Groundwater Restoration at

Wyoming Uranium Solution Mining Sites
By

Glenn Catchpole, Project Manager,

OPI-Western Joint Venture

Roger Garling, Operations Superintendent,

UNC Teton Exploration Drilling, Inc.

Mike Neumann, Senior Licensing Specialist,

Solution mining, or in-situ leaching, is the process of recovering uranium from a water-saturated, underground ore body in a manner which leaves overlying rock strata and the land surface intact. The process involves the installation of a series of wells through which a chemical solution (lixiviant) is injected into the uranium-bearing formation, passed through the formation, and pumped back to the surface. From the recovery or production well, the uranium-bearing solution is piped to a surface plant where a series of conventional chemical processes extract uranium from the solution. The resulting solution, now barren of uranium, is then refortified with leach chemicals and reinjected into the ore body. This process continues until uranium levels in the production fluid (pregnant liquor) drop to a point where recovery is no longer economical.

Once all uranium has essentially been recovered from the ore body, groundwater affected by the leaching solution must be "cleaned up" to a condition which allows appropriate future use of the resource. Generally, regulatory agencies require that groundwater be returned to a quality as close to premining (baseline) conditions as can practically be achieved. Recognizing that restoration to exact baseline characteristics for each groundwater constituent may not be physically possible, the State of Wyoming requires that, at a minimum, groundwater be returned to a condition compatible with the premining use or potential use of the water.

Concerns have been expressed by the public, landowners, regulatory agencies, and special interest groups regarding the amount of information which exists that demonstrates groundwater can be restored to acceptable conditions following in-situ uranium mining. Because the future viability of the domestic uranium production industry is expected to rely heavily upon this relatively low cost production method, it is important to make known the successes which industry has experienced in Wyoming. This paper will, there re, focus on the groundwater restoration aspects of uranium solution mining and present case histories of successful groundwater restoration at three different mine sites in Wyoming.

Project Development

Before a property becomes a candidate for solution mining, several years of extensive data gathering programs will have been completed. The first of these involves exploration drilling, typically over a period of several years, to locate uranium mineralization and define an ore body. If early drilling results are favorable, other studies may be initiated to determine the feasibility of developing the project from an economic, engineering, regulatory, and environmental perspective. Assuming preliminary indications from these investigations are all positive, attention begins to focus on environmental considerations since no project will be approved absent a determination that potential impacts are acceptable.

For a proposed solution-mining project, environmental concerns relate primarily to protection of the groundwater resource both during and following mining. It must be shown that solution movement can be controlled once injected the ore body and that groundwater can be restored to acceptable condition following mining. Well pump tests be performed to define the hydrologic characteristics of ore zone and determine if adjacent geologic strata are suit to prevent vertical movement of leaching solution into underlying or overlying aquifers, if present. Additional information such as the direction and velocity of groundwater flow porosity, permeability, and hydraulic gradients within the zone is obtained from the pump tests. This information is t used to design the optimum pattern for injection and recovery well spacing, or wellfield configuration, and assess potential groundwater impacts from mining operations. Other w called monitor wells, are completed for aquifer sampling poses so that a thorough documentation of surrounding groundwater quality is obtained prior to mining.

In Wyoming, permits for a commercial scale, in-situ will not be issued until regulatory agencies are satisfied t groundwater can be restored to an acceptable condition. That reason, legislation was passed (W.S. 35-11-431) in I which specifically provides for research and develop (R&D) facilities. Such facilities are designed to evaluate feasibility of mining and restoring groundwater at a scale indicative of an operators ability to prevent significant environmental impacts. The R&D or test facility allows operator to determine the best procedure for and define costs of restoring groundwater. Naturally, if restoration c are excessive, a commercial-scale operation may not economically viable. A comprehensive understanding regulatory requirements is essential to properly evaluate economic feasibility of restoration costs. The following describes current regulations applicable to groundwater restoration in Wyoming.

