RANCHO MURIETA, CA (MPG) - Rancho Murieta Community Services District operators dumped approximately 200,000 gallons of treated water into Lake Clementia, temporarily shut down both water treatment plants, and relied on water already stored in the system to prevent elevated manganese from reaching customers during last week’s precautionary water advisory on June 19 and 20.

Chief Plant Operator Travis Bohannon said he chose to notify residents before manganese levels in the district’s storage tanks exceeded the district’s operating threshold because the situation was still unfolding.

“I felt it was better to do that while I was trying to resolve the issue,” Bohannon wrote. “Not knowing how long or how bad this manganese flare-up was going to last or how long it was going to take me to get it under control, I made this decision out of concern for the district’s residents.”

The June 19 advisory was issued after manganese levels in treated water leaving Water Plant 1 exceeded the district’s 0.05 milligrams-per-liter operating threshold. Rather than continue sending that water into the distribution system, operators temporarily diverted treated water away from customers while they corrected the problem, relying instead on treated water already stored in the Rio Oso and Van Vleck tanks.

The new information, provided by Bohannon in response to questions from the River Valley Times, explains how the district managed the incident without interrupting water service and provides additional details that were not available before the newspaper’s initial story went to press.

Storage Tanks Keep Water Flowing

One of the biggest unanswered questions after the advisory was how Rancho Murieta continued receiving water after Bohannon wrote that Water Plant 1 had been put “to waste” and Water Plant 2 had been shut down.

Bohannon said the district had sufficient treated water in storage to meet customer demand throughout the incident.

“At the time that I started wasting, there was plenty of water in the tanks to supply the district with water,” he wrote. “I was monitoring the tank levels at all times, and the tanks never got below an acceptable level. There was never any danger of the tanks running empty at that time.”

Approximately 200,000 gallons of treated water were diverted into Lake Clementia rather than being delivered to customers.

Why 0.05 mg/L Matters

The district repeatedly referred to the 0.05 milligrams-per-liter manganese level during the incident because it corresponds to California’s secondary drinking water standard for manganese. The standard is intended primarily to prevent yellow or brown water, staining of plumbing fixtures and laundry, and other aesthetic problems.

State health officials have also expressed growing concern about prolonged manganese exposure in sensitive populations, particularly formula-fed infants and young children, who absorb and retain more manganese than adults. Earlier this month, the California Division of Drinking Water revised its health-based notification and response levels after reviewing studies linking elevated manganese exposure to potential neurological and developmental effects in formula-fed infants.

According to Bohannon’s report, the flare-up began when raw water entering Water Plant 1 measured 0.171 milligrams per liter of manganese. After treatment, the plant’s finished water measured 0.077 mg/L: an improvement, but still above the district’s 0.05 mg/L operating threshold. Those measurements were included in the district’s report posted after the River Valley Times’ initial story went to press.

During the incident, Bohannon used the 0.05 mg/L level as his operational threshold and issued a public advisory before manganese concentrations in the storage tanks reached it. According to his report, the highest manganese reading in the Rio Oso tank was 0.01 mg/L, while the Van Vleck tank reached 0.04 mg/L.

Echoes 2019 Yellow-Water Event

The incident echoes Rancho Murieta’s well-publicized 2019 yellow-water episode, when elevated manganese caused discolored tap water and generated approximately 80 customer complaints.

District officials reported at the time that the newer membrane-based Water Plant 1 could not adequately remove dissolved manganese by itself, while the older filter-bed Water Plant 2 continued producing water with non-detectable manganese after treatment. Operators resolved the problem by adding pre-oxidants that converted dissolved manganese into particles that could then be removed during treatment.

Bohannon said the same approach helped to resolve last week’s flare-up.

“The numbers were the initial numbers that were initially reported to me,” he wrote. “Once pre-oxidants were turned on, that is when I started to get better results. There were no pre-oxidants being fed at the time this incident started due to not being needed until this flare up happened.”

Plants Monitored Separately

Bohannon also clarified how the district monitors water quality when both treatment plants are operating.

He said “finished water,” also known as potable water, refers to treated water leaving each individual treatment plant. Each plant is monitored separately before the two water supplies are blended.

“We have analyzers for each individual plant,” Bohannon wrote. “Once the water leaves the water plant, it is blended in the distribution pipes going to the tanks.”

In-House Testing Speeds Response

Bohannon said the district’s in-house manganese analyzers allow operators to make immediate operational decisions while certified laboratory results, which typically take about two days, are pending.

“The in-house testing meters provide enough information to make on-the-spot operational decisions for process control,” he wrote. “The samples sent to the lab just confirm that what we are doing is correct. The meters don’t provide extremely accurate information, but good enough to make sure the right decisions are being made.”

Bohannon said he still does not know what triggered the manganese flare-up, describing it as more severe than he had previously experienced. After treatment adjustments and consultation with a chemical engineering specialist, manganese levels dropped to non-detectable levels, allowing the district to return both treatment plants to normal operation and lift the advisory the following morning.