COMPLETED ~B-~ 7(FA c[ RI 96041 9 REPORT OF INVESTIGATIONS/1996

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Midnite Mine Summary Report

UNITED STATES DEPARTMENT OF THE INTERIOR

44,

o w U' 4 'NT UNITED STATES BUREAU OF MINES I / 7. -- U. S. Department of the Interior Mission Statement

As the Nation's principa! conservation agency, the Department of the Interior has responsibility for most of our nationally-owned public lands and natural resources. This includes fostering sound use of our land and water resources; protecting our fish, wildlife, and biological diversity; preserving the environmental and cultural values of our national parks and historical places; and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to ensure that their development is in the best interests of all our people by encouraging stewardship and citizen participa- tion in their care. The Department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration.

I0 Report of Investigations 9604

Midnite Mine Summary Report

By N. E. Dean, C. M. K. Boldt, L. E. Schultze, D. N. Nilsen, A. E. Isaacson, B. C. Williams, F. E. Kirschner, B. W. Moore, W. P. Stroud, and D. C. Peters

UNITED STATES DEPARTMENT OF THE INTERIOR Bruce Babbitt, Secretary

BUREAU OF MINES Rhea Lydia Graham, Director

This report has been technically reviewed, but it has not been copy edited because of the closure of the agency.

1/ CONTENTS

ABSTRACT ...... 1

INTRODUCTION ...... 2

SITE DESCRIPTION ...... 2

RELATED STUDIES ...... 3

METHODOLOGY...... 4 WATER TREATMENT STUDIES ...... 5 HYDROGEOLOGY ...... 5 RADIATION SURVEY ...... 6 SOLID MATERIAL REACTIVITY ...... 6

RESULTS...... 7 WATER TREATMENT ...... 7 HYDROGEOLOGY ...... 9 RADIATION SURVEY ...... 10 SOLID MATERIAL REACTIVITY ...... 10

GEOGRAPHIC INFORMATION SYSTEM...... 11

CONCLUSIONS ...... 11 WATER TREATMENT ...... 11 BASELINE RECLAMATION STUDIES ...... 11

REFERENCES ...... 13

ILLUSTRATIONS

1. PRE-MINING TOPOGRAPHY ...... 15 2. POST-MINING TOPOGRAPHY ...... 16 3. SCREENING OF REMEDIAL TECHNOLOGIES ...... 17 4. COMPREHENSIVE DRILLING AND CHARACTERIZATION OF THE MIDNITE MINE ...... 18

TABLES

1. PROTOCOL FOR DETERMINING ACIDIC SAMPLE CLASSIFICATION ...... 14 2. SOIL SAMPLE ANALYSIS ...... 14

4'470 MIDNITE MINE SUMMARY REPORT

By N. E. Dean', C. M. K. Boldt 2, L. E. Schultze3, D. N. Nilsen , A. E. Isaacson5 , B. C. Williams, F. E. Kirschner', B. W. Moore', W. P. Stroud', and D. C. Peters10

ABSTRACT

The Midni'e Mine is an inactive, hard-rock mine in Stevens County, WA. Oxidation of sulfide-containing minerals in the ore body produces large quantities of acidic water. The U.S. Bureau of Mines was directed by Congress in Fiscal Year 1994 to perform technological research on the treatment of radioactive water and disposal of treatment residues at the Midnite Mine and en overall site reclamation. This Report of Investigations summarizes the studies that were completed on: 1) treatment alternatives for uranium contaminated acid mine drainage, and 2) overall site reclamation, including: ground water flowpaths in the bedrock, radiation, and waste rock reactivity. As an aid to site reclamation, a Geographic Information System database was also produced that contains available current and historic data and information on the Midnite Mine. This report explains the scope of the Bureau's study and summarizes the results of its investigations.

'General Engineer

2Civil Engineer

3Chemist

4Chemical Engineer

5Chemical Engineer

6Civil Engineer

"Hydrologist

8Chemical Engineer

9Physical Scientist

'0Mining Engineer 2

INTRODUCTION

The U.S. Bureau of Mines (USBM) was directed treatment, there would be a major problem with by Congress in Fiscal Year 1994 'to perform disposal of the generated sludge. The goal of the technological research on the treatment of USBM was to provide the Secretary of the radioactive water and disposal of treatment Department of the Interior (DOI) with less costly residues at the Midnite Mine and on overall site alternatives should they be needed. Water reclamation.' In response, the USBM initiated a treatment. technologies that would limit the need two year program of technical studies. The for offsite disposal were particularly examined. USBM worked closely with the Bureau of Indian The second goal was to address a limited Affairs (BIA), the Bureau of Land Management number of technical issues involved with overall (BlM), and the Spokane Tribe of Indians to site reclamation that responded to major issues of develop the work plan on which the technical concern by stakeholders at the Midnite Mine. studies summarized in this report are based. 'T'hese studies developed 1) a conceptual The primary focus of the first of this two hydrogeologic model of the mine site's principal part study was to determine alternate treatment groundwater fh (paths and a conceptual geologic technologies for contaminated water that has model, 2) an assessment of the acid generation collected in Pits 3 and 4 onsite. The lessee potential of the various waste rocks at the mine (Dawn Mining Co.) built and is operating a lime-- site and gross characterization of the South Spoils based water treatment plant.. The treatment and Hillside Dump. 3) radon and gamma radiation produces a large volume of sludge that, because surveys, and 4) a database containing an extensive of residual radioactive materials associated with collection of information on the Midnite Mine. the current water treatment system, must be This report is a summary of Reports of disposed of in an facility regulated by the Investigations which contain the results of the Nuclear Regulatory Commission (NRC). Should specific studies described above. the Dawn Mining Co. be unable to continue water

