Column: A different angle on water

Aquifer supply is much more than story indicated

Last Sunday, there was an article in the Daily Miner about the U.S. Geological Survey and Arizona Department of Water Resources status report to the county supervisors. The report is part of the Rural Water Initiative study being conducted across the state.

We have three major aquifers in this part of Mohave County - the Detrital, Hualapai and the Sacramento Valley. The Detrital flows from Dolan Springs to Lake Mead, the Hualapai flows from the Hualapai Mountains and Kingman north toward the Colorado River, and the Sacramento Valley begins at Chloride/Golden Valley and flows south through Yucca and Topock to the Colorado River. The various mountain ranges form the dividing lines (and the natural blocks) between the aquifers.

The crucial question is just how much water is available to serve our future needs in the county. Unfortunately, the article "muddies" the water by reporting only part of the story from a 2007 study, and it expresses a fundamental misunderstanding of the recently completed groundwater "budgets" in these three basins. It presents a picture that doesn't accurately portray just how much water is available.

First, the article reports from the USGS 2007 study about occurrence and movement of groundwater, and also well water level changes in 330 wells across the three aquifers. The article quotes from the introduction that there were substantial declines in well levels, "... as much as 55 feet." However, it fails to note that that same introduction reports that many, if not most, of the wells were at the same level or even increased in water levels in all three basins.

Furthermore, when you look further into the body of the report, including a map showing all the wells, you see a much greater discrepancy. Of the 330 wells studied, the overwhelming majority showed negligible drops to gains of up to 20 feet since 1980. In fact, several wells in the study even showed major increases in water levels throughout the county. The study, in spite of its bias, basically reports that water levels are stable throughout the county, with the exception of some wells north of Kingman.

Second, it expressed a fundamental misunderstanding of the recent report, about the water budgets in the three aquifers. The story accurately reports the amount of water in the three basins. Those amounts, in millions of acre-feet, were 15 in Hualapai, 16 in Sacramento Valley, and 4.5 in Detrital. However, the reporter noted that only 15 percent of the amounts in each basin was available. That is a crucial mistake.

The presentation by Ms. Truini stated that due to the coarseness of the ground, there was a 15-percent water yield from the ground in the Hualapai and Sacramento Valleys. However, in the Detrital, due to the fineness of the sandy soil, there was only the potential of an 8-percent yield.

So instead of the small amount of water available, according to the report, only 8- to 15-percent of the figures above, the FULL amount stated in the article is the amount of water in the first 1,300 feet below land surface! That's a huge difference of available water that needs to be explained further.

The amount of water a normal household uses in a year is between one-quarter and one-half acre-foot per year, or about 80-160,000 gallons annually. My household in Golden Valley used only 5,300 gallons last month. According to the study, we were withdrawing about 2,400 acre feet per year in 2007-2008, in the Sacramento Valley.

That doesn't include the Mineral Park mine, which uses much more than that. For sake of argument, let's assume with future growth in population and industry, we start withdrawing 10 times that much, or 25,000 acre feet per year. If there was that much withdrawal of water from the water storage area above 1,300 feet below the surface, it would take 160 years to withdraw only one-fourth of the total water in the Sacramento Valley aquifer!

If I apply the same analysis to the Hualapai, but only increase the withdrawal five-fold to 49,000 acre feet, it would take over 100 years to withdraw one-third, or 5 million acre feet of the water available in that aquifer.

This is a far different picture than the one painted in the article, one that I believe is more reflective of the information in these two reports. That is the real story.