Regulatory Requirements

Two major permits (or licenses) are required for the construction and operation of an in-situ uranium solution mining Additionally, there are numerous minor permits required solution mining. The two major permits are a "permit mine" from the Wyoming Department of environmental Quality (DEQ), Land Quality Division (LQD), and a "so material license" from the U.S. Nuclear Regulatory Commission (NRC). The fulfillment of the U.S. Environmental Protection Agency's Underground Injection Control (U.I.C.) Program requirements are realized through the DEQ Water Quality Division's (WQD) interaction with the Land Quality Division in the review of the mine permit application.

The DEQ's requirements for restoration are stated in the Wyorning Environmental Quality Act, 35-11-426 through 3511-536, and in Chapter XXI of the Land Quality Division Rules and Regulations. The Land Quality Division rules state in Section 2.d (1)(a) and (b) That "The condition and quality of all affected groundwater will be returned to background or better, or: (b) the requirements of Section 2.d (])(a) cannot be achieved. In this event, the condition and quality of all affected groundwater will at a minimum be returned to a quality of use equal to and consistent with uses for which the water was suitable prior to commencement of the operation." The rules and regulations also mention That the operator is to employ the best practicable technology in the restoration effort. The NRC does not have specific restoration criteria but normally is in agreement with the DEQ on restoration requirements for an individual mine. However, the NRC is required by Federal regulations to conduct a separate and independent review of restoration results to ensure protection of public health and the environment.

In practice, the DEQ has been requiring operators to return most water quality parameters to respective baseline values with a tolerance of 20 percent to allow for analytical tolerances and natural variations in the water quality. This requirement may be on a well-by-well basis or by wellfield area depending upon agreements between the agencies and the individual operator. If it is not practical at a specific mine to return water quality to baseline conditions, then the restoration requirement is tied to the premining use or potential use of the water as classified by the Water Quality Division.

The WQD's water classification system is discussed in their Rules and Regulations, Chapter VIII. Briefly, the classification system allows for six (6) classes of water as listed:
Class Description

1. Domestic

2. Agriculture

3. Livestock

4. Industrial

5. Commercial (Hydrocarbon, Mineral and Geothermal

6. Unsuitable

If the WQD classifies the ore body aquifer as Class I (e.g., there is a domestic well nearby completed in the same aquifer), then all parameters must be returned to baseline including uranium. Normally, an ore zone aquifer will be classified by the WQD as Class 5 due to the typical natural groundwater quality in a uranium mineralized sandstone unit. If the ore body aquifer is classified as Class 5 and it is not practical to return a given water quality parameter to baseline, then That parameter must be returned to a value consistent with Class 5 waters. For example, uranium would have to be returned to 5 mg/ I (the Class 5 standard for uranium) or less. Generally, the WQD also requires That total dissolved solids (TDS) which gives a general indication of overall water quality, be returned to within baseline plus 20 percent regardless of class.

Regardless of the specific restoration goal, efforts must be undertaken to mitigate the effects of mining on aquifer water quality. A wide variety of techniques for restoring groundwater have been used by the in-situ mining industry with varying degrees of success. A discussion of the methods most commonly used within the in-situ industry and specifically those methods successfully employed at projects cited in this paper follows.

Restoration Techniques

To achieve restoration, constituents added to the groundwater for mining and those mobilized during the mining process must be removed or rendered nonmobile. In some cases, it may also be necessary to chemically treat the geologic formation in order to reverse or inhibit reactions initiated during the mining phase.

Prior to aquifer restoration, the operator should have adequate background data to determine the following:

1. Groundwater baseline conditions;

2. The balance between process chemicals injected into and recovered from the wellfield;

3. Knowledge of both the constituents mobilized in the formation during mining and a general understanding of the area and volume of the affected groundwater; and

From the process chemistry and operation, the optimum equipment, chemistry, and pumping patterns required to achieve restoration and maintain a favorable equilibrium between the resulting groundwater and the formation.

This information is derived from data collected prior to and during initial phases of the R&D operation. The optimum restoration technique for a given site will be largely determined by inherent geologic and hydrologic conditions of That site and observations made during the initial R&D phase. In general, however, combinations of two basic approaches have been used most extensively within the industry.

