DWP to Try Natural Filter for Reclaimed Water

Los Angeles Department of Water and Power officials launched a test program Wednesday to determine if the filtering action of the soil--the principle that cleans the Earth’s water in natural springs--will work as well on the city’s reclaimed sewage.

As the officials looked on, water gurgled from a pipe into a brush-filled basin near Griffith Park, initiating the Headworks pilot project.

The $800,000, two-year study is meant to support efforts to use reclaimed water from the city’s sinks and toilets for up to 10% of the city’s supply--not just to irrigate fairways and parks, as in most current water reclamation projects, but to replenish aquifers tapped by city drinking water wells.

Early Wednesday, DWP officials inflated a black rubber dam across the bottom of the Los Angeles River’s concrete channel near the Ventura Freeway and Forest Lawn Drive. The dam partially blocked the flow of the river, at least 80% of which is discharge from the Tillman Water Reclamation Plant in the Sepulveda Basin.

Water pumped from the river took at least 30 minutes to flow through 1,000 feet of galvanized steel pipe and begin soaking weeds and wildflowers in the Headworks spreading grounds, a nearby series of dry, shallow basins.

About 750,000 gallons of water per day will be diverted from the river to the spreading basin and allowed to percolate into the ground. The water will slowly seep in the direction of the river, and in six months to a year reach an extraction well that will pump it out to return it to the river.

The water will undergo laboratory tests both when it is pulled from the river and again when it is returned, measuring the cleansing power of soil bacteria and subsurface sand and gravels. DWP officials hope the tests will show that reclaimed water filtered through soil becomes fit to drink, or would be with minor additional treatment.

Department officials said that if the results are favorable, they may be able to divert large amounts of Tillman water that now flows to the ocean. The water could be spread in the Headworks basin to sink into the ground and replenish city water supply wells near Griffith Park.

According to department engineers, Tillman effluent is clean enough that it has improved the water quality of the Los Angeles River, perhaps making it possible to return the now idle Headworks spreading grounds to use.

Years ago, the department regularly diverted storm water from the river to the Headworks, but had to stop because the runoff was too dirty, said Stephen A. Ott, a waterworks engineer with the DWP.

“When it rains, the water that runs off our surface streets” is laced with “greases and oils and pesticides that people apply to their lawns,” Ott said. The Tillman water, which receives advanced treatment, is much cleaner, he said.

Under current state health guidelines, the DWP would be required to dilute the reclaimed water with at least four times as much storm or surface water, Ott said. He said the Headworks study may show that such large dilutions are unnecessary.

Using reclaimed water to boost ground water supplies is not a new idea. Since the 1960s the Los Angeles County Sanitation Districts have been using reclaimed water from two sewage treatment plants, diluted with large amounts of surface water, to replenish aquifers tapped by cities and water districts in southern Los Angeles County.

The DWP currently operates only one reclaimed water project, using 1,000 acre-feet per year of reclaimed water to irrigate the Griffith Park golf courses and landscaping along the Golden State Freeway. One acre-foot is enough to supply a Los Angeles family of five with water for 18 months.