Three holes that opened on Hilton Head Island roads in recent weeks are likely the result of aging and improperly installed pipes, according to town staff.
The metal pipes under the sinkholes -- each of them a few feet wide -- are reaching the end of their 30 to 40-year lifespan, assistant town manager Bryan McIlwee said. That could mean more pipe failures or complications in coming years, he said.
"Up to this point, it's been rare," McIlwee said. "But people should expect it."
The first two sinkholes appeared on Governors Drive and Greenwood Drive in Sea Pines within the last two weeks. The third opened on Yacht Cove Drive next to the Hilton Head Diner on Wednesday afternoon, McIlwee said.
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Crews have patched the hole at Governors Drive and replaced two sections of pipes, whose incorrect installation caused the sinkhole, according to Charles Seasons, town director of public projects and facilities. That repair cost about $26,000, McIlwee said.
It's too early to say how much it will cost to update the stormwater pipes at the Greenwood Drive sinkhole, which is located at a pump station, McIlwee said. The multi-step process will begin next week when crews remove one of the stormwater pumps with a crane, leaving one in service in case of heavy rain, he said.
Engineers will seal the pipe and assess the stormwater system to plan their next move. An initial check by a diver revealed one of three 48-inch pipes in the system had separated at a joint, though it's not clear why, McIlwee said.
The layer of dirt above it then leaked into the pipe and was washed away, causing the section of road to crumble.
A similar process likely caused the hole at Yacht Cove Drive, a private road owned by Yacht Cove and several other parties, Seasons said.
DruBrown, president of Yacht Cove's board of directors, said property owners will likely split the cost of repairs. A cost estimate for the project should be available Monday, board vice president Bruce Pitkin said.
The community plans to defer to the Town of Hilton Head Island to coordinate the work and ensure it's done properly, according to Brown.
McIlwee said he has been in touch with Yacht Cove but has not finalized an agreement.
In the mean time, the hole is covered by steel plates and blocked by traffic cones. Brown said the damage has him questioning the safety of other pipes across the island.
"I think it's definitely a concern," he said. "The water has to go somewhere and you really want it to be the best situation for everyone involved."
Follow reporter Rebecca Lurye on Twitter at twitter.com/IPBG_Rebecca.