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50 Ways Farmers Can Protect Their Groundwater
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36. Know Your Well Site Conditions


Certain characteristics of the land where your well is located have a significant effect on water movement and the risk of groundwater contamination. The major characteristics to consider are: soil type, depth to aquifer, type of aquifer, other geologic conditions, precipitation, and temperature.

An "aquifer" is an underground zone saturated with water and capable of delivering water to a well at a usable rate. If the aquifer from which you draw water is within 50 feet of the surface, it is generally considered to be a shallow aquifer. These aquifers are more likely to become contaminated than deeper aquifers.

well log The best way to determine the aquifer's depth is to obtain a well log. If you do not have the log, check with the previous property owners or the company that dug the well. Otherwise, contact the Illinois State Geological Survey, Illinois State Water Survey, or local well drillers.
unconfined aquifer The potential for contamination also depends on the type of aquifer. An unconfined aquifer is bounded by geologic materials through which water easily moves.
confined aquifer A confined aquifer is bounded on the top by geologic materials through which water moves very slowly, such as clays, shales, dense crystalline, and sedimentary bedrock. Generally, confined aquifers offer cleaner, safer water; but if chemicals enter them, it takes a long time to decontaminate them.
shallow limestone or dolomite deposits Regions with shallow limestone or dolomite deposits can be particularly susceptible to groundwater contamination because water may move rapidly through dissolved caverns or sinkholes.
sinkhole Once water enters a sinkhole, it receives little filtration or chance for degradation of the chemical. Fractured rock systems also allow rapid movement of contaminant-bearing water.

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