spills relative to Alternative WM1 (because of
baseflow treatment); exceedances of the PCTR would be more
frequent than exceedances of the SBPS. Targeting SCDD
operations to attain PCTR would be expected to cause more
frequent spills'and SBPS exceedances. .
The treatment of Slickrock Creek base flows will reduce metals
loads by 30 to 35 percent (copper) and 20 to 25 percent (zinc and
cadmium) and significantly reduce metals concentrations in SCR,
Keswick Reservoir, and the Sacramento River.
Spring Creek arm of Keswick Reservoir continues to have regular
exceedances of the SBPS and PCTR.
Mass metal loads from (MM AMD reduced by 30 to 35 percent
(copper) and 20 to 25 percent (zinc and cadmium) on average, but
loading to State waters still very large; releases continue to pose risk
to benthic, water column, and other species because of continuous
exposure to large loads of dissolved and particulate heavy metals.
Potential for minor environmental improvement above SCDD.
Human hearth risk is expected to be low.
Provides significant environmental impact reduction by reducing
SCDD spill frequency to once in 100 years or better (assuming
SCDD targets compliance with the SBPS below Keswick Dam) and
by reducing toxicity of spills relative to Alternative WM1 (because of
baseflow treatment) and WM2 (due to purchased dilution water);
exceedances of the PCTR would be more frequent than exceed-
ances of the SBPS. Targeting SCDD operations to attain PCTR
would be expected to cause more frequent spills and SBPS
exceedances.
The treatment of Slickrock Creek base flows will reduce metals
loads by 30 to 35 percent (copper) and 20 to 25 percent (zinc and
cadmium) and significantly reduce metals concentrations in SCR,
Keswick Reservoir, and the Sacramento River.
Because dilution water is available, severity of uncontrolled SCDD
spills can be reduced.
Spring Creek arm of Keswick Reservoir continues to have regular
exceedances of the SBPS and PCTR.
Mass metal loads from IMM AMD reduced by 30 to 35 percent
(copper) and 20 to 25 percent (zinc and cadmium) on average, but
loading to State waters still very large; releases continue to pose risk
ROD4.DOC
67
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TABLE 2
Summary of Overall Protection of Human Health and the Environment
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
to benthic, water column, and other species because of continuous
exposure to large loads of dissolved and particulate heavy metals.
Potential for minor environmental improvement above SCDD.
Alternative WM4-Rely on the
existing SCDD for backup for
plant failures, build two alter-
native dams (one in Slickrock
Creek and one in Boulder
Creek), build clean-water
diversions, and collect and
treat all contaminated water.
Human health risk is expected to be low.
The treatment of all AMD will essentially eliminate the IMM metals
discharge and greatly reduce metals concentrations in SCR,
Keswick Reservoir, and the Sacramento River.
The SCR can be relied upon to prevent spills to the Sacramento
River.
SBPS and PCTR expected to be met in Spring Creek arm of
Keswick Reservoir except during most extreme and unusual events.
Increased potential for environmental improvement above SCDD
relative to other alternatives.
Alternative SR1-Construct a
dam in Slickrock Creek and
clean-water diversions, collect
and treat all contaminated
Slickrock Creek runoff, and
build a retaining structure for
the hematite pile.
Human health risk is expected to be low.
The treatment of Slickrock Creek AMD will reduce under all
conditions the metals load by 60 to 70 percent (copper) and 40 to 50
percent (zinc and cadmium), and significantly reduce the metals
concentrations in SCR, Keswick Reservoir, and the Sacramento
River below Keswick Dam.
SCDD spills will be less toxic and reduced to once every 8 to 10
years if SCDD operated to target compliance with the SBPS below
Keswick Dam; SCDD spills expected every 4 to 8 years if the SCDD
is operated to target compliance with the PCTR below Keswick
Dam.
Spring Creek arm of Keswick Reservoir continues to have regular
exceedances of the SBPS and PCTR.
Potential for some environmental improvement above SCDD.
Mass metal loads from IMM AMD reduced by 60 to 70 percent
(copper) and 40 to 50 percent (zinc and cadmium) under all flow
conditions. Reduction in risk to benthic, water column, and other
species due to decrease in exposure to large loads of dissolved and
particulate heavy metals.
Alternative SRI can later be combined with an appropriate area
source remedial alternative for Boulder Creek (such as those devel-
oped and evaluated in EPA's Boulder Creek Remedial Alternative
Study).
Combining Alternative SR1 with a subsequent Boulder Creek area
source remedy could reduce spills to once in 100 years and reduce
spill toxicity and duration. Additional source controls could provide
further reductions as necessary; combined remedy could potentially
ROD4.DOC
66
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TABLE 2
Summary of Overall Protection of Human Health and the Environment
Record of Decision 1997, Iron Mountain Mine Superiund Site
Alternative Component
reduce mass loading from IMM AMD by significant amount and
permit attainment of standards in the Spring Creek arm of Keswick
Reservoir and restoration of at least some beneficial uses to Spring
Creek watershed waters.
VIII.2 Criterion 2—Compliance with Applicable or Relevant and Appropriate Requirements
and To Be Considered Standards
Applicable requirements are those cleanup standards, standards of control, and other sub-
stantive requirements, criteria, or limitations promulgated under Federal or State environ-
mental or facility siting laws that specifically address a hazardous substance, pollutant,
contaminant, remedial action, location, or other circumstance at a CERCLA site. Relevant
and appropriate requirements are those cleanup standards, standards of control, and other
substantive requirements, criteria, or limitations promulgated under Federal or State environ-
mental siting law that, while not "applicable" to a hazardous substance, pollutant, contami-
nant, 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.
Compliance with ARARs addresses whether a remedy will meet all Federal and State envi-
ronmental laws and/or provide a basis for a waiver from any of these laws. These ARARs
are divided into chemical-specific, action-specific, and location-specific groups.
In addition to legally binding laws and regulations, EPA is to consider proposed standards
and other guidance that, while not legally binding, provide useful information regarding the
performance of the remedy. These other standards are referred to as 'To Be Considered"
standards or TBCs. As discussed above, the EPA recently promulgated draft statewide
numeric water quality criteria (the PCTR). If the criteria had been finalized by the time of
ROD signature, the criteria would apply to this action. The EPA considers these criteria as
TBC because the criteria provide useful information regarding risks posed by AMD releases.
The PCTR are based on well established procedures for deriving water quality criteria, and
the criteria take into account a wide array of aquatic toxicity issues. Consideration of the
criteria will enable EPA to predict ARARs that are likely to apply to future response actions.
The EPA has therefore evaluated the extent to which the proposed remedy would comply
with Uiese proposed standards. In general,~targeting SCDD operations to attain compliance
with the PCTR increases the frequency of exceedances of the SBPS because water must be
released from the SCR more slowly. Targeting SCDD operations to attain compliance with
the SBPS results in frequent exceedances of the PCTR chronic water quality criteria for
copper because the SBPS are less stringent than the PCTR with respect to copper.
ROD4.DOC 69
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ARAR Compliance Upstream of Spring Creek Debris Dam
None of the alternatives fully complies with ARARs because none of the alternatives would
achieve SBPS or the PCTR in Spring Creek, Slickrock Creek, or Boulder Creek. Depending
upon subsequent remedial decisionmaking, EPA may ultimately need to waive at least some
of the ARARs for these heavily impacted water bodies on the basis of technical impractica-
bility. The EPA requested comment on a proposed ARAR waiver for these streams during
public comment period.
None of the streams above the SCDD currently support aquatic life, and no option has yet
been developed which would effectively restore all these streams to life. The remedial
actions implemented to date, and those considered in the 1994 FS and 1996 FSA, may allow
for the restoration of some beneficial uses to these surface waters. It is expected that any
ARAR waiver would be limited to those response actions which would be technically
impracticable, and would not extend to clearly feasible measures, such as compliance with
Best Management Practices, SBPS, other ARARs for current control measures at IMM, or
feasible actions to provide incremental improvements of the toxicity criteria which may
improve conditions for more tolerant life forms, such as plants and invertebrates, even if
more stringent toxicity criteria cannot be met.
ARAR Compliance in Keswick Reservoir
Alternative WM4 would achieve compliance with ARARs in Keswick Reservoir in most
circumstances, but occasional exceedances in Keswick Reservoir may occur as a result of the
difficult operations that are required to manage the safe dilution of the peak discharges of
stormwater runoff. Alternative SRI, in combination with certain potential remedial actions
for the Boulder Creek area source AMD discharges, could also allow for compliance with
ARARs in Keswick Reservoir in most circumstances. Alternatives WM2 and WM3 are
expected to result in some improvement in water quality in Keswick Reservoir over Alter-
natives WMO and WM1 because of the increased treatment.
ARAR Compliance below Keswick Dam
Alternatives WM1 through WM3 would meet SBPS below Keswick Dam in all but the most
unusual events, projected at one to three times per century, depending on the availability of
dilution water in those years (with slightly a greater frequency of spills expected if the SCDD
is targeting compliance with the PCTR below Keswick Dam). Alternatives WM2 and WM3
would more reliably meet the SBPS than Alternative WM1 because those alternatives remove
a significant concentration of metals from the water impounded behind SCDD. Of the two,
compliance with SBPS and PCTR may be somewhat more reliable in the extreme events
under WM3 because Alternative WM3 would rely upon the exercise of water rights (to the
extent they become available), while Alternative WM2- contains no such protection.
Alternative SRI would meet the SBPS below Keswick Dam except during IMM AMD spills
from SCDD, which are projected to occur on a frequency of once every 8 to 10 years (when
the SCDD is operated to target compliance with the SBPS below Keswick Dam). The metal
concentrations and thus the toxicity of the spills would be reduced because of the treatment of
the Slickrock Creek area source discharges. Alternative SRI would also significantly reduce
the duration of the spill events, because treatment would cause the SCR water to be less toxic
ROD4.DOC 70
-------
and therefore permit release at a faster rate. Operating the SCDD to target compliance with
the PCTR below Keswick Dam is predicted to result in exceedances every 4 to 8 years.
Of the five alternatives, Alternative WM4 best complies with water quality standard ARARs
and TBCs below the SCDD.
All treatment options (Alternatives WM2 through WM4 and SRI) rely upon established
treatment technologies. To the extent that any treated sludge exceeds the standards for haz-
ardous waste under applicable California law, the treatment option would require a variance
from standards applicable to the disposal of mining waste. Current response actions (includ-
ing the ongoing treatment plant operations and sludge disposal) rely upon a variance from
such standards. Since each of the treatment alternatives relies upon the same treatment plant
and technology, it is not anticipated that there will be any significant degree of difference
among the treatment alternatives in their relative compliance with the State mining waste
standards.
Insofar as all the action alternatives further the goals of the various natural resource protec-
tion ARARs identified for this Site, they all help in meeting ARARs. Of the treatment
options, however, Alternative WM4 best achieves the goals of Fish and Game Code Section
5650, which prohibits the discharge of material deleterious to fish life, and Section 5651,
which encourages the implementation of best available control technology on chronic
pollution sources. Alternatives WM1 through WM3 and SRI all further this goal to some
degree, relative to the degree by which they reduce the metals loading from Site discharges
and permit compliance with the SBPS and PCTR in receiving waters.
Alternatives WM1 through WM4 and SRI also all help achieve the ends of the State
Endangered Species Act and Federal Endangered Species Act because all will result in
substantial improvements in water quality below Keswick Dam, which is the location of the
endangered winter-run chinook salmon and other important species such as the steelhead
trout and spring run salmon. Alternative WM4 best achieves this ARAR because it provides
a more consistent level of protection. Alternatives.WMl through WM3 and SRI also
provide substantial protection because the chances of a spill event are reduced to one to seven
per century. Alternative WM3 is the best option of the three alternatives that rely on an
enlarged SCR in that it provides both treatment and a more reliable dilution option in those
spill years in which dilution is feasible. Alternative SRI provides greater reduction in the
metals discharge than these three alternatives, but would allow for more frequent, although
less toxic, spills. Alternative SRI, in combination with an appropriate subsequent remedy for
the Boulder Creek area sources, could potentially provide protection from SCDD spills
essentially equivalent to Alternatives WM1 through WM4 and additional reduction in the
Site metals discharge loads both above and below the SCDD.
Alternatives WM1 through WM4 and SRI would comply with the Fish and Wildlife Coordi-
nation Act, an ARAR for those actions. Significantly less mitigation for remedial actions
SRI and WM4 is expected because the areas in which containment ponds would be estab-
lished are currently highly impacted by the past mining activity.
ROD4.DOC 71
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ARAR Exceedances Because of Sediments
With respect to all options, it is anticipated that occasional re-suspension of sediments now
located in the SCAKR could result in exceedances of ARARs, notably Fish and Game Code
Section 5650 and SBPS, both in Keswick Reservoir and below Keswick Dam. Because these
sediments are not being addressed in this action, but will be addressed in a subsequent study,
it would be appropriate to invoke an interim remedy ARARs waiver to the degree it is antici-
pated these sediments may result in ARARs exceedances.
Alternative SRI would also achieve compliance with state mining laws with respect to
control of the hematite piles.
Table 3 below presents a summary of each alternative's compliance with ARARs.
TABLE 3
Summary of Compliance with ARARs
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
Alternative WMO-No Further
Action.
Alternative WMl-Enlarge
SCR to 15,000 acre-feet and
dilute uncontrolled spill water,
if dilution water is available.
If the SCDD is operated to achieve the SBPS below Keswick Dam,
uncontrolled SCDD spills are expected to occur on average every 3
to 4 years. SBPS attained below Keswick Dam during non-spill
periods but PCTR exceeded below Keswick Dam even during non-
spill periods. Operating the SCDD to target the PCTR below
Keswick Dam would cause the spills to occur every 2 to 3 years on
average. Spills would occur even more frequently if the SCR were
operated to target compliance with these standards in Keswick
Reservoir rather than downstream of Keswick Dam.
PCTR and SBPS would'continue to be exceeded in Keswick
Reservoir and the creeks that drain Iron Mountain.
Does not further the goal of Rsh & Game Code Sections 5650 and
5651.
No archeological and/or historical sites would be disturbed. No flood
plains or wetlands would be disturbed.
Uncontrolled SCDD spills of toxic AMD discharges threaten the
endangered winter-run Chinook salmon.
SCDD spill frequency reduced to two to three times in 100 years if
SCDD targets compliance with the SBPS below Keswick Dam; SBPS
attained below Keswick Dam during non-spill periods but PCTR
exceeded below Keswick Dam even during non-spill periods. AMD
spills expected to occur more frequently if SCDD targets compliance
with the PCTR below Keswick Dam.
The SBPS are expected to be exceeded in the Sacramento River
below Keswick Dam because of AMD spills one to three times per
century.
PCTR and SBPS would continue to be exceeded in Keswick
Reservoir and the creeks that drain Iron Mountain.
Exceedances of the PCTR would be more frequent than exceed-
R004.DOC
72
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TABLE 3
Summary of Compliance with ARARs
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
ances of the SBPS; targeting SCDD operations to attain PCTR would
cause more frequent spills and SBPS exceedances.
Furthers goal of Fish & Game Code Sections 5650 and 5651 only
below SCDD.
Exceedances because of sediments to continue.
No archeological and/or historical sites will be disturbed.
No harmful impacts to endangered species are anticipated. The
EPA continues to coordinate with State and Federal Natural
Resource Trustees, and consult with NMFS consistent with the
provisions of the Endangered Species Act.
Mitigation is required related to expected unavoidable impacts to
chaparral and riparian habitat. In accordance with the Fish and
Wildlife Coordination Act, EPA would consult with the USFWS during
design of this alternative.
Alternative WM2-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water,
if dilution water is available.
Alternative WM3-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water
with purchased dilution water.
SCDD spills expected once in 100 years if SCDD targets compliance
with the SBPS below Keswick Dam; SBPS attained below Keswick
Dam during non-spill periods but PCTR exceeded below Keswick
Dam even during non-spill periods. AMD spills expected to occur
more frequently if SCDD targets compliance with the PCTR below
Keswick Dam. Exceedance of SBPS and PCTR reduced during spill
periods due to baseflow treatment.
PCTR and SBPS would continue to be exceeded in Keswick
Reservoir and the creeks that drain Iron Mountain.
Furthers goal of Rsh & Game Code Sections 5650 and 5651 pri-
marily below SCDD.
Exceedances because of sediments to continue.
No archeological and/or historical sites would be disturbed.
No harmful impacts to endangered species are anticipated. The
EPA continues to coordinate with State and Federal Natural
Resource Trustees, consistent with the provisions of the Endangered
Species Act.
Mitigation is required related to expected unavoidable impacts to
chaparral and riparian habitat. In accordance with the Fish and
•Wildlife Coordination Act, £PA would consult with the USFWS during
design of this alternative.
SCDD spills expected once in 100 years if SCDD targets compliance
with the SBPS below Keswick Dam; SBPS attained bebw Keswick
Dam during non-spill periods but PCTR exceeded below Keswick
Dam even during non-spill periods. AMD spills expected to occur
more frequently if SCDD targets compliance with the PCTR below
Keswick Dam. Exceedance of SBPS and PCTR reduced during spill
ROD4.DOC
73
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TABLES
Summary of Compliance with ARARs
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
periods due to baseflow treatment and purchased dilution water.
PCTR and SBPS would continue to be exceeded in Keswick
Reservoir and the creeks that drain Iron Mountain.
Furthers goal of Fish & Game Code Sections 5650 and 5651 pri-
marily below SCDD.
Exceedances because of sediments to continue.
No archeological and/or historical sites would be disturbed.
No harmful impacts to endangered species are anticipated. The
EPA continues to coordinate with State and Federal Natural
Resource Trustees and consult with NMFS consistent with the
provisions of the Endangered Species Act.
Mitigation is required related to expected unavoidable impacts to
chaparral and riparian habitat. In accordance with the Fish and
Wildlife Coordination Act, EPA would consult with the USFWS during
design of this alternative.
Alternative WM4-Rely on the
existing SCDD for backup for
plant failures, build two alter-
native dams (one on Slickrock
Creek and one on Boulder
Creek), build clean-water
diversions, and collect and
treat all contaminated water.
SCDD spills expected once in 100 years if SCDD targets compliance
with the SBPS below Keswick Dam; SBPS attained below Keswick
Dam during non-spill periods but PCTR exceeded below Keswick
Dam even during non-spill periods. AMD spills expected to occur
more frequently if SCDD targets compliance with the PCTR below
Keswick Dam.
SBPS and PCTR attained in Keswick Reservoir except in unusual
circumstances.
PCTR and SBPS expected to be exceeded in the creeks that drain
Iron Mountain but to a lesser degree than the other alternatives.
Furthers goal of Fish & Game Code Sections 5650 and 5651 both
above and below the SCDD.
Exceedances because of sediments to continue.
No archeological and/or historical sites would be disturbed.
No harmful impacts to endangered species are anticipated. The
EPA continues to coordinate with State and Federal Natural
Resource Trustees and consult with NMFS, consistent with the
.provisions of the Endangered Species Act.
Mitigation may be required related to expected unavoidable impacts
to chaparral and riparian habitat that is currently highly impacted by
historic mining. In accordance with the Fish and Wildlife
Coordination Act, EPA would consult with the USFWS during design
of this alternative.
ROD4.DOC
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TABLE3
Summary of Compliance with ARARs
Record of Decision 1997, Iron Mountain Mine Supertund Site
Alternative
Component
Alternative SR1 -Construct a
dam in Slickrock Creek and
clean-water diversions, collect
and treat all contaminated
Slickrock Creek runoff, and
build a retaining structure for
the hematite pile.
SCDD spills expected every 8 to 10 years on average if SCDD
targets compliance with the SBPS below Keswick Dam; SBPS
attained below Keswick Dam during non-spill periods but PCJR
exceeded below Keswick Dam even during non-spill periods. AMD
spills expected to occur more frequently if SCDD targets compliance
with the PCJR below Keswick Dam.
SBPS and PCTR are also expected to be exceeded in Keswick
Reservoir and the creeks that drain Iron Mountain.
Furthers goal of Fish & Game Code Sections 5650 and 5651 below
the SCDD and to some degree on Slickrock Creek and bwer Spring
Creek.
Exceedances because of sediments to continue.
No archeological and/or historical sites would be disturbed.
Alternative SR1 does not fully eliminate all spills from SCDD, does
not delay spills as the enlarged SCDD alternatives do, and would not
prevent all harm to endangered species. Additional actions in
Boulder Creek could further reduce the frequency, toxicrty, and
duration of spills, providing significant additional protection to
endangered species. The EPA continues to coordinate with State
and Federal Natural Resource Trustees and consult with NMFS,
consistent with the provisions of the Endangered Species Act.
