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Notification levels are health-based advisory levels established by the Division of Drinking Water (DDW) for chemicals in drinking water that lack maximum contaminant levels (MCLs). When chemicals are found at concentrations greater than their notification levels, certain requirements and recommendations apply. The level at which DDW recommends removal of a drinking water source from service is called the "response level."

f a chemical concentration is greater than its notification level in drinking water that is provided to consumers, DDW recommends that the utility inform its customers and consumers about the presence of the chemical, and about health concerns associated with exposure to it. To provide consumer notice, the utility may want to consider using its annual Consumer Confidence Report, a separate mailing, or other method. SOURCE REMOVAL (RESPONSE LEVEL):

If a chemical is present in drinking water that is provided to consumers at concentrations considerably greater than the notification level, DDW recommends that the drinking water system take the source out of service. The level prompting a recommendation for source removal is the "response level" of Health and Safety Code §116455, and depends upon the toxicological endpoint that is the basis for the notification level.

For four chemicals considered to pose a cancer risk—RDX, TBA, and TNT—this response level recommendation occurs at 100 times the notification level, which is established at a de minimis risk level (a theoretical lifetime risk level of 1 X 10-6, or up to one excess case of cancer per million people exposed daily for 70 years). Thus, the response level for these chemicals corresponds to a lifetime cancer risk of 1 X 10-4. The 10-4 value is at the upper end of the 10-6 to 10-4 cancer risk range. Exposures to environmental chemicals resulting in risks within the 10-6 to 10-4 range are generally considered by public health and environmental regulatory agencies to be "acceptable."

When the notification level for chemicals considered to pose a cancer risk is set at higher than the 1 X 10-6 risk, the response level—still at the 1 X 10-4 risk—occurs at a lower multiple of the notification level: For 1,4-dioxane, this recommendation occurs at 35 times the notification level, and for the nitrosamines NDEA, NDMA, and NDPA this recommendation occurs at 10, 30, and 50 times the notification level, respectively. ADDITIONAL NOTIFICATION WHEN WATER IS SERVED ABOVE THE RESPONSE LEVEL:

• Notification of the water system’s customers and other water consumers that the contaminant is present in their drinking water at a concentration greater than its response level, the level at which source removal is recommended by DDW, and the reason for the continued use of the source.

• Thereafter, DDW recommends the following: (1) Monthly sampling and analysis of the drinking water supply for as long as the contaminant exceeds its response level, and quarterly sampling for 12 months, should the concentration drop below the response level. (2) Quarterly notification of the water system’s customers and other water consumers for as long as the contaminant is present at a concentration greater than its response level, using the methods described above.