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OCR for page 141
APPENDIX D
hater Quality Issues Associated
with Surface Coal Mining
Comprehensive studies confirm that water quality
can be adversely affected by pre-mining, mining,
and post-mining activities associated with surface
coal mining (NRC, 1981a; Western Water Consultants,
Inc., 1985~. During the pre-mining period
exploration boreholes may intersect aquifers
allowing communication of ground water, which could
result in deterioration of deeper, more pristine
waters. Blasting activities during mining fragment
rock materials, thus expose fresh mineralized
surfaces. In the post-mining period, ground water
recharge, in the form of atmospheric precipitation,
surface water, and lateral or vertical ground water
flows, may wet loosely consolidated overburden.
This process initiates chemical reactions with
exposed minerals, which could ultimately result in
serious deterioration of ground water quality.
Affected ground water quality parameters can
include pH, specific conductance, acidity,
alkalinity, physical appearance, total dissolved
solids, ionic composition, and trace metal burden.
This appendix reviews criteria used to evaluate
ground water quality; describes factors affecting
the chemical composition of waters infiltrating
unconsolidated overburden; surveys the methods for
assessing and monitoring water quality; and
investigates issues concerning water quality
protection in surface coal mined areas.
-141
OCR for page 142
-142-
GROUND WATER QUALITY: EFFECTS OF
COAL SURFACE MINING
Water Quality Criteria
Several criteria are used to determine which
chemical constituents must be analyzed when
assessing the impact of surface coal mining on
water quality (Turk et al., 19869:
1. Constituents specifically required by the
Permanent Regulatory Program (Office of Surface
Mining Reclamation and Enforcement);
2. Constituents required at the discretion of
the regulatory authority;
3. State and federal drinking water standards;
4. Irrigation criteria;
5. Aquatic life criteria;
6. Minimum groups of constituents necessary to
perform routine quality control checks; and
7. Minimum groups of constituents necessary to
evaluate possible geochemical controls on the
hydrologic system.
Constituents that may be analyzed by these criteria
include a number of chemical and physical
constituents as well as biological aspects (Table
D.1~. Water quality standards are established by
the U.S. Environmental Protection Agency; the
Office of Surface Mining Reclamation and
Enforcement is responsible for enforcing these
standards relative to coal surface mining activity.
Factors Affecting the Quality of Ground Water
Geochemical and biogeochemical processes that
affect water quality as a result of coil surface
mining are oxidation of mineral and organic matter,
the reaction of carbon dioxide and water to form
carbonic acid, precipitation and dissolution of
OCR for page 143
-143-
TABLE D.] Chemical, Physical, and Biological
Constituents and Parameters That May Be Measured As
Required by Several Criteria
Measured Onsite
Measured in Laboratory
Temperature
pH (in standard
units)
Specific conduct-
ance (in
micromhos/cm)
Acidity
Alkalinity
Total dissolved solids (TDSs)
Carbonate and bicarbonate
Trace metals:
Iron
Manganese
Arsenic
Mercur r
Boron
Lead
Zinc
Silver
Copper
Chromium
Calcium
Magnesium
Sodium
Potassium
Chloride
Aluminum
Selenium
Fluoride
Radium-226
Nitrogen species
Nitrate
Ammonia
Organic nitrogen
Total suspended solids (TSSs)
(surface water only)
Microbiology
SOURCE: Turk et al., 1986.
OCR for page 144
-144-
calcite and dolomite, precipitation and dissolution
of gypsies, cation exchange and adsorption, and
transport of solutes (Forstner and Wittmann, 1979;
Groenewold et al., 1983; Western Water Consultants,
Inc., 19851.
Important Oxidation Reactions
The most significant reaction contributing to
ground water degradation in the post-mining
environment is sulfide mineral oxidation. Common
sulfide minerals associated with coal surface
mining overburden are pyrite and marcasite. In
the presence of oxygen introduced into the
overburden during the mining process, these
minerals will slowly oxidize:
FeS2 + 7/2 O2 + H2O (chemical) >
Fez+ + 2 SO42 + 2 H+ [1]
However, in 2the presence of the aerobic,
acidophilic bacterium Thiobacillus
ferrooxidans, this oxidation rate is increased by
500,000 times:
2 FeS2 + 15/2 O2 + H2O (bacteria) >
2 Fe3+ + 4 SO42- + 2 H+
Thiobacillus are ubiquitous and proliferate rapidly
in sulfide-containing coal spoils. Under acid
conditions (pH < 3) the Thiobacilli directly attack
the sulfide minerals and also oxide the ferrous
ion:
1Pyrite and marcasite are both designated by the
formula FeS2.
