Crews will be working at the Chapel Hill Public Library again after heavy summer rains gouged an already damaged stormwater basin behind the building.
The library reopened in April after a $16.2 million expansion more than doubled its size to 62,000 square feet. That same month, however, a town inspection found landscaping materials slipping along the basin’s west bank.
Construction company Clancy & Theys, which is responsible for repairs under its original contract, was notified. However, before repairs could be made, spring rain and two heavy storms in June worsened the problem, officials said.
Scott Cutler, vice president of Clancy & Theys, said they were concerned about the continuing damage, but they also had to wait for the project engineer to draw a new plan.
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“If it’s already not working, going back and putting it in again is not going to fix it,” he said.
The basin, hillside and a walking path below have since been stabilized with fences and matting. The path will be closed temporarily while crews repair the hillside and basin. That work started Thursday and will take about three weeks, town officials said. The cost hasn’t been determined yet, they said.
“The damages from the large storm events were unfortunate, however, all parties worked together immediately to install measures to trap sediment and stabilize the areas of impact. These measures were inspected periodically after significant storm events and adjusted as necessary,” town spokeswoman Catherine Lazorko said.
Public Works Director Lance Norris told town leaders in an email last week that the first step is to grade and stabilize the berms surrounding the basin. Then they’ll add an impermeable liner to the basin’s top edge and more drainage below the soil surface to brace it against future storms. The town will have an independent soil engineering firm inspect and approve the work, he said.
Modern stormwater systems are engineered to gradually filter and release the runoff, rather than release the water all at once or hold it for an extended period of time, Cutler said.
Sue Burke, the town’s stormwater engineer, said the 3,600-square-foot rain garden is designed to hold up to 12 inches of water during storms and funnel another 12 inches from heavier storms through an outlet and underground pipe.
The system is still a relatively new way to control stormwater, so there isn’t a lot of practical history behind it, Cutler said. This time, it didn’t work as intended.
“There was too much force on it, and it pushed the dirt out,” he said.
Project engineer Mike Hammersley, with Corley Redfoot Architects, hung up twice when contacted by phone last week for more information. According to a timeline that he provided to town officials, Hammersley worked with the town’s Stormwater Division and the N.C. Division of Environment and Natural Resources in June and July to craft a repair plan.
Corley Redfoot Architects ordered Clancy & Theys to start the repairs Aug. 7. Cutler said Wednesday they were waiting for the final documents authorizing the work.