In May 2017, the Superior Court of Sacramento County issued a judgment invalidating the new California MCL of 10 ppb for Cr+6. 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 Therefore, as of September 11, 2017 the 10 ppb MCL for Cr+6 is no longer in effect.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.

The Water Board has notified agencies, such as Vacaville, that were previously under compliance orders to address Cr+6 that the new 10 ppb MCL for Cr+6 is voided and no longer has to be met. The Water Board has determined that it will begin the process of adopting a new MCL for Cr+6, following Safe Drinking Water Act requirements. The Water Board will utilize scientific and economic data obtained during the past three years to establish a new Cr+6 MCL, but it is too early to project what that new MCL will be. The Water Board estimates it will take approximately two years to establish a new Cr+6 MCL.

The City of Vacaville continues to deliver the highest quality drinking water, meeting all federal and state drinking water requirements, to our customers.

In 2014, the State of California created a new maximum contaminant level, or MCL, for hexavalent chromium, also known as chrome 6, or Cr+6. The new MCL was adopted at 10 micro-grams per liter, or 10 parts per billion (ppb). Previously, the State regulated Cr+6 through a MCL of 50 ppb for Total Chromium, which includes all forms of chromium, including Cr+6. California's 50 ppb MCL for Total Chromium has been in place for a number of years. The federal Environmental Protection Agency (EPA) has an established MCL for Total Chromium of 100 ppb. All of the states in the United States, with the exception of California, use EPA's MCL of 100 ppb for Total Chromium.  Neither the EPA nor any individual state, other than California, has an MCL specifically for Cr+6.

Cr+6 is a naturally occurring ionic form of the element chromium. It is found in the geologic soils throughout California, and is mined as an ore to be used in industrial processes. The ore is used in making stainless steel, textile dyes, wood preservatives, leather tanning, paints, inks, plastics, and various coatings. Cr+6 is a known carcinogen, primarily entering the body through the lungs inhaled as dust or in a vapor form due to high-heat industrial processes. Scientific studies have been inconclusive to date though as to whether Cr+6 is a proven carcinogen when ingested by drinking water containing trace levels of Cr+6. In creating the new MCL, the State was concerned that the risk of getting cancer could potentially be increased after decades of drinking large amounts of water containing elevated levels of Cr+6.

Five of the City's eleven municipal drinking water wells have Cr+6 at levels between 10 ppb and 24 ppb. The source of Cr+6 in Vacaville's deep groundwater wells is from the naturally occurring mineral deposits in the geologic formation of the Sacramento Valley. It is not a result of any industrial pollution. There are no known Cr+6 industrial pollution sites in Vacaville. Many other cities in the region, and throughout California, are also dealing with Cr+6 in their water supply wells. As a result of the 2014 regulations, Vacaville has been working with the State Water Resources Control Board's Division of Drinking Water (DDW) to design treatment systems or modify the five source water wells to produce drinking water with Cr+6 less than the new 10 ppb MCL by the lawful deadline of January 1, 2020.

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 Cr+6 in drinking water would require decades of drinking large volumes of drinking water with elevated levels of Cr+6. 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 Cr+6 under compliance plans approved by DDW. Vacaville has been working with DDW under such an approved compliance plan.