A new study of Santa Monica Bay beaches by the city of Los Angeles confirms long-held beliefs that contaminated rainwater pouring into the bay from storm drains significantly increases the levels of bacteria associated with health risks to swimmers.
Water biologists sampled runoff rainwater in the surf at 17 testing stations from Topanga Beach to Palos Verdes and, for the first time, measured how frequently bacteria levels exceed safe-swimming standards. The 2 1/2-year study was performed by the biologists at the city's Hyperion treatment plant at the request of the Board of Public Works.
The study showed that levels of coliform bacteria, which scientists regard as an indicator of fecal and other contamination, increased dramatically at each of the 17 stations during rainy periods from January, 1985, through June, 1987. Rainy periods were defined as a day of rain plus the following two days, when runoff is still working its way toward the bay.
Some of the highest levels of bacteria during both dry and rainy periods were found near the so-called Pico-Kenter storm drain at the foot of Pico Boulevard in Santa Monica, which has long been regarded as one of the worst sources of pollution among the 64 storm drains that empty into the bay. County officials are currently working on plans to extend a portion of the drain 600 feet into the bay so that at least some of the runoff can be kept off the beaches.
The study found that bacteria counts near the Pico-Kenter drain exceeded the state standard 21.9% of the days during rainy periods and 4.6% of the days during dry weather.
The state considers the bay safe for swimming if levels are not greater than 1,000 coliform bacteria organisms per 100 milliliters of water more than six days a month. For purposes of the study, any measurement higher than 1,000 was counted, regardless of how frequently it occurred.
Ballona Creek Higher
The Pico-Kenter levels were surpassed only by sampling stations near Ballona Creek, which acts as a natural storm drain at the entrance channel to Marina del Rey. Rainy-day levels south of the creek exceeded the state standard 26.6% of the time. Those north of the creek exceeded the standard 23.4% of the time. During dry weather, the standard was rarely reached--less than 1% of the time at each station.
Water biologists who worked on the study said it revealed a general pattern of contamination: that bacteria levels were higher along northern beaches than South Bay beaches, with the exception of the area around the Avenue I storm drain in Redondo Beach. The biologists speculated that runoff from the Santa Monica Mountains and heavily urbanized areas on the Westside contributed to the difference. County officials also noted that a more extensive network of storm drains feeds into the north bay and that much of the runoff in the south empties into San Pedro Bay.
John H. Dorsey, Hyperion's supervising water biologist who participated in the study, characterized the findings as predictable and unspectacular to those who work with pollution problems in the bay. Water biologist Melinda S. Bartlett, who presented the study to the Board of Public Works on Wednesday, said city officials have used the testing stations for years to take samples and record the results but never separated the data into rainy and dry categories to analyze over a specific period of time.
'We've Known All of This'
"We've known all of this, we just never had anything to back it up," Dorsey said.
But to beachgoers, the biologists said, the information establishes an important statistical link between storm drains and the potential dangers associated with swimming near them. As a result, the study will probably do more to educate the public than make inroads into research on bay pollution, they said.
"The most salient message is don't swim around or near a storm drain in wet weather," Dorsey said. "The bacteria are indicators that something harmful may be present. And since we don't know what is there, we have to be conservative."
The study did not deal with nonorganic pollutants commonly associated with urban runoff--such as harmful chemicals, toxic metals and grease that is flushed into storm drains from city streets--which the city biologists said also pose an unknown threat to swimmers during rainy periods. Nor did it address pollution caused by dumping of various levels of treated sewage into the bay.
Storm drains are usually easy to recognize along the beach. They are typically made of concrete or metal pipe that abruptly ends in the sand or the surf. During rainy periods, large puddles and pools of water form near some of them. While recommendations vary, officials generally agree that swimmers and beachgoers should stay 50 yards away from drains that have material flowing from them.