SITE DESCRIPTION

The Midnite Mine is an inactive uranium mines, is within a sulfide- hosted orebody which surface mine located on the Spokane Indian produces acid mine drainage and associated heavy Reservation in WellpiniL, . The site is metal contamination. There are several open pits approximately 50 miles northwest of Spokane, and impoundments of heavy metal contaminated Washington and four miles from the Spokane water on site. The major pits are designated as Arm of the Grand Coulee Dam National pit 3 and pit 4. In figure 2, Pit 4 is the northern Recreation Area which is jointly administered by most pit and Pit 3 is located due south of Pit 4. two Indian 'T'ribes, the National Park Service, A pollution control pond, seen at the toe of the Bureau of Reclamation, and the Bureau of Indian southern most spoil pile in Figurc 2, is a collection Affairs. The mine is roughly 320 acres of point for most of the contaminated seep water disturbed area (% mile wide by 1 mile long) and which is then pumped back and stored in pit 3 the site is relatively steep with 1000 feet of prior to treatment and discharge. Water from the relief between the north and south ends of the Boyd Seep, located in the drainage east of the mine. There are 2 %million tons of low grade Mine, is pumped directly to Pit 3. Water from the ore, 33 million tons of waste rock, and 100,000 pollution control pond and Pit 3 must be pumped tons of topsoil stockpiled on the mine site. and treated to avoid a water level rise and Figure 1 and 2 show the pre mining and post subsequent outflow that could result in increased mining surfaces of the site respectively. seepage through reactive mine wastes. Pits 3 and The Midnite Mine, unlike most U.S. uranium 4 currently contain about 500 million gallons of 3 contaminated waters. The Dawn Mining Co. built infiltration, and because water is being pumped and is operating a lime-based water treatment into it from seepage collected below the mine via plant at a 500 gallon per minute capacity. the pollution control pond and from Boyd Seep. The Midnite Mine lies on the southwest slope Many waste rock piles and eight low-grade of Spokane Mountain at the southern end of the material pits remain on the mine site. The two Huckleberry Mountains, a minor range in the largest waste rock piles have been designated north-south trending Selkirk system. Altitude of Hillside Dump and South Spoils. In figure 2 the mine ranges from 1036 m above mean sea Hillside Dump is the waste rock pile located level at the northern end to 730 m at the southwest of Pit 4. South Spoils is the curvilinear southern end. During the period the mine was feature in Figure 2, located about 457 m south of active, six pits or subpits were opened. Four of Pit 3. The pollution control pond was constructed these were subsequently backfilled with in 1979 below the South Spoils to intercept overburden and waste as mining progressed, seepage that flows along the now buried upper while two pits (3 and 4) were left open. The reach of the unnamed central drainage. Water present bottom of pit 3 is about 130 m lower in from seeps that have formed since that time are elevation than the bottom of pit 4. Pit 3 pumped to the pollution control pond and then to contains approximately 430 million gallons of Pit 3, except for water from the Boyd Seep which water and is more contaminated than pit 4. Pit is pumped directly to Pit 3 4 contains approximately 70 million gallons of Precipitation at Wellpinit averaged 48 cm/yr water. Pit 4 was used as a repository during from 1951 through 1980. Recharge to the site dewatering of pit 3 that began around 1979. The consists of rainfall and snowmelt from the water level in Pit 4 appears to be in dynamic immediate vicinity. Discharge consists of equilibrium, responding primarily to seasonal evaporation, surface stream runoff, and a small variations from precipitation, ground water amount of ground water flow, Sumioka [1991, (1)]. inflow, and seepage loss to down gradient Three unnamed tributaries to Blue Creek carry portions of the mine. The water in pit 3, less most of the water from the site; these streams ongoing mine water treatment, is constantly were informally designated East Drainage, West increasing because of precipitation and Drainage, and Central Drainage.

RELATED STUDIES

Previous research on the Midnite Mine and within fractures, shear zones, and focused primarily on the geology and hydrology clay-rich layers within the calc-silicate rock. of the mine. Nash and Lehrman [1975, (2)] and -bearing phyllite schist is the Nash [1977 (3)] established the geologic setting predominant rock type on the northern wall of pit of the mine on the southwest slope of Spokane 3. Mountain and in the western edge of the Freshman and Dodd [1982, (5)] described the metasedimentary Togo Formation in the Belt Late Cretaceous porphyritic quartz monzonite Supergoup. This Precambrian sequence is 900 m intrusive that crops out along the west side of the thick and contains graphitic and pyritic mica mine and underlies the eastern portion of the phyllite and muscovite schist with interbeds of mine. The contact between the quartz monzonite marble, calc-silicate, hornfels, and quartzite. and the ore-bearing metasediments was described They described the ore deposition as as running north-south from the middle of pit 4 hydrothermal in a contact metamorphic- through pit 3 near the west wall. Intrusive rock metasomatic system that produced sulfide forms the west highwall of pit 4, the ridge above minerals. Uranium within the ore zone was the highwall, and the west highwall of pit 3. Ore described by Nash and Lehrman [1975, (2)] and bodies were described as being 18 m wide, 366 m Ludwig, et al. 11981, (4)] as being disseminated long, and 46 m thick and 4.6 to 91 m below the along foliations in muscovite schist, phyllite, and surface. Oxidized uranium minerals occurring 4

