Biosolids Mine Reclamation History
In the 1970s, federal mining laws established mandatory standards for reclamation following the disturbance by surface mining. At the same time, marine protection legislation banned the practice of ocean disposal of biosolids. Taken together, the need to reclaim mine lands and to recycle biosolids lead to the two programs joining together in the late 1970s in the experimental use of biosolids for mine reclamation.
A key objective in the new regulatory standards for reclamation is good vegetative cover re-establishment. These were difficult for mining companies to achieve. The three steps of reclamation required were:
Stage 1: Rough grading of the site with backfill
Stage 2: Planting of groundcover vegetation
Stage 3: Achieving 5 years of full performance of vegetation
Failure of the third stage resulted in mining companies returning multiple times to attempt vegetation coverage. With biosolids, companies discovered a sure-fire, one-time application solution.
Biosolids Delivery and Application to mining sites
Biosolids are typically trucked to mine sites using dump trucks. They are emptied into a bermed staging area, typically formed by excess backfill material. If biosolids are scheduled to be held for more than 30 days, the staging area is equipped with a leachate collection system, commonly a tarp-lined sump.
Any farm tractor and spreader equipment may be used to apply biosolids to the mine surface. Application rates change by state and are measured in dry tons per acre. Biosolids may be applied in flat areas in one pass, while hillsides may require several passes. The biosolids are then incorporated into the soil with a chisel plow or large disc plow with at least three passes and occasionally more (the last pass will be pulled along the contour of a sloping hill)
Using biosolids provides near certainty that Stage 3 requirements are met. During and after biosolids are land applied the soil pH, water quality, surface vegetation coverage, and surface stability are monitored.Achieving stage 2 and stage 3 requirements has been successful for coal mine operators in all cases in which biosolids have been used.
A drill seeder is used to sow a blend of legumes and grasses. The land owner, who may not be the coal mine operator, is involved in selecting the cover. The permitting authority also has a say in choice of seeding because it is dependent on the state-approved revegetation plan for the reclamation project. The most popular use for a reclamations are to restore the land back to a wildlife habitat. The rich nutrient composition of biosolids creates an environment for plant growth. Reclaimed sites are known to have dense vegetation with substantial water holding capacity in the soil.
In addition to vegetation, the establishment of permanently improved wildlife habitat has been observed in various projects. Herbivores are attracted to the rich vegetation, and predators follow.
Biosolids virtually eliminates erosion at reclamation sites. Part of this is due to plowing directed across the slope.creating contours. Root mass is another key factor in erosion prevention. Furrows created during biosolids application act as small diversions where grasses and legumes can develop their root systems.
Water Quality Benefits
Although no comprehensive study has been made of the changes to acid mine drainage (AMD),, quarterly monitoring data collected over the past decades have shown AMD is significantly reduced from sites where biosolids is used.
There is potential for the release of nitrogen from mine reclamation sites in large dosage. The nitrogen composition of dry biosolids is 5% in the nitrate form, 15% in the ammonium form, and the remaining 80% is organic nitrogen. Over the years of groundwater monitoring, some release of nitrate nitrogen has been observed. In general sites where mining reclamation is done are deficient in nitrogen, and the organic nitrogen in biosolids serves to benefit plant growth.
Biosolids application yields about 3,000 to 5,000 pounds per acre. No water monitoring samples have yielded phosphorus concentrations above background. This suggests that phosphorus from biosolids stays locked in the soil’s mineral matrix, benefiting plant growth while not negatively impacting the local watershed.
Metals Contamination and Movement
Metals are present both in the surface level rock layers (overburden) of the mining site and in biosolids. Data show that metals are not released in significant quantities from reclamation sites. This is based on research work performed in the 1980s as well as ongoing monitoring. Monitoring data reviewed does show an elevated level of metals in water after initial biosolids application, but concentrations fall to background quickly.
The use of biosolids for mine reclamation came at a time where both industries were looking for solutions to increased regulations. The cooperation has proven to be a benefit to both the industries and the habitats they have reclaimed. While coal mining activities are not as strong today as they were in previous decades, some 250,000 acres of previously disturbed mine land remain un-reclaimed. These could be a resource for use of biosolids in the future, to the benefit of watershed and wildlife.
For a deeper exploration of biosolids being used for mine reclamation check out these papers and blogs: