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United States
Environmental Protection
Agency
Office of
Emergency and
Remedial Response
EPA/ROD/R06-89/050
September 1989
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Record of Decision: '£*
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Homestake Mining, NM
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50272-101
REPORT DOCUMENTATION
PAGE
1. REPORT NO.
EPA/ROD/R06-89/050
X Recipient. Acceeaion No.
4. Title and Subtitle
SUPERFUND RECORD OF DECISION
Homestake Mining, MM
First Remedial Action - Final
S. Report Oil*
09/27/89
7. Author(a)
8. Performing Organization Rept No.
9. Performing Orgainiatfon Name and Addrtaa
10. ProftcVTaak/Work Unit No.
11. ContracqC) or Gr«nt(G) No.
(C)
12. SpoMoring Organization Namt and Addraaa
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
Typa of Report 1 Period Covarad
800/000
14.
15. Supplementary Nolea
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ri
16. Abetrtct (Umit: 200 word*)
The Homestake Mining Company (HMC) site consists of a uranium processing mill and two
tailings embankments in Cibola County, New Mexico, about 6 miles north of Milan. The
tailings embankments contain a combined total of 22 million tons of tailings material
covering 225 acres. Four housing subdivisions are south and southwest of the mill with
the nearest residence approximately 0.6 miles from the tailings embankments. In 1983
^elevated levels of selenium were found in offsite ground water prompting EPA to require
.MC, under a consent agreement, to supply municipal water to residents in the
subdivision south of the mill. Furthermore, HMC implemented an aquifer protection and
restoration program including ground water injection/collection efforts at the site,
which was subsequently formalized, modified and approved pursuant to requirements of the
New Mexico Water Quality Control Commission. The restoration program continued to
operate and has been largely successful in onsite containment of tailings seepage. This
Record of Decision addresses possible radon releases from the uranium mill operations
into residential subdivisions. From 1987-1989 HMC, under an Administrative Order on
Consent, conducted an investigation as to whether radon associated with the uranium mill
tailings operation might be influencing outdoor and indoor radon levels in the
subdivisions. Based on the results of HMC's investigation, EPA has determined that the
uranium mill and tailings embankments at the site are not contributing significantly to
offsite subdivision radon contamination and that it does (Continued on next page)
17. Document Analyai* a. Dmcrlptora
Record of Decision - Homestake Mining,
First Remedial Action - Final
Contaminated Media: None
Key Contaminants: None
tx Menmiara/Open-Ended Term*
NM
c. COSAT) Reid/Group
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AvailaMIt*
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None
20. Security OM« (IN* Page)
None
21. No. ofPagea
58
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(Sec ANSI-ZM.U)
See Jnenucltone en ftmara*
OPTIONAL FORM 272 (4-77)
(Formerly NT1S-35)
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EPA/ROD/RO6-89/050
Homestake Mining, MM
16. Abstract (Continued)
)
not have authority under CERCLA to address radon levels due to natural soil
concentrations. In June 1986 the Nuclear Regulatory Commission (NRC) resumed
jurisdiction over uranium mills in the State of New Mexico and issued HMC a radioactive
materials license. NRC intends to close the site pursuant to their regulations and will
coordinate their requirements with EPA.
The selected remedial action for this site is no further action for the Radon Operable
Unit. However, EPA is recommending radon reduction techniques to residents having
elevated indoor radon levels.
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RECORD OF DECISION
HOMESTAKE MINING COMPANY
RADON OPERABLE UNIT
CIBOLA COUNTY, NEW MEXICO
SEPTEMBER 1989
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION 6, DALLAS, TEXAS
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DECLARATION
FOR THE
RECORD OF DECISION
SITE NAME AND LOCATION
Homestake Mining Company
Cihola County, New Mexico
Radon Operable Unit
STATEMENT OF PURPOSE
This decision document presents the radon decision for the Radon Operable
Unit of the Homestake Mining Company (HMC) site selected by the United States
Environmental Protection Agency (EPA) 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 Oil and Hazardous Substances Pollution Contingency
Plan (NCP).
STATEMENT OF BASIS
The decision is based upon the administrative record for the Homestake Mining
Company Superfund Site. The attached index (Appendix C) identifies the items
which comprise the administrative record upon which this decision is based.
DESCRIPTION OF THE SELECTED REMEDY
The EPA has decided that it will take no further action for the Radon Operable
Unit as defined by indoor and outdoor radon concentrations in four subdivisions
near the HMC site.
This action is part of a comprehensive response action for the HMC site. To
date, pursuant to a 1983 Consent Agreement signed by HMC, alternate water has
been supplied to residents in subdivisions near the HMC site whose wells were
contaminated by tailings seepage. Remedial activities addressing remaining
tailings contaminated ground water, source control and onsite surface reclama-
tion have been and will continue to be implevented by HMC under the direction
of the U.S. Nuclear Regulatory Commission (NRC), pursuant to the facility's
NRC license, and integrated with the New Mexico Environmental Improvement
Division's (NMEID) approved aquifer protection and restoration program as
authorized by the facility's state-required Ground water Discharge Plan (DP-200)
Agency responsibilities for the remedial action at the HMC site will be
formally delineated in an agreement to be signed by the EPA and NRC.
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DECLARATION
Based on the results of the remedial investigation, EPA has determined that
the uranium mill and tailing embankments at the HMC site, though a potential
source of radon near the site, are not contributing significantly to off-site
subdivision radon concentrations. EPA has concluded that the principle cause
of elevated indoor radon in homes (homes having annual average radon concentr-
ations exceeding 4 pCi/1) is related to local, native soil sources of radon
in the subdivisions, and is a function of the type and quality of housing
construction. As a result of this finding, EPA has determined that it does
not have authority under CERCLA Section 104 to address indoor radon concentr-
ations identified as elevated in the Radon Operable Unit. The no action
decision formalized in this ROD, however, does not constitute a finding by
EPA that adequate protection has been achieved in the subdivisions. Because
8 out of 66 residences investigated for radon had annual indoor radon concen-
trations above the 4 pCi/1 action level guideline (between 4.1 and 6.7 pCi/1),
EPA is recommending radon reduction techniques to residents having elevated
indoor radon levels. House-specific radon reduction techniques were
identified during the remedial investigation and feasibility study in a
manner consistent with EPA's national radon policy.
The Nuclear Regulatory Commission and the State of New Mexico have reviewed
the proposed plan, as identified in the remedial investigation/feasibility
study (RI/FS), and Proposed Plan Fact Sheet, and support the remedy described
in this Record of Decision. (Appendices D,E)
Robert E. Layton J/., P.ET
Regional Administrator
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TABLE OF CONTENTS
PAGE
1. Site Name, Location, and Description 1
2. Site History and Enforcement Activities 1
3. Community Relations History 3
4. Scope of Radon Operable Unit 4
5. Site Characteristics 5
5.1 Meterology * 5
5.2 Geology and Hydrology 5
5.3 Radon 6
6. Summary of Site Risks 9
7. Description of Alternatives and Comparative Analysis 9
8. Selected Remedial Approach 10
9. Statutory Authority Findings 11
Figures 1-6 and Tables 1-8
REFERENCES
APPENDICES
A. Evaluation of Applicable or Relevant and Appropriate Requirements
B. Agency for Toxic Substances and Disease Registry (ATSDR)/Center for Disease
Control (CDC) Evaluation
C. Administrative Record Index
D. U.S. Nuclear Regulatory Commission Correspondence
E. State of New Mexico Correspondence
F. Responsiveness Summary
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LIST OF FIGURES
1. Site Location Map
2. Local Site Map
3. Regional Map
4. Subdivisions Map of Annual Average Indoor Radon Concentrations
5. Subdivisions Map of Annual Outdoor Radon Concentrations
6. Probability Distribution of Corrected Indoor Radon Concentrations
in Subdivisions
LIST OF TABLES
1. Measured and Corrected Indoor Radon Concentrations
2. Measured and Corrected Outdoor Radon Concentrations
3. Summary of Corrected Indoor Radon Levels by Quarterly Averages and
Subdivisions
4. Summary of Corrected Outdoor Radon Levels by Quarterly Averages
5. Indoor Radon Concentrations: Corrected Twelve-month Averages in
pCi/1 for Frame Houses and Trailers
6. Indoor Corrected Radon Concentrations (Twelve-month Averages)
Based on General Construction Type and Quality of Residence
7. Comparison of Indoor and Outdoor Corrected Radon Concentrations
8. Recommendations for Reducing Radon Concentrations in Residences
Above 4 pCi/1
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1. SITE NAME. LOCATION. AND DESCRIPTION
The Homestake Mining Company (HMC) site is located in Section 26, Township
12N, Range 10W of Cibola County, New Mexico, about 5.5 miles north of Milan
(figure 1). The site consists of a uranium processing mill and two tailing
(byproduct materials generated from milling operations) embankments situated
in the San Mateo drainage at an elevation of approximately 6,600 feet (figure
2). One tailings embankment, which is still in use, consists of two cells
covering approximately 175 acres, with tailings totaling 21 million tons
and measuring 95-100 feet high. This tailing embankment is constructed of
coarse tailings material, and is largely covered with water on top. The
second tailings embankment has not been in use since 1962, covers approx-
imately 45 acres, measures 25 feet high, and contains 1.225 million tons of
tailings. This embankment has greater than 95% of its top covered with at
least 6 inches of soil.
Four housing subdivisions are located south and southwest of the mill and
associated tailings embankments, and are known as Murray Acres, Broadview
Acres, Felice Acres, and Pleasant Valley Estates. The nearest residence
is located in Murray Acres and is approximately 0.6 miles from the center
of either tailings embankment.
2. SITE HISTORY AND ENFORCEMENT ACTIVITIES
The HMC mill has been in operation since 1958 and was originally licensed
by the Atomic Energy Commission. Milling operations were constructed and
originally operated as two distinct partnerships, the Homestake-Sapin
Partners with a milling capacity of 1,750 tons per day (tpd) and Homestake-
New Mexico Partners with a milling capacity of 750 tpd. In November 1961,
the Homestake-New Mexico Partnership dissolved and the property was ultimately
acquired by the Homestake-Sapin Partnership. The operating facilities from
both operations were combined and expanded to bring the optimal operating
capacity of the mill to 3,400 tons per day. In April 1968, the name of the
Partnership was changed to United Nuclear-Homestake Partners and in March
1981, Homestake purchased United Nuclear Corporation's interest and the
operation became Homestake Mining Company - Grants.
