A milky white substance discovered in Los Trancos Creek on the evening of Tuesday, Feb. 1, did not significantly infiltrate the creek, did not appear hazardous in a field test, and seems not to have killed any aquatic or riparian creatures, said Waymond Wong, supervisor of the San Mateo County Hazardous Materials and Pollution Prevention Program.
"Technically, we could consider it a toxic substance," but to be certain would require several thousand dollars in further testing, Mr. Wong told the Almanac.
A call came in at about 5:45 p.m. to the Environmental Health offices about a possible release of hazardous material near the intersection of Alpine Road and Interstate 280. Firefighters from the Woodside Fire Protection District were already on the scene when he got the call, Mr. Wong said.
Onsite testing showed the substance to be a water-based aqueous solution that was also present in the drain across Alpine Road, inferring that someone had poured it into the drain and that it had traveled through the culvert under the road to the creek, he said.
Debris in the culvert outlet slowed the flow and substantially reduced creek infiltration, Mr. Wong said.
There were no reports of dead or injured creatures, he added.
The West Bay Sanitary District responded and pumped out the drain, flushed the culvert and attended to the creek, Mr. Wong said. The next day showed no evidence of the incident, he added.
While the aftereffects of this incident appear to have been relatively benign, whoever did it violated several laws, including the federal Clean Water Act, Mr. Wong said. "You're not supposed to be (dumping) any type of hazardous substance into the storm drains," he said.
The law applies to restaurants using a parking lot to wash out oil-soaked mats or dump mop water, and auto body shops washing cars on the street.
While the county does not regulate residents' washing of cars or rinsing of oily mats, they, too, should not be doing it on impervious surfaces that can lead to storm drains, Mr. Wong said. Choose a location that can absorb the water, such as grass, he said. Soil microbes are proficient at detoxifying substances that may be toxic to aquatic creatures.