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Locating Your Well

High-Quality Water

Are you planning a new home on a site that is not served by a community water sysem? Or are you thinking of replacing your water well with a new well? If so, the importance of having a depend-able supply of safe, high-quality water cannot be overstated. Family health is at stake, and the market value of a home will refl ect any serious shortcomings in the water supply. The fi rst step in planning a new well is to fa-miliarize yourself with the geologic conditions of your site. If you plan to install a new well, these conditions will infl uence the kind of well you put in, how deep you will have to drill to obtain a dependable supply, and even the potential for future water contamination. To learn about the condition of your site, you can contact local well drillers, geologists, soil scientists, agricultural and civil engineers, and University of Illinois Extension staff. In addition, specialists at the Illinois State Water Survey

and the Illinois State Geological Survey can pro-vide advice on developing new wells and solving problems with old wells.

How Geology Affects Groundwater

Although groundwater occurs everywhere, its quality and the amount available varies from one location to the next. The variation is due to geo-logic formations underlying different areas, which affect impurities found in the water and the rate of water withdrawal. Some of the geologic fac-tors that affect groundwater are: permeability, depth to aquifer, and type of aquifer.

Permeability

Clay and Shale. Certain geologic materials, such as clay and shale, may contain abundant supplies of water in their minute pores. However, the movement of water between pores in clay and shale is so restricted that water cannot fl ow into a well in usable quantities. These formations

When water fi lls all of the spaces between soil particles or rock, it is called groundwater. The upper level of the groundwater is the water table.

Figure 1. Groundwater

have low water-yielding capability, or what is called low permeability.

Sand and Gravel. Other geologic materials capable of transmitting and storing signifi cant quantities of water, such as sand and gravel, are referred to as aquifers. In Illinois, aquifers are commonly found in bedrock (such as sandstone, dolomite, and limestone) and in overlying uncon-solidated deposits (such as sand and gravel). These materials have varying degrees of permeability.

Depth to Aquifer

If the aquifer from which you draw water is within 50 feet of the surface, it is generally con-sidered to be a shallow aquifer. Wells fi nished in very shallow aquifers may cost less to drill and may require a smaller pump, but they are subject to seasonal varia-tions in precipitation that can cause the water table to rise or drop signifi cantly. They are also more susceptible to surface sources of contami-nation than wells drawing from deeper aquifers.

If you drill into a deeper aquifer, however, there are no assurances that the quality of water will be good. Some deep aquifers are too highly mineralized or salty for most domestic uses. The best way to determine the aquifer’s depth is to obtain a well log. If there is an exist-ing well on the property, there should be a well log. If you do not have one, check with the pre-vious property owners or the company that dug the well. Otherwise, contact the state geological survey, state water survey, local well drillers, or your nearest Extension offi ce.

Type of Aquifer

There is a strong association between the detection of agrichemicals in rural wells and the type of aquifer from which water is drawn. The potential for contamination depends a lot on whether the aquifer is “confi ned” or “uncon-fi ned.”

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Figure 2. Aquifers

An unconfi ned aquifer is bounded by geologic materials through which water easily unconfi ned a q u i f e r i s b o u n d e d b y g e o l o g i c m a t e r i a l s t h r o u g h w h i ch w a t e r e a si l y unconfi nedmoves. A confi ned aquifer is bounded on the top confi ned a q u i f e r i s b o u n d e d o n t h e t o p confi ned by geologic materials through which water moves very slowly. Because of pressure inside a confi ned aquifer, the water level sometimes naturally rises in the well. This is called the “pressure head.” With an uncon-fi ned aquifer, however, water in the well remains at the same level as the water table—un-less it is being pumped upward. The water table is the upper level of the groundwater.

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Confi ned Aquifers. An aquifer is confi ned when it is bounded on the top by what is called an “aquitard”—geologic materials through which water moves very slowly. This material, such as clay, shales, dense crystalline, and sedimentary bedrock, helps prevent contaminants from enter-ing the aquifer.

Unconfi ned Aquifers. An unconfi ned aquifer is bounded by permeable layers—geologic mate-rial through which water moves rapidly. Generally, confi ned aquifers offer cleaner, safer water; but if chemicals should enter them, it takes a long time to decontaminate them. Con-fi ned aquifers may also be harder to fi nd and can be expensive to tap.

