Sewer overflow leads to high levels of E. coli in Granite Creek, Watson Lake

Crews with the City of Prescott’s Wastewater Treatment Division continued work in Granite Creek Park in downtown Prescott on Monday, March 27, 2023 to clean up the sewage overflow that occurred into Granite Creek during heavy rainfall on March 21, 22, and 23, 2023. (Cindy Barks/Courier)

Crews with the City of Prescott’s Wastewater Treatment Division continued work in Granite Creek Park in downtown Prescott on Monday, March 27, 2023 to clean up the sewage overflow that occurred into Granite Creek during heavy rainfall on March 21, 22, and 23, 2023. (Cindy Barks/Courier)

As Prescott’s Wastewater Treatment Division continued the cleanup of sewage overflow in Granite Creek Park this week, testing at Watson Lake and Granite Creek is indicating high levels of E. coli bacteria in the water.

And that will lead to a restriction on kayaking, fishing, and paddle boarding in the lake until the levels come down, said Prescott Utilities Manager Steven Olfers.

On Monday, March 27, crews were working at Granite Creek Park in downtown Prescott to vacuum up traces of wastewater that remained from an overflow of sewage from a number of manholes located near Granite Creek last week.

Starting just after noon on Tuesday, March 21, and continuing until early Thursday morning, March 23, sewage was overflowing into Granite Creek from about a half-dozen manholes that are located near the creek at Granite Creek Park located on Sixth Street.

The overflow occurred in the midst of heavy rainstorms that brought between 1.5 to 2 inches (more in some locations) to the Prescott area over the three-day period.

Runoff water from nearby streets and properties reportedly cascaded down toward the creek and into the manholes, causing them to overflow into the creek. Also, in several manholes that are located right along the creek bank, the creek ultimately rose high enough to submerge the manholes, said Prescott Utilities Manager Steven Olfers.

Workers were onsite Monday with a large vacuum truck to start the vacuum and disinfecting process. Olfers had reported on Friday, March 24, that the first step was to allow the area to dry out somewhat. On Monday, he said that had occurred over the weekend.

The next step for workers was vacuuming up remaining standing water. “We’ll assume that all of this water is contaminated, so they’ll be taking all of this out,” Olfers said Monday afternoon, pointing to puddles of water that remained near the banks of Granite Creek.

In addition, crews were raking up grass and debris and removing it into wheelbarrows. Other workers were spraying down the area with clean water and then using a large vacuum on the truck to vacuum it up.

After that, crews would be applying disinfectant to the area and then vacuuming that up as well. “They’ll disinfect and then we’ll back it all up and do it again,” Olfers said, noting that the process would be repeated at least three times.

Meanwhile, the city’s Environmental Division has been taking water samples in Granite Creek and in Watson Lake, which is fed by Granite Creek, to test for E. coli bacteria (described by the University of Arizona Cooperative Extension website as “a type of fecal coliform bacteria commonly found in the intestines of animals and humans.”)

Olfers and Prescott Wastewater Superintendent Scott Gregorio noted that three recent rounds of sampling and testing had shown E. coli levels above the maximum allowed for both full-body contact (swimming, which is already prohibited in Watson Lake), and partial-body contact (boating, fishing, and kayaking).

The U of A Cooperative Extension website lists the maximum for full-body contact at 235 CFU (colony-forming unit) per 100ml, and a 575 maximum for partial-body contract. The recent tests have exceeded both levels, Gregorio said.

Olfers said the city would be putting out a notice to the public about limited contact. “We’re on our third round of testing, and bacteria counts are higher than normal in the lake and in the creek,” he said.

Olfers and Gregorio said there is currently no prediction on how long it might take for the E. coli levels to drop.

“I think it will go down quicker in the creek, but the lake is really going to be a challenge,” Olfers said. “We’re going to have to keep testing until such a time that we show we’re below the limits.”

Throughout the cleanup, the city has been following a procedure required by the Arizona Department of Environmental Quality (ADEQ).

Olfers said city staff spoke with ADEQ representatives by teleconference on Monday morning. “They’re very much assisting us as much as they can,” he said, noting that much of the process involves getting data to the state agency. “Our response (to the overflow) – all of that is documented and sent to ADEQ,” he said.

Among the data will be the quantity of sewage that flowed into the creek, although Olfers and Gregorio said that figure was still being calculated on Monday.

Olfers said that the city still has a goal of having Granite Creek Park opened back up to the public by Tuesday, March 28.

Follow Cindy Barks on Twitter @Cindy_Barks. Reach her at 928-445-3333, ext. 2034, or cbarks@prescottaz.com.


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