State Water Board Approves Drinking Water Standard For 1,2,3-Trichloropropane

Public Water Systems Expected to Begin Sampling for the Contaminant in 2018

Recently the State Water Resources Control Board adopted a drinking water standard for the regulation of the contaminant 1,2,3-Trichloropropane in tap water. Under the regulation, public water suppliers will be required to notify their customers and take corrective action when drinking water exceeds the allowable limit.

The man-made chemical, used historically in industrial cleaning solvents and some soil fumigant pesticides, is a recognized carcinogen that may cause cancer after long-term exposure. Commonly known as 1,2,3-TCP, it has been found in groundwater sources, primarily in the Central Valley.

“1,2,3-TCP is not naturally occurring and too many Californians have been exposed to it for far too long, which is why it has been our top priority for standard setting this year,” said Felicia Marcus, chair of the State Water Board. “This standard will better protect public health and allow communities and the state to get on with the job of getting it out of our water supplies.”

The State Water Board’s Division of Drinking Water set the standard for 1,2,3-TCP at 5 parts per trillion (ppt). The drinking water standard, also known as a maximum contaminant level, is a set limit on what’s an allowable concentration of a contaminant in tap water. This is the first drinking water standard adopted by the State Water Board since the Division of Drinking Water joined the Board from the Department of Public Health in July 2014.

Based on 2015 data, the Division of Drinking Water has estimated that 103 water systems serving approximately 920,000 Californians have detected 1,2,3-TCP above 5 ppt in at least one drinking water source. Communities in several counties within the Central Valley are particularly impacted due to their reliance on groundwater and past use of pesticides containing 1,2,3-TCP in many agricultural areas.

The regulation will require that more than 4,000 public water systems statewide begin quarterly sampling for 1,2,3-TCP in their drinking water sources in January 2018. Systems will be in or out of compliance with the new drinking water standard based on the average of four quarters of sampling.

If a water system’s four-quarter average is above the 5 ppt standard, it must publicly notify its customers of the violation and take corrective action to resolve the exceedance and avoid future violations of the standard. The Division of Drinking Water encourages systems with previous monitoring data indicating a high potential for future violations to begin taking corrective action prior to January 2018.

The State Water Board will assist water systems in violation of the 1,2,3-TCP standard reach compliance by offering technical help. In some instances for certain communities, funding assistance might be available through the State Water Board’s regular financial assistance programs.