WHO'LL CATCH THE RAIN? STORM RUNOFF TO BE TESTED AS POSSIBLE WATER SOURCE.

Byline: Kerry Cavanaugh Staff Writer

For a cleaner Santa Monica Bay and improved water supply, experts have been advocating projects to catch storm-water runoff and let it seep back into groundwater.

But until recently, nobody has studied whether urban runoff- with all its pesticides, lead, oil and bacteria - could taint otherwise good-quality groundwater.

``There's not universal agreement that infiltration won't impact the groundwater,'' said Suzanne Dallman, who manages the storm-water program for the Los Angeles & San Gabriel Rivers Watershed Council. ``The science really was the big question.''

Dallman has undertaken a four-year study to measure how quickly pollutants seep into the soil at sites in Pacoima, Santa Monica and South Central Los Angeles. She is trying to determine whether the soil filters out pollutants, or whether the toxics find their way into the groundwater.

Many businesses and developers are already using infiltration systems.

Since 2000, large shopping centers and new housing developments, gas stations and restaurants have been required to control storm-water runoff. One of their options is to add swathes of grass, flower beds and shrubs to collect runoff on site and allow it to soak into the ground.

Cities in Los Angeles County face dozens of strict new rules to curb urban runoff, and infiltration appears to be a cheap and easy solution to storm-water pollution.

Some water experts also estimate Southern California could cut in half its reliance on imported water by infiltrating storm water back into the aquifer. The region buys two-thirds of its water supply from Northern California and the Colorado River.

``If these measures work out, then that's an additional source of water,'' said Steven Kasower, Bureau of Reclamation planning officer for Southern California. ``But everybody involved is careful to make sure we touch every scientific base before we get really excited.''

During storms, rain hits the pavement; picks up the oil, chemicals and animal waste accumulating on the street; and carries them down the gutter and into the storm drain, which eventually empties into Santa Monica Bay.

With infiltration, there is less pavement. Grassy patches dot parking lots, and sidewalks are lined with flower beds to catch runoff and allow it to soak into the ground, rather than run straight to the storm drain.

The chemicals, heavy metals and bacteria in storm water are supposed to collect in the top two inches of dirt and decompose over time.

At least that's the idea.

``Soil captures pollutants, but it doesn't capture all the pollutants all the time,'' Dallman explained.

So Dallman is studying how storm water and pollutants move through different soils in different locations.

Dallman has set up monitoring sites at Hillery T. Broadous Elementary School in Pacoima, Imax Corp. offices in Santa Monica and a house in South Central Los Angeles built to catch all storm water on site.

Each site is equipped with groundwater monitoring wells and soil moisture gauges to track how fast storm water moves through different types of soil.

So far, Dallman and her consultants have detected copper, zinc, lead and cancer-causing gasoline additive MTBE in runoff. She intends to see how deeply those pollutants travel once seeped into the soil.

Dallman has $2.6 million from various governmental agencies through 2005.

One sponsor is the Los Angeles County Department of Public Works, which is partnering with environmental group TreePeople to develop a massive infiltration project in flood-prone Sun Valley. There, engineers are designing a system to catch the rivers of storm water and recycle it or let it seep into the ground to replenish the aquifer.

``If you can catch water where it falls, you don't have to worry about cleaning it up,'' said David O'Donnell with TreePeople. ``This flood water we're always talking about, it's water just being flushed away.''

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Photo:

Suzanne Dallman of the Los Angeles & San Gabriel Rivers Watershed Council installs a weather station at Broadous Elementary School in Pacoima Thursday as part of a study of the safety of urban runoff and storm water.

Tom Mendoza/Staff Photographer