Chromium 6 Informational Page
Hexavalent Chromium (Cr6)
Chromium is found naturally in rocks, plants, humans and animals. The most common forms of chromium that occur in natural waters are trivalent chromium (chromium 3) and hexavalent chromium (chromium 6). Hexavalent chromium, in high doses, can be identified as a carcinogenic. However, Patterson’s water has always had a small trace amount of chromium 6 that is naturally occurring and not caused by industrial contaminants.
The City of Patterson's water supply currently averages between 14.2 and 20.3 parts per billion – far BELOW the levels set by the State and current Federal limits. The following information on chromium levels can be helpful to keep in mind:
- 100 parts per billion (ppb) is the federal maximum contaminant level (MCL) set by the EPA for total chromium. Total chromium includes both trivalent chromium (chromium 3) and hexavalent chromium (chromium 6).
- 50 ppb is the total chromium MCL for the state of California set by the State Water Resources Control Board, Division of Drinking Water (DDW), and is still in effect. Patterson is in compliance with this standard.
2014 California Regulation for Hexavalent Chromium
In 2014, the State of California created a new maximum contaminant level, or MCL, for hexavalent chromium. The new MCL was adopted at 10 micro-grams per liter, or 10 parts per billion (ppb). DDW was careful to point out that the new 10 ppb MCL did not create an urgent drinking water crisis. Any potential health risks regarding Cr6 in drinking water would require decades of drinking large volumes of drinking water with elevated levels of Cr6. Therefore, DDW determined that communities with groundwater wells exceeding the new MCL could continue to use those wells while they implemented proposed system improvements to address Cr6 under compliance plans approved by DDW.
State Rescinds 2014 MCL for Hexavalent Chromium
In May 2017, the Superior Court of Sacramento County issued a judgment invalidating the new California MCL of 10 ppb for Cr6. The court determined the State Water Resources Control Board (Water Board) failed to properly follow the requirements of the Safe Drinking Water Act for establishing the new MCL. The court ordered the Water Board to delete the new hexavalent chromium MCL from the California Code of Regulations. This change became effective on September 11, 2017. Therefore, as of September 11, 2017 the 10 ppb MCL for Cr6 is no longer in effect. The regulation of hexavalent chromium in drinking water reverts back to the previous State of California MCL of 50 ppb for Total Chromium, to which the city is in compliance.
Future Chromium 6 Announcements
Although the MCL was rescinded, the court ordered the State Water Board to adopt a new MCL for hexavalent chromium. In February 2020, the State Water Board staff published the White Paper Discussion on Economic Feasibility Analysis in Consideration of a Hexavalent Chromium Maximum Contaminant Level.
On April 27, 2020, State Water Board staff held a public workshop on the White Paper. The public comment period ended on May 15, 2020. Preliminary occurrence data and treatment cost estimates were released in October and November 2020, with public workshops on the cost estimates held on December 8 and 9, 2020.
The Notice of Preparation of an environmental impact report is available. The Division of Drinking Water is soliciting early public consultation via a scoping meeting to be held virtually on November 29th at 3pm. More information is available in the Notice of Preparation.
In June 2023, the State Water Board released the Notice of Proposed Rulemaking for the Hexavalent Chromium MCL and associated Draft Environmental Impact Report. A hearing is scheduled on August 2, 2023 and written comments are due August 4, 2023.
What We Have Done To Address Chromium 6
Following the July 1, 2014 adoption (since rescinded) of the Chrome 6 MCL by DDW, the City initiated quarterly monitoring for Chrome 6 in their potable wells and submitted a Corrective Action Plan (CAP) outlining the steps and estimated timeframe needed to achieve Chrome 6 compliance. Using the mitigation/treatment approach, the City completed the following steps:
- Field testing of wells to determine the potential for Chrome 6 source control.
- Feasibility study to evaluate and screen treatment and facility siting alternatives.
- Pilot Testing to develop/confirm site specific design criteria for the selected Chrome 6 treatment process.
What We Are Currently Doing
We continue to monitor our pilot-tested well site on a quarterly basis. Design and installation of a centralized facility or on-site treatment is placed on hold until a new MCL is established by the State. The City can then identify which wells will require treatment, if any, and which treatment alternative will be able to meet the new standard.
To visit the state's website regarding chromium 6, click here.