DI sewer main collapses second time in just over a month

Daniel Island has a foul smell still lingering above the surface of one of its main streets, but the problem stems from below. Seven Farms Drive has suffered a second sewer main collapse in just over a month and the two incidents are connected.

 

On July 28, Charleston Water System responded to a sewer main line break that created a sinkhole near Guggenheim Terrace. The hole was 20-feet wide and 10-feet deep. The cause of the collapse was classified as a pipe failure due to corrosion from sewer gasses and direct contact with sewage material.   

 

CPW discovered and removed 20 feet of collapsed 24-inch ductile iron sewer main and installed a cured-in-place 150-foot long structural liner expected to extend the life of the sewer mainline segment by 50 years. 

 

On Sept. 1, the same sewer main on Seven Farms Drive across the LTP Tennis Center collapsed for the same reason ­- deterioration due to hydrogen sulfide gas, according to Public Information Administrator Mike Saia. 

 

Saia estimated that approximately 100 feet of pipe is deteriorating and could collapse. He compared the pipe’s state of deterioration to “as brittle as aluminum foil.”

 

One attributing cause of the collapse was that the lines, which were installed more than 30 years ago, lacked a protective cement lining common in today’s usage. Another detriment has been the recent heavy rainfall with increased groundwater levels.      

 

In the first few hours, CPW established a temporary bypass pump and improved that bypass system later that day to carry the wastewater to a solid section of pipe.   

 

“Thankfully, we never had a sewer overflow or any loss of sewage,” Saia said.

 

Portions of adjacent pipe were found in good condition within about 75 feet on both sides of the current hole. Saia said that CPW is planning to install a new pipe this week to effect the repair once the materials are available.   

 

As soon as weather permits, CPW will reroute the flow and send a robot through the pipe to determine how much pipe needs to be replaced. The investigation can’t be done during wet weather due to increased sewer flows.  

 

The repair is expected to take up to two weeks or longer to get the brick pavers installed. There is a plan in place to remove the flows from this pipe in the future, but there is no estimated timetable for this to happen.

 

“We’d really like to ask residents to please stay away from the area and any construction that may arise in the next two weeks,” Saia added.

 

CPW doesn’t anticipate any rerouting of traffic or road closure on Seven Farms Drive to execute the repair. There have been no service outages reported by customers at this time.