Mobile’s water system shared a sneak preview Thursday of a multimillion-dollar construction project designed to prevent storm-driven sewage overflows into Halls Mill Creek.
Officials with the Mobile Area Water and Sewer System held the project up both as an example of how MAWSS is making progress in addressing a longstanding environmental problem – and of how real long-term solutions are neither simple nor cheap.
The project is officially known as a SWAB, for Severe Weather Attenuation Basin. On a 12.4 acre site off Riviere du Chien Road near Halls Mill Road, three giant earthen basins are taking shape. The "cells" – which eventually will be lined with PVC and have their banks covered in sod – are big enough to make the bulldozers and trackhoes moving around inside them look like toys.
Despite some sticker shock at the price tag of more than $7.5 million, MAWSS approved the project in March. It’s now about 50 percent complete, and should be operational by the beginning of this summer, according to MAWSS officials.
When completed the cells will have a combined volume of 19 million to 20 million gallons, said Doug Cote, assistant director of operations for MAWSS. While it’s hard to image that capacity being maxed out, it will relieve a system that all too frequently is.
Mobile has a sanitary sewer system meant to carry sewage to treatment plans, and it has storm drains to direct runoff to waterways. In theory, the sanitary sewer lines should operate normally during heavy rains. In reality, a lot of stormwater gets into the sanitary lines through breaks and improper connections. That causes overflows in which untreated sewage escapes into the storm drains and from there into the creeks and rivers that area residents used for recreational purposes.
Structures such as the new SWAB are designed to buffer the overflows caused by major rain events such as Tropical Storm Cindy, which cause more than 9 million gallons of overflows in June. That included more than a million gallons that went into Halls Mill Creek.
As Cote explained, when sensors at a Halls Mill lift station detect that the system is flooding, pumps will divert untreated water into the basin. As soon as possible – which should be within a few days after the rain has stopped, Cote said – it’ll be gradually pumped back into the system, which will carry it off for treatment. (MAWSS officials said the water will be treated to control smell while it is held.)
The SWAB’s capacity is far larger than any spills recorded in that specific area. But Cote said MAWSS "didn’t want to be marginal" and that it just made sense to make the basin as big as the site would allow. He also said that "this is not a local pump station just for localized wastewater." The lift station serves a big swath of western Mobile, not just the relatively small Riviere Du Chien area.
The basin doesn’t solve the fundamental problem of stormwater getting into the sewer lines. Barbara Shaw, public affairs manager for MAWSS, said, "We feel that this project is a way to help reduce those overflows until we can get to rehabbing all the pipes."
That is a big, ongoing undertaking, Shaw said. MAWSS is responsible for 3,200 miles of sewer lines, and a little over half of them are made of brittle old clay pipe.
"It’s easy to say, ‘Just fix ’em,’" she said. "Fixing it is going to take decades, and it’s probably going to cost hundreds of millions of dollars." And most if not all of that will come from the people who pay MAWSS bills for water and sewer service.
"This is not just a MAWSS problem, this is a community problem," said Cote.
Cote and Shaw said that Halls Mill Creek isn’t the only waterway due to get overflow protection. Next up is Three Mile Creek, another waterway prone to receiving overflows. Instead of an open basin, that project will use storage tanks, to be located at a site near Tricentennial Park. That project should be finished by late 2019, followed by another on Eslava Creek.