Orange County Water District (OCWD) is using four full-scale versions of its patented Basin Cleaning Vehicle (BCV) hood technology to clean its percolation lakes.
OCWD's cleaning method is unique in that a BCV hood -- similar to a swimming pool cleaner -- cleans the lake while it is full of water.
Traditional methods involve emptying the lake, drying it out and scraping the bottom with heavy equipment to remove one-quarter to one-inch thick clogging layer. The four new barge-like BCV's cost $4 million and are projected to help increase the amount of water available for Orange County residents.
"In a tight urban environment like Orange County, we have been forced to push the envelope to find new ways to put more water into our groundwater basin," said Board President Denis R. Bilodeau. "Since it is difficult and expensive to obtain additional land to build more percolation lakes, developing the BCV significantly increases the efficiency of our existing lakes and is a very innovative and remarkable achievement."
OCWD's percolation lakes act as both a filter and funnel to replenish Orange County's deep groundwater basin with Santa Ana River water and imported water from the Colorado River or Northern California. The groundwater stored beneath Orange County is later pumped out by retail water agencies that provide that water to more than half of Orange County's citizens.
As the water is filtered by the sand and gravel at the bottom of the lake, the clay and silt in the water collects at the bottom. Under the pressure of millions of gallons of water in the lake, the silt is compacted to form a thin "clogging layer" -- similar to concrete -- that stops or slows percolation into the groundwater basin below.
"We started a six-month percolation study in January of this year to document the specific impact of operating the new shallow lake BCVs on groundwater percolation rates," said OCWD General Manager Virginia Grebbien. "Previous full-scale tests in 2001 and 2002 in another basin not only showed a 30 percent increase in percolation, but also that a basin can operate perhaps twice as long before needing cleaning in the conventional way."
After ten years of research and development, OCWD is now using two models of the BCV -- one to clean deep lakes and one for shallow lakes. The shallow lake version -- recently installed in four lakes and currently being tested -- are towed along the lake bottom by a cable system, while the deep lake model, still under development, can actually drive itself back and forth along the lake bottom using a global positioning system (GPS).
Both versions of the BCV stir up the clogging layer at the bottom of the lake and pumping the clay and silt ashore. Since percolation lakes are used to replenish many groundwater basins around the world, this new, patented BCV technology has potential global application.