Constellation Power Source Generation Inc., which owns and operates three coal-fired power plants in Maryland, has contracted with Charah Inc., an ash management company, to build a landfill to strict environmental requirements for the disposal of its plants’ coal combustion by-products that can’t be recycled for other uses.
Coal-fired power plants produce approximately 40% of the electricity generated in Maryland. Constellation Power Source Generation Inc. (CPSGI), an affiliate of Baltimore-based Constellation Energy, owns and operates three of these plants that help meet the growing demand for electricity. Although more than half of the coal combustion by-products (CCBs) produced by these three plants is recycled for reuse in products such as cement and concrete, not all can be reused due to a lack of market demand. The remainder is placed in landfills permitted to dispose of such materials.
Overview of Coal Combustion By-products
Approximately 43% of CCBs were recycled for “beneficial uses” in 2008, according to the American Coal Ash Association. The remainder were landfilled, placed in mine shafts, or stored on site at coal-fired power plants.
The University of North Dakota has extensively researched the characteristics of different types of CCBs typically produced by coal-fired power plants. Here are the main types of CCBs the university has identified:
- Boiler slag is a molten ash collected at the base of slag tap and cyclone boilers that is quenched with water and shatters into black, angular particles having a smooth glassy appearance.
- Bottom ash consists of agglomerated ash particles formed in pulverized coal boilers that are too large to be carried in the flue gases. Consequently, they impinge on the boiler walls or fall through open grates to an ash hopper at the bottom of the boiler. Bottom ash is typically gray to black in color, is quite angular, and has a porous surface structure.
- Fluidized bed combustion (FBC) materials consist of unburned coal, ash, and spent bed material used for sulfur control. The spent FBC material (removed as bottom ash) contains reaction products from the absorption of gaseous sulfur oxides (SO2 and SO3).
- Flue gas desulfurization (FGD) materials are derived from a variety of processes used to control sulfur emissions from boiler stacks. These FGD systems include wet scrubbers, spray dry scrubbers, sorbent injectors, and a combined sulfur oxide (SOx) and nitrogen oxide (NOx) process. Sorbents include lime, limestone, sodium-based compounds, and high-calcium coal fly ash.
- Fly ash is the coal ash that exits a combustion chamber in the flue gas and is captured by air pollution control equipment such as electrostatic precipitators, baghouses, and wet scrubbers.
Charah’s Decision to Develop a CCB Landfill
In the fall of 2007, CPSGI voluntarily began hauling and placing its nonbeneficially reused CCBs at privately owned lined landfills in Virginia and western Maryland as part of a consent decree signed with the Maryland Department of the Environment (MDE).
At that time, CPSGI’s evaluation of alternative disposal locations to manage its CCBs in a manner that ensured the health, safety, and welfare of the community intensified. In addition, CPSGI was determined to secure a disposal site for its sole use, as a monofill for CCBs. To facilitate this evaluation, CPSGI turned to Charah Inc., a Louisville, Ky.–based leading ash management provider for the coal-fired electric utility industry. Charah was initially tasked with evaluating long-term, cost-effective CCB disposal opportunities, including beneficial mine reclamation, industrial waste landfills, and additional beneficial reuse applications. In 2008, more than 300 sites in four states were evaluated for environmental, regulatory, capacity, and operational feasibility.
By late 2008, Charah presented CPSGI with a recommendation to purchase and develop an existing, unused 65-acre industrial waste landfill, located in Baltimore City, just miles away from the plants. The site identified by Charah was already permitted as an industrial waste landfill and was located within a heavy industrial zoning district separated from any residential land use. In addition, no private wells were located within the vicinity of the site. The site conformed to CPSGI’s strict environmental requirements and provided for long-term and cost-effective CCB disposal. The site would also reduce CPSGI’s carbon footprint by decreasing CCB disposal hauling distances and travel times.
CPSGI accepted Charah’s site recommendation and shortly thereafter secured an option to purchase the property. Having successfully completed the site selection process, and having met the day-to-day needs of CPSGI, Charah was then tasked with providing the design and engineering for converting the industrial waste landfill into a newly permitted landfill for disposal of CCB materials.
While CPSGI and Charah were evaluating alternative disposal locations for CPSGI’s CCBs, the MDE began reforming its regulatory program and issued a 68-page report detailing proposed action on regulations associated with CCBs. The purpose of this action was to establish requirements pertaining to the generation, storage, handling, processing, disposal, recycling, beneficial use, or other uses of CCBs.
