MWSD Program Should Reduce Groundwater Leaking into Sewer System

Jul 03, 2013 at 02:00 pm by bryan


The Murfreesboro Water and Sewer Department has begun a program to rehab private sewer connections from the house to the street where cracked or broken pipe is allowing groundwater to infiltrate into the sanitary sewer system. This infiltration and inflow (I/I) creates high peak flows at the wastewater treatment plant and increases costs to all City sewer customers. 

The City spends approximately $1.25 million dollars each year repairing and replacing broken sanitary sewer lines.  The City’s rehabilitation efforts have been ongoing in full force since 2005.  Until now, the repairs were only to public sewer lines and did not address private laterals, which is the portion on private property that connects the home or business to the sanitary sewer main. 

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Before the City could begin the private lateral rehabilitation program, a change in law was required to allow City funds and employees to work on private property. 

The City recognized from other successful I/I reduction programs that replacing and repairing only the public sewer lines in the street was not successful enough in eliminating the infiltration and inflow to the system.  There is significant groundwater entering the public sewer from the private laterals in certain areas of the system. In many cases, the private property owner is not aware of the problem and may not have the financial resources to replace the lateral. 

One problem of infiltration and inflow is cost, MWSD Director Darren Gore said. “Though it’s highly diluted, groundwater must be treated as sanitary sewer; it must go through the same process.”

MWSD has divided the city into 19 geographic ‘drainage basins’.  Within those basins, there are 19 flow monitors that keep track of water levels in the sewer system.  Each year MWSD staff receives reports from the flow monitoring that pinpoints locations with significant infiltration.  These are the locations where sewer rehabilitation takes place.  Valerie Smith, Assistant Water and Sewer Director said, “MWSD crews are beginning to rehabilitate and replace private laterals in areas where the public sewer mains have been previously rehabilitated to eliminate infiltration and inflow.  These areas typically have old cast iron or clay pipe that degrades over time. “

If during investigations it is determined that a private lateral is allowing infiltration and inflow into the sewer system, Smith said, the property owner will receive a letter explaining the process and program first. The property owner must sign a hold harmless agreement for the City to proceed with the repairs on private property at no cost to the owner.

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