Mitigation may be required related to expected unavoidable impacts
to chaparral and riparian habitat that is currently highly impacted by
historic mining. In accordance with the Rsh and Wildlife Coordina-
tion Act, EPA would consult with the USFWS during design of this
alternative.
VIII.3 Criterion 3—Long-Term Effectiveness and Permanence
Long-term effectiveness and permanence refers to the ability of a remedy to maintain reliable
protection of human health and the environment over time. This criterion includes the con-
sideration of residual risk and the adequacy and reliability of controls.
Under the No Further Action Alternative, WMO, long-term effects would continue as under
their present condition. The discharge of areawide sources of AMD would continue for
thousands of years if left unabated. The affected portion of Spring Creek watershed will
continue to be devoid of aquatic life, amphibians, and other affected resources. Sediments
containing elevated levels of metals would continue to be deposited in the creeks, behind
SCDD, and in SCAKR. Uncontrolled spills of IMM contaminants would continue to occur
every 3 to 4 years if the SCR is operated to target the SBPS below Keswick Dam and every 2
to 3 years if the SCR is operated to target the PCTR below Keswick Dam.
ROD4.DOC
75
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RECORD OF DECISION
IRON MOUNTAIN MINE
SHASTA COUNTY, CALIFORNIA
SFUND RECORDS CTR
1652-04373
THE DECLARATION
I. SITE NAME AND LOCATION
Iron Mountain Mine (IMM)
Shasta County, California (approximately 9 miles northwest of Redding, California)
II. STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected interim remedial action for control of releases
of hazardous substances from widespread area sources in the Slickrock Creek watershed at
the Iron Mountain Mine Site. The selected interim remedial action was chosen in accordance
xwith the Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA), as amended by the Superfund Amendments and Reauthorization Act (SARA),
and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). This
decision is based upon the Administrative Record for this Site.
The State of California concurs with the selected interim remedial action for the Slickrock
Creek area source acid mine drainage (AMD) discharges at the Iron Mountain Mine Super-
fund Site.
III.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from this Site, if not addressed by
implementing the response action selected in this Record of Decision (ROD), may present an
imminent and substantial endangerment to public health, welfare, or the environment.
The Slickrock Creek area sources of AMD include the numerous waste piles on the mine
property, disturbed areas related to mining activity, contaminated groundwater and interflow
seepage, underground mine workings, and underground mineralization exposed through
mining-induced hydrologic and physical changes. The general disturbances in this area of
Slickrock Creek are shown in Photo Exhibit 1. The releases from these sources consist of
highly acidic, heavy metal-bearing waters, termed acid mine drainage, or AMD. The heavy
metals contained in the AMD from Slickrock Creek area sources include, among others, cop-
per, cadmium, and zinc. The AMD contains acidity and concentrations of copper, cadmium,
and zinc that are toxic to aquatic life and harmful to humans. The response action will also
address the hematite mine waste piles, which contain high levels of arsenic and are actively
eroding into Slickrock Creek and thence to downstream areas.
The principal threat posed by these releases is the creation of conditions toxic to aquatic life
in the receiving waters downstream of the Site, Surface water is the primary exposure path-
OfiC-J?
U.S. EPA CONCURRENCES
• s
OFFICIAL FILE COPY
-------
Alternatives WM2 and WM3 would remove an estimated 30 to 35 percent (copper) and 20 to
25 percent (zinc and cadmium) of the remaining uncontrolled Site discharge by treating up to
50 percent of the Slickrock Creek area source AMD metals discharge load. The remedy
would treat a larger percent when flows are low and a smaller percent when flows are high.
Alternative SRI would remove essentially all of the Slickrock Creek area source AMD
discharge load. (In the EPA Water Quality Model, EPA generally relied upon an efficiency
of 90 percent as a conservative estimate, but EPA anticipates that the remedy will be more
effective than that estimate.) The Slickrock Creek area sources comprise approximately 60 to
70 percent of the remaining uncontrolled copper and 40 to 50 percent of the remaining
uncontrolled zinc and cadmium site discharges. Alternative WM4 would remove essentially
100 percent of the remaining Site discharge load. Alternative SRI, in combination with a
subsequent Boulder Creek area source remedy, could equal or approach the metal reduction
provided by Alternative WM4. Alternatives WM1 and WMO would not provide for any
additional metals removal.
Enlarging the SCR to a capacity of 15,000 acre-feet, as proposed in Alternatives WM1,
WM2, and WM3, is expected to provide significant, effective, long-term protection to human
health and the environment below Keswick Dam. An enlarged dam would require periodic
maintenance, but is expected to have a project design life in excess of 100 years. The
enlarged SCR is a passive device that is expected to provide significant additional hydrologic
controls. The additional hydrologic controls would provide for a significant reduction in
toxic spill frequency and greater compliance with the protective SBPS and PCTR below the
SCDD than is possible under current conditions. Enlarged SCR capacity would also provide
additional protection with respect to treatment plant upsets because the enlarged reservoir
would increase the ability to control the dilution of highly polluted water from the SCR.
Reducing the metal load to the SCR reduces the frequency of SCDD spills. If the water in
the SCR contains lower concentrations of metals, the reservoir can release the water at faster
rate because less dilution water would be needed. Alternatives WM2, WM3, WM4, and SRI
reduce metals discharges and therefore reduce spill frequency associated with operation of
either the enlarged SCR (in the case of Alternatives WM2 and WM3) or the existing SCR (in
the case of Alternatives WM4 or SRI). When coupled with the other response actions, this
additional reduction in SCDD spills associated with the metals removal provides significant
additional compliance with the protective SBPS and the PCTR below the SCDD and thus
protection to the Sacramento River fishery and ecosystem. The metals reduction also
decreases the overall metals discharge loading, the exposure of aquatic resources to heavy
metals, and the resultant amount of metals deposition in the sediments behind SCDD and in
the SCAKR. The continued deposition of sediments poses a threat to benthic and water
column organisms as well as hindering the ability to effectively respond to the sediments
caused by past IMM AMD releases. Removal of metals also increases the potential for the
beneficial uses of Spring Creek and its tributaries to be restored.
All the alternatives would rely on the release of dilution water, if possible, to mitigate dam-
age from the uncontrolled spills. Dilution water would be more likely to be available under
Alternative WM3 because that alternative provides for the purchase of water rights for dilu-
tion water.
ROD4.DOC 76
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Alternative WM4 would provide the greatest long-term effectiveness by significantly
reducing the metals discharged to the environment The proposed treatment of all areawide
sources by capturing the creek flows on Boulder and Slickrock Creeks and treating all con-
taminated flows would reduce the amount of metals by an estimated 99 percent Contami-
nated creek sediments in the contaminated reaches of the Spring Creek watershed would
continue to discharge metals for some period of time. The existing heavy metal-laden
sediments in SCAKR could also act as a metal source as metals re-dissolve into the water.
The operation of a treatment scheme that requires the collection and treatment of all storm
flows is a difficult task, and cannot be expected to function perfectly. Some upset condition
operations should be anticipated to reduce the overall effectiveness of this approach. Alter-
native SRI could potentially be coupled with other response actions to achieve protection
that is comparable to Alternative WM4.
Table 4 below presents a comparison of each alternative's ability to meet this criterion.
TABLE 4
Summary of Long-Term Effectiveness and Permanence
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
Alternative WMO-No Further Action.
Not effective. Because no additional remedial action is imple-
mented, environmental impacts will continue over the long
term under their present condition.
Metals releases and current risks may continue for thousands
of years.
Alternative WM1-Enlarge SCR to
15,000 acre-feet and dilute uncon-
trolled spill water, if dilution water is
available.
Provides substantial long-term effectiveness for protection of
human health and the environment. Infrequent fishery impacts
below Keswick Dam are expected because of SCDD spills that
would occur two to three times in 100 years.
Aquatic resources below SCDD continue to be exposed to
large loads of total and dissolved heavy metals.
Receiving waters upstream of SCDD continue to be devoid of
aquatic life; portion of Keswick Reservoir remains impaired.
Heavy metal-laden sediments would continue to accumulate.
Better control over SCDD releases during storm events is
anticipated.
Alternative WM2-Enlarge SCR to
15,000 acre-feet, collect and treat
the base flow from Slickrock Creek,
and dilute uncontrolled spill water, if
dilution water is available.
Provides significant long-term effectiveness for protection of
human health and the environment. Rare fishery impacts
below Keswick Dam are expected because of spills that would
occur less than once in 100 years.
Below SCDD, baseflow treatment permits reduction in metal
loading (on average 30 to 35 percent [copper] and 20 to 25
percent [zinc and cadmium]), thereby reducing the exposure of
aquatic resource to large loads of total and dissolved heavy
metals. Heavy metal-laden sediments would continue to
accumulate, but at a reduced rate.
ROD4.DOC
77
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TABLE 4
Summary of Long-Term Effectiveness and Permanence
Record of Decision 1997, Iron Mountain Mine Superiund Site
Alternative
Component
Receiving waters upstream of SCDD continue to be devoid of
aquatic life; Keswick Reservoir remains impaired.
The collection system, pipelines, and treatment plant should
operate effectively. Treatment of the AMD with the HDS plant
is very reliable, and the plant would remove 99 percent of the
metals discharged. Disposal of the treatment sludge in Brick
Rat Pit would be effective over the long term.
Better control over SCDD releases during storm events is
anticipated.
Alternative WM3-Enlarge SCR to
15,000 acre-feet, collect and treat
the base flow from Slickrock Creek,
and dilute uncontrolled spill water
with purchased dilution water.
Provides significant long-term effectiveness for protection of
human health and the environment. Rare fishery impacts
below Keswick Dam are expected because of SCDD spills that
would occur once in 100 years. Mitigation with dilution water
would reduce the impact of the rare spill.
Below SCDD, basef low treatment permits reduction in metal
loading (on average 30 to 35 percent [copper] and 20 to 25
percent [zinc and cadmium]), thereby reducing the exposure of
aquatic resource to large loads of total and dissolved heavy
metals. Heavy metal-laden sediments would continue to
accumulate, but at a reduced rate.
Receiving waters upstream of SCDD continue to be devoid of
aquatic life; Keswick Reservoir remains impaired.