At this time the MDE announced that “Additional controls are needed to ensure that we protect the public health and the environment. While the U.S. Environmental Protection Agency (EPA) has been developing a proposal to regulate the disposal and use of coal combustion byproducts since 2000, no federal program currently exists. Therefore MDE believes it is necessary to move forward with our own regulatory program (1).”
In February 2008, both Charah and CPSGI submitted comments and recommendations to the MDE on the proposed regulations. The MDE’s CCB regulations were published on November 21, 2008, in the Maryland Register, and they took effect on December 1, 2008. The regulations provide a regulatory framework for the disposal of CCBs and the use of CCBs for mine reclamation. Disposal facilities now need to meet all the standards required for industrial solid waste landfills, including a leachate collection system, groundwater monitoring, the use of liners, and routine analysis of CCBs. Requirements were also specified for CCB transportation and air quality controls.
To comply with the new MDE regulations, Charah navigated the site design and engineering, permitting, and construction process with the State of Maryland and City of Baltimore over a period of over two years. Throughout the process, Charah and CPSGI actively included the participation of the public and environmental groups, allowing all parties’ concerns to be voiced and addressed. Multiple community association meetings, public hearings, and collaboration meetings with nongovernmental environmental groups were held.
“There was never any question that the site design was outstanding,” CPSGI Project Manager Beth Pittaway said. “MDE was ahead of other agencies, including EPA, when they implemented the regulation. Even after design and operations plans were accepted by MDE, CPSGI met with national and local environmental group representatives to address their concerns. The project gained their support with some minor operational changes and increased bonding on the site for long-term care and closure.”
The project resulted in Maryland’s first permitted CCB landfill following enactment of the state regulations. “This project serves as a model of how industry and state regulators worked together to implement practical, safe, and environmentally conscious CCB regulations,” stated Charles Price, Charah’s president and CEO. “Additionally, the design conforms to the EPA’s proposed approach [to coal ash disposal] under Subtitles C or D [of the Resource Conservation and Recovery Act].”
“Coal will continue to be a viable part of the country’s generation mix. This site is a great example of how the by-products of coal-fired generation can be addressed in an environmentally responsible way,” said John Long, president of Constellation Power Generation, the Constellation Energy affiliate that oversees the company’s Maryland-based coal plants. He added, “we’ve always been keenly aware of the need to manage coal combustion byproducts in a manner that ensures the health, safety and welfare of our community. For a lot of reasons this site was one that allowed us to meet our own high expectations.”
Property Characteristics and Engineering Design
The property presented a unique and natural environmental buffer, as it is situated over a 100-foot-thick clay base at a permeability of 1 x 10-7 cm/sec or less. This buffer allowed Charah to place 60-mil high-density polyethylene (HDPE) liner directly on the graded subbase (Figure 1). The liner preceded installation of the leachate collection system, which consists of a network of 8-inch perforated HDPE pipes surrounded by coarse aggregate, all encased in filter fabric.
|1. The final act. Layout of a typical landfill used for the disposal of coal combustion by-products (CCB). Courtesy: Constellation Power Source Generation Inc. (CPSGI)|
The leachate system also includes a 12-inch drainage layer and 12-inch protection layer. Both specify a minimum hydraulic conductivity of 4 x 10-3 cm/sec. The leachate collection system was designed to maintain the leachate depth over the bottom liner to no more than one foot. The pipe network drains to a leachate sump that discharges into a double-lined collection basin on site. The leachate collection system is equipped with a telemetered and audiovisual alarm system to provide continuous monitoring. Once collected, the leachate will be transported to an approved wastewater treatment facility.
Long-Term Design and Permitting
Upon reaching fill capacity, the cells will be closed by placing a 24-in clay cover layer on top of the CCBs and a 40-mil HDPE liner system over top of the cover layer (Figure 2). A geocomposite drainage layer will be installed above the 40-mil liner, followed by 18 inches of protective soil, 6 inches of topsoil, and vegetation. This will provide a fully encapsulated system and will promote stormwater flow across and off of the landfill to the designed stormwater conveyance infrastructure.
|2. Topping it off. Upon reaching fill capacity, the cells of the CCB landfill will be closed by placing a 24-inch clay cover layer on top of the CCBs and a 40-mil HDPE liner system over top of the cover layer. Courtesy: CPSGI|
A permanent stormwater management (SWM) system will be implemented to closely maintain the predevelopment runoff characteristics after site development and to enhance water quality at permitted discharge points, as designated according to the National Pollutant Discharge Elimination System (NPDES) under the Clean Water Act. Design parameters will provide protection of natural resources by integrating erosion and sediment (E&S) controls with SWM practices, minimizing site imperviousness, taking advantage of the natural hydrology, and implementing the use of smaller controls to capture and treat stormwater closer to the source.
