Assessing the Risk of Groundwater Contamination From Drinking-Water Well Condition
Farm•A•Syst: Farmstead Assessment System Worksheet #1
Included when you order this worksheet: MU publication WQ675, Reducing the Risk of Groundwater Contaminationby Improving Drinking-Water Well Conditions, the fact sheet that corresponds with this worksheet.
Approximately 95 percent of this country's rural residents use groundwater to supply their drinking water and farmstead needs. Wells are designed to provide clean water. If improperly constructed or poorly maintained, they can allow bacteria, pesticides, fertilizer or oil products to contaminate groundwater. These contaminants can put family and livestock health at risk.
Cases exist that document well contamination from farmstead activities near drinking-water wells. The condition of your well and its proximity to contamination sources determine the risk it poses to the water you drink. For example, a cracked well casing allows bacteria, nitrates, oil and pesticides to enter the well more easily. Spilling pesticides being mixed and loaded near the well could result in the contamination of your family's drinking-water supply. Feedlots, animal lots, septic systems, fertilizer applications and waste storage areas could release large amounts of nitrate, contaminating your well.
Preventing well-water contamination is important. Once the groundwater supplying your well is contaminated, it is difficult to clean up. The only options may be to treat the water, drill a new well or get water from another source. A contaminated well also can affect your neighbors' wells, posing a serious health threat to your family and neighbors.
The goal of Farm•A•Syst is to help you protect the groundwater that supplies your drinking water.
How will this worksheet help me protect my 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.
How do I complete the worksheet?
Follow the directions at the top of the following chart. It should take you about 15 minutes to 30 minutes to complete this worksheet and determine your ranking.
Focus on the well that provides drinking water for your home or farm. If you have more than one drinking-water well on your farmstead, fill out a worksheet for each one.
Drinking-water well condition: Assessing drinking-water contamination risk
- Use a pencil. You may want to make changes.
- For each category listed on the left that is appropriate to your farmstead, read across to the right and circle the statement that best describes conditions on your farmstead. (Skip and leave blank any categories that don't apply to your farmstead.)
- Then look above the description you circled to find your "rank number" (4, 3, 2 or 1) and enter that number in the blank under "your rank."
- Directions on overall scoring appear at the end of the worksheet.
- Allow about 15 minutes to 30 minutes to complete the worksheet and figure out your risk ranking for well-management practices.
||Low risk, rank 4
||Low to moderate risk, rank 3
||Moderate to high risk, rank 2
||High risk, rank 1
|Position of drinking-water well in relation to pollution sources
||Upslope from all pollution sources. No surface-water runoff reaches well. Surface water diverted from well.
||Upslope from or at grade with pollution sources. No sureface water runoff reaches well.
||Downslope from most pollution sources. Some surface-water runoff may reach well.
||Settling or depression neare casing. Surface-water runoff from livestock yard, pesticide and fertilizer mixing area, fuel storage or farm dump reaches well.
|Separation distances between well and farmstead contamination sources1
||Meets or exceeds all state minimum-separation distances.
||Meets most minimum-separation distances.
||Meets minimum-separation distances only for sources required to be at least 100 feet from well2
||Does not meet all minimum separation distances for sources required to be at least 100 feet from well.3
|Soil and/or subsurface potential to protect groundwater
||Fine-textured soils (clay loams, silty clay). Water table or fractured bedrock deeper than 20 feet.
||Medium-textured soils (silt loam, loam). Water table or fractured bedrock deeper than 20 feet.
||Medium- or coarse-textured soils. Water table or fractured bedrock deeper than 20 feet.
||Coarse-textured soils (sands, sandy loam). Water table or fractured bedrock shallower than 20 feet.
|Condition of casing and well cap seal.
||No holes or cracks. Cap tightly secured. Screened vent. Casing properly grouted.
||No defects visible. Well vented but not screened.
||No holes or cracks visible. Cap loose.
||Holes or cracks visible. Cap loose or missing. Can hear water running.
||Cased more than 30 feet below water level in your well.
||Cased 15 feet to 30 feet below water level in your well.
||Cased less than 15 feet below bedrock in your well. No casing.
|Casing height above land surface
||More than 12 inches above grade.
||8 inches to 12 inches above grade.
||At grade or up to 2 inches to 8 inches above.
||2 inches or below grade or in pit or basement.
||Less than 20 years.
||21 years to 50 years.
||51 years to 70 years.
||More than 70 years.
||Anti-backflow devices (such as check valves) installed on all faucets with hose connections. No cross-connections between water supplies.
||Anti-backflow devices installed on some faucets with hose connections.
||No anti-backflow devices. Air gap maintained.
||No anti-backflow devices. Air gap not maintained. Cross-connections between water supplies.
||No unused unsealed .
||Unused well capped and protected.
||Unused, unsealed well in field. Not capped or protected.
||Unused, unsealed well in farmstead. Not capped or protected.
||Consistent satisfactory water quality. Bacteria, nitrate and other tests meet standards.
||Occasional deviation from standards with bacteria, nitrate and other tests.
||Bacteria, nitrate and other tests mostly do not meet standards.
||No water tests done. Water discolored after rainstorms or during spring melt. Noticeable changes in color, clarity, odor or taste.
|Use this total to calculate risk ranking in Equation
1See MU publication WQ675,Improving Drinking-Water Well Condition.
2Should be a minimum distance of 150 feet for fertilizer and chemical storage.
3Besides representing a higher-risk choice, this practice also violates Missouri law.
What do I do with these rankings?
Begin by determining your overall well management risk ranking using Equation 1. Total the rankings for the categories you completed, and divide by the number of categories you ranked:
|(total of rankings)
1Carry your answer out to one decimal place.
|If your risk ranking is
||Your risk is
|3.6 to 4
|2.6 to 3.5
||low to moderate
|1.6 to 2.5
||moderate to high
|1 to 1.5
This ranking gives you an idea of how your well management practices as a whole might be affecting your drinking water. This ranking should serve only as a general guide, not a precise diagnosis. Because it represents an average of many individual rankings, it can mask any individual rankings (such as 1s or 2s) that should be of concern. (Step 2.)
Enter your well management risk ranking above in the first table in Worksheet #9 (MU publication WQ659). Later