British Columbia Mine Reclamation Symposium

Reclamation of surface coal mine disturbed lands in western Washington Wisch, John 1985

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th  Proceedings of the 9 Annual British Columbia Mine Reclamation Symposium in Kamloops, BC, 1985. The Technical and Research Committee on Reclamation  RECLAMATION OF SURFACE COAL MINE DISTURBED LANDS IN WESTERN WASHINGTON  by John Wisch INTRODUCTION  The physiographic and climatic conditions in the Pacific Northwest, including deep soil profiles, poorly indurated and steeply dipping rock sequences, and high rainfall, combine to create the potential for severe soil erosion. The potential is increased where land-based industries disturb the natural conditions. In a large surface mining operation, like the Centralia Coal Mine, large areas are exposed and disturbed, creating the potential for increased erosion and heavy sedimentation to adjacent streams. Mine owners, early in the planning stages, committed themselves and the operator of the mine, Washington Irrigation & Development Company, to addressing these and other soil related problems. Goals were outlined and implemented in both the mining and reclamation program, and since then have been expanded and honed to their current state of the art. Specifically, the thrust of WIDCO’s reclamation program is to return mined lands, which will eventually encompass half of the 20,000 acres involved in the operation, to the same uses which were prevalent prior to disturbance. These are principally intensive tree farming on the uplands and agricultural uses in the valley bottoms. Contemporaneous with mining is surface restoration of surface drainage patterns and channels, moderation of slopes to aid slope stabilization (20% or less) and aggressive revegetation of all exposed surface areas to a permanent, productive vegetative cover. Major drainages remain undisturbed. REVEGETATION AND SOIL HISTORY Early in the mine's genesis it soon became apparent that intensive revegetation and soils studies were called for. Baseline information on each soil type was obtained. Study plots were established both in the mine and in the greenhouse in cooperation with the Soil Conservation Service and Washington State University, to assess the growth performance of selected annual grasses: rye grass (Lolium multiflorum); field brome (Bromus arvensis); grass-legume mixtures; orchard grass (Dactylis glomerata), timothy (Phleum pratense), fescues (Festuca rubra), bent grasses (Argrostis tenuis), New Zealand white clover (Trifolium repens), Marshfield trefoil (Lotus species), and several tree species indigenous to the area: Red alder (Alnus rubra), Sitka alder (Alnus sinuata) and Douglas-fir (Pseudo-tsuga menzesii). Results were positive for erosion control but revealed an incompatability  83  th  Proceedings of the 9 Annual British Columbia Mine Reclamation Symposium in Kamloops, BC, 1985. The Technical and Research Committee on Reclamation  between grasses and trees. As might be expected, early attempts to plant trees in disced grass residues resulted in high mortality from burgeoning rodent populations (Microtus townsendii). Lighter seeding with bunch grasses proved not much of an improvement. Proliferous seed production by brome and rye grasses caused dog-hair stands creating moisture competition during droughty periods in addition to the rodent problem. Rapid establishment of grasses to stabilize exposed slopes was essential, but it was obvious that follow-up grass control was necessary if trees were to be successfully reestablished. Current State permits and Federal law mandate that all surface mined lands be restored to the same use that existed prior to their disturbance. Soil, being one of the basic resources most severely impacted by surface mining, was immediately analyzed from top to bottom, since disturbance occurs from the surface to depths in excess of 300 feet (91.44 m). Nutrient status and procedures for correlating greenhouse tests with field tests were developed for the purpose of arriving at ongoing soil fertility-management practices specifically tailored for WIDCO's edaphic conditions, recognizing WIDCO's management goals. As a result, selected strata of subsoil overburden showing the most desirable characteristics are now placed as the surface layer to be reclaimed on all lands disturbed prior to 5/13/78, the date that the new federal surface mining law was implemented. Ongoing soil testing monitors nutrient and biomass accretion or depletion, nutrient imbalances, physical changes in soil structure, biological and chemical imbalances, etc., with follow-up management prescriptions based upon test results. Plant nutrients, outside of nitrogen, were found adequate for subsoil revegetation needs. Soil biological components essential for plant development and growth were found somewhat deficient in subsoils, but more than adequate in topsoils. (Trappe, O.S.U. 1981) SOILS HANDLING Topsoil removal and handling practices became of prime importance with the passage of PL 95-87, the federal Surface Mining Control and Reclamation Act (SMCRA) of 1977. Nutrient, biological and physical changes during the handling, storage and redistribution of topsoil were of concern, particularly how they might impact the establishment and successful growth of such reclamation species as Red alder, Sitka alder or Douglas-fir. Results of nitrogen fixation studies under young Red alder stands