Cleaning up sewer spills
For many years, Atlanta’s population has been growing, but its wastewater infrastructure has been crumbling. Prompted by a lawsuit filed by several groups, including the U.S. Environmental Protection Agency, Atlanta officials agreed to two separate consent decrees in 1998 and 1999 to settle the lawsuits, created a Department of Watershed Management and crafted the Clean Water Atlanta sewer improvement plan.
The city contracted with Broomfield, Colo.-based MWH and locally based KHAFRA Engineering Consultants to manage the capital improvement program. The team divided the project into two categories: the combined sewer system, which carries sewage and stormwater runoff for approximately 15 percent of the city, and the separate sanitary sewer system. Atlanta officials decided to separate combined sewers in a few areas, and improve storage, conveyance and treatment systems in the remaining areas.
One of the largest projects under the plan called for constructing an 8.5-mile, 16-foot-wide separate sewage tunnel in the northern part of Atlanta to alleviate spills from the combined sewer that had plagued the area since the 1980s. The $173 million project, dubbed the Nancy Creek Tunnel, began in 2002 and was completed in December 2005, under budget and in time to comply with a consent decree. The system consists of three construction shafts that anchor the tunnel, which is situated 150 feet below street level, and eight intake shafts that divert sewage from shallow sewers to the tunnel. A 100 million-gallon-per-day-capacity lift station was built at the treatment center at the end of the tunnel to carry sewage up from the tunnel for treatment.
Today, sewer spills in metropolitan Atlanta are down 60 percent compared to earlier this decade, and more than 200 miles of sewer lines have been rehabilitated. The projects have been financed through a combination of $500 million in low-interest state loans, the sale of local bonds, higher water and sewer rates, a one-cent sales tax increase and a $1.2 billion line of credit. About 90 percent of the work on the combined sewer improvements has been completed, which puts that portion of the project on track to meet its 2008 deadline. Work continues on the separate sanitary sewer system, with a deadline for the entire overhaul set for 2014.
Clean Water Atlanta plan
Broomfield, Colo.-based MWH; Atlanta-based KHAFRA Engineering Consultants