A Cat D6 low ground pressure dozer placing soil cover over cap liner.
North Carolina’s Asheville Regional Airport expansion project features an environmentally responsible component: the use of coal combustion products as fill material.
A regional partnership composed of the airport, Raleigh, N.C.-based utility company Progress Energy Carolinas Inc. and Charah Inc., of Louisville, Ky., cooperated on the project, which began in 2009 when the airport identified opportunities to develop a new taxiway and general aviation commercial parcel in the southwest portion of the airport property.
“The site identified for development contains approximately 53.5 acres of land that was partially wooded with a couple of drainage features passing through the property providing outfall for stormwater runoff from the airport’s existing infrastructure,” said Norman Divers, senior engineer of Charah Inc. “To facilitate the future development of a new taxiway and commercial aviation site, known as the Westside Development project, significant site grading would be required.
“Charah approached the airport’s management staff to present a solution to the significant site development economics for the Westside Development project,” Divers went on. “The solution involved the use of Coal Combustion Products (CCPs) as a suitable engineered structural fill material that would facilitate the rough grading needed to make the Westside Development project a reality. Using CCPs as an eco-fill material would offset the significant cost that soil structural fill material was presenting to the development of the project, as well as provide the means to conserve a natural resource by allowing any offsite soil borrow to remain undisturbed and left in place.”
Coal combustion products have been recycled and used for decades for various construction purposes, including on such historic projects as Boston’s Big Dig and the Hoover Dam. CCPs also have been utilized for airport construction in Pennsylvania, Texas, and Wisconsin. Use of these by-products saves natural resources ton for ton and space at landfills, and in addition there are significant cost savings for the client.
“This project is the first of its kind, being an ’encapsulated’ engineered fill meeting stringent protective features as found in the EPA’s proposed rules for the reuse of Coal Combustion Products,” stated Danny Gray, Charah’s executive vice president.
Development of the site required approximately 2.1 million cu. yds. (1,614,434 cu m) of structural fill to establish the necessary rough grade elevations across the site, an amount of suitable structural soil that would be both hard to locate in western North Carolina and would involve the use of several borrow sources, as well as presenting a significant financial strain on the project. Estimates for suitable structural soil fill ranged from $7 to $8 per cu. yd. providing an overall cost of approximately $15.8 million dollars.
“In addition to the fill requirements, the site presented a drainage challenge which involved the preservation of the existing runway stormwater drainage patterns, while still allowing the engineered fill material to be placed. Significant drainage improvements were constructed along the eastern side of the engineered fill project to re-direct runoff around the work area and continue to maintain stormwater drainage as needed to maintain safe maneuvering, take-off and landing of airplanes,” said Lew Bleiweis, A.A.E., airport director at the Asheville Regional Airport Authority.
The Asheville Airport project, which is expected to be completed in 2014, will create 15 acres of aeronautical use land. The project created approximately 50 jobs for local residents and utilized numerous pieces of equipment.
“The engineered fill project was extensive and required a vast array of earth moving equipment. Large track excavators, Caterpillar 330CL, were used to remove soils to develop the subgrade surface of the engineered fill. Artic 40-ton end dumps were used to transport soils throughout the project to allow for the construction of containment berms, sediment basins and haul roads needed to serve the project,” Charah’s Vice President of Operations, Scott Sewell, said.
“Large bulldozers including the Caterpillar D6R were used to move soils as needed to achieve final grade elevations along slopes and the base surface of the engineered fill surface,” he continued. “Compaction was achieved using a Cat 815 compactor. Fine grading was performed using a Case 885 motorgrader and rolled to a final surface ready for deployment of liner using a Dynapac vibratory smooth drum roller.”
Liner was deployed by Chesapeake Containment Systems (CCS), Charah’s liner installation subcontractor, using retractable forklifts fitted with spreader bars. Rubber tired mules and rubber tracked mini-excavators were the only types of equipment allowed for use in placing the liner materials. Seaming for HDPE liner materials was performed principally using a double hot shoe welder that matched liner panels together. Seams were tested on-site using both vacuum and air test equipment and destructive testing also was performed on-site as well as sent to a lab for Construction Quality Assurance purposes.
“CCPs were spread using a Caterpillar D6N LGP dozer equipped with grade control to ensure the material was placed within the specified elevation tolerance of +/-0.25 feet,” Sewell stated. “Compaction of the CCP material was achieved using a Dynapac vibratory smooth drum roller. Numerous passes were made throughout each day, varying in direction achieving the compaction requirement of 95 percent modified Proctor. Compaction was confirmed using both nuclear and standard density testing methods.”
