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EnWonmental Protection
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Office 01
Emergen~ and
Remedial Response
EPAlRODtR08.88I019
March 1988
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&EPA
Superfund
Record of Decision:
~ 2>q-I2..~3.83
Central City / Clear Creek, CO
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50272 -1111
REPORT DOCUMENTATION 11. REPORT NO. 12.
PAGE EPA/ROD/R08-88/019
J. Recipient'. Acc..alon No.
.. Title and Subtitle
SUPERFUND RECORD OF DECISION
Clear Creek/Central City, CO
Second Remedial Action
5. Report Date
03/31/88
,-
6.
7. Author(l)
8. Performin. O,.anlutlon RePt. No.
9. Perform In. O,.ani%8tlon Name and Address
10. Project/Task/Work Unit No.
-- ._-
11. Contract(C) or Grant(G) No.
(C)
(G)
--
12. Sponlorinll Or.aniution Name and Address
U.S. Environmental Protection
401 M Street, S.W.
Washington, D.C. 20460
13. Type of Report & Period eove,.d
Agency
800/000
14.
15. Supplemantary Notes
16. Abstract (Limit: 200 words)
The Clear Creek/Central City site is located approximately 30 miles west of Denver in
Clear Creek and Gilpin Counties, CO. The site consists primarily of acid mine drainages
from five mines/tunnels and adjacent milling and mining wastes. Currently, acid mine
dralnage and runon and runoff from the tailings and waste rock piles have affected
downstream surface water qual1ty. In add1tion to the direct discharge from the mine
tunnels, contaminatec water may enter Clear Creek and North Clear Creek during overland
sheet flow. Th1S occurs during rapid snowmelt and storms. The resulting surface flow
across the ta1l1ngs ana waste rock piles dissolves soluble minerals and transports
particulate tailin~s and waste rock mater1als into the creeks. All this results in
elevated creek acid1ty ana metal loads. The introduction of tailings and waste rock
into the creeks could also occur due to catastrophic collapse of tailings and waste rock
piles dur1ng a flash flood or as a result of undercutting of the base of the pile under
any flow regimen. The ciscr.arges fror tr.e five tunnels were addressed in the first
remedial action operable unit for this site. The primary contaminants of concern for
human receptors 1n surface water 1nclude: aluminum, arsenic, cadmium, chromium (IV),
lead, manganese, nickel, and silver. For aquatic receptors, the above list expands to
include: copper, fluoride, and Zinc.
(See .Attached Sheet)
-
--
17. Document Analysis a. Descriptors
Record of Decision
Clear Creek/Central City, CO
Second Remedial Action
Contaminated Media: sw
I
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EPA/ROD/R08-88/019
Clear Creek/Central City, CO
Second Remedial Action
16.
ABSTRACT (continued)
The selected remedial action for this site includes: slope stabilization at the Bi9
Five Tunnel and Gregory Incline; monitoring,.of the gab ion wall at the Gregory Incline:
and run-on control at the Argo Tunnel, Big Five Tunnel, Gregory Incline, National
Tunnel, and the Quartz Hill Tunnel. The estimated present worth cost for this remedial
action is $1,049,600.
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DECLARATION
FOR THE
RECORD OF DECISION
SITE NAME AND LOCATION
Clear Creek/Central City Superfund Site
Clear Creek and Gilpin Counties, Colorado
Operable Unit No. Two
Tailings and Waste Rock Remediation
STATEMEN~ OF PURPOSE
This decision document represents the selected remedial
action for Operable Unit No. Two (Tailings and Waste Rock
Remediation) of the Clear Creek/Central City Superfund Site
developed in accordance with the Comprehensive Environmental
Response, Compensation and Liability Act of 1980 (CERCLA), as
amended by the Superfund Amendments and Reauthorization Act of
1986 (SARA), and the National Contingency Plan (40 CFR Part 300).
The State of Colorado has been consulted on the Proposed
Plan and has indicated that it will concur on the selected remedy
for Operable Unit No. Two.
STATEMENT OF BASIS
This decision is based upon the Administrative Record for
Operable Unit No. Two of the Clear Creek/Central City Superfund
Site. The attached index identifies the items which comprise the
administrative record upon which the selection of the remedial
action was based.
DESCRIPTION OF SELECTED REMEDY
The Clear Creek/Central City Superfund Site is located
approximately 30 miles west of Denver, Colorado and primarily
consists of acid mine discharges and milling and mining wastes
from five mines/tunnels in the Clear Creek and North Clear Creek'
drainages. These are the Argo Tunnel and Big Five Tunnel in the
Clear Creek drainage; and the Gregory Incline, National Tunnel,
and the Quartz Hill Tunnel in the North Clear Creek drainage.
Conditions at the five tunnels and tailings and waste rock pile
locations pose potential impacts to human health and the
'environmen~.
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More specifically, potential impacts to human health and the
environment resulting from the acid mine discharges include:
degradation of downstream surface water quality resulting
from dissolved and suspended metals in the discharges and
resuspended metal laden sediments below the discharges; and
reduction in aquatic habitat quality or productivity in
Clear Creek and North Clear Creek resulting from
contaminated surface water.
These impacts were addressed in the September 30, 1987 Record of
Decision for the Discharge Treatment Operable Unit or Operable
Unit No. One for the site.
Operable Unit No. Two for the site, the Tailings and Waste
Rock Remediation Operable Unit, considers potential impacts to
human health and the environment resulting from:
degradation of downstream surface water quality due to
collapse of the piles into either Clear Creek or North Clear
Creek;
degradation of downstream surface water quality due to runon
and runoff from the tailings and waste rock piles; and
human uptake of metals from the inhalation of dust or
ingestion of material from the tailings and waste rock
piles.
These impacts are addressed in this Record of Decision.
EPA is. undertaking an additional feasibility study, Operable
Unit No. Three or the Blowout/Discharge Control Operable Unit, to
evaluate remedial action alternatives for remediating impacts to .
human health and the environment resulting from a potential
blowout of the Argo Tunnel. In addition, the State of Colorado
has submitted an application to EPA for monies to fund an
investigation to identify other areas within the mining district
which may be significantly impacting North Clear Creek and Clear
Creek. The State will also investigate the quality of
groundwater in the area. Depending upon the results of the State
study, EPA may consider additional operable units.
The selected remedy for Operable Unit No. Two consists of
slope stabilization at the Big Five Tunnel and Gregory Incline
and runon control at all five tailings and waste rock piles. No
action will be taken at this time to address potential impacts
from inhalation and ingestion of material from the piles.
2
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The unstable slopes at the Big Five Tunnel and Gregory
Incline could collapse into Clear Creek and North Clear Creek,
respectively, and the resulting metals loading into the creeks
would adversely affect the water quality of the creeks. Slope
stabilization at the Big Five Tunnel will consist of regrading
portions of tha piles to a stable configuration and placing large
boulders at the base to minimize erosion. The current gabion
wall at the Gregory Incline will be maintained until monitoring
indicates remediation is necessary or until the tailings are
removed for reprocessing. At that time, a permanent solution
will be implemented.
Runon control will reduce the metals loading to Clear Creek
and North Clear Creek resulting in an improvement of stream water
quality. Runon control at all five locations will consist of
installing diversion ditches on the upgradient sides of the
piles.
No action will be taken at this time to address potential
impacts from inhalation and ingestion of material from the piles
because the Public Health Evaluation for the site indicated that
current or episodic human health and environmental risks
resulting from these exposure pathways were minor. Current use
consists of periodic visits to the sites by local residents and
visitors. The Public Health Evaluation indicated, however, that
for a potential future residential scenario, risks resulting from
the inhalation and ingestion exposure pathways are of some
concern. Therefore, EPA will evaluate this No Action decision
when the final remedy is selected for the site. . EPA, in
coordination with the State of Colorado and local officials, will
evaluate the use of institutional measures which would control
any human health or environmental threat that could be created by
future development upon these tailings and waste rock piles and
any other piles which the State identifies in its study. In
addition, pursuant to SARA Section 121(c), EPA will review no
less than every five years all properties where hazardous
substances continue to remain onsite and, if necessary, will
reconsider this No Action decision.
Estimated costs for slope stabilization at the Big Five
Tunnel and Gregory Incline and runon control at all five sites is
approximately $1.0 million.
The selected remedy for Operable Unit No. Two has been
chosen to mitigate and minimize potential impacts resulting from
the tailings and waste rock piles and to protect human health and
the environment. The selected remedy for Operable Unit No. Two
is an interim remedy because the net beneficial impact to Clear
Creek and North Clear Creek will not be realized until the' .
completion of remedial actions for the other operable units~ The
selected remedy therefore requires the exercise of the "interim
remedy" waiver (SARA Section 121(d)(4)(A)) from contaminant-
3
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specific ARARs listed in the Feasibility Study. The interim
remedy waiver allows for the selection of a remedial action that
does not attain ARARs if "the remedial action selected is only
part of a total remediation action that will attain such level or
standard of control when completed." The interim remedy is
consistent with the final site remedy. Location- and action-
specific ARARs will be met.
DECLARATION
The selected remedy for Operable Unit No. Two of the Clear
Creek/Central City Superfund Site is a cost-effective remedy
which is protective of human health and the environment. The
selected remedy is an interim remedy which does not attain
Federal and State public health and environmental requirements
that are applicable or relevant and appropriate and therefore the
SARA Section 121(d)(4)(A)) interim remedy waiver is required.
The statutory preference for treatment is not satisfied
because treatment was found to be impracticable at this time.
However, EPA leaves open the opportunity for any future treatment
or reprocessing which can be shown to be protective of hum~n
health and the environment and which attains Federal and State
public health and environmental requirements that are applicable
or relevant and appropriate.
James 3Cher;rt /.
Regional Administrator
Environmental Protection Agency
Region VIII
~iJ~~.
Date
.J I, /;,~
- -...
4
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SUMMARY
FOR THE
RECORD OF DECISION
SITE NAME AND LOCATION
Clear Creek/Central City Superfund Site
Clear Creek and Gilpin Counties, Colorado
Operable Unit No. Two
Tailings and Waste Rock Remediation
SITE DESCRIPTION
The..Clear Creek/Central City Superfund site is located
approximately 30 miles west of Denver,JColorado, and primarily
consists of acid mine drainages and milling and mining wastes
from five mines/tunnels in the Clear Creek and North Clear Creek
drainages. The site encompasses the northeastern portion of
Clear Creek County and southeastern portion of Gilpin County.
Specifically, the focus of the Remedial Investigation was
five abandoned mines/tunnels proximal to the cities of Idaho
Springs, Black Hawk, and Central City (Figure. 1). The tunnels
are the Argo Tunnel and Big Five Tunnel in the Clear Creek
drainage and the National Tunnel, Gregory Incline, and the Quartz
Hill Tunnel in the North Clear Creek drainage. The Argo portal
is within the city limits of Idaho Springs. The Big Five portal
borders the Idaho Springs city limits. The Gregory Incline is
within the Black Hawk city limits. The National Tunnel is within
a mile of the City of Black Hawk. The Quartz Hill Tunnel is
within a mile of the City of Central City.
The waste rock/tailings piles considered in this Operable
Unit were selected based on their location close to the acid mine
discharges. Currently, the major impacts on the water quality of
Clear Creek are the Big Five and Argo mine tunnel discharges.
The water quality of North Clear Creek is affected by the
National Tunnel discharge and seepage from the Gregory Incline
and the Quartz Hill Tunnel. The discharges from the five sites
were addressed in Operable Unit No. One.
In addition to Idirect discharge from the mine tunnels,
contaminated water may enter the creeks during overland sheet
flow. Overland runoff occurs during rapid snow melt and
thunderstorms. The resulting surface flow across the tailings
and waste rock piles dissolves soluble minerals and transports
. particulate tailings and waste rock material into the creeks.
These mechanisms result in elevated creek acidity and metal
loads. The introduction of tailings and waste rock into the
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creeks could also occur due to catastrophic collapse of tailings
and waste rock piles during a flash flood or aS'a result of
undercutting of the base of the pile under any flow regime.
SITE HISTORY
The Clear Creek/Central City hard rock mining district is
historically one of the most mined areas in Colorado. At one
time, gold mining accounted for 85 percent of the activity,
silver for 10 percent and other minerals, (e.g., copper, lead,
and zinc) the remaining 5 percent. The area includes over 800
abandoned mine workings and tunnels. Recent data indicate that
up to twenty-five mines and six milling operations are currently
operating in Gilpin and Clear Creek counties. The intensity of
mining operations has varied in recent years, due largely to
fluctuating market prices for precious metals.
Mining activity in the Central City/Black Hawk area
commenced in 1859. Placer gold was found at the mouth of Chicago
Creek, near Idaho Springs, in January of 1859 and, in May of the
same year, the first lode discovery in the Rockies was made in
Gregory Gulch between Central City and Black Hawk. Initially,
mining was concentrated in the Gregory Gulch area, including the
Gregory Incline. Exploration via adits and shafts rapidly
expanded to the south and west of Central City. Excavation of
the Quartz Hill Tunnel was begun in 1860, largely for the purpose
of transporting ore from the overlying surface Glory Hole Mine to
mills in Central City. The tunnel is over a mile long. National
Tunnel construction was initiated in 1905 and continued to 1937.
The tunnel is believed to be over 3,100 feet in length.
The Argo Tunnel was constructed from 1893 to 1904. The
tunnel was built for the dual purpose of mine drainage and ore
transport. The total tunnel length is 4.16 miles, extending from
the portal in Idaho Springs in a northward direction to beneath
the headwaters of Gregory Gulch, west of Central City.
In July, 1982, the Clear Creek/Central City site was ranked
as Site No. 174 on the Interim Priorities List of 400 sites. The
site was added to the final National Priorities List (NPL) in
September, 1983. EPA began the Remedial Investigation (RI) of
the site in July, 1985. The RI Report was issued in June, 1987
and reported results ,from the study period of July, 1985 through
December, 1986. An addendum to the RI was issued in January,
1988 to report results from additional studies conducted in April
and May, 1987.
A removal action was conducted by EPA's Emergency Response
Branch at the Gregory Incline in March, 1987 to protect human
health and the environment from hazards associated with the
collapse of a retaining crib wall. A collapse would have allowed
3
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the tailings to slide into North Clear Creek and EPA was
concerned that a large load of metals-laden tailings would wash
downstream into Clear Creek and contaminate the municipal water
supply of the City of Golden, Colorado. EPA removed an old
deteriorated crib retaining wall and decreased the slope of the
tailings pile to stabilize it. EPA then constructed a gabion-
basket retaining wall.
SCOPE AND ROLE OF THE OPERABLE UNIT
During the course of the RI, EPA determined, in accordance
with 40 CFR Section 300.68(c), that the Feasibility Study (FS)
should be divided into Operable Units in order to remediate site-
specific problems.
The Operable Units include:
Operable Unit No. One - Mine Tunnel Discharge Treatment
(Record of Decision signed in September, 1987)
Operable Unit No. Two - Tailings and Waste Rock Remediation
Operable Unit No. Three - Blowout/Discharge Control
In addition, the State of Colorado has submitted an
application to EPA for monies to fund an investigation to
identify other areas within the mining district which may be
significantly impacting North Clear Creek and Clear Creek. The
State will also investigate the quality of the groundwater in the
area. Depending upon the results of the State study, EPA may
consider additional operable units.
SITE CHARACTERISTICS
A public health evaluation was conducted to identify
compounds which could pose a significant threat to human health
and the environment. Based on sampling of environmental media
and consideration of toxicity, twelve contaminants of concern
were identified and potential exposure pathways were analyzed.
Impacts on human health and the environment were assessed for
exposures due to inhalation and ingestion of material from the
piles and due to runoff from the piles and catastrophic slope
failure of the piles into the streams.
As stated, twelve contaminants were identified during the
public health evaluation as contaminants of concern in the Clear
Creek/Central City study area. Contaminants of concern were
chosen separately for human receptors and aquatic organisms.
Arsenic, chromium (VI), and nickel are present in relatively high
concentrations in the tailings and waste rock and have been rated
by EPA as Group A human carcinogens by the inhalation pathway.
Cadmium is a Group 81 carcinogen by inhalation and is a potent
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kidney toxin when ingested. Lead and silver are toxic
noncarcinogens and are present in relatively high concentrations
in the tailings and waste rock.
Contaminants of concern for aquatic life were chosen based
on their concentration in water, published criteria values (e.g.,
Ambient Water Quali~y Criteria (AWQC», and supplemental data for
chemicals that lacked criteria. Contaminants include aluminum,
arsenic, cadmium, chromium, copper, fluoride, lead, manganese,
nickel, silver, and zinc.
Exposure to metals in tailings or waste rock can potentially
occur through inhalation of dust by people at or near the sites.
Two mechanisms for dust generation were considered in the
evaluation: (1) dust resulting from wind entrainment of tailings
or soil particles; and (2) dust generated from human activities
(in particular, riding of dirt bikes on the tailings piles). The
Gregory tailings pile is readily accessible and in some areas is
quite compacted or has a surface crust. Dirt-bike riding is
known to occur at the Gregory tailings pile. The A~go tailings
are also readily accessible and are less compacted and more
friable than the Gregory tailings. The Argo tailings are not
used extensively by dirt-bike riders due to their steepness.
