A public hearing is set for Wednesday in San Bernardino County to review a state report on the health problems from drinking contaminated water that came from wells in the 1980s.
The concern covered possible exposure dating back to the '80s from "well 22" in the West Valley Water District.
For years, the well, originally drilled by the federal government, was thought to possess high levels of perchlorate.
State officials now say that danger was overstated.
"I'm hopeful they're going to back away from saying it was as severe as maybe they thought it was," said Antony Araiza, General Manager of the West Valley Water District. "I don't believe it was as severe as they first brought out in the report."
The initial problem started when the U.S. military used the site to store and test munitions.
Perchlorate is used as a propellant in those weapons.
But the chemical seeped into the ground water table that supplies 60,000 people in Rialto, and another 50,000 in the surrounding area.
"If you're exposed to it for long periods of time like through your drinking water, there are apparently health risks associated with that, like thyroid problems and things like that," said UC Riverside chemist, Dr. Chris Bardeen.
State investigators say they based an August draft report on a worse case scenario that the concentration of perchlorate was high because the water in well 22 wasn't mixed with other water.
New information from the water district shows the water from well 22 was blended with cleaner water from six other sources.
And the risk of contamination is low, significantly dropping the likelihood of adverse health effects.
"It was a dynamic system that was fed by several wells and water from our Lila Creek area which is the most pristine water," said Araiza. "So there was always a blend of water in there."
State department health officials say there's no exposure to perchlorate in the drinking water now.
State officials will present the updated report with their new findings in Rialto on Wednesday and ask for public feedback.
A final report is due out next year.