News: New MCL Proposed for Chromium-6 in Drinking Water

Today, a long-awaited draft maximum contaminant level (MCL) for Chromium-6 was proposed by the California Department of Public Health at 10 (ten) parts per billion (ppb).

Chromium-6 is a groundwater constituent found in over 30% of groundwater basins in California, including Riverside County’s Coachella Valley and various basins in Los Angeles, San Bernardino, Solano, Santa Barbara, San Mateo, Santa Cruz and Yolo Counties. For example, affected cities include Glendale, Burbank, North Hollywood, Pomona, Monterey, Chino, Joshua Basin, Phelan, Twentynine Palms, Solano, Daly City, Santa Ynez, Soquel Creek, Davis, Woodland, and parts of San Francisco.   It also naturally occurs in the Cadiz Valley aquifer system at levels consistent with the proposed MCL.

Cadiz has long anticipated the imposition of a new Chromium-6 MCL and has prepared an on-site treatment program  in the event that a final Chromium-6 MCL is ultimately adopted that is lower than measured levels in the Cadiz Valley.  Cadiz water can either be blended with existing water in the Colorado River Aqueduct or a portion will be treated on site at a nominal cost.   Water will never be delivered to any end user of the Cadiz Project that exceeds an MCL for any constituent, including Chromium–6.

The entire expense, if any, to treat for Chromium-6 or any other constituent will be borne by Cadiz.  All water supply agreements with Project participating agencies reflect our responsibility for water quality.


About Chromium-6

Chromium is a heavy metal and the 11th most common element in the earth’s crust. It can be found as Chromium-3 or Chromium-6.  Chromium-3 and Chromium-6 are naturally occurring and are often found in groundwater when manganese in groundwater oxidizes. The current California State MCL for Chromium, a combination of both Chromium-3 and Chromium-6, is 50 ppb. The Federal MCL for total Chromium adopted by the United States Environmental Protection Agency is 100 ppb. There is presently no state or federal MCL specific to Chromium-3 or Chromium-6.

In 2011, as part of the process of developing an MCL for Chromium-6, the CA Office of Environmental Health Hazard Assessment (OEHHA) issued a public health goal for Chromium-6 at .02 ppb.  A public health goal is advisory and not regulatory; it is not an enforceable state standard (MCL) for drinking water that public water systems must meet.  According to the California Department of Public Health, close to 2,500 public drinking water sources in California have measured levels of Chromium-6 greater than 1 ppb. At these sites, Chromium-6 primarily occurs naturally. (

Since issuing the public health goal, OEHHA has been developing an MCL for Chromium-6 that is subject to public comment and review. A draft MCL of 10 ppb was announced on August 22, 2013. All comments are due on October 11, 2013.

About Water Quality at Cadiz

Overall water quality at Cadiz is excellent.  Our water currently meets all State and Federal water quality standards without treatment.  It is suitable for both domestic and agricultural use.  The vast watershed in which the water originates has very few overlying land uses and is free from the threat of bacterial waste and industrial contamination.

Cadiz water is also substantially better than state and federal standards for total dissolved solids (TDS) and much softer than California’s Colorado River supply.  The MCL for TDS is 1,000 mg/L.  TDS concentrations at Cadiz average approximately 300 mg/L.

By comparison, the Metropolitan Water District of Southern California (MWD) has set a target for TDS in its service area at 500 mg/L.  However, the actual concentration of TDS in its Colorado River Aqueduct, one of the main sources of supply in the MWD service area, is generally around 700 mg/L, and its water must be treated or blended with lower TDS water before reaching the end-user.

High levels of TDS create aesthetic issues and create negative economic consequences for affected residential and business customers.  Hard water clogs pipes and machinery, drives up water heating prices and can damage agricultural crop production.

According to the Southern California Salinity Coalition, increased salinity is one of the most under-recognized water quality threats in the Southwest. A recent report from engineering consulting firm CH2M Hill reveals that blending Cadiz water into the CRA will provide Southern California ratepayers $7.89 million per year in annual savings and $395 million over the life of the Cadiz Project.


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