073019 CHA Ninigret Pond water quality 26.JPG

View of algae bloom along shore of Ninigret Pond on Tuesday, July 30, 2019. URI is asking Charlestown residents to help with study on nutrients entering salt ponds via groundwater. Harold Hanka, The Westerly Sun

CHARLESTOWN — A new study of two salt ponds in Charlestown is measuring nutrients and pollutants entering the ponds in groundwater.

The $400,000 research project, funded by the Southern New England Program of the U.S. Environmental Protection Agency, will assess the environmental impact of groundwater, a significant source of fresh water entering salt ponds, but one that is poorly understood. Greenwich Bay is also part of the study.

Rebecca Robinson is the principal investigator on a team of scientists from the University of Rhode Island, which is leading the study. Partners include the state Coastal Resources Management Council, the Natural Resources Conservation Service, the Salt Ponds Coalition, the Friends of Green Hill Pond, the towns of Charlestown and South Kingstown, and the city of Warwick.

At least 12 sites, six at Green Hill Pond, which is mostly in South Kingstown, and six at Ninigret Pond, just to the west, will be chosen for the Charlestown component of the study. Homes must be near the salt ponds and owners must be willing to allow the installation of temporary water sampling wells. 

Sea Grant Extension Specialist Teresa Crean said several Green Hill and Ninigret homeowners have already signed up for the two-year study, which began in June.

“We’ve been getting quite a few volunteers that have come forward to offer their sites, so now the researchers are going through the sites and selecting the ones that are the best candidates for the study,” she said. 

Oceanographer John King, a member of the URI research team, said the role of groundwater in transporting nutrients and pollutants to the salt ponds has been underestimated until recently.

“The amount of nutrients coming in, in groundwater inputs, was always assumed to be small enough that you could ignore it, and that’s what the models did. They just basically ignored it,” he said. “To many of us, that really didn’t make a whole lot of sense, because the materials that the ponds and bay are in are surrounded by pretty porous glacial materials.”

Previous studies used infrared to measure warmer groundwater entering the colder water of the salt ponds. The assumption was that the pond bottoms consisted largely of mud and therefore, groundwater would not flow into the ponds on a  significant scale.

But when King began modeling the bottoms of the salt ponds, he found they were most sandy, not muddy.

“Groundwater can easily come up deep enough that you can’t see it in these infrared surveys,” he said. 

King’s study, and an earlier study done by the U.S. Geological Survey, confirmed that a large volume of groundwater, much more than previously assumed, was entering the salt ponds.

“One of the characteristics of groundwater, particularly in suburban and developed areas, is the concentration of nutrients in the groundwater tends to be sometimes orders of magnitude higher than it would be in the coastal waters that it’s coming into,” he said. “That’s the whole point of this, is to try and quantify how much groundwater is coming in and how many nutrients are in that groundwater.”

Matthew Dowling, Charlestown onsite wastewater manager, said that the high-density development typically found near the salt ponds compromised groundwater quality. The impact is felt acutely in Charlestown, which relies entirely on septic systems and private wells.

“Septic systems are a large contributors of nutrients and bacteria, mostly nutrients, to the groundwater,” he said. “We sponsored the sampling of private wells throughout the coastal watershed of Charlestown over the last eight or so years and we’ve looked at all of those data points and analyzed them and run some statistical analyses on them, which indicates that there is a correlation between the density of development, ie., density of septic systems, and groundwater nitrogen concentrations.”

Arthur Ganz, president of the Salt Ponds Coalition, welcomed the groundwater study.

“We’re interested in this, because we want to know what the groundwater impact is to the ponds,” he said. “How much groundwater is really coming in? That’s the big issue with a lot of the contamination we have in these areas, particularly in Green Hill Pond. There are so many houses that were built in areas with really high groundwater levels, and it’s not uncommon in these neighborhoods to have flooded basements. And if there’s a flooded basement, there’s a flooded septic system and you wonder how much of that material is carried with the groundwater, both bacteria and in terms of the nitrogen, nitrates and so forth. This is one more piece of the puzzle.”

Homeowners interested in participating in the study can contact the Salt Ponds Coalition at: saltpondscoalition@gmail.com 

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