Saying they are doing so only to reassure the public, city water officials have decided to filter chemical vapors that would be emitted by the aeration tower they plan to build in North Hollywood to clean up solvent-tainted well water.
Rick Caruso, vice president of the Los Angeles Board of Water and Power Commissioners, said the decision to run tower emissions through carbon filters was made Thursday during a discussion among members of the Board and the staff of the Department of Water and Power.
Caruso said Water and Power officials remain confident that the amount of uncontrolled emissions would be too low to endanger the health of people nearby. The decision to use filters, which would trap 90% of the vapors, "is really more of an act by this department to make the people feel more comfortable about having that tower" in the San Fernando Valley, Caruso said.
Carbon filtration, which department officials said Thursday will add $100,000 to the cost of the $2.2-million project, is a "worthwhile investment if it makes the public feel more secure," Caruso said.
Despite the relatively modest cost of controlling emissions, department officials up to now have balked at the idea because they believed it was not needed.
The project would be built on city property at 11845 Vose St. and could be operating by late next year.
The 45-foot tower would treat 2,000 gallons of water a minute from Valley ground-water supplies that have been contaminated by suspected cancer-causing solvents, particularly trichloroethylene (TCE) and perchloroethylene (PCE). Water drawn from the ground would be pumped up the tower and blasted with air, causing most of the solvents to evaporate.
TCE Levels Above Limit
TCE levels in many Valley wells exceed state advisory health standards. As a result, the DWP is diluting some of the tainted water with cleaner water but has had to shut down the most contaminated wells.
Solvent levels in the water are in the parts-per-billion range. Without controls, the aeration tower would emit airborne vapors in the parts-per-trillion range, according to DWP data. The maximum emissions, according to the DWP, would be 20 pounds of solvents a day, about the amount given off by the average dry-cleaning shop.
Thursday's decision is a victory for critics of the proposal, who turned out in force last week at a public hearing in North Hollywood. The hearing was sponsored by the South Coast Air Quality Management District, which is expected to issue the DWP an emissions permit this summer.
Transfer of Pollution
Environmental activists and a number of North Hollywood residents and politicians testified that the project would merely transfer pollution from one medium to another. In light of the overwhelming opposition, Caruso said, DWP officials decided they should be "responsive to the people who are out there in that area and go the extra mile in allaying" their fears.
Air district officials had indicated that they would issue a permit for the project without emissions controls, because there was no evidence that vapors from the tower would pose a significant health risk.
State health officials who reviewed the DWP data had said that living and working for years next to the tower would not increase a person's risk of getting cancer by more than one chance in a million.
The use of emissions controls is certain to neutralize some opposition but will not appease all opponents. Some critics have called on the DWP to scrap the tower in favor of direct carbon filtration of the tainted well water. DWP officials have said this alternative is more expensive and that the used filters may create a toxic disposal problem.
The DWP previously estimated the cost of filtering air emissions at $20,000 to $30,000 a year, not including installation. Officials said Thursday they believe the annual cost, counting installation, will be $50,000 to $100,000.
Caruso said the DWP commissioners will hold their own public hearing on the proposal at 7 p.m. June 10 at DWP headquarters downtown.
On June 12, the board is scheduled to decide whether to issue a "negative declaration"--essentially a statement that a comprehensive environmental review is not needed.
The aeration tower has been proposed as a way to deal with the spread of chemical contaminants to an increasing number of Valley wells. Eventually, the spread of polluted well water could be a serious constraint on use of this supply.
15% of City Water
Valley wells furnish 15% of the city's drinking water and are counted on more heavily in dry weather. Ironically, water from the wells is piped over the Santa Monica Mountains to be used in almost every part of the city but the Valley.
In a related development, DWP officials said this week that they have launched a $200,000 project to regain use of some highly contaminated wells by sealing off pockets of dirty ground water.
The effort involves installation of devices similar to inner tubes, called "well packers," in 13 North Hollywood wells that have not been pumped in recent years because TCE levels range from about 30 ppb to 235 ppb--far above a state advisory health limit of 5 ppb.
According to DWP officials, the well packers will allow water to be drawn almost exclusively from deep-water zones that are fairly clean and will block dirtier water in upper layers from flowing through the wells.
Laurent McReynolds, assistant chief engineer for the water system, said the well packers, which are expected to be installed by July, should allow drawing of water that can at least be blended to meet health limits.