New Arsenic Treatment is Online
Arsenic is an element that is found in combination with other substances to form many different compounds. When present in food and water, its concentration is expressed in micrograms per liter (mg/L), or parts per billion.
Inorganic arsenic compounds are found in soils, sediments, and groundwater, and can occur either naturally or as a result of mining, ore smelting, and other industrial uses. In the past, inorganic forms of arsenic were used in pesticides, paint pigments, wood preservatives, and as a medicinal. Usage of arsenic-containing products today is mostly restricted.
Inorganic arsenic has been recognized as a human poison since ancient times, with large oral doses in food and/or water (above 60,000 mg/L) producing death. Ingestion of moderate to elevated levels of inorganic arsenic (greater than 300 mg/L) may cause irritation of the stomach and intestines, with symptoms such as pain, nausea, vomiting, and diarrhea. Ingestion of arsenic has also been reported to increase the risk of cancer in the liver, bladder, kidney, lungs, and skin. As a result, California revised its Maximum Contaminant Level (MCL) for arsenic in drinking water from 50 mg/L to 10 mg/L back in November 2008.
As you may know, the District’s primary source water is groundwater from the pristine Mt. Tamalpais watershed. Naturally occuring arsenic deposits are present in this watershed and when groundwater comes into contact with those deposits, some arsenic ends up dissolving into the water. The District conducts regular and robust water quality testing in all its raw and treated water. In some raw water sources, arsenic has been found at levels as high as 14 mg/L, which is above the State’s MCL.
In the past before we had the ability to treat for arsenic, we would blend our raw water sources so the resulting treated water delivered to you would always have an arsenic concentration below the MCL. This often resulted in a restriction of how much water could be drawn from certain wells. Recently, the District installed and commissioned a new arsenic treatment system at the water treatment plant that now removes any arsenic present to below the MCL and allows us full capacity at all of our wells.
For more information on Arsenic:
- Agency for Toxic Substances and Disease Registry, Public Health Statement for Arsenic: http://www.atsdr.cdc.gov/toxprofiles/phs2.html
- California Water Boards Groundwater Fact Sheet on Arsenic: https://www.waterboards.ca.gov/water_issues/programs/gama/docs/coc_arsenic.pdf
Rules Regarding Your Backflow Prevention Device
“Backflow” is a term the District uses to describe the undesirable reversal of flow and possible contamination back into a public drinking water system. A backflow prevention device is a testable and repairable in-line assembly that is used to keep undesirable water from entering the drinking water system during a backflow event. In layman's terms, it's essentially a device that stops water from flowing backward in your pipes and into the public water supply. These devices are essential to protect our drinking water system from contamination or pollution due to backflow, and must be tested annually, so please make sure they are easily accessible and free of obstruction.
The District’s Title III – Water System Management Code (“Code”), was recently updated by Ordinance 2024-03 in December 2024. Section 3.07.010 of the Code requires that all new and existing water service connections from the District must have a backflow prevention device installed. Section 3.07.300 of the Code also states that it shall be customer’s responsibility, at their own expense, to provide and install a new backflow prevention device in accordance with District standards at a location approved by the District. Installation must be performed by a licensed plumbing contractor and is subject to District inspection, testing and approval following installation. The customer will retain full ownership and responsibility of their backflow prevention device.
District staff are now starting to inspect properties for backflow prevention devices as part of your regular OWTS inspection. Installation of a properly installed device is a condition of continued water service from the District.
For more information, please visit:
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