EFFECTS OF COVER SOIL THICKNESS ON REVEGETATION OF ACIDIC APPALACHIAN COAL REFUSE

摘要

Appalachian coal processing wastes are typically acid forming with potential acidities in Virginia ranging from an average of 12 Mg CCE demand/1000 Mg waste up to > 50 Mg/1000 Mg where higher sulfur coal seams are cleaned. Direct seeding of these materials is further complicated by high rock fragment content, low water-holding capacity, and high summer surface soil temperatures. In Virginia, conventional revegetation protocols established by the Virginia Division of Mined Land Reclamation (DMLR) in the early 1980's required the return of 1.2 m of soil cover over all actively permitted coal wastes. Unfortunately, most active piles at the time had no available topsoil reserves, so the only alternative was to disturb adjacent properties via blasting to generate spoil derived topsoil substitutes. Between 1982 and 1990, we investigated a number of direct seeding and reduced topsoil cover alternatives in an effort to determine the optimal combination of soil amendments and cover soil thickness for the successful revegetation of varying coal waste acidity conditions. The centerpiece of this research effort was a series of topsoil wedge experiments established over three different coal waste materials where cover soil depth was varied from 0 to 125 cm, with and without lime (15 to 25 Mg/ha) at the soil/coal waste contact. Multi-year vegetation and soil sampling results indicated that a minimum of 45 to 75 cm of cover soil was required over highly acid-forming refuse (47 Mg CCE demand/1000 Mg), with the shallower depth sufficient when a lime layer was applied at the contact zone. Over moderately acid-forming materials (15 to 35 Mg CCE /1000 Mg), as little as 25 cm of cover soil was adequate as long as lime was added to the soil/waste contact zone. Coal waste materials that are < 15 Mg CCE/1000 Mg net acid forming can be direct seeded if high P applications are coupled with heavy mulch or organic amendments, especially when the fill faces are not south-facing. These results were implemented into permit review and oversight by Virginia DMLR in the early 1990's and over the past 15 years, a wide range of active coal waste piles have been successfully revegetated with soil covers of 50 cm or less.