Since the onset of milling operations at the HMC site, an alkaline leach-
caustic precipitation process has been employed to extract and concentrate
uranium oxide from uranium ores that have historically averaged from 0.05
to 0.30 percent U308. The concentrate is a semi-refined uranium compound
known as yellowcake that averages 92 percent U308. Ore processed at the HMC
mill has primarily come from 5 underground uranium mines and an Ion Exchange
Facility in Ambrosia Lake, New Mexico. These facilities are operated by
HMC and are located about 18 miles northwest of Grants, New Mexico in the
southeastern part of McKinley County.
Tailings at the site are composed of uranium-depleted fine and coarse sand
fractions and slimes. The tailings have been and continue to he deposited
above ground on and within the active embankment by means of wet cyclones
which separate the material into coarse and fine fractions. The tailing
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piles are treated to minimize water and wind erosion. Treatment has included
stabilization with solid objects such as erosion control blankets and used
tires, by wetting with water, and with chemical agents which form a crust
on the surface of the sands.
In 1974, the State of New Mexico signed an agreement with the U.S. Nuclear
Regulatory Commission (NRC - formerly the Atomic Energy Commission) authorizing
the State to regulate uranium milling activities under the Atomic Energy Act,
as amended. After becoming an "Agreement State" in 1974, New Mexico issued
HMC a radioactive materials license for their uranium mill.
In that same year, the New Mexico Environmental Improvement Agency (now the
New Mexico Environmental Improvement Division, or NMEID) requested EPA to
assist in a survey of uranium mining and milling activities in the Grants
Mineral Belt to determine the impact of these activities on surface and
ground water in the area. The sampling program was undertaken early in 1975,
and results indicated that ground water in part of the alluvial aquifer
downgradient from the Homestake mill exhibited elevated selenium concentra-
tions. A number of residential wells in two subdivisions south of the HMC
site were subsequently found to be contaminated.
The site was placed on the National Priorities List (NPL) of Superfund sites
in September 1983, primarily due to ground water contamination. In June of
1983, as a result of the elevated selenium concentrations in off-site loca-
tions, HMC signed a consent agreement with EPA to supply municipal water to
residents in the subdivisions south of the mill. All water supply hookups
were completed during April 1985.
As a result of elevated selenium concentrations detected in the neighboring
subdivisions, HMC implemented an aquifer protection and restoration program
at the site. This program was subsequently modified and approved pursuant
to requirements of the State of New Mexico Water Quality Control Commission
under Ground Water Discharge Plan DP-200. DP-200 was initially submitted
to the NMEID in November of 1981 and last renewed in July of 1989. DP-200
requires continued operation of ground water injection and collection systems
at the site and quarterly and semi-annual monitoring of water-level and
water quality conditions with time. Monitoring results to date indicate
that injection/collection efforts under DP-200 have been largely successful
in flushing previously contaminated zones in the alluvium and underlying
Upper Chinle aquifer resulting in onsite containment of tailings seepage.
On June 30, 1987, HMC voluntarily entered into an Administrative Order on
Consent (AO) with EPA to conduct a Remedial Investigation (RI) and Feasibility
Study (FS) on radon in accordance with CERCLA. Limited data collected by
NMEID at that time suggested that radon associated with HMC's uranium mill
tailings operations might be significantly influencing indoor and outdoor
levels in the neighboring subdivisions. To address this concern, the AO
called for the performance of a RI/FS to address the levels and sources of
radon that may impact the four subdivisions southwest of the HMC mill and
tailings embankments. HMC conducted the RI/FS studies with oversight by
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EPA between October 1987 and January 1989, and completed final RI/FS documents
in July 1989. The contents of these documents form the basis of this ROD.
In June 1986, at the request of the Governor, the State of New Mexico returned
its regulatory responsibility for uranium mills hack to NRC. NRC subsequently
issued HMC Source Materials License SUA-1471 governing mill operations and
tailings disposal activities at the site. Discussions between EPA, NRC, and
the NMEID followed in order to determine the most timely and effective way
to oversee regulatory requirements at the site. Results of these discussions
are to be formalized in an agreement between EPA and NRC governing remedial
action at the HMC site. In this regard, NRC will coordinate its ground
water requirements pursuant to 10 CFR 40, Appendix A with NMEID, and when
mill operations are discontinued will require HMC to implement a final mill
site reclamation plan for long-term stabilization and closure (200-1000
years).
Present milling rates continue to be approximately 18,000 to 19,000 tons
per month with an operating schedule of seven days per week.
3. COMMUNITY RELATIONS HISTORY
There has been some media interest in the HMC Superfund site, most of which
occurred during the site's initial NPL listing and in response to EPA's
decision to extend the Milan public water supply to subdivision residents.
Since installation of alternate water supplies in 1985, interest from
individual citizens in subdivisons near the HMC site has been low to moderate.
EPA published and distributed a fact sheet in October 1986 updating interested
citizens on the status of the HMC site, and announcing plans for further
radon studies in subdivision areas. In August of 1987, in accordance with
the June 1987 AO, a letter was sent to all subdivision homeowners inviting
them to participate in a 15-month radon study. In order to answer questions
related to the proposed study, EPA distributed a second fact sheet in
September 1987 and on September 22, 1987, held a public information meeting
at the Cibola County Convention Center in Grants, New Mexico.
HMC received acceptance letters along with completed questionaires from 66
of a possible 67 homeowners for preliminary and long-term indoor radon
monitoring. Participating residents received results of the first 6 months
of monitoring in June 1988, were sent monitoring results for months 7 through
9 in October 1988, and results for months 10 through 15 in September 1989.
Notice of EPA's Proposed Plan was provided to potentially affected persons
through newspaper notice on July 19, 1989, and was followed by a direct
mailing to individuals and groups on the site mailing list. The mailing
consisted of a fact sheet describing the results of the radon investigations
and the Proposed Plan for no action. The Administrative Record for the
Radon Operable Unit was sent to the New Mexico State University Grants
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Library on July 17, 1989. The public comment period on the Proposed Plan
was established from July 31, 1989, through August 28, 1989. The fact sheet
provided the opportunity for a public meeting on the Proposed Plan, and a
request for such a meeting was received on August 17, 1989. The requested
public meeting was announced in the local newspaper on August 18 and held in
Grants, New Mexico on August 28, 1989. To accommodate the public meeting,
the comment period was extended by EPA through September 1, 1989. Comments
received are addressed in the Responsiveness Summary (Appendix F).
4. SCOPE OF RADON OPERABLE UNIT
Environmental concerns at the HMC site involve potential or actual releases
of hazardous substances, pollutants, or contaminants to air, groundwater,
and soils. As a result, EPA has grouped environmental concerns at the site
into three categories or operable units. These are:
- OU One: Tailings seepage contamination of ground water aquifers.
- OU Two: Long-term tailings stabilization, surface reclamation, and
site closure.
- OU Three: Radon concentrations in neighboring subdivisions.
As discussed in Section 2.0 above, specific environmental concerns and
problems at the HMC site have been addressed by either EPA, NMEID, or NRC
since inclusion on the NPL. To date, OU One has been addressed by both EPA
and NMEID. EPA required HMC to provide neighboring subdivisions with alternate
water supplies (1983 Consent Agreement with HMC) in response to off-site
tailings seepage contamination of domestic wells, while NMEID has required
HMC to operate an aquifer protection and restoration program in areas
contaminated by tailings seepage pursuant to New Mexico Water Quality Control
Commission Regulations (Ground Water Discharge Plan DP-200). Alternate water
was extended to the neighboring subdivisions in 1985, usage costs pre-paid by
HMC for ten years, and the Water Right transfered to the Village of Milan,
New Mexico by quitclaim deed. As discussed earlier, the aquifer protection
and restoration program has been effective in reversing natural ground water
flow gradients in the San Mateo alluvial and Upper Chinle aquifers and
containing tailings seepage contamination on HMC property. On July 27, 1989,
this restoration program was renewed for a period of 5 years by NMEID.
OU One is also being addressed by NRC under mill tailings regulations in
10 CFR 40, Appendix A, pursuant to the Atomic Energy Act of 1954, as amended.
To date, NRC has implemented a detection monitoring and hazardous constituent
data gathering program at the site and has established ground water pro-
tection standards and points of compliance for the tailings disposal area.
Monitoring data collected under the direction of NRC indicate that ground water
protection standards are exceeded at established onsite point of compliance
wells, and therefore NRC has requested HMC to submit a corretive action plan
for ground water. NRC will, in conjunction with NMEID's requirements, require
HMC to implement a corrective action program at the site, with the objective
of long-term remediation of tailings contaminated ground water.
OU Two above is being addressed by NRC under mill tailings regulations in
10 CFR 40, Appendix A. In accordance with these regulations, NRC will
require HMC to submit a final reclamation plan for NRC approval, and upon
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HMC's decision to terminate its operations, to implement the plan for the
tailings disposal area which meets the technical requirements of 10 CFR 40,
Appendix A, as amended, which conform with EPA standards in 40 CFR 192.
These activities will address long-term stabilization and closure of the
tailings disposal area. To date, HMC has implemented a land clean-up program
for windblown tailings as required by 10 CFR 40, Appendix A and NRC licensing
requirements, and will continue this program pursuant to NRC requirements
until the site is closed. HMC has also submitted a reclamation plan to NRC
as required by Source Material License SUA-1471. NRC is currently reviewing
this plan.
The third OU is authorized by this ROD and addresses radon concentrations
in neighboring subdivisions. The subdivisions themselves are located south
and southwest of the HMC site. Limited data collected by NMEID prior to
conduct of the radon RI suggested that the HMC mill and tailings embankments
might significantly influence radon concentrations in the subdivisions and
thus pose a threat to human health and the environment. As a result, EPA
required an investigation addressing the concentrations and possible sources
of radon in the subdivisions. The purpose of this ROD is to discuss the
results of the radon investigation and formalize EPA's decision that no
additional action for off-site radon is necessary.
5. SITE CHARACTERISTICS
5.1 Meterology
The HMC site area has an arid to semi-arid continental climate which receives
more than 60 percent sunshine each day, on average, throughout the year.
On an annual basis, winds are moderate and are primarily from the southwest.
Average yearly precipitation is about 10 inches, most of which occurs in
the summer with generally dry conditions persisting year-round.
