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PasswoYds The Importance of Groundw r Groundwater fills the spaces between soils particles. and fractured rock underground Image compliments of LIS Geological Survey, adapted by The Groundwater Foundation ooking through my files, I discovered articles on groundwater dating back to 1968. Re-reading some of the data makes it clear that the immense value of groundwater has gradually moved it to the forefront of concern, study, and action. Yet, I will bet that the public as a whole does not have a firm understanding of what groundwater is. Groundwater obviously deals with water and the ground, but how? In my understanding, there are four zones involved in groundwater: surface, or free-water, zone: water on or at the surface of the ground, which includes our lakes, rivers, bogs, and marshes; capillary or unsaturated zone: water drawn into the soil by capillary action and seepage that dampens the soil. If you dig a hole in the soil it will not fill with water; saturated zone: the true groundwater zone-also called an aquifer if it extends over a large area underground- where water has filled, or saturated, the pores in soil or in rock. If you dig a hole here, water accumulates. The top of this zone of saturation is called the water table; and, bedrock: this serves as an impervious floor to the aquifer. Aquifers can lie above other aquifers. Geologic formations can have impervious layers of bedrock interspersed with porous bedrock. A well can be drilled through more than one aquifer. Precipitation is the main source of groundwater recharge. The depth. of the water table from the surface varies from place to place, depending upon the character of the soil or rock, the amount of precipitation, and the amount of water drawn from the aquifer. It is often stated that of all the water in the world, only three percent is fresh. The rest is saline, or salt water. Of the three percent that makes up fresh water, two-thirds is locked up in ice caps or glaciers. That leaves only one percent of the world's water available for our use. A User's Guide to Ground Water, published by two Minnesota state agencies in 1984, tells us that nearly two-thirds of the fresh water available in Minnesota is groundwater. The balance is in our lakes, rivers, marshes, soil, or atmosphere. Another interesting statistic on groundwater: If all of the groundwater in Minnesota were somehow brought to the surface, every inch of the state would be covered with ten feet of water. The state of our state depends upon usable groundwater. Nearly all of our rural communities get their drinking water from wells. In the United States, 45% of the groundwater is used by agriculture and 45% by industry, leaving FACETS December 2003 Grottndzoater continrted on next page Fractured rock Gravel