The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 1 of 11

Global Comments

1. EPA appears to be extending its authority into implementation of the 40 CFR Part 192 

standards, which oversteps its authority under the Atomic Energy Act (AEA). The 

AEA confers jurisdiction over the operations of conventional, heap leach, and in situ 

uranium recovery facilities where source material is milled or processed on the U.S. 

Nuclear Regulatory Commission (NRC). As discussed in Section 275(b) of the AEA, the 

Uranium Mill Tailings and Radiation Control Act of 1978 (UMTRCA) amended the AEA to 

give EPA the authority to develop generally applicable standards for protection of public 

health, safety, and the environment from the radiological and non-radiological hazards 

associated with processing and with the possession, transfer, and disposal of byproduct 

material at sites where ore is processed primarily for its source material content or at site 

which are used for the disposal of such byproduct material. EPA’s generally applicable 

standards are contained in 40 CFR Part 192. Section 275(d) states that “[i]mplementation 

and enforcement of the standards promulgated pursuant to subsection b. of this section 

shall be the responsibility of the [NRC] in the conduct of its licensing activities under this 

Act.” Section 84 of the AEA directs the NRC to develop standards that conform to EPA’s 

general standards. The NRC’s conforming standards are contained in 10 CFR Part 40, 

Appendix A. 

Throughout the revisions to 40 CFR Part 61 in this draft proposed rule, EPA proposes that it 

will be responsible for ensuring that liner requirements under 40 CFR 192.32 are met. We 

interpret that the following statements would authorize EPA to review and approve liner 

system designs for impoundments at uranium recovery facilities and would be duplicative of 

and create a conflict between the NRC’s implementation of EPA’s generally applicable 

standards and the proposed regulations: “[t]hird, we are proposing to clarify what specific 

liner requirements in 40 CFR 192.32 apply and that EPA, rather than NRC, will ensure 

those requirements are met under subpart W.” (page 48 – 49); and “[h]owever, when 

referenced in Subpart W, the requirements in 40 CFR 192.32(a)(1) would also be 

implemented and enforced by EPA as the regulatory authority administering Subpart W 

under its CAA authority.” (page 97)(note that several other locations within the document, 

such as pages 71, 72, 74, 96, and 97, discuss the relationship between the 40 CFR Part 

192 standards and 10 CFR Part 40, Appendix A, requirements). However, statements on 

pages 74, 98, and 107 of the proposed revisions correctly point out that the 40 CFR Part 

192 standards are currently implemented and enforced by the NRC. It is unclear to us what 

additional benefit would be obtained by implementing the 40 CFR Part 192 standards under 

the CAA as uranium recovery facilities are already subjected to these standards. The 

NRC’s conforming regulations in 10 CFR Part 40, Appendix A, currently require installation 

of liner systems to protect groundwater resources in the vicinity of an impoundment. 

Additionally, the aspect of the proposed rule requiring both NRC and EPA implementation 

of the 40 CFR Part 192 standards may lead to more confusion because while NRC’s 10 

CFR Part 40, Appendix A, standards conform to the 40 CFR Part 192 standards (including 

the cross reference to 40 CFR 264), the Appendix A standards are not identical to the 40 

CFR Part 192 standards. Note the NRC’s final rulemaking related to the development of 

groundwater protection standards for uranium recovery facilities (52 FR 43553; November 

13, 1987) includes a table identifying the applicable EPA regulation, subject, and location of 

the comparable NRC regulation in Appendix A. 

 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 2 of 11

EPA Response: EPA agrees that under UMTRCA, it has the authority to promulgate 

standards applicable to uranium recovery facilities, and NRC has the authority to implement 

and enforce these standards through its licensing activities. See 42 U.S.C. §§ 2022(b), 

2022(d); 40 CFR Part 192. However, as explained in Sections II.A. and II.B. of the Subpart 

W proposed rule, EPA also has authority under the Clean Air Act (CAA) to regulate the 

emissions of radionuclides from these same facilities. EPA originally promulgated 40 CFR 

Part 61, Subpart W, in 1989 under its CAA section 112 authority, and it is under that 

authority that EPA now acts to propose revisions to Subpart W. 