2Acidophilic (acid-loving) bacteria grow at pH
values between 1 and 3.
OCR for page 145
-145-
2 Fez+ + 3 SO42- + 2 H+ + 1/2 O2 (bacteria) ~
2 Fe3+ + 3 SO42- + H2O
Ferric iron is a strong oxidizing agent, chemically
attacking sulfide minerals:
FeS2 + 14 Fe3+ + 21 SO42- + 8 H2O (chemical) >
15 Fez+ + 23 SO42 ~ 16 H+
Hence, the reactions become cyclic, creating
conditions that further enhance the production of
acid and cause bacterial proliferation (Hutchins et
al., 1986~. Reactions [13 through [43 are
responsible for the creation of acid mine drainage
(AMD), a familiar problem in the Appalachian region
of the United States; however, these reactions also
play a major role in the salinity problem
associated with western coal surface mining. If
unabated by deliberate control or by natural
buffering reactions, the acid can become
concentrated enough to solubilize deleterious trace
metals, such as aluminum, arsenic, zinc, copper,
and selenium.
Organic matter associated with coal spoils is
oxidized by a complex biota existing in coal spoils
(Miller, 1973; Harrison, 1978~. The resulting
products--organic acids and carbon
dioxide--undoubtedly alter the chemistry of
interstitial waters of the coal spoil, but this
aspect has had limited study. -
Buffering Reactions, Salinity Production, and
Sulfate Precipitation
Backfill systems of coal surface mines are
chemically complex with a series of acid-generating
and acid-consuming reactions occurring. Ferric ion
hydrolysis is an acid3generating process which also
precipitates jarosite
3Jarosite is a basic ferric sulfate mineral.
[4]
OCR for page 146
-146-
Fe3+ + 7/3 H2O + 2/3 SO42------->
5/3 H+ + 1/3 Fe3(SO4~2(0H)5~2 H2O
The most important acid-consuming reaction, which
buffers the coal spoil system and contributes
calcium and magnesium to waters percolating through
overburden spoil, is the dissolution of the
carbonate minerals, calcite and dolomite4:
CaCO3 ~ 2 H + SO42 + H2O ----->
CaSO4 + 2 H2O + CO2
Carbonate minerals are also soluble in the presence
of carbon dioxide:
CaCO3 + H2O + CO2
t5]
[6]
2+
Ca + 2 (HCO3)- [7]
Reaction [6] is very important in understanding
the chemistry of overburden materials, because this
reaction decreases sulfate concentration in
solution through the precipitation of gypsum. The
solubility of gypsum in water controls sulfate
concentration in interstitial waters in the
mine-waste overburden.
Cation Exchange and Adsorption
Clay minerals, precipitated iron hydroxides,
amorphous silicic acids, and organic matter are all
capable of sorbing cations from solution and
releasing equivalent amounts of other cations into
solution. The mechanism of cation exchange is
based on the metal-binding properties of negatively
charged hydroxyl groups on clays, metal
precipitates, and organic substances. Cation
4Dolomite is a carbonate mineral containing both
calcium and magensium.
OCR for page 147
-147-
adsorption, which is also an important chemical
phenomenon in backfill materials, occurs when
~~ ~ ~ ~ having a large surface area
fine-grained materials
accumulate metals in the solid-liquid interface as
a result of intermolecular forces, such as
electrostatic attraction, hydrogen bonding, or Van
der Waals forces. In backfill materials cation
exchange and adsorption increase the concentration
of dissolved salts, particularly sodium, in the
infiltrating waters.
occurs when
Transport of Solutes
When water and solutes move together through
vadose zones or aquifers, chemicals that are
adsorbed to ~ ~~ ~
me ta1 ~ and
the soil materials (trace elements,
~ , _ _ certain organic compounds, for example)
move more slowly than the water. This is of great
importance in ground water quality monitoring,
especially, for example, to assess offsite effects
of surface mining. As contaminated ground water
moves laterally through an aquifer, an offsite
monitoring well will first show the arrival of
sulfate, chloride, and other nonsorbing chemicals.
