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Tue, Oct. 15

Scientists pull 'plug' on aquifer flow<BR>Say that hydrology does not support city's contention pumping won't affect Verde

PRESCOTT – The notion of an underground "clay plug" that would protect the headwaters of the Verde River from the pumping that the City of Prescott might choose to do in the future took a beating Saturday.

In front of a packed room of about 100 people, two retired U.S. Geological Survey (USGS) scientists punched holes in the theory that an underground clay formation separates the CV/CF Ranch area from the area where the Verde River originates.

"The implication of (the clay plug) is that you can pump water to your heart's content, and you won't affect the flow of the Verde River," said Ed Wolfe, a retired USGS volcanologist. But, he maintained, neither the hydrology nor the geology support that idea.

Bill Meyer, a retired USGS hydrologist, agreed, pointing out that the Big Chino Valley basin has been the topic of a number of studies through the years. The first and only mention of the existence of a clay plug turned up in a 1990 study that the City of Prescott paid for, he said.

Meyer explained that groundwater is always moving through the system. As new water recharges in, he said, "it has to come out somewhere. If the water weren't able to get out, (the area above the barrier) would be a lake."

He theorized that the water comes out at the lowest point – the headwaters of the Verde River. "You know it's going somewhere; that's gravity," he said.

The presentation by Meyer and Wolfe was a part of the regular meeting of the local Citizens Water Advocacy Group (CWAG). The topic was obviously a popular one among the group's members and others in the community, with the meeting attracting more than double the number of dues-paying members.

Indeed, the Big Chino basin is once again under intense scrutiny in the community, because of the City of Prescott's interest in buying 50,000 acres of ranchland in the area. For nearly a year now, the city has been studying the possibility of spending $30 million to buy the Paulden-area CV Ranch as a future source of water for the tri-city area.

Since the spring of 2003, when Prescott's year-long option to buy the ranch began, the city has been conducting a number of studies to determine whether to go ahead with the purchase.

As recently as November 2003, in a report to the Prescott City Council, consultant hydrologist Bill Wellendorf reported on the existence of a formation that he said would slow the flow of the groundwater within the basin.

Wellendorf stopped short of calling the formation a clay plug. Instead, he said it is "playa" material similar to clay. Although Wellendorf said the formation would not stop all water movement in the basin, he maintained that it would be "an impediment to the groundwater flow."

But Meyer said that even a slow movement of groundwater would have an eventual detrimental effect on the Verde River.

"Any drop of water that you take out of the basin is water that will not reach the Verde River," Meyer said. "But it's a question of time. It happens slowly over time."

Assuming that the City of Prescott would pump just over 10,000 acre-feet of water per year, Meyer and Wolfe calculated that the Verde River would not see much of an impact within the first five years. But at about 10 years, they said, the river would experience a noticeable decrease in flow. Ultimately, they predicted a 60-percent impact.

"Most of us could live our lives out and never see the impacts," Meyer said. "But the pumpage will affect the Verde River within decades, not hundreds of years."

CWAG's president, Kay Lauster, said City of Prescott officials plan to give a report on their findings about the CV Ranch at the group's March meeting.

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