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The California EPA's Office of Environmental Health Hazard Assessment (OEHHA) released their draft PHG for arsenic that is proposed at 4ppt (or 0.004 parts per billion). It is set (technically, it is "prepared and published") based exclusively on public health considerations without any weight given to practical factors such as laboratory capability to analyze, availability of treatment systems, or costs. The Drinking Water Division of the California Department of Health Services is charged with establishing a legally enforceable MCL that is as close to the PHG as is "technologically and economically" feasible.
Even though California is required to adopt an MCL at least as stringent as the USEPA's 10 ppb MCL and do it by 2006, the California Legislature passed a law that requires the state MCL be adopted by July 1, 2004. It is not expected that utilities will be required to come into compliance with the new California MCL earlier than the federal regulation. (That law had required the PHG to be set by December 31, 2002. Publication of the draft PHG sets in motion a 45-day review period and a public workshop before it can be finalized.)
Under California law, the PHG is somewhat parallel to the USEPA's MCLG. However, for carcinogens such as arsenic, EPA is required to set the MCLG at ZERO. For various reasons, the fact that OEHHA never sets their PHGs at zero but does theoretical risk calculations to come up with a very small but finite number somehow gives that number a greater significance in the eyes of the media, environmental activist groups and subsequently the general public.
OEHHA's PHG for arsenic was set based on a theoretical one-in-a-million risk of cancer based on epidemiological studies from China, Argentina and Chile. Like USEPA, OEHHA gave little credence to an epidemiological study from Utah which showed significantly lower cancer risk. The National Academy of Science's arsenic review and guidelines were relied upon heavily. OEHHA's risk assessment was peer-reviewed by scientists in the University of California system.
CDHS is in the process of completing a series of stakeholders meetings getting input from the public on the arsenic standard-setting. The California legislation mandating the state arsenic MCL specifically requires the department to consider "emerging technologies that may cost-effectively reduce exposure to arsenic in drinking water." Advocacy organizations are pressing DHS to set the MCL at 2 ppb.
The analytical detection level for arsenic in drinking water set by the state as the DLR (Detection Level for purposes of Reporting) is 2 ppb.