Reducing the Risk of Groundwater Contamination by

Fact Sheet 1

Whether a well taps water just below the ground or hundreds of feet deep, its location on top of the ground is a crucial safety factor. Locating a well in a safe place takes careful planning and consideration of such factors as where the well is in relation to surface drainage and groundwater flow. A well downhill from an animal lot, a leaking tank, or a failing septic system runs a greater risk of contamination than a well on the uphill side of these pollution sources. The general rule for protecting the water supply is to keep a well upslope and as far as possible from potential sources of contamination.

Surface slope does not always indicate the direction a pollutant might flow once it gets into the ground. In shallow aquifers, groundwater flow is usually in the same direction as surface water flow. If the aquifer supplying water to your well is deep below the surface, however, its slope may be different than that of the land surface.

Many states encourage good well location by requiring minimum separation distances from sources of potential pollution, thus using the natural protection provided by soil. Washington well regulations, WAC 173-160-205(2), require that new wells be constructed a minimum of 100 feet from all potential sources of pollution or contamination. In many Washington counties, the local health, planning, or zoning department may have specific regulations requiring greater separation from some potential contamination sources.

There is no specific distance that will guarantee the well will not be affected. Make every effort, however, to provide as much separation as possible between your well and any potential contamination source—especially if your homestead is on highly permeable soils or thin soil overlying bedrock, or if the contamination source or activity presents a high risk of contamination.

Both soil and slope can make siting a well tricky business. Keep in mind that separation distances required by the state are minimums. You may want to choose greater separation distances in some cases, depending on factors at your site. All surface runoff should be diverted away from the well. Consider contamination sources on adjacent properties as well.

Changing the location of contamination sources in relation to your well may protect your water supply, but not the groundwater itself. Any condition likely to cause groundwater contamination should be improved, even if your well is far away from the potential source. Whether or not drinking water is affected, groundwater contamination is a violation of Washington law.

Simply separating your well from a contamination source may reduce the chance of pollution, but it does not guarantee that the well will be safe. Stormwater and groundwater can carry bacteria, oil products, and pesticides from one place to another. Wells located in the path of that water run a risk of contamination from overland flow washing into an improperly sealed well. Some wells become contaminated through polluted recharge at great distances, depending on the depth of the aquifer and the well intake.

Figure 1: Required construction components for new wells.

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Poor well design can allow contamination by letting rain or snowmelt reach groundwater without filtering through the soil. Wells located in pits, or constructed without grout or a sanitary well seal, can allow surface water to carry bacteria, pesticides, fertilizer, or petroleum products into your drinking water supply. Proper well design reduces the risk of pollution by sealing the well from anything that might enter it from the surface (Figure 1).

The way in which a well is constructed, even if the design is sound, affects its ability to keep out contaminants. Several things that should be checked are described in the following sections. Well construction information may be available from the person who drilled your well, from the previous owner, or from the well construction report. The Water Resources Program in the Department of Ecology regional office for your area will have the well construction report on file, if it was turned in to them by the driller.

The following overview of well construction and inspection can help you understand your drinking water contamination risk ranking. For more information, contact a well driller licensed by the state of Washington, or contact the Water Resources Program in the Department of Ecology regional office for your area (see contacts and references section).

The well driller installs a steel or plastic pipe (casing) during construction to prevent collapse of the borehole. All openings in the casing should be sealed, and if water pipes exit through the side of the casing, they must do so through an approved fitting called a pitless adapter.

The space between the casing and the sides of the borehole provides a direct channel for surface water—and pollutants—to reach groundwater. To seal off that channel, the driller fills the space with grout (cement, neat cement, or a special type of clay called bentonite). The grout seal should extend at least 18 feet in depth from the surface. Grouting should also seal the casing within confining layers. The grout seal, pitless adapter, and casing help to prevent pollutants from seeping into the well. The ground surface should slope away from the well in all directions as well.

You can visually inspect the condition of your well casing for holes or cracks at the surface, or look down the inside of the casing with a light. If you can move the casing around by pushing against it, you have a problem with your well casing's ability to keep out contaminants. In areas of shallow (less than 20 feet from surface) fractured bedrock, check on the condition of your well casing by listening for water running down into the well. (Pump should not be running.) If you do hear water, there could be a crack or hole in the casing, or you are not cased down to the water level in the well. Either situation is risky.

