An Analysis of Constructed Treatment Wetlands to Purify Coal Slurry

 Simone Knowlden, Timothy Ryan, Michael O’Donnell


If Big Coal’s reputation did not already precede itself, recent high profile cases have been surfacing more evidence of the industries malpractices. Earlier this year, the nation sympathized with 300,000 West Virginians when headlines revealed that 4-methylcyclohexane methanol (MCHM), a chemical used to clean coal, was leaked into the Elk River, contaminating their drinking water supply (Dizard, 2014). One month later, a reported 100,000 gallons of coal slurry flooded Fields Creek, through a valve malfunction by Patriot Coal (Conlon, 2014). The stark truth is that these are not isolated incidences, the coal industry has been inundating watersheds with toxic waste throughout Appalachia since the 19th century; degrading their single most essential resource, water. Poor enforcement of already lenient regulations has given many coal preparation plants the freedom to utilize unsafe disposal methods. America’s dependency on coal-powered energy has degraded regions like West Virginia for the sake of cheap energy. In a fiscally driven industry market incentives and more stringent regulations, along with constructed treatment wetlands could be a temporary concession.

Historically, the impact of coal mining has been significant upon the communities where it has taken place. From economic turmoil to environmental damage, the negative influence of the industry has been particularly strong throughout the Appalachian Mountain range in the eastern United States. A number of events have brought the sustainability and safety of coal into question. In 1972, the Buffalo Creek Flood event released 500,000 cubic meters of coal slurry into the Buffalo Creek hollow due to the failure of a containment dam. With 125 deaths and 4,000 residents left homeless, it remains one of the most costly coal disasters in United States history, and the environmental damage continues to be a blight upon the region to this day (Kelley, 1972). The impact of the Buffalo Creek (1972) disaster pales in comparison to more recent events, particularly the dike breach at the Kingston Fossil Plant of the Tennessee Valley in 2008. Though no deaths resulted, the release of 4.2 million cubic meters of toxic coal slurry decimated local wildlife populations, contaminated local aquifers with dangerous levels of heavy metals, and cleanup costs are estimated at up to $975 million. (Ray, 2014)

Coal Slurry is a black byproduct of the process referred to as wet-washing, where noncombustible materials, such as clay and rocks are separated from coal prior to mining. The preparation of coal consists of unloading, storing, conveying, crushing and classifying different grades of coal. Fine and coarse coal are then fluidized with water, magnetite, and organic chemicals, separating the impurities (Davidson, 2004). According to Davidson (2004), the final step in processing is dewatering the processed coal; removing excess water through screens, cyclones or thickeners . This water slurry can contain heavy metals (ie arsenic, lead, cadmium, chromium, iron, manganese, aluminum, and nickel), polyacrylamides, hydrocarbons and organic compounds that are known carcinogens to the human body. The large quantity of chemically treated water that remains is known as “coal slurry”.

This heavy metal and chemically laden mixture is then disposed of in impoundment ponds or alternatively injected into abandoned mines. Coal Slurry injection is regulated under the Groundwater Protection Unit’s Underground Injection Control and is presently classified as a Class 5 well for the injection of non-hazardous fluids, requiring a permit with a fixed term of no longer than 5 years or approval by the State. The chemicals used during the preparation process must be approved as non-hazardous. The West Virginia DEP is required to protect underground drinking sources that include entire aquifers in any amount, which supplies any municipal water system; groundwater reserve able to or currently supplying public water use, or contain fewer than 10,000 mg/l total suspended solids and is not an exempt aquifer (West Virginia Department of Environmental Protection 2009).

The Appalachian Basin has approximately 1,000 slurry impoundments containing anywhere from tens of thousands to billions of gallons of slurry. These toxic lakes often leach, resulting in catastrophic spills that could decimate many miles of a watershed, rendering water supplies undrinkable. Among the 23 impoundment spills on Massey Coal Co. owned sites, the Inez disaster was the worst. “Black lava” flowed through 100 miles of waterways of Kentucky on October 11, 2000 after a 68-acre impoundment pond failure at Martin County Coal Corp. Massey eventually settled with $3.5 million in state fines and paid $46 million for the clean up (Donovan, 2010). Coal preparation plants have been injecting slurry as early as the 1960’s and this practice peaked in the 1980’s when more than 60 plants utilized this cheaper and presumably safer alternative. This also occurred prior to the State receiving primacy for the US EPA.  According the Underground Injections Control data in 2008, approximately 15% of all active preparation plants inject slurry into abandoned underground mines and there are currently 13 active sites (West Virginia DEP 2009).

