monitoring requirement for conventional impoundments in existence on
December 15, 1989. Commenters provided information demonstrating that
the conventional impoundments previously required to monitor radon
emissions (i.e., Cell 3 at the White Mesa Mill and the impoundments at
Shootaring Canyon and Sweetwater) are unable to meet the GACT-based
standards. Although we agree with the other commenters that the GACT-
based standards are effective in limiting radon emissions, they were
predicated on the impoundments meeting certain minimum requirements.
Because comments included information demonstrating some conventional
impoundments in existence on December 15, 1989 do not meet these
minimum requirements or did not enter closure as the EPA expected, it
is necessary and appropriate to retain the radon flux standard and
monitoring requirement for these units.
    Comment: A number of commenters expressed the view that monitoring
should not be limited to conventional impoundments constructed before
December 15, 1989. They asserted that they have little confidence that
the management practices in place for newer impoundments are
effectively being implemented, and argue that it is not possible to
verify their effectiveness without monitoring. The commenters

also expressed concern that impoundments that are drying out
(``dewatering'') are emitting larger amounts of radon, and that without
monitoring the operators are not compelled to provide additional soil
cover.
    Response: The EPA reviewed the management practices prescribed for
conventional impoundments constructed after December 15, 1989 and
reaffirmed its determination that they effectively reduce radon
emissions. The radon flux standard and monitoring requirement were
instituted in the 1989 rulemaking to provide a means to control radon
emissions from impoundments that were constructed and operated
according to earlier industry practices. The EPA found that the
management practices would represent a demonstrable improvement
compared to those industry practices. The Agency has concluded that the
appropriate action to satisfy its CAA review is to establish these
management practices as GACT-based standards. We agree that operators
need to take appropriate action to control radon during the period when
the impoundment is operating, and not allow excessive drying during
standby or other periods of limited activity. The management practices
are intended to limit radon emissions. For conventional impoundments
and heap leach piles, the management practices limit the exposed area
and/or number of impoundments at a uranium recovery facility, which
effectively limits the opportunity for radon emissions. For non-
conventional impoundments, ensuring that the material is saturated will
limit radon emissions by approximately 95% compared to dry materials.
    Comment: Some commenters favored retaining the emissions standard
for conventional impoundments constructed before December 15, 1989, but
at a more stringent level. One commenter stated that a standard below
10 pCi/m\2\-sec would be appropriate, and also that a review of current
control technologies would support a standard of 1 to 5 pCi/m\2\-sec.
Another commenter noted that the 1989 Background Information Document
found that a 6 pCi/m\2\-sec standard was achievable and cost effective.
This general view was supported by other commenters, with one stating
that the 20 pCi/m\2\-sec standard was established ``for economic
reasons.'' One commenter also expressed concern that the EPA did not
evaluate monitoring methods other than Method 115, and specifically
referred to the Landauer RadTrak.
    Response: Because the proposal involved eliminating all monitoring,
the EPA did not evaluate the impacts of implementing other standards or
monitoring methods. However, we did reaffirm that the 20 pCi/m\2\-sec
standard remains protective, and we also find that Method 115 remains
an appropriate method to measure radon emissions from conventional
impoundments.\15\ We disagree with the characterization of the 20 pCi/
m\2\-sec flux standard as based on economics. As stated in the preamble
to the 1989 final rule, when determining an ample margin of safety for
the rule, ``As explained above, the risks from current emissions are
very low. A NESHAP requiring that emissions from operating mill
tailings piles limit their emissions to no more than 20 pCi/m\2\-sec
represents current emissions. EPA has determined that the risks are low
enough that it is unnecessary to reduce the already low risks from the
tailings piles further'' (54 FR 51680, December 15, 1989). The update
of the 1989 risk assessment conducted for this rulemaking confirms that
the risk to public health from uranium byproduct material or tailings
managed at operating uranium recovery facilities is comparable to, if
not lower than, the level of risk considered presumptively acceptable
in the 1989 rulemaking. See Section IV.B.2.
---------------------------------------------------------------------------

    \15\ ``Report on the Review of Method 115 to Monitor Radon
Emissions From Uranium Tailings,'' prepared by S. Cohen &
Associates, September 2008, Docket No. EPA-HQ-OAR-2008-0218-0122.
---------------------------------------------------------------------------

C. GACT for Conventional Impoundments Constructed After December 15,
1989

1. How did we address conventional impoundments constructed after
December 15, 1989 in the proposed and final rules?
    We proposed to designate the management practices promulgated in
the 1989 rulemaking for impoundments constructed after December 15,
1989 as GACT-based standards for all conventional impoundments. In
doing so, we evaluated the reasoning used in the 1986 and 1989 Subpart
W rulemakings to determine that the phased disposal and continuous
disposal management practices protect public health with an ample
margin of safety (54 FR 51681).
    We initially defined these two management practices because they
provided a means for newly-designed impoundments to limit radon
emissions, either by limiting the overall size of the impoundment or by
limiting the area of dried (dewatered) uranium byproduct material or
tailings that can be exposed at any time. We found the two management
practices to improve performance (risk to exposed individuals and
population) by approximately 35% to more than 50%, respectively,
compared to earlier practices of constructing larger impoundments
without limiting their number or the exposed area. The potential for
larger impoundments or many smaller impoundments to remain uncovered
and their radon emissions uncontrolled if bankruptcy prevented proper
closure was considered to provide a further advantage to the two
management practices (54 FR 51680).
    Owners and operators of uranium recovery facilities in the United
States have all used the phased disposal method for management of
uranium byproduct material or tailings in conventional impoundments,
making it a generally available management practice to control radon
emissions. We have found no reason to believe that this method is
unworkable, unreasonably burdensome or ineffective in limiting radon
emissions. Keeping the uranium byproduct material or tailings wet or
partially covered, as is typical practice, further reduces radon
emissions. These industry practices also clearly demonstrate that the
phased disposal method is a generally available technology. In
addition, while there has been no use of the continuous disposal method
in the United States, it has been successfully employed in other
countries, and was proposed for use by some U.S. companies in the
1980s. Therefore, this final rule designates the phased disposal and
continuous disposal methods as elements of GACT-based standards for
conventional impoundments constructed after December 15, 1989. Because
these impoundments are separately required to comply with the
requirements at 40 CFR 192.32(a)(1), we concluded that such a
management practice is generally available and contributes to the
control of radon emissions as described more fully in Section IV.A.2.
Conventional impoundments must also comply with the construction
requirements in 40 CFR 192.32(a)(1).
2. What key comments did we receive on conventional impoundments
constructed after December 15, 1989?
    We received some comments questioning the effectiveness of the 1989
management practices and our decision to adopt those practices as GACT-
based standards. These commenters argued that there is no basis for
concluding that these practices are effective in limiting radon
emissions when no confirmatory monitoring has been done. They further

assert that the work practices were inadequate because practices that
are actually effective in reducing radon emissions, such as maintaining
a soil or water cover, were not elements of the 1989 work practices or
the proposed GACT management practices.
    Comment: Several commenters believe our GACT standards are
unsupported because there is no monitoring data to demonstrate the
effectiveness of the measures for post-1989 impoundments. Commenters
criticize the analysis of control technologies in the BID prepared to
support the proposal as flawed and insufficient. One commenter states
that limiting the size of the impoundment is not in itself an effective
means to limit radon emissions without monitoring, reporting, and the
requirement of liquid or soil application. This and another commenter
also believe that any new impoundments should be required to use the
continuous disposal method, as the commenters view the phased disposal
method as ineffective in controlling radon emissions, particularly when
using water cover. The first commenter further disputes the reliance on
40 CFR 192.32(a)(1) as an effective control technology to limit radon
emissions. Another commenter also suggests that the most effective
control technology is an emissions limit coupled with monitoring, and
believes the rule should be re-crafted along those lines.
    Commenters also asserted that we have not sufficiently examined
other technologies employed either in other countries or in related
industries. One commenter argues that other technologies (e.g., dry-
stack placement, paste tailings, solidification) may be superior to
open-air storage and cover in conventional impoundments, but were not
evaluated in the BID.
    Response: Our review under CAA section 112(q)(1) focused on the
management practices applicable to post-1989 conventional impoundments
(i.e., continuous or phased disposal). However, as noted in the
proposal, we also considered control technologies employed at other
facilities in the same industrial sector and internationally. We found
that the continuous and phased disposal methods adequately control
radon emissions and meet the requirements for GACT--these management
practices are generally available and effectively prevent adverse
health impacts from radon emissions. We recognize the commenter's
position that the design and engineering requirement in 40 CFR
192.32(a)(1) does not directly limit radon emissions. However, the
design requirement serves two purposes. Retaining moisture or
maintaining liquid levels within the impoundment does effectively
inhibit radon flux while at the same time preventing releases to ground
water. It is possible and important to achieve both goals.
    Regarding the area limitation, we disagree with the commenters. The
focus of the 1989 analysis was on limiting the surface area from which
radon would be emitted.\16\ Surface area is directly correlated with
radon emanation--the smaller the surface, the lower the overall
emissions, given similar materials. While the 1989 rulemaking clearly
recognized that the use of soil cover or water are also effective in
reducing radon emissions and were commonly employed by industry, the
acceptability of the promulgated work practices was not predicated on
those additional measures being employed, except to the extent that it
was necessary to limit the exposed area when using the continuous
disposal method.
---------------------------------------------------------------------------

    \16\ ``Either one of these technologies will ensure that future
risks will be kept under control by assuring that only small amounts
of tailings are uncovered at any time'' (54 FR 51681 (emphasis
added)).
---------------------------------------------------------------------------

    Comment: Some commenters stated that the designation as an area
source is not in itself sufficient to justify use of GACT. Commenters
cite the legacy of contamination associated with the uranium industry
as justifying the ``strongest preventive measures.'' Similarly, other
commenters accuse the industry of ``cutting corners'' and believe GACT
``runs counter to everything EPA knows'' about past practices. Another
commenter argues that the Agency's ``discretion'' must be supported by
full and complete explanation and justification. These and other
commenters also believe the EPA has not sufficiently considered MACT
approaches.
    Response: When setting standards, the EPA aims to ensure that the
promulgated standards effectively protect against adverse environmental
and health impacts, regardless of whether such standards are based on
GACT or MACT. For area sources, the Administrator has the discretion
under CAA section 112(d)(5) to set standards based on GACT in lieu of
setting MACT standards under sections 112(d)(2) and (d)(3), which is
required for major sources. See Section IV.A.2 for discussion of
regulating these units as area sources. Under CAA section 112(d)(5),
the Administrator may elect to promulgate standards or requirements for
area sources ``which provide for the use of generally available control
technologies or management practices by such sources to reduce
emissions of hazardous air pollutants.'' Consistent with section
112(d)(5), we are revising Subpart W to reflect GACT-based standards.
Based on the EPA's evaluation of available information, the GACT-based
approach in the final rule provides the necessary protections from
management of uranium byproduct material or tailings. The emission
standards and management practices established in Subpart W will
appropriately reduce radon emissions from uranium recovery facilities.

