There are over 138 miles (nearly 730,000 linear feet) of sanitary sewer lines in the City of Marshfield, WI which provide the wastewater conveyance or collection system with 2,500 manholes at 200-600 ft. intervals to facilitate inspections, cleaning, maintenance, investigations, and sampling within the collection system.
Wastewater that cannot flow by gravity to the wastewater treatment plant must be pumped from four separate lift station locations on the east, north, and west sides of the city.
One major concern in the proper operation of the collection system, and ultimately the wastewater treatment facilities itself, is clearwater (rain, snow melt, and groundwater) infiltrating into the collection system. This clearwater causes excessive flows and hydraulic problems at the wastewater treatment facilities and in the collection system itself. Some results of this excess clearwater are basement backups, increased operation and maintenance costs, and failure to meet discharge permit parameters required by the Wisconsin Department of Natural Resources.
Wastewater staff employees work diligently to identify, prevent and correct the sources of this clearwater infiltration. Sources may be from:
- Cracked or broken mainline pipes
- Cracked or broken home or business laterals
- Home or business sump pumps routed directly to their sanitary sewer lateral
- Yard drains routed to the sanitary sewer
- Eave troughs directed to sanitary sewer
Collection System Mainline Televising
The only way to investigate these clearwater entry sources in the underground lines is to insert a television camera inside the line. This camera is powered through the line on tracks or wheels and the picture is monitored from inside the televising trailer.
This procedure is recorded and backed up on the cloud so it can be viewed later by wastewater staff and engineering design staff to identify and prioritize the needed repairs or replacements of lines.
Collection System Maintenance
Routine cleaning of the collection system is necessary to assure that the wastewater continues its gravitational flow to the wastewater treatment plant. This is done with a truck using water under high pressure through the hose. The hose travels through each line, flushing built up sand, grit, or debris back to the manhole where the wastewater staff can remove it with a vacuum tube attached to the truck. A root cutter device also removes tree roots which may impede the flow in a line. These procedures avert flow constrictions within the lines which could cause sanitary sewer backups into homes or businesses. All 138 miles of lines are cleaned within the city on a three year rotation with other known debris buildup areas routinely cleaned more often.
Other maintenance performed within the collection system is for manholes. Wastewater staff inspects all manholes regularly to log any deterioration and repair or replacement needs. Manhole cover leaks, joint leaking, and wall cracking are some common clearwater entry concerns which the wastewater staff repairs as necessary.
Another part of the collection system is the lateral piping which extends underground from the home or business all the way out to the mainline in the street or terrace. These laterals can also become constricted or leak. The maintenance of each lateral is the owner's responsibility and corrective actions must be done by them. At times, it may be necessary for an owner to televise the inside of their lateral in order to identify the source of clearwater entry or a blockage. The Marshfield Wastewater Treatment Facility provides this service for the owner who has a blockage by placing a lateral camera device within their line which assists in identifying the clearwater source or blockage source. To make an appointment to have this service provided, call (715) 486-2007.