To prevent contaminants from flowing down inside the well casing, the driller installs a tight-fitting, vermin-proof well cap to prevent easy removal by children and entry by insects or surface water. The cap should be firmly installed, with a screened vent incorporated into it so that air can enter the well. Check the well cap to see that it's in place and tightly secured. Electrical wires entering the well should be in an approved conduit. If your well has a vent, be sure that it faces the ground, is tightly connected to the well cap, and is properly screened to keep insects out. Well regulations require a vermin-proof seal for all private wells. (Not all wells have caps. Some may have pumping equipment attached at the surface.)

The minimum depth of casing required for your well is stated in Washington regulations (WAC 173-160). All wells are required to have a durable, watertight casing extending into the water-producing aquifer. In no event should this watertight casing extend less than 18 feet below ground level. This ensures that water is filtered through soil and geologic materials before entering the well. You may want to consider exceeding the minimum casing depth. Since most contamination comes from the surface, casing the well deeper can provide greater protection.

Typically, the casing extends one to two feet above surrounding land, preventing surface water from running down the casing or on top of the seal and into the well. Washington well regulations require that at least 6 inches of casing pipe extend above the final grade of the land. In areas subject to flooding, the casing must be extended above the estimated flood elevation, but such well locations are discouraged. Check with your county for local regulations concerning casing construction.

Dug wells may pose some of the highest risk of drinking water supply contamination. They are shallow, and often poorly protected from surface water. A dug well is a large-diameter hole, typically three to six feet wide, which is often constructed by hand, and lined with rock, brick, or concrete. Hand dug wells as small as two feet, and larger than 30 feet are known to exist. Dug wells will usually be 15 to 50 feet deep.

Driven-point (sand point) wells are constructed by driving assembled lengths of pipe into the ground. These wells are normally smaller in diameter (two inches or less) and less than 50 feet deep. They can only be installed in areas of relatively loose soils, such as sand.

All other types of wells, including those constructed by a combination of jetting and driving, are drilled wells. Drilled wells are commonly 6 to 12 inches in diameter. Depth will vary depending on the aquifer.

Shallow wells draw from the groundwater nearest the land surface, which may be directly affected by farmstead activities. Depending on how deeply the well is cased and sealed below the surface, rain and surface water soak into the soil, and may carry pollutants into the well.

Local geologic conditions determine how long it takes for this to happen. In some places, this process happens quickly, in weeks, days, or even hours. Areas with thin soils over fractured bedrock or sand and gravel aquifers are particularly vulnerable. On the other hand, thick clay soils can prevent contaminants from reaching the water table.

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Existing wells were most likely located according to traditional practice or regulations in place at the time of construction. While these wells may yet be producing potable water, you may want to consider how well yours conforms to current standards and recommendations. Current standards can be found in the state well design and construction regulations, WAC 173-160. Recommendations to better protect your drinking water supply can be found within the Homestead Assessment System, as well as other publications. Consult the contacts and references section.

Move pesticide mixing, tank rinsing, or fuel storage further from your well. You might want to upgrade your well, to include getting rid of well pits, installing seals, or extending casings.

Changing the location of other practices may prove expensive. (You can't move an animal lot or a silo overnight.) Until you can meet minimum separation distances, change the way you manage such structures to control contaminants.

If your silo is too close to your well, for example, you may want to install a system for collecting any drainage from freshly ensiled forage. You could install a diversion ditch to direct animal lot runoff away from the well. (See fact sheet 9, Improving Silage Storage, for further information.)

Short-term manure storage is another example. These areas pose a risk of well contamination by bacteria or nitrates. Locate storage areas on clay soil or, better yet, a concrete slab to reduce the chance of polluting your drinking water. Also, protect storage sites from rain and surface runoff. (See fact sheet 7, Animal Manure Storage, for further information.)

Additional Home·A·Syst fact sheets and worksheets provide more information on various potential contamination sources around your farmstead. Several management practices you may want to consider to help maintain the quality of your well water include:

• Do not use petroleum products, solvents, or lawn and agricultural chemicals near your well.
• Protect wells from wastes stored or disposed of around the farmstead.
• Protect wells from household wastewater treatment systems. Consider the possibility of upgrading or better management of your current system.
• Move traffic areas and chemical or fuel storage areas away from the well.
• Limit the number of activities and structures located within 100 feet of your drinking water well.
• At least once a year inspect your septic system, septic tank, and all other tanks used with the system and drainfield to make sure it is operating properly. If you think there are problems, call the local health department and a licensed pumper or installer.