above the water table were identified as autunite Williams and Riley 11993, (8) investigated head and meLauLunite; reduced uranium minerals distribution within the mine and the potential for found in the deep ore bodies below the water ground water recharge of the excavated pits after table were identified as and . dewatering. head data from wells in the vicinity Pyrite and rnarcasiLe are associated with these of pit 4 indicated that if pit 4 were dewatered, it latter minerals. Several other sulfide minerals would refill with ground water and would continue were also identified in minor amounts: to discharge water to the ground water flow pyrrhotite, molybdenite, chalcopyriLe, sphalerite, system. Pit 3 water quality data, prior to and galena. pumpback of water from the pollution control Hydrologic studies by Marcy 11993, (6)1 made pond, was examined and was shown to exceed several conclusions based on water quality data: uranium concentrations for current NPDES 1) sources of acid water were indicated as the discharge limits. The water quality data from low grade ore piles, waste rock, and other spoils wells near pit 3 also indicated that future piles, 2) seasonal flushing of contaminated water recharge to pit 3 will have poor water quality. was attributed to rainwater moving through the Other work at Midnite Mine included reactivity waste rock and migrating downgradient to studies by Altringer and Froisland |1993, (9)1. emerge at seeps, with concentrations of toxic These studies were preliminary tests using surface metals increasing as the flow rate increases, 3) grab samples from low grade ore piles and the degradation of water in pit 3 was attributed to Hillside Dump, and subsurface samples taken after not only the pumpback system from the trenching Pit 2 and two of the low grade ore piles. pollution control pond but to the infiltration and Samples were tested for reactivity using a runoff directly entering pit 3 as well, 4) a percolation column leach system. Five of the low hydraulic connection between pit 4 and the grade ore piles sampled were found to have acidic seeps on the north headwall of pit 3 was leachate. Two of the low grade ore piles exhibited indicated by hydrochemical models describing alkaline conditions. Hillside dump exhibited the seeps as predominantly pit 4 water, and 5) primarily alkaline conditions. Pit 2 waste rock hydrochemical models of ground water from produced the most acidic leachates of any Boyd Seep, located in the southeastern portion samples. Leachates from pit 2 samples contained of the mine, indicated that the existence of a uranium and other metals, including manganese, flowpaLh between pit 3 and Boyd Seep was and zinc. Uranium was also found to be mobile in unlikely. the low grade ore piles. lHillside Dump, however, Additional work by Marcy, et al. [1994, (7)1 showed variability in metal leaching. Conclusions concluded that there is recharge from the waste of the study were that low grade ore pile were piles of low grade ore into the metasediments reactive and will need isolation from ground and and that a probable flow path exists along the surface waters, and that other waste materials on contact of the metasediments and the intrusive. site needed further evaluation. A flow path model was used to show that Other reports, studies, and maps, including contaminated water from the areas around the those produced by the Dawn Mining Co. are low grade ore piles and degradation of identified in the bibliographic portion of the infiltration water within the South Spoils could Geographic Information System Database contribute to the contaminated water emerging assembled by the USBM and available through at the South Spoils Seep. NTIS.

