Hanover
The contaminant, a solvent component known as 1,4-dioxane, previously had been found at low levels in a stream, which was its first recorded appearance in surface water.
In these latest tests, the chemical compound showed up at more than 10 times the state standard for water quality, suggesting that an underground plume of the chemical is nearing the stream, along which several homes are located.
Maureen O’Leary, the college’s director of environmental health and safety, said over the weekend that the latest discovery had prompted Dartmouth to propose installing five new monitoring wells, farther from the dump site, to determine the extent of the plume.
“These new monitoring locations are intended to identify the outer limits of the contamination and serve as an early detection system in case of further migration,” she said in an email to neighbors on Saturday.
O’Leary said the college would soon be submitting to state regulators a work plan to dig the new wells.
The 1,4-dioxane is believed to have come from the wooded hill in rural northern Hanover where, in the 1960s and ’70s, Dartmouth buried thousands of pounds of lab animals, many of which had been used in radiological experiments.
The college’s environmental contractors say the contaminant likely was disturbed by a 2011 excavation of the site, which set the plume on a downhill path to the north.
About a year ago, tests of a nearby private well found 1,4-dioxane was present there at twice the state standard for ambient water quality. The residents who used that well, the Higgins family, reported adverse health effects that they said subsided when they stopped using the water.
Last month, the chemical, which the Environmental Protection Agency classifies as a probable carcinogen, was found in a stream that runs beyond the Higgins residence to the north and feeds into Hewes Brook, which in turn is a tributary to the Connecticut River.
Last week’s results came from two test wells located along the suspected path of the plume, to the south of the stream.
At one well, “GZ-25,” which is just yards from the stream, test results topped out at 0.54 parts per billion — less than New Hampshire quality standard of 3 ppb.
Another well to the south, called “GZ-26,” registered much higher levels: between 17 and 33 ppb.
Water regulators at the New Hampshire Department of Environmental Services say these results suggest that GZ-26 is close to the “main axis” of the plume, whereas GZ-25 is closer to its boundary.
“The non-detectable to trace levels found at the more distant new well GZ-25 suggest that well may be near the current limit of the plume,” spokesman James Martin said in an email on Monday.
Meanwhile, Dartmouth is working to install a “pump-and-treat” system that could siphon away the contaminated water. College administrators have said they hope to have the system in place by the end of the year, and in an email last week, officials said they were obtaining the necessary permits and equipment.
O’Leary also advised residents who would like to have their wells sampled to contact her at maureen.oleary@dartmouth.edu or by phone at 603-646-1762.
Dartmouth officials and their environmental contractor are scheduled to visit the site today at 4 p.m., and will be available to answer residents’ questions, O’Leary said in her email. The entrance to Rennie Farm is at 572 Hanover Center Road.
Rob Wolfe can be reached at rwolfe@vnews.com or at 603-727-3242.