Louisville Water Co., Louisville, Ky., will complete a 7,800-ft tunnel next month as part of a $50-million riverbank filtration project, the Business First of Louisville reported. The tunnel is in the final stages of construction, as crews are lining the tunnel walls with concrete, narrowing the space to 10 ft in diameter.
The tunneling process, which represents a key component of the water company’s riverbank filtration project, has taken more than a decade of planning and two years of construction.
The system’s goal is to filter water naturally using the sand and gravel layer of the riverbank, said Kay Ball, an engineer and the water company’s riverbank filtration project manager.
The water will then flow into four underground collector wells and be pumped through the tunnel to an above-ground pump station.
The entire project is slated for completion in spring of 2010, when the riverbank filtration process will replace the B.E. Payne Water Treatment Plant’s current system of pumping and treating raw water from the Ohio River.
The Payne plant pumps an average of 30 million gal per day (mgd), and it has capacity for 60 mgd.
The riverbank filtration process will have a capacity of 75 mgd, although Louisville Water will need to upgrade its treatment facility and obtain necessary approvals before it makes full use of that capacity.
Louisville Water will continue to operate its Crescent Hill Water Treatment Plant, which pumps 100 mgd. They are considering alternative treatment options for that facility.
Riverbank filtration is a “green” alternative to traditional methods, Ball said. Before being treated, bank-filtered water has the desired level of turbidity, or cloudiness, as river water that already has been treated.
Riverbank filtration also protects the water source from pathogens, herbicides and pesticides.
While Louisville Water still will run the water through the Payne treatment plant to chlorinate it, less treatment will be required.
The process should also mean fewer water main breaks because the constant temperature of bank-filtered water reduces the amount of contraction in the pipelines, and mussels and clams will not clog water intakes.
Louisville Water is the first water utility in the U.S. to combine the technologies of underground collector wells and tunneling.
Ball said the utility, a for-profit entity owned by Louisville-Jefferson County Metro Government, initially planned to build a series of 15 to 20 pump stations above collector wells.
Concerns about how the pump houses would affect the river view sent officials back to the drawing board. According to Ball, someone almost in jest suggested building an underground tunnel to connect the collector wells to one pump house on the B.E. Payne property. “It was thinking out of the box,” Ball said.
Officials talked to tunneling companies and soon realized the option was truly viable.
A group from Okaloosa County, Fla., visited the construction site in April 2008 to get a look at the technology.
Robert Renner, executive director of the Water Research Foundation, a Denver-based nonprofit organization, said Louisville likely will see other utilities visiting to better understand how riverbank filtration works.
Riverbank filtration has been used in Europe for years, Renner said, but it has not been a common practice in the U.S.
The Water Research Foundation worked with Louisville officials to research the technology. The foundation published riverbank filtration reports in 2002 and 2006, and a third report is scheduled for release this year.
Source: Business First of Louisville