The first, and simplest of these techniques, is referred to as "groundwater sweep" in which both chemical constituents and groundwater are removed from the affected area by pumping selected wells. Although this technique has been successfully employed at the R&D level, several considerations may preclude total reliance on the groundwater sweep method for commercial- scale operations. Disadvantages of the sweeping method include consumptive use of large volumes of groundwater and extensive waste water storage facilities or evaporation ponds which, in turn, require large surface disturbances.

A more accepted technique utilizes treatment equipment to remove chemical constituents from the groundwater which renders the resulting water fit for reinjection to the aquifer. Several processes exist for continuous water treatment. Those processes most common to ISL restoration follows:

1. Reverse Osmosis: Process utilizes high pressure across semi-permeable membranes to physically remove soluble molecular and ionic species. This process was successfully used at the OPI-Western joint venture Bison Basin project in the Red Desert area of Wyoming.

2. Electrodialysis: Process utilizes electrical current passed across a stack of alternating cation and anion selective membranes in order to achieve an electrochemical separation of ionized species in aqueous solutions. The UNC-Teton Leunberger project used this process to demonstrate restoration in the southern Powder River Basin, Wyoming.

3. Ion Exchange: Ion exchange systems have been used in conjunction with water treatment equipment, typically for the removal of residual mobile uranium, although the process can be used for effective deionization of recovery streams. A modified version of this process was successfully used by Rocky Mountain Energy (RME) at the RME-Halliburton- Mono Power Reno Creek joint venture project in the northern Powder River Basin, Wyoming.

In all three cases, clean water generated from the treatment unit was reinjected into the mined aquifer in order to restore affected groundwater and help in guiding fluid movement to pumping wells. Chemical additions to the reinjection stream, such as reductants or pH adjusters, have in some cases been used to chemically stabilize the formation. In high clay content, formations, benign cation species may be reinjected with the treated water in order to reverse ion exchange reactions which occurred during mining.

The advantages of utilizing continuous water treatment systems in aquifer restoration, or a combination of groundwater sweeping followed by treatment and reinjection, include:

1. Reduction in groundwater consumption and waste generation by up to 90 percent;

2. Provides a means to direct groundwater flow in the aquifer through selective well pumping and reinjection; and

3. Provides a means of introducing chemicals to the formation to reverse or inhibit continuing chemical reactions.

Certainly experience gained at the Bison Basin, Leunberger, and Reno Creek sites confirms the advantage of using a reinjection process combined with limited groundwater sweeping. Restoration results at all three sites are considered demonstrated evidence by the DEQ and NRC of the respective operator's ability to restore groundwater to acceptable conditions at the R&D level. Further, both the DEQ and NRC have accepted the R&D restoration results as being sufficient to justify commercial-scale operations at these sites.

Summary and Conclusions

The groundwater restoration, or cleanup of an aquifer impacted by in-situ uranium solution mining is technically and economically achievable as demonstrated by results of three successful pilot projects operated in different geographic regions of Wyoming. In each of the three projects, appropriate regulatory agencies have concurred That aquifer restoration was adequately demonstrated. Key ingredients for successful restoration appear to be lixiviant (leach chemicals) selection coupled with detailed planning of the restoration phase of the project.

Regulatory agencies and special interest groups have voiced the concern That adequate restoration of a commercial sized solution mining wellfield may not be achievable since no mining company in Wyoming has yet to restore a commercial sized wellfield. There is no basis for this concern in That the technical and physical processes for restoring a solution mined aquifer have been successfully demonstrated. In fact, aquifer restoration of a commercial wellfield is expected to be less difficult than restoring an R&D wellfield from both an economic and technical standpoint. Economy of scale associated with a commercial size operation will lower the cost of restoration. From a technical standpoint, improved flow patterns and decreases in perimeter area per production well will make restoration quicker and more complete. Quoting from the NRC's final Environmental statement on the commercial-scale license application for-the Bison Basin project (NUREG-0687), "The staff conclusion is That fewer treated pure volumes will be needed for restoration than appears necessary because the percentage volume affected external to the injection well perimeters decreases radically with an increase in wellfield area."

The second article in this two part series will address in detail restoration results obtained at the Bison Basin, Leunberger, and Reno Creek sites. Case histories will describe changes in water quality That occurred during mining operations, and complete results of respective restoration programs will be presented along with regulatory agency evaluations.