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PREDICTED VERSUS ACTUAL WATER QUALITY AT HARDROCK
MINE SITES: EFFECT OF INHERENT GEOCHEMICAL AND
HYDROLOGIC CHARACTERISTICS
1
Ann Maest
2
, James Kuipers, Kim MacHardy, and Gregory Lawson
Abstract. The Environmental Impact Statements (EISs) for 70 large modern-era
hardrock mines in the United States were reviewed to determine their predicted
impacts to water resources. EIS predictions were then compared to actual water
quality conditions for 24 of the 70 mines (case studies), and the effects of
geochemical characteristics and hydrologic conditions on operational water
quality were evaluated. Nearly all case study mines with close proximity to water
resources and moderate to high potential for acid drainage or contaminant
leaching had operational water quality impacts ranging from increases over
baseline concentrations to exceedence of water quality standards, with most
having exceedences of standards. EIS water quality predictions made after
considering the effects of mitigations largely underestimated actual impacts to
groundwater, seeps, and surface water. EIS water quality predictions made before
the ameliorating effects of mitigations were considered were more accurate at
predicting operational water quality. Of the case study mines with these inherent
geochemical and hydrologic characteristics, at least three-quarters underestimated
operational water quality impacts in their pre-mining EIS predictions.
______________________
1
Poster paper presented at the 7
th
International Conference on Acid Rock Drainage (ICARD),
March 26-30, 2006, St. Louis MO. R.I. Barnhisel (ed.) Published by the American Society
of Mining and Reclamation (ASMR), 3134 Montavesta Road, Lexington, KY 40502
2
Ann Maest, PhD, is an aqueous geochemist with Buka Environmental, 729 Walnut Street, Suite
D5, Boulder, CO 80302. James Kuipers, PE, is a mining engineer with Kuipers and
Associates, PO Box 641, Butte, MT 59703. Kim MacHardy is with Kuipers and Associates,
and Gregory Lawson is with Buka Environmental.
1122
Introduction
This study is part of a larger study on the reliability of water quality predictions in
Environmental Impact Statements (Kuipers et al., 2005). The larger study compares predictions
about operational water quality with predictions made about operational water quality in EISs.
Such a comprehensive comparison has never before been completed for hardrock mines.
Regulatory agencies, the pubic, and the mining community need to know the reliability of water
quality predictions in order to set adequate bond amounts and to reduce future liability associated
with hardrock mining. The public accessibility of documents under the National Environmental
Policy Act (NEPA) made the collection of EISs for this study possible.
Methods and Approach
After identifying 182 major hardrock mines and 136 major mines eligible for National
Environmental Policy Act (NEPA), the Environmental Impacts Statements or Assessments were
reviewed for 70 NEPA-eligible mines. Two levels of study were undertaken for this project:
reviewing all available EISs for information relevant to water quality predictions; and a more in-
depth study of a more limited number of mines for a comparison of predicted and actual water
quality. The primary goal of the in-depth studies is to gain insights into the methods and
approaches used to predict water quality and to determine whether these tools were successful.
For the 70 NEPA-eligible mines with reviewed EISs, the information gathered from the
NEPA documents was scored numerically for entry into an Excel database. The scoring allowed
statistics to be performed on the information in the NEPA documents. The information collected
consisted of the following elements: geology/mineralization; climate; hydrology; field and lab
tests performed; constituents of concern identified; predictive models used; water quality impact
potential; mitigations; predicted water quality impacts; and discharge information. For each
element and sub-element, a score was derived to characterize the element (e.g.,
geology/mineralization used six scores, including one for no information provided). Scores
generally included zero (no information available), 1 for low (acid generation potential, far from
water resources, low potential to impact water resources, etc.), 2 for moderate, and 3 for high or
closer proximity to water resources. For mines with multiple EISs, the highest score was used
(i.e., score for the EIS that predicted the highest acid generation potential or closest proximity to
water resources, etc.) when discussing the mine as a whole. However, the scores for the
individual EIS were also maintained in the database. The details of the scoring are contained in
Kuipers et al. (2005), and specific scoring details for this paper will be provided when the results
are presented in later sections.
Each case study includes a brief description of the information contained in the NEPA
documents for each mine, along with information on water quality impacts either included in the
NEPA documents, or contained in other documents as referenced. A summary of information on
the water quality impacts and their causes is then provided for each mine in the larger study
(Kuipers et al., 2005).
The availability of water quality information after mining began was one of the primary
factors in selecting a mine for in-depth study. For example, a number of operating or recently
closed open-pit mines in Nevada and other states have no or very limited information on pit
water quality because the mines have not stopped dewatering operations. These mines may have
water quality information on groundwater or leachates, but no information is currently available
1123
that can be used to compare pit-lake water quality predictions in the EIS to actual water quality.
In addition to the availability of water quality information, the selected mines are also intended
to represent a cross-section of commodities, mining types, and climates. In making the final
selection of mines for in-depth study, the following priorities were identified: mines with long
histories and NEPA documentation from new project through reclamation and closure; mines
with different proximities to water resources; mines that conducted some geochemical testing,
and if possible, some water quality modeling; and mines with different potentials to generate
acid and leach contaminants to water resources.
There are two types of “predictions” made in EISs: “potential” water quality (a prediction
that does not take mitigations into account) and “predicted” water quality (a prediction that does
take mitigations into account). Nearly all the EISs reviewed reported that they expected
acceptable water quality (concentrations lower than relevant standards) after mitigations were
taken into account. Indeed, if this prediction was not made in the EIS, the regulatory agency
would not be able to approve the mine (with certain exceptions, such as pit water quality, in
states where pit water is not considered a water of the state). For the 70 mines with EISs
reviewed (including the case study mines), we recorded both “potential” and “predicted” water
quality from information in the NEPA documents. For the case study mines, comparisons were
made between potential, predicted, and actual water quality conditions.
The list of mines that meet these criteria and had publicly available operational water quality
information is limited. In some cases, later EISs include an evaluation of operational water
quality conditions. These cases provide the most readily accessible, although not only,
opportunities for insight into the accuracy of water quality predictions made in EISs. In addition
to data from NEPA documents, operational water quality data were obtained from State agencies
or consultant or agency report for mines in Arizona, Nevada, California, and Wisconsin.
Selected Case Study Mines
In all, 22 different mines with complete NEPA documents and additional water quality
information were selected for a comparison of water quality predictions (made in EISs) and
actual water quality conditions after mining began. In addition, two mines presently being
constructed (Safford, AZ and Pogo, AK) were selected to compare NEPA information and
mining practices at new mines with mines that have been operating for various time periods.
Table 1 shows the complete list of 24 mines selected for case studies.