  Figure 1. UIC Historical and Current Sites ( WV DEP, 2009)


Need for Regulations

EPA reports state that portions of at least 100 aquifers supplying drinking water have been declared exempt from regulation, and are now poorly documented waste sites. An investigation by ProPublica reveal that the EPA’s records do not track exactly where or how many exemptions have been issued or who is impacted (Lustgarten, 2012). Aquifers and groundwater sources that are exempt are no longer protected by the Underground Injection Control program and the Safe Drinking Water Act. The agency relied heavily on the assumption that once waste is injected, it will not mobilize and remain confined within the boundaries of the exempt aquifer. Mike Wireman, a senior hydrologist with the EPA commented, “Over decades, that water could discharge into a stream. It could seep into a well. If you are a rancher out there and you want to put a well in, it’s difficult to find out if there is an exempted aquifer underneath your property (Lustgarten, 2012).” The EPA has since appointed a special unit to re-assess exemptions policies.

There is a great need for further and more comprehensive research on the health risks associated with water sources contaminated by coal slurry. The little research concerning the impacts have only been able to comment of the need for further data, partially due to lack of knowledge but also lack of funding. In 2009 the West Virginia DEP Secretary Randy Huffman reported on a The Phase 1 Environmental Investigation conducted by the department assessing the impacts of coal slurry injections and the results were inconclusive due to some challenges the team faced; though they could not identify clear evidence that coal slurry injections were unsafe but they did recognize the need for significant improvement of the process (West Virginia DEP 2009). Following the study the state DEP placed a temporary ban on new injection sites until further studies could be conducted.

 The US Department of Interiors, Geological Survey (USGS) (2010) report on the Health Effects of Energy Resources published in 2010 investigates the implications of toxic substances from coal leaching into water supplies on human health. A disease model they examined called the Balkan Endemic Nephropathy, linked chronic exposure of toxic organic substances from coal in their water supply to kidney failure and high instances of renal/pelvis and ureter cancer. Each of these study areas in Southwestern Europe had primary water sources downstream from coal deposits. Similarly, the highest instances of renal pelvis cancer in Louisiana are found in Northwestern Louisiana, where high concentrations of the same toxic organic compounds are present in the drinking supply. Chronic exposure to aromatic amines, heterocyclic compounds, and terpenoids are known to cause kidney disease and cancer; the researchers hypothesized that the presence of these compounds along with other environmental and genetic factors result in these conditions in both regions. Further studies are planned for Texas, Wyoming and North Dakota to further investigate the relationship between long-term exposure to potentially toxic organic compounds in water sources and the effect on public health.


In the aftermath of these events, one fact has become abundantly clear: our current methods for dealing with the waste created by coal mining are not sustainable given the demand for cheap energy. Containment on such a massive scale is dangerous to the environment and surrounding communities, so the demand for effective treatment procedures is vital. Active treatment, utilizing chemical catalysts to render coal slurry safe for disposal or further refining, is too expensive given the output of resulting forms of fuel (Hedin, 2013). Therefore, passive treatment methods become more attractive, as they require minimal upkeep and can even help to improve the health and biodiversity of land that would otherwise remain barren. In addition to passive treatment options, increase legislation and government incentives will help ensure these treatment methods as priority over the current ones which do little to protect and ensure potable drinking water

Multiple forms of passive treatment have shown effective, and the strengths of each render them well suited to different environments and industrial processes. Described below are five types of treatments for coal slurry.

  1. Settling ponds are used for removal of iron and aluminum hydroxide from mine runoff. They do so by letting gravity do the work, and solids suspended in the water settle on the bottom before proceeding to further treatment processes. (Hedin, 2013) (Sunnyside, 2014)

  2. Constructed treatment wetlands (CTW) are used in unison with settling ponds to remove contaminants from wastewater. The use of reed plants and fish creates a biofiltration mechanism by which nitrogen, ammonia, heavy metals, and mine water acid drainage can be mitigated. (Hedin, 2013) (EPA, 2009)

  3. Vertical flow ponds make use of limestone to condition pH towards alkalinity, and remove aluminum and ferrous solids. Because this method does not address organic contaminants, it is also used along with a settling pond. (Hedin, 2013)

  4. Anoxic limestone drains (ALD) also utilize subsurface limestone to add alkalinity, yet are not effective in removal of aluminum or ferric iron due to their reactivity with limestone, which shortens the lifespan of the drain. (Hedin, 2013)

  5. Oxic limestone beds (OLB) use exposed limestone for removal of manganese and pH neutralization, and do so faster than the use of a CTW.  Recent developments have also shown that if drained regularly, they can also handle aluminum and ferric iron, which is superior to the use of an ALD. (Hedin, 2013)

As each of these methods is best suited to a specific family of contaminants, use of several in tandem is required for complete reconditioning of wastewater. A strong benefit lies in the use of constructed treatment wetlands, in that they are beneficial to all other processes as a final step to purification and also increase biodiversity (EPA, 2009).

