EPA-600/7-34-006
January 1984
AN ENVIRONMENTAL OVERVIEW OF
UNCONVENTIONAL EXTRACTION OF URANIUM
by
James I." Marlowe
WAPORAj Inc.
Chevy Chase, Maryland 20815
Contract No. 68-03-3035
Task No. SAW01
Project Officer:
Mary Ann' Curran. "
Energy Pollution Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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TECHNICAL REPORT DATA
(Plccsc read /nu/uctwns on the reverse before eompfciuit*)
REPORT MO. 12.
EPA-600/7-84-006 j
3. RECiPIENT'S ACCESSION NC.. _
i. TITLE anosubtitle
An Environmental Overview of Unconventional Extraction
5 REPORT DATE
January 1934
or Uranium
6. PERFORMING ORGANIZATION CODE
7. AUThCfllSI
James I. Marlowe, Ph.D.
B. PERFORMING ORGANIZATION REPORT \0.
9. performing organization name and address
WAPORA, Inc.
6900 Wisconsin Ave.
Chevy Chase, MD 20815
10. PROGRAM ELEMENT NO.
CB3M1G
11. CONTRACT/GRANT NO.
68-03-3035
Task No. SAW01
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
13. TYPE OF REPORT AND PERIOD COVERED
Final Report 11/80-02/81
Oitice of Research and Development
US Environmental Protection Agency
Cincinnati, OH 45268
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This study was performed to provide information on the status of technological and
environmental aspects of unconventional extraction of uranium for use by the Industrial
Environmental Research Laboratory of the U.S. Environmental Protection Agency in
developing research programs related to this method of uranium extraction.
Uranium mining areas in the United States are identified and briefly described, and
the geologic, geochemical, and hydro Logic factors associated with the various types of
ore deposits are discussed. Uranium deposits that are now being mined or have recently
been mined by solution-mining techniques are identified and briefly described; as well,
deposits for which licenses have been obtained, but which thus far have not been mined,
are listed.
The techniques used in these processes of uranium extraction are described and
discussed. The environmental impacts specifically associated with these methods of
extracting uranium are identified, using examples from case histories of in situ mining
operations. Impacts on groundwater are of the greatest concern, and problems associated
with these impacts are discussed. The major adverse impact is contamination from the
effects of lixiviant chemicals. Restoration to acceptable post-mining conditions is a
major concern and technical problem. Existing or proposed technologies to prevent or to
control pollution from in situ mining of uranium are identified and discussed, with
emphasis on the problems associated with groundwater.
17, KEY WORDS AND DOCUMENT ANALYSIS
a. ' DESCRIPTORS
b.IDENTIFIERS/OPEN ENDEDTERMS
c. COSATl I:irld'Group
19. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19 SECURITY CLASS fThitRtpO'tj
UNCLASSIFIED
21. NO. Of PAGES
20 SECURITY CLASS (This page}
UNCLASSIFIED
22 PRICE
EPA Form 2220-1 <9-73)
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
ii
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on
our health often require that new and increasingly more efficient pollution
control methods be used. The Industrial Environmental Research Laboratory -
Cincinnati (IERL-Ci) assists in developing and demonstrating new and improved
methodologies that will meet these needs both efficiently and economically.
This report deals with the status of unconventional extraction of uranium
ore including in-situ mining and, to a lesser degree, heap leaching. The
purpose of this report is to determine the status of such extraction techniques
so that a long term environmental research plan may be developed. Extraction
techniques have been described, environmental impacts have been identified,
case histories have been presented and areas of additional research have
been recommended. This report should be of value to those individuals concerned
about the environmental consequences of unconventional uranium extraction
and those involved in such research. For further information regarding
this report, contact the Energy Pollution Control Division.
David G. Stephan
Direc tor
Industrial Environmental Research Laboratory
Cincinnati
iii
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ABSTRACT
This study was performed to provide information on the technological
and environmental aspects of unconventional extraction of uranium. It is
to be used by the Industrial Environmental Research Laboratory of the U.S.
Environmental Protection Agency in determining" the "need for and, .-ifv necessary,
developing research^ programs related "to this'" method " of Uranium extraction.
Uranium mining areas in the United States are identified and briefly
described, and the geologic, geochemical, and hydrologic factors associated
with the ore deposits are discussed. Uranium deposits that are now being
mined or have recently been mined by solution-mining techniques are identi-
fied and briefly described; also, deposits for which licenses have been
obtained but which thus far have not been mined are listed.
The techniques used in uranium extraction are described and discussed.
The environmental impacts specifically associated with methods of extrac-
ting uranium are identified using examples from case histories of in situ
mining operations. Impacts on groundwater and problems associated with
these impacts are discussed. The major adverse impact is contamination
from lixiviant chemicals. Restoration of the mine site to acceptable post-
mining conditions is a major concern and technical problem. Existing or
proposed technologies to prevent or to control pollution from in situ mining
of uranium are identified and discussed, with emphasis on the problems
associated with groundwater.
Partial case histories of in situ mining operations are presented in
order to describe instances of resulting degradation or non-degradation of
groundwater quality. Information in this report also documents the develop-
ment of monitoring and control technologies associated with in situ uranium
mining. Specific problems and the actions taken to remedy them are
described.
Research projects that address environmental impacts from unconven-
tional extraction of uranium are identified. Also, areas of potential
research are identified. The Federal and state laws which are applicable
to unconventional extraction of uranium are listed.
IV
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CONTENTS
INTRODUCTION
CONCLUSIONS AND RECOMMENDATIONS
EXTRACTION TECHNIQUES
3.1 INTRODUCTION
3.2 SOLUTION, MOBILIZATION, AND EXTRACTION OF ORE
Lixiviants
Well Field Design and Operation
3.3 RECOVERY PROCESSES
3.4 PILOT PLANT PROGRAM
3.5 RESTORATION
3.6 HEAP LEACHING
ENVIRONMENTAL IMPACTS OF IN SITU HEAP LEACH
MINING OF URANIUM
4.1 INTRODUCTION
4.2 GROUNDWATER CONTAMINATION
Alteration of pH
Introduction of Ammonium Ion
Mobilization of Metals
Other Salts from Leaching Solutions
Leach Liquor Excursions
Radioactive Materials
4.3 SURFACE WATER CONTAMINATION
4.4 ATMOSPHERIC CONTAMINATION
Radioactive Emissions
Non-Radioactive Emissions
v
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CONTENTS (continued)
Page
4.5 GROUNDWATER CONSUMPTION 31
SECTION 5. CONTROL TECHNOLOGY 32
5.1 MINING OPERATIONS 32
Water Barriers 32
Control of Water Movement by Pumpage 33
Grouts 33
5.2 CLEANUP AND RESTORATION 35
Ion Exchange 35
Reserve Osmosis 38
Pretreatment of Ore-Bearing Aquifers 39
Removal of Ammonium Ions After Leaching 40
5.3 DISPOSAL OF WASTES THROUGH INJECTION WELLS 41
SECTION 6. IN SITU MINING OPERATIONS AND THEIR EFFECTS ON
WATER QUALITY 47
6.1 THE CROWNPOINT MINE, MCKINLEY COUNTY, NEW MEXICO 47
Introduction 47
The Pilot Plant 47
Groundwater Effects 52
Processing and Waste Disposal 56
Restoration 58
6.2 THE EL MESQUITE MINE, DUVAL COUNTY, TEXAS 58
Introduction 58
Groundwater 61
The Mine Plant 64
Restoration 65
Excursions 65
6.3 THE IRIGARAY MINE, JOHNSON COUNTY, WYOMING 65
Introduction 65
Proposed Operation 67
Operational History 76
6.4 HEAP LEACH FACILITY AT AMBROSIA LAKE, N.M 79
Introduction 79
Hydrology 79
Mine Plant 80
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CONTENTS (continued)
Page
6.5 THE HIGHLAND MINE, CONVERSE COUNTY, WYOMING 82
Introduction 82
Proposed Operation 82
Operational History 83
SECTION 7. PAST AND CURRENT RESEARCH 86
APPENDIX A. URANIUM MINING AREAS IN THE UNITED STATES 98
A.l TYPES OF MINEABLE URANIUM DEPOSITS 98
Sandstone Deposits 98
Deposits in the Wyoming Basin 101
Deposits in South Dakota 103
Deposits in New Mexico 103
Deposits in Arizona 106
Deposits in Colorado 108
Deposits in Texas 108
Uranium Vein Deposits in Plutonic Rocks 110
Colorado Mineral Belt 112
Midnite District, Washington 112
Other Vein Deposits 115
APPENDIX B. PERTINENT FEDERAL AND STATE LAWS AND REGULATIONS 117
B.l FEDERAL LAWS AND REGULATIONS 117
B. 2 STATE LAWS AND REGULATIONS 119
REFERENCES 94
vii
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FIGURES
In Situ Leaching Process
Typical Well Field Configurations
Mining and Monitoring Wells
Ion Exchange Processing Plant
Ion Exchange Column
Industrial Waste Injection Well
Selection of Formations and Areas for Waste Injection
Location Map, Crownpoint Mine
Crovmpoint Pilot Plant
Crownpoint Well Completion Design
Crownpoint Process Plant Flow Chart
Location Map, El Mesquite Mine
Generalized Geologic Cross-Section, Irigaray Mine ....
Location Map, Irigaray and Highland Mines
Pilot Plant Arrangement at the Irigaray Mine
Expected Processing Circuit, Irigaray Mine
Uranium-Producing Areas in the United States
Typical Rollfront and Tabular Uranium Ore Deposits ...
Uranium Deposits in the Wyoming Basins
Uranium Deposits in the Southern Black Hills
Uranium Deposits in New Mexico
Uranium Deposits in Utah and Arizona
Uranium Deposits in the Uravan District
Uranium Deposits in South Texas
Uranium Deposits in the Colorado Mineral Belt
Uranium Deposits In the Midnite Mining District
viii
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TABLES
Number Page
1 Concentrations of Trace Metals and Inorganics,
Willow Creek, Wyoming 18
2 Compositions of Typical Lixiviants 21
3 Typical Compositions of Leach Liquor 22
4 Water Quality in Texas Ore Production Zones 23
5 Water Quality Data for Typical Wyoming Area
Groundwater 24
6 Groundwater Quality at Nine-Mile Lake, Wyoming 26
7 Wastewaters Generated by Ion Exchange 30
8 Ion Exchange Resins Employed by the In Situ Uranium
Mining Industry 35
9 Factors to be Considered in Evaluating the Suitability
of Untreated Wastes for Deep-Well Disposal 45
10 Groundwater Quality in the Crownpoint Region 53
11 Radiation Levels of Groundwater in the Crownpoint
Region 54
12 Groundwater Quality in the Grants Mineral Belt 55
13 Baseline Groundwater Quality, El Mesquite Mine 62
14 Production Zone Water Quality, El Mesquite Mine 63
15 Restoration Test Results for the O'Hern Project 66
16 Excursion of November 27, 1979, El Mesquite Mine 66
17 Excursion of January 23, 1980, El Mesquite Mine 67
18 Expected Composition of Pregnant Liquor, Irigaray Mine .... 71
19 Estimated Feed Rates, Irigaray Mine 75
20 Estimated Liquid Wastes, Irigaray Mine 75
21 Ambrosia Lake Groundwater 81
22 Analysis of Water from Ore Zone, Highland Mine 83
23 Analysis of Water from Pilot Plant Area, Highland
Mine 85
24 Licensed Uranium Solution Mining Operations in the U.S. ... 116
ix
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SECTION 1
INTRODUCTION
In situ uranium mining has resulted in a technology which is
efficiently applied to the extraction of low-grade uranium deposits from
permeable host rocks. This technology makes available as part of the national
resources many such deposits that could not be economically mined by other
existing methods.
The introduction of solvent chemicals, or lixiviants, into uranium-
bearing geologic formations that are also reservoirs of groundwater causes
severe deterioration of the groundwater quality; this constitutes the major
environmental effect of the in situ mining operation. Included in the
resulting negative effects are: the release of metals in toxic concentra-
tions from minerals in the formation; the introduction of hazardous concen-
trations of materials in the lixiviants themselves; and the alteration of
oxidation-reduction and pH conditions in the groundwater. Groundwater
supplies may be locally depleted as a result of the operation.
Federal and state laws aimed at controlling the negative environmental
effects of in situ uranium mining require that the groundwater in the mined
zone be restored to near pre-mining conditions. Monitoring wells and water
sampling and analysis programs are required to detect any excursions of the
chemically altered groundwater outside the intended mine area. In most
cases of excursions, differential pumping of the well field brings the
excursion under control. In some cases, unexpected geologic features allow
the fluids to breach aquitards. In others, failures of well structures
permit leaks between formations.
Surface restoration to the required levels can be accomplished with
relative facility. Restoration of the underground aquifer can be complex
and time-consuming. This is particularly true in operations where lixi-
viants utilizing ammonium-based compounds have been used. This type of
lixiviant is very effective in extracting uranium but sorbs to clay minerals
and is not readily removed after the operation is completed.
Operators, regulatory authorities, and residents sometimes disagree
what level of groundwater restoration is acceptable in return for the ex-
traction of the uranium. Land use priorities, the demand for uranium and
what constitutes pre-mining water quality are factors affecting these
disagreements.
1
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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
The information gathered for this project showed that a considerable
gap exists between regulatory expectations and the ability of the industry
both to comply and to carry out an effective minerals e>traction program.
Some operators have been unable to meet restoration requirements, while
others have done so only after substantial effort and cost. Although much
innovative work is being done to improve the technology, it appears that
given the state-of-the-art, groundwater quality cannot be readily restored
to pre-mining levels.
Realistic evaluation of the demands and utilization of groundwater
should be considered when restoration criteria are established.
Materials and the technology to construct tight wells that will with-
stand the conditions of in situ mining are costly but will probably prove
economic in the long term.
Detailed and realistic assessments of the fate of dissolved ammonium
ions under deep groundwater conditions are also needed to determine the
probability of nitrate formation and the health hazards associated with
nitrates.
The development of a reagent that would promote the precipitation of
dissolved contaminants, including ammonium, within the formation, without
itself causing contamination would greatly facilitate groundwater restoration.
Similarly, the improvement of lixiviant formulations and an improvement in
the knowledge of metal solubilities under the special geochemical conditions
of an in situ mine could decrease the contamination caused by associated
minerals that are dissolved with the uranium. Until such technical develop-
ments occur, however, it appears that site-specific assessment of restora-
tion criteria, in terms of land use priorities, may offer a potential for
reduction of the difficulties encountered by many in situ operations.
Areas in..which...research is needed to provide better knowledge and
control of the various processes associated with solution mining of uranium
ore are described for exploration, environmental baseline characterization,
well field and monitor wells, operation and restoration.
2
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EXPLORATION
a) Means of adequately sealing exploration borings to prevent the
inter-aquifer transfer of fluids. In the in situ raining industry
and in the groundwater exploration and development industry in
general, there is ample and widespread evidence that improperly
cemented we?Is are responsible for breaches in aquicludes that
would otherwise act as impermeable barriers to the movement of
groundwater. The standardization of techniques that can be applied
to remedy the further spread of this problem is of great importance
to the control of leach-liquor excursions.
b) Knowledge of the extent of groundwater pollution associated with
present drilling practices. In order to fully understand base-
line water quality at a given site, it is important to know how
much disturbance to natural values is caused by drilling and well
completion activities, including the use of drilling fluid
additives.
c) Development of means to obtain representative samples for the
determination of water quality during exploration drilling.
Because the numerical levels of control parameters of water quality
as applied to in situ mining are very small, the impact of erroneous
values due to using the results from non-representative samples
can be great. Procedures and equipment used in obtaining water
samples during exploration should be designed to produce values
representative of formation-water conditions, apart from the
influence of the drilling operation.
d) Improvement of the capability to predict the mobility of trace
metals and their probable concentrations in leach liquors, by the
Study of core samples obtained during exploration drilling.
e) Knowledge of the effects of the opening of exploration borings
on oxidation-reduction potentials and groundwater quality in
uranium orebodies. Where holes are closely-spaced, the effects
of ventilating the formation water may cause significant changes
in the ambient geochemistry.
ENVIRONMENTAL BASELINE CHARACTERIZATION
a) Refinement of various aspects of the procedures used to character-
ize groundwater quality in the vicinity of uranium orebodies.
Though procedures for acquiring this information are generally
well understood, additional studies directed toward optimum location
of wells, well sampling, and analysis of data would probably
prove beneficial in establishing reliable and representative
baseline water-quality values.
b) Improvement of the capability of defining directional properties
in aquifers and aquicludes in the vicinity of uranium orebodies,
for optimum well field and monitor well design.
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WELL FIELD AND MONITOR WELLS
a) Improvement of techniques of computer-aided well field and
monitor well design, using directional properties of aquifers and
aquicludes.
b) Improvement of design and construction techniques of wells, for
maximum aquifer protection and cost-effectiveness. Several
instances of excursions have been attributed to breakdowns in
well integrity, due either to material or construction failure.
Research and development in this area may produce results of
direct benefit to the in situ raining industry.
c) Improvement of logging and testing methods for verification of
well integrity.
OPERATION
a) Improvement of lixiviant formulations to minimize mobilization of
trace metals attendant to the mobilization of uranium.
b) Improvement of processes to selectively remove trace metals from
leach liquor during processing and regeneration.
c) Improvement of techniques for the definition and identification
of leach liquor excursions. These might include geophysical
methods.
d) Development of methods of pretreatment of the ore-bearing
formation to minimize problems of contamination resulting from
the in situ mining operation.
e) Improvement of techniques for extracting hazardous wastes from
the leach-liquor stream, in order to minimize the volume of waste
and to maximize the volume of reinjected water.
RESTORATION
a) Development of treatment techniques to remove mobilized trace
metals from solution in the formation.
b) Improvement of knowledge of the fate of ammonium and other nitrogen
compounds under deep, mineralized aquifer conditions, and the
associated health-hazard implications.
c) Study of the feasibility for permanent isolation of production
zones from the rest of the aquifer by grouting or other artificial
means, to prevent the spread of contaminants after completion of
mining, as an alternative to complete restoration.
d) Evaluation of aquifer restoration criteria, in light of pre-
mining acceptability of groundwater, potential future use, and
alternative potable groundwater sources.
e) Evaluation of existing criteria and development of standards for
long-term monitoring of sites mined by in situ leaching.
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SECTION 3
EXTRACTION TECHNIQUES
3.1 INTRODUCTION
In situ and heap leaching of uranium are alternative methods of metal
extraction which only minimally disturb the host rock but utilize moving
fluids that pass through the rock, dissolve the uranium, and transport
the dissolved metal to a collection and concentration site. In situ leaching
of unmined rock may be applied to low-grade deposits situated below deep
overburden, with relatively little impact on the original surface and
subsurface of the mined site. The mining operation does not involve the
removal of large volumes of bulk rock from the ground; hence it is not
attended by continuous traffic of heavy vehicles, blasting, or dust clouds.
No subsidence results from this method of mining, as only a very small
proportion of the rock, usually intergranular and non-supportive, is removed.
Because the method is based upon both the chemical and physical alteration
of groundwater conditions, the major and most immediate environmental
effect of an in situ mining operation is on the ambient groundwater. Thus,
the planning and operation of an in situ leach mine necessarily involves
the observation and control of groundwater conditions. This is necessary
to avoid both the loss of leached metal from the mine site and the contami-
nation of underground water supplies that would otherwise be utilizable
resources.
Basically, an in situ leaching operation includes 1) the design of
chemical solutions or lixiviants that will dissolve the uranium-bearing
minerals and transport the uranium through the host rock; 2) the installation
of injection wells which are used to introduce the lixiviant to the uranium
ore and to maintain an elevated hydraulic pressure in the pore spaces
or fractures of the rock; 3) the installation of production wells which
maintain a lowered hydraulic pressure and thereby cause the uranium-bearing
solution to flow toward them. The solution is pumped up the production
wells to a processing facility on the surface, where the uranium is extracted
and the lixiviant is reconditioned for re-injection to the orebody (Figure
1).
Continued movement of lixiviant through the orebody is necessary
to remove the uranium. The amount of leaching necessary to achieve cutoff
grade is clearly time-dependent and will vary with size of the orebody,
solvent/mineral chemistry, permeability, and design factors associated
with the well-field.
Licensing regulations require that groundwater be restored to or
nearly to its original condition. Thus, the operation of the well field
includes a period after production has ceased during which restoration
must be accomplished.
3.2 SOLUTION, MOBILIZATION, AND EXTRACTION OF ORE
Lixiv iants
The selection of a solvent for use in the leaching process must involve
the consideration of the rate at which uranium minerals dissolve at the
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INJECTION
LIXIVIANT
IN
PRODUCTION
PREGNANT
LIQUOR
OUT
INJECTION
LIXIVIANT
IN
rlh
-CASING-
-CEMENT'
SUBMERSIBLE
PUMP>
^ ^rxt I
r1^
WELL
SCREEN
WATER
TABLE
f;t:AQUiCLUDE:y
VlfniT lr>n |
SANDSTONE
Figure In Situ Leaching Process
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specific site, interaction of the solvent with non-ore minerals, effects on
permeability of the rock, effects on well casings, pumps and other material of
construction, cost availability, and handling problems (Huff, et al., 1980).
Further, the ease with which toxic constituents of the solution can be removed
from the mine site after production has ceased is of prime significance in the
selection of a lixiviant.
The chemistry of uranium is such that its hexavalent form is soluble in
either acid or alkaline leaching solutions. If the uranium in a particular
deposit does not occur in the hexavalent state, it must be oxidized to that form
by the use of an oxidizing agent (Kasper, et al. , 1979). Thus, a lixiviant
consists of two major components: 1) an acidic or a basic solvent to maintain
a desirable pH range; and 2) an oxidant to convert tetravalent uranium to the
hexavalent state and to maintain it in that state. Various combinations of
solvents and oxidants may be used, depending upon conditions.
Only a few proposed in situ operations have been planned around the use of
acidic lixiviants, and only two pilot operations have actually used acid. These
operations utilized sulfuric acid, which is the least costly of the technically
feasible acids. Oxidants that can be used in acidic lixiviants include sodium
chlorate, manganese dioxide, ferric sulfate, and oxygen. Hexavalent uranium in
the form U02++ is the soluble ion where acidic lixiviants are used; this forms
an anionic complex with sulfate as follows:
7 U02++ + 3S04 -> U02 (S04)3==
Rocks that contain large proportions of acid-soluble minerals such as
calcite will consume significant or prohibitive quantities of acid solutions
and hence are generally not suited for the use of acidic lixiviants. Also,
reactions with phosphates, clay and oxide minerals may produce dissolved metal
and other ions which present problems in regeneration of the lixiviant or in the
potential contamination of water supplies.
Two types of alkaline lixiviants are commonly used, based on sodium
carbonate-bicarbonate and ammonium carbonate-bicarbonate. In the solubiliza-
tion process, uranium takes the form of uranyl tricarbonate anion, U02(C03) .
In clay-rich rock, swelling clays may make the use of sodium carbonate-
bicarbonate solvents unfeasible, as decreased permeability and eventual plug-
ging of the formation may result. The use of an ammonium carbonate-bicarbonate
system, on the other hand, involves the possibility of sorption of NH^+ ions by
clays and the formation of nitrates in groundwater. The use of either of the two
carbonate-based solvents may result in the precipitation of calcium carbonate or
the formation of free CO2 gas, if the carbonate-bicarbonate equilibrium within
they system shifts adversely. Potassium carbonate has also been used experi-
mentally as an alkaline solvent, producing a potassium carbonate-bicarbonate
system which is reported to be comparable in effectiveness to ammonium carbonate
solvents. (Kasper, et al., 1979).
In alkaline solutions, the hexavalent uranium forms stable, complex anions
which combine with ammonium or alkaline metals as follows (Cowan, et al., 1980):
UO3 + 2NH4HCO3 -> (NH4)2 U02 (C03)2 + H20
UO3 + Na2 CO3 + 2NaHC03 -> Na4 UO2 (C03)3 + H20
7
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Alkaline solvents have an advantage over acidic solvents in that they react
less with the country rock and their pH is therefore more stable. Acidic
solvents tend to increase the permeability of the rocks through which they pass,
but in so doing increase their pH. Sulfuric acid solvents may cause the
precipitation of sulfates such a gypsum near the "downstream", or higher pH,
end of the flow path, producing problems in wells, pumps, screens and other
associated equipment. Oxidants used in the in situ mining of uranium are free
oxygen and hydrogen peroxide. Of these, oxygen is perhaps the most commonly
used, being cheapest. A disadvantage is that it may cause plugging of the
formation or may migrate vertically. Hydrogen peroxide is more convenient to
inject, but decomposes to produce oxygen in the formation. Its cost per pound
of uranium produced is about 10 times that of gaseous oxygen (Huff, et al«,
1980).
The uranium mining industry considers the oxidation phase of leaching to
have a controlling influence upon the rate of leaching of uranium. Precise
control over oxidant injection, relative to site-specific conditions, must be
maintained in order to keep production at desired levels and to avoid wastage of
oxidant through reactions with non-ore minerals. Thus, it is important to match
oxidant and ore chemistry, and this match is achieved through field trials.
Some laboratory techniques have been developed, however, which closely simulate
down-hole conditions and provide design information early in the development of
an in situ mine (Carlson, et al. , 1980). The effects of oxygen and hydrogen
peroxide, respectively, in an ammonium carbonate lixiviant were compared on
samples of south Texas uranium ore. These tests indicated that desired initial
high concentrations of oxidant can be economically achieved using a blend of
hydrogen peroxide and oxygen.
Well Field Design and Operation
The design of the well field must be tailored to fit the conditions of the
mine site- These conditions must be thoroughly understood prior to development,
not only to optimize the mining operation but to comply with Federal and State
regulations which require monitoring of the operation and post-production
restoration. The boundaries of the orebody, its internal structure and grade
variations, and geohydrologic factors must all be defined by a detailed
subsurface geologic investigation. The development of the orebody is planned
according to these defined characteristics.
The leaching and extraction of uranium under controlled conditions is
basically a geohydrologic problem; therefore, a detailed analysis of hydrologic
conditions at the site must be carried out. This may require studies of areal-
or even regional-scale. Groundwater conditions must be defined in terms of
depths, gradients, rates and direction of flow, veritical fluctuations, recharge
and discharge, and relationships among individual aquifers and aquicludes-
Test wells and laboratory analyses are used to determine porosities, permea-
bilities, rates of drawdown, and other hydraulic parameters of the ore zone or
zones. The effectiveness of aquicludes in sealing off non-orebearing aquifers
is also evaluated. Groundwater chemistry and its variations both vertically and
laterally must be understood; it is equally important to understand the clay
mineralogy of the formations involved, in order to forecast interactions among
clays, lixiviants, and dissolved ions from the orebody and host rock. It is to
the operator's benefit to carry out a very detailed evaluation of exisiting
groundwater conditions, not only to provide better control for the design of the
operation, but to supply information for use as a reference when post-production
restoration is initiated.
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A typical well field consists of injection wells, production wells, and
monitoring wells. Injection and production wells are arranged in patterns
designed to provide optimum leaching and flow through the formation. A typical
and widely used configuration is the 5-spot pattern, in which a single
production well is surrounded by four injection wells. This and other commonly
used patterns are depicted in Figure 2.
Ideally, all lixiviant introduced into the formation would be recovered by
the production wells. In practice, the injected fluids move in directions other
than toward production wells, and because of this, monitoring wells are placed
around the mine site. These wells are designed to provide information on
variations in groundwater properties outside the production zone that may be
indictative of "excursions" or movements of solutions from the production zone
outward or vertically into other groundwater zones. Monitoring of several
parameters in these observation wells provides the information with which to
control the flushing of the orebody. This process can be regulated by adjusting
rates of injection and withdrawal. Monitoring also alerts the operator to
problems of contamination of groundwater resources outside the permitted
production zone.
In order to assure the hydraulic integrity of the injection well-orebody-
production well system, the ore-bearing formation must be isolated from
communication through the drill hole with underlying or overlying formations.
This is accomplished through the use of a continuous casing between the surface
and the production formation. The casing is perforated or terminated at the
level of the production zone and is cemented in the hole with a cement that is
formulated to be stable in the presence of the injected fluids.
Materials used in the casing oust also be resistant to attack from
lixiviants. PVC or fiberglass casing is commonly used in in situ mining
operations. Where steel casing is used, inner liners of corrosion-resistant
materials must be used to protect the steel, unless the considerably more
expensive stainless steel is used. Pumps, valves, packers and other mechanical
components of the system all must be chosen to withstand the corrosive effects
of the solutions as well. Huff, et al., (1980) point out that engineering
problems peculiar to the in situ mining industry include the difficulty of
maintaining dispersion of gaseous oxygen in liquid solvents during the passage
of the lixiviant down the injection well and the difficulty of obtaining
downhole pumps for production wells that can withstand the ambient corrosive
conditions over long periods of time.
When production is initiated, the orebody is flooded with injected
lixiviant at elevated pressure. At the same time, withdrawal of groundwater is
begun through the production wells at a slightly higher rate, setting up a
hydraulic gradient that, ideally, causes the subsurface fluids to move from
injection points toward withdrawal points. These relationships are illustrated
diagramatically in Figure 1. Rates of injection and withdrawal must be adjusted
to one another to ensure complete and continuous flooding of the production
zone by the lixiviants, a residence time in the formation that will allow
optimum use of the leaching capability of the lixiviant, without premature
depletion, and the desired hydraulic gradients. The slight excess of production
volume over injection volume, which is maintained in order to preserve a
hydraulic gradient into the well field is called the bleed stream. Obviously,
a major consideration in controlling passage of lixiviant through the orebody is
the grade of recovered uranium at the surface, which must be sufficient over a
defined time period to show a healthy profit margin for the mining operation.
