[Federal Register Volume 62, Number 146 (Wednesday, July 30, 1997)]
[Proposed Rules]
[Pages 40784-40786]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-19940]



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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 300

[FRL-5864-3]


National Oil and Hazardous Substances Pollution Contingency Plan; 
National Priorities List

AGENCY: Environmental Protection Agency.

ACTION: Notice of intent to delete Silver Mountain Mine from the 
National Priorities List.

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SUMMARY: The Environmental Protection Agency (EPA) Region 10 announces 
the intent to delete the Silver Mountain Mine site (``the site'') from 
the National Priorities List (NPL) and requests public comment on this 
proposed action. The NPL constitutes Appendix B of 40 CFR part 300 
which is the National Oil and Hazardous Substances Pollution 
Contingency Plan (NCP), which EPA promulgated pursuant to section 105 
of the Comprehensive Environmental Response, Compensation and Liability 
Act (CERCLA) of 1980, as amended. EPA and the State of Washington 
Department of Ecology (Ecology) have determined that the remedial 
action for the site has been successfully executed.

DATES: Comments on this site may be submitted to EPA on or before 
August 29, 1997.

ADDRESSES: Comments may be mailed to: Anne D. Dailey, U.S. 
Environmental Protection Agency, 1200 Sixth Avenue, Mailstop ECL-111, 
Seattle, WA 98101.
    Comprehensive information on this site is available through the 
Region 10 public docket which is available for viewing by appointment 
only. Appointments for copies of the background information from the 
Regional public docket should be directed to the EPA Region 10 docket 
office at the following address: SUPERFUND Records Center, U.S. 
Environmental Protection Agency, Region 10, 1200 Sixth Avenue, Seattle, 
WA 98101.
    The deletion docket is also available for viewing at the following 
location:
    County Clerks Office, Okanogan County Courthouse, 149 N. 3rd, 
Okanogan, Washington 98840.

FOR FURTHER INFORMATION CONTACT: Anne D. Dailey, U.S. Environmental 
Protection Agency, 1200 Sixth Avenue, Mailstop ECL-111, Seattle, WA 
98101, (206) 553-2110 or 1-800-424-4372.

SUPPLEMENTARY INFORMATION:

Table of Contents
I. Introduction
II. NPL Deletion Criteria
III. Deletion Procedures
IV. Basis of Intended Site Deletion

I. Introduction

    The U.S. Environmental Protection Agency (EPA) Region 10 announces 
its intent to delete the Silver Mountain Mine site in Okanogan County, 
Washington, from the National Priorities List (NPL) and requests public 
comment on this proposed action. The NPL constitutes Appendix B of 40 
CFR part 300 which is the National Oil and Hazardous Substances 
Pollution Contingency Plan (NCP), which EPA promulgated pursuant to 
section 105 of the Comprehensive Environmental Response, Compensation 
and Liability Act (CERCLA) of 1980, as amended. EPA identifies sites 
that appear to present a significant risk to public health, welfare, or 
the environment and maintains the NPL as the list of these sites. EPA 
and the State of Washington Department of Ecology (Ecology) have 
determined that the remedial action for the site has been successfully 
executed.
    EPA will accept comments on the proposal to delete this site for 
thirty (30) days after publication of this document in Federal 
Register.
    Section II of this document explains the criteria for deleting 
sites from the NPL. Section III discusses the procedures EPA is using 
for this action. Section IV discusses the Silver Mountain Mine site and 
explains how the site meets the deletion criteria.

II. NPL Deletion Criteria

    Section 300.425(e)(1) of the NCP provides that releases may be 
deleted from, or recategorized on the NPL where no further response is 
appropriate. In making a determination to delete a release from the 
NPL, EPA shall consider, in consultation with the state, whether any of 
the following criteria have been met:
    i. Responsible parties or other parties have implemented all 
appropriate actions required;
    ii. All appropriate response under CERCLA has been implemented, and 
no further action by responsible parties is appropriate; or
    iii. The remedial investigation has shown that the release poses no 
significant threat to public health or the environment and, therefore, 
taking remedial measures is not appropriate.
    Even if a site is deleted from the NPL, where hazardous substances, 
pollutants, or contaminants remain at the site above levels that allow 
for unlimited use and restricted exposure, EPA's policy is that a 
subsequent review of the site will be conducted at least every five 
years after the initiation of the remedial action at the site to ensure 
that the site remains protective of public health and the environment. 
If new information becomes available which indicates a need for further 
action, EPA may initiate additional remedial actions. Whenever there is 
a significant release from a deleted site from the NPL, the site may be 
restored to the NPL without application of the Hazard Ranking System.
    In the case of this site, the selected remedy is protective of 
human health and the environment. Consistent with the State Superfund 
Contract, Ecology has agreed to take over operation and maintenance of 
the site and conduct an annual inspection. EPA has conducted the first 
five-year review of the final remedy, and will also perform future 
five-year reviews.

