HANOVER — An ongoing investigation into animal remains found this fall buried at the Cold Regions Research and Engineering Laboratory has revealed high concentrations of a likely carcinogen, but no evidence of groundwater contamination so far.

The remains are likely tied to former Dartmouth College research.

Half of the soil samples collected since the discovery of decayed animals and black plastic bags by construction workers at the site off Lyme Road in September had levels of formaldehyde above state regulatory limits, according to a December announcement from Dartmouth.

Formaldehyde is considered a probable human carcinogen by the U.S. Environmental Protection Agency. The risks posed by formaldehyde exposure generally come from inhaling the chemical or contact with the skin, according to the EPA. Serious risks such as cancer come from long-term exposure to the material, while short-term exposure can cause irritation that stops when contact ends.

Because the concentrations were found in soil samples, “where direct exposure is highly unlikely,” CRREL does not believe that the results “pose a health threat to CRREL employees or the surrounding area, nor has it impacted our operation,” spokesperson Justin Campfield said via email Thursday.

In general, no test results so far “have altered our scientific or research activities,” Campfield said, but “we continue to assess test results as they come in, and stand ready to implement operational changes if needed.”

Dartmouth’s environmental consultants, GZA Geoenvironmental, plan to conduct further testing in response to the formaldehyde results, Senior Vice President of Capital Planning & Campus Operations Josh Keniston said Wednesday.

Engineers also conducted preliminary tests on groundwater at the site and found no contamination, including when testing for another probable carcinogenic material previously found at the former Rennie Farm site — 1,4 dioxane — and for volatile organic compounds. Preliminary tests conducted at the site also found no concerning radiation levels, according to a November update.

A portion of the Rennie Farm property, which is several miles from CRREL, was a state-licensed burial site for animal carcasses used in medical testing, including radioactive material, throughout the 1960s and 1970s.

In 2011, Dartmouth College began excavating and cleaning up the site, revealing chemical contamination including elevated levels of 1,4 dioxane. Beginning in 2015, the contamination was found in the drinking water of one nearby home prompting outcry from residents.

Test results are still returning for some of the samples collected at the CRREL site and Dartmouth expects to have them by the end of January, said Keniston. The overall project is likely to continue for “another couple months” to “really understand what’s there.”

The U.S. Army Corps of Engineers bought the 28-acre property off Lyme Road from Dartmouth College in 2012, after previously serving as tenants, according to property records.

The lab’s construction began in 1960.

The college does not have a clear record of what it used the site for in the past, Keniston told the Valley News in October. Test results and the remains themselves have since led the college to believe that it used the site for “something related to research activities,” Keniston said Wednesday.

The actual species of the animals is still unknown, Keniston said, but they are slightly larger than a small rodent and smaller than a dog. In addition to the animal remains, “in at least one case” the excavation has uncovered other materials related to lab work, “like a bottle,” Keniston added.

“This is an ongoing process, I don’t think we’re at a point where we feel like we have fully concluded anything,” Keniston said, though he added that some of the results have been “encouraging.”

One thing investigators do know is that there are likely more remains than those uncovered by the original excavation as a result of a construction project in September. However, they have not decided whether they will excavate more of the site to uncover the other remains, Keniston said. The decision will be made based on remaining test results.

“We know that it goes a little bit beyond what was actually revealed during the excavation, so we’re still delineating exactly where it goes,” Keniston said.

The two locations where animal remains were found are about 200 feet apart.

In October, Campfield told the Valley News that CRREL did not know about the animal remains before they were uncovered.

However, since then the laboratory has found a set of 1976 blueprints from a construction project that advise “special care” when digging wells because of the presence of an “old cadaver bed” in the area.

Dartmouth also has uncovered “a few correspondences” between the college and the Army Corps of Engineers from when the facility was being built that “indicated” the remains were there, Keniston said. But the documents did not clarify “the nature” of how the property had been used “with any specificity.” A Dartmouth spokesperson declined to share these documents.

The remains were originally uncovered by construction workers digging a culvert; CRREL paused this work after finding them. The construction team was able to continue some of the paving work before pausing for the winter. Work is expected to resume again in April, Campfield said.

The Dartmouth College Environmental Health and Safety website, dartmouth.edu/ehs/campuscommunications, will continue to be updated as new information about the remains at CRREL becomes available.

Clare Shanahan can be reached at cshanahan@vnews.com or 603-727-3216.