(Sarah L. Voisin/The Washington Post)

After the longest zoning proceeding in official memory, a Montgomery County hearing examiner has recommended denial of Costco’s request to place a 16-pump gas station at its store at Wheaton Westfield mall.

Martin Grossman, hearing examiner for the Office of Zoning and Administrative Hearings, said in a 492-page report released Friday that Costco had failed to meet the burden of justification for a special exception to existing zoning in the Kensington Heights neighborhood. Among the concerns he cited were the impact of fumes from idling vehicles at the unusually large station, which would be less than 400 feet from a community swimming pool and less than 1,000 feet from a school with disabled children, some with chronic lung disease.

The matter now goes to the county’s Board of Zoning Appeals.

The proposed station has been a focus of intense neighborhood opposition since 2010, when Costco announced plans for a store, which opened in April 2013. Wheaton and Kensington residents welcomed the convenience of having a mega-discounter, the world’s third-largest retailer, nearby. But some balked at the prospect of a gas station they said would be a source of polluted storm runoff, increased traffic and noxious gas fumes. Opponents formed the Stop Costco Gas Coalition.

Costco, which operates eight gas stations at warehouses in Maryland — including in Beltsville, Columbia and Frederick — said all its stations meet or exceed state requirements.

Costco first sought the special exception in 2011, with a proposal that would have placed the station less than 300 feet from the Kenmont Swim & Tennis Club. In 2012, the Montgomery County Council, citing neighborhood protests, passed a measure requiring large gas stations to be more than 300 feet from schools and recreation centers.

Costco took a revised proposal to the county’s zoning office in April 2013. The case generated 36 hearings spread across 17 months, with more than 40 witnesses — opponents, supporters and experts — generating 9,540 pages of transcripts of testimony.