III. Deletion Procedures

    The following procedures were used for the intended deletion of 
this site: (1) All appropriate response under CERCLA has been 
implemented and no further action by EPA is appropriate; (2) Ecology 
has concurred with the proposed deletion decision; (3) a notice has 
been published in the local newspapers and has been distributed to 
appropriate federal, state, and local officials and other interested 
parties announcing the commencement of a 30-day public comment period 
on EPA's Notice of Intent to Delete; and (4) all relevant documents 
have been made available in the local site information repositories.
    Deletion of the site from the NPL does not itself create, alter, or 
revoke any individual's rights or obligations. The NPL is designed 
primarily for informational purposes and to assist Agency management. 
As mentioned in section II of this notice, Sec. 300.425(e)(3) of the 
NCP states that the deletion of a site from the NPL does not preclude 
eligibility for future response actions.
    For deletion of this site, EPA's Regional Office will accept and 
evaluate public comments on EPA's Notice of Intent to Delete before 
making a final decision to delete. If necessary, the Agency will 
prepare a Responsiveness Summary to address any significant public 
comments received.
    A deletion occurs when the Regional Administrator places a final 
notice in the Federal Register. Generally, the NPL will reflect 
deletions in the final update following the Notice. Public notices and 
copies of the Responsiveness Summary will be made available to local 
residents by the Regional Office.

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IV. Basis of Intended Site Deletion

    The following site summary provides the Agency's rationale for the 
proposal to delete this site from the NPL.

Site Background and History

    Silver Mountain Mine is an abandoned heap-leach mining operation 
located approximately six air miles northwest of Tonasket, in Okanogan 
County, Washington. The site consists of five acres of range land on a 
358-acre tract of privately owned land. The site was placed on the NPL 
in 1984 due to concerns about a cyanide-contaminated leachate pond, 
saturated mine tailings, and the potential for arsenic and cyanide 
contamination of the regional ground water aquifer.
    The risk assessment identified arsenic and cyanide as the primary 
contaminants of concern. The Remedial Investigation (RI) identified and 
evaluated three potential sources of contaminants at the site: the heap 
leach pile, the unprocessed rock, and the mine drainage water. 
Potential exposure pathways for contaminants were identified as: On-
site soils, on-site surface water, on-site ground water in a shallow 
aquifer, and off-site ground water in the region. During the RI, the 
highest arsenic levels found were in the mined material (1080 mg/kg) 
and in the water from a stock water tank (95 ug/l). Both arsenic and 
cyanide were also found in the perched shallow aquifer just at the edge 
of the heap leach pile.
    The Feasibility Study screened twenty-three various methods of 
cleaning up the site. From this list, eight alternatives were developed 
and evaluated against criteria listed in the NCP. Alternatives ranged 
from capping on-site to treatment and off-site disposal.

Response Actions

    The Record of Decision (ROD) for Silver Mountain Mine was signed on 
March 27, 1990, and included a number of construction elements to 
implement the Remedial Action. In October 1994, EPA completed an 
Explanation of Significant Differences (ESD) to document changes in the 
Remedial Action due to unforeseen conditions encountered at the site 
during implementation of the selected remedy. The remedial action at 
the site ultimately included:

--Consolidating and contouring contaminated mine waste overburden and 
tailings,
--Covering and capping the site with a soil and clay cap,
--Fencing the site to protect the cap and allow seeded grass cover to 
develop,
--Closure of the mine entrance and diversion of the mine drainage so 
that it flows away from the site, and
--Deed restrictions on property to protect the cap.

