MARTINEZ -- A mistake by a vendor contributed to erroneous messages being sent out to the public during a gas leak in Alamo on Wednesday, a Contra Costa Sheriff's Office spokesman said Friday.

The leak, caused by an East Bay Municipal Utility District crew striking a gas line with a backhoe about 10:30 a.m. at 3195 Danville Blvd., forced the evacuation of homes and businesses in a three-square-block area.

A Contra Costa County Supervisor said Thursday the issue traced back to an upgrade to the National Integrated Public Alert and Warning System that had not been received by the Contra Costa County Community Warning System.

Further investigation revealed that a technical error made by Alerting Solutions, the vendor for the Contra Costa CWS, caused the message to go through the county's Wireless Emergency Alert System, Sheriff's Office spokesman Jimmy Lee said.

The message was not supposed to go through that system, Lee said, because the WEA system does not have the ability to alert an audience smaller than the entire county and it can't customize messages.

Thus, alerts advising people to leave the county were sent to areas and people not affected by Wednesday's gas leak. Lee said the CWS is working with the vendor to avoid the error from happening again.

Lee also said Contra Costa's CWS is up to speed with the national IPAWS upgrade.

Contact Rick Hurd at 925-945-4789 and follow at Twitter.com/3rdERH.