Currently, however, waste rock at Argo is being removed for use
in constructing roads. This activity, which involves operation
of dump trucks and front-end loaders, increases dust emissions
from this area.
In addition to inhalation, exposure to metals in soil or
tailings can also occur by incidental ingestion. Tourists
visiting the mines may contact the tailings, although the
potential for significant exposure is low. Older children living
in the area, particularly those from ages 6 to 16 who have less
parental supervision than younger children, may play or ride dirt
bikes at the tailings piles especially during the summer months
when school is out.
Future use of the sites may include residential development.
Under this scenario, potential exposure pathways would inc:~de
incidental ingestion of contaminated material by the residents
over their life time. This potential future use residential
exposure scenario was also evaluated.
In summary, the major potential impacts at the site due to
tailings and waste rock are:
o
Degradation of surface water quality caused by runoff from
the piles;
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o
Degradation of surface water quality caused by collapse of
the piles into the creeks; and,
o
Human uptake of metals through inhalation or ingestion.
Exposure to humans
Under both current land use conditions and potential future
use scenarios, the principal po~ential pathways by which human
receptors could be exposed to site contaminants from the tailings
and waste rock piles is through inhalation or ingestion of
material from the piles. Impacts resulting from ingestion of
surface water were evaluated as part of Operable Unit No. One~
Exposure scenarios for average and maximum plausible cases
were developed for both the inhalation and ingestion potential
exposure pathways. Based on estimates of exposure and a
quantitative description of each contaminant's toxicity, human
health risks were then assessed. The major conclusions of this
assessment are presented in Table 1 and can be summarized as
follows:
o
Inhalation of wind-entrained dust from the Gregory Tailings
pile-5esults in_~pperbound lifetime excess cancer risks of
7xl0 and 3xl0 for the average and maximum plausible
cases, respectively, primarily from exposure to arsenic.
Inhalation of wind-entrained dust from the Argo Tailing pi!!
results !g upperbound lifetime excess cancer risks of 2xl0
and 3xl0 , for the average and maximum plausible cases,
respectively. Generation of dust by dirt bikes ridden at
the 95egory Tai!~ngs piles results in upperbound" risks of
Sxl0 and lxl0 , for the average and maximum plausible
cases, "respectively. Risks from inhalation of dust from the
other tailings and waste rock piles are similar.
o
Ingestion of arsenic-contaminated material from the tailings
and waste rock piles under current use, or the episodic
exposure scenario, poses an upper bound lifetime excess
cancer risk of 2Xl0-S for the average case and 1xl0-4 under
maximum plausible conditions.
o
Ingestion of arsenic-contaminated material from the tailings
and waste rock piles under the potential future use
residential scenario poses an upper bound lifetime excess
cancer risk of lxl0-4 under average conditions and 9Xl0-4
under maximum plausible conditions.
The risks for individual sites are provided in Table 1 and a
more detailed discussion of these exposure pathways and the
resulting risks can be found in the Public Health Evaluation,
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TABLE I
SUMMARY OF RISK ASSESSMENT RESULTS FOR HUMAN EXPOSURE
TO CONTAMINANTS AT THE CLEAR CREEK/CENTRAL CITY SITE
Total Excess Upper-Bound
Lifetime Cancer Risk
Exposure Pathway
Average
Case
Maximum Plausible
Case
Inhalation of
by \lind
Gregory.
Argo
Dust Entrained
7x10-65
2x10-
3Xl0-55
3x10-
Inhalation of Dust Generated
by Motorcycles
Gregory
5xIO-6
lxlO-4
Incidental Ingestion
and Tat 11 ngs
Episodic Exposure
Gregory
Argo
Big Five
National
Quartz Hill
of Soil
2XIO:;
2xlO -5
lxlO -5
2xlO_S
2xI0
lxl0-4
lx10-4
8xIO-5
lx10-4
lxlO-4
Incidental Ingestion
and Tailings
Residential Exposure
Gregory
Argo
Big Five
National
Quartz Hill
of Soil
-4
IxlO-4
IxlO-5
8xlO-4
hlO -4
hlO
6xlO-4
6xlO-4
4xlO-4
6xlO-4
6x10-4
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Section 10 of the Remedial Investigation Report. Impacts on
aquatic life due to catastrophic slope failure and runoff during
storm events are discussed in the following paragraphs.
Exposures to Aquatic Life
The exposure of aquatic life in Clear Creek and North Clear
Creek were considered. The principal potential pathways by which
the tailings and waste rock piles impact aquatic life are:
o
Degradation of surface water quality caused by collapse of
the piles into the creeks; and
o
Degradation of surface water quality caused by runoff from
the piles.
Catastrophic Slope Failure:
The failure of a slope results in movement of a mass of
waste rock and/or tailings into the adjacent creek. If these
materials are reactive or toxic and are introduced into a water
or air stream, where exposure to environmental or human receptors
can occur, then a hazard exists. The potential for catast~ophic
slope failure was assessed for each site.
Argo Tunnel: A geotechnical evaluation was performed on the
waste rock/tailings pile at the Argo Tunnel and Mill. The
evaluation concluded that the toe of the slope behind the
commercial buildings had been cut away and the slope was
marginally stable and increased weakness could result from
further activities or disturbance. A slope failure would impact
the buildings but materials would probably not reach Clear Creek.
The volume of such a failure was estimated at 11,200 cubic yards
( Cy ) .
Big Five Tunnel: A geotechnical engineering evaluation was
conducted on two mine waste rock piles (one on the north side of
Clear Creek and one on the south side) created from material
excavated from the Big Five Tunnel. The conclusions of these
evaluations included: .
o
The eastern portion of
of Clear Creek and the
pile on the south side
to unstable;
the waste rock pile on the north side
western portion of the waste rock
of Clear Creek are marginally stable
o
A lOa-year flood could erode the toe of existing slopes back
seven to ten feet and decrease slope stability. A SOO-year
flood could erode the slope back an additional two feet;
and,
o
All slopes are subject to erosion if left exposed.
8
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Based on the results of the geotechnical investigations,
volumes of marginally stable and unstable mine waste rock have
been calculated to be 2000 and 6200 cy for the north and south
banks, respectively. In addition, the volumes of waste rock
which could become marginally stable or unstable after seven to
ten feet erosion back from the toe of the existing waste piles
due to a lOa-year flood were also determined. The volume was
calculated to be 7200 and 7900 cy for the north and south banks,
respectively.
Quartz Hill and National Tunnel:
the National Tunnel is considered
Quartz Hill Tunnel are marginally
recontouring is recommended.
The waste rock pile adjacent to
stable. Some slopes near the
stable and some minor
Gregory Incline: In 1987, the tailings pile at the Gregory
Incline was recontoured to a 2:1 (horizontal to vertical) slope
and a gabion-basket retaining wall was constructed. The gabion-
basket wall is partially immersed in creek water and is exposed
to acid drainage. Without maintenance, the wall has an estimated
life of five years. The wall is supporting an estimated 1,100
cubic yards of tailings which would otherwise collapse into North
Clear Creek.
More details on the geotechnical evaluations conducted at
the Clear Creek/Central City Superfund Site can be found in
Section 8 of the Remedial Investigation Report and Section 5 of
the Addendum to the Remedial Investigation Report.
Estimated Impact Due to Catastrophic Collapse:
A computer model was used to predict water quality in Clear
Creek and North Clear Creek in the assessment of human health and
environmental impacts resulting from the catastrophic failure of
the Big Five Tunnel and Gregory Incline waste rock and tailings
piles. The collapse of the Big Five waste rock piles was modeled
under realistic, worst case conditions. In particular, a total
of 8,200 cubic yards of material (both north and south banks
collapse) was instantaneously introduced into Clear Creek during
normal low flow (40 cubic feet per second (cfs». The 8,200
cubic yards is the quantity of material currently unstable and
which could collapse into Clear Creek at any time, including
during low flow conditions. Zinc and aluminum were selected to
represent the variety of geochemical behavior expected from the
twelve identified contaminants of concern. Arsenic was not
modeled because measured concentrations in the streams and
leachates were below detection limits. Lead and copper were not
modeled because leachate concentrations were low.
A collapse of the Big Five pile into Clear Creek would
result in a peak dissolved concentration of 1,000 ug/L of
aluminum at the point of collapse. After one day, the
9
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contamination would reach Golden where a maximum concentration of
730 ug/L of aluminum is predicted. The aluminum concentration at
Golden under ambient conditions is 200 ug/L. A collapse of the
Big Five pile would result in a maximum dissolved concentration
of 1,100 ug/L of zinc at the collapse point, an increase from
400 ug/L of zinc under ambient conditions. This translates into
a maximum concentration of 960 ug/L of zinc at Golden after two
days which would gradually decrease to 400 ug/L after eight days.
The zinc concentration at Golden under ambient conditions is
about 300 ug/L. The modeling results indicate that maximum
concentrations of aluminum and zinc would exceed AWQC in all
stream segments down to Golden. At Golden, the AWQC would be
exceeded by a factor of 24 and 89, respectively for aluminum and
zinc. Based on the modeling of zinc and aluminum, it is
estimated that concentrations of selected parameters in Clear
Creek at Golden would also exceed maximum contaminant levels
(MCLs) established under the Safe Drinking Water Act. The
results of the model clearly indicate an adverse impact on Clear
Creek due to collapse of the waste rock piles at the Big Five
Tunnel.
Similar analyses of collapse of the Gregory Tailings into
North Clear Creek have been performed. Results from this effort
indicate that both AWQC and MCL values would be exceeded in Clear
Creek at Golden as a result of a collapse.
Impact Due to Runoff:
In addition to collapse of the tailings and waste rock
piles, materials will also enter the stream due to runoff from
the piles during snow melt and storm events. The results of the
analyses of samples taken on Clear Creek and North Clear Creek
during storm events indicate that the average total aluminum and
zinc concentrations exceeded AWQC values by factors of 69 and 15
times, respectively. The results indicate potential impact on
aquatic life due to runoff during storm events. Impacts on human
health due to runoff from the sites are minimal because the storm
events are of limited duration.
Summary of Exposures to Aquatic Life:
The major conclusions of the assessment of exposure to
aquatic life can be summarized as follows:
o
Several of the chemicals of concern are at concentrations
that exceed the ambient water quality criteria for the
protection of freshwater aquatic life (AWQC). In
particular, concentrations of zinc, copper, and aluminum
consistently exceed the acute and chronic AWQC. In
addition, concentrations of manganese in the water exceed
the lowest observed effect level in rainbow trout. Because
aquatic organisms are exposed to a mixture and not
1 0
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individual chemicals, toxic effects may be even greater than
indicated by comparison to the AWQC. Although some fish may
tolerate the chemicals in the creeks, it is highly unlikely
that the populations of fish found in these creeks are free
of toxic effects.
A more detailed discussion of these exposure pathways and
the resulting risks can be found in the Public Health Evaluation,
Section 10 of the Remedial Investigation Report. It is clear
that a release or substantial threat of release of a hazardous
substance or pollutant or contaminant into the environment has
occurred at the Clear Creek/Central City Superfund site and that
remedial action is justified.
COMMUNITY PARTICIPATION
On October 26, 27, and 28, 1987, announcements for the
public comment period and the public meeting to be held
concerning the Operable Unit No. Two Feasibility Study (FS) were
published in the Weekly Register Call, the Golden Transcript, and
the Clear Creek Courant. The ads announced the November 9
through December 8, 1987 public comment period and the November
24 public meeting, gave a brief description of the remedial
action alternatives, and stated the rationale for the Proposed
Plan. The press release, along with the Proposed Plan, was
mailed to the approximately 300 names on the EPA-compiled Clear
Creek/Central City Superfund Site mailing list.
The press release notified the public of the availability of
the Administrative Record for the site and informed them of
location of the information repositories which had previously
been established for the site. Those information repositories
are located at the EPA library in Denver, the Gilpin County Court
House in Central City, the Idaho Springs Public Library and the
Idaho Springs City Hall in Idaho Springs, and the Golden Public
Library in Golden, Colorado. The Administrative Record is .
located at the Gilpin County Courthouse and the EPA Library. An
index of the Administrative Record is located at each information
repository and is also attached to this Record of Decision.
On November 24, 1987, EPA held a public meeting concerning
the Operable Unit No. Two FS and the Proposed Plan.
Approximately SO people attended. Major concerns raised were how
EPA's presence in the area was affecting the economy of the area,
the perceived large amounts of money which EPA is spending on
studying the site, and whether remedial action at the site is
warranted. At the request of several who attended the public
meeting, EPA extended the public comment period on the Operable
Unit No. Two FS to December 18, 1987 and assured concerned
individuals that late comments would be accepted up until the
decision was made (late March).
--
1 1
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The Operable Unit No. Two Responsiveness Summary contains
the official transcript of the public meeting, describes in more
detail the nature and level of the community's concern, and
includes EPA's responses to all comments received during the
public review of the Operable Unit No. Two FS.
ENFORCEMENT
A responsible party search for the Clear Creek/Central City
Superfund Site has been initiated. The search has revealed
information on ownership of the mine tailings and waste rock
piles. At this time, however, this search has not been
completed. EPA does not feel that response actions should be
delayed pending finalization of the responsible party search.
Upon finalization of the search, the status of responsible
parties will be determined and evaluated and, if appropriate, EPA
will formally notify them of the selected remedy for Operable
Unit No. Two and will initiate negotiations for the implemen-
tation of the remedy. If the potentially responsible parties do
not formally commit to performing the remedy in a timely manner,
or if no potentially responsible parties are found, EPA will
proceed with a Fund-financed remedial design and remedial action
and will attempt to recover EPA's response costs from the
responsible parties.
IDENTIFICATION AND SCREENING OF ALTERNATIVES
The EPA evaluated potential remedial action alt~rnatives to
abate the threat posed by contamination from the five mine
tailing and waste rock piles by progressing through the series of
analyses which are outlined in the National Contingency Plan
(NCP), in particular, 40 CFR Section 300.68, the Interim Guidance
on Superfund Selection of Remedy, December 24, 1986, (OSWER
Directive No. 9355.0-19) and the Additional Interim Guidance for
FY '87 Records of Decision, July 24, 1987, (OSWER Directive No.
9355.0-21). This process, in part, enables the EPA to address
the SARA Section 121 requirements of selecting a remedial action
that is protective of human health and the environment, that is
cost-effective, that attains Federal and State requirements that
are applicable or rele~ant and appropriate, and that utilizes
permanent solutions and alternative treatment technologies or
resource recovery technologies to the maximum extent practicable.
Additionally, SARA Section 121 and the guidance documents
referenced above require that EPA give preference to remedies
which employ treatment which permanently and significantly
reduces the mobility, toxicity, or volume of hazardous substances
as their principal element.
1 2
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The selection of remedy process begins by identifying
certain site-specific information to be assessed in determining
the types of response actions that will be considered for the
site. A general list of site-specific information is contained
in Section 300.68(e)(2) of the NCP. This list was used to
identify specific site and waste characteristics for Operable
Unit No. Two of the ~lear Creek/Central City site. Based upon
these site and waste characteristics, the EPA was able to reduce,
from the universe of many possible response actions, a set of
response actions and associated technologies to be considered for
Operable Unit No. Two.
Section 121(b)(1) of SARA requires that an assessment of
permanent solutions and alternative treatment technologies or
resource recovery technologies that, in whole or in part, will
result in a permanent and significant decrease in the toxicity,
mobility;" or volume of the hazardous substance, pollutant, or
contaminant be conducted. The alternative treatment and resource
recovery technologies considered included chemical fixation and
reprocessing.
The next step of the selection of remedy process is
assembling the technologies and/or disposal options into remedial
action alternatives. Pursuant to OSWER Directive No. 9355.0-19,
"Interim Guidance on Superfund Selection of Remedy", remedial
action alternatives were considered ranging from those that would
eliminate the need for long-term management (including
monitoring) at the site to alternatives involving treatment that
would reduce mobility, toxicity, or volume as their principal
element. Remedial action alternatives developed in this way will
vary mainly in the degree to which they rely on long-term site
management. Further, a no action alternative was developed as
required by Section 300.68(f)(1 )(v) of the NCP.
The remedial action alternatives developed in the
Feasibility Study for Operable Unit No. Two for the Clear
Creek/Central City site are:
No Action
Slope Stabilization
Capping
Off-site Disposal
Chemical Fixation
Reprocessing
and Runon Control
Alternatives were subjected to an initial screening to
narrow the list of potential remedial actions for further
detailed analyses using the criteria of cost, effectiveness, and
implementability (acceptable engineering practices) as directed
by 40 CFR Section 300.68(g). A description of each alternative
follows along with the results of the initial screening analysis.