5.2 Geology and Hydrology
The HMC site and subdivisions are located on the northeast flank of the Zuni
Uplift, a tectonic feature which is characterized by a core of Precambrian
crystalline basement rocks partially mantled by Permian and Triassic sedimen-
tary rocks. The Zuni Uplift is surrounded by several tectonic depressions,
including the Gallup Sag to the west-southwest and Acoma Sag to the southeast,
Major faults occur along the southwest flank of the Zuni Uplift and a number
of minor faults are mapped in the remainder of the region. No active major
or minor faults are known to be in the vicinity of the site. Figure 3
summarizes the region's geography.
The site is underlain by the San Mateo alluvium to depths of over 120 feet.
The alluvium is generally sandy silt; however, two distinct sand and gravel
horizons occur at the top and bottom of the unit. The lower sand and gravel
horizon is relatively continuous throughout the area and is a source of
water in the region. Ground water in the San Mateo alluvium flows south-
west north of the HMC site. Directly underlying the alluvium is the Chinle
Formation (with Upper and Lower members) which is in turn underlain by the
San Andres Limestone. As discussed earlier, the San Mateo alluvium and
Upper Chinle formations are aquifers, have been locally affected by seepage
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from the tailings facility, and have been addressed hy NMEIO's Ground Water
Discharge Plan.
The HMC mill and subdivisions are located in the Arroyo del Puerto Valley
which is encircled by a number of mineral deposits. To the west-northwest
is Haystack Mesa where uranium was first discovered in the Grants Mineral
Belt. To the north is Ambrosia Lake, the densest uranium mining and mine
ventilation location in the United States. There are also open pit uranium
mines, and therefore, outcropping mineralizations at the surface located in
the various mesas between Ambrosia Lake and the Arroyo del Puerto Valley.
A number of surface excavations are also found in and around the mesas to
the east and northeast. To the northeast is the San Mateo Valley which
drains air flow from the north side of Mount Taylor where the largest and
deepest uranium mine is located. To the east is the Lobo Canyon drainage
which also exhibits the residues of several past mining ventures.
The surface water regime of the Mill Site is influenced by the arid to
semi-arid climate of the region, the relatively medium to high permeability
of the soils and the exposed bedrock in the watersheds. The San Mateo
drainage basin which includes the mill site has a drainage area of approx-
imately 291 square miles. The only surface water bodies are several stock
ponds, some small ephemeral ponds, and an undetermined number of springs on
the flanks on Mount Taylor. Nor\g of these water bodies are affected by the
Mill operations, because they are geographically remote and not hydrologically
connected with the site.
5.3 Off-site Radon
The specific element of concern addressed for this Operable Unit is radon-222,
which is the first decay product of radium-226. Radon is an inert gas that
decays with a half-life of 3.8 days into short-lived, primarily alpha-emitting
radon progeny. Radon levels were monitored in the following subdivisions
south and southwest of the HMC site during the RI: Murray Acres, Broadview
Acres, Felice Acres, and Pleasant Valley Estates. The primary objectives
of the radon RI were:
- to accurately measure the annual average indoor radon concentrations in
dwellings located near the mill;
- to accurately measure the annual average outdoor radon concentrations in
air in the vicinity of the residences located in the subdivisions; and
- to access the significance of the potential influence of the mill and
tailings embankments on radon levels in the subdivisions.
A preliminary radon screening program was initiated in October of 1987, after
66 of a possible 67 homeowners indicated their willingness to participate
in the study. Results of the preliminary three-day screening indicated a
range of indoor radon concentrations from 1.6 to 12.1 pCi/1. In the absence
of finding any acute concentrations (exceeding 20 pCi/1), the radon RI
focused on long-term radon evaluations. Integrated radon concentrations
were measured during a fifteen-month period in three-month intervals. Con-
currently, similar integrated radon measurements were made at 28 outdoor
locations within the four subdivisions.
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A fifteenth-month period (five quarters: October - December 1987, January -
March 1988, April - June 1988, July - September 1988, and October - December
1988) was selected to cover the four seasons of the year and to provide
measurement for two winter month periods when radon concentrations are
usually the highest inside houses due to the homeowner attempts to keep homes
tightly sealed against the weather.
Indoor radon data are presented in Table 1 for each residence studied, by
lot and block number within each housing subdivision and for each of the
five quarters. Both measured and corrected values are presented in this
Table. Measured concentrations were corrected by determining the response
of a detector to known radon concentrations.
Measured values were calibrated by the following factors for each successive
quarter: 1.21, 1.22, 1.18, 1.15, and 1.14. The annual average columns in
Table 1 reflect the average for the first four quarters; the second four
quarters; and the annual average obtained by combining and averaging the
first and fifth quarters (both winter quarters - October through December)
with the middle three quarters, respectively. This third calculation gives
equal quarterly weight to the first and fifth quarters of the radon survey
period. Averages were not calculated for residences where some portion of
the data was missing. Collectively, data is missing for one or more quarters
for seven residences. In four cases only one" quarter's data is missing, in
two cases two quarter's data are missing, and in the third case, data are
not available for three of the five quarters studied. As Table 1 indicates,
the highest measured quarterly radon concentration in homes with incomplete
data is 2.9 pCi/1, which is equivalent to a corrected radon concentration
of 3.5 pCi/1. Primary reasons for loss of data were monitors which were
not collected due to inability to contact the residents. As a result,
complete data are available for 59 living units. Footnotes to Table 1
describe the specific reasons for incomplete data. Figure 4 shows the
corrected annual average radon concentrations for each of the 59 residences.
These averages were obtained by combining and averaging both winter quarters
with the middle three quarters.
Measured and corrected outdoor radon data for twenty-eight locations are
presented in Table 2. Detector locations are identified in terms of the
nearest residence and cover the same period of five quarters covered by the
indoor radon study. The calibration factors determined for each quarter
for the first through the fifth quarters were 0.75, 0.47, 0.53, 0.79 and
0.95. The last 3 columns of Table 2 contain the corrected annual average
radon concentration for the first 4 quarters; the second 4 quarters; and
the annual average obtained by combining and averaging the first and fifth
quarters results (both winter quarters - October through December) with the
middle three quarters, respectively. Figure 5 shows the 28 outdoor monitor
locations and corresponding corrected outdoor annual average radon
concentrations. These averages were obtained by combining and averaging
both winter quarters with the middle three quarters.
Table 3 presents a summary of corrected indoor radon concentrations by
quarter and subdivision, and Table 4 a similar summary for corrected outdoor
concentrations. The overall annual average indoor radon concentration in
the 59 houses is 2.7 pCi/1. The annual average outdoor radon concentration
for the 28 monitoring stations is 1.9 pCi/1. Seasonal variation occurred
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in the indoor radon concentrations evidenced hy higher levels in the quarters
having the coldest weather. Only eight residences have annual average
radon concentrations greater than 4 pCi/1 (12% of the total houses in the
subdivision). These eight values are 6.7, 6.2, 5.1, 4.6, 4.5, 4.2, 4.2,
and 4.1 pCi/1. There are seventeen residents residing in these eight
residences.
Tables 5 and 7 present and compare indoor and outdoor radon concentrations
hy subdivision and by the quality and type of home construction. Table 6,
together with Figure 6, present indoor radon data in three concentration
groupings as a function of the quality and type of home construction.
Analysis of the radon data collected during the RI, and summarized in
Tables 1-7 and Figures 4-6, allow the following observations to be made:
- Average radon concentrations for trailers are consistently lower than
the average concentrations for houses;
- Dwellings with the highest radon concentrations (4.7-6.7 pCi/1)
consists of frame houses, two with crawl spaces, one with a slab,
and no trailers;
- In most cases, trailers have indoor concentrations which are comparable
with outdoor radon concentrations indicating significant indoor/
outdoor air exchanges;
- No definitive correlation is apparent between the distance of individual
homes from the HMC mill and tailings embankments and annual average
indoor radon concentrations;
- No definitive correlation is apparent between the distance of outdoor
radon monitors from the HMC mill and tailings embankments and annual
average outdoor radon concentrations (correlation coefficients for
regression analyses of data for different wind rose sectors varied
between 0.07 and 0.56, with a combined four sector coefficient of 0.05).
These observations indicate that:
1) outdoor radon concentrations do not exhibit the degree of variability
with distance from the mill and tailings embankments which would suggest
atmospheric dispersion of radon from these is significantly elevating
the average radon concentration in the subdivisions;
2) indoor radon concentrations are influenced primarily by structural
characteristics of individual homes which allow indoor radon concen-
trations to be dominated by build-up from local sources of radon in
the subdivisions.
Potential local radon sources evaluated were building materials used in
house construction and soils under or adjacent to the homes with the most
elevated radon concentration. Gamma radiation levels inside and exterior
of homes with elevated radon did not identify radioactive sources in home
building materials. Uranium and radium levels in surface soils collected
beneath or adjacent to homes with elevated indoor radon concentrations were
8
-------
indicative of background levels and provided no evidence that tailings were
significant in the soil in the vicinity of these residences. In view of
these findings, it is concluded that the primary source of indoor radon in
homes in the subdivisions is local soil which emits radon gas. Primary
radon entry routes are through cracks and other openings in dwelling floors,
with higher indoor levels in frames houses with a crawl space or slab.
6.0 SUMMARY OF SITE RISKS
An Endangerment Assessment of the risks to radon exposure was performed for
the seventeen individuals residing in the eight houses having annual average
radon levels of > 4 pCi/1.
Four conservative models which are in current use for setting regulatory
standards were used to provide upper-bound risk estimates for radon concen-
trations measured in the eight houses. The first three are based on relative
risk and are the Time Since Exposure and Internal Analysis models used in
the Biological Effects of Ionizing Radiation IV Report (BEIR IV) and the
model employed in Report 50 of the International Commission on Radiological
Protection (ICRP 50). A fourth model, used in a National Council on Radiation
Protection and Measurements 78 Report (NCRP 1984), is based on absolute
risk and is used for comparison. The Relative Risk models assume that the
risks of exposure from radiation is proportional, or relative to the normally
occurring, or background, risk of lung cancer. The Absolute Risk models
assume that the risk of radiation exposure adds to the underlying background
risk of contracting lung cancer. Lifetables used are from BEIR IV and are
corrected for United State background exposure to average indoor and outdoor
radon concentrations based on average values from the 1988 Report of the
United Nations Scientific Committee on the Effects of Atomic Radiation
(UNSCEAR). This UNSCEAR Report was also used to obtain conservative occupancy
factors of 80% indoor and 20% outdoor for residents and average radon daughter
equilibrium factors of 0.4 and 0.8 for indoor and outdoor radon concentrations,
respectively. These latter factors are then used to convert the various
radon concentrations into exposures as expressed by working level months
per year (WLM/y).
