The need for more water for urban and agricultural uses has drive even more competition for limited supplies in stressed basins. The effects of urbanization and agriculture on surface water supplies are obvious to most people. We have also seemed the ecosystem impacts from surface water diversions and pollution. As a result, many areas have pursued groundwater, the unseen resource.
I have been touting a USGS report (#1323 by Reilly, et al, 2009) to many in the water industry. It is an important report that gives us a little insight on state of groundwater supplies in the US. As we have developed arid regions and developed better pumps to irrigate in dry places, groundwater has been the obvious choice. And it is not regulated in some states. However the extensive and in many cases excessive use of groundwater creates the long-term potential for loss of water supplies in many jurisdictions. Determining groundwater availability involves more than calculating the volume of groundwater within any given aquifer: it requires a consideration of recharge, water quality, the economics of recovery or of poor quality, interconnectedness with the hydrologic system and ecosystem/user demands. Rarely is a consultant paid to determine that sustainable water supplies are not available. The result is the potential for aquifer drawdown that are accompanied by aquifer mining and land subsidence. The result is declining water levels in aquifers.
Confounding the situation are confined aquifers that are disconnected for localized recharge and often have overestimated recharge. The common practice to evaluate aquifer productivity is pump wells that have a significant drawdown for only a few hours each day, allowing an extended period for the aquifer to recover. Reilly et al, 2009 estimates that the pumpage of fresh ground water in the United States is approximately 83 billion gallons per day (Hutson et al, 2004), which is about 8 percent of the estimated 1 trillion gallons per day of natural recharge to the Nation’s ground-water systems (Nace, 1960), which sounds like it is not a serious issue. However, Reilly et al, 2009 found that the loss of groundwater supplies in many areas will be catastrophic, affecting economic viability of communities and potentially disrupting lives and ecological viability.
Drilling deeper is not a solution. Deeper waters tend to have poorer water quality as a result of having been in contact with the rock formation longer and dissolving the minerals in the rock into the water. Additional power will be required to further treat limited, lower quality supplies. Therefore, while some deep aquifers may be prolific, the quality of water obtained from a well may not be desirable or even usable for drinking water without substantial amounts of treatment. In addition, most deeper aquifers are confined and therefore do not recharge significantly locally. The withdrawal of water may appear to be a permanent loss of the resource in the long-term. For example, portions of the aquifer in eastern North and South Carolina were virtually denuded in due to pumpage because there is no local recharge. As a result the aquifer was mined, exceeding its safe yield, and the large utilities converted to surface water. Likewise, most of the aquifer use in the western states of the U.S. are poised similarly since they have minimal potential for recharge. In parts of the western plains state and Great Basin, the aquifers have dropped hundreds of feet, but with an average of 13-18 inches per year of rainfall, and high evaporation rates throughout the summer, little of this water has potential to recharge the aquifer (Bloetscher and Muniz, 2008).
Rarely will permit writers or consultants tell you there is no more water available, but if groundwater levels keep declining, clearly the groundwater is over allocated. It also appears that we have misjudged recharge to most confined aquifers. They simply do not recharge at the rates estimated creating a long-term decline. In some cases, maybe many cases, recapturing the water needed to recharge the aquifer will not happen in our lifetimes without specific capital to do otherwise. Nature just doesn’t recharge confined aquifers quickly. One reason we like them for water supply.
So the questions are these:
Are many confined aquifers better suited to be drought protection, backup supplies to surface supplies, as opposed to primary water supplies?
- What is the solution for agricultural operations and utilities where groundwater is quickly diminishing?
- When can we start the dialogue to manage groundwater resources better in the US without all the legal and political constraints that currently work against protecting our nation’s groundwater supplies?
Clearly we won’t make everyone happy, and may make a lot of people very unhappy. But better to make those decisions now, than in 20 or 30 years when the groundwater runs out?