The U. S. Army Corps of Engineers Louisville District held a public meeting Feb. 4, to give the community and other stakeholders an opportunity to review and comment on the Proposed Plan for the Former Raco Army Airfield and Missile Site, located near Raco, Michigan.
“The Corps has been conducting environmental investigations at the Former Raco Army Airfield since the 1980’s, so it is always nice to give the public an update on the progress of where we are in the process and allow them to comment on the proposed plan,” said Aaron Steele, Louisville District environmental engineer.
The Raco Army Airfield and Missile Base site occupies approximately one square mile and is located southwest of Sault Ste. Marie, Michigan, in the Hiawatha National Forest. The Department of Defense used the site as an airfield for 21 years and as a missile base for approximately 13 years, ending in 1972. After its use, the U.S. Air Force released the property to the U.S. Forest Service.
USACE Louisville District is currently conducting an investigation of a trichloroethene, also known as TCE, groundwater plume at the site under the Defense Environmental Restoration Program-Formerly Used Defense Sites Program. Louisville District’s investigation in 2009 specifically focused on the TCE groundwater plume and included the installation of five new monitoring wells. In 2014 and 2015 over 400 groundwater samples were collected to better delineate the extent of the plume, and additional monitoring wells were installed.
During the Remedial Investigation, TCE was detected in groundwater from depths of 287 to 344 feet in the borehole where the most down-gradient well was installed in the TCE plume. The TCE plume was found to be more than ½ mile away from the nearest residential wells, which also take in water from much shallower depths (less than 100 feet deep).
“Fortunately these wells are not likely to be affected by the plume based on available data,” said Nicole Toth, project manager. “But the proposed plan does include routine well sampling for private lands located downgradient of the Raco site.”
Pure TCE is a volatile chemical that is a colorless or blue non-flammable liquid with a sweet odor. It was historically used as a metal parts degreaser and industrial solvent/cleaner. The Environmental Protection Agency classifies TCE as carcinogenic (cancer-causing) to humans if they are exposed to high enough levels over a long period of time.
“Members of the public expressed appreciation of the work that has been done to date to delineate the TCE (trichloroethene) plume, as well as the proposed plan,” Toth said.
During the field investigation in 2016, a partially demolished tank filled with TCE contaminated sludge, 18 feet in depth, was discovered. Since the tank was too large to be removed using the equipment available on site at the time, the removal of this vault and its contents was later accomplished in October 2019 as a Non-Time Critical Removal Action, also known as NTCRA.
“The NTCRA was well-planned and well-executed,” Toth said. “This was attributable to an exceptional team, and superior communication between USACE, the contractor and their sub-contractor. The work was accomplished on time with no issues or surprises in the field, and no TCE contamination was detected in the underlying soil above Michigan clean up levels for protecting groundwater or above U.S. Environmental Protection Agency regional screening levels.”
USACE is proposing long term groundwater monitoring (monitored natural attenuation) for the site.
A 30-day public review period for the proposed plan is underway, and the review period ends Feb. 26, 2020.