Location Requirements

When locating a new well, most people do not have a site large enough to offer a wide range of options. This is because a well’s location is ex-pected to meet several requirements. The following specifi cations are described in the Illinois Water Well Construction Code. Any variances must be approved in writing by the local health department or the Illinois Department of Public Health.

Figure 3. Minimum Setbacks

In the illustration above, the well is placed out of reach from several sources of contamination. The well is more than 25 feet from the stream, more than 50 feet from the barnyard, more than 100 feet from the manure pile, and more than 200 feet from the sand/salt storage pile and the underground fuel storage tank.

Boundaries. The well must be within your property lines. Its exact distance from property lines is governed by local codes.

Maintenance. The well must be acces-sible for maintenance, inspection, and pump replacement. For example, wells should not be located directly under trees or power lines or inside a house or basement. Wells also must be at least 2 feet clear of an overhang.

Groundwater Flow. Ideally, the well should be placed on the side of the contami-nant source opposite the fl ow of groundwater. For example, if you know groundwater fl ows to the south, place the well as far north of the contaminant as possible. To fi nd out the direc-tion of groundwater fl ow in your area, contact a well driller, an engineering fi rm, or the Illinois State Water Survey.

Contamination Sources. The well must be as far removed as possible from potential contamination sources and routes, such as septic tanks, road salt, underground gas stor-age tanks, manure piles, fertilized cropland, and solid waste disposal sites. The Illinois Department of Public Health has established the following minimum set-backs for common sources and routes of contamination:• At least 200 feet from potential sources and routes of contamination. However, if

What About Surface Water

as Drinking Water?

Surface waters (lakes, steams, ponds) generally are undesirable sourc-es of drinking water for private water systems because they require a high degree of treatment and are easily con-taminated. However, if groundwater is unsuit-able for a domestic supply in your area, then you may need to consider this op-tion. For technical assistance and advice on the potential costs and effectiveness of a surface water supply, contact the nearest offi ce of the USDA Natural Re-sources Conservation Service or Univer-sity of Illinois Extension.

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September 2007 September 2 0 0 7 September • Number 15

Sources

Bob Frazee, University of Illinois Extension natural resources educatorJerry Dalsin, Illinois Department of Public HealthBrian Kaiser, Illinois State Water Survey

Land & Water Coordinator

Michael C. Hirschi, U of I Extension soil and water specialist

the owner of the private well is the same as the owner of the potential source or route of contamination, the setback is 75 feet. (For information on sources and routes of contamination, see the sidebar below.)• 150 feet from existing cesspools. New installations of cesspools are not approved in Illinois.• 100 feet from leaching pits.• 75 feet from a pit privy or a septic seepage tile, which should be downslope from a well.• 50 feet from a barnyard, animal confi ne- ment lot, or septic tank.• 25 feet from lakes, ponds, and streams.• 10 feet from a sewer with watertight joints.• 2 feet from a pump house fl oor drain• 100 feet from a temporary manure stack. (This is an Illinois EPA setback require- ment.)

These lateral distances apply to clay- and loam-textured soils; they should be increased for more permeable soils. For example, these dis-tances should be doubled for highly permeable, coarse-textured soils, such as loamy sand. As you evaluate a site for your well, also consider future land uses near the site, as well as pesticides that will be applied nearby. Some pesticides, such as atrazine, require setback zones around wells where the chemical cannot be applied.

Sinkholes

Regions with shallow limestone or dolomite can be particularly susceptible to groundwater contamination because water may move rapidly through dissolved caverns or sinkholes. Once water enters a sinkhole, it receives little fi ltration or chance for degaradation of the chemical. Fractured rock systems also allow rapid movement of contaminant-bearing water.

Potential Routes of Contamination

• Abandoned and improperly plugged wells• Injection wells (most commonly used to drain surface water and dispose of indus- trial and municipal waste water)• Excavations related to the production of stone, sand, and gravel

Potential Sources of Contamination

• Landfi lls and land disposal areas for mu- nicipal, special, and hazardous wastes• Underground storage tanks containing more than 500 gallons and aboveground tanks containing more than 25,000 gal- lons of petroleum products• Storage and handling areas for de-icers, hazardous substances, road oils, agricul- tural chemicals, and animal waste