Treating Large Ponds on a Multi-Year Construction Project

In 2002, the Florida Department of Transportation began a multi-year construction program designed to modernize Interstates 10 and 110 in Escambia County. The program came to close at the end of 2009 and represented more than $400 million in construction work to improve mobility and enhance safety on the local interstate highways.

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By Frank Kneib

In 2002, the Florida Department of Transportation began a multi-year construction program designed to modernize Interstates 10 and 110 in Escambia County. The program came to close at the end of 2009 and represented more than $400 million in construction work to improve mobility and enhance safety on the local interstate highways.

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Figure 1: The photo shows the suction float where the inlet water is drawn into the pump for filtration. The road construction project is located just beyond the pond.
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Inset: The Florida DOT project aimed to improve mobility and enhance safety on the local interstate highways.

The I-10/I-110 and I-10/Davis Highway interchanges are located north of Pensacola and are closely spaced, essentially operating as a single interchange and referred to as the I-10/I-110/Davis Highway interchange.

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Figure 2: The largest pond, shown here, is 16 acres in size. The construction in the foreground shows how the pond is being filled in to reduce its size. Discharge from this pond averaged between 5 and 10 NTUs at 700-1,500 gpm.

The construction work comprised a number of projects, including widening portions of I-10 and I-110 to six lanes; replacing a bridge that was destroyed in 2004 by Hurricane Ivan; and construction of a new I-110 interchange.

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Figure 3: The mobile treatment systems and equipment were staged on dams between the ponds.

Throughout the construction site, the project involved work on several very large stormwater collection ponds. The ponds needed to be dewatered to retain storage capacity for future rain events. Because the panhandle of Florida receives some of the state’s highest rainfall averages, the project expected to receive around 60 inches annually.

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Figure 4: Shown here, the 4-pod sand filtration systems, which used the GelFloc as a filter aid.

Mobile filtration systems, provided by Rain for Rent, proved extremely successful throughout this large construction project. Using a product called StormKlear, the systems were able to easily meet the Florida NTU turbidity requirements, which state that discharge cannot exceed 29 NTUs over background waters. Background historically is around 5 NTUs in this part of the state.

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Figure 5: The filtration system viewed from the discharge point.

Archer Western, the contractor for the project, called in the services of Rain for Rent to build the mobile treatment system. Rain for Rent incorporated several sand filtration systems and recommended the use of the StormKlear product in their systems because of previous success with it on projects in both Maryland and Washington.

Starting in February 2008, the contractor began running two multi-pod sand filter systems to dewater a 16-acre stormwater collection pond. The systems were required throughout the ‘wet season’ (spring, summer and fall). Each treatment system was capable of treating 1,000 gpm, but average flow rates were around 700 gpm per system. The total amount of water treated is estimated to be around 150 million gallons of stormwater.

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Figure 6: The discharge area is the point at which samples are taken for NTU measurement and occasionally pH levels. Testing for free residual chitosan is also tested here.

The nature of the material keep it in suspension, thus Rain for Rent chose the biopolymer GelFloc product, which is made from crustacean shells, a waste product of the seafood industry. Because of its performance with sand filtration and its ability to field detect against residual polymer, the system successfully met the contractor’s needs.

Starting turbidity levels in the ponds fluctuated between 75 and 400 NTUs depending on rainfall and pond water level. Discharge was between 0.5 and 28 NTU with average discharge between 5 and 10 NTUs. Turbidity measurements were taken manually three or four times per day or if any significant change occurred.

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Figure 7: Discharge runs into the creek, which drains into a stream.

The particles that caused the turbidity were very small and didn’t want to settle out with gravity. The GelFloc aided the systems by floccing the small particles together so the sand filters could remove them. Because the GelFloc is biodegradable, there was not a concern of bioaccumulation.

Because the system was able to operate in a flow-through model, it was the best model for this application. This project has now come to a close and demonstrates the value of a mobile treatment process for a multi-year project of this magnitude.

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Figure 8: Close-up of the water clarity at the discharge pipe.

About the Author:

Frank Kneib has been managing the StormKlear stormwater business for HaloSource Inc. since 2007 and is a Certified Erosion & Sediment Control Lead with Washington State. Prior to that, he was the Commercial Manager for the company’s recreational water and aquarium business.

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