The leak is also in the vicinity of four city-operated water wells near the Ventura (134) Freeway, but it did not appear to pose any direct threat to the city's water supply, Steve Cain, a representative for the Water Quality Control Board, said.
Three of the wells penetrate 200 feet deep, the other 400 feet, said Peter Kavounas, the city's water services administrator. The water level there is at about 100 feet deep, he added.
Additionally, water from those wells is pumped directly to the Glendale Water Treatment Plant, where any contamination would be found and removed anyway, he said.
Still, officials for the L.A. Regional Water Quality Control Board conceded that MTBE plumes can be difficult to fully assess until the remediation process gets underway.
The project manager for the case could not be reached for comment Monday.
Crescenta Valley Water District has had to deal with its own MTBE plume since it was discovered in 2004. Vigilant monitoring at its water wells and testing throughout the Foothill Boulevard corridor has tried to track the ever-changing size and movement of the plume there.
Plans to clean similarly contaminated soil beneath twoMobil and 76 gas stations on Foothill are underway.
Glendale water officials said no MTBE has been found in the city's water supply.
The gas additive was banned in 2003 amid health concerns, although its ill effect on humans has never been proven. As such, federal and state health agencies have rated it under secondary standards for drinking water, which regulate odor and taste.
Water officials have been using those secondary standards to enforce abatement and remediation, Kavounas said.
"The understanding is that there are likely health implications," he said.