An air-quality panel Friday agreed to hold a public hearing on a request by the Los Angeles Department of Water and Power for a permit to build an air-stripping tower in North Hollywood to purge drinking water of chemical pollution.
The South Coast Air Quality Management District governing board had received at least six requests for a hearing from businessmen and residents near 11845 Vose St., the city-owned site where the DWP wants to build the 45-foot tower.
The board, which granted the requests during its monthly meeting at air-district headquarters in El Monte, specified that the hearing be held at night in the San Fernando Valley. But it will be early next week before a meeting place and date are set, air-district spokesman Ron Ketcham said.
An air-stripping, or aeration, tower is a device that cleanses water of volatile solvents by transferring them to the air.
In its application for an air emissions permit, the DWP says it should not be required to install controls to capture solvent vapors, although the cost of doing this might be as low as $20,000 a year.
The tower project, which would cost about $2 million, is aimed at cleaning water in wells in the eastern San Fernando Valley, which furnish about 15% of the city's water supply. Many of the wells are contaminated by small but increasing amounts of toxic solvents, particularly trichloroethylene and perchloroethylene--TCE and PCE for short.
Both compounds are dry-cleaning agents and industrial degreasers that have caused cancer in tests on laboratory animals, leading to fears that they may slightly raise the cancer risk for people chronically exposed to them in drinking water.
1 Billion Gallons a Year
An aeration tower cleans such chemicals from water by accelerating the natural process of evaporation. Water is pumped from wells to the top of the tower and blasted with air, causing a high percentage of the contaminants to leave the water in vapor form.
The tower, which the DWP hopes will be operating in about 18 months, would treat up to 2,000 gallons of water a minute, or about 1 billion gallons a year.
In the process, according to DWP calculations, the tower would emit a maximum of 20 pounds of solvent vapor a day--or up to 3.7 tons a year, most of it TCE.
The air district has severely restricted use of TCE because its vapors react with sunshine and other chemicals to form ozone, a lung-irritating gas that is the most persistent pollutant in Greater Los Angeles.
But, in its permit application, DWP says it should not have to use carbon filters to trap solvent emissions from the tower, citing an air-district cost-benefit formula.
Controls Too Costly
According to that formula, controls aren't warranted unless the cost of removing pollution is held to $4,700 a ton. The DWP says that filtering tower emissions would cost at least $5,500 a ton--or about $20,000 a year.
The DWP says the tower is needed because pollution is slowly increasing and invading more of the wells, which furnish water to customers south of the Santa Monica Mountains.
Up to now, the DWP has coped with the problem by shutting down the most polluted wells and blending the contents of others with clean water from the Owens Valley Aqueduct system. Most of the time, this has assured that water reaching customers is well below state advisory health guidelines.
But, over the last three years, TCE levels exceeded the state guideline during eight months, DWP lab data show.