PERFORMANCE OF ALTERNATIVE ENGINEERED COVERS-- RESULTS OF 12 YEARS OF COVER PERFORMANCE IN LYSIMETERS AT A HUMID REGION SITE, BELTSVILLE, MARYLAND

This project addresses a need for confirming methods of keeping water from waste. The concepts under investigation are applicable to near surface facilities as well as mined caverns. The project is significant in that it presents results of 12 years of actual cover performance at a humid region site. Long-term field projects on this scale are rare because of cost. Consequently, most reports on cover performance appearing in the literature are computer simulations. Of the concepts under investigation, two are particularly promising and are unique to this project. The first is a surface cover called bioengineering. Because it is a surface cover it is easy to maintain should there be subsidence. Bioengineering has the capability of (1) reducing infiltration of water through a cover to zero and (2) the remedial action capability of lowering the water table beneath a cover. The latter capability is a very important property for cleaning up sites in which there is water in disposal units. The second promising concept is called a conductive layer barrier. This is a special application of a capillary barrier, in which a capillary break is placed below a conductive layer. The conductive layer consists of material (e.g. fine sandy loam) which is capable of conducting water around waste under unsaturated flow conditions. In the absence of subsidence, such a system offers a significant margin of safety to cover performance particularly when it is placed below a geomembrane or a clay layer or a GCL, and it has a wide range of possible applications ranging from a tumulus to mined cavern disposal where there is intermittent fracture flow of water.