Water superintendent says Elk Fire and summer storms caused turbidity spikes; operators kept drinking-water standards

Tom Nolis, the city’s water treatment superintendent, told the City Council Sept. 15 that Sheridan’s raw water comes entirely from Big Goose Creek and its tributaries and that the plant consistently produces treated drinking water well below EPA turbidity limits.

“Right now it's at 0.15 turbidity units. And our drinking water right now, we consistently put out water that's less than 0.05 turbidity units,” Nolis said, describing the treatment process of coagulation, flocculation, sedimentation, filtration and disinfection required under the Safe Drinking Water Act.

Nolis explained seasonal variation in raw water quality: winter produces low turbidity; spring runoff can push turbidity to around 40 NTU and sometimes higher; and the city has experienced extreme, unusual events. He recounted a 2019 mudslide that spiked raw‑water turbidity to about 3,400 NTU but said operators maintained treated water below the compliance threshold. He also described a taste‑and‑odor event in 2012 and said the Elk Fire in 2024 produced a burn scar that has altered runoff chemistry and contributed to higher‑than‑typical turbidity during recent heavy summer storms.

This summer, Nolis said, the plant saw spikes near 800 NTU during storm events on burn‑scar slopes. The treatment response required as much as seven times the normal chemical dose, producing more sludge and significant overtime for operators. “Two and a half months into the fiscal year, we've used over half of our chemical budget already,” he said, and the department anticipates a possible budget amendment later in the fiscal year to cover higher chemical costs.

Nolis described operational responses: adding a turbidometer upstream of the intake to provide earlier alarms; drafting revised standard operating procedures and recipes for treating different turbidities; and installing operational measures to bypass the intake during the worst flows. He told council that while long‑term effects of the Elk Fire are uncertain, the plant is capable of producing compliant drinking water under the changing raw‑water conditions.

Council members thanked Nolis for the detailed explanation; a resident speaker praised the staff’s expertise in keeping water safe despite unusual events.

Ending: Nolis said the department will monitor watershed conditions, update operations guidance, and likely seek a budget amendment if high chemical usage continues.