(E)X Marks the Spot

Municipalities in Florida know the importance of having a sanitary sewer rehabilitation program.

Ask anyone living in a coastal community, the soil conditions are different. Typically in areas with a high water table, such as Florida, sanitary sewer lines tend to be shallower than other areas of the country.
For example, in the Midwest, it is not uncommon for lines to be in excess of 20 ft deep but lines that deep are rare in Florida. However, the lines in Sun City — a community in Hillsborough County, Fla. — are buried 14 to 20 ft deep, which in turn fuels their rigorous, proactive rehabilitation program.

As part of this program, directors monitor the amount of time the lift station pumps run in comparison to the anticipated run time based on the predicted amount of sewage to be produced. Engineers can calculate the amount of sewage normally produced by looking at the number of homes feeding into the lift station. When the run times fluctuate one way or another, it alerts the directors of a potential problem.

Trenchless Chosen

After the analysis of the data related to run times and further testing in Sun City, county personnel knew exactly what needed to be done.

“The lines in Sun City were huge candidates for rehabilitation,” said Jim Adair, project manager for Hillsborough County. “We knew using a trenchless technology was the route we wanted to take.”

Since lines in Sun City run an above average depth of 14 to 20 ft deep, rehabilitation before failure is extremely important to avoid having to dig up the lines, as excavating to repair can be difficult and costly, given the soil conditions and high water table. Hillsborough County designed a publicly bid project in an attempt to eliminate infiltration into its systems. Miller Pipeline was awarded the contract, which included rehabilitating a total of 127,405 ft of combined 8-, 12-, 18- and 24-in. lines and encompasses approximately 2,000 to 3,000 homes. The sheer amount of footage is unique in itself.

“A job of this magnitude is rare,” said Louis Woska, manager of the south region municipal services division for Miller Pipeline. “We were thrilled to have this opportunity to work with Hillsborough County again.”

The trenchless technology being used on this project is Miller Pipeline’s EX Method, also known as expanded-in-place PVC relining. Miller’s EX is a manhole-to-manhole rehabilitation technique that has been used extensively in the sewer rehabilitation market for two decades. It represents a large share of sewer rehabilitation business and many customers who have tried it once keep using expanded in place PVC for its consistency, environmental friendliness and over quality of the finished product.

To start the rehabilitation process, a subcontractor is called in to clean and televise all of the lines to verify footage, service counts and diameters. Once this is complete, the lining crew marks the services for reinstatement and records the footage for house connections. The installation procedure consists of the pulling of the heated PVC material through one manhole to another manhole by means of a winch. The speed at which the winch pulls is critical. Keeping the pipe heated for the entire pull is vital to minimizing the “pull stress” on the pipe. This stress is closely monitored during installation. Rollers are used to further reduce stresses. Once the pipe is installed, both ends of the pipe are fitted with end caps that facilitate the introduction of steam and air, as well as regulating the exhaust of both and any condensate from the cooling steam. Through the use of carefully regulated steam, air and pressure, the EX liner unfolds or expands against the wall of the host pipe. The pipe is heated to a required temperature and while maintaining the pressure, the steam is discontinued and air is induced to reduce the temperature. During the process, a hydrophilic gasket may be added to both ends of the new PVC pipe between it and the host pipe to inhibit any infiltration between the two.

After the cooling of the EX pipe, the house service connections are re-opened using a specially designed robotic cutting device and closed circuit television camera. As mentioned earlier, coastal communities are a bit unique in the fact that their soil conditions are slightly sandier and relatively close to sea level. Because of the elevation, coastal communities that use this rehabilitation method often require the use of grout at the service-to-mainline connection. Grout is pumped in between the liner and the host pipe to further protect the line from infiltration and inflow (I/I). The entire process tends to take less time per installation than other forms of manhole-to-manhole rehabilitation methods.

The benefits of using manhole-to-manhole rehabilitation are:

  • prevention of infiltration and inflow (I/I)
  • eliminates the added cost of having to process groundwater mixed with wastewater
  • the finished product is a new, joint less PVC pipe
  • trenchless technology is usually less expensive than open-cut alternatives
  • less disruptive to homeowners
  • can be completed in a faster timeframe

Miller Pipeline’s EX is an environmentally safe, practical and economical method for the manhole-to-manhole rehabilitation of gravity sewer lines. Having no hazardous ingredients or odors and the ability to perform more installations per day in many cases are obvious advantages. Additionally, those municipalities wishing to make physical connections of laterals will have the flexibility of making PVC-to-PVC connections for a leak-free system.

“We are currently 25 percent through the project and things are going very well,” said Louis. “Everything is being completed in a timely, trenchless-manner without disruption to the great residents of Hillsborough County.”

Kim Lyon is a marketing communications specialist at Miller Pipeline.
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