Metals can arrive much later. Thus, to get the
full effect of mining on offsite ground water
quality, long-term monitoring programs (lasting
decades and perhaps even centuries) are required.
Preferential channeling flow processes, however,
can result in rapid breakthrough of strongly
adsorbing solutes.
Biogeochemical Reactions
Other than the important role of Thiobacillus,
and the possible contribution of several recently
characterized thermophilic bacteria that also
oxidize sulfide minerals on a geologic scale,
little is known about the overall contribution of
biogeochemistry to the fate and transport of
deleterious ions in coal mine waste overburden.
OCR for page 148
-148-
Biological sulfate reduction has been implicated
in anoxic coal overburden environments to account
for sulfide production in spoils that have a
sparsity of sulfide minerals (Olson et al., 1981~.
Because these spoils have a high salinity due
principally to sodium, it is believed that sulfide
oxidation must occur to initiate the sequence of
reactions necessary for salinity to occur
(Groenewold et al., 1983~. This would be expected
if the water infiltrating the spoils is of ground
water origin and is anoxic (Olson et al., 1981~.
Nitrate concentrations sometimes increase in coal
surface mine spoils. This increase is believed to
be due, in part, to the solubilization of nitrate
from nondetonated blasting compounds at the mine
site. A variety of microorganisms are active in
nitrogen cycling: conversion of organic nitrogen
to ammonium; oxidation of ammonium to nitrate;
nitrate reduction to free nitrogen and ammonium;
and free nitrogen fixation to organic nitrogen.
Biogeochemical processing of nitrogen species in
coal spoils has been demonstrated (Williams, 1975~.
Onsite Disposal of Wastes
Fly ash, scrubber sludges, wastes from coal
cleaning, spent machine oils, municipal waste, and
industrial waste have been buried in the backfill
of surface coal mines (NRC, 1981a). Such burial
requires a solid-waste permit. Burial of waste is
accompanied by isolation practices, whereby the
wastes are encapsulated in clay materials that are
designed to minimize leakage or leaching of toxic
materials. Care is taken to avoid placement of
wastes in areas where a high contamination
potential exists. However, little is known about
the long-term effects of such burial practices on
the quality of recharge to ground water.
OCR for page 149
-149
-
Monitoring and Assessing Ground
Water Quality Impacts
Monitoring Ground Water Quality
Surface and ground water samples are collected
during pre-mining, mining, and post-mining phases
of surface coal mining and analyzed for various
constituents among those listed in Table D.1.
Monitoring wells for ground water sampling are
constructed in aquifers within the pre-mining
overburden and coal Dermis) to tee' mined as well as
in the aquifers) that are belong' the eventual mine
floor. Pre-mining water samples are evaluated to
obtain baseline data for mine permits. Samples
collected during and after mining are used to
evaluate water quality as a result of mining
activities. Monitoring wells often disappear
during mining, and new wells are constructed in the
backfill. Post-mining monitoring continues until
the property is released for post-mining use.
There are essentially no regulatory requirements
or guidelines mandating (1) correct procedures'for
collecting ground water samples, (2) proper
handling and storage procedures of collected
samples, (3) selection and execution of analytical
techniques (Western Water Consultants, Inc., 1985),
and (4) the reporting of a cation-anion balance.
Failure to perform a cation-anion balance often
results in reporting erroneous water quality data
(A. E. Whitehouse, Office of Surface Mining
Reclamation and Enforcement, personal
communication, 1989~. Approved methods include
those published by the American Public Health
Association et al. (1985) and the U.S.
Environmental Protection Agency (1986~.
Pre-Mining Overburden Assessment to Evaluate
Impacts
During the pre-mining phase of coal surface
mining, overburden is assessed, when the need i
s
OCR for page 150
-150-
evident or
attempt to
quality
mining is to occur in a new area, in an
predict mine drainage and ground water
Assessments are assigned to two test
r~=t~crr~r' "C _ _ Patti ~ Ann rl~rn~m; ~
__ Ho . Static tests
entail whole-rock analyses for total sulfur and
neutralization potential, and from these analytical
data an acid and base accounting is made. Dynamic
tests involve simulated weathering of the
overburden material. This is accomplished by
placing crushed rock materials in a humidified
atmosphere and leaching periodically by adding
water to the rock material. Chemical analysis of
the effluents from these tests determines
leachability of the material. As with analytical
techniques, there are no prescribed standards for
evaluating surface coal mine overburden materials
by testing category. Several different methods for
overburden assessment have been employed (Table
D.2~. There are advantages and disadvantages of
each method. In addition to those methods listed
in Table D.2, several techniques, including the
American Society for Testing and Materials (ASTM)
method "B" and the U.S. Environmental Protection
Agency's extraction procedure (EP), have been
evaluated (Schuller et al., 1981~. The ASTM-B and
EP tests, which use acetic acid as an extractant,
were not predictive of field conditions (Schuller
At zip 1 9~1 ~
- ~_., _,_,. Nine comparative evaluations of
static and dynamic tests tabulated in Table D.2
indicate that, in fact, none of the test results
predicts observed field conditions, because of the
complex geochemical and hydrologic system that
Column leach tests
exists at each mine site.
