DROUGHT AND GROUND WATER
This article, written by the American Ground Water Trust was originally published in
THE AMERICAN WELL OWNER, 2002, Number 3]
"We know the value of water when the well runs dry." - Benjamin Franklin
A drought is defined as a period of abnormally dry weather that persists long enough to produce significant water supply problems in a particular area. The severity of a drought is related to the size of the area affected, the magnitude of the water deficiency and how long the drought condition persists. Currently about one-third of the United States is in a moderate to extreme drought condition.
A drenching rain storm is a welcome event during a drought, but it may not have a big impact on replenishing the ground water supply if the stormwater runoff volume is high because of large areas of impervious development (pavement, roof tops, lawns vs. woods), or if the volume of water exceeds the ability of the natural soil to accept the flow as fast as it arrives at the earth’s surface. Once infiltration begins it still may take weeks for the water to seep down to become ground water. During drought, well owners may deepen wells seeking to find additional water-bearing fractures. Storage capacity may be increased by drilling wells deeper or by installing tanks in basements (follow local regulations for this work), but the total amount of ground water available on a daily basis to private well owners or a municipal well system will not increase until infiltration and recharge increase as the drought abates.
During drought, water well yields may decline and potentially cause a change in the quality of the water. Changes result from the drought’s affect on the “mixture” of water in the well. As we draw water from a well new (i.e., recharge) water flows into the well from fractures and pore spaces in the rocks surrounding the drilled hole.
There may not be enough rain during a drought to replenish the water in a shallow bored or dug well because the recharge is typically obtained from recent precipitation (rain or snow) in a matter of hours or days. The water quality usually remains consistent in a shallow well even with a reduction in the quantity of water because the water recharging the well has had little time to react chemically with the surrounding rock. However, the quality (increased odor, cloudiness [sediment], and bacteria, etc.) may change quickly just before the well actually goes dry, especially if the pump intake is near the bottom of the well.
Water from deep bedrock wells may represent a “cocktail mixture” of water added from different fractures and rock layers that the recharge water contacts during its travel to the well from the surface. Generally, the fracture supplying the most of the water will have the greatest impact on the quality of the water in the well. This might not be true if a “small” fracture supplies a modest volume of water, but with an unusually high concentration of a particular substance (e.g., sediment, radon, hydrogen sulfide (rotten egg odor), etc). In this case, the concentration of the substance in the well water may be significantly affected by this part of the cocktail mixture. During a drought or period of seasonally low water, some fractures may go dry before others and thus change the chemistry of the water. When the “normal” water level returns the former water chemistry conditions are likely to return.
The Trust recommends testing well water annually for bacteria and nitrates, or whenever you notice a significant and persistent (continuous for several days) change in the aesthetic quality (odor, taste, color) of your well water. Before making an investment in a water treatment system it may be prudent to wait a few months to see if the quality will return to normal as the ground water levels change with the seasons or the end of the drought. In most cases ground water levels are highest in the spring and lowest in the fall.
Additional Sources:
National Oceanic and Atmospheric Administration (NOAA) Website:
What is drought?: http://www.drought.noaa.gov/
What regions of the United States are in drought?:
http://www.cpc.ncep.noaa.gov/products/expert_assessment/drought_assessment.html
[© American Ground Water Trust. This article may be reprinted for non-commercial educational purposes provided it is used in its entirety and that reference is made to its source as an article in THE AMERICAN WELL OWNER, 2002, Number 3]