Editor's note: This story includes a correction.

State regulators plan to fine the East Bay Municipal Utility District $426,000 for polluting a creek in Oakland's Upper Rockridge neighborhood last year.

EBMUD crews were working on a major pipeline replacement project near Glen Echo Creek on April 8, 2015, when a worker accidentally opened an old out-of-service water pipe, dumping more than 34,000 gallons of cellular concrete into the waterway.

The spill violated state water law, prompting the proposed fine by the California Regional Water Quality Control Board, which the local agency has agreed to pay.

"It's an expensive mistake and East Bay MUD has learned its lesson," said EBMUD spokeswoman Andrea Pook. "For us as a water agency, stewardship of the environment is our main value and our main goal and it's important to us that we fix this ... and that it doesn't happen again."

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The tentative fine comes on the heels of an investigation by state fish and game officials that determined the water district accidentally polluted state waters.

The creek is still suffering damage from the spill, and Pook says efforts to restore Glen Echo will take several years.

The East Bay Municipal Utility District's map of the areas affected by a 2015 concrete spill into Glen Echo Creek. (Click for larger image.) (EBMUD)

EBMUD's latest restoration job will include placing 8 cubic yards of rocks in the creek to prevent erosion and improve wildlife habitat, Pook said. The agency plans to monitor the health of the creek for years, she said.

The spill also changed how the water district handles some of its major infrastructure projects.

During last year's pipeline replacement work, an employee thought a valve on the 24-inch water pipe was closed when it was actually open, leading to the spill of about a dozen truckloads of cement.

Now, EBMUD requires crews to conduct air-pressure tests on water pipes before placing any material in them.

"We instituted a pressure-testing procedure which makes sure that this can't occur again," Pook said.

Because the spill was judged to be an accident, state officials decided not to file criminal charges and instead agreed to a civil settlement, according to Andrew Hughan, a California Fish and Wildlife spokesman who said his department conducts investigations into hundreds of similar incidents yearly.

The proposed penalty is the result of an agreement between several state and local agencies, including Fish and Wildlife, the California Regional Water Quality Control Board and EBMUD. The public can comment on the tentative fine for the next several weeks.

If the agreement is adopted, the penalty would go to the regional water board for water pollution cleanup, the San Francisco Estuary Institute to study water quality and the state Office of Spill Prevention and Response.

Correction: We initially reported that the proposed fine was being issued by the California Department of Fish and Wildlife. The agency proposing the fine is actually the California Regional Water Quality Control Board.

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