however, were found to more closely approximate
field conditions, and data generated from such
tests are useful in identifying potentially toxic
strata and formulating overburden-handling plans to
dispose of problem spoils (Perry, 1985; Caruccio
and Geidel, 1986~.
Although still limited in use, computer models
are gaining popularity as a method to simulate
ground water quality as a result of coal surface
mining (Western Water Consultants, Inc., 1985;
OCR for page 151
-151-
TABLE D.2 Overburden Assessment Methods
Tost Procedure Advantages Disadvantages References
Static teats
Acid/base Perform whole Quick and easy Does not provide Sobek et al.,
accounting rock analysis test with low rate data; 1978; Sturey et
and relate acid cost. OK for assumes parallel al., 1982; Perry,
potential to qualitative release of 1985; Caruccio and
sulfur con- prediction. acidity and Geidel, 1986;
tent; relate alkalinity, Eledin and
neutralization giving Erickson, 1988
potential to erroneous
hot HC1 results.
digestion .
B.C. Perform whole Quick and easy Does not provide Bruynesteyn and
research rock analysis; test with low rate data; Duncan, 1979;
test relate acid cost. OK for assumes parallel Caruccio and
potential to qualitative release of Geidel, 1986
total sulfur prediction . ac idity and
content; alkalinity,
relate giving erroneous
neutralization results.
capacity to
sulfuric acid
titration.
Dynamic test
So~chlet Pulverize Quick and easy Apparatus is Renton et al.,
reactor supple and test, report- expensive; 1973; Caruccio
leach in edly providing leaching is and Geidel, 1986;
Soxhlet rate data. aggressive and Renton et al.,
extractor; dry not related 1988
sample and to natural
reteach in weathering
extractor. processes.
OCR for page 152
- 152 -
TABLE D. 2 continued
Humidity Place crushed Yields rate Long turn- Caruccio, 1968;
chamber rock in humidity data and around time Perry, 1985;
chamber; leach mimics required and Caruccio and
periodically weathering. large data Geidel, 1986
with water; base generated.
relate leachate
character to
acidity,
aLlcallnity, and
rock weight.
Beaker Place pulverized Simulates Oxygen transfer Sobek et al.,
leach test sample in beaker submerged is limited, 1978; Schuller
with water and conditions; and therefore et al., 1981;
monitor provides some rate data may Caruccio and
chemistry over rate data. not be Geidel, 1986
time. representative.
B.C. Place pulverized Similar to To date data Bruynesteyn and
research sample in beaker beaker leach from this test Duncan, 1979;
test with with water and test; oxygen have not been Caruccio and
bacteria bacteria and is not limited correlated to Geidel, 1986
agitate to and text any other
incorporate incorporates test data.
Oxygen; monitor bacteria.
pH and analyze
leachate .
Column Place samples Results Long turn- Hood and Oerter,
leach in columns approximate around time 1984; Sturey et
test and leach field required and al., 1982; Perry,
periodically conditions. large data 1985; Caruccio
with water; base generated. and Geidel, 1986.
bacteria can Solutions can
be added. channel, giving
Analyze erroneous data.
leachate and
correlate data
with rock weight.
SOURCE: Perry, 1985; Caruccio and Geidel, 1986 .
OCR for page 153
-153-
Perry, 1985; Rymer II et al., 1988;~Renton et al.
1988~. Computer models consist of algorithms~to
simulate pyrite weathering and ground water flow.