General Characteristics of Case Study Mines
The general characteristics of the case study mines, including location (state), commodity,
extraction and processing methods, and operational status, are similar to those of the larger set of
NEPA mines with reviewed EISs (Table 2). The mines studied in detail include two from
Alaska, three from Arizona, three from California, two from Idaho, six from Montana, seven
from Nevada, and one from Wisconsin. Sixteen primary gold and/or silver mines were selected
for study in detail. Three of the mines selected are primary Cu or Cu/Mo mines. Three mines
selected are polymetallic mines (Au, Ag, Cu, Pb, Zn). One Pt group metals mine and one
primary Mo mine were also selected.
1124
Table 1. Case Study Mines.
Mine State
Greens Creek AK
Pogo AK
Bagdad AZ
Ray AZ
Safford AZ
Jamestown CA
McLaughlin CA
Royal Mountain King CA
Grouse Creek ID
Thompson Creek ID
Beal Mountain MT
Black Pine MT
Golden Sunlight MT
Mineral Hill MT
Stillwater MT
Zortman and Landusky MT
Florida Canyon NV
Jerritt Canyon NV
Lone Tree NV
Rochester NV
Round Mountain NV
Ruby Hill NV
Twin Creeks NV
Flambeau WI
Five of the mines selected for study are underground mines, 17 are open pit mining
operations, and two are combined open pit and underground mining operations. For ore
processing, six of the mines use flotation (and in some cases gravity), two use both flotation and
dump leach solvent extraction electrowinning (SX/EW), one uses dump leach SX/EW
processing, one uses flotation with vat leaching, and 14 use either heap leaching, vat leaching, or
a combination of both processes.
EIS Information for Case Study Mines
Table 3 contains a summary of the information obtained from the NEPA documents for the
case study mines, including: geology and mineralization; geochemical characterization
(including constituent of concern) and modeling performed; water quality impact potential
(including acid drainage and contaminant leaching potential and groundwater, surface water, and
pit water impact potential); predicted water quality impacts (for surface water, groundwater, and
pit water); and discharges (zero discharge, surface water discharge, or groundwater discharge).
The results and discussion in the following sections refer to information presented in Table 3.
1125
Table 2. Comparison of General Characteristics for NEPA Mines with Reviewed EISs and Case
Study Mines.
1126
Characteristic Feature
NEPA-Eligible
Mines with
Reviewed EIS’s
(% of Total)
Case Study
Mines
(% of Total)
Alaska 10%
8%
Arizona 11%
13%
California 11%
13%
Colorado
0% 0%
Idaho 8.6%
8.3%
Michigan
0% 0%
Montana 19%
25%
Nevada 33%
29%
New Mexico 2.9%
0%
South Carolina
0% 0%
South Dakota 1.4%
0%
State
Utah 1.4%
0%
Washington
0% 0%
Wisconsin 1.4%
4.2%
Primary Gold 20%
17%
Primary Silver 7.1%
4.2%
Gold and Silver 54%
54%
Primary Copper 20%
8.3%
Copper and Molybdenum 1.4%
4.2%
Molybdenum 1.4%
4.2%
Lead and Zinc 5.7%
4.2%
Platinum Group 2.9%
4.2%
Underground 19%
21%
Open Pit 71%
71%
Underground and Open Pit 10%
8.3%
Heap or Vat Leach 61%
63%
Flotation and/or Gravity 27%
33%
Dump Leach (SX/EW) 11%
13%
Heap Leach only 26%
21%
Vat Leach only 14%
13%
Heap Leach and Vat Leach 21%
21%
Smelter 1.4%
4.2%
Operating 49%
54%
Closed 37%
38%
In Construction 1.4%
4.2%
Permitting 7.1%
4.2%
Withdrawn 5.7%
0%
Total Number
70 24
Commodity
Extraction and
Processing
Methods
Operational
Status
Table 3. EIS Information for Case Study Mines.
Greens Creek Pogo Bagdad Ray Safford Jamestown McLaughlin Royal Mountain
King
Grouse Creek Thompson
Creek
Beal Mountain Black Pine
AK AK AZ AZ AZ CA CA CA ID ID MT MT
Sulfides present,
carbonate or
mod/high NP
rock present
No/insufficient
information
available
Sulfides present,
no carbonates/
carbonates not
mentioned or
associated with
ore body.
No/insufficient
information
available
Sulfides present,
no carbonates/
carbonates not
mentioned or
associated with
ore body.
No/insufficient
information
available
No/insufficient
information
available
No/insufficient
information
available
Sulfides present,
no carbonates/
carbonates not
mentioned or
associated with
ore body
Sulfides present,
carbonate or
mod- high NP
rock present
Sulfides present,
no carbonates/
carbonates not
mentioned or
associated with
ore body.
Sulfides present,
no carbonates/
carbonates not
mentioned or
associated with
ore body.
Testing
Methods
Static, short-
term leach,
kinetic
Static and kinetic Static None/unknown Static and short-
term leach
Short-term leach Static and short-
term leach
Static Static and short-
term leach
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
No information
Constituents
of Concern
zinc No information
available
arsenic, fluoride,
lead, metals,
sulfate
copper,
beryllium, zinc,
turbidity, pH
Pit: aluminum,
copper, iron,
manganese,
nickel, zinc,
thallium, sulfate
Tailings
leachate:
barium, arsenic,
chromium
copper No information lead, arsenic,
cyanide,
ammonia, nitrate
cadmium,
copper, iron,
lead, zinc,
selenium, sulfate
arsenic,
cadmium, lead,
nitrate, sulfate,
cyanide, TDS
sulfate, copper,
zinc, iron,
cadmium, low
pH
Predictive
Models
Water quality
and quantity
Water quality
and quantity
None None Water quality
and quantity
None None None Water quantity Water quality
and quantity
None None
Acid Drainage
Potential
Moderate Low Low No information Low Low Low Low Moderate Moderate Moderate High
Contaminant
Leaching
Potential
Low Moderate No information No information Low Low Moderate No information Low Low Low Moderate
Groundwater
Impact
Potential
Moderate High Low No information No information Moderate High Moderate Moderate Moderate Moderate No information
Surface
Water Impact
Potential
Moderate Low Low No information No information Moderate Moderate No information Moderate Moderate Moderate No information
Pit Water
Impact
Potential
No pit lake
expected to form
No pit lake
expected to form
Low No information High Moderate High No information Moderate Moderate No information No pit lake
expected to form
Groundwater Low High Low No information Low Low High No information Low Moderate Low Low
Surface
Water
Low Moderate Low No information Low Low Moderate No information Low Moderate Low Low
Pit Water No pit lake
expected to form
No pit lake
expected to form
No information No information Low Moderate High No information Low Low Low No pit lake
expected to form
Zero
Discharge
Yes No information Yes Yes Yes
Surface
Discharge
Yes Yes Yes Yes Yes Yes No information Yes
Groundwater
Discharge
No information
Predicted
Water Quality
Impacts
Discharges
NEPA EIS Water Quality
Category
Geology and Mineralization
Geochemical
Character-
ization and
Modeling
Water Quality
Impact
Potential
1127
1128
Table 3. EIS Information for Case Study Mines.