The collection system, pipelines, and treatment plant should
operate effectively. Treatment of the AMD with the HDS plant
is very reliable, and the plant would remove 99 percent of the
metals discharged. Disposal of the treatment sludge in Brick
Rat Pit would be effective over the long term.
Better control over SCDD releases during storm events is
anticipated.
Alternative WM4-Rely on the
existing SCDD for backup for plant
failures, build two alternative dams
(one on Slickrock Creek and one on
Boulder Creek), build clean-water
diversions, and collect and treat all
contaminated water.
Provides significant long-term effectiveness for protection of
human health and the environment. SCDD spills would be
expected to occur only under the rarest of circumstances.
Essentially eliminates the IMM metals discharge. Heavy
metal-laden sediments would not continue to accumulate.
Significant reduction in exposure of aquatic resource to large
loads of total and dissolved heavy metals.
The dams, pipelines, and treatment plant should operate effec-
tively. Treatment of the AMD with the HDS plant is very
reliable, and the plant would remove 99 percent of the metals
discharged. Disposal of the treatment sludge in Brick Flat Pit
would be effective over the long'term.
R004.DOC
78
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TABLE 4
Summary of Long-Term Effectiveness and Permanence
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
Alternative SR1-Construct a dam in
Slickrock Creek and clean water
diversions, collect and treat all con-
taminated Slickrock Creek runoff,
arid build a retaining structure for
the hematite pile
Provides significant long-term effectiveness for protection of
human health and the environment. Occasional fishery
impacts below Keswick Dam are expected because of spills
that would occur once every 8 to 10 years.
Provides significant reduction (60 to 70 percent copper and 40
to 50 percent zinc and cadmium) in metals load discharge
under all conditions. Heavy metal-laden sediments would
continue to accumulate, but at a much reduced rate.
Potential for restoration of some beneficial uses of waters in
Spring Creek Watershed. The collection system, pipelines,
and treatment plant should operate effectively. Treatment of
the AMD with the HDS plant is very reliable, and the plant
would remove 99 percent of the metals discharged. Disposal
of the treatment sludge in Brick Rat Pit would be effective over
the long term.
Alternative SR1 can later be combined with an appropriate
area source remedial alternative for Boulder Creek (such as
those developed and evaluated in EPA's Boulder Creek
Remedial Alternative Study).
Alternative SR1, combined with an appropriate Boulder Creek
source control and treatment remedy, is expected to be able to
achieve further significant metal load reductions. The further
load reductions in Boulder Creek could reduce spill frequency
to less than once per century, which is comparable to
Alternatives WM2, WM3, and WM4 and increases the potential
for restoration of the beneficial uses of Spring Creek and its
tributaries.
VIII.4 Criterion 4—Reduction of Toxicity, Mobility, or Volume through Treatment
Reduction of toxicity, mobility, or volume through treatment refers to the preference for a
remedy that uses treatment to reduce health hazards, contaminant migration, or the quantity
of contaminants at the Site.
The No Further Action Alternative, WMO, is not expected to provide a reduction in toxicity,
mobility, or volume because no-further reductions in the EMM metal discharges would occur,
and SCDD would continue to spill at its current frequency. Therefore, metals would continue
to accumulate in the environment.
The SCDD enlargement alternatives will reduce the toxicity of the AMD discharge at the
point below Keswick Dam to the SBPS through dilution, except during the one to three spills
in 100 years. Exceedances of the PCTR below Keswick Dam would also be reduced. Alter-
native WM1 does not contain any treatment components; therefore, there will be no reduction
R004.DOC
79
-------
in mobility or volume of AMD discharge. Alternatives WM2 and WM3 would treat up to
approximately 750 gpm of Slickrock Creek base flow, thereby reducing the volume of AMD
discharge by about 240 gpm on average. On an annual average, baseflow treatment is
expected to reduce the uncontrolled release of copper by 30 to 35 percent and the
uncontrolled release of zinc and cadmium by 20 to 25 percent The mobility of the untreated
AMD discharge would remain unchanged. Ensuring the availability of dilution water in
Alternative WM3 increases the probability that the toxicity of an uncontrolled SCDD spill
can be reduced. Alternative WM4 treats all the areawide sources of AMD discharge
collected in dams constructed on Slickrock and Boulder Creeks. Alternative WM4 would
provide the greatest decrease in the toxicity and volume of these discharges and would reduce
the mobility of the metal contaminants by separating and binding the metals in a sludge,
which will be disposed of in a landfill to limit future re-mobilization.
Alternative SRI.provides greater reductions in the volumes of IMM area source contaminants
discharged than Alternatives WM2 and WM3, and less than under Alternative WM4. Alter-
native SRI would collect and treat (under all conditions) essentially all Slickrock Creek area
source discharges, which comprise approximately 60 to 70 percent (copper) and 40 to 50
percent (zinc and cadmium) of the currently uncontrolled IMM AMD discharge. Alternative
SRI provides for a significant reduction in toxicity of the SCR waters. Because Alternative
SRI does not include the increased hydrologic controls of Alternatives WM2 and WM3,
Alternative SRI does not ensure the same degree of reduction in the toxicity in the
Sacramento River. Alternative SRI is estimated to reduce spills from the SCR to once every
8 to 10 years (when the SCDD is operated to target compliance with the SBPS below
Keswick Dam). When combined with a remedy for the Boulder Creek area sources (to be the
subject of additional study and a later EPA decision), the Alternative SRI could potentially
be comparable to the other alternatives with respect to reduction in toxicity in the Sacramento
River and an equivalent or greater reduction in volume and mobility both above and below
the SCDD.
Table 5 below presents a comparison of each alternative's ability to meet this criterion.
TABLES
Summary of Reduction of. Toxicity, Mobility, or Volume through Treatment
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative Component
Alternative WMO-No Further No reduction in toxicity, mobility, or volume.
Action.
Alternative WM1-Enlarge Reduces the toxicity to SBPS below Keswick Dam of SCDD
SCR to 15,000 acre-feet and discharge except for one spill event per century (if SCDD operated to
dilute uncontrolled spill water, target compliance with SBPS below Keswick Dam). Also reduces
if dilution water is available. exceedance of PCJR below Keswick Dam.
No reduction in volume or mobility.
Alternative WM2-Enlarge Reduces the toxicity to SBPS below Keswick Dam of SCDD
SCR to 15,000 acre-feet, discharge except for one spill event per century (if SCDD operated to
ROD4.DOC BO
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TABLE 5
Summary of Reduction of Toxicity, Mobility, or Volume through Treatment
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water,
if dilution water is available.
target compliance with SBPS below Keswick Dam). The
uncontrolled SCOO spill should be less toxic than WM1. Also
reduces exceedance of PCTR below Keswick Dam.
Provides some reduction in volume and mobility of AMD by treating
750-gpm base flow of Slickrock Creek. Also reduces exceedance of
PCTR below Keswick Dam.
Provides some reduction in volume of heavy metal precipitates, but
large volumes of precipitates continue to settle into reservoirs and
riverbeds
Alternative WM3-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water
with purchased dilution water.
Alternative WM4-Rely on the
existing SCDD as backup for
plant failures, build two alter-
native dams (one in Slickrock
Creek and one in Boulder
Creek), build clean-water
diversions, and collect and
treat all contaminated water.
Alternative SRl-Construct a
dam in Slickrock Creek and
clean-water diversions, collect
and treat all contaminated
Slickrock Creek runoff, and
build a retaining structure for
the hematite pile.
Reduces the toxicity to SBPS below Keswick Dam of SCDD
discharge except for one spill event per century (if SCDD operated to
target compliance with SBPS below Keswick Dam). The
uncontrolled SCDD spill should be less toxic than WM1.
Provides some reduction in volume and mobility of AMD by treating
750-gpm base flow of Slickrock Creek.
Guaranteed dilution water increases probability of reducing toxicity of
uncontrolled SCDD spill.
Provides some reduction in volume of heavy metal precipitates, but
large volumes of precipitates continue to settle into reservoirs and
river beds.
Reduces the toxicity to SBPS below Keswick Dam of SCDD
discharge except for one spill event per century (if SCDD operated to
target compliance with SBPS below Keswick Dam). The
uncontrolled SCDD spill should be less toxic than Alternatives WM2
and WM3 because of increased removal of metals through
treatment. Also reduces exceedance of PCTR below Keswick Dam.
Greatly reduces toxicity, mobility, and volume of AMD by collecting
and treating all IMM area sources of AMD.
Greatly reduces volume of heavy metal precipitates and new sedi-
mentation, thereby increasing potential for effective remediation of
existing sediments.
Treatment will improve the water quality in the Spring Creek
watershed.
Reduces the toxicity to SBPS below Keswick Dam of SCDD
discharge except for one spill event every 8 to 10 years (if SCDD
operated to target compliance with SBPS below Keswick Dam). The
uncontrolled SCDD spills should be less toxic than Alternatives WM2
and WM3 because of increased removal of metals through
treatment. Also reduces exceedance of PCTR below Keswick Dam.
Significantly reduces the toxicity, mobility, and volume of AMD
ROD4.DOC
81
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TABLES
Summary of Reduction of Toxicity, Mobility, or Volume through Treatment
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative Component
discharges by collecting and treating essentially all Slickrock Creek
area sources of AMD under all conditions.
Some reduction (greater reduction than Alternatives WM1 and WM2)
in volume of heavy metal precipitates and new sedimentation.
Alternative SR1 can later be combined with an appropriate area
source remedial alternative for Boulder Creek (such as those
developed and evaluated in EPA's Boulder Creek Remedial Alter-
native Study).
Alternative SR1, in combination with a Boulder Creek area source
remedy, would be expected to provide equivalent reductions in the
toxicity and frequency of spills provided under Alternatives WM2 and
WM3 and greater reductions in volume and mobility of the contam-
inants. Combined remedy could potentially greatly reduce the
volume of heavy metal precipitates and new sedimentation, thereby
increasing the potential for effective remediation of existing
sediments.
Treatment will improve the water quality in the Spring Creek
watershed.
VIII.5 Criterion 5—Short-Term Effectiveness
Short-term effectiveness refers to the period of time required to complete the remedy and any
adverse impacts on human health and the environment that may be posed during the con-
struction and implementation of the remedy.
