By Hub-LA.

What do dairy farms, landfills, and giant heaps of decaying food have in common? Culver City’s big green buses, which are getting even greener and running cleaner thanks to all that dirty waste.

In the coming months the city will begin using renewable natural gas, or RNG, to fuel its already low-emission natural gas fleet including its buses, trash trucks, and utility vehicles.

Transportation director Art Ida announced the decision to incorporate RNG last year and the transition will be complete by summer. The fleet has run solely on compressed natural gas since 2004, but he acknowledged that the fuel still has sustainability problems.

“One of the comments about … getting [compressed natural gas],” he said. “Is fracking and going down and digging.”

Traditionally, natural gas has been harvested from underground geologic formations often trapped in layers of rock through a process called hydraulic fracturing, or fracking. It involves injecting water, chemicals, and other material at extremely high pressure into the deposit to fracture the rock and release the gas.