Neabsco District Supervisor John Jenkins last week named Ben Chavez, a productions manager at S&J Industries, to replace Chris Thomaidis on the county's Planning Commission.

Jenkins had often publicly expressed his desire to replace Thomaidis, whose term expires Dec. 31. He said last week that Thomaidis was not "responsive to the community or to me." Thomaidis, who has served on the Planning Commission for 12 years, several of them as chairman, was appointed by Jenkins' predecessor, Jim McCoart, who resigned in 1982.

"I opposed Jenkins in the race to finish McCoart's term of office and I don't think that sat well," Thomaidis said.

Thomaidis said he is disappointed in what he sees as a "development-at-all-costs board" and said he doesn't think he wanted reappointment to the commission. "I'd rather be on the outside taking shots at them."

Chavez, a former administrator for the Dale City Sanitary District, resigned from the county's Industrial Development Authority to take the Planning Commission post. Donald Chendorain resigned from the Dale City Sanitary District board to accept the post vacated by Chendorain. Patricia Cosand, a Dale City resident who led the unsuccessful fight to retain a popular Gar-Field high school principal after he was abruptly transfered to Osbourn Park in June, will replace Chendorain on the Sanitary District board.

In other business, the board approved the hiring of an Arlington firm to study potential risks from air emissions from a Woodbridge fiber glass plant that residents say are causing lung problems and skin rashes. Although recent tests show that United Fiberglass is operating within state-approved emissions limits, the board said that the plant's emissions may still be a health risk.

County Attorney John Foote will negotiate a contract with Clement Associates to determine whether emissions from the plant's twin stacks are enough of a health risk to require local air pollution control regulations. The State Air Control Pollution Board said the plant's emissions were well within allowable limits, but residents of the nearby Featherstone community continue to call county officials with health problems they say are due to fiber glass particles, too small to be seen, that they claim get into the lungs and under the skin.

The U.S. Environmental Protection Agency has not declared fiber glass a hazardous substance, officials said. According to deputy county attorney Stephen MacIsaacs, state air control officials intend to work with the county until the issue is resolved. The study, which will take about four months, is expected to cost $25,000.

In other business, the board agreed to ask the county delegation to the General Assembly to change the length of time an offense is prosecutable. Under current law, according to Foote, the county has been forced to hold a felony warrant for 15 years and a misdemeanor warrant for five years, even though witnesses or victims can no longer be found or are dead and evidence has deteriorated. Under the proposed bill, there would be no limit for holding a warrant. County investigator D.L. Cahill told the board that if a case is no longer prosecutable the warrant should be destroyed after one year; if it remains prosecutable the warrant should remain open.

The board also:

*Approved a 1,460-unit development near Lake Ridge.

*Authorized $50,000 to the county park authority for general park improvements.

*Heard a report from auditors from Arthur Anderson Inc. that the county's books are in good standing and its fiscal management is sound.