A blockage on a public sewer line caused raw sewage to leak unchecked from a manhole for more than 27 hours earlier this week, spilling an estimated 23,834 gallons of wastewater and human waste in a creekbed behind several homes in Greenbrae, according to the the Ross Valley Sanitary District.
District officials notified the California Emergency Management Agency, the Marin County Department of Environmental Health, and the San Francisco Bay Regional Water Quality Control Board.
"Water testing of the area within the seasonal creek bed is being performed under the guidance of Environmental Health," Greg Norby, interim general manager of the sanitary district, said in a statement distributed Thursday Feb. 28. "Warning signs have been posted in the area."
Workers spotted the spill Monday morning and left a note for a resident, but the spill went unreported until mid-morning Tuesday.
The spill apparently started about 8 a.m. Feb. 25 at 495 Los Cerros and it was reported at 11 a.m. Feb. 26, Norby said.
"It appears the spilled sewage may have been contained on the grounds of 2 properties and within the bed of a seasonal creek behind the properties," Norby said. "However, we are still confirming this through visual inspection and water quality testing.
"Because we are still unable to confirm if or how far the spill traveled down the creek bed, we are operating under the assumption that some of the spill may have entered Corte Madera Creek or the Creekside Park marshland," Norby said.
Sanitary district workers responded to a call reporting the spill at 11 a.m. Tuesday, removed the blockage in the public sewere line, and stopped the overflow by 11:38 a.m. Feb. 26, Norby said.
"This particular line and the manhole from which the sanitary sewer overflow occurred are located in an easement behind several properties on Los Cerros," Norby said.
Cleanup of the affected properties on Los Cerros was complete by Thursday, according to Norby.
Property owners in the area "provided insight into the duration" of the spill, Norby said.
The sanitary spill had been ongoing since 8 a.m. Feb. 25, when construction workers noticed the overflowing manhole, Norby said.
The construction workers placed a note on the property owner's door, but the property owner did not immediately report the spill, Norby said.
"It was not until the property owner was advised by another party that this may be serious that the call was placed to RVSD, delaying our ability to respond by more than a full day," Norby said.
"Based on the timing of the initial call to RVSD, the removal of the blockage, and on-scene interviews, the duration of this sanitary sewer overflow was estimated to be 27 hours 38 minutes," Norby said.
"Using this information, along with a count of the properties served upstream on this line, the spill volume is estimate at 23,834 gallons," Norby said.
The blockage was caused by a structural failure within the sewer pipeline, Norby said. That allowed roots to invade the pipe and create an area where debris was caught up, creating a blockage in the line.
An investigation by the Ross Valley Sanitary District was ongoing, Norby said.
"After the investigation is complete, RVSD crews will be evaluating this line and performing appropriate repairs," Norby said.
Details may change as more information is discovered and reported, Norby said.
Norby urged all Ross Valley residents to call the sanitary district office at (415) 259-2949 if they see, smell, or hear water coming out of manholes or pipelines.
"Staff will mobilize at any time of the day or night and check to see if sewer infrastructure is leaking," Norby said. "If it is not the RVSD sewer system, our first responders with make sure that the appropriate agency is contacted."
Ross Valley Sanitary District is based in San Rafael. For more information visit http://rvsd.org.
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