Some degree of increased traffic and related impacts are expected during construction, but
none of the alternatives pose a substantial threat to the local communities. The alternatives
with construction components expose workers to normal construction-related impacts and
expose the environment to minor impacts which can be mitigated during construction. The
alternatives with treatment components expose treatment plant operators to some risk from
being exposed to AMD, but through proper operation, maintenance, and protection, the risk
is minor.
The No Further Action Alternative does not propose any new construction that would
adversely affect the environment. -This alternative will not meet the remedial action objec-
tives and does not mitigate the present environmental risks.
For the SCDD enlargement alternatives, Alternatives WM1 through WM3, there is no
substantial threat to local communities because of the remote location of the IMM Site. Iron
Mountain Road would be permanently relocated, which would minimize traffic conflicts
associated with the project. During construction, however, there would be increased traffic
ROD4.DOC 82
-------
on Iron Mountain Road. The project is large, but construction would be staged to reduce
noise and dust impacts.
Environmental impacts of construction of an SCDD enlargement are expected to be minor,
and it is anticipated that these impacts can be mitigated. The inundation of an additional
180 acres of land is an unavoidable minor impact. The EPA has consulted with USFWS
regarding appropriate mitigation measures for an SCDD enlargement.
The two alternatives that treat the base flow from Slickrock Creek (Alternatives WM2 and
WM3) will have only minimal additional short-term impacts because only minimal con-
struction is required to modify the treatment plant and build conveyance pipelines to the
existing treatment plant. Alternative WM4 requires a substantial amount of additional
construction, including construction of two small dams, other water management projects,
new pipelines, a significantly expanded treatment plant, and additional sludge handling
facilities. During construction, Iron Mountain Road would experience greater traffic, as well
as construction-related impacts such as dust and noise. Because the two new dams would be
constructed upstream of the existing SCDD, a failure of one of these dams during
construction would not present a threat to downstream residents.
Alternative SRI requires substantial additional construction with a containment dam, the
hematite containment structure, clean-water conveyances, new pipelines, and an expanded
treatment plant. However, there would be less traffic and construction-related impacts such
as dust and noise than in Alternatives WM1 through WM4. Because the new dam would be
constructed upstream of the existing SCDD, a failure during construction would not present a
threat to downstream residents. In the absence of rapid implementation of the remedy for
Boulder Creek area sources, Alternative SRI would be less effective in short-term reduction
of metals, toxicity, and mobility than Alternative WM4. Investigation of Boulder Creek is
continuing, so a remedy for those sources could potentially be implemented in the near-term.
The treatment alternatives share the common short-term advantage that the process can be
readily modified to take advantage of improvements in treatment technology or changed eco-
nomic conditions which may in the future favor resource recovery processes.
Table 6 below presents a comparison of each alternative's ability to meet this criterion.
TABLE 6
Summary of Short-Term Effectiveness
Record of Decision 1997, Iron Mountain Mine Supertund Site
Alternative Component
Alternative WMO-No Further Does not meet remedial action objectives.
I0n' Workers at the treatment plant are exposed to work risks similar to
those of chemical industry workers.
Alternative WM1-Enlarge No substantial threats to the local communities are anticipated.
SCR to 15,000 acre-feet and Increase in traffic and related impacts during construction.
dilute uncontrolled spill water, ... , .. . ... . . . . .
r Workers exposed to normal construction-related nsks.
ROD4.DOC 63
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TABLES
Summary of Short-Term Effectiveness
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
if dilution water is available.
Minor environmental impacts during construction, which can be
mitigated.
Workers at the treatment plant are exposed to work risks similar to
those of chemical industry workers.
Alternative WM2-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water,
if dilution water is available.
No substantial threats to the local communities are anticipated.
Increase in traffic and related impacts during construction.
Workers exposed to normal construction-related risks.
Minor environmental impacts during construction, which can be
mitigated.
Workers at the treatment plant are exposed to work risks similar to
those of chemical industry workers.
Alternative WM3-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water
with purchased dilution water.
No substantial threats to the local communities are anticipated.
Increase in traffic and related impacts during construction.
Workers exposed to normal construction-related risks.
Minor environmental impacts during construction, which can be
mitigated.
Workers at the treatment plant are exposed to work risks similar to
those of chemical industry workers.
Alternative WM4-Rely on the
existing SCDD as backup for
plant failures, build two alter-
native dams (one in Slickrock
Creek and one in Boulder
Creek), build clean-water
diversions, and collect and
treat all contaminated water.
No substantial threats to the local communities are anticipated.
Increase in traffic and related impacts during construction. These
impacts are greatest with this alternative because of the size of the
project.
Workers exposed to normal construction-related risks.
Minor environmental impacts during construction, which can be
mitigated.
Workers at the treatment plant are exposed to work risks similar to
those of chemical industry workers.
ROD4.DOC
84
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TABLES
Summary of Short-Term Effectiveness
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative Component
Alternative SR1-Constaict a No substantial threats to local communities are anticipated. Increase
dam in Slickrock Creek and in traffic and related impacts during construction.
clean water diversions collect
^sed nomia| construction.related risks
and treat all contaminated *~
Slickrock Creek runoff, and Workers at the treatment plant are exposed to work risks similar to
build a retaining structure for those of chemical industry workers.
the ema e pt e. Minor environmental impacts during construction, which can be
mitigated.
The short-term effectiveness of an alternative that combines
Alternative SR1 with a subsequent Boulder Creek remedy would be
similar to other action alternatives; substantial delay in implementing
a Boulder Creek remedy would cause Alternative SR1 to be less
effective in the short-term than the other action alternatives.
Alternative SR1 can later be combined with an appropriate area
source remedial alternative for Boulder Creek (such as those
developed and evaluated in EPA's Boulder Creek Remedial Alter-
native Study). Short-term impacts of those projects would likely be
comparable to the SR1 projects because of the similarity in the
nature of the problem being addressed and location.
VIII.6 Criterion 6—Implementability
Implementability refers to the technical and administrative feasibility of a remedy, including
the availability of materials and services needed to implement the chosen solution. It also
includes coordination of Federal, State, and local governments to clean up the Site.
All the technologies are readily implementable. All the materials and work force necessary
for each alternative are readily available. The administrative implementability for each alter-
native is straightforward and easy.
The No-Action Alternative, WMO, requires no additional effort and is readily implementable.
The only aspect of this alternative that requires active implementation is the operation of
existing facilities. The continued implementation of this alternative is straightforward.
The technical implementability of an enlargement of SCDD proposed in Alternatives WM1,
WM2, and WM3 is relatively straightforward." All of the technologies and construction tech-
niques for dam enlargement required for these alternatives are well understood. Construction
sequencing will be carefully planned and phased to minimize environmental and construction
hazards.
The treatment of the Slickrock Creek base flow in Alternatives WM2 and WM3 will require
minor modifications to the construction of the HDS treatment facility. The modifications to
the HDS treatment process are readily implementable because they involve only flow control,
ROD4.DOC 85
-------
treatment, and existing sludge disposal facilities. All of these facilities involve well estab-
lished technologies with known costs, effectiveness, and reliability.
Alternative WM3 would explore and secure options to guarantee the availability of water to
ensure the dilution water for the uncontrolled spills from the existing SCDD through the pur-
chase of necessary rights to the required amounts of water. These options include possible
purchase of water from the CVP and from individual holders of water rights. Water right
purchasing is a relatively new development in California; therefore, its implementability is
uncertain.
Alternatives WM4 and SRI propose standard construction and treatment processes, dam con-
struction, and HDS treatment. The implementability of these alternatives is complicated by
the difficult Site conditions, such as the narrow ravines and lack of relatively flat terrain.
These Site features will complicate the design, construction, and maintenance of the dams,
diversions, roads, pipelines, and treatment plant modifications. Operation of the treatment
plant to treat all contaminated runoff during storms is expected to be difficult and challeng-
ing. The existing SCR provides a backup for episodic plant discharges of untreated waters.
The Boulder Creek Remedial Alternatives Study indicates that response actions for Boulder
Creek area sources would be implementable. The appropriateness and feasibility of
responding to other sources (including but not limited to contaminated stream sediments)
could be evaluated in a further remedial investigation and feasibility study, if necessary.
Table 7 below presents a comparison of each alternative's ability to meet this criterion.
TABLE?
Summary of Implementability
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
Alternative WMO-Np Further
Action.
Readily implementable.
Alternative WM1-Enlarge
SCR to 15,000 acre-feet and
dilute uncontrolled spill water,
if dilution water is available.
Readily implemented, as it uses well established technologies with
known costs, effectiveness, and reliability.
All materials and work force are readily available.
Administrative implementability is straightforward.
Alternative WM2-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water,
if dilution water is available.
Readily implemented, as it uses well established technologies with
known costs, effectiveness, and reliability.
All materials and work force are readily available.
Administrative implementability is straightforward. .
ROD4.DOC
86
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TABLET
Summary of Implementability
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Component
Alternative WM3-Enlarge
SCR to 15,000 acre-feet,
collect and treat the base flow
from Slickrock Creek, and
dilute uncontrolled spill water
with purchased dilution water.
Readily implemented, as it uses well established technologies with
known costs, effectiveness, and reliability.
All materials and work force are readily available.
Administrative implementability is straightforward.
Securing of water rights is uncertain and may not be implementable.
Alternative WM4-Rety on the
existing SCDD as backup for
plant failures, build two alter-
native dams (one in Slickrock
Creek and one in Boulder
Creek), build clean-water
diversions, and collect and
treat all contaminated water.
Readily implemented, as it uses well established technologies with
known costs, effectiveness, and reliability.
All materials and work force are readily available.
Administrative implementability is straightforward.
Site conditions will complicate the implementation of dams.
Stormwater treatment may present operational difficulties.
Alternative SR1-Construct a
dam in Slickrock Creek and
clean-water diversions, collect
and treat all contaminated
Slickrock Creek runoff, and
build a retaining structure for
the hematite pile.
Readily implemented, as it uses well established technologies with
known costs, effectiveness, and reliability.
All materials and work force are readily available.
Administrative implementability is straightforward.
Site conditions will complicate the implementation of dams.
Stormwater treatment may present operational difficulties.
Alternative SR1 can later be combined with an appropriate area
source remedial alternative for Boulder Creek (such as those
developed and evaluated in EPA's Boulder Creek Remedial Alter-
natives Study). The implementability of an alternative that combines
SR1 with a subsequent Boulder Creek remedy would be similar.