Construction was completed during 1992 and the deed restrictions were 
finally obtained in December 1996.
    The five-year review inspection occurred on May 27, 1997, and 
determined that the remedial objectives have been achieved. The 
constructed remedy is performing as designed and is controlling the 
risks to human health and the environment as specified in the ROD and 
ESD. The cap was in excellent shape with no evidence of subsidence, 
erosion, or animal burrows. The grass cover is well established and 
provides thorough coverage of the cap; minimal weeds and woody 
vegetation were growing on the cap. The mine entrance and mine vent 
were both closed and covered with rocks.

Cleanup Standards

    The remedial action cleanup activities at the Silver Mountain Mine 
site are consistent with the objectives of the NCP and will provide 
protection to human health and the environment. The cleanup standards 
for the heap leach pile and mine dump materials and the surrounding 
soils are 200 mg/kg for arsenic and 95 mg/kg for total cyanide. 
According to the data obtained during the construction work, the 
cyanide in the soils is below detection (0.5 mg/kg), and the 
concentrations of arsenic that remain in the areas that were cleaned up 
are less than 100 mg/kg. Risks at the site have been reduced below the 
Hazard Index of 1.0 or health based levels; and for arsenic, a human 
carcinogen, the cancer risk factor has been reduced below one in ten 
thousand.
    The major source of contaminants identified in the ROD, the rock 
material from the mining operations (heap and mine dump), has been 
addressed. The mine drainage was reevaluated in the Explanation of 
Significant Differences and it was determined that the mine drainage 
did not pose an ecological threat. According to the risk assessment and 
amended risk assessment, the inhalation and ingestion of the 
contaminated soils were the major routes of exposure. The arsenic-laden 
waste rock from the mine was contained and capped. The cleanup also 
reduced the impacts to the ground water by diverting the run-on water 
away from the capped mine waste and by limiting potential leachate 
generation.

Operations and Maintenance

    The site is designed to require very little maintenance. The area 
is remote and the semi-arid climatic conditions suggest that only 
minimal maintenance is expected. The mined rock material under the 
cover is not expected to settle which is often the major cause of cap 
disturbance. The rainfall is low with an annual average precipitation 
of 11 inches/year which is primarily as snow and spring rain. It is 
expected that the Ecology personnel, per the State Superfund Contract, 
will be able to provide the annual maintenance with a minimal amount of 
work.

Five-Year Review

    The Comprehensive Environmental Response, Compensation and 
Liability Act (CERCLA or Superfund) requires a five-year review of all 
sites with hazardous substances remaining above the health-based levels 
for unrestricted use of the site. Since the cleanup of the Silver 
Mountain Mine site utilized containment of the hazardous materials as 
the method to reduce the risk, the five-year review process will be 
used to insure that the cap is still intact and blocking exposure 
pathways for human health and the environment. As indicated above, EPA 
has conducted the first five-year review and has determined that the 
remedy selected for Silver Mountain Mine remains protective of human 
health and the environment. For future five-year reviews, EPA will 
review Ecology's annual reports on the operation and maintenance at the 
site and as needed perform a five-year review inspection.

Community Involvement

    EPA published its Community Relations Plan in December 1987, after 
interviews with local residents and officials. An information 
repository was established at the Okanogan County Courthouse and all of 
the documents used to make the decision were placed there before the 
final Record of Decision was signed. All other reports and fact sheets 
were sent to the repository as they were completed. Those individuals 
on the mailing list were informed by fact sheet prior to construction 
activities on-site. No public meetings have been requested thus far.

Applicable Deletion Criteria

    One of the three criteria for site deletion specifies that EPA may 
delete a site from the NPL if ``all appropriate Fund-financed response 
under CERCLA has been implemented, and no further response action by 
responsible parties is appropriate.'' 40 CFR 300.425(e)(1)(ii). EPA, 
with the concurrence of Ecology, believes that this criterion for 
deletion has been met. Subsequently, EPA is proposing deletion of this 
site from the

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NPL. Documents supporting this action are available from the docket.

State Concurrence

    The Washington Department of Ecology concurs with the proposed 
deletion of the Silver Mountain Mine Superfund site from the NPL.

    Dated: July 17, 1997.
Charles Findley,
Acting Regional Administrator, U.S. EPA Region 10.
[FR Doc. 97-19940 Filed 7-29-97; 8:45 am]
BILLING CODE 6560-50-P