Modeling techniques require a considerable amount
of input of site-specific hydrogeochemical
information, including static or dynamic overburden
assessment test data and detailed geologic and
hydrologic data. Computer simulations are tools
for evaluating the short- and long-term ground
water quality impacts of geochemical and
biogeochemical factors operating in backfill
material. Software programs to evaluate the
hydrologic impacts, including ground water quality
of coal surface mining are available (Whitehouse et
al., 1989; Rymer II et al., 19889. Computer
modeling is expected to assist in providing
information on a topic of considerable concern:
What are the cumulative effects of multiple coal
surface mines on the ground water quality of..a
region, and how long is this impact expected to
last? .
is expected to
CONTROLLING WATER QUALITY
Controlling Acid Mine Drainage
Acid mine drainage (AMD) is.usually thought of as
a surface water phenomenon; however, ground water
can also become acidified as a result of an influx
of contaminated water emanating from pyrite- and
marcasite-containing spoils.
AMD is usually treated by the conventional
technique of neutralization.of the acidic water.
with caustic, lime, limestone, or soda ash or
mixing of these materials with acidic spoils. To
terminate the geochemical and biogeochemical
processes of iron oxidation and its concomitant
production of acid, attempts have also been made to
diminish oxygen availability through selective
spoils handling. Several new alternative
technologies have been introduced for both
treatment of AND as well as prevention:
OCR for page 154
-154-
1. Wetlands - - In this approach artificial
wetlands are constructed with the typical
components of limestone, compost, and cattail
{T=-h= N ^1=~= As the wetlands mature a complex
ecosystem is established in which higher plants,
algae, and microorganisms are inhabitants. AMD is
directed through the wetlands where geochemical and
biogeochemical processes neutralize the acid and
remove dissolved metals through plant uptake,
microbial accumulation and immobilization, or both
(Kolbash and Romanoski, 1989; Hammack and Hedin,
1989; Wenerick et al., 1989~. A variation of the
wetlands approach is the use of a microecosystem
employing a collection of encapsulated
microorganisms (immobilized microbial pollution
purification systems, IMPPS) (Davidson, 19899.
2. Phosphatic clay abatement--AMD is limited at
its source with the addition of phosphatic clay
from the Florida phosphate mining operations. The
phosphatic clay reduces AMD by (a) forming a
low-permeability clay layer around spoils and (b)
precipitating soluble iron that is formed by pyrite
and marcasite oxidation (Bowders et al., 1989~.
3. Bactericides--Surfactants can be added to
acidic spoils to minimize microbial growth.
Re-mining to Control Water Quality
Much of the current ground and surface water
pollution in the Appalachian region is associated
with abandoned coal mines. Re-mining of abandoned
coal mines, which contain substantial mineable coal
reserves, is a viable means of minimizing a
significant water quality problem. Strict
regulations and modern technology can reclaim these
lands after re-mining to diminish further
contamination of ground water (Giovannitti and
Merritt, 1989~.
DISCUSSION
Communication of water between aquifers during
exploration and mining and interaction by drainage
OCR for page 155
-155-
-
water and lateral inflow with chemically reactive
backfill material contribute to contamination of
ground water. What is difficult to predict is the
overall extent of water quality deterioration over
both time and space. How extensive will ground
water quality deterioration be due to cumulative
mining efforts--i.e., multiple mines in an area?
How long will the deterioration last? Decades?
Centuries? The presumption among many experts and
the coal industry is that time and dilution will
diminish the impacts of coal surface mining on
water quality. Part of the problem in predicting
short- and long-term impacts is inadequate
standards for pre-mining sampling, assessing, and
analytically evaluating overburden samples to
generate data that can be used to predict effects.
As a result of pre-mining overburden assessment,
there is some selective materials handling,
blending of spoils, encapsulation of toxic and
reactive spoils, special contouring, and controlled
revegetation to minimize ground water
contamination. These techniques at this time are
"more art than science."
Selective materials handling, blending, and
isolation have been particularly practiced with
sulfidic overburden, but greater consideration
should be given to selective materials handling to
avoid dissolution of soluble salts in western coal
surface mining operations. In reclamation one
objective is to restore ground water recharge.
This restoration can sometimes compromise ground
water quality. There should be serious attention
given to controlling recharge through spoils
handling in those areas where water quality is at
risk.
More emphasis needs to be placed on collecting
and making available relevant data that can be
applied to predict short- and long-term impacts on
ground water quality as well as estimate the
effects of cumulative mining on regional ground
water quality. Further research and development
are needed to enhance the science of spoils
handling.
,
Representative terms from entire chapter:
water quality
