Florida's First RBF Project Brings Reliable, Sustainable Drinking Water to Residents

Construction is now complete on Florida's first riverbank filtration (RBF) test well, part of an alternative water supply and reverse osmosis (RO) water treatment project that, when completed in 2012, is anticipated to bring a reliable, sustainable, year-round source of drinking water to the residents of the North Port community as well as to the region.

The City of North Port, Florida, is developing a new facility that has been partially funded by the Southwest Florida Water Management District and will use RBF and RO to produce 1.5 million gallons per day (mgd) of water. The water produced by the new RO treatment plant will be combined with water from the existing Myakkahatchee Creek Water Treatment Plant, which will allow the City of North Port to consistently produce approximately 3.5 mgd of potable water. The City provides water service to over 18,000 customers, each of whom uses an average of 4,000 gallons of water per month.

"The City's goal is to have a reliable water supply that will meet our current needs and also set a foundation for future water supply needs for our City, in addition to helping augment the regional supply," said Cindi Mick, North Port's Utilities Director. "Equally as important is to provide better water quality, because we believe our citizens deserve the highest-quality water at a reasonable cost. Our third goal is to increase the reliability of our system year-round so as not to burden the regional system during the dry times of year. By this project, we expect to meet all these goals efficiently, effectively and at a lesser cost than currently purchased water."

Additional Water Source Needed

Partnering with regional water suppliers is something North Port is familiar with. The City is fortunate to have its own supply and also to be connected to the regional supply. The City's water comes from the Myakkahatchee Creek and the Cocoplum Canal, and is treated at the Myakkahatchee Creek Water Treatment Plant. However, the City cannot operate the plant at full capacity year-round because, during dry seasons, the concentration of total dissolved solids and sulfates increases in these sources. This makes it difficult to meet established regulatory requirements. To fulfill customer needs during these periods, the City must, at times, rely solely upon purchased water from the Peace River/Manasota Regional Water Supply Authority.

When the RBF/RO project is completed, treated water produced by the RO plant will be blended with water treated at the existing Myakkahatchee Creek Water Treatment Plant in ratios that will meet regulatory requirements, improve water quality, maximize the use of surface water supplies, and more efficiently manage the water resources in the region during the dry times of the year.

"Novel" Technology

This project represents the first time RBF has been used in the state of Florida, according to Phil Locke, PE, a project manager with McKim & Creed, which is providing planning and design services. "Soil in Florida is typically not conducive to riverbank filtration technology," Locke said.

RBF technology is fairly simple. Horizontal wells are built near the surface water source. Over a period of time, water flows toward the wells, traveling through sediment along the riverbank. The sediment filters impurities, reduces turbidity and breaks down biological components in the water. The pre-filtered water is then pumped from the wells to the treatment facility. "The water is basically filtered through the riverbank, so by the time it gets to the well, it's clean and doesn't need pretreatment," said Locke.

"The concept of using a horizontal well to pull water out of the creeks is fairly novel. It's used more in Europe than in America," said John Ferguson, a hydrologist in the Water Supply and Resource Development Section of the Southwest Florida Water Management District.

As for being the first municipality in Florida to use RBF technology, Mick said that she generally likes others to try out new technologies first. "But since this has worked in other places in the world and in the country, and with the expertise of our consultants, we feel confident that this small risk is worth the financial gain in the end. We are really excited about starting an innovative project."

Green and Sustainable

The City plans to have its new treatment facility LEED-certified. This internationally recognized green building certification was developed by the U.S. Green Building Council. LEED-certified buildings feature energy savings, water efficiency, CO2 emissions reduction, improved indoor environmental quality, and stewardship of resources and sensitivity to their impacts.

Because the new plant will allow year-round water treatment, the City will be able to reduce the amount of water purchased from the regional wholesale provider, which means less pumping and less energy used in transferring water throughout the region. And it is anticipated that the RO concentrate from the water treatment plant will be treated at the City's Wastewater Treatment Plant for beneficial reuse through the municipal reclaimed water system.

Future

The RO/RBF facility is scheduled for completion in June 2012. According to Mick, "It is important to our future, important for the quality of service we give to our customer, and important financially, because it is by far the most financially feasible water supply source delivery that we could plan for our citizens."

Well alignment, layout and setbacks were carefully planned out to assure quality installation and compliance with regulatory requirements.

The riverbank filtration well was installed approximately 70 feet deep in the dolestone formation, approximately 10 feet from the northern bank of the Cocoplum Canal. Monitoring wells were installed on either side of the alignment to record groundwater levels during operation.

Construction of the riverbank filtration well used standard horizontal directional drilling equipment with a wire line control system to ensure the installation was within the production zone/fracture identified in the original geotechnical investigation.

A biodegradable drilling fluid was used to protect the environment and to make cleaning the open production hole easier.

A high-density polyethylene well casing was installed at either end of the open hole to seal the well. The casing pipe was placed in compression with drill rods and pulled back until the first casing section was in place. Once the horizontal well was completed, the wire line as-built data were plotted, reflecting a very successful installation. The riverbank well was then developed by flushing the well with water and jetting it using the drilling rods and heads already in place. The solids were removed using a suction lift pump connected to the drilling head and drawn through the open hole.

The well casing was equipped with integrally molded spacers from the manufacturer to keep the casing centered in the open hole.

An electro-fusion coupling (left) was used to hold the two sections of well casings together while the full pipe section was pulled back. Once the first section of well casing was in place, the compression assembly was disconnected, releasing the well seal and remaining casing pipe (right) to be pulled into place.

City staff, McKim & Creed (engineer), Leggette, Brashears & Graham (hydrogeologist), and Trenchless Specialties (drilling contractor) worked closely together to develop the installation approach and assure its success. "This is our first experience working with McKim & Creed and it's been an absolute pleasure. We're looking forward to long-term relationship," said Cindi Mick, Public Utilities Director of the City of North Port.