Golden
Sunlight
Mineral Hill Stillwater Zortman and
Landusky
Florida Canyon Jerritt Canyon Lone Tree Rochester Round
Mountain
Ruby Hill Twin Creeks Flambeau
MT MT MT MT NV NV NV NV NV NV NV WI
High sulfide
content,
carbonates
low/not present
Sulfides present,
no
carbonates/carb
onates not
mentioned or
associated with
ore body.
Sulfides present,
carbonate or
mod- high NP
rock present
Sulfides present,
no
carbonates/carb
onates not
mentioned or
associated with
ore body.
Sulfides present,
carbonate or
mod- high NP
rock present
Low sulfide
content,
carbonate
present or
hosted in
carbonate
Sulfides present,
carbonate or
mod- high NP
rock present
Low sulfide
content,
carbonate
present or
hosted in
carbonate
Sulfides present,
carbonate or
mod- high NP
rock present
Sulfides present,
carbonate or
mod- high NP
rock present
Sulfides present,
carbonate or
mod- high NP
rock present
Sulfides present,
no
carbonates/carb
onates not
mentioned or
associated with
ore body.
Testing
Methods
Static, short-
term leach,
kinetic
Short-term leach
and kinetic
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
Static, short-
term leach,
kinetic
Constituents
of Concern
aluminum,
arsenic,
cadmium,
copper, zinc, pH,
sulfate,
chromium, iron,
lead,
manganese,
nickel, selenium,
nitrate
arsenic, cyanide,
manganese,
nitrate
nitrate aluminum,
cadmium, iron,
copper, fluoride,
zinc, cyanide,
metallocyanide
complexes, low
pH, sulfate,
nitrate, arsenic
aluminum,
antimony,
arsenic,
cadmium, iron,
lead, mercury,
thallium, TDS,
cyanide
arsenic,
selenium,
nitrate, sulfate
arsenic, iron,
cyanide,
antimony,
cadmium, nickel,
fluoride, sulfate,
TDS
iron, aluminum,
copper, lead,
cadmium, zinc,
pH
aluminum,
arsenic, fluoride,
nickel, zinc,
antimony,
selenium, iron,
mercury, lead,
manganese,
nitrate, sulfate,
TDS
arsenic,
aluminum,
antimony, TDS,
pH
pH, TDS, zinc,
beryllium,
cadmium,
selenium,
aluminum,
antimony,
arsenic, iron,
manganese,
mercury, nickel,
thallium, sulfate
iron,
manganese,
sulfate
Predictive
Models
Water quality
and quantity
Water quantity Water quality
and quantity
Water quantity Water quantity None Water quality
and quantity
None Water quality
and quantity
Water quality
and quantity
Water quality
and quantity
Water quality
Acid Drainage
Potential
High Low Low High Low Moderate Moderate Moderate Low Low Moderate No information
available
Contaminant
Leaching
Potential
High Moderate Moderate Moderate High Moderate High Moderate High Moderate High Moderate
Groundwater
Impact
Potential
High Moderate Low Moderate High Moderate Low Moderate High Low Moderate Moderate
Surface
Water Impact
Potential
Low Low Low High No information
available
Moderate Moderate Moderate Moderate Low High Moderate
Pit Water
Impact
Potential
High No pit lake
expected to form
No pit lake
expected to form
No information
available
No information
available
No pit lake
expected to form
High No pit lake
expected to form
Moderate No pit lake
expected to form
High High
Groundwate
r
High Low Low High Low Low Low Low Low Low Low Low
Surface
Water
Low Low Low High Low Low Low Low Low Low Low Low
Pit Water
High No pit lake
expected to form
No pit lake
expected to form
High No pit lake
expected to form
No pit lake
expected to form
High No pit lake
expected to form
Moderate No pit lake
expected to form
High High
Zero
Discharge
No information Yes No information No information Yes Yes
Surface
Discharge
No information Yes Yes Yes No information Yes No information Yes Yes
Groundwater
Discharge
No information Yes No information No information Yes
Predicted Water
Quality Impacts
Discharges
NEPA EIS Water Quality
Category
Geology and Mineralization
Geochemical
Character-
ization and
Modeling
Water Quality
Impact Potential
Inherent Factors Affecting Water Quality at Mine Sites
One of the goals of the larger study (Kuipers et al., 2005) was to determine if there are
certain factors that make a mine more or less likely to cause water quality problems. Some of
the characteristics that may influence the environmental behavior of a mine include:
• Ore type and association (e.g., commodity, sulfide vs. oxide ore, vein vs. disseminated)
• Climate (e.g., amount and timing of precipitation, evaporation, temperature)
• Proximity to water resources (distance to surface water resources, depth to groundwater
resources, presence of springs)
• Pre-existing water quality (baseline groundwater and surface water quality conditions)
• Processing chemicals used
• Type of operation (e.g., vat leach and tailings vs. heap leach facility; underground vs.
surface mine)
• Constituents of concern
• Acid generation and neutralization potentials (and timing of their release)
• Contaminant leaching potential
Of these, the ore type and association, climate, proximity to water resources, constituents of
concern, acid generation potential, and contaminant leaching potential are considered inherent
factors that are a function only of the mine’s geochemical characteristics and physical location.
The acid generation and contaminant leaching potential refer to the potential of the mined
material before mitigations are put in place. While these potentials can have different
environmental effects depending on mitigation, their pre-mitigation potentials are considered
inherent in this study. For this study, the proximity to water resources was considered to be a
function of climatic conditions (as shown in Kuipers et al., 2005); therefore, climate will not be
discussed separately. Similarly, the constituents of concern will be reflected in the contaminant
leaching potential and will not be discussed separately. The characteristics listed above that are
not considered inherent factors are the type of processing chemicals used, the type of operation,
and the pre-existing water quality. These characteristics are instead more dependent on
economics or site history (which in turn is a function of both inherent and non-inherent factors)
than on geochemical and geographic factors.
The following sections examine the influence of inherent factors on operational water quality
for the 24 case study mines. Information from the EISs was used to identify the inherent factors
listed above, and operational water quality was used to determine if water quality impacts were
present after mining began. The inherent factors evaluated below include: geology and
mineralization, proximity to water resources, and geochemical characteristics of mined materials,
such as acid drainage and contaminant leaching potential.
Geology and Mineralization
For five of the 24 case study mines, little or no information was available on rock type or
mineralization, as shown in Table 3. Geologic and mineralogic information available in the EISs
was generally insufficient to make even general predictions about contaminant leaching potential
1129
or acid generation potential based on mineralogy (e.g., identification of arsenic-containing
minerals).
