About 3.5 billion gallons of contaminated water have been pumped from the 1-by-3-mile toxic plume beneath the former base.
Despite these reassurances, members of the council and the public voiced doubts during the meeting.
Councilman Steven Choi expressed concern over the length of time in which the plume clean-up would take.
"Forty years is a long time," Choi said. "It is my concern that what happens if it stays stagnant or travels to drinking water?"
John Hills, director of water quality for the Irvine Ranch Water District, assured the council and community that water is being pumped from the plume at a rate to prevent the chemical plume from spreading.
Additionally, the treated water has no detectable traces of TCE and is used for nondrinking purposes, such as watering greenbelts, he added.
However, well-known environmentalists, including Roger Butow of Laguna Beach, questioned whether the public has been properly kept in the loop in the process.
Councilwoman Christina Shea pressed for transparency during the ongoing clean-up process and disclosure of reports between the city attorney's office and URS, an independent environmental consultant retained by the city.
"I believe in transparency," Shea said, "especially when it involves real or perceived health risks to the public."
Richard Montevideo, an attorney from Rutan and Tucker, which represents the city, said that it was in Irvine's best interest to keep some dealings with URS privileged.
"You have to protect your client's interests and the outside world is not entitled to know what your lawyer's legal thoughts are," Montevideo said, and added that a consultant is the legal arm of the lawyer. "Second, you don't want a draft memo to be disseminated because it's a work in process and that creates confusion."
Drafts and reports from URS will be made available to the public once the city attorney's office has provided advice, Montevideo said.
After expressing dissatisfaction with the answers provided, Shea called for an immediate meeting between council members and city staff as early as next week.
"I think it would be of value to have much more regular updates," Shea said. "I feel that a lot goes on at the staff level that is missed by policymakers, and I feel that's not the right avenue to be traveling down."