Backflow or backsiphoning from pesticide mixing tanks allows chemicals to flow back into the well through the hose. Use an anti-backflow device when filling pesticide sprayer tanks to prevent the chemical mixture from flowing back into the well and contaminating groundwater. Inexpensive anti-backflow devices for hoses used to fill farm sprayers may be available from irrigation or spray equipment suppliers. Provide an air gap of at least six inches between the hose and the top of the sprayer tank being filled. As an additional safety factor, pesticides could be added after the tank has been filled.

Consider purchasing an inexpensive plastic nurse tank. A nurse tank is filled with water at the well and then used to fill the sprayer away from the homestead and away from the well. (For more information about preventing well contamination from pesticide mixing and loading practices, see worksheet and fact sheet 2, Pesticide Storage and Handling.)

You should consider anti-backflow devices on all faucets with hose connections, and maintain air gaps between hoses or faucets and the water level during all activities. Otherwise, you risk having contaminated water from laundry tubs, sinks, washing machines, pressure washers, outside hydrants, and swimming pools flow back through plumbing to contaminate your water supply. Water supplies that have cross-connections between them (connections between two otherwise separate pipe systems, such as potable and nonpotable) also put your drinking water at risk.

Although not required by state law, your county may mandate the use of backflow or backsiphoning prevention devices. Check with your county health department for additional information.

Keep an eye on water quality in existing wells by testing them annually. Although you cannot have your water tested for every conceivable pollutant, some basic tests can indicate whether or not other problems exist.

At a minimum, test your water annually for bacteria and nitrates using a Washington certified laboratory. If the well draws from sandy materials or granite bedrock, testing once for corrosivity is also important. A good initial set of tests for a private well includes hardness, alkalinity, pH, conductivity and chloride.

In addition, you may choose to obtain a broad scan of your water quality for a number of contaminants. Some labs offer a screening for metals, inorganic chemicals, volatile organic chemicals, and herbicides/pesticides. These tests can be expensive, so you will probably not have them unless you suspect a specific problem.

When testing for additional contaminants, be sure to select contaminants that are most likely at your farmstead. Test for lead if you have lead pipes or soldered copper joints. Test for volatile organic chemicals (VOCs) if there has been a nearby use or spill of oil, petroleum, or solvent.

While testing for pesticides can be very expensive (often $80-$100 per compound analyzed), the expense may be justified if:

• Your well has nitrate levels greater than 10 mg/l (reported as nitrate-nitrogen, NO₃-N) or 45 mg/l (reported as nitrate, NO₃).
• A pesticide spill has occurred near the well, or backsiphonage has occurred.
• Your well is shallow or is located in sandy soil and down gradient from irrigated croplands where pesticides are used.

You can seek further advice on appropriate tests to run from your local health department or county Cooperative Extension office.

You should test your water more frequently if:

• There are unexplained illnesses in the family.
• There are individuals who may be at increased risk like infants and pregnant or nursing women.
• There are noticeable changes in livestock or poultry performance.
• Your neighbors find a particular contaminant in their water.
• You note a change in water taste, odor, color or clarity.
• You have a spill or backsiphonage of chemicals or petroleum products near your well or on your homestead.
• You apply chemicals or manure to your fields within 100 feet of your well.
• Your animal operation inspectors require it.

You can have your water tested by a commercial laboratory. A list of Washington certified labs is available from your county Cooperative Extension office or health department, or contact the Washington State Department of Health (WDOH) Certification Officer at (206) 361-2822. Follow the lab's instructions for water sampling to assure accuracy of the results. Use only the container provided, and return samples promptly. Bacteria sample bottles are sterile and must be returned to the lab within specified time limits. Request that drinking water methods be used to test your water.

Because many materials, including bacteria and nitrate-nitrogen, naturally occur in minor amounts in groundwater, and the levels can vary seasonally, you may want to contact a specialist for help in interpreting test results. Contact the WDOH district office for your area for assistance. Several Cooperative Extension and WDOH publications may be of help as well (see contacts and references section).

Nitrates and bacteria are acute contaminants. Nitrate levels greater than 10 mg/l should not be consumed by infants under 1 year of age. The standard bacteriological test conducted on drinking water supplies is the test for Total Coliforms. If any bacteria are detected in a water system, resample the system. If a presence is confirmed by the second test, a water system is said to have an "acute MCL" and well owners must take action to correct the problem, i.e., disinfection, and must notify water system users. The presence of total coliforms is an indicator of system vulnerability. If a presence is detected in any bacterial analysis, the lab will automatically test for the presence of fecal coliforms. The presence of fecal coliforms is a more serious matter since it indicates that the well is vulnerable to contamination by fecal material and may also contain other pathogens as well. There is no acceptable level for coliform contamination. If coliforms are present, the water does not meet drinking water standards.