Lung cancer lifetime risks per year for the seventeen residents of the eight
houses having more than 4 pCi/1 average annual indoor radon concentrations
are given in Table 8. The data range from 3.1 x 10 to 5.9 x 10"^
and center around 1 in 10,000 per year of residency for all houses exceeding
4.0 pCi/1 and for all age groups. These risks from radon exposure are
slightly above EPA's threshold level for remedial action, and therefore EPA
is recommending that radon reduction measures he employed by these eight
homeowners.
-------
7. DESCRIPTION OF ALTERNATIVES AND COMPARATIVE ANALYSIS
Based upon the results of the RI, EPA has determined that the uranium mill
and tailings embankments, though potential sources of radon in the area,
are not contributing significantly to subdivision radon levels. Therefore,
alternatives addressing radon emanations from the mill and tailing embankments
were not developed, evaluated or compared. No action for off-site radon was
the only remedial alternative examined in relation to the site itself.
However, since 8 residences in the subdivisions had annual average indoor
radon concentrations above EPA's radon guideline of 4 pCi/1, house by house
evaluations were conducted during the RI in order to identify construction
features causing indoor radon buildup.
House by house evaluations also permitted the selection of appropriate radon
reduction methods for each of the residences with radon levels above 4 Ci/1.
These house-specific radon reduction methods were summarized in the July
1989 FS, as recommendations to homeowners (these recommendations *ill be
sent directly to the individual homeowners as well). In accordance with
EPA's Citizen's Guide to Radon, radon reduction efforts are recommended
within 2 to 3 years of indoor measurements if annual radon levels are between
4 and 20 pCi/1.
8. SELECTED REMEDIAL APPROACH
Based on:
A. Long-term outdoor radon monitoring which does not indicate a definitive
relationship between concentration and proximity to the HMC mill and
tailings embankments;
B. Long-term indoor radon monitoring which indicates that the primary cause
of elevated radon concentrations is related to local soil sources and
construction features of homes which allow radon build up; and
C. The fact that tailings materials were not identified during sampling in
crawl spaces of, or adjacent to residences with elevated radon;
EPA has determined that it does not have the authority under CERCLA Section
104 to address radon concentrations identified in the subdivisions and
therefore has selected no further action for the Radon Operable Unit.
Although results of the RI indicate that the mill and tailings embankments
are not significant in causing elevated indoor radon in the subdivisions,
eight homes marginally exceed EPA's radon actions level guideline. As a
result, house by house evaluations were conducted during the RI to identify
construction features responsible for radon build up. As detailed in the
FS report, house by house evaluations permitted the selection of radon
reduction methods for each home (see figure 8). These radon reduction
recommendations will be made available to individual homeowners.
10
-------
While EPA believes that continued subdivisions monitoring is unwarranted
at this time, EPA recognizes the need to monitor outdoor radon and windblown
participate levels south of the disposal area to assure that conditions in
the subdivisions do not significantly change prior to final site closure.
In this regard, EPA will continue to review outdoor radon monitoring and
particulates data collected at the facility boundary pursuant to NRC-
license requirements. Should an increasing trend in either radon or
particulates levels be noted, EPA and NRC will require monitoring or
corrective action in the subdivisions, whichever is appropriate.
9. STATUTORY AUTHORITY FINDINGS
Based on the results of the remedial investigation, EPA has determined that
the uranium mill and tailing embankments at the HMC site, though potential
sources of radon near the site, are not contributing significantly to off-site
subdivisions radon concentrations. EPA has concluded that the principle
cause of elevated indoor radon concentrations is related to local soil sources
of radon in the subdivisions, and is a function of the type and quality of
housing construction. As a result of this finding, EPA has determined that
it does not have authority under CERCLA Section 104 to address indoor radon
concentrations identified as elevated in the Radon Operable Unit. The no
action decision formalized in this ROD, however, does not constitute a
finding by EPA that adequate protection has been achieved in the subdivisions.
Because 8 out of the 66 residences investigated for radon had annual indoor
radon concentrations above the 4 pCi/1 action level guideline (between 4.1
and 6.7 pCi/1), EPA is recommending radon reduction techniques to residents
having elevated indoor radon levels. House-specific radon reduction tech-
niques were identified during the the RI and FS in a manner consistent with
EPA's national radon policy.
11
-------
FIGURES 1-6
AND
TABLES 1-8
-------
FIGURE 1
AMBROSIA LAK[ TO
i SAN MATEO
HOMESTAKE
MINING COMPANY
TO
AlHl Ql IRQl'f
NEW
MEXICO
N
HOMESTAKE MINING COMPANY
SITE LOCATION
-------
HMC MILL AND SUBDIVISIONS LOCATIONS
1546000 -
1542000 -
1538000 -
1534000 -
483400
495*::
-------
Figure 3. Map pf Regional Area.
.wuy..^. :
//.t \ipc\: /
>-3S^? v<£r >: ^^'O
^^S^^1
y '. / '--- - -/-.y / .- I TV.
^?S>
i-S?^-- ;: **:
Wfa X
near surface
uranium
mineralization
-------
1546000 -
154200C - PLEASAWT-VA^EY-ESTATS , \
1538000
1534000 -
483400
-------
1546000 -!
1542000 -li PIZAS4NT-VAUPT-ESTATES I \
I ' i
1538000 -
1534000 -
I i_ I
493400
-------
2 333
H
2
H
c/5
Z H
a a
w as
H 3
U M
u
DS Z
OS I-H
o
cj en
Bug
Z U
O >
CQ H
1-1 Z
as o
H S
tn i
-" CM
a -i
> OS
e
CQ
GO
c
en
CU
I
FIGURE 6
v.-
'NOI1V^1N3DN03 NOOVH HOCX1NI
-------
Table 1
aOXESTAlE llNiNG ;0)IF.AHY - GRA8TS QPERATIQS
i'JsJ!7;S!CSS JACOI STUDY
IgDOOR QUARTERLY SADCN 'SACI-JTCH CCICZITRATIMS
COORD
"OAOfiil ACRES
!!-L23
31-LS
B1-L5
51-L3
31-L13
81-L3/10
B1-L6
31-L4
-"-4 t
52H22
EM-llI
E2-L13
u-L'.l
11. J^^
U1V
W-Jtf
82A-L10
B2A-L5
t"2A-L2
E3A-L3
E!A-:2
83A-L3
:3A-L1
S4A-L2
!2-Ll
J2A-L3
PELICE AC5ES
?A-2
FH
?A-i
?H
FH
FA-'
?A-3
ICRRAY ACRES
81-L;
W-ll
IMS
J2-L5
48361"
45374C
490225
490825
490775
(39450
490375
490600
490875
uo <
11 « »
b *
2.1 : :
:» : :
-------
Table 1 (.cone 'd)
MEASURED
CORRECTED
RM'
n-::
;H5
23-LI
34-L5
34-13C
34-L2D
54-12
34-L1A
51-1!
34-L5
PLEASAJT WlIT
LI3
' *
b*
17
»t
u<
15
L6
is
L12
LH
487550 1540125
483550 1540335
488550 1540275
485250 15335:5
487200 1529775
486700 1523825
48'5CO 1539025
487125 1533045
488075 1539075
(38540 1539025
487850 1540675
487150 15287^5
485700 1541325
484000 1540275
484550 1539775
484500 1539775
484300 1533675
484850 15(0425
48(330 1540125
4851CO 1540200
485120 1540575
485320 1540575
435400 1540200
485500 1533125
435475 1529175
2.4
3.1
2.4
5.5
3.4
5.1
2.5
3.0
2.2
4.0
2.4
3.0
1.8
2.1
1.4
IA
2.1
2.9
1.5
2.2
2.2
i i
2.5
2.7
2.7
3.2
2.3
2.0
9.5
2.4
5.4
2.2
2.3
1.7
1.5
1.4
2.4
1.5 .
1.5
1.1
IA
2.1
1.4
0.3
1.6
1.2
1.4
1.4
2.4
2.9
3.0
2.9
2.5
2.9
1.5
1.3
1.2
2.8
1.5
3.5
1.8
2.2
2.0
2.2
1.3
IA
1.6
IA
1.2
1.5
1.5
2.0
1.4
1.7
4.9
1.8
2.3
2.4
3.3
2.2
3.0
2.1
3.0
1.0
4.6
1.4
1.1
1.7
2.2
l.J
1.5
I.i
IA
1.5
1.3
1.0
1.6
1.5
1.7
1.3
4.2
2.}
4.2
4.0
3.3
5.2
3,1
3.8
IA
3.3
2.3
4.0
2.7
2.5
1.8
2.0
IA
2.6
2.4
2.7
1.3
2.3
2.4
3.3
3.5
, j mirM
2.3 TRAILER
2.7 PEAIE/CEAIl
8.1 PSAXg/CEAVL
2.3 mi LEE
5.2 PRAXE/CEAll
2.4 TRAILER
2.7 PRAXE/SLAB
2.0 PEAIE/CE1IL
1.8 PEAXE/SLAB
1.3 mint
2.7 PRAXE/SLAB
1.7 TEA1LK
1.3 PEAII/3ASHEIT
1.1 TEA1LK
IA PEAIE/CUII
2.1TUIIZE
2.2 TEAI LEE
1.2 TEAILZE
2.0 TEAL LEE
1.7 TUIltt
2.1TEAIL1E
2.0 TRAIL!?
2.6 PSAXE/CRAVl
1.3 FRAIE/CRAIL
3.4
2.5
3.2
3 <
5.4
2.9
3.2
2.4
4.5
2.3
3.3
2.1
2.2
1.5
IA
2.6
2.6
1.4
1.4
2.1
2.5
2.4
3.1
4.9
2.4
4 4
<4 i M
3.1
5.7
2.4
3.2
2.2
4.5
2.2
3.1
2.2
2.2
1.5
IA
2.3
1.7
1.4
2.2
2.0
2.4
2.1
t
4.5
2.1
1.5
1 '
* 1
I > W
1
5.2
2.4
3.3
1.9
4.7
2.1
2.5
2.1
2.4
1.7
IA
2.3
IA
1.5
2.3
1.3
2.3
2.0
2.5
4.3
i"! (
3.5
5.2
4
c :
1 C
4. «
3.5
li
4.5
2.2
: 3
2.3
2.5
1. 3
IA
IA
IA
1. 7
i.i
1. 5
M t i
2.0
2.3 (
2.3
2.:
f.'
c
:.i
* *
u
4.5
fc. ^
:."
te »
J.I
i »
i . >
!A
!l
DA
:."
ir '
i.
