Assessing the Risk of Groundwater Contamination from Drinking Water Well Condition

About 90 percent of this country's rural residents use groundwater to supply their drinking water and homestead needs. Wells generally provide clean, safe water. If improperly located, constructed, or maintained, however, they can allow bacteria, pesticides, fertilizer, or oil products to contaminate groundwater. These contaminants can put family and animal health at risk.

There are many documented cases of well contamination from homestead activities near drinking water wells. The condition of your well and its location in relation to contamination sources determine the risk it poses to the water you drink. For example, a cracked well casing may allow bacteria, nitrates, oil, and pesticides to enter the well. A spill of pesticides being mixed and loaded near the well could result in a serious contamination of your family's drinking water supply. Feedlots, septic systems, fertilizer applications, and waste storage areas can release large amounts of contaminants which may contaminate your well.

Preventing well water contamination is very important. Once the groundwater supplying your well is contaminated, it is very difficult to clean up. The only options may be to treat the water, drill a new well, or obtain water from another source. A contaminated well can also affect surrounding wells, posing a serious health threat to others.

The goal of Home A·Syst is to help you protect the groundwater that supplies your drinking water.

• It will take you step-by-step through your drinking water well condition and management practices.
• It will rank your activities according to how they might affect the groundwater that provides your drinking water supplies.
• It will provide you with easy-to-understand rankings that will help you analyze the "risk level" of your drinking water well condition and management practices.
• It will help you determine which of your practices are reasonably safe and effective, and which practices might require modification to better protect your drinking water.

 Follow the directions at the top of the chart on the next page. It should take you about 15 to 30 minutes to complete this worksheet and summarize your risk rankings.

Focus on the well that provides drinking water for your homestead. If you have more than one drinking water well on your homestead, fill out a worksheet for each one.

Abandoned water well: A well that is unused, unmaintained, and is in such disrepair as to be unusable.

Air gap: An air space (open space) between the hose or faucet and water level, representing one way to prevent backflow of liquids into a well or water supply.

Anti-backflow (anti-backsiphoning) device: A check valve or other mechanical device to prevent unwanted reverse flow of liquids back down a water supply pipe into a well.

Aquifer: An underground formation containing, and capable of supplying, groundwater.

Backflow: The unwanted reverse flow of liquids in a piping system.

Backsiphonage: Backflow caused by formation of a vacuum in a water supply pipe.

Casing: Steel or plastic pipe installed while drilling a well, to prevent collapse of the well bore hole and entrance of contaminants, and to allow placement of pumping equipment.

Decommissioned well: A well that has been permanently closed according to Washington regulations.

Cross-connection: A link or channel between pipes, wells, fixtures, or tanks carrying contaminated water and those carrying potable (safe for drinking) water. Contaminated water enters the potable water system if it has higher pressure.

Drilled wells: Any drilled excavation that is constructed when the intended use of the well is for the location, diversion, artificial recharge, observation, monitoring, dewatering, or withdrawal of groundwater.

Driven-point (sand point) wells: Wells constructed by driving assembled lengths of pipe into the ground with percussion equipment or by hand. These wells are usually small in diameter (two inches or less), less than 50 feet deep, and installed in areas of relatively loose soils, such as sand.

Dug wells: Large-diameter, relatively shallow wells lined with rock or brick and often hand constructed. Typical dug wells are three to six feet in diameter and 15 to 50 feet deep.

Groundwater: Subsurface water in a zone of saturation.

Grout: A fluid mixture of cement, bentonite, and water used to seal the annular space around or between well casings, or to fill and seal abandoned wells.

Milligrams per liter (mg/L): The weight of a substance measured in milligrams contained in one liter. It is equivalent to 1 part per million in water measure.

Parts per million (ppm): A measurement of concentration of one unit of material dispersed in one million units of another.

Pitless adapter: An assembly placed below the frost line which permits pumped well water to pass through the casing without allowing contaminants to enter.

Water table: The upper level of groundwater in a zone of saturation. Fluctuates with climatic conditions on land surface, and with aquifer discharge and recharge rates.

Well cap: A manufactured device installed at the top of a well casing which creates an air- and watertight seal to prevent surface water and contaminants from gaining access to the groundwater supply.

 Step 2: Look over your rankings for individual activities:

• High risk practices (1's) pose a high risk of polluting groundwater.
• Moderate-to-high risk practices (2's) are inadequate protection in many circumstances.
• Low-to-moderate risk practices (3's) provide reasonable groundwater protection.
• Low risk practices (4's) are ideal; should be your goal despite cost and effort.

Any shaded rankings require immediate attention. Some concerns you can take care of right away; others could be major or costly projects, requiring planning and prioritizing before you take action. The long term goal of the Home·A·Syst program is to improve homestead practices and structures, so that they are classed as low risk. Activities classed as low risk generally reflect best management practices.

Transfer any activities that you ranked in the shaded areas in step 1 to the "High-Risk Activities" on pages 2-3 of worksheet 12.

Step 3: Read fact sheet 1, Improving Drinking Water Well, if you haven't already. Consider how you might modify your homestead practices to better protect your drinking water.

The Homestead Assessment System is a cooperative project of Washington State University Cooperative Extension, Washington Department of Ecology, and the U. S. Environmental Protection Agency Region X.

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

Drinking Water Well Technical Review Team; Enid Cox, Cooperative Extension, Klickitat County; Jerry Stonebridge, Sr., Washington OnSite Septic Association.; Cheryl Freeman, Inland Empire Public Lands Council; Richard F. Szymarek, Washington Department of Ecology, Water Resources Program.

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.

Information derived from Home·A·Syst worksheets is intended only to provide general information and recommendations to rural dwellers regarding their own homestead practices. It is not the intent of this educational program to keep records of individual results.

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, gender, national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may be reported to 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-W1