Salt Water Intrusion Testing and Monitoring

The Plymouth Saltwater Intrusion Task Force is collecting data and setting up monitoring to assess the potential for intrusion of marine water into Plymouth's coastal groundwater aquifer. The Town of Plymouth is situated above the second largest sole-source aquifer in the Commonwealth: the only source of drinking water for our 63,000 residents and a key component of a unique, biodiverse ecoregion that includes over 400 ponds and 75 state-listed species. Coastal portions of our aquifer are potentially at risk of saltwater intrusion (SWI) due to rising sea levels and rapidly increasing groundwater withdrawals aimed at meeting growing demand.
In 2019 the Town participated in an Municipal Preparedness Vulnerability (MVP) planning process where our vulnerability to SWI was identified and acknowledged. In 2021, the Town and a consortium of 12 non-profit organizations (collaborating as the Task Force) received an MVP grant from the State to begin planning for climate change resiliency to address the risks of SWI, with the ultimate goal of developing action-oriented resiliency plans. Under this grant, the Task Force will collect data about current conditions in coastal portions of our aquifer, engage the University of Massachusetts-Amherst to further characterize the aquifer and develop a groundwater model to predict SWI potential, and educate the public about SWI risks and realistic mitigative actions.
The data collection element of the project requires the assistance of private well owners by allowing us to sample their wells. Data collection addresses two key parameters: groundwater salinity and water-level elevation relative to mean sea level. In order to measure groundwater salinity, we simply collect samples of well water taken from a spigot or faucet and measure the electrical conductance (EC) of the water (an indicator of total dissolved salts) and its chloride concentration. For water-level elevation, we use a specialized water-sensing measuring tape (“electric well sounder”) to measure depth to water in your well. The data are maintained in a project database (respecting homeowner privacy) and will be used to identify coastal areas where EC, chloride or groundwater elevation suggest vulnerability or resiliency to saltwater intrusion.  

Training Session for gathering well data

Training session for well data. Well on Old Sandwich Road

Recent Updates

Tidal Signature in Coastal Well

By Peter Schwartzman on August 7, 2023
Under its data collection program, the Plymouth Saltwater Intrusion Task Force installed a datalogging transducer in a coastal Ellisville well located about 450 feet from the shoreline. The transducer measured water level, specific conductance (SC) and temperature. The plot below shows how tidal variations in Cape Cod Bay affect water levels in the well. The salinity (expressed as SC) was not affected by tidal variations. Groundwater quality shows low salinity and is not impaired relative to drinking water standards.


Peter Schwartzman
Hampton Watkins