METHODOLOGY

The direction and scope of technical studies requested two principal projects be completed by reported in this document were decided upon by the USBM: 1) identification and assessment of a technical working group composed of staff alternatives for water treatment, and 2) studies to from the USBM, BIA, BIM, and representatives of support overall site reclamation, including a the Spokane 'ribe of Indians. The working group conceptual hydrogeologic model of the mine site's 5 principal bedrock ground water flowpaths and a remediation technologies. Figure 3 shows the conceptual geologic model, further various technologies screened and why they were characterization of ground water quality, included or excluded. Five technologies developed material characterization of the two largest by the USBM and one commercial technology were waste piles at the site, radon anu gamma tested at the bench scale. In addition, a Request surveys, and a database containing an extensive for Information was advertised in the Commerce collection of information on the Midnite Mine. Busoess jai/y for innovative, commercially available, water treatment methods. Three of the WATER TREATMENT STUDIES twenty -three submittals reviewed by the USBM were identified as having application to the mine A major reclamation issue at the Midnite water and treatability studies were performed. Mine is the two pits containing approximately Technologies examined were those that could 500 million gallons of water contaminated with provide suitable pre-treatment to remove uranium uranium, radium, manganese, and other heavy and radium prior to the current precipitation metals. The lessee at the site must comply with technology. This would prevent the generation of a National Pollutant Discharge Elimination an NRC source material and eliminate the need for Systems (NPDES) permit, and is currently expensive disposal. The alternatives were tested operating a water treatment plant At Lhe Midnite for their effectiveness in removing uranium and Mine that uses a combination of lime and radium prior to precipitation of a sludge. The barium chloride additions to precipitate the uranium could then be sold and only a small radionuclides and other metals. This produces a quantity of radium would require disposal. sludge that is classified as a source material by Treatability tests were completed on eight the NRC. The lessee now trucks this sludge off alternative water treatment methods, including: the site to a mill in Ford, Washington. The ion exchange resin (Dowex 21K), ion elutriation, sludge is treated at the mill to remove uranium liquid emulsion membrane, biogenic hydrogen and the remaining slurry is periodically pumped sulfide treatment, immobilized extractants, into the tailings impoundment located at the waterglass process (Westinghouse Electric, Corp.), mill. Diphonix resin (Eichrome Industries) and a solid It was anticipated that, should the lessee be phase extractant (ChromatoChem, Inc.). In unable to meet their commitment to treat the addition an advanced dewatering method {or contaminated water at Midnite Mine, the DOI treatment of the sludge was examined to reduce might have to assume contingency treatment. sludge volume. Since the )01 would not have access to the offsite mill or tailings pond, this would require HYDROGEOLOGY disposal of .he sludge in a regulated landfill. Cost of commercial disposal is estimated to be Hydrogeology of the bedrock at the Midnite $28 per 1000 gallons of mine water treated. At Mine was selected by the technical working group the current treatment rate of up to 500 gallons as a focused study. This study was selected in per minute, the disposal costs would be order to determine the flow of contaminated approximately $5,443,200 per year. This cost is ground water and the potential for offsite based on continuous operation of the plant over migration effecting valuable water resources. It a 270 day period (the plant is closed during was recognized that further studies of the winter months due to freezing conditions and localized ground water flow through the disturbed county road load restrictions) and does not areas within the mine will be necessary in order to include transportation, sludge drying, or ensure reclamation options limit seepage through applicable licenses and permits. the mine site, however, an understanding of the In order to provide cost-effective options for bedrock flow is essential to assessing off-site contingency water treatment that would not contamination and was a necessary first step. require landfill disposal of an NRC source Hydrogeologic studies of the Midnite Mine included material, the USBM screened physical, chemical, hydraulic stress testing, structural analysis, resource recovery, biological, and passive water development of geologic and hydrologic models, 6 and additional collection of water quality data. such as drains, at a localized scale without having Analysis of structural geology included to reconstruct/redescretize the model domain. It assessment of fractures, fracture density, width, also allows for localized hydrologic areas and orientation, and the relative influence of results in a more realistic model capable of fractures on ground water flow through the utilizing structural and geomorphic information. bedrock. Wells were chosen for hydraulic stress tests RADIATION SURVEY based on their likelihood to bound the range of permeabilities in bedrock at the site. Previous Two radiation sruvey were selected by the estimates of specific capacity were based on technical working group as focused areas for short pump tests of the wells. The specific study. The proposed studies would provide capacity data were used as a gross estimate of baseli: radiation data needed for reclamation of hydraulic conductivity to rank the wells. Wells the site. were then identified as to their productivity and A ground radiation survey was conducted at location near localized hydraulic features the Midnite Mine. Two types of information were needing assessment, i.e. backfilled pit 2 and the developed from the survey: 1) gross gamma area between pits 3 and 4. radiation measurements related to health risk to Two types of hydraulic stress tests were individuals at the site, and 2) Ra -226 analyses of performed: slug tests and pump tests. Slug tests the soil required for site remediation planning, were performed in three wells. A cylindrical slug A square sampling grid was constructed using was instantaneously lowered into the well, 150 -m spacings between points over the mined causing the water level to rise. The subsequent area. Survey points were laid out using a portable rate of fall of water level as the head CI'S receiver. The Ra -226 survey was completed reequilibrated to prestress conditions was using URINCO 'face scanners, originally developed recorded with a transducer and data recorder. for use in uranium ore reserve evaluation. A falling water level test was used in each case As part of the radiation survey, 17 soil samples because the equilibrium water level was above were collected at the mine site. Splits of the the screened section of the well. The slug test samples were loaded into steel cans, sealed with data was analyzed using the Bouwer and Rice paraffin wax, and allowed to equilibrate for 3 solution for determining hydraulic conductivity. weeks. The samples were then analysed for Ra Pumping tests were performed in four wells. A 226 and Th-232 using gamma spectroscopy. submersible pump was used to pump at low flow Spectral analysis was done using a sodium iodide rates, ranging from approximately 1 to 3 detector and a Canberra Model 35 multichannel liters/minute. Drawdown and recovery responses analyzer. were monitored with transducers and data loggers in the pumping well. SOLID MATERIAL REACTIVITY Two models were developed as a part of the hydrogeologic analysis of the mine site and are The site contains a variety of wastes both available on disk through NTIS -l/dr/e he stockpiled on the surface and used as backfill in Croud #'/Ier/Yow i/ode/. A shell model of the the course of previous mining operations. geology was developed with fourteen filterable Characterization of the reactivity of materials in layers that can be viewed/modified using the waste piles containing the largest volume of AutoCAD Release 13. The shell model is a visual materials at the Midnite Mine was selected as a tool designed to aid the modeler with developing focused study area. The technical working group or modifying the model. anticipated that these studies would provide A ground water flow model was developed information on: whether material from either of using MODFI,0W/MODPATH. The model discretizes the spoils piles (the most readily available the study area using 25,536 blocks that are 200 materials) could be used in reclamation of the feet long by 200 feet wide by 100 feet high. This site, which rock types were reactive and what fine discretization enables the model to conditions might develop if the piles are disturbed. accommodate proposed reclamation alternatives, It was recognized that further studies will be 7 necessary to examine the low grade ore piles testing for their acid-generation (AP) and and other wastes on site to determine how they neutralization potential (NP). should be handled during reclamation. Samples were collected and blended in five- Seventeen holes were drilled using a Becker foot sections. The samples were examined by a hammer drill into the two large waste rock piles geologist using light microscopy, a scanning at the Midnite Mine - South Spoils and Hillside electron microscope, and x-ray diffraction. Dump. Nine sample holes, shown in Figure 4, Samples were then screened to a maximum of a were drilled in the outer edge over the deepest inch, blended, and split. A split of the samples part of the South Spoils. Holes were drilled were pulverized to -200 mesh and were analyzed every 400 feet. Two holes were drilled 550 feet using inductively coupled plasma (ICP), flame apart in the Boyd Dump area of the South atomic absorption (AA), ion chromatograph, Leco Spoils. Six holes, shown in Figure 4, were drilled carbon-sulfur analysis, neutron activation, and on the perimeter of the top level of the Hillside sequential ICP. Paste pH and NP were measured. Dump and on the access road to the top of the Samples that fell between acidic and non- dump. acidic conditions, as defined in Table 1, were Chemical analyses were used to asses which tested in humidity cells which are designed to rock samples were expected.to turn acidic. accelerate weathering. Samples were tested for 20 Samples containing less than 0.5 percent sulfur weeks. A chemical analysis was made of the are considered nonacidic. Samples containing leachate from the humidity cells, using ICP, AA, greater than 0.5 percent sulfur received further and sequential ICP.

