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The Latest From GSA: Groundwater, Public Health, and A New Shallow Well Design

April 1st, 2019

Not long ago, HRP’s geologists attended the Geological Society of America (GSA) 54th Northeastern Section meeting in Portland, Maine. Their goal was to harvest the latest knowledge from New England’s most robust environmental/geological research to date. One of the most interesting GSA technical oral presentations was given by Ian Carlisle.

Recent studies in New England have identified naturally-occurring arsenic in groundwater at concentrations that exceed drinking water standards. Mr. Carlisle’s presentation focused its scope on technological efforts to provide safe drinking water.

Mr. Carlisle asks two questions; “Is it prudent to drill new wells in formations that contain consistent high arsenic water?” and “By treating the water, does it mitigate the actual human health risks?” Well, not exactly for all private domestic wells, and here’s why: the traditional shallow well design itself is to blame. More importantly, we must ask ourselves, which geologic formation is best to install a dug shallow well into? In New England we have both fractured bedrock aquifers and glacial aquifers through which drinking water can be sourced.

Mr. Carlisle spoke to the benefits of installing wells near glacial till deposits. Glacial aquifers are far less likely to contain dangerous concentrations of arsenic as compared to fractured bedrock aquifers. However, glacial aquifers have been under-utilized due to the poor design of current shallow well technology. So what can we rely on then?

Although glacial till provides great hydraulic conductivity for groundwater, it generally percolates through the relatively small surface area at the bottom of the well. The small area of inflow at the bottom and sides creates a low yield, and sometimes periods of no water. To counter this problem, Mr. Carlisle points to research hydrologist, Joe Ayotte’s proposal for a new shallow well design. This design calls for 5-10 times more surface area of groundwater inflow, using a 15 x15-foot square-shaped well. This will allow for better water storage, recharge rate, and even drought resiliency.

A second problem is that traditional well-liners are often cracked, allowing for entrance of fertilizer and pesticide contamination as well as entrance of small animals, whose wastes can generate harmful bacteria. Ayotte proposes a sealed PVC entrance, similar to those used on drilled wells, which elongates the route for direct animal and bacteria contact to the water.

In 2018, the new well design was put to the test at two sites in northern New England. During a year of sampling, neither of the shallow wells had detectable concentrations of arsenic, above the reporting limit. Two bedrock wells, near the new shallow well locations, were sampled, and found to have elevated arsenic concentrations.

The research of Carlisle et. Al. presents a new shallow well design that could eliminate many of the issues associated with shallow bedrock aquifers, while also providing safe drinking water.

Carlisle I, Belaval M, Gordon RP, Simbliaris H, Bryce J, Ayotte JD. Ground Water and Public Health: A Novel Shallow Well Technology to Provide Safe Drinking Water for Private Domestic Wells. 2019.

Trevor D. Cazlan, Project Geologist at HRP Associates, Inc.

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