EPA’s authority under the CAA includes the authority to implement and enforce the 

standards it promulgates. Subpart W, as promulgated in 1989, requires uranium recovery 

facilities to comply with certain Part 192 requirements. Specifically, Subpart W currently 

requires: “All mill owners or operators shall comply with the provisions of 40 CFR 192.32(a) 

in the operation of tailings piles, the exemption for existing piles in 40 CFR 192.32(a) 

notwithstanding.” 40 CFR 61.252(c); see also discussion in Section II.E. of proposed rule. 

The fact that EPA cross-references the Part 192 requirements in Subpart W does not 

change the authority EPA is acting under when requiring compliance with these 

requirements. EPA is acting under the CAA when it includes these Part 192 requirements 

in Subpart W. Cross-referencing these provisions instead of copying them directly into 

Subpart W is done as a matter of convenience and is a convention often used in 

rulemakings. The proposed revisions clarify the particular Part 192 requirements that apply 

to uranium recovery facilities under Subpart W. 

EPA does not believe that its proposed revisions to Subpart W will lead to confusion as to 

the requirements that uranium recovery facilities must meet. The proposed revisions to 

Subpart W simply clarify the particular Part 192 requirements that apply. The proposed 

revisions also propose that uranium recovery facilities keep records that confirm that the 

conventional impoundments, nonconventional impoundments and heap leach piles meet 

the requirements in 40 CFR 192.32(a)(1), which we have incorporated by reference into 

Subpart W. See 40 CFR 61.255(a) in the proposed rule. These recordkeeping 

requirements help assure compliance with the requirements of Subpart W. If we adopt the 

proposed recordkeeping requirements in Subpart W, EPA expects that most facilities will 

demonstrate compliance with the Part 192 requirements in Subpart W by showing 

compliance with the same requirements for NRC purposes. The recordkeeping 

requirements included in the proposed rule are not burdensome and enable EPA to assure 

compliance with the requirements of Subpart W. As has been the case since 1989, EPA 

can take enforcement action if necessary under its CAA regulatory authority if the 

requirements of Subpart W are not met. 

2. EPA lacks the authority to assume jurisdiction over heap leach uranium recovery 

operations. On page 23 of the proposed rule, EPA states that it is proposing to regulate 

heap leach uranium extraction under Subpart W. As EPA appropriately described, the 

heap leach treatment processes uranium ore in such a manner that the uranium content is 

removed. Licensing and regulatory authority over this process rest with the NRC pursuant 

to the AEA. 

EPA Response: We disagree that EPA lacks the authority to regulate radon emissions 

from the heap leach pile under the CAA. See discussion in Section IV.B.4 of the proposed 

rule. While we agree that NRC possesses the licensing authority pursuant to the AEA, EPA 

has authority under the CAA to regulate radon emissions generated from the uranium 

byproduct material in the heap leach pile, and we are exercising that authority in the 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 3 of 11

proposed rule. Regulating radon emissions from heap leach piles is no different than 

regulating radon emissions from uranium byproduct material in conventional tailings 

impoundments or evaporation ponds. As discussed in Section IV.B.4 of the proposed rule, 

EPA believes that once the extraction solution removes uranium from the ore, what remains 

is uranium byproduct material; thus, under the CAA, EPA may require such facilities to limit 

radon emissions from the heap leach pile. 

3. Various definitions may not be consistent with other regulations or used consistently 

within the proposed rule and could lead to confusion. The AEA, UMTRCA, 40 CFR 

Part 192, and 10 CFR Part 40 all define byproduct material as “[t]he tailings or wastes 

produced by the extraction or concentration of uranium or thorium from any ore processed 

primarily for its source material content.” However, Subpart W defines uranium byproduct 

material or tailings as the waste produced by the extraction or concentration of uranium 

from any ore processed primarily for its source material content. Under the Subpart W 

definition, all byproduct material are tailings, which is a different from the approach taken in 

the AEA, UMTRCA, 40 CFR Part 192, and 10 CFR Part 40. Our interpretation under the 

AEA, UMTRCA, 40 CFR Part 192, and 10 CFR Part 40 is that tailings are merely one type 

of byproduct material. In addition to using a different definition, the proposed rule revisions 

do not appear to use the terms “byproduct material” and “tailings” consistently. For 

example, page 18 of the document discusses evaporation or holding ponds that contain 

byproduct material, page 49 discusses ponds that contain tailings (but the material is liquid 

byproduct material), and page 53 uses both terms “byproduct material” and “tailings” in the 

title and following paragraph. We also observe that the proposed rule uses several different 

terms when referring to structures that contain byproduct material (impoundment, mill 

tailings pile, evaporation pond, holding pond, heap leach pile, tailings impoundment, 

collection pond, non-conventional impoundment). We agree that it does not particularly 

matter what the structure is called; however, it may be helpful to identify and define one 

term near the beginning of the proposed rule and use it consistently throughout the 

document. We observe that the definition of a surface impoundment in 10 CFR Part 40, 

Appendix A, may be an appropriate term to use. 