1 3
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No Action Alternative
Under the No Action Alternative, there would be no
monitoring activities and no new barriers would be constructed to
restrict access to the tailings and waste rock piles. The
analysis of the No Action Alternative analysis was summarized
earlier in this document in the section entitled "Current Site
Status". The evaluation indicated that potential human health
and environmental impact could result from the tailings and waste
rock piles. In particular, catastrophic failure and runoff could
affect aquatic life and downstream water users. In addition,
ingestion of tailings or waste rock may have some effects on
human health under the future residential use scenario. The No
Action Alternative serves as a baseline and was retained for
further analysis and consideration as required by Section
300.68(f)(1 )(v) of the NCP.
Slope Stabilization and Runon Control Alternative
Slope stabilization measures eliminate or reduce
contamination of surface water resulting from collapse of
tailings and waste rock piles into the stream. Slope
stabilization measures can include excavation, grouting and
construction of retaining walls. In addition, contamination of
surface water resulting from sheet flow over the piles can be
reduced by providing runon control to the piles. Runon control
can include diversion ditches around the 'piles or culverts
through the piles.
Initial assessments indicated that slope stabilization and
runon controls are effective and can be implemented. Therefore,
these alternatives were considered further in the detailed
screening of' remedial action alternatives. The initial screening
of stabilization alternatives identified the following
alternatives by site for further study: '
Gregory Incline
o
o
o
o
Concrete Crib Wall
Timber Crib Wall'
Box Culvert
Runon Control
Big Five
o
o
o
Excavation and Slope Layback
Erosion Protection at Toe
Runon Control
National, Argo, and Quartz Hill
o
Runon Control
1 4
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The initial screening evaluation indicated that grouting and
retaining walls at the Big Five were not technically feasible.
These alternatives were eliminated and not considered in the
detailed screening.
Capping Alternative
Surface control measures will eliminate contamination of
surface water due to runoff from the mine tailings and waste rock
sites and prevent human exposure through inhalation and
ingestion. Such measures could include regrading the site to
stabilize existing slopes and control surface water runoff,
providing a containing cap over the tailings and waste rock
material, or revegetation of the site.
Six types of caps were evaluated for each site including
synthetic liners, bituminous pavement, soil cement layers, soil
cover, clay barrier/soil cover, and a modified Resource
Conservation and Recovery Act (RCRA) cap - a frost-resistant clay
barrier/soil cover).
The capping analysis indicated that containment is
effective, technically feasible and can be implemented.
Therefore, these alternatives were considered further in
detailed screening of remedial action alternatives. The
screening resulted in the following capping alternatives
further evaluation:
the
initial
for
National Tunnel
o
o
Synthetic liner
Soil cement cover
Argo Tunnel
o
o
Synthetic liner
Soil cement cover
Gregory Incline
o
o
Replacement of existing gabion wall
Synthetic liner or soil cement cover
Quartz Hill Tunnel
'0
o
Pavement of parking lots
Synthetic liner or soil cement cover
1 5
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Big Five Tunnel
o
South Side of
creek or off-
North Side of
cement cover.
Clear Creek - Remove to north side of
site disposal.
Clear Creek - Synthetic liner or soil
o
Various caps were eliminated during the initial screening.
Those caps screened out included soil cover, clay barrier/soil
cover, bituminous cover and modified RCRA cap. Most of these
covers could not be implemented on the steep slopes. More
details concerning the screening evaluation can be found in
Section 2 of the Feasibility Study Report.
Off-Site Disposal Alternative
The off-site disposal alternative considers the option of
transporting the mine tailings and waste rock material to either
a local municipal landfill or to a RCRA permitted landfill.
The most likely municipal landfill would be a facility
operated by Browning Ferris Incorporated (BFI) near 88th and
Tower Road northeast of Denver. This is a relatively new
facility which replaces a BFI facility along Colorado State
Highway 93 between Golden and Boulder, which has now been closed.
The primary concern with this alternative, however, would be
whether or not the appropriate regulatory agencies or the
operator would allow disposal of materials from a CERCLA site at
a municipal landfill even if it was not a RCRA characteristic
waste. A second concern would be the impact of such a large
volume of material on a landfill designed primarily for municipal
use.
. The second alternative for disposal of the material is
landfill at a permitted RCRA landfill. Three sites were
investigated, including the new Last Chance site, operated by BFI
near Limon, Colorado; the u.S. Ecology disposal site near Beatty,
Nevada; and the USPCI disposal site at Grassy Mountain, Utah.
Construction of the BFI site has not yet begun, but will probably
commence within the next year. The BFI site is scheduled to
provide cells of approximately 158,000 cubic yard capacity.
Several of these cells could be dedicated to disposal of the
Clear Creek mining waste. The U.S. Ecology and USPCI sites are
presently in operation.
The off-site disposal analysis indicated that off-site
disposal is a technically feasible alternative that is effective
and can be implemented. Therefore, this alternative was
considered further in the detailed analysis of remedial action
alternatives.
1 6
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Chemical Fixation Alternatives
Modifying the chemical environment within the Clear
Creek/Central City tailings and waste rock piles is a means of
reducing the mobility of metals in the piles. By changing the
chemical environment of the tailings through the addition of
neutralizing materials, the generation of acid and the subsequent
dissolution of metals can be eliminated. Such changes also would
limit dust generation and could potentially reduce the impact of
direct ingestion.
Several methods exist for the modification of the chemical
environment in the piles. The effects on the metal-specific
species present will vary according to the technique chosen for
modification. The addition of materials with large
neutralization (basic) capacity, such as kiln dust, is a common
method available for raising the pH of an acidic material with
the accompanying "fixation" of metals as metallic hydroxides.
This is a cost-effective option but its total effectiveness is
limited by the fact that some metals may remain slightly
leachable by this method. .
Another approach is fixation of contaminant metals by
chemical binding with an accompanying physical encapsulation.
This is accomplished by the addition of fixation and
solidification agents that make the contaminan~s unavailable to
oxidation and leaching. Metals that cannot be fixed by simple pH
adjustment respond to this technique. Pozzolans and cements
constitute the major portion of these fixation agents. Their
addition to an acidic material also causes an increase in pH.
Approximately thirty different fixation agents were
evaluated during the screening process. These materials were
screened for effectiveness as shown by actual leach results,
implementability and cost per unit neutralization capacity. The
details of this evaluation are provided in Section 2 of the
Feasibility Study. Based on the screening evaluation, fixation
appears to be a technically feasible containment option and was,
therefore, further investigated in the detailed analysis of
remedial action alternatives. In particular, the following
techniques/fixation agents were considered:
o
Kiln dust
o
Three proprietary fixation agents
Each of these fixation agents were subject to bench scale
tests. The resulting fixed materials were also tested for
.effectiveness by using leaching tests. The results of these
tests are summarized in the Detailed Analysis Section.
1 7
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Reprocessing Alternatives
There are many processes that have been developed to remove
metals from ores and these processes could potentially be applied
to remove toxic metals from the five waste piles. The processes
fall into two categories: pyrometallurgical - processes using
heat; and hydrometallurgical - processes using water solutions.
Facilities using these processes exist in several parts of the
country and could potentially reprocess materials from the Clear
Creek/Central City site. These processes could also potentially
be used at a facility constructed in the Clear Creek/Central City
site area.
The screening of technologies for reprocessing of tailings
and waste rock piles indicated that flotation as a reprocessing
alternative is technically feasible and can be implemented. In
addition, reprocessing of Gregory Tailings by gravity separation
to recover pyrite is technically feasible. To determine the
effectiveness and cost of reprocessing, laboratory bench scale
studies were conducted. The results are summarized in the
detailed analysis of remedial action alternatives.
Summary of Initial Screening
/
The following alternatives were considered for remediation
of the tailings and waste rock piles:
o
No Action
o
Slope Stabilization and Runon Control
o
Capping (with soil cement or synthetic liners)
o
Off-site disposal
o
Chemical Fixation (with kiln dust and three proprietary
agents)
Reprocessing (flotation or gravity concentration)
o
Various options under each alternative were. evaluated for
effectiveness, implementability and cost. Based on this
screening evaluation, options were selected for detailed
analyses. The results of the detailed analyses are provided in
the next section.
DETAILED ANALYSIS OF REMEDIAL ACTION ALTERNATIVES
Consistent with Section 300.68(h) of the NCP, the Office of
Solid Waste and Emergency Response (OSWER) Directive No. 9355.0-
19, and OSWER Directive No. 9355.0-21, the remedial action
1 8
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alternatives remaining after initial screening were further
refined and then subjected to detailed analysis. Detailed
analysis of each remedial action alternative entailed evaluation
based on the criteria derived from the NCP and SARA. These
criteria relate directly to factors mandated by SARA in Section
121, in particular Section 121(b)(1 )(A-G). The criteria follow:
o
Protection of human health and the environment
o
Compliance with legally applicable and/or relevant and
"appropriate requirements
o
Reduction of mobility, toxicity, or volume
o
Short-term effectiveness
o
Long-term effectiveness and permanence
o
Implementability
o
Cost
o
Community acceptance
o
State acceptance
The evaluation of alternatives reflects the mandate to
utilize permanent solutions and alternative treatment
technologies to the maximum extent practicable, as specified in
Section 121 of SARA.
Description of Alternatives
No Action Alternative: The No Action alternative assumes that
" there will be no remediation of tailings and waste rock piles.
The potential impacts on human health and the environment
include:
o
Collapse of tailings and waste rock piles into Clear Creek
and North Clear Creek;
o
Runoff from the waste rock and tailings piles contaminating
Clear Creek and North Clear Creek; and
o
Inhalation or ingestion of material from the piles.
The impact due to potential collapse of the Big Five and
Gregory Incline waste rock/tailings piles were evaluated in the
section entitled "Site Characteristics". As discussed in that
1 9
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section, both AWQC and MCLs would be exceeded in Clear Creek and
North Clear Creek.
The Site Characteristics section also summarized the effects
of runoff during storm events. Actual data indicate that AWQC
are exceeded in Clear Creek and North Clear Creek.
In addition to potential impacts due to runoff and collapse,
the adverse effects of inhalation of ingestion of material from
the piles were evaluated and summarized in the Site
Characteristics section (Table 1). Under current (episodic
exposurel4worst case conditions, the risk for ingestion of soil
was 1x10 (one excess cancer death in 10,000 people oveS a
lifetime). Under average conditions, the risk was 2x10- .
Inhalat!gn of dus~4under average and worst cases indicated risks
of 5xl0 to 1x10 . Under a potential future use residential
scenario, the risk of ingestion under average conditions ranged
from 8X10-5 to 1x10-4. Under maximum plausible exposure
conditions the risk ranged from 4x10-4 to 9X10-4.
Slope Stabilization and Runon Control Alternative: Based on the
detailed evaluation of criteria cited previously, slope
stabilization at the Big Five waste rock piles would be
accomplished by excavation, slope cutback and toe rip-rap to
prevent erosion and tailings collapse into Clear Creek. Based on
detailed evaluation at the Gregory Incline, the current gabion
wall would be maintained until monitoring--indicates remediation
is necessary or until the tailings are removed for reprocessing.
At that time, a permanent solution will be implemented. Runon
controls such as diversion ditches or culverts would be placed on
the upgradient side of all sites.
Slope stabilization would be a permanent solution that
eliminates collapse of the tailings and waste rock piles. The -
potential for catastrophic contamination of Clear Cre~k and North
Clear Creek would be eliminated. The runoff would also be
reduced by eliminating runon at the upgradient sides of the
piles. No reduction in impact due to dust or ingestion would be
achieved.
Cappinq Alternatives: Results of the screening analysis
indicated that because of the steep slopes only two technically
feasible capping alternatives exist for waste piles at the
National Tunnel and Argo Tunnel: synthetic liners or soil cement
covers. Because of the steep slopes at both sites, a soil cover
would not remain on a synthetic liner. A bare liner would be
extremely susceptible to damage and/or vandalism with frequent
replacement required. The soil cement cover retains the natural
color of the tailings and waste rock material and is prob~bly
preferred by the Colorado Historical Society and local residents
over a liner. Thus, a soil cement cover is the preferable
20
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capping alternative which could be implemented at the National
Tunnel and Argo Tunnel waste piles.
Before the Gregory Incline can be capped, the temporary
gabion wall would be replaced. A timber crib wall is priced
comparably with other alternatives and would probably be
preferred by the Colorado Historical Society. Alternatives
evaluated for capping were a synthetic liner and soil cement
cover. The soil cement cover is a permanent cover and is
probably preferred by the Colorado Historical Society over other
capping alternatives.
The Big Five waste rock pile provides a technical challenge
for capping and protection against flood erosion. Physical
constraints imposed by the original topography and the location
of Clear Creek along one side of the piles dictate that piles
would be regraded and rip-rap would be placed for flood
protection. The regraded piles would then be covered by a soil
cement cap. A synthetic liner could be placed, but no soil cover
could be put on the liner.
Capping of the Quartz Hill waste rock pile was evaluated for
three areas: parking lots with adjoining side slopes, an area
near the tunnel entrance, and all remaining areas from the
parking lots to the tunnel portal. The screening analysis
indicated that soil cement covers were more feasible than
synthetic liners for non-auto traffic areas. Selection of soil
cement covers would also probably be preferred by the Colorado
Historical Society over a liner. The most feasible capping
alternative for the parking lots is paving.
In all cases discussed above, runon and runoff control would
be provided. This would consist of ditches upgradient of the
capped area to divert water and ditches or culverts below the
sites to divert runoff. Capping of the tailings and waste rock
piles would be a permanent solution that removes exposure to,.
human health and the environment.
Off-Site Disposal: Under the off-site disposal alternative,
tailings and waste rock piles would be excavated and transported
for disposal at a municipal landfill site such as the landfill
operated by SFI at 88th and Tower Road northwest of Denver.
Leachate tests indicate that the tailings and waste rock are not
RCRA characteristic waste and therefore do not have to be sent to
a RCRA landfill.
Removal of the tailings and waste rock piles is a permanent
solution that removes exposure to human health and the
environment. Dust control measures must be implemented during
excavation and trucks would have to be lined and covered during
transportation.
2 1
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Chemical Fixation: In the initial screening process, kiln dust
and three proprietary materials were selected for detailed
evaluation. Waste rock/tailings from Gregory and Argo were
treated with each of the four selected fixation agents. The
resultant fixed materials were then subjected to a series of
leaching tests to document the effectiveness of the treatment.
In all cases, the fixation agents tested were effective in
reducing leachate concentrations. In some cases, leachate
concentrations were below AWQC for zinc. However, in one case,
the leachate contained extremely high values for aluminum
(27,700 ug/L). Because of this result, this fixation agent was
eliminated from evaluation. Kiln dust and two proprietary agents
were all considered further. Based on cost and leachate quality,
kiln dust is the most cost-effective. Kiln dust would be applied
at an application rate of approximately 0.58 tons per cubic yard
of available tailings and waste rock material. Approximately 9
inches of kiln dust would be mixed in with the top 9 inches of
tailings and waste rock material and then compacted.
Fixation of the tailings and waste rock piles is a permanent
solution that removes exposure to human health and the
environment.
Reprocessing Alternative: The reprocessing alternative considers
the tailings and waste rock piles as an economic resource and
recovers the inherent monetary value while generating a waste
which may not be detrimental to the environment. In order to
evaluate this option, a three-phase characterization task was
undertaken:
o
Evaluating the parameters necessary to process the waste
rock/tailings;
Determining if the resultant waste is a hazardous waste; and
o
o
Performing a cost analysis of all options.
The reprocessing studies were conducted on a bench scale
level by International Process Research Corporation of Golden,
Colorado. Two options were evaluated, namely:
o
Reprocessing of all materials; and
o
Reprocessing of all materials less than two inches with
disposal of coarse fraction as a waste rock.
22
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The results of these types of tests were evaluated to
determine if the tailings and waste rock could be reprocessed.
These tests included:
o
Tests on characterizing the waste rock with respect to
particle size distribution and selected contaminant
concentrations (copper, zinc, lead, chromium, and arsenic),
total sulfur, and precious metals (silver and gold) in
different size fractions;
o
Froth flotation tests for recovery of an economic product;
and
o
Leaching tests on waste rock and new tailings to determine
potential environmental impacts.
Results of the tests indicate that the quantities of
contaminants remaining in the new waste tailings were
significantly reduced. However, leachate concentrations were
greater than AWQC for selected contaminants such as,zinc.
Reprocessing would be a permanent solution
collapse of the tailings and waste rock piles.
tailings is produced. Leaching tests show that
can be disposed in a municipal landfill.
that eliminated
A new waste
the new tailings
Comparison of Alternatives
Listed in Table 2, in matrix format, are the key criteria
considered in evaluating and comparing alternatives. These
criteria are specified in J. Winston Porter's memorandum
"Additional Interim Guidance for FY '87 Records of Decision,"
dated July 21, 1987 and include:
o
Protection of human health and the environment
o
Compliance with legally applicable and/or relevant and
appropriate requirements
o
Reduction of mobility, toxicity or volume
o
Short-term effectiveness
o
Long-term effectiveness and permanence
o
Implementability
Cost
o
o
Community acceptance
o
State acceptance
23
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Table 2 summarizes the data developed in the Detailed
Analysis of Remedial Action Alternatives and provides a
comparison for selecting a preferred alternative for each
location. The following paragraphs summarize the evaluation
criteria for all sites.
