OUR MISSION: To provide our customers with high-quality, efficient and reliable water, power and sewer services in a manner that values environmental and community interests and sustains the resources entrusted to our care.
Water Quality Division
1657 Rollins Rd
Burlingame, CA 94010
T 650.652.3100
F 650.652.3142
October 25, 2022
M E M O R A N D U M
To: Commissioner Newsha Ajami, President
Commissioner Sophie Maxwell, Vice President
Commissioner Tim Paulson
Commissioner Tony Rivera
Commissioner Kate Stacy
Through: Dennis J. Herrera, General Manager
Steven R. Ritchie, Assistant General Manager, Water Enterprise
From: Andrew DeGraca, Water Quality Division Director
Subject: Chlorate Notification Level Exceedance at Moccasin, Early Intake and O’Shaughnessy Water Systems
We have prepared this memorandum pursuant to California Health and Safety Code §116455 to provide notification of confirmed detections of chlorate in the subject public water systems. The detections exceed the Notification Level established by the State Water Resources Control Board (SWRCB). Notification Levels are nonregulatory, health-based advisory levels established by the SWRCB for contaminants in drinking water for which Maximum Contaminant Levels have not been established. The Notification Level is the concentration of a contaminant in drinking water that the SWRCB has determined, based on available scientific information, not posing a significant health risk but warrants notification.
The Notification Level for chlorate is 0.8 mg/L. The California Office of Environmental Health Hazard Assessment (OEHHA) developed the Notification Level for chlorate based on animal studies that demonstrated chlorate exposure in rats caused adverse effects (noncancer) to the pituitary and thyroid glands. The SWRCB has not established a Response Level, where additional actions are required, for chlorate.
On August 24, 2022, the San Francisco Public Utilities Commission (SFPUC) was informed by our outside laboratory that the treated water sample collected from Early Intake Water System on June 8, 2022, contained a chlorate concentration of 1.1 mg/L.
Early Intake is a SWRCB permitted public water system operated by Hetch Hetchy Water and Power.
A second treated water sample was collected from Early Intake on September 6, 2022, and again sent to our outside laboratory for expedited analysis. On September 21, 2022, the outside laboratory reported the second sample contained a chlorate concentration of
0.99 mg/L. This result confirmed the detection of chlorate in excess of the SWRCB’s
Notification Level. Additional treated water samples were collected from Moccasin and O’Shaughnessy Water Systems on September 6, 2022, and showed chlorate levels of
1.9 mg/L and 1.7 mg/L, respectively. Moccasin and O’Shaughnessy are also SWRCB permitted public water systems.
Per State of California’s Health and Safety Code §116455, we are notifying you of this occurrence. We have also notified the Tuolumne County Board of Supervisors, as required by the Health and Safety Code.
The SFPUC is conducting an ongoing investigation to determine the cause of the elevated chlorate. Chlorate is not a naturally occurring contaminant and has not been detected in our Hetch Hetchy water source. It is speculated that the elevated level was from the degradation of sodium hypochlorite used for disinfection. We further believe that the degradation could have been exacerbated by a combination of long chemical storage time and high storage temperatures.
The SFPUC is reviewing existing protocols for managing water disinfectant chemicals at these facilities and will improve them to minimize chlorate formation potential. We have ordered sodium hypochlorite from a new source and have disposed of our existing stock from these drinking water treatment facilities. We will monitor chlorate concentrations as the new batches of sodium hypochlorite are deployed in each system until chlorate levels are below the Notification Level. The water systems will remain in operation while the investigation is ongoing.
A notification (attached) is being distributed to all the people served by these water systems.
Please contact me at (650) 652-3102 or [email protected] if you have any questions.
Cc: Margaret Hannaford, HHWP Division Manager
Records Management, WQD
Moccasin Records
Attachment: Chlorate Notification
IMPORTANT INFORMATION ABOUT YOUR DRINKING WATER
Levels of Chlorate have been Measured Above the Drinking Water Notification Level at the Moccasin, Early Intake and O’Shaughnessy Water Systems
The above water system s have recently experienced elevated levels of chlorate in the treated water. This is not a health emergency; however, as our customers, you have a right to know what happened, what you should do, and what we are doing to correct this situation.
What happened?
We routinely monitor for the presence of drinking water contaminants. The result of a w ater sample collected from the storage tank at Early Intake Compound Water System on June 8 th showed a chlorate level of 1.1 mg/L. This is above the California Notification Level, of 0.80 mg/L.
A second sample taken on September 6th had a chlorate concentration of 0.99 mg/L. Additional samples collected at Moccasin and O’Shaughnessy showed chlorate levels of 1.9 mg/L and 1.7 mg/L, respectively, in the treated water. The California State Water Resources Control Board has not established a response level or Maximum Contaminant Level for chlorate.
What should I do?
• You do not need to use an alternative water supply (e.g., bottled water). • This is not an immediate risk. However, animal studies have demonstrated chlorate exposure in rats caused adverse effects (noncancer) to the pituitary and thyroid glands. • If you have other health- related concerns about the consumption of this water, you may wish to consult your doctor.
What is being done?
The SFPUC is conducting an ongoing investigation to determine the cause of the elevated chlorate. Chlorate is not a naturally occurring contaminant and has not been detected in our Hetch Hetchy water source. It is speculated that the elevated level was from the degradation of sodium hypochlorite used for disinfection. We further believe that the degradation could have been exacerbated by a combination of long chemical storage time and high storage temperatures.
The SFPUC is reviewing the existing protocols for managing water disinfectant chemicals at these facilities and will improve them to minimize the chlorate formation potential. We have ordered sodium hypochlorite from a new source and have disposed of our existing stock from these drinking water treatment facilities. We will monitor chlorate concentrations as the new batches of sodium hypochlorite are deployed in each system until chlorate levels are below the Notification Level. The water systems will remain in operation while the investigation is ongoing.
For more information, please contact Chris Graham at 209-989-2132 or [email protected] Please distribute to all personnel / staff members who live or work in Moccasin, Moccasin Fish Hatchery, Early Intake and O’Shaughnessy.