D. GACT for Heap Leach Piles

1. How did we address heap leach piles in the proposed and final rules?
a. When are heap leach piles regulated under Subpart W?
    We proposed to regulate the heap leach pile from the moment that
uranium begins leaching from the ore pile. This approach was based on
the view that uranium byproduct material or tailings is produced the
moment the lixiviant passes through on its first pass and uranium
begins to be leached from the ore (79 FR 25403). At the point of
uranium movement out of the heap, what remains is uranium byproduct
material or tailings as defined by 40 CFR 61.251(g). In other words,
what remains in the heap is the waste produced by the extraction or
concentration of uranium from ore processed primarily for its source
material content. The heap leach pile manages that uranium byproduct
material or tailings, even as the pile is further leached to extract
uranium. The proposal placed the emphasis on the presence of uranium
byproduct material or tailings in the heap leach pile.
    We also requested comment on an alternative approach we described
in the proposal (79 FR 25398). Under this approach, heap leach piles
would not fall under Subpart W until after leaching is permanently
discontinued. This approach is based on the view that, as long as the
heap is being leached, the ore on the heap leach pad is being
processed. While uranium byproduct material or tailings may exist in
the heap, the heap does not become engaged in managing uranium
byproduct material or tailings until leaching is permanently
discontinued. This view places the emphasis on the continued extraction
of uranium from the heap leach pile. Only after that extraction
potential is exhausted, and only uranium byproduct material or tailings
remains, would the pile fall under Subpart W.
    Many commenters (primarily those from industry) supported basing
the

final rule on this alternative view. These commenters argued that the
heap leaching cycle is essentially serving the same function as the
successive leaching of uranium that occurs in the leach and counter
current decantation circuits of a conventional mill, where the ore pulp
is successively leached in a series of leach tanks and thickeners. The
material does not become uranium byproduct material or tailings (i.e.,
waste) and fall under the requirements of Subpart W until it leaves the
final thickener and is discharged to the tailings impoundment.
    Although we proposed to bring the heap under the jurisdiction of
Subpart W based upon the presence of uranium byproduct material or
tailings within the pile, after further consideration we find the
commenters' reasoning compelling and more consistent with previous
application of the rule. Subpart W has historically not regulated radon
emissions from the milling or extraction process, even at the
intermediate points where residuals from uranium extraction make up the
bulk of the material being processed, which may be the situation as
processing of the heap progresses. Subpart W has regulated only the
disposition of the wastes at the end of the separations process.
Consistent with this precedent, the heap leach pile is like a
conventional impoundment and will be subject to Subpart W once uranium
extraction is complete and only uranium byproduct material or tailings
remains. Until that time, the heap is considered to be either an
unprocessed ore pile or a uranium recovery facility. Thus, heap leach
piles are regulated by Subpart W only during the period between the end
of processing (i.e., after the pile's operational life) and the
beginning of closure. As described in Section IV.F.1.a, and consistent
with the requirements applicable to conventional and non-conventional
impoundments, the final rule requires that operators provide written
notification to the EPA and the NRC that the heap leach pile is being
managed under an approved reclamation plan for that pile or the
facility closure plan. Impoundments used to manage liquids resulting
from the heap leach operation, to the extent they contain uranium
byproduct material or tailings, are considered non-conventional
impoundments subject to Subpart W, as defined in today's final rule.
    There is a significant aspect of heap leach pile management that is
important to these regulations. Several commenters from industry stated
that a heap leach pile, unlike a conventional impoundment, will
immediately begin closure after processing has concluded (either
closure in place, or possibly removal for placement in a conventional
tailings impoundment). If that is the case, there will be no period
when the heap is subject to the requirements of Subpart W. Because
there are no heap leach facilities operating in the United States, we
have no basis for disputing these statements of industry's intent.
Nevertheless, we have concerns that these good intentions may prove
insufficient to ensure that closure takes place as expeditiously as the
commenters believe. There is some potential that heap leach piles will
complete processing but not immediately enter closure. During such a
period the owner or operator is only using the pile to manage uranium
byproduct material or tailings, and the heap leach pile is then subject
to the requirements of Subpart W. The specification in the final rule
that final closure does not begin until the operator has provided a
written notification to the EPA and the NRC will minimize the potential
for confusion regarding the applicability of Subpart W. A further
concern might be that operators continue ``processing'' the pile
indefinitely, thereby postponing the costs associated with closure.
This would be a matter for the NRC or NRC Agreement States to consider.
    We recognize that heap leach piles will emit radon while they are
being processed. However, as explained above, Subpart W has
traditionally been applied to uranium byproduct material or tailings
after exiting the extraction process. Thus, Subpart W has not been
applied to other sources of radon at uranium recovery facilities where
wastes are present, such as material in thickeners or other processing
units. The NRC, or NRC Agreement State, regulates the radionuclide
emissions from all sources at a uranium recovery facility. The operator
is required to report particulate radionuclide and Rn-222
concentrations at the facility boundary. Thus, radon emissions from
sources not covered under Subpart W, including those from the raw ore
in heap leach piles or processed yellowcake, are captured by the NRC
reporting requirements. However, we emphasize that the best way to
control radon emissions from heap leach piles after they have completed
processing is to expeditiously close them and install a permanent radon
barrier.
b. Phased Disposal
    As described in the preceding section, after reviewing comments, we
have decided to require that heap leach piles conform to the standards
for other uranium recovery facility impoundments only during the period
between processing (i.e., after the pile's operational life) and
closure. Heap leach piles meeting this description will conform to the
GACT-based standard of phased disposal (piles that are 40 acres or less
in area, and no more than two in this status at any time) and follow
the construction requirements of 40 CFR 192.32(a)(1). We note that
piles that will close in place would separately be required by NRC or
Agreement State license to meet the construction requirements.
    Since heap leach piles are in many ways similar to the design of
conventional impoundments, the same combination of phased disposal
management practices (limitation to no more than two heap leach piles
that are no longer being processed but have not yet entered closure,
each one no more than 40 acres in area) that limit radon emissions from
conventional impoundments will also limit radon emissions from heap
leach piles. Because this management practice is generally available
for conventional impoundments, heap leach piles can control radon
emissions through the same practice. We determined that phased disposal
is a GACT-based management practice that will effectively limit radon
emissions from these units. Use of the phased disposal management
practice will limit the amount of exposed uranium byproduct material or
tailings that can emit radon. Because these units will be separately
required to comply with the requirements at 40 CFR 192.32(a)(1), we
concluded that such a management practice is generally available and
contributes to the control of radon emissions as described more fully
in Section IV.A.2.
c. Regulating the Moisture Content of Heap Leach Piles
    The third issue we are addressing is the proposed requirement for
heap leach piles to maintain a 30% moisture content. In the proposal we
recognized that owners and operators of conventional impoundments also
limit the amount of radon emitted by keeping the uranium byproduct
material or tailings in the impoundments covered, either with soil or
liquids (79 FR 25398). At the same time, we recognized that keeping the
uranium byproduct material or tailings in the heap in a saturated or
near-saturated state (in order to reduce radon emissions) is not a
similarly practical solution. In the definitions at 40 CFR 61.251(c) we
have defined ``dewatered'' tailings as those where the water content of
the tailings does not

exceed 30% by weight. We proposed to require operating heaps to
maintain moisture content of greater than 30% so that the uranium
byproduct material or tailings in the heap is not allowed to become
dewatered, which would allow more radon emissions. We specifically
asked for comment on the amount of liquid that should be required in
the heap, and whether the 30% figure was a realistic objective.
    After considering stakeholder comments and information, we conclude
that it is physically impossible to maintain a 30% moisture content
within the heap leach pile and have it remain stable.\17\ Calculations
submitted by numerous commenters showed that maintaining a 30% moisture
content across the heap leach pile would require the pile to be almost
submerged. Further, such a condition would place a great amount of
hydraulic head on the liner system, potentially causing failure. So,
the final rule does not include the requirement to maintain 30%
moisture content, even for the period between the end of processing and
the beginning of closure, when the pile will be allowed to ``dry'' in
preparation for placing a permanent radon barrier. We do encourage the
NRC and facility operators to consider the appropriate use of soil and
liquid to limit radon emissions from heap leach piles, as well as
methods to reduce the potential for wind erosion (e.g., by spraying or
covering the pile when not actively being leached). However, we
emphasize that the best way to control radon emissions from heap leach
piles after they have completed processing is to expeditiously close
them and install a permanent radon barrier.
---------------------------------------------------------------------------

    \17\ EPA-HQ-OAR-2008-0218-0144, -0162, -0169, -0170.
---------------------------------------------------------------------------

2. What key comments did we receive on heap leach piles?
    Comments submitted on heap leach piles focused on the proposed
approach to regulation and the proposed requirement to maintain a 30%
moisture content.
    Comment: Most commenters on this topic disagreed with our proposal
to regulate heap leach piles under Subpart W while they are being
processed. These commenters expressed the view that material in the
heap leach pile does not become uranium byproduct material or tailings
until processing is complete, including a final rinse. As stated by one
commenter, ``Heap leaching is part of the milling process, and the
proposed rules would interfere with such processing operations.'' The
commenter believes that, in essence, the heap leach pile is analogous
to the conventional mill, which we have not previously proposed to
regulate under Subpart W.
    Further, several of these commenters stated that heap leach piles
will immediately enter into closure upon the cessation of processing,
so there is no period when they are ``operating'' simply as uranium
byproduct material or tailings management units. As a result, they see
no time at which Subpart W can apply to heap leach piles.
    Some commenters raised the distinction between ``close in place''
piles and ``on-off'' piles. Commenters explain that the latter
operations involve the removal of the processed heap and placement in a
conventional impoundment. In this case, the commenters agree that the
uranium byproduct material or tailings from the heap, and the
impoundment into which it is placed, would be subject to Subpart W.
    Response: The final rule does not include requirements related to
heap leach piles undergoing processing. We acknowledge the comments
that indicate that uranium byproduct material or tailings is generated
once processing begins. To ensure that heap leach piles are regulated
consistent with other units subject to Subpart W, we conclude that the
heap leach pile is, for purposes of Subpart W, more appropriately
considered part of the milling process than as an impoundment whose
function is to manage uranium byproduct material or tailings. In other
words, while the pile may contain uranium byproduct material or
tailings, the pile itself is the ore from which uranium is being
extracted, and does not become a waste until that process is completed.
The rule does, however, cover the other impoundments used to manage the
uranium byproduct material or tailings associated with the heap
leaching operation.
    We appreciate the commenter's description of the ``on-off'' heap
leach piles and agree that if a processed heap is removed and placed in
a conventional impoundment, that impoundment is subject to Subpart W.
    We emphasize the importance of closing piles ``as expeditiously as
practicable considering technological feasibility'' once processing
concludes. Industry commenters provided assurances that there would be
no untoward delay in beginning the closure process. We encourage NRC to
ensure that this is the case. Closure is a more comprehensive system to
assure that emissions are minimized for the long term. Once processing
has ended, the heap leach pile serves only as a uranium byproduct
material or tailings management structure. Such a pile will be subject
to Subpart W if the operator has not informed regulators that it is
being managed under an approved reclamation plan. As set forth in the
final rule, in such a situation, the phased disposal restrictions will
apply (no more than two such piles at any time, with area no greater
than 40 acres each). Heap leach piles subject to Subpart W must also
comply with the construction requirements at 40 CFR 192.32(a)(1).
Timely closure of heap leach piles will be better for public health
than maintaining piles in an interim state in which they fall under
Subpart W.
    Comment: Some comments supported our proposed approach, and
recommended that we establish an emissions standard and monitoring
requirements for heap leach piles. These commenters agree that, because
uranium byproduct material or tailings is generated within the heap
leach pile at the time processing begins, the pile serves to manage
that material during the operation of the facility. These commenters
believe this function brings it under the scope of Subpart W. These
commenters also take a more expansive view, and believe the EPA is
obligated under the CAA to address the entire process at heap leach
facilities in the final rule. In this approach, Subpart W would apply
to ore stockpiles, ore crushing and heaps that are awaiting processing,
as well as to the heap until placement of the final cover. One
commenter further recommends that open-air heap leaching not be
approved, when leaching can be conducted more safely and with lower
emissions inside a designed enclosure.
    Response: As stated in the response to the previous comment,
Subpart W will not regulate heap leach piles while they are being
processed (i.e., during the heap leach pile's operational life). We
proposed to apply certain management practices to heap leach piles, but
did not propose to establish a radon emission standard and monitoring
requirements. Regarding the extension of Subpart W to ores and other
similar materials, when the EPA initially promulgated Subpart W in
1986, we identified radon as the radionuclide released to air that
presented the highest risk at uranium recovery facilities and
determined that units managing uranium byproduct material or tailings
were the most significant source of radon emissions (51 FR 34056).
Since 1986 and re-promulgation in 1989, Subpart W has only regulated
units that manage uranium byproduct material or tailings

at uranium recovery facilities. 40 CFR 61.250. Other potential emission
points in these facilities were not previously the subject of Subpart W
regulation and were not assessed for the 1989 rulemaking. The EPA's CAA
section 112(q) review of Subpart W was limited to the existing
standard. Because Subpart W did not regulate other potential emission
points, the EPA did not include any other potential emission points in
its CAA section 112(q) review. In this final rule, the EPA continues to
regulate the management of uranium byproduct material or tailings from
conventional mills, from in situ leach facilities and from heap leach
piles.
    Comment: A significant number of commenters raised objections to
the proposed requirement that heap leach piles be maintained at 30%
moisture content as a means to limit radon emissions. Calculations
submitted by numerous commenters have shown that to maintain a 30%
moisture content across the heap leach pile would require the pile to
be almost submerged. The commenters broadly agreed that this is an
unrealistic goal that could severely undermine the stability of the
pile. Further, it would result in a significantly greater hydraulic
head, which raises the risk of liner failure. Several commenters also
consider the monitoring requirement to be difficult to implement. As
with the proposal to maintain one meter of liquid in non-conventional
impoundments, concern was also expressed regarding the source of the
water. Commenters suggested that a simpler water balance, which would
involve calculations of the amount of liquid entering and leaving the
pile, would be a more implementable method of estimating moisture
content.
    Response: Recognizing the difficulties associated with maintaining
a 30% moisture content across the heap leach pile, the final rule does
not include a requirement related to the moisture content of heap leach
piles. That being said, keeping the pile wet or covered will help
reduce radon emissions. We encourage operators as well as the NRC and
NRC Agreement States to consider methods that can be applied during the
operational life of the heap leach pile.

