SOUTH LAKE TAHOE - A section of a pipeline that pumps treated sewer water over Luther Pass blew a gasket Saturday night and sent between 200,000 and 400,000 of gallons of muddy water into the Upper Truckee River.
The wastewater sprayed out of a manhole from pressurized pipe behind the South Tahoe Public Utility District's Grass Lake Road pump station. The accident was likely caused by a faulty gasket or because bolts holding gasket failed, said Dennis Cocking, district information officer.
"They are doing some testing on the bolts," Cocking said. "And they've got the gasket, but it's hard to tell too much because it's pretty well torn up."
A Lahontan Regional Water Quality Control Board investigator arrived on scene Sunday at 8 a.m.
"The river was brown for a long time a number of miles downstream," said Erika Lovejoy, an environmental scientist at Lahontan, who investigated the spill. "It was pretreated wastewater, nothing like raw sewage. Sewage would be much worse from a human-health standpoint."
But the soil-laced wastewater did contain trace amounts of chlorine, ammonia, nitrogen and phosphorous which ended up in the Upper Truckee River - the largest tributary to Lake Tahoe.
Phosphorous and nitrogen can increase algae growth in the lake. Enough chlorine can kill or affect fish and other aquatic species. So far no dead fish have been spotted.
"Chlorine levels were non-detect in the river, but we still don't have the results for everything else," Lovejoy said. "There is no doubt there was sediment input and nutrient input that is going to go to the lake, but the amounts are unclear."
Much more dirt would have ended up in the river if the district's pump house, which provides power to pump the wastewater out of the basin so it doesn't get into the lake, had not acted like a dam. About 3 feet of mud and sand collected behind the building.
Cocking guessed that it will not much to repair mechanical damage caused by the gasket rupture because the pump house and pipeline were intact.
The El Dorado County Department of Environmental Management on Monday asked people to stay away from the river at least until final water quality tests have been analyzed. Those test results are expected within a day or so.
The section of line was just replaced by the district. Tests on the line had been done, and the pipeline was at the end of its first full week of operation. The last inspection was on Saturday around 5 p.m., Cocking said.
Gregory Crofton can be reached at (530) 542-8045 or by e-mail at gcrofton@tahoedailytribune.com.
