Professional Engineers Of North Carolina

SUM 2014

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10 the Professional Engineer Summer 2014 modeling to support a given design. Absent data and analysis, there is no indication that the proposed CFA cannot be used at the Charlotte airport to provide sufcient strength and stability. One might argue that CFA could perform better than natural soils given its uniformity. Soils in the Piedmont include moisture-sensitive silts and intermittent strata of high plasticity clay colloquially referred to as "bull tallow." Moreover, the use of CFA is likely to involve more frequent testing and a stringent construction quality assurance plan. Te proposed design for the Charlotte airport includes encapsulating CFA in multiple layers to minimize infltration and isolate the material from the environment. One concern is that encapsu- lated ash flls can't be moved without breaching the liner and cover system. Te location of future runways and taxiways is generally well-defned by the location of existing runways and overall site constraints. Still, fxing site topography could theoretically present obstacles to airport ofcials as they optimize the airfeld for growth. In that situation it may be advisable to increase the depth of cover soils above encapsulated ash and/or explore alternate methods of encapsulation, such as the use of lime or water-repellent additives. Another concern is FAA approval. Airports are generally eligible to have 90% to 95% of runway work funded by FAA, consistent with the recently signed FAA Modernization & Reform Act of 2012 on Feb. 14, 2012, (PL 112-95). Such support comes with expectations. Te FAA has numerous advisory circulars and design standards that engineers can consult. Typically engineers can specify materials as can be demonstrated appro- priate for a given application. Tis includes CFA. Tere are airport construction standards for CFA use as a partial replacement for Portland cement in runways as well as for stabilizing soil, typically by decreasing plasticity and increasing strength. Tere is no specifc standard that prevents CFA from being a fll material. Apart from Asheville, another example is the Rostraver Airport runway in Belle Vernon, Pa., where CFA was mixed with fue gas desulfurization gypsum, bottom ash and lime to form a cement-like product. Historically, the extent CFA is handled as a solid waste as opposed to a benefcial product is a function of the building needs of the construction industry, not the disposal needs of electric utilities. Upstream and down- stream concentrations of unfltered samples after the Dan River spill (arsenic and copper visible in charts bellow). Upstream and down- stream concentrations of arsenic and copper in unfltered samples after the Dan River spill. F E AT U R E S T O R Y 0 1 2 3 4 5 6 7 8 Upstream - Total - µg/L Aluminum Arsenic Iron Copper Feb. 3 Feb. 4 Feb. 5 Feb. 6 Feb. 7 Thousands µg/L Arsenic: 10 µg/L Copper: 7 (human health) (Aquatic health) Applicable Standard: Downstream - Total - µg/L Thousands 0 1 2 3 4 5 6 7 8 Feb. 3 Feb. 4 Feb. 5 Feb. 6 Feb. 7 Upstream - Total - µg/L 0 10 20 30 40 50 Feb. 3 Feb. 4 Feb. 5 Feb. 6 Feb. 7 Downstream - Total - µg/L 0 10 20 30 40 50 Feb. 3 Feb. 4 Feb. 5 Feb. 6 Feb. 7

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