The search continues for whatever is polluting Santa Rosa Creek on B Street near downtown.
After years of questions, city public works officials this week ripped up a part of parking lot at the corner of Ross and B streets to see if there was a leaking underground fuel tank that might be contaminating the soil and nearby waterways.
After digging a six-foot deep, L-shaped trench and sampling the soil, they came up empty, failing to find any tanks or contamination.
"We sampled the heck out of the soil and it's squeaky clean," said Andy Rodgers, president of the Sebastopol-based environmental consulting firm ECON.
That's good news for the city, which would have been on the hook for the costly clean-up of the site. The city paid about $35,000 for the work, which has been sought by regulators with the North Coast Regional Water Quality Control Board since 2007.
But it leaves unsolved the mystery of what's causing the pollution. Water quality officials have been wondering what's going on beneath B Street for years.
The area is home to some of the city's oldest buildings, many of which had heating oil tanks in their basements. Several gas stations and garages once occupied the area, which is one block east of Highway 101.
At least five other sites along B Street have been identified by the board as possibly being the source of pollution reaching the creek through the city's storm drains.
One of the most significant sites is a former Pacific Gas & Electric Company property on First Street along Santa Rosa Creek near the B Street intersection.
A manufactured gas plant operated on the site from 1876 to 1924, turning coal into gas for heating and cooking. After natural gas came to the area, the plant was dismantled and the property was later used as a natural gas distribution center. The utility sold the property in 1987, but remains involved in the clean-up.