At least 25,500 uninsured Sonoma County residents are expected to get health insurance by the end of the first year of full implementation of President Obama's health care law, county health officials say.

The figure represents 36 percent of the 70,000 county residents who have no health insurance. About 20,000 county residents will not be eligible for expanded health coverage because of their undocumented immigrant status.

During the Board of Supervisors meeting this week, county health and human services officials summarized steps the county has been taking to prepare for the last stages of the health care law, commonly known as Obamacare. Officials assured supervisors that the county is ready for what could be an unprecedented sudden wave of newly insured residents.

"We do believe we are ready," said Rita Scardaci, director of the Sonoma County Department of Health Services. "This is the beginning and it's always good to start on a strong foot."

The final components of the law take effect Jan. 1, 2014, including a massive expansion of the federal Medicaid program, known in California as Medi-Cal, and the so-called individual mandate, a requirement that most people obtain health insurance or pay a penalty.

An even more timely deadline is just three weeks away, when the state launches its Covered California health insurance marketplace. Open enrollment for Covered California begins Oct. 1 and runs through March 31, 2014.

A new coalition of local health care professionals, known as Covered Sonoma County, is expected to spearhead efforts to get people enrolled. The coalition includes employees at community health centers, hospitals, health insurance groups and county health and human services departments.

Scardaci said that an estimated 18,000 Sonoma County residents will become eligible under an expanded Medi-Cal program. The cut-off for Medi-Cal eligibility is now set at 138 percent of the federal poverty guideline. It was previously 100 percent of the poverty level.

The coalition has set a goal of getting 13,500 new Medi-Cal residents insured by Dec. 31, 2014, Scardaci said. Also, by that date an additional 12,000 local residents are expected to become insured through Covered California, which will offer subsidized health plans on a sliding scale for those making from 139 percent to 400 percent of the poverty line.

According to Covered California, a family of four with an annual household income of $31,900 could potentially receive an $11,100 tax credit toward the family's $12,300 annual premium. In such a case, the monthly premium is $100.

For a family of four earning $88,800, the annual federal subsidy would be $3,900 for a monthly premium of $700 a month.

During the Board of Supervisors meeting, county risk manager Marcia Chadbourne briefed supervisors on the impact the new health care law will have on the county as an employer.

Chadbourne said the provision in the law that requires large employers to provide health insurance to at least 95 percent of their employees — known as the employer mandate — had been postponed until 2015. She said the county government already meets that requirement.

But another provision of the law that would levy an excise tax on "Cadillac" health plans could cost the county $4.1 million by the time the provision takes effect in 2018.

"Our goal is to work with labor organizations to align our health plans with the Affordable Care Act requirements to minimize or avoid excise taxes," Chadbourne said.

A majority of county employees, about 2,700, are covered by Kaiser health plans that do not meet the "Cadillac" threshold and therefore trigger no tax, she said. But some of the county's higher wage earners are covered by the county's "self-insured" health plan, which qualifies as a Cadillac plan.

Several supervisors expressed concern about the $4.1 million excise tax and encouraged county staff to figure out ways to minimize the financial impact, which could involve negotiating a reduction in benefit levels.

(Contact Staff Writer Martin Espinoza at 521-5213 or martin.espinoza@pressdemocrat.com.)