RESULTS

Results of individual technical studies are Tests on the DOWEX 21K, a strong base ion reported in the following USBM Reports of exchange resin, known to have good Investigation: 1) Midnite Mine Water Treatment characteristics for uranium recovery, were Studies [1995 (10)], 2) Hydraulic Characterization performed in single and multiple test columns of Midnite Mine [1995 (11)], 3) Hydrologic and containing 25 grams of resin and operated at 1 Geophysical Studies at Midnite Mine [1995, (12)], mL/min. Analyses showed <0.2 ppm uranium in 4) Ground Water Flow Model (GWFM) Development: treated effluents. Comparison tests were also Midnite Mine, [1995, (13)], 5) Reactivity in the conducted on a new resin formulation, DOWEX 21K South Spoils and Hillside Dump at the Midnite XLT. The DOWEX 21K XLT was shown in contact Mine [1995, (14)], 6) Midnite Mine Radiation tests, using .5 grams of the resin and 200 mL of Survey [1995, (15)], and 7) Data Dictionary and water, to be more efficient in removing uranium Discussion for the Midnite Mine GIS Database than the DOWEX 21K. Continuous column test were [1995, (16)]. A brief discussion of findings from then run using DOWEX 21K XLT resin. Calculations these studies is given below. showed that uranium loading was 24 percent of that obtained using the DOWEX 21K. WATER TREATMENT Field tests used the DOWEX 21K XLT in two separate column treatment circuits. A three Early treatability tests and cost evaluation column circuit was used for water pretreated for indicated the best options for water treatment radium. A five column circuit was used for that would remove uranium prior to lime untreated water - three columns were loaded with treatment arc: 1) ion exchange using a DOWEX DOWEX 21K XLT and the last two columns were 21K XLT, and 2) a Liquid Emulsion Membrane filled with an adsorbent for radium. Results from (LEM) technology. These technologies were field the first treatment circuit were difficult to tested on site along with a radium adsorption evaluate since the pretreatment for radium and a radium precipitation method that had removal also removed as much as 80 percent of received laboratory trials and showed favorable the uranium. The second circuit of treatment results. column treated 345 L of water and achieved 8 removal of uranium to <5 ppb. Breakthrough then contacted with a sodium carbonate solution was not achieved, indicating that maximum to strip the uranium. uranium loading was not achieved. Calculated The pilot scale plant was operated for ten days uranium loading was 56 mg/g. The first column on a continuous basis. Results indicated that the from the five treatment column circuit was uranium level in the water was reduced from an stripped using 3 1, of 2 M NaCI adjusted to pH 1 initial level of 21 ppm to 120 ppb. Uranium with IICL. The stripping solution, containing 1.7 levels in the stripping solution reached 9,400 ppm. g/l uranium was treated with hydrogen peroxide Other major metals (Mn and Zn) passed through to precipitate the uranium. X- ray diffraction the LEM and exited the system in the treated analysis did not detect any impurities in the water. Specifications for yellow cake were met by product. the field test. The LEM was also tested in the laboratory for Pre and post treatment of radium during field the recovery of uranium from Midnite Mine tests were accomplished using two different water. The lEM method has been proven to be methods. Radium precipitation was used as a very successful for removing metal ions from pretreatment. Four precipitation tanks, a rapid dilute solutions. In the LEM process, metal ions mix tank, two aging tanks and a thickener for in waste water are selectively extracted through solid--liquid separation were the components of direct contact with an emulsion that is made the system. Barium chloride solution was added to from an organic phase and an aqueous internal the mine water in the first tank to precipitate the phase. The organic phase contains the metal radium. The water containing the precipitated extraction reagent that selectively removes the radium was then fed to the rapid mix tank and metal. A number of extractants were tested. the two aging Lanks in series. A ferric chloride Alamine 336 showed the best selectivity for solution was fed to the rapid mix tank to uranium. Flowsheeting of the process revealed precipitate ferric hydroxide as a collector for the the relative simplicity of the system and a bench radium precipitate. The slurry was then fed to a scale, continuous flow circuit was constructed. thickener to produce an underflow containing Laboratory tests showed that uranium in the about three percent solids and a clarified overflow. mine water was reduced to s150 ppb while The overflow was filtered with a sand filter to producing a concentrated and pure uranium in remove any unsettled precipitate and then fed to the stripping solution. Concentrations were either the LEM or the three column DOWEX 21K XIT reached with only one extraction stage and a resin circuit. For the five column DOWEX 21K XLT residence time of five minutes. resin circuit, the last two columns were loaded Based on the laboratory investigations, a with zeolites. Radium was removed by the zeolites small pilot plant-scale LEM was tested on site. but the kinetics were very slow. In the emulsion generation step, recycled organic Results of the field tests demonstrated that phase and internal solution were combined in an treatment with either a strong base anion emulsion premix stage at a 2:1 ratio. exchange resin or LEM will decrease uranium to Composition of the organic phase was 5.0 weight less than 0.7 ppm -- the level required to avoid percent Alamine 336, 1.0 weight percent P100 generation of a low level radioactive waste during surfactant, 4.0 volume percent Isodecanol and lime neutralization. Uranium removal by the balance Isopar L kerosene. The internal pretreatment would be cost effective since cost solution was composed of 50 g/L sulfuric acid. estimates are $1.41 per 11000 gallons using ion The emulsion then flowed to the dispersion unit exchange or $2.72 per 1000 gallons using the LEM. that generated the stable emulsion. The emulsion Radium removal as a pretreatment can be and water were combined in a four stage achieved through the use of barium chloride and concurrent flow extraction unit. After the would cost $2.12 per 1000 gallons of water treated. emulsion and treated water were separated in Barium chloride treatment should be done after the final extraction stage, the emulsion was uranium removal since the process removes broken into the two original phases using a high uranium as well as radium. The barium chloride voltage. The organic phase containing the pretreatment also produced a problem in the LEM uranium in the form of a uranyl complex was circuit by introducing iron and flocculent into the 9 mine water that created a problem in separating waste effluent were reduced to about .01 ppm the emulsion. uranium using the waterglass process. The Bench scale tests of three other water waterglass was re-dissolved in caustic, producing treatment methods were completed as part of a uranium rich solid containing greater than 4,000 this study. A Diphonix Resin produced by ppm uranium and a recycle stream containing Eichrome Industries to remove uranium from about 70 percent of the silica with between 2 and highly acidic solutions was compared with DOWEX 200 ppm uranium. The concentration of zinc, 21K XIT in flask tests. Diphonix showed removal copper, manganese, iron and cadniiun were all of uranium from Midnite Mine water, however the reduced in the mine effluent along with the kinetics were much slower than those of the uranium. DOWEX 21K XLT. A fast solid phase extractant developed by HYDROGEOLOGY ChromatoChem, Inc. was