9
-------
FIVE-SPOT LINE DRIVE * SEVEN-SPOT
o o 04-00 o
+
o o
Q INJECTION WELL
o • o ^ 0
O o
o >- o
o 4- o
Note: Typical well spacings range from 12 to 33m
PRODUCTION WELL j ,(40 to 100 ft),
I
f
Figure. 2. Typical Well Field Configurations
-------
Initially, production values should be low, as native groundwater is moved
out of the production zone; as it is replaced by lixiviant, the uranium content
of recovered liquid increases. As the production zone is flooded with lixiviant
and a near-equilibrium flow condition achieved between the injection and
production wells, the recovered uranium will maintain an essentially constant
range of values. As leaching proceeds, recoverable uranium is gradually
depleted and values begin to decrease, eventually reaching some level below
which it is no longer economical to mine the deposit. The economics of in situ
mining consider the number of pore-volumes (the total volume of displaceable
fluid in the production zone) that must be exchanged to extract the ore-grade
uranium. The number of pore-volume exchanges needed to deplete the deposit
obviously will have a major influence on the life of the mine, while the time
required to effect a pore-volume exchange is a function of many variable factors
including hydrogeologic characteristics, number of wells, and pumping capaci-
ties. Fifteen or more pore-volume exchanges are expected to be required to
recover the uranium values from Mobil's Mesquite Mine in Texas (Eng. and Min.
Jour., Jan. 1981).
As ore is depleted from a given production zone, well patterns may be
placed in new production zones in the orebody in order to maintain an acceptable
overall grade of production for the mine. An orebody may be progressively mined
over a predetermined period of time by staged depletion, in which new production
zones are opened as old ones reach the cutoff grade for production.
Well spacing may vary with transmissive characteristics of the formation.
Most host rocks for sandstone-type uranium deposits are anisotropic; it is
therefore to be expected that internal fabrics, and hence transmissive
properties, will vary directionally. Directional variations in flow velocities
can be compensated for by adjusting the spacings between wells in such a way as
to provide equal flow times from injection well to production wells, regardless
of direction of flow. Typical spacings range from 12 to 33 m (40 to 100 feet).
At the Clay West Mine in Texas, 66 injection wells and 46 production wells
are located within an area of less than 1.2 ha (3 acres). The wells are
regularly-spaced on a 15 m (50 foot) grid pattern, with each production well
being surrounded by four injection wells. A ring of monitoring wells surrounds
the mine site at an average distance of about 61 m (200 feet).
Monitoring wells (Figure 3) are observed in order to detect fluctuations in
physical or chemical parameters that might serve as indications of excursions or
other alterations of ambient groundwater conditions. Such parameters might
include changes in water level, conductivity, temperature, pH, and various
chemical constituents such as sulfate, nitrate, bicarbonate, trace metals, and
uranium. Generally, various permits issued by state authorities specify which
parameters must be monitored. These specifications vary from mine to mine, and
are usually determined on a case-by-case basis (Section 6).
Volurtes of injected lixiviant vary with the size and transmissive
properties of the production zone. At the Wyoming Minerals Comporation's
Irigaray Mine near Buffalo, Wyoming, 50 L/s (800 gpm) were being injected into
200 wells in June, 1980 (Mining Record, 6-25-1980). The El Mesquite Mine, in
Texas, is designed to handle 200 L/s (3200 gpm) in a total of 45 production
areas, each of which is a complete well pattern.
11
-------
PRODUCTION-
ZONE
MONITORING
I WELLS
PRODUCTION-ZONE
MONITORING
WELL
NJECTION AND PRODUCTION WELLS
DEEP
MONITORING
WELL
SH ALLOW -
AQUIFER
MONITORING
WELL
SHALLOW I.
MONITORING
WATER
TABLE
.V
Figure 3: Mining and Monitoring Wells
I
-------
In the event of an excursion of leachate or lixiviant into non-producing
zones within an ore-bearing stratum, initial efforts to control the excursion
consist of increasing the rate of production and decreasing the rate of
injection. This produces an increased hydraulic gradient which tends to draw
the excursion back toward the production zone. Experience has shown, however,
that excursions into non-ore-bearing strata occur raore often than those into
strata being mined. Such excursions may be difficult to detect unless
monitoring wells are proerly located in view of the stratigraphic and structural
framework of the mine site. While these excursions may be due to natural
features such as through-going fractures or discountinuities in aquicludes,
they often are caused by leaky wells. Incompletely sealed cement plugs may
allow vertical migration of fluids from the mined strata to other aquifers,
while damage to PVC tubing by tools and samplers is a common source of leaks in
the casing. In areas where considerable subsurface exploration has been carried
out, unplugged exploration wells may also be a source of interformational leaks.
3.3 RECOVERY PROCESSES
The uranium-laden leachate, on reaching the surface through the production
well, is pumped to a processing plant where the uranium is extracted and waste
materials are separated out. In the plant, the leachate is passed through an
ion-exchange resin in an extraction column. Here, the dissolved metal is
retained in the resin, which at the same time releases displaceable ions into
the leachate stream. When the resin has become "loaded" with uranium, it is
transferred to an elution column where, by exposure to an eluant of suitable
ionic strength, the uranium is displaced from the resin and the resin
regenerated>by the addition of (usually) chloride ions. The uranium concentrate
from the elution column is then precipitated by the addition of a suitable
reagent. The resulting uranium oxide is then filtered and dried to produce
"yellowcake", U3O8. (Kasper, et al., 1979; Alvarez, 1980). Figure 4 depicts
schematically these generalized steps in the process. The details of these
steps vary from plant to plant; however, the flow lines and waste streams shown
in the diagram are typical of all processing plants.
Waste streams are produced at the filter and drier, as the precipitate is
separated from the eluant solution. At the extraction column, the leach
solution, after losing its contained uranium to the resin, is returned to the
well field for re-injection. Before this can take place, however, it must be
renewed by the addition of fresh solvent and oxidant. Also, to avoid the
recycling of dissolved ions which may descrease permeability by precipitation
in the host rock, the water is processed through a purification unit before
these renewal chemicals are added. Wastewater from both the extraction column
and the purification unit is removed from the cycle. The compositions of the
lixiviant and the minerals in the mined zone determine what types and amounts of
dissolved materials remain in the leachate after the uranium is stripped from
it. If significant quantities of heavy metals or toxic trace elements are
present, special processing of the recycled leaching fluid may be necessary to
control the increase of these materials in solution. This increase of dissolved
toxic elements in the leaching fluid, through continued dissolution of the
containing solid minerals, can have-adverse environmental consequences.
The bleed stream, which is tapped off the leach circuit in order to
maintain production at a higher rate than injection, is also a source of
wastewater after it is processed.
13
-------
DISSOLVED ION-EXCHANGE
GASES
LOADED RESIN
URANIUM
CONCENTRATE
ELUTION
FLUID
BARREN RESIN
BARREN
LEACH
LIQUOR
YELLOWCAKE
SLURRY
LIXIVIANT
MAKEUP
CHEMICALS
NqCI.CO.
CONDENSATE
WATER
STEAM
YELLOWCAKE
POWDER
WASTE TO
DISPOSAL OR
RECIRCULATION
WASTE TO
DISPOSAL
PRODUCTION
WELL
INJECTION
WELL
STORAGE
SURGE
TANK
FILTER
WATER
TREATMENT
ADSORPTION
COLUMNS
ELUTION
MAKEUP
DRYER
MIXING
TANK
ELUTION
COLUMNS
FILTER
PRECIPITATOR
Figure 4'.;. Ion Exchange Processing Plant
-------
Wastewater from the production process is collected and stored for
disposal through evaporation/concentration or deep well injection. Potential
environmental problems are inherent in both of these methods, because toxic or
radioactive materials may accidentaly be introduced to the air, the soil, or
ground- or surface water during the disposal process. Various Federal and State
regulations govern the design and operation of facilities that store or dispose
of hazardous wastes. The effects of such facilities at uranium ore processing
plants are discussed in Chapter 4.
3.4 PILOT PLANT PROGRAM
Regulatory agencies require that, prior to the issuance of an operating
license for an in situ uranium mine, the applicant operate the plant on a pilot
scale for a period long enough to demonstrate that lixiviant can be controlled,
that any excursions can be remedied, and that satisfactory restoration can be
achieved. Should problems be encountered during this pilot operation,
mod_ifications to the design of the plant may be made. Should irremedial_.p_rob-
lems occur, any negative environmental impact will be minimized due to the
¦' small area involved. " / ~ --
Pilot-scale operations are run over periods ranging from one to several
years. The general practice is to mine the deposit for several months and then
to restore the aquifer. Exxon's pilot plant in Valencia County, New Mexico, was
expected (at startup) to operate for two .months, .and to conduct.restoration for
nine months before the feasibility of a full-scale mine could be evaluated
(Mining Record, 6-^25"1980). Obviously, the cost of the pilot operation must be
considered in evaluating the economics of a prospective in situ uranium mine.
During the pilot-plant test, the effects of mining the deposit are closely
monitored, both to evaluate the efficiency of the operation and to detect any
environmental degradation that may occur.
3.5 RESTORATION
Restoration programs are also an inherent part of the mining operation and
must be included in the initial planning. They are conducted in response to
regulations that require the operator to restore environmentally acceptable
conditions to the in situ mine and surface site. Surface restoration can be
accomplished with relative facility. Restoration of the underground aquifers
affected by the operation, however, can be complex and time-consuming and is the
major concern of the restoration program. Basic to the restoration program is
the cessation of injection of lixiviant. Beyond that initial step, the approach
to restoring the quality of affected groundwater may vary from mine to mine.
One alternative method that has been suggested involves natural physical
and chemical processes which under near-neutral pH and in the absence of an
oxidant, tend to result in precipitation and sorption of dissolved materials
(Riding, et al., 1979). Other studies, however, suggest that oxidation-
reduction conditions prevailing in groundwater of one ore-bearing stratum in
Texas are not such that dissolved molybdenum (and, possibly, other metals) is
removed by these processes (Henry, 1980); thus, this does not appear to be a
universally applicable alternative but it has received attention by investi-
gators (e.g., Buma, 1979). Some investigators (Riding, et al., 1979) believe
15
-------
that bacterial reduction and introduced chemical reductants such as hydrogen
sulfide can be effectively used to restore groundwater. Natural restoration has
not been demonstrated to be a viable method, nor has its use received approval
from any regulatory agency.
Currently the most common approach to restoration is to flush the mined
zone with clean water through the injection wells, extracting the altered
groundwater through the production wells and processing it to remove un-
desirable constituents before re-injecting it. The continuous "rinsing" of the
production zone with clean water was used to restore the pilot plant at Nine-
Mile Lake, Wyoming, over a period of eight months (Engelman, et al., 1980). It
is also planned as the major restoration method for several currently operating
pilot plants and commercial-scale mines and at the Bruni and Palangana mines in
Texas (Kasper, et al. , 1979). Data presented by Kasper, et al. , 1979 on the
effectiveness of excursion cleanup demonstrations during pilot plant operations
suggest that restoration may be accomplished in relatively short periods of time
under some conditions. Molybdenum, sulfate, and conductivity values were all
restored to within 95% of baseline values after 35 days of restoration efforts
in those examples.
As displaced and diluted leachate is pumped to the surface, it may be
treated by any of several processes to remove unwanted materials and to prepare
it for re-injection. Reverse osmosis, electrodialysis, ion exchange, and
distillation are among the available methods to accomplish this (Riding, et al.,
1979). Ion exchange and reverse osmosis are presently the only feasible
methods; ion exchange is utilized in the extraction of the uranium, while
reverse osmosis has been used to treat wastewater prior to its disposal.
The separated hazardous materials must then be disposed of according to
practices approved by regulatory authorities. Two proven methods for accom-
plishing this are deep well injection and solar evaporation ponds. Both methods
require careful planning, engineering, and closure.
3.6 HEAP LEACHING
The technology of heap leaching as applied to the extraction of uranium is
similar to methods developed for the heap leaching of other metals, such as
copper. Essentially, heap leaching consists of passing solvents through piles
of crushed, low-grade ore, tailings, or mineralized rock that was originally
discarded as waste. The solvent solubilizes the metal and carries it in
solution to a collection point. The liquor is then processed to remove the
dissolved metal. Heap leaching is normally an above-ground operation and can be
completely isolated from ground and surface water bodies by engineered struc-
tures. Thus, the threat of contamination of water resources by leach liquor is
far less than it ia in in situ mining. At the time of this writing, only six
licenses were known to have been issued for heap-leach operations (see Table 24
in Appendix A).
The exact processes used in heap leaching uranium are highly proprietary and
closely guarded by the companies that own them. Therefore, the example cited
here as representative of heap leaching should be considered generally rather
than specifically descriptive. This information was obtained from the public
record, as part of material submitted In support of an application for an
operating license (Cotter Corp., 1978).
16
-------
In March, 1978, the Cotter Corporation, of Lakewood, Colorado, applied to
the USNRC for a license to operate a pilot-scale test of a heap leaching process
for the extraction of uranium (Cotter Corp., 1978). In the supporting
documentation, the proposed operation was described.
The process is thin-layer (TL) acid leaching, developed by Holmes and
Narver, Inc., of Anaheim, California. The purpose of the pilot operation was to
evaluate the process in terms of economic production, using ore obtained from
the Charlie orebody at Willow Creek in an open-pit mining operation. The ore
occurred as uraninite and associated vanadates as coatings on sand grains,
located along oxidation-reduction zone interfaces in sedimentary deposits of
the Wasatch Formation. Approximately 6,000 to 8,000 tons of ore were exposed in
the pit.
The process generally was to consist of crushing the ore, mixing it with a
strong acid (93% H2SO4) and allowing it to "cure" in a specially-designed
container for 16 to 24 hours. The acidized ore would then be transferred to a
leach pad, where it would be washed with a weak acid solution for approximately
48 hours. The leachate would be collected and sent to a precipitation tank,
where U3O8 and V2O5 would be precipitated by addition of MgO. After thickening
and filtering, the yellowcake would be packaged for shipment. The plant was
expected to have a daily capacity of approximately 25 tons.
The ore was to be transported to the mixing tank by conveyor belt, and, to
minimize dust generation, was to be wet down by water sprays. For the same
reason, the crusher and screens were to have dust hoods.
At the leach pad area, acid spray nozzles were to be placed below the grade
of the pad. They were set to produce a coarse spray, in order to minimize acid
mist generation. No acid spray effects were expected outside the leach pad
area.
All liquid wastes were to be stored and treated before release or disposal.
Accidental spills were to be contained by dikes. Disposal cells were to be lined
with clay.
Seventeen batches, approximately 23 metric tons each, were processed in
the pilot plant over a 46-day period in late 1979. Test data from samples
collected during this period showed that concentrations of airborne uranium in
various operating areas of the plant were two or more orders of magnitude below
the allowable levels, and atmospheric radon levels in the vicinity of the pilot
plant were one to two orders of magnitude below allowable concentrations (Cotter
Corp. , 1980).
Analyses of water draining from tailings produced some results that,
according to the Cotter Corporation, were not representative of wastes from a
commercial-scale plant. Table 1 presents concentrations of trace metals in
samples from the above mentioned sample program. Cotter has stated that these
more closely represent the projected characteristics affecting groundwater in
the immediate vicinity of a saturated, below-grade tailings disposal cell.
No environmental problems had been reported from this operation in early
1981.
17
-------
Table 1. Concentrations .(mg/L) o£ Trace Metals and_Inorganics, Willow
Creek, Wyoming, Stage 2, Leach Potential" -Test. (without 'clean
water wash)
Column No./Batch No.
Chemical Parameters
1/1
2/1
3/2
A1
<1.0
<1.0
<1.0
Ca
84.0
80.0
80.0
Fe
<0.12
<0.12
<0.12 •
K
3.0
2.5
3.0
Mn
<0.05
<0.05
<0.05
Na
240.0
235.0
240.0
Ni
<0.15
<0.15
<0.15
VA
6.0
8.0
8.0
<1.7
<1.7
<1.7
Zn
<0.018
<0.018
<0.018
pH
8.21
8.29
8.23,
Reference: Cotter Corporation, 1980
18
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SECTION 4
ENVIRONMENTAL IMPACTS OF IN SITU AND HEAP LEACH MINING OF URANIUM
4.1 INTRODUCTION
The discussions in this chapter are focussed upon the environmental
impacts inherent in the processes of solution mining of uranium and are not
intended to cover all the environmental impacts that are associated with the
setting up, operation, and dismantling of mines and mills in general. An in situ
operation has some obvious environmental advantages over an open-pit or
underground mine in that little or no dust, vibration, or objectionable noise is
generated. However, due to its basic nature, this method of mining alters
drastically the quality of groundwater at the mine site and can potentially
contaminate surface or shallow subsurface water resources as a result of mill
operations. Another major environmental concern is the release of radioactive
substances from the mining operation.
Maintenance of water•quality during and following in situ leaching of
uranium is the fundamental problem which must be considered in an environmnental
assessment of such operations. Prior to any leaching activity, a realistic
baseline by which to judge groundwater quality must be established for any given
operation. Monitoring programs will be required to evaluate subsurface
restoration efforts and to assess.the containment of the lixiviant and the
solubilized ions witjiin _the -mining area of the ore—bearing aquifer.;
In the Grants, New Mexico, mining district, studies have indicated that
major impacts on groundwater levels and flows will result from the extensive
dewatering that is necessary to carry out a conventional underground mining
operation (Stone, 1979). As in situ mining requires that the ore-bearing zone
be flooded at all times, and as groundwater conditions must be restored after
completion of mining, this impact is minimal or non-existent in a solution
mining operation.
4.2 GROUNDWATER CONTAMINATION
Groundwater contamination may result from excursions of lixiviant from the
production zone either laterally, into non-producing parts of the aquifer or
vertically, into overlying or underlying aquifers and from increases in
dissolved trace elements caused by the solvent action of the lixiviant and
reactions between the lixiviant and the minerals of the formation.
It is significant that contamination in a solution mining operation is
defined on the basis of the condition of the groundwater and not with reference
to drinking water or other standards. Thus, the groundwater in the production
zone before the lixiviant is introduced may not meet standards for potable
water. Induced toxicities may therefore be increases in dissolved materials
that were already considered toxic or otherwise unacceptable.
- 19 -
-------
Table 2 presents compositional parameters for typical lixiviants.
Table 3 lists compositions of leach liquors, as identified in analyses at
typical mining operations (Kasper, et al., 1979).
Alteration of pH
Solvents used in lixiviants are designed to alter the pH of native water in
orebodies to a range in which solution can take place efficiently. This results
in strongly acidic or moderately alkaline pH values in the groundwater in the
zone of influence of the injection wells. Reaction with minerals within the
formation tends to neutralize the pH of the leach liquor, which may be
maintained at desired levels by the addition of appropriate chemicals at the
surface. Generally, water' "showing"' "pE values outside "the; range "of 6.5 to~8.5^is
considered unsafe for drinking (US EPA, 1975). Excursions of lixiviant outside
the bounds of the production zone may therefore result in undesirable or
hazardous pH values in groundwater used for drinking. Restoration of pH baseline
levels after intensive mining operations appears to require a relatively long
time. In the pilot restoration program at the Nine-Mile Lake Mine in Wyoming
(Engelman, et al., 1980), where a sulfuric acid lixiviant was used, flushing
with native groundwater over a period of seven months resulted in a pH of 6.0,
as compared to 6.8 in native groundwater outside the ore zone. The relatively
slow recovery of this parameter is thought to be due in part to the presence of
clay minerals above and below the ore body, which tend to retain sorbed H+ ions
and to release them gradually.
Introduction of Ammonium Ion
Where ammonium carbonate-bicarbonate lixiviant is used, ammonium ion
presents a special problem in its impact on the subsurface environment. Most
clay minerals have sites on or in the crystal structure which are occupied by
ions sorbed to the clay by electrical bonds that are relatively weaker than the
internal bonds of the crystal lattice. These ions are subject to replacement by
other ions which are preferentially sorbed to the clay by bonds that vary in
strength. Ammonium ion (NH4+) has a strong affinity for clay and will be sorbed
preferentially where strong concentrations are available (Degens, 1965).
Sodium, calcium, and other cations may be displaced by ammonium ion, which is
held by the clay during the leaching operation and given up only gradually
during restoration. Adsorption of NH4+ by clay in producing formations may
result in concentrations in groundwater many times higher than baseline values.
The presence of this ammonium is considered to be an environmental concern and
permitting regulations require its reduction to acceptable levels. While these
levels have not been determined yet, NH3 levels of 10 ppm have been suggested for
Texas mines (Yan, 1980). Natural waters in five Texas ore production zones had
ammonia contents ranging from 0.01 to 2.1 mg/L, four of them being 0.2 mg/L or
less (Table 4). Values were generally higher at three typical Wyoming study
areas, in which ammonia concentrations were 0.1, 1.8, and 1.5 mg/L (Table 5).
Neither ammonium ion nor ammonia is considered to be toxic. Under cetain
conditions, however, either of these compounds can produce nitrate ion (NO3-),
small concentrations of which have been associated with metheglobinemia in
infants. Because of this association and other health concerns, primary
drinking water standards set the limit of acceptability for nitrate at 10 mg/L.
_ 20:
-------
Table 2. Compositions of Typical Lixiviants
Concentrations of Typical Components
of Acid lixiviants
Concentration
Range
Component (g/I)
Acid
Sulfuric Acid 3.0 to 20.0
Oxidant
Hydrogen Peroxide (50%) 0.5 to 2.0
Oxygen 0.5 to 4.0
Concentrations of Typical Components
of Alkaline Lixiviants
Concentration
Range
Component (g/L)
Base
Carbon Dioxide 0.5 to 15.0
Ammonia 0.2 to 5.5
Oxidant
Hydrogen Peroxide (50%) 0.5 to 2.0
Oxygen 0.5 to 4.0
Modified from Kasper, et al., (1979)
-------
Table 3. Typical Compositions of Leach Liquor
Partial Composition of Recirculated
Acid Lixiviant
Concentration
Constituent
(*/L)
Arsenic
0.05
Copper
1.00
Zinc
4.30
Lead
0.70
Manganese
1.20
Iron
25.40
Nickel
0.60
Chromium
0.15
Strontium
3.70
Zirconium
3.30
Vanadium
1.00
Cobalt
0.20
Ra-226
390 pCi/L
Partial Composition of Recirculated
Alkaline Lixiviant
Concentration
Constituent
(mg/L)
Arsenic
0.05
Copper
0.04
Zinc
0.10
Lead
0.20
Selenium
1.60
Iron
0.60
Nickel
0.06
Chromium
0.07
Molybdenum
0.90
Strontium
1.50
Zirconium
0.90
Ra-226
1750 pCi/L
Modified from Kasper, et al., (1979)
22
-------
Table 4. Water Quality in Texas Ore Production Zones - mg/L Except pH,
Conductivity, and Radon 226
Parameter Location A B C D E
No. of Wells 15 wells 18 wells 3 wells 17 wells 5 wells
Calcium
42
52
80
267
14.
5
Magnesium
9
10
11.
,6
68
2.
9
Sodium
212
341
163
413
337
Carbonate
0
0
0
0
0
Bicarbonate
197
285
281
121
347.
.8
Sulfate
41
51
142
142
141
Chloride
280
436
143
1090
289.
.4
Fluoride
1.
.02
0.
.91
-
0.
, 17
1.
,31
Nitrate
0.
.07
-
0.
,05
0.
.05
2.
78
pH
7.
.94
7.
.6
7.
,3
7.
.4
8.
,05
TDS
699
931
764
2312
1052
Conductivity (F)
1281
1589
1310
3835
1154
Arsenic
0.
.003
0.
.074
0,
,01
-
0.
,2
Barium
0,
, 1
0.
.2
0,
.5
0.
.05
0
Boron
0.
.53
1.
.2
0,
.57
0.
.19
2.
,15
Cadmium
0.
.001
0.
,0001
0,
,0025
0.
.007
0.
01
Copper
0,
.007
0.
,004
0.
,015
0.
.007
0.
64
Chromium
0.
.01
0.
,01
0,
,01
-
0.
,24
Lead
0.
.009
0.
.004
0.
.02
0.
.052
0.
.25
Manganese
0.
,01
0.
.02
0.
.046
-
5.
,06
Mercury
0.
.0001
o;
;ooo3
0,
.0001
0.
,0007
0,
,36
Nickel
0.
.02
0,
.03
-
0,
.037
0.
.01
Selenium
0,
.012
0.
.002
0,
.005
0,
.005
0.
,61
Silver
0.
.01
-
0,
.0023
0,
.007
0.
.1
Zinc
0.
.37
0,
.03
0,
.02
0,
.04
0.
. 18
Ammonia
0,
.15
0.
.2
0.
.01
0,
.17
2.
.1
Uranium
0.
.07
0.
.1
0.
.181
0,
. 15
0.
.17
Molybdenum
0,
.05
0.
.03
0,
.2
0,
.05
0.
.25
Vanadium
0,
.1
-
0,
.003
0,
.05
0.
.2
Radium-226(G)
96
349
274
19.
.2
52.
.3
Iron
0,
.02
2,
.6
-
-
2.
,06
A - TWQB Permit No. 02025, Dalco-U.S. Steel Burns Lease
B - TWQB Permit No. 01890, ARCO Clay West Mine
C - TWQB Permit No. 02050, IEC Pawnee Plant
D - TWQB Permit No. 01942, Wyoming Mineral Corporation Bruni Site
E - TWQB Permit No. 01941, Mobil Oil Corp. O'Hern Uranium Plant
F - Micromhos per centimeter
G - Picocuries/liter
Table from Kasper, et. al., 1979.
23.
-------
Table ;5. Water Quality Data for Typical Wyoming Area Groundwater
Constituent/Site
A
B
C
D
E
F
Calcium
17
7.8
20.5
63
230
12
Magnesium
9.6
1.5
16
40
17
2.3
Potassium
2.5
7.3
7.9
-
-
-
Sodium
66
325
700
69
530
170
Bicarbonate
188
374
643
281
0.1
67
Chloride
9.0
12
21
8
360
51
Carbonates
0
7.4
120
-
170
18
Sulfate
14
202
880
130
950
220
TDS
288
917
1860
430
2300
560
Ammonia
0.1
1.8
1.5
-
-
-
Uranium
0.006
0.002
0.85
-
0.11
0.006
Selenium
0.003
0.005
0.22
-
0.01
0.01
Barium
0.5
0.5
0.5
-
1.0
1.0
Arsenic
0.01
0.02
0.02
-
0.01
0.01
Nitrate
0.05
0.85
0.32
-
0.62
0.18
PH
7.7
9.4
8.3
7.9
8.7
8.5
All concentrations are expressed in terms of mg/L except for pH.
Table from Kasper, et al., (1979).
24
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Because nitrate ion in groundwater is very mobile, it is a major concern to the
quality of water in aquifers. Nitrate can form from the oxidation of ammonium
ion in a strongly oxidizing environment, where it is stable. In shallow
groundwater bodies, a shift toward reducing conditions can lead to denitri-
fication or breakdown of nitrate into nitrogen (N2) or nitrous oxide (N2O);
these are innocuous in drinking water. Denitrification is promoted by a number
of processes that are effective in shallow soil zones, including bacterial
action, oxygenation, and heating. Denitrification below the water table,
however, is incompletely understood. It appears that the scarcity of
denitrifying bacteria in the groundwater may inhibit the conversion of nitrate
to other forms. Theoretically, denitrification should occur in deeper
groundwater under reducing conditions, producing N2C). N2> or ammonium ion
(NH4+) (Freeze and Cherry, 1979). Thus, it may be argued that under low-oxygen
neutral-pH conditions, nitrate is unlikely to form from NH4+ in deeper
groundwaters. While highly oxidizing conditions are maintained^ during the
mining operation, restoration to baseline Eh values should result in a
geochcmical environment that does-. not favor nitrification of .ammonium," so"-long
it remains in the restored formation. Further, in most situations, contTnufecr
desorption of ammonium by ammonium-saturated clays probably would not result in
widespread contamination of non-producing zone aquifers.
Transport of NH4+ into areas of ammonium-poor clays should result instead in the
fixation of the ion by resorption.
Mobilization of Metals
Sandstone-type uranium deposits are the result of precipitation of
dissolved metals from groundwater, under conditions of changing Eh, from
oxidizing to reducing conditions. Uranium and other metals with similar
solubility are deposited together or in close proximity, often under the
influence of reducing conditions brought about by the organic matter in the
sediment. Therefore, alteration of ambient Eh and pH conditions to promote
solubilization of uranium in this type of deposit unavoidably mobilizes other
metals and introduces them into the leach liquor. Obviously, these dissolved
metals vary greatly in composition and concentration from site to site, as they
are dependent upon original mineralogy and the chemistry of the in situ mining
operation; typical trace metals found in association with sandstone-type
uranium deposits include selenium, lead, copper, nickel, arsenic, chromium, and
molybdenum (Table 5), all of which are considered to be toxic above certain
concentrations in drinking water. To reduce the potential for contamination of
drinking water resources, permitting regualtions require that the dissolved
metal content of formation waters be returned to defined levels near baseline
values.
Table 4 lists the dissolved constituents in waters of typical orebodies of
Texas, under natural pH and Eh conditions. Ideally, the flushing of lixiviant
from the aquifer after completion of the mining operation should result in the
restoration of these conditions and the consequent reduction and precipitation
of metals that were mobilized during the operation. Recent studies, however,
show that the behavior of dissolved trace elements that are mobilized under
-------
oxidizing conditions does not follow this predicted path, at least within a short
time period. The reasons for this discrepancy between observed and predicted
behavior are not understood; however, possible explanations include: (1): an
incomplete understanding of thermodynamic relationships among these trace
metals; (2) an incomplete understanding of all factors affecting solubility,
including complexing by organic compounds; and (3) reaction times that are much
slower than expected. Observation shows that some trace metals persist in the
dissolved form even though they have been transported from mined areas into
reducing environments- (Henry, et al., 1980).
The restoration pilot program at the Nine-Mile Lake site, near Casper,
Wyoming, required approximately 100 days of flushing to restore arsenic levels
at one well to primary drinking water standards, while selenium values became
asymptotic over a period of more than 200 days of restoration, reaching low
values between 10 and 20 ppb (slightly above the standard of 10 ppb). A
comparison of total dissolved solid values before and after the pilot restora-
tion operation shows that restored values fall within measured concentration
ranges inside the production zone but are slightly above values measured
outside the zone (Table 6; Engleraann, et al", 1980).
