As the Alabama Department of Transportation (ALDOT) constructs the $110 million State Road 158 extension to connect with the new U.S. 98 west of Mobile, Alabama, many factors make stormwater management critical, including the project’s history.

When ALDOT started work on the new alignment in 2007, stormwater runoff into wetlands and the City of Mobile’s drinking water supply prompted litigation, regulatory fines, and loss of funding. By the time the project restarted in 2017, ALDOT had refined their stormwater management approach. Special roles within the contractor team manage the efforts, and measures such as sediment and detention basins, level spreaders, and enclosed drainage systems control water flow.

Most importantly, “We limit our disturbance to 17 acres at a time – small portions that we stabilize as we go to keep problems down,” said Sam Fountain, Construction Engineer for ALDOT. “We implemented lessons learned from way back to now, the contractors bought in, and everything has progressed very smoothly.”

The new alignment improves safety and provides extra capacity for the heavily traveled, rural route. ALDOT divided the 12-mile corridor into seven separate projects (see “Project Breakdown”). All the projects were funded by state and federal funds, and the first five (two now complete and three under construction) also included money from the BP oil spill settlement. The last two projects will start construction in February 2022 and Fountain expects them to finish in mid-2024.

Throughout the corridor, work includes building the foundation and performing earthwork for four lanes, creating interchanges, and paving two lanes. The timing to expand the roadway into a divided, four-lane facility will depend on future need and funding.

Volkert, Inc., headquartered in Mobile, provides construction management for the projects. ALDOT wanted to reassemble team members who helped regain regulatory compliance in 2008, and two of those individuals – Joey Fresolone, who serves as Project Manager, and Barry Fagan, Environmental Quality Assurance – now work for Volkert.

In addition to the history of the project, several other factors contribute to the need for strict water, erosion, and sediment control.

First, with the new alignment through rural areas, “It was over 75 percent wooded, with some pastures and open land,” Fagan said. “When you turn an area from trees to asphalt, the rate of water leaving speeds up and the volume of water increases.”

The quantity of water adds to the complexity.

“Mobile gets 67 inches of rain each year over about 59 days,” Fagan explained. “That means really intense rains; it’s not unusual to get a 4-inch rain event. We’re also right on the coast with tropical storms and hurricanes coming out of the Gulf of Mexico. Because Mobile is so wet, there are lots of streams, wetlands, and ponds within the project limits and alongside the project.”

In addition, three of the seven projects cross the watershed for Big Creek Lake, the drinking water source for over 250,000 people.

“ALDOT is treating all the projects the same,” Fagan said. “We’re doing everything we can to protect all the waters.”

Contracts for all the projects specify that the work can’t disturb more than 17 acres at a time, unless altered by a plan note. That results in only a small piece of the project exposed to rainfall and potential erosion.

“We don’t want the risk of those heavy, intense downpours washing all the work away,” Fagan said. “If that happens, you’ve got not only a repair on the slope, but a bunch of sediment in the creek downstream.”

To avoid that, “ALDOT has standard requirements that the contractor can’t clear an area until they’re ready to start grading,” Fagan said. “Once they start grading, ALDOT doesn’t want them to stop until they reach final grade. Once they reach final grade, they need to apply topsoil within so many hours, then the erosion control.”

In these projects, “There are areas where we seed and put down erosion control product, but 70 to 75 percent of the corridor uses solid sod to get to permanent stabilization as quickly as possible,” Fagan said.

The limited chunks of work and continuous pursuit of final stabilization require extensive planning and an intentional shift in project phasing and sequencing.

In addition to multiple mobilizations for subcontractors like logging and sod companies, “In the contractor’s own workforce, they can’t just have a grading crew out there then bring in the fine grading and cleanup crews later,” Fagan said. “They need the pans, trackhoes, and rock trucks running at the same time the small dozers and skid steers work on the slopes to get them covered up.”

To offset the increase in water leaving the corridor, ALDOT incorporated multiple detention basins. During construction, those areas act as sediment basins.

“The best way to manage sediment is to slow stormwater down so it’s harder for it to carry sediment,” Fagan explained. “Baffles in the basins calm the water and promote settlement of soil particles. Floating dewatering devices or skimmers on the outfalls withdraw water from the surface, which in theory is the cleanest part of the water column.”

When everything works ideally, “We just have a film of clay particles or a half-inch of sediment across the bottom of the basin and there’s no need to clean it out,” Fagan said. “However, sometimes we get really big storms, or it comes at a stage of construction that’s not ideal, and we end up with sediment that’s sand and heavier particles.”

In those cases, an onsite erosion and sediment crew cleans the basin. “The good news is that sediment didn’t leave the project,” Fagan added.

After construction, contractors will retrofit the sediment basins into permanent detention basins.

As part of the stormwater management plan, every project in the corridor requires a designated erosion and sediment control crew.

“If a storm creates maintenance issues, the contractor has dedicated people, equipment, and materials on hand to fix those problems as soon as possible,” Fagan said. “You wouldn’t want those folks sitting around waiting for a storm, so they’re typically part of the contractor’s onsite road-building crew – but there’s an expectation that their first priority is taking care of any stormwater issues that occur.”

To lead the stormwater management efforts, each contract also requires a Qualified Credentialed Professional (QCP).

“Contractors usually don’t have a QCP on staff, so they hire a consultant – someone with training and experience in erosion and sediment control and credentials as specified by the state’s environmental regulator,” Fagan said.

Contractors also need a Qualified Credentialed Inspector (QCI), with training defined by the state regulator. Typically, a foreman or superintendent fills that function.

Those roles add cost, as does the requirement for sequencing to delay and limit disturbance. ALDOT’s mandatory pre-bid meetings, plan notes, and other communication allowed contractors to account for those costs in their bid packages.

• Owner – Alabama Department of Transportation; Matt Ericksen, P.E., Southwest Region Engineer; Sam Fountain, P.E., Construction Engineer; Jenifer Eubanks, P.E., Assistant Construction Engineer
• Construction Manager – Volkert, Inc., Mobile, Alabama; Joey Fresolone, Project Manager; Barry Fagan, Environmental Quality Assurance; Eric Gautreau, Stormwater Inspector
• Prime Contractors – see “Project Breakdown”

ALDOT divided the corridor into seven contracts:

• Extend eastbound bridge on U.S. 98 over Big Creek – $5.4 million; Tanner Construction, Laurel, Mississippi, started work September 2017 and finished October 2018
• Extend SR 158 from east of Lott Road to Schillinger Road – $16 million; John G. Walton Construction Company, Mobile, Alabama, started work April 2018 and finished November 2020
• Extend SR 158 from east of Glenwood Road to west of Lott Road – $27.9 million; H.O. Weaver & Sons, Inc., Mobile, Alabama, started work November 2018 and expects to finish June 2022
• SR 158 extension, Lott Road overpass, and jug handle – $16.8 million; McInnis Construction, LLC, Summerdale, Alabama, started work April 2020 and expects to finish May 2022
• Glenwood Road bridge replacement – $9 million; H.O. Weaver & Sons, Inc., is scheduled to start work February 2022 and finish mid-2024
• Bridge on Wilmer-Georgetown Road over U.S. 98 with jug handle – $7.7 million; HCL Contracting, LLC, Semmes, Alabama, started work May 2021 and expects to finish September 2022
• Base and pave on U.S. 98 eastbound lanes from Mississippi line to half-mile east of Glenwood Road – $25.8 million; Mobile Asphalt Company, LLC, Mobile, Alabama, is scheduled to start work February 2022 and finish mid-2024