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Superfund

How Superfund Addresses Groundwater Contamination

Groundwater contamination is a common issue at Superfund sites. Of the National Priorities List sites where EPA has selected remedies, EPA addressed groundwater contamination at approximately 85 percent of them.

Superfund response actions at contaminated groundwater sites protect human health and the environment by:

  • Remediating contaminated soils;
  • Restoring contaminated groundwater to beneficial uses;
  • Preventing migration of contaminant plumes; and
  • Protecting groundwater and other environmental resources.

Superfund responses to contaminated groundwater generally address all exposure pathways that pose an actual or potential risk to human health and the environment. For example, groundwater response actions should generally address the actual or potential direct contact risk posed by contaminated groundwater (e.g., human consumption, dermal contact or inhalation), and should also consider the potential for the contaminated groundwater to serve as a source of contamination into other media (e.g., sediment, surface water, wetlands, or vapor intrusion into buildings).

EPA expects to return usable groundwaters to their beneficial uses wherever feasible and within a reasonable timeframe given the site’s circumstances. When restoration of groundwater to beneficial uses is not feasible, EPA expects to prevent further migration of the plume, prevent exposure to the contaminated groundwater, and evaluate further risk reduction.

Common Remedies

Superfund prefers to treat contaminants to reduce their toxicity, mobility or volume. As part of the overall site cleanup, groundwater remedies may be combined to clean up groundwater contamination. Groundwater remedies may also be used with other remediation technologies to address different media, contaminants, or contaminant levels. Controlling the source of groundwater contamination (such as treating contaminated soil) and containing the contaminated plume (such as pumping to control groundwater flow) are often critical to the success of groundwater restoration efforts.

The following are common Superfund remedies for groundwater contamination:

Pump and treat is a common method for cleaning up groundwater contaminated with dissolved chemicals, including industrial solvents, metals, and fuel oil. Groundwater is extracted and conveyed to an above-ground treatment system that removes the contaminants. Pump and treat systems are also used to contain contaminant plumes. Pumping draws contaminated water toward the wells, keeping the contaminant plume from spreading. This pumping helps keep contaminants from reaching drinking water wells, wetlands, streams, and other natural resources.

In situ treatment occurs when groundwater is treated in place without extraction from the aquifer. In situ treatment technologies can destroy, immobilize or remove contaminants. Examples include in situ chemical oxidation and chemical reduction, and permeable reactive barriers.

Containment is used to keep groundwater plumes from migrating. This is achieved by using a vertical, engineered, subsurface, impermeable barrier. These vertical engineered barriers (VEBs) are walls built below ground to control the flow of groundwater. VEBs may be used to divert contaminated groundwater flow to keep it from reaching drinking water wells, wetlands or streams. They may also be used to contain and isolate contaminated soil and groundwater to keep it from mixing with clean groundwater. VEBs differ from permeable reactive barriers in that they do not clean up contaminated groundwater and do not allow groundwater to pass through them. Common types of VEBs include slurry walls and sheet pile walls. Contaminant remedies may also rely on pump and treat to keep groundwater plumes from spreading.

Monitored natural attenuation is the reliance on natural processes to achieve remediation objectives within a reasonable timeframe. These include a variety of physical, chemical or biological processes that can act without human intervention to reduce the mass, toxicity, mobility, volume or concentration of contaminants. These processes include dispersion; dilution; sorption; volatilization; radioactive decay; and biological stabilization, transformation, or destruction (biodegradation) of contaminants. When relying on natural attenuation processes for site remediation, EPA prefers those processes that degrade or destroy contaminants. Monitored natural attenuation is generally only appropriate for sites that have a low potential for contaminant migration.

Institutional controls are non-engineered instruments, such as administrative and legal controls, that minimize the potential for human exposure to contamination and/or protect the integrity of a response action. Institutional controls typically limit land and/or resource use or provide information that helps modify or guide human behavior. Some common examples include zoning restrictions, building or excavation permits, well drilling prohibitions, easements and covenants.

Alternative water supply: EPA can provide drinking water and household water supplies under Superfund when drinking water wells or a principal drinking water supply become contaminated. Providing an alternative water supply may involve furnishing clean, drinkable water on a permanent or temporary basis. Examples of providing a permanent drinking water supply include installing a new private well, connecting to a municipal water system, or drilling a new community water supply well. Examples of providing a temporary water supply include installing individual treatment units or delivering bottled water.

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