E. GACT for Non-Conventional Impoundments

1. How did we address non-conventional impoundments in the proposed and
final rules?
    The purpose of non-conventional impoundments, also known as
evaporation or holding ponds, is to manage liquids generated during and
after uranium processing operations. We proposed to require one meter
of liquid to remain in the impoundment at all times (79 FR 25411). The
liquid cover was proposed as a management practice that would limit
radon emissions from the uranium byproduct material or tailings.
    The Subpart W regulation as promulgated in 1989 did not clearly
distinguish between conventional tailings impoundments and those
operating as ponds (i.e., those defined as ``non-conventional
impoundments'' in this final rule). The proposed regulation intended to
clarify this distinction.
    For non-conventional impoundments, the proposed rule allowed for an
unlimited number of units to be operating, with no size limitation, but
required that a depth of one meter of liquid be kept above any
precipitated solids (uranium byproduct material or tailings). The use
of the word ``liquid'' is important here. Typically, operators divert
process water to evaporation or holding ponds, where it may be
recycled, treated, evaporated, or disposed by injection. Thus, it is
likely that the liquid entering the impoundment will contain uranium
byproduct material or tailings in solution or suspension. Some portion
of this uranium byproduct material or tailings will settle out into
sediments. In our proposal we did not specify that the one meter of
liquid covering a non-conventional impoundment be fresh water; however,
we did refer to ``water'' in the preamble, and the comments demonstrate
that there has been some confusion about this point.
    Various commenters described the cost of locating fresh water in
the semi-arid and arid western portions of the United States in order
to meet the one meter requirement. Other comments focused on the
limitations in operational flexibility that a fresh water cover would
create by changing the chemistry of a stream that is often recycled
back into the extraction process, or noted that this requirement would
require re-design of impoundments.
    We recognize that this requirement could result in the need to use
large volumes of water that may not be readily available in the arid to
semi-arid areas in which most uranium recovery facilities operate. Even
for facilities that maintain large volumes of process water in ponds,
there would likely be some demand for fresh water as a supplement to
maintain the required liquid level. Further, maintaining this level of
liquid cover would result in placing significantly more hydraulic head
on the liner systems for the impoundments, which is counter to existing
state and federal regulations and guidelines for operating these
systems, as well as a concern to the Agency that the liner would be
more susceptible to failure.
    In light of these comments, we took a closer look at the proposed
requirement. The best indicator of potential Rn-222 emissions during
the impoundment's operating period is the concentration of Ra-226 in
the liquid and sediment. The BID to support the 1989 rulemaking
indicates that the Ra-226 concentrations in conventional uranium
byproduct material or tailings is as much as an order of magnitude
higher than evaporation pond sediments at the same uranium recovery
facility (1989 BID Volume 2, Risk Assessments, EPA/520/1-89-006-1,
Table 9-2, Docket No. EPA-HQ-OAR-2008-0218). We have recognized that
keeping uranium byproduct material or tailings in conventional
impoundments wet helps to limit radon emissions. Moreover, this
management practice is used throughout the industry, even in arid
regions, and can thus be considered ``generally available.'' We have
further recognized that the difference between uranium byproduct
material or tailings that are saturated and those covered with one
meter of liquid is negligible (79 FR 25398). Therefore, the final
rule's requirement that solids remain saturated achieves the same goal
as the proposed standard of maintaining a one-meter liquid cover.
    Commenters also expressed concern over Rn-222 emissions resulting
from Ra-226 dissolved in the liquid present in non-conventional
impoundments, as opposed to solid materials in the bottom of the
impoundment. A number of commenters questioned our conclusion that
radon emissions from uranium byproduct material or tailings in non-
conventional impoundments could be greatly reduced by keeping the
solids saturated, and reduced to nearly zero by maintaining a liquid
cover. The BID shows in Figure 12 that 100% saturated soil reduces
radon emanation by nearly 95% compared to dry material, while one meter
of liquid provides a further reduction of about 93%, or an overall
reduction of greater than 99% (BID Equation 5.1).\18\ In either case,
radon emissions from non-conventional impoundments would be controlled
to levels that represent limited risk to public health. However,
commenters argued that actual data on the liquid contents of non-
conventional impoundments (primarily from the

White Mesa mill), when evaluated using a correlation in the updated
risk assessment, showed radon emissions well in excess of 20 pCi/m\2\-
sec.
---------------------------------------------------------------------------

    \18\ See also ``Risk Assessment Revision for 40 CFR part 61
Subpart W: Task 5--Radon Emissions from Evaporation Ponds,'' S.
Cohen & Associates, November 2010, Docket No. EPA-HQ-OAR-2008-0218-
0123.
---------------------------------------------------------------------------

    We carefully evaluated the data and emissions analyses submitted by
commenters. We determined that the data cited by the commenters did not
support their conclusions. We conclude that our analysis in the
proposal was correct regarding the characteristics of non-conventional
impoundments and the radon attenuation that could be achieved. See
Section IV.E.2 for more detail on this issue.
    To summarize, we received comments that raise concerns regarding
the economic and technical feasibility, as well as the practical
effect, of specifying a liquid level for non-conventional impoundments.
We further confirmed that keeping the sediments in a non-conventional
impoundment at 100% saturation is nearly as effective as maintaining
one meter of water (liquid) cover (Figure 12 in the BID for the final
rule). The cost and logistics of maintaining a one-meter liquid cover
in arid regions also favor maintaining saturation, especially given
that saturation effectively controls emissions and will limit economic
impacts.
    We evaluated management practices in use at non-conventional
impoundments in the industry that could achieve the goal of limiting
radon-222 emissions from these units. These units are designed to hold
liquid, and typically any uranium byproduct material or tailings
contained in these impoundments is covered by liquid. Maintaining a
liquid cover over the uranium byproduct material or tailings would
effectively control radon and is a practice that is generally available
to owners and operators of non-conventional impoundments. Therefore, we
have revised the proposed rule language to indicate that the solids in
a non-conventional impoundment must remain saturated at all times. In
this final rule, we are establishing this condition, along with the
liner requirements in 40 CFR 192.32(a)(1), as GACT-based standards for
non-conventional impoundments. As noted above, this will reduce radon
emissions by approximately 95% compared to dry conditions. We recognize
that operators may still have to add water at times to ensure that the
uranium byproduct material or tailings remain saturated, particularly
during standby or high-evaporation periods. However, we anticipate that
the need for additional water will be much less than would be necessary
to maintain one meter of liquid. Because these impoundments are
separately required to comply with the requirements at 40 CFR
192.32(a)(1), we concluded that such a management practice is generally
available and contributes to the control of radon emissions as
described more fully in Section IV.A.2.
    The final rule requires that visual evidence of saturation must be
recorded and maintained by the owner/operator of the non-conventional
impoundment, which we anticipate can be obtained using a smartphone or
a digital camera during the routine daily inspections required by NRC
regulations. Written observations must be recorded daily, with digital
photographs to be taken at least weekly. Photographs including embedded
metadata must be uploaded to the Subpart W Impoundment Photographic
Reporting (SWIPR) Web site maintained by the EPA on at least a monthly
basis, beginning on the effective date of this final rule.\19\ Until
that time, and subsequently should the SWIPR site be unavailable,
digital photographs must be maintained by the facility owner/operator
and provided to the EPA or authorized State upon request. Should the
operator determine that the liquid has fallen to a level that exposes
solid materials, the operator must correct the situation within one
week, or other such time as specified by the EPA or the authorized
State. This provides flexibility if the operator needs to take the
impoundment out of service for a longer period to address the
situation, such as to repair the liner. Photographs must be taken that
show conditions before and after the liquid level is adjusted to verify
that appropriate corrective actions have been taken. There is no limit
on the size or number of non-conventional impoundments.
---------------------------------------------------------------------------

    \19\ SWIPR is accessed through the EPA's Central Data Exchange
(CDX) (https://cdx.epa.gov). Information submitted to SWIPR is
available to the public after review.
---------------------------------------------------------------------------

2. What key comments did we receive on non-conventional impoundments?
    We received a variety of comments related to non-conventional
impoundments. Many were related to the proposed requirement to maintain
one meter of liquid in the impoundment. Others related to the potential
for radon emissions from liquids in the impoundments, and whether those
risks were properly characterized.
    Comment: Many commenters opposed the proposed requirement to
maintain one meter of liquid in the impoundment. Commenters primarily
cited cost and the logistical difficulty of obtaining and transporting
water as making this proposed requirement overly burdensome,
particularly in the arid West. A few commenters noted that impoundments
that had already been approved and operating were not constructed with
a depth that could accommodate an additional meter of water,
potentially necessitating costly renovation. Other commenters noted
that this requirement would have effects on the facility operation,
where it is necessary to manage evaporative or holding capacity, and to
control the characteristics of liquids that may be recycled through the
process. The additional stress on the impoundment liner was also
raised.
    Some commenters questioned the need for this requirement, and noted
statements in previous rulemakings that the difference between
saturation and one meter of water is negligible. Commenters further
argued that non-conventional impoundments present a small risk in any
case. A few commenters suggested that a better approach would be to
require that solid materials in the impoundment remain saturated, with
no solids visible above the liquid level.
    Response: We recognize the concerns raised regarding maintaining
one meter of liquid in non-conventional impoundments. Because we
determined that radon emissions can be controlled if the solids in non-
conventional impoundment remain saturated, the final rule does not
include a requirement to maintain one meter of liquid in the
impoundments. Instead, the final rule adopts the approach suggested by
the commenters. Solid materials in the impoundment must remain
saturated, with no solids visible above the liquid level. This will
achieve a reduction of roughly 95% compared to emissions from dry
material. Saturation must be documented by written and visual records,
with digital photographs taken on at least a weekly basis. We disagree
that the non-conventional impoundments present such a small risk that
they need not be regulated under Subpart W.
    Comment: Commenters find difficulties in measuring compliance with
the proposed one meter liquid requirement. One commenter believes
direct measurements will be difficult because of the density of
sediments and may present health and safety risks to workers. The
commenter suggests that calculations based on mass and liquid balances
would be more effective. Another commenter makes a similar suggestion,
that the one meter requirement be replaced with a calculation to take
into account site-specific factors and give operators

greater flexibility. A third commenter sees problems with the slope of
the impoundment and the distance that must be observed, and notes that
past experience suggests that measuring devices (such as pressure
transducers) will need frequent maintenance and calibration. The
commenter prefers to have a simple permanent indicator allowing visual
confirmation, rather than measurement.
    Response: We appreciate these comments and thoughtful suggestions.
The final rule does not include a requirement to maintain one meter of
liquid in the impoundments. Instead, the final rule requires that solid
materials in the impoundment must remain saturated, with no solids
visible above the liquid level. Although we proposed a one meter liquid
cover, comments and further evaluation persuaded us that keeping solids
saturated controls emissions nearly as effectively as maintaining a
one-meter liquid cover. As explained in Section IV.E.1, we have
recognized that keeping uranium byproduct material or tailings wet
helps to limit radon emissions. We have further recognized that the
difference between uranium byproduct material or tailings that are
saturated and those covered with one meter of liquid is negligible. See
Section IV.E.1 and 79 FR 25398.
    Comment: Some commenters argue that the potential for radon
emissions from non-conventional (liquid) impoundments has been greatly
understated. They state that the general position taken by regulatory
agencies (including the EPA) and industry that these impoundments
represent a negligible source of radon compared to the solids in
conventional impoundments is not supported by data. In particular, the
commenters believe that radium in solution or suspension in the liquids
has been overlooked as a potential source of radon, compared to solids
or sediments in the bottom of the non-conventional impoundments.
Commenters cited data from the 2013 and 2014 ``Annual Tailings System
Wastewater Sampling Report'' submitted by Energy Fuels to the State of
Utah to support this contention. Using radium data from liquid samples
collected from Cells 1, 3, 4 and 4A at the White Mesa Mill and a
correlation to radon flux from liquids in the EPA's risk assessment to
support the rulemaking (the ``Task 5'' report, Docket No. EPA-HQ-OAR-
2008-0218-0123), the commenters calculate radon fluxes well in excess
of 20 pCi/m\2\-sec (up to 2,317 pCi/m\2\-sec from Cell 1 in 2014). The
commenters further note a significant increase in the radium
measurements for three of the four impoundments from 2013 to 2014,
likely attributable to evaporation and concentration of the radium in
solution (Cell 3 showed a significant increase from 2012 to 2013, but
dropped in 2014). They conclude that the risk to public health
associated with radon emissions from non-conventional impoundments is
much greater than the EPA has acknowledged.
    Response: The EPA disagrees that the data provided by commenters
support their conclusion that the liquids have been underestimated as a
source of radon. First, the laboratory analyses included in the
sampling report refer to ``Total Alpha Radium'' (or ``Gross Radium
Alpha'') and specify the analytical method as EPA Method 900.1.\20\
This method cannot distinguish between different alpha-emitting
isotopes of radium, which are all chemically identical. In addition to
Ra-226, the isotope of concern that decays to form Rn-222, the sample
may also contain Ra-224 (a decay product of Thorium-232) and Ra-223 (a
decay product of Uranium-235). Because of the vast difference in their
decay rates,\21\ Ra-224 and Ra-223 need be present in much smaller
amounts (by mass) to have the same activity as Ra-226. For example, one
gram of Ra-226 will have the same activity as about 6.25 micrograms
(6.25 x 10-\6\ grams) of Ra-224. It is known that the White
Mesa Mill has processed materials containing Th-232, which makes it
likely that Ra-224 is present in some amount. Given these sources of
uncertainty, these results cannot definitively represent Ra-226
concentrations. Other sources of uncertainty could include interference
from barium present in the liquid sample, as Method 900.1 relies upon
precipitation with barium sulfate to separate the radium. Moreover,
while Method 900.1 can essentially separate uranium from the sample, it
is less effective at separating other alpha-emitting radionuclides,
such as isotopes of thorium. Thus, some small amounts of uranium and
thorium could solubilize and ``carryover'' into the precipitated
sample, which would also affect the analysis. Given the numerous
uncertainties associated with the data relied upon by the commenters,
these data cannot reliably serve as a surrogate for Ra-226. Without
specific isotopic analyses, which were not performed on the samples
presented in the 2013 and 2014 reports, the actual Ra-226
concentrations cannot be determined.
---------------------------------------------------------------------------

    \20\ ``Prescribed Procedures for Measurement of Radioactivity in
Drinking Water,'' EPA-600/4-80-032, August 1980, Docket No. EPA-HQ-
OAR-2008-0218.
    \21\ Radium-226 has a half-life of 1,600 years, while Radium-224
and -223 have half-lives of 3.66 days and 11.43 days, respectively.
EPA Method 900.1 has been used by drinking water systems to show
compliance with the regulatory standard of 5 pCi/L for combined Ra-
226 and Ra-228, which is well below the activity found in effluents
from uranium processing. Ra-228 is a pre-cursor of Ra-224 that
decays by beta emission and has a half-life of 5.75 years. If the
result is below 5 pCi/L using Method 900.1, there is no need for
additional analysis. Half-life is the amount of time for one-half of
the radionuclide to decay. Further, although Ra-223 and Ra-224 decay
to form Rn-219 and Rn-220 (also known as ``thoron''), respectively,
these isotopes of radon are also very short-lived (half-lives less
than one minute each) and therefore are not considered to be of
concern for exposures to the public.
---------------------------------------------------------------------------

    The 2015 annual wastewater sampling report for White Mesa \22\
contains additional information to clarify this situation. Samples
taken on two separate occasions from each of the cells (compared to the
single sampling conducted in previous years) were analyzed not only for
total alpha radium, but also for the isotope Ra-226, using EPA Method
903.1 (``Prescribed Procedures for Measurement of Radioactivity in
Drinking Water,'' Docket No. EPA-HQ-OAR-2008-0218). These results
confirm that total alpha radium is not the correct basis for
calculations of radon emissions. Table 4 below shows the 2015 results
for Cell 1, compared to the 2013 and 2014 results that were cited by
the commenters. Cell 1 has been in use since 1981, and has only been
used to manage liquids (i.e., no solids from the mill have been placed
in it). It consistently shows among the highest levels of total alpha
radium.
---------------------------------------------------------------------------

    \22\ Environmental reports for the White Mesa Mill are available
from the Utah Department of Environmental Quality at http://www.deq.utah.gov/businesses/E/energyfuels/whitemesamill.htm.

     Table 4--Monitoring Results From Cell 1 at the White Mesa Mill
------------------------------------------------------------------------
                                   Total alpha
                                 radium (pCi/L)       Ra-226 (pCi/L)
------------------------------------------------------------------------
2013...........................          32,700  Not analyzed.

2014...........................         331,000  Not analyzed.
2015 Sample 1..................          73,800  829.
2015 Sample 2..................         735,000  1,110.
------------------------------------------------------------------------
Source: ``2015 Annual Tailings System Wastewater Sampling Report,''
  Energy Fuels.

    The Ra-226 concentrations found in 2015 are consistent with
historical data, also included in the sampling reports. For the period
1980-2003, the maximum concentration of Ra-226 recorded is 1,690 pCi/L,
based on sampling from Cell 1, Cell 2, and Cell 3 (it is not specified
which cell recorded the maximum concentration). Table 6 of the Task 5
report estimates that, based upon site-specific conditions at the White
Mesa Mill, a Ra-226 concentration of 1,000 pCi/L in impoundment liquids
would result in a radon flux of approximately 7 pCi/m\2\-sec. Using
this correlation, the average radon flux from Cell 1 in 2015 would be
slightly less than 7 pCi/m\2\-sec. The highest level of Ra-226 in 2015
from the other impoundments was 772 pCi/L in Cell 4A, which translates
to a radon flux of about 5.4 pCi/m\2\-sec. Further, based on the
maximum Ra-226 concentration recorded from 1980-2003, the calculated
radon flux would be roughly 11.8 pCi/m\2\-sec. These results indicate
that the radon flux from Ra-226 suspended or dissolved in liquids in
the non-conventional impoundments at White Mesa is controlled to a
level that is within the range that the EPA determined to be acceptable
during the development of Subpart W, without taking additional
measures.
    These results are also consistent with information reported for
liquid impoundments at ISL facilities (see Tables 7, 8 and 9 of the
Task 5 report). They also suggest that the noteworthy fluctuations in
recent years may not be directly attributable to the radium content of
the liquids, but may result from the analytical method used. ``Total''
or ``gross'' analytical methods are generally considered screening
tools whose results are more susceptible to other influences. Energy
Fuels states that the individual isotopic analyses ``show that the
increasing gross alpha results are being caused by matrix interference
due to the nature of the tailings solution and are not representative
of gross alpha from radium concentrations in the solution'' (Energy
Fuels, 2015 annual wastewater sampling report, page 15). Similar
fluctuations occurred for all the impoundments (although, as noted
earlier, Cell 3 showed a significant increase in 2013, with a decrease
in 2014).
    As an additional source of information, the facility's 2015 ``Semi-
Annual Effluent Monitoring Report'' (July through December) provides
radon monitoring data from air monitoring stations posted around the
impoundments. The facility resumed monitoring for radon in 2013 and the
data presented in Attachment J of the report show that emissions have
been within the limits calculated to correspond to a 25 mrem annual
dose for continuous exposure at each monitoring station. These limits
serve as As Low As Reasonably Achievable (ALARA) goals for the
facility.
    In most cases, results are well below that level. The highest
annual result (four consecutive quarters) can be seen for Station BHV-
4, which is located directly south of the impoundments but still within
the White Mesa facility boundary. A person located at this point during
2015 would have incurred a dose of approximately 16 mrem \23\ (average
quarterly results of roughly 0.31 pCi/L, compared to a calculated limit
of 0.5 pCi/L). The single highest quarterly reading is listed at
Station BHV-6, which is to the southeast of the impoundments at the
facility boundary. The reading for the fourth quarter of 2013 is
approximately 88% of the calculated limit (0.73 compared to 0.83,
translating to a quarterly dose of about 5.5 mrem at that location).
However, readings for the previous two quarters were recorded as zero
and readings for the next quarters were significantly lower as well.
There is fluctuation in these results as well, which depends to some
extent on wind direction, but overall the results indicate that radon
from the impoundments is not a significant public health concern.
---------------------------------------------------------------------------

    \23\ Corresponding to an annual risk of fatal cancer of less
than 1 x 10-\5\. See Section 4 of the BID.
---------------------------------------------------------------------------

    Both the sampling data from the non-conventional impoundment cells
and the radon data from the air monitoring stations at the White Mesa
Mill support the EPA's conclusion that emissions from the liquids in
non-conventional impoundments represent a limited source of radon and
does not support commenters' argument to the contrary.
    Comment: Some commenters request clarification that Subpart W
should not apply to impoundments that only contain water that has been
treated to meet effluent limits. The commenters see this as having no
regulatory benefit, but a potential additional cost to operators who
must meet the more stringent requirements in 40 CFR 192.32(a)(1).
Commenters also suggest we define a threshold level of radium or
uranium content below which liquids no longer must be managed as
uranium byproduct material or tailings.
    Response: The purpose of Subpart W is to control radon emissions
from sources containing uranium byproduct material or tailings at
uranium recovery facilities. The EPA agrees that if an impoundment does
not contain uranium byproduct material or tailings, it is not subject
to the requirements of Subpart W. The EPA is not defining a
concentration or level of radium or uranium at which treated liquids
would no longer be considered uranium byproduct material or tailings.
Instead, such impoundments can be identified and their status can be
addressed during the construction application review under 40 CFR part
61, subpart A.
    Subpart W also does not apply to impoundments constructed for the
purpose of managing liquids generated by closure or remediation
activities, when they are used solely for that purpose. Impoundments
that do not contain uranium byproduct material or tailings resulting
directly from uranium recovery operations are not considered to be non-
conventional impoundments as defined in Subpart W.
    However, non-conventional impoundments remain subject to the
requirements of Subpart W until they enter final closure pursuant to an
approved reclamation plan for that impoundment, even if at some point
in their operational life they are used for the purpose of managing
liquids from closure or remediation activities. EPA recognizes that
non-conventional impoundments that are subject to