Keep in mind that activities off your property can affect your groundwater. Chemical spills, changes in land use, underground storage tanks, and the presence of landfills can increase the chance of pollutants getting into your water. Bacteria and nitrates are two important indicators which may suggest problems with the well's location or construction, and at excessive levels, they can cause health problems. If your water has a high nitrate or bacteria level, you may want to talk with a specialist about the need for additional testing, disinfection, or other treatment.

It is also important to record test results and to note changes in water quality over time. In addition to water analysis test results, you should keep records of a few other things to tell what is happening with your water system. These include well construction details and dates and results of maintenance intervals for the well and pump.

Well equipment doesn't last forever. From time to time, your well may require attention to its mechanical parts. Well maintenance also includes protecting your well from contamination sources.

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New wells are expensive, but they are a good investment for the future. Getting the most from such an investment means locating the well away from contamination sources and working to maintain the quality of the well. Some simple principles are:

• Follow the required minimum separation distance of 100 feet from potential contamination sources, as well as any local ordinances, when locating your new well. WAC 173-160 contains requirements for drinking water wells. A full listing of requirements is also available from either your county health department, a Washington licensed well driller, or the Water Resources Program in the Ecology regional office for your area (see contacts and references section).
• Locate your well on ground higher than such surrounding pollution sources as fuel tanks, livestock lots, septic systems, or pesticide mixing areas. Where practical, locate the well as far as possible from pollution sources. There is no specific distance from a potential pollution source that will guarantee the well will not be affected.
• Build soil up around the well so that all surface water drains away from it, maintaining the minimum 6 inches of casing above the soil surface.
• Avoid areas that are prone to flooding.
• Make the well accessible for pump repair, cleaning, testing, and inspection.
• Hire a competent, licensed well driller. Make sure the driller disinfects the well with chlorine after construction, tests the water for bacteria after drilling, and provides you with a copy of the water well record, which includes detailed information about the well's depth and construction. Encourage the driller to file a copy of the well record with Ecology.

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Many rural homesteads have abandoned wells. It is not uncommon to visit a homestead and find three or four wells, with only one or two currently in use. Old homesteads with shallow wells are common. No one knows how many of these wells there are in Washington, although estimates range in the hundreds of thousands.

If not properly filled and sealed, these wells can provide a direct conduit for surface water carrying pollutants to enter groundwater without filtering through soil or can allow contaminant movement from one aquifer to another.

In addition to these wells being a threat to groundwater, large open wells pose safety hazards for people and animals. Washington law makes the landowner responsible for decommissioning wells and test holes, and therefore liable for any occurrence of contamination.

You may perform well decommissioning work on your own land. A license is not needed, but you must meet the minimum regulatory requirements for Washington. A Washington licensed well driller can also be hired to close these wells. A local well driller will have experience with well construction materials and methods as well as a working knowledge of the geology of the well site.

Special equipment is often required to remove old pumps and piping and to properly install sealing material inside the well. Use of inappropriate materials and methods can lead to well settling, collapse, and continued groundwater contamination.

The Washington Department of Ecology administers the laws regulating construction, reconstruction, and decommissioning of wells. Chapter 173-162 of the Washington Administrative Code specifically addresses the decommissioning of wells. The regulations provide instructions for all types of wells and aquifer conditions. Well drillers and landowners are required to follow these procedures.

Proper well closing takes time and money. Costs will vary with the well depth, diameter, and geology of the area. However, spending a few hundred dollars decommissioning an abandoned well near your home may prevent contamination of your drinking water. Contact the Ecology regional office for your area for additional information.

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Certified water testing laboratories
A listing is available from your county health department, or Cooperative Extension office, or contact the Washington Department of Health (WDOH) Laboratory Certification Officer, (206) 361-2822.

Interpreting well water test results, installation of home water conditioning and treatment devices
Your county health department, or the WDOH office for your area:

Southwest: (206) 753-4152
Northwest: (206) 464-7670
Eastern: (509) 456-3115

Or, contact the WDOH Hotline, 1 (800) 521-0323.