'.
'
=A 51-L5: USI9EIT OIA?AlUfllS EDO OP 4T! VUITR, 5T! QI. USOLTS CC»EE 4TJ i 5TH 4UAITEES
3* Bl-LI/IO: SSSiOEiT «0?EO OOEIIC 5TH QOAirES, IOSITOE LOST
;A-i OEICIIAL SSSljiiT X07ED, LOST DETSCTCK2 FOJ 320 t 4T3 iDAETEE
(A 84-L2: SESiCEiT COT OP ASSA OliSISC LAST WAlTZt, DETSCTOE LOST
-1-L7: HO'JSJ IO?5D 0»TO LOT D0611C 3ED QUART'S RESULT! POB 4Ti AID 5TH QOARTERS OILT
FMS: TSAlLIi SiIC?EO fRCI LOT DUB! 1C 5TH QOART1R. DETSCTOE LOST
.:?-L5: ORCI.HAL SESiiJEiT K07ED, LOST DETECTORS POE 3RD I 4TI (JOAETEES
-------
Table 2
IGWSTUE I1IIIG COIPAIT - GUITS 3PHATIQI
SUJCUISiOIS SADOI 2TUDT
OlittOCS. WAiTMl! TJACI-JTCH UOOI CGICZ»TSA!iC
EAST Km FIRST 4: SEC. QT TEISD L5
jfm.1
/WrL5
» 32-13
U B2-L1
1A B4-U
1* S4-L2
1* 8I-L5
PT-L12
PT-12
P?-LI2
PH13
MEASURED
13 ^X
OJT! tf PI FT! «
C08C U COIC
PIC/L PIC/l PIC/l PIC/l PIC/l
(88825
4I3?!0
450?35
439450
490355
489025
490055
4JC775
490240
491005
483835
490460
483725
*39225
490350
435355
(85200
433110
485310
487540
438540
486700
48806!
427150
485 'oo
4S4000
435400
485(55
1538490
153S53C
1538475
1538220
153822!
15J3015
1538005
1537915
1537750
1537690
1537425
1527500
1535865
1535215
1535415
1535315
1540630
1540725
1540125
1543125
1540275
1538815
1533075
1533755
1541335
1540265
1540210
1539175
3.0
2.3
l.T
2.9
2.8
2.5
2.3
2.5
1.3
3.0
3.4
3.3
2.3
4.3
2.0
1.5
1.9
2.3
6.3
3.0
4.0
2.9
4.3
3.4
2.4
3.5
1.5
2.8
1.5
1.1
1.7
2.9
1.3
3.2
2.9
2.7
1.7
2.5
1.9
2.2
1.6
S.I
3.3
2.7
4.3
2.4
1.1
2.3
2.3
1.9
2.1
1.9
1.5
2.9
1.2
1.2
4.0
2.4
1.4
4.1
1 '
!» I
2.8
2.9
2.4
1.7
1.7
2.6
1.7
3.2
4.3
2.3
4.2
2.6
3,4
3.7
6.6
4.2
5.7
J.T
4.0
1.2
2.1
2.9
1.3
1.9
1.1
1.9
2.3
I.fl
2.3
i.fl
3.5
1.3
0.9
1.5
1.9
1.3
1.7
1.2
1.5
1.5
3.5
1.2
1.3
1.1
1.6
1.1
1.2
2.6
1.0
1.2
1.4
3.4
4.7
6.9
3.3
2.8
5.9
3.9
6.0
3.4
3.T
4.3
7.6
5.6
7.4
3.J
5.2
6.5
5.9
5.!
5.1
5.1
4.1
8.1
4.2
9.2
5.1
3.9
3.3
CORRECTED
' 5 W
«. 112 4T. 1-2 4T. 1-4 V. 2-5 PIM tf 2-4
PlUSSC.AfG iA 19G 1A AfG )A A!G W A!G U
QT. AJG ADJOSTSt ADJCSTED 4DJU5TH ADJflSTM AOJ11STS3
PIC/l BT
2.3
1.7
l.T
3.4
2.1
2.9
2.6
2.7
1.5
2.3
2.7
2.6
2.0
4.5
2.T
2.1
3.0
2.3
4.0
2.T
3.2
2.3
3.5
2.6
2.9
2.2
1.4
2.0
QT. 3T QT. BT
1.5
l.l
I.fl
2.1
1.4
1.7
1.5
1.6
fl.J-
1.7
l.T
1.5
1.2
2.T
1.5
1.2
1.5
1.3
2.9
l.T
2.0
1.9
2.3
l.T
1.2
2.0
0.8
1.3
l.T
1.2
0.9
2.2
1.4
1.5
1.5
1.5
0.9
1.4
1.5
1.4
1.4
»2.5
1.6
1.5
1.7
1.8
2.5
2.3
2.1
2.3
2.4
1.9
1.0
l.T
1.1
1.1
«. BT
1.6
l.l
1.1
2.0
1.2
1.6
1.3
1.2
0.9
1.2
1.5
1.4
1.4
2.2
1.4
1.5
1.6
2.0
2.1
2.1
l.l
2.3
2.0
1.6
1.1
1.5
1.0
l.l
ff. BT
1.9
1.8
2.4
2.2
1.4
2.5
1.3
2.2
1.5
1.6
2.0
2.7
2.:
3.2
2.0
2.4
2.B
2.3
2.2
3.0
2.2
1.3
3.0
2.0
2.6
2.0
l.T
1.4
B.
1.7
1.4
1.7
2.1
1.2
2.1
1. 6
1.7
1.2
1.4
1.9
2.3
1.3
2.7
1.7
2.0
2.2
2.4
2.2
2.5
1.0
2.1
2.5
1.9
1.9
1.7
1.4
1.2
1.5
1.5
1.5
2.2
1.3
-------
TABLE 3
SUMMARY OF CORRECTED INDOOR RADON LEVELS (pCi/1)
BY QUARTERLY AVERAGES AND SUBDIVISIONS
SUBDIVISION
Broadview Acres
Felice Acres
Murray Acres
Pleasant Valley Estates
Corrected Total Average
QUARTERLY AVERAGE RADON CONCENTRATION,
1-2 1-3 1-4 2-5
2.8 (27)b
2.0 ( 7)
4.1 (19)
2.4 (12)
3.0 (65)
2.
1.
3.
2.
2.
6
9
8
3
8
(27)
(-6)
(19)
(12)
(64)
2.5
1.8
3.6
2.2
2.7
(26)
( 6)
(19)
(11)
(62)
2.
1.
3.
2.
2.
6
7
7
3
8
(25)
( 6)
(18)
(10)
(59)
, PCl/1
1 & 5 f
2.5
1.7
3.6
2.2
1.7
2-4*
(25)
( 6)
(18)
(10)
(59)e
a The values in this column were calculated by averaging the values for
the 1st and 5th quarters and using this average (representing a weighted
1st quarter) to then average with quarters 2-4.
b The numbers in parentheses represent the number of measurements.
c This value is the twelve-month average radon level in pCi/1 for the 59
residences studied in the four subdivisions.
-------
TABLE 4
SUMMARY OF CORRECTED OUTDOOR RADON LEVELS (pCi/1)
BY QUARTERLY AVERAGES
PARAMETER
QUARTERLY AVERAGE RADON CONCENTRATION, pCi/1
1-2 1-3 1-4 2-5 1&5 + 2-4*
Corrected Total Average
Number of Measurements
1.6
28
1.6
28
1.5
28
2.2
28
1.9"
28
a The values in this column were calculated by averaging the values for
the 1st and 5th quarters and using this average (representing a weighted
1st quarter) to then average with quarters 2-4.
b^This value is the twelve-month average radon level in pCi/1 for the 28
outdoor monitoring stations studied in the four subdivisions.
-------
TABLE 5
INDOOR RADON CONCENTRATIONS
(CORRECTED TWELVE-MONTH AVERAGES IN pCi/1)
FOR FRAME HOUSES AND TRAILERS
SUBDIVISION FRAME HOUSES TRAILERS
Radon (pCi/1) Number Radon (pCi/1) Number
Broadview Acres
Felice Acres*
Murray Acres
Pleasant Valley Estates
All Subdivisions
3.1
4.0
3.0
3.6
12
12
3
27
2.0
1.7
2.6
1.9
2.0
13
6
6
7
32
a Felice Acres contains only trailers.
-------
TABLE 6
INDOOR CORRECTED RADON. CONCENTRATIONS (12-MONTH AVERAGES)
BASED ON GENERAL CONSTRUCTION TYPE AND
QUALITY OF RESIDENCE
RADON
GROUP,
1.5 -
22.2 -
24.7 -
Totals
24.0 -
PROBABILITY
pCi/1
<2.2
4.7
6.7
6.7
TOTAL NUMBER
OF RESIDENCES
24
32
3
59
8
NUMBER OF
FRAME/CRAWL
0
17"
2
19
6
NUMBER OF
FRAME/SLAB
1*
6
1
8
2
NUMBER OF
TRAILERS
23
9c
0
32
0
a The lowest indoor radon level in a house is 2.0 pCi/1.
b This includes one house with a basement.
c The highest indoor radon level in a trailer is 3.4 pCi/1
-------
TABLE 7
COMPARISON OF INDOOR AND OUTDOOR
CORRECTED.RADON CONCENTRATIONS
SUBDIVISION
Pleasant Valley Estates
Murray Acres
Broadview Acres
Broadview Acres
Broadview Acres
Murray Acres
Murray Acres
Broadview Acres
Broadview Acres
Murray Acres
Pleasant Valley Estates
Pleasant Valley Estates
Broadview Acres
Murray Acres
Murray Acres
Broadview Acres
Broadview Acres
Pleasant Valley Estates
Broadview Acres
Broadview Acres
Felice Acres
Fel ice Acres
Murray Acres
Felice Acres
Broadview Acres
Felice Acres
TYPE OUTDOOR
RESIDENCE RADON, pCi/1*
Frame/Crawl
Frame/Crawl
Frame/Crawl
Trailer
Frame/Crawl
Frame/Crawl
Frame/Crawl
Trailer
Frame/Crawl
Frame/Slab
Trailer
Frame/Basement
Frame/Slab
Frame/Crawl
Frame/Crawl
Trailer
Trailer
Trailer
Trailer
Trailer
Trailer
Trailer
Trailer
Trailer
Trailer
Trailer
1.2
2.1
2.1
1.2
1.4
2.4
2.0
1.4
1.8
1.8
1.4
1.7
1.7
2.2
2.5
1.6
1.7
1.8
1.7
2.0
1.8
1.7
2.2
2.0
2.1
2.7
INDOOR/
OUTDOOR*
3.25
2.43
2.14
2.08
1.79
1.71
.1.65
1.64
1.61
1.50
1.43
1.41
1.35
1.32
1.32
1.31
1.24
1.22
1.06
1.00
1.00
1.00
1.00
0.95
0.86
0.67
INDOOR
RADON, pCi/1*
3.9
5.1
4.5
2.5
2.5
4.1
3.3
2.3
2.9
2.7
2.0
2.4
2.3
2.9
3.3
2.1
2.1
2.2
1.8
2.0
1.8
1.7
2.2
1.9
1.8
1.8
The values used are the 12-month averages calculated by averaging the
1st and 5th quarters and using this value to average with the 2nd, 3rd,
and 4th quarters.