Subpart W may subsequently transition to a use that supports facility
closure or site remediation (e.g., when an ISL wellfield enters into
the groundwater restoration phase, and is no longer recovering
uranium). Some parties may argue that a non-conventional impoundment's
receipt of waste associated with facility closure or site remediation
appears analogous to the ability of licensees to obtain a license
amendment and have a reclamation plan which provides for placement of
remediation wastes in conventional impoundments during the closure
process. Using this analogy, some may contend that non-conventional
impoundments should not be subject to Subpart W when receiving such
wastes. However, such a non-conventional impoundment could later be
used to manage liquids from uranium recovery operations at the next
wellfield. To ensure that non-conventional impoundments that receive
uranium byproduct material and tailings are managed in accordance with
Subpart W, and to promote clarity and consistency with the promulgated
regulations, Subpart W applies to non-conventional impoundments during
the entire operating life of an impoundment which receives, or has
received, uranium byproduct material or tailings directly from active
uranium recovery operations. Changing a non-conventional impoundment's
Subpart W applicability based on the primary use of the impoundment at
any particular time during its operational life would cause unnecessary
confusion and would be inconsistent with the regulations.
    Operationally, this should not represent a burden to licensees. If
the impoundment is being used to manage liquids from closure or
remediation activities, it should remain in compliance with the
requirement to retain sufficient liquid to cover solid materials in the
impoundment. Further, because there is no restriction on the number of
such impoundments that may be operating at one time, the licensee will
not face the same pressure to begin closure as applies to conventional
impoundments using the phased disposal approach.
    Comment: A commenter finds the discussion of non-conventional
impoundments confusing. The commenter believes we have inconsistently
and inaccurately described the purpose of these impoundments, the
nature of the materials in them, and our regulatory approach. The
commenter wishes us to clarify that the liquids are not held in the
impoundments for the purpose of covering uranium byproduct material or
tailings, but the liquid in fact contains (or is) uranium byproduct
material or tailings. The commenter questions how the liquid can be
used to control radon emissions, when the liquid is itself in need of
control, and requests that we consider that liquids high in radium
content may actually cause an increase in emissions.
    Response: The purpose of non-conventional impoundments (evaporation
or holding ponds) is to receive liquids generated by the uranium
processing operation. Uranium byproduct material or tailings may be
suspended or dissolved in these liquids. Some portion of the material
will precipitate out and settle on the bottom of the impoundment. In
some sense, the liquid itself is uranium byproduct material or tailings
because it is a waste from the concentration or extraction process. The
definition of ``non-conventional'' impoundment accurately conveys the
concept that these impoundments ``contain uranium byproduct material or
tailings suspended in and/or covered by liquids.'' As noted in the
previous comment response, impoundments containing only treated water
and impoundments constructed for the purpose of managing liquids from
closure or remediation activities are not non-conventional impoundments
as defined by Subpart W, because they do not contain uranium byproduct
material or tailings resulting directly from active uranium recovery
operations.
    While radium contained in the liquid will contribute to radon
emissions, those emissions will be attenuated to some degree by the
liquid in which it is contained. Further, liquid on top of solid
materials will effectively limit radon emissions from those solids
reaching the air, even if the liquid itself contains radium. While
higher concentrations of radium in the liquid will generate more radon,
concentrations in non-conventional impoundments have not been seen to
reach levels of concern. See the response to the earlier comment in
this section.
    Comment: Many commenters expressed opinions related to limiting the
size of impoundments. Some commenters believe Subpart W should contain
limits on the size of non-conventional impoundments. The commenters
believe that larger impoundments are more likely to fail and limits
must be imposed to minimize the potential for ground water
contamination. One commenter also believes the number of impoundments
should be limited. Another commenter does not believe we have
adequately supported our conclusion that the requirements of 40 CFR
192.32(a)(1) will provide protection against extreme weather events and
may be subject to greater turbulence. Regarding our reference to an
impoundment of 80 acres, one commenter wishes us to clarify that no
actual impoundment has been as large as 80 acres, but this size has
been used only for modeling purposes. Another disputes our statement
that it is reasonable to assume that such impoundments will not exceed
80 acres in area, simply because one never has.
    Response: We have chosen not to limit the size of non-conventional
impoundments because they are not as significant a source of radon
emissions and can be readily controlled by maintaining saturation of
solid materials, but also because they provide operational flexibility
to uranium recovery facilities that may need to manage, on a temporary
basis, large volumes of water that can then be recycled into the
process. Regarding the maximum size of such impoundments, we referred
to 80 acres as a ``reasonable maximum approximation'' for estimating
cost, clearly noting that it is ``the largest size we have seen'' (79
FR 25401).
    Comment: A commenter states that the current and proposed rules do
not actually contain any measures to control releases of impoundment
contents to the surface or subsurface during extreme weather events.
The commenter asserts that the EPA has not provided any data to support
the conclusion that the requirements of 40 CFR 264.221 will prevent
dispersion of contents in severe events. The commenter expresses
concern that generally available technologies do not exist that could
prevent dispersion of contents or failure of the impoundment in a
severe event such as a tornado or hurricane.
    Response: As discussed in the proposal, we believe the design and
engineering requirements for impoundments in 40 CFR 264.221, referenced
in 40 CFR 192.32(a)(1), provide a sound basis for protection against
reasonably foreseeable weather events. The provisions related to
avoiding overtopping (essentially, spillage or dispersion) from
``normal or abnormal operations,'' ``wind and wave action,'' or
``rainfall,'' as well as the requirement to maintain integrity and
prevent massive failure of the dikes, lay a foundation for addressing
the commenter's concerns. To satisfy these conditions, design of
impoundments at any specific site would likely take into account
regional climate and the

magnitude of events such as 100- or 500-year precipitation, or the
likelihood of tornados or hurricanes.

F. Definitions, References and Conforming Editorial Revisions

1. How did we address definitions, reference and conforming editorial
revisions in the proposed and final rules?
a. Definition of ``Operation'' and ``Final Closure''
    We proposed a relatively minor change to the definition of
``operation'' (79 FR 25404). Under Subpart W as promulgated in 1989, an
impoundment was in operation when new tailings were being emplaced,
from the day that tailings are first placed in the impoundment until
the day that final closure begins. There has been some confusion over
this definition. We proposed to amend the definition of ``operation''
in the Subpart W definitions at 40 CFR 61.251 to replace the reference
to ``new'' tailings with the broader term ``uranium byproduct material
or tailings'' at 79 FR 25405.
    We received comments from across the spectrum of stakeholders who
disliked this definition. Commenters from industry said we did not take
into account the period between cessation of placement of uranium
byproduct material or tailings into an impoundment and physical closure
with an approved closure plan. This period can sometimes last for years
while the uranium byproduct material or tailings are dewatered to an
extent that heavy machinery can be used to emplace the final closure
radon barrier. Also, the impoundment(s) are often used for dismantling
the facility, for disposal of other liners, etc. Extending the
operational period and Subpart W jurisdiction during the entire closure
period could result in a milling facility having two operating
impoundments in the closure process and no ability to operate a third
impoundment to receive uranium byproduct material or tailings from
operations. Other commenters claimed that operators were taking
advantage of the existing definition by claiming that an impoundment is
``in closure'' but taking no concrete action to implement a closure
plan or apply a final cover.
    We do not intend to extend the jurisdiction of Subpart W to include
the period during which closure activities are being conducted. The
proposal was intended to clarify that an impoundment remains
``operating'' until it enters closure, even if it is not receiving
newly-generated uranium byproduct material or tailings from facility
processing (79 FR 25405). Further, we note that the definition in
Subpart W is consistent with those in 40 CFR 192.31 and 10 CFR part 40,
Appendix A, which were in fact derived from Subpart W. Thus, we find
this concern to be misplaced. The final rule adopts the definition of
``operation'' as it was proposed.
    We did not propose to include a definition of ``closure''; however,
we realize that a lack of clarity on the concept of closure, what it
involves and when it begins has affected the understanding of Subpart
W. In particular, the use of the term ``final closure'' in the
definition of ``operation'' does not, by itself, provide sufficient
clarity on the end of operation. As described earlier, we received a
number of comments making suggestions or raising concerns on this
point. As noted above, the definition of ``operation'' in Subpart W
served as the basis for the definitions later adopted in 40 CFR part
192 and 10 CFR part 40, Appendix A. Further, both 40 CFR part 192 and
10 CFR part 40, Appendix A adopted definitions and requirements related
to closure that address some aspects of the comments we received
related to Subpart W. The more appropriate action is to retain the
definition of ``operation'' and clarify the meaning of final closure in
a separate definition. Therefore, the final rule incorporates a new
definition of ``final closure'' at 40 CFR 61.251(n).
    We emphasize two aspects of this new definition that we believe
will help address concerns regarding the timeliness and predictability
of closure activities. First, impoundments or heap leach piles will
remain subject to Subpart W until the owner or operator provides
written notice that the impoundment is entering final closure. Second
is the reference to the reclamation plan for the impoundment or heap
leach pile. We have heard some comments, specifically related to the
Cotter mill, that the facility should still be subject to Subpart W
because it has never had an approved reclamation or closure plan;
however, the facility no longer has an operating license under which it
would conduct activities subject to the requirements of Subpart W.
    The reference to a reclamation plan in the definition of ``final
closure'' does not affect that Subpart W only applies to operational
units and does not cover units that are in closure. Rather, it makes
clear our expectation, also found in 40 CFR part 192 and 10 CFR part
40, Appendix A, that the NRC or the Agreement State require and approve
such a plan. It also establishes that notice to the NRC or the
Agreement State and an approved reclamation plan are necessary
prerequisites for determining that the impoundment in question is no
longer subject to the requirements of Subpart W. The final rule is
adopting the terminology employed in NRC regulations. In 10 CFR part
40, Appendix A, NRC identifies a reclamation plan as applicable to
individual impoundments, while the closure plan is a more comprehensive
document that addresses all aspects of facility closure and
decommissioning, including any necessary site remediation. A
reclamation plan prepared and approved in accordance with NRC
requirements in 10 CFR part 40, Appendix A, is considered a reclamation
plan for purposes of Subpart W. The reclamation plan may be
incorporated into the larger facility closure plan.
    A number of commenters expressed concern that the issue of delayed
closure would have been addressed by 40 CFR part 61, subpart T (40 CFR
61.220-226), which required that impoundments that are no longer
accepting tailings be brought into compliance (i.e., covered) within
two years, or in accordance with an approved compliance agreement if it
is not feasible to complete closure within two years. In accordance
with a 1991 Memorandum of Understanding (MOU), the EPA and the NRC
amended 40 CFR part 192 and 10 CFR part 40, Appendix A, respectively,
to incorporate provisions related to the timing and requirements of
activities conducted during the closure period. The EPA subsequently
rescinded subpart T in 1994, finding that the NRC regulatory program
protected public health with an ample margin of safety to the same
level as would implementation of subpart T (59 FR 36280, July 15,
1994). The commenters correctly noted that in that action the EPA
retained the authority to reinstate subpart T should we determine that
the NRC was not implementing it as we intended. The Agency has no plans
to reinstate subpart T at this time, but takes this opportunity to
emphasize that closure of impoundments should be conducted
expeditiously, taking only the time that is truly necessary to dewater
or otherwise prepare the uranium byproduct material or tailings before
application of interim and final covers.
b. Liner Requirements in 40 CFR 192.32(a)(1)
    We proposed specific provisions for conventional impoundments, non-
conventional impoundments and heap leach piles to explicitly convey
that any impoundment at a uranium recovery

facility that contains uranium byproduct materials or tailings would be
subject to the Subpart W liner requirements. The 1986 and 1989 versions
of Subpart W included a reference to 40 CFR 192.32(a); 40 CFR 192.32(a)
incorporates the surface impoundment design and construction
requirements of hazardous waste surface impoundments regulated under
the Resource Conservation and Recovery Act (RCRA), found at 40 CFR
264.221. Those requirements state that the impoundment shall be
designed, constructed and installed to prevent any migration of wastes
out of the impoundment to the adjacent subsurface soil or ground water
or surface water at any time during the active life of the impoundment.
Briefly, 40 CFR 264.221(c) requires that, for new impoundments
constructed after January 29, 1992,\24\ the liner system must include:
---------------------------------------------------------------------------

    \24\ 57 FR 3487, January 29, 1992. These specifications also
apply to lateral expansions of existing surface impoundment units or
replacements of existing surface impoundment units beginning
construction or reuse after July 29, 1992. At the time of the 1986
and 1989 Subpart W rulemakings, double liners and leachate
collection systems were specified for new impoundments, but the
requirements did not contain this level of detail. The requirement
for double liners was promulgated on July 15, 1985 (50 FR 28747).

    1. A top liner designed and constructed of materials (e.g., a
geomembrane) to prevent the migration of hazardous constituents into
the liner during the active life of the unit.
    2. A composite bottom liner consisting of at least two
components. The upper component must be designed and constructed of
materials (e.g., a geomembrane) to prevent the migration of
hazardous constituents into this component during the active life of
the unit. The lower component must be designed and constructed of
materials to minimize the migration of hazardous constituents if a
breach in the upper component were to occur. The lower component
must be constructed of at least three feet of compacted soil
material with a hydraulic conductivity of no more than 1 x
10-\7\ cm/sec.
    3. A leachate collection and removal system between the liners,
which acts as a leak detection system. This system must be capable
of detecting, collecting and removing hazardous constituents at the
earliest practicable time through all areas of the top liner likely
to be exposed to the waste or liquids in the impoundment.

