Groundwater well construction in the Central Valley, California. Photo Credit: Chad Ress (www.chadress.com).
Humans rely on two main sources of freshwater: surface water and groundwater. Groundwater is often considered an invisible resource, difficult to understand, and challenging to manage sustainably. Unlike surface water resources, groundwater flows slowly under our feet through cracks in rocks and spaces in sediments. Unlike surface water’s grand infrastructure (e.g., reservoirs, dams) groundwater infrastructure (i.e., groundwater wells) is small, distributed, and often lost among landscapes. People map surface water infrastructure and photograph iconic reservoirs and dams, but can the same be said for groundwater infrastructure? Have you ever wondered where we get groundwater from or who uses groundwater?
A recent analysis of groundwater infrastructure analyzed 12 million well construction records, mapping wells for domestic, agricultural and industrial uses across the United States. Groundwater wells are distributed densely across the United States—from California to New York City and from Washington State to Florida.
The analysis shows that groundwater wells are being drilled deeper over time across much of the United States. The decision to drill deeper wells may be motivated by many and multiple reasons. Factors that may drive a person to drill a deeper well include (i) improvements in pump and bore technologies, augmenting abilities to construct deeper wells, (ii) “discoveries” of deep productive aquifers, (iii) more lenient rules governing use of deep groundwaters, (iv) real or perceived contamination of shallower aquifers, and (v) declining water tables that threaten to leave existing, shallow wells high and dry.
Irrigated agriculture in the Central Valley, California. Photo Credit: Chad Ress (www.chadress.com).
Regardless of the factors driving groundwater users to drill deeper for water, the finding that water wells are being drilled deeper across large swaths of American has several ramifications.
First, drilling deep wells is costly. For example, constructing a domestic well in California typically costs tens of thousands of dollars. Irrigation wells can cost upwards of hundreds of thousands of dollars. Not all groundwater users can afford new or deeper wells, even where constructing deeper wells is feasible.
Second, the level of water in a well tends to be farther underground in deeper wells. Therefore, pumping water from deeper wells usually requires more energy to lift well waters up to the land surface relative to shallower wells with shallower water levels, all else being equal. The ramification: drilling deeper wells is likely increasing the energy intensity of groundwater use, which could increase greenhouse gas emissions for pumps powered by fossil fuels.
Third, drilling deeper is becoming impractical in some places because of the properties and quality of the groundwater system. At some depth, stored groundwaters become too saline for use without desalination. Further, some deeper rock formations have low permeability, meaning wells perforated in these zones are unable to pump water at useful rates. For example, wells cannot be drilled deeper in some parts of the central and southern High Plains without entering zones of low permeability that also contain brackish water. Groundwater levels are declining in these same parts of the High Plains. Because wells cannot be drilled any deeper, existing wells may run dry if groundwater levels continue to decline.
This work concludes that deeper well drilling is widespread in the USA; this strategy represents no more than a stopgap to many groundwater problems.