Dewatering Challenge In Pensacola

By Steve Hudson | September 28, 2010

In Pensacola, FL, Roads Inc. was recently called on to tackle a number of site work, road building and infrastructure construction challenges at a project located along Highway 98. The job was to install a new turning lane on U.S. 98 at the site of a recently constructed bank.

Work included not only constructing the new turn lane but also installing new guard rail and an 80-foot-long double run of 36-inch-diameter stormwater pipe. Subcontractor Gulf Beach Construction, Pensacola, handled the culvert construction portion of the project, removing a portion of an existing box culvert under the highway, and constructing a new 10-foot-long extension on the north side of the culvert.

Roads Inc. also handled construction of the bank's new parking lot, as well as related construction of a new lift station, installation of new sewer and water lines, and installation of a Stormtech underground stormwater retention chamber.

But before any of this work could move ahead, it was necessary to deal with water.

Keeping The Water At Bay

The job site, located just a stone's throw from the bay, faced not only the usual groundwater challenges encountered in the area but also faced tidal fluctuations in a small stream which drained the site. Thus, the water management challenge was twofold: to transfer the stream flow around the work area, allowing construction of several key elements to proceed, and also to isolate the construction area from the tidal fluctuations.

Step one in the dewatering plan was thus to keep the tidal fluctuations in the small creek from periodically inundating the work area. To that end, crews went to work inside the culvert to construct a barrier wall of sandbags. The sandbag wall effectively kept tidal backflow from impacting the site, setting the stage for the next phase of the dewatering operation.

Diverting A Stream

To bypass the stream around the work area, Robby Williams of Roads Inc. worked with Matt Hall of Holland Pump to design and install a suitable bypass system. Using D8 and D6 hydraulic trash pumps, the resulting system had a capacity of about 4,600 gallons per minute. This was enough to handle not only normal stream flow but also to take care of peak flows following storms.

The pumps pulled water from sumps cut about 1.5 feet below the work area, drawing water through rock screens and running 24 hours a day. Excess water was sent around the work area through a 200-foot-long discharge line that passed through the tidal barrier. The discharged water was filtered before being discharged back into the bay.

Effective Dewatering

The multi-pronged dewatering system worked well, notes Robby Williams of Roads Inc., allowing the project to be completed as scheduled despite several challenges from the weather.

"Though the creek was just a gentle flow under normal conditions," Williams says, "it turned into a roaring flow when rains came."

The pumps, which ran 24 hours a day, were up to the task. They were also environmentally safe, using 100-percent vegetable oil.

But, adds Holland Pump's Matt Hall, "You definitely needed both pumps running when storms came."