EPA Response: The various definitions for impoundments in the proposed rule were 

defined specifically to avoid confusion among the owners and operators of uranium 

recovery facilities. Many have argued that Subpart W did not apply to evaporation ponds 

because they did not hold “tailings.” However, by defining “uranium byproduct material or 

tailings” in the original Subpart W final rule (see 40 CFR 61.251(g)), as well as proposing 

definitions for the types of pits, ponds or impoundments that hold the uranium byproduct 

material or tailings (see the proposed definitions of these terms in 40 CFR 61.251), we 

believe operators understand whether they fall under the regulatory umbrella of Subpart W. 

We attempted to maintain consistency with the definition of impoundment as found in the 

RCRA program, and by reference, under EPA’s definitions in 40 CFR Part 192. 

 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 4 of 11

4. Concern about timing as to when Subpart W would apply. On page 86 of the proposed 

rule, EPA states its intention to have Subpart W apply as soon as lixiviant is placed on a 

heap leach pile. This approach may lead to challenges from an operational standpoint. 

Based on discussions with potential operators, we understand that lixiviant may be applied 

on different portions of a heap pile at different times, which would allow a portion of the pile 

to drain. Additionally, an operator may propose to place ore in multiple lifts of material, so it 

may be possible to end up with a situation where material not yet subject to Subpart W 

overlies material subject to Subpart W. From a regulatory compliance perspective, it may 

be more practical to follow the approach proposed on pages 91 and 92. Under this 

approach, Subpart W would apply after the final rinse of a heap leach pile is complete. 

Note that the definition of tailings in UMTRCA and 40 CFR Part 192 is “[t]he remaining 

portion of a metal-bearing ore after some or all of such metal, such as uranium, has been 

extracted.” We observe that under this definition, ore is considered to be tailings after the 

uranium has been extracted, not when it is in the process of being extracted. 

EPA Response: EPA agrees that there may be comments on our interpretation of when 

material in the heap leach pile becomes subject to the requirements of Subpart W. It is 

important to note that since this is a proposed rule, we specifically laid out several options 

for regulation of the byproduct material in a heap leach pile. Our preferred option is to 

require regulation of the heap as soon as the material in the heap contains uranium 

byproduct material. We recognize, however, that some commenters may disagree with this 

approach, and argue that the material only becomes a waste when it is no longer used for 

the purpose for which it was intended. EPA will carefully consider all comments before 

making a determination in the final rule. 

5. Concern about the 30 percent moisture content requirement for heap leach piles. 

EPA is proposing that heap leach piles maintain a minimum moisture content of at least 30 

percent to minimize radon emissions. We have several comments related to this proposed 

requirement: 

General EPA Response: There are a few general stipulations that are common to all of 

the responses below. They are summarized here. 

First, it is important to understand that the basis for applying the 30% moisture content 

requirement to a specific heap leach pile is very much dependent on the characteristics of 

the pile itself. Some of the pile’s characteristics that might influence the application of the 

requirement include the topography of the site, the site’s net evaporation rate, the pile’s 

height, the ore’s initial moisture content, permeability of ore, etc. Because of this 

dependency, each site will be affected differently by the 30% moisture content GACT, 

making it difficult to provide generic responses to some of the comments. 

Second, it is recognized that imposing a 30% moisture content requirement on the pile 

might (and likely, would) require certain design changes to the pile (e.g., lower slopes, 

higher liquid application rates, additional monitoring, etc.). Nonetheless, as described in the 

specific responses, it is believed that successful designs can be developed. 

