Vacaville officials report chromium‑6 above new state limit in some wells; compliance plan due 2026

Vacaville water officials told the City Council on Aug. 12 that routine testing found chromium‑6 (hexavalent chromium) in groundwater wells serving the city and that four of the nine municipal wells exceeded California''s new maximum contaminant level (MCL) of 10 parts per billion adopted in October 2024.

The city's water quality manager, Mindy Bolli, and Utilities Director Justin Cole said the triennial public health goals report (covering 2022''–2024) shows five constituents that exceed California public health goals — including arsenic, coliform bacteria, gross alpha, PFOA and PFOS — but that none of those five require additional treatment because the public health goals are more stringent than enforceable MCLs and reducing to those goals would be technically and financially infeasible.

The nut graf: City staff emphasized Vacaville meets its current federal and state MCLs overall, but compliance with California''s chromium‑6 MCL of 10 ppb is required by Oct. 1, 2026; staff are preparing a state-approved compliance plan and will send required customer notifications.

City water staff said all nine groundwater wells tested above 1 ppb for chromium‑6 and four wells produced chromium‑6 concentrations above 10 ppb. Staff stated the weighted average for the distribution system is 5.76 ppb and that chromium‑6 constitutes an average of 17.8% of the city's supply by volume in the sampling period reported.

Assistant Director Hawkins (presenting the chromium data) said the state-set MCL that took effect in October 2024 requires Vacaville to come into compliance by Oct. 1, 2026. Hawkins said staff is working with the California Division of Drinking Water (DDW) on a compliance plan and that the city will send quarterly notification letters to customers explaining the exceedance and the city's plan. Hawkins said the letters are not violation notices but are required public notifications and will be reviewed by the state before mailing.

Council members asked about sampling locations and frequency, whether residents can test individual taps, and the health significance of chromium‑6. Bolli explained the triennial report covers all sources (surface water purchased from North Bay Regional and local wells) and that the state requires raw-well sampling plus 26 designated distribution sampling sites across pressure zones. She said some analytes are sampled yearly, some quarterly, and some at other intervals depending on state rules.

On health effects, Bolli said the state derived the 10 ppb MCL to align with an estimated 1-in-1,000,000 lifetime cancer risk for a person drinking roughly a half-gallon per day for 70 years at that level. Bolli and Hawkins said Vacaville's water system continues to meet other federal and current state MCLs and that residents with concerns can have samples tested by commercial labs or the Solano County public health lab.

No formal action was required; staff said they will finalize the compliance plan with DDW, mail state-approved notices, and return to council with updates as needed.

Ending: Staff reiterated that current required MCLs (state and federal) are being met for most regulated contaminants, that chromium‑6 is naturally occurring in the region's geology, and that the city will provide periodic updates and customer notifications about the compliance steps.

"Per requirements of the state Health and Safety Code, the triennial report is intended to inform the public of the performance of the city's water system and provide the opportunity for public comment," Hawkins said.