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Thursday, Apr. 17, 2014

Power company asked to share in repair costs

Thursday, April 15, 2010

Shelbyville's utility company has yet to respond to a letter from the mayor that asks for the power company to pay for half of the damage costs to the city's underground flume system caused by flooding nearly a year ago.

Mayor Wallace Cartwright sent the letter to Shelbyville Power, Water and Sewer manager David Crowell on March 31, which requested that it was the city's belief that sharing the repair costs for the flume should be the responsibility of the utility "or its agents and contractors."

Last May, part of North Main Street and a grassy area next to it began to collapse following a weekend of heavy rains.

When workers began work to replace the underground structure, engineers discovered that the collapse was caused by two sources of water intrusion into the space around the flume -- an open, but unused sewer line and a broken pressure relief valve on the flume itself.

Cartwright stated that the city had already requested restitution from Mayse Construction Co., the contractor that had uncovered the area where the collapse occurred, but they have denied the claim.

Mayse had excavated the section of the flume in November 2008 as part of the power system's Northeast Area Sewer Replacement project.

"Before seeking relief through litigation, the City suggests that the matter be settled completely with a contribution by the Power Company to the City for half of the repair costs," which totaled $457,394.12, the letter stated.

The mayor also said he appreciated the recent vote of the Power Board "to waive any potential statute of limitations concern" and said it was the city's hope that the matter could be resolved "amicably and without further delay."

According to the conclusion of last year's report by CBC Engineers & Associates, the flume's collapse "was the result of the foundation support below the pipe arch being compromised by the intrusion of water from the ... non-abandoned old sanitary line and damaged pressure relief valve."

Cartwright said that both of the conditions that caused the collapse "were under the direct control of the Power System," and since it owns the old sewer line and was responsible for the excavation of the area, and had these things not occurred, the flume would not have failed.

How it happened

The engineering report says that the water that was introduced to the soil below the flume "during the May storm event caused the erosion of the bedding material ... and likely caused softening of the remaining bedding material."

The valves are placed down the length of the flume to allow water from outside the structure to flow inside the flume to relieve the outside pressure. Instead, the valve that had been knocked off allowed water that was inside the flume to go into the area surrounding it.

After the repair last year, public works director Mark Clanton traveled the length of the flume several times taking photos and he said that no other valves had been knocked off except the one highlighted in the engineering report.

The failure of the flume ran for 125 feet toward Duck River, but the report notes that the steel on the rest of the flume "appeared to be in relatively good shape after 40+ years of service" with minor corrosion visible.

The broken valve was located 10 feet downstream of the upstream end of the failed section of the flume, the report reads. Also, the backflow preventing gate for the valve was missing and "backfill material was visible on the outside of the valve."

After the failed part of the flume was removed, engineers returned to inspect the area and that's when the open sewer line was discovered.

The report states that during the preparation work for placing in the new flume section, "the new sanitary manhole was plugged in order to bypass sewage around the sanitary lines in the excavation area."

"Shortly after the manhole was plugged, sewage was observed discharging out underneath the flume into the excavation in the same area ...."

The report also says that Shelbyville Power performed a leak test with fluorescent green dye, and the dye was seen discharging from underneath the flume. The old line was also examined with a video camera by the utility and "it was determined that this line has been compromised and was leaking under the flume," the report reads.

The report also says that the valve on the old sewer line had remained open instead of being shut, which allowed water and sewage to continue to flow in the old line, which crossed under the flume.