Island County has given the Federal Emergency Management Agency, or FEMA, the first evidence that the agency erred when it revised flood-risk maps this summer, Hiller West, director of current-use planning and community development, told the county commissioners during a work session Wednesday.

The county now wants FEMA to extrapolate from that evidence, which pertains only to two sites on Whidbey, and agree to reexamine its conclusions about the entire county, at its own cost.

The alternative — paying an engineering firm to study each of the many county shoreline areas that FEMA recently declared to be flood zones — would be too burdensome and costly, the commissioners worried.

West said he would relay the extrapolation request to the FEMA office in Lynnwood, where the decision would be made. He also agreed to invite FEMA to a meeting with the commissioners. That meeting could include Coast & Harbor Engineering, the Edmonds engineering firm the county hired for $43,000 in late 2015 to perform the initial studies.

The new maps, which were issued free to any waterfront homeowner who requested one, show the elevation that one would have to build at to avoid flooding during the most violent storm likely to occur within a 100-year period, a so-called 100-year flood.

Areas that received “questionable” flood-hazard designations from FEMA include Glendale, Hidden Beach, Possession Beach, Sandy Point and Sunlight Beach, according to a presentation made in September by David Simpson, an engineer with Coast & Harbor, to a group of Realtors.

But the new maps also show flood areas on the east side of Whidbey and the west side of Camano — inclusions that West has described as “so counter-intuitive that they suggest there’s a problem” with FEMA’s modeling.

The only permissible basis for appeals of FEMA’s determinations is information indicating the determinations are “scientifically or technically incorrect,” FEMA has said.

Unless the county wins area-by-area appeals — or FEMA agrees to a county-wide reassessment of its conclusions — the county eventually must adopt floodplain-management measures based on those conclusions in order to remain qualified for the National Flood Insurance Program. A county must be qualified in order for its residents to buy flood insurance from that program.

Some federally backed mortgages require federal flood insurance, though flood insurance is also available commercially. The commissioners have emphasized how costly the new maps could prove for property owners who formerly faced no flood risk. Island County this past summer sent postcards to 4,260 residents who it said might be affected by the changed maps.

Today, however, only 1,015 island residents appear to be using the federal flood-insurance program.

In zip codes 98278 and 98277, only 40 federal flood-insurance policies are in force, with an average annual premium of $595, FEMA said. In zip code 98260, five policies are in force, with an average annual premium of $893.

Zip code 98239 has five policies in force, at an annual average premium of $1,013. And the island’s other zip codes — 98253, 98249 and 98236 — combined have 965 policies, at an average annual premium of $1,293.