Wannacomet Water Company public water supply well sampling results have been below the Maximum Contaminant Level (MCL) Massachusetts Department of Environmental Protection (MassDEP) set as safe for PFAS in drinking water, with most wells showing no PFAS. Wannacomet public water supply wells draw water from below confining units. A confining unit may help prevent PFAS from moving vertically, deeper underground where the Wannacomet public water supply well screens are located. For comparison, most private residential (domestic) wells are screened in the upper Unconfined Aquifer, thus withdrawing groundwater from above the confining unit.
Groundwater sample results have been reported by Nantucket Memorial Airport for on-airport shallow monitoring wells and adjacent residential drinking water wells, the Town’s Wannacomet Water Company public water supply wells, and by a limited number of private residents. This data is not a complete picture of PFAS in the Island’s aquifer. The Airport is continuing to advance its investigation through ongoing sampling and source identification activities. The Town is developing a groundwater sampling program, and the Siasconset Water Department will test their wells by October 1, 2021. The Town sampling program is scheduled to begin in Spring 2021 and will focus on the landfill site. Once we have that information, we will better understand if PFAS impacts the groundwater aquifer.
An aquifer is underground layer of water bearing rock and/or granular materials from which water can be extracted using a well.
A confining unit is relatively dense and contains impermeable materials, such as clay, that may prevent transport of groundwater and pollutants deeper into the subsurface.