Nassau County is conducting a study on what is causing the water contamination that has kept Glen Cove’s Crescent Beach closed since 2009.

But don’t expect the beach to open this summer. The study likely won’t be complete until the end of June. Even if the source of contamination is found, cleanup could take months or years, said Brian Schneider, assistant to the deputy commissioner of public works.

The county health department will decide when the beach is safe.

The main reason swimmers and bathers have been barred from wading into Long Island Sound from Crescent is high levels of bacteria. The county has tried before to determine the reason for the contamination, but it’s still a mystery.

“This is like finding a needle in a haystack,” Glen Cove Mayor Reginald Spinello said at a recent City Council work session discussion on the problem.

Schneider said the current study, by Woodbury-based D&B Engineers and Architects, is more detailed than previous ones.

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“We’re looking at pathogens and bacteria, and we’re looking at nitrogen,” Schneider said. “We’re looking at any potential contaminant that would reduce the water quality.”

D&B will begin taking groundwater samples this month. Samples will also be taken from a stream after rainstorms. Holbrook-based Long Island Analytical Laboratories will analyze the samples.

The $51,000 for the study is from $12 million in bonds the county approved in 2014 to look into expanding sewer systems on the North Shore. Schneider said the problems in the Crescent Beach area could stem from groundwater that has been contaminated from septic systems that are faulty or not properly maintained.

Even if that is not the source, the septic systems may be causing other contamination or could do so in the future, Schneider said. That is why the county is looking into alternatives.

A sewer system in areas near Crescent Beach would cost about $37.5 million for 152 homes — or $247,000 per home, plus homeowners’ costs to connect with the sewer system, Schneider said. The high cost is due in part to the neighborhood’s hilly topography.

“That’s just not economical,” Schneider said. “There have to be other — and there are other — mechanisms that are being explored.”

One much cheaper potential alternative the county is examining is installing technologically advanced sewage-treatment equipment in residents’ basements or garages, Schneider said.