Groundwater Restoration at

Wyoming Uranium Solution Mining Sites

(PART II)

By

Glenn Catchpole, Project Manager,

OPI-Western Joint Venture

Roger Garling, Operations Superintendent (Former),

UNC Teton Exploration Drilling, Inc.

Mike Neumann, Senior Licensing Specialist,

Rocky Mountain Energy
INTRODUCTION

In the first issue of this two part article (see The Mining Claim, June 1984) an introduction to uranium solution mining was presented along with a review of the various groundwater restoration methods and the regulatory requirements that apply to groundwater clean-up. By way of review, solution mining is the process of recovering uranium from a water-saturated, underground orebody 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 orebody (See Figure 1). Typically, the leach chemicals consist of nothing more sophisticated (or non-toxic) than sodium bicarbonate (baking soda) and, oxygen.

Once all uranium has essentially been recovered from the orebody, 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. 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.

The second part. of this two part series will focus on the groundwater restoration results from three Research and Development (R&D) uranium solution mining operations conducted in the late 70s and early 80s at three geographically separated sites in Wyoming. The water quality data from the three sites demonstrate that groundwater affected by solution mining activities can be restored to acceptable conditions. For background information the reader is encouraged to read Part I of this article.

REVIEW OF 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. 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 in Wyoming.

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 into the aquifer. Several processes exist for continuous water treatment. Those processes most common to ISL restoration are reverse osmosis, electrodialysis, and ion exchange. The advantages of utilizing continuous water treatment systems in aquifer restoration, or a combination of groundwater sweeping followed by treatment and reinjection, include:
· Reduction in groundwater consumption and waste generation by up to 90 percent;

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

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

SUCCESSFUL CASE HISTORIES
A. Bison Basin Mine

The Bison Basin in-situ leach uranium mining project, located in southern Fremont County, Wyo., is a joint venture between Ogle Petroleum Inc. of Calif., the operator, and Western Fuel Inc., a subsidiary of the Duke Power Company. In the summer and fall of 1979 the OPI-Western Joint Venture conducted an R&D pilot scale uranium solution mining test to assess both the amenability of the orebody to in-situ mining, and the technical and economic practicality of restoration of the groundwater quality following mining.

The Bison Basin R&D project utilized sodium carbonate/bicarbonate as the lixiviant and oxygen as the oxidant. Due to the high sodium levels in the groundwater (400-500 mg/ 1) it was felt that sodium carbonate/bicarbonate would be an excellent choice of lixiviant from both a mining and restoration standpoint. The R&D wellfield consisted of four injection wells and three recovery wells arranged in a line-drive configuration, and operated at a flow rate of about 25 gallons per minute. Wells were completed within the mineralized zone of the Laney member of the Green River formation, which is of lower Eocene age.

The mining phase of the pilot operation lasted three months during which the amenability of the orebody to solution mining was adequately demonstrated. Target values for total number of pounds recovered, product purity, and quantity of uranium in solution (head grade) were achieved.

As part of the planning and procedures for the aquifer restoration phase of the project, the OPI-Western Joint Venture followed a step-by-step program designed to terminate each leaching reaction in the proper sequence. Following the sequential mining termination process, the restoration activity of circulating clean, surface treated water through the orebody aquifer was initiated. The surface water treatment system consisted of a reverse osmosis (R.O.) unit rated at 30,000 gallons per day (21 gpm).

TABLE I

BISON BASIN MINE
R & D RESTORATION DATA
(units: mg/l unless otherwise indicated)

NOTES

(1) The majority of the restoration requirements are baseline plus
ten percent.
(2) "-" means not detected at level indicated.
(3) The restoration requirement for total carbonate (carbonate plus
bicarbonate is 500 mg/l.
(4) The 0.04 mg/ I manganese value was not considered a significant
factor in the overall restoration results as 4 of the 5 restoration sampling wells had final restoration values of -0.01 mg/l for manganese

Groundwater restoration values acceptable to both the NRC and the DEQ were met in a little over one month of restoration after circulating about six pore volumes of R.O. treated water through the aquifer. A pore volume is simply an estimate of the quantity of groundwater contained within a specific volume of formation material. A total of nine pore volumes during a two month time period were eventually circulated through the aquifer to collect additional data on the slope of the restoration curves, and to obtain cost-benefit information. Table I presents the baseline and restoration water quality data at the Bison Basin R&D project.>

The two main regulatory agencies concerned with solution mining in Wyoming, the NRC and DEQ, both found the results of the OPI-Western Joint Venture aquifer restoration test acceptable which led to their respective approvals of a commercial scale license for the Bison Basin project. The DEQ expressed their approval of the restoration results in correspondence dated April 9, 1980 and May 5, 1980. The NRC expressed their approval of the restoration results in the Final Environmental Statement (FES) on the commercial scale license application (NUREG-0687).

B. Reno Creek Project

The Reno Creek R&D in-situ leach project is a joint venture between Rocky Mountain Energy Company (RME), Halliburton Company, and Mono Power, a subsidiary of Southern California Edison Company. RME operates the project which is located in southern Campbell County, approximately nine miles southwest of Wright, Wyo. Uranium in this portion of the Powder River Basin is found within the Wasatch Formation of Tertiary Age, as a typical roll front deposit.

