Recycling and reusing coal ash are big business today, since it reduces costs for disposal while making good use of the waste material. While nearly half of all coal ash produced by power plants in the U.S. is reused today, that means 50% of it still needs disposal through some other method. It’s unlikely that 100% recycling rates will be achieved for coal ash within the next few decades. Make use of one or more of the following disposal methods still approved for use today, to deal with remaining coal ash residues that can’t be recycled or reused.
Buried Pit
With careful design and extra work put into the construction, it’s possible to build extra deep pits that can hold the coal ash permanently. These impoundments are built around the coal fired plant and need the extra depth to compensate for the 8 to 18 feet deep cap of soil required on top. These burial pits are generally only allowed for dewatered slurries and relatively dry ash products. Slurries with a high water content will settle too much over time and cause the cap on top to sink and potentially release waste. Buried pits are allowed for disposal-in-place methods by the EPA even under their most stringent set of regulations, but only with reinforced and lined pits that won’t collapse or leak over time.
Sedimentation Ponds
Sedimentation is a powerful tool for dewatering ash slurries, that relies only on gravity and time to slowly settle ash and other particulates out of the wastewater mixture. This allows for reuse of the water for cooling or sluicing more ash out of the boiler, while eventually accumulating the sludge at the bottom for recovery and disposal. Sedimentation ponds absolutely must be lined since they accumulate thick layers of particulate at the bottom. The only way to continue using these impoundments long-term, is to routinely empty them with dredging equipment and send the solid waste to a landfill or burial pit. Sedimentation ponds need controlled evaporation rates, to maintain the right sedimentation speed, so that valuable and reusable water isn’t lost in the process.
Direct Release into Waterways
Many coal powered, power plants release the majority of their coal ash slurry into a nearby waterway with EPA approval. In these cases, the ash residues are generally sorted by volatility and contamination risks so that the most hazardous material is disposed in a different way. Only well-diluted and relatively inert coal ash products are generally approved for direct release into waterways; although this can vary by state. Since most discharge permits will involve a waterway considered one of the official waterways of the United States, this means that the EPA can get involved in the process due to the Clean Water Act.
Well Injection
Deep well injection is a disposal method more commonly used for waste produced during oil and gas drilling, especially hydraulic fracturing. However, it is being investigated as a disposal method for many other types of hazardous waste products, included concentrated slurries of coal ash residues. It’s a potential alternative to landfill disposal for concentrated waste products, but it can waste water since the slurry has to be thinner than it would be for the usual hazardous waste landfill methods. Thick slurries that are too dewatered are hard to inject smoothly into the well and may break up the rock formations designed to contain the waste products. This method isn’t as easy to get approved as above-ground lined impoundments, so most facilities simply stick to the traditional methods of long-term and short-term disposal.
Landfill Disposal
For dewatered slurries that are 20% water or less by volume, disposal in a hazardous waste landfill is the most common method of disposal. Almost all coal ash disposed of today eventually ends up in these landfills unless it’s approved for direct burial at the power plant site. Yet the amount of space available for this kind of controlled, lined, and capped disposal shrinks each year. Eventually landfill costs will become so high that coal plant operators will be forced to find new alternatives. It’s worth investigating other options now, rather than waiting, since coal ash will continue to be produced in large volumes for many years to come.
Coal ash residues deserve proper handling and disposal, regardless of the specific type of ash or its environmental risks. Increasing recycling and reuse opportunities is the best way to reduce disposal costs, but it comes with an eventual limit as well. Consider investing in direct burial pits lined with materials from BTL Liners to save money on landfill and direct discharge costs. BTL has plenty of liner products that can last for decades, even when buried deep underground in a challenging environment.
