CH Library Stormwater System Crumbled Prior To June Floods
CHAPEL HILL- The Town of Chapel Hill just spent $16 million to expand the library, but part of the newly installed stormwater management system began to fail months ago.
David Tuttle lives on Estes Drive. From his backyard he says it’s just a short walk to Pritchard Park, which surrounds the Chapel Hill Public Library. But he says lately, that walk is anything but soothing.
“I almost try to avoid walking back there in the woods, because to walk through there now and see what’s happened and see that nothing’s being done to keep it from getting even worse, it’s just disheartening,” says Tuttle.
The recent flooding scoured the forest floor, wiping away low-lying vegetation and spreading silt everywhere. Though scenes of flood damage have become common since the June 30 rainstorm that dumped more than five inches in just a few hours, Tuttle says this is different.
He says the part of the new stormwater management system at the library began to fall apart before the flood, and he’s got the pictures to prove it.
“I saw where the rain garden structure right behind the library building had completely given way and had caused the entire area to wash out and go across the greenway path that goes along there and deposited into the creek,” says Tuttle. “So I took pictures of all that.”
The pictures, dated June 25, show an eroded gulley where the side of the man-made pond intended to capture rainwater collapsed.
The bioretention basin is the central feature of the rain garden at the back of the library. It’s designed to slow down run off and direct overflow into a stormwater grate instead of flowing downhill.
It’s also brand new, part of the $16 million dollar library expansion project that was completed in April, which increased the library’s square footage by 35,500 square feet and added a second parking lot.
But an email to town officials reveals that the bioretention pond began to fall apart as early as April 10, the same week the library reopened.
And according to a report prepared by the project engineer, two months passed before a contractor came out to inspect the damage. Shortly after that, in early June, summer rain storms caused the embankment to crumble further, allowing water to wash silt and sediment into Pritchard Park.
All that happened before the torrential rain at the end of June that flooded parts of Chapel Hill. Pictures taken after that storm show sediment piled at the base of trees that escaped plastic fencing put in place as a temporary measure.
John Holley, the regional engineering supervisor with the state Department of Environment and Natural Resources, was contacted in mid-July to evaluate the damage. He says the town will be responsible for cleaning up the forest.
“I’m going to be asking them to retrieve the visible siltation that was lost into the channel in the affected areas down below the basin,” says Holley. “We’re going to ask them to clean all that up as they do the repairs.”
Holley says in the past month the town has worked quickly to address the problems at the site.
“The town has responded immediately and started cleaning up, or putting in containment for the sediment and they are working with the stormwater people to get the measures in appropriate shape,” says Holley. “As long as they are working with us, that’s where we want the focus.”
Multiple town officials as well as the project engineer declined to go on record for this story. No one would comment on the likely costs to repair the bioretention pond, the cost of cleaning up the park, or who might ultimately foot the bill.
Meanwhile, David Tuttle is left wondering if the repairs will be enough to prevent this from happening in the future.
“Are they just going to stay with these rain ponds, which are not meant to retain stormwater, or are they going to look at going the next step and finding a way to not pass water down Bolin Creek to Camelot Apartments and University Mall? Because the library at this point is basically passing all its water down there,” says Tuttle.
Clean-up and repairs are slated to start this week and take three weeks to complete.
Public Works Director Lance Norris wrote to Town Manager Roger Stancil on Friday to update him on the planned repairs. You can read that full email below:
From: Lance Norris
Sent: Friday, August 09, 2013 6:00 PM
To: Roger Stancil
Subject: Library Bioretention Repairs
In response to concerns raised about needed repairs to part of the stormwater management system at the Library I requested that Mike Hammersley, the project engineer, put together a brief report describing the scope of the issue, the background of correspondence requesting corrective actions, and a summary of what will be done next. A copy of Mike’s report is attached. The issue involves needed repairs to bioretention cell #5, one of several stormwater mitigation improvements installed when the Library expansion project was built. I have also attached two pictures showing existing conditions on the site. The first shows erosion caused by water overtopping the bioretention basin in recent storms. The second shows sediment that was transported during these heavy rains to the wooded area between the basin and the creek.
Working with the Town’s Stormwater Management Division and the State Division of Environment and Natural Resources, Mike has developed a plan to make the necessary repairs. This work will include re-grading and stabilizing the berms around the bioretention cell and installing some supplemental measures, including an impermeable basin edge liner and additional sub-surface drainage to assure the repairs will hold up to anticipated future storm events. The repairs will also include the removal and/or stabilization of sediment that has been deposited below the basin as recommended by the State Division of Environment and Natural Resources. To assure that the repairs are properly done the Town will involve an independent soil engineering firm to inspect and approve the work. The work is scheduled to begin next week and is expected to take approximately three weeks to complete.
Please let me know if you need additional information.
Public Works Director
Town of Chapel Hill
6850 Millhouse Road
Chapel Hill, NC 27516-8173