The implementation of these new treatment processes is not easy, and upfront costs are considerably higher in the short term compared to active treatment. Why do we care about reforming current standards, when the cost is so high and economic benefit nearly zero? As the disasters described earlier show, continued reliance upon outdated solutions carries a high cost.

In an industry where short-term profits are chased due to looming “threats” of government regulation, we should be employing programs that incentivize the treatment of coal slurry prior to injection or impoundment. This way the government absorbs some of the cost preventing the loss of jobs or substantial profit or increasing the cost of energy. Constructed treatment wetlands are a viable option because they are a low cost and effective solution. If legislators provide a tax expenditure for the construction of these treatment facilities, this option may become even more appealing than paying millions in fines and litigation fees.

There are two different basic types of CTW’s: surface flow and subsurface flow. The main difference is that in a surface flow CTW, the wastewater flows above the ground through channels, whereas in a subsurface flow wetland the wastewater travels below the surface (Halverson, 2004). In subsurface flow wetlands, the water still travels through channels, but unlike in surface flow systems these channels are filled with rock, gravel, or sediment, and the water line is generally kept below the top of the sediment. This material that the water runs through acts as an extra filter for the wastewater. The flow direction in a surface flow wetland is always horizontal, whereas in a subsurface flow wetland the water travels generally horizontally but can also travel vertically within the filter medium. Although subsurface flow systems generally remove water pollutants slightly more effectively, they also cost far more and are much harder to design and construct that surface flow systems(Halverson, 2004). Because of this, there are far more surface flow CTW’s than subsurface flow CTW’s in the U.S.

The location of the wetland on the surface or subsurface is tied to the overall implementation. Subsurface-flow wetlands do not suit animal life; yet require a smaller surface footprint. Surface-flow CTW’s support both plant and animal life, but are not ideal due to their footprint (Davis, 2013). Tidal-flow wetlands, which denitrify water by cycling through wetlands, achieve the goal in a shorter amount of time with a smaller footprint. This is particularly helpful for high-nitrogen waste sources.

According to Haderl, et al. (2003), reviewed journal article on Constructed Wetlands for the Treatment of Organic Pollutants, removal mechanisms are dependent upon  hydraulic conductivity of the media, types and number of microbes present, oxygen supply for microbes and  chemical conditions of the media. The mechanisms that come into play within the wetland are the settling of suspended particulate matter, filtration and chemical precipitation, chemical transformation, absorption and ion exchange, breakdown and transformation and uptake of pollutants and nutrients by microbes and plants. Adjusting wetland characteristics of the CTW to accommodate the volume and composition of effluent being treated is key to achieving high rates of contaminant removal. For coal slurry high in heavy metals and special organic compounds choosing the proper plants can enhance the efficiency of pollutant removal. The flora play an important role in contaminant uptake as they can absorb pollutants into their tissues while providing surfaces for microbes to flourish. The root system also prevent clogging within the system. Phragmites australis commonly known as the Reed is a highly productive grass found in wetlands in toxin removal (Haberl et al., 2003). The microorganisms are the most vital component of the ecological food web within a wetland. They are the driving force behind transformations of nutrients into varying biologically useful forms.

Figure 2. Table of plant types used for specific organic pollutants (Haberl et al, 2003)

There are, however, a significant number of general design characteristic rules that should be followed when designing any constructed treatment wetland. First and foremost, a general rule is that design should be based off of the function of the wetland and not any aesthetic features. The design of a CTW should be kept as simple as possible. Even though the processes that take place in the CTW are fairly complex chemically, the simpler the overall design is the less chance there is of the CTW not working properly. Another general design rule is that the CTW should take advantage of natural forces, specifically the use of gravity to control the flow of water through the wetland. If designed properly, a CTW should function completely free of outside input. When designing a CTW, one should also take advantage of any natural features of the land, while creating as little detrimental effects on the natural surroundings as possible. The most effective CTW designs are the ones that closely mimic natural wetland systems(Davis, 2013).

             Along with these basic rules of design, all CTW’s must be constructed around their own specific purpose. For instance, a CTW that is to treat only a small amount of runoff water from a small mining operation would not require that the CTW be nearly as large of an area as one would have to be for a major mining operations. The safest method for designing a CTW is to model it after a natural local wetland, only changing the design minimally to meet the wastewater treatment needs. Channels and paths for the water to follow should run along with the naturally occurring contours of the land. Various types of vegetation, can be used for various functions, such as erosion control, water pathway control, and more obviously water treatment. Aesthetic appeal should be taken into consideration only once all of the functionality needs have been met.

