More Air-Stripping Towers on Way as Water Cleanup Efforts Intensify

A proposed aeration tower in North Hollywood that has raised fears about air pollution is but one of many such towers planned or already in use to treat chemically tainted ground water in greater Los Angeles.

At least 10 aeration towers are operating or have construction permits, and applications are pending for about 20 others, including several in the San Fernando Valley and eastern Ventura County, according to the South Coast Air Quality Management District and Ventura County Air Pollution Control District.

And officials expect more businesses and water utilities to seek permits for aeration towers in the coming months.

Aeration, or air-stripping, towers remove chemicals from water through evaporation. There is no ironclad rule that emission controls be installed. Whether controls are required depends on the cost in relation to pollution removed or on a demonstration that uncontrolled emissions might increase health risks for people living or working nearby.

Agreed to Use Filters

Because of complaints from neighbors, the Los Angeles Department of Water and Power recently agreed to use carbon filters to cut emissions from the tower it has proposed in North Hollywood. The tower would remove suspected cancer-causing solvents--principally trichloroethylene (TCE) and perchloroethylene (PCE)--from ground water that replenishes city drinking water wells.

PCE, commonly used in dry cleaning and metal degreasing, was the subject of a hazard alert issued Friday by state health officials to an estimated 20,000 dry cleaning workers in California who may be exposed to significant levels of PCE vapor.

According to DWP, the filters will reduce solvent vapor emissions by at least 90%--or from a maximum of 20 pounds a day without controls to a maximum of two pounds daily. The average dry-cleaning shop emits roughly 20 pounds of vapor a day, according to air quality officials.

Yet the filters would not be required, according to air district officials, because the cost is too high for the amount of emissions involved, and because a health assessment showed no significant cancer risk to people in the neighborhood.

Emission Controls Not Required

For these reasons, none of the five aeration projects that have operating permits from the South Coast air district is equipped with emission controls, according to officials with the district, which regulates air quality in Los Angeles, Orange and Riverside counties, as well as part of San Bernardino County. Similarly, many of the proposed towers probably will not be required to have emission controls, district officials say.

Whether this could pose a problem is debatable. Chemical emissions from such towers are relatively slight, usually ranging from less than a pound to 25 pounds a day, and dilution in the surrounding air is tremendous.

On the other hand, stripping chemicals from water into the air is an example of a problem environmental regulators are trying to avoid: cleansing one site or medium at the risk of polluting another.

Not an Optimum Solution

Even if the risk is minute, “It does not seem like the best way of handling something,” said Norman Gravitz, toxicologist and science adviser with the state Department of Health Services. Shifting contaminants from water to air “does not, from my personal perspective, solve a problem,” Gravitz said.

Some environmentalists also point out that tower emissions, although small, combine with trace levels of chemicals already in the air.

“We don’t need to exacerbate an air toxics problem, or create an air toxics problem where one doesn’t exist,” said Mark Abramowitz, an official with the environmental group Citizens for a Better Environment.

DWP hopes to have its tower in operation by next year to intercept a plume of TCE- and PCE-tainted water that is polluting more wells, knocking some out of service.

Officials with the cities of Burbank and Glendale, which also have some solvent-contaminated wells, said they are not planning to build aeration towers but will closely monitor the effectiveness of the DWP project.

Used by Industry

Air-stripping is also used by some industries that are under orders to clean up ground water pollution from past spills or leaky tanks. The major alternative is direct carbon filtering of tainted water, a technique that is usually more expensive because of the need to clean spent filters or dispose of them as hazardous waste.

Air-stripping “seems to be the method of choice,” said Ray Delacourt, a senior water resources control engineer with the Los Angeles regional office of the state Water Quality Control Board. “It’s a very simple technology that’s cheap, and that’s the attractiveness of it.”

At the former computer components plant of Burroughs Corp.’s Memorex unit in Westlake Village, an aeration tower is used to purge ground water of solvents, including TCE concentrations as high as 5,000 parts per billion--1,000 times higher than would be allowed in drinking water. The problem was discovered last year when the company closed the plant and removed underground solvent storage tanks, according to regional Water Quality Control Board officials.

There are no emission controls on the tower, which air district officials estimate emits only about one pound of vapor a day.

Talley Corp. in Newbury Park has begun using an aeration tower in its cleanup of ground water polluted by very high levels of TCE and heavy metals from a leaking waste pond. Tower vapors are being filtered, according to an official with the Ventura County Air Pollution Control District.

Ventura-Hayvenhurst Inc. is seeking a permit for an aeration tower that would remove gasoline from ground water at an Encino site where it is building a six-story office building. The ground water, encountered during excavation of a parking garage for the building at 16501 Ventura Blvd., apparently was contaminated by tank leaks from a nearby Mobil service station.

Rocketdyne Seeks Permit

The Rocketdyne division of Rockwell International, which operates the Santa Susana Field Laboratory west of Canoga Park, is seeking permits from the Ventura County air district for two aeration towers to treat ground water. TCE levels of up to 11,000 parts per billion have been found in water beneath the property, which is on the state Superfund list of hazardous waste sites needing priority attention.

Steve Lafflam, an environmental control specialist with Rocketdyne, said the company also is likely to seek approval from the South Coast air district to install one or more aeration towers at the company’s Canoga Park production complex, where ground water tests have revealed benzene, PCE and TCE concentrations of up to 26,000 parts per billion.

Air quality officials in Ventura County have said they will require emission controls on the towers at the Santa Susana lab, Lafflam said. Rocketdyne also would install vapor capture equipment on any tower at the Canoga Park site, whether or not the South Coast district required the controls, he said.

Officials with the South Coast district said they require emission controls on new pollution sources unless the cost of the equipment exceeds certain guidelines. For organic compounds such as TCE and PCE, the main test is whether the cost of controls exceeds $4,700 for each ton of pollution removed, according to air district officials.

Such a cost-benefit test is easily met for large pollution sources, said Robert C. Murray, senior air quality engineering manager for the South Coast district. But for small pollution sources, such as aeration towers, the cost-benefit guidelines are often not met.

In such cases, Murray said, emission controls would be required only if calculations showed a health risk from long-term exposure.

In the past, South Coast air district officials have said they might consider revising their approach if cumulative emissions from aeration towers significantly increased. No such revision, however, is under consideration, district officials said.

Dick Johnson, engineering section manager for the Ventura County air district, said the district also weighs economic arguments. But, he said, the district is not locked into a cost-benefit formula and would normally require controls on aeration towers.