Above: Cal Water used grants to help fund its new strong-base anion exchange chromium-6 treatment system.
Several days ahead of the release of the Environmental Working Group’s (EWG) report, “‘Erin Brockovich’ Carcinogen in Tap Water of More Than 200 Million Americans,” which focused on the prevalence of chromium-6 in the nation’s water supply, California Water Service (Cal Water) finalized a $15 million project to reduce chromium-6 levels to below California’s stringent 10-ppb regulation at several locations across the state.
While the district’s wells once had naturally occurring chromium-6 levels of about 16 ppb, the water supply has remained in compliance with the new state standard since treatment plants were constructed and brought online. All of Cal Water’s service areas now comply with the state mandate, and a ribbon-cutting ceremony commemorated the completion of the final chromium-6 treatment plant in Cal Water’s Willows District, which serves approximately 2,400 connections, on Sept. 15, 2016. This final treatment plant enabled the district to utilize an additional source of supply for local customers, augmenting water supply reliability.
“At Cal Water, we actively monitor and participate in the regulatory process,” said Sophie James, director of water quality for Cal Water. “We knew this constituent would eventually be regulated, so we kicked off our internal research and pilot projects long beforehand to determine the types of technologies (and other associated items) that would best serve our needs and those of our customers in the most cost-effective manner. We wanted to be thoroughly prepared by the time the regulation finally came out.”
The system was debuted on “Imagine a Day Without Water” in September 2016.
Ahead of the Curve
California’s new regulatory level is progressive, requiring a sizable up-front investment, which can be difficult for some utilities. “California is the first state in the nation to adopt such a regulation,” James said. “On the federal level, there is a maximum contaminant level (MCL) of 100 ppb for total chromium, which encompasses all chemical species (e.g., hexavalent and trivalent chromium). The MCL for total chromium for California is 50 [ppb].”
In early 2015, Cal Water received two state grants to offset chromium-6 treatment costs in the Willows District, one of two Cal Water districts where the entire water system is affected by the new regulation. The larger $5 million grant was awarded by the Department of Water Resources via Proposition 50 funding and supported a full-scale demonstration of strong-base anion exchange (SBA-IX) technology, which Cal Water’s research team had identified as the most cost-effective method for reducing chromium-6 levels. The technology also minimizes the amount of waste generated from the treatment process and recycles a portion of the salt-brine regeneration stream. The technology has turned out to be so effective that Cal Water has partnered with local municipalities to identify research and development cost efficiencies and has been featured in industry journals.
“The treatment plant is great example of how private, local and state entities can partner together to provide much needed water infrastructure for our communities,” said state Assemblyman James Gallagher in a statement for the Willows District ribbon cutting ceremony.
While various treatment methods had been tested due to the need to determine the best-performing ion exchange resin, empty bed contact time and hydraulic loading rate, SBA-IX was chosen due to cost, estimated efficiencies observed during pilot work and readiness of implementation, since Cal Water had a tight timeline for installation. Previously, a reduction, coagulation, filtration treatment method had been tested; however, the site-specific water supply in the Willows and Dixon districts was not ideal for this type of process. Weak-base anion exchange also was investigated; however, it requires a reduction of the pH level in water that is treated. Large volumes of acid would be required to lower pH levels in large volumes of water and, once treated, most utilities must then raise the pH to an appropriate level to ensure the water is not “aggressive” when it is dispersed system-wide. (Aggressiveness is the tendency for water to cause chemical leaching, e.g., from pipes and fittings.)
Understanding Chromium’s Origin
Chromium is found within serpentinite rock formations. When groundwater comes into contact with these rocks, certain chemicals start to leach out, including hexavalent chromium. Thus, wells in the Willows District are impacted with chromium-6 simply due to the fact that rocks contained in the wells leach chromium. “The chemical characteristics in the groundwater have been relatively constant throughout the time we have been gathering data, which is since the 1980s—and I’m sure well before that,” James said. “Chromium has really been at the same levels in perpetuity. The only thing that has changed in California is the adoption of this regulation, establishing a really low limit.”
The recently released EWG report concluded that chromium-6 is actually in the tap water of more than 218 million Americans nationwide. “That’s two-thirds of the U.S. being served water with chromium-6 at, or above, the level that California state scientists consider safe,” according to the World Health Organization. EWG previously set a public health goal that allowed a chromium-6 level expected to cause no more than one case of cancer in 1 million people who drink it for lifetime.
The September 2016 ribbon cutting ceremony in the Willows District was held in conjunction with the Value of Water Coalition’s “Imagine a Day Without Water.” “This is appropriate, as now our customers won’t have to go a day without high-quality water,” James said.
The ceremony included State Water Resources Control Board member Steven Moore; Department of Water Resources’ Chief of Financial Analysis and Risk Management Linda Ng; representatives from the city of Willows and city council; representatives for Gallagher and state Sen. Jim Nielsen; and local residents. “The citizens of Willows are very fortunate that we received grants for this project and that Cal Water and their consultants have cleaned up chrominum-6 for all of us,” said Willows council member Larry Mello.
The Water Research Foundation awarded another $175,000 grant for research and treatment, which also will help offset future rate impacts for Willows customers. “Cal Water is one of only a few water utilities that is in compliance with this regulation at this date,” James said.