Originally Published: March 2, 2017 6:02 a.m.
The bright yellow warning signs said it all: “Water may be sewage contaminated. Do not drink. Do not fish. Avoid contact.”
If the signs did not get the attention of visitors to Prescott’s Granite Creek Park this week, the “caution” tape strung along the bank of Granite Creek, as well as the two city wastewater trucks that were vacuuming water from a small pond, probably did.
In fact, the downtown-area park was closed to vehicle traffic from early Tuesday morning, Feb. 28, until this morning, Thursday, March 2.
The reason for the warning signs, say city officials, was an “inundation of inflow and infiltration” to the city’s sewer system.
In other words, Prescott Utilities Manager Craig Dotseth said, the 2.25 inches of rain that fell in the Prescott area Monday and Tuesday, Feb. 27 and 28, caused flooding, which inundated the sewer lines.
He explained that in flooding situations, water gets into the system through manholes, as well as through cracks in sewer lines.
Ultimately, the flood water caused untreated sewage to breach the wastewater treatment system and spill into the nearby Granite Creek.
That set off a state-required cleanup procedure, which started with the city’s sanitization of the area with a chlorine solution.
“ADEQ (Arizona Department of Environmental Quality) has requirements for cleanup,” Dotseth said. Along with the sanitization early Tuesday, crews also were busy raking up the grass and dirt in the area and hauling it away.
In addition, Dotseth said, the city sent in two large wastewater trucks, which are equipped to vacuum up the contaminated water and haul it off to be treated. The city also brought in bypass pumps that transferred the overflow water from one part of the system to another.
As the flow started to subside Tuesday evening, crews were able to discontinue the use of the pumps. By about noon Wednesday, the two wastewater trucks were still on site, vacuuming up the remaining contaminated water.
Because of the volume of runoff water involved, Dotseth said the sewage that flowed into Granite Creek was “drastically diluted.”
Prescott Recreation Services Director Joe Baynes said the dilution of the sewage would mitigate the impacts to the recreation uses of the creeks and lakes.
Although the signs at Granite Creek Park warned against use of Granite Creek on Tuesday and Wednesday, Baynes said no similar warning was needed for Watson Lake, which receives the flow of Granite Creek. He said fishing would still be safe at the lake.
“The sewer’s just inundated with rainwater,” Baynes said, maintaining that the impact from the sewage “is so minor in the big scheme of things.”
Still, Watson Lake and Granite Creek have for years been designated as impaired bodies of water for E. coli contamination and other pollutants. A 2015 ADEQ report on the Granite Creek contamination identified “sanitary sewer overflows and septic seepage” as two of the causes of the pollution.
While overflows of the wastewater treatment system have happened before, Dotseth said the most recent such incident was about seven years ago. The city dealt with a spill in 2010, he said, as well as in 2005 and 2008.
Coincidentally, Dotseth said, on the same day his department was dealing with this week’s spill at Granite Creek Park, the Prescott City Council was approving several multi-million-dollar wastewater improvement projects that are intended to prevent such incidents in the future.
In a series of votes on Tuesday, Feb. 28, the council approved: a $2.3 million Sundog trunk main project; a $2 million wastewater treatment plant lift station; a $2 million design for a Highway 89 lift station; and a $220,000 design for design of a second phase of a Sundog trunk main.
Although the improvements are part to the city’s goal to centralize its wastewater treatment at the airport plant, Dotseth said, “The projects the council approved yesterday are all directly related to solving the capacity issues of this storm event.”
ADEQ Public Information Officer Caroline Oppleman said Wednesday afternoon that the City of Prescott was required to report the spill to the state within 24 hours, and “they fulfilled that requirement.”
The city is now required to file a report about the spill with ADEQ within five days. Part of the information expected in that report is the approximate amount of the discharge.
Dotseth said late Wednesday that city does not yet have an estimate on the volume.