2020 Interceptor Rehabilitation




WHAT IS AN INTERCEPTOR SEWER?   
An interceptor sewer is a large pipe that receives flow from smaller local sewers and directs it to the wastewater treatment plant.
                                          

 

        


 

ABOUT THE PROJECT
The 2020 Interceptor Rehabilitation project will rehabilitate 3,900 feet of the District's West Interceptor Spring Street Relief (installed in 1940) and 600 feet of the old West Interceptor (installed in 1916). Both interceptors are 24” cast iron pipe draining to Pumping Station 2 in Brittingham Park. The rehabilitation method will be cured in place pipe (CIPP). CIPP involves installing a new felt pipe liner inside the existing pipe. The felt liner, which is impregnated with resin, takes the shape of the host pipe and is heated with hot water or stream. The heat causes the resin to cure and the liner essentially becomes a new pipe inside the existing host pipe.   

This project has been publicly advertised and bids have been opened. The project has been awarded to Visu-Sewer, Inc. Construction is expected to begin in late summer and continue into the fall.

The liner will be installed in sections from one manhole to the next. Installing and curing the liner can take up to 16 hours for each section. During that time pumps will be used to bypass wastewater around the section being lined and any properties connected directly to the pipe will not be able to discharge to the sanitary sewer pipe that is being lined. Typically, single family homes connected to the host pipe will need to minimize water use for up to 16 hours during the installation. The contractor will make special arrangements to maintain wastewater flow from higher flow properties such as apartment buildings. After the new liner is fully cured, robotic cutters with cameras will be used to reopen service connections to the host pipe. Affected properties will be notified at least a day before their service connections are blocked by the liner installation.

The installation takes place completely within the existing pipe through existing manholes and typically there will be no excavations. Equipment used in the process includes refrigeration trucks, boilers, pumps and possibly generators. The new pipe liner needs to be refrigerated during storage and transportation to prevent premature curing. The boilers provide hot water or steam to cure the new liner pipe, which is soft when first installed but hard, similar to fiberglass, after curing.  

On rare occasions odors may be detected during the CIPP installation and curing. To prevent odors from entering buildings, residents in properties connected to the pipe section being lined will be encouraged to pour approximately one gallon of water down floor drains and traps.

Preparatory work prior to lining includes pipe cleaning and setting up bypass pumping. Pipe cleaning is accomplished with a tanker truck, a high pressure water jetter inserted into the pipe through a manhole, and rotary cutting tools if required for heavier deposits. Cleaning can be done while wastewater is flowing through the host pipe. Although the liner installation itself will only take approximately 16 hours, the whole process, including prep work and break down, can take up to a week or more for each section.

In addition to the work described above 189 feet of the Northeast Interceptor Relief near the intersection of First Street and East Johnson will be rehabilitated with CIPP. The NEI Relief is 30” cast iron pipe installed in 1937. Also at this location 700 feet of the East Johnson Street Relief will be rehabilitated by pressure testing and grouting the pipe joints. This method robotically tests each pipe joint with air pressure. Joints that are found to be leaky are robotically sealed with grout. The East Johnson Street Relief is 36” reinforced concrete pipe installed in 1979. The testing and grouting process can typically be accomplished without the need for bypass pumping.

The CIPP lining and the joint testing and grouting will improve flows, prevent infiltration of groundwater into the pipe and extend the life of the existing pipe. A general overview of the project location can be seen at the following link Project Overview Map.

PROCESS PROTECTS ENVIRONMENT, SAVES TIME AND MONEY
Since the cured-in-place process does not require digging, it is significantly less costly, time consuming and disruptive to the public and the environment than excavation and pipe replacement with traditional open-cut methods. However, the use of bypass pumps and other equipment is expected to have short term traffic impacts and to generate some noise between 7 p.m. and 7 a.m. The lining process also will temporarily (up to 16 hours) limit sewer use for some residents.

The project reflects the District’s efforts to maintain aging infrastructure in a way that protects public health and the environment while delivering reliable services at an acceptable cost. Questions may be directed to project engineer Eric Hjellen, Madison Metropolitan Sewerage District, at (608) 222-1201, ext. 348 or at erich@madsewer.org.