             Economic function of a CTW must also be met. One of the biggest oppositional views on CTW’s is that they cost a significant amount of money more than the current wastewater treatment methods. If designed properly, however, these opponents would be silenced. Initial economic factors are based on the amount of water that must be treated, the specific pollutants that must be treated, and the amount of land that the CTW will take up (Davis, 2013). Choosing the properly suited site can be an extremely important economic aspect of the CTW. Improper site selection could lead to the need for excessive land manipulation, wasting both time and money. The proper site is one that it is located in close proximity to where the wastewater is produced, that has a downhill grade allowing for natural water flow through gravity, and that doesn’t already serve as an important natural system. Other factors that can also affect site choice are the ability of the soil to be manipulated properly and the ease of human accessibility to the CTW.

             When compared with other treatment options, CTW’s are more economically viable if properly constructed (Davis, 2013). One of the current methods of coal mine wastewater treatment being commonly used is pumping all of the wastewater from the mine into a large tank that is then mixed with lime as well as other chemical-cleansing microbes. This is an extremely expensive option because not only must a properly sized tank be purchased, but this system also requires the purchase of several pumps to get the water into and out of the tank, and testing equipment to monitor that the water is being successfully treated. Once water has been pumped into the tank and treated, it is then pumped out into the environment, eventually getting into local bodies of water. This method is often extremely expensive and highly problematic. These systems require constant maintenance and monitoring, and if any one of the components of the system stops working properly then the entire system is compromised and will most likely fail. Compared to these tank systems, CTW’s leave many ways to cut down on these unnecessary costs. Being as the materials used in a CTW are all natural, the material costs can be significantly less. The need for maintenance is also significantly smaller, as once the CTW is constructed and functioning it performs most of its own maintenance naturally (Halverson, 2004). Wastewater that fails to be treated properly can lead to companies getting substantial fines. These fines are generally much less likely in mines using CTW’s as opposed to tanks because CTW’s use gravity to move the water as opposed to mechanical systems (Davis, 2013). Another very similar method to the fixed-tank method is to bring mobile tanks and pumps to a mine to be used and then removed. This method is far more expensive than both other methods, as there are added transportation costs. A benefit of this method over the fixed-tank method is that there is the potential for financial  savings when retiring a mine, as there are far less fixed materials and systems to be uninstalled.


Resistant Audience

Coal is the largest source of energy in America, and with such a powerful industry comes financial interest that seeks to maximize profits. The influence of political posing and lobbying has always been negative for environmentalists. In the case of Buffalo Creek (1972), politicians supportive of coal industry covered up the risks of contamination, and even today the West Virginia Coal Association continues to deny culpability for coal mining accidents in the state. Bill Raney, the president of WVCA, claims that with government regulation, could come the loss of thousands of West Virginia jobs that rely on coal (Dizard, 2014). However, Democratic Senator of West Virginia and former Governor, Jay Rockefeller (2014), commented after the recent chemical spill:

“Many people (2014) have the view, particularly those in the industry, that if you regulate them, they’ll go out of business and people get laid off. Well, this is a perfect example of, when you don’t regulate them, dozens and dozens, maybe hundreds of businesses have to close down, schools close down. People can’t go to school. People can’t do anything. People can’t escape… It’s a travesty really beyond description (p. 1)”.


While the threat of job loss is very real for families who must deal with the destruction of their local watershed, the reality remains that sustainable economic growth through wetland construction can become a reality. By providing thousands of construction jobs and removing the source of environmental damage, the economies of these regions can grow. Strong government regulation does not necessarily have to equate to increased coal prices, and while coal will never be a completely clean source of energy, the possibility of balance between economic success and environmental sustainability is nearing closer by the day.


Access to potable water is a basic human right; unfortunately for many years this liberty has been compromised in places like West Virginia. A tremendous need for a paradigm shift is apparent in areas scarred by Big Coal; one where the cost of human health is not foreshadowed by the loss of jobs and profits by multi-billion dollar companies. Although much is still unknown about coal slurry, current evidence does indicate that the health implications posed by this substance in water supplies should not be taken lightly. “Levying fines after the fact does nothing for the communities and waterways already harmed,” said Mary Anne Hitt, director of the Sierra Club’s coal campaign (Dizard, 2014). These communities are pleading with governmental officials to make them a priority. Action needs to be taken to ensure that basic human needs are being met.


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