Groundwater contaminated from past fuel tank leakage is thought to be responsible for combustible gas recently detected in the sewer system near 23rd and Alabama streets, a state geologist said Tuesday.
The contaminated groundwater is near the Total gas station along 23rd, west of Alabama, said Dan Wells, an environmental geologist for the Kansas Department of Health and Environment. The tank currently in use by the station is not leaking.
A KDHE crew was boring small holes in the ground at the site Tuesday, taking soil samples. The contaminated water, between Total and O'Reilly Auto Parts, was pooled close to a concrete stormwater box buried underground and sitting on top of 4 to 6 inches of crushed rock, Wells said..
The box was installed by the city of Lawrence in 1977 to collect stormwater runoff and direct it into the sewer system.
"We think that's where the source is, and now we just need to prove it," Wells said.
High levels of combustible gas initially were discovered more than a week ago by Lawrence Utility Department crews conducting a routine sewer inspection. The high levels re-emerged at least twice last week. The gas always dissipated when firefighters from Lawrence-Douglas County Fire & Medical flushed the sewers.
The next step is to dig a trench along the east side of the stormwater box to interrupt the flow of the contaminated water to the box, Wells said.
KDHE will install equipment that will, over a period of time, exfiltrate the gas from the water, Wells said. The equipment will be housed inside a box the size of a dog house or small storage shed, he said. It will be left in place until KDHE is convinced the gas is gone.
How long the process will take is not known, Wells said.
"It could take a couple of years," he said.
Firefighters have not been called back to the area to flush the sewer system since late last week, Chief Jim McSwain said.
The process of finding the source of the gas has been difficult. KDHE officials said there have been several gasoline stations along 23rd Street that no longer exist and have been taken over by other businesses.
"There were too many possibilities," Wells said.