Other Salts from Leaching Solutions
In addition to ammonium, other components used in lixiviants and mill
processes can build up concentrations in the groundwater that exceed baseline
values and therefore must be restored by post-operational remedial actions.
These components are discussed below.
Table 6- Groundwater Quality at Nine-Mile Lake, Wyoming, Comparison of
Native, Preleach, and Restored Groundwater^
Native groundwater
outside ore zone
Preleach pattern
groundwater
Restored
groundwater
PH
6.8
5.8-7.9
6.0
Free acidity
10
10
20
Calcium
110
20-360
65
Sulfate
1,620
300-3,600
2,200
TDS
2,660
680-5,450
3,000
All values in parts per million (except pH).
a) Sulfates--sulfate ion (S0^+) is introduced to groundwater ; at sites
where sulfuric acid is used as a lixiviant; however, it may also appear at
sites where alkaline lixiviants are being used' as a result of oxidation of
pyrite or other sulfides under the induced highly-oxidizing conditions.
Sulfate readily combines with calcium, which is commonly abundant in sedi-
mentary rocks, to form gypsum. Sulfate in drinking water may cause gastro-
intestinal irritation, and the U.S. Secondary Drinking Water Standards accord-
ingly set the acceptable maximum at 250 mg/L; however, this value may be
exceeded by several multiples in natural waters, particularly those associated
with concentrations of minerals. As an example, Englemann, et al., (1980),
26
-------
cite preleach sulfate concentrations of 300 to 3600 ppm in ore-zone ground
water at the Nine-Mile Lake mine in Wyoming, while concentrations outside the
ore zone averaged 1620 ppm.
b) Chlorides--this ion commonly enters the leach liquor streams at the
extraction column, where it is used as the exchangeable ion in resins. Sodium
chloride (NaCl) is the most widely used agent for regeneration of ion-exchange
resins, as chloride causes only minimal interference with the leaching process
(Kasper, et al., 1979). The U.S. Drinking Water Standard maximum for chloride
is 250 mg/L. As this value is commonly exceeded in natural waters, it is in
the mine operator's interest that a detailed baseline sampling program be
carried out./be'fore lixiviants^Jare injected, j*.
Although the major effect of excessive chloride content on drinking water
is aesthetic, in that an unpleasant taste is produced, Galloway, et al.,
(1981, p. 283) note that chloride may act as a complexing ion for base metals
and hence should increase the solubility of those metals.
c) Total Dissolved Solids--Drinking water standards set the acceptable
limit for total dissolved solids (TDS) at 500 mg/L; however, in many regions,
groundwater" used for drinking exceeds this limit and water from mineralized
formations would commonly do so. Baseline values for groundwater .at the
Nine-Mile Lake mine were 2660 mg/L outside the ore zone and 680 to 5450 mg/L
in the ore zone. As values of 1,000 to 3,000 mg/L are typical for uranium
leaching operations (Kasper, et al., 1979), careful compilation of baseline
data will provide for optimum differentiation between the effects of solution
mining and the ambient chemistry of natural waters.
Leach Liquor Excursions
The possibility of an excursion occurring in an in situ mining operation
,is -moderately lively"- ^"Tfiis poislb'i-iity^ decreases. with the degree of under-
standing of subsurface geohydrologic conditions, which would strongly affect.,
well field design, construction, and operation. On the other hancT, -'the poss'i-^
bility tends to increase with nunber of wells and the period of time ove»- which
"the mine is operated _ ~ _
Galloway, et al., (1981) discuss the geochemical implications of both
alkaline and acid leach liquors in Texas aquifers. In the case of an alkaline
leach-liquor, they conclude that an excursion from an ore zone into a mineral-
poor, normally oxidizing zone would be influenced by only few reactions tend-
ing to alter its chemical nature over a short time span. The introduction of
a high-pH lixiviant into an environment dominated by quartz and aluminum
silicates, they believe, would produce the slow formation of silica and
aluminum hydroxides, allowing the pH to remain high while the fluid moved
along under hydrodynamic impetus. Similarly, they postulate that the oxidant
content of the lixiviant would remain high for considerable distances of
travel. An excursion passing into a reduced zone outside the ore production
zone would have effects similar to those in the production zone, that is, pH
would be lowered, the oxidant would be consumed in reactions with reduced
metals, and trace metals would be dissolved into the groundwater.
Although acid lixiviants were not in use in Texas, Galloway, et al., also
considered the effects of an acid leach-liquor excursion. In that case, they
27
-------
hypothesized that, even if the pH of the liquor were raised to a near-neutral
range by reaction with wallrock minerals such as carbonates, the solubility of
trace elements would not be immediately affected.
The conclusion that dissolved trace elements will probably not quickly
reprecipitate or be adsorbed is supported by the observations of Henry, et
al., (1980), who offer evidence that trace elements tend to remain in solution
even after Eh conditions have changed from oxidizing to reducing.
Thus, the environmental threat presented by excursions of leach liquor is
one that must be controlled by artificial means, as natural controls that
would remove the threat in an acceptably short time period appear to be lack-
ing.
Radioactive Materials
The radiological effects of uranium and its decay products constitute a
health hazard that is distinct from the hazard due to its toxic properties.
These ..effects" are a special concern where excursions of leach liquor threaten
potential drinking water supplies and at surface facilities where leach liquor
and process wastewater are. in;"cpritac.t~,wifh humans-arid'the environment.
Most uranium contains more than 99 percent of uranium 238, which^evolves
through radioactive decay 2§§r period of time (4.5 x 10 years)
into an isotope of lead, Pb . Num^gus othgg^unstable daughter products are
formed during the transition from U to Pb , and in many ore deposits all
of the daughter isotopes are pi^ent in constant proportions. Of these
daughter products, radium 226 (Ra ) is considered to present the greatest
threat to groundwater resources because of the potential radiat^op effects of
its daughter products. Its immediate daughter, radon 222 (Rn ) is a gas
which can be released into the atmosphere.
Excursions of leach liquor transport radioactive materials'"as- well"
as other dissolved metals. Kasper, et al.~ (1979), state that the data base
covering the long-term effects of such excursions is very small, but that
available evidence from cleanup operations suggests that the radioactive
materials are returned to the producing zone along with the other contami-
nants- when remedial measures are taken. They also point out that there is a
significant difference between the solubility of radium in acid and alkaline
lixiviants; in a typical acid leach operation, only 0.38 percent of the total
radium 226 in the ore is dissolved, '_whereas in .a t^pjical alkafine leach'ope.ra-
.tion, about;.' 2_per.cent'- of-'thcr radium in thf -ore was 'dissolved-..- Thus, ..the p'oten-
..t'ial. impact of radioac.tiye -contamination..by -an. excursion ..from..an._a_lkaline-—_ ~
leach .mine_can -be, .expected. to- be::.considerably- gr.eater-than.;an..excursi-on, from
an .acid-leach mine. . - — — .
"473 SURFACE WATER CONTAMINATION
.Leach 1 iquors'...an3...mill. pro*cess_ waters-.that .arc not _ re'-'injected. niay...con-__
.tamiriate. surface waters".- ..The. waste streams depicted schematically in .Figure^
4 -,al't contain,.non-radioactivV'potential contaminants in various .concentrations,
'that- mus-t_.be handled to avoid..contamination of...sur.fajce^wat:evs"," These waste
streams all contain^ trace: amounts of r adioactive ifiatcyial .'.tHat' cannot~ be. .released.,
into the'environment even 'in dilutedform. "
-------
Because disposal of radioactive wastewater is expensive, most plants are
designed to recirculate and to reuse process waters. A summary compiled by
Kasper, et al. , (1979), of annual volumes of wastewaters generated by a
hypothetical plant is presented in Table 7. The authors point out that the
wastewaters produced during the restoration period is based on a 10-pore volume
flushing program to be carried on in one-year-long increments for a total of
nine years. Such an estimate may be low, as flushing volumes as high as 25-pore
volumes have been required to attain baseline or acceptable restoration in some
cases. At the Nine-Mile Lake mine, more than 20 pore volumes (estimated) of
flushing were required to achieve near-baseline values for the groundwater in
the production zone (Englemann, et al., 1980).
As many of these waste streams are characterized as brines (1500-5000 mg/L
TDS), they would have an adverse effect on surface waters if discharged into
the environment.
Where liquids are transferred from point to point, either through pipes or
in open settling or evaporation pond systems, the possibility of system failure
or operator error exists. The accidental escape of hazardous or otherwise
undesirable materials into the environment can be minimized by incorporating
safety factors or backup features in the design of the facility. However,
because there is great variation among in situ mining operations and their
associated environments, specific environmental impacts must be evaluated case
by case.
4.4 ATMOSPHERIC CONTAMINATION
Atmospheric emissions at an in situ solution mining operation are slight
compared to those from conventional surface or underground mining operations,
but radioactive emissions pose the most important health concerns.
Radioactive Emissions
Radon gas from the pregnant liquor surge tank and uranium 238 oxide dust
from the yelloweake dryer are the primary emissions from an in situ mining
operation and its recovery plant (Kasper, et al., 1979). Evaporation ponds are
also a potential source of radon. Because of the difference in solubility of
radium 226 in acid and alkaline solutions, approximately 0.02 percent of radium
in an ore body is precipiated as yelloweake at a typical acid leach operation,
as opposed to about 2.0 percent at an alkaline leach operation. Measured
values at the Irigarary mine in Wyoming support the conclusion that human
populations are characteristically exposed to doses of less than 0.1 percent
of the allowable maximum under NRC standards and 5 percent under proposed USEPA
standards.
The effect of atmospheric emissions from the Irigaray mine on the popu-
lations within an 80.5 km (50 mile) radius was estimated by the NRC to be less
than 5 x 10~^ percent of the dosage provided by natural background radiation
(USNRC, 1978).
Ledbetter (1980) summarized the occurence and effects of radioactive
materials in and near uranium mines and concluded that the hazard from radon is
practically eliminated at above-ground operations by natural ventilation.
29
-------
Table 7, Wastewaters Generated by Ion Exchange, b00,000 Pounds Uranium per
Year In Situ Solution' Leaching Operation Main Lixivant Circuit
Flowrate = 63 1/sec (1,000 gpm), ?/i-hour operation
W0 monitoring
wells (? 250 gallons twice
per month.
1.25 1/sec (20 gpd)/employee
x 60 employees
Water Hushed through
leached areas to remove
all traces of 1ixiviants.
JfJowrate
1.25 1 /see (20 gpm)
0.63 1/ser (10 gpm)
0.63 I/sec (!0 gpm)
0.2 1/sec (3 gpfn)
0.02 1/sec (0.3 gpm)
0.05 1/sec (0.3 gpm)
6.4 I/sec (102 gpm)
Annual Volume
2 7 HO m
(32 AF)
1390 m (16 At)
1390 m (16 AF)
420 rrT (5 AF)
42 ra (0 r> AF)
110 m (1.3 AF)
14, 170 !.r ( 164 Al* )
(a) Lixiviant hired can be used - l.fowrate in then contained in 11 em 1.
(h) I.ow water use fixtures, assumes showers for 80 percent of employees.
Ref: Kasper, et al., 1^79.
-------
effects. He pointed out that uranium itself presents little or no external
body hazard. Measures to prevent the inhalation and ingestion of dust are
effective in controlling the internal hazard.
Non-radioactive Emissions
Non-radioactive atmospheric emissions that are specific to in situ
uranium plants include ammonia, ammonium salts, and carbon dioxide. These
materials are emitted at the yellowcake dryer, from the surface of storage and
disposal ponds, and at water purification units. Ammonium chloride partic-
ulates may be emitted from evaporation ponds; however, the transport of
particulates from pond areas is minimized by the maintenance of a supply of
liquid in the ponds. All of these are relatively low-level emissions and have
minimal or no adverse environmental impact (Kasper, et al., 1979).
4.5 GROUNDWATER CONSUMPTION
Because of restoration requirements, there may be relatively little net
removal of water from subsurface aquifers as a result of in situ mining
operations. Kasper, et al., (1979) point out that the hypothetical plant
described in Table 7 can produce as little as 1.47 L/sec. (23.3 gpm) of
radioactive wastewater if maximum in-plant reuse of water is practiced.
Restoration water is treated at the surface and re-injected, producing a
relatively small waste stream for each pore-volume of flushing water. Kasper,
et al., (1979) conclude that consumptive water use would have only local
effects and would not adversely affect regional water supplies in either the
Texas or the Wyoming type ore-bearing formations. Galloway, et al., (1981),
however, conclude that the projected increase of in situ mining in Texas will
have an increasing effect on regional hydrology, and recommend detailed pre-
operational tests and post-restoration monitoring programs to provide more
information on the sensitivity of aquifers there.
As not all mining operations recycle the produced water, consumption of
water varies. Net removal may be large in some operations.
31
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SECTION 5
CONTROL TECHNOLOGY
Technologies for the control of pollution from in situ and heap-leach
extraction of uranium include many which are common to the mineral processing
industry or other industries in general, such as dust and noise control
technologies. Several areas, however, are more specific to the solution mining
and processing of uranium, and they are discussed in this chapter. These
technologies can be grouped into three broad categories: (1) mining operations;
(2) cleanup and restoration; and (3) waste disposal.
5.1 MINING OPERATIONS
Water Barriers
To be suitable for in situ leaching, a uranium deposit should be bounded
above and below by impermeable strata and be located below the water table
(Riding, et al., 1979). Impermeable strata or aquicludes vertically bounding
the uranium deposit figuratively function as dams which prevent leach solution
from flowing into the overlying or underlying strata. Water flows through these
aquicludes but the rate is so slow that vertical migration of the leach solution
can be avoided if the aquiclude is isotropic throughout. Aquicludes, however, are
not always isotropic in their permeabilities. Anomalies in the permeability of
an aquiclude may result from fracturing, lithologic differences, and improperly
sealed wells. Potential breach zones of the aquiclude such as fractures and
high permeability zones can be sealed by grouts or slurries. Grouts and
slurries are discussed later in this report.
Wells that are drilled into the ore bearing strata but improperly sealed
are the most vulnerable locations through which migration of the leach solution
may occur. It is imperative that the annular space and fractures produced
adjacent to the drill hole as a result of the drilling operation can be sealed
off. Sealing of the annular space and associated drilling fractures is commonly
done with cement. To maintain the integrity of the well, the cement seal and
well casing should be stable in the presence of the injected leaching solution.
Centralizers used during placement of the cement will help to insure that all of
the annular space is sealed off. Cement or cement grout placed under pressure
will permeate naturally present fractures and those induced by drilling. The use
of cement grouts is limited by the size of the spaces which they are capable of
penetrating. It may be necessary to use clay or chemical grouts to seal off
small fractures.
Abandoned exploration wells in the vicinity of in situ uranium mines must
be adequately plugged in order to prevent the migration of contaminants through
them. Most states have adopted regulations governing the abandonment of
exploration wells.
32
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In the event of an excursion through a jwell _during,.the. active
life of an in situ mine, the location of the break in the well seal can be
determined by pressure testing. Pressure testing entails establishing a
relatively high pressure within a packer and measuring any loss in pressure.
Should pressure drop, it may be inferred that a break exists in the well
casing or well seal within the increment being tested.
Control of Water Movement by Pumpage
Current technology used to control the flow of lixiviant in the strata
containing the ore body "involves /establishijig~Jsubsur face flow systems"
between the injection and pumping weils by differentiaf pumping. The leach
solution injected into the ore body will initially flow out in a radial
pattern. Pumping of the production well controls the outward flow of the
leach solution by creating a low pressure area to which the injected solution
will flow. The resulting flow pattern from the injection well to the produc-
tion well approximates a tear shape with the large end .of the tear at the
injection well and the smaller end at the production well.
The distance which the fluid lines extend from the injection well deter-
mines the areal extent of the leach solution and is dependent upon the amount
of fluid injected and pumped out. The greater the differential between
volumes of pumping and injection, the lower the pressure at the production
well and the smaller the areal extent of the lixiviant. In the event of an
excursion, Ihe differential pumping scenario described above creates an in-
creased hydrodynamic gradient which tends to draw the excursion toward the
pumping well.
Another method of controlling lixiviant migration is the establishment of
a pumping trough. In the event of an excursion, wells surrounding the ore
body are pumped. The pumping wells then form a trough in the piezometric
surface into which the leach solution flows. The hydrodynamic gradient thus
created initially limits leachate excursion. Eventually, the contaminants
will be removed, as the aquifer is flushed by inflowing groundwater. _ How-
ever, such a method reduces the usable storage capacity of the aquifer and
utilizes large volumes of native groundwater.;-
A pressure ridge, or water barrier, can also be used to control excur-
sions. This method involves the use of a line of recharge wells that pump
water into the formation to form a ridge in the piezometric surface. The
pressure ridge must be initiated outside the lixiviant-fresh water front in
order to prevent driving the excursion further away from the leach zone.
Lixiviant will not transgress the pressure ridge if the ridge is of signi-
ficant pressure and a pumping well is used to provide a low pressure zone into
which the lixiviant can flow. The ridge produced by the recharge wells would
consist of a series of peaks at each well with saddles in between. The neces-
sary elevation of the saddles to displace the lixiviant would govern the well
spacing and the recharge rates required. This method of control does not
restrict usable groundwater.; storage capacity but has the disadvantage of
requiring supplemental water.
Grouts
Migration of the lixiviant in the vertical and horizontal planes can be
restricted by decreasing the natural permeability via grouting.
33,
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While the use of grouting techniques in the in situ mining industry appears
to be rare, the method has potential application in isolating difficult- to
restore zones from regional circulation and in controlling leakage through
aquicludes. Grouting is usually relatively expensive, and may be economical
only in certain situations.
Common grouting procedures involve drilling through casing anchored
sufficiently to withstand the applied pressure. The permeability of the strata
is tested, grout is chosen in accordance with the conditions and objectives of
the grouting program and then it is injected. Deep holes are commonly grouted
in stages; for example, the hole is drilled until a permeable zone is found and
then grout is injected. After the grout has set, the hole is drilled out,
deepened, and grouted again (Int. Soc. Soil Mech. and Found. Engnrg., 1963).
In order to permeate the rock, the grout pressure should exceed the
hydrostatic pressure but not the vertical stress (Cummins and Given, 1973).
Injecting grout at pressures greater than the vertical stress can open
additional fractures in the rock.
There are basically three types of grout: cement, clay, and chemical. Of
these, only the first two are considered here, because the polymerizing
compounds used in chemical grouting may contaminate the area. The objectives of
a grouting program and the funds available for it control the choice of grouts
to be used.
Cement Grout—
Cement grout is commonly used to fill moderate or large voids in component
rock. Cement slurries enter fractures and pores larger than 1 millimeter at the
rate of about 0.3 cm/sec in coarse sand. Penetration can be improved with sodium
silicate or clay lubricant, but even with these admixtures medium porosity sands
are the penetration limit (Cummins and Given, 1973).
Bentonite will improve the pumpability of cement slurries and prevent the
separation of water in the grout mixtures; however, it decreases the strength of
the grout (Int. Soc. Soil Mech. and Found. Engnrg., 1963). Clay-cement grouts
will bond with native clays, unlike neat cement and cement-sand grouts. The
setting times of clay-cement grouts are slow and inexactly known.
The water-cement ratio is important in controlling the behavior of cement
slurries. When a large number of small openings are to be plugged, a relatively
thin slurry with a ratio of five parts water to one of cement is commonly used.
If a large quantity of grout is accepted without a pressure increase, it is
probably running through a conduit in the material which is to be grouted.
Remedies include decreasing the water-to-cement ratio, adding bridging material
such as gravel, reducing the rate of pumping, and letting the hole stand for
several hours (Cummins and Given, 1973).
Clay Grout—
Clay grout is commonly used to fill small void spaces in weak ground to
resist low pressure gradients. The advantage of colloidal suspensions with clay
is that they can fill voids as small as 0.1 millimeters at a rate of .001 cm/sec
in medium sand. Clay grouts will bond with native clay, unlike neat-cement and
cement-sand grout. However, setting time is indefinite and some clays are
thixotrophic, that is, they may become fluid when disturbed (Cummins and Given,
1973).
34
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5.2 CLEANUP AND RESTORATION
Ion Exchange
Ion exchange is a hydrometallurgical concentration method based on the
selective adsorption of metal-bearing ions onto ion exchange resins. The
resins consist of an elastic, three-dimensional network of hydrocarbon mole-
cules which carry fixed charges. They "are "formed "into' spheri"caT~nbeads ," . \
which range in diameter from 0.5 to 2 mm.
There are two basic types of resins: 1) cationic resins, which exchange
cations; and 2) anionic resins, which exchange anions. Anionic resins are
used for the recovery of uranium. A typical anionic exhange mechanism is
shown in the following reaction:
2 R - Cl" + U02 (CO ) " = R2- U02 (C03)2" + 2Cl"
Resin Uranyl dicarbonate
The resin carrying the chlorine anion is reacted with uranyl dicarbonate (or
tricarbonate, depending on solution pH), causing the complexed uranium to
adsorb onto the resin while the chlorine ion goes into solution. The selec-
tivity of the resin for metal ions is a prime factor in resin selection.
Generally, however, ions having high charges that are opposite, to tRe_cfiajge _of '.¦>
the resin are favored for adsorption; for ions of the same charge, those with
the smaller solvated volumes are favored. The problem of co-adsorption of
metal ions is lessened in the uranium exchange procedure because few metal
ions form aaonic complexes. A partial list of resins commonly used for
uranium recovery is shown in Table\j8. The theoretical capacity of all these
resins is approximately the same; however, actual tests have shown variations
from 77 to 385 KG of U^Og per cubic meter of resin. The wide variation in
loading is due to differences in lixiviant concentration, grade of pregnant
liquor, pH, and purity of the feed solution.
Table '8. Ion Exchange Resins Employed by the In Situ Uranium Mining Industry
Resin Manufacturer
Amberlite IRA 430 Rohm & Haas Company
Dow X 21K Dow Chemical Company
Duolite A-101D Diamond Alkali Company
Ionac A-580 Ionac Chemical Company
Permutit S-700 Permutit Research and Development
Center
35
-------
Figure 5 ; is a schematic illustration of an ion exchange column. The
pregnant leach solutions from the well field pass into the ion exchange column
and percolate through the resin column. The barren lixiviant passes out the
bottom of the ion exchange column.7 It is then .chemically refortified_to
/restore' reagent." 1'ost to^iihe hos~t formation, through .'chemical "and/or sorption
reactions and is'reinjected into the formation. .-Some- prov is ion must ¦ also
>_be incorporated -in alkaline leach "circuits "'for .£aicium_control, since-'ai-
/ ka 1 ine^J.gsch^so.lL^t_i_ons.J~a're jas.ua 1 l'y. supersaturated "with" "respect* .to__calcium
..carbonate¦ Such _prov ision_jnay .be"~ either/upstream or downstream from the,...., .J.
' ion .exchange process"" '"
When available ion exchange sites are filled, the ion exchange column is
either taken off stream (fixed bed) or the most heavily loaded beads are
extracted and fresh ones added (fluidized bed). In the former case, the pro-
cess stream is diverted to another ion exchange column while the_lo_aded beads
are eluted. In the..latter cquntercurrent circulat.ion.,.is._employed. .Wh"en„„. --
/ the .beads are- loaded ,f. the current direction is reversed and the most heavily
loaded "beads, i.e., ""the oldest, are flushed from the column while fresh beads
are loaded at the other end. The fixed bed is most commonly employed since it
requires a less sophisticated mill circuit. The fluidized bed, however, has
certain advantages in that only the most heavily loaded resins go to the elu-
tion stage, and column down time is reduced.
To remove the adsorbed uranium from the ion exchange beads, the original
process is reversed during an elution stage based on the following reaction:
R2 - U02 (C03)2" + 2C1~ = 2R-C1 + U02 (CO^"
The elution process ,'strips.,•.uranium, from the""resi"n-and concentrates it _in.^/V
solution. ' "The • uranium concentration._of "the'.'.preghantf" eluanC• • is.".npp,roximately-
40 to_.6"0/times''greater than that of''the pregnant lixiviant." ' " r ' •
In general, most plants use a chloride based salt (NaCl or NH^Cl) to re-
generate the loaded resin. However, although chloride is an effectxve eluant"",
a small amount will be transferred to the barren liquor and eventually will be
recycled to the injection wells. This buildup in chloride content will
eventually impair the loading capacity of the resin. For this reason some
plants are switching to ammonium carbonate-ammonium bicarbonate. While not as
effective as chloride, . these,,.d6,; not /cause..extraneous ions ..to, be/introd.uced . _ 1
to. the...aquifer."
The stripped beads are returned to the process stream for reloading. In
the fixed bed concept, the column merely goes back on stream, while in the
fluidized bed concept, the beads are returned to the column as fresh beads.
The pregnant eluate goes to precipitation tanks where the uranium is re-
covered as U02- Various systems are used. Conventional resin elution with
NaCl solution is followed by a caustic precipitation. For circuits using
NH^Cl, the pregnant liquor is acidified with HC1 prior to precipitation with
36
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PREGNANT SOLUTION
> RESIN BEADS
BARREN LIXIVIANT
Figure 5.. .Ion Exchange Column
'37
-------
Reverse Osmosis
Osmosis is a process in which two solutions of different concentrations are
separated from the same solvent by means of a permeable membrane. If the
membrane is permeable to the solvent and not the solute, then the solvent will
flow from the dilute to the concentrated solutions until equilibrium is
established. In reverse osmosis, the procedure is reversed by application of
pressure to the more concentrated solution. Thus, it becomes possible to
separate dissolved solids from water, resulting in clarified water and a
concentrated brine solution.
Commercially available systems force water through a semi-permeable
membrane at pressure of 410 to 4,100 kPa (60 to 600 psi). Two types of membrane
configurations are available—spiral wound and hollow fine-fiber. Spiral wound
modules have better-defined flow channels than the hollow fiber modules and
therefore are more readily cleaned if fouled or scaled. The spiral wound
modules also have a lower feedwater pretreatment requirement.
Newly developed systems are highly selective and will reject most metals.
Field demonstrations have shown that for every four liters of influent, three
liters of purified water are obtained and 99% of the dissolved metals are
removed. More recent studies of the in situ uranium industry (Kasper, et al.,
1979) have indicated that on the average, every five liters of influent water
yields four liters of purified water that exceeds potable quality.
Despite its widespread adoption by the uranium industry, reverse osmosis
is not without significant problems. It has proven too costly for adoption by
other industries, coal mining, for example, and for the smaller in situ
operation, it may not be economically practical. Furthermore, waste solutions
require pretreatment, and this can be complex, depending on the nature of the
waste solutions. At minimum, influent solutions with significantly high
concentrations of iron, that is, those operations employing acid lixiviant,
must also maintain pH values below 3.0 to prevent iron precipitation on the
membrane. Perhaps the greatest problem may be the high concentrations of
calcium sulfate or calcium carbonate in influent water. Further concentration
of this dissolved constituents by the reverse osmosis process results in
precipitation of the calcium sulfate or calcium carbonate on the membrane.
Pretreatment processes, such as calcium removal by ion exchange or lime
softening can precipitate the calcium and thus reduce membrane fouling.
Disposal of the resultant brine continues to remain a problem. The size of
evaporation ponds can be reduced significantly but, in areas where net
evaporation does not exceed precipitation, deep well injection is still
necessary and the processed, concentrated solutions may be even more environ-
mentally objectionable. The decrease in volume of the injected solution does,
however, decrease disposal costs. Deep-well injection as a method of waste
disposal is discusssed in Section 5.3.
38
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Pretreatment of Ore-Bearing Aquifers
In order to facilitate the in situ mining process, ore-bearing aquifers
may be treated using a variety of techniques. Usually, these treatments are
aimed at improving the permeability or flow characteristics of the formation.
This may consist simply of producing and re-injecting native groundwater; this
establishes flow gradients and often flushes out intergranular fines. Pres-
surization by air has also been used to "clean" the aquifer prior to injection
of lixiviants at some operations.
Recent work indicates that chemical pretreatment of the formation may
also reduce the formation of calcium carbonate in the low-pressure zones
around production wells. Where potassium carbonate-bicarbonate lixiviants are
used, this treatment also has the advantage of drastically lowering the rate
of consumption of the solvent (Tweeton, et al., 1980). This study tested the
advantages of using potassium chloride as a pre-flush solution.
Permeability loss occurs near the production well screen when CaC03,
which is supersaturated in the lixiviant, precipitates out. Preflushing with
KG1 removes calcium from the orebody prior to leaching with a carbonate lixi-
viant. CaCl2 is more soluble than CaC03 and will not precipitate as readily
when entering the area of reduced pressure near the well screen, thus reducing
the scaling problem.
Test results indicated that permeability loss was reduced with a chloride
preflush before leaching with either NH4CI or K2CO3. The reduction in per-
meability loss was found to be most effective where the loss without the pre-
flush would be greatest.
Uranium recovery percentages were not reduced by the chloride preflush.
In one test using the ammonium carbonate lixiviant with the NH4CI preflush,
the recovery percentage increased. The high cost of NH4CI, however, effec-
tively prohibits its commercial use at this time.
This study also tested the feasibility of using potassium carbonate as a
lixiviant. Potassium carbonate is much more expensive than ammonium carbonate
($27.60/lb-mole vs. $4.08/lb-mole); this cost can be reduced by flushing the
leach zone with much cheaper potassium chloride prior to solution mining.
Potassium chloride satisfies cation exchange sites in the leach zone, thereby
reducing consumption of the more expensive potassium carbonate by 83%. The
advantage of using K2CO3 as a lixiviant is that the baseline potassium concen-
tration is normally high for groundwater and is not considered harmful. Re-
storation parameter levels are therefore easier to achieve.
