Push on for Tower to Aid Water Cleanup

The Los Angeles Department of Water and Power is pushing ahead with plans to build an air-stripping tower in North Hollywood, a project heralded by department officials as “the first step being taken by the city to clean up and prevent the further spreading of ground-water contamination.”

An air-stripping, or aeration, tower is a device that strips chemical solvents from water by accelerating the natural process of evaporation. Water is pumped from wells to the top of the tower and blasted with a stream of air, causing a high percentage of these volatile chemicals to leave the water in vapor form.

The $2-million project would be built on DWP property at 11845 Vose St., about half a mile north of another proposed site that sparked controversy earlier this year.

The DWP has applied to the South Coast Air Quality Management District for a permit to operate the tower and hopes to have it running in about 18 months.

Hearing May Be Called

DWP officials will hold a public meeting on the project at 7:30 p.m. Tuesday in the auditorium of the Fair Avenue School, 6501 Fair Ave., North Hollywood. The air quality district’s governing board is expected to decide on Dec. 6 whether to call a public hearing before taking action on the permit request.

DWP wells in the eastern San Fernando Valley provide about 15% of Los Angeles’ drinking water. Many of the wells are contaminated by low, but increasing, levels of solvents, particularly trichloroethylene and perchloroethylene, or TCE and PCE. These chemicals, used extensively for industrial de-greasing and dry cleaning, have caused cancer in laboratory animals and may slightly raise the cancer risk for people exposed to low levels in drinking water over a long period of time.

Because solvent levels have increased in recent years and the pollution is spreading to more wells, “we have reached the point where we must implement cleanup measures with a sense of urgency,” said Duane L. Georgeson, DWP assistant general manager for water, referring to the air-stripping tower.

The DWP’s Valley water wells normally do not serve Valley customers, but instead supply water to areas of central, eastern and western Los Angeles and as far south as Los Angeles Harbor. According to the DWP, as many as 1 million of the 3 million people it serves get at least some of their water from the Valley wells.

State advisory health standards restrict the amount of TCE in drinking water to less than 5 parts per billion. The state limit for PCE is 4 ppb. Scientists estimate that persons drinking water containing that much pollution over a lifetime would raise their risk of getting cancer by one chance in a million.

By shutting off the most polluted wells and blending others with clean water from the Owens Valley Aqueduct system, the DWP says it has been able to keep its customers’ water below the advisory levels most of the time.

Pollution Limits Exceeded

However, some customers were supplied water that exceeded the TCE limit during eight months over the last three years, according to DWP laboratory data regularly filed with the state. In September and October, for example, when the DWP increased use of the Valley wells because of repair work to the aqueduct system, average TCE levels in a supply conduit serving about 600,000 people were 5.9 ppb the first month and 10.4 ppb the next.

DWP officials point out that levels at the tap probably were lower because of solvent evaporation during reservoir storage. Moreover, they contend, the advisory levels were based on the assumption of long-term exposure, which has never occurred.

The proposed aeration tower would be about 45 feet tall and would treat as many as 2,000 gallons of water per minute, or about 1 billion gallons per year, Laurent McReynolds, assistant chief engineer for the water system, said. McReynolds said the price of the tower will be about $300,000. The remainder of the $2 million will be used to drill wells and install collector lines, pumps and related equipment.

The proposed Vose Street site, a DWP storage yard, is in a largely industrial neighborhood with some homes and apartments nearby. Original plans called for use of DWP property at 11850 Vanowen St., North Hollywood, which is ringed by homes and apartments.

Residential Site Abandoned

The DWP had obtained an air quality district permit for that location but decided not to use it by the time its plans became widely known last spring. The utility said it abandoned the Vanowen Street site because of “aesthetic considerations,” not health concerns.

Although the DWP scrapped the site on its own, state Sen. Alan Robbins (D-Van Nuys) and some North Hollywood residents assailed the DWP and the AQMD for making a decision without public hearings.

In April, Robbins introduced a bill to ban air-stripping towers within 100 meters of residential property. The measure was weakened and, as signed into law, requires the DWP to inform property owners within 100 meters of a planned aeration tower of their rights to ask the air quality district for a public hearing. McReynolds said property owners near Vose Street have been notified.

DWP officials say the solvent levels in the air near the tower would be too low to create a health risk. They say the solvents, while present in the water at parts-per-billion concentrations, would be at parts-per-trillion levels in the air around the tower.

Data submitted by the DWP to the air district shows that at the most, the tower would emit about 20 pounds of solvent vapors each day, or about 3.7 tons per year--most of that TCE.

Ozone-Producing Vapors

TCE vapors, even if too diluted to be toxic, can react with other chemicals and sunlight to form ozone, a lung irritant that is the most widespread pollutant in the South Coast Air Basin. Because TCE is so reactive, the air-quality district has adopted rules severely restricting its use.

According to DWP figures, the cost of filtering solvent emissions from its tower would be about $20,000 per year, not including installation. But the DWP says it should be spared the effort because air district guidelines do not require that much expense.

Those guidelines call for carbon filtering if solvent vapors can be removed for less than $4,700 per ton.

But according to the DWP, the filtering cost for its project would be at least $5,500 to $5,800 per ton of emissions removed--about $20,000 per year.

Therefore, the DWP application says, the use of the “emissions-control equipment is not cost-effective and therefore not required.”

Mandatory Filtration Unlikely

Robert C. Murray, senior engineering manager with the air quality district, agreed that air filtration normally is not required unless the cost is within the guidelines. He said an exception could be made if there were a toxic-exposure hazard to people nearby. But, Murray said, while the application is still being reviewed, it is unlikely that any toxic risk can be shown to exist. Therefore, Murray said, it is unlikely that the DWP will be required to filter the air.

McReynolds said the DWP would not hesitate to install filters “if there’s a significant improvement to be made.”

But, he said, the tower emissions without filtering would be insignificant--about the same amount of solvent vapor that escapes from dry-cleaning establishments.

Murray confirmed that the average dry cleaner produces similar emissions--roughly 18 pounds a year. But dry cleaners generally use PCE, which does not readily react to form ozone. In contrast, the air-stripping tower would mainly give off the highly reactive TCE vapors.

More Tower Proposals Expected

According to air district records, there are 19 air-stripping towers proposed or in operation in the South Coast Air Basin, which includes Los Angeles, Orange and Riverside counties and a portion of San Bernardino County. Maximum daily emissions from these towers is about 115 pounds, a small fraction of the area’s total solvent pollution.

However, other water utilities and industries that have polluted ground water are likely to propose new stripping towers in the next several years.

“We’re seeing more and more of them,” Murray said. “It wouldn’t be inconceivable that the district would find the need to pass a regulation relative to control of water strippers.”