A massive wastewater treatment plant upgrade near Birmingham, Ala., will help keep residents living along a flood-prone urban creek from being exposed to raw sewage and pollutants.

Alabama's Jefferson County is in the midst of a major expansion of the Village Creek Wastewater Treatment Plant, the second largest of nine plants in the county. The $71.87 million project is scheduled for completion in June.

The project is the result of a settlement of a federal lawsuit alleging violation of the Clean Water Act. The county admitted dumping untreated or partially treated sewage into creeks that feed the Warrior River, including Village and Valley creeks, as well as into the Cahaba River.

In a 1995 settlement, the county agreed to upgrade the sewer systems, with a major part of the money going to upgrade the Valley and Village Creek wastewater treatment plants. The Village Creek plant, northwest of Birmingham, receives sewage flow from most of the downtown Birmingham area.

The biological facility already had been upgraded and expanded several times since it was first built in 1905 and currently has a capacity of 60 million gallons per day. When torrential downpours result in increased flows, wastewater can flow in excess of 400 MGD. The excess has in the past been forced to bypass the treatment plant, resulting in untreated sewage going directly into Village Creek.

The new expansion is adding "peak flow facilities" to provide full treatment for the high volume of wastewater that flows to the plant during wet weather.

Birmingham-based Brasfield & Gorrie, ranked fourth among the nation's top wastewater treatment contractors by Engineering News Record, is a major contractor on the project. The firm recently completed the Village Creek pumping station, a $44.94 million project, and 20 large surge basins in a $45.25 million project.

Project manager Dennis Hill said that in times of peak flow, the upgraded facility will pump stormwater into the new surge basins. The stormwater will be aerated, partially treated and held in these basins until the flow goes back down enough so the water can be sent through the plant.

Hill said this job is big. "I've been working with the company for 21 years now, and it seems like the plants get bigger and bigger," he added. "It used to be a good-size treatment plant could be built in 12 to 18 months. Now it seems they're two to three years."

"There's a huge volume of work we have to do in a relatively short period of time. Everything has to be coordinated closely. You start at your deepest point and work your way up. You have to make sure you don't install something too early. For instance, a lot of electrical work has to be done, but it can't be installed until near the end - you have to get the piping in first."

The recently completed deep-pump station features eight pumps that can pump 45 MGD each, and another four pumps that can pump 15 MGD each. These are the largest sewage pumps in the county, Hill said. The pump station required more than 26,000 cu. yds. of concrete. It's roughly 90 ft. below grade, with a total height of about 120 ft. above the base floor slab.

On the pumping station, a big obstacle was a requirement in the specs that backfill had to settle for six months before laying pipe or pouring concrete on top of it. This spec made it very difficult to complete the job in the 19 months allotted in the contract.
Brasfield & Gorrie came up with an unusual solution. A grid of concrete columns and grade beams, supported from the bedrock, allowed workers to support the pipe and critical structures such as transformer and generator pads without waiting six months for the backfill to settle.

"As we brought our fill up from bedrock, we'd pour another 8 ft. of columns," Hill said. "We no longer had to rely on the fill to support these things."

The biological facility is actually a number of structures. There are eight large clarifiers, two pods of four each, requiring more than 63,500 cu. yds. of concrete. The clarifiers are 140 ft. in diameter and 34 ft. high. "It's a pretty big concrete structure," Hill said.

There are also large aeration basins, a blower building for the aeration basins and the sludge thickeners. There's a pump station for return-activated sludge and waste-activated sludge.

There is a tremendous amount of excavation and backfill involved on the facility - close to 900,000 cu. yds. of material.

Then there's the pipe. For instance, a deep plant drain line of 24-in. ductile iron pipe was more than 3,000 lin. ft long. The project requires more than 39,000 lin. ft. of other iron ductile yard piping, and more than 2,300 lin. ft. of steel end ring RCP pipe, up to 120 in. in diameter.

One of the unusual features of the new facility is the offices being built inside the water tank at the site.

"I used to build water tanks, and I've never seen someone use one for an office facility," Hill said. Brasfield & Gorrie put in floors and finished offices to create three levels of offices inside the big steel column that supports the water tank. By using this space for offices, the design engineer reduced the total project cost.

Building it is much like building any other office space, he said, "but there are no square corners," Hill added. "We've built all shapes and sizes of office buildings in our commercial building division, but this is pretty unique."