Begin Main Content Area

Other Geologic Hazards

Methane Gas Migration

In some areas of Pennsylvania (especially areas of coal mining and gas well activity), stray methane gas in the subsurface can be a hazard. Under certain conditions, methane can migrate to private water-supply wells and ultimately into a house or structure.

Unmitigated, methane can build to explosive concentrations. A proper well vent allows methane to escape to the atmosphere rather than build up to explosive levels.

Chemical analyses of natural-gas samples taken from suspected problem sites have been recognized as a “fingerprinting” tool for methane-source tracing.

Pennsylvania methane gas resources include:


Radon is a naturally occurring, colorless, odorless, inert, radioactive gas that has been linked to lung cancer. It is estimated that 40 percent of homes in Pennsylvania have radon levels above the U.S. EPA action guideline of 4 pCi/l. Radon in groundwater also is a health concern.

Radon is a decay product of the most abundant naturally occurring isotope of uranium -- U238. Uranium and radon are found nearly everywhere in very small concentrations.

Pennsylvania radon resources include:

Subsidence Caused by Underground Mining

Subsidence associated with the underground extraction of coal and minerals is a geologic hazard with a human twist.

After a resource is removed from the ground, there may not be enough remaining material to support the roof of the mine. If that is the case, over time, the roof will collapse, and the sagging rock layers may propagate to the surface.

Land subsidence can be devastating to building foundations and road surfaces, and can alter groundwater and surface water flow.

For risk assessment and insurance information for homeowners, see DEP’s Mine Subsidence Insurance.


Flooding is well known as a hazard across Pennsylvania. Although it is influenced by the landscape and precipitation, modification and use of the land by humans can worsen flooding and put more people and structures at risk.

Avoiding development or encroachment on floodplains allows floodwaters to rise without harm. Dams and floodwalls can protect some critical areas, but even with proper planning, floods cannot be completely controlled.

Pennsylvania flood resources include:

Carbon Dioxide

Elevated concentrations of carbon dioxide (CO2) and associated reduced concentrations of oxygen (O2) in building spaces are a growing environmental hazard in western Pennsylvania.

During the past, this problem was generally the result of blackdamp (a miner’s term for gas composed of CO2 and nitrogen) from abandoned underground coal mines. During recent years, serious CO2 hazards related to reclamation of surface coal mines have emerged.

Pennsylvania carbon dioxide resources include: