Natural Resources Conservation Service s27

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NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION PRACTICE STANDARD

MINE SHAFT AND ADIT CLOSING (No.)

CODE 457

DEFINITION Fences, gates or other closure techniques that maintain or enhance bat and other wildlife Closure of underground mine openings by habitat shall be considered where habitat filling, plugging, capping, installing barriers, exists. Where bats or other wildlife inhabit the gating or fencing. mine, and wildlife friendly closures are not feasible, an exclusion plan for the bats or other PURPOSE wildlife shall be written and implemented.  Reduce hazards to humans and/or animals Fencing, gates, caps, and walls shall be used only where periodic inspection and  Maintain or improve access and/or habitat maintenance is ensured through a for wildlife maintenance agreement with a responsible  Protect cultural resources government entity, landowner, or organization.  Reduce subsidence problems Stockpiled soil or rock materials shall be protected from erosion until used.  Reduce the emission of hazardous gases Safety. Teams consisting of a minimum of two  Reduce or prevent contamination of surface persons each are required to conduct searches and ground water for concealed shafts and adits, leaving their specific schedule with others. Safety barriers, CONDITIONS WHERE PRACTICE APPLIES ropes, safety belts, gas detectors, and other equipment must be used as necessary during This practice applies to the investigation, site reconnaissance, surveying and foundation design and treatment of locations where investigation activities. shafts, subsidence pits or adits of underground mines are open or where prior closures can be If hazardous gas is present, a person with modified to accomplish one or more of the United States Mine Safety and Health above purposes. Administration (MSHA) certification for underground work shall be on site to monitor This practice may be associated with surface safety during the site investigation and practice treatment to reclaim the area surrounding the installation. mine opening. During construction, a collapse zone shall be established, clearly marked with fencing and CRITERIA warning notices, and no person shall enter this General Criteria Applicable to All Purposes zone without wearing proper safety equipment. The closure of mines shall be planned, Bumper blocks or other devices must be used designed and constructed to comply with all to keep machinery and trucks from falling into local, state, federal and tribal laws and shafts and subsidence pits. If possible, regulations. Fences or gates shall be used equipment blades and buckets shall be larger where it is essential to occasionally enter or than the opening being filled. gain access to shafts or adits.

Conservation practice standards are reviewed periodically, and updated if needed. To obtain NRCS, NHCP the current version of this standard, contact your Natural Resources Conservation Service State Office, or download it from the electronic Field Office Technical Guide for your state. February 2005 457 - 2

If explosives or items that resemble explosives Fences or gates shall be made of steel, are found, do not handle them and report the concrete, masonry, or "anti intruder" chain link findings to the local MSHA office. and barbed wire fences or a combination of these materials. At the completion of the closing, filled or plugged shaft or adit locations shall be marked Additional Criteria for Designed Filling or in the field and an affidavit of mine closing shall Sealing be recorded with the local register of deeds to Shafts and adits shall be cleaned of all trash, reduce the risk of future development over the debris, metal, timber, wire and other materials shaft or adit. that could hinder an effective designed filling or REPORT. A SITE INVESTIGATION REPORT sealing. SHALL DOCUMENT THE FOLLOWING INFORMATION: The finished surface of the filled or plugged shaft or adit shall be graded to provide free  Geology and groundwater conditions at the drainage away from the opening and site vegetation established in accordance with  Access conditions into mine NRCS standards.  Risks to life and property associated with All materials removed shall be disposed of by the mine burning or burying at approved sites or transported to approved landfills.  Equipment and trash within mine Designed Filling. Shafts or adits shall be  Presence of hazardous gases filled to about 3 feet from the surface with a  Presence of acid mine drainage designed filter consisting of nonacid-forming, free-draining materials or polyurethane foam.  Mine history including mine plan if available The remainder of the shaft or adit shall be filled  Inventory of plant or animal species using with earth materials including a minimum of 3 the mine feet of clay compacted in 9-inch lifts or other  Potential for surficial changes due to water impervious materials that would retard the table variation passage of water or gas. Shaft openings shall be overfilled 10 percent of the depth of the Design References. Agricultural Engineering shaft, or 3 feet, whichever is less to allow for Note 1, January 1981, contains guidance on settlement. investigation, safety, design and construction and is to be used as a procedural guide with Subsidence pits that are open, active, and/or this standard. Agricultural Engineering Note 1 passing a significant quantity of water require a was developed specifically for coal mines and designed filter of nonacid-forming, free- all information does not apply to other types of draining material. Sufficient soil covering shall mines. be placed to sustain planned vegetation. Guidance for enclosures and gates for bat Subsidence pits that are closed, inactive and conservation purposes is found in Bats and not passing a significant quantity of water shall Mines by Merlin D. Tuttle and Daniel A.R. require only backfilling with suitable soil Taylor, Bat Conservation International, Inc., material. 1998 Revision. Sinkhole openings shall be overfilled 10 Additional Criteria for Fences and Gates percent of the fill depth, or 3 feet, whichever is less to allow for settlement. Fences or gates shall be constructed to keep unauthorized persons out and shall be located Sealing with Plugs. Shafts shall be closed where subsidence or caving will not break their with plugs only if another practical solution is integrity. Where applicable, fences and gates not available. Installed below the ground shall be designed to maintain or improve surface, plugs are used where the shaft is to habitat and access for bats and other wildlife. be filled to the surface but the shaft below is to remain open.