Finally, it may be feasible that for some piles, the 30% moisture content requirement could 

be applied in a stepped manner. For example, the 30% moisture content might only be 

applied to the top “×” feet of the pile, where “×” feet would be determined on a site by site 

basis. Or, if there are inter-lift liners in a multi-lift pile, the 30% moisture content requirement 

might only apply to the top lift. 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 5 of 11

 Comment: EPA should provide an objective, or goal, for radon emissions at heap 

leach piles. This would allow potential commenters to compare the reduction 

afforded by the 30 percent moisture content criterion. Without a goal or objective, it 

is unclear how EPA will judge any information submitted, and no basis is given for 

people to supply the further information that is requested. The reduction factor is a 

critical factor in assessing the risk from radon emissions from a heap leach pile. It is 

not clear if there is any data available (either actual data or modeling) demonstrating 

that a 30 percent moisture content requirement provides sufficient reduction in 

radon emissions. 

EPA Response: The goal of the 30% moisture content requirement is not so much to 

reduce the radon flux, as it is to prevent the flux from increasing. When moisture is 

introduced the radon flux first increases due to an increasing emanation (diffusion) 

coefficient and then, as more moisture is applied, the radon flux decreases due to the 

reduced diffusion coefficient. The figure below shows that the radon flux is a maximum at 

about 8% moisture content, and that at 30% moisture content the flux is back below what it 

is for dry ore. In other words, since the heap leaching process intentionally introduces 

moisture to the ore and since that moisture can result in an increased radon flux, the 30% 

moisture requirement is an attempt to ensure that heap leaching will not enhance the 

release of radon over what would occur from the dry ore. 

Therefore, the objective or goal of this GACT is to maintain the radon flux during the heap 

leach process at or below the flux from dry ore. 

We have not being able to identify, so far, “actual” data associated with radon emissions 

from a heap leach operation. There were a couple of novice attempts at heap leaching in 

the 1980's in the Gas Hills of Wyoming. These piles were composed of low-grade ore and 

overburden that was saturated with an acidic leaching solution. The resulting uranium rich 

solution was recovered and processed. There were no licensing conditions requiring radon 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 6 of 11

emission measurements (to our knowledge) associated with this specific operation. Rather 

track-etch canisters were placed a strategic down-wind points. The continuous and 

sometimes violent winds in this area of Wyoming caused sufficient mixing of the 

atmosphere to make any data extrapolation to the radon emission from the heap leach pile 

unreliable to reference. Often upwind radon measurements exceeded downwind radon 

measurements. 

Additionally, there were several low-grade ore piles that were established within the 

perimeter of mill tailings impoundments. These low grade ore piles were leached by various 

solutions. However, no radon emission data specific to these operations were collected. 

Rather perimeter radon monitoring as well as beach monitoring data were collected. Again 

attempting to apply any of these radon measurements to the presence of the heap leaching 

area would be scientifically invalid. 

In the absence of operational data, it is difficult to establish a performance standard for 

radon emissions for heap leach sites. This apparent data void, resulted in the performance 

standard of a 30% moisture requirement. This moisture requirement has been determined 

to appropriately reduce radon emissions (see Figure 16, on Page 72). 

 We recommend that “actual” data ought to be collected from an operational site to 

determine the effect of the 30% moisture requirement.. An operational license condition 

may need to be included in the licensing package to monitor the moisture content and the 

radon emission. Comparison of these data with background conditions will allow a scientific 

determination of radon emission and risk to be evaluated. 

 COMMENT: EPA should provide its estimate of the reduction factor for radon 

emissions that would be obtained by the 30 percent moisture content requirement. 

We observe that such an estimate was provided for the requirement for 1 meter of 

water covering nonconventional impoundments. 

EPA Response: The reduction factor associated for radon emissions from water covered 

impoundments can be calculated by the well known radon attenuation equation, shown as 

Equation 6-1. The water radon attenuation factor is independent of the site’s location and 

all other site specific characteristics, and depends only on the depth of the water cover. 

Contrary to this, the radon reduction factor resulting from the application to the 30% 

moisture content GACT is heavily dependent on each site’s characteristics. As the figure 

below shows, at 8% moisture content the radon flux is a maximum of about 2.3 times the 

dry ore flux. At 30% moisture content the radon flux has been reduced to below the dry ore 

flux. Therefore, this GACT results in a potential 2.3 reduction in the radon flux from the 

heap leach pile. Of course the exact reduction will depend upon the specific heap pile. For 

example, if a heap pile is operating at 20% moisture content without the GACT, then 

imposing the GACT would result in a radon flux reduction of about a factor of 1.6. Also, (see 

below), the response of the radon emanation coefficient to increasing moisture is very 

dependent on the material. This relationship between the emanation coefficient, moisture 

content, and material also influences the amount of reduction provided by the GACT. 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 7 of 11

As we cited earlier, the 30% moisture content effectiveness can be determined based on 

operational data, if and when heap leach sites are built and operated. An operational 

license condition may need to be included in the licensing package to monitor the moisture 

content and the radon emission. 

 COMMENT: The moisture content within a heap pile is variable with time and heap 

leach piles are designed to drain, so it is not clear how the moisture content could 

be maintained above 30 percent once liquid application has stopped. 

EPA Response: Of course, the moisture content of a heap leach pile is continuously 

changing, from saturation to some percentage of moisture. It is very likely (more probably 

assured), that in the western United States semiarid areas that the upper layer of the heap 

leach may reach air-dry moisture content which is much less than the 30% moisture content 

that has been established. The high evaporation rate, combined with brisk winds and 

almost constant sun will result in rapid drying of the surfaces of heap leach sites. This is 

particularity the case in the semiarid western United States, where there is the highest 

probability of a viable heap leach industry. To manage the drying that took place licensees 

were required, by license condition, to sprinkle beach areas, or otherwise maintain a water 

cover. This operation reduced radon exhalation and minimized the dispersal of wind-blown 

tailings. Operational inspections by regulatory individuals noted that this was a labor 

intensive and effective process, if the appropriate effort was devoted to the management 

practice. 

To manage the 30% moisture requirement an operational license condition may need to be 

implemented. The actions associated with the license condition will need to be assessed 

during the active heap leaching cycle to determine what response is appropriate to 

reasonably maintain the 30% moisture requirement. Numerous environmental conditions 

are present in the semiarid high desert areas of the western United States. High summer 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 8 of 11

temperatures are countered by below zero conditions in the winter. Additionally, near 

constant winds which are sometimes violent are not uncommon. Maintaining the moisture 

content at a predetermined value will be an operational challenge that will be unique to 

each heap leach site. 

In order to maintain the 30% moisture content once liquid application has stopped (i.e., after 

active uranium leaching has ceased), it will be necessary for the licensee to continue to 

apply water to the pile. Because the purpose of the 30% moisture content requirement is to 

reduce radon emissions, and because radon emissions occur mainly from the top surface 

of the pile, it would not be necessary to maintain the entire pile at 30% moisture content, 

but only the upper portion of the pile. The exact depth to which the 30% moisture content 

requirement would apply would be determined on a site by site basis. 

After active uranium leaching has ceased a final engineered cover would be constructed 

over the exhausted heap leach pile. Similar to the reclamation cover that was constructed 

over the Gas Hills heap leach piles, a final heap leach pile engineered cover would contain 

a radon barrier layer. Once the engineered cover has been constructed, than the 30% 

moisture content requirement would be withdrawn. 

 COMMENT: Potential operators have described using multiple lifts within a heap 

leach pad; it is not clear how the 30 percent requirement would be applied in this 

situation. 

EPA Response: Heap leach operations routinely utilize multiple lifts of ore. Commonly the 

ore is end dumped into the leaching area and then spread into a lift of varying thicknesses. 

This process does not lack science, in that ore simply needs to be placed into the leaching 

area. Each truck load of ore contains some degree of moisture; however, it is unlikely that 

incoming ore would have moisture content at or above the 30% level. To assure a 30% 

moisture content of the ore, an operational condition may need to be established during the 

licensing process and implemented at the site. Each lift will need to be monitored and have 

the moisture amended accordingly. In addition, it is important to manage the moisture 

content so as to minimize the compaction of the ore. The heap leach operator needs to 

avoid compacted areas of ore that could slow the movement of leaching solutions. 

Considering this situation and the 30% moisture requirement, the heap leach operator 

would add moisture as required. 

Since the purpose of the 30% moisture content requirement is to control the radon 

emissions, it may not be critical to maintain the 30% moisture content in the lower 

lifts/levels of the pile. The reason for this is two-fold; first, radon generated in the lower lifts 

would have to travel further in the pile before it would escape to the atmosphere, thereby 

giving it more time to decay within the pile, and second, radon from the lower layers will be 

slowed due to the 30% moisture content in the upper lift layers. 

Additionally, in some cases inter-lift liners are provided when the pile is composed of 

multiple lifts (Thiel and Smith 2004). If that is the case, the inter-lift liner would act as a 

barrier to the emission of radon from the lower lifts, and thus mitigate the need for those 

lower lifts to maintain the 30% moisture content. 

