10/29/2009 5:15:00 PM Big Chino well level report is open to interpretation
Graphics courtesy of ADWR
A recent report from the Arizona Department of Water Resources shows that well water levels with the embattle Big Chino Basin have changed little over the last 10 years. On average the water levels of wells being monitored have changed less than one foot.
YAVAPAI COUNTY - The Arizona Department of Water Resources (ADWR) has released its first report on well water level changes in the Big Chino Valley in almost 15 years.
However, what the report has to say is a matter of interpretation.
The Big Chino report and its corresponding maps are just the fourth in a series of reports ADWR calls its Water Level Change Map Series.
According to Frank Corkhill, chief hydrologist for the agency's hydrology division, the maps and reports provide well level data for wells located in critical groundwater areas of the state, such as the Big Chino, upper San Pedro River and the Willcox basin.
The report on the Big Chino, which is available on ADWR's Web site, www.azwater.gov, covers the years 1999 to 2009.
According to the report, most of the wells levels in the Big Chino are at or near the same levels they were 10 years ago. Some areas, such as around the middle and lower valley, along with the communities of Paulden and in Williamson Valley's Mint Wash, have seen declines.
Some areas in the upper valley have actually seen water levels rise over the last 10 years.
Overall, according to the report, well levels throughout the Big Chino have changed less than one foot on average.
"The report shows that over time there has been a long-term balance between the amount of recharge and the amount of discharge to the groundwater system," Corkhill says. "It shows there are no significant impacts from groundwater withdrawals at this time."
The report also shows that well water levels vary significantly during the year as irrigation pumps are turned on and off, a situation Corkhill says is to be expected.
John Munderloh, water resource manager for the Town of Prescott Valley, notes the report is limited in its ability to show the workings of the aquifer but he agrees with Corkhill that it does show there is a long-term balance.
"The report is limited to single point comparisons of water levels year to year, and it doesn't necessarily demonstrate the overall aquifer.
"However, it demonstrates to me that the aquifer is resilient to both drought and pumping," Munderloh says. "And that the upper Chino remains a full aquifer. You just can't get much more water in it."
The Town of Prescott Valley and the City of Prescott own property in the upper Big Chino from which they plan to pump and transfer water to augment their municipal water supplies. Opponents feel the pumping will eventually impact the flows of the upper Verde River.
"I think the report also indicates the basin has separate characteristics in different locations. It shows the upper Big Chino has different influences than, say, the Williamson Valley arm or the Paulden area," Munderloh says.
Hydrologist Bill Meyer, who has authored several cautionary reports on large-scale pumping in the Big Chino, is complementary of the ADWR report, but does not see it as a validation that the aquifer is either in balance or resilient.
"I don't see the report as one of stability as much as I see it as an indication of how dynamic the system really is," Meyer says. "To say the system is stable is to say that pumpage is not affecting the system. That's not accurate.
"You can turn a well pump on for one second and the fact remains, that water is removed and will never make it to the Verde River. It may not show up for many years, but that water won't make it."
A similar report on well water levels in the Verde Valley is due out at end of November or early January, according to Corkhill.
