Coal mining on or under highly productive farmlands can have negative consequences for the land’s productivity, both in the short term and the long term. Different mining techniques and waste disposal practices affect farmlands in different ways, but farmers and landowners need to be aware that coal mining can alter the topography, drainage, and fertility of agricultural lands, in addition to the negative impacts that may be had on local water and air quality.
Room and Pillar Mining
Underground room and pillar mining removes roughly 50% of the coal seam, leaving the rest in place as “pillars” to provide surface support. This practice inevitably causes subsidence, which can potentially destroy both natural and installed drainage systems, although these effects may not be seen for many years.
Room and pillar subsidence results from several factors. In some cases, the rock strata above or below the coal seams are too soft, which can causes the pillars to sink over time. Also, coal pillars left to support the material above the mined coal seam will deteriorate over time thereby reducing their ability to bear weight. In both cases the result is the formation of surface depressions and sinkholes.
Subsidence severely damages houses, buildings, and roads, necessitating costly fixes that are often funded by taxpayers (see here and here). The potential for subsidence also complicates later construction because it necessitates special engineering and higher costs to prevent damage to new projects.
Additionally, associated underground blasting can damage nearby wells.
Longwall mining removes nearly all of the coal in panels that are over 1,000 ft wide and can extend for miles.
The land above these panels subsides immediately, while the space in between the panels where the underground conveyor belts carry coal from the working face to the slope (~200ft in width) remains at its previous elevation. This leads to an immediate bathtub effect where the surface above the panels sinks ~6 ft within two weeks, while the land above the conveyor belts remains elevated. Especially on flat farmland, massive investments in ditches and tiles may be required to achieve any drainage at all.
Of course, this subsidence also places severe strains on surface structures – homes, wells, roads, and other buildings – and while the coal operator is supposed to pay for any damage they cause, surface owners are not able to prevent their property from being damaged by the longwall machine in the first place if they no longer have control over their mineral rights.
Landowners who decide to lease their coal may write restrictions into their lease prohibiting the use of longwall techniques, thereby protecting them from the effects of immediate subsidence (see Lease with Landowner Protections).
For more information, consult The Strip Mining Handbook, available in full online.