US groundwater supplies are smaller than originally expected, according to a new research study that includes the University of Arizona's hydrology.
The study provides important information on the depths of underground fresh and brackish water in some of the most important sedimentary basins across the US
Research by scientists from the University of Saskatchewan, UA and the University of California, Santa Barbara was published November 14 in Environmental research letters.
"We have found that supplies of drinking groundwater in the US are not as deep as previously mentioned, meaning that there is less groundwater for human and agricultural use," said Jennifer McIntosh, Arizona University Science Professor and Professor of Hydrology and Atmospheric Sciences .
Drilling deeper boreholes may not be a good long-term solution to offset the growing demands on groundwater.
"We show that there is potential for contamination of deep fresh and brackish water in areas where the oil and gas industry injects sewage into or near these water bodies," McIntosh said. "This drinking water supply is already exhausted from bottom-up activity of oil and gas.
"Groundwater is the primary source of household supplies by about half of people living in the US," said McIntosh, who reports that about 40 percent of all water used in the US for irrigated farming comes from groundwater. "In Tucson, Arizona, about half of the drinking water comes from groundwater."
Many rural areas in Arizona and other parts of the US rely solely on groundwater for both agricultural and domestic use, she said.
To find out how deep drinking groundwater is expanding, scientists analyzed data on chemical properties of water from the US Geological Survey for 28 key sedimentary basins in the US and examined the correlation between well depths and the depth of transition between fresh and brackish water.
So far, attention has been focused on the monitoring of declining surface areas, said lead author Grant Ferguson, principal investigator of the Global Water Futures project led by the University of Saskatchewan.
In parts of the western US, known to geologists as the catchment area and area, fresh groundwater spreads on an average of 3,400 feet, McIntosh said. This province includes Nevada, southern Arizona and New Mexico, and is located in parts of California, Utah, Oregon and Idaho.
A new survey found that the average depth of transition from fresh to brackish groundwater in the US is roughly 1800 feet, which is in contradiction with previous studies suggesting that fresh groundwater extends to 6500 feet.
Especially in parts of the eastern US he found that the transition from fresh to brackish water was less than 1000 feet. In such areas, drilling deeper wells is not a long-term solution to the need for fresh water, he wrote.
"There are a number of scenarios where you could potentially go up to a kilometer or so deep for fresh groundwater, but there are other areas of the United States where you might encounter saltwater groundwater in no more than 200 or 300 meters – basically you made in terms of water resources, "said Ferguson, a professor at the University of Saskatchewan, Saskatoon, Canada.
In addition, water, chemical or sand injection, such as hydraulic fracturing or "fractionation", or injection of waste water can cause water containing hydrocarbons to adjacent areas containing potable water.
Collaborator Debra Perrone, an environmental scientist at the University of California at Santa Barbara, said: "In some river basins, the wells are installed shallower than the transition from fresh to brackish water."
Addressing how much separation of groundwater resources and oil and gas activities is needed to protect groundwater will require further research, the team writes.
Based on US findings, the authors suggest that the amount of fresh groundwater available around the world may also be less than previously thought. They note that it is estimated that more than five billion people live in precious areas, many of which rely on groundwater and where, in some cases, much more water is removed from the groundwater basin than it is near.