No Action: As previously indicated, collapse would
degradat~on of stream quality below AWQC and MCLs.
does not meet AWQC. No action would not reduce the
toxicity or volume of the contaminants.
result in
Runoff also
mobility,
Stabilization and Runon controls: Degradation of stream quality
due to collapse will be eliminated. Runoff quality will not meet
AWQCi however, the volume of runoff will be reduced as a result
of runon control. As a result, contamination to the stream will
be reduced. Overall mobility of contaminants are reduced.
Relative to other alternatives (except no action), this option
has the lowest cost. The remediation is not a permanent solution
for all contamination and does not eliminate all risks to human
health and the environment.
Capping: Runoff quality will meet AWQC. Capping reduces
mobility of contaminants. Risks to human health due to .
inhalation of dust and ingestion of materials are eliminated.
Capping is a permanent remediation that removes exposure to human
health and the environment.
Off-Site Disposal: Off-site disposal reduces the mobility and
toxicity of contaminants on the site. However, the materials are
placed in another location and the ultimate volume anq toxicity
is not reduced. Existing risks to human health and the
environment are eliminated. Off-site disposal is a permanent
remedy. The cost for off-site disposal is the second highest of
the six alternatives evaluated.
Chemical Fixation: Runoff quality will meet AWQC for most
parameters. Fixation reduces mobility and possibly toxicity of
the contaminants. However, the volume of contaminated material
is increased. Fixation is a permanent remedy and eliminates
existing risks to human health and substantially reduces risk to
the environment. .
Reprocessing: Reprocessing will result in new tailings that are
not RCRA wastes. However, potential leachates from the waste
will exceed AWQC. Reprocessing reduces mobility, toxicity and
volume of the contaminants. This alternative is the only option
that reduces volume. Reprocessing reduces existing risk to human
health and the environment. This option is the most expensive of
the six alternatives evaluated even considering the value of the
minerals extracted (See Table 2). Overall, reprocessing is a
permanent solution that reduces exposure to human health and the
environment.
24
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TA8LI 2
COfGIARtSON OF ALTERNATIVES
Stabili.aUon/
Criteria 110 Action Runon Control OIppinCJ Off-Site Disposal a..ldcal Fiution Raproce..inCJ
Ar'JO 'l\lnnel
1. COllphance wi th Runoff doe. not _t Runoff wi 11 not -et Runoff will _et Ri.t. ar. r88Oved. IIunoff will -t Ii.k. ar. r88DV8d.
ARARs NoJQC. Collapse AWQC. AIiQC's. Dispo.al will _et -.t ANQC.. a.proce..ed tailinCJ.
would re.ult in RCRA. are not RCRA ...tes.
daCJradation below Laachat.. will
ttCLs and .wQC. exceed ANQCs.
2. Reduction of 1'10 reduction of R.duce. _bility Reduc.. _bility of Reduce. _bility and Reduces _bility of Reduce. ",7 and V.
8Obility, M,T,V. contaainants of toxicity --sit. contaainants of
toxici ty or concern. ..terial. ar. placed concern.
vol 1188 in another location.
]. Short Tel""8 No reduction of Eli.inate. so- Eli.inate. exi.tinCJ ExistinCJ risk to Bliainate. .xi.tinCJ Eliainat.. ..i.tinCJ
Effectiveness existinCJ risk. fro. conta.ination to risk to hU88ft h.alth hU88ft health and the ri.k to huaan health ri.k to buaan b.alth
cata.trophic .tr.a.. am be and the environaent. envir_Dt are and the .nvironaant. and the 8ftvi ronaant .
collapse of pile. cOllpleted in 6 80. CappinCJ can be eliainated. Fixation can be Reproce..iDCJ can be
and fro. runoff or coapieted in 12-18 Off-site dispo.al cOllpleted in 12-18 cOllpleted in 5 to 9
inCJe.tion. 8Onths. can be cOllpleted in . _nths. years.
t- years.
4. LonCJ Ter. Doe. not pr..ent a Doe. not present a CappinCJ is a Off-site disposal is Fixation 18 a ReprocessiDCJ is a
Effectiveness per_nent solution pal""88nent .olution per..nent re_dy a pel""88nent re_dy pel""8anent re~ pel""8anant re~
to re~atin9 risks to all risks. that eli.inate. the that eliainates the that eliainate. the that ellainates the
fro. the tailin9. need for 10n9 ter. need for 10nCJ tel""8 need for lonCJ t.1""8 nead for 10DCJ tel'.
and waste rock site ..naCJa-nt. site ..naCJa_nt. .ite 88nage-nt. si te 88naCJe-Dt.
piles.
5. IlIple_ntability Constructed with Constructed with Constructed with Constructed with Local .ills can be
available aqui~nt available available available used but are
construction constnaction constnaction currently
aqulpaant. aquip88nt. aquip818nt. inoperable.
6. Cost ($1
- Capital 0 40,000 1,969,800 7,347,800 I,Ul,800 ',~12,12',OOO
- Present Worth 0 80,000 1,969,800 7,347,100 1,.'1,100 ',~12,12',OOO
10'
7. Co~ity No A/::tion is No A/::tion is No .Action is No Action is 110 Action 18 110 A/::tiCID is
Acceptance preferred pr.ferred preferred preferred preferred preferred
alt.mative. alternative. alternative. alternative, alternative. alternative.
I. State Acceptance 110 action 18 state's preferred CappinCJ should be Cost. are the ..jor May be considered in St.t. ~d
acceptable a. an alternative. considered in future concern. future .tudie.. ancouraCJe
interi. solution studies. reproces.iaCJ if
only. -_cally
f.a.ible.
9. Overall May re.ult ill ltunon control CappinCJ is a Off-aite dispo.al i. Fix.Uon 18 . Iaproce..iDCJ i. .
Protection of adv.r.e effects due eli.inate. so- of peraanent solution a peraaneDt solution pa~t .oluUon per88llant solution
Huaan Health and to runoff and direct the risk to the that re_ve. that r88Ove. that reduce. that ra4lce.
the Environaent contact with piles. enviro_t. exposure to hU88n exposure to huaan expo.ure to huaan exposure to .......
health and the health and the beal th and the health aDd the
environaent. enyi r_t. envir-nt. 8ftvir-nt.
-------
TABU Z .cont.1
caG'1\JlI SOIt ~ -.t.TEIIJV.rtV!iI
stabUbation/
Cdtel'ia 80 Action ltuDon Contl'ol CappillCJ Off-site Di.po..l ~cal Piaation bpI'OCe.dDC)
8il) rive TUnnel
1. coat>liance vith 8uDoff~. DOt _t llUnoff vi 11 not ..et Runoff vi 11 ..et alsks al'e 1'88DY8d. 8uDoff will _t alata are 1'880¥8d.
NWts MIQC. CoUapse MIQC. MIQC's. Disposal viii ...t _st ANQCs. 88pl'ocesaed tailin'JI
_ld I'..ult in 8CRA. al'e DOt ICIA vastea.
da9l'adation below ..achate. will
..:La and MIQC. e.ceed MlQCs.
2. Reduction of 80 l'8&lction of Reduce. _bility and Reducea _bility of Reduces "ilit, and Reduce. ~ility of Reduces ",T and 9,
_bility, ",T,V. volU88 1 if contaainants of toaicity oa-site coataainants of
toaicity 01' I'epl'oc.ssed). concern. ..tel'ial. al'e placed canc:ern.
volU88 in anothel' location.
). Shol't Tera 110 reduction of Eli.inates collapse Eli8inate. e.istinC) bistinCJ !'ist to Ili8inatea eaistinC) Ili8inat.. eaiatinC)
Effectiveness eaistinC) I'iaka fl'08 potential and _st I'isk to hU8&R health hu88n heal th and the I'i.k to hu.an health risk to huaan bealth
catastrophic cotaainants in the and the enviroD88nt. enviroD88nt al'e and the envil'onMnt. and the IDvil'0D88nt.
collap.. of pil.s stl'ea.; can be C.-ppinCJ can be di8inated. ri.atiOD can be Repl'ocessinC) can be
and fl'08 runoff or C08pleted in 6 _. c08pleted in 12-18 off-site disposal C08pleted in 12-18 C08pleted in 5 to 9
inCJestion. 8Onths. can be c08pletad in 8ODtha. yeal's.
two yeal's.
4. LonCJ Tel'Wl Doea not preaant a Pl'ovides a per8&Dent c..ppinCJ is a off-site dispoaal ia ria.tiOD h a .eprocessiDC) ia a
Effectiveness perwanent solution solution to per8&Dent re..
-------
TABLE 2 (Cont)
COMPARISON OF ALTERNATIVES
criteria
.eprocessinq
110 Action
Stabi li zati on/
Runon Control
Cappinq
Off-site Disposal
Cb88ical Fixation
Gre90ry Incline
1.
COllphance wi th
MARs
2.
Reduction of
8Obility,
toxicity or
volU88
3.
Short Ter..
Effectiveness
4.
1.on9 Te rm
Effectiveness
IV
-....J
5.
laple..ntability
6.
Cost ($)
- Capital
- Present
10\
Worth
1.
Co.-mity
Acceptance
8.
State Acceptance
9.
Overall
Protection of
Huaan Health and
the Environaent
Runoff does not ...t
MIQC. Collapse
would result in
de9radation belov
ttCLs and MIQC.
No reduction of
M,T,V.
No reduction of
existin9 risks froa
catastrophic
collapse of piles
and frba runoff or
inqestion.
Does not present a
peraanent solution
to re..diatinq risks
froa the tailinqs
and waste rock
piles.
o
o
No Action is
preferred
alternative.
No Action is
acceptable a. an
interi. solution
only.
Kay re.ult in
adverse effect. due
to runoff and
collapse of vaste
rock/tailinqs piles
and direct contact
wi th plies.
Runoff will not ..et
AWI;JC.
Reduces aobility
Eliainates collapse
potential and 80st
contaainants in the
streaa; can be
cOllpleted in 6 180.
(processinq in 2
yr).
Provides a peraanent
solution to
collapse; eliainates
80st of lonq tera
site aanaqe..nt
Constructed with
available equipment.
32,500
50 , 100
No Action is
preferred
alternative.
state's preferred
alternative.
Stabilization is a
peraanent solutlon
that eli8iMtes
collapse and reduces
potential huaan and
envi ronaental
exposure.
Runoff will ..et
AWQC's.
Reduces mobility of
contaainants of
concern.
Eliainates existinq
risk to huaan health
and the environaent.
Capping can be
coapleted in 12-18
8Onths.
Capping is a
permanent re_dy
that eli8inates the
need for long ter.
site aanaCJe..nt.
Constructed with
available
construction
equip_nt.
498,300
498,300
No Action is
preferred
alternative.
Cappinq should be
considered in future
studies .
Cappinq is a
peraaneDt solution
that re80ves
exposure to huaan
health and this
environaent.
Risks are re80ved.
Disposal will ..et
RatA.
Reduces aobility and
toxicity on-site
..terials are placed
in another location.
Existinq risk to
huaan health and the
environaent are
eliainated.
Off-site disposal
can be c08lpleted in
Two years.
Off-site disposal is
a peraanent re..dy
that eliainates the
need for long tera
site aanaqe..nt.
Constructed with
available
construction
equipment.
816,400
816,400
No Action is
preferred
alternative.
Costs sre the ..jor
concern.
Off-site dispo.al i.
a peraanent solution
that re80Ve.
exposure to huaan
health and the
environaent.
Runoff viII ...t
80S t ANQC:s.
Reduce. aobility of
contaainants of
concern.
Eli8inates existinq
risk to buaan health
and the eDvironaent.
Fixation can be
coapleted in 12-18
80Dtbs .
Fixation is a
pe.--nent re..dy
that eli8inates the
need for 10n9 tera
site aanaqe..nt.
Constructed with
available
construction
equi.-nt.
395,800
395,800
No Action is
preferred
alternative.
Kay be considered in
future studies.
riuUaa 18 a
per88Dant solution
that racluce.
exposure to hu8aa
health and the
envir_t.
Risks are reaoved.
Reprocessed tailinqs
are not RatA WAstes.
lAachates will
exceed AWQCs.
Reduces H,T and V.
Eli8inates existinq
risk to huaan health
and the environaent.
Reprocesslnq can be
coapleted in 5 to 9
years.
Reprocessin9 is a
peraanent re..dy
that eliainates the
need for 10n9 tera
site aanaqe_nt.
Local aills can be
used but are
currently
inoperable.
3-3,480,000
]-3,480,000
No Action is
preferred
alternative.
State would
encourage
reproceninq if
econo8ically
feasible.
leproce.sinq is a
paraanent solution
that reduces
eXposure to huaan
heal th and the
envir_nt.
-------
rAllu.. l ant'
C'CftPAill SOlI 0' 'i.TERRATt'VES
StabUbation/
Cdtada 80 Action Runon control CappinCJ off-Sita Disposal c::ha8ical riaation Itaproca..inq
National 'l'Unnal
1. C08Iplianca with -.-ff cIoaa not _t Itunof f vi 11 not _at lunoff viiI ..at lisk. ara ra80vad. ItImoff will _t aisks ar. r880vad.
AIWts AMQC. Collaps. AMQC. ~'s. Dispo.al will _t 8O.t MIQCa. a.proc...ad tailin98
~d r..ul t in JICItA. ar. not ICItA ~st...
de9radation below Leachata. vill
~ and AMQC. a.caad ~5.
2. Reduction of 80 r~ion of Reducad 8Obility. Reduca. 80bility of 8educas 80bility and Reduc.. .ability of Iteducas ",1' and V.
8Obility, ",T,V. contaainants of todcity on-sita contaailYDt. of
toaicity or concarn. ..tarials ara placad conc.m.
vol\188 in anothar location.
3. Short T.r8 110 r~ion of EU.inat.s '0- Eliainat.. aaistinq bistin'1 risk to Eliainat.. ..i.tin'1 Eliainat.s ..i.tin'1
Effectivana.. ..istinq risk. froa contaaination to risk to hu..n h.alth h- h.al th and the risk to buaaD health risk to huaan h.alth
catastrophic straa.; can be and the anvi rOll88nt. anviron88nt ara and the anvironaant. and the anvironaant.
collaps. of pilas coaplatad in 6 80. CappinCJ can be ahainatad. riaatiOD CaD be Reproca..inCJ can be
and froa nmoff or coaplated in 12-18 off-sita di.posal coaplatad in 12-18 coaplatad in 5 to 9
in'1a.tion. _nth.. can be coapletad in 8Onths. yaar..
t- yaars.
t. Lon'1 Tar. Does not pr.s.nt a Ooa. not pra.ant a CappinCJ is a off-sita di.posal is rbati- is a Reprocassinq is a
Effectivana.s per88Dant .olution per..nant .olution panunant ra..dy a par..nant ra..dy per88R8Dt r.-dy paraanant ra_dy
to raaadiatinq risk. to aU risks. that aliainates the that ali81nahs tha that .liainatas the that aUainata. tha
froa the tailinCJs need for 10nCJ tant need for 10nCJ tar8 n..d for IODCJ tar8 naed for lon'1 tar8
and vast. rock .ita 88n8CJa..nt. sita aana'1e..nt. sita _~nt. sit. aanaCJa..nt.
pilas.
tV s. lapla..ntability Con.tructad vith Constructed vith Constructad with Conatructad with Local aiU. can be
CO
avaUabl. availabl. availabla avaUabla used but ara
aqui~nt. construction construction constructi- currently
aquipaent. aquipaant. aquipll8Dt. inoperabla.
6. COlt 1$1
- Capital 0 25,200 275.100 1,809,300 :nO, 400 1,9-3,190,000
- Prasant Worth 0 41,400 275,100 1,809,300 :UO,400 1,9-3,190,000
10'
7. Co_ity 110 Action is 110 Action is 110 Action is 110 Act i on is 110 Acti- is 110 Action is
Accaptanca prafarrad praf.nad prafanad prafeuad pr.farrad prafarrad
anarnativ.. anarnativ.. altarnativ.. altarnativa. altarnativa. altarnativ..
8. Stata Acc.ptanc. 110 Action is stata's prafarred CappiRCJ .hould b8 Co.t. ara tha ..jor Nay be conaiderad in Stat. would
acceptable a. an an.mativa. considerad in future concarn. future .tudi.s. ancoura'1.
intaria .olution studia.. reprocassinCJ if
only. aconoaicaUy
f..sibl..
9. OV.rall IIay r..ult in .- control Cappi.nc) is a Off-sit. disposal i. riaati- is a 88procaa.iDq is a
Protection of adv8r.a affect. due aliainata. 1088 of p8C'8811ent solution a p8l'8811ent solution pe~t solution pal'88llant solution
IlU88n Haal th and to ~ff and direct tha risk to the that ra80vas that r88Dvas that reca.c.. that reduc..
tha Enviroft88nt contact with pil... .nvhonaant. ..posura to huaan ..posur. to bu8an ..posur. to huaan ..po.ar. to huaan
haalth and this baal th and the haalth and the haal th and tha
anvir_nt. aDvi ronaant. anvh-t. anvh-nt.