    There are other requirements for the design and operation of the
impoundment, and these include construction specifications, slope
requirements, sump requirements and liquid removal requirements. As
part of the proposed rule, we examined these provisions to help
determine whether Subpart W adequately addresses extreme weather
events. We determined that the requirements in 40 CFR 264.221
satisfactorily address such events.
    The proposal did not adopt a new approach. Instead, it carried
forward the approach adopted in the 1989 rulemaking. That rulemaking
included Sec.  61.252(c), which broadly required all impoundments,
including those in existence prior to the promulgation of 40 CFR part
192, to comply with the requirements of 40 CFR 192.32(a). The 1986
rulemaking had not applied the requirements of 40 CFR 192.32(a) to
impoundments in existence when the 1986 rule was promulgated, as these
impoundments were anticipated to cease accepting uranium byproduct
material or tailings by the end of 1992 (51 FR 34066). The 1989
rulemaking lifted this restriction as well as the exemption from the
requirements of 40 CFR 192.32(a) (54 FR 51680).
    We did not propose to remove the liner requirements or request
comment on whether they should be retained. We proposed to refer only
to 40 CFR 192.32(a)(1) because Sec.  192.32(a) includes provisions that
extend well beyond the design and construction of impoundments, such as
ground water monitoring systems and closure requirements. These aspects
do not fall under the purview of Subpart W, and they are removed in
this action.
    This final rule incorporates the revised reference to 40 CFR
192.32(a)(1) for all impoundments that contain uranium byproduct
material or tailings and establishes this requirement as an element of
GACT-based standards for conventional impoundments, non-conventional
impoundments, and heap leach piles. The provision in the 1989 rule that
extended this requirement to conventional impoundments in existence as
of December 15, 1989 is moved to Sec.  61.252(a)(1), which addresses
those impoundments.
    We received a comment suggesting that we explicitly cite 40 CFR
264.221(c) as the criteria that all impoundments are required to meet.
This provision was not incorporated into regulation until 1985 (50 FR
28747). Adopting the commenter's approach would require impoundments
constructed before 1985 to upgrade or close, which we did not propose
to require. Those older impoundments are required to comply with the
provisions of 40 CFR 264.221 that are applicable to them. The
commenter's approach would also eliminate consideration of Sec.
264.221(d), which allows for an alternative design or operating
practices if ``such design and operating practices, together with
location characteristics'' would prevent migration of hazardous
constituents and allow detection of leaks at least as effectively as
the requirements of Sec.  264.221(c). It is not appropriate to
eliminate this flexibility, particularly for sites that may employ
improved liner materials or have exceptional natural characteristics
that lend themselves to such a demonstration.
c. Eliminating ``As Determined by the Nuclear Regulatory Commission''
    As described in the preceding section, Subpart W as promulgated in
1989 required impoundments to be constructed in accordance with the
requirements cited in 40 CFR 192.32(a). This provision also included
the phrase ``as determined by the Nuclear Regulatory Commission.''
    As described in the preceding section, 40 CFR 192.32(a) also
contains provisions related to ground water protection and closure
activities, which are not within the scope of Subpart W. It is
appropriate that the NRC be the sole regulatory agency for implementing
and enforcing these provisions. We proposed to eliminate the phrase
``as determined by the Nuclear Regulatory Commission'' from Subpart W
to clarify that EPA is an approval authority for Subpart W, but
specifically for the impoundment engineering and construction
requirements in 40 CFR 192.32(a)(1).
    We received a number of comments from industry objecting to this
change on the grounds that it would create dual regulation with NRC,
thus leading to inefficiencies and the potential for one agency to
approve an application while the other denied it. We disagree with
these commenters, as described in detail in the next section. The final
rule eliminates the phrase ``as determined by the Nuclear Regulatory
Commission'' from 40 CFR 61.252(a)(2)(i) and (ii).
2. What key comments did we receive on definitions, references and
conforming editorial revisions?
    We received a number of comments related to the issue of operation
and closure, either to extend the jurisdiction of Subpart W or to limit
it. Commenters also expressed views on the liner requirements and their
relation to groundwater protection or older impoundments. In connection
with the liner requirements, a number of commenters disagreed with the
proposal to eliminate the phrase ``as determined by the Nuclear
Regulatory Commission,'' suggesting that it will create dual regulation
and exceeds our rulemaking authority. Although we did not propose to
revise it, we also received some comment related to the definition of
``uranium byproduct material or tailings.''

    Comment: A number of commenters advocated that the scope of Subpart
W be extended to include all activities undertaken to achieve final
closure of the impoundment (see also the next comment in this section).
As defined in Subpart W, ``operation'' ends ``the day that final
closure begins'' (40 CFR 61.251(e)). Many of the commenters would like
this definition extended and explicitly stated that Subpart W should
apply until the final cover is installed on the impoundment (or, for
non-conventional impoundments, until the impoundment is removed, if
that is the closure approach).
    Response: Subpart W has never addressed remediation or reclamation
activities undertaken to close the impoundment or the site and EPA did
not propose to expand the scope of the rule to cover such activities.
Comments on whether the separate regulations that apply during closure
and until the final cover is installed are sufficient or whether
additional regulations are needed to cover activities during that time
period are beyond the scope of this section 112(q) review of Subpart W
and thus EPA has no obligation to respond. However, a goal of this
rulemaking was to provide clarity regarding when the management of
uranium byproduct material or tailings is no longer subject to Subpart
W. The final rule specifies that Subpart W no longer applies at the
beginning of closure and further defines when closure begins. For
informational purposes only, EPA discusses below some of the
regulations that apply during the closure period. EPA did not reopen or
accept comment on any aspects of these regulations.
    In 1989, in conjunction with the promulgation of Subpart W, the EPA
promulgated 40 CFR part 61, subpart T (40 CFR 261.220-226) to address
the closure period and final disposal for conventional tailings
impoundments (54 FR 51682). Subpart T required closure of impoundments
to be complete within two years after ceasing operations.
    In 1991, by Memorandum of Understanding (MOU) with the NRC, the two
agencies agreed to take action to clarify the timing for closure of
impoundments and processing sites. As part of this agreement, the EPA
amended 40 CFR part 192 (58 FR 60341, November 15, 1993) and rescinded
subpart T (59 FR 36302, July 15, 1994). The NRC subsequently amended 10
CFR part 40, Appendix A, consistent with the EPA's amended 40 CFR part
192 (59 FR 28220, June 1, 1994). The MOU included the goal that all
sites could be closed and in compliance with radon emission standards
by 1997 or within seven years of the date on which existing operations
cease and standby sites enter disposal status. The MOU did not address
Subpart W because Subpart W does not apply during closure.
    The MOU and subsequent regulatory actions created a more
comprehensive and coordinated framework for managing uranium processing
wastes. Further, a settlement agreement with stakeholders provided
additional detail to the MOU that, in part, allowed the EPA to make a
finding under the CAA that the NRC's regulatory program protected
public health with an ample margin of safety. This supported the
Agency's decision to rescind subpart T.
    In their respective rulemakings, the agencies essentially adopted
the Subpart W definition of ``operation'' and included provisions
related to closure that would allow certain activities related to waste
management during the closure process. Among these were provisions that
would allow wastes to be placed in impoundments that were also either
in closure or had completed closure (final cover). These authorizations
would not change the status of the impoundment or site, as we explained
in our rulemaking to amend 40 CFR part 192: ``Even if a portion of a
site is authorized to remain accessible for disposal of byproduct
materials during the closure process or after placement of a permanent
radon barrier consistent with the Settlement Agreement, as described
above, this will not cause a nonoperational uranium mill tailings
disposal site to revert to an operational site as defined by 40 CFR
192.31(q)'' (58 FR 60348, November 15, 1993).
    Similarly, the NRC addressed this point in its 1993 proposed rule
to amend 10 CFR part 40, Appendix A in response to a comment from an
NRC Agreement State:

    [Agreement State] Comment. The word ``portion'' should be
deleted from paragraph (3) of Criterion 6A.
    [NRC] Response. This provision allows limited disposal during
closure as an exception to the definition of operation. If the whole
impoundment is involved in waste disposal and no reclamation
activities are proceeding, the impoundment would be considered
operational and continue to be under appropriate requirements for
operation. Note, one site may have both an operational impoundment
and a non-operational impoundment with the applicable regulations
applying to each (58 FR 58659, November 3, 1993, emphasis in
original).

    The final rule includes the definition of ``operation'' as it was
proposed, which makes it fully consistent with the definitions in 40
CFR part 192 and 10 CFR part 40, Appendix A. We are also adopting a
definition of ``final closure'' that clarifies that Subpart W does not
apply to impoundments that are being managed under an approved
reclamation plan for that impoundment or the facility closure plan.
    Comment: Several commenters stated that the current regulatory
scheme allows an unacceptable period during closure activities when
impoundments are not being monitored or otherwise managed to limit
radon emissions. They further argue that closure is not being conducted
in a manner that will lead to timely installation of a final cover or
removal of an evaporation or holding pond. They cite periods of decades
during which tailings are being ``dewatered'' or impoundments are used
to deposit wastes from decommissioning activities, while the drying-out
of impoundments allows increased radon emissions. Commenters attribute
this in some part to the Agency's rescission of subpart T, which called
for installation of final covers on conventional tailings impoundments
within two years of the cessation of operations. One commenter notes
that an impoundment undergoing closure will be required to demonstrate
compliance with the 20 pCi/m\2\-sec radon emissions standard only if it
requests extension of the milestones in the closure plan, where it may
not have been required to monitor previously under Subpart W.
    Response: The EPA did not propose to extend the jurisdiction of
Subpart W beyond the operational phase, nor did we request comment on
regulations that are applicable to closure activities. We are under no
obligation to respond to such comments. However, one purpose of this
rulemaking was to clarify at what point Subpart W no longer applies to
the management of uranium byproduct material or tailings. The final
rule specifies that Subpart W no longer applies at the beginning of
closure and further defines when closure begins. The following response
is provided in the interest of further clarifying this issue.
    As described in the response to the previous comment, the EPA and
the NRC entered into an MOU in 1991, after industry efforts to stay the
implementation of subpart T, due, in part, to the fact that the
requirement to complete closure of impoundments was unrealistically
stringent. As part of the MOU, the EPA rescinded subpart T and modified
its UMTRCA standards at 40 CFR 192.32 to address activities conducted
during closure, including allowing placement of decommissioning wastes
in non-operating impoundments. The EPA and the NRC agreed that such
activities can, for the most part, be

conducted and a final cover installed within seven years of the end of
operations. Similar timeframes should be possible for non-conventional
impoundments, which are likely to be removed altogether. We note that
both 40 CFR 192.32(a)(3) and 40 CFR part 40, Appendix A were modified
and require that closure take place ``as expeditiously as practicable
considering technological feasibility.'' They further state that such
placement of wastes during closure will not be approved if it would
cause delays in emplacement of the final radon barrier to meet the
disposal requirements. The MOU did not address Subpart W because
Subpart W does not apply during closure.
    The Agency has no plans to reinstate subpart T, although EPA is not
precluded from doing so (40 CFR 261.226). Nor is the final rule
extending the scope of Subpart W to cover closure activities. While
this does leave a period of time when conventional and non-conventional
impoundments are more likely to have increased radon emissions because
they are not managed as they would be during operations, such a period
is necessary to facilitate final closure activities. However,
``dewatering'' tailings for decades, particularly in the arid West, is
certainly not consistent with the seven-year period envisioned by both
the EPA and the NRC. Most conventional tailings are emplaced using the
phased disposal method. To avoid extended dewatering periods, sites may
consider using the continuous disposal method, in which tailings are
dewatered before emplacement and immediately covered. Regardless of the
method of emplacement, we emphasize the importance of timely closure in
achieving the safe end state of these sites, and encourage the NRC and
NRC Agreement States to give appropriate attention to controlling radon
emissions during closure activities.
    Comment: Some commenters expressed concern that impoundments are
not being closed in accordance with closure plans, because the plans do
not exist, milestones are absent or unclear, or milestones are not
being enforced. One commenter states that the EPA should not consider
an impoundment in closure until such plans are incorporated into the
facility license. Another commenter recommends that we amend 40 CFR
part 192 to include a provision that the EPA will verify the existence
of a closure plan. Several commenters offer specific comments related
to the White Mesa and Cotter sites and what they perceive as a lack of
closure plans.
    Response: Activities related to closure or closure plans are beyond
the scope of this rulemaking and the EPA is under no obligation to
respond to comments on that topic. However, one purpose of this
rulemaking was to clarify at what point Subpart W no longer applies to
the management of uranium byproduct material or tailings. This final
rule specifies that an approved reclamation plan is a prerequisite for
entering closure, thereby removing a unit managing uranium byproduct
material or tailings from the jurisdiction of Subpart W. The response
below is provided in the interest of clarity in conveying the
provisions of the final rule. The EPA does not require, review, approve
or enforce reclamation or closure plans.
    As noted by one commenter, closure plans with milestones are
required under 40 CFR part 192 and 10 CFR part 40, Appendix A. Closure
plan requirements, closure activities and revisions to part 192 are not
within the scope of this Subpart W rulemaking. The EPA typically does
not see closure plans when reviewing construction applications under 40
CFR part 61, subpart A. The NRC or the Agreement State is responsible
for enforcement of reclamation or closure plans. The Cotter site ceased
operations several years ago, no longer has an operating license and is
therefore no longer subject to the requirements of Subpart W. The site
is currently a Superfund site and is conducting activities under a
decommissioning license from the State of Colorado.
    The final rule includes a definition of ``final closure'' that
specifies notification that the impoundment in question is being
managed according to the requirements and milestones in the approved
reclamation plan. This should provide clarity when determining whether
an impoundment is in closure, and whether Subpart W still applies.
    Comment: A few commenters took the opposite view of that addressed
earlier in this section. These commenters wish us to clarify that the
period of operations for either a conventional or non-conventional
impoundment only extends to the management of uranium byproduct
material or tailings produced by the concentration or extraction of ore
processed primarily for its source material content (which may include
the commercial management of such wastes produced at other facilities),
and not to the management of wastes (byproduct material or otherwise)
generated during closure or decommissioning activities.
    Response: The final rule clarifies that Subpart W does not apply
during closure activities, and further defines when final closure
begins. As described above in this section, this is essentially the
position agreed to in the 1991 MOU between the EPA and the NRC. Both 40
CFR 192.32(a)(3) and 10 CFR part 40 Appendix A, Criterion 6(A) provide
for the use of impoundments while they are undergoing closure. However,
impoundments that are used to manage uranium byproduct material or
tailings generated during closure or remediation activities, while
remaining open to manage operational wastes, would continue to fall
under Subpart W until they formally enter the closure process and
implement the approved reclamation plan for that impoundment. The
definition of ``final closure'' adopted in the final rule makes clear
that Subpart W does not apply to impoundments that are being managed
under an approved reclamation plan.
    In addition to the use of an impoundment for wastes generated
during closure or remediation activities, NRC regulations also provide
for waste from other sources to be emplaced in the impoundment during
the closure process (10 CFR part 40, Appendix A, Criterion 6(A)(3)).
Approval of such emplacement requires a license amendment and must not
delay complete closure of the impoundment. Subpart W does not apply to
such authorized emplacements while the impoundment is undergoing
closure because the unit is subject to an approved reclamation plan
and, therefore, no longer operating. Depending on the terms of the
license amendment, authorized emplacements at impoundments may include
waste from ISL sites, which are not expected to construct permanent
impoundments, thereby facilitating the overall goal of limiting the
number of small disposal sites. Authorization to allow emplacement of
waste from other sources during the closure process must be reflected
in both the facility license and the applicable reclamation plan.
    Comment: One commenter disagreed with comments described earlier
and pointed out that maintaining impoundments under Subpart W
jurisdiction while they are undergoing closure may cause facilities to
be out of compliance with the restriction on the number of conventional
impoundments. The commenter posits that this situation could arise if a
facility opened a new conventional impoundment for operational uranium
byproduct material or tailings, while having another one in operation
and one in closure (or multiple impoundments in closure). To avoid
compliance issues, the commenter explained that facilities may have to