Should permitting regulations require it, however, it may be necessary to
inject a solution of high ionic strength to remove the potassium ions adsorbed
on the clays in the formation. This depends on the stringency of the restora-
tion parameters regarding potassium. The calcium from the solution produced
during the chloride preflush would be an ideal cation for exchange with
potassium, as it is already in the ore-bearing formation and would not lead to
further restoration problems.
39
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Removal of Ammonium Ions After Leaching
Uranium deposits that occur in calcareous sandstones have presented
special problems to in situ leach operations. Acidic lixiviants cause dis-
solution of carbonate minerals, which subsequently precipitate during proces-
sing, thereby fouling equipment. To avoid this problem, alkaline lixiviants
are widely used. Ammonium carbonate and bicarbonate solutions have become
the preferred solvents in lixiviants. The use of alkaline lixiviants, how-
ever, is not without problems.
Most uranium orebodies contain up to 20% clay. The clay acts as an ion
exchange medium for the leach solution, according to the following equations:
Na Clay + NH4+ = NH4 Clay + Na+
Ca Clay + 2NH4+ = (NH4)2 Clay + Ca4"1"
The selectivity of clays for NH4+ is high and the overall post-leaching con-
centrations of NH4 in the formation can become quite high (in excess of 2000
ppm). If not removed during restoration, the NH4+ ions will be released
slowly by exchange with incoming cations in the groundwater, resulting in
pollution of the aquifer.
Post-restoration concentrations of ammonium on the order of 0.01 to
10 ppm are required if regulations are to be met. Computer models indicate
that such a restoration could take decades if simple flushing alone is
employed. In fact, field restoration tests have shown that it is extremely
difficult to reduce NH4 concentrations to less than 100 ppm even after
flushing with 6 to 10 pore volumes of water.
Mobil Oil Corporation (Yan, 1980) has developed the following three-
step process which an result in a more rapid reduction of the ammonia con-
centrations :
1) The leached formation is flushed with connate water to remove
the initial easily soluble ammonia
2) Chlorinated water or hypochloric solution is injected at a pH
of 8 to 10
3) The formation is flushed to lower the Total Dissolved Solids to
the desired level.
The overal reaction between NH3 and chlorine can be summarized as
follows:
2NH3 + 3C12 6H+ + 6 CI" + N2(gas)
The normal decompositon reaction is quite rapid, producing nitrogen gas
and chloride ion. The overall reaction is irreversible, making the com-
plete removal of the ammonium ion possible; because the nitrogen is removed
as a gas, the volume of water to be disposed of is reduced.
Controlled laboratory experiments have shown that flushing with less
than three volumes of pore water have effectively reduced ammonia concen-
40
-------
trations to less than 3 ppm. The only drawback to the method is the large
volume of Cl£ necesary to treat the NH3 (6 pounds CI2 per 1 pound NH3).
Commercial application of this process has not been reported, and it remains
to be seen if ammonia concentrations can be reduced to less than 1 ppm with
this method.
5.3 DISPOSAL OF WASTES THROUGH INJECTION WELLS
Deep-well injection has become a widely-used procedure for the disposal
of liquid wastes. From 1964 to 1973, the number of waste injection wells
(excluding oil-field brine wells) increased from 30 to more than 280 in 24
states. The injection of brines separated from crude oil production wells
is a common practice in the petroleum industry; over 100,000 of these wells
existed in North America in 1979 (Freeze and Cherry, 1979, p. 454).
The diposal of liquid waste by injection involves essentially the same
mechanical and hydrogeological principles as does the withdrawal of subsur-
face fluids. As in the latter case, formation permeability characteristics
strongly influence the volumes and flow rates of fluids that can be accepted
by a given aquifer, while fluid and chemical characteristics of the injected
liquid may affect equally strongly the behavior of the waste as it moves
through the formation.
Most injection wells are completed in formations 300 to 2100 m (1000 to
7000 feet) beneath the surface. For obvious reasons, disposal aquifers must
be selected only from among those which have no potential for use as suppliers
of water to the surface. It is equally important that no hydraulic connec-
tions exist between aquifers used for waste disposal and aquifers which con-
tain potentially usable groundwater.
In practice, waste liquid is injected under pressure into the formation.
A pressure mound results. The size and shape of this mound varies with rate
and pressure of injection and the ambient flow characteristics of the ground-
water already in the formation; generally, however, as injection continues,
the presure mound spreads over a widening area. The spread of the injected
waste itself increases at a slower rate as the formation water is displaced
before the advancing front (Freeze and Cherry, 1979).
The volume of wastewater to be handled is of primary importance on that
it limits the feasibility of using subsurface injection in many instances.
In areas of favorable geology such as the Texas Gulf Coast rates of injec-
tion through a single well can be as high as several hundred gallons per
minute on a sustained basis. In contrast, in the interior geologic basis
of Wyoming and New Mexico injection rates are more commonly limited to
tens of gallons per minute. This difference in injection reservoir capa-
bility is one of the reasons why injection wells have been frequently used
in conjunction with uranium leaching operations in the Texas Gulf Coast
region, whereas impoundment and evaporation has been the principal disposal
method selected for operations in the Rocky Mountain states.
Systems for injection of low level liquid radioactive wastes are care-
fully designed and constructed to minimize the potential for contamination
of useable groundwater. Figure 6 diagrammatically shows the design features
that are routinely incorporated in such injection wells. The actual de-
41
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PRESSURE GAGE
NJ WELLHEAD PRESSURE
FRESHWATER-BEARING -vo
.SURFACE SANDS AND.I' v ^
;Gravels ;
u "'°''
^IMPERMEABLE SHALE
CONFINED FRESHWATER-
BEARING SANDSTONE
IMPERMEABLE SHALE:-:-:1:-:
IMPERMEABLE SHALE
PERMEABLE SALTWATER
.•BEARING SANDSTONE
^.INJECTION HORIZON
KD PRESSURE GAGE
.• -v'; ?. •:; ¦ - ;• ;.o\. •. '•. •
= .~ •' * •''/"«.* *' r '' 'i'*' * -
,, t \ -o',' , . - ^ .0 . . ' *
c--' 0 *.o'' a''¦ 1; •*•
• _» - - _o_ _ * . _ _ — • a i
"SURFACE CASING SEATED
BELOW FRESHWATER AND
CEMENTED TO SURFACE
INNER CASING SEATED IN
OR ABOVE INJECTION HORI-
ZON AND CEMENTED TO
SURFACE
-r _ IN[JECTIC>_N__T_U B IfJ G: ^
ANNULUS FlULED WITH
N 0 N CO R R_0_S IV EFLUJ D_=:
PACKERS TO PREVENT"
FLUID CIRCULATION IN*:
ANNULUS
OPEN HOLE COMPLETION
N COMPETENT STRATA
IMPERMEABLE SHALE
Figure 6.. Industrial, Waste Injectioil Well Completed; iri
_ /.Competent^ Sandstone (after Warner. 1965) ....
42_
-------
sign of a particular well is dictated by the site geology and wastewater
volume and chemistry.
In addition to technical and economic factors, Federal and State regu-
lations must be considered when the use of injection wells is contemplated
(Appendix B). In particular, the recent promulgated Underground Injection
Control Regulations (U.S. EPA, 1980) dictate many aspects of injection well
design, construction, testing and operation.
The local geologic and hydrologic conditions necessary for successful
and safe subsurface injection are shown in diagram form in Figure 7. Very
briefly, a potential disposal site and injection interval should have the
following characteristics (Warner and Lehr, 1977):
a. Injection interval should be sufficiently thick, with adequate porosity
and permeability to accept waste at the proposed injection rate with-
out necessitating excessive injection pressures.
b. Injection interval should be of large enough areal extent so that
injection pressure is minimized and so that injected waste will
not reach discharge areas.
c. Injection interval should be "homogeneous" (without high-permeabi-
lity lenses or streaks), to prevent extensive fingering of the waste-
vs-formation water contact, which would make adequate modeling and
monitoring of waste movement extremely difficult or impossible.
d. Overlying and underlying strata (confining bed) should be suffi-
ciently thick and impermeable, to confine waste to the injection
interval.
e. Structural geologic conditions should be simple, that is, the site
should be reasonably free of complex faulting and folding.
f. Site should be an area of low seismic activity so that the hazard
of earthquake damage or triggering of seismic events is minimal.
g. Lateral movement of fluid in the injection interval should be slow
under natural conditions.
h. Formation-fluid pressure should be normal or low, so that excessive
fluid pressure is not needed for injection.
i. Formation temperature should be normal or low, so that the rates
of undersirable reactions are minimized, including corrosion.
j. Wastewater should be compatible with formation fluids and minerals
or capable of being made compatible by treatment, emplacement of
buffer zone, or other means.
k. Formation water in the disposal formation should be of no apparent
economic value, that is not potable, unfit for industrial or
agricultural use, and not containing minerals in economically
recoverable quantities.
43
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"CLCSEfi" 2CSES, NO
S'JBSwRIACS DISPOSAL
ALLOWED
YES
YES
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SATOJU. ?£S017RC£S
and ?£Sfxrac2 uses
F7ALWri3N OF
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PRIORITIES
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EVALUATION CP
LOCAL
HYDRODYNAMICS
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EVALCATICH CF
LOCAL
sravcruRE
disposal fowaticm
OF ADEQUATE THICKNESS
ECIE*T, PERMEABILITY
AW P0RGSI7Y
PICZOHETRIC MAPS,
SECEAPjCE/OISCdARCS
DATA. ETC.
02TAILE0 GEOLOGICAL
MAPS, Sj'IS'JBFACE
DATA, ETC.
DETAILS STRUCTURE
KA?S, SUBSITRFACE
3aTA, SIC.
-VALUATION OF
LOCAL
STEATIGRAPKY
subsurface
DISPOSAL CONFLICTING
WITH R£C0V1KY OF
COAL. CEL,GAS, MTXERaLS
POTENTIAL 3AS CP.
c**SH-VA?£& STORAvi,
rRE'a-WATER R-SC-.-RCZ5
HOMOGENEOUS
~3RMmTION» AE EQUATE
?ORC S IZf. ?EE>£5ABIL IT/,
IDU FLl'lO ?BISSUR£,
SLCV HCRI20!JTAL >93VtXEKT
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VERTICAL GRADIENT,
.'
-------
1. Injection interval should be adequately separated from potable water
zones, both horizontally and vertically.
m. Waste injection should not endanger present or future use of mineral
resources (coal, oil, gas, brine, others).
n. Waste injection should not affect existing or planned gas-storage
or freshwater-storage projects.
o. No unplugged or improperly abandoned wells should penetrate the
disposal formation because other resources in the vicinity of the
disposal site could be contaminated.
At the same time that the geologic and hydrologic conditions are being
evaluated, the suitability of the wastewater for injection must be deter-
mined. Table 9, lists the factors to be considered in determining the
injectability of a wastewater.
A major hazard associated with the practice of wastewater injection in
many areas is the presence of abandoned, unplugged wells, which may provide
vertical conduits for inter-aquifer migration of contaminants. There may be
as many as 1 million unplugged wells in North America, the locations of which
are unknown (Freeze and Cherry, 1979).
As has been demonstrated in the solution-mining of uranium, the excursion
of injected liquid through mechanical faults in well casing is a serious
Table 9. Factors to be Considered in Evaluating the Suitability of
Untreated Wastes for Deep-Well Disposal
A. Volume
B. Physical Characteristics
1. Density
2. Viscosity
3. Temperature
4. Suspended solids content
5. Gas content
C. Chemical Characteristics
1. Dissolved constituents
2. pH
3. Chemical stability
4. Reactivity
a. With system components
b. With formation waters
c. With formation minerals
5. Toxicity
D. Biological Characteristics
45
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potential threat to usable groundwater supplies. Careful work and the use of
durable materials in well completions may overcome this potential threat on a
practical level; however, continued and careful inspections and monitoring are
necessary to ensure the continued integrity of injection wells.
46
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SECTION" 6
IN SITU MINING OPERATIONS AND THEIR EFFECTS ON WATER QUALITY
In this chapter, partial case histories of operating solution mines are
presented, in order to provide practical information on the effects of mining
operations on ground and surface water. Information included here was ob-
tained from the public record (i.e., NRC Dockets) and from interviews with
representatives of mine operators and regulatory agencies.
6.1 THE CROWNPOINT MINE* > MCKINLEY COUNTY, NEW MEXICO
Introduction
Crownpoint Mobil Energy Minerals Division (Nufuels Corp.) operates an in
situ uranium leaching project in McKinley County, New Mexico. This pilot test
site is located 8 km (5 miles) northwest of the town of Crownpoint, on land
leased from the Navajo Indian Reservation (Figure '8). It is on the Chaco
Slope, north of the northwesterly trending Zuni uplift along the southwestern
flank of the San Juan Basin of the Colorado Plateau. The terrain is charac-
terized by broad expanses of open range land, bounded by cuesta ridges .such
as Mesa de los Lobos, 8 km (5 miles) south of the project site-* Elevation at
the site is approximately 2,000 m (6,700 ft). The east-west-trending escarp-
ment of Mesa de los Lobos rises to 2,400 m (8,000 ft), and is the northern
edge of the Continental Divide in this region.
In the region, surface waters are limited to intermittent streams with
broad valleys, heading in incised arroyos against the mesas. Flow is
northerly to the San Juan. Vegetation consists of grassland and scrub trees.
The climate of the San Juan Basin is semi-arid, with an average rainfall of 26
cm (10.22 inches). Most of the precipitation occurs in late summer as
thunderstorms, and there is no base flow in the numerous stream channels of
the project area. All channels flow northerly from the high mesa south of
Crownpoint and eventually join Indian Creek, an intermittent stream which is a
tributary of the Chaco River. The Chaco River, also an intermittent stream,
flows northwest 72 km (45 miles) to the San Juan River, a tributary of the
Colorado River.
Scream gradients in the arroyos along Mesa de los Lobos are initially-high,
as the'escarpment drops approximately 390 m there, but level out in the gently
rolling basin lands of the project area. Most precipitation either infiltrates
or evaporates before it reaches the larger stream beds to the north. ¦ The
possibility of flooding in the area is very slight and would not affect the pilot
site.
The Pilot Plant
Mobil's Section 9 pilot in situ leaching operation occupies 2 ha (5
acres) of an allotted lease of 65 ha (160 acres), which was obtained in 1972.
It consists of the wellfield, processing facilities, an evaporation pond, and
access roads to all wells (Figure 9). The well field dimensions are 61 ra
(200 feet) by 61 m (200 feet). The wells are arranged as four 5-spot patterns.
The corner wells of each 5-spot pattern are used as injector wells. All wells
-------
NEW MEXICO
NAVAJO INDIAN
RESERVATION
_.J
LOCATION DIAGRAM
Standing Rock
,Crowri point
PROJECT AREA
Gallup
,40,
miles
Thoreau
KILOMETERS
MC KINLEY COUNTY
"VALENCIA COUNTY
I
Grants 14ml.
Figure v8. Location Map, Crownpoint Mine
-------
ACCCV5 HOAO fHOM
OU-?«W
OPF&ATOft In
FACILITY— f
TiuRKACF. PROCCSSiNG MCII 17 0S
WASJt O^rOSAl. POND
?A0'X 2*0' TOP
"1 INJECTION well
PRODUCING WELL
t"l MONITOR WELL
Figure '.v9. Crownpoint Pilot Plant
-------
are capable of either injection or production to facilitate complete ore zone
leaching in a commercial operation. Well spacing is 30 m (100 feet) between
corners.
The lixiviant is composed of a sodium carbonate-bicarbonate solvent and
hydrogen peroxide. The ore zone is in the Westwater Formation, approximately
610 m (2,000 feet) beneath the surface. The uranium occurs as coffinite, in a
carbanoceous matrix, with quartz and feldspar.
Six monitor wells surround the production field. The New Mexico Environ-
mental Improvement Division (NMEID) required that the wells be place in a cir-
cular pattern with a 120 m (400 ft) radius from the center production well with
no more than a 60° arc between the monitor wells. One well (9u 201) was set
only 91 m (300 ft) away from the center well because of a property boundary.
In addition, NMEID requested that 3 more wells be placed to the northeast, in
the direction of groundwater movement. The central well in this direction is
perforated in the Dakota sandstone and the Westwater Canyon aquifers. Monitor
well 9u 207 is in the northeast corner of the production pattern and was
completed in the Dakota Formation to detect any vertical excursions. All the
other monitoring wells were completed in the Westwater Formation to detect any
horizontal excursions that might occur in the ore-bearing unit.
Hydrogen peroxide was used as an oxidizer in this plant. The depth of
the ore body (610 m or 2,000 feet) made it difficult to use oxygen, which
costs less, but which must be dispersed as a gas in the liquid lixiviant.
Mobil now has the technology to deliver the oxygen at the necessary pressure
to this depth, and plans to utilize oxygen in subsequent operations in the
Crownpoint area. The H2O2 and the Na2C03 are mixed at the surface injection line.
Oxygen transforms the quadravalent uranium to an oxidized hexavalent state,
and the bicarbonate ion combines to form a soluble uranyl tri-carbonate complex.
The pregnant lixiviant is pumped to the surface, fed through a sand trap to
remove entrained sediments, and pumped into storage tanks for loading into the
ion exchange column.
The concentration of uranium in the pregnant lixiviant ranges from 50 to
250 ppm. The leach rate is typically adjusted to 6.3 L/s (100 gpm) in this
operation. High concentrations of molybdenum occur in this ore body, and
this metal is oxidized and solubilized along with the uranium.
The wells were drilled to total depth with a 20 cm (7-7/8 inch) drill bit
and cased with 13.97 cm (5-1/2 inch) steel, internally plastic—coated, casing
to the top of the Westwater formation. A 13.97 cm (5-1/2 inch) fiberglass
casing was set from the top of the Westwater to the bottom of the drill hole.
Use of fiberglass casing in the lower part of the well will prevent corrosion
caused by the oxidant in the injection stream. Hydrogen peroxide, the oxi-
dant, is injected with the solvent. The well design shown in Figure 10 will be
used when gaseous oxygen is the oxidant (it will be injected through a 1.59 cm
(5/8-inch) diameter, fiberglass injection line). This tubing string terminates
just below a packer set at the top of the ore-bearing zone in the fiberglass
casing. The lixiviant is injected through a separate 5.08 cm (2-inch) diameter
fiberglass tubing string which also terminates just below the packer. Centrali-
50
-------
INJECTION WELL
PRODUCTION WELL
}
Leachate Injection thru
2" Fiberglass Tubing
0^ Injection thru 5/8"
Fiberglass Tubing
8-5/8" Steel Casing Shoe,
Cemented from Surface to 60'
5-1/2" Steel Casing,
Surface to 1850*
¦ llowcolite and Cement,
to Surface
5-1/2" Fiberglass Casing,
1850' - 2080'
! Perforations,
1955' - 1985*
5-1/2" Fiberglass Casing Shoe
Total Depth 2100'
Production
8-5/8" Steel Casing Shoe,
Cemented from Surface to
60'
5-1/2" Steel Casi ng, Plastic
,Coated on Inside, Surface to
1850'
5-H.P. Reda Pump; 28 gpm
at 300 ft. head
Howcolite and Cement, to
Surface
5-1/2" Fiberglass Casing,
1850* - 2080'
Perforations,
1955' - 1985'
5-1/2" Fiberglass Casing
"'ioe
otal Depth 2100'
J
Figure 10. Crownpoint Well Completion Design
-------
total depth to surface by circulation of the cement through the casing and up
zers are used to center the well casing and the well casing is cemented from
the annulus to the surface.
The fiberglass casing opposite the uranium ore-bearing zone is perforated
by jet perforators over an interval of 6 to 8 m (20 to 25 feet). The total
flooded zone is 18 to 23 m (60 to 75 feet) thick. The zone to be leached is
injected with air under pressure prior to mining to improve its permeability.
The air pressure, however, must be kept below 6,900 kPa (1,000 psi), in order
to avoid shattering the formation. The wells conform with all applicable Fed-
eral and New Mexico well completion standards.
The casing design for the production wells is similar to that of the in-
jection wells. However, no packer was used in the production wells. Instead,
each well contains a 3.7 kw (5-HP) submersible pump, which is attached to a
production tubing string and set several hundred feet below the surface. The
production tubing is coated on the inside with plastic to prevent corrosion
of the steel by any residual oxidant in the production stream.
Groundwater Effects
The baseline water quality was analyzed in the Crownpoint area and for
all wells on the project site when drawdown tests were conducted. Table 10
compares average baseline parameter levels for the aquifers affected by the
pilot mine with State and Federal drinking water standards. Table 11 is a
summary of various baseline radiation parameters sampled prior to solution
mining from wells in the region. High concentrations of natural uranium in
the Crownpoint public water supply and the Thoreau public water supply are
within EPA established parameters for drinking water in the Grants Mineral
Belt (Table 12).
A computer model was developed to simulate underground leachate flow and
to calculate the leachate front advance within the ore body during solution
mining operations. Reservoir and ore body data were obtained from pumping
tests and core analyses which were done in wells on the mine site.
The leachate is produced at about 1.3 L/s (20 gpm) per well. The ion
exchange system can accept flow rates as high as 6.3 L/s (100 gpm), but nor-
mally runs at about 4.7 L/s (75 gpm). Flow rates for injection and production
wells are controlled separately to enable manipulation of the hydraulic bal-
ance within the production zone.
During the leaching phase, approximatley 4.6 L/s (73 gpm) of fresh leachate
are pumped down the injector wells, and 4.7 L/s (75 gpm) retrieved. The 3%
excess is bled to the evaporation pond from the ion exchange to control excess
chemical buildup in the lixiviant and to maintain a cone of depression.
The production zone at Crownpoint is in the Westwater "A" and "B" zones
which are delineated by shale units within the Westwater member. These shale
units confine the movement of liquids in the production zone.
The NMEID has proposed that the following parametric variations which
would constitute a significant increase, or potential excursion:
52
-------
U-t
Tabic
1Q. Ground Water Quality.in
rhn Crownpoi nt
Region
M*:w KckI^u
Nat, i:iterl.-n
i
! &
CrontiJ Watpr
Prinaiy Drink-
We atvu r e r
Lowe I
1 .nyi't
Htiiiidai Js
ing W/itei R«**p,»
Pav*r#n:tcM '
Canyon Men:.
(la 1 1 up SOS
Gallup SI)S
: • JH1L
(Uec . . 1925}
1 !>« (SU)
/,9*«-5
7. Ci >H . 4
i Lund. (;wiiua)
74« -X72S
stoaiso
CibO
_
j AlkjIiriUy
14J0
150 -220
-
-
17H
178-1-2 {6
190-194
_
I Ca J
S.U-71
0,2-32,0
\2>\Q
cri
20 *4
3.0-/. '>
2jUrt
-
' i*
¦ 0 J . ¦>
O.J2HJ.d4
'0.^6
1 .6
i.-w.i
.v.i
12 >/2
i .3 -9 3
-
i M-jKo
0.6-2.0
0.2*8. 1
$.9-9.2
; N-jn-N
vO. 1 *12
¦ 0. !
10''
10
f 3
-
0.0?-HI. H»
0.20
.
_
K
J . 1 -?.(!
2-4 *b. >
1.6 *2 . 3
Sit*,
-
i 5*54
/9
-
H,i
82 "'as
h<)<> 'jH
120>2.'(y
_
S«J,
4 y ^>60
88 >4 20
S?4(U4
600J
.
Al"(yg/I>
-200 oco
'100*500
vIOO
1000*
-
a-i (wg/n
<2 *20
J 0 * i 0
<10
I00C
50
l)a (VR/1)
<^1)
<100*100
100
10fWc
iOOD
Be (yg/l)
-
^'1
-
H (ue/1)
150 '4^0
IS0-»1S()
}V)e
_
€d 50
, ^
1000
Cyunide t :¦ B./1 >
-
<10
^100
200
_
Ft'
a.Ul>2.00
•0.1-2.5
0. 39
.J)d
rb <
< Ul 'i 'i
<1
• f3. ?
<0.4
2
«.i (a;;/))
60 '1330
«-i
< i
1000*
tU
• V)
<•10
<10
200*'
_
, Phenols
-
<1
-
rd
J
_
Si: ilig/l)
<1 »J
u
<10
¦)0C
10
H (Mg'i)
-10
< 1
*n)
•50
•-10
- 1U
-
la ImtI)
mo-moo
u7-*sm
*)¦*
io.ooo]}
TDS
IflllM?'!'}
^00 *760
*2/-748
1000.
_
. Co (i-e/i)
<3
< I
<1
¦iO1-'
-
Km:. Mux
I'crinisii-ib
LjuiIL fur
Dr ink inp,
W4t*sc
US PUS
(J96?)
250
i -2.4
(O.b-1.7)
"I
250
">'[ei n rrporiod as Mg/I vmlur,;; (toted oi her wIh^ .
\>hi-n iin cxtuMng pli or rmiociitrrt t ion »f ar.y wufaoinant exceeds ihe btand-nd specified, ilie r.xl&ting pit or cuncefilrrtil <>n
ihest startdjtds .shall apply lt> c it£* dissolved portion *jf the cuntaj»iDi ruercuty (total) .
SfaiuJaidsj i\u human healib (ptiuictry).
£»L.'trul.-trd«j for flom<»st It; u.'if^r supply (so.ratui.ity).
i>la«dasds foi ii r iihc, dl-,o include* human health and d«»ue*t Lc waLei Supply hiandaids,
ftecoucni'nded limit for drinking w.itm .
For valets used continuously on all
ihill be th<- «1 lovable limit.
-------
'iam£_ling_ hoc,ion
AntisnzJ; slock t;ink
In Section 16 E
Well 4il9; Seclion
4 NF.
Wel l I 7-If.5015 I ;
Set- I inn 4 SW
Cr'v.-npoint public
watel" supply
Tlnucau public
walcr supply
We 1 I BU12; Sect ion
8 ME
W?ll 41.60; Sci ( Ion
4 NK
11/04/75
0S/I1//6
08/28/76
I 1/08/76
1 1/04//!>
03/12/7ft
00/28/76
11/08/76
i 1/04/75
OS/12/76
08/28//6
11/08/76
I I/0S//5
05/12/76
08/28//6
I I/08/76
05/12/76
OR/78/76
1 I /08/76
11/04/7 ">
08/28/76
Grn;;:;
(pjy/ii
0. 1
10.3
*0. 2
10.3
I • 0
10.4
Groundwater in
the' Crowripoint Region
f.ross
0
u
lh23°
1' is solved
R,j2h
(pci/i)
Aii&Zll
(vet/I)
2.9
0.71
40120
>0.6
n. 21
_
0.70
0. 1
10. 1
0.31
--
0.056
0.7*0.1
0.1810.02
0 . 33
0 .6*0. 1
0.2S-.0.02
4-6
0.05
1 10 < 70 ¦
t0.6
0.5?
0.73
to . 1
±0.1
o. /y
—
0- 14
1 . HO. 2
0.4510.01
0.16
2.910.3
1.0210.04
—
O.06
--
0.81)
0.29
~0. 1
to.2
0.14
~
0.64
0.6 »0.1
0- 38'0.02
--
0. 21
0.310. 1
0.72*0.03
2.1
3.4
__
<>(M,'()
10.6
0. 11
—
4 . 7
0.4
tO. 3
0. IB
7.4
1.filC.7
0. 79 *0 •02
--
5.2
2.2 <0.2
0.2/10.02
.....
7.8
0.0
i0.2
0.20
—
7.0
l.lt0.2
0. 37+0.02
—
8.2
2.010.7
0.2 310.02
0.03
--
0. ?flc
__
0.095
1 .2 Ml. 2
0-<>~(). 03
-------
Table .12. •
Groundwater Quality in the Grants Mineral Belt"'"
Background Levels in Groundwater
Radionuclide Range Average
Radium-226 0.060 - 0.310 pCi/1 0.160 pCi/1
Polonium-210 0.270 - 0.570 pCi/1 0.360 pCi/1
Thorium-230 0.013 - 0.051 pCi/1 0.028 pCi/1
Thorium-232 0.010 - 0.024 pCi/1 0.015 pCi/1
Natural U 21 to 100 ug/1 52 ug/1
Radium and Gross Alpha Concentrations for Municipal Water Supplies
Location
Radium-
-226
Gross Alpha
Grants
0.42
+
0.022
19 + 132
Milan
0.14
+
0.01
12 + 10
Bluewater
0.22
+
0.01
8 + 10
Gallup
0.68
+
0.03
10+9
Paguate
0.18
+
0.02
2 + 4
Churchrock
0.12
+
0.01
3+7
^"Data extracted from ORP/LV-75-4, US EPA
2
All error terms are at the 95 percent confidence level,
from: Mobil Oil Corp., 1978.
-------
Conductivity: a 25 percent increase above the highest baseline
value of all the wells,
Uranium: a 5 mg/L increase above the baseline value, and
Sulfate: a 10 mg/L increase above the baseline value.
Biweekly data reports are filed for pH, conductivity, sulfate, uranium,
molybdenum, sodium, gross alpha and gross beta values in the monitor wells.
In the latest available quarterly report (covering November, 1979, through
January, 1980), the operators stated that none of the permitting criteria had
been exceeded.
Processing and Waste Disposal
The uranium is extracted from the pregnant liquor by an ion-exchange
process. The barren lixiviant goes from the ion-exchange adsorption column to
a surge tank, where additional CCL and NaOH are added before reinjection to
the ore body. The 0.06 to 0.13 L/s (1 to 2 gpm) bleed stream to the evapora-
tion pond (Figure 11) makes up 75% of all discharges entering the pond. A
small portion of this bleed stream also enters the elution circuit and is
eventually disposed of as excess decant. This stream contains up to 5 ppm
U3°8"
The loaded resia is transferred to the elution column where the uranium
is stripped from the resin. The fresh resin is returned to the top of the
loading column to repeat the circuit. An acid regeneration system was in-
stalled in this loop to remove calcite from the resin. Pregnant eluate is
composed of:
Concentration Range
Constituent (ppm)
Chloride
20,000 -
30,000
Carbonate
2,000 -
5,000
Bicarbonate
10,000 -
20,000
Sodium
20,000 -
30,000
Sulfate
1,000 -
3,000
Calcium
50 -
300
Uranium
6,000 -
15,000
A circuit takes the precipitate and the decant to a thickener where a
spiral classifier stirs the precipitate at the bottom and the barren eluent
floats to the top as a decant. The decant is stored and regenerated before
being returned to the elution column. A small percentage (0.06 L/s or 1 gpm)
is bled to remove excess NaCl and diverted to the evaporation pond.