indicated substantial N fixation rates of up to 100 Kg/ha (89 lbs./ac.). (Tripp, Bezdicek & Heilman - W.S.U. 1977) Juvenile and pole-sized Red alder volunteer stands on orphan mine spoils in the area dating back 30 to 50 years exhibit near normal growth compared to adjacent, non-disturbed alder stands. Douglas-fir, being more site selective and less tolerant than Red alder was not as prevalent on orphan mine spoils. One exception to this is the Black Prince abandoned mine Douglas-fir planting on carbonaceous subsoils with good survival and fair growth; howbeit, some vegetation appears chlorotic which is a sign of nitrogen deficiency. Topsoil plantings of 2-1 Douglas-fir dating back to 1977, with only native grasses, forbs and 84  th  Proceedings of the 9 Annual British Columbia Mine Reclamation Symposium in Kamloops, BC, 1985. The Technical and Research Committee on Reclamation  woody plants to stabilize the reclaimed areas, show excellent survival (97%+) and promising juvenile growth with 4-year old outplanted seedlings on topsoils averaging 6' 7" (2 m) in height compared to 6' 11" (2.44 m) for the same age seedlings growing on non-disturbed adjacent lands. It should be noted that with the passage of SMCRA, complete topsoil salvage and redistribution is mandated on all lands disturbed by surface coal mining after May 13, 1978. Current soil replacement and revegetation practices, following backfilling and grading of mine overburden, are conducted in the following sequence. Topsoil and select subsoils are removed during the driest summer months (usually July-September) to minimize moisture related structural damage. This occurs generally 12 months in advance of overburden removal (mining). Topsoil or select subsoil redistribution occurs concurrently with removal to avoid rehandle. Topsoil storage, which is shown to be detrimental to both biota and stored nutrients (Quam, O.S.U. 1982), is avoided if at all possible. Removal and placement of topsoils and subsoils is carefully engineered to assure desired quantity and quality control. Upon redistribution of subsoils and topsoils, compaction is addressed by ripping subsoils to depths of 30 inches (76 cm) and chisel plowing topsoils if necessary. Select buffer soils are redistributed to minimum depths of four feet while topsoils are redistributed to depths of 18-24 inches (46-61 cm) which are the predisturbance topsoil depths. REVEGETATION Subsoil reclaimed areas (those disturbed before May 13, 1978), are revegetated initially with selected grasses or grains, and proceed through a multi-year sequence of tillage, sewage sludge injection (50 T/ac. topsoils and 100 T/ac. subsoils; 18,357 kg/ha topsoils and 36,713 kg/ha subsoils) and cropping until nutrient levels have reached target levels (6,000-7,000 lbs.; 1,100-1,146 kg/ha) of total nitrogen per acre. This may take from 3-6 years to accomplish. Douglas-fir is then planted at 10 x 10 spacing resulting in 400+ trees per acre. Reestablishment of internal drainage in reconstructed soil profiles is a long-term process, but is somewhat accelerated with the rapid root development of Red alder and other volunteering plants. Essential mycorrhiza fungi are found to be deficient in subsoils, so must be reintroduced at planting time by placing background soils into the tree planting bags. Topsoil reclaimed areas (disturbed after May 13, 1978) are treated with sewage sludge, monitored for effective (but not excessive) groundcover vegetation, and then planted with Douglas-fir at a spacing of 10 x 10 (435 trees/acre). Sitka alder has been experimentally interplanted with Douglas-fir as a biological site enhancer. Within 10-15 years, Douglas-fir will completely occupy the site forcing the Sitka alder to succumb. Disintegration and assimilation of the alder is rapid. Sitka alder's  85  th  Proceedings of the 9 Annual British Columbia Mine Reclamation Symposium in Kamloops, BC, 1985. The Technical and Research Committee on Reclamation  intended contribution is to provide 30-50 lbs. (5-8 kg/ha) of N annually over the 10-15 years that it survives, establish early site occupancy with select vegetative species to forestall encroachment of non-desirable competing vegetation requiring brush control, and to assist in the redevelopment of internal structure and surface stability which was lost through massive mine disturbance. Site productivity of the newly established forest plantations initially match or exceed adjacent, nondisturbed areas. Careful ongoing growth assessment work will document this comparison. EROSION CONTROL  Erosion control, touched on earlier in this report, is of major importance throughout the active mine area. Rapid revegetation of all disturbed areas, except for the active coal removal areas, is a must to minimize surface erosion and resultant sediment laden runoff. Extensive systems of gradient terraces and rocklined waterways are constructed to accommodate surface runoff, thereby minimizing the erosive action of water as it travels from upper slopes to valley bottoms. Tolerable soil loss rates (<5 ton/acre/year; <1,335 kg/ha/year) are being achieved through these practices. Streamside zones and pond areas are revegetated with riparian species and developed as wildlife enhancement areas.  86  th  Proceedings of the 9 Annual British Columbia Mine Reclamation Symposium in Kamloops, BC, 1985. The Technical and Research Committee on Reclamation  87  


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