(WSB Radio) -- An underground methane gas explosion shutdown a busy Gwinnett County roadway for nearly 12 hours. 

The blast, which occurred around 12:45 p.m. Sunday, blew off several manhole covers along Lawrenceville Highway, between Mountain Industrial Boulevard and Pounds Road. 

Gwinnett Fire Captain Tommy Rutledge told WSB firefighters aren't sure where the methane came from.  He said "there are several underground AT&T vaults that have high concentrations of methane gas and there was also concentrations of methane gas found in the sewer and water system in that general area."

The Gwinnett County Fire Department worked closely with AT&T and the Environmental Protection Division to ventilate the underground vaults and monitor methane gas readings.  They used industrial fans to bring the readings down to normal levels.

Captain Rutledge said "it is unknown at this point what may have ignited the methane and caused the explosion." 

There were no structures damaged and no injuries reported.  When firefighters arrived, crews found obvious damage to three manhole covers as well as slight damage to the roadway.  Traffic is expected to be impacted during the morning rush hour commute.

The northbound lanes of Highway 29 are now open.  The southbound lanes will remain closed in an area just north of Jimmy Carter Boulevard.  Captain Rutledge said "even though the southbound lanes will remain closed during the rush hour, Gwinnett County Police are developing a traffic management plan that will allow traffic to flow in both directions for the morning commute."

Captain Rutledge said "traffic in the area will be slowed, but will be moving in both directions.  Motorists should expect a slight delay and should make travel plans accordingly.  If possible, motorists should avoid the area and take an alternate."