The City of Thomasville on Wednesday released an executive summary from a sewage spill assessment, outlining the events that led to last summer’s multi-million gallon wastewater spill into High Rock Lake and how to prevent another system failure. Despite the latest report, City Manager Kelly Craver said some things will never be known for sure.

“We had hoped for more definitive answers,” Craver said. “We had a lot of professionals studying what happened, but nothing was conclusive. The most important thing was the reassurance from scientists that they don’t expect any environmental impact at High Rock Lake.”

Last summer, the city reported an estimated 15 million gallons of untreated wastewater spilled from a manhole and associated pipeline near Baptist Children’s Home Mills campus between July 31 and Aug. 4. Brown and Caldwell Environmental Engineers and Consultants prepared the summary, stating that “the likely cause of the failure was a combination of compromised structural integrity due to corrosion and high flows resulting from intense rainfall.” City workers were first called to the manhole on Aug. 3 and within a day had a bypass installed around the failed section of pipe. On Aug. 8, repairs to the pipeline were completed and it was returned to service. The report stated “insufficient data exists to quantify the duration and volume of the sanitary sewer overflow with certainty.”

Reduced flows to the wastewater treatment plant on Lake Road initially were observed on July 14 when influent flow levels dropped. Brown and Caldwell developed a model to estimate the difference between measured and expected flows at the treatment plant between July 14 and Aug. 4. The model indicated that metered flows were between 12.5 and 15 million gallons lower than typical volumes under the rainfall conditions during that timespan.

“The release of this document is an essential component of the City of Thomasville’s comprehensive strategy to address sewer collection issues,” said Craver. “The city is moving forward to correct sewer collection system shortcomings, better train its personnel and better equip itself to meet future sewer challenges.”

Brown and Caldwell listed five measures the city should take to avoid another spill due to pipe failure. The city has to replace the remaining corroded sewer pipe and manhole downhill of the spill location at BCH, implement standard operating procedures for review of wastewater treatment plant influent flow data, conduct a critical analysis of the system to identify high risk assets likely to result in another failure, inspect high risk sewers and manholes using closed-circuit television and digital cameras, and develop and implement a repair and replacement plan.

Craver said the city has already appropriated $600,000 to replace the BCH collector line, but another $2 million is needed. Craver said he is seeking help from Congressmen Mel Watt and Howard Coble to get money from the state to avoid passing the expense on to taxpayers.

“There is never a good time for a massive expense like this,” Craver said. “Had we had plans in place before stimulus money became available, I’m sure we would’ve qualified for some of it. That time has passed. I’m looking under every rock possible so we can continue making improvements to our collection system.”

Craver added that work is expected to start on the BCH collector line with 60 days.

Staff Writer Eliot Duke can be reached at 888-3578, or duke@tvilletimes.com.