Carol Johnson, the park district's assistant general manager, said the pact means "the public can fully enjoy the holiday weekend in our parks this weekend."
Cliff Rocha, a park ranger who is president of Local 2428 of the American Federation of State, County and Municipal Employees, said union negotiators are recommending that members approve the new four-year contract in a vote that will take place soon.
The union represents more than 600 rangers, naturalists, supervisors, firefighters, lifeguards, clerical workers and other employees.
The park district has 65 regional parks in Alameda and Contra Costa counties.
Johnson said the two sides have been in contract talks since February and finally reached the tentative agreement about 9 p.m. Monday after what she described as "quite a long discussion" in what was to be the last mediation session.
Johnson said the contract provides a 9.5 percent salary increase to park district over four years, which she said is more than double management's original salary offer to employees in February.
She said the district initially had asked employees to contribute to their health care costs but ultimately agreed to continue paying for full family medical coverage.
However, Johnson said the union agreed to have employees contribute an additional 4 percent of their wages to help pay for their pensions, bringing their total contribution to 8 percent of their wages.
Rocha declined to comment on the specifics of the tentative agreement because the union hasn't yet presented it to its members.
But he said he believes it's a fair agreement that addresses the union's goals for wage increases and retirement and health care contributions.
Rocha said employees' take-home pay has "eroded" during the economic downturn but the new contract will allow them to "share in the recovery" that is bringing more revenue to the park district.
The union's threat to strike on Thursday and Friday wouldn't have shut down the district's parks but it would have disrupted swimming, boating and other activities at some of the parks.
The union's previous contract expired on March 31. The park district declared an impasse in contract talks two weeks later and a mediator was called in to assist the two sides.
The new contract will be retroactive to April 1.
Park District General Manager Robert Doyle said in a statement that the tentative agreement is "a fair contract that provides meaningful wage increases to our employees and employee contributions to retirement costs."
Doyle said, "We've averted a strike on the Fourth of July and can assure the public that the regional parks, campgrounds and water facilities will be open and fully-staffed."