Soil material in the final cover was moved and placed by using the Artic end dumps, D6 dozer, and motorgraders, and compaction was achieved using the 815 compactor and smooth drum roller. Soil materials were screened using a Chieftain Powerscreen to ensure particle size requirements were met as well as establishing an organic free soil material.
Protection for the environment and public concerns as related to the use of CCP materials was not limited to maintaining stormwater runoff for the existing runway. Additional measures of environmental and public health protection were provided in the design of the Westside Development engineered fill project, as Divers explained.
“A comprehensive liner system consisting of two layers of non-woven geotextiles encapsulating a layer of bentonite, commonly referred to as a geocomposite clay liner (GCL) in conjunction with a 60-mil high density polyethylene (HDPE) textured liner was provided between the excavated subgrade of the engineered fill limits and the CCP material. The GCL and HDPE liners act as a barrier layer preventing any CCP material or related moisture to pass through the comprehensive liner system into the subgrade soils or underlying groundwater table,” Divers said.
Presenting a hydraulic conductivity less than 5x10-9cm/s, the GCL provides 200 times the protection currently required by Subtitle D regulations for clay that is a part of a liner system serving a municipal solid waste landfill.
“Closure of the engineered fill project included the installation of a 30-mil textured HDPE cap liner that was extended across the limits of the engineered fill providing a complete ’encapsulation’ of the CCP material,” Divers noted. “In addition to the HDPE cap, six feet of soil cover was installed across the CCP fill limits at a compaction rate of at least 95 percent modified Proctor meeting FAA fill placement requirements for the development of aviation facilities and infrastructure. These improvements provide the necessary site conditions conducive to the continued development of the new taxiway and commercial aviation site.”
Speaking of the various complications involved in the Asheville Airport project, Sewell observed that “In an industry not traditionally known for its innovation, Charah has remained committed to developing and providing innovative solutions that are environmentally conscious. With nearly 20 years of engineered fill experience, our team of experts not only has done this before but we also are well versed in complying with government regulations as well as implementing the most up-to-date solutions.”
At the time of the project, state regulations allowing the use of CCP materials as suitable fill did not require the added use of the comprehensive liner system nor the provision for an HDPE cap liner. Charah and Progress considered the application of these design elements environmentally responsible and progressive to industry standards, while the project solved the economic strains that were preventing a much-needed infrastructure and commercial development for the airport, as well as providing an advanced and conscientious use of CCP material.
“Charah provides a broad base of services to the coal-fired utility industry to assist them in meeting the increasing environmental requirements under which they operate. We are committed to providing our utility partners innovative, environmentally conscious solutions to meet all of their ash management and power plant support services needs. In approaching the Asheville Regional Airport about this idea, we were able to provide a solution for Progress Energy and the airport, solving two problems at the same time,” said Charles Price, president and CEO of Charah Inc.
“As a group, Progress Energy, Charah and the Asheville Airport agreed to utilize only state-of-the-art products and materials for this project. We worked hard to design and construct the first of its kind, next generation facility utilizing the latest in environmentally sound engineering,” added Rob Reynolds, project manager at Progress Energy.
The Asheville Airport project was recently recognized by the South-East Chapter of the American Association of Airport Executives when it was presented with their General Aviation Project of the Year Award for creative use of a regional partnership to efficiently, effectively, and safely conduct a major fill project.
About the Company
Charles Price founded Charah Inc., in 1987 and has more than 35 years of experience in the construction industry. In 1992, he began focusing exclusively on ash management and is now recognized as an industry leader and expert. He currently serves on the board of directors of the American Coal Ash Association as Secretary/Treasurer.
Based in Louisville, Ky., Charah Inc., is a coal combustion products (CCP) management company working in the coal-fired electric utility industry. In operation for more than twenty years and handling more than six million tons of various CCPs annually, its areas of expertise include support services for power plants, construction of ash ponds and landfills and development of markets here and abroad for client’s CCP material as well as assistance in meeting industry-wide environmental requirements.
Charah’s work in the coal by-product industry earned it the 2005 Innovation Award from the EPA’s Coal Combustion Products Partnership (C2P2) for increasing the use of coal-combustion products with its ash-based packaged concrete. The company is currently processing bottom ash that is being sold to Quikrete for production into packaged concrete at an Ameren facility outside St. Louis. The final product is being sold into Home Depot locations in Missouri.
The company’s current projects include the design, permit, construction, and operation of a 65-acre landfill for and in partnership with Constellation Power Source Generation Inc., of Baltimore. With a capacity of about seven million tons of CCBs and an anticipated life span of 22 years, it will be the first in Maryland featuring CCPs and built to the EPA’s new potential regulations. Special features include a leachate collection system, groundwater monitoring wells, stormwater management system and CEthe preservation of on-site wetlands. CEG