defer opening new impoundments, which could lead to temporary shutdown
of the facility's processing operations if there is no outlet for the
wastes. The commenter specifically notes that non-conventional
impoundments may continue in operation when conventional impoundments
are in closure.
    Response: We did not propose to extend the scope of Subpart W to
apply during closure activities and thus did not open this issue as
part of our review under CAA section 112(q). Also, we are neither
finalizing such an extension of applicability, nor limiting the number
of non-conventional impoundments that may be in operation at any one
time.
    Comment: Several commenters stated that definitions in or proposed
for Subpart W are inconsistent with the NRC's definitions in 10 CFR
part 40 (and Appendix A). For example, two commenters state that
``[t]he definition of Operation conflicts with existing regulations,
specifically those in 10 CFR part 40 Appendix A following the
rescission of 40 CFR part 61 Subpart T.'' These commenters also suggest
that we look to the Appendix A definition of ``closure'' and they note
that the closure period is tied to the ``end of milling operations'' in
Criterion 6.
    One commenter requests clarification of the term ``day that final
closure begins,'' which the commenter believes has never been
adequately explained. Another commenter requests clarification on the
steps that must take place for closure to begin. Commenters also stated
that we did not include non-conventional impoundments in the definition
of operation.
    Response: It is important to make the distinction between closure
of an impoundment and closure of a facility. Subpart W applies to
impoundments that are operating. An individual impoundment may enter
and complete the closure process, thus removing it from Subpart W
jurisdiction, while other impoundments and the facility continue to
operate. When the facility (site) itself enters the closure process,
and is no longer operating (and generating uranium byproduct material
or tailings), impoundments will also be managed according to the
overall site closure plan. Tying Subpart W to the ``end of milling
operations'' in NRC regulations, as suggested by the two commenters,
would essentially preclude the closure of individual impoundments until
overall site closure begins. This is likely contrary to the commenters'
intentions. We also note that the NRC definition of ``closure'' cited
by these commenters clearly refers to activities undertaken to close
the entire site and is not directed specifically at impoundment
closure.
    Additionally, commenters have misinterpreted our proposal. The
Agency does not intend to apply Subpart W to impoundments that have
entered the closure process. The proposed modification of the
definition of ``operation,'' which we are adopting in the final rule,
clarifies that impoundments that have not yet entered closure remain
subject to Subpart W, even if the material they are receiving is not
newly-generated uranium byproduct material or tailings (``new
tailings'' in the original). This also makes the definition more
consistent with those in 40 CFR part 192 and 10 CFR part 40, Appendix
A. See the proposed rule at 79 FR 25405, May 2, 2014. To further
clarify this situation, the final rule includes a definition of ``final
closure'' specifying that closure begins upon written notification that
the impoundment is being managed according to the requirements and
milestones in the approved reclamation plan for that impoundment.
    This definition of ``final closure'' adopts a suggestion provided
by one commenter. The commenter proposed tying ``closure period'' to a
written notification from the licensee that the impoundment is no
longer being used for emplacement of tailings or for evaporative or
holding purposes, and is also no longer on standby for such purposes.
The commenter suggests that it would be useful to explicitly address
both conventional and non-conventional impoundments in the definitions,
as there may be situations where non-conventional impoundments continue
to operate when conventional impoundments are in closure. We are also
adopting this suggestion in the definition of ``final closure.''
    Adding this language should eliminate some uncertainty regarding
impoundment status. This uncertainty is reflected in a statement by the
same commenter regarding the White Mesa Mill. In providing information
about the different impoundments, the commenter notes that ``. . . Cell
3 could be considered to have already commenced the closure process''
(emphasis added). The written notification requirement will help
eliminate such ambiguous situations. There should be no question as to
whether an impoundment is undergoing closure, and similarly no
ambiguity regarding the applicability of Subpart W.
    Regarding the perceived conflicts with NRC regulations, we do not
see such a conflict, and note that the definition of ``operation'' in
existing and proposed Subpart W is substantively identical to and
served as the basis for that in 10 CFR part 40, Appendix A (we note the
NRC's statement in its proposal that ``the definition of operations is
in conformance with the definition of `operational' in the proposed EPA
amendment to [40 CFR part 192] subpart D and in 40 CFR part 61, subpart
W'' (58 FR 58659, November 3, 1993). The commenters did not suggest
that the NRC's definition is in conflict with its own regulations.
Further, the same definition is used in 40 CFR 192.31(p). As noted
above, we are also adding a definition of ``final closure'' in the
final rule. This will provide additional clarity as to what steps the
operator must take to remove an impoundment from the jurisdiction of
Subpart W while remaining consistent with the definitions in 10 CFR
part 40 and 40 CFR part 192. The definition of final closure explicitly
addresses conventional impoundments, non-conventional impoundments and
heap leach piles.
    The phrase ``day that final closure begins'' was included in the
original promulgation of Subpart W in 1986 (51 FR 34056, September 14,
1986). ``Final closure'' is a term defined under RCRA hazardous waste
regulations in 40 CFR 260.10. ``Final closure'' in that context refers
to the closure of all hazardous waste management units at a site, and
is distinguished from ``partial closure,'' which refers to closure of
individual units. However, as the term is used in Subpart W, and as it
is being adopted in the final rule, it refers to individual
impoundments, not the entire site (so is more like ``partial closure''
in the RCRA context). Subpart W differs in this respect from 40 CFR
part 192 and 10 CFR part 40, Appendix A, which are both also concerned
with closure of the overall site. We also note that, as described
earlier, the definition of ``operations'' in Subpart W served as the
basis for corresponding definitions in 40 CFR part 192 and 10 CFR part
40, Appendix A, and this phrasing has also been adopted in and provides
consistency with those regulations. We did not propose to change it and
we are not finalizing any changes.
    Comment: The State of Utah commented on the status of liners at two
of the facilities regulated by the State under its Subpart W
delegation. The conventional impoundment at the Shootaring Canyon Mill
was constructed in 1981 and ``was not required to be constructed in
accordance with'' the requirements of 40 CFR 192.32(a). However, the
State will require the liner to be upgraded if the mill goes back into
production. The Shootaring Canyon Mill operated for

only a short period and has been in standby for nearly 35 years. The
State also addresses Cell 1 at the White Mesa Mill, which is a non-
conventional impoundment also constructed in 1981. The State has not
considered this impoundment to be subject to Subpart W and believes
that EPA must conduct a cost-benefit analysis if the liner is required
to be upgraded.
    Response: Comments indicate that some stakeholders have not always
clearly understood the true scope of the 1989 Subpart W rulemaking. The
1989 rulemaking revised the approach taken in 1986, which required
impoundments existing at that time to cease operations by December 31,
1992 unless they could receive an exemption or extension (51 FR 34066).
These impoundments were not required by Subpart W to meet the
requirements of 40 CFR 192.32(a). The 1989 rulemaking lifted the
operating restriction on older impoundments, but also removed the
exemption from the requirements of 40 CFR 192.32(a) (54 FR 51680). This
provision, promulgated as 40 CFR 61.252(c), explicitly addressed the
exemption for impoundments constructed prior to the promulgation of 40
CFR part 192 and established that all impoundments used to manage
uranium byproduct material or tailings became subject to the liner
requirements in 40 CFR 192.32(a) when the 1989 rule became effective,
regardless of when they were constructed. These liner requirements have
remained in place because CAA section 112(q) explicitly retains
standards that were in effect before the date of enactment of the CAA
Amendments of 1990, unless and until the EPA revises them.
    The two impoundments identified by the State of Utah are both
required to comply with the liner requirements in 40 CFR 192.32(a)(1),
and by extension 40 CFR 264.221. The standby status of the Shootaring
Canyon Mill makes no difference in this regard. We understand that some
stakeholders did not view the 1989 rulemaking as applicable to liquid
(non-conventional) impoundments. This final rule clarifies that non-
conventional impoundments did fall under the 1989 rule and are also
subject to the requirements in 40 CFR 192.32(a)(1). We note that
Denison Mines, the previous owner of the White Mesa Mill, stated in its
response to the EPA's section 114 request for information that Cell 1
meets the requirements of 40 CFR 264.221(a).
    Comment: Many commenters objected to the proposal to eliminate the
phrase ``as determined by the Nuclear Regulatory Commission'' from
provisions related to review of the impoundment construction
requirements in 40 CFR 192.32(a)(1). Commenters in general argued that
eliminating the phrase ``as determined by the Nuclear Regulatory
Commission'' would result in unnecessary dual regulation if both the
EPA and the NRC need to review and approve construction applications,
with limited if any benefit. One commenter suggests this will have
significant cost implications that were not considered during the
rulemaking. Another commenter questions how disagreements between the
agencies will be resolved, and suggests that appeals will be
``inappropriately complicated''.
    A number of these commenters asserted that our proposal was
contrary to the legal framework established by Congress for management
of byproduct material as defined in Section 11e.(2) of the AEA.
Commenters cite to the framework in Section 275 of the AEA, which
directs the EPA to establish standards for management of byproduct
material and which gives the NRC sole authority over implementation and
enforcement of the EPA's standards through its licensing process (one
commenter cites Title 42 of the United States Code, Section 2022(d)
rather than Section 275 of the AEA). Several commenters refer
specifically to that section's statement that ``no permit issued by the
Administrator is required . . . for the processing, possession,
transfer, or disposal of byproduct material, as defined in section
11e.(2) to this subsection.'' Another commenter suggests that the EPA
is attempting to expand its role by improperly assuming or duplicating
the NRC's responsibilities.
    One commenter does not make these specific statutory references,
but more generally criticizes the EPA for ``grossly inefficient, dual
regulation'' that is ``inconsistent with efficient regulatory
practices'' and goes against previous efforts by the two agencies to
avoid such situations, as illustrated by the EPA's rescission of 40 CFR
part 61, subparts I and T. The commenter suggests that Subpart W could
also be rescinded, and notes that the EPA's separate rulemaking related
to 40 CFR part 192 may be used to incorporate elements of Subpart W as
needed.
    We also received some comments in support of the proposal to remove
the phrase ``as determined by the Nuclear Regulatory Commission.'' One
commenter believes this is a welcome clarification that the EPA is
administering the NESHAP program. Another commenter notes that it is
not unusual for an industry to be regulated under more than one statute
or agency. A third commenter points out that this situation has existed
for several decades. A fourth commenter agrees and cites the EPA
approvals under 40 CFR part 61, subpart A, as well as the division of
responsibilities at the state level in Utah as they relate to the White
Mesa Mill.
    Response: The EPA disagrees that the change will be burdensome to
licensees or create additional barriers to regulatory approval. We
proposed this change to be consistent with the proposal to narrow the
reference to the impoundment engineering and construction requirements.
As explained in the preamble to the proposed rule, the requirements at
40 CFR 61.252(b) and (c) required compliance with 40 CFR 192.32(a) (79
FR 25406). However, we focus the Subpart W requirements on the
impoundment design and construction requirements found specifically at
40 CFR 192.32(a)(1). The remainder of 40 CFR 192.32(a) goes beyond this
limited scope by including requirements for ground-water detection
monitoring systems and closure of operating impoundments. These other
requirements, along with all of the part 192 standards, are implemented
and enforced by the NRC through its licensing requirements for uranium
recovery facilities at 10 CFR part 40, Appendix A. It is appropriate
for compliance with those provisions to be solely determined by the
NRC. However, when referenced in Subpart W, the requirements in 40 CFR
192.32(a)(1) would also be implemented and enforced by the EPA as the
regulatory authority administering Subpart W under its CAA authority.
Therefore, we revised 40 CFR 61.252(b) and (c) to specifically define
which portions of 40 CFR 192.32(a) are applicable to Subpart W. Section
61.252(b) is re-numbered as 61.252(a)(2) and section 61.252(c) is
incorporated into 61.252(a)(1) in the final rule.
    The comments confirm that there is a misimpression that this
reference to the NRC precluded the EPA from reviewing applications for
compliance with 40 CFR 192.32(a)(1) in its pre-construction and
modifications reviews under 40 CFR 61.07 and 61.08. That is an
incorrect interpretation of the 1989 rule. To the contrary, in
promulgating the 1989 rule, we stated ``Mill operators will not be
allowed to build any new mill tailings impoundment which does not meet
this work practice standard. EPA will receive information on the
construction of new impoundments through the requirements for EPA to
approve of new construction under 40 CFR part 61, subpart A'' (54 FR
51682). The referenced ``work practice standard'' includes the
requirement for