56
-------
NaCI
C02
u>
"-vl .
M
NaOH
ION
XCHANGE
ELUTIOf
DISPOSAL
PRECIPITATION
C02
(NaOH)
u3oe
(TO FILTERING,!
DRYING) I
OXIDANT
INJECTION WELL
-r~rirry
SURFACE -E3S3:
r/v // J //// /~7
PRODUCTION WELL
7~7 7 7~7~7~7~7
PUMP
- - ^ 9 m a _
K-.-!*-) LEACHATE CIRCUIT
i
| | RESIN TRANSFER I
Effgj ELUTION CIRCUIT I
URANIUM
-LESS PERMEABLE FORMATION:
Figure
11. Crownpoint Process Plant Flow Chart
-------
An evaporation pond is located just west of the well field and processing
facilities (Figure 9). Total pond capacity is approximately 7.6 million liters
(2 million gallons), which can accept flow rates of 0.32 L/s (5 gpm) for one
year. This figure is over twice the bleed stream rate from the lixiviant and
elution circuits. The pond will also provide extra disposal capacity in the
event of a lixiviant excursion in the well field, or spills anywhere in the
process circuit. It also provides a site for the disposal of chemicals from
the testing lab and brine from the reverse osmosis unit during restoration.
The surface area of the pond is designed to evaporate 0.15 L/s (2.3 gpm)
liquid at half volume.
The evaporation pond leak detection system consists of a riser from the
PVC drain underlying the pond and four shallow wells at the lagoon perimeter.
Water samples from these are analyzed bi-weekly for uranium, sodium, bicar-
bonate, and conductivity. No excursions have occurred since plant operations
began.
Restoration
The 14-month restoration phase of the Crownpoint Section 9 pilot plant
began in November, 1980. The New Mexico Environmental Improvement Division
(NMEID) requires that the 27 parameters for drinking water standards be re-
turned to near-baseline conditions.
Restoration is being accomplished by withdrawing groundwater from the
leach zone aquifer at 4.4 L/s (70 gpm), passing it through the ion-exchange
unit and then running the effluent through a reverse osmosis unit. The clean
water, or permeate, is then reinjected.
The permeate leaving the reverse osmosis unit for reinjection is moni-
tored every hour at a small testing laboratory on the mine site. Chloride and
molybdenum levels are tested by titration to insure that the water is of suf-
ficient quality to be injected to an aquifer used for drinking water. A
composite sample from every shift goes to a larger laboratory near Crownpoint
at Mobil's Nufuels field office for a re-check. Mobil will sample the permeate
stream biweekly to determine values for the existing excursion monitoring para-
meters of conductivity, uranium, sulfate, molybdenum, and sodium. A quarterly
analysis will include testing of all parameters required by the State of New
Mexico Water Quality Control Commission Regulations, plus gross alpha, gross
beta, Ra228f combined Ra^26 and Ra^®, Th^30> Pb^O, spcific conductance,
and alkalinity. Brines recovered from the reverse osmosis unit are pumped to the
evaporation pond for disposal.
6.2 THE EL MESQUITE MINE, DUVAL COUNTY, TEXAS
Introduction
The El Mesquite Mine of the Mobil Oil Corporation is located on 906 ha
(2,240 acres) of land in Duval County, 6.4 km (4 miles) east of Bruni, Texas
(Figure 12). Forty-five production zones have been defined; they range in
size from 0.97 to 14 ha (2.4 to 35 acres), within the property.
58
-------
281
44
lAlic*
m
"^MOBIL OIL
EL MES QUITE
MINE-.
159,
Brgni
[285,
GULF
OF
MEXICO
MEXICO
miles
: " Fipure 12, Location Map, El Mesquite Mine
i __
59
-------
Exploration leading to the development of the El Mesquite Mine began in
1969 at the O'Hern lease. During the ensuing years, new leases were added
until the total lease block encompassed 3,240 ha (8,000 acres), of which 906
ha (2,240 acres) were named the El Mesquite property.
Exploration was followed by injection and production flow-rate tests
using water. In 1975, a pilot plant was constructed on the O'Hern property.
It was started as an 5 L/s (80 gpm) operation and scaled up to higher flow
rates of 32 L/s (500 gpm). In 1977, well field development began and in
mid-1978 plant construction was initiated. The project was completed and
brought into production September 18, 1979.
The El Mesquite Mine site lies within the Gulf Coastal Plain physio-
graphic province. This area is characterized by low rolling hills with maxi-
mum relief at the mine site less than 10 meters (30 feet). Red-brown fine to
medium grained Holocene sands cover fifty percent of the mine site with the
remainder consisting of"outcropsof the Goliad Sand, of Late Pliocene age.
Vegetation in the mine area consists of a thick growth of mesquite, sage,
mountain laurel and cactus.
The uranium ore deposits occur in the Soledad Conglomerate, or middle
member, of the Catahoula Formation of Miocene age. The Soledad Conglomerate
averages 76 m (250 feet) in thickness within the mine area. It consists of
interbedded gravels, sands and minor shale beds all of which were deposited in
a fluvial environment. The major production horizon is restricted to a 15 to
24 m (50 to 80 foot) thick zone composed of interbedded sands with local shale
lenses. The sands range in grain size from fine to medium. Both sands and
clays are highly tuffaceous. The lower member, or Fant Tuff, averages 152 m
(500 feet) thick in the Bruni area. It is comprised of tuffaceous silt and
silty clay with lenses of fine to very fine sand. This member is a major
aquitard and has been recognized in the past as water of .jus enable 'q.u'a'1'ity.
The Soledad Conglomerate is overlain by the Chusa Tuff, a clay-rich unit
which functions as an aquiclude at the mine site. The Catahoula Formation is
underlain by the Frio Formation. This formation was not encountered during
drilling and was not expected to be affected by leaching of the uranium ores
in the overlying Catahoula Formation.
The mine area is situated along the northeast flank of the Rio Grande
Embayment. Sediments dip east-southeast at one to two degrees 20-40 m/km „
(100 to 200 feet per mile). The only known notable structural features within
Duval County are three small growth faults with less than 61 m (200 feet) of
throw. These strike northeast-southwest and dip steeply to the southeast.
They do not intersect the mine site.
The drainage basin upgradient from the mine lies partly in Duval County
and partly in Webb County to the west. All stream channels within the mine
area are dry except during and briefly following periods of heavy rainfall.
Mesquite Creek is the only intermittent stream that crosses the mine area.
The mine lies in an "undefined" area, for which insufficient data are avail-
able to allow use of available analytical methods for estimating flows in
ungauged watersheds.
-------
Groundwater
Fresh to moderately saline groundwater occurs in three stratigraphic
horizons within Duval County. The three aquifers are located in the Cata-
houla Sand, the Oakville Sandstone, and the Goliad Sand. The aquifers are
generally confined except at shallow depths in the outcrop areas. At the
mine site the Oakville Sandstone is absent, the Catahoula and Goliad Sands
constituting the only aquifers.
In general, groundwater movement within the region is to the southeast.
The average gradient is 2.1 m/km (11 feet per mile). Centers of heavy pump-
ing by municipalities and ranchers have locally altered the regional grad-
ient. Average groundwater velocity is approximately 463 mm (0.152 ft) per
day.
As only regional-scale hydrologic information was available for the mine
site, Mobil conducted detailed hydrolic studies of each production area prior
to operation. These tests indicated that there are no boundary conditions
and there do not appear to be any significant variations in permeability over
the subject area. The mean permeability is 282 millidarcies. A slight in-
crease of permeability, however, was noted within the production area. It
was felt that because of their fluvial origin, the sediments would vary
widely in local permeability. Tests of cased wells in the underlying aquifers
indicated no hydrologic interconnection within aquifers during the above pump-
ing test. No overlying confined aquifers were detected during these investi-
gations.
Baseline values of water quality for the mine area and each production
zone were established prior to solution mining. In addition, water quality
was analyzed from all domestic water wells within a two-mile radius of the
mine. Table 13 shows values of baseline water quality compiled from samples
taken from regional wells. The wells were not selected geometrically, but
rather so as to provide the maximum amount of data on the geochemistry of the
groundwaters within the mine area.
In general, the regional groundwater quality in the mine area is variable
due to the presence of differing geochemical environments in the subsurface.
Groundwater from reduced zones is of significantly better quality than that
from oxidized zones.
The fact that the quality groundwater was found to vary regionally
established the need to monitor groundwater quality within each production
zone, as final restoration values generally must be within 10% of baseline
values.
Table 14 summarizes the baseline water quality for the EOA #1 production
zone. Note the major differences in several parameters when compared with the
regional values. Metals, in particular, vary in abundance over several orders
of magnitude, which reflects the presence of reducing conditions in the pro-
duction zones.
61
-------
Table 13.' Baseline Groundwater Quality in Region of El Mesquite Mine
Constituent
Calcium
18.18
mg/1
Magnesium
5.50
mg/1
Sodium
348.68
mg/1
Potassium
7.63
mg/1
Carbonate
5.20
mg/1
Bicarbonate
265.75
mg/1
Sulfate
86.65
mg/1
Chloride
420.32
mg/1
Fluoride
0.74
mg/1
Nitrate
20.60
mg/1
Ammonia
0.41
rag/1
Arsenic
0.02
mg/1
Barium
0.20
mg/1
Boron
1.58
mg/1
Cadmium
0.01
mg/1
Chromium
0.03
mg/1
Copper
0.02
mg/1
Iron
2.48
mg/1
Lead
0.05
mg/1
Manganese
0.05
mg/1
Molybdenum
0.30
mg/1
Nickel
0.02
mg/1
Selenium
0.01
mg/1
Silica
19.86
mg/1
Silver
0.02
mg/1
Urani urn
0.11
mg/1
Vanadium
0.20
mg/1
Zinc
0.03
mg/1
Radium 226
4.39
pCi/1
pH
8.09
std.
TDS
1,120.25
mg/1
Conductivity
1,894
umhos
Alkalinity
221.25
std.
SOURCE: Mobil Oil Corp., 1979.
-------
Table 14, Baseline Water Quality, EOA #1 Production Zone
El Mesquite Mine
Parameter Average Value Unit
(9 wells)
Calcium
6.16
mg/L
Magnesium
0.79
t!
Sodium
382
tt
Potas's'iuir.
7.96
tt
Carbonate
6.4
tt
Bicarbonate
234
M
Sulfate
58
M
Chloride
423
tt
Fluoride
0.50
tt
Nitrate-N
2.8
! f
Silicon
17.5
tl
PH
8.43
Std.
TDS
1071
mg/L
Conductivity
1885
|Jmhos
Alkalini ty
202.8
Std.
Arsenic
0.007
mg/L
Barium
0.117
Boron
0.925
Cadmium
0.0005
tt
Chromium
0.0046
M
Copper
0.015
If
Iron
0.12
tf
Lead
0.119
II
Manganese
0.014
11
Mercury
0.0002
It
Nickel
<0.01
H
Selenium
0.004
f 1
Silver
<0.01
M
Zinc
0.024
II
Ammonia
0.023
tl
Uranium
0.039
tt
Molybdenum
0.015
II
Vanadium
0.03
It
Radium 226
3.20
pci/L
SOURCE: Mobil Oil Corp., 1979.
63
-------
The Mine Plant
The production facilities consist of a well field, a processing plant,
storage tanks, shops and offices. The plant was originally designed to pro-
cess 130 L/s (2,000 gpm), but with more efficient operation can now operate at
200 L/s (3,200 gpm). Design production capacity is 295,000 kg/yr (650,000
lb/yr) of yellow cake.
The well field consists of 45 production areas. Each area is surrounded
by production zone monitor wells and includes several shallow monitor wells.
Production and injection wells are drilled on staggered straight lines with an
average distance of 21 m (70 feet) between injection wells. This is more
commonly known as the five spot pattern with four injection wells at the
corners of a square centered on a production well.
All production and injection wells are completed in the middle Catahoula
Formation, at depths ranging from 91 to 275 m (300 to 900 feet). There are
surface gravels overlying the well which are monitored by shallow wells.
Aquifers underlying the well field are not monitored, as the clay of the lower
Catahoula serves as an aquiclude.
Production and injection wells normally are cased with 11.43 cm (4-1/2
inch) fiberglass tubing. The completion technique for these wells includes
drilling the wells through the completion interval, running casing to total
depth and cementing the annulus back to the surface. Three centralizers are
run on the casing string, evenly spaced across the sand intervals. The wells
are screened at the producing intervals.
Monitor wells are cased with PVC, fiberglass, or steel casing, dependent
on completion depth. Monitor wells are drilled through the desired completion
interval, and the casing is run with a wire-wrapped screen on the bottom, a
double cement basket above the screen, and three centralizers evenly spaced
across the sand intervals, it is then cemented to the surface.
The extraction of uranium involves the following: leaching, ion ex-
change, elution, precipitation, dewatering, packaging and shipping. Uranium
minerals are leached in situ from the sand host by a lixiviant solution com-
posed of a bicarbonate anion complexing agent (CO^ or soda ash) and oxygen.
It is expected up to 15 pore volumes of leach solution will be necessary to
recover the easily leachable uranium. Produced fluids pass from the produc-
tion wells into surge tanks and from the surge tanks into one of five ion-
exchange trains, each equipped with three 10.3 m3 (365 ft3) columns, from
which the uranyl tricarbonate complex is adsorbed by ion exchange.
The barren leach solution passes to recharge tanks, through sand filters,
and then is reinjected into the formation for a new leach cycle. The loaded'
resin is transferred to an elution column and stripped of uranium through the
addition of sodium chloride. The stripped resin is returned to the ion ex-
change column and the pregnant . eluat'e,. containing 15,000 to 20,000 ppm
uranium, is precipitated by the addition of hydrochloric acid (HC1) and hydro-
gen peroxide (H^O^). The resultant uranium slurry is then washed, thickened
until the uranium content increases to about 30%, and subsequently centrifuged
until it reaches 50-60%. This product is dried in an oil-fired dryer to
reduce moisture in the y^ellowcake.'to^'_l to. 2/'.'-.. The yellowcake is lueri" • loaded
into 208 L (55 gal) drums for shipping.
64'v
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Restoration
Mobil has announced the planned restoration at El Mesquite, but has not
released specific information on the proposed method of aquifer restoration.
They have provided a restoration progress report for the adjacent O'Hern well
field, which is considered to be geologically and hydrologically similar.
At O'Hern, Mobil used the groundwater sweep method. Table 15 presents
the analytical results of a three-month test conducted after the formation had
been flushed with 3.5 pore volumes of water. Ammonia test restoration values
were not reported. With few exceptions, all measured parameters were within
25% of their initial baseline values. Ammonia and nitrates, not reported, are
thought to be considerably above the original baseline conditions.
Excursions
On November 28, 1979, Mobil Oil formally notified the Texas Department of
Water Resources (TDWR) of a leachate excursion at its El Mesquite Mine. Two
monitor wells showed significant increases in conductivity, SO4, U3O8 and HCO3
(Table 16) during the normal bimonthly sampling on November 27. Immediate cor-
rective action was initiated. Seven injection wells were shut down and three
of these wells were converted to production wells. Sampling and analysis of
water from monitor wells were conducted every other day.
During the subsequent week, a total of 15 injection wells were shut down
with three continuing as production wells. When the piezometric surface had
dropped sufficiently to induce a gradient back into the production area, 10
wells were reactivated at reduced injection rates. By the end of the second
week both monitor wells were below the upper clean-up limits specified by TDWR
for all parameters except bicarbonates. On December 21, 1979, Mobil notified
the TDWR of its intent to return to bimonthly sampling for one of the two wells,
as the results of analyses from five consecutive samples had been below the
specified upper limit. One week later, the second well was taken off excursion
status and the mine was returned to normal injection and pumping status.
On January 23, 1980, Mobil notified the TDWR of a second excursion in
another production area. One monitor well showed significant increases in
conductivity, SO4, and HCO3 (Table 17). Three injection wells were immedi-
ately shut down and a fourth converted into a production well. In addition,
production rates were increased in four other wells. Within three weeks,
values had returned to baseline levels and the well was taken off excursion
status. No additional excursions had been reported by January, 1981.
6.3 THE IRIGARAY MINE, JOHNSON COUNTY, WYOMING
Introduction
The development of this mine has taken place over a period of approxi-
mately seven years, since 1974. Its history involves modifications to the
operation to overcome environmental and technical problems and thus serves
as an example of complex relationships that can exist among mining operations,
ambient conditions, regulatory bodies, and public concerns. These relation-
ships are summarized in this section.
65
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Table 15. Restoration Test Results for the O'Hern Project
Non-Ammonia Non-Ammonia Test
Test Means* Final Restoration"
Calcium
11.27
21
Magnesium
3.02
4
Sodium
305.83
338
Potassium
10.87
8.1
Carbonate
5.67
3
Bicarbonate
374
369
Sulfate
118
180
Chloride
210.67
216
Fluoride
0.65
0.6
Arsenic
0.027
0.061
Barium
0.61
0.065
Boron
1.73
1.115
Cadmium
0.1
0.0003
Chromium
0.03
0.003
Copper
0.02
0.007
Iron
0.77
0.04
Lead
0.05
0.002
Manganese
0.023
0.022
Mercury
0.3
0.5
Molybdenum
0.14
0.01
Nickel
0.02
0.01
Selenium
0.01
0.007
Silica
45.33
40
Silver
0.02
0.01
Uranium
2.36
1.7
Vanadium
0.2
0.045
Zinc
0.023
0.015
PH
8.23
8.35
TDS
909.5
1036
-Average UI-94 & UI-95
SOURCE: Mobil Oil Corp., 1979. All', units in mg/L except for pH.
Table' 16. Excursion of November 27, 1979, El Mesquite Mine
Conductivity SO, U„0o HC0o Ca CI
4 JO J
Upper Limit
1875
138
5.3
424
10
321
Well UI 974
2100
155
2.8
544
3
245
Well UI 973
1850
145
30.9
458
6
245
Underlined values are in excess of exceptable upper limit.
SOURCE: Mobil Oil Corp., 1979a; units in mg/L.
66.'-
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Table 17. Excursion of January 23, 1980, El Mesquite Mine
Conductivity
SO4
u3o8
HCO3
Ca
CI
Upper Limit
1875
138
5.3
424
10
321
Well UI-714
2100
220
0.4
519
8
240
Underlined values are in excess of exceptable upper limit.
SOURCE: Mobil Oil Corp., 1980; units in mg/L.
The geology of the Irigaray Site and three other uranium deposits in
Wyoming and South Dakota was described generally as "normal western sandstone,"
consisting of sandstone beds below the water table, some 15 to 30 m (50 to 100
ft) thick and overlain and underlain by impermeable shale beds. The porosity
was characterized as being about 30%, with lateral permeabilities of 200 to
400 millidarcies (md) and vertical permeabilities of 10 to lOOmd. The ore
occurred in zones between oxidizing and reducing mineral facies in channel
deposits of the Wasatch Formation, of Eocene Age. The dip of these beds was
about 2° W at Irigaray. Thickness ranged from 30 to 43 m (100 to 140 ft).
The ore occurred in mineralized bands about 24 m (8 feet) thick (Figure 13).
Proposed Operation
On March 29, 1974, Wyoming Mineral Corporation filed an environmental
report to support its application for a license to operate a research and
development (R&D) solution mine for uranium, at Irigaray, Wyoming (Wyoming
Mineral Corporation, 1974, Figure 14). This pilot operation was to occupy
approximately one acre of land, on which a four-spot pattern of three in-
jection wells and one production well was to be situated. A carbonate lixi-
viant was to be injected at a rate of approximately 1.6 L/s (25 gpm), for a
volume of about 140,000 1 (37,000 gallons) in the ore zone and 56,8000 1
(15,000 gallons ) in the plant at any one time. It was estimated that 60
cycles of fluid exchange through the entire circuit would be involved, for a
total volume of some 11 million liters (3 million gallons). It was expected
that about 1,300 kg (3,000 pounds) of U30g would be produced from this pilot
operation. The processing plant was modular and contained in trailers (Fig-
gure 15). As no processing was was to be produced, no tailing's ponds were
planned.
Surface water at the site was to be protected by bentonite clay liners in
surge pools and dikes surrounding the processing plant. A pattern of 3 monitor
wells was laid out to provide information on the lateral extent of the zone
affected by the mining operation (Figure 15).
The expected composition of the pregnant solution was estimated to be as
shown in Table 18. The pregnant solution was to be processed in ion-exchange
columns, where the uranium would be extracted. Approximately 3 to 7 ppm of
U3O8 was expected to remain in the barren solution leaving the ion-exchange
columns. The carbonate lixiviant was to be reconstituted at a mixing tank to
the required pH (6 to 10), after which it was to be reinjected.
67
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WELLS
IMPERMEABLE-
SHALE
SANDSTONE
100-140 FEET THICK
(30-45 METERS)
IMPERMEABLE _ SHALE
MINERALIZED BANDS
_ 2-l2_FEE.T THICK -
(1-4 METERS) |
Figure 13. Generalized Geologic Cross-Section, Irigaray Mine
-------
BUFFALO'
IRIGARAY
MINE
#HIGHLAND
MINE
CASPER
Figure 1A ; Location Map, Irip.aray and Highland Mines
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rSURGE POOLS
DIKE
TRAILERS
ACRE
o © o
PRODUCTION INJECTION MONITOR
WELL WELL WELL
Figure Pilot Plant Arrangement at the Irigaray Mine
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Table 18. Expected Composition of Pregnant Liquor, Irigaray Mine
U (as U3O8)
Basic strength (as HCO 3)
1 g/L
50 g/L
6-10
pH
Ca++
NH4+
0.5 g/L
0.2 g/L
The loaded resin was to be eluted by chloride ions, with an expected
efficiency of stripping of 95%. Precipitation was to be attained by the addi-
tion of HC1 to lower the pH to about 2, driving off any dissolved CO2; fol-
lowed by the addition of ammonia, to neutralize the pH and to cause ammonium
diuranate to precipitate. The resulting yellowcake would be a slurry of about
50% solids. The processing circuit was shown schematically as in Figure 16.
The only effluent stream expected from this pilot plant was uranium concen-
trate. A daily production of approximately 20.4 kg (45 pounds) was antici-
pated.
Wyoming Mineral Corporation cited their experience in Texas to support
their position that no excursions would occur at the Irigaray research and
development plant. Safeguards against excursions were provided by cementing
of the wells to the mineralized zones, and perforating or slotting the casing
in the ore zone only. They felt that little if any negative impact on the
environment would occur because of the presence of existing carbonate systems
in groundwater, and placed reliance on dilution and buffering by the existing
calcite system to maintain natural pH values.
Monitored wells were to be sampled daily for pH, Eh, HC0~3, and U30g.
Wells and streams within a 8 km (5-mile) radius were to be samples one month
prior to the operation and twice afterward (at 3-month intervals) for pH, Eh,
U, V, Mo, Se, As, and alpha and beta activity.
The research and development operation commenced in November, 1975, and
lasted until October, 1976. The results of tests during this pilot operation
showed that optimum well spacing for the site was about 12.2 m (40 feet), and
that a 7-spot configuration in a hexagonal array was best suited for the opera-
tion.
Restoration tests, which began in May, 1977, indicated that sweeping of
the production zone by clean, injected water reduced most contaminants in the
groundwater. Flusing of the production zone by concentrated solutions of Ca,
Na, or Mg brought levels down to 120 ppm. Neither method, however, was
satisfactory in removing NH3 from the formation. Reverse osmosis treatment
of the extracted water, followed by reinjection, was able to reduce the
content of the formation water to 35 ppm (USNRC, 1978).
A Final Environmental Statement relative to Wyoming Mineral Corporation's
application for a license to operate on a commercial scale was issued by the
U.S. Nuclear Regulatory Commission (USNRC) in September, 1978. The document
summarized the findings of the USNRC regarding the feasibility of the proposed
operation and the associated effects on the environment and was based upon:
71
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BARREN LIQUOR TO
RECONSTRUCTION AND
PREGNANT
LIQUOR
FROM
PRODUCTION
WELL
PRECIPITATED
YELLOWCAKE
SLURRV
PRECIPITATION
* TANK
ELUTION
COLUMN
EXTRACTION
COLUMN
FLOW OF ION EXCHANGE
RE&IN
FLOW OF ELUTION
SOLUTION
Figure 16. Expected Processing Circuit, Irigaray Mine
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1. A Source Material License, dated January 28, 1976;
2. An environmental survey dated January 28, 1976, and supporting cor-
respondence dated May through November, 1976;
3. Responses to questions of the USNRC, dated March 1, 1977;
4. A revised environmental report, of November ,1977; and
5. A restoration demonstration in March ,1978.
The Environmental Report, as was submitted by Wyoming Mineral Corpora-
tion, is required as a supporting document to every application for a Source
Material License, to be used by the NRC in assessing potential environmental
effects (in accordance with 10 CFR Part 51). The content of the Environmental
Report is specified in Regulatory Guide 3.8 of the USNRC.
In addition to the reports and other materials which Wyoming Mineral
Corporation had submitted to the USNRC by September 1978, the company was
required by the State of Wyoming to obtain the following approvals or permits
before starting a commercial, in situ mining operation:
1. License to Mine - issued by DEQ/LQD*
2. Permit to Mine - issued by DEQ/LQD
3. Air Permit to Construct - issued by DEQ/AQD
4. Air Permit to Install Recovery Plant - issued by DEQ/AQD
5. Sanitary Sewage Disposal - issued by DEQ/WQD
6. Potable Water Supply - issued by DEQ/WQD
7. Water Wells - issued by SE
8. Construction of an Impoundment - issued by DEQ/WQD, SE
9. Industrial Siting Permit - issued by Wyoming Office of Industrial
Siting
10. Air Permit to Operate - issued by DEQ/AQD
11. Industrial waste disposal site - issued by DEQ/Solid Waste Management
Division
Abbreviations as follows:
AQD = Air Quality Division
LQD = Land Quality Division
WQD = Water Quality Division
DEQ = Department of Environmental
Quality
SE = State Engineer
73
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As of September, 1978, two pilot-scale tests were in operation in the
Irigaray Site. The property as described in the report contained 8,540 ha
(21,100 acres), of which the initial well field was to occupy 20 has (50
acres). It was anticipated that solution mining would eventually affect about
400 ha (1,000 acres), only part of which was covered under the initial license.
The USNRC summarized salient aspects of the proposed operation as follows:
Groundwater—Groundwater from the Wasatch Formation in the area generally
meets drinking water standards, with the exception of one well which produced
water containing 0.07 ppm of selenium (the Federal limit is 0.01 ppm and the
Wyoming level for livestock consumption is 0.05 ^pm). Total dissolved solids
(TDS) were generally less than 500 ppm, with Na and S0^ as the predominant
cations. In the mineralized zone, drinking water standards were exceeded by
2^226 (radium), gross alpha, and uranium contents; a few hundred feet from the
ore zone, however, formation waters generally met the standards.
The main uses of groundwater in the area of the site are livestock watering
and private, domestic water supplies. Well tests showed the presence of an
artesian head in the aquifer, with a consequent flow toward the northeast.
Transmissivities were 53.6 to 58.9 m^/s (373 to 410 gpd/ft).
Proposed Operation
Expected injection pressures were 340 to 690 kPa (50 to 100 psi), at rates
of 0.25 to 0.32 L/s (4 to 5 gpra) per well. The "production cell" was defined as a
7-spot configuration consisting of six injection wells and one production well.
All wells were 10.16 cm (4 inch) diameter borings, which were logged, cased,
and screened. Production wells contained downhole pumps suspended on a 2.54 era
(1 inch pipe). Restoration was to commence in each completed cell when pro-
duction had moved 3 cell widths about 73 m (240 feet) away, in order to minimize
interference between restoration and mining activities. Estimated feed rates,
based on a 230,000 kg/yr (500,000 lb/yr) production rate and an 0.84 L/s (800
gph) injection rate, were shown as in Table 19.
Liquid wastes were expected to consist of solutions of NH4CI, carbonates,
and other dissolved solids. Total expected volumes of liquid wastes were as
shown in Table 20, totalling 25,000 m^ (20 acre-ft)/yr. The proposed evapora-
tion ponds were designed to evaporate 4,300 m^ (3.5 acre-ft)/yr; thus, 2.43 ha
(6 acres) of evaporation ponds could handle the expected total volume of waste-
water. The pond design included impermeable plastic liners and an underlying
gravel and pipe collection system.
Prior to reinjection of depleted lixiviant, calcite was to be removed by
precipitation. It was believed by the applicant that much of the other dis-
solved contaminants would co-precipitate with the calcite, producing about 95%
removal of Ra^26> Vanadium was to be removed by the use of activated charcoal
and sulfate by precipitation with barium, should those two dissolved con-
stituents have built up to levels above pilot-scale values.
74
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Table 19. Estimated Feed Kate Ranges for 500,000 lb/yr Production,
Irigaray Mine
a) Lixiviant for 800 gph injection
lb/hr Tons/yr
CO 75-225 325-985
* 40-120 175-525
50% H2°2 75"25° 325"1100
b) Reagents for 4.5 gpm Eluant Bleed
NH HCO 35-100 150-440
m7C1 75-200 325-875
NH4
35% HC1 25-70 110-305
NH3 5"20 22"90
c) Fuel
Propane 20-60 90-260
Table 20. Expected Volumes of Liquid Wastes for a 500,000 lb/yr Production
Rate, Irigaray Mine
Overproduction of well field at 1% of design
production rate 14.6 acre-ft/yr
Well cleaning to maintain flows 5.5 acre-ft/yr
It was estimated by the NRC that the crystalline concentrates in the
evaporation ponds would accumulate assorted ammonium and alkaline earth salts
(e.g., NH^Cl, NH^SO^, RaSO^, and CaCO^) at a rate of about 500 tons/yr, all
containing radioactive materials.