also examined. The process uses polyethylene glycol molecules lHydraulic conductivity calculated from slug covalently bonded to the surface of silica tests range from 7x10 7 to lxl10 3 m/min. particles. The long polyethylene glycol molecule Hydraulic conductivities of moderately fractured has a chelating agent attached on the end which bedrock were calculated as 2x10 6 and 1x 10 binds uranium. The material removed uranium, m/min. Unweathered monzonite had the lowest and also manganese and zinc. However, the cost measured hydraulic conductivities of 7x10 7. of the material is forty times that of the DOWEX Ilydraulic conductivity is anisotropic, with a strong 21K XI;' resin, which makes it prohibitive for use north -south component related to major geologic in treatment of the Midnite Mine water. structures at the mine. Pumping tests indicated The Waterglass process developed by that the weathered monzonite has a vertical Westinghouse involves adding dilute waterglass hydraulic continuity that extends 23 m (74 ft) (sodium silicate) to a process stream to form a below ground surface. precipitate which captures the uranium and Responses to drawdown in wells adjacent to pit other heavy metals. The precipitate is removed 4 during pumping of the pit water indicated that from the process stream using d continuous pit 4 is in hydraulic connection with adjacent pressure filter. The waterglass portion of the ground water via fractured bedrock and the buried precipitate is then dissolved in sodium hydroxide original topography. Long--term trends in water solution leaving a concentrated heavy metal elevation at the site also support the general sludge. Waterglass technology was batch tested conclusion that the pits are in dynamic on Midnite Mine water. The optimum equilibrium with the ground water system. Wells concentration of waterglass for the process was upgradient of the pits show response to recent between 700 and 1677 ppm silica. At a drought conditions with progressively decreasing concentration of 1677 ppm silica, the uranium water levels. Possible influence of the drought extraction is 99.6 percent. Precipitated solids upon the downgradient wells is damped, or were then contacted with sodium hydroxide for buffered, by the water stored in the pits. removal of the silica. Filtrate from redissolution Water quality changes over the 3 to 5 years of of the waterglass had 'ih concentrations of monitoring were examined. Using pH, sulfate, zinc uranium and would ge to undergo multiple and uranium as indicator constituents, only wells contacts with sodium hydroxide for waterglass located near low grade ore piles exhibited water redissolution. Tests were then done to extract quality degradation. Other well locations with poor uranium from the sludge with hydrogen sulfate. water quality have not changed over time. An acid/sludge ratio of 3:1 was found to be the Two steady-state simulations were produced of optimum ratio to facilitate mixing. Uranium was ground water flow within the bedrock units. Flow reduced to 8 ppm after four washes; uranium in data for the bedrock units was not available at filtrate from the rinse was reduced to non the time of the simulation and the current model detect. Hydrogen peroxide was then added to renders non-unique solutions. However, the model the solids to precipitate uranium, however test does present useful results with respect to results were inconclusive. Uranium levels in the direction of flow. Results of both simulations are 10 typical of steep, rugged, mountainous basins. fifty-nine percent feldspar. Other rock types in Simulation 1 is a steady-state simulation the South Spoils and Hillside Dump also contain consisting of a homogeneous isotropic hydraulic significant amounts of feldspar. These feldspars conductivity domain. Simulation 2 is a steady- have been weathered and altered to clays by the state simulation consisting of a heterogeneous sulfuric acid produced within the dumps from isotropic domain in which the upper 100 feet of oxidation of pyrite. These clays contain alkali and bedrock and the faults exhibits a hydraulic alkaline earth cations (ie., calcium, magnesium, conductivity that is two orders of magnitude sodium and potassium) that act to neutralize higher than lower blocks. Simulation 2 was further acid production in the dumps through ion produced to exhibit the effects of exfoliation in exchange. Rainfall and weathering of the dump the monzonite, dilation of fractures withing the decomposes silicates and puts acid neutralizing metasediments, and preferential flow associated cations into solution. In the dry season, acid with faults. neutralizing cations are not flushed out of the dumps but instead accumulate. These acid RADIATION SURVEY neutralizing cations can accumulate for years and act to neutralize acid. Complete data from the radiation survey are In the South Spoils numerous voids were available on CD ROM through NTIS - hilile ime drilled where no sample was recovered. In Summary M eporl Daa . addition, samples collected in one hole between 20 Gross gamma readings measured at the mine - 60 feet showed indications of high moisture site ranged from a low of 15 yR/h tu a high of content. highly weathered and oxidized rocks, and 800 .R/h. NRC radiation dose limits for an absence of carbonate. These are indications individuals is 100 mrem/yr, or about 12 yR/h that water is flowing through channels within the (10 CFR - 20.1301). Ra-226 survey values spoil pile. The South spoils was constructed in ranged from a low of 3.1 pCi/g to a high of twenty foot lifts, with an oiled road on top of each 479.8 pCi/g, compared to the average worldwide lift. These oiled roads were observed while drilling. concentration of Ra-226 (Clarke level) of The compaction of the road surface has produced approximately 1 pCi/g. further conduits that are channeling water. Results of the soil sample analysis are found The most recently collected samples at the in Table 2. Thorium-232 was consistently South Spoils were acquired using a Becker drill present in all samples analyzed. Radon and were dry, therefore accumulations of acid emanation coefficients for the soil samples are salts and the NP from the altered silicates could also presented in Table 2. be assayed. These samples could be used to The Ra-226 survey results were in generally determine conditions within the dump. Only four good agreement with the soil sample assays. percent of the samples tested were discharging When the data are corrected for the presence of acid in the dump and seventy--nine percent of potassium and thorium, they should be in those were the samples collected from the hole excellent agreement with the soil sample assays, containing voids indicative of water flow. Most of particularly at the low activity sites. the samples classified as acidic or potentially Finally, linear regression analysis of 126 sets acidic showed accumulated neutralization of data points showed good correlation between potential. Since so few potentially acidic samples the gross gamma measurements at ground level are producing acid, conditions are not favorable and the Ra-226 soil assays. for rapid pyrite oxidation. Of the twenty-three samples classified as potentially acidic that had an SOLID MATERIAL REACTIVITY NP measurement, eighteen had a higher NP than carbonate value. This indicates that silicate Examination and analysis of samples indicate decomposition is occurring and that acid that the acid producing rock type at the Midnite neutralizing cations accumulating within the dump Mine is the quartz mica schist. Pyrite and are playing a major role in inhibiting acid calcite concentrations were low in the quartz discharge from the South Spoils. monzonite, but they did contain approximately The Hillside Dump contains both low levels of 11