-------
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-------
REFERENCES
ICRP, 1987. Lung Cancer Risk from Indoor Exposure to Radon Daughters.
ICRP Publication. 50, Annals of the ICRP 17 (1).
Feasibility Study Report, June 1989. Grants. New Mexico Subdivisions
Radon Study. Homestake Mining Company, Grants Operation.
NAS, 1988. Health Risks of Radon and Other Internally Deposited Alpha-
Emitters: BEIR IV. Committee on the Biological Effects of Ionizing
Radiations, National Research Council, National Academy of Sciences,
Washington, D.C.
NCRP, 1984. Evaluation of Occupational and Environmental Exposures to
Radon and Radon Daughters in the United States. NCRP Report No. 78,
National Council on Radiation Protection and Measurements, Bethesda,
Maryland.
Remedial Investigation Report, June 1989. Grants, New Mexico Sub-
divisions Radon Study, Homestake Mining Company, Grants Operation.
UNSCEAR, 1988. Source, Effects and Risks of Ionizing Radiation. United
Nations, New York.
-------
Appendix A
EVAL!!S"?|!J?F APPLICABLE OR RELEVANT
AND APPROPRIATE REQUIREMENTS
-------
Appendix A
EVALUATION OF APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS
INTRODUCTION
Section 121(d)(2) of CERCLA as amended in 1986 by SARA requires that the
selected remedy attain certain requirements adopted under Federal and State
environmental laws. These requirements are called "ARARs" or "applicable
or relevant and appropriate requirements".
The Feasibility Study for the Homestake Mining Company Radon Operable Unit
included a review of these laws, and identified those which could be ARARs
based on the types of wastes and concentrations and sources of radon at the
site. This appendix lists all the laws which the Feasibility Study identified
as potential ARARs for the site.
EPA Guideline of 4 pCi/1 (Indoor Radon)
The 4 pCi/1 indoor exposure level is not a regulatory requirement hut a
guideline. EPA's radon guidance states that where indoor radon concentrations
range from 4 pCi/1 to 20 pCi/1, homeowners should undertake action to lower
levels to 4 pCi/1 or below within a few years, or sooner if levels are at the
upper end of this range.
10 CFR Part 20, Standards for Protection Against Radiation
These regulations are considered ARARs. They are promulgated and enforced
by the NRC and create standards for protection against radiation exposure
which apply to all facilities licensed pursuant to the Atomic Energy Act.
These regulations limit the concentration of radon-222 to 3 pCi/1 above
background at the boundary of HMC's property (a "restricted area"). The
NRC license and regulations are designed to ensure achievement of this
applicable maximum permissible concentration limit for exposure to indivi-
duals off-site of HMC facility.
Regulations in 10 CFR Part 20 give the NRC authority to limit a licensee's
radon emissions to 1 pCi/1 above background at the facility boundary. This
limit is considered relevant and appropriate and it is within NRC's regulatory
authority to enforce this concentration limit.
10 CFR Part 40, Appendix A, Criteria Relating to the Operation of Uranium Mills
and the Disposition of Tailings of Wastes Produced by the Extraction or
Concentration of Source Material from Ores Processes Primarily for Their Source
Material Content
These regulations, established by NRC, govern the operation and decommissioning
of licensed uranium mills and tailings piles, and are considered applicable or
relevant and appropriate for mill closure. They specifically address
clean-up standards for Ra-226 in soil, and involve the removal of Ra-226
contaminated soil in areas impacted by wind blown tailings. These regulations
also require active mitigation of airborne emissions during operation,
particularly particulates, by wetting or partially covering the tailings
pile.
-------
40 CFR Part 192. Health and Environmental Protection Standards for Uranium
and Thorium Mill Tailings
EPA has established these standards under the authority of the Atomic Energy
Act and the Uranium Mill Tailings Radiation Control Act for clean-up of
land and buildings. They are considered relevant and appropriate in that
they relate to reduction of radon concentrations in any occupied or habitable
building to 4 pCi/1 (or 0.02 WL, equivalent to EPA's radon action guideline),
as well as to establishing a soil clean-up standard for radium.
State of New Mexico ARARs
The State uses EPA's recommended action level of 4 pCi/1 for indoor radon,
and the airborne concentration limits in 10 CFR Part 20. Other requirements
conform with Federal regulations.
-------
APPENDIX B
AGENCY FOR TOXIC SUBSTANCES AND DISEASE CONTROL (ATSDR)/
CENTER FOR DISEASE CONTROL (CDC) EVALUATION
-------
DEPARTMENT OF HEALTH & HUMAN SERVICES Public Health Service
Agency for Toxic Substances
and Disease Registry
Atlanta GA 30333
MEMORANDUM
Date : September 15, 1989
From : Senior Regional Representative
ATSDR/Region VI
To : William D. Rowe, RPM
6H-EO
Subject: Health Consultation - Homestake Mining Company
Cibrola County, New Mexico
The Agency for Toxic Substances and Disease Registry (ATSDR) has
been requested to review and comment on the proposed remedial
decision identified by EPA in the draft ROD document (September 1989)
for the Radon Operable Unit, Homestake Mining Company (HMC), Cibrola
County, New Mexico. °
BACKGROUND
ATSDR and the Center for Environmental Health, Centers for Disease
Control (CDC) have previously had the opportunity to review and comment
upon various aspects of the radon sampling program in the four sub-
divisions southwest of the HMC mill and tailings einbankment areas. Most
recently, the ATSDR Preliminary Health Assessment for Homestake (dated
August 12, 1988) in discussing the off-site radon concern reiterated the
CDC 1984 recommendation that all homes in the affected community should
be included in the indoor monitoring program.
Other recommendations from previous reviews of site related documents
have identified the need:
- to determine whether or not preliminary data on indoor radon
concentrations were really above what might be typical from back-
ground in this region of the country, and
- to consider the influence of housing construction on radon build-up
when designing the study.
FINDINGS
Areas of previous concern to ATSDR were addressed and summarized in the
draft ROD document. These included:
1. Involvement of all homeowners in the four affected subdivisions
in the 15-month radon study.
a. Sixty-six of the 67 homeowners did participate.
b. Twenty-eight outdoor sampling locations within and adjacent to
-------
the four subdivisions were also monitored.
2. The influence of home construction on indoor radon concentrations.
a. Data collected from the study indicated that the concentrations
were closely related to the type and quality of housing construc-
tion.
b. The average concentrations in trailers were lower than those found
in homes and, in general, were approximately those found outside.
c. The highest concentrations were found in frame houses.
3. Whether concentrations found in the homes were related to normal
regional background variations.
a. No definitive correlation was found between the distance of the
individual homes from the site and the annual average indoor
radon concentrations.
b. No correlation was found between the distances to outdoor sampling
locations from the site and annual average outdoor concentrations.
c. Gamma radiation measurements did not identify significant radie
contributions from building materials.
d. No evidence of significant radon was found in the water supply
or heating systems.
e. Uranium and radium levels in surface soils collected beneath or
adjacent to homes with elevated indoor radon concentrations were
typical of background levels and provided no evidence that tailings
had been transported to the location of these residences.
CONCLUSIONS
EPA has concluded based on the Remedial Investigation that the uranium
mill and tailing embankments at the HMC site, though potential sources,
of radon near the site, are not contributing significantly to off-site
subdivision radon concentrations. For the eight residences where radon
concentrations were above the 4 pCi/1 action level guideline esta-
blished by EPA, specific guidance was provided for achieving reductions.
EPA does not feel that they have the authority to further address indoor
radon problems that have not been demonstrated to be site related. They
are therefore proposing no further action other than reviewing outdoor
radon monitoring and particulate data collected at the HMC facility
boundary pursuant to their NRC-license requirements.
ATSDR after reviewing EPA proposed actions and the reasons for the
actions, concurs with the decision proposed.
*-
Carl R. Hickam
-------
APPENDIX C
ADMINISTRATIVE RECORD INDEX
<
-------
Appendix D
U.S. NUCLEAR REGULATORY COMMISSION CORRESPONDENCE
-------
UNITED STATES
NUCLEAR REGULATORY COMMISSION
REGION IV
URANIUM RECOVERY FIELD OFFICE
BOX2S32S
DENVER. COLORADO 80225
SEP 8 1989
URFO:GRK
Docket No. 40-8903
U.S. Environmental Protection Agency
ATTN: William Rowe
1445 Ross Avenue, Suite 6H-EE
Dallas, Texas 75202-2733
Dallas, Texas
Dear Mr. Rowe:
Our office is in receipt of your draft decision document for the Radon Operable
Unit of the Homestake Mining Company (HMC). The Nuclear Regulatory Commission
has regulatory oversight for the HMC site, which involves enforcement of
applicable regulations and license conditions ensuring protection of human
health and the environment. We are currently requiring the control of blowing
tailings through the utilization of interim soil covers. The inactive tailings
have been completely covered and thereby isolated from the environment.
Additionally, due to the exceedance of ground-water protection standards, a
ground-water corrective action program is being required of HMC. These two
actions are consistent with your Record of Decision and the 1983 Consent
Agreement signed by HMC. We will continue to pursue these items to ensure that
regulatory requirements are satisfied.