Implementability of other responses would be evaluated in
subsequent investigations, if necessary.
VIII.7 Criterion 7-Cost
This criterion examines the estimated costs for each remedial alternative.
Table 8 below presents estimates of the 30-year present worth for each alternative. The table
shows the initial capital investment, the initial annual operations and maintenance costs, the
present worth of 30 years of operation (at 5 percent interest rate), and the total 30-year cost.
The 30-year basis is selected to compare the costs of the alternatives, but remediation is
expected to continue beyond 30 years.
ROD4.DOC
87
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TABLES
Summary of Cost
Record of Decision 1997, Iron Mountain Mine Superfund Site
Alternative
Total Capital Total Annual
Costs O&M Costs
($x 1,000) ($x 1,000)
Present Total 30-Year
Worth O&M Present
Costs Worth
($x 1,000) ($x 1,000)
Alternative WMO-No Further
Action.
Alternative WMl-Enlarge SCR to
15,000 acre-feet and dilute
uncontrolled spill water, if dilution
water is available,
74,240
60
922
75.162
Alternative WM2-Enlarge SCR to
15,000 acre-feet, collect and treat
the base flow from Slickrock
Creek, and dilute uncontrolled spill
water, if dilution water is available.
77,531
273
4,196
81,727
Alternative WM3-Enlarge SCR to
15,000 acre-feet, collect and treat
the base flow from Slickrock
Creek, and dilute uncontrolled spill
water with purchased dilution
water.
77,531
899
13,816
91,347
Alternative WM4-Rely on the
existing SCOD as backup for plant
failures, build two alternative
dams (one in Slickrock Creek and
one in Boulder Creek), build
clean-water diversions, and collect
and treat all contaminated water.
116.215
928
14,271
130,486
Alternative SRl-Construct a dam
in Slickrock Creek and clean-
water diversions, collect and treat
all contaminated Slickrock Creek
runoff, and build a retaining
structure for the hematite pile.
18,709
160
2,460
21,169
Most expensive Boulder Creek
alternative developed to date
30,374
320
4,920
35,294
SR1 combined with most
expensive Boulder Creek alter-
native developed to date
49,083
480
7,380
56.943
Alternative SRI can later be combined with an area source remedial alternative for Boulder
Creek. For purposes of cost comparisons between SRI and other sitewide remedies, this
analysis relies on AJtemative No. 2H, Combined Area Source AJternative, as the appropriate
ROD4.DOC
88
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Boulder Creek remedy. That remedy is the most costly feasible alternative considered in the
Boulder Creek Remedial Alternatives Study. Even when combined with the most expensive
remedy for Boulder Creek area sources, Alternative SRI provides the most cost-effective
response to sitewide releases.
In general, these cost estimates are the product of the "order-of-magnitude" estimating
procedures based upon conceptual layouts and preliminary cost information. Estimates of
this nature are subject to changes as more detailed engineering and cost information becomes
available. It is commonly assumed that actual cost may vary from the stated amounts by as
much as -f 50 percent to -30 percent Cost information for the enlargement of the SCDD
would be significantly more reliable because of the more detailed studies conducted by EPA
on that issue.
The costs shown for the alternatives do not include costs associated with future reliance on
the existing SCDD to provide emergency storage during treatment plant failures or any other
use of the existing SCDD. The cost of continued SCDD operations is comparable to the No-
Action Alternative, which is assumed to have a cost of zero for purposes of the comparative
analysis.
VIII.8 Criterion 8—State Acceptance
State acceptance refers to the State's position and key concerns related to the preferred alter-
native and other alternatives, and State comments on ARARs or the proposed use of waivers.
Throughout the development of this operable unit, EPA has worked closely with the Cali-
fornia Department of Toxic Substances Control (DTSC) (the State lead agency), RWQCB,
and CDFG. All three agencies support the selection of Alternative SRI as described in the
May 1996 Water Management FSA.
VIII.9 Criterion 9—Community Acceptance
This criterion refers to the community's stated preferences through oral and written comments
on EPA's Proposed Plan regarding which components of the alternatives interested persons in
the community support, have reservations about, or oppose.
There was significant community interest in EPA's June 1994 and May 1996 Proposed Plans.
The public meeting held in connection with the May 1996 Proposed Plan was attended by
approximately 25 people. The general public did not submit any comments on the May 1996
Proposed Plan, but comments submitted in connection with the May 1994 Proposed Plan
expressed overwhelming support in favor of taking immediate action at the Site. In the
context of the 1994 Proposed Plan, several community members supported onsite treatment
in lieu of enlarging the SCDD. Prior comments from the community also supported the use
of the inactive open pit mine, Brick Flat Pit, for sludge disposal.
Rhone-Poulenc submitted detailed comments in support of its conclusion that no further
action is warranted at this time. If EPA selected additional response action, Rhone-Poulenc
urged EPA to select treatment of Slickrock Creek baseflows. Rhone-Poulenc recently
requested that EPA defer remedy selection to permit Rhone-Poulenc to investigate the
feasibility and effectiveness of implementing limited surface-water collection in the Big Seep
ROD4.DOC
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area of Slickrock Creek and a groundwater collection program that would rely on intercept
trenches to collect limited groundwater from Slickrock Creek area sources.
IMMI did not submit any comments on EPA's 1996 Proposed Plan.
Responses to the above comments are presented in the Response to Comments document.
IX. THE SELECTED REMEDY
The EPA is selecting Alternative SRI as described in the May 1996 Water Management
FSA. The selected remedy incorporates a retention dam within the Slickrock Creek drainage,
a clean water diversion system, and upgrades to the pipeline and treatment plant The selec-
ted remedy relies on the collection and treatment of the AMD-contaminated surface-water
discharges from the area sources in the Slickrock Creek watershed that discharge to the reach
of Slickrock Creek below the heavily disturbed mining area. The remedy, as finally designed
and implemented, may rely to some extent on source control of specific sources and on water
management technologies to ensure collection of the contaminated surface flows as well as to
minimize the amount of water that could become contaminated by the area source discharges
and require treatment (such as a collection system for seeps under the hematite pile and the
flows from Brick Flat Pit).
The major components of the selected remedy include:
Construct a retention dam and necessary surface water diversion facilities to ensure the
collection and storage of contaminated surface runoff, interflow, and groundwater in the
Slickrock Creek watershed at IMM.
Construct facilities to provide controlled release of contaminated waters from the
retention dam to the AMD conveyance pipeline to the IMM HDS/ASM lime
neutralization treatment plant.
Construct facilities to divert relatively uncontaminated surface water from the area
upstream from the highly disturbed mining area of the Slickrock Creek basin and divert
that water around the Slickrock Creek retention reservoir. The diversion shall also divert
around the retention reservoir the water from the unmined side of the Slickrock Creek
watershed.
Take appropriate steps (including consideration of emergency failure scenarios) to
integrate into the operation of the reservoir the collection and conveyance of the Old/No.
8 Mine Seep AMD to the IMM HDS/ASM lime neutralization treatment plant.
Construct a hematite erosion control structure consistent with California mining waste
requirements.
Construct one or more sedimentation basin(s) or other EPA approved control structures in
the Slickrock Creek watershed to minimize sedimentation of the Slickrock Creek
retention reservoir and to ensure proper functioning of the controlled release facilities.
R004.DOC 90
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• Upgrade the hydraulic capacity of the existing pipeline (or if necessary construct a new
pipeline) from Slickrock Creek to the Boulder Creek crossing as required to ensure
adequate reliable capacity to convey Slickrock Creek and Old/No. 8 Mine Seep AMD.
• Construct an additional pipeline to reliably convey Slickrock Creek and Old/No. 8 Mine
Seep AMD from the Boulder Creek Crossing to the IMM HDS/ASM lime neutralization
treatment plant.
Modify the IMM HDS/ASM lime neutralization treatment plant to ensure proper
treatment, using the HDS/ASM treatment process, of the Slickrock Creek area source
AMD discharges in conjunction with AMD flows collected pursuant to other Records of
Decision.
Construct a tunnel to provide for gravity discharge of the high volumes of effluent from
the IMM HDS/ASM treatment plant to Spring Creek below the Upper Spring Creek
diversion to Flat Creek.
Construct facilities to assure collection of significant identified sources (including but not
limited to seeps from Brick Flat Pit and the hematite piles) and convey those releases to
the Slickrock Creek Retention Reservoir.
Perform long-term operations and maintenance (O&M) of all components.
X. STATUTORY DETERMINATIONS
The EPA's primary responsibility at Superfund sites is to select remedial actions that are
protective of human health and the environment. CERCLA also requires that the selected
remedial action for the Site comply with applicable or relevant and appropriate environ-
mental standards established under Federal and State environmental laws, unless a waiver is
granted for a particular ARAR. The selected remedy must also use permanent treatment
technologies or resource recovery technologies to the maximum extent practicable and be
cost-effective. The statute also contains a preference for remedies that include treatment as a
principal element. The following sections discuss how the selected remedy meets these
statutory requirements.
X.1 Protection of Human Health and the Environment
The selected remedy protects human health and the environment from the exposure pathways
that are being addressed in this interim action. The selected remedy addresses IMM AMD
releases from essentially all of Slickrock Creek area sources and the hematite pile. The alter-
native will permit treatment of essentially all of the IMM AMD from the Slickrock Creek
area sources, which comprise approximately 60 to 70 percent of the remaining uncontrolled
copper and 40 to 50 percent of the remaining uncontrolled zinc and cadmium releases from
IMM. These collected releases will be treated to neutralize the acidity of the water and
remove more than 99 percent of the metals. The concentrations in the contaminated Spring
Creek watershed would be expected to decrease proportionately under all hydrologic
ROD4.DOC 91
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conditions. The remedy will also control releases from the hematite pile. The selected rem-
edy is an interim remedy that is not expected to be final and does not address all of the
sources of discharges from the Site. The selected remedy therefore cannot be expected to be
fully protective of human health and the environment.
The primary human health-related exposure pathway is the ingestion of contaminated surface
waters. The selected remedy would ensure that State and Federal drinking water standards
are not exceeded at the point of withdrawal for the Redding Municipal Water District, except
during extreme spill events. The alternative will improve water quality in the creeks draining
Iron Mountain, in SCR, and in the lower portion of Keswick Reservoir, but the remedy will
not ensure compliance with human health standards in these water bodies. The human health
threat posed by potential exposure to contaminated sediments through ingestion is not
addressed by the selected remedy. However, control of the hematite pile will reduce the
release of airborne arsenic into the environment.