-------
TABLE 2 ,':ontl
COMPARISON ~ AL'I'EIUtA'I'IVES
Stabilhation/
Crit.da 110 Actioa Runon Control cappinCJ Off-Sit. Dilposal dM8ical PbaUon 1teproc.sdft9
Quart& Rill TUnn.l
1. COIlpUanc. vith 8I8off doe. DOt _t ItUnoff vUl not ...t Runoff will ...t Risks ar. r880¥8d. IIImoff will -t lisk. II'. r88D¥8d.
AltARs ANQC. Collllp8. MoJQC. AWQC's. Disposal will _t -t ANQCa. aeproc.ssed tailinlJl
_ld r.sult in RatA. II'. not 8CIA ~st.s.
d8C)rldatioa below Lalchlt.S will
fICL8 and ANQC. .acaad AWQCs.
2. Reduction of 110 raduction of Reducas 8Obility. Reducas 80bility of Reducas .ability and R8cb:.s .ability of lt84Jca. M, T and V.
8Obility, M,T,V. contaainants of toxicity on-sit. CUltaainaDtS of
toaicity or concarn. ..tarial. ar. placed cOllCam.
VOIU88 in anothar location.
3. Short Tar8 110 ra41cUon of I:li81nat.. so.. I:li81natas a.iltinCJ EailtinCJ rilk to Ili8iDat.. .aJ.tinCJ I:li8inat.s ..istinCJ
Effactivan.sl ..istinCJ risks fro. conta.ination to risk to huaan haalth hU8Ut haal th and the risk to hU88D bealth rilk to hu8an h.alth
catastrophic straa.; can be and tha anviroft88nt. anvir_nt ar. and the anvb-t. and the .nvir0R88nt.
collapsa of pil.s cOllplatad in 6 80. CappinlJ can be ahainated. riaati- can be ..procassinlJ can be
and fro. runoff or coaplatad in 12-18 Off-sit. disposal c08pl.ted in 12-1' coaplated in 5 to 9
inCJ..tion. 8Onths. can be co.platad in _t.h.a. y.ars.
two yaars.
4. LonlJ T. r8 Does not pr..ant I Oo.s not pr.sant a CappinlJ is a Off-sita disposal is rbaU- i8 a ..proc.ssinCJ is a
Effactiv.nesl pel'88ftant solution p8E"88nent solution peE"88Dant ra..
-------
SELECTED REMEDY
Description of Selected Remedy
The selected remedy for Operable Unit Two of the Clear
Creek/Central City site consists of slope stabilization and runon
control.
The Remedial Investigation identified four potential
exposure pathways by which the tailings and waste rock piles
could impact human health and the environment. These potential
pathways are:
o
Collapse of tailings and waste rock piles into streams;
o
Runoff from tailings and waste rock piles into streams;
o
Inhalation of dust from the piles; and
o
Ingestion of material from the piles.
Two sites were identified that had tailings and waste rock
piles that had the potential to collapse into Clear Creek or
North Clear Creek because of unstable slopes. The two sites are
the 8ig Five Tunnel and the Gregory Incline. The Argo Tunnel
tailings and waste rock pile was also identified as being
unstable because of being undercut. If the Argo waste rock pile
fails, the structures below it would be affected, however, the
waste rock would not reach Clear Creek. Based on the effects on
human health and the environment from the potential collapse of
the 8ig Five waste rock pile into Clear Creek, it is "recommended
that the slopes on both sides of the creek be regraded and
stabilized and that rock rip-rap be placed on the toe to protect
the slope from eroding and collapsing into Clear Creek. Based on
the effects on human health and the environment from the
potential collapse of the tailings and waste rock pile at the
Gregory Incline, it is recommended that the gabion-basket wall be
maintained until monitoring indicates remediation is necessary or
until the tailings are removed for reprocessing. At that time, a
permanent solution will be implemented. Specific details
concerning the stabilization remedial actions will be developed
during Remedial Design~ The cost of this remediation is provided
in Table 3.
The second exposure pathway is contaminated water from both
runoff and runon over the tailings and waste rock piles. Runoff
can be controlled by alternatives such as: capping, chemical
fixation, reprocessing, and off-site disposal. Because of the
high cost to control runoff and the fact that the quantity of
runoff, as opposed to runon, from the five sites is small when
compared to the total runoff from the mining district (less than
0.01 percent of the total during storm events), no large-scale
30
-------
TABLE 3
SUMMARY OF COST FOR PREFERRED OPTION
Cost
Slope
Stabilization
Runon
Control
CAPITAL
Gregory Incline
National Tunnel
Quartz Hill
Argo TUflnel
Big Five
$
o
$ 25,300
19,700
154,300
31,900
231,400
Subtotal
207,800
$207,800
$462,600
Engineering, Management
and Contingency
Total Capital
$ 58,200
$266,000
129,500
$592,100
OPERATIONS AND MAINTENANCE
Five Year Evaluation
Annual Repair
$ 10,000
9,000
$ 10,000
25,000a
Annual Total
(including 20% contingency)
10,800
30,000
Five Year Recurring Total
(including 20% contingency)
12,000
12,000
PRESENT ~ORTH COST
,)
(Inflation = 4% and Interest = 10%)
330,900
718,700
TOTAL BOTH OPTIONS
$1,049,600
a
Includes repair of five percent. of the total length each year.
31
-------
remediation to eliminate runoff is proposed. However, runon
controls (upgradient ditches) have been incorporated into the
proposed remediation. The costs for runon control are shown for
all five sites in Table 3. Runon controls will substantially
reduce the quantity of water flowing over the waste rock and
tailings piles. A detailed evaluation of these quantities is
provided in the Operable Unit No. Two FS (Appendix J). Based on
the benefit achieved by providing runon control and the
relatively small cost of these measures, runon controls are
recommended. '.
When final designs
under Operable Unit No.
from tailings and waste
will be evaluated.
are completed to treat acid mine drainage
One, collection and treatment of runoff
rock piles at the treatment facilities
The third and fourth exposure pathways of concern are
ingestion and dust inhalation. As previously discussed,
acceptable risks are present for tourists and the occasional site
visitors (episodic exposure), therefore, no remedial actions are
currently recommended to alleviate ingestion and dust inhalation.
However, the Public Health Evaluation. for the site indicated
that, for a residential scenario, risks resulting from the
inhalation and ingestion exposure pathways are of some concern.
Therefore, EPA will evaluate this No Action decision when the
final remedy is selected for the site. EPA, in coordination with
the State of Colorado and local officials~ will evaluate the use
of institutional measures which would control any human health or
environmental threat that could be created by future development
upon these tailings and waste rock piles and any other piles
which the State identifies in its study. In addition, pursuant
to SARA Section 121(C), EPA will review no less than every five
years all properties where hazardous substances continue to
remain onsite and, if necessary, will reconsider this No Action
decision.
Documentation of Significant Changes
EPA identified the Slope Stabilization and Runon Control
Alternative as the preferred alternative in the Proposed Plan
which was released to the public on November 9, 1987. The key
elements of this alternative as stated in the Proposed Plan were
runon control on all five tailings and waste rock piles and slope
stabilization of the Big Five and the Gregory Incline.
At the time of the release of the Proposed Plan, EPA was
proposing to remove the gabion-basket wall at the Gregory Incline
and replace it with a crib wall. EPA intended to take the.
property owner's desire to reprocess tailings at the Gregory
Incline into account when replacing the gabion-basket wall. Since
that time, EPA has received extensive comment on this portion of
the Proposed Plan and has modified the selected remedy to address
32
-------
these concerns. The primary difference between the preferred
remedy as presented in the Proposed Plan and the selected remedy
as presented in this Record of Decision is that EPA no longer
plans to immediately replace the gabion-basket wall, but will
instead maintain the wall until monitoring indicates that the
wall needs to be replaced or until the tailings are removed for
reprocessing. The EPA will still take the owner's reprocessing
concerns into account while monitoring and maintaining the wall.
The selected remedy is a logical outgrowth of the remedy
identified in the Proposed Plan and other alternatives developed
and evaluated in the Operable Unit No. Two FS. The components of
the selected remedy were conceptually evaluated in the FS and the
selected remedy is well within the range of alternatives the
public could have reasonably anticipated EPA to be considering.
STATUTORY DETERMINATIONS
Protectiveness:
The Public Health Evaluation
City Superfund Site clearly shows
Clear Creek are being impacted by
the tailings and waste rock piles
site. These impacts include:
for the Clear Creek/Central
that Clear Creek and North
the acid mine discharges and
which are associated with the
degradation of downstream surface water quality resulting
from dissolved and suspended metals in the discharges and
resuspended metal laden sediments below the discharges;
degradation of downstream surface water quality due to
potential collapse of the tailings and waste rock piles into
either Clear Creek or North Clear Creek; and
degradation of downstream surface water quality due to runon
and runoff from the tailings and waste rock piles.
These impacts pose no immediate danger to public health because
the cities of Idaho Springs, Blackhawk, Central City, and Golden
have municipal water supply systems that meet MCLs. However,
these impacts result in severely degraded water quality affecting
aquatic life and productivity and reduced or destroyed aquatic
habitat in Clear Creek and North Clear Creek.
The first impact mentioned above is associated with the acid
mine discharges and was addressed under Operable Unit No. One.
The other two impacts are associated with the tailings and waste
.rock piles and are addressed in this Operable Unit.
The selected remedy for this Operable Unit includes slope
stabilization which will reduce the potential for a collapse of
33
-------
~
unstable tailings and waste rock piles into the creeks and runon
control measures which will divert water around the piles thereby
eliminating the impact due to runon. This portion of the
selected remedy is therefore protective and will result in an
improvement of the water quality in Clear Creek and North Clear
Creek.
The Public Health Evaluation also considered impacts to
human health resulting from inhalation or ingestion of material
from the tailings and waste rock piles. However, as discussed
earlier in this document and as shown in Table 1, there are no .
current impacts to human health from these exposure pathways.
For this reason, the selected remedy for this portion of the
Operable Unit, No Action, is protective of human health.
Under the potential future residential use scenario the risk
from ingestion of soil is of some concern. For this reason, EPA,
when selecting the final remedy, will consider institutional
measures to control future development upon the tailings piles.
Consistency With Other Laws:
Pursuant to SARA Section 121(d), remedial actions shall
attain a degree of cleanup of hazardous substances, pollutants,
and contaminants released into the environment and control of
further release which at a minimum assures protection of human
health and the environment. In addition, remedial actions shall,
upon their completion, reach a level or standard of control for
such hazardous substances, pollutants, or contaminants which at
least attains legally applicable or relevant and appropriate
Federal standards, requirements, criteria, or limitations, or any
promulgated standards, requirements, criteria, or limitations
under a State environmental or facility siting law that is more
stringent than any Federal standard (ARARs).
On December 23, 1986 EPA requested that the State of
Colorado provide a list of applicable or relevant State
requirements, standards, criteria and limitations for the Clear
Creek/Central City Site. The State responded on May 14, 1987
with a list of requirements pertaining to Operable Unit No. One.
The State did not formally submit a list of requirements for
Operable Unit No. Two. Subsequently, however, probable State
requirements were identified by State and EPA staff through
informal discussions. These informally identified requirements
were taken into account during the development of alternatives
for tailings and waste rock remediation.
EPA classified all Federal and State public health and
environmental requirements applicable or relevant and appropriate
to the tailings and waste rock remediation into three categories:
contaminant-specific ARARs, action-specific ARARs, and location-
specific ARARs. A description of each of these categories is
34
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provided in Section 2 of the Operable Unit No. Two FS. Tables
2-1 and 2-2 in the FS contain a brief description of each
potential Federal and State public health and environmental
requirement identified and EPA's analysis of each requirement's
applicability or relevance and appropriateness to the operable
unit.
EPA has determined that the contaminant-specific ARARs for
Operable Unit No. Two are the Maximum Contaminant Levels (MCLs)
established under the Safe Drinking Water Act, Ambient Water
Quality Criteria (AWQCs) established under the Clean Water Act
and State Water Quality Standards. There are currently no
identified contaminant-specific ARARs for metals in soils so EPA
relied on action-levels established through the risk assessment.
These action levels are contained in Table 2-3 of the Operable
Unit No. Two FS.
The selected remedy for Operable Unit No. Two is an interim
remedy which is consistent with the final remedy and which,
pursuant to SARA Section 121(d)(4)(A), requires the "exercise of
the "interim remedy" waiver from the contaminant-specific ARARs
mentioned in the previous paragraph, that is, the selected remedy
is only part of a total remediation that will attain such a level
or standard of control when completed. Location- and action-
specific ARARs will be met.
In accordance with SARA Section 121(d)(2)(A)(ii), EPA
intends that the final remedy will at least attain water quality
criteria established under the Acts mentioned above. However,
additional data collection and use attainability analyses are
necessary for EPA to determine if such criteria are appropriate
under the circumstances of the release or whether site-specific
modification to the criteria would more appropriately establish
clean-up goals for the site. EPA will make this determination as
part of the final remedy selection.
Cost-effectiveness and Utilization of Permanent Solutions and
Alternative Treatment Technoloqies or Resource Recovery
Technoloqies to the Maximum Extent Practicable:
The Slope Stabilization and Runon Control Alternative is a
cost-effective remedial action alternative which effectively
mitigates and minimizes threats to and provides adequate
protection of public health and the environment. Other than the
No Action Alternative, this is the least expensive alternative of
those considered. (See Table 2.) The estimated total cost for
the selected remedy is anticipated to be $1,049,600. This cost
includes operation and maintenance activities and the cost of the
five-year evaluation.
."
35
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The selected remedy does not satisfy the statutory
preference for treatment as a principal element because treatment
was found to be impracticable at this time. However, EPA leaves
open the opportunity for any future treatment or reprocessing
which can be shown to be protective of human health and the
environment and which attains Federal and State public health and
environmental requirements that are applicable or relevant .nd
appropriate.
36
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i
J
1
,
ft
o
lNTED STATES ENVIRONMENTAL P.AOTECTION AGENCY
REGION VI
999 18th STREET - SurE 500
DENVER, COlORADO 80202-2405
RESPONSIVENEss SUMMARy
CLEAR CREEK/CENTRAL CITY SUPERFUND SITE
CLEAR CREEK AND GILPIN COUNTIES. COlDRADO
OPERABLE UNIT NO. 'NO
TAIUNGS AND WASTE ROCK REKEDIATION
MARCH 29. 1988
-------
FIlW.
USPORSIVERESS SDIDIARY
OPERABLE UNIT 80. 'NO OF '1'HI
CLEAR CREEK/CEN'l'RAL CITY SUPERFUND SITE
. .
CLEAR CREEK AND GILPIR COOR'l'IES. COIDRADO
Karch 1988
This Responsiveness Summary for Operable Unit No. Two of the Clear
Creek/Central City site was prepared by the U.S. Environmental Protection
Agency (EPA) to describe the issues raised by residents of Clear Creek and
Gilpin Counties, the Colorado Department of Health, and other interested
parties regarding EPA's activities in the area and to summarize EPA',
responses to those issues. EPA is conducting a Remedial Investigation and
Feasibility Study (RI/FS) at the site to determine the nature and extent of
contamination that has resulted from historic mining activities in the area,
to develop ways of remediating the contamination found at the site, and,
finally, to select the most appropriate remedial actions.
A Responsiveness Summary is required under the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA) of 1980 (the
"Superfund" program) as amended by the Superfund Amendments and
Reauthorization Act (SARA) of 1986. The purpose of the Responsiveness Summary
is to document public concerns about proposed remedial action. and to present
EPA's responses to those concerns. This document summarizes public comments
for the period that began with the initiation of the Feasibility Study (FS)
for Operable Unit No. Two in June 1987 continuing through the public comment
period on the Operable Unit No. Two FS Report. The public comment period
closed on December 18, 1987; however, EPA accepted comments through March
1988. This report is divided into the following sections:
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 2
Section 1.
Section II.
Section III.
Appendix.
1.
Introduction and Back,round. Thi. .ection provide. a
brief introduction to the site and de.cribe. ErA'.
preferred alternatives for remedial action on Operable
Unit No. Two.
The Community Relations Prolram at the Clear Creek/Central
City Site. This section provides a brief history of
community relations activities that EPA has conducted
throughout the RI/FS at the site.
Summary of Public Comments Received and EPA's Responses.
This section summarizes comments received by EPA on
Operable Unit No. Two, categorized as follows:
. Comments and EPA's Responses. Comments received from
inception of the Operable Unit No. Two FS until the
selection of remedy was made (in Karch 1988) and
.
EPA's responses to those comments; and
Remaining Comments. Comments received for which EPA
will provide more complete answers after further
study.
