PG&E has a 100-year-old problem on its hands. Waste products from the messy process of creating manufactured gas — the fuel used to power lamps back at the turn of the 20th century — still exist in underground storage tanks in downtown Santa Rosa. Worse still, the tanks are in an area near Santa Rosa Creek.

One particular problem is a 10,000-gallon steel tank filled with coal tar that sits beneath the site of a manufactured-gas plant that operated from 1876 to 1924 on First Street near Santa Rosa Avenue. Some of the contamination, but certainly not all of it, was cleaned up when a four-story office building was built on the site in 1989.

The challenge now is figuring out how to get the rest of the messy stuff out of the soil.

PG&E, which has taken financial responsibility for the cleanup and says it has spent $10 million on the mission to date, had proposed building a 300-foot cutoff wall to channel and treat any contaminated groundwater from the property. But construction would require rerouting Santa Rosa Creek and shutting down and dismantling sections of the Prince Memorial Greenway, the bike and pedestrian path along the creek.

The utility is now looking at alternative plans that would not require such a disruption while still ensuring the protection of groundwater. PG&E officials presented an overview of the alternatives this week, including the possibility of constructing two smaller concrete walls that would be built next to a retaining wall that was installed as part of the construction of the Prince Memorial Greenway nearly 10 years ago.

The key question is whether the sludge that exists in the soil is mobile. PG&E contends, because of the thick nature of the material and the soil, it's not.

Council members, who did not take a vote, wisely showed some skepticism about going to an alternative plan. But PG&E deserves a chance to make its case, particularly if it means there will less disruption to the path — and to the soil — in the area while still ensuring the protection of groundwater.

Any alternative would have to be approved by the North Coast Water Quality Control Board, which is hardly prone to letting responsible parties take the easy way out when it comes to protecting groundwater.

Santa Rosa should keep an open mind as to the right solution, at least until the water board weighs in on the matter.