Chromium-6, also known as hexavalent chromium, occurs naturally in many water sources. In 2014, the State Water Resources Control Board’s (State Board) Division of Drinking Water (DDW) adopted a new chromium-6 standard of 10 parts per billion (ppb); however, in August 2017, DDW rescinded the regulation due to adequate documentation on the economic feasibility of meeting the standard.
Water supplies in our Willows and Dixon Districts, and in our Salinas District’s Las Lomas and Oak Hills systems, exceeded the maximum contaminant level (MCL) without treatment. After taking cost, method effectiveness, waste disposal, and raw water quality all into consideration, our crews installed strong base ion-exchange treatment facilities at each affected location to meet the standard while in effect.
Protecting our customers’ health and safety is our highest priority, and we have always been committed to meeting all water quality regulations set by the public health experts. Although the State Board removed the MCL for chromium-6 due to insufficient documentation on the economic feasibility of compliance, the State Board continues to believe that chromium-6 is a threat to public health and is working to establish a new MCL, which could be the same as the previous MCL.
When the MCL was originally established, the deadline for compliance was very short. Although we challenged the timeline for compliance in an effort to reduce the cost impact to our customers, the compliance deadline remained under six months. Because we have a duty to protect our customers’ health and safety, we installed treatment facilities at the water sources we needed to use to serve our customers. Prior to installing treatment facilities, however, we thoroughly investigated treatment methods to meet the new standard as cost-effectively as possible.
As DDW works to establish a new MCL and because of chromium-6’s risk to public health, the State Board has also encouraged water utilities that had already installed treatment facilities to continue treating the water for the contaminant. And, because we have treatment facilities already in place, we know our customers’ health and safety will continue to be protected.
Chromium-6 is a subset of total chromium. The state has had an MCL of 50 ppb for total chromium since the 1970s. The Environmental Protection Agency has a federal limit of 100 ppb for total chromium and no standard for chromium-6.
- Optimization of strong-base anion exchange O&M costs for hexavalent chromium treatment (Science Direct)
- California Water Service, Willows Proposition 50, Chapter 6(b), Grant Number P50-1110002-290: Strong Base Anion Exchange Treatment and Brine Minimization for Hexavalent Chromium Removal Final Report (December 12, 2017)