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Nitrogen problem in perspective: Unique challenges for Islanders

Flowers grow alongside a nitrogen-reducing septic system on a Midway Road property.

With the issue Shelter Islanders have with nitrogen in their drinking water — especially those in the Center —Town Engineer John Cronin said he’s focusing on how to overcome a problem that seems overwhelming.

Unlike most of Long Island, where there is a public water supply, Islanders are dependent on wells on their properties, and many are poisoned by nitrogen leaking from faulty and/or outdated septic pools.

Suffolk County, at best, can process about 900 applications for nitrogen-reducing Innovative Alternative (I/A) septic systems per year, while in the Center alone, there’s a need for up to 600 to address the problem.

A primary installer of I/A systems has speculated that 600 systems could be installed in 2.5 years if the county could process the applications. But that would assume a five-day work week installing a fully functional system each day, he said.

“That would be an ambitious undertaking, if it is even possible,” Mr. Cronin said.

It would also assume a “cookie cutter” model for all installations, ignoring specific needs at individual sites, he said.

“Of course the alternative to installing individual I/A systems is fast adoption of public water,” Mr. Cronin said, while making it clear he’s not advocating any particular approach to the problem.

Instead, he means to inform people about the problems that exist and ways to address them, the town engineer said, since an informed public can make the most appropriate decisions.

Mr. Cronin offered some significant clarifications to recent statements about dealing with the town’s efforts to reduce nitrogen content in its water.

On the drawing board for the Center is a so-called “clustered” or unified septic project that could serve the Legion Hall; the school; Shelter Island Library; the Center Firehouse; and eventually the Town Hall complex of buildings. If the town and the other institutions installed that shared, unified nitrogen-reducing system, it would still address just 3% of the problem, which 500 to 600 property owners in the Center could solve completely if they put in I/A systems, Mr. Cronin said.

At the same time, that 3% represents a consistent year-round reduction of nitrogen, which would not be the case for the home systems, since some are used only part of the year by second home-owners.
The model

A model of the Center’s aquifer, created last summer by town engineering and enhanced by data received as a result of a Freedom of Information request by Mr. Cronin from Suffolk County’s water test data, indicates the following:
• It would take about 54 nitrogen-reducing septic systems just to “hold the line” on nitrates in the Center, representing the treatment of about 16,000 gallons of sewage per day.
• Approximately 163 I/A septic systems would be needed to reduce Center nitrates by 10%, treating about 49,000 gallons of sewage per day.
• The entire Center would need to convert to nitrogen-reducing systems to regain what’s called the “pastoral” level of less than 3 milligrams per liter of nitrates in the aquifer.

Shelter Island is “anxious to find a practical way to address the problem we have in the Center, as it is a primary impactor of drinking water quality there,” Mr. Cronin told Suffolk County officials in a series of emailed communications.

“No one is modeling Shelter Island’s aquifer with great precision — not us, not the United States Geological Survey, not the county, not the county’s consultant, CDM Smith, not the New York State Department of Environmental Conservation,” Mr. Cronin stated. But he said the town’s own model, while not perfect, is a tool to help guide a strategy.

“In the absence of any other tool, it is the one to use currently,” he said.