The identification of geology and mineralization, as currently conducted in EISs, is generally
a blunt tool for predicting water quality impacts. Geologic and mineralogic information is
usually focused on the ore body rather than on all mined materials that could potentially impact
water resources. We found relatively weak relationships between geology and mineralization or
ore association and identified acid drainage potential. For example, nine of the case study mines
indicated that either sulfides were present or there was a high sulfide content and that there was
no carbonate material present. However, five of these identified low to moderate acid drainage
potential.
The reasons for the low acid drainage potential scores may be related to different rocks being
evaluated for mineralization and acid drainage potential or to other factors that were considered
by the mine in determining the potential for acid drainage. However, the discrepancy or lack of
good agreement between identified mineralization and acid drainage potential highlights the
importance of coordinating mineralogic and acid drainage potential evaluations in the NEPA
process. As noted in Maest et al. (2005), the same geochemical test units should be used for
testing of all parameters used to predict water quality impacts. In addition, more extensive
information on mineralogy and mineralization should be included in EISs.
Geochemical Characteristics of Mined Materials
This section discusses changes in geochemical characterization approaches over time, as
reflected in the reviewed EISs. It also discusses combinations of geochemical characteristics and
proximity to water resources, and examines linkages between these combinations of inherent
factors and operational water quality.
Changes in Geochemical Characterization Testing over Time. The use of geochemical
characterization testing in EISs has changed somewhat over the years. Mines with EISs or
Environmental Impact Reviews (EIR’s), are expected to have more geochemical characterization
information than mines with EAs. The EISs reviewed in detail spanned a period from 1978 to
2004. The first EISs (for Troy Mine in Montana in 1987 and Zortman and Landusky Mine in
Montana in 1979) did not provide any information on geochemical characterization. Starting in
1980, mines began to provide basic information on geochemical characterization, such as static
and short-term leach testing.
The first kinetic tests performed at the group of 70 mines with reviewed EISs were five-day
“weathering” tests conducted in 1981 at the Stibnite Mine in Idaho. Kinetic testing was
combined with other types of geochemical characterization testing (static and/or short-term leach
tests) beginning in 1986 at the Mineral Hill Mine in Montana. After 1990, many of the mines
were conducting combinations of kinetic testing and static or short-term leach testing. However,
a number of mines still used only static testing to help predict acid drainage potential. The
availability of geochemical characterization data affects our ability to determine the potential for
mines to release contaminants to water resources.
Identified Acid Drainage and Contaminant Leaching Potential. Two of the case study mines had
no information on acid drainage potential (Ray, AZ and Flambeau, WI) in their NEPA
documents (see Table 3). Eleven of the 24 case study mines (46%) identified low acid drainage
potential, eight (33%) identified moderate acid drainage potential, and only three (Black Pine,
Golden Sunlight, and Zortman Landusky – all in Montana) identified high acid drainage
1130
potential. Generally the potential for acid generation was presented verbally in the text of the
NEPA document, even though the basis may have been extensive acid-base accounting (ABA)
and/or kinetic testing. In a number of cases the ABA testing results suggested that the mined
material could be acid generating, but kinetic testing produced neutral leachate and the material
was considered to have low acid generation potential.
The potential for contaminant leaching was generally based on information from short-term
leach tests or kinetic testing. The geochemical testing results presented in the NEPA documents
were used to score the mine as having low potential for contaminant leaching if leachate from the
tests did not exceed water quality standards, moderate potential if the leachate exceeded water
quality standards by one to ten times, and high potential if the leachate exceeded water quality
standards by over 10 times. The verbal summaries, as discussed above for acid generation
potential, were used if no quantitative information was available in the NEPA documents. Three
mines (Bagdad and Ray, AZ and Royal Mountain King, CA) had no information on contaminant
leaching potential in their NEPA documents. Royal Mountain King had information on
contaminant leaching potential in its Report of Waste Discharge, but this information was not
transferred to the EIR and was therefore not readily available to the public. Six mines (25%)
identified a low potential for contaminant leaching; 11 (46%) identified a moderate potential;
and four (17% - Golden Sunlight, MT; Lone Tree, Round Mountain, and Twin Creeks, NV)
identified a high potential for contaminant leaching.
Relationships between Inherent Factors and Operational Water Quality at Case Study
Mines
This section examines the relationships between multiple inherent factors (proximity to water
resources and geochemical characteristics) and operational water quality. For this evaluation, a
water quality impact is defined as increases in water quality parameters as a result of mining
operations, whether or not an exceedence of water quality standards or permit levels has
occurred. Information on whether groundwater, seep, or surface water quality exceeded
standards is also included. For this section, EIS predictions and information are compared to
operational water quality; therefore, the Pogo Mine in Alaska and the Safford Mine in Arizona
are excluded because they have not yet become operational. Mines with close proximity to water
resources and moderate to high acid drainage or contaminant leaching potential are examined
together to determine if this combination of inherent factors results in a higher risk of adverse
water quality impacts. Results for case study mines with this combination of factors are included
in Tables 4a (surface water) and b (groundwater and seeps). Table 4 lists the following
information: acid drainage and contaminant leaching potential; whether or not there was a
surface water or groundwater impact; whether or not acid drainage has developed on the site;
whether or not standards have been exceeded in surface water, groundwater or seeps; which
constituents have seen increases over baseline conditions or exceed standards; and whether there
are perennial streams on site or there is a discharge to surface water, or both. The discharges to
surface water are usually permitted National Pollution Discharge Elimination System (NPDES)
discharges under the Clean Water Act. Table 4 also includes information from the EISs on
predictions. The last two columns list the highest potential (pre-mitigation) impact to surface
water, groundwater and seeps, and the highest predicted (post-mitigation) impact to these
resources. More information on mines with other types of inherent characteristics and conditions
is provided in Kuipers et al. (2005).
1131
1132
Mines with Perennial Streams on Site or Direct Surface Water Discharges and Moderate to High
Acid Drainage or Contaminant Leaching Potential
This section addresses mines with close proximity to surface water that also have moderate to
high potential for developing acid drainage or contaminant leaching. The next section addresses
mines with close proximity to surface water that have the same geochemical characteristics.
Mines with Moderate to High Acid Drainage Potential. The following case study mines have
perennial streams on site or discharge directly to surface water and have a moderate to high acid
drainage potential:
• Greens Creek, Alaska
• Grouse Creek, Idaho
• Thompson Creek, Idaho
• Beal Mountain, Montana
• Black Pine, Montana
• Zortman and Landusky, Montana
• Jerritt Canyon, Nevada
• Lone Tree, Nevada
• Twin Creeks, Nevada
Of these nine mines, all had some impact to surface water quality (Table 4a). Of the nine
mines with identified moderate to high acid drainage potential and close proximity to surface
water resources, four have currently developed acid drainage on site. Impacts to surface water
from the other five mines resulted from CN, NO
3
-
, SO
4
-2
, metalloids, ammonia, or other anions.
