Regulation

On October 1, 2024 the Maximum Contaminant Level (MCL) of 10 ug/L for Hexavalent Chromium, also known as Chromium 6 or Cr VI, came into effect. This means that each community water system must test water sources for Cr VI to ensure the concentration is below 10 ug/L or 10 parts per billion (ppb). Testing must be completed by April 1, 2025. Since Sunnyslope has fewer than 10,000 water service connections, compliance with this regulation is required by October 1, 2027. This regulation does not apply to private domestic wells.

Health Effects

Cr VI is a chronic health concern. This means that its health effects are due to long term, decades-long exposure.  Drinking water with low amounts of Cr VI, even for several years, is not believed to have negative health effects. At the MCL of 10 ug/L the health risk will be limited to a one-in-two-thousand or 0.05% chance of developing cancer during a lifetime (70 years) of exposure. Such lifetime exposure may result in liver toxicity, gastrointestinal tumors, and liver cancer.

Cr VI in Sunnyslope Water Sources

Around Hollister, Cr VI occurs naturally in portions of the groundwater aquifer due to the mineral composition of the local geology. Sunnyslope has tested and will continue testing all its wells for Cr VI, and average concentrations range from 3 ug/L in the lowest concentration well to 13 ug/L in the highest concentration well. Cr VI has always existed here naturally, and is not the result of man-made industrial pollution.

In some situations pollution can cause elevated Cr VI groundwater levels, as was the case in Hinkley CA.  There PG&E severely contaminated the local groundwater with high levels of Cr VI which caused higher than normal rates of cancer in that local population. This tragedy became notorious as the basis for Hollywood film "Erin Brockovich" starring Julia Roberts in 2000. However, most instances of Cr VI in California are entirely due to naturally occurring minerals in the existing soil, as is the case in Hollister.

Future Steps

Sunnyslope will continue to conduct quarterly testing and reporting of all our water sources for Cr VI. If any sources appear to have concentrations higher than the 10 ug/L MCL, Sunnyslope will create and submit a Compliance Plan to Division of Drinking Water.

Sunnyslope will most likely utilize a blending treatment strategy at any wells that exceed the MCL. This would require that water from a low Cr VI source is mixed with the water from the higher Cr VI well before it is pumped to customers through the water distribution system. Essentially, that treatment dilutes the Cr VI to below the MCL. Low Cr VI water sources include Sunnyslope's Well #11 and treated surface water from West Hills or Lessalt.

Implementing the blending treatment strategy may require some Capital Improvement Projects at Sunnyslope's wells and the West Hills and Lessalt treatment plants. Staff are currently evaluating the cost, design, and schedule for these projects and how they might impact future water rates.