Century-old pipes show their age
Baton Rouge, La., is rehabilitating its 100-year-old sewer collection system to reduce sanitary sewer overflows (SSOs) and to provide growth capacity in the city. The SSO Program is the largest capital improvement initiative undertaken by the city and will include $100 million worth of sewer rehabilitation over the next 10 years.
For several years, the city has had problems with the aging wastewater collection system, which includes more than 400 pump stations and 2,000 miles of pipe. In 1988, it received an Environmental Protection Agency (EPA) consent decree because of inadequate treatment of sewage flow. Then in 1995, while working to improve the sewer treatment plants, the city received an EPA administrative order for collection system deficiencies. At that time, the sewer system experienced numerous overflows and system backups, which led to roughly 7,000 customer complaints annually or almost 20 per day. In late 1999, the city entered into consent decree negotiations because of more violations to the Clean Water Act because of SSOs. In 2000, as a show of good faith during negotiations, the city began addressing the violations.
During the early 1990s, efforts were made to control the overflows by sealing known overflow locations; however, that usually only moved the overflow to another location in the system. The poor condition of the aging infrastructure, the complex system hydraulics and inadequate capacity led to an urgent need for remedial action. “We were in a difficult position,” says Kent Mudd, Baton Rouge SSO Program manager and special projects engineer. “We needed to determine not only if rehabilitation alone was the right solution, but also how we were going to prioritize and pay for the overwhelming number of needed projects.”
In 1998, the city completed an SSO Corrective Action Plan following an evaluation of the system. The plan focused on increasing system capacity through new facilities or cost-effective rehabilitation, as appropriate. It also established an Asset Management Program to begin a long-term sewer rehabilitation effort focused on preventive maintenance. The city hired a consultant to assist with program management and to develop GIS-based decision support software that would prioritize sewer inspection and direct preventive maintenance based on closed-circuit television inspection data.
The Sewer Rehabilitation Decision Support System (RDSS) has improved the consistency of sewer defect data, reduced design time and capital costs, reduced time between analysis and construction, and improved engineering flexibility. In addition to the RDSS, a detailed hydraulic model of the collection system has analyzed system capacity. The model is directly linked to the GIS management system, which allows the city to view its wastewater system problems, causes and solutions. The model and mapping system help the city identify the causes of sewer problems, optimize existing system operation, analyze the effect of future development and prioritize capital improvements.
In 2000, the city launched an SSO Program to implement recommendations of its SSO Corrective Action Plan. So far, 24 projects have been initiated, and 11 of those are focused strictly on sewer infrastructure rehabilitation. To date, the city has spent $32 million on collection system upgrades as part of the program, of which $10 million is rehabilitation-related. Thus far, the city has been able to fund the program almost solely with user fees, sewer impact fees and federal grants. “With the implementation of the current program, we are providing a long-range solution to the overflows that are occurring in our system and providing capacity for more growth throughout our community,” Mudd says.
Christopher Young, senior engineer for Broomfield, Colo.-based Montgomery Watson Harza (MWH), and Rod Moeller, consultant for TAG The Asset Group, an MWH business.