It looks like there will be enough valid signatures to qualify a tunnel referendum for Seattle's ballot.

As of Tuesday morning, King County Elections said they had reviewed nearly half of the signatures submitted and about 72 percent were valid, more than enough to certify the referendum, if the trend continues.

Kim van Ekstrom, spokeswoman for the elections office, said of the 12,658 signatures reviewed through Monday, 9,139 were valid and 3,519 had been challenged.

The measure needs 16,503 valid signatures from registered Seattle voters to qualify for an election. Nearly 16,000 remain to be reviewed.

Once enough signatures are verified, the results will be forwarded to the Seattle City Clerk to certify. The clerk then will forward the referendum to the City Council for action.

City Attorney Pete Holmes last week brought a lawsuit to stop the referendum before it can be placed on the ballot. Holmes argued that it isn't legal because it concerns agreements between the city and state that are administrative in nature and therefore not subject to referendum.

The city now expects the court to take up the issue in May. The City Council must act by May 24 to place the measure on the August primary ballot.