Covering surface impoundments

An enclosure is usually an air-supported structure which permits the collection and treatment of gaseous wastes produced by surface impoundments. Enclosures are susceptible to wind damage and can be harmed by the wastes they cover. Subject to these limitations, control effectiveness approaches 100 percent (University of Arkansas and Louisiana State University, 1985). 

A variety of containment strategies employ floating solid objects to control the rate of gaseous emissions from surface impoundments. These include synthetic membrane covers, rafts, and hollow plastic spheres. Synthetic membrane covers are feasible where the out-gassing of volatiles due to biological activity is not expected. Selection of the liner material must be... 

U.S. EPA, Technical Guidance Document Final Covers on Hazardous Waste Landfills and Surface Impoundments, EPA/530-SW-89-047, U.S. Environmental Protection Agency, Washington, DC, July 1991. 

Long-term exposure can be stopped using either soil or a nonwoven fabric to cover the membrane in a surface impoundment. Another option is to drape a heavy, nonwoven fabric with base anchors in it over the membrane. This nonwoven material is cheaper, safer, and more readily repaired than a soil cover. 

Several approaches have been suggested for the future implementation of biofilm barrier technology. There are several potential applications of the technology, including liners for landfills or surface impoundments, covers for landfills, and in situ vertical cutoff walls. 

Technical Guidance Document Final Covers on Hazardous Waste Landfills and Surface Impoundments... 

Environmental regulations dictate that landfills and surface impoundments for the disposal of hazardous and non-hazardous waste have liners (base, side-slope, and cover liners) and a leachate (contaminated water that emanates from a disposal site) collection and removal system in order to protect air, water, and land resources. Base and side-slopes of containments are lined with compacted clay or geomembrane (commonly HDPE) or both. Cover liners generally incorporate a foundation material overlain by a clay and/or geomembrane (commonly VLDPE which is more flexible than HDPE) liner. Geosynthetic clay liners may be used in place of clay. The leachate collection and removal system is... 

Uncontroited hazardous waste site means an area identified as an uncontrolled hazardous waste site by a governmental body, whether Federal, state, local or other where an accumulation of hazardous substances creates a threat to the health and safety of individuals or the environment or both. Some sites are found on public lands such as those created by former municipal, county or state landfills where illegal or poorly managed waste disposal has taken place. Other sites are found on private property, often belonging to generators or former generators of hazardous substance wastes. Examples of such sites include, but are not limited to, surface impoundments, landfills, dumps, and tank or drum farms. Normal operations at TSD sites are not covered by this definition. 

From 1949 to 1958, Nor-Acme Gold Mine piped 227,000 tonnes of refractory gold-bearing sulfide concentrate into a rock-walled impoundment (Richardson Ostry 1996, Salzsauler et al. 2005) in hope of finding a means to extract the gold. The ARS remained uncovered until 2000 when a cover was placed to inhibit sulfide oxidation and prevent further contaminated surface runoff. Arsenic is... 

Figure 14 Schematic diagram of a mine-waste impoundment with a combined remediation approach, including a cover to prevent O2 and water ingress, in situ mixing to geochemically stabilize waste, permeable reactive barrier in aquifer to treat subsurface drainage, and wetland for surface treatment of drainage.

To prevent the release of contaminants from an inactive Cu-Zn mine-tailings impoundment near Joutel, Quebec, a geomembrane and a protective clay cover overlain by 0.5-1.5m of till were placed on the impoundment surface (Lewis et al., 2000). The performance of this barrier is the subject of a long-term monitoring program. 

Cover (or cap) system One or more layers of material, such as soils, suitable mineral wastes, and geosynthetics, constructed on the surface of a site or waste impoundment and designed to control egress of contaminants from and infiltration of precipitation into a source of contamination. 

Once the discharge of tailings ceases, the surface of the impoundment is allowed to dry. Drying of the decant pond may take place by evaporation and/or by drainage to an effluent plant. Desiccation and consolidation of the slimes may take considerable time. Stabilization can begin once the surface is firm enough to support equipment and normally involves the establishment of a vegetative cover. 

The determination of the volume of free water is difficult because the free water level may vary across the tank bottom surface. The bottom is often covered by pools of free water or water emulsion impounded by layers of sludge or wax. 

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