The City of Cedar Rapids has reduced sanitary sewer backups by more than 80 percent — proof that its aggressive war on blockages is working.
The Sewer Maintenance Division’s key weapons against blockages include a comprehensive preventive maintenance program (PMP) and a targeted capital improvement program (CIP) to upgrade the infrastructure.
Cedar Rapids has a population of 125,000, but it has a large industrial base. The wastewater flow is 30 mgd, more typical of a city of 1.2 million. For years, the city took a reactive approach to blockages, which occurred at the rate of 500 to 700 per year.
No longer willing to accept the service interruptions and high costs and risks of blockages, the city implemented a mandatory grease trap program in 1994. As county and building inspection teams enforced those rules, backups dropped to 120 by 2003.
“In that year, we implemented our PMP and CIP and reduced sewer blockages by 60 percent in three years,” says Public Works maintenance manager Craig Hanson, P.E. “These programs have also helped decrease the average flow of wastewater to our treatment plant by almost 15 percent and peak flow by 25 percent.
“We accomplished this by combining several tools and technologies. Our PMP uses geospatial technologies, work order management, and CCTV pipe inspection to provide us with accurate information on the location and condition of our sanitary sewer pipes. Our CIP involves rehabilitation of more than 25,000 feet of line with cured-in-place liner and replacement of over 5,000 feet each year.”
Building a database
The Cedar Rapids sanitary sewer system serves a population of about 155,000, including residents of Marion, Hiawatha and Robins, part of Fairfax, and a small portion of Linn County. The 31 members of the Sewer Maintenance Division operate and maintain the sanitary and storm sewer systems. The city maintains more than 650 miles of sanitary sewer pipes in sizes from 6 to 96 inches with an average age of 53 years. The Water Pollution Control Department takes care of the system’s six lift stations.
“Although the system is simple, it takes careful review and coordination to ensure that more than 1,300 annual preventive maintenance actions are completed and documented,” Hanson says.
In fighting any battle, it is critical to know the geography and history of the battlefield. In Cedar Rapids, a geographic information system (GIS) supplies the geography, and a work order management system provides the history.
In 2004, the Sewer Maintenance Division performed a thorough review of the previous three-year period to locate sites of backups and document past cleaning efforts. The team then inspected each location to identify specific pipe defects. This helped them build a database of nearly 1,000 locations. Since then, crews regularly review work orders from inspections and blockage responses and enter more information into the database. That has added 300 more locations.
The GIS provides an inventory of pipes and structures. Global positioning systems (GPS) are used for accurate field-data collection and condition analysis. The GIS was developed 10 years ago using ESRI shape files, and the staff has refined it over the last five years into a robust enterprise Geodatabase.
The city began using a Sokkia survey-grade GPS for data collection in 2002, and also uses recreational-grade and GIS-grade GPS units for locating and other data-collection tasks. New sewers are located with GPS and entered into the GIS along with attribute data, such as elevations, diameter, material, and project number. Data for existing sewers is field verified using GPS and, if necessary, revised in the GIS.
