Use of injection wells for disposal of brine and industrial waste is more common in the western U.S. than the eastern U.S., because the geology of the eastern U.S. makes it more difficult to find suitable sites. One of the most important features of an underground injection well is that the fluid will stay in the formation into which it is being injected, without migrating to other formations. Properly sited and executed, an underground injection well is currently the only disposal option that completely prevents wastewater from entering surface and groundwater. It is not without its risks, however.
Underground injection wells involve pumping billions of gallons of fluid into rock formations, orders of magnitude more than hydraulically fractured wells for natural gas extraction. High pressures are sustained for weeks at a time for fluid injection. This is useful because it means that the well can be used over years to dispose of the fluids. It is potentially hazardous, however, because it means that injection wells have the potential to cause induced seismicity (human-caused earthquake activity). For example, a swarm (a large number of very small earthquakes) was caused in central New York in
2001 as a result of injection wells in the cases of Avoca, NY in 200124 and Dale, NY25 in 1970. For a more
detailed explanation, please see Marcellus Issue 3: Making the Ground Shake: Understanding Induced Seismicity.