Road salt in drinking water? How Merrimack’s water utility is targeting sodium chloride pollution
While winter salt application provides safer travel conditions, it has another legacy, too: polluted surface and groundwater throughout the state. Here, a plow truck clears a road in Laconia. (Getty Images)
New Hampshire applies more salt to its roads in the winter than the majority of the country, as do most New England states. And it doesn’t just disappear. Some people end up drinking it.
A public water supply well owned by the Merrimack Village District had to be officially taken offline earlier this year because it was “so adversely impaired” by increasing sodium and chloride concentrations over the last three decades — as a result of salt contamination of streams, rivers, ponds, lakes, and wetlands within the watershed area.
Between 1992 and 2019, that particular well saw a 734 percent increase in sodium and a 702 percent increase in chloride, according to data from Emery and Garrett Groundwater Investigations. Overall, trends in the district’s wells have shown a more than 1,000 percent increase in both sodium and chloride over the last 30-plus years.
While winter salt application provides safer travel conditions, it has another legacy, too: polluted surface and groundwater throughout the state. In 2008, 19 bodies of water in New Hampshire were listed as chloride-impaired on the 303(d) list under the Clean Water Act. On the state’s list for 2020-2022, that number had increased to 46.
The state’s Department of Environmental Services says elevated sodium levels can affect drinking water taste and alter soil chemistry, while high levels of chloride are corrosive, leading to the leaching of metals from plumbing systems. Chloride is also toxic to aquatic life at certain thresholds.
The Merrimack Village District — the town’s water department — relies exclusively on groundwater to supply nearly 1 billion gallons of water annually to approximately 9,300 customers. DES announced this month the district will receive federal funding for a first-of-its-kind project in the state to mitigate winter salt pollution in the Naticook Brook watershed area.
Funding from the Bipartisan Infrastructure Law funneled through a DES grant program will help the district develop a sodium chloride-based watershed restoration plan, targeting winter salt as a pollutant impacting both surface and groundwater resources.
Road salt problems in Merrimack
Located in the watershed area in question are paved roads, parking lots, and other impervious surfaces that all require winter maintenance such as plowing, sanding, and salt application. Because of associated runoff and infiltration, all three public water supply wells in the Naticook Brook watershed have experienced rising sodium and chloride levels, while one was taken offline as public water supply.
Jill Lavoie, business manager and water quality specialist at the Merrimack Village District, said they’ve been working for many years to reduce salt application as a means of improving water quality. The water utility had a study done on sodium and chloride in 2012, funded by a grant from the state, that evaluated salt load around its seven wellhead protection areas.
Lavoie said the district established a Sodium and Chloride Reduction Committee several years ago that includes the Department of Public Works, police, DES, the state Department of Transportation, property management companies, contractors, and Emery and Garrett Groundwater Investigations.
In 2020, they sent a letter to property owners saying it is “imperative” the town protect its drinking water from the rising trends in sodium and chloride.
Because it was already embarking on a more than $20 million water treatment investment to reduce PFAS in wells, any additional costs to treat and remove sodium and chloride would be “cost prohibitive,” Merrimack Village District Superintendent Ronald Miner Jr. wrote.
The district has already invested more than $50,000 in salt load issues within the designated area. The new $80,000 in federal funding will be used to evaluate winter salt use throughout the Naticook Brook source water protection area, and to develop a sector load allocation for salt and priority-based reduction goals for surface and groundwater. The plan will recommend a series of actions for municipal, state, private, commercial, and nonprofit partners with the intention of meeting the salt reduction goals within 10 years.
The district hopes the most-impacted well will be able to resume service sometime in the future, “as it has been taken offline at great expense to the local community,” according to the grant application.
The state of New Hampshire has been trying to cut back on its salt application, balancing the improvement of water quality with the prioritization of road safety. There are more than 500 commercial salt applicators in New Hampshire certified through DES’ Green SnowPro program, which offers snow and ice management professionals training and certification in salt reduction practices that “prioritize public safety while mitigating salt usage.”
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