Algae blooms cover Shawme Pond in Sandwich. Is it affecting the spring and drinking water?

SANDWICH — As Sara Price collected water from the celebrated town hall spring, she said she worries about the water's quality due to a thick layer of moss-like sludge that stretches across nearby Shawme Pond.

"We could be drinking sewage and we could also be drinking fertilizer that's coming from people's lawns," said Price, a pastor who lives on Cape Cod. "This is a really big concern for me."

Price is one of many people concerned about pond's water quality surrounding Shawme Pond, said Dave Mason, director of health for the town of Sandwich.

For the last week, Mason has fielded dozens of calls from neighbors of the kettle pond who are not only watching the vegetation grow day-to-day but are also gagging from its smell.

Some residents fearthe vegetation indicated cyanobacteria, Mason said the the multi-colored muck is actually algae. While it's one of the worst accumulations he's seen in years, it's the same problem that continues to plague the pond.

"This has been occurring for the last eight years in different levels of intensity," he said. "It's growth is due to rainfall, water temperature, the biology of the town and the inputs of nutrients into the pond."

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The nutrient inputs, said Mason, come primarily from wastewater in septic systems. The nutrients also contain phosphorous, which is present in lawn and turf fertilizer. Phosphorus helps grass grow lush and thick because it promotes strong root growth. But it's also detrimental to the health of the pond.

"Those nutrients are a direct result of everyone that has a green lawn that lives around the pond," Mason said. "The same people screaming at me telling me I'm not doing anything about it - are the ones contributing to the problem."

Warmer temperatures are making things worse. Mason said pond water is heating up earlier in the spring - more than it ever has before. Once waters reach 68 degrees, whatever phosphorous is bound up with the iron in the pond, is released. This reaction fertilizes the pond and causes excessive growth. Once the oxygen is used up, there is a massive die off.

"That die off is what you are seeing at the top of the pond," Mason said.

Is the algae affecting the drinking water?

Located next to Shawme Pond is the Dexter Grist Mill, where people from throughout the Cape collect water from the town hall spring. On Wednesday, there was a line of people holding containers - many of them snapping pictures of the adjacent algae bloom. Despite the smell, and the startling size of the bloom, most residents were not deterred from filling up their plastic containers and bottles.

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The spring water source stems from an artesian well, with pressure forcing freezing cold water above ground from Upper Shawme Pond springs, as well as the Cape's water supply.

"If you go to the most southern point (of Shawme Pond), you can see what looks like boiling water coming up from the sand in the pond bottom," Mason said. "It's infiltering up into the pond and runs through a number of underground channels, which the well is tapped into."

According to Mason, the Massachusetts Department of Environmental Protection required microscopic particulate analysis in 2003. The testing evaluated the biological make-up of the water source by microscopic examination and helped determine if the well source is groundwater under the influence of surface water. During the week-long testing, conducted by geological field services, it was determined there was no infiltration of pond water into that water source, said Mason. The Department of Environmental Protection has not required any testing since.

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"That town hall spring is monitored, as is the water supply. There are certified operators for that town hall spring," he said.

Algae blooms anticipated 20 years ago

Mason said town officials in the early 2000s anticipated algae blooms, which sparked a series of public presentations about how the problem could worsen in years to come. The concerns were so great that the town consulted with Lycott Environmental, Inc, to initiate remedies for possible future algae blooms - which have now become a yearly reality.

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A subsequent Lycott report, said Mason, made several suggestions including using alum (aluminum sulfate) to treat the water. Alum, according to HAB Aquatic Solutions,

is a nontoxic liquid commonly used in water treatment plants to clarify drinking water. The liquid was initially used in lakes and ponds in the 1970s, and was found to have the capacity to reduce phosphorus in the water. Lower amounts of phosphorus lead to lower amounts of algae and symptoms associated with poor water quality.

Recommendations in the report also suggested vegetation removal during winter was also an option. That could be accomplished by lowering the level of pond in colder months, and allowing it to freeze.

Mason said Sandwich residents were against all report recommendations.

"Townspeople in public meetings opposed both of those measures," he said. "They were vehemently against it."

Long- and short-term studies and solutions

In 2018, environmental engineering firm Wright-Pierce was employed by the town to conduct a study on 12 Sandwich ponds, including Upper and Lower Shawme Pond.

The investigation found that, for the most part, the ponds met their designated uses, but showed signs of excessive rooted plants and algae, which indicated that larger problems could exist "in the not too distant future."

Since then, Wright-Pierce has continued to work with the town's Sandwich Water Quality Advisory Committee to develop its Comprehensive Water Resource Management Plan, which is being executed in two phases, said Mason.

Phase 1, according to the plan's executive summary, includes wastewater collection, and construction of two wastewater treatment and disposal facilities – one at the Sandwich Industrial Park, and another near the Sandwich Marina. Phase 1 is also evaluating how the Forestdale School, Oak Ridge School and the high school can be connected to the Sandwich Industrial Park wastewater treatment facility.

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Throughout the process, Mason said Wright-Pierce and town officials also identified drainage watersheds in both Lower and Upper Shawme Pond, and designed systems that could contain road runoff. The committee also looked into the possibility of running discharge underground for filtering, said Mason.

"Sandwich is the first town in the state of Massachusetts to approve a water infrastructure investment fund and the first to utilize it," he said. "The town approved funding in 2021 for the design and the construction of new drainage systems for Upper and Lower Shawme pond."

Phase two of the management plan includes a possible partnership with Joint Base Cape Cod, said Mason.

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"We are in the process of evaluating whether we can either build a treatment plant at the end of Jan Sebastian Drive or we can go to Joint Base Cape Cod," he said. "Joint Base Cape Cod offers the best scenario at this point."

In the interim, Mason is also considering using an aquatic weed harvester to clean up the pond. Harvesters, said Mason, have been used at kettle ponds in Brewster to rid them of thousands of pounds of vegetation. The efforts have the capacity to also cut down the amount of phosphorus in the water.

"Whether or not that will work, we are not sure yet," he said.

Susan Bridges, president of Brewster Pond Coalition, said the harvester is a floating mower used to cut aquatic plants several feet below the water's surface. The town of Brewster's Department of Natural Resources houses and operates the harvester, and  successfully removed plants and roughly 110 pounds of phosphorus from Elbow Pond between three removals in 2020 and 2021.

"The town is interested in loaning it," she said. "It doesn't get used often enough."

Regardless of any short- or long-term solutions, Mason said nothing can fix the pond tomorrow but he is adamant problems with Shawme Pond and other waterways are not being ignored.

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"Most of the people calling in are those that live abutting the pond - it mostly impacts them. So those calls are understandable. It (the pond) is a mess. No one likes that," he said. "But other than me going down with waders on, and raking out the pond, there's not much else that can be done yet."

This article originally appeared on Cape Cod Times: Shawme Pond: Algae blooms stretch across Sandwich waterway