BMPs for Wellhead Protection

Idaho's Water
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 water.

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 same fate.

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 areas include:

1. Well location.
2. Well construction.
3. Well management and maintenance.
4. New wells.
5. Unused wells.

• 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 surface runoff.
• 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 following:
• 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.

• 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.
• Inspect:

Check to see that the space between the casing and side of hole is grouted. Visually inspect the well casing with a flashlight for holes or cracks at the surface or down inside. Well cap should be firmly installed with a screened vent. 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 from contamination. 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 contamination sources.
  • Older wells are more likely to have thinner casing that is corroded through.
• 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.

• 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 tanks.
• Consider installing anti-backflow devices on all faucets with hose connections.
• 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.

• Make the well accessible for pump repair, cleaning, testing, and inspection.
• 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 wells.

This brochure, WQ-30, was prepared by R. L. Mahler and K. A. Loeffelman, Soil Science Division, University of Idaho, Moscow, Idaho 83844.

2M 6-94

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College of Agricultural and Life Sciences, University of Idaho.
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Revised: January 3, 2003

URL: http://www.uidaho.edu/wq/wqbr/wqbr30.html