carbonate and sulfide. Only seven of one Preliminary studies conducted to study hundred and ten samples were classified as uranium discharge indicated that uranium is being potentially acidic and of the two samples solubilized as a sulfate. Seven samples containing selected from the seven for humidity cell testing, high concentrations of uranium were selected for just one generated acid. Silicate alteration humidity cell testing. The largest concentrations within the dump is also low. With low levels of of uranium occurred during the initial leach of carbonate or other neutralization potential, samples from the Hillside Dump. Uranium in hydrogen sulfate has reacted with silicates in the these samples was being oxidized and solubilized dump to form acid salts. Although sulfate within the same week. Material balances showed discharged from pyrite that oxidizes in a year is over seventy five percent of the uranium in three low, the lack of water flow through the dump of the acidic samples were leached in less than a has caused the acid salts to accumulate in the year of testing. Non -acidic samples seldom dump. Consequently there is a potential for discharged uranium above NPDES permit levels discharge from the accumulated acid salts. after the initial leach.

GEOGRAPHIC INFORMATION SYSTEM

A CIS database was developed for the Midnite (Shepherd Miller, Inc.), 4) the Bonneville Power Mine as a means of consistently compiling Administration (BPA), 5) the U.S. Geological Survey historical site information and as support for (USGS) Water Resources Division, and 6) Washington government study and planning at the mine. State University (WSU) researchers. Data was collected from 1) USIIM researchers The data is available on CD ROM from NTIS. involved in the mine analysis, 2) I3LM and the The title of the CD ROM is 4ihdrle k'ine Summary 131A, 3) the Dawn Mining Co.'s archives and recent Repor i/ala. The database was created using data collection activities by their consultant ARC/INFO and the data is available in that format. CONCLUSIONS

WATER TREATMENT exchange technology would be significantly less than that of the LEM. Costs are $1.41 per 1000 'Technical data produced by the US3M gallons for ion exchange compared to $2.72 per supports the implementation of two 1000 gallons for the LEM. The cost for commercial pretreatment methods, should they be needed, disposal of the sludge currently being produced by for removal of uranium prior to the current the Dawn Mining Co. lime treatment plant was water treatment system. Addition of either one estimated to be $28 per 1000 gallons. Addition of of these methods to the current water treatment either pretreatment technology (ion exchange or system will eliminate the generation of an NRC LEM) would produce substantial cost savings if the regulated source material and reduce the cost of DO1 had to assume responsibility for treatment of disposal. The two recommended methods are: 1) the mine water. ion exchange using DOWEX 21K XL'l', and 2) Liquid Emulsion Membrane (LEM) technology. l3oth BASELINE RECLAMATION STUDIES technologies reduced uranium to below discharge limits in the treated water and were able to hydraulic studies at the Midnite Mine produced produce a reusable yelloweake product from the two steady-state simulations of ground water flow uranium. Ion exchange is a conventional within the bedrock units. 'These simulations as technology that can be readily scaled up for well as the geologic model and the ground water implementation at the site. The l;M technology flow model developed using MODFLOW/MODPATl can is an innovative technology that would require be used to determine the effects of various additional pilot scale work prior to projected reclamation alternatives on offsite flow implementation. Cost of operating the ion of contaminated ground water. 12

The radiation surveys produced data studies showed the Hillside Dump contains little according to appropriate NRC regulations that sulfide or carbonate, however the dump has can be used in mine reclamation planning and accumulated acid sulfate salts. These salts could determinations of exposure risks to individuals discharge excessive metals if contacted by water. on site. Consequently if the South Spoils or Hillside dumps Reactivity studies of the South Spoils are moved, acid mine drainage could increase and indicated 14 percent of the waste rock has the accumulated sulfate and oxidized metals could be potential to produce acid mine drainage. washed from the dumps. Currently only a fraction of this acidic material All data in support of these studies, as well as is discharging acid because of the accumulation historical records and reports, is available on a of neutralization cations in the spoils from GIS database. Data is filed on CD-Rom and is weathering and oxidation of feldspars. Reactivity available through NTIS.

REFERENCES

1. Sumioka, S. S. Quality of Water in an Investigations 9484, 1994, 40 pp. Inactive Uranium Mine and Its Effects on the 8. Williams, B. C., and Riley, J. A., Midnite Quality of Water in Blue Creek, Stevens County, Uranium Mine - Hydrologic Research and Washington. U.S. Geological Survey Water Characterization. Paper in Proceedings of the Resources Investigations, Report 89-4110, 1991, Annual Meeting of the American Society of Surface 62 pp. Mining and Reclamation ( Spokane, WA, May 16- 19, 2. Nash, J. T., and Lehrman, N. J. Geology of 1993). American Society of Surface Mining and the Midnite Uranium Mine, Stevens County, Reclamation, 1993, pp. 455-466. Washington. U.S. Geological Survey Preliminary 9. Altringer, P. B., and Froisland, L. J., Reactivity Report, Open File Report 75-402, 1975, 36 pp. of Stockpiled Material at Midnite Mine: A 3. Nash, J. T. Geology of the Midnite Uranium Preliminary Evaluation. Paper in Proceedings of Mine, Stevens County, Washington. U.S. Geological the Annual meeting of the American Society of Survey Preliminary Report, Open File Report 77- Surface Mining and Reclamation (Spokane, WA, May 592, 1977, 38 pp. 16-19, 1993). American Society of Surface Mining 4. Ludwig, K. R., Nash, J. T., and Naeser, C. W. and Reclamation, 1993, pp. 489-501. U-Pb isotope systematics and age of uranium 10. Schultze, L. E., Nilsen, N., and Isaacson, A. E. mineralization, Midnite Mine, Washington. Midnite Mine Water Treatment Studies. U. S. Bureau Economic Geology, v. 76, No. 1, pp. 89-110. of Mines, Report of Investigations 9605, 1995, 35 5. Fleshman, B. R., and Dodd, S. P. National pp. Uranium Resource Evaluation, Ritzville 11. Williams, B. C., and Riley, J. A. Hydraulic Quadrangle, Washington. Bendix Field Characterization of Midnite Mine. U. S. Bureau of Engineering Corp., Grand Junction, CO, 1982, pp Mines, Report of Investigations 9606, 1995, 22 pp. 62. 12. Williams, B. C., Riley, J. A., Montgomery, J. R., 6. Marcy, A. D. Identification of Probable and Robinson, J. A., Hydrologic and Geophysical Ground Water Flow Paths at an Inactive Uranium Studies at Midnite Mine. Report of Investigations Mine Using Hydrochemical Models, Paper in 9607, 1995, 31 pp. Proceedings of the Annual Meeting of the 13. Kirschner, F. E., Ground Water Flow Model American Society of Surface Mining and (GWFM) Development: Midnite Mine. U. S. Bureau Reclamation (Spokane, WA, May 16-19, 1993), of Mines, Report of Investigations 9608, 1995, 17 American Society of Surface Mining and pp. Reclamation, 1993, pp. 467-488. 14. Moore, B. W., Gardner, T. H., and Price, J. W. 7. Marcy, A. D., Scheibner, B. J., Toews, K. L., Reactivity in the South Spoils and Hillside Dump at and Boldt, C. M. K. Hydrogeology and the Midnite Mine. U. S. Bureau of Mines, Report of Hydrochemistry of the Midnite Mine, Northeastern Investigations 9609, 1995, 219 pp. Washington. U. S. Bureau of Mines, Report of 15. Stroud, W. P., and Droullard R. F. Midnite 13

