The Tibbetts Road site is located in a rural residential area of Barrington just south of Swains Lake. In addition to maintaining a residence at the site, the property owner collected and stored flammable hazardous wastes in drums on the property and used this waste to help burn out the interiors of junked automobiles, which were subsequently sold for scrap. The wastes included various solvents, automotive fluids, petroleum products and PCBs. Dioxins and furans were detected in the soils at the site and are thought to have formed as a combustion byproduct of PCBs. The site was discovered in 1982 by DES following a complaint from an abutter. Sampling of residential water wells in the area indicated VOC contamination at relatively high levels.
In 1984, EPA and DES conducted an emergency response action to remove the drum wastes from the site. That same year, DES began a hydrogeological study to determine the extent and nature of groundwater contamination. Several plumes of contamination were found to be emanating from the site. The site was added to the National Priorities List in June 1986.
In 1986, the State and EPA excavated and hauled PCB and VOC contaminated soils to a secure out-of-state hazardous waste disposal facility. Dioxin contaminated soils were treated on-site using an infrared thermal treatment process.
As an interim measure, the affected residences were supplied with bottled water, first by the town of Barrington, then by DES. Through cooperative federal, state and local efforts, an emergency water supply system was constructed. Funded with federal Superfund money, the project included: the construction of an infiltration well system; a pump station; and a storage facility adjacent to Swains Lake, which serves as the water source. The water supply system is designed to service up to 70 residences in designated risk areas and is managed by the Swains Lake Village Water District (SLVWD).
The remedial investigation/feasibility study was completed in 1991. The September 1992 Record of Decision included: upgrading the existing drinking water treatment and distribution systems; capturing and treating highly contaminated groundwater and soil vapors; and discharging treated groundwater into the overburden and bedrock aquifers.
A Vapor Extraction and Groundwater Recovery (VER) system was constructed in the spring of 1995 to remove soil and groundwater contaminants. The system was in operation for three years during warm weather conditions, ending in December 1997.
Phytoremediation was implemented in the spring of 1998. Phytoremediation is a process that uses trees and plants to achieve or assist in the environmental cleanup of hazardous waste sites. At the site the ultimate goal is to develop a system that is densely vegetated and deeply rooted with hybrid poplar trees that dewater the upper overburden deposits and maintain an aerobic environment. Phytoremediation will become complete when these trees reach the end of their life expectancy of 30 or more years.
The VER system was restarted in June 2000 to augment the phytoremediation effort. The VER system treated water from two on-site bedrock wells for seven to eight months of the year. The system was shut down and drained during the winter months due to the shallow burial of the piping network.
The first Five-Year Review Report for the site was completed in June 2003. The assessment of the Five-Year Review found that the remedies implemented at the site remain protective of human health and the environment and that progress is being made at the site to achieve the cleanup levels identified in the ROD.
A small portion of the weathered bedrock aquifer located to the northeast of the site has shown more limited progress in achieving the required cleanup levels. To see if the cleanup processes in this area can be accelerated, a pilot-test was performed during the fall of 2003 using in-situ chemical oxidation technology. An initial injection of sodium permanganate (20 percent solution) was injected into shallow bedrock in three injection/monitoring wells in early November 2003. A second injection was performed in late December 2003.
Following the analyses of post pilot-test data obtained through the fall of 2004, it was observed that reductions in VOC concentrations in groundwater in the pilot-test area were significant. It was recommended that permanganate oxidation be used in other portions of the site. Implementation of an injection of sodium permanganate commenced in late November and continued through early December 2006. Post-injection monitoring was conducted in December and monitoring results were evaluated in early January 2007. Based upon the evaluation, it was determined that additional injections would be beneficial to further reduce VOC concentrations in the area. Injections were performed in early summer of 2007 and continued through 2008.
EPA and DES conducted a Five-Year Review inspection of the site in the spring of 2008 assuring that the recommendations made in the first Five-Year Review Report have been implemented. During the review, an evaluation of the vapor intrusion pathways was completed by using both EPA and DES guidance. The second Five-Year Review Report was completed in the summer of 2008. The report identified potential future issues that may affect protectiveness; primarily that the water supply system that serves the residents surrounding the site has operational issues. The general deterioration of the surface water supply (Swains Lake) will likely compromise the ability of the water treatment system to deliver safe drinking water into the future.
The SLVWD is currently exploring alternatives for upgrading the existing treatment facility and for developing a new drinking water source for servicing the impacted area in the Tibbetts Road area. Their engineering consultant completed a Water System Evaluation Study in July 2009. The study identified alternatives for upgrading the existing water system, including developing a groundwater source. A bedrock well installation and pumping test program was conducted during 2010 and development of supplementary bedrock water sources is on-going.
On-site investigation and monitoring activities are also continuing during 2011-2012, including the installation and sampling of additional bedrock monitoring wells, source area delineation and vapor intrusion studies.