For years, municipal utility managers, public works directors and engineers across the country have realized that in order to mitigate inflow and infiltration (I&I) in the sewer collection system, they must adopt a holistic approach to their rehabilitation efforts to include all aspects of the collection system.
By only performing mainline cured-in-place pipe (CIPP) or manhole rehab, the groundwater will eventually just get pushed to the next defect in the line, usually to the lateral/main connection.
Industry-leading organizations such as the Water Environment Federation (WEF) and the Environmental Protection Agency (EPA), have all published dozens of papers reinforcing comprehensive collection system rehabilitation to eliminate I&I, which not only has a positive fiscal impact on a municipality as less clear water is treated at the plant, but also reduces the occurrence of sanitary sewer overflows (SSO) resulting in a healthier environment for all.
With the continuous emergence of new technologies in this sector, there are several, financially viable solutions available to municipalities to address the issues they face with their sewer systems. And as documented in this case study, Jefferson County, Alabama, used multiple rehabilitation techniques in the rehabilitation of its Chapel Drive pump station to achieve a result that went far beyond anyone’s expectations.
Chapel Drive Pump Station
Jefferson County Environmental Services Department (JCESD) is responsible for sanitary sewer collection and treatment in Birmingham, Alabama, and the surrounding municipalities. During heavy rain events, JCESD noticed a huge increase in the influent flow rate and SSO’s in the Chapel Drive pump station even though 85 percent of the mainlines had been previously rehabilitated using CIPP between 1996–2006.
In order to get a better understanding of exactly what issues the County was facing, JCESD teamed up with Hazen and Sawyer for an in-depth asset evaluation of their underground infrastructure. After performing a cost comparison between upsizing the pump station vs. a full system rehabilitation of the basin, JCESD and Hazen and Sawyer determined the most cost-effective solution would be to rehabilitate the remaining part of the system, ultimately less than half the cost of upsizing in this particular case.
After a full assessment of the 15,000 lf of the Chapel Drive basin, which included CCTV of all main lines, manhole inspections, and CCTV lateral launching inspection, Hazen and Sawyer concluded that:
• Twenty-six percent of the system was newer ductile iron pipe.
• Sixty percent of the main lines had been previously rehabilitated using CIPP.
• Fourteen percent was vitrified clay.
• The manholes adjoining the CIPP pipes had also been previously rehabilitated.
• The manholes adjoining the ductile iron pipe were new concrete.
• None of the service laterals had been taken into consideration during JCESD’s previous rehabilitation program.
The results of the assessment showed that more than half of the service laterals were inactive, and infiltration was gushing through this connection at an enormous rate. At this point, JCESD concluded that to see a significant reduction in I&I at this pump station, all the remaining issues needed to be addressed, including every service lateral connection:
• Suncoast Infrastructure Inc. installed CIPP on the remaining 14 percent of mainline VCP (approximately 2,000 LF) and rehabilitated the manholes.
• BLD Services LLC installed the full-wrap Service Connection Seal + Lateral (SCS+L) on the active service connections and completed CIPP point repairs to cover inactive services to prevent infiltration at the interface.
JCESDs comprehensive approach, which included upfront spending for lateral launch CCTV to determine the best method of lateral rehabilitation, ultimately saved the County hundreds of thousands of dollars in the short-term and will save millions in treatment, pump run-times, and SSO consent decree fees in the long-term.
Preliminary data is already showing a remarkable 89 percent reduction in volume and 79 percent reduction in peak flow for the Chapel Drive Pump Station, requiring only minor upgrades to the station and not the expensive capacity upgrades which were initially considered. By using a holistic approach to sewer rehab, these results have persuaded JCESD to incorporate lateral rehabilitation along with manholes and mainlines into all future projects.
This case study clearly shows that by rehabilitating sewer systems as a whole and not simply the separate components, there is a greater over-all return on investment for the municipality, not to mention the money saved from having to upgrade pump stations and treatment plants.