Solid wastes were to be stored temporarily in lined ponds under liquid
seals. A maximum accumulation time of f;ive-ey.®%rswwaa
JL'ifc'en's'e.
Atmospheric emissions were expected to be limited to combustion bypro-
ducts and ^yei'lowcake- fines from the dryer. The latter were expected to total
about 45 kg (100 lb)/yr, after passing through a high-int^q^ity venturi
scrubber. These losses, equalling approximately 0.15 Ci of U jua] the
natural background value. The USNRC estimated that 1.4 Ci/yr of Rn (Radon)
would be emitted from the evaporation ponds and 76 Ci/yr from the surge tanks.
-7:5.'-.
-------
The recommendations of the USNRC showed concern with: 1) The effective-
ness on a production scale of the reverse osmosis treatment, which was in a
developmental stage; and 2) the residual NH3 in the aquifer. The NRC recom-
mended that, until the ammonia problem is resolved, the use of ammonia-based
lixiviant by the applicant be limited in volume.
According to the USNRC, unavoidable adverse environmental impacts caused
by the operation were:
1) Air emissions - (These were judged to be of negligible magnitude.)
2) Surface water contamination - (Some possible local deterioration was
expected.)
3) Groundwater consumption - (An estimated 1.2 x 10^m^ would be perma-
nently removed, mostly during restoration operations.)
4) Radioactivity - (Some small increase in the level of local radio-
activity was expected.)
The question of the residual ammonia in the aquifer was addressed by the
Wyoming Department of Environmental Quality in a letter of August, 1978, in
which the Department stated its intention to require the applicant to meet any
restoration standards that might be developed in the future, consistent with
the state of the art of solution mining in Wyoming. The Department also stated
a requirement for sampling of nitrosamines on a quarterly basis.
Operational History
On March 27, 1979, approximately six months after the operation began, an
excursion was detected with the use of three shallow monitoring wells. Subse-
quently, nine exploratory wells were drilled to assess the cause of this problem.
Possible causes of this excursion were:
1) Natural hydrologic connections between the shallow aquifer and the
deeper, production zone;
2) Interaction between the two aquifers through abandoned and unplugged
drill holes;
3) Ineffective cement around one or more well casings; and
4) Loss of casing integrity due to flaws or damage .
In order to assess the cause of the excursion, a program of packer tests and
a televiewer examination of the well field was initiated. Packer tests showed
that two injection wells in Well Field C were leaking. These injections wells
were converted to production wells and overproduction was commenced at several
nearby production wells. Pumping of contaminated water from the shallow aquifer
was then initiated, through additional shallow wells. In July, a televiewer
survey of the wells suspected of having casing damage, as wells as representative
wells in Production Units I through IV, was carried out. On July 16, Wyoming
Mineral Corporation requested a 30-day extension to the required period for cor-
76
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rection of excursions; this extension was granted by DEQ. By August 24, 1979,
a correctional trend had been established and maintained in the shallow aquifer,
while production operations continued. This trend was the result of:
1) Direct withdrawal of water from the shallow aquifer through two wells
at a combined rate of 0.066 to 0.11 L/s (1500 to 2500 gpd); and
2) Indirect withdrawal from the shallow aquifer through pumpage from the
production zone through converted injection wells, at a combined rate
of 0.123 to 0.438 L/s (2800 to 10,000 gpd).
At that time, cleanup of the shallow aquifer had progressed to the point that the
shallow monitor wells that originally had detected the excursion were reported
as being off "excursion status."
Analysis of all test data led to the conclusion that casing leaks resulting
from well completion and stimulation practices were responsible for the excur-
sion. Pumping from the shallow aquifer reduced rather than increased the level
of contamination; therefore, it was inferred that no stratigraphic connection
existed between the two aquifers.
On October 29, 1979, Wyoming Mineral Corporation stated its intention to
continue the cleanup operation by continuing to pump from the shallow aquifer at
maximum capacity through some wells, in order to exaggerate the cone of depres-
sion around offending wells. It was also suggested that Cl~ be used as an
indicator of excursions for monitoring purposes. At that time chloride levels
were reported to be below the limit for drinking water, and V, As, and Se were
below the limits of detection.
In June, 1979, Wyoming Minerals Corporation had requested an amendment to
its license from the USNR.C to allow an increase of leachate flow from 50 to 130
L/s (800 to 200 gpm). This was followed in February, 1980, by a request to the
Wyoming DEQ for a permit to change to a non-ammonia type of lixiviant, with a
restoration demonstration, and to expand its permitted operating area by 20%.
In the same month, plans to mine an alternative lixiviant field using Na, Mg,
and Ca bicarbonate as a solvent were submitted to the USNRC, together with a
groundwater restoration plan for that field. Restoration was to be accomplished
by recycling clean water through the production zone, using an ion-exchange unit.
The area in the shallow aquifer to be cleaned up was defined as being en-
closed by the 18 ppm CI- isopleth. It was estimated that approximately 37.8
million liters (10 million gallons) of cleanup water would be required to reduce
the Cl~ concentration to about 11 ppm. This would involve the exchange of 1
to 1.5 pore volumes at a rate of flow of 1.8 L/s (28 gpm) at the recovery wells,
over a period of one year. The installation of forty-eight additional wells in
the cleanup zone was also recommended (Wyo. Min. Corp., 3-7-80).
Restoration of the production zone in the initial well field was to begin
in Hay of 1980. This process included soda-lime softening to reduce a carbonate
and bicarbonate levels; the addition of CaCl2 to elute NH and the use of
reverse osmosis to remove residual solubles and trace elements. A water fence
was to be used to isolate restoration areas from active mining areas. In ac-
cordance with the conditions of the license, a minimum of two wells in the mined
77
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zone, two wells in the direction of maximum transmissivity, and two wells on
the trend of the ore body were to be monitored at quarterly intervals for one
year after completion of the restoration operation. Both of the above plans
were approved by the Wyoming DEQ on March 7, 1980.
On March 21, 1980, Wyoming Mineral Corporation was notified by the Wyoming
DEQ that an uncontrolled excursion existed at the site, based on their discovery
of two consecutive, excessive Cl~ concentrations in Well Field F. (Wyo. DEQ,
3-21-80). Four days later, Wyoming Mineral Corporation requested approval of a
plan to remedy this condition. This plan involved a continuation of withdrawal
from production wells in the affected area and shutdown of injection wells with-
in a 1-cell radius. In addition, a series of shallow exploration holes around
the offending well was proposed to locate the excursion, followed by execution
of the cleanup plan already submittted (Wyo. Min. Corp., 3-25-80).
Because restoration had not been accomplished in the ammonia-leach pro-
duction units to levels of 0.5 ppm or less, the Wyoming DEQ declined to issue
a permit to proceed with mining using a non-ammonia lixiviant (Wyo. Min. Corp. ,
4-16-80). The USNRC then issued an order to Wyoming Mineral Corporation to sus-
pend the operation (USNRC, 1980), because the excursions of March an early April
were not attributable to defective well casings, and that hydraulic communica-
tion existed between the production zone and the shallow aquifer. The order
directed Wyoming Mineral Corporation to cease injection of refortified ammonia
lixiviant, to continue to circulate unrefortified (barren) leach liquor, to
continue current activities toward the cleanup of the shallow aquifer, and to
commence preparations for restoring and decommissioning the site.
On May 23, 1980, the shutdown order was terminated and permission was given
to proceed with operations using a sodium lixiviant. Conditions for this permit
included 1) monitoring CI- around the production zone; 2) drilling additional
test wells; 3) conducting pump tests to evaluate hydrogeologic conditions; 4)
continuing the cleanup of the shallow aquifer; and 5) carrying out geophysical
tests to further define the hydrostratigraphy of the area.
On June 27, 1980, Wyoming Mineral Corporation reported to the USNRC that
further excursions had been detected, in Production Unit 5. Chloride and
alkalinity values in shallow monitor wells there exceeded baseline values es-
tablished a month earlier, although Unit 5 was only recycling unfortified
lixiviant. Unit 5 was accordingly shut down and pumping begun at the shallow
monitor wells. On July 3, an excursion condition was reported in another
monitor well, followed on August 12, by still another.
In December, 1980, Wyoming Mineral Corporation was able to report to the
Wyoming DEQ that the non-ammonia field had been restored to baseline values,
drinking water standards, or Wyoming groundwater standards, and the essentially
all heavy metals and radionuclides had been restored to pre-mining conditions.
This restoration program involved the exchange of 11.5 pre-volumes at 1.9 to
3.2 L/s (30 to 50 gpm).
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6 .4 HEAP LEACH FACILITY AT AMBROSIA LAKE, N.M.
Introduction
The United Nuclear Corporation (UNC) operates an experimental heap leach
facility for uranium extraction at the Old Phillips Mill in the Ambrosia Lake
Mining District, located. 40 km...(.2 5 miles) north of Grants, New ^Mexico (Appe.ndix A,
2l), This facility uses tailings and low-grade ore from conventional mining
and milling operations in the area as feed stock. Water for the process is
obtained from underground workings in UNC's Section 27 Mine. The uranium-rich
liquor from the heap leach operation is processed in an ion exchange plant
which was originally built to extract uranium from the water pumped from the
underground mines.
The Ambrosia Lake Mining District lies to the west of Mt. Taylor along a
series of southward facing cliffs, mesas, cuestas, and intervening soft rock
valleys. It is in a valley three miles wide and seven miles long eroded into
the Mancos Shale Elevation is approximately 2,000 m (7,000 feet) above sea
level. Physiographically, Ambrosia Lake is on the south rim of the San Juan
Basin, east of the Zuni uplift.
The Old Phillips Mill is situated above a 9 to 12 m (30 to 40-foot) thick
layer of alluvium that is underlain by the Mancos Shale, the Dakota Sandstone,
and the Morrison Formation.
— Hydrology
The Westwater Canyon sandstone member of the Morrison Formation is the
principal aquifer for the region, as well as the principal ore horizon in the
Ambrosia Lake Mining District. Water pumped through the ion exchange plant
from the Phillips mine dewatering operation is from this aquifer.
Overlying the Morrison Formation is the Dakota Sandstone which is also a
regional aquifer, but wells completed in this horizon are less productive and
the water from them is not considered potable. The Mancos Shale overlies the
Dakota Sandstone, and was originally reported to be an aquiclude. However,
numerous drill holes, ventilation holes, and abandoned mine shafts in the
district are of concern as possible routes of vertical migration of water from
the overlying alluvium to the underlying Dakota aquifer.
An upward flow gradient exists between the Dakota Sandstone and the
Mancos shale. This gradient serves as a hydraulic barrier, but the numerous
mine dewatering projects in the Grants region could reverse its direction in
the future. Direction of flow in the Dakota aquifer is to the northeast,
following the regional dip of the beds.
A shallow aquifer exists in the alluvium overlying the Mancos Shale,
approximately 12 m (40 feet) below the surface; the water, however, is of poor
quality because of mineralization from the Mancos Shale. Water quality has
continued to degrade in this aquifer since the onset of mine dewatering in the
1950's. Direction of flow is towards the northeast, following the topography.
Fine silt and clay beds overlie this aquifer and would impede downward move-
ment of any contaminated water from the holding ponds, tailings pile and
ion-exchange operation.
-------
Annual rainfall in the Ambrosia Lake area averages 35.13 cm (13.83 inches).
A maximum rainfall for a storm was calculated at 51 (20 inches) by UNC for the
site. Berms designed to exclude flooding from this storm were constructed
around the heap leach pads. Within a 1.6 km (1 mile) radius of the heap leach
pads, the only surface waters consist of mine-water holding ponds. Arroyo Del
Puerco, to the northeast of the Old Phillips Mill, is an intermittent stream
channel. No discharge to this stream will occur as a result of plant operations.
Mine Plant
On July 17, 1980, UNC began to carry out experimental heap leaching of mine
tailings at the Ambrosia Lake Old Phillips Mill. Prior to 1971, an ion exchange
unit had been installed to extract uranium for water in UNC's Section 27 Mine.
The heap leach operation was built as an additional loop within this closed-
circuit system.
The plant was designed to operate for less than one year and to provide
operational data for possible future commercial-scale, heap leach operations.
These data included flow rates to the pile, collection rate below the pile,
changes in water quality and the economic feasibility of such an operation.
The leaching pad holds 20,200 tons of low-grade ore and tailings; it was ori-
ginally designed to contain two ore piles but was modified to hold a single
pile with two sets of ponds. Feed water from either the mine water pipeline
or the ion exchange holdings ponds is applied at a rate of 3.2 L/s (50 gpm)
for five hours every 10 days. The uranium content of water leaving the leach
pad will be below 500 mg/1. The pad is underlain by 6 mil-thick, polyethylene
plastic sheeting, on top of a permaprime sealant sprayed onto the ground.
Leachate from the leach pad is pumped to the ion exchange plant, where the
dissolved uranium is removed. The processed water is then returned to the under-
ground mine workings. The pregnant eluant from the ion exchange plant is trans-
ported by truck to the UNC-Homestake Partners Mill, where the uranium is
precipitated out. The barren solution is then returned by truck to the Old
Phillips Mill, where it is re-inserted into the closed circuit between the under-
ground workings and the ion exchange plant.
Three monitoring wells were installed on the north, east, and west sides of
the leach pad approximately 6.1 m (20 feet) outside of the berm surrounding the
pads. The wells were drilled through the alluvium and 0.9 m (3 feet) into the
Mancos Shale, in order to monitor the shallow aquifer. Groundwater in this
aquifer would be the first to be affected by contamination from the leach opera-
tion. The casing of these wells was perforated along the lower 9.1 m (30
feet). The wells were sampled for molybdenum, selenium, IDS, vanadium, total
uranium, and dissloved radium 226 before heap leaching began, and on a quarterly
basis thereafter. Results of the baseline sampling and the first quarterly
report to NMEID are shown in Table 21.
80
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Table 21. Ambrosia Lake Groundwater
PRE-OPERATIONAL
May 6, 1980 - May 15,-1980 June 18, 1980
Well #1
Mo 0.007 <0.001 0.014
Se 0.110 0.034 0.024
TDS 4,289.3 4,314.4 4,705.8
V 0.007 <0.001 0.009
U 0.16 0.13 0.15
*Ra22S 1.8 1.9 3.1
Well #2
Mo 0.006 <0.001 0.022
Se 0.124 0.033 0.024
TDS 2,886.3 2,985.2 3,379.3
V 0.007 <0.001 0.013
U 0.10 0.11 0.09
*Ra226 2.8 1.7 4.4
Well #3
Mo 0.003 <0.001 0.014
Se 0.121 0.0817 0.044
TDS 4,189.0 3,786.0 3,944.0
V 0.010 <0.001 0.016
U 0.05 0.04 0.04
*Ra226 0.7 0.9 1.8
OPERATIONAL
Aug. 3, 1980 Nov. 4, 1980
Well n
Mo
0.10
0.003
Se
0.008
0.016
TDS
5,413.3
5,561.5
V
0.016
0.018
U
0.12
0.12
*Ra226
7.16
4.63
Well #2
Mo
0.015
0.006
Se
0.024
0.039
TDS
4,092.3
3,750.3
V
0.015
0.014
U
0.04
0.07
*Ra226
1.88
2.26
Well #3
Mo
0.007
0.005
Se
0.042
0.055
TDS
4,320.2
4,102.5
V
0.016
0.019
U
0.04
0.05
*Ra226
1.56
1.83
All parameters reported in rag/L except those indicated as * (pCi/L).
81
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Upon completion of the experimental heap leaching operation, residual
materials on the pads and the polyethylene liner will be sent to the UNC
Church Rock Mill and combined with their present tailings pile.
As of February, 1981, no problems of environmental contamination had
developed at the plant (as a result of the operation of the heap leach and ion
exchange).
6.5 THE HIGHLAND MINE, CONVERSE COUNTY, WYOMING
Introduction
This commercial-scale operation is carried on by the Exxon Minerals Company
in Converse County at the south edge of the Powder River Basin, some 32 km (20
miles) northwest of the town of Douglas (Figure 14). Uranium is produced from
sandstone ore in the Fort Union Formation, of Paleocene age. The production
zone is overlain and underlain by shale formations some 4.6 m (15 feet) thick.
Drinking water is produced from an aquifer located about 46 m (150 ft) above
the ore-bearing unit, supplying 3 wells within 3.2 km (2 miles) of the site.
Several sandstone and shale units lie between the production zone and this
aquifer.
Proposed Operation
In September, 1970, Humble Oil and Refining Company applied for a Source
Material License from the U.S. Nuclear Regulatory Commission, proposing to
carry out pilot testing at the site. Pump tests to prove pressure communication
between injection and production wells in a 7-spot pattern (one injection well,
six production wells) were carried out. Tracer studies, using a saline solution
of 250 mg/L NaCl, were carried out to confirm the hydraulic properties of the
formation. It was proposed that sodium carbonate-bicarbonate lixiviant, using
oxygen as an odixizer, would be injected at a rate of 7,938 to 15,876 liters
(50 to 100 barrels per day for a total volume of 6,032 million liters (38,000
barrels or 1,596,000 gals). Production wells then would be started and a
balance would be established to cycle approximately 20 million liters (128,000
barrels or 5,376,000 gals) of lixiviant through the ore zone. The pregnant
liquor was to be processed in an ion-exchange plant, which would leave approxi-
mately 60 ppm of dissolved uranium in the liquor. Elution of the ion-exchange
columns was to be accomplished using ammonium nitrate and nitric acid.
Wastes were to be discharged into an evaporation pit. Solid wastes were
to be buried and seeded at the end of the operation. No airborne particulate
contamination was expected because all processing was to be done with wet
materials. The precipitated yellowcake was to be packaged while still wet
enough to prevent dust generation.
Restoration was to be accomplished by pumping all lixiviant from the for-
mation, removing introduced materials, and pumping water to a tailings pond.
It was expected that approximately 8.3 million liters (52,000 barrels or
2,184,000 gals) of clean water would be required to remove essentially all of
the leach solution.
82
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Expected environmental Impacts were:
1) Removal of approximately 12.7 million liters (80,000 barrels or
3,360,000 gals) of groundwater
2) Residual traces of carbonate-bicarbonate solution in the formation;
and
3) Creation of evaporated residues in surface pits.
No long-term, adverse effects were foreseen. An operating license was
issued by the USNRC in November, 1970.
The pilot well pattern was a symmetrical spacing of the six production
wells on 27 m (90-ft) radii around the injection well. In addition six minitor
wells were placed on 46 m (150—ft) radii from the center well. Results of
analysis of water pumped from the ore are shown in Table 22.
Table 22. Analysis of Water from Ore Zone—Highland Mine*
Na 161 ppm HCO3 237 ppm
Ca 77 ppm Se <0.5 ppm
Mg 13 ppm U 212 ppm
CI 27 ppm R^oon ^ x uc/ml
So. 119 ppm Th230 8.6 x 10"8 uc/ml
* Based on an average of 3 samples from production wells.
On January 1, 1973, the license was amended to reflect the merger of Humble
Oil with the Exxon Corporation.
Operational History
Operations in the initial pilot plant production area were carried on from
March, 1972, to November, 1974. During that period, 38.74 million liters
(10,248,000 gals) of lixiviant were injection through the production well, with
38.90 million liters (10,290,000 gals) being produced. After injection was
stopped, 78.38 million liters (21,000,000 gals) were pumped from all 7 wells.
Monitoring efforts emphasized the detection of increases in uranium con-
tent of water in the six monitoring wells. Detectable changes were observed in
mid-1973 and mid-1974; each time, the excursion was controlled by adjusting in-
jection and production rates to pull the leach liquor plume back into the
production zone. Arrival times of the plume at the monitoring wells were earlier
than had been anticipated, due to the presence of stratigraphic non-uniformities
in the ore-bearing beds.
After cessation of injection in November, 1974, uranium concentrations in
observation wells decreased, passing the limit of detectability by June, 1975.
By that time, Exxon reported that carbonate and bicarbonate ion were essen-
tially at baseline levels, and that trace metals, with the exception of arsenic
83
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and selenium, were not mobilized in sufficient amounts to be of concern to
groundwater quality. During the pilot operation, concentrations of radon
daughter products occasionally exceeded acceptable levels. New filters and
blower systems were installed to overcome that problem.
In October, 1977, Exxon applied for a permit to drill a new test pattern
of four injection wells, ten production wells, nine observation wells, and two
monitor wells. The monitor wells were to be located in the middle of this
double-5 spot pattern and were completed above and below the production zone
aquifer. At that time, pumping from the initial production area continued, at
a rate of about 0.95 L/s (15 gpm). Baseline samples obtained from this pattern
of wells produced the results shown in Table 23. A license to operate the
second pilot area was issued in May, 1978.
In March, 1979, Exxon reported that bicarbonate values in some observa-
tion wells exceeded the control limits by small amounts; also, in two wells,
conductivity values were high. Exxon did not believe that this was due to a
leach-liquor excursion. By mid-April, 1979, Exxon reported that a new obser-
vation well had been drilled between the ore zone and the wells showing high
bicarbonate values. Samples from this well did not have similar concentra-
tions of bicarbonate, and this demonstrated that a plume of leach liquor did
not extend between the two areas.
In December, 1979, a minor casing leak was discovered in an injection well.
This was the result of a pressure test, using down-hole packers. The leak was
determined to be adjacent to an aquifer lying above the production zone. To
determine the extent of any excursion, an additional observation well was
drilled 3 ra (10 ft) from the leaky injection well, and water samples were
obtained from this aquifer. Comparison of analytical data with baseline values
showed that an excursion had occurred through the leaky casing. Pumping was
begun through the new well, resulting in a significant decline of initially
excessive concentrations of excursion parameters after 96 hours. By March,
1980, the clean-up of this excursion was completed.
Exxon conducted a downhole television survey of the leaky well, and deter-
mined that the leak was the result of hairline cracks and a bad joint in the
PVC tubing. Exxon indicated that they would not longer use PVC tubing in their
wells, but would instead utilize fiberglass or steel pipe.
As of November, 1980, no further excursions or environmental problems had
been reported at the mine.
84
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Table 230 Analysis of Water—Pilot Plant Area, Highland Mine
¦R-
Wyoming DRQ1
Guideline
No. 4
•Sample
Well
an
Pilot
Well
#6
Pilot
Wcl 1
# 3
Obsev
Well
it 7
Obsev
Well
09
{'"lit rol*
We i1 In
Ore Zone
Con! ro I
WHl
Out aide
Ore Zone
Date of Sample
2/1/77
2/15/773
4/21/77
4/21/77
4/21/77
4/21/77
2/1/77
2/2/773
2/14/77
2/15/77
A1 nmimurt-ntg/1
0.5
. 46
.049
.03
. 13
17
.009
.123
Arsenic-mg/1
0.2
.30
.15
.065
.023
.014
.0015
<.001
Boron-mg/1
5.0
. 1
. 1
.1
<. 1
. 1
0.2
.2
Cadmium-mg/1
0.05
<.001
<.001
.001
<.001
.005
.002
.001
Chrom i um-mp,/l
1.0
.002
.002
.004
.010
.003
<¦001
.0345
Coppei -nig/1
0.5
.016
.13
.004
.019
.069
<.001
< .001
Fliioride-mg/1
2.0
1. 15
0.6
0.3
0.7
0.2
0.2
0.25
Lcad-mR/I
0.1
.005
.013
.002
.037
.16
.002
.010
Mercury-mg/1
0.01
.0003
<¦0001
<.0001
<.0001
<.0001
<.0001
<•0001
Seleninm-mg/l
0.05
. 145
.30
.003
.004
<001
<.001
.001
Zinc-mg/l
25
.010
.020
.029
15
16
.007
.016
Sill fat e-mg/1
3000
189r'
252
155
136
114
141®
1328
Cliloridc-mg/1
2000
18
9
12
27
10
6
17
Radium-226 pCi/1
302
200
92
500
125
4.9
470
.3.3
Thorium-230 pCi/1
20002
160
113
48
230
3.8
0.55
0.2
Uranium-nig/1
l»t,. 32
7B
15
4. 1
3.4
. 15
.095
.045
1 Wyoming Department of Environmental Quality, Division of land Quality Guideline No. 4 (revised) November 9,
1976. Part II: Water Quality Criteria for Wildlife and Livestock Impoundments.
2 MPC above background for release to an unrestricted area, 10 CFR 20, Appendix B, Table IT.
3 Average of two samples.
* Located 700 feet east of pilot injection well in the same sand.
51 Located 1100 feet southeast fit pilot injection well in the same sand.
6 All sulphur calculated as SO^.
Analyses are by mass spectrometry except for R.1-226 and Th-Z:ln.
Reference: Exxon Minerals Co., 1978
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SECTION 7
PAST AND CURRENT RESEARCH
This section presents brief summaries of past and ongoing research pro-
jects that address the environmental effects from unconventional extraction of
uranium and the technologies to mitigate such effects. A primary source of
information that was used in compiling this list was two computer searches of
the Smithsonian Scientific Information Exchange (SSIE) data base, which main-
tains "notices of research projects." Because it is not always possible to
determine project completion dates, several of the projects that are identi-
fied as current research may have been completed and the results published.
Another major source of information is a U.S. Bureau of Mines (1980) publica-
tion that lists minerals environmental research for FY 1980. A similar report
for FY 1981 will be available after April 20, 1981, from the Division of Minerals
Environmental Technology. Information regarding all other research projects was
obtained from proceedings of symposia and from other published literature.
These project summaries are provided below.
Effect of Sodium Silicate on Leaching Uranium Ores with Hydrogen Peroxide
Laboratory experiments demonstrate that additions of small amounts of
sodium silicate to hydrogen peroxide (H2O2) leaching solutions prevents the
loss of permeability. With some ores, it also helps stabilize H2O2 against de-
composition. This research project was conducted by E.I. duPont de Nemours and
Co., Inc., Chemicals, Dyes and Pigments Department, Wilmington, Delaware (Lawes,
1978).
Environmental Assessment of In Situ Mining
This study evaluates selected environmental effects of in situ leaching and
hydraulic borehole mining of uranium, copper, and phosphate ores. The study
specifically discusses the impacts associated with in situ uraniun leaching in
Texas and Wyoming. For each of the in situ processes and ores investigated, the
physical and chemical characteristics of the systems are described, the toxic-
ity of the leaching solutions are presented, and the potential environmental
effects are discussed. The assessment was conducted by PRC Toups under a
Bureau of Mines contract, which was administered under the direction of the
Twin Cities Research Center, Minnesota. The final report was published
December, 1979 (Kasper, et al., 1979).
Geochemical Changes During In Situ Uranium Leaching with Acid
The Bureau of Mines measured the geochemical changes as sulfuric acid was
used for in situ uranium leaching by Rocky Mountain Energy Company near Casper,
Wyoming. Cores and groundwater were analyzed before leaching. Water samples
were taken from observation wells located between injection and production wells
as the leach solution was brought up to full strength in several steps. Measure-
ments were made of pH, Eh, temperature conductivity, total dissolved solids,
dissolved oxygen, HCO3, U, V, Na, K, Ca, Mg, SO4, CI, Mo, Mn, Fe, Al, Si, F, P,
As, and Se. The data were gathered to assist in geochemical modeling of leaching
and to study the potential environmental effects of acid leaching. Environ-
86
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mental considerations appear favorable. For example, the concentration of Se,
a toxic element often found in uranium deposits, stayed below the EPA standard
for drinking water (Tweeton, et al., 1979).
Ground Water Restoration for In Situ Solution Mining of Uranium
This paper, a summary of a study funded by the Bureau of Mines, reviews the
state of the art in restoring groundwater quality after in situ uranium leach-
ing. Current restoration practices discussed include disposing of liquid wastes
in deep disposal wells and evaporation ponds, producing from all wells during
restoration, and recirculating water purified in surface plants. Methods for
predicting the effectiveness and cost of current techniques are presented. Pos-
sible alternative techniques are also described. TVo restoration operations
are discussed (Riding, et al., 1979).
The Push-Pull Test: A Method of Evaluating Formation Adsorption Parameters for
Predicting the Environmental Effects of In Situ Coal Gasification and Uranium
Recovery
The push-pull test, which is a simple injection and pumping sequence of
groundwater spiked with solutes of interest, is presented as a method of deter-
mining the adsorption characteristics of a formation. Adsorption properties
are necesary to predict restoration from both in situ coal gasification and in
situ uranium extraction. Two field push-pull tests were conducted on uranium
formations in Wyoming. Adsorption properties estimated from these tests on
the basis of a simple cell model were compared to the laboratory values. In
the first case, excellent agreement was observed between the values estimated
from the field test and the values measured in the laboratory. In the second
case, the value for k^ determined in the laboratory was five times higher than
the field value. It was concluded the the push-pull test is a viable technique
for comparing laboratory to field adsorption values (Drever and McKee, 1979).
Analysis of Groundwater Criteria and Recent Restoration Attempts
The objectives of this work effort are to present, compile, and compare the
criteria for groundwater quality restoration and the effectiveness and costs of
the methods used, to develop empirical expressions for predicting the amount of
aquifer flushing that is required, and to improve predictions for the costs of
restoration. This is an ongoing effort by Resource Engineering and Development,
Inc. (U.S. Bureau of Mines, 1980).
Assessment of Leachate Movement from Ponded Uranium Mill Tailings
This research project was designed to determine the interaction of tailings
leachate with clay liner material and subsurface sediments that are representa-
tive of the Morton Ranch site. Using obtained interaction data, numerical
models then were to be used to describe and predict the groundwater leachate
movement beneath the tailings pond. The project was scheduled to be completed
by early 1980. The project was supported by the U.S. Nuclear Regulatory
Commission and was conducted by Battelle Memorial Institute in Columbus, Ohio.
The project sponsor was R.J. Serne of the Pacific Northwest Laboratory (SSIE,
1980).
