Considerations for Sustainable and Resilient Coal Ash Cover Systems

Presentation Summary:In the aftermath of the catastrophic 2008 Tennessee Valley Authority (TVA) Kingston Power Plant coal ash containment dam disaster and the 2014 Duke Energy Dan River coal ash spill, US EPA and state agencies have developed more stringent rules for regulation of containment and storage of Coal Combustion Residuals (CCR). Regulations to protect ground and surface water as well as suppress airborne dust are under auspices of US EPA 40 CFR Part 257 Subpart D Standards for the Disposal of Coal Combustion Residuals in Landfills and Surface Impoundments. Additionally, state regulations have been implemented such as the North Carolina Coal Ash Management Act (CAMA) and the Commonwealth of Virginia Waste Management Act. Traditional closure capping methodology from past requirements under the Resource and Conservation Recovery Act (RCRA) for Municipal Solid Waste Landfills has been the placement of 18-inches of “earthen cover material” topped with 6-inches of a "vegetative soil layer" capable of sustaining “native” plant growth over a geomembrane, geosynthetic clay liner, or soil of low permeability to keep incident water from entering the waste as leachate. In recent years alternative cover system technologies have been introduced to save money and improve performance, but how sustainable are they? How can we maximize sustainability of these cover systems to create functional ecosystems and sequester more carbon? Then, how can we effectively convert these brownfield sites into tangible assets such as solar energy fields, industrial sites or even recreational opportunities? This presentation will compare costs and sustainability of three cover system methodologies throughout their installation and effective design lives.
Full Abstract: Design and construction of cost-effective cover systems are critical to successful Coal Combustion Residuals (CCR) closure projects. Traditional cover system designs typically have involved comprehensive specifications for placement of highly specialized barrier and drainage systems with 18 inches of cover soils, that are then capped with 6 inches of a "vegetative soil layer" that is "capable of supporting the growth of vegetation" (US Environmental Protection Agency (EPA) CFR 40 Part 257.102) - Criteria for conducting the closure or retrofit of CCR units - updated May 9, 2022). A sustainable stand of vegetation will provide enduring erosion control, capture precipitation to reduce and improve stormwater runoff quality, reduce surface and water runoff temperatures, enhance visual aesthetics, and foster carbon sequestration while returning oxygen to our atmosphere.

Fertile and productive soils are essential to the development of sustainable vegetative covers. However, obtaining acceptable soil can be problematic as closure sites rarely have salvageable onsite cover soil and topsoil after decades of operation. The costs of procurement, transportation and placement of suitable imported offsite soils can be significant on large closure projects. Fortunately, emerging technologies such as "engineered soil amendments" can help make marginal soils suitable for vegetative establishment with significant cost savings to utilities, tax and rate payers, and other stakeholders.

The ASTM International D5268-19 "Standard Specification for Topsoil Used for Landscaping and Construction Purposes" describes Engineered Soil Amendment as "an alternative to topsoil to accelerate development of depleted soils/substrates with low organic matter, low nutrient levels and limited biological activity. "Engineered soil and/or organic amendments" are also referenced as topsoil alternatives in the US EPA Publication "Revegetating Landfills and Waste Containment Areas Fact Sheet" - Office of Superfund Remediation and Technology Innovation (5102P) - EPA 542-F-06-001 (October 2006). This informative publication recommends and details the keys to successful establishment of native plants for improved habitat in support of bees, butterflies, and other important pollinators of agricultural and horticultural crops. Moreover, several ecological values of native plants for ecosystem integrity are introduced including the elimination of chemical inputs and reductions in mowing frequency to significantly reduce post-closure maintenance costs.

A study by Applied Ecological Services (2013) documented a three-to-eight-year return of investment in reduced maintenance costs when employing native vegetation is lieu of turf grasses. Moreover, a native grassland community can sequester 57 tons of carbon per acre versus 25-30 tons per acre from turf grasses. This bodes particularly well for the progression of solar energy development on post-closure CCR sites as utilities and other entities transition from fossil fuels to renewable energy sources in their quest for carbon neutrality.

This presentation will address pros and cons of current state of the practice versus alternative cover systems with an examination of installation and life-cycle costs coupled with long-term environmental impacts; especially when considering mitigation of climate change via environmentally sensible, sustainable, and resilient closure practices.