A MASS BALANCE APPROACH TO EVALUATING SALT LOADING OF A STRATIFIED DRIFT AQUIFER, MERRIMACK, NEW HAMPSHIRE

The Merrimack Village District (MVD) obtains drinking water from two wells sited in the highly transmissive stratified drift deposits that comprise the Naticook Brook Aquifer in Merrimack, New Hampshire. Sodium chloride levels in the production wells have been increasing steadily over the past several years in this urbanizing watershed, prompting concern for the future water quality of the aquifer. A mass balance approach was used to evaluate salt loading impacts to the aquifer, and as a tool to help manage future impacts. Over 500 tons of salt are applied in the wellhead protection area annually. Though most of that salt is removed from the aquifer each year, approximately 18 tons of salt remain in storage, contributing to the salinization of the groundwater.