For the more information about the geologic resources of the National Park Service, please visit http://www.nature.nps.gov/geology/.
Mitigation and Restoration
The mitigation and reduction of hazards from abandoned mineral lands are often complicated and expensive procedures. The National Park Service establishes the priority for mitigation by considering the level of danger and degree of resource damage. Each site is unique. The chosen method for mitigating features at a hazardous or contaminated site depends on numerous variables such as available materials at the site, the type of rock, the difficulty of reaching the site, and money. Parks use a variety of methods to close hazardous mine openings. Because of limited funding, parks can usually afford only temporary solutions such as fencing and posting signs, until funding for more long-term solutions becomes available. Common long-term mine closure techniques include backfilling, blasting, expandable polyurethane foam ("PUF"), rock and mortar walls, steel grates, bat gates, and bat cupolas. For more information, see the AML Closures and Photos pages.
During mitigation of abandoned oil and gas sites, well bores are properly plugged and capped. Cementing the wellbore with concrete at the production zone and the groundwater zone prevents contamination of water supplies.
Reclamation and Restoration
Scars on the land may last thousands of years even if mined areas stabilize and the vegetation recovers. Carefully planned reclamation can restore natural processes and greatly speed site recovery. Reclamation in the National Park System focuses on reestablishing landscapes and environments that mimic the surrounding undisturbed lands. Mine structures such as mills, shops, headframes, and others of historic value are stabilized and preserved. Otherwise, the pre-mine condition is restored wherever possible. Reshaping the surface stabilizes slopes and drainages, waste rock piles, tailings ponds, highwalls, and access roads. This reshaping often requires the use of heavy equipment to contour the land to look and function like the surrounding undisturbed lands. The restoration of stream channels also provides for the reintroduction of plants and animals that were lost because of mining. The same type of earthmovers that created the mineral extraction scars are often the best suited to remove them.
Cleanup or treatment of toxic materials prevents further impairment of the environment. Small quantities of mining related materials, such as chemicals or fuels used in mining and milling are completely removed. Large quantities of naturally occurring materials such as acid-generating waste rock may be treated on-site. Applications of lime may provide a buffer to prevent the generation of acids. In more severe cases, limestone drains or artificial wetlands filter heavy metals and reduce acidity. In worst-case scenarios, active water treatment systems may be necessary.
The goals for revegetation of mine sites in the National Park System are the restoration of native plant populations and patterns. The first consideration is the suitability of the soil for revegetation. In harsh conditions, topsoils, compost, or specific nutrients can be added. Specialized nurseries may be needed to propagate suitable plant materials. Sometimes, revegetation work is focused on establishing pioneering species to allow for natural succession. Time and nature then restore the natural productivity in the site.
Last Updated: February 28, 2013