Federal drinking water quality standards and other drinking water concerns
U.S. Environmental Protection Agency's Safe Drinking Water Hotline. Call toll free 1(800) 426-4791 from 5:30 a.m. to 2 p.m. Pacific Standard Time.

Locating possible sources of contamination
Your local health department, county Cooperative Extension office, a licensed well driller, or the WDOH office for your area (see phone numbers above). Besides locating contamination sources, they can also recommend improvements to decrease contamination potential.

Well construction or inspection, and decommissioning of abandoned wells
(206) 695-5215

A copy of your well construction record
If a report was filed with the state, then it will be on file at the Ecology regional office for your area:

Northwest: (206) 649-7038
Southwest: (206) 586-6380
Central: (509) 575-2597
Eastern: (509) 456-6188

Be prepared to provide the legal description (county, township, range, section and quarter section) of the well's location. (If your property covers more than one section, make a note of that in case well drillers reported the wrong section.) If known, provide the year the well was installed and the owner's name at the time.

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Publications are available from sources listed at the end of the reference section. Refer to number in parentheses after each publication.

Groundwater contamination and protection

Washington Groundwater: A Vital Resource EB1622. (1)
Protect Your Groundwater: Survey Your Homestead Environment EB1631. (1)
How Fertilizers and Plant Nutrients Affect Groundwater Quality EB1722. (1)
Role of Soil in Groundwater Protection EB1633. (1)
Water Quality Improvements for Farmstead and Rural Home Water Systems F2274. (1)
Water Quality for Domestic Use: Resource Handbook, 1988. (1) A wide-ranging collection of information including a list of certified water testing laboratories, drinking water standards, bulletins on various water quality contaminants, and the Private Water Systems Handbook, MWPS-14 (see below).
Private Water Systems Handbook. 1979. Fourth edition. MWPS-14. (2) Includes information on wells and other water supply systems; pumps, piping and water treatment. (Recommendations may not meet Washington codes.)
Selecting a Site and Constructing a Well. 1990. ACRE Fact Sheet #7. (3)

Domestic Water Quality

Drinking Water: Bacteriological Safety and Treatment EB0995. (1)
Turbidity, Color, Odor, and Taste in Domestic Water EB0994. (1)
Stainers: Iron and Manganese Removal EB1500. (1)
Sodium Content of Your Drinking Water EB1525. (1)
Corrosion from Domestic Water EB1581. (1)
Home Water Softening EB1583. (1)

Water testing, interpretation and treatment

Safe Drinking Water, 1990. (4) A short handbook that gives an overview of drinking water sources, regulations, protection, and testing.
Water Quality for Domestic Use: Resource Handbook contains several publications addressing water testing.
Testing Well Water for Contamination. 1990. ACRE Fact Sheet #19. (3)

Abandoned Wells

Abandoned Wells: Forgotten Holes to Groundwater EB1714. (1)
The Importance of Sealing an Abandoned Well. 1990. ACRE Fact Sheet #6. (3)

Publications available from...

1. Your county Cooperative Extension office. There may be charges for publications, postage, and sales tax.
2. Your county Cooperative Extension office or the Midwest Plan Service, Iowa State University, Ames, Iowa, 50011, (515) 294-4337. There may be charges for publications, postage, and sales tax.
3. Alliance for a Clean Rural Environment (ACRE), P.O. Box 413708, Kansas City, Missouri 64141, 1 (800) 545-5410.
4. Washington State Department of Health, Drinking Water Program, PO Box 47823, Olympia, Washington, 98504-7823.

Home·A·Syst team members: Christopher F. Feise and Edward B. Adams, WSU Cooperative Extension Water Quality Coordinators; James D. LaSpina, Homestead Assessment System Project Associate.

Drinking Water Well Condition Technical Reviewers: Enid Cox, WSU Cooperative Extension, Klickitat County; Jerry Stonebridge, Sr., Washington Onsite Association; Karen Paugh, Yakima Health District; Cheryl Freeman; Richard F. Szymarek, Washington Department of Ecology; Belle Fuchs, Washington State Department of Health.

Adapted for Washington from material developed by the Wisconsin, Minnesota, and Kansas Extension Services and Farm·A·Syst Programs. Washington Home·A·Syst development was supported by the National Farmstead Assessment Program.

Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8, and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, religion, national origin, gender, age, disability, and gender preference. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intended. Published September 1993. Subject Code 376. A. EB1746-F1