Mr. Gary Konwinski of my staff will continue coordinating the efforts
associated with the proposed Memorandum of Understanding between the NRC and
the EPA. He will also be the contact for all environmental issues associated
with the site. Please feel free to contact him directly concerning these
activities.
Sincerely,
Ramon E.
Director
Hall
-------
Appendix E
STATE OF NEW MEXICO CORRESPONDENCE
-------
__
All
New Mexico Health and Environment Deoartment
DENNIS BOYD
Secretary
MICHAEL j BURKHAP
Oeoucy Secretary
RICHAPO MITZELFEl/
Director
September 12, 1989
Allyn M. Davis, Director
Hazardous Waste Management Division
U.S. Environmental Protection Agency
1445 Ross Ave.
Dallas, Texas 75202-2733
RE: Proposed Record of Decision for Homestake Mining Company,
Radon Operable Unit
Dear Mr. Davis: +
The Environmental Improvement Division (EID) has reviewed the
draft Record of Decision (ROD) for the Radon Operable Unit of the
Homestake Mining Company (HMC) Superfund site.
The EID agrees that the results of the remedial investigation
indicate that the uranium mill and tailings embankments at the
HMC site are not contributing significantly to radon
concentrations in the subdivisions near the site. Therefore,
the EID concurs with the selected remedy of no further action for
the Radon Operable Unit as proposed by EPA.
It is understood that this action is only one part of a more
comprehensive response action for the HMC site which includes
three operable units: radon, groundwater, and source control. As
you are aware, EID currently requires HMC to have an approved
ground water protection and restoration program as authorized by
the facility's Ground Water Discharge Plan (DP 200). Remedial
activities addressing source control, onsite surface reclamation,
and contaminated ground water are regulated by the U.S. Nuclear
Regulatory Commission (NRC), pursuant to the facility's NRC
license. The EID in conjunction with the NRC will continue to
require HMC to implement a ground water remediation program after
closure of the mill.
The uranium mill and tailings embankments are potential sources
of radon in the area. As we discussed at a meeting with your
staff on August 29, 1989, a^provision will be included in the ROD
for continued review of outdoor radon monitoring and particulate
data by EPA, and the monitoring of radon in the subdivisions if
warranted by future data.
- ENVIRONMENTAL IMPROVEMENT DIVISION -
Harold Runnaia Building
1 1 9O St. Franoa Or.
Santa Fa. Naw Maxico S7SO3
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Allyn M. Davis
September 13, 1989
page 2
The EID is in agreement with the evaluation of applicable or
relevant and appropriate requirements (ARARs) in Appendix A of
the ROD.
Thank you for the opportunity to review the Record of Decision on
HMC and for keeping us involved.
Sincerely,
Richard Mitzelfelt
Director
RM:DMD:dmd
cc: Steve Gary, NMEID
William Rowe, USEPA
Gary Konwinski, NRC
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Appendix F
RESPONSIVENESS SUMMARY
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Homestake Mining Company Site
Community Relations Responsiveness Summary
The Community Relations Responsiveness Summary has been prepared to provide
written responses to comments submitted regarding the proposed plan at the
Homestake Mining Company hazardous waste site. The summary is divided into
two sections:
Section I: Background of Community Involvement and Concerns. This
section provides a brief history of community interest and concerns
raised during the remedial planning activities at the Homestake site.
Section II: Summary of Major Comments Received. The comments (both
oral and written) are summarized and EPA's responses are provided.
I. Background of Community Involvement
Individual interest or attention to the site has been very low-key.
Individual residents are concerned about their health as well as the economy
of the area. Frequent reports by a potentially responsible parties to
residents kept them up to date.
EPA issued fact sheets and press releases to update area citizens of site
activities. An information meeting was held in September 1987, prior to
the start of the in-home detection study. No additional concerns were
raised by these activities.
II. Summary of Major Comments Received
The Proposed Plan fact sheet announcing the public comment period and
opportunity for a public meeting were distributed on July 20, 1989. The
comment period began on July 31 and was extended to September 1, 1989. At
the request on four local homeowners a public meeting was held on
August 28, 1989, at the Cibola Hall. The purpose of this meeting was to
explain the results of the Remedial Investigation and the Feasibility Study.
Fourteen people attended the meeting, and five asked questions. One addi-
tional letter was received signed by four residents.
The comments/questions received during the public comment period concerned
interagency requirements at the site, and specific findings in the radon
RI/FS. Comments received are summarized below, along with EPA's responses:
Question 1.
Homestake installed the monitors, hut how was EPA involved, and who was
responsible for assuring data quality and correct field procedures?
Response: Under the Administrative Order (AO) signed by Homestake,
the remedial investigation and feasibility studies (RI/FS) would he
performed by Homestake as a potential responsible party under an EPA
approved workplan, mainly developed by the State of New Mexico.
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As part of this workplan, a quality assurance/quality control plan (QA/QC)
was developed and approved by EPA. The plan included controlled calibration
of detectors, duplicate detectors and analysis of unexposed detectors
to assess accuracy and precision. All detectors were purchased from
and analyzed by Terradex for long-term indoor and outdoor radon
monitoring. Although the detectors were in Homestake's possession,
EPA through its oversight contractor, Jacobs Engineering Group, audited
all work performed by Homestake staff to insure the integrity of the
results and compliance with QA/QC goals and requirements.
Under Superfund, the potential responsible party is encouraged to
conduct the RI/FS work with EPA oversight in accordance with an
approved work plan, which includes a QA/QC plan, as well as a worker
health and safety plan.
Question 2.
Were controls applied?
Response; In all cases, controls were applied to determine the accuracy
of the measurements. Each quarter, seven indoor and three outdoor
detectors, 10% of each type of detector, were exposed to known radon
concentrations and analyzed to establish calibration factors to adjust
the field measurements. Placement and retrieval of five quarters of
radon monitoring was audited by EPA's oversight contractor.
Question 3.
How is the outdoor air tested for radon?
Response: Air containing radon diffuses through a filter into a
detector chamber containing a special plastic detector. Alpha particles
from the decay of radon or daughter products produced within the
detector volume strike the plastic detector and produce a track in the
plastic. The integral number of alpha-tracks generated over a given
exposure period are chemically enhanced, counted and calibrated
relative to the response of the detector system to known radon concen-
trations. Since an integral number of alpha-tracks accumulated for a
given exposure period are counted, usually three-months, the system
measures the average radon concentration for the period.
Question 4.
Would the outdoor results have been different if monitors were placed close
to the ground, or at a higher elevation?
Response: Probably to some extent, but the objective was to measure
radon at breathing height.
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Question 5.
What was EPA trying to measure with outdoor monitors?
Response: The purpose of the outdoor monitors was to detect radon
levels in the subdivisions, and to determine whether there was a
significant contribution of radon to the subdivisions from the Homestake
facility.
Question 6.
How was it concluded that the main source of indoor radon was from the homes?
Response: It was noted that the outdoor radon concentrations were
typically less than the indoor radon levels and there did not appear
to be an obvious relation between indoor and outdoor radon concentrations
and the mill. Local radon sources under the buildings that exceeded 4
pCi/1, combined with the quality of home construction provided a reasonable
interpretation of the elevated radon concentrations observed in eight
homes. Any small outdoor increment produced by the mill did not
significantly effect the indoor radon levels.
Question 7.
Was there sampling made north and east of the mill and how do the measurements
correlate with this study?
Response: As a license requirement windblown tailings in these areas
were scrapped and placed back on the tailings pile. Perhaps a square-
mile of surface was involved. These actions are under NRC supervision
and authority.
There are 19 outdoor radon monitors distributed throughout these areas,
at least four on the southwest Homestake boundary, which are required
by the NRC operating license. The average historical results from the
four monitors were in the range 1.8-2.7 pCi/1, with two of the monitors
averaging slightly higher than the annual outdoor average of 1.9 pCi/1
in the subdivisions. The radon 'averages north of the Homestake facility
(15 monitors) ranged from about 0.8 to 4.7 pCi/1, with the highest
concentrations near uranium mine shafts. These data were compared
only qualitatively with the study results.
Question 8.
Are the results of the NRC monitoring variable or consistent?
Response: Average outdoor radon concentrations range from about 0.8
to 4.7 pCi/1 according to data collected under NRC supervision and
authority. The highest radon levels are associated with uranium mine
areas between four and five kilometers north of the Homestake facility.
Monitors located north of the facility, and within a two kilometer radius,
range between 1.4 and 2.9 pCi/1.
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Question 9.
Why can't radon get into the water pipes?
Response: Radon from radium in the soil under a dwelling can move into
the house by passing through the space around pipes where the pipes
pass through the dwelling floor. However, radon cannot diffuse through
the pipes and enter the water, since the diffusion of radon through
plastic or metal pipe is very low, and the radon would radioactively
decay before it reached the water. In order that the water supply
contribute to the indoor radon concentration due to domestic water
usage, the radon levels in water must he relatively high. For example,
10,000 pCi of radon per liter of water is estimated to produce an
increase in the indoor radon concentration of about 1 pCi/1. The
subdivisions are on the Milan water supply.
Question 10.
Please re-iterate the distribution of dwellings having annual indoor radon
concentrations exceeding 4 pCi/1 and there respective relation to outdoor
radon levels.
Response: Six homes are in Murray Acres, two in Broadview Acres. As
noted in the viewgraph, the houses with elevated indoor radon concentra-
tion are not distributed in a discernable pattern relative to the mill
location. High indoor concentrations were found only in frame houses
and not in a single trailer. Also the outdoor radon concentrations
observed near each dwelling were lower.
Question 11.
Explain why windblown tailings are not a source of radon in the subdivision?
Response: For the houses exceeding 4 pCi/1 annual average, gamma
exposure measurements were made in the near vicinity of the dwellings
and in each room of the houses. In addition, a limited soil sampling
program was undertaken in crawl spaces or adjacent to slabs on grade.
The results from this limited assessment of potentially windblown
material did not indicate that windblown tailings were significant in
the soil in the vicinity of these houses. Soil sample analysis also
did not indicate the presence of elevated radium or uranium.
Question 12.
Discuss the groundwater discharge plan.
Response; The groundwater discharge plan is a state responsibility
and this plan has been recently renewed. Present results of water
sampling in the subdivision indicate that the groundwater quality,
particularly selenium, has largely returned to essentially background
conditions. Information is available at the state office in Santa Fe.
