SOUTH PORTLAND — Spring Point Ledge Lighthouse faces an uncertain future, after a study concluded it could cost up to $500,000 to repair deterioration of the 19th-century structure.

Lighthouse keepers said they are not worried about the structure’s safety and short-term viability, but they are concerned about their ability to raise enough money to make the repairs.

If the money isn’t found, and if Gov. Paul LePage’s budget is passed and previously tax-exempt properties are taxed, “we probably would be out of business,” Spring Point Ledge Lighthouse Trust Chairman Keith Thompson said this week. “Frankly, I don’t think we could even come close to covering taxes on a facility like that.”

Built in 1897 to warn ships of the ledge at Fort Preble, at the mouth of  Portland Harbor, the light sits at the end of a nearly 900-foot breakwater on Lighthouse Circle, off the Southern Maine Community College campus.

Ownership of the lighthouse was transferred from the U.S. Coast Guard to the trust in 1998. It continues to be used as a navigational aid by the Coast Guard, and the lighthouse’s foghorn can still be heard on the peninsula in Portland.

The trust, governed by an 11-member board, operates the lighthouse on a volunteer basis on weekends from June to September, when visitors can pay $5 to visit the site.

Last year was the “most successful year in our history,” trust Chairman Keith Thompson said this week. Approximately 3,500 people visited the site – triple the  attendance in 2012. 

Spring Point is notable because it is the only caisson-style lighthouse in the country that is accessible by land. Yet in this case, its most distinct characteristic is also its most susceptible.

Formed by the banding and bolting of five large cast-iron flanged plates, the cylindrical caisson, which has a diameter of about 25 feet and is 30 feet tall, was initially installed by constructing it above water, and then sinking it. 

In order to make it impervious to water and to act as a primary support for the lighthouse, the bottom 12 feet of the caisson was filled with a mixture of cement, broken stone and sand, according to original construction guidelines, detailed in a structural study completed in early October. 

With the ebb and flow of tides, the portion of the caisson in the intertidal zone has been submerged in sea water constantly for more than 100 years, making the steel particularly susceptible to corrosion, Thompson said.

To curb this issue, the caisson has been rebanded twice, in 1915 and again in 1929.

In recent years the caisson’s top band, along with lower portions of the cast iron itself, have cracked, which has allowed water to enter and weaken the cement mixture at the base of the caisson. This is evident on the outside of the structure at low tide, as well as in the basement, formerly the coal room, where parts of the 24-inch-thick cement and brick mixture are peeling off due to intensified moisture, Thompson said. 

The installation of the breakwater in 1951 has prevented the inspection of the caisson’s lower bands, Thompson said.

Complications caused by the broken bands are exacerbated in the winter, when the ocean water seeps in behind the cast-iron plates and freezes, expanding the cement mixture and forcing the plates outward.

“The water gets in the cracks, freezes, and forces new ones,” Thompson said.

Preliminary findings of a study last October by Becker Structural Engineers of Portland, with assistance from Gredell & Associates of Newark, Delaware, and Ocean Technical Services of League City, Texas, showed that, in some places, functionality of the caisson had deteriorated as much as 62 percent, he said. 

Repairs to the caisson could be extensive, costing up to $500,000, but nothing can be done until the rest of the structure is tested, Thompson said.

In keeping with the study’s findings, he said he believes a “worst-case scenario” might require the removal of all rocks around the base in order to install a cement collar around the caisson.

Removing any portion of the breakwater also requires permission from the U.S. Army Corps of Engineers.

Masonry and caisson repairs are expected to be extensive and take several years, Thompson said. 

“That hardest part, first of all, is that each one of these projects is going to take multiple grants,” he said. Not only are there limited funds available through each grant, but “there’s a lot of competition.”

The cost will be so large that if the trust can’t find enough grant money, “our best hope is for something with deep pockets to come along and write us a check,” Thompson said.

For the time being, he said, “the structure is not unsafe,” since the report found “there is currently no indication of structural instability.”

Rather, Thompson said, “this is something we need to find out to prevent further deterioration. It’s not something we are worried about to the extent where we can’t open it during the summer like we normally do.”

Alex Acquisto can be reached at 781-3661 ext. 106 or aacquisto@theforecaster.net. Follow Alex on Twitter: @AcquistoA. 

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Spring Point Ledge Lighthouse in South Portland stands against a morning sky Thursday, Feb. 12, as a ferry plies toward Peaks Island. A recent study concluded that repairing the 19th-century landmark could cost up to $500,000.

A close-up of some the deterioration around the base of Spring Point Ledge Lighthouse in South Portland.