Six-Mile Richardson Highway Areawide Groundwater Investigation

Site Narrative

Background

Trichloroethene, also known as trichloroethylene or TCE, was discovered in groundwater and drinking-water wells serving homes and businesses in the Six Mile Richardson Highway area of Fairbanks in 1995. TCE is an industrial solvent and degreaser that has been shown to cause adverse health effects in humans. The Alaska Department of Environmental Conservation (DEC) has been monitoring groundwater quality and other environmental conditions in the area since the 1990s, to evaluate the potential risk to human health.

The TCE groundwater contaminant plume in the area measured slightly more than a mile long, up to 1,200 feet wide, and more than 100 feet deep when it was discovered in the 1990s. The plume originates from multiple sources in an industrial area south of the Richardson Highway, near the intersection with Davison Street, and extends northwest toward the Six Mile Village Subdivision. DEC has been studying the plume by measuring concentrations of TCE and other volatile organic compounds (VOCs) in drinking-water wells and monitoring wells of various depths. TCE concentrations in the plume have gradually decreased since 1995 as the result of natural breakdown and dilution.

Drinking Water Treatment Systems

Activated carbon water treatment systems that remove TCE from drinking water were installed in qualifying homes where TCE concentrations were greater than the regulatory limit in the Six Mile area. The DEC paid for water testing and the installation and maintenance of the treatment systems.

Based on the data collected from 2017, private wells affected by the TCE contamination plume are now below DEC cleanup levels. Therefore, DEC no longer provides free water testing or treatment system maintenance.

TCE may remain at low concentrations in drinking water wells in the Six Mile area. If you are installing a drinking water well in the Six Mile area, DEC recommends that you test your water for VOCs using Method 524, as well as other water quality parameters typically tested in private drinking water wells. It is important to note that there are many types of contaminants other than TCE that can affect your drinking water quality. DEC does not regulate or test private drinking water wells. If you have a treatment system to improve water quality, proper maintenance of your system is necessary. Improper maintenance may worsen water quality.

• Find additional information about your water quality

Vapor Intrusion

Certain chemicals, including TCE, give off vapors that can travel through air spaces within the soil. If the pressure inside a building is lower than in the soil, or if the amount of chemicals in the soil gas is high, the vapors can enter buildings through cracks in foundation, crawl spaces and basements. This is termed “vapor intrusion”. Sometimes people in the buildings can smell a chemical, however, often the chemicals are odorless or too faint to smell. The best way to assess the potential for vapor intrusion is to evaluate indoor air quality and soil gas beneath or near buildings. In order to evaluate soil gas beneath a building, sampling is conducted through the foundation by drilling a small hole to sample the interface between the foundation and soil.

In 2009, the DEC began monitoring TCE vapor concentrations in and around occupied homes to investigate the potential for TCE vapor intrusion. The vapor intrusion investigation has focused on permanent buildings within 100 feet of the TCE contaminant plume. Vapor intrusion sampling was conducted between 2009 and 2023 and included evaluation of indoor air quality, sub-slab soil gas, and soil gas near buildings above the TCE contamination plume. The findings from the investigation do not indicate a high potential that vapor intrusion remains in the Six Mile area.

Recent Updates

In 2020, monitoring wells were evaluated statistically to determine whether the TCE concentrations in the groundwater are changing over time. The results show evidence of decreasing contaminant levels. The concentrations of TCE in groundwater have been monitored for more than twenty years and indicate substantial decreases from the concentrations that were found during the initial investigation. During a 2022 sampling event, only one monitoring well contained concentrations of TCE above DEC groundwater cleanup levels. DEC continues monitoring groundwater to evaluate contaminant trends. A site history evaluation is being conducted to identify outstanding data gaps to facilitate site closure.

Additional information and ongoing site updates can be found at the Six Mile Richardson Highway Groundwater Investigation Contaminated Site Database Page.

More Information

For detailed information and documents related to the cleanup of this site, visit the Contaminated Sites Database.

• Contaminated Sites Program’s Vapor Intrusion Web page, DEC
• Fact sheet (2019) – “ToxFAQs for Trichloroethylene (TCE),” Agency for Toxic Substances Disease Registry, U.S. Department of Health and Human Services.