Office of Environmental Health Hazard Assessment


Notification Levels are health-based advisory levels for chemicals in drinking water that are established for chemicals for which there are no formal regulatory standards (Maximum Contaminant Levels, or MCLs). Notification Levels may be established by the State Water Resources Control Board’s Division of Drinking Water (DDW) when a chemical is found in or threatens drinking water sources. Upon request by DDW, OEHHA performs a risk assessment of the chemical using standard risk and exposure assumptions and proposes a health-protective level. A notification level is then established by DDW, and amended as necessary as conditions or risk assessment methods change. The OEHHA letters to DDW, which provide brief summaries of the toxicological literature and proposed Notification Levels, can be accessed through the links below.

When notification levels are exceeded, the drinking water system is required to notify the local governing body of the local agency in which the users of the drinking water reside. If the notification level is exceeded, the State Water Resources Control Board (SWRCB) recommends that the utility also inform its customers and consumers about the presence of the contaminant and about the health concerns associated with its exposure. Response levels are levels of the contaminant at which SWRCB recommends the drinking water system take the affected water source out of service. These levels range from 10 to 100 times the notification level depending on the chemical. Further information on notification and response levels can be found at the SWRCB Web site. The California legislation covering notification and response levels is Health and Safety Code 116455 and can be found at


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Notification Level (ug/L)

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1,2,3-trichloropropane 0.005 53kb
1,2,4-Trimethylbenzene (1,2,4-TMB) and 330 171kb
1,3,5-Trimethylbenzene (1,3,5-TMB) 330 same as above
1,4-Dioxane 3 91kb
2-Chlorotoluene 140 143kb
Carbon Disulfide 160 93kb
Chlorate 800 200kb
Methyl Isobutyl Ketone 120 141kb
Naphthalene 17 141kb
n-Propylbenzene (isocumene) 260 171kb
sec-Butylbenzene and 260 170kb
tert-Butylbenzene 260 same as above
Tertiary butyl alcohol (TBA) 12 178kb
Vanadium 50 143kb
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