Mine Radiation Survey. U. S. Bureau of Mines. A. Data Dictionary and Discussion for the Midnite Report of Investigations 9610, 1995, 21 pp. Mine GIS Database. U. S. Bureau of Mines, Report 16. Peters, I). C., Smith, M. A., and Ferderer, D. of Investigations 9611, 1995, 33 pp. 14

Table 1. Protocol for Determining Acidic Sample Classification

2 2 Classification of Rock S mole ratio C03/S-

non acidic any > 3.0 non acidic <0.5% any possibly acidic >0.5% > 1.0 and < 3.0 possibly acidic >0.5% and <1.0% < 1.0 Acidic >0.5% < 1.0

* expanded protocol

Table 2. Soil sample analysis Sample site ID Uranium-238 Thorium--232 Potassium Emanation soil sample, soil sample, soil sample, coefficient, ppm ppm % % 109 ...... 6.4216.16 2.67 10.4 158 ...... 8.3924.14 3.96 9.6 160 ...... 73.06 28.88 3.56 28.7 162 ...... 67.44 16.20 2.67 32.6 122 ...... 656.12 44.92 4.27 14.5 213 ...... 2,712.30 101.69 --0.52 17.6 213B ...... 2,769.02 112.28 0.66 N.A. 233 ...... 95.76 23.56 2.85 28.6 238 ...... 73.60 22.61 3.32 30.3 260 ...... 91.78 24.26 3.53 12.9 263 ...... 20.20 20.04 3.26 9.5 309 ...... 31.7 ) 21.44 4.17 17.0 310 ...... 365.98 36.72 4.35 34.6 312 ...... 122.04 24.33 2.83 22.4 359 ...... 177.31 30.22 4.17 42.3 362 ...... 71.52 24.33 3.59 25.6 439 ...... 15.57 18.15 3.17 13.2 463 ...... 228.88 27.32 3.49 25.9 15

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Figure 1. Pre-mining Topography 0 t ** -t he$? 5%IQRtrIayeE

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Figure 2. Post-mining Topography

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General Resonrise Actions Ronedial jjIehnoloa Process Option DescrI lion Screening Connents These are primary These options offer little Neutralisction/precipitalioo nn Irealnent techniques select ivily inthis siteudion Phys ic l/Chenicul/ for removing nelals However a conbinat ion of firon AMD through floculat lon and Resourte Recovery polyner pH adjousrnenl neutrulr7olion will be {Polyner Floculal on - investigated us a nelhod to produce a cansalidt led turanrun free sludge Retain polyner floccilato

lhis energing technique USBM experience has shown -fCo- precipitation uses co-precipilotion this approach is ineffective and adsorption lo renove inwater cleanup neals fron solution Not retained Porous---sdse-- Ihese are associated with These techniques offer innovative tenerging) potential for low cost 1 LEM and SLM techniques for the and/or improved perfornence renovol of netals fron over traditional Ireulnenl AMD options Fulure bench scale --- on lidion i testing will provide insight into their opplicobi lily iII the present situation Hydrogen Sulf da IH ge nIt) Retained

fhis convent ional This opt ion has c history treulnent option is used of use in the uroniun for netal extract ion industry but questions of through the exchange extrCt Imu effect iveness of ions needs to be answered Retained

This convenional This option will be Solvent Ex ract ion Ireotnent option is used investigated indirectly for nel extraction through Ie LEM work through the exchange ta related technique! of ions As a direct application solvent extruclion will not be retained

This energing techique This opt iin offers little tons pr incipally -Zeal Ies I funi potential for the extract on through the exchange of uraniun Not retained of ions

this conventional Iretneanl This option offers lillle opt ion is often associated polenlil for select vely Cryslull n liuonj with evaporatlon and separating uranun ftren renoving netlts by using the olher contained nelats their solubility linits Energy costs are an added concern Not retained

[his is associated with This technique offers in ovatlive tenerging) potential for low cost BacIerial Exrs ct ion techniques for the and/or inpioved renoval of netals Tron performance over traditional AMD opt ios Future bench- scale testing will provide insight into its appticability in Biological the present situation Reloined

TIh s technique uses At present I his option Wetlands] constructed wellands offers tittle potent ial In renove nelols for the renoval of fron AMD uraniun Not retained

his convent ronol This o lion offers lillle _ P---- technique uses ponds Possiv --- [evaporation Poiids potent - for selectively to evaporate AMD water separating uraniun fron the other contained nelats Not retained

Figure 3. Screening of Remedial Technologies

BEST COPY AVAILABLE 18

90PRt 4

Hikide Oump

PIt 3

South spobS

Figure 4. Comprehensive drilling and characterization of the Midnite Mine; drilling sites indicated by squares.

INT.BU.OF MINES,PGH.,PA 30240