conformance with 40 CFR 192.32(a). We are eliminating the reference to
the NRC to clarify that the EPA is an approval authority for the
impoundment engineering and construction provisions in 40 CFR
192.32(a)(1). This change will have no effect on the licensing
requirements of the NRC or its regulatory authority under UMTRCA to
implement the part 192 standards through its licenses.
    Commenters' references to AEA Section 275 as limiting our authority
are incorrect. The commenters have overlooked a salient point, which is
that the Subpart W rulemaking is being undertaken pursuant to our CAA
authority, not under the AEA. Another relevant provision in Section
275, 275e (42 U.S.C. 2022(e)), states: ``Nothing in this Act applicable
to byproduct material, as defined in section 11e.(2) of this Act, shall
affect the authority of the Administrator under the Clean Air Act of
1970, as amended, or the Federal Water Pollution Control Act, as
amended.'' The Federal Water Pollution Control Act is also known as the
Clean Water Act.
    Further, commenters who cited the prohibition on EPA permitting
neglected to note the context for this provision and the specificity of
the language regarding the standards of general application to be
developed by the EPA. AEA section 275b.(2) reads as follows: ``Such
generally applicable standards promulgated pursuant to this subsection
for nonradiological hazards shall provide for the protection of human
health and the environment consistent with the standards required under
subtitle C of the Solid Waste Disposal Act, as amended, which are
applicable to such hazards: Provided, however, That no permit issued by
the Administrator is required under this Act or the Solid Waste
Disposal Act, as amended, for the processing, possession, transfer, or
disposal of byproduct material, as defined in section 11e.(2) to this
subsection'' (emphasis in original). Thus, Congress required the EPA's
standards to be consistent with standards applicable to nonradiological
hazardous waste (subtitle C of the Solid Waste Disposal Act, better
known as the Resource Conservation and Recovery Act, or RCRA) in lieu
of the Agency exercising permitting authority under either the AEA or
RCRA. The EPA is not contravening this restriction by exercising
regulatory authority under the CAA. Responses to other comments on our
legal authorities for this action may be found in Section IV.A.2.
    Regarding the view of appropriate and efficient regulation, our
action will not have such far-reaching consequences. The EPA and the
NRC have not examined the prospect of rescinding Subpart W. As with the
rescission of 40 CFR part 61, subparts I and T, and in accordance with
CAA section 112(d)(9), the EPA would need to determine that the NRC's
regulatory program will protect public health with an ample margin of
safety. The EPA's separate rulemaking under 40 CFR part 192
specifically addresses ground water protection at ISL facilities.
    Comment: Several commenters addressed the definition of ``uranium
byproduct material or tailings'' in Subpart W. Commenters generally
raised the distinction between ``tailings'' and ``byproduct material''
under the AEA as germane to the scope of this rulemaking. One commenter
suggests that the historical focus on conventional mill tailings
impoundments (or ``piles'') is linked to the CAA, and that we are
impermissibly re-defining non-tailings byproduct material as
``tailings'' as a means to address them under the CAA. Another
commenter noted the following in reference to the AEA definition: ``All
tailings are byproduct material, but not all byproduct materials are
tailings.'' A third commenter asks for clarification on how restoration
fluids may be considered byproduct material. Several commenters
suggested that we adopt the NRC's definition in 10 CFR 40.4 as a means
to improve clarity and consistency.
    Another commenter raised a question regarding wastes at uranium
recovery facilities that are not derived from ores. The commenter
stated that such wastes may derive from ``alternate feed'' materials
that contain sufficient uranium to make processing worthwhile (e.g.,
tailings from other mineral extraction operations), or could include
wastes placed directly into conventional impoundments because they are
physically or chemically similar to the material already being managed.
    Response: Although we received suggestions to adopt the AEA's and
the NRC's definition of byproduct material, we did not propose to
revise the definition of uranium byproduct material or tailings. CAA
section 112(q) explicitly retains standards such as Subpart W that were
in effect before the date of enactment of the CAA Amendments of 1990,
so the existing definition of uranium byproduct material or tailings
remains unless or until the EPA revises it. Because we did not propose
to revise the definition of uranium byproduct material or tailings, we
did not open it for comment. The EPA first defined the term ``uranium
byproduct material or tailings'' in 1986 and has generally used the
term ``tailings'' in Subpart W for simplicity. This rulemaking
clarifies the scope of the EPA's term ``uranium byproduct material or
tailings'' and provides reassurance that it is not in conflict with
NRC's definitions. The following discussion is provided for
informational purposes to further clarify this issue.
    We note that the EPA has clear authority to promulgate definitions
under the CAA as it deems appropriate and is not limited to the AEA's
definition of ``byproduct material'' or the NRC's definition in 10 CFR
40.4. The EPA's definition identifies the scope of material covered by
the Subpart W regulations and does not preempt the NRC's AEA authority.
See Section IV.A.2 for more discussion of legal authorities as they
relate to this issue.
    The definition of ``uranium byproduct material or tailings'' in
Subpart W, as it was promulgated in 1989 and not modified by this rule,
establishes that Subpart W broadly addresses radon emissions from
operating structures used to manage wastes produced during and
following the concentration or extraction of uranium from ore processed
primarily for its source material content. The EPA acknowledges that
the definition of ``uranium byproduct material or tailings,'' as
originally promulgated in 1989, may not wholly conform with the common
understanding of ``tailings.'' However, the scope and applicability of
Subpart W is determined by the regulatory definition of ``uranium
byproduct material or tailings,'' not the common understanding of
tailings. Subpart W applies to the structures at uranium recovery
facilities that are used to manage or contain ``uranium byproduct
material or tailings'' during and following the processing of uranium
ores. Common names for these structures may include, but are not
limited to, impoundments, tailings impoundments, tailings piles,
evaporation or holding ponds, and heap leach piles. However, the name
itself is not important for determining whether Subpart W requirements
apply to that structure; rather, applicability is based on what these
structures contain. To clarify any potential confusion created by the
Subpart W definition, any references to ``uranium byproduct material''
or ``tailings'' are now references to ``uranium byproduct material or
tailings.'' These changes reaffirm the scope of Subpart W and are not
substantive.
    The defined scope of materials subject to Subpart W becomes more
meaningful when one considers the current

dominance of ISL in uranium recovery. At these sites, where
conventional impoundments are not present, non-conventional
impoundments managing uranium byproduct material or tailings are the
most significant potential source of radon during operations. Although
we do not generally expect non-conventional impoundments to be as large
a source of potential emissions as conventional impoundments, non-
conventional impoundments manage uranium byproduct material or tailings
and emit or have the potential to emit sufficient radon that it is
appropriate for the EPA to address them under Subpart W.
    The designation of restoration fluids as uranium byproduct material
or tailings is consistent with the approach taken by the NRC. See Staff
Requirements Memorandum--SECY-99-013, ``Recommendation on Ways to
Improve the Efficiency of NRC Regulation at In Situ Leach Uranium
Recovery Facilities,'' July 26, 2000.
    It is not necessary for us to explicitly address waste not
resulting from the concentration or extraction of ores because Subpart
W applies to impoundments, both conventional and non-conventional, that
are used to manage uranium byproduct material or tailings. Such
impoundments that also contain non-ore wastes continue to be subject to
Subpart W. It is unlikely that an operator would construct impoundments
for the sole purpose of managing wastes that do not derive from the
processing of ores. As explained in Section IV.E.2, the purpose of
Subpart W is to control radon emissions from sources containing uranium
byproduct material or tailings at uranium recovery facilities. If an
impoundment does not contain uranium byproduct material or tailings, it
is not subject to the requirements of Subpart W. If construction of
such impoundments is planned, they can be identified and their status
can be addressed during the construction application review under
subpart A.
    Comment: Commenters requested clarification regarding whether
liquids in impoundments contain byproduct material or are byproduct
material. One commenter asked us to clarify that solids and liquids in
impoundments are byproduct material.
    Response: Subpart W applies to conventional and non-conventional
impoundments to the extent they are used to manage uranium byproduct
material or tailings, with the primary concern being the potential to
emit radon. The uranium byproduct material or tailings may be in
solution or suspension in liquids that are discharged to these
impoundments, or in sediments after settling out from the liquids.

V. Summary of Environmental, Cost and Economic Impacts

    As discussed earlier, uranium recovery activities are carried out
at several different types of facilities. We are revising Subpart W
based on how uranium recovery facilities manage uranium byproduct
materials during and after the processing of uranium ore at their
particular facility. As discussed in Sections III and IV, we are
establishing GACT-based requirements for three types of affected
sources at uranium recovery facilities: (1) Conventional impoundments;
(2) non-conventional impoundments; and (3) heap leach piles.
    For purposes of analyzing the impacts of the final rule, we assumed
that approximately five conventional milling facilities, 50 ISL
facilities (although this is only a projection since only 12 are fully
licensed) and one heap leach facility, each with at least one regulated
impoundment, are subject to the final Subpart W. The following sections
present our estimates of the final rule's air quality, cost and
economic impacts. For more information, please refer to the Economic
Impact Analysis (EIA) report that is included in the public docket for
this final rule (EPA-HQ-OAR-2008-0218).

A. What are the air quality impacts?

    The requirements in this final rule should eliminate or reduce
radon emissions at all three types of affected sources. The GACT-based
standards being established by this action are based on control
technologies and management practices that have been used at uranium
recovery facilities for the past twenty or more years. These standards
will minimize the amount of radon that is released to the air by
keeping the impoundments wet or covered with soil and/or by limiting
the area of exposed uranium byproduct material or tailings.

B. What are the cost and economic impacts?

    Table 5 presents a summary of the unit cost (per pound of
U3O8) for implementing each GACT-based standard
at each of the three types of uranium recovery facilities. Because the
requirements for liners are not attributable to Subpart W, but are
required by other regulations, the only costs attributable to this
rulemaking are related to maintaining liquids in non-conventional
impoundments. In addition to presenting the GACT costs individually,
Table 5 presents the total unit cost to implement all relevant GACT-
based standards at each type of facility. For example, the table shows
that conventional mills will have both conventional impoundments and
non-conventional impoundments, and will also be required to maintain
saturation in the non-conventional impoundments.

                              Table 5--Final GACT Standards Costs per Pound of U3O8