The State Water Resources Control Board, on April 15, 2014, announced a new Maximum Contaminant Level (MCL) of 10 parts per billion (ppb) for chromium-6, a mineral that occurs naturally at levels above the new MCL in the City of Patterson’s groundwater. The newly established MCL is one fifth the current total chromium standard in California of 50 ppb, which includes both trivalent chromium (chromium-3) and chromium-6. The federal MCL for total chromium is 100 ppb.
We routinely monitor for the presence of drinking water contaminants. Water sample results received on September 21, 2016, showed chromium-6 levels between 15.6 to 38.2 ppb. These results raised the annual average of all our potable supply wells to be above the new MCL of 10 ppb for the State of California. California is the first and only state in the nation to establish a maximum contaminant level specifically for chromium-6 in drinking water.
Our water system recently violated the new drinking water standard for chromium-6. Although this is not an emergency, as our customers, you have a right to know what happened, what you should do, and what we are doing to correct this situation.
Please click on the attachments below to learn more about the new regulations and what the city is doing to address it.