Groundwater is the water underneath the earth's surface and in the rocks and soil. When groundwater pools in large volume, an aquifer is formed. Aquifers supply wells and springs, and due to ground water flow, also eventually move into lakes, rivers and wetlands. Since groundwater accounts for 95% of the freshwater resources in the United States, groundwater resources are monitored by the Environmental Protection Agency (EPA), which governs groundwater cleanup in the event of environmental contamination. Some different methods of groundwater cleanup include bioremediation, carbon adsorption, air stripping, and the physical removal of contaminated substances.
Bioremediation is one form of groundwater cleanup. Organisms that are present at the contaminated site are given fertilizer and oxygen in order to grow stronger. The organisms eat the contamination, which allows the site to revert back to its natural state. This is often used when the groundwater contamination is an oil spill because organisms can clean up the site much faster and more cost effectively than other types of groundwater cleanup.
When the water table is low, groundwater pumping and treatment is often used since groundwater remediation may not be effective. The contaminated groundwater is pumped from the aquifer, run through a treatment system, then returned to the ground. Treatments include carbon adsorption and air stripping.
Carbon adsorption is a treatment technique that works by soaking up contaminants through porous particles. Once the contaminants are fully absorbed, the water can be reintroduced to the environment. Air stripping works by forcing the groundwater through an aeration tank that separates the groundwater from the contaminants; cleaned water then flows back to the aquifer.
Groundwater cleanup may also involve incineration. One incineration method is to burn the carbon that was used during the carbon adsorption treatments so that the contaminants present in the carbon after treatment can be destroyed. This method of groundwater cleanup is also used when there is a significant amount of soil to process and the contaminants are not a kind that can be eaten by organisms. Incineration occurs in encapsulated towers at extremely high heat in order to break down the contaminants and destroy any organic compounds present.
When the size of the contamination site and type of chemicals that need to be extracted do not lend themselves to on-site groundwater cleanup methods, the EPA will direct the contaminants be removed. This requires heavy duty front loaders and dump trucks to be brought in and the ground actually dug up and removed from the site. The materials are transported to a hazardous waste facility and disposed of under the direction of the EPA.