The environmental threats posed by these sources are the very significant releases of copper,
cadmium, zinc, and acidity into surface waters. The selected remedy will essentially elimi-
nate the discharges from the sources being addressed in this interim action. The removal of
these metal loads associated with the Slickrock Creek area sources will significantly improve
the surface water quality below the SCDD and provide significant protection to aquatic
resources below Keswick Dam. The metal removal will decrease the frequency, duration,
and toxicity of SCDD spills of IMM AMD, make significant progress toward the attainment
of appropriate water quality criteria in and below Keswick Reservoir, and provide some
improvement in receiving waters above the SCDD.
The removal of metals will make significant progress toward compliance with the SBPS and
the PCTR in the Spring Creek arm of the Keswick Reservoir. Currently, water quality
criteria in that water body are exceeded on a regular basis, and only limited beneficial uses
are attainable under current conditions.
The anticipated reduction in SCDD spill frequency associated with the selected remedy is not
as great as Alternatives WM1, WM2, WM3, and WM4; however, the spills occurring after
implementation of the selected remedy will tend to be less toxic and require less dilution
because the SCR water will contain lower concentrations of metals. When combined with a
remedy for the Boulder Creek area sources (to be the subject of additional study and a later
EPA decision), the selected remedy could potentially be comparable to the other alternatives
with respect to reducing SCDD spills and protecting the environment below SCDD.
The current uncontrolled IMM area source AMD discharges are estimated to result in SCR
waters with copper concentrations of approximately 400 to 800 ppb, and zinc concentrations
of approximately 600 to 1,200 ppb; The selected remedy is expected to decrease the SCR
water concentrations in proportion to the load reduction to approximately 150 to 250 ppb
copper and 300 to 600 ppb zinc (with similar proportional reductions for cadmium).
Although less polluted than current conditions, these levels will remain well in excess of the
existing standards for copper (5.6 ppb) and zinc (16 ppb). Since the water will be less
contaminated, the water will require less dilution to meet protective standards, so the SCR
waters could generally be discharged from the SCR under controlled conditions at higher
ROD4.DOC 92
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rates than the current discharge. The ability to discharge greater quantities of water creates a
greater capacity to manage the discharge of the large flows of contaminated stormwaters.
This greater water management capability reduces the frequency of uncontrolled spills from
SCDD, which in turn reduces the frequency of SBPS and PCTR exceedances below Keswick
Dam.
Water quality modeling using the most recently acquired data indicates that the selected rem-
edy will provide significant additional protection to the environment. The model takes into
account all the remedial actions implemented to date and calculates the frequency at which
the SBPS and the PCTR would be exceeded in the main stem of the Sacramento River below
Keswick Dam over the 31-year study period (1965 to 1995). The model is capable of taking
into account the uncertainties inherent in real-time operation of CVP facilities. For the
modeling conducted in 1996, EPA generally assumed that these uncertainties could be
accounted for by targeting SCDD operations to meet a value equal to 75 percent of the actual
standard. Comments submitted by the USBR indicate that this assumption might be overly
optimistic, which would cause the model to understate the frequency and duration of
exceedances. Since 1996, EPA has conducted additional analysis of the difficulties inherent
in trying to predict metal concentrations below the SCDD in real-time under highly variable
conditions. This additional investigation indicates that, even if significant resources are
expended to perform an intensive monitoring program and make frequent operational
adjustments, achieving a 75 percent SCDD operational efficiency under all conditions could
be an overly optimistic assumption. EPA therefore considers a range of operational
efficiencies in evaluating the probability of future SCDD spills under variable hydrologic
conditions, including a straight 75 percent assumption and a split operational efficiency that
varies the assumed efficiency from 50 to 75 percent depending on the SCR inflows (75
percent is used for SCR inflows less than 50 cfs and 50 percent is used for SCR inflows
greater than 50 cfs).
Considering concentration and flow information developed since 1994 and a range of SCDD
operation efficiencies indicates that, in the absence of further remediation, uncontrolled spills
of IMM contaminants would continue to occur every 3 to 4 years if the SCR is operated to
target the SBPS below Keswick Dam and every 2 to 3 years if the SCR is operated to target
the PCTR below Keswick Dam. Implementing Alternative SRI would reduce the expected
SCDD spill frequency to once every 8 to 10 years if the SCR is operated to target the SBPS
below Keswick Dam and every 4 to 8 years if the SCR is operated to target the PCTR below
Keswick Dam. Alternative SRI is also expected to decrease by approximately 80 percent the
days that the Sacramento River below Keswick Dam experiences a violation of a water
quality criteria. See responses to comments in the technical memorandum responding to the
Evaluation of Revised IMM Water Quality Model and its Application to Slickrock Creek
Remediation, by Spaulding Environmental, dated July 1,1996 and Additional Water Quality
Model Simulations Using Data Collected Through June 1997 and Proposed Water Quality
Standards. The Alternative is also expected to improve water quality in Keswick Reservoir,
part of which currently experiences exceedances of the SBPS and PCTR for much of each
wet season.
ROD4.DOC 93
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The selected remedy would also protect the environment by significantly reducing the mass
loads of copper, cadmium, and zinc through removal of approximately 60 to 70 percent of the
remaining uncontrolled copper and 40 to 50 percent of the remaining uncontrolled zinc and
cadmium Site discharges. The release of these metals causes heavy metal precipitates to
form in the water column, some of which settle in the SCAKR and the Sacramento River
below Keswick Dam. The heavy metal-laden precipitates threaten the environment through
the physical processes of settling, which could smother benthic organisms, and the inherent
toxicity of the heavy metal-laden sediments and the associated pore water (i.e., water in the
space in between sediment particles) to benthic organisms. These releases also interfere with
remediation of the heavy metal-laden sediments currently in place in SCAKR and other State
waters (by continuing the introduction of new sediments on a regular basis). Remediation of
these sediments could allow for the restoration of beneficial uses for the affected water
bodies which would eliminate the threat of releases of toxic metals through mobilization of
the sediments. -
The selected remedy also protects the environment from the releases being addressed by
improving water quality in Spring Creek and Slickrock Creek. While it is too early to deter-
mine the extent to which beneficial uses could be fully restored to those waters, removal of
these significant metal loads is anticipated to improve the beneficial uses of these impaired
waters. Since this is an interim remedy that does not control all releases, however, EPA does
not expect that this action will be capable of restoring all beneficial uses to those water
bodies.
Reducing metal loads from IMM also produces ancillary environmental benefits by reducing
the need for special dilution releases. For example, if special releases of water are required
for dilution of IMM AMD, those releases reduce the amounts of water in storage that would
otherwise be available for temperature control in the Sacramento River or other environmen-
tal needs. An additional ancillary benefit can be realized with reduced reliance on the current
use of the Spring Creek Power House discharges to ensure regular flushing of the heavy
metals from SCAKR (as described in the USER Operation Criteria and Plan 1993, pages 44
and 45). Demand for water from the Trinity River and upper Clear Creek would be reduced,
increasing its availability for beneficial uses in those watersheds.
As part of the Site investigation, EPA has concluded that Site remedies that rely on the
selected remedy as a component are feasible, and can ensure that releases associated with an
extreme hydrologic event would be rare.
In summary, current conditions are not protective and do not meet the remedial action objec-
tives for the Site. The implementation of the Slickrock Creek Retention Dam remedial action
is not expected to fully meet the remedial action objectives for the Site without further
actions, but would significantly reduce the exceedances of the water quality standards and
production of toxic sediments. These beneficial effects are expected to significantly improve
the protectiveness of the Superfund cleanup.
With respect to this criterion, the selected remedy, in conjunction with a subsequent Boulder
Creek remedy, is preferable to Alternatives WMO, WM1, WM2, and WM3. The remedy,
which can easily be implemented in conjunction with a Boulder Creek remedy, would
ROD4.DOC 94
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remove a significant amount of heavy metals from the system rather than simply diluting the
heavy metal discharges or treating only the Slickrock Creek baseflows. Alternative SRI, in
conjunction with an available Boulder Creek remedy, could provide protection approximately
equivalent to Alternative WM4, but at less cost.
X.2 Compliance with ARARs
The selected remedy provides for significant progress toward meeting ARARs for the
Superfund cleanup action at IMM by reducing the discharges of copper, cadmium, zinc, and
acidity from the Site. In particular, the remedy will result in better water quality in the
Sacramento River by limiting discharges of copper, cadmium, zinc, and acidity from the Site,
thereby reducing the number of days and/or the degree of exceedances of the State Basin Plan
standards (and the PCTR) in the Sacramento River and Keswick Reservoir. This section
discusses the ARARs which the action will meet and identifies the ARARs which are being
waived.
The Slickrock Creek area discharges are similar in nature and characteristics to the IMM
AMD sources addressed in the September 30, 1992, Record of Decision for the Boulder
Creek Operable Unit at IMM. The September 30,1992, Record of Decision thoroughly dis-
cusses the ARARs for this type of source (AMD containing high concentrations of copper,
cadmium, and zinc) and ARARs for the selected remedy (treatment with onsite sludge dis-
posal or discharge of the treated effluent to lower Spring Creek and waste pile management).
The September 30,1992, Record of Decision discussion regarding ARARs in Section X.2 is
incorporated fully by reference, except as modified below.
Compliance with Chemical-Specific ARARs
The selected remedy makes significant progress toward complying with chemical-specific
ARARs below Keswick Dam, but the remedy does not ensure compliance with the SBPS
under all circumstances and in all locations. The reduction in the IMM metal discharges
would significantly increase compliance with the SBPS in the Sacramento River except in
unusual circumstances. The treatment plant will continue to meet the effluent standards as
set forth in the 1992 ROD.
The selected remedy would improve water quality in Keswick Reservoir but would not assure
compliance with the SBPS under all circumstances. Combining the selected remedy with an
available Boulder Creek Remedy could potentially attain compliance with the ARARs for
Keswick Reservoir.
In the 1992 ROD, EPA identified the California Inland Surface Waters Plan as an ARAR.
