Engineered Soils for Cost Effective Coal Ash Cover Systems

摘要

Design and construction of cost effective cover systems are critical to successful coal ash closure projects.Traditional cover system designs have involved comprehensive specifications for placement of highly specialized geosynthetic barrier and drainage systems with 18-24 inches(457-610 mm)of cover soils,then capped with 4-8 inches(102-204 mm)of a”vegetative soil layer”often with vague requirements such as”capable of(or suitable for)supporting the growth of vegetation”.Detailed specifications for soils used to establish vegetative cover should be fundamental components of any construction project.Sustainable vegetation will provide enduring erosion control,capture precipitation to reduce and improve stormwater runoff quality,improve visual aesthetics and foster carbon sequestration.Soil specifications should include detailed requirements for properties such as texture,pH,nutrient content,organic matter,soluble salts and additional provisions for soil testing to insure specification compliance and quality assurance.Obtaining candidate cover soils at fossil plants can be problematic,as these”soil poor”sites rarely have salvageable topsoil over decades of operation.The costs of procurement,transportation and placement of suitable offsite soils can be exorbitant on large coal ash closure projects.Fortunately,emerging technologies,such as biotic soil media and prescriptive agronomic amendments,can make marginal soils suitable for vegetative establishment with significant cost savings to utilities and other stakeholders.This paper presents an overview of soil specifications,soil testing requirements,biotic soil media,agronomic formulations,and complementary erosion control techniques with case histories documenting successful,yet cost-effective coal ash cover systems.