The sand filling Treasure Island canals isn't likely coming from nearby Sombrero Beach, according to a nearly-complete study commissioned by the City of Marathon.

The city will have to wait to hear what options are available to block sand migration into the canals, but the City Council on Tuesday shot down a staff initiative to seek matching state funding for a rock "groin" that may be part of the proposed solution.

The study, conducted by Weiler Engineering Corporation, analyzed sand migration patterns at Sombrero Beach to determine if sand from the beach is filling up the canals of nearby Treasure Island. Weiler was also tasked with determining "the preferred project alternative to prevent the canals from shoaling and control beach erosion."

According to background information Marathon Director of Community Services Susie Thomas provided council Tuesday at its general meeting, the sand grain size in the canals appears to be larger than the grain size found on Sombrero Beach. But sand is nevertheless eroding from Sombrero Beach, as well as accumulating in the canals from some source.

The groin, according to Thomas' agenda item information, would be "the most likely alternative which would be acceptable for permitting" with the Florida Department of Environmental Protection.

Councilman Pete Worthington -- the lone council supporter of filing for a grant application to help pay for installing a rock groin on Sombrero Beach -- asked the question that seemed to be on the minds of all five council members.

"Do we know that this mechanism would solve the Sombrero/Treasure Island [issue]?," Worthington said to Weiler Engineering's Ed Castle.

"This will keep your sand put in place under normal conditions," Castle responded.

The issue came up quickly with little chance for review at or before the Tuesday meeting because a state Bureau of Beaches grant that would provide 50 percent funding for the project has an Aug. 6 deadline.

The project was estimated to cost just under $500,000 over two years, with the city paying its portion of about $125,000 per year for two years out of its capitol infrastructure budget, according to Finance Director Peter Rosasco.

Those costs were too much for the majority of the council, especially when paired with short notice and little in the way of information on a groin's impacts.

"Right now, in my mind, this is a lot," said Vice Mayor Mike Cinque. "I'm not willing to spend the money. ... There's way too many unanswered questions for us to be spending this kind of money."

Worthington, however, continued to press for a groin as a possible solution to Treasure Island residents' issues, as well as a safeguard for hundreds of thousands of dollars soon to be spent on a beach renourishment project.

"If we're putting in $525,000 in sand and we're getting complaints that says it's our sand [in the canals] ... I think we gotta do something out there," Worthington said. "I think the city wants to protect that beach. We have a significant investment up there. It is getting eroded. I'm not going to allow our sand to possibly migrate down to be their problem."

But the rest of the council disagreed with Worthington's assertions on the impacts to the canals -- and to beach erosion after some questioning.

"This is not going to keep the canal from silting up," Councilman Richard Keating said before further questioning Castle on the groin's effectiveness. "Will this keep our sand on our beach?"

"Under normal conditions," Castle said. As for hurricanes, "Some storms it will keep the sand on the beach. Other storms it wouldn't."

The council voted, 4-1, to not allow staff to apply for the state money.

Even with the grant funding for a groin off the table, residents spoke out about the need to find a solution to the canals filling.

"Twice [the canal] has filled in, they dredge it out and it fills right back in," said Bill Wilkenson.

Steve Errera, who lives in the Treasure Road area and has spoken at a number of council meetings on the subject of the canals filling with sand, told the Free Press in Marathon that more than $450,000 has been spent over the years -- all by residents, save for one FEMA project 10 years ago -- to dredge the canals. Without the dredging, the canals are nearly unusable in all but the highest of tides.

The full results of Weiler's study are due to be released in the next 30 days. Council will review those findings, expected to include recommended solutions to the sand migration issue.

mphelps@keysnews.com