Since that time, the plan has been held to be invalid on procedural grounds, so the standards
are not ARARs for this response action. Once the plan was invalidated, California no longer
had statewide numeric water quality criteria. On August 5,1997, EPA promulgated the
PCTR, which are draft statewide water quality criteria for California (62 Federal Register
42160 [1997]). If adopted, the standards would apply to subsequent response actions at IMM
to the extent the standards are more stringent than the SBPS. Because the SBPS do not
currently have a 96-hour standard (the SBPS are stated as instantaneous maximums), the
PCTR would likely serve as that standard. As discussed above, the selected remedy will
ROD4.DOC 95
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make significant progress toward enabling management of Site discharges in a manner that
would comply with the PCTR.
The selected remedy does not ensure compliance with the SBPS or PCTR above the SCDD,
and continuous exceedances in those bodies are expected to remain even after
implementation of Alternative SRI. Since Alternative SRI removes significant metal loads
from Slickrock Creek, some of the beneficial uses of that stream could potentially be restored
over time (particularly if additional steps are taken to address the remaining sources in that
watershed).
The disposal of sludge from the treatment effluent would be required to meet State standards
applicable to mining waste. Sludge from treatment of the Slickrock Creek contaminated
waters would be disposed of in the onsite landfill constructed pursuant to ROD2 and ROD3.
The disposal facility was constructed in accordance with the State standards for disposal of
mining wastes.
Compliance with Location-Specific ARARs
The selected remedy shall address and comply with all location-specific ARARs. Significant
action-specific ARARs include those relating to disposal of treatment sludge and ARARs
directing activity to protect affected fisheries, aquatic resources and their habitat
The action would need to comply with the substantive requirements of the Fish and Wildlife
Coordination Act because the action will result in the regular inundation of an area on the
mine property. Areas that would be unavoidably impacted by the selected remedy include
chaparral and riparian habitat that is currently significantly impaired because the area is
highly disturbed by past mining activity. The EPA will consult with the USFWS to develop
appropriate mitigation measures.
The requirements for protection of habitat in the Endangered Species Act are also ARARs for
this action. The selected remedy would have a potential impact on a federally endangered
species because the action would reduce the toxic releases from IMM that threaten the
winter-run Chinook salmon. Although it is anticipated that such impacts will be beneficial
and would further the goals of the Endangered Species Act, EPA has been consulting with
the NMFS in accordance with the provisions of the Endangered Species Act. The EPA has
also worked closely with the appropriate Natural Resource Trustees to ensure protection of
natural resources.
This action will not impact archaeological and/or historic sites of significance.
Compliance with Action-Specific ARARs
The selected remedy shall address and is expected to comply with all action-specific ARARs.
The action would have a potential impact on a federally endangered species. Although it is
anticipated that such impacts would be beneficial, EPA has been coordinating the devel-
opment and evaluation of potential IMM remedial actions with the Federal and State Natural
Resource Trustees. Consistent with the provisions of the Endangered Species Act, EPA has
been consulting with the NMFS regarding proposed remedial actions for the Site.
ROD4.DOC 96
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In prior actions, the State of California has identified State requirements for seismic safety as
requirements for construction projects generally (see CDFG letter of March 27,1992). The
Dam Safety Act also serves as an ARAR for the construction of any dam, including the dam
to be constructed as part of this response action. (See DTSC and RWQCB letter of
March 30,1992).
The selected remedy involves control of the large hematite pile located in the Slickrock Creek
watershed. The inactive mining waste unit shall be controlled in the manner required by the
California Mining Waste Requirements identified in the 1992 ROD.
ARAR Waivers
The EPA is waiving compliance with certain ARARs on the basis that this proposed action is
an interim action that will not respond to all releases of hazardous substances from the
facility. Since the dam and treat interim remedial action for the Slickrock Creek area source
AMD discharges does not address releases other than area sources discharging to the reach of
Slickrock Creek below the heavily disturbed mining area, such as releases from area sources
in the Boulder Creek watershed and the existing sediments in SCR and Keswick Reservoir,
this interim action is not expected to provide for compliance with all ARARs at all times.
Since the action selected in this Record of Decision is an interim action that leaves some
releases of hazardous substances unabated, EPA is relying on the ARARs waiver for "interim
measures" (CERCLA § 121(d)(4)(A); 40 CFR § 300.430(f)(l)(ii)(C)(l)) for this remedial
action. That section provides that ARARs may be waived if "the remedial action selected is
only part of a total remediation that will attain such level or standards of control when
completed."
The EPA anticipates that the remedy will improve water quality in Spring Creek, Spring
Creek Reservoir, Keswick Reservoir, and the Sacramento River, but EPA does not anticipate
that this remedy, in conjunction the other remedies implemented to date, will be sufficient to
ensure compliance with (1) the numeric, chemical-specific standards contained in the SB PS
for copper, cadmium, or zinc, and (2) California Fish and Game Code § 5650 (which
prohibits discharge of contaminants "deleterious to fish, plant life, or bird life"). The EPA is
therefore waiving compliance with those standards for the interim action to the extent those
standards cannot be achieved by the remedy selected in this Record of Decision in
conjunction with the remedies implemented under prior RODs.
The EPA anticipates that a permanent waiver for certain ARARs might ultimately be required
for certain receiving waters above the SCDD, but EPA is deferring a final decision until
additional information is known regarding the feasibility and degree to which some beneficial
uses could be restored to those water bodies.
X.3 Cost-Effectiveness
Section 300.430(f)(l )(ii)(D) of the NCP requires EPA to evaluate cost-effectiveness by
0 comparing the alternatives that meet the threshold criteria against three additional balancing
criteria: long-term effectiveness and permanence; reduction of toxicity, mobility, or volume
through treatment; and short-term effectiveness. The selected remedy is cost-effective with
respect to meeting these criteria.
ROD4.DOC 97
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The total cost of the selected remedy (including both the capital and O&M costs based on a
30-year present worth cost using a 5 percent interest rate) is estimated to be about
$21,169,000. Since EPA has not yet addressed further Boulder Creek remedial actions or
continued SCDD operations as part of the selected remedy, the costs described above for
implementation of the selected remedy do not include the expected costs associated with
potential remedies for the Boulder Creek area sources or continued operation of SCDD.
To more fully evaluate the cost-effectiveness of the selected remedy, EPA considered the cost
of combining the selected remedy with the most expensive technically feasible Boulder Creek
remedy from EPA's Boulder Creek Alternatives Study (which is referred to below as the
Combined Alternative SRI). The 30-year present worth cost of the Combined Alternative
SRI is estimated to be less than $57 million. (EPA is still investigating the appropriate
response action for Boulder Creek area sources, so the response action for those sources
could be greater.or less than the amount used in this analysis.) The Combined Alternative
SRI is less costly than the other remedial alternatives, which range in cost from approxi-
mately $75 million to approximately $130 million. As discussed above, this combined rem-
edy would provide a response action that is at least equivalent to the other remedies with
respect to (1) long-term effectiveness and permanence; (2) reduction of toxicity, mobility, or
volume through treatment; and (3) short-term effectiveness. The selected remedy is therefore
a cost-effective component of the overall response action.
The cost estimates for these alternatives do not include the cost of continuing to operate the
SCDD as a component of the remedies because the cost of continued SCDD operations is
comparable to the No-Action Alternative, which is assumed to have a cost of zero for
purposes of the comparative analysis.
X.4 Utilization of Permanent Solutions and Alternative Technologies or Resource Recovery
Technologies to the Maximum Extent Practicable
The EPA has determined that the selected remedy represents the maximum extent to which
permanent solutions and treatment technologies can be employed in a cost-effective manner
for the interim remedial action.
The EPA recognizes that the mineralization at IMM will continue to generate AMD unless
additional remedial actions are developed, evaluated, and selected for implementation to
reduce or eliminate the AMD-forming reactions. The EPA has developed and evaluated
alternatives as part of the ongoing remedial investigation and feasibility study activities at
IMM that could reduce or eliminate the AMD-forming reactions. Resource recovery
alternatives have also been proposed and evaluated. The EPA has concluded that further
information is required to be developed and evaluated before one of these approaches could
be selected for implementation. The needed further information would address technical
feasibility, implementability, effectiveness, and cost-effectiveness concerns and risk factors
with respect to these approaches. The EPA encourages the further development of
alternatives that could control the AMD-forming reactions and resource recovery alternatives
for future evaluation and potential selection in a subsequent action.
The selected remedy will provide for a significant reduction in the copper, cadmium, zinc,
and acidity discharges from the Site. The current water supply and fishery conditions are
ROD4.DOC 98
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critical. There is a need to implement controls on these discharges as expeditiously as possi-
ble, while studies are ongoing with respect to further source control or resource recovery
approaches. Treatment is effective, a part of each approach developed to date, and is
consistent with implementation of a subsequent action.
X.5 Preference for Treatment as a Principal Element
The selected remedy relies on treatment as a primary component to reduce the toxicity and
mobility of the AMD which is being generated. The HDS neutralization treatment process is
expected to be very effective in preventing the discharge of metals from the Slickrock Creek
contaminated flows that are collected and conveyed to the treatment plant for treatment The
HDS neutralization process is expected to remove more than 99 percent of the metals from
the treated contaminated Slickrock Creek flows.
The EPA is not selecting a remedy that treats the source in a manner that prevents the
formation of AMD because EPA is not currently aware of such an approach that could be
effectively implemented at IMM. The EPA encourages the continued development and
evaluation of alternatives that may partially satisfy the preference for treatment as a principal
element, and this issue will be addressed in the final decision document for the Site. The
EPA has concluded that further development and evaluation of the above approaches is
necessary to address significant uncertainties with respect to technical feasibility,
implementability, effectiveness, cost-effectiveness concerns, and risk factors.
XI. DOCUMENTATION OF SIGNIFICANT CHANGES
The EPA is today approving the Proposed Plan with no significant changes.
ROD4.DOC 99
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PHOTOGRAPHY DATED 9-3-06
DIGITAL ORTHOPHOTO MEETS NA:ONAL
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P-!OTO EXHIBIT 1
MINE WORKINGS 4 DRILL HOLES
SLICKROCK CREEK
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-------
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APPROXIMATE AREA COLLECTED FOR TREATMENT
APPROXIMATE AREA NOT COLLECTED FOR TREATMENT
PHOTOGRAPHY DATED »•>«>
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MAP ACCURACY :-AWARDS FOR I- • XW SCALE
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PHOTO EXHIBIT 2
CONCEPTUAL DEPICTION OF SELECTED REMEDY
SLICKROCK CREEK AREA SOURCES
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