County supervisors approved an expansion of the Big West of California refinery Tuesday after nearly two years of community debate and a packed, hours-long public hearing.

The board's unanimous approval came after the company agreed to several new conditions, including one that requires an independent safety audit of the refinery's operations and equipment before the expansion can operate.

The $700 million expansion is expected to nearly double the facility's gasoline and diesel output and create 100 new jobs.

The project, which Big West has been proposing for nearly two years, became highly controversial for several months due to the company's plans to start using a highly toxic chemical called hydrofluoric acid.

Big West last month agreed to instead pursue an alternative expansion plan that would create less pollution and eliminate the use of the HF acid.

However, community concerns erupted again last week when it was revealed that Big West already uses a solution containing a 1 to 5 percent concentration of HF a couple times of year to maintain injection wells.

The news shook the trust of some groups that cheered Big West's recent decision not to use HF in its expansion. However, county planners determined that the use of diluted HF is a safe process and should be allowed to continue.