For monitoring during and after CCB placement, the site is surrounded by six perimeter groundwater monitoring wells. An active groundwater monitoring plan requires semi-annual sampling to document groundwater quality, to demonstrate that the background groundwater quality is not affected by present operations on the property, and to record groundwater quality directly downgradient of the limits of CCB placement. Groundwater levels in the wells are monitored monthly.
Long-term engineering design includes the development of future cells and the installation of mechanically stabilized earthen walls for the environmental conservation of existing wetlands located onsite. The landfill is expected to accommodate approximately 7 million tons of CCBs over a projected lifespan of 22 years.
“The design of this project incorporates the environmental criteria which will be the standard for next-generation CCB landfills,” said Bobby Raia, Charah’s project coordinator. “As we move forward with the design and permitting associated with the development of future cells and the overall landfill expansion, we will continue to provide innovative and environmentally beneficial solutions to CPSGI.”
Current Project Status
With several years of evaluation, design and engineering, and permitting completed, approval was granted by the MDE for the first two of six cells. In March, Charah began construction of the new CCB landfill, which is expected to take between eight and 10 months to complete. Construction efforts include the excavation of more than 1,000,000 cubic yards of clay, the deployment of nearly 12 acres of HDPE liner, and installation of the leachate collection system (Figures 3 and 4).
|3. The landfill’s layout. The CCB landfill site features side slopes at 2:1 extending 60 feet vertically. Crews deploy liner from the top to the bottom of the cell floor. Once in place and shingled properly to ensure free drainage from panel to panel, fusion welding commences. Courtesy: Photography by David Starling of CPSGI|
|4. Installing the liner. Crews complete the installation of a 60-mil textured HDPE liner at the site of the future CCB landfill in Maryland. Upon installation, welds are tested for their conformance with the technical specifications by third-party testing. The test must be submitted for approval to third-party construction quality assurance personnel and the MDE. Courtesy: Photography by David Starling of CPSGI|
Charles Price, Charah’s president and CEO, added that “the uniqueness of this project not only lies in the site’s characteristics and design but also in the partnership between CPSGI and Charah. Our involvement from the beginning of this project, starting with site selection, has forged a knowledgeable, trustworthy, and transparent relationship with CPSGI.” Charah expects to begin placement of CCB material in the initial cell by October 2011 (Figure 5).
|5. Successful teamwork. Charah President and CEO Charles Price (left) and CPSGI President John Long discuss the 60-mil textured HDPE liner used at the CCB landfill called “Lot 15.” Courtesy: Photography by David Starling of CPSGI|
Upon completion of construction, Charah will begin the landfill management phase, providing day-to-day operations that will include hauling, placement, and compaction of CCBs produced by CPSGI’s plants. Trucks owned and operated by Charah will haul CCBs from the plants to the landfill and will feature a cable-type tarp system that encapsulates the CCBs, thus avoiding and controlling any potential for dusting during transit. After placing the CCBs within the active working area, and prior to leaving the landfill site, trucks will travel through a self-contained truck and wheel wash system. The system includes a wash unit and recycling/filtration tank designed to clean and remove any CCB residue that may remain on the truck prior to returning to the public roadways. Any potential for onsite dusting will be further controlled by watering the access road, and other landfill areas as needed, via water truck (Figure 6).
|6. Hands-on management. CPSGI Project Manager Beth Pittaway (left) and Charah Project Coordinator Bobby Raia review and discuss the landfill’s liner layout drawings prior to the final installment of liner. Courtesy: Photography by David Starling of CPSGI|
To secure the active area and avoid dusting after hours, Charah will apply hydro-mulch on a daily basis across the exposed CCB surface. Hydro-mulch is a hydrated straw mulch that contains tacking agents that allow the material to adhere to the CCBs. The hydro-mulch will provide an initial barrier that will mitigate any possible wind or stormwater runoff erosion.
— Angela Neville, JD, is POWER’s senior editor.