TCP is exclusively a man-made chemical. The primary source of TCP in groundwater is past agricultural use of soil fumigants that contained TCP as an impurity.
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TCP has not been detected in the District wells that currently supply drinking water. The Maximum Contaminant Level (MCL) for TCP is 5 parts per trillion (ppt). Country Club Well has TCP levels above the MCL - with an average of 8.7 ppt, and a maximum of 15 ppt. As of July 2017, Country Club Well has been temporarily shut off pending installation of a TCP treatment plant.
The most likely source of the TCP in Country Club Well was as a known impurity in the soil fumigants (nematicides) D-D and Telone. The immediate area around Country Club Well was agricultural in the 1950s and 1960s. We do not know how long the TCP has been in the groundwater.
The District has been testing for TCP since 1989. TCP was first detected in 2008 using an improved analytical method, capable of detecting very low levels.
The District’s water meets or exceeds all current drinking water testing requirements and regulations. The experts at the State Water Resources Control Board, Division Drinking Water (DDW) say that some people who drink water containing TCP over many years may have an increased risk of getting cancer, based on studies of laboratory animals.
A new Maximum Contaminant Level (MCL) for 1,2,3-TCP of 5 ppt was established by DDW. The new standard takes effect in 2018.
The District is currently evaluating potential treatment options for the TCP in order to utilize this important drinking water supply source. If you have additional questions about TCP and your health, you should visit the DDW’s TCP page.