A 36-inch water pipeline that the City of Prescott built late last year to bring water from Chino Valley to Prescott may not be safe.
At issue is the compaction of dirt along the pipeline. Engineering plans and specifications called for a 95-percent compaction for the pipeline that runs south of Center Street through the town.
Prescott said it ran compaction tests after construction and that 100 percent of the line passed those tests.
Then, residents and council members noticed that the ground around the pipeline was showing considerable signs of settling in some areas.
"The last time it rained, the pipeline trench on Road 4 South settled four feet," said Vice Mayor Russ St. Pierre. "The chip sealing from the road was falling into the trench. I’d say that’s a good indication that the compaction isn’t there."
So Chino Valley ordered its own tests, said Stu Spaulding, Public Works manager, and all pipeline areas tested failed compaction testing.
At that point, Spaulding asked the Arizona Department of Environmental Quality (ADEQ) to work with Chino Valley and Prescott to ensure the integrity of the Prescott pipeline.
In a third test, ADEQ asked the engineering company that passed pipeline compaction at 100 percent to perform tests again. This time ADEQ, Prescott and Chino Valley supervised testing, and more than 85 percent of the pipeline trench tests failed.
"This 36-inch-diameter water pipeline is under 4,000 pounds of pressure, and if the line separates because of improper compacting, it is a serious danger to the citizens of both Chino Valley and Prescott," Spaulding said. "The line was not compacted to the standard 95 percent compaction specified by engineers."
Town Council members approved a resolution they hope will expedite repairs of the line.
Chino Valley, in cooperation with Yavapai County, is planning to build roads over a large portion of the pipeline. But they can’t build roads until the entire line passes compaction testing at the specified 95 percent.
Peter Foster, ADEQ community liaison, said he is negotiating with Prescott officials about bringing compaction up to the expected standard and thinks they are close to an agreement. But Prescott reportedly wants to compact one section at only 85 percent.
"Don’t you require engineers to adhere to a set of plan specifications as originally submitted?" St. Pierre asked Foster. Pipeline compaction of 95 percent is a standard requirement throughout the Prescott area.
And now, town officials and Chino Valley citizens are questioning the integrity of the entire 20-mile pipeline.
They wonder if the improper compaction has affected pipeline bedding. Foster said he is inspecting other construction documentation to make sure that pipeline bedding is sound before they go ahead with compaction of the top four feet of soil.
Chino Valley resident Norm Freeman asked ADEQ and the town to "look beyond just re-compacting. The pipeline may need other stabilizing because it has had an opportunity to move because of poor compaction during original construction."
Another resident asked if we should be concerned about the quality of installation of earlier, smaller water pipelines that Prescott installed through Chino Valley.
Resident Mike Nelson urged Chino Valley officials to notify local emergency agencies "that there is the potential for breakage," and the council directed staff to take that action.
Foster said ADEQ considers the compaction problem "a potential threat to health and safety."
The 36-inch pipeline is carrying water from Chino Valley to Prescott and the pipeline could leak or break because of poor compaction.
"If the pipeline is taken out of service for any reason, it would be a danger to residents of both Prescott and Chino Valley," Spaulding emphasized.
A Prescott official confirmed that the city is working with ADEQ to determine what, if any problems exist.