Click for next page ( 142


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

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 141
-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 141
-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 141
-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 141
-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 141
-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 141
-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 141
-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 141
-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 141
-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 141
-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 141
- 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 141
-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 141
-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 141
-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. ,