The Board of Supervisors and county residents are getting one step closer to knowing how future growth will affect groundwater levels in the county.
Officials from the U.S. Geological Survey and the Arizona Department of Water Resources updated the Board on the ongoing studies of the Detrital, Hualapai and Sacramento Valley aquifers on Monday.
The Detrital aquifer serves the areas of Dolan Springs and White Hills. The Sacramento aquifer serves Chloride, Golden Valley, Yucca and parts of Kingman. The Hualapai aquifer serves Valle Vista, Hackberry, parts of Kingman and includes Red Lake.
Work on the studies started during the housing boom in 2005, said ADWR Statewide Rural Water Planning Manager Tom Whitmer. Federal, state and local officials became concerned that the county's groundwater resources wouldn't be able to support the population and commissioned the study.
According to information from ADWR, the last groundwater studies in the area were completed in the 1980s.
The new study of all three aquifers is nearly complete, Whitmer said. The only thing that remains unfinished is the numerical groundwater flow model, which should be finished next year.
The model is a tool the county, developers and others can use to project the impact of future development might have on the aquifers in the area, he said.
The first part of the study was completed in 2006 and includes the movement and current levels of water in the three aquifers as well as the geological makeup of the aquifers, said Margot Truini from the USGS.
The geological makeup of the aquifers is important because it determines how much water the ground can store, how quickly the aquifer will recharge and how much water you can get out of the ground, she said.
The 2006 study shows that the three aquifers all drain into the Colorado River. It also showed between 1943 and 2006 in the Detrital Valley Aquifer, water levels have either remained the same, or have steadily increased as much as 3.5 feet since the 1980s. Similar conditions were observed for much of the northern and central parts of Hualapai Valley Aquifer and in the Yucca and in the Dutch Flat area.
However, steady water level declines as much as 60 feet were found in wells in areas near Kingman, northwest of Hackberry, and northeast of Dolan Springs within the Hualapai Valley Aquifer and as much as 55 feet within the Sacramento Valley Aquifer for wells in the Kingman and Golden Valley areas.
The USGS estimates that there are around 15 million acre-feet of water in the Hualapai aquifer, 4.5 million acre-feet of water in the Detrital and around 16 million acre-feet in the Sacramento aquifer.
An acre-foot equals 325,851 gallons. According the USGS' website, the average person uses between 80 and 100 gallons of water a day.
However, not all of that water may be useable, Truini said. She estimated that because of geological formations and water quality, the Hualapai aquifer will only yield about 15 percent of its stored water; the Detrital will yield about 8 percent and the Sacramento about 15 percent.
She also warned that while that there might be a lot of water available, it might not be water that you would want to drink and the cost to drill to reach water in some areas may be prohibitive for some people.
The latest addition to the study is a water budget, said Brad Gardner from the USGS. The budget gives people an idea of how much water is entering the aquifers through recharge from rain, how much leaves through natural discharge to the Colorado River and human activity and how much returns to the aquifer.
According to USGS' calculations, 95 percent of the rain that falls on the three aquifers evaporates, is taken up by plants, or is runoff that never soaks into the soil, Gardner said. On average the three aquifers have seen a 24 to 50 percent increase in the rate of natural discharge and recharge from previous studies. According to the report, that is not unusual considering that previous reports used different approaches to measure the water.
The Hualapai aquifer is experiencing the greatest withdrawal rate at 9,800 acre-feet per year, he said. The aquifer is the main source of water for Kingman, but is also connected and flows into the Sacramento aquifer. The report estimates that since 2007 the aquifer is losing around 5,600 acre-feet per year of stored water.
The Detrital aquifer has a withdrawal rate of less than 300 acre-feet per year and is losing less than 300 acre-feet a year in storage, Gardner said. The Sacramento aquifer has a withdrawal rate of about 4,500 acre-feet per year and is losing around 2,400 acre-feet of storage a year.
At the same time, long-term natural recharge rates between 1940 and 2008 for the aquifers were estimated to be 1,400 acre-feet per year for Detrital Valley, 5,700 acre-ft/yr for Hualapai Valley, and 6,000 acre-ft/yr for Sacramento Valley, he said. Those numbers are based on the idea that the aquifers are recharging at the same rate as they are discharging water into the Colorado River.
Recharge from leaking water-supply pipes, septic systems, and wastewater-treatment plants accounted for about 35 percent of total recharge between 2007 and 2008 across the study area, he said.
Gardner warned that the numbers for the water budgets and the amount of water stored in each aquifer were estimates and not exact. There are a number of variables that cannot be accounted for such as the amount of rainfall in future years and the amount of runoff during a storm that ends up seeping into the ground to recharge the aquifer. All of that could change the figures.
The USGS has an interactive chart on each of the aquifers and their recharge, withdrawal and discharge rates online at http://pubs.usgs.gov/sir/2011/5159/. Residents can use sliders on the website to change a number of variables that effect the aquifers such as the amount of precipitation, the amount of water use by humans, the amount of evaporation and more. Each time a person changes one of the sliders the chart will recalculate all of the other variables on the chart.
The USGS and ADWR are still working on a numerical groundwater model which will allow someone to plug in theoretical numbers from possible future developments and see what effect those developments would have on the aquifers, said Fred Tillman, also from the USGS. The final report and model should be finished by September.