At the Greens Creek Mine, elevated concentrations of SO
4
-2
and Zn and lower pH values
have been measured in smaller streams, most likely as a result of leaching of high sulfide
material (tailings or waste rock) lying outside of the tailings pile capture area. At the Grouse
Creek Mine, tailings impoundment leakage into groundwater resulted in Cn in surface water. At
the Thompson Creek Mine, creeks downgradient of the waste rock dumps had increasing
concentrations of SO
4
-2
(to values in excess of water quality standards) over a six-year period.
At the Beal Mountain Mine, NO
3
-
, TDS, and SO
4
-2
concentrations in streams have increased
relative to baseline conditions, and CN exceeded aquatic life standards. At the Black Pine Mine,
springs impacted by waste rock flow into Smart Creek and have elevated concentrations of
SO
4
-2
, Cu, Zn, Fe, and Cd, and low pH values. At the Zortman and Landusky Mine, streams
have been impacted by acid drainage from waste rock and the heap leach pad. The Lone Tree
Mine has been in general compliance with overall permit requirements for discharge of its
dewatering water to the Humboldt River, but there have been some exceedences of permit limits,
and Newmont has been fined for these exceedences. Although no information was obtained on
stream water quality at the Twin Creeks Mine, dewatering water discharged to Rabbit Creek has
shown exceedences of TDS and arsenic standards by up to ten times.
These results, although not comprehensive, suggest that the combination of proximity to
surface water resources (including direct discharges to surface water) and moderate to high
potential for acid drainage does increase the risk of water quality impacts. All of these nine
mines predicted a low impact to surface water after mitigations were in place in at least one or all
of the EISs. For the Thompson Creek and Zortman Landusky mines, later EISs predicted a
Table 4a. EIS and Operational Water Quality Information on Case Study Mines with Moderate to High Acid Generation or
Contaminant Potential and Perennial Streams on Site or Discharge to Surface Water.
Site State
Acid
Drainage
Potential
Contaminant
Leaching
Potential
SW
Impact?
Acid Drainage
Developed on
Site?
Standards
Exceeded?
Constituents Increasing or
Exceeding
Perennial or
Discharge?
Highest
Potential
Impact to SW
Highest
Predicted
Impact to SW
Greens
Creek
AK 2 1 Yes Yes Yes
low pH, Cd, Cu, Hg, Zn,
SO
4
Both 2 1
McLaughlin CA
12
Yes Yes Yes
SO
4
, As, Cr, Cu, Pb, Mn,
Ni, Hg, Fe, Zn
Discharge 2 2
Grouse
Creek
ID 2 1 Yes No Yes
CN exceeded in surface
water
Perennial 2 1
Thompson
Creek
ID 2 1 Yes Yes Yes
Cd, Cu, Pb, Zn, SO
4
Both 2 (1) 2 (1)
Beal
Mountain
MT 2 1 Yes No Yes
NO
3
, TDS, SO
4
, CN
Both 2 1
Black Pine MT 3 2 Yes Yes Yes
SO
4
, Cu, Zn, Fe, Cd, low
pH
Perennial 0 1
Mineral Hill MT 1 2 Yes No Yes
CN, NO
3
, Mn, SO
4
, As,
TDS
Discharge 1 1
Stillwater MT 1 2 Yes No No
NO
3
Discharge 1 1
Zortman
and
Landusky
MT 3 2 Yes Yes Yes
metals, metalloids, NO
3
,
low pH, CN
Both 3 3 (1)
Jerritt
Canyon
NV 2 2 Yes No Yes
TDS, SO
4
Perennial 2 1
Twin
Creeks
NV 2 3 Yes No Yes TDS, As Both 3 1
Lone Tree NV 2 3 Yes No Yes
pH, TDS, F, B, NH
4
Discharge 2 1
Flambeau WI 0 2 No Yes No
SO
4
, Mn, low pH, Fe
Discharge 2 1
1=low; 2=moderate; 3=high. SW=surface water; GW=groundwater.
1133
Table 4b. EIS and Operational Water Quality Information on Case Study Mines with Moderate to High Acid Generation or
Contaminant Potential and Shallow Depth to Groundwater on Site or Discharge to Groundwater.
Site State
Acid
Drainage
Potential
Contaminant
Leaching
Potential
GW or
Seeps
Impacted?
Acid Drainage
Developed on
Site?
Standards
Exceeded?
Constituents Increasing or
Exceeding in GW or Seeps
Shallow GW
or GW
Discharge?
Highest
(Lowest) GW
Impact
Potential
Highest
(Lowest)
Predicted GW
Impact
Greens
Creek
AK 2 1 Yes Yes Yes - seeps
GW: SO
4
; seeps: SO
4
, Zn,
pH, Cu, Pb, Se
Shallow GW 2 1
McLaughlin CA
12
Yes Yes Yes - GW
TDS, Cl, NO
3
, SO
4
, Cu,
Fe, Mn, B, Zn
Shallow GW 3 3
Grouse
Creek
ID 2 1 Yes No Yes - GW
CN; Al, Cu, As, Se, Ag, Zn,
CN in tail pore water
Shallow GW 2 (1) 1
Thompson
Creek
ID 2 1 Yes Yes Yes - seeps
Seeps: Fe, Zn, SO
4
, Se;
GW: no info
Shallow GW 2 (0) 2 (1)
Beal
Mountain
MT 2 1 Yes No
Yes - GW
and seeps
GW: NO
3
, Fe, CN; TDS.
Seeps: CN, Se, SO
4
, NO
3
Shallow GW 2 1
Black Pine MT 3 2 Yes Yes
Yes -
Seeps; NA -
GW
Seeps: low pH, SO
4
, Cu,
Zn, Fe, Cd; GW: no info
Shallow GW 0 1
Golden
Sunli
g
ht
MT 3 3 Yes Yes
Yes - GW
and seeps
CN, Cu, low pH Shallow GW 3 (2) 3 (1)
Stillwater MT 1 2
No - GW;
Yes - adit
No
No - GW;
Yes - adit
Adit: Cd, Cu, Pb, Mn, Zn,
NO
3
. GW: Cr, Fe, SO
4
, Cl,
PO
4
, Cd, Zn
Both 1 1
Zortman
Landusky
MT 3 2 Yes Yes
Yes - GW
and seeps
low pH, As, metals, NO
3
,
CN
Shallow GW 2 (1) 3 (1)
Florida
Can
y
on
NV 1 2 Yes No Yes
CN, Hg, NO
3
, Cl, TDS
Shallow GW 3 1
Jerritt
Can
y
on
NV 2 2 Yes No Yes - GW
CN, Cl, TDS, SO
4
Shallow GW 2 (1) 1
Lone Tree NV 2 3 No? No
Yes
(baseline?)
