The Bayside Bridge is an arterial roadway that parallels U.S. 19 and connects Largo to Clearwater, Florida. It also spans a sensitive Florida waterway, the Old Tampa Bay, which is a Designated Aquatic Habitat and Outstanding Florida Water source, required to have the highest level of treatment.
As part of its ongoing maintenance activities, the Environmental Division of Pinellas County Public Works Department (PCPWD) wished to rehabilitate the existing stormwater pond that provided water quality treatment to the bridge’s north end.
The County faced two specific problems with the existing stormwater pond. First, while the existing system provided treatment, it also short-circuited and sent water back into Old Tampa Bay prematurely. Second, trash and sediment were washing off the bridge, collecting along the side and eventually going into the retention pond, filling it up.
The PCPWD considered its options. Large fiberglass pipes could take the stormwater under the bridge, but large volume pushed the water directly into the bay. Site limitations prohibited expansion of the pond. A treatment plan could not be put on the bridge. Plus, stormwater had to stay off the bridge for safety reasons.
The county installed a Continuous Deflective Separation (CDS) stormwater treatment device that uses hydraulic techniques in a compact footprint to treat large stormwater flow volume. “We’ve used other such units down here, and they work well,” ” said Sr. Engineer Mike Maroney, P.E., of PCPWD’s Surface Water Division.
A Contech engineer worked closely with County staff to understand the objectives, design challenges and site data to effectively treat the 13 acres of bridge deck. After reviewing multiple CDS models, the County selected the CDS PSW70_70, that has a rated treatment capacity of 26 cubic feet per second. Further, this device was selected based on its ability to treat the first inch and a half of runoff, which mimics the level of service provided by the stormwater pond.
Contech assisted with preparation of the final bid documents, and event had a representative on-site while contractor Keystone Excavating was installing the device to ensure proper installation and help minimize potential construction delays.
The majority of the installation was completed in one day, and the contractor finished the construction by making pipe connections and completing field-cast concrete work.
Maroney outlines some of the problems the highly-developed Pinellas County faces: “The area has a relatively high water table and, with all the construction that took place in the 1960s and ‘70s when there were no retention ponds required, a lot of the County is covered with impervious pavement. We have a lot of streams and creeks which are now eroding, then depositing sediment into the bay.”
Pinellas County received state funding assistance for the Bayside Bridge project.
“We’re very proud of our surface-water program, and we should be,” Maroney concludes. “However, we’re always fighting projects built in the ‘60s and ‘70s, when the goal was to get the water to the Gulf ASAP. Who knew about environmental impacts then?”