87
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Biochemistry of Uranium Mill Wastes
Studies in the southwestern U.S. are being conducted by personnel at the
Los Alamos Scientific Laboratory (DOE) to evaluate the transport and environ-
mental fate of contaminants associated with uranium mill tailings and to in-
vestigate methods of containment of these waste materials. Contaminants of
interest include Se, Mo, As, V, U, and Ra^26. Field studies at inactive tailing
piles have included groundwater quality monitoring, measurement of radon-222
flux, investigation of contaminant uptake by vegetation, and stabilization of
sites by establishing native vegetation. The primary investigator on this
project is D.R. Dreeson. (SSIE, 1980).
Cleanup and Recycle Technology for Mine and Mill Waters
The objective of this project is to devise process-water treatments that
permit water reuse or safe discharge and recovery of minerals and metals con-
tained in the waters. Work will include the removal of heavy metals from
ammoniacal process solutions used in permit fertilizer production; removal of
selenium from uranium mine wastewater in Ambrosia Lake, New Mexico; and recovery
of molybdenum catalyst preparation wastewater. (U.S. Bureau of Mines, 1980).
Computer Simulation of Chemical Concentrations During In Situ Leaching
A solute transport model is to be developed using the ISL-50 hydrology
model and a simulation of leaching chemistry kinetics. Use of the model would
enable site operators to predict recovery rates for in situ leaching of copper
and uranium and to assist in the optimal selection of well locations, pumping
rates, and leachant and oxidant concentrations. Project completion was sched-
duled for the end of FY 79. This project was performed by the Bureau of Mines,
Twin Cities Metallurgy Research Center, Minnesota. Project contact is R.D.
Schmidt (SSIE, 1980).
Contamination of Ground and Surface Waters by Uranium Mining and Milling
This project will involve work efforts to measure rate of pollutant migra-
tions from uranium mining and milling operations, to develop improved techniques
for describing these migrations and predicting their rates, to determine if algae
and bacteria can be used to lower pollutant concentrations and hence, to reduce
water pollution. This effort is through the University of Colorado (U.S.
Bureau of Mines, 1980),
Detection of Lixivlant Excursions with Geophysical Resistance Measurements
During In Situ Uranium Mining
Westinghouse Electric Corp. of Annapolis, Maryland, is planning to develop,
test, and demonstrate a commercially acceptable resistance measuring system.
The system would detect the excursion of a lixiviant, with a resistivity of
about half of the groundwater it displaces, before it reaches a monitoring well
at a depth of 120 m (400 feet). This work is sponsored by the Bureau of Mines,
TVin Cities Mining Research Center, Minnesota (SSIE, 1980).
88
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Development of Field-Demonstration of Environmentally Attractive Leachants
Project objectives are to determine whether sodium carbonate or potassium
carbonate, with or without clay-encapsulating additives, can be substituted
for ammonium carbonate as a leachant without excessive cost or loss or per-
meability, and to determine the optimum strengths of these leachants for ex-
tracting uranium from several types of sandstone ores. This is an ongoing
effort by the University of Texas. In a new follow-up project, the techniques
that are developed will be field-demonstrated (U.S. Bureau of Mines, 1980).
Development of In Situ Leaching Technology for Uranium
The objective of this project is to improve the following processes for
in situ uranium leaching: the construction of injection wells, the selection
of lixiviants, and the restoration of groundwater quality after leaching. The
Bureau of Mines, TVin Cities Metallurgy Research Center, is performing the
research (SSIE, 1980).
Environmental Aspects of Uranium Mining in Minesota
During this project, the possible environmental problems will be defined,
baseline environmental monitoring programs will be developed, and environmental
effects research will be initiated. This project will involve work, with the
State, landowners, and potential mining companies. This is an ongoing project
(U.S. Bureau of Mines, 1980).
Evaluation of Best Management Practice for Mining Solid Waste Storage,
Disposal, and Treatment
The objective of this program is to extensively monitor ground and surface
water and air quality at approximately eight waste disposal sites including
metallic ores, phosphates, and uranium. In order to comply with sections 3004
and 4004 of the Resource Conservation and Recovery Act, EPA is sponsoring this
study with the Bureau of Mines cooperation. EPA will use the results of this
study in their development of standards for "Best Management Practice" for
disposal of metallic ores, phosphate, and uranium wastes. This is an Inter-
agency Agreement with EPA, and contract to PEDCo (U.S. Bureau of Mines, 1980).
Evaluation of Lixivlation of Mine Wastes
The purpose of this project is to determine which types of, and to what
extent, mineral wastes contaminate groundwater through leaching of acid-forming
or toxic-forming materials. This is an ongoing effort by Calspan Corp. (U.S.
Bureau of Mines, 1980).
Geochemistry of Uranium Leaching
This project involves a study of the processes that are involved in the
leaching of uranium ores. The studies concentrate on the interactions between
the host rock and leaching agents. Empirical and theoretical models of the
89
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interactions are to be developed so as to enable operators to minimize their
impact on the environment. The principal investigator is R.W. Potter, of the
U.S. Geological Survey (USGS), Geologic Division (SSIE, 1980).
Hydrochemical Controls on the Migration of Radionuclides from Uranium Mill
Tailings
As of FY 79, research was being conducted to characterize the physical,
chemical, and mineralogic nature of uranium mill tailings, to determine the
mobility of radium associated with the tailings, and to examine the hydro-
geochemical controls on the groundwater transport of radium. Parts of this
research project involved core sampling of tailings piles, analysis of tail-
ings, examination of radium leaching behavior and distribution, radium trans-
port modeling, and literature review. E.R. Landa is the principal investi-
gator and is with USGS, Water Resources Division, Reston, Virginia (SSIE,
1980).
Hydrologic Impact of In Situ Mining, Weld County, Colorado
The objective of this project is to develop a non-conservative solute
transport model that is capable of simulating the in situ solution mining of
uranium. The model would be used to determine the hydrologic impacts of the
Wyoming Minerals Corporations's in situ mining activities on the groundwater
resources in that mining area. Subtasks include: termination of aquifer
hydraulic properties and regional groundwater flow patterns, monitoring of an
installed observation well for chemical leachate, adaption of the Intercomp
Model to simulate the leachate distribution with time, and model verification.
As of FY 1979, this program was being conducted USGS, Water Resources Division,
Lakewood, Colorado. J.W. Warner is the project contact (SSIE, 1980).
In Situ Leaching Studies on Uranium Ores
The objectives of this study were to develop a technique for the labora-
tory simulation of in situ uranium leaching and to determine the effects of
leaching variables on the permeability and uranium extraction from ores found
in Texas and Wyoming. The project was to have been completed by late 1978 by
Westinghouse Electric Corp., Pittsburgh, Pennsylvania, and was supported by
the Bureau of Mines, Salt Lake City, UTAH (SSIE, 1980).
In Situ Uranium Leach Mining: Consideration of Monitor Well Systems
David L. Durler of United States Steel Corp., and Arthor L. Bishop of
Uranium Resources Inc., discuss the importance of certain geologic factors
that can influence the groundwater regime and, hence, can affect the adequacy
of groundwater monitoring programs. Case histories of three in situ projects
are presented (Durler and Bishop, 1980).
New Mexico's First Uranium In Situ Solution Extraction Project
Mobil Oil Corporation began operation of a pilot plant in November, 1979
in northwestern New Mexico. the 3-year pilot test program is intended to
determine the technical feasibility, environmental impact, and economics of
90
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the operation prior to expansion into commercial production. Initial data
indicate that the leach front behavior has been acceptable and that there has
been no increase in radon-222 levels at the pilot plant site. No data were
available on product shipment or aquifer restoration because neither of these
project phases had begun, as of September, 1980 (Coleman and Stewart, 1980).
Operating Experience in the Recovery of Uranium at the Pawnee and Zamzow Sites
Intercontinental Energy Corporation (IEC) is recovering uranium by in situ
leaching at the Zamzow site and has completed its production at the Pawnee site;
both sites are in South Texas. The authors, Velu Annamalai of IEC and Francis
X. McGravey of Ionac Chemical Co. (1980), discuss the solution mining methods
that have been used and the problems related to the ion exchange process. The
Pawnee site restoration program methods for handling wastes, and approaches to
the control of groundwater contamination also are discussed. Additionally,
Zamzow plant practices and economics are outlined and process modifications are
suggested.
Radiation Dose Models Application to Uranium Solution Mining
Models to estimate radiation exposure from nuclear facilities are to be
adjusted to determine the doses that might arise from uranium solution mining,
waste spills, and waste storage facility leaks. Using potential theory for
fluid flow under a gravity head, the flow to drinking water and irrigation
reservoirs can be estimated. This was to be a FY 77 research project conducted
by Professor T.A. Parish and C.W. Bishop of the University of Texas, Department
of Mechanical Engineering, Austin, Texas (SSIE, 1980).
Research Within the Coordinated Program on Bacteria Leaching of Uranium Ores
Part of this FY 1977 project included an evaluation of the effectiveness of
biocide applications in order to prevent bacterial activity in dumps that con-
tain uranium waste material. Delaying the biochemical processes, which inten-
sifies uranium leaching from waste piles, should mitigate adverse environmental
effects. This project was conducted by the Rudarski Institute in Yugoslavia
(SSIE, 1980).
Restoration of Groundwater Quality After In Situ Uranium Leaching
The purposes of this project were to evaluate existing methods of restor-
ing groundwater quality after in situ uranium leaching, to evaluate alternative
methods, to rank the methods according to their effectiveness, and to identify
technological deficiencies in the state of the art. Information sources were
to include published literature, contacts with leaching companies, and the
project staff experience in water treatment. The project was to have been
completed during FY 1977 by the Bureau of Mines, Twin Cities Mining Research
Center, Minnesota, under the direction of D.R. Tweeton (SSIE, 1980).
Restoration of Groundwater Quality Following Pilot-Scale Acidic In Situ
Uranium Leaching at Nine-Mile Lake Site Near Casper, Wyoming
Engelman, et al. (1980) report on the methods used and the results of the
9-month restoration program that began in November 1978. The project was con-
ducted under a cooperative agreement between the Bureau of Mines and a joint
91
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venture consisting of Rocky Mountain Energy, Halliburton, and Mono Power Co.
About 25 water quality parameters were monitored. pH returned to the pre-
leached baseline at the slowest rate; nearly all others returned within 6
months. Restoration of the Nine-Mile Lake site was considered successful,
which should add to the viability of sulfuric acid as an alternative leachant
for uranium contained in low-calcium carbonate ores. The acid leachant also
sidesteps many of the environmental problems associated with some alkaline
leachants.
Environmental Assessment of Fuel Cycle Facilities
The objective of this project is for Oak Ridge National Laboratory to
provide technical assistance to the NRC in the preparation of detailed assess-
ments of the environmental impacts associated with or potentially associated
with existing or proposed fuel cycle facilties. Included in such facilities
may be in situ uranium solution mines and above-ground uranium leaching opera-
tions, as well as uranium mills, ore buying stations, and fuel fabrication
facilities. H.E. Zittel and M.J. Kelley are the principal investigators (SSIE,
1981).
Evalution of Mass Transport Models for Groundwater Systems
The purpose of this program is to evaluate and develop reliable models that
can predict changes in groundwater quality due to the transport and dispersion
of dissolved chemical constituents. Models are developed or applied to a
variety of problems or areas. One city research plan is the analysis of in
situ uranium leaching or of heavy metal transport from mining waste dumps
or tailings ponds. The principal investigator is L.F. Konikow, who is with
the USGS, Water Resources Division, Denver, Colorado (SSIE, 1981).
Extraction of Radionuclides from Low-Grade Ores and Mill Tailings
The objectives of this program are to investigate the removal, by leaching,
of radium-226 and thorium-230 from uranium mill tailings and ores; and to de-
rive solvent extraction methods for the recovery of radionuclides from the
leach liquors in a form that is easily handled and disposed. The New Mexico
Institute of Mining and Technology, Socorro, New Mexico, is conducting the
research for the Office of Surface Mining Reclamation and Enforcement. The
project contact is A.E. Torma (SSIE, 1981).
Groundwater Management
New computer models will be developed or existing models will be modified
to predict the movement of groundwater and its pollutants. One aspect of this
project will involve the use of models in the study of uranium solution mining.
Artificial groundwater recharge techniques and pollution from sanitary land-
fills also will be studied. The Colorado State government is sponsoring the
work effort that is being performed by Colorado State University, Fort Collins,
Colorado. R.A. Longenbaugh and D.K. Sunada are responsible for this project.
(SSIE, 1981).
92
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In Situ Uranium Mining
Various energy companies are planning to test the feasibility of uranium
solution mining on the Long Pines Area of eastern Montana. This study will
monitor the ecosystem effects of solution mining techniques and wildlife popu-
lations and will develop guidelines for reducing these conflicts. Studies will
be conducted to furnish the baseline data needed to monitor the effects of solu-
tion mining. Long Pines will be used as a model demonstration site for re-
searching the compatibility of wildlife, vegetation, and solution mining. The
project will also review Montana's environmental protection statutes in terms
of protection of the environment. The U.S. Fish and Wildlife Service, Fort
Collins, Colorado, is the sponsoring organization. The research will be con-
ducted by the Montana Department of Fish and Game, in Helena. R. Martinka
is the principal investigator (SSIE, 1981).
93
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REFERENCES
Alvarez, J. J. The Elution and Precipitation Systems at URI's In Situ
Solution Mining Plants In: Proceedings of Fourth Annual Uranium Seminar,
Soc. Min. Eng., Corpus Christi, Texas, 1980. pp. 145-147.
Bowman, W. G. Record Grout Curtain Seals Nile's Leaky Bed. Engineering News-
Record., Feb. 29, 1980. pp. 22-24.
Buma, G. 1979. Geochemical Arguments for Natural Stabilization Following In-
Place Leaching of Uranium: In: Proc. Symposim on In Situ Uranium Mining
and Groundwater Restoration, Soc. Min. Eng., New Orleans, 1979 meeting,
p. 113-124.
Carlson, R. H., R. D. Morris, and R. Schoellinger. 1980. Oxidant Effectiveness
in In Situ Uranium Leaching: In_: Proc. of Fourth Annual Uranium Seminar,
Soc. Min. Eng., Corpus Christi, pp. 149-156.
Colorado State University, Waste Guide for the Uranium Milling Industry, U.S.
HEW, Public Health Service Pub. TW-W62-12.
Cotter Corporation. 1978. Application for License, USNRC Docket No. 40-8692,
March 24, 1978.
Cotter Corporation. 1980. Letter from Mr. Timothy Smith to Mr. Jack
Rothfleisch, USNRC, August 25, 1980. USNRC Docket No. 40-8692.
Cowan, C- E., M. A. Parkhurst, R. J. Cole, D. Keller, P. J. Mellinger, and
R. W. Wallace, 1980. Some Implications of In Situ Uranium Mining Tech-
nology Development: Battelle Pacific Northwest Laboratory, for U.S.
Dept. of Energy, Report PNL-3439, UC-11.
Cummins, A. B., and I. A. Given. 1973. Society of Mining Engineers Handbook,
Volume 2. Society of Mining Engineers of the American Institute of
Mining, Metallurgical and Petroleum Engineers, Inc.
Degens, E. T. 1965. Geochemistry of Sediments: Englevrood Cliffs, New Jersey,
Prentice-Hall, Inc. , 324p.
De Voto, R. 1978. Uranium Geology and Exploration: Colorado School of Mines,
Golden, Colorado.
Durler, D. L. and A. L. Bishop, 1980. In Situ Uranium Leach Mining:
Considerations for Monitor Well Systems: Soc. Petr. Eng., Ann. Meeting,
Dallas (preprint)
Engineering Mining Journal, Jan. Article on Mobil's New Mesquite Plant. 1981.
P. 54-57.
Englemann, W. H., P. E. Philips, D. R. Tweeton, K. W. Loest, and M. T. Nigbor.
Restoration of Groundwater Quality Following Pilot-Scale Acidic In Situ
Uranium Leaching at Nine-Mile Lake Site Near Casper, Wyoming: Soc.
Petr- Eng., Ann. Meeting, Dallas, Texas, 1980. (preprint)
94
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Exxon Minerals Co. 1978. Application of Amendment to License, to USNRC,
Jan. 19, 1978: USNRC Docket No. 40-8064.
Freeze, R. A., and J. A. Cherry, 1979. Groundwater: Englewood Cliffs,
New Jersey, Prentice-Hall, Inc., 604p.
Galloway, W. E., C. D. Henry, and G. E. Smith, 1981. Predicting Response
of an Aquifer System to Uranium Extraction: Report IERL of U.S. EPA,
Cincinnati, 414p. (draft).
Hart, 0. M. 1968. Uranium in the Black Hills.
Henry, C. D. 1980. Uranium and Molybdenum in Groundwater of the Oakville
Sandstone, South Texas: Implications for Restoration of Uranium Mines:
in Proc. of 4th Ann. Uranium Seminary, Soc. Min. Eng., Corpus Christi,
Sept. 1980, pp 19-34.
Huff, R. V., D. H. Davidson, D. Baughmann, and S. Axen. 1980. Technology for
In Situ Uranium Leaching: Mining Eng., Feb., pp. 163-166
International Society of Soil Mechanics and Foundation Engineering. 1963.
Grouts and Drilling Muds in Engineering Practice: London Symposium, May
1963, Butterworths.
Rasper, D. R., H. W. Hartin, L. D. Munsey, R. B. Bhappu, and C. K. Chase,
1979. Environmental Assessment of In Situ Mining: U.S. Bureau of Mines
Report, Contract No. J0265022, PRC Toups, 292p.
Kelley, V. C. , D. F. Kittel, and P. E. Melancon. Uranium Deposits of the
Grants Region: In: Ore Deposits of the United States, 1933-1967, Vol. I,
John D. Ridge (ed.)
Langen, R. E. and A. L. Kidwell. 1971. Geology and Geochemistry of the
Highland Uranium Deposit, Converse County, Wyoming: Earth Science
Bulletin, vol. 6, pp. 41-48.
Ledbetter, Joe 0. 1980. Health Physics for the Above Ground Uranium Miner
and Producer: in Proc., 4th Annual Uranium Seminar, Soc. Min. Eng.,
Corpus Christi, Sept. 1980 Mtg.
Mining Record, June 25, 1980-
Mobil Oil Corporation, 1978, Interim Mining and Reclamation Plant for Pilot
Testing of In Situ Uranium Leaching, Crownpoint Project, McKinley County,
New Mexico.
Mobil Oil Corporation, 1979, Report on Mesquite Mine to Texas Dept. of Water
Resources.
Mobil Oil Corporation, 1979a, Letter from Wm. A. Trippet II to Texas
Department of Water Resources, Nov. 30, 1979.
Mobil Oil Corporation, 1980, Letter from Wm. A. Trippet II to Texas Dept. of
Water Resources, received Jan. 29, 1980.
95
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Nordhausen, E. A., 1980. The States of Permitting for an Uranium Mine and
Mill: in Proc. , 4th Annual Uranium Seminar, Soc. Mining Engrs., Corpus
Christi, Sept. 1980 Mtg.
Ogle Petroleum Mine at Bison Basin, Fremont County, Wyoming - Environmental
Report: USNRC Docket No. 40-8745.
Rex Chainbelt, Inc. 1970. Treatment of Acid Mine Drainage by Reverse Osmosis:
Penn Dept. of Mines and Mineral Industries, Rpt., Contract No. FWPCA
14010 DYK.
Riding, J. R. , F. J. Rosswog, G. Buma, and D. R. Tweeton. 1979. Groundwater
Restoration for In Situ Mining of Uranium: ^n Proc., Symposium on In
Situ Uranium Mining and Groundwater Restoration, Soc. Min. Eng., New
Orleans, 1979 meeting, pp. 67-86.
Siras, P. U. , and Sheridan, D. M. 1964. Geology of Uranium Deposits in the
Front Range, Colorado: U.S. Geological Survey Bulletin 1159.
Stone, W. J., 1979. Hydrologic Constraints and Impacts Associated with Uranium
Extraction, San Juan Basin, New Mexico. Presented at the Geological
Society of America 92nd Annual Meeting, San Diego, California, November
5-8, 1979. Geological Society of America Abstract Programs, Volume 11,
No. 7, Page 524.
Taylor, W. R. 1979. Groundwater Quality Protection in In Situ Uranium Mines.
Texas Department of Water Resources. Proceedings of the New Orleans
Symposium, Feb. 19, 1979.
Todd, D. K. 1967. Groundwater Hydrology. John Wiley & Sons, Inc. New York,
New York.
Tweeton, Daryl R. , Gregory R. Anderson, Jon K. Ahlness, Orrin M. Peterson, and
William H. Engleman. 1979. Geochemical Changes During In Situ Uranium
Leaching with Acid: In: In Situ Uranium Mining and Groundwater Restoration,
Proc. of Symposium, New Orleans, Soc. Min. Eng., Amer. Insti. Min. Eng.,
pp. 23-51.
Tweeton, D. R. , T. R. Guilinger, W. M. Breland, and R. Schecter. 1980. The
Advantages of Conditioning an Orebody with a Chlorite Solution Before
In Situ Uranium Leaching with a Carbonate Solution: Soc. Petrol. Engrs.,
Ann. Mtg., Dallas.
U.S. Department of Energy. 1980. Statistical Data for the Uranium Industry:
Rpt. GUO-100(80), Grand Junction, Colorado.
U.S. Environmental Protection Agency. 1975. Primary Drinking Water Regula-
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U.S. Environmental Protection Agency.
Permit Regulations and Technical
ground Injection Control Programs:
42472-42512.
1980. Water Programs; Consolidated
Criteria and Standards; State Under-
Federal Register, June 24, pp.
96
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U.S. Nuclear Regulatory Commission. 1978. Final environmental statement
related to the operation of Irigaray Uranium Solution Mining Project,
Wyoming Mineral Corporation (NUREG-0481): USNRC Docket No. 40-8502
Sept. 1978.
U.S. Nuclear Regulatory Commission. 1980. Order to show cause, to Wyoming
Minerals Co., April 21, 1980: USNRC Docket No. 8502.
Van Everdingen, R. 0. and R. A. Freeze. 1971. Subsurface Disposal of Waste
of Waste in Canada, Technical Bulletin No. 49, Inland Waters Branch,
Department of the Environment, Ottawa, Canada.
Warner, D. L. 1965. Deep Well Injection of Liquid Waste, U.S. Dept. of
Health, Education and Welfare, Public Health Service Publication No.
99-WP-21, 55p,
Warner, D. L. and J. H. Lehr. 1977. An Introduction to the Technology of
Subsurface Wastewater Injection, U.S. Environmental Protection Agency,
EPA-600/2-77-240, 344p.
Wyoming Department of Environmental Quality. 1978. Letter from Mr. W. C.
Ackerman to Mr. W. A. Eisenbarth, WMC, Aug. 18, 1978: USNRC Docket No.
8502.
Wyoming Department of Environmental Quality. 1980. Letter from Mr. Dennis
Morrow to Ms. Donna Wickers, WMC, March 21, 1980: USNRC Docket No. 8502.
Wyoming Mineral Corporation. 1974. Environmental Survey Supporting the Appli-
cation for a Source Material License for a Solution Mining R&D Program:
USNRC Docket No. 40-8502, March 29, 1974.
Wyoming Mineral Corporation. 1979-80. Correspondence to various individuals
in the USNRC and Wyoming DEQ: USNRC Docket No. 8502.
Yan, Tsoung-yuan. 1980. A method for Removing Ammonium Ions from Subter-
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Ann. Mtg., Dallas, 1980.
97
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APPENDIX A
URANIUM MINING AREAS IN THE UNITED STATES
In this chapter, areas of uranium mining in the United States are identi-
fied. Figure 17 shows the areas reporting uranium production through 1979. The
largest proportion of production has come from Wyoming, western South Dakota
and the Colorado Plateau regions of Utah, Colorado, New Mexico, and Arizona.
Texas has assumed an increased proportion of the production in recent years.
Within the United States the known uranium reserves and reliably delineated
resources are sandstone ores, magmatic-hydrothermal vein systems, and vein or
breccia deposits in sedimentary rocks. The sandstone ores constitute the
greatest proportion of the known U.S. reserve.
A.1 TYPES OF MINEABLE URANIUM DEPOSITS
Sandstone Deposits
It is estimated that 90% of the proven uranium in the United States occurs
in sandstone ores. The bulk of this reserve and all of the active mines of
this type located in the western Cordillera and on the Texas Gulf Coast.
The two types of uranium deposits found in sandstone are differentiated by
their geometric and morphologic relationships to the enclosing host rocks.
These two types are known as roll front and tabular deposits. Often the actual
deposit is a gradation between the two.
Roll front deposits—Typical roll front deposits are peneconcordant to
bedding, display sharp contacts between ore and gangue, and are curvilinear in
cross section. Localization of the ores is controlled by the oxidation-reduc-
tion (redox) boundary. The roll front cuts across sandstone bedding, and the
ore deposit is situated on the downdip (unoxidized) side of the boundary
(Figure 18). The host sandstone is commonly overlain and underlain by unoxi-
dized, less-permeable sediments.
The grade of this type of deposit averages 0.2 to 3.0% l^Og, decreasing
with increasing distance from the redox boundary. In plan, ore bodies are
sinuous, reflecting the geometry of the channel-fill sandstone host rock.
Although the sand might extend laterally for many miles, the metal deposits
are not necessarily present along the entire redox boundary.
Carnotite, uraninite, and coffinite are the most abundant uranium-bearing
ores. Individual deposits range in size from small pods containing a few tons
of ore to large deposits of several million tons. In general, however, ore
deposits are small, with lengths and widths rarely exceeding 305 m (1,000 feet).
98
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Figure 17Uranium-Producing Areas of the United States
(U.S. DOE, 1980)
99
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-------
Roll front deposits have no recognizable spatial relationship to igneous-
hydrothermal or tectonic activity. The uranium contained in them is thought
to have originated from the weathering of volcanic rocks. Groundwater carried
the oxidized, dissolved hexavalent uranium down gradient to reducing environ-
ments where it was deposited. Reducing environments seem to have formed where
carbonaceous material was abundant. Many roll front ores appear to be the
result of the remobilization by groundwater of previously deposited ores.
Tabular deposits—Tabular uranium deposits are conformable with the bed-
ding of the host sandstone and are generally oriented subparallel to the strike
of the host rock (Figure 18). Grain size of the sandstone host varies from
coarse, where tabular deposits occur in paleochannels , to fine in crevasse-
splay paleoenvironments. Sorting is usually poorer in tabular sandstone hosts.
Tabular deposits occur in locally reduced environments in otherwise oxidized
sandstone and, unlike roll front deposits, show little evidence of remobili-
zation. Typically, tabular deposits contain a higher ratio of vanadium to
uranium, a lower than average uranium grade and a larger areal extent than
roll front deposits. Uraninite and coffinite are the dominant ore minerals,
wtih little carnotite. Area often exceeds 305 m (1,000 feet).
The mechanism of formation for tabular deposits is thought to be similar
to that for roll fronts. However, evidence for secondary remobilization is
absent. Among the explanations offered for the apparent lack of remobili-
zation are low permeability of the poorly sorted, tabular host sandstone and
the ability of the vanadium to fix uranium in relatively stable uranyl vanadate
compounds.
Most uranium in the United States comes from sandstone deposits in Wyo-
ming, Texas, and the Colorado Plateau region. The deposits of these regions
are discussed below.
Deposits in the Wyoming Basin—
Figure 19 shows the major uranium mining areas of the Wyoming Basin. Most
of these areas are within the state of Wyoming, but a portion of the Poison
Basin and the entire Maybell District are in northwest Colorado.
The Wyoming Basin formed during the Cretaceous Period. Later, uplift along
the margins of the basins in the lower Tertiary Period resulted in the deposi-
tion of thick sequences of terrestrial clastic sediments that were subsequently
buried and later exhumed during the upper Tertiary period. After deposition
of these beds, uranium was leached from outcropping granites and volcanic rocks,
transported in solution by groundwater, and deposited in the permeable sand-
stones of the basin.
The Wasatch, Wind River and Battle Spring Formations of early Eocene age
and the Fort Union Formation of Paleocene age contain most of the known reserves.
The deposits occur in fluvial carbonaceous sandstones in the Crooks Gap, Gas
Hills, Southern Powder River, Great Divide and Shirley Basins. They are typical
roll front deposits with uranium concentrated along the redox boundary. Tongues
of altered sandstone characterized by the presence of hematite, and an alteration
envelope of siderite, sulfur, and ferrosalite extend downdip into unaltered,
101
-------
MONTANA
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Significant uranium occurrences
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—
100
KILOMETERS
IX
_)
Figure 19, Uranium Deposits in the Wyoming Basins (DeVotcr, 1978).
102
-------
pyritic gray sandstone. Oxide staining is marked within the Powder River Basin
but subtle in the Gas Hills and Shirley Basin.
Other formations in Wyoming with reported uranium reserves include the Tea-
pot Sandstone Member of the Cretaceous Mesaverde Formation along the southwestern
flank of the Powder River Basin, the Cretaceous Louise Formation in the north-
eastern portion of the Powder River Basin and the Miocene Browns Park Formation
in the Washakie and Sand Wash Basins. Known mineable reserves in Wyoming also
occur in the Hanna, Big Horn, and Green River Basins.
Deposits in South Dakota—
The only significant uranium production in South Dakota has come from the
Southern Black Hills district, a portion of the larger Inyan Kara belt of min-
eralization along the southeast flank of the Black Hills (Figure 20).
The uranium mineralization occurs in the Lower Cretaceous Inyan Kara Group
which consists of interbedded fluvial and marine-fluvial sandstones. The bulk
of the reserve is restricted to a single deposit, the Harber Mine, containing
600,000 tons of uranium ore with an average grade of 0.23% U3O3. Ores are
localized in the basal Dakota Sandstone Formation, just above its contact with
the underlying Morrison Formation. The Dakota is a fluvial, carbonaceous,
arkosic sandstone.
The major deposit is tabular in shape with an average thickness of 1.2-
1.8 m (4 to 6 feet), although thicknesses of 3.7 m (12 ft.) are not uncommon.
