DWP Drew From Well With High TCE Level

A city well in North Hollywood, tapped for one day last month after a year of disuse, disgorged water that contained more than 85 times the state-recommended limit for a suspected cancer-causing solvent into the Los Angeles drinking-water supply.

The water containing the solvent trichloroethylene, or TCE, was pumped to the Silver Lake Reservoir before the problem was detected, said Raul Sosa, engineer in charge of water quality for the Los Angeles Department of Water and Power. But “it’s almost certain” that no excessive pollutants reached customers, he said.

By the time the water left the reservoir, it was blended with clean supplies and most of any solvent would have evaporated, lowering the concentration below the 5 parts-per-billion standard, he said.

Fault in Monitoring

Although customers were probably not affected, the incident pointed up a hazard in the DWP system of monitoring wells, Sosa said in a report to the state Department of Health Services. After the incident, on May 6, DWP changed its procedure so that water from newly activated wells is now tested for solvents almost immediately after pumping begins, Sosa said.

The well, at the corner of Vanowen Street and Beck Avenue, is in the middle of one of three zones where the natural subterranean reservoir beneath the East San Fernando Valley has been contaminated with two industrial solvents, TCE and perchloroethylene, or PCE.

About 40 of the 80 DWP wells in the area contain excessive levels of the chemicals. Many of the contaminated wells can still be pumped, but the water must be blended with clean supplies to keep solvent concentrations down.

Blending Done Daily

The blending is done each day as DWP engineers predict levels of pollution in active wells and mix the water with varying amounts of clean water to keep the final concentration of TCE below 5 parts per billion and PCE below 4 parts per billion.

When DWP engineers reactivated the Vanowen Street well, they expected it would produce water with 20 or 30 ppb of the solvent, as it had in the past, Sosa said.

Instead, the TCE concentration jumped to 440 ppb, he said.

Water officials, taken by surprise, did not blend the tainted water with enough clean water to bring the solvent level below the state standard, he said. It entered the reservoir at 6.3 ppb, according to the DWP report.

The well has not been pumped since that day, Sosa said. The reason for the dramatic increase in TCE concentration is not known. Adjacent wells have shown no similar rise in TCE levels, he said.