Byline: Marisa Lagos; Chronicle Staff Writer

The state's top environmental official has called for an independent investigation of the agency that regulates Bay Area water pollution after the botched response by Marin County officials to two spills that dumped more than 5 million gallons of raw and partially treated sewage into the bay last month.

In a letter, Linda Adams, secretary of the state Environmental Protection Agency, faults the San Francisco Bay Regional Water Quality Control Board for not immediately investigating a decision to release 2.5 million gallons of untreated sewage into Richardson Bay on Jan. 25. A larger spill occurred less than a week later.

It took the Sewerage Agency of Southern Marin several days to tell the water board the extent of the Jan. 25 incident. Emergency officials never were told about it. And on Jan. 31, it took officials about 20 hours to notify the public of a 2.7 million-gallon spill of treated and untreated sewage.

Both spills posed health risks to people using the bay, officials said. Raw sewage contains illness-causing bacteria, viruses, parasites and chemicals.

State law requires the sewage-treatment plant to notify emergency officials of any dangerous spill as soon as possible and to tell the water board within 25 hours.

Sewage plant officials did not return calls seeking comment.

In a letter to the water board dated Tuesday, Adams said the Mill Valley plant's delay in reporting the first spill is "disturbing because of the potential environmental effects to the bay through the lack of aggressive action."

She also blamed the San Francisco Bay Regional Water Quality Board for failing to immediately investigate the incident.

"This is, in my opinion, a disservice to the citizens of the Bay Area and, therefore, unacceptable," Adams wrote.

Bruce Wolfe, executive director of the Regional Water Quality Board, said he looks forward to the investigation, which not only will review his agency's procedures but also will look at how sewage plants around the region notify the public in the case of potential contamination.

State Sen. Carol Migden, D-San Francisco, said this week that she would request a legislative investigation into the incident.

"We want to look both at the notification procedures from wastewater plants in general and the procedures at our office," Wolfe said. "Obviously, the plants have a requirement in their permits that anybody causing a spill make notifications, but if they are not going to be diligent on doing that, then we need to fill the gaps."

The spills on Jan. 25 and Jan. 31 came from the Marin sewerage agency's facility and eventually flowed through a tidal marsh into Richardson Bay.

In the first instance, a worker intentionally released 2.5 million gallons of untreated sewage from an overflow pond at the treatment plant because recent storms had inundated the facility with too much water, Wolfe