Water Well Journal

September 2015

Water Well Journal

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A cross the country and around the world, climate change is altering the hydrologic cycle. These changes have caused moderate to severe drought conditions in some areas, resulting in increased reliance on groundwater wells. The design of a water supply well relates specifically to the well's hydrogeologic environment and its intended use (public supply, in- dustrial use, agricultural, etc.). Because climate change or drought conditions will impact the water table depth or groundwater quality in a well, the de- sign of the well should accommodate those changes. California is a prime example of the effect drought conditions have on an area's reliance on groundwater supplies. California has been in the throes of "severe," "extreme," or "exceptional" drought conditions for several years. As can be seen from Figure 1, drought conditions are a lingering problem in California, as well as several other western states. In response to these extraordinary drought conditions and associated re- ductions of surface water allotments, California farmers and homeowners have contracted for the drilling of liter- ally hundreds of new agricultural and domestic wells during the past few years. Capital Public Radio reported the rate of agricultural and domestic well installation in Fresno County almost doubled—from 362 wells in 2012 to 705 wells in 2013, with a further in- crease to 804 wells through September of 2014. Although the number of wells doesn't necessarily reflect the quantity of groundwater being pumped, increases in groundwater withdrawals will likely result in water table declines, which will cause or intensify one or all of these problems: • Reduced flow rate (gpm) and reduced well performance (specific capacity) from wells • Increased potential for cascading water • Potential need for deeper pump settings • Higher energy costs to lift the water from deeper levels in the well • Increased risk of seawater intrusion (for wells in close proximity to a shoreline) • Potential for land subsidence, with associated infrastructure damage • Potential to create or increase sand invasion during pumping • Potential degradation of water qual- ity, which may necessitate wellhead treatment. The last three items listed may not be intuitively obvious. When over-pumping of an area results in a significant drop of the water table, fine-grained sediment layers containing substantial quantities of groundwater may be drained, and will collapse—resulting in an actual drop of the land surface. This has already been documented to have caused 30 feet of land subsidence in California and 18 feet of land subsi- dence in Arizona (Figure 2). Additional drops in the water table may cause this trend to resume, which can collapse well casings, disrupt drainage structures, and cause earth fissures. The potential for sand production from a well is enhanced by increased velocities of the groundwater entering the well. When water flows into the well at higher speeds, it becomes capable of Flexibility is key when installing a water well system today. By Donald P. Hanson, RG, and Marvin F. Glotfelty, RG DROUGHT continues on page 18 Figure 1. U.S. drought monitor map for July 14, 2015. WWJ September 2015 17 Twitter @WaterWellJournl

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