Uraninite and coffinite are the principal ore minerals. Genesis of the ores is
thought to be related to uplift of the Black Hills during the Oligoecene Epoch,
subsequent leaching of tuffaceous beds by groundwater, and deposition of leached
uranium in a reducing environment in the Inyan Kara Group.
Deposits in New Mexico
The major unranium-producing mines in New Mexico lie within the 137 km (85
mi.) long Grants Mineral Belt in the northwestern corner of the state, with the
bulk of the production coming from the Ambrosia Lake and Laguna districts (Figure
21). The Grants District lines within the Colorado Plateau physiographic province.
The Colorado Plateau is a region of uplifted sedimentary igneous and volcanic
rocks which range in age from Precambrian through Tertiary. The Plateau was
tectonically stable during much of the Paleozoic. Deformation, beginning in the
Pennsylvanian Period, form the Zuni uplift. Detritus shed by the uplift filled
the San Juan Basin to the north. Rejuvenation during the Cretaceous Laramide
orogeny resulted in the deposition of additional sediments in the San Juan Basin.
The uranium occurs predominantly in terrestrial sandstone of the upper part
of the Morrison Formation of Jurassic age, but less important deposits are found
in the Todllto Limestone (Jurassic) and Dakota Formation (Cretaceous). The
major producing horizons in the Morrison (the Westwater Canyon and Jackpile Sand-
stone) are fluvial, lenticular, quartzose or arkosic sandstone interbedded with
claystone and mudstone. The sandstones are paleochannel systems ranging in
width from tens of feet to many miles.
103
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MONTANA
WYOMING
Devils Tower
BUTTE
CROOK
MEADE
Riv.
Belle Fourche
Sturgis
LAWRENCE
Rapid City
PENNINGTON
a
Newcastle
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OUTCROP OF INYEN KORA GROUP
© SOUTHERN BLACK HILLS DISTRICT
© CARLILE DISTRICT
@ HULETT CREEK DISTRICT
MILES
KILOMETERS
fall river
Figure/ 70 Uranium Deposits in the Southern Black Hills
/'(Hart, 1968)
1G4
-------
108'
106'
REGION
108'
-CHURCHROCK
SMITH LAKE
/'«¦
Block Jock No 2
GALLUP ~ Hoobock No.
Block Jock No. I
56° 30*
Diamond
No. 2
55° 30'
jr. AMBROSIA
LAKE
Mian.:\ .-'Canton
GRANTS
NORTH
LAGUNA
MILES
U.S. 66
SOUTH
LAGUNA
100
107'
Figure 2lt Uranium Deposits in •New Mexico
(Kelley, et al., 1968)
-------
The uranium is disseminated in the sandstone. The average grade is 0.20 to
to 0.30% t^Og and deposit size varies from a few hundred tons to several million
tons. The ore consists mainly of uraninite, coffinite and secondary oxides,
including carnotite and uranophase.
The history of the Grants District ores is complex. At Ambrosia Lake, two
principal stages of ore formation are recognized, separated by Laramide faulting.
It is generally agreed that the original ores were deposited during the Cretaceous
by groundwaters moving down dip from eroded volcanic and sedimentary rocks.
Subsequent oxidation, particulary during the Quaternary, has significantly modi-
fied many deposits.
Deposits in Arizona—
Uranium mining areas in Utah and Northern Arizona are limited to four dis-
tricts (Figure 22). Of these, only the Lisbon Valley District has recorded signi-
ficant production. The uranium generally occurs in disseminated form in sandstone
but in the Grand Canyon District it is found in breccia pipes. The age of host
rocks varies from Triassic to Upper Permian, the older host rocks lying to the
southwest.
The Lisbon Valley or Big Indian District is an arcuate belt of scattered
deposits 15 miles in length, lying on the southwest flank of the Lisbon Valley
anticline. The uranium deposits range in size from 500 to 1,500 tons and have
an average grade of 0.35% U^O . Uraninite is the principal uranium mineral.
Ore bodies average 2 m (6 feet) thick, are tabular, amoeba-shaped masses and are
concordant to bedding.
The host rock for the ores is the Moss Back Member of the Chinle Formation,
a fluviatile, calcareous arkosic sandstone. Coalified plant material occurs in
sandy lenses and pockets above the basal portion of the sandstone.
The uranium ore deposits are thought to have formed during the Triassic
Period. Anticlinal uplift (of the ancestral Lisbon Valley anticline) resulted
in deposition of the fluvial elastics of the Chinle Formation, of Triassic age,
along the flanks of the anticline. Subsequent Triassic, Jurassic and Cretaceous
sediments buried the Chinle to depths of several thousand feet. Uranium was
leached from interbedded volcanics by oxidizing connate groundwaters and de-
posited downdip under reducing conditions. This emplacement occurred prior to
the Laramide Orogeny, as evidenced by the fact that mineralized beds are offset
by Tertiary faulting.
The Monument Valley-White Canyon District is situated in northeastern
Arizona and southeastern Utah. Production from the district has been limited
due to the small size of the ore bodies. Approximately half of them contain
less than 1,000 tons of ore.
Most of the deposits are in an arcuate belt 5 to 19 km (3 to 12 miles) wide
extending from Monument Valley northward nearly 209 km (130 miles). Uranium
deposits are primarily restricted to favorable carbonaceous sandstone and con-
106
-------
^9 Grand
° Junction
Durango
UTAH
COLORADO
NEW MEXICO
ARIZONA Qr)
Gallup
Flagstaf f
Albuquerque
MILES
Q LISBON VALLEY
WHITE CANYON
(j) MONUMENT VALLEY
@ GRAND CANYON
.A:
Figure^22V Uranium Deposits in Utah and Arizona
107
-------
glomerate beds in the lower part of the Shinarump Member of the Chinle Formation.
Ore deposits are generally linear to curvilinear in outline with lengths of a
few feet to several thousand feet and the thickness of 0.3 to 3.7 m (1 to 12
feet). Uraninite and coffinite are the primary ore minerals. The average
U3O8 grade is unreported, but vanadium (V2O5) averages 0.6% and copper 0.7%.
The ores occur in the Shinarump (the lowermost member of the Chinle), a
fluvial-channel sandstone with interbedded lenticular siltstones and mudstones.
Ore emplacement was similar to that described for the Lisbon Valley district.
Minor uranium production has also come from the Grand Canyon District of
Arizona. Uranium-vandium ores in this district are localized in collapse struc-
tures in the Coconino and Supai Formations of Permian age. The collapse struc-
tures are circular in plan with diameters of a few feet to over 91m (300 feet).
Uranium ore occurs as the cement for the breccia matrix commonly associated
with sulfide mineralizations. Little is known of the genesis of this type of
deposit and its limited areal extent has not made it a candidate for detailed
study. This very small size of th breccia structures also limits to total
reserve potential.
Minor production also comes from deposits in the Toreva Formation of the
Black Mesa Basin, and the Dakota Sandstone in the San Juan Basin of Arizona.
Deposits in Colorado—
Much of the uranium production from Colorado has come from the Uravan
mineral belt (Figure 23). This is a narrow north-northwesterly trending belt
of deposits 97 km (60 miles) in length and 24 km (15 miles) in width. It is char-
acterized by numerous ore bodies of relatively large size in close proximity
to one another. The average grade of U30g is 0.27% and of V2O5 1.46%. Urani-
nite, cof finite and camotite are the main uranium minerals, while vanadium-
bearing chlorite and hydromicas are the major vanadium minerals.
The ore deposits occur principally in the uppermost sandstone unit of the
Saltwash Member of the Mossison Formation of Jurassic age. This unit consists
of sandstone lenses formed by a meandering, braided stream system. These lenses
or channel fills are usually over 1.6 km (1 mile) in length and 15 m (50 feet)
in thickness. The ore-bearing sands are generally fine to medium grain, com-
posed predominantly of quartz with minor amounts of clay minerals, feldspar and
heavy minerals.
The ore minerals are believed to have been precipitated from laterally
migrating solutions. There is no apparent integral relationship between ore
deposits and tectonic structural features, but some deposits do appear to be
grouped in association with buried anticlinal folds.
Deposits in Texas—
Uranium was first discovered in South Texas in 1954. During the following
decade and a half little interest was generated in the deposits, principally
due to their low grade. In the 1970s, solution mining or uranium became econ-
omically feasible and the South Texas deposits began to receive considerable
attention. Today, they have become a center of in situ solution mining study
and are accounting for an increasing share of the annual U3O8 production of the
nation.
108
-------
, o
:
MONTROSE CO.
5W
POLAR
MESA
MOOR
LA SAL
MESA CO
GRAND CO
SAN JUAN CO.
MOUNTAN
l>OJRAVAN
SLICK l/At
ROCK y4L
•^EGNaA
monhcello
abajo
MOUNTAINS
SAN MIGUEL CO.
i
J UTAH
i
COLORADO
L...
...L
...J
¦ naturita
MONTROSE CO.
SAN MIGUEL CO.
Hi
~
MORRISON ANO YOUNGER
FORMATIONS
PRE-MORRISON FORMATIONS
URAVAN MINERAL BELT
ORE DEPOSITS OR GROUP
OF DEPOSITS
MILES
_J_
— t r—
15
KllCMtTERS
J5
OELORES CO.
1
Figure 23. Uranium Deposits of the Uravan District
-------
The uranium deposits occur in a belt of Eocene- to Pliocene-age rocks that
stretch along the entire length of the Texas Gulf Coastal Plain (Figure 24).
The Catahoula Formation of late Oligocene age is the major ore host.
The Catahoula Formation ranges in thickness from 61 m (200 feet) to 305 m
(1,000 feet), thinning over the San Marcos Arch and thickening in the Houston
and Rio Grande embayments. Most of the known deposits occur in the Rio Grande
embayment. The fluvia system in the embayment (the Gueydan Fluvial System) is
characterized by recognizable terrestrial, floodplain, and river channel facies.
It differs from classic systems in the low sinuosity of the river channels. The
ore deposits are usually associated with the thickest and coarsest sand sequences
(channel-fill sands) but isolated deposits occur in sandy siltstone facies (cre-
vasse splays).
Mineralization is typical roll front, redox boundary-controlled in the chan-
nel fill sands, but distinct relationships to redox boundaries are more dif-
ficult to establish for crevasse splay ore deposits. Fault zones appear to have
some effect on localization of ore bodies but little or no effect on others.
Mineralization occurs as disseminated reduced uranium (coffinite) within
medium- to fine-grained sand beds which contain mud lenses and abundant clay.
The redox boundary is often ragged where clay content is higher. The thickest
and more easily mineable ore bodies are restructed to sections that have well
sorted sand and high sand-to-clay ratios
Ore bodies average 4.6 to 6.1 m (15 to 20 feet) in thickness, with lengths
varying from hundreds of feet to thousands of feet. Ore grades are quite low,
often less than 0.1% l^Oy.
In addition to the aforementioned mining areas, minor production occurs from
sandstone uranium deposits in the Permian Cutler Formation of the Paradox Basin,
Utah.
Uranium Vein Deposits in Plutonic Rocks
Uranium production from vein deposits in plutonic rocks has not reached the
proportions of that from sandstones; however, vein-type ores do constitute a
small though significant share of the total production.
Uranium vein ores occur dominantly in felsic igneous rocks and metamorphic
rocks, and the mineable veins are generally restricted to granitic rocks. The
ores are deposited as open-space or fracture fillings along brecciated fault
zones or in stockworks. The major ore mineral is pitchblende (fine-grained,
botryoidal uraninite) with gangue minerals including quartz, calcite, and pyrite/
marcasite. Wall rock alteration is limited, indicating low temperatures of
deposition (i.e., <200° C.) A two-fold model is postulated to account for
uranium in hydrothermal vein deposits. The uranium is thought to be derived
originally from differentiation of MgO-CaO-deficient magmas and transported by
hydrothermal solutions to dilation zones where reducing conditions caused pre-
cipitation. Later, oxidizing groundwaters dissolved some of the near-surface
uranium and reprecipitated it at the redox boundary, causing the formation of
a supergene enrichment zone.
110
-------
GULF
OF
MEXICO
I^SMzone of uranium-bearing rocks
0 APPROXIMATE LOCATION OF IN SITU
MINING OPERATION
Figure 24. Uranium Deposits in South Texas
-------
Colorado Mineral Belt—
The major uranium vein deposits are found in the Colorado Front Range.
They occur in a thick sequence of complexly folded and metamorphosed, Pre-
cambrian sedimentary and volcanic rocks and granitic intrusions. The ore-stage
mineralization appears to be related to early Tertiary hydrothermal activity
associated with the granitic intrusions in the northeast-trending Colorado Mineral
Belt (Figure 25). Localization of the vein ores was strongly influenced by the
prevailing structural trends, northeast-trending Precambrian shear zones, north-
northwest -trending Laramide faults and fracture zones, and east and northeast-
trending folds in Precambrian metamorphic rocks.
The mineable uranium vein orebodies are concentrated in the east-central
Front Range as open space fillings along fractures and faults. The veins occur
within certain preferred host horizons which are characterized by brittleness
(i.e. , they are easily fractured) and anomalous pyrite or graphite content
(indicating the presence of reducing environments). The Schwartzwalder Mine
is the largest and most extensively studied of the vein-deposit reserves, where
the ore occurs as brecciated vein fillings which are estimated to exceed 9.1-11
million kg (20-25 million pounds) of l^Og (DeVoto, 1978).
The richest ore usually occurs where fractures branch or dips change ab-
ruptly. Host rocks include graphitic, pyritic schists, gneiss, quartzite, and
granite pegmatite. Uranium is thought to have been deposited by solutions
carrying in saline, low temperature, aqueous brines which boiled at low
temperatures and subsequently reacted with pyrite and graphite to precipitate
U02.
Midnite District, Washington—
A second district which has recorded major production is the Midnite Mining
District, Washington (Figure 26). Ore has been mined from the Midnite and Sher-
wood Mines with the Spokane Mountain deposit currently under development.
The ore occurs as vein deposits in Cretaceous age, quartz nionzonite and
metasedimentary rocks of Precambrian age. Mineralization is concentrated along
shears and fractures within the intruded granite and the metamorphosed pelitic
sedimentary rocks. Both reduced and oxidized minerals are present in the ores.
Pitchblende is the dominant reduced uranium mineral while autunite, uranophase
and phosphuranylite are common oxidized uranium minerals. Pyrite-marcasite and
pyrrhotite account for as much as 3 to 5% of the ore.
Deposits in the Midnite District average 305 m (1,000 feet) in length and
30 m (100 feet) in width, with thicknesses varying from 0.31 m (1 foot) to over
12 m (40 feet). Ore grade fluctuates widely from 0.01% to 2.8% with averages
of 0.25 to 0.30% U30g.
Ore genesis is complex and as many as five periods of mobilization, trans-
portation and concentration may have occurred. The uranium is thought to have
been present initially as syngenetic accumulations, and subsequently to have
been metamorphosed, intruded and retransported by groundwaters. Recent ground-
water activity is thought to have concentrated the ores to their presently
mineable state.
112
-------
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IGNEOUS ANO METAMORPHIC ROCKS
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^TERTIARY
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tertiary
I
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SEDIMENTARY ROCKS
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KC
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> PRECAMBRIAN
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> ANO
j QUATERNARY
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> AND
J CRETACEOUS
Hlgh-anglo fault dashed where inferred
Thnisl foull samieetti or unper plate
URANIUM OCCURRENCES
O Au-Ag, uraninlte, sulfides
A fluorite, uraninite
q uroninite, adularia, jordlsite,
carbonate
Figure 25. Uranium Deposits in the Colorado Mineral Belt
(De Voto, 1978)
/'
-------
Chewelah
Newport J
Hunters
(
J /
b { * x
DAYBREAK \
-tflfoo
48" 00
SPOKANE MOUNTAIN DEPOSI
MIDNITE
\SHERWOOD
I,
Coeur d Alene
W Reordon
Spokane
T TERTIARY ROCKS
IGNEOUS GRANITIC ROCKS
M METAMORPHIC ROCKS
2? URANIUM MINES
3 Mll.ES ,0
10 is
KILOMETERS
Figure 26- Uranium Deposits ih the Midnite Mining District
/-/
-------
Other Vein Deposits—
Other vein deposits occur in the Copper Mountain District of northwestern
Wyoming, the Sawatch Mountains of central Colorado, the Marysville District,
Utah, and the Bokan Mountain District, Alaska. Production from these districts
is relatively small and the deposits are therefore not discussed here. In
situ mining is not practiced in any of these districts.
A.2 ACTIVE OR PROPOSED IN SITU OR HEAP LEACH OPERATIONS
Known active or proposed leach-mining operations in the United States are
listed in Table 24. These operations have been identified from information
obtained by contacts with state licensing authorities and the U.S. Nuclear
Regulatory Commission.
115
-------
Table 24. l~i"censed-Urariium--Solu"t'iorilMining Operations in the U. S.
State Location or Mine Type of License Operator
Colorado
New Mexicc
Miami
S. Tucson
Maybe11
Naturi La
Grover
Crown Pt.
S. Tread-Grants
L-Bar Ranch
Crovripoint
Church Rock
Heap leaching
Heap leaching
Heap leaching
Vat leach
Id situ
In situ Pilot plant
In situ Cu.Timercial
Scale
In situ Pilot plant
Ir. situ License
Heap leach
Tots: McClary
Ar.ama.x Mininp
Union Carbide
Gates anc Fox
Wyoamg Minerals-
Power kesources
Hob il
Mobi 1
Exxcn
Phillips
United Nuclear
Oregon
McDer/nott, Nevada
In situ License
Placer A.1AX
Kcbryde Mine
In
situ;
lie. issued
Caithness
Trevino Mine
Ir
situ;
lie. issued
Conoco
Hobson Mine
In
situ;
active
Everest
fit. Lucas Mine
In
situ;
lie. issued
Everest
Las Paloas Mine
In
6 itu;
active
Everest
Pawnee Mine
In
situ;
active
IEC
Zaazov Mine
In
situ;
active
IEC
O'Hern Mine
In
situ;
acti ve
Mobil
Holiday Mine
In
Situ;
active
Mobil
El Mesquite Mice
In
situ;
active
Mobil
Fiedrt: Lumbrsf
Mine (3;
In
situ;
active
Mobil
Brelura (2) Mine
In
s i tu;
active
Mobil
Nell Mine
In
situ;
active
Mobil
Karnes County
Heap Leach
Solution En^rg
Palaagana Mine
In
e i tu;
active
Union Carbide
Moser Mine
In
situ;
active
U.S. Steel
Burns Mine
In
situ;
active
U.S. Steel
Clay West
In
situ,
active
U.S. Stee2
Bocts/Brovn
In
situ;
active
U.S. Steel
Pawelek
In
situ;
a ctive
U.5. Steel
Longoria
In
6itw;
active
URI
3enavides
In
situ;
active
UP I
Bruoi
In
01
ft
c
active
Wyo. Mm. Corp
Lasprecht
In
situ;
active
Wyo. Mir*. Corp
Benhatr
In
situ;
lie. issued
Wye. Min. Corp
Washington
Wyoming
Ford, Washington
Mt. Spokane
Highland Mine
Jrcmont Cc.
Nine Kile Lake
Leuenfcerger Mine
Irigaray Mine
North Rolling Pin
Site
Peterson Mine
Charley Pty.
Johnson Co.
Carbon Cc.
Sweetwater Co.
Sundance Project
R?no Creek
Ruth Site
Red Desert
Collins Draw
Bill Saiith Pty.
Willow Creek
Pilot Plant
In situ lie. pending
Commercial in situ
Commercial In situ
Pilot In situ
Pilot 3n situ
Commercial In situ
Pilot In situ
Pilot In situ
Pilot In 61tl
Pilot In bitu
Pilot In situ
Pilot In situ
Pilot In situ
Cornmercial In situ
Pilot In situ
Pilot In situ
Pilot In situ
Pi jot In s i tu
Pilot heap leach
Dawn Mining
Mineral Associates
Exxor.
Ogle Petroleum
Rocky Mtn. Energy
Teton Exploration
Wyoming Minerals Corp.
Clevrland C2: ffr.
Arizoua Public Service
Co.
Cotter Corporation
J & P Corporation
Kerr-McGse
Minerals Exploration
Nuclear Dynamics
Rocky Mtn. Energy
Uranerz U.S.A., Inc.
Void Nuclear
Cleveiand-Cliffs
Kerr-McGee
Cotter Corporation
February,/1981
- . 116-
; i
h L>~
-------
APPENDIX B
PERTINENT FEDERAL AND STATE LAWS AND REGULATIONS
In this chapter, a list of laws and regulations that are applicable to solu-
tion mining and heap leaching of uranium is presented. These laws and regulations
were identified from published Federal sources and by contacting responsible
agencies in the states where unconventional extraction of uranium is going on or
is contemplated.
B.l FEDERAL LAWS AND REGULATIONS
Uranium Mill Tailings Radiation Control Act of 1978 (PL-95-502)
This Act, also referred to as the Mill Tailings Act, authorized the Depart-
ment of Energy to enter into cooperative agreements with certain states to per-
form remedial actions involving residual radioactive materials at existing sites.
The Act also amends the Atomic Energy Act of 1954 and gives NRC direct licensing
authority over uranium mill tailings; prior to this enactment, tailings were
controlled indirectly through licensing of mill operations (Nordhausen, 1980).
By-product materials, which are defined as including wastes produced by the ex-
traction or concentration of uranium or thorium from any ore processed primarily
for its source material content, also are regulated by the Mill Tailings Act.
Other requirements of this regulation include obtaining an additional NRC
license; conducting an environmental impact analysis if required for the permit
application; and providing for the decontamination, decommission, and reclamation
of sites at which ores were processed for their source content and at which by-
product materials were deposited.
Safe Drinking Water Act of 1974 (PL-93-523)
The SDWA is of particular consequence to the in situ uranium leaching industry,
specifically with regard to its Underground Injection Control (U1C) Program
requirements. This provision requires that states develop UIC programs to pro-
tect their underground sources of drinking water from well injection practices
and that they establish permit systems to authorize injection wells. Permitting
of these wells has been incorporated into the Consolidated Permit regulations.
The UIC program is primarily intended to protect existing and potential
groundwater sources for public water supplies. Public water supply systems
include those that have at least 15 service connections or that serve a minimum
of 25 persons. The quality of a potential groundwater source must be such that
the water contains less than 10,000 mg/L IDS and that there Is a sufficient yield
(Riding, et al, 1979). There are provisions, however, that allow state program
administrators to designate aquifers or parts thereof to be exempted from the
regulations. An "exempted aquifer" might be identified if it were mineral pro-
ducing, if the depth precluded the economical feasibility of pumping, or if the
water were unfit for public consumption (Kasper, et al, 1979).
117
-------
EPA categorized injection wells into five classes. Three of these types of
wells could conceivably be used for extraction or disposal activities at an in
situ uranium leach site:
° Class III wells are those used to inject fluids for the solution mining
of minerals, for in situ combustion of fossil fuel, for sulfur mining
by Frasch process, or for recovery of geothermal energy.
° Class IV wells are those used by generators of hazardous or radioactive
wastes, or by owners or operators of hazardous waste management facili-
ties or of radioactive waste disposal sites to dispose of these wastes
into or above a formation which within one quarter mile of the well
contains an underground source of drinking water.
° Class V wells are those injection wells not otherwise classified. (This
includes deep well wastewater disposal at an in situ uranium leach site.)
Operators of permitted Class III wells must comply with requirements for
continuous monitoring, quarterly reporting, well construction, and aquifer re-
storation, among others (Nordhausen, 1980). There is also a general prohibition
against the migration of any injection fluid from a well into an underground
source of drinking water.
EPA has established drinking water standards under the SWDA. Primary standards
are enforceable; secondary standards are recommendations. Although these drinking
water regulations do not specifically regulate in situ leaching, they may be
considered by regulatory agencies when establishing groundwater restoration ob-
jectives. For example, a mine operator may be required to restore an aquifer
to the baseline condition or to the EPA drinking water standards, whichever is
less restrictive.
Energy Reorganization Act of 1974 (PL-93-438)
This Act amended the Atomic Energy Act of 1954 and established the U.S.
Nuclear Regulatory Commission (NRC) as the agency responsible for issuing permits
for uranium mines and mills. In situ uranium mines also are within NRC juris-
diction. For most of the states with know uranium reserves, NRC has delegated
this permit-issuing authority to the states, which are referred to as "agreement
states." In these states, in situ mine operators must apply to NRC for a source
material license and to the state for a mine or mill permit; in non-agreement
states, the miner must apply to NRC for the permits.
National Environmental Policy Act of 1969 (PL-91-190)
NEPA requires a detailed "environmental impact statement" (EIS) on actions
significantly affecting the environment that involve Federal agencies or funds.
The source material license from NRC or state regulations may require the pre-
paration of an EIS for a proposed in situ uranium mining operation. To determine
the necessity of an EIS, a mining applicant would submit an environmental report
to the permitting agency for review. If the review indicates that the action
may significantly affect the environment, an EIS would have to be prepared.
118
-------
Federal Water Pollution Control Act Amendments of 1972 (PL-92-500)
This Act and its subsequent "Clean Water Act" amendments of 1977 have several
provisons that might affect in situ uranium mining operations. Two requirements
that could apply are:
° Obtainment of a permit, under the National Pollutant Discharge Elimina-
tion System (NPDES), for the discharge of pollutants into navigable
waters.
° Compliance with Federal effluent limitations for specific pollutants in
the ore mining industry category.
Prior to the operation of an in situ uranium mine and associated activities
that will involve the discharge of pollutants into navigable waters, an NPDES
permit must be obtained from EPA or the designated state water pollution control
agency. The term, navigable waters, has a very broad definition which encompasses
even surface drainage ditches and intermittent streams. NPDES permitting has
been incoporated into EPA's "Consolidated Permit" regulation.
If contaminants are to be discharged to surface waters, then the effluent
must meet the applicable EPA limitations. For conventional uranium mines and
mills, the effluent guidelines for Ore Mining (40 CFR 400) apply. These set
pollutant-specific daily maximums and monthly averages that are not to be ex-
ceeded. The provision, however, establishes a zero discharge standard for in
situ uranium leaching. The effluent limitations are included in the NPDES permit,
which basically establishes the conditions under which a discharge is permissible
so that state water quality standards for the receiving waters will not be vio-
lated.
B.2 STATE LAWS AND REGULATIONS
Arizona
In Arizona, USNRC regulations cover primary mining and milling operations.
State regulations are being formulated. Existing state regulations govern
secondary processing operations.
California
California has no regulations that are specific for the mining and processing
of uranium and USNRC regulations apply to such operations within the state. Min-
ing activities, including in situ mining, are governed by the California Surface
Mining and Reclamation Act of 1975, administered by the State Mining and Geology
Board. The California Environmental Quality Act of 1970, administered by the
State Resources Agency, specifies requirements for environmental impact state-
ments.
Colorado
Regulations that may be applicable to in situ mining include:
1) The Colorado Mined Land Reclamation Act, revised in December, 1980.
119
-------
2) Rules and Regulations of the Radiation and Hazardous Waste Control
Division, Colorado Department of Health; and
3) The Uranium Hill Licensing Guide, issued by the same organization. A
representative of the Department of Lands stated that solution mining
is governed more by policy than by specific laws.
Idaho
No regulations specific to the mining and processing or uranium exist in
Idaho. The Idaho Department of Health and Welfare's Division of the Environ-
ment is responsible for the administration of the following rules and guidelines:
1) Technical Guide for Control of Water Pollution from Mining and Milling
Operations;
2) Rules and Regulations for the Control of Air Pollution in Idaho; and
3) Water Quality Standards and Wastewater Treatment Requirements for Idaho.
Montana
The Montana Water Quality Act sets water quality standards and regulates
the discharge of pollutants. This Act is administered by the State Department
of Health and Environmental Science. The Department of State Lands administers
the Strip and Underground Mine Reclamation Act of April 1, 1980, and regulations
governing the reclamation of mined lands.
New Mexico
The New Mexico Environmental Improvement Agency, Division of Water Quality
Control, administers the New Mexico Water Quality Control Act and the Environ-
mental Quality Control Act. The regulations of the Water Quality Control Com-
mission establish standards for ground and surface waters. The Radiation
Protection Regulations of the radiation Protection Bureau of the State Department
of Health apply to radiological aspects of uranium mining operations.
South Dakota
Existing regulations for this state are at present incomplete. Presently
applicable regulations include the Surface Mining Land Reclamation Act; other
aspects of uranium mining operations are governed by USNRC regulations.
Texas
The Texas Department of Water Resources administers the following regulations:
1) The Texas Water Code;
2) Texas Underground Injection Control Regulations; and
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3) Texas Consolidated Waste Discharge Permit Regulations.
The Texas Department of Health Resources administers:
1) Radioactive Materials Licences
2) Regulations of the Radiation Control Branch for environmental assess-
ment of in situ uranium mines.
These state agencies review proposed in situ operations and act to ensure
that design, operation, and restoration requirements are met.
Utah
The State Department of Natural Resources, Division of Oil, Gas and Mining,
administers:
1) The Oil and Gas Conservation Act;
2) The Mined Lands Reclamation Act;
3) General Rules and Regulations; and
4) Rules of Practice and Procedure to control underground and surface mining
and drilling activities.
Washington
The State of Washington Department of Ecology administers the State Environ-
mental Policy Act, and has issued Regulations Regarding the Stabilization of
Uranium and Thorium Mill Tailings Piles. These regulations are currently under-
going review and are expected to be modified in the near future.
Wyoming
The State Department of Environmental Quality administers the Wyoming Environ-
mental Quality Act, which governs solution mining and processing of uranium, as
well as effects on the land, air, and water and solid waste management. Regulations
of this Act are the responsibility of the three Divisions of Land, Air, and Water
Quality, respectively. Water Quality Rules and Regulations of immediate concern
to in situ mining operations are set forth in Quality Standards for Wyoming
Ground Waters and Wyoming Ground Water Pollution Control Permit conditions, of
the Division of Water Quality. Wyoming is not an agreement state and licenses
to mine uranium there are obtained from the USNRC.
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