Thiel, Richard, and Mark E. Smith, 2004, “State of the Practice Review of Heap Leach Pad 

Design Issues,” Geotextiles and Geomembranes, 22(5): 555-568. 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 9 of 11

 COMMENT: The 30 percent moisture content requirement appears to be based 

solely on radon emissions and does not appear to take into account the engineering 

properties of heap materials. This could result in slope stability or other operational 

issues within a heap. 

EPA Response: It is agreed that the 30% moisture content requirement will impact the 

design of the heap leach pile. Principal concerns to be addressed during pile design are 

slope stability and the liquefaction potential. The impact that 30% moisture content will have 

on each of these parameters must be addressed during pile design. Nonetheless, it is 

believed that heap leach pile can be successfully designed, constructed, and operated with 

30% moisture content mandate. 

Regarding slope stability, many leach piles are provided with containment dikes which 

provide structural support to the pile. These dikes would not be affected by the 30% 

moisture content requirement, and thus would continue to provide support. Additionally, the 

pile design may be altered to increase its stability. For example, lower slopes, higher 

confinement dikes, the construction of stair-step pad grade, or the installation of textured 

(as opposed to smooth) geomembrane liner in critical areas would enhance pile stability. 

The 30% moisture requirement will have little or no effect on the moisture requirements 

associated with the containment dikes. The containment dikes represent geotechnical 

structures that are constructed in compacted lifts to assure stability of the dikes 

Regarding liquefaction potential, it has been estimated that liquefaction is unlikely if the 

degree of saturation in the pile is less than about 85% (Sassa 1985, as referred to in Smith 

2002, Thiel and Smith 2004). Assuming a 2.7 ratio between moisture content and saturation 

(NRC 1984), the 30% moisture content require translates into 81% saturation, which is 

slightly below the level required for liquefaction. Needless to say, with the increase in the 

saturation that will result from the imposition of the 30% moisture content requirement, 

more attention will need to be paid to the pile design to minimize the liquefaction potential. 

NRC (U.S. Nuclear Regulatory Commission) 1984. “Radon Attenuation Handbook for 

Uranium Mill Tailings Cover Design,” V.C. Rogers, K.K. Nielson, Rogers and Associates 

Engineering Corporation, and D.R. Kalkwarf, Pacific Northwest Laboratory, NUREG/CR3533, PNL-4878, RAE-18-5, April 1984. 

Sassa, K. 1985. The mechanism of debris flows. Proc. of the 11th Intl. Conf. on Soil Mech. 

and Foundation Engineering, San Francisco, V. 3, pp. 1173-1176. 

Smith, Mark E., 2002, “Liquefaction in Dump Leaching,” Mining Magazine, July 2002. 

Thiel, Richard, and Mark E. Smith, 2004, “State of the Practice Review of Heap Leach Pad 

Design Issues,” Geotextiles and Geomembranes, 22(5): 555-568. 

 COMMENT: We attempted to verify the make-up water application rate calculation 

on pages 89 and 90. It appears that the makeup water rate is close to the 

evaporation rate. If that is correct, the makeup water would be sufficient to make up 

for that water lost to evaporation. However, that does not mean that the water flow 

rate through the heap leach pile is sufficient to keep the pile at 30 percent moisture. 

The water flow rate required to keep moisture content at 30 percent would be based 

on how fast the water percolates through the heap leach pile. It appears that EPA 

has not provided any basis for concluding that a flow rate of 0.005 gpm/ft2

 is 

sufficient to maintain 30 percent moisture. 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 10 of 11

EPA Response: We are proposing as GACT that the heap leach pile constantly maintain a 

moisture content of at least 30% by weight. By requiring a moisture content of at least 30%, 

the byproduct material in the heap leach pile will not become dewatered, and we think that 

the heap leach pile will be sufficiently saturated with liquid to reduce the amount of radon 

that can escape from the heap leach pile. We have defined this moisture content as 

sufficient in earlier rulemakings, and it is defined in the current Subpart W rule. However, 

we are requesting further information on all the chemical mechanisms in place during the 

leaching operation, and whether the 30% moisture content is sufficient for minimizing radon 

emissions from the heap leach pile. We are also requesting comment on the amount of time 

the 30% moisture requirement should be maintained by a facility. We are proposing the 

term “operational life” of the facility. We are aware of several operations that take place 

during the uranium extraction process at a heap leach pile. After an initial period of several 

months of allowing lixiviant to leach uranium from the pile, the heap leach pile is allowed to 

“rest,” which enables the geochemistry in the pile to equilibrate. At that point the heap leach 

pile may be subjected to another round of extraction by lixiviant, or it may be rinsed to flush 

out any remaining uranium that is in solution in the heap leach pile. After the rinsing, the 

pile is allowed to drain and a radon barrier required by 40 CFR 192.32 can be emplaced. 