Testing to evaluate the amenability of the ore deposit to solution mining with a sodium carbonate/bicarbonate lixiviant began in October of 1980. The wellfield consisted of two recovery wells ringed by four injection wells and an outer ring of monitor wells. This well configuration is known as a modified "five-spot pattern," illustrated in Figure 2.

Leaching operations were conducted over a 10-week period during which the feasibility of recovering uranium using a sodium carbonate/bicarbonate lixiviant was confirmed. Groundwater restoration began in December 1980 by pumping production fluid from the wellfield through the surface plant facilities where an ion exchange (IX) process was used to remove undesirable constituents. This process continued for a one-month period and was followed by a groundwater sweep which also continued for about one month.

At the close of the restoration program, all groundwater constituents, except uranium, were restored to levels below or within baseline ranges. Uranium was reduced to less than five parts per million which is the standard for drinking water in Wyoming. This was accomplished through the circulation of about seven pore volumes of groundwater through the aquifer. Total groundwater consumption during restoration was equivalent to 5 pore volumes or 1.3 million gallons. A representative comparison of premining and restored groundwater quality is shown on Table 2.

Groundwater restoration and stabilization monitoring data were thoroughly evaluated by the Land and Water Quality Divisions of the DEQ and by the NRC. Both agencies concluded that the goal of restoring groundwater to premining baseline conditions was achieved for all parameters except uranium which met WDEQ's water use class standards. Further, the NRC and DEQ acknowledged that restoration results would be suitable to support commercial-scale operations at Reno Creek. See copies of DEQ and NRC correspondence approving the restoration results pages 18 and 19.
C. Leuenberger Project

The Leuenberger site is located approximately seven miles northeast of Glenrock in the southern portion of the Powder River Basin. The R & D project was originally a joint venture between NEDCO and UNC Teton, operator, designed to evaluate the feasibility of solution mining within the Fort Union Formation of Paleocene Age.

UNC Teton began test operations in April 1979 also using a sodium bicarbonate/carbonate lixiviant. Uranium mineralization within this portion of the Fort Union Formation frequently occurs as "stacked" or layered zones in different sand units so two separate test patterns were constructed at different depths. Both wellfield configurations were typical five-spot patterns consisting of four injection wells surrounding a central recovery well (see Figure 2).

The first of the patterns to undergo active groundwater restoration was the N sand which is the shallower sand unit. The test pattern was successfully restored using a groundwater sweep method initiated June 1980 and completed in November 1980. Following a 14-month groundwater stability monitoring period, DEQ agreed that the aquifer restoration had been effective and met license requirements. Although restoration was successful, groundwater consumption was high due to the sweep method.

Leaching operations within the lower ore zone, or M sand, were terminated in February 1981 after confirming the viability of uranium recovery using the sodium bicarbonate/carbonate lixiviant. The restoration program was designed to recapture all groundwater affected by leaching constituents while minimizing the consumptive use of groundwater. This was accomplished through the use of electrodialysis (ED) treatment which is basically a water purification process. The ED concentrates undesirable groundwater constituents into an effluent or brine for disposal and produces "clean" water which can be reinjected into the wellfield.

By the end of the restoration program, approximately half (46 percent) of the affected groundwater recovered from the pattern was sent to the ED unit for treatment. Of this amount, approximately 8 percent was disposed of in an evaporation pond. The ED product, or "clean" water was then mixed with untreated groundwater from the pattern and reinjected to improve overall groundwater quality. The total restoration process resulted in the consumption of 1.7 million gallons of groundwater which represents a 90 percent improvement in water conservation compared to the groundwater sweep method.

Restoration was terminated in December 1981 when water quality in all pattern wells was at or below restoration goals contained in the R & D permit. Comparison of baseline and post restoration water quality indicated that all parameters except radium were restored to specified levels or well within baseline water quality ranges. Radium levels were reduced to an average of 350 pCi/l compared to a baseline average of 185 pCi/I. Wyoming DEQ standards for Class I (Domestic), Class II (Agricultural), and Class III (Livestock) groundwaters are 5 pCi/ 1. Therefore, post restoration radium levels did not impair groundwater use suitability.

The Final Environmental Statement (FES) prepared by the NRC for the commercial-scale license application concluded that " . . . the applicant has demonstrated that restoration of the ore zone aquifers to their original potential use condition is achievable."

Reno Creek

Pattern 2 Production Wells

Restoration Data

All values expressed as mg/I except pH (standard units), conductivity (umhos/cm), radium and thorium (pCi/1).
Baseline range is for all pattern production zone wells following outlier
removal.
NML values are U308; CDM values are U nat.

Conclusion

In-situ leaching of uranium is a mining method undergoing rapid technological development. Experience to date confirms that this method can compete favorably with traditional open pit or underground mine operations from an economical standpoint. An advantage of solution mining is that surface facilities and disturbances are significantly less extensive than those associated with open pit or other surface mining methods. Consequently, protection of groundwater resources is of greatest environmental concern, particularly the restoration of affected groundwater to premining conditions. At least three different operators in Wyoming have demonstrated, in different geographical and geological settings, that groundwater restoration to the original use suitability can be achieved.

Domestic marketplace requirements for uranium are currently quite depressed as imported uranium is readily available and utilities are deferring construction on existing and proposed power plants. When market demand increases, however, the domestic industry is expected to rely heavily on in-situ mining as an economical means of production. As documented in this article, the mining industry has shown that in-situ mining can be done in an environmentally acceptable manner which protects land and water resources for future use.