CARY, N.C. — Improper excavation led to a ruptured pipe and a massive sewage spill in June, according to a report released Monday by Cary officials.
A pipe at Cary's Swift Creek Regional Pump Station failed June 23, forcing the town to shut the station down and causing almost 8 million gallons of raw sewage to flow into Swift Creek and Lake Wheeler and Lake Benson downstream. The lakes were closed to the public for several days, but no fish kills were reported.
Brown and Caldwell, an engineering consultant hired by Cary officials in August to review the spill and the town's response, found that excavation work done by a private contractor as part of the pump station's expansion was too close to the main pipe and didn't provide the necessary support for the pipe. The pipe was dislodged after heavy rains caused an embankment to give way.
A forensic team from the California-based company spent six weeks visiting the pump station, conducting interviews and analyzing data before issuing its report. Its findings included the following:
Excavation around the pipe was too sharp and steep, causing the surrounding soil to become unstable. The incident would likely have happened even without the heavy rains. Town officials and the engineers on the project should have stopped the construction before the pipe failure because of the slope problems. In addition to the short-term impacts of the sewage spill, there could be long-term impacts on Swift Creek and Lake Wheeler.Cary hired Brown and Caldwell after Town Manager Bill Coleman said an assessment provided by Black & Veatch, the engineering firm handling the pump station expansion, was inadequate.
"As an open, learning organization, we needed to know exactly what happened so we can continue to improve," Coleman said.
Cary now has the piping on hand to create a bypass line in case a similar incident occurs in the future. Permanent bypass valves have been standard at all new pump stations in Cary for the last three to four years, and officials said town engineers are evaluating older pump stations to determine the best way to create bypasses.
The town also is working with state and local environmental experts and others to assess the long-term health of Swift Creek and Lake Wheeler.
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