Chronolo2'V of Community Relations Activities at the "Clear
Creek/Central City Site.
INTRODUCTION AND BACKGROUND
Since February 1985, EPA has been investigating public health and
environmental risks posed by mining wastes at the Clear Creek/Central City
site. The mining wastes are associated with the Argo Tunnel and Big Five
Portal on Clear Creek and the National Tunnel, Gregory Incline and Quartz Hill
Tunnel in the North Clear Creek drainage. These investigations are part of
the RI/FS at the Clear Creek/Central City Superfund site in Gilpin and Clear
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 3 .
Creek Counties.
There has been one RI conducted at the .ite; the FS h.. been
divided into the following operable unit.:
.
Operable Unit No.
Operable Unit No.
Operable Unit No.
One, Acid Kine Di.charge:
Two, tailing. and Va.te Rock Re..ediation; and
Three, Discharge and Blowout Control.
.
.
In addition to the above operable units, the State of Colorado will
investigate 1) contamination upstream of the sites and 2) regional ground
water contamination. Based on these investigations, remedial actions may be
recommended. .
The RI Report and the draft FS Report on Operable Unit No. One, which
considered mine drainage issues, .were completed and released to the public in
June 1987. The RI Report describes the results of EPA's investigation of the
entire site to date. The draft FS Report on Operable Unit No. One discusses
and evaluates methods for cleaning up contaminated mine drainage. The Record
of Decision (ROD) for Operable Unit No. One was signed September 30, 1987.
The selected remedy for Operable Unit No. One, mine drainage discharges,
included both passive and active treatment of mine drainage. Community
response to the Proposed Plan for Operable Unit No. One was guarded -- that
is, residents expressed concerns about EPA's plans and actions to solve at
great expense problems that residents believe to be ..inor.
The draft FS Report on Operable Unit No. Two discusses and evaluate.
methods of remediating contamination resulting from waste rock and tailings
piles. Alternatives for remediation of tailings and waste rock contamination
were presented to residents in EPA's Proposed Plan, dated November 9, 1987,
which was mailed to the approximately 100 individuals on the Clear
Creek/Central City mailing list. EPA's major concerns associated with
Operable Unit No. Two are potential human and environmental effects resulting
from contaminant and sediment loading caused by water running over the.
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 4
. " "\'10
tailings and waste rock pHes and into surface water bOdifi"''jotentft}lbts abuut tb
collapse of the piles, which could result in contaminatlon ot~...~am:~a r~h1~~
direct contact through inhalation or ingestion of materliFJfroirtfi. ~fli.. the fiv(" ;,
; on "~"'tta ,dn8.tJon in the. ar.'",
Six remedial alternatives were considered for remedi.f~:of~et~ittft,~~re tria
and waste rock contamination at the five lIining tunne18 9f Eli,::' ~ ..:ork At the ~itc" N-
a110.., ()l"o~erty owners tCl r~p:
'. R, .,idt: 'tE also are COTicen"
.
no action;
.
slope stabilization and runon control;
capping;
off.site disposal;
chemical fixation; and
reprocessing.
19~ f.:' 1.1:.:'(
investment in mi11ir,
.
ldit'~ .Jonf, tc -d"te ir.dic"ItL2
.
:: ail. :n5s
I1C ",",. S t£
r~'ck yil(>~
t ,', ;, II}. ~ 1 i~
.
;~1 '::-, 'h1--: r,.l...t,;cl
.
, ,
EPA's selected a1 t~rnative's vary for each of the Di1n~ ";tUr\rtJf11Jcatfbn~v'''!J1'';,
because of the different conditions at each property. t~~g~rieral,
alternatives were selected that would minimize costs and remediate the most
critical risks present at the properties.
3 r"I' ''!OJ 3ctilln at t.he:: Gr(;';l'
7 t:. ("\r-e\', .~t.
the p("\ssibJe ,=",':-':
EPA's selected alternative for dealing with potendA1"talrtngs lO'!lapsecor,c"l"1if-:
at the Gregory Incline and at the Big F1ve Tunnel 1s' slope~stiti~liiaf!onf ~Th~'
gabion wall at the Gregory Incline will be carefully monitoied:8nd~'pfac.d:~ ~
only if necessary. The selected alternative for dealing.~th'tW.ter running
over the tailings and waste rock piles and entering the creek. at the five
mine portals is to reduce wrunonw (water running on to tH~ipfli.'fr&i j'~15
by building diversion ditches above the piles. The sel~Ct.d'art.fniEiv~ for
inhalation or ingestion of material from tailings and wi8{.~~~'pii.. 1. no
action. This is an interim remedy, because some risk e~lsts for possible
future residential exposure. EPA will work with State atd local officials to
evaluat~ land use controls that will mitigate risks assdbiated with future
development.
; p,
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 5
As with Operable Unit No. One, residents expressed doubts about the need
to solve a problem they believe to be minor or nonexistent. Many re.ident.
expressed the opinion that EPA's efforts to solve proble.. at the five aines
would not have a significant overall effect on contamination in the area or in
the creeks because of the large 'quantity of waste ..terial el.ewhere that
would not be addressed during this portion of EPA's work at the .ite. Many
commenters said they would prefer that EPA allow property owner. to reprocess
the tailings as a means of cleaning them up. Residents also are concerned
that EPA's long-term presence will discourage future investment in mining in
the area. They dispute the findings of studies done to date indicating that
there is an imminent danger of collapse of tailings and waste rock piles and
the findings that there may be potential health risks related to inhalation or
ingestion of tailings dust.
Several technical activities with high visibility in the community have
been conducted thus far. They are described below.
.
Gre~ory Tailinis: EPA conducted a removal action at.~he Gregory
Incline and Tailings in March 1987 to prevent the possible collapse
of the tailings pile into North Clear Creek. EPA was concerned that
collapse of the tailings would wash a large load of metals
downstream into Clear Creek and contaminate the Colden municipal
water supply that is drawn from Clear Creek.
EPA decreased the slope of the tailings pile to stabilize it and
built a retaining wall. EPA originally planned to build a culvert
at the Cregory Tailings through an Expedited Response Action (ERA)
in the Fall of 1986. Engineering reports vere released in April and
June 1986, followed by a public comment period July 7-28, 1986. EPA
was unable to proceed with construction at that time, however, due
to the shortage of funds that preceded reauthorization of ~he
Superfund program. The temporary retaining wall was built in March
1987 under the EPA Emergency Response program. .
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 6
II.
.
Residential Yells Survey: During the RI, EPA found that shallow
ground water, a common source of water for shallow domestic vells,
is contaminated in places with metals, including lead, arsenic,
cadmium, zinc, copper, nickel, and chromium. In March and April
1987, EPA conducted a survey of area households to discover whether
residents were using shallow wells. The 8urvey revealed the
existence and use of a few shallow wells, one of which vas
contaminated with elevated levels of cadmium. EPA informed the
owner of that well of the elevated levels of cadmium, and EPA's
Emergency Response Branch conducted a Superfund removal action to
provide the well owner with clean water from the Idaho Springs
municipal water supply.
.
Passive Treatment Pilot Pro,ect: As part of the remedy for Operable
Unit No. One, a pilot project for passive treatment of mine
discharge is now underway at the Big Five Tunnel portal. EPA has
built a concrete box at the mine portal to treat some of the mine
discharge. An artificial wetland has been created in the box to
study the efficiency of this technology in reducing the levels of
metals and neutralizing the acid drainage. EPA expects to use the
results of this project to refine estimates of land requirements for
passive treatment and the types of vegetation most suited to this
technology for Operable Unit No. One.
THE COKKUNITY RElATIONS PROG'RAK AT THE CLEAR. CREEK/CENTRAL CITY SITE
EPA's community relations activities at the Clear Creek/Central City site
began in the fall of 1982 after the site was listed on EPA'. interim National
Priorities List (NPL) in July 1982. The site was placed on the final NfL in
September 1983. Community concern about EPA's activities at the site has
tended to be moderate, with occasional periods of high interest caused by
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 7
residents' concerns about the action at the Gregory Ta1l1n&., the 11& Five
pilot project, and EPA's plans for the tailin&s and wa.te rock pil... In
addition, many residents are concerned that two local property owner. will be
expected to pay for cleanup cost.. ~y resident. do not believ. local
property owners should be liable for the.e co.t. becauae they di4 not cr.ate
the problems. These two land owners purchased the properties after the
original mining that created the problems took place. loth of th... property
owners are private citizens who live near the site and have aany frien4a in
the communities. In response to community comments about the local property
owners' potential liabilities for their mining properties, EPA representatives
have had several conversations with local officials, residents, an4 the press
to listen to concerns and provide information. Much of the community concern
expressed at these meetings has focused on residents' beliefs that mine wastes
do not present a problem worthy of the high level of attention given to this
site. In additioD, there is a general
agencies because of mining regulations
restricted mining activity in the area.
antagonism toward other Federal
that are~ residents believe have
On several occasions, new information about ongoing work at the site has
been the subject of extensive news and editorial coverage in local newspapers,
in particular during EPA's removal action at the Gregory Tailings in the
Spring of 1987. Residents expressed concern about the cost and necessity of
conducting the work, particularly in light of the possibility that the
property owner, a local resident, might have to repay the &overnment later for
the costs. The pilot passive treatment project at the Big Five Tunnel portal
has been closely followed in the local newspapers as well. Local interest
among residents and in area newspapers increased again during the public
comment period on the Operable Unit No. Two FS Report on tailings and .aste
rock piles. In general, citizens have questioned the need for remed1al work
on the tailings and waste rock piles, which have been in place for many years.
Area residents and local newspapers have expressed relatively less interest in
the overall mine drainage problem than in the Gregory Tailings or the Big Five
Tunnel projects.
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 8
In preparing the Revised Community Relations Plan (CRP) completed in
January 1986, EPA conducted discussions with local official. and c08DUnity
members in September 1985. The original CRP was prepared in the fall of 1982.
To facilitate the flow of information to the c08mUnit1e., inforaation
repositories were established at the Gilpin County Court Hou.e in Central
City, the Idaho Springs Public Library in Idaho Springs, and the EPA Library
in Denver in the Fall of 1985. In December 1985, EPA prepared and distributed
to residents an initial Fact Sheet describing the site and the potential
contaminants of concern.
EPA prepared and distributed a second Fact Sheet in July 1986 regarding
the Emergency Removal Action (ERA) planned at the Gregory Tailings for the
Fall of 1986. The Agency held a public comment period on the proposed action
and held a public meeting with local residents. As described in the
Responsiveness Summary prepared for Operable Unit No. One, the ERA was later
conducted as a Superfund removal action in the Spring of 1987. Public concern
at that time was focused on the cost of the removal action, the potential
liability of the property owner (who is a life-long resident of the
community), the potential loss of an historic site, and the potential for EPA
to conduct other similar actions in the area. During this period, EPA also
expanded the number of information repositories to include the Golden Public
Library in Golden and the Idaho Springs City 8a11 in Idaho Spring., to aake
site-related documents more accessible to the community.
In August 1987, EPA placed the entire Administrative Record for the site
in the Gilpin County Court House and the EPA Library. An index to the
Administrative Record was placed in all five information repositories. In
addition, EPA further revised the CRP and signed a Memorandum of Understanding.
with the Colorado State Historical Society concerning the Gregory Tailings
removal action to assure that the action that EPA undertook at the site was
carried out in accordance with State guidelines for preserving historic sites.
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 9
The Colorado Historical Society ha. determined that the 8il Five Tunnel
portal is eligible to become a national hi.toric landmark. Federal la.
requires that any Federal agency proposing to undertake work at a location
eligible for listing as a national historic landmark demonstrate it he. taken
into account historic preservation considerations. Thua, EPA .ub.itted to the
State Advisory Council on Historic Preservation drawing. of the pa..ive
treatment system at the Big Five Tunnel portal. Upon recommendation of the
Advisory Council, EPA changed the location and materials of the fence to be
built around the passive treatment plant. These changes were deemed important
in preserving historic aspects of the tunnel.
During the survey of shallow domestic wells in the spring of 1987, EPA
prepared a letter to residents and a question-and-answer Fact Sheet -- both
designed to provide residents with information about the survey and it.
purpose -- to be handed out by the individuals taking the survey. EPA
representatives also met with local officials and area residents to discuss
the survey.
After release in June 1987 of the FS Report on Operable Unit No. One, EPA
published a question-and-answer Fact Sheet and held two public meetings in
conjunction with the public comment period from June 8 through July 7, 1987.
At the first meeting in Central City on June 16, approximately seventeen
people attended, and only one person asked a question of EPA. A local
property owner later commented to EPA that he thought the public notice for
this meeting had been insufficient, and requested an extension of the Public
comment period. About forty people attended the second meeting on June 17 in
Idaho Springs. These people had numerous questions and comments about EPA's
plans for the site. Residents again expressed doubt about the neces.ity of
taking action on mine drainages when local people do not perceive them to be
causing any problems. They also said that the high cost of the treatment cast
further doubt on the need for remediation and expressed concern about the
effects of EPA's activities on the local economy.
These concerns are
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 10
described in greater detail in the Responsiveness Suaaary prepared for
Operable Unit No. One.
The draft FS Report for Operable Unit No. Two, Tailing. and Vaste Rock
Remediation, was released on November 9, 1987. On the ...e day, EPA
published a Proposed Plan for the site, prefaced by an explanatory letter. A
public meeting was held on November 24, 1987 in Idaho SpriDg8, Colorado.
Prior to the meeting, EPA mailed copies of the Propo8ed Plan and letter to
local residents and officials. Legal announcements of the meeting were
published in the Clear Creek Courant (Idaho Springs) on October 28, 1987, in
the Weekly ReJister-Call (Gilpin County) on October 26, 1987, and in the
Golden TranscriDt (Golden) on October 27, 1987. EPA provided these newspapers
with press releases that were also published in each of these three newspapers
during the week of October 26, 1987. The public meeting occurred midway
through the public comment period, on November 24, 1987, and was attended. by
approximately fifty people. Copies of the Proposed Plan for Operable Unit No.
Two were available at the meeting. The atmosphere of the aeeting was heated,
as residents strongly expressed their doubts about EPA's plans.
Community members attending the meeting had numerous questions and
comments regarding EPA's activities in the area. Many of the residents'
comments were made in regard to the local economic effects of EPA's
activities. Several residents questioned EPA'. justification for it.
activities in the area and the accuracy of findings related to Operable Unit
No. Two. Residents were concerned that the cost of EPA'. effort. to clean up
the mine tailings and waste rock at the five mine tunnel. would be exce..ive
in light of the lar&~r volume of such materials elsewhere in the area.
Residents' concerns are described in greater detail below.
~
In response to requests made at the November 24 public meeting for an
extension of the comment period, EPA extended the closing date of the comment
period by ten days until December 18, 1987. This extension wa. announced in
press releases in the Clear Creek Courant, the Weekly Re2ister-Call, and the
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 11
Golden TranscriDt during the veek of December 7, 1987. EPA announced through
local media the delay in signing of the ROD on Operable Unit No. Tvo. '1'he
Agency accepted public comment until the final selection vas ..cIe.
III.
SUKKAllY OF POBUC COMKENTS RECEIVED AND EPA' S USPORSES
This section summarizes public concerns about the FS Report on Operable
Uni t No. Two expressed during the public cOlDIDent period. COllllllUDity cOlllllents
generally addressed: issues about the reduction of contamination from vaste
rock or tailings piles at the five tunnels relative to the total volume of
mining wastes in the area, particularly when the costs of this effort are
considered; issues about Superfund procedures, studies, and actions, such as
cleanup of the Gregory Tailings site; issues about the methods, costs, and
conclusions of the studies; issues about local economic impacts of Superfund
activities; and technical issues, raised primarily by the Colorado Department
of Health.
Many residents expressed concern about the effects of the Superfund
process on investment in future mining development. Several residents also
commented about the possible loss of the value of the metals in tailings piles
because of the liability associated with extracting metals from an NPL site.
Several local officials and two of the owners of mining properties that
are part of the Superfund lite attended the public meeting held on November
24, 1987 in Idaho Springs. Aside from county and municipal governments, the
Clear Creek and Gilpin County Metal Miners' Association (CCGCMHA) 1s the only
citizens' group that has consistently expressed interest in EPA's activities
at the site. The CCGCKHA includes a broad membership throughout the two
affected counties, as well as areas downstream of the site. As with many of
the comments made at the public meeting held for Operable Unit No. One,
residents and representatives of the CCGCHMA suggested that EPA evaluate
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 12
reprocessing of the tailings piles as a way of reducing public health and
environmental risks while providing an economic return to the c08aUD1tie..
A major concern at the site throughout the Superfund proce.. bas been the
extent to which EPA's Superfund activities may adversely impact local property
owners and future prospects for mining. A number of citizens have expre..ed
support for area property owners, both encouraging EPA to limit the financial
liabilities for local property owners, and discouraging EPA from de.troying or
removing the mining wastes before the minerals can be extracted from them.
