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Over 90 percent of the drinking water consumed in Idaho is supplied by groundwater.
This resource is vital to homeowners and industry as well as Idaho's agricultural
community. Best management practices (BMPs) for wellhead protection have been
and are becoming more important.
Recent surveys by Idaho water quality specialists have found trace amounts of
chemicals--nitrates--and, in some cases, pesticides in some of Idaho's drinking
Wellhead Protection Concerns
Why should you be concerned? Ninety-five percent of rural residents in
Idaho use groundwater obtained from private wells to supply drinking water. Your
well is your own private gold mine! Improperly constructed and maintained wells
can put both your family and the health of your pets and/or livestock at risk.
Large areas that contain groundwater are called aquifers. Wells are drilled into
aquifers that are found in many areas of Idaho. The water in aquifers is a finite
resource. Without an aquifer containing potable water many of you could not live
in a rural area. In effect, your well drilled into an aquifer provides you with
independence! The contamination of drinking water obtained from your well could
compromise this independence and perhaps even force you off your property.
Within a given geographic area many landowners obtain their drinking water from
wells drilled into the same aquifer. In fact, it is not uncommon to find hundreds
of rural wells drilled into the same aquifer. The prevention of well
contamination should be your top priority because once contaminated, it becomes
very difficult, if not impossible, to clean up the aquifers. Since the water
produced from your well comes from the same underground body of water as your
neighbor's well, if your well becomes contaminated your neighbor may suffer the
To protect your well and its water quality you should use best management
practices, which are defined as implemented strategies that eliminate or minimize
environmental pollution. BMPs are designed to be compatible with good, sound
wellhead protection. BMPs can protect the environment and eliminate or minimize
the threat of environmental pollution.
Wellhead Protection BMPs
There are five major areas where BMP implementation should be considered. These
1. Well Location
- Well location.
- Well construction.
- Well management and maintenance.
- New wells.
- Unused wells.
The location of your well is a crucial factor determining the safety of your
drinking water. Consider:
2. Well Construction
- Well location in relation to surface drainage.
- Good--The well is high in the landscape so surface water drains away from
the wellhead; little chance for contamination.
- Fair--The well is on level ground; moderate chance for contamination by
- Poor--The well is poorly located on the landscape; surface water runoff may
move toward the well with a high chance for contamination.
- Separation distances from potential contaminants.
- Provide as much separation distance between your well and the
- septic tanks and drain fields
- chemical storage
- gas tanks
- manure storage
- liquid manures/wastes
- animal feed storage
- The separation distance that is advised depends on: (1) type of potential
contaminant, (2) soil type, and (3) slope of the land.
- Also consider contamination sources on adjacent properties.
Properly designed and constructed wells minimize the risk of pollution by sealing
the well from anything that might enter it from the surface. Well construction
information may be available from the driller, the previous owner, or the well
construction report. Five items dealing with well construction deserve detailed
consideration. These items include: (1) casing and the well cap, (2) casing depth
and height, (3) well age, (4) well type, and (5) well depth.
3. Well Management and Maintenance
- Casing and the well cap.
- Casing is a steel or plastic pipe installed during construction to
prevent collapse of the borehole.
- The space between the casing and sides of the hole should be sealed with
grout to prevent pollutant seepage into the well.
- A well cap is a tight-fitting, vermin-proof seal designed to prevent
contaminants from flowing down inside of the well casing.
- Check to see
that the space between the casing and side of hole is grouted.
inspect the well casing with a flashlight for holes or cracks at the surface or
- Well cap should be firmly installed with a screened
- Listen for water running down into the well--a signal that you
have casing leaks.
- Casing depth and height.
- The wells
should be cased below the water levels in the well to afford greater protection
- The well casing should extend 1 to 2 feet above the
surrounding land to prevent surface water from running down the casing or on top
of the cap and into the well.
- Well age.
- An important factor in predicting the likelihood of contamination.
- Older well pumps are more likely to leak lubrication oils.
- Older wells are usually at the center of a farm and surrounded by potential
- Older wells are more likely to have thinner casing that is corroded
- Well type.
- Well type is related to potential contamination risks.
- Three common well types:
- Dug wells
- large diameter,
- usually shallow,
- highest risk of contamination.
- Driven-point or sand wells
- small diameter (< 2 inches),
- <50 feet in depth,
- moderate-to-high contamination risk.
- Drilled wells
- casing diameter between 4 and 8 inches,
- lower contamination risk.
- Well depth.
- Shallow wells draw from groundwater nearest the land surface;
this water is most likely to be adversely impacted by human activities.
- Well depth depends on depth of the well casing below the water table and
local geologic conditions.
Good maintenance means testing your water every year, keeping the well area clean
and accessible, keeping pollutants as far away from the well as possible, and
periodically having the well mechanics checked. Additional items to consider
4. New Wells
- Better management of your existing well.
- Consider if your existing well conforms to current standards.
- Consider moving traffic areas and chemical or gas storage away from the well
and upgrading or better managing of your septic system.
- Backflow prevention.
- You should use an anti-backflow device when filling pesticide sprayer
- Consider installing anti-backflow devices on all faucets with hose
- Maintain air gaps between hoses or faucets and the water level.
- Cross-connections are connections between two otherwise separate pipe
systems. Water supplies with cross-connections between them put your drinking
water at risk. Eliminate cross-connections.
- Water testing.
- Observe water quality in existing wells by testing them annually.
- Test for contaminants that are most likely on your property.
- Further advice on testing can be obtained from your local health department
or local Extension office.
- Water testing is done by both public and private laboratories. Consult your
local health department.
- Record test results and note changes in water quality over time.
- Well maintenance.
- Your well should require mechanical attention every 10 to 20 years.
Contact a qualified well driller or pump installer.
5. Unused Wells
- Make the well accessible for pump repair, cleaning, testing, and
- Hire a competent, licensed well driller and pump installer.
- Unused wells can provide a direct path for surface water carrying
pollutants to groundwater--shut down any unused wells.
- Hire a licensed, registered well driller or pump installer to close unused
It is apparent that many factors affect the quality of drinking water obtained
from your well. Remember that owning a well is a large responsibility because it
can impact the health of your family. You do not live on an island--your
neighbors can impact the quality of your well. Finally, to protect the
environment, the management of your well and potential pollutants on your
property must consider BMPs for water quality protection.
This brochure, WQ-30, was prepared by R. L. Mahler and K. A.
Loeffelman, Soil Science Division, University of Idaho, Moscow, Idaho 83844.
Comments to webmistress:
All contents copyright © 1997-2003.
College of Agricultural and Life Sciences, University of Idaho.
All rights reserved.
Revised: January 3, 2003