We are proposing that the operational life of the heap leach pile be from the time that 

lixiviant is first placed on the heap leach pile until the time of the final rinse. We believe this 

incorporates a majority of the time when the heap leach pile is uncovered and when the 

ability for radon to be emitted is the greatest Again, though, we are asking for comment on 

these processes and procedures in order to make an informed decision for the final rule. 

6. Prescriptive nature of requirement to maintain 1 meter of water within 

impoundments. We note that the requirement to maintain 1 meter of water within an 

impoundment containing byproduct does not provide operators much flexibility. For 

example, a licensee may use an impoundment in conjunction with a land application 

system. The land application system may only be able to operate in warmer weather, and 

may need to have an impoundment nearly empty to provide sufficient disposal capacity for 

the time period during which the land application system is not capable of running. 

Additionally, if a liner is found to be leaking, the water level within the pond may need to be 

lowered to repair the liner system. As currently structured, this requirement does not give 

licensees any flexibility. We are also concerned that maintaining 1 meter of water over the 

liner may significantly increase the amount of liquids requiring disposal, especially at sites 

relying on some form of evaporation. 

EPA Response: While the one meter liquid requirement may be prescriptive, we have 

been in contact with uranium recovery operators who have been making the claim that 

because of the liquids in the impoundments, there are no radon emissions. Therefore, EPA 

decided to formalize in a regulation what owners and operators have been claiming for 

years. Also, it is important to note that this is a proposed rule, and the Agency has asked for 

comment on this approach. 

7. EPA inspection and oversight. As currently structured, it appears that uranium recovery 

facilities with impoundments would be subject to EPA inspection and oversight. It is not 

clear to us if this is a regulatory burden that is calculated (in terms of the burden imposed 

on licensees). 

 

EPA Response: Under Subpart W, uranium recovery facilities with impoundments have 

always been subject to EPA inspection and oversight. This cost has been included in the 

ICR for this rulemaking, and are also included in Table 1 of the preamble, roughly page 66. 
The comments below reflect interagency review of the draft rule under EOs 12866 and 13563. They are subject to further policy review.

Page 11 of 11

Specific Comments

1. Page 22, item A, describes the processes involved in a heap leach operation and identifies 

that potential liner systems could be constructed of plastic, clay, or asphalt. Based on 

discussions with potential heap leach licensees, we understand that modern geosynthetic 

liners will likely be used. Corrected. 

2. Page 22, item B, describes liquid application practices that have previously been used at 

heap leach operations. Past practices likely did involve spraying acid on a heap leach pile, 

but potential operators have discussed using drip irrigation systems. For the rule language, 

it may be more accurate to say that acid would be applied by spraying, dripping, or 

flooding. Corrected

3. Page 22, items D and E, discusses using ion exchange as part of the uranium extraction 

process. It is our understanding that either ion exchange or solvent extraction techniques 

can be used to recover uranium at heap leach facilities. The decision to use one type or 

the other depends largely on the quality of the ore at a particular site. Corrected 

4. Titan Uranium has been acquired by Energy Fuels; however, several sections of the 

proposed rule refer to potential future actions proposed by Titan Uranium. We recommend 

updating sections of the text to reflect that future actions for the Sheep Mountain site will be 

led by Energy Fuels. Examples of this issue that should be addressed can be found on 

pages 37 and 119. Corrected 

5. Several dates or anticipated milestones have already passed. We recommend updating 

text to reflect current timelines or that anticipated activities have (or have not) occurred. 

Examples of this that should be addressed can be found on pages 37 and 41. Note that 

the anticipated applications table can be found at this location: 

http://www.nrc.gov/materials/uranium-recovery/license-apps/ur-projects-list-public.pdf. 

Corrected 

6. Page 90 has an incorrect Table reference. The text in the make-up water discussion 

should refer to Table 3, not Table 1. Corrected.