As the old adage goes, ground water is "out of sight, out of mind." Unlike surface water, which can be readily seen, there are a number of misconceptions and myths surrounding ground water. As NYRWA’s groundwater/source protection specialist, I have had to dispel many of these commonly held misconceptions at public meetings and gatherings. In the future, I hope to write a series of articles about groundwater conditions throughout New York State. Therefore, I thought that it would be best if I cleared up some of these misunderstandings first. So here goes…..

Misconception #1

Ground water occurs in underground lakes and streams.

99.9 times out of one-hundred, this statement is false. Ground water is subsurface water that fills the tiny spaces between mineral grains or cracks (fractures) in rock (see Figure 1). This is analogous to water being held in a sponge or a tiny pipe network. Only in rare instances, in so-called karst terranes, does ground water flow in underground lakes or streams. Karst terranes are found where fractures in limestone or dolostone have been significantly enlarged by chemical solution. This solution activity (i.e. dissolving of the rock) can eventually result in localized cavernous conditions. Large-scale cavernous conditions only potentially occur in a very narrow belt of carbonate rock that stretches up the Hudson Valley and across central and western New York. Howe Caverns in Schoharie County is arguably the largest example of a well-developed karst feature in this carbonate rock belt.

Figure 1: Ground water occurs in pore spaces or fractures

Misconception #2

All water beneath the land surface is ground water.

Ground water occurs in the saturated zone beneath the land surface, where all open spaces are completely filled with water. The upper boundary of the saturated zone is the water table. This is illustrated in Figure 1. Above the water table, the open spaces in soil and rock are filled with air and water. This is the unsaturated zone. Water found in the unsaturated zone does flow to wells and is not ground water.

Misconception #3

Ground water, such as spring water, comes from deep within the Earth.

All ground water originates as precipitation that has infiltrated through the soil and into the saturated zone. Once in the saturated zone, ground water flows at relatively slow rates of a few feet per day or year. However, ground water has different residence times from the point where it originates as precipitation recharge to where it reaches wells, springs, and surface water. As Figure 2 illustrates, this residence time may range from days or months in the case of a spring to several months or years for a typical well. For deep or highly confined aquifers, the ground water may be several years, even decades or centuries old. In New York, with our hilly topography, much of groundwater flow is local in origin and occurs at shallow depths. Flow lines are relatively short, from local topographic highs to local topographic lows such as along lakes and streams.

Figure 2: Typical groundwater flow and aquifer settings

Misconception #4

High-producing wells should be located using dowsing.

For every successful well that has been sited by a dowser, there are many more unsuccessful wells that you never hear of. Have you ever wondered why dowsers never charge for their services? Scientific studies have shown that dowsing does not improve your chance of finding suitable a ground water supply. This is especially true of locating a municipal or other high-yielding well. Such wells are located using a hydrogeologic investigation typically beginning with a desktop study of available information. I have helped many water systems with this initial phase of study since wellhead protection is a critical consideration in planning for a new supply well.

Misconception #5

Ground water and surface water are not closely linked.

Both ground water and surface water are part of the hydrologic cycle. As illustrated in Figure 3, ground water flows toward and is discharged into streams, lakes, and wetlands. For example, in summer months, ground water sustains the flow of most streams. This is termed baseflow. Under some natural conditions, such as flooding events, surface water can flow toward and replenish ground water. Under pumping conditions, surface water can be induced to flow toward a well. This is illustrated in Figure 3. This condition can be favorable for increasing yields, but can lead to water quality difficulties if there is inadequate ground water travel time from the surface water body to the well. The latter situation is termed ground water under the direct influence of surface water.

Questions??

If you have any questions about ground water or your groundwater sources, please do not hesitate to call me at 1-888-NYRURAL. Remember that ground water is an ample resource if properly managed, but it is more prone to contamination or over utilization compared to surface water. To prevent this, it is a good idea to develop a wellhead protection plan with NYRWA’s free assistance.