Residents suggested that EPA should reevaluate the need for the cleanup at
this site. Residents have consistently suggested that blowout control is
important; however, few appear to support the need to clean up or stabilize
the tailings and waste rock piles. Blowouts are large releases of mine
drainage from mines whose tunnels have been temporarily blocked for a period
of time through natural silting or collapse of mine workings. The Argo Tunnel
has experienced blowouts in the past, with resulting contamination of Clear
Creek downstream to Golden. Residents criticized EPA for continuing its study
of mine tailings at the site without considering the length of time the
tailings have been in place without any perceived endangerment of human health
or the environment.
During the public meetings, EPA responded that it would consider
proposals to reprocess-~he tailings piles and that the proposed remedial
alternative would not affect the future economic value of the tailings piles.
The Agency has al.o consistently agreed that blowout control is an 18portant
issue and noted that the problem is currently under study.
The first subsection below provides a summary of
responses; the second subsection summarizes remaining
will be able to provide more complete responses after
comments and EPA'.
comment. for which EPA
further study.
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 13
A.
Summary of Comments Received During the Public Co88ent Period 8D4 BrA'.
Responses
This section categorizes questions and comments received durins the
public comment period and EPA's responses to those comments in the catesorie.
below:
1.
.
Policy Issues;
Study Methods and Findings;
Government and Superfund Procedures and Activities; and
Economic Issues
.
.
.
Policy Issues
.
Comment:
Two commenters asked what th~. cost of EPA'. studies has
been to date. One of these commenters questioned whether the high
cost of EPA's efforts is worth the outcome.
~
EPA's ReSDonse: Actual costs of the studies to date were compiled
and sent to the commenters. This same information is available to
any individual who requests it. With regard to the tailings and
waste rock, EPA has selected those actions that effectively address
the identified problems.
.
Comment: The Colorado Department of Health (CDH) recommends that
Operable Unit No. Two be redirected to evaluate all major sources of
contamination from mining waste piles in the study area to determine
the relative contribution of each source, to develop a quantitative
estimate of the environmental improvements from remediation of any
and all sources relative to the district-wide impact of mining
waste, and to select the necessary remediation based on the
significance of each source. CDH also recommends that the selection
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 14
of Applicable or Relevant and Appropriate Requirement. (ARARa), with
respect to technical feasibility and cost effectivene.., ahould also
be reexamined as a part of this redirected effort.
EPA's ResDonse: EPA has evaluated the district-wide t.pact of
mining waste in relation to the proposed remediation. EPA
recognizes the potential contamination from other .ources and these
sources will be studied in -the future by the State of Colorado. EPA
believes, however, that the current remedies are cost-effective and
will reduce contamination to the surface water.
current remediation should proceed as scheduled.
Therefore, the
.
Comment: With regard to ARARs, CDH made the following comments:
selection of the preferred alternative will require waiving several
ARARs, such as revegetation standards under the Colorado Mined Land
Act and prohibition of waste disposal in ground water (Gregory
Tailings), as they will not be met under the remediation. Discharge
standards under Colorado 40 CFR 440 are relevant and appropriate
based on past activity on the site. Resource Conservation and
Recovery Act (RCRA) ARARs are not relevant because of the mineral
waste exclusion and because testing showed them to be nonhazardous.
The wording in paragraph 5, page 2-28 of the draft FS Report, where
it is stated that Federal Water Quality Criteria (WQC) for, certain
parameters are relevant, should be changed to .ay that VQC are
relevant, with only the specifically noted parameters identified as
exceeding the criteria. As noted above, CDH believes that ARARs
should be related to the overall remedy rather than just the five
piles that now constitute the site.
EPA's ResDonse: EPA will incorporate CDH's luggestions concerning
the WQC parameters exceeding the criteria. EPA's preferred remedy
for the five piles is an interim measure. EPA will continue to
evaluate these ARARs as part of the overall remedy for the site.
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2.
For example, Colorado 40 CFR 440 will be considered ln the de.lan-
of Operable Units One and Three.
Study Methods and Findinls
.
Comment: The City Administrator of Central Clty. re.pondlna on
behalf of the City Council to EPA'. request for pUbllc coaaent.
expressed concern about the possible impacts of EPA'. preferred
cleanup alternative on the community's businesses~ In reference to
controlling runon to the parking area near the Quartz Hill .ite by
building ditches to divert water around the parking lots, the City
Administrator noted that even the presence of construction equipment
could be detrimental to the businesses because of the confusion and
noise that potential customers might find intimidating.
The City
Administrator believes that closure of the lots, even temporarily,
could cause serious problems. Construction during the 90-4&y peak
business season would be most detrimental to the businesses
according to the City Administrator. He is also concerned about the
effect of the ditches on entrances and exits. In addition, he is
concerned about the loss of parking spaces in the lots if efforts to
stabilize the slopes reduce the size of the lots. He noted that
asphalt capping, if capping is part of the solution, could enhance
the parking lots and would be beneficial to the community. The City
Administrator asked that EPA provide the City with any plana or
drawings that would affect the parking lots.
EPA's ResDonse: EPA will consider these issues during remedial
design and will consult with the City during this process.
.
Comment: The City Administrator of Central City also questioned
whether the runon control system would have an effect on the City's
drainage system. He asked where runon water would be diverted and
whether the changes created by the runon solution could create
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Clear Creek/Central City Site
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Page 16
additional risks of flood hazard for the City. The City 18 .eeking
Community Development Block Grant fund8 to resolve concerna
identified in its flood hazard report. He asked whether IPAls
efforts to control runon and the City's efforts to control
stormwater drainage could be mutually beneficial. He requested that
the City be kept informed of EPA's intentions so that the City and
EPA can coordinate future efforts.
EPA's ResDonse:
EPA will consider the effect of diverted runon
water on the City's drainage system during
will consult with the City during remedial
City informed of plans that may affect the
drainage system.
remedial design. EPA
design.~nd will keep the
City's stormwater
.
Comment: A mining engineer commented that the FS finding that
slopes at the site are unstable contradicts common sense and good
engineering practice. He said that the fact that the slopes have
stood in place for over eighty years, and probably have been subject
to some measure of flooding during that time, are indicative of
their stability. The Mayor of Idaho Springs also commented that the
mine dumps are more stable than most soils becau.e of a cementing
action that takes place in the tailings piles, and requested that
this cementing action be discussed in the FS leport. Another
commenter indicated that, because of the length of ti8e the tailings
have been in place, he does not believe that there are any
particular time pressures for removal of the tailings.
EPA's ResDonse: The stability of the
evaluated using accepted geotechnical
of the material was considered in the
waste rock at the Big Five was
techniques. The .cementing-
evaluation. After further
review of the evaluations and site inspections, EPA believes the
conclusions are correct. It should be noted that since Clear Creek
was re-routed due to the construction of Interstate Highway 70, the
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Clear Creek/Central City Site
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~
river channel has been narrowed and has undercut the toe of the
waste rock pile. This undercutting ha. resulted in some f.ilure of
the lig Five pile and has caused the current UD8table conditi0D8.
.
Comment: Regarding dhe conclusion in the FS Report that the aine
tailings must be cleaned up to prevent them from washing down8tream
and contaminating the Golden water supply during. flood, . aining
engineer said that under flood conditions, the creeks would be
contaminated with or without mine tailings. The Golden water 8upply
would be contaminated from many sources in addition to mine
tailings, so the conclusion that potential flood conditions justify
slope stabilization is not supportable. He commented that EPA
should focus its attention on preparing the Golden water treatment
plant for flood conditions rather than attempting to stabilize the
tailings and waste rock piles in the area. The Mayor of Idaho
Springs also commented that the RI report "...assumes a worst case
scenario, the collapse of tailings from a SOO-year flood collapsing
into low stream flow conditions. It would take flood conditions to
cause collapse. Flood conditions are not low stream flow
conditions. I believe these conditions are mutually exclusive, and
that 'worst case condition' is not possible."
EPA's ReSDonse: The RI Report considered a realistic scenario.
Simply, the volume of waste rock currently evaluated to be un.table
was placed in the river under low flow conditions. Under flood
conditions, the volume of unstable waste rock would have been much
greater than that used in the evaluation.
Currently, Golden can treat contaminated water. It cannot treat
large volumes for long periods of time, however. It i8 EPA'.
position to prevent contamination rather than treat it after the
fact.
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.
Comment: Several residents commented that they and other. bad Irown
up in the area and have never experienced adver.e health effect.
from the tailings. Many residents expressed .keptici.. that health
risks were of any significance. One commenter .aid that the rs
Report and Proposed Plan presented data that did not .bow or explain
risks or reach any conclusions or recommendations about ri.k8. He
said that statistical estimates of risk alone did not help bia
understand whether site contamination poses a genuine threat to
human health.
EPA's ResDonse: Risk calculations, such as those presented in the
Proposed Plan and in the FS Report, provide estimates of risk.
These estimates are based on a consistent set of assumptions, 80
that these standards can be applied to all types of conditions and
locations at a variety of Superfund sites across the country.
Current EPA guidance states that the risk for carcinogenic materials
at a site should not exceed 10-4, and preferably should be less
(e.g., 10-7). These figures refer to a range of risks that a
population may face when exposed to a specific hazard. For example,
a 10-4 risk is the risk assessors' projection that a population
exposed to a particular hazard may suffer one extra cancer death per
10,000 persons; a risk of 10-7 means there might be one excess
cancer death per 10,000,000 among a population exposed to the
hazard. The risks at the Clear Creek/Central City .ite are
presented in Table 1 of the ROD and in Chapter 10 of the II Report
issued June 8, 1987. As can be .een in table 1, current human
health risks resulting from the inhalation and ingestion exposure
pathways are minor. However, under an assumed future residential
exposure scenario, risks are present for people who .ight live on
the waste rock/tailings piles. Therefore, EPA has selected the no
action alternative for current episodic use of the piles. For
future residential use, EPA will work with State and local officials
to pursue controls to limit future residential development.
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For noncarcinogenic ..terial., EPA ha. e.tabli.hed 88X~
acceptable exposures (.reference doses.) that should not be
to protect human health.
exceeded
.
Comment: A newspaper reporter commented that so.e of the wording in
the FS Report and other documents was tentative or inexact. The
commenter noted that as a result, EPA's remedial actiona ..y not
actually occur as stated or may be only hypothetical. She also
questioned selection of passive treatment as a final alternative
when it 15 still considered experimental. An owner of one of the
mining properties at the site commented also that the use of the no
action alternative in the study made no sense and was used only as a
"scare tactic" to convince people of the necessity of EPA'. actions.
EPA's ReSDonse: When possible, EPA will change the words to be more
specific. Selection of the passive treatment system was part of the,
remedy for Operable Unit One. Passive treatment effectiveness is
currently being studied at a pilot plant at the Big Five. These
data will be used to determine final design. Final design .ay
include additional treatment to meet standards. Consideration of
the no action alternative is required under Superfund and other
environmental regulations to provide an esti8ate of the risk or
damage that will result if no remedial action is taken.
.
Comment:
One resident asked that source control be defined.
EPA's ReSDonse:
Source control is the identification and
elimination or blockage of mine drainage at it. source to prevent
further flow of contaminated water through the environment.' In
order to be more specific, EPA has changed the term to discharge
control. Discharge control includes any method to control or
eliminate the drainage from the tunnels.
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.
Comment:
A commenter asked why fresh water runon baa to be
controlled if it does not carry acid8 when it run. OV8r the tailings
piles.
EPA's ResDonse: As it mixes with .inerall in the tailina., fr..b
water will turn acidic and leach metals from the pil... Th. vater
will also carry suspended materials.
.
Comment: A newspaper reporter asked why reprocessing of tailings
was not the preferred alternative, since the Proposed Plan indicates
that reprocessing of tailings is the only way to reduce the
mobility, toxicity and volume of the tailings. Several other
commenters said they thought the costs of reprocessing presented in
the study were extremely high, relative to their own estimates. A
commenter employed by a company that conducts feasibility analyses
of reprocessing mine dump and mill tailings materials in the Clear
Creek/Central City area said that EPA's estimate of $27 million for
reprocessing the tailings at the five mine properties is
overestimated by a factor of at least ten. He asked why EPA has the
right to evaluate the proposals as if the Agency owned the property
in question. Several residents asked why the mine property owners
could not reprocess the tailings on their own as the primary means
of cleaning them up.
EPA'. ResDonse: Although reprocessing the tailing. is tbe only
alternative that meets the criterion of reduction of mobility,
toxicity and volume of the tailings piles, this criterion i. only
one of nine criteria against which an alternative is evaluated.
Other alternatives that EPA considered also were expected to reduce
mobility and toxicity but not necessarily volume. Cost estimates to
reprocess the tailings were prepared by metallurgical engineers
considered to be experts in the area of reprocessing. To ensure the
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Responsivenes. Summary on Operable Unit No. Two
Page 21
tailings had a reduced toxicity after reproce..ins. ..tal
concentrations had to be reduced to low level.. Thi. requir..ent
precludes 80me types of reprocessing. EPA ha. authority under the
Superfund law to take actions to protect public health and the
environment.
.
Comment: CDH expressed concern about conclU8ions regarding leaching
problems with the waste and tailings pile. and .aturation of .ome of
the piles. CDH said that sufficient data may not be available to
justify these conclusions. CDH also questioned whether air
monitoring data have been collected and how such data are related to
risk analyses or action levels. CDH said that the conclusion that
the inhalation pathway does not present a significant hazard may be
based on an unsubstantiated risk analysis. if air quality monitoring
has not been conducted. CDH recommends reconsidering the air
quality action levels, and suggests specific action levels in
addition to establishing background levels by air quality monitoring
prior to remedial action. Lastly. the State requests EPA to verify
that sampling of runoff from piles included maximum runoff events.
[PA's ResDonse: Site-specific air quality sample. were not
collected. Rather, site-specific data for soils and regional/local
air data were used to model worst-case scenarios. Given that worst-
case model. revealed low concentrations. no further evaluations had
been planned. However. the State ..y conduct limited air .ampling
a. part of their upstream sources study.
Runoff from the piles was collected during two .torm event. that
occurred during the RI. These storms were not maximum .torm events.
The concentrations in the runoff were extremely high. however. and
may represent maximum levels.
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,
.
Comment:
CDH commented that the statement that the abundance and
diversity of aquatic life in Clear Creek ba. been reduced due to
acid mine drainage (FS Report, page 1-32) ne~d8 to be verified by a
comparison of historic and current populationa. If the 8tat...nt
cannot be verified with data, CDH .ugge.ted qualifyina it.
EPA's lesDonse:
The statement was based on data collected before
the II was initiated. No studies were performed as part of the RI.
EPA will make that clear in the FS Report. Additional .tudies are
planned to be completed.
.
Comment: CDH commented that the discussion of tunnel discharge flow
paths (FS Report, page 1-35) should be checked for accuracy. By
example, CDH states that discharges from the Argo Tunnel and the
National Tunnel travel some distance before flowing into the creek,
and that movement through the discharge channel may affect the
suspected contribution to ground water contamination.
EPA's ResDonse: Currently, it is believed that iron hydroxide
precipitates create a .sea1. in the discharge channels, thus
minimizing infiltration. This is verified at the Argo Tunnel in
that no seeps are observed on the bank below the discharge channel
and no general ground water mound i. observed. That 18, no general
ground water rise is observed around the di8charge area.
.
Comment: CDH commented that EPA must provide further justification
for its use of the mine waste material underlying the tailina. and
waste rock piles to determine the baseline elemental analy..s or
-background,- due to the possibility that this .aterial i.
contaminated both by mine wastes above the material and by ground
water below it.
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Responsiveness Summary on Operable Unit No. Two
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EPA'. Res'Donse:
All available data were ex8llined to cleteraine
bacqroUDd conc~tration8. Some material below the tailiD18
contained elevated concentrations of .etal.. IPA deterained that
these samples were not repre.entative of background conditions, and
they were eliminated from the background .&llple.. To verify that
the background concentrations were rea.onable, the value. were
compared to published data for western .0i18. In addition, IPA
recently took additional samples both above and below the Big Five
tailings on the south side of Clear Creek. Based on analysi. of
these samples and comparisons of all gathered data, EPA ha.
concluded that the identified background concentrations are
reasonable.
.
Comment: Yith regard to slope stabilization (FS Report, page 2.41),
CDH commented that: 1) a discussion of the proposed no action
alternative at the Argo, National, and Quartz Hill Tunnels should be
included; and 2) stabilization of the undercut portions of the Argo
pile should be included in the preferred alternative 'because a slope
failure could impact people inside the structures on the slope, not
just the structures.
.
EPA's ResDonse:
The no action alternative was discussed for each
property in the ROD. The owner of the Argo pile has recently
performed .ome slope stabilization. The Superfund program i.
authorized to address human health and environmental problema only
as they are cretted by hazardous substances, pollutant., or
contaminants. Safety concerns, such as those at the Argo wa.te rock
pile, are aore appropriately addressed by other program., .uch a.
the Colorado Mined Land Reclamation Board, or by owner. of the
affected property.
.
