City outlines Chromium‑6 compliance plan and pilot testing after lowered state limit

Interim City Manager Gary Vriese reported to the council on Oct. 15 that the city’s second quarter Chromium‑6 testing exceeded California’s revised maximum contaminant level (MCL) of 10 parts per billion at some well sources.

Vriese said the city submitted the required compliance plan to the State Water Board (Division of Drinking Water) on Sept. 29 and that the state approved the plan on Oct. 1. Under the approved plan the city intends to pursue wellhead treatment for its affected wells, using a reduction‑coagulation‑filtration (RCF) approach that staff and consultants judged most viable. The Division of Drinking Water provided the city a compliance schedule with a target completion date of Dec. 31, 2030 for implementation across the city’s 13 wells.

Vriese said staff began pilot testing of the RCF approach at one well site; the pilot unit will move to a second well for additional testing. Pilot testing is expected to continue for several weeks at each site while samples are analyzed. The city will use those data to refine treatment designs and then move into detailed design, vendor selection and construction. Vriese estimated the engineering cost to implement wellhead treatment across the city’s 13 wells at roughly $60 million, and he said staff will explore funding options.

The city sent required written notices to utility account customers after the exceeded MCL results, consistent with state requirements. Vriese emphasized that the state has not told the city its drinking water is unsafe to drink and that the compliance plan seeks to reduce Chromium‑6 concentrations below the regulatory limit. Staff said they will return with pilot results and proposals for financing and construction once testing and design work are complete.

Quotes are drawn from the city manager’s presentation to the council and the city’s public comments during the Oct. 15 meeting.