Officials say it will take three-to-four weeks to finish removing contaminated soil and other potentially toxic debris from the rubble-strewn lots of homes destroyed by a gas pipeline explosion in Northern California.

San Mateo County officials say they've received permission from the property owners to clean the lots of 29 of the 37 homes destroyed by the fireball that erupted from the ruptured gas transmission line in San Bruno on Sept. 9.

Crews are removing three-to-four inches of soil from each lot, which will be tested for toxic substances like asbestos and dangerous metals.

Dean Peterson, director of San Mateo County's environmental health services division, says he hopes the work will give the survivors and their families peace of mind that they can rebuild in a safe environment.