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Question 13.
Uhat is the situation of windblown tailings in the subdivisions, and what
has NRC required of Homestake on this topic?
Response: Analysis of windblown tailings was limited to the area in
the vicinity of those houses that exceeded the 4 pCi/1 annual indoor
radon guideline. The NRC has identified areas to the north and east
of the mill that have been impacted by windblown material and has
required and overseen Homestake's cleanup efforts as part of Homestake's
license requirement. NRC also requires outdoor radon monitoring at 19
locations surrounding the Homestake site, four of which are situated
between the subdivisions and the Homestake mill and tailings embankments.
Question 14.
Can EPA say that there are not substantial amounts of windblown tailings in
the subdivision?
Response: See response to question 13.
Question 15.
To what extent have tailings been stabilized?
Response: there are two tailings piles on the Homestake site, one
active, the other inactive. The inactive pile has been stabilized to
date with an interim soil cover, approximately 6 inches in thickness.
Measures taken to date to reduce erosion of the active tailings pile
include use of erosion control blankets, used tires, wetting with water,
and with chemical agents which form a crust on the tailings surface.
Question 16.
What would you expect indoor-outdoor radon concentrations to look like over
the next couple of years in the subdivisions?
Response; Provided that meterological conditions do not change abruptly
in the Grants area, and assuming that homeowner living habits remain
pretty much the same as over the previous two years, EPA would not
expect radon levels in the subdivisions area to be substantially
different in the future.
NRC license requirements, which include continued outdoor radon
monitoring and the delineation of windblown tailings through radio-
logical surveys, are intended to assure compliance with human health
standards for radioactivity at uranium mill facilities.
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Question 17.
What are EPA's future plans related to Homestake?
Response: Licensing conditions will continue to he implemented and
overseen by the NRC. Continual surveying and cleanup of windblown
tailings will be required. Eventually, complete reclamation of the
site and impacted vicinity properties will occur as required hy NRC
regulations. In place boundary radon monitors will continue to ensure
that regulatory compliance is met. The EPA and the NRC will have an
agreement to delineate respective regulatory responsibilities for the
Homestake site.
The following are responses to one written comment received hy EPA during
the public comment period.
Concern 1.
HMC's erosion protection efforts to mitigate windblown tailings from its
main tailings embankment are judged to be insufficient since wind blown
material is still observed in the direction of the subdivisions when the
wind direction is from the north/northeast.
Response: Windblown tailings are a concern in so far as the radon
produced potentially may impact public health in the unrestricted,
off-site environment. It is EPA's understanding that improvements to
reduce the extent of wind erosion have been made through the use of
crust forming agents, net blankets, tires and fencing. To compliment
these activities, cleanup requirements for the off-site environment
have also been imposed as a licensing condition by the NRC. Recent
implementation of these requirements took place in 1988 resulting in
the cleanup of the main impacted areas to the north of the county road
adjacent to the main property, as well as east of Hwy. 53 (RI Figure 15).
Such efforts are expected to periodically continue, and a complete
survey and cleanup of all potentially impacted vicinity properties will
be a NRC imposed condition of final remedial action and mill closure.
Public exposure to radioactive, airborne particulates in the off-site
unrestricted areas to the south and southwest of the site is continually
assessed on the site boundaries as a NRC licensing requirement.
Compliance with 10 CFR 40 will be overseen by the NRC and reviewed hy
the EPA.
However, from the prospective of this radon study the issue of concern
is whether the windblown tailings significantly impact indoor radon
concentrations in the subdivisions. This issue will be addressed more
fully in response to concern 5.
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Concern 2.
EPA has stated that the in-pi ace aquifer restoration program has largely
flushed mill generated groundwater contaminants from the alluvium and Upper
Chinle aquifers. Would EPA provide evidence to support this observation
and state its official opinion as to the how long this restoration program
will be continued?
Response: The New Mexico Environmental Improvement Division (NMEID)
monitors wells in the subdivisions to assess the performance qf the
pump back system on a semi-annual basis. The water sampling data is
a matter of public record and may be obtained from the NMEID. A
review of this data can be made to individually judge the success of
this system to restore water quality in the alluvial and Upper Chinle
aquifers.
The maintenance of a groundwater control program and associated
downgradient well monitoring probably will be required throughout the
operation of the mill to ensure that groundwater contamination is
restricted to the on-site environment. Upon mill closure, site reclama-
tion is expected to occur in accordance with NRC regulations (10 CFR 40,
Appendix A) and licensing requirements. NRC requirements will dictate
design conderations to comply with appropriately accepted long-term
groundwater quality relative to the stabilized tailings piles. Long-
term groundwater corrective action will include points of compliance,
and ground water protection standards to be met (such as background
water quality, maximum or health based alternate concentration limits).
The NMEID will work closely with NRC on the direction of the corrective
action program.
Concern 3.
The historical section of the RI has mistakenly portrayed the community's
irrigation well as 1000 feet deep. The actual Murray Acres irregation well
of 585-feet pumping water from the San Andres formation. Furthermore, most
of the homeowners use shallow wells, 90-300 feet deep, to irrigate yards
and gardens using the alluvial and Upper Chinle formations.
Response; The Final RI Report acknowledges that the San Mateo alluvium,
Upper CMnle and San Andres Formation aquifers have been used for
irrigation water in the past. The FS states that significant irrigation
is derived from the San Andres formation (approximately 1000 feet deep).
This statement was not intended to refer specifically to the 585-foot
deep irrigation well in Murray Acres (well log #806 on file with NMEID).
There are a number of San Andres wells in the subdivisions area which are
used for irrigation. These wells have a range of depths, and have an
average depth of approximately 1000 feet.
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Concern .4.
In an off-the-record statement by Mr. Kennedy of HMC, it was devulged that
there was no evidence of windblown tailings outside of HMC's property. This
statement directly contradicts a 1979 NRC study, which implied that Ra-226
and Pb-210 surface soil contamination could be distinguished above background
at distances up to 5 miles from HMC's mill. In addition, this article
indicated that windblown contamination residing in the uppermost four
centimeters (cm) of topsoil is contributing about 1.6 Ci per day above the
natural background.
Response: EPA was not a party to the refered conversation and, therefore,
will restrict its response to a substantive interpretation of the article
cited.
The soil sampling plan implemented was limited to radial transects
(22.5 degree) with soil samples collected at 0.5, 1.0, 2.0, 3.0, 4.0
and 5.0 mile increments. Approximately 20 soil samples were in the
subdivisions area. The radium-226 soil concentration isopleths
essentially reflect the wind rose distribution with the major windblown
contamination plume in the north/northeastern directions. Soil concen-
trations elevated 2.3 pCi/g above background are observed as far as 5
miles to the north/northeast of the HMC site. However, in the south/
southwest direction, this 2.3 pCi/g contour is only about 1.2 miles
from the main embankment center. The next highest concentration
contour in this area, 4.5 pCi/g, lies about 0.75 miles from the site
followed by a 9 pCi/1 contour at 0.5 miles. The 9 pCi/1 isopleth
appears to be almost entirely within the HMC property boundary.
From the limited analysis performed on this study, it appears that any
windblown tailings in the subdivisions would be on the order of the
surface soil cleanup standard adopted by the EPA for remediation of
inactive uranium mill sites, 40 CFR 192, and contained in 10 CFR 40,
Appendix A for active mill sites: 5 pCi/g above background averaged
over the top 15 cm soil depth and a 100 m 2 area. The radiological
impact of this material in the subdivisions would be considered
minimal.
The areas to the north, northeast and east of the site, that the
study indicates may be contaminated above the 5 pCi/1 cleanup criteria,
roughly correspond to those on-site and off-site areas recently cleaned
by HMC as an NRC licensing requirement (RI Figure 15). Accordingly,
the radon flux capacity of this distributed material has been returned
to the north side of the main embankment. Since the contamination is
mixed with uncotitaminated soil in the removal operations, the effective
emission rate is probably reduced in its present disposition.
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From the above discussion it is reasonable to assume that the dominant
potential outdoor radon source in the vicinity of the subdivisions
would be the main tailings embankment, and not off-site windblown
tailings.
Concern 5.
The evidence supporting the notion that the main embankment is not signif-
icantly impacting the radon levels in the subdivision is insubstantial and
the conclusions may or may not be valid.
Response: The main objectives of the study's work plan was to determine
whether indoor radon concentrations in subdivision residences exceeded
the 4 pCi/1 annual guideline, to identify sources and contributing
mechanisms for residences that exceeded this recommended limit, and
determine appropriate remedies. The study was limited to only the
residences in the subdivisions and not a general study of indoor
residential radon, nor was an extensive determination of background
included as part of the work plan. Therefore, the inclusion of homes
outside the study area was not considered appropriate or relevant to
the analysis of the probable causes of indoor radon concentrations
in a particular subdivision residence that exceeded 4 pCi/1.
The fact that the length of time that a residence has been situated on -
a site was not considered in the study does not appear to be a signif-
icant flaw. Presummably this issue was raised to imply that the long-term
accumulation of windblown tailings within or around the dwelling could
significantly affect indoor levels. As noted in the discussion of the
1979 NRC report, windblown tailings in the area of the subdivisions appears
to he minimal. Although the gamma-exposure measurements and soil sample
analysis performed as part of the RI study were limited and considered
only dwellings with indoor concentrations exceeding the adopted guidelines
they did not indicate that a more comprehensive study of windblown
tailings was justified. Also, it should he noted that a six-inch deep
soil sampling protocol is considered appropriate to assess windblown
contamination.
The issue of interest is not whether the mill incrementally increases
the outdoor radon concentrations in its vicinity, hut whether the
increment signifcantly influences indoor concentrations. The general
structure for atmospheric dispersion of radon from the main tailings
embankment would be similar to that for particulates. If the measured
outdoor concentrations consistently exceeded indoor levels one would
reasonably assume that the outdoor air could potentially influence the
indoor environment. However, the RI results indicate that indoor
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concentrations, for the most part, are higher than the nearby outdoor
levels. Furthermore, there is a correlation of indoor radon concen-
trations with construction quality and dependance of outdoor radon
concentrations will mill location is not readily apparant. Accordingly,
it is not unreasonable to conclude that any incremental radon contribution
from the mill is not significantly impacting indoor radon concentrations
and that construction characteristics of the individual dwellings
relative to local soil radioactivity tend to dominate.
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