Comment: With regard to comments made at the November 24, 1987
meeting about the Gregory Tailings retaining wall, CDH recommends
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Responsiveness Summary on Operable Unit No. Two
Page 24
that efforts at that property be directed toward a negotiated
settlement with the landowner to reprocess the pile within 8
reasonable time frame, maintain the gabion wall until completion of
the project, and construct a final 810pe that does not require a
permanent retaining wall. If settlement i8 not possible, the State
recommends that remediation plans utilize rather than remove the
gab ion wall as part of the final plan.
EPA's ResDonse: Use of the current gabion wall as part of a more
. permanent wall has been evaluated and determined not to be cost
effective. That is, the gab ion wall cannot be made more permanent
without major costs. EPA is recommending that the current gabion
wall be maintained and monitored, and replaced only when necessary.
EPA will continue discussions with the landowner about reprocessing.
.
Comment: The State commented that active erosion at the Quartz Hill
parking lot is not addressed in the FS Report, noting that this
issue should be considered. Problems associated with this erosion
include environmental and health concerns about the sediment, and
the possible safety hazard posed by cars parked on the edges of the
lot. The Department recommends regrading of the lots to provide
more stable side slopes; construction of berms around the parking
surface perimeter to control runon to the side slopes; routing of
runoff to stabilized channels; and extension of the lot back to the
Quartz Hill tailings to recover lost parking spaces. The State also
recommends that EPA consider paving the parking su~ace and sealing
the side-slopes because of the district-wide significance of this
pile. .
EPA's ResDonse: EPA has studied the active erosion at the parking
lots. As recommended by CDH, berms and ditches will be constructed
for runon control. Runoff ch~~nels will also be stabilized.
Detailed designs will be provided during the remedial design.
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Clear Creek/Central City Site
Re.pon.ivene.. Summary on Operable Unit No. Two
Page 25
Detailed de.igns will be provided during the re.ed1al de. 11ft.
Paving i. currently not planned, because analy.i. .howed there are
no potential human health effect. from inhalation of blowing dust at
the parking lots. EPA acknowledge. CDH', plana to evaluate t.pact.
due to blowing dust fro. the parking lots.
.
Comment: CDH commented that the use of .011 cover (capping) .. a
remedial technique was discarded too early in the .creen1ng procell.
CDH believes that, in contrast to the statement in the FS aeport on
page 2-61, the soil cap may have sufficient storage capacity to
reduce percolation of water into the waste significantly. In
general, the state recommends reconsideration of 80il cover and/or
revegetation as a viable leachate and erosion control technology.
EPA's ReSDonse: EPA has concluded that generation of leachate due
to infiltration is not a problem, and'therefore, a cover or .011 cap
is not needed for leachate control. Regarding erosion control,
runoff due to direct precipitation on the surface i8 a relat1~ely
minor source of contamination versus runon to the tailings and waste
rock piles. Therefore, even though a soil cap can be effective in
preventing erosion, EPA has determined that it would be
significantly less cost-effective than use of the preferred runon
controls in preventing erosion.
.
Comment: With regard to neutralization agent. (FS Report, page 2-
83), CDH commented that no discussion is given to the volume of
neutralizing agent that would be needed. The State believe. that it
is possible that the volume of kiln dust needed would negatively
impact the project to the extent that use of the next .ost
inexpensive agent (commercial lime) may be warranted.
EPA's ReSDonse: In evaluating the proposed alternatives, EPA
considered fixation of only the upper 18 inches of waste material.
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Responsiveness Summary on Operable Unit No. Two
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Given this limited depth of fixation, the volU8e incre..e (even
though significant on a small scale) 18 not a concern. For exaaple,
even a volume increase of 50 percent would add only nine incbe. to
the top of the pile.
.
,.
Comment: The State recommends that the diver.ion ditches that viII
be used to control runon at the site be lined vith .o..thina le.s
costly than concrete. The State believes that ditches .hould be
constructed in undisturbed ground if possible to minimize contact
with waste. The State also says that an operation and maintenance
(0 and M) component should be added to the cost estimate.
EPA's ResDonse: EPA has re-evaluated the lining material for the
ditches and currently believes that soil cement may be a more cost-
effective option. CDH's other recommendations will be evaluated in
the remedial design phase. 0 and M costs have been added to the
cost estimate and are provided in Table 3 of the ROD.
.
Comment:
CDH noted several typographical errors in the FS Report.
EPA's ResDonse:
corrected.
EPA appreciates the comment; these errors will be
3.
Government And Sunerfund Procedures and Activities
.
Comment: A mining engineer and representative of a local mining
organization asked what weight community comments have in the
selection of the final alternative and in EPA's decisions about the
Clear Creek/Central City site.
EPA's ResDonse: Under the Superfund program, Congress requires EPA
to consider community comments along with eight other criteria in
making a final selection of remedies. At the Clear Creek/Central
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 27 .
City aite, EPA has modified ita original plans and ia currently
considering aeveral additional changes, baaed on public C08Denta.
Superfund requirements dictate, however, that BPA clean up the aite.
These requirements do not permit the Agency to abandon. aite that
poses a threat to public health and the environment or to lover its
cleanup standards.
The other eight criteria that EPA considers in choosing. r...dy
include compliance with ARARs; reduction of mobility, toxicity, or
volume of contaminants; short-term effectiveness; long-term
eff~ctiveness; implementability; cost; State acceptance; and overall
protection of human health and the environment. These criteria are
discussed in the ROD.
.
Comment: Several residents, including owners of two of the five
mining properties, said that EPA's actions do not take property
owners' rights into account, tie up their properties for long
periods of time, have no regard for the hardships that the process
creates for them, and involve them in legal and bureaucratic issues
that put their lives as well as their properties on hold. One of
the owners alleged that EPA staff have trespassed on his property
without permission, have not properly informed his family of the
Agency's plans for the property, and have not shown concern for them
or for their rights. Another property owner said that EPA ataff,
particularly at the Gregory Tailings project, would not clean up the
area after they were finished with their work and did not follow EPA
rules for managing a hazardous waste site.
[PAIs Res~onse: [PA obtained a signed access agreement from the
property owner in question before going onto the property. BPA has
provided public notification of its activities in the past and will
provide all property owners with information and direct notification
of all Agency activities in the future. [PA staff recognize the
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 28
burdens as.ociated with being a part of the Superfund proce.. and
are committed to working a. clo.ely a. pO'lible with property owner.
in the future to resolve as aany issues a. po.sible within the
constraints of the laws and regulations under which the Agency IIUIt
operate.
.
Comment: Several commenters had questions about the co.t. of the
work that has been done for the Clear Creek/Central City .ite and
asked if EPA is under pressure to spend a .pecific amount of aoney
by a given date, regardless of needs or accomplishments. In a
similar vein, commenters challenged the motivation. of both EPA and
its contractors suggesting that the work was being done only to
maintain jobs and profits and not to accomplish necessary tasks.
EPA's ResDonse: Budgets are allocated to each site based on the
needs and requirements of that site. EPA approves each work
assignment to be performed by its contractor. on an -as needed-
basis. EPA staff are assigned to projects as needed and as 8taff
are available. The Superfund legislation was intended to accomplish
very specific goals. EPA and its contractors have met both the
spirit and the letter of the law in carrying out the required work
at this site.
.
Comment: One property owner expressed concern about the l1alted
..ount of time available to hill to cOllllent on EPA'. work on Operable
Unit No. Two and to provide a proposal to EPA for cleanup of hi.
property. The 88111e property owner commented that EPA had reque.ted
his ideas and comments, yet the Agency did not provide .ufficient
information for him to prepare a cleanup proposal. Other commenters
asked how EPA could evaluate proposals in two weeks, even if the
property owners were able to submit proposals within the time-frame
of the comment period.
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[PAIs Resoonse: EPA extended the comment period for ten day.,
through December 18, to allow more time for community C0aa8Dt on the
Proposed Plan. EPA also delayed making a decision OD the Operable
Unit until Karch 1988 to provide for a thorough review of a11
technical information and public comments. EPA .taff a,reed to
accept any comments up until the remedy was selected. In addition.
EPA staff agreed to review all plans and specifications for each
property with the property owners, as requested. EPA bas provided
the property owner with all of the technical information that is
currently available.
.
Comment:
Many citizens commented on the removal action that took
place at the Gregory Tailings in the spring of 1987. Commenters
raised several issues about the action, including the cost of the
action relative to what was accomplished; the fact that a temporary
solution rather than a permanent solution was carried out; the
contradiction between EPA's original statement that the corrective
action would last for twenty-five years and the current statement
that the solution was designed only as a short-term remedy; the fact
that solutions previously dismissed as inappropriate. such as
construction of a retaining wall, are now being considered; and the
concern of residents that work was being performed at the Gregory
Tailings only because EPA wanted to take action of some kind and the
Emergency Response division had the funding to do .0. A son of the
owner of the Gregory Tailings property said that reclaimable
tailings are nov.mixed with dump dirt and more tailings are washing
into the creek than before the removal action.
EPA's Resoonse: EPA initiated the removal action at the Gregory
Incline and Tailings to prevent a potential collapse of tailings
into North Clear Creek. The Emergency Response Branch (ERB) of EPA
is a separate branch of the Agency that is designated to respond to
emergency and short-term needs to protect public health and the
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4.
environment.. ERB typically develop8 and implellent. .hort-tem
temporary solutions under ti&ht tille constraint.. Such actions ..y
or may not have to be addressed permanently at a later date, under
less critical conditions. EPA believes that the DB re.ponded with
an appropriate solution.
.
Comment: Several citizens expressed concern about EPA'. pa.t
activities and motives, stating that EPA appeared determined to
carry out the Gregory Tailings removal action regardle8s of its
. effects on human health and the environment.
[PA's ResDonse: EPA is committed to cleaning up Superfund sites
that have been determined to be hazardous to human health or the
environment.
This is the Agency's only motive and the 80le reason
for its activities at the Clear Creek/Central City site.
Economic Issues
.
Comment: One commenter expressed concern that EPA's proposed
solutions will destroy the economic value in the tailings and create
more problems than will be solved. In reference to plans for slope
stabilization, another commenter said that a 2-to-1 slope (a 30.
gradient) as described in the Proposed Plan would ruin the property
associated with the Big Five tunnel becau8e the .lope. would be cut
back 80 extensively that there would be no flat ground left on them
where future mining or reprocessing activities could be conducted.
EPA's ResDonse: EPA selected options that would not interfere with
future reprocessing (e.g., no covers or fixation). In the area of
the Big Five, where the slopes are unstable, very little horizontal
surface area exists. As a result, very little useful area would be
affected. In addition, the stabilization would preserve waste
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
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rock/tailings for future reprocessing that would be eventually lo.t
due to collapse into the streams.
.
Comment:
Several commenters noted that inve.tor. would be reluctant
to invest in the area as long as EPA's Superfund activities vere
ongoing. One commenter noted that even the State of Colorado 1.
concerned about permitting mining properties because of the State's
potential liability under Superfund. The commentera asked how long
EPA planned to be at work in the area and when the work would be
completed, so that those who may be interested in further
development in the area could proceed.
EPA's ReSDonse: EPA's primary concern at all Superfund s1tes 1s the
protection of human health and the environment. Since the public
meeting, EPA has re-evaluated and scaled back the extent of its
planned activities in the area.
.
Comment: A local newspaper reporter requested that EPA use local
labor when doing site work in the area.
EPA's ReSDonse:
EPA is committed to
using local labor when
and other contracting
law to follow.
local
contractors can meet the regulations
requirements that EPA is required by
B.
SUMMARY OF REKAINING COKKENTS.
Several commenters asked questions that will be answered more thoroughly
during later studies, when additional and more definitive information 1s
available. These three remaining comments are summarized below, followed by
EPA's preliminary response.
.
Comment: Referring to EPA's Proposed Plan and FS Report, several
commenters asked what overall effect EPA's efforts at the five mine
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 32
properties would have on contamination in the ar.a, given the large
volume of disturbed lands, tailings, va.te rock, runoff, runon and
erosion throughout the two counties. The commenter. al.o asked if
EPA intends to clean up all of the mined area. in the two counties
and, if not, what difference will be made by cleaning up the
tailings at only the five properties that together make up the
Superfund site. In a related question, a mining engineer a.ked if
drainage might have been naturally acidic before any mining or
settlement took place in the area. If this is the ca.e, he asked
whether cleanup standards might exceed previously natural
conditions. He also asked whether improvements to water quality
from cleanup efforts at the five mine properties would be difficult
to measure because of the extensive overall contamination in the
region that continually enters the creeks from many other sources.
EPA's ResDonse: EPA and the State are currently evaluating these
issues to determine the overall effect of cleanup of the Clear
Creek/Central City site given other possible sources of
contaminants. Information regarding comparative volumes of mining
waste and disturbed lands was included in the FS Report and the
Proposed Plan to indicate that these issues are being considered.
The cleanup efforts currently proposed and selected in Operable
Units One and Two will result in a distinct and measurable
improvement in water quality.
.
Comment: One commenter expressed concern that a study of the total
effects of Superfund cleanup on the area has not been done. As an
example, this commenter questioned if a decrease of minerals in the
creek might adversely affect crops grown downstream as allegedly
occurred in the Arkansas River Valley when the Arkansas River was
cleaned up several years ago.
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 33
EPA's ResDonse: EPA'. first responsibility under the Superfund
program is to protect public health and welfare at de.isnated
Superfund sites. Established procedures have been followed
throughout the RI/FS process at the Clear Creek/Central City .ite.
As noted above, EPA is currently considering the i..ue. of natural
contamination and contamination from other .ource., a. well a. the
question about the overall effect of cleanup effort.. !PA'. .tudies
will not include a total environmental assessment for the entire
Clear Creek drainage, however.
.
Comment: The issue of blowout control was raised by several
commenters. In particular, a mining engineer commented in a letter
read at the November 24, 1987 public meeting on the possibility of
blowout at the Argo Tunnel, the inadvisability of plugging the
portal and the importance of reopening the tunnel. This commenter
advised that the tunnels be cleaned out, the water be diverted, and
the water channels be grouted to bring the mine back into
production.
EPA's ResDonse: EPA has initiated a study of blowout control.
draft FS Report on blowout control will be available for public
review in July 1988. EPA will consider the commenter's
recommendations during this study.
A
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Responsiveness Summary on Operable Unit No. Tvo
Page 34
APPENDIX
CHRONOLOGY OF COMKDHITY IELAUOHS AC'l'IVIUa AT DIE
CLEAR CREEK/Cmmw. CITY SITE
The list below summarizes community relations activities at the Clear
Creek/Central City site. In addition to the activities li.ted below, EPA has
met with area residents and local officials throughout the RI/FS.
.
EPA prepares Community Relations Plan (CRP). (October 1982)
EPA conducts on-site discussions with local officials and area residents.
(September 1985)
EPA establishes information files at three locations accessible to the
.
.
.
local communities: the Gilpin County Court House, the Idaho Springs
Public Library, and the EPA Library. (November 1985)
EPA distributes a kick-off Fact Sheet about the site. (December 1985)
EPA completes the draft Community Relations Plan. (January 1986)
EPA releases a question-answer Fact Sheet on the proposed Expedited
Response Action at the Gregory Tailings, holds a public comment period,
and sponsors a public meeting on the ERA. (July 1986)
EPA holds a public meeting on the proposed Emergency Removal Action at
the Gregory Tailings, and signs a Memorandum of Understanding with the
Colorado Historical Society. (Karch 1987)
EPA releases a question-and-answer Fact Sheet on the well survey and
.
.
.
.
.
writes an open letter to
In response to community
information repositories
residents. (April 1987)
requests, EPA expands the number of local-area
to include the Golden Public Library and the
.
Idaho Springs City Hall. (May 1987)
EPA revises the draft CRP. (June 1987)
EPA delivers historic preservation plans for the Big Five property to the
Colorado State Historical Society. (June-July 1987)
EPA distributes a question-and-answer Fact Sheet, conducts two public
meetings, and holds a public comment period on the RI/FS and Proposed
Plan for Operable Unit No. One. (June-July 1987)
.
.
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Clear Creek/Central City Site
Responsiveness Summary on Operable Unit No. Two
Page 35
.
EPA places the complete Operable Unit No. One Administrative Record for
the site in the information repositories at the Gilpin County Court House
and the EPA Library, and an index to the Administrative Record .t .11
five repositories. (August 1987)
EPA distributes the Proposed Plan for Operable Unit No. Two and . public
comment letter. (November 1987)
EPA conducts a public meeting, and holds a public comment period on the
draft FS Report and the Proposed Plan for Operable Unit No. Two,
providing notification of the public comment period in local newspapers
in legal notices and press releases. (November-December 1987)
EPA extends the public comment period through December 18 and provides
notification of the public through press releases in local newspapers.
(December 1987)
EPA announced through local media the delay in signing of the ROD on
.
.
.
.
Operable Unit No. Two. The Agency remained open to public comment until
the final selection of remedy for the operable unit was made on Karch 29,
1988.
.
RI Addendum distributed to information repositories.
(January 1988)
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