NRCS, NHCP February 2005 457 - 3

Plugs shall be constructed of reinforced Concrete or masonry wall may be used to concrete designed to support anticipated support the barrier. Barriers not supported by loads. The reinforced concrete shall be placed concrete or masonry walls shall have 3 on firm bedrock. Plugs may be designed to be horizontal to 1 vertical or flatter slopes. watertight and gastight or to allow drainage Barriers at the ground surface shall be covered and venting of gases. with soil materials to a minimum vertical Shaft above the plug shall be filled to about 3 thickness of 4 feet and vegetation shall be feet from the surface with a designed filter established in accordance with NRCS consisting of nonacid-forming, free-draining standards. materials or polyurethane foam. Where needed, a permanent drainage system The remainder of the shaft above the plug shall using pipe or rock toes shall be installed be filled with earth materials including a through this covering. Traps to prevent air or minimum of 2 layers of clay, approximately 2 gas passage shall be used where necessary. feet thick, or other impervious materials that Sealing with Dams. Dams are constructed to would retard the passage of water or gas. prevent water flow into or out of adits. Shaft openings shall be overfilled 10 percent of the depth of the shaft above the plug to allow Dimensional requirements are those stated for for settlement. barriers in the previous section. The finished surface of the plugged shaft shall The fill shall be essentially watertight and be graded to provide free drainage away from designed to support anticipated structural and the opening and vegetation established in hydraulic loads. Designed filters shall be accordance with NRCS standards. incorporated to prevent piping of the fill material. Sealing with Caps and Walls. Caps and walls shall be constructed of reinforced concrete or steel beams and grates or solid CONSIDERATIONS steel plates to completely close shaft or adit Consider the following for maintaining or openings. enhancing bat and other wildlife habitat: Caps and walls shall be designed with  Species using the mine. sufficient strength to support anticipated loads and shall be securely anchored.  Seasons and purpose mine is used by bats or other wildlife. The cap, wall, fittings, access holes and vent pipe shall be reasonably vandal proof. The  Effects on airflow and temperature of the surface of a cap over a shaft must be raised mine caused by a closure. Small changes not less than 1 foot above the surrounding in environment can have significant terrain to provide good visibility and positive negative or positive effects on suitability for drainage away from the cap installation. bat use. D. Sealing with Barriers. Barriers shall be constructed to restrict humans and animals PLANS AND SPECIFICATIONS from entering adits, and may be used to Plans and specifications for closing shafts and prevent lateral spreading of backfill material adits shall be in keeping with this standard and and to support fill used to cover adit openings. shall describe the requirements for applying Barriers shall be constructed of stones, the practice to the specific site to achieve its crushed rock, quarry-run rock, gravel or similar intended purpose or purposes. nonacid-forming, free-draining materials. The minimum filled length of the barrier shall OPERATION AND MAINTENANCE be three times the maximum adit height or Barriers, fences, gates and caps are to be width within the barrier section, whichever is maintained to accomplish their purpose. greatest.

NRCS, NHCP February 2005 457 - 4

A site-specific operation and maintenance plan shall be carried out. Additional maintenance shall be developed for all gated, fenced and activities shall be outlined in the maintenance capped closures. Regular inspections shall plan. take place and prompt repair and follow-up

NRCS, NHCP February 2005