F, Fe, Mn, TDS, Al, B,
NH
4
, pH
Shallow GW 1 1
Rochester NV 2 2 Yes No Yes - GW
CN, Hg, Cd, NO
3
, As
Shallow GW 2 1
Twin
Creeks
NV 2 3 Yes No
Yes -
perched
GW
TDS, SO
4
, Cl , CN, Al, Sb,
As, Mg, Fe, Hg, Mn
GW
Discharge
21
Flambeau WI 0 2 Yes Yes Yes
Fe, Mn, pH, SO
4
, TDS
Shallow GW 2 1
1134
higher potential impact to surface water, but in both cases the initial EIS, on which the
mitigations were based, predicted a low impact to surface water resources. These results suggest
that even though mines may identify a moderate to high acid drainage potential, they predict that
surface water resources will not be impacted after mitigations are implemented. In all cases
examined, these predictions underestimated the eventual impact to surface water resources.
Mines with Moderate to High Contaminant Leaching Potential The following mines have
perennial streams on site or discharge directly to surface water and identified a moderate to high
potential for contaminant leaching in their EISs:
• McLaughlin, California
• Black Pine, Montana
• Mineral Hill, Montana
• Stillwater, Montana
• Zortman and Landusky, Montana
• Jerritt Canyon, Nevada
• Lone Tree, Nevada
• Twin Creeks, Nevada
• Flambeau, Wisconsin
Of these nine mines, five also have moderate to high acid drainage potential and proximity to
surface water resources, as discussed above. All of these have had some impact to surface water
quality from mining operations, as shown in Table 4a. Of the remaining four mines, the
McLaughlin Mine has had some impact to surface water quality, including high concentrations
of SO
4
-2
(showing steady increases since mining has begun) and nickel. Downstream surface
monitoring locations show exceedences of SO
4
-2
, and occasionally large exceedences of As, Cr,
Cu, Pb, Mn, Hg, Fe, and Zn. Apparently no violations of surface water quality have been
recorded for the McLaughlin Mine. At the Mineral Hill Mine, tailings leachate containing CN,
NO
3
-
, Mn, SO
4
-2
, As, and TDS has escaped the liner system and caused exceedences in surface
water. The Stillwater Mine does not have perennial streams on site, but it does have a NPDES
permit for discharge of mine water to surface water. However, this permit has never been used.
Nitrate concentrations in the Stillwater River have increased to as high as 0.7 mg/l (limit is 1.0
mg/l) as a result of mining activity, but no standards or limits have been exceeded. At the
Flambeau Mine, there have been no observable changes in surface water quality, but there is
some concern that surface water sample locations may not capture all releases from mine. The
Flambeau Mine has had groundwater impacts from the backfilled pit. More monitoring of
additional locations and over a longer time period is required before we will know if observed
poor groundwater quality will adversely affect downgradient surface water.
Therefore, for nine mines with proximity to surface water resources and moderate to high
contaminant leaching potential, eight have shown some impact to surface water quality. Seven
of the nine mines have had exceedences of standards in surface water. These results, although
not comprehensive, suggest that the combination of proximity to surface water resources
(including direct discharges to surface water) and moderate to high potential for contaminant
leaching does increase the risk of water quality impacts. In terms of EIS predictions, six of the
nine mines identified a moderate to high potential for surface water impacts without mitigations,
1135
but eight of the nine predicted a low impact to surface water after mitigations were in place (as
noted above, the Zortman Landusky Mine initially predicted a low impact to surface water
resources). To date, predictions for surface water impacts at the McLaughlin, Stillwater, and
Flambeau mines have been accurate, but the remaining six mines underestimated the actual
impact to surface water in their EISs.
Overall, for the 13 mines with close proximity to surface water and high acid drainage or
contaminant leaching potential (see Table 4a), 12 (92%) have had some impact to surface water
as a result of mining activity. Eleven of the 13 (85%) have had exceedences of standards or
permit limits in surface water as a result of mining activity. Of the 11 with exceedences, ten
(91%) predicted that surface water standards would not be exceeded. Considering the two mines
that accurately predicted no surface water exceedences (Stillwater and Flambeau), and the one
that accurately predicted exceedences (McLaughlin), 77% of mines with close proximity to
surface water or direct discharges to surface water and moderate to high acid drainage or
contaminant leaching potential under predicted actual impacts to surface water. EIS water
quality predictions made before the ameliorating effects of mitigations were considered
(“potential” water quality impacts) were more accurate at predicting operational water quality
than predictions based on assumed improvements from mitigations. Mines with these inherent
factors are the most likely to require perpetual treatment to reduce or eliminate the long-term
adverse impacts to surface water resources.
Mines with Shallow Depth to Groundwater or Discharges to Groundwater and with Moderate to
High Acid Drainage or Contaminant Leaching Potential
Mines with close proximity to groundwater resources are often close to surface water as well.
Therefore, a number of mines evaluated above will also appear in this section. Mines that
discharge to groundwater usually do so through infiltration basins or some other kind of land
application. Although this is not a direct discharge to groundwater, it does increase the
likelihood that the discharge water and any associated contaminants will reach groundwater.
Mines with Moderate to High Acid Drainage Potential. The following mines have a relatively
shallow depth to groundwater (0 to 50 feet), have springs on site, or discharge to groundwater –
and have a moderate to high acid drainage potential:
• Greens Creek, Alaska
• Grouse Creek, Idaho
• Thompson Creek, Idaho
• Beal Mountain, Montana
• Black Pine, Montana
• Golden Sunlight, Montana
• Zortman and Landusky, Montana
• Jerritt Canyon, Nevada
• Lone Tree, Nevada
• Rochester, Nevada
• Twin Creeks, Nevada
1136
Of these 11 mines, we obtained some groundwater quality information for all but two
(Thompson Creek, Idaho and Black Pine, Montana). However, there is information about
seepage water quality from both of these facilities. Of the nine mines with shallow depths to
groundwater, springs on site, or that discharge to groundwater and that have moderate to high
acid drainage potential, all have had some impact to groundwater quality from mining operations
(see Table 4b).
The Greens Creek Mine in Alaska has a depth to groundwater that ranges from the ground
surface up to 50 feet deep. Seepage/runoff from the waste rock piles has an average Zn
concentration of 1.65 mg/l, and tailings seepage water (including underdrain water) has had pH
values as low as 5.8, with elevated SO
4
-2
(up to 2,400 mg/l), Zn (up to 3.6 mg/l), Cu, Pb, and Se
concentrations. Anomalously high SO
4
-2
concentrations have been observed in groundwater
monitoring wells, but metal concentrations have not increased as of 2000.
No groundwater data were obtained for the Thompson Creek Mine, which has flowing
artesian wells, alluvial groundwater that is connected to streams, and some groundwater in
bedrock fractures. However, tailings seepage water quality has shown increases in Fe and Zn,
and SO
4
-2
and Se concentrations in waste rock seepage have been increasing since 1991, with
selenium concentrations in excess of water quality standards.
At the Beal Mountain Mine in Montana, there is limited information on groundwater depth,
but there are springs on site, and groundwater depth below the pit is 25 to 50 ft. Groundwater in
the land application area exceeded standards for NO
3
-
, Fe, and CN and has elevated total
dissolved solids. Springs below the land application area also show appreciable increases in CN
and Se. Concentrations of Se, SO
4
-2
, NO
3
-
, and total dissolved solids are elevated in springs
sampled at the toe of the waste rock dump. At the Black Pine Mine in Montana, groundwater
depths are approximately 45 feet in the impoundment area, and there are 30 springs in project
area. Although we have no direct information on groundwater quality, seeps downgradient of
waste rock and the soils barren areas are acidic (pH 2.6-4.7) and have elevated concentrations of
SO
4
-2
, Cu, Zn, Fe, and Cr. The Golden Sunlight Mine has alluvial groundwater at 50 to 60 feet
deep and numerous springs on site. Tailings effluent has contaminated downgradient wells with
CN and Cu (up to 65 mg/l Cu). Acid drainage is being produced from the waste rock dumps, ore
stockpiles, tailings, and adits. The Zortman and Landusky Mine in Montana has perched
groundwater at 150 to 150 feet, an overall depth to groundwater of <200 ft, and springs and
seeps on site. Karst features control groundwater flow in some areas. Acid drainage has been
generated from waste rock dumps (as low as pH 3.9), the ore heap retaining dikes, pit walls and
floors, and leach pads and pad foundations. Sulfate concentrations have increased in alluvial
groundwater downgradient of the heap retaining dikes.
The Jerritt Canyon Mine has perched groundwater at 8 to 70 feet deep, and 23 springs and 8
seeps on site. The regional groundwater depth is approximately 700 feet. Groundwater has been
impacted by seepage from the tailings impoundment, and a CN plume exists on site.
Groundwater in the vicinity of the tailings area also has exceedences of Cl
-
(up to 12,000 mg/l),
TDS (up to 30,000 mg/l), and SO
4
-2
. Groundwater at the Lone Tree Mine ranges from 10 to
>200 feet deep. Pre-mining groundwater levels have scored the mine as being close to
groundwater resources, but the large dewatering rate for this mine has lowered groundwater
levels considerably. The Lone Tree Mine in Nevada has had exceedences of primary and
secondary drinking water standards in groundwater, but it is not clear if the cause is baseline
conditions or seepage from mine facilities. Depth to groundwater at the Rochester Mine ranges
1137
from <1 to 20 feet in the alluvial aquifer and from the ground surface to approximately 400 feet
in the bedrock aquifer. There are springs on site. Leaks from the heap leach pad and the barren
solution pond have caused numerous exceedences of WAD CN, Hg, Cd, NO
3
-
, and As in
groundwater. The Twin Creeks Mine, which has a large dewatering operation, has a
groundwater depth of over 100 feet over most of the mine site, and the pit floor is approximately
400 feet below pre-mining groundwater levels. However, the mine discharges to groundwater
through infiltration basins. Degradation of groundwater (perched water) with CN and other
constituents has occurred as a result of seepage from the tailings impoundment. The vadose zone
monitoring wells that were added during 2003 to monitor seepage from the tailings
impoundment have shown multiple exceedences of total dissolved solids, SO
4
-2
, Cl
-
, CN, Al, Sb,
As, Fe, Hg, and Mn.
Therefore, for the 11 case study mines with close proximity to groundwater resources or that
discharge to groundwater and that have moderate to high acid drainage potential, eight (73%)
have shown some adverse impact to groundwater quality from mining activity. Of the remaining
three mines in this category, two have contaminated seeps flowing from tailings and/or waste
rock storage areas (Thompson Creek and Black Pine mines), but no groundwater quality data
were obtained. Therefore, a total of 10 mines (91%) have had mining-related impacts to
groundwater or seeps. One mine in this category, the Lone Tree Mine, has had no groundwater
impacts. However, the groundwater table at the Lone Tree Mine has been lowered considerably
from dewatering operations, and it is unlikely that groundwater impacts would be evident at this
time. These results, although not comprehensive, suggest that the combination of proximity to
groundwater resources (including direct discharges to surface water) and moderate to high acid
drainage potential does increase the risk of water quality impacts.
Mines with Moderate to High Contaminant Leaching Potential. The following mines are have a
relatively shallow depth to groundwater (0 to 50 feet), have springs on site or discharge to
groundwater, and have a moderate to high contaminant leaching potential:
• McLaughlin, California
• Black Pine, Montana
• Golden Sunlight, Montana
• Stillwater, Montana
• Zortman and Landusky, Montana
• Florida Canyon, Nevada
• Jerritt Canyon, Nevada
• Lone Tree, Nevada
• Rochester, Nevada
• Twin Creeks, Nevada
• Flambeau, Wisconsin
Of these 11 mines, all but four (McLaughlin, Stillwater, Florida Canyon, Flambeau) also
have moderate to high acid drainage potential and were discussed above. As noted above, all of
these seven mines have had some impact to groundwater or springs/seeps as a result of mining
activity with the possible exception of the Lone Tree Mine in Nevada, which has exceedences in
groundwater that may be related to baseline conditions.
1138
The McLaughlin Mine in California has been touted by the mining industry as an example of
a mine with laudable environmental behavior and has received numerous environmental awards.
When the state of Wisconsin passed a requirement for new mines in sulfide ore bodies to
demonstrate that other mines with net acid generation potential have operated and been closed
for at least 10 years with out polluting groundwater or surface water (Wisconsin Act 171 (Statute
§293.50), passed in 1997), the McLaughlin Mine was one of the three examples used by Nicolet
Minerals in their application for a permit for the Crandon Mine (Nicolet Minerals, 1998). The
McLaughlin Mine has a regulatory exclusion for groundwater at the site, so no groundwater
enforcement actions can be brought by Regional Water Quality Control Board (RWQCB). At
the McLaughlin Mine, wells downgradient of the tailings impoundment had exceedences of TDS
(up to 12,000 mg/l), Cl
-
, NO
3
-
(up to ~37 mg/l), and SO
4
-2
, and increases of Cu (up to 280 μg/l)
and other metals from 1984 – 1992 (mine began operation in 1985). Wells downgradient of
waste rock dumps had increasing concentrations of SO
4
-2
(up to 5,000 mg/l), B, TDS, Ca, Fe,
Mn, and other constituents from 1985 to 1998 and Zn (up to 1.7 mg/l) after this timeframe.
The Stillwater Mine in Montana has also received environmental awards, and acid drainage
has not developed on the site to date, likely due in part to the unique ultramafic host rock and
associated mineralogy. Depth to groundwater at the mine is 40 to 90 feet, and there are three
springs on site. The mine discharges adit water to percolation ponds and a land disposal area on
the site. Groundwater at the Stillwater mine in the area of the East Land Application Disposal
Area has exceeded drinking water standards for Cr, but the cause appears to be tailings from an
historic government-operated World War II-era mine. The adit water that percolates to
groundwater is unimpacted except for NO
3
-
contamination but contains Cd, Cu, Pb, Mn, Zn, and
N concentrations in excess of baseline surface water values. Groundwater downgradient of the
land application facility has slight elevations of SO
4
-2
, Cl
-
, P, Cd, Fe, and Zn, but these appear to
be a baseline issue.
The pre-mining regional groundwater table at the Florida Canyon Mine was quite deep (~400
feet), but alluvial groundwater exists at 0 to 250 feet deep. A contaminant plume with elevated
concentrations or exceedences of WAD CN, Hg, NO
3
-
, Cl
-
, and TDS exists in groundwater
downgradient from the leach pad. Other groundwater monitoring wells on the site show
exceedences of drinking water standards for Al, As, Cd, Cl
-
,Fe, Mn, Ni, and TDS.
Depth to groundwater at the Flambeau Mine is Wisconsin before mining began was generally
<20 feet and flowed toward the Flambeau River. Samples taken from a well between the river
and the backfilled open pit showed elevated levels (compared to baseline values) or exceedences
of drinking water standards for Fe, Mn, pH, SO
4
-2
, and total dissolved solids. Concentrations
appeared to peak in 2000 and have been slowly decreasing for Mn, SO
4
-2
, and TDS, but are
continuing to increase for Fe. Zinc concentrations are variable and still (as of 2003) ~700 μg/l
(Lehrke, 2004).
Of the mines that have close proximity to groundwater, springs on site, or that discharge to
groundwater – and have a moderate to high contaminant leaching potential, 8 of 11 mines (73%)
had groundwater quality impacts, and two of the remaining three had seeps that were adversely
impacted from mining activity (91% have mining-related impacts to groundwater, seeps, springs,
or adit water). The remaining mine, the Lone Tree Mine in Nevada, has had exceedences of
primary and secondary drinking water standards in groundwater, but it is not clear if the cause is
baseline conditions or seepage from mine facilities. All of the 11 mines have exceedences of
standards in groundwater (8), or seeps, springs, or adits (4). Therefore, the combination of close
1139
proximity to groundwater and elevated contaminant leaching potential appears to be a good
indicator of future adverse groundwater quality impacts. Of the 11 mines in this category, all but
one (the McLaughlin Mine) predicted low groundwater quality impacts after mitigations were
installed. The Stillwater Mine predicted low impacts to groundwater, and no exceedences of
standard have thus far resulted from current operations or operators. The Lone Tree Mine in
Nevada also predicted low groundwater impacts, and current information suggests that this is
true (assuming the exceedences are a baseline issue). However, the lowered water table likely
prevents the observation of impacts to groundwater. EIS water quality predictions made before
the ameliorating effects of mitigations were considered (“potential” water quality impacts) were
more accurate at predicting operational water quality than predictions based on assumed
improvements from mitigations. Therefore, of the 11 mines in this category, eight (73%)
underestimated actual impacts to groundwater resources from mining activity.
Taken as a whole, there are 15 mines with close proximity to groundwater, springs on site, or
discharges to groundwater – and with moderate to high acid drainage or contaminant leaching
potential (see Table 4b). Of these 15 mines, all but one (93%) have had mining-related impacts
to groundwater, seeps, springs, or adit water (with the one possible exception being the Lone
Tree Mine in Nevada). Eleven of the 15 mines (73%) have had adverse mining-related impacts
to groundwater; of the remaining four mines, three have mining-related impacts to spring, seeps
or adit water, and only one (the Lone Tree Mine) has exceedences in groundwater that may be
related to baseline conditions. These results, although not comprehensive, suggest that the
combination of proximity to groundwater resources (including discharges to groundwater) and
moderate to high acid drainage or contaminant leaching potential does increase the risk of water
quality impacts.
Conclusions
The identification of geology and mineralization, as currently conducted in EISs, is generally
a blunt tool for predicting water quality impacts. Geologic and mineralogic information is
usually focused on the ore body rather than on all mined materials that could potentially impact
water resources. We found relatively weak relationships between geology and
mineralization/ore association and acid drainage potential. Similarly, we found a relatively weak
relationship between geology and mineralization and the potential for water quality impacts. The
discrepancy or lack of good agreement between identified mineralization and acid drainage
potential highlights the importance of coordinating mineralogic and acid drainage potential
evaluations in the NEPA process. As noted in the companion report (Maest et al., 2005), the
same geochemical test units should be used for testing of all parameters used to predict water
quality impacts. In addition, more extensive information on mineralogy and mineralization
should be included in EISs.
The EISs reviewed in detail spanned a period from 1978 to 2004. The availability of
geochemical characterization data affects our ability to determine the potential for mines to
release contaminants to water resources. Starting in 1980, mines began to provide basic
information on geochemical characterization, such as static and short-term leach testing. After
1990, many of the mines were conducting combinations of kinetic testing and static or short-term
leach testing. EISs performed after about 1990 should have more reliable information on water
quality impact potential than those with EISs completed before this time.
1140
Mines with close proximity to surface water or groundwater resources and with a moderate to
high acid drainage or contaminant leaching potential have a relatively high risk of impacting
water quality and must rely on well executed mitigation measures to ensure the integrity of water
resources during and after mining. These results, although not comprehensive, suggest that the
combination of proximity to water resources (including discharges to surface water or
groundwater) and moderate to high acid drainage and contaminant leaching potential does
increase the risk of water quality impacts. These combined factors at a mine appear to be a good
indicator of future adverse water quality impacts. Mines in this category are also the most likely
to require perpetual treatment to guarantee acceptable water quality.
Acknowledgements
The authors wish to acknowledge helpful reviews of the manuscript by Tom Myers, PhD and
David Chambers, PhD.
Literature Cited
Kuipers, J., A. Maest, K. MacHardy, and G. Lawson. 2006. Comparison of Predicted and
Actual Water Quality at Hardrock Mines: The Reliability of Predictions in Environmental
Impact Statements. Available at: www.kuipersassoc.com.
Lehrke, S. 2004. Memorandum from Stephen Lehrke, Foth & Van Dyke, to Jana Murphy,
Flambeau Mining Company. Re: Flambeau Mining Company – 2003 Annual Report
Groundwater and Surface Water Trends. January 1, 2004.
Maest, A., J. Kuipers, C. Travers, and D. Atkins. 2005. Predicting Water Quality at Hardrock
Mines: Methods and Models, Uncertainties, and State-of-the-Art. Available at:
www.kuipersassoc.com.
Nicolet Minerals Company, 1998. Wisconsin Statute §293.50 Compliance Demonstration.
Submitted to Wisconsin Department of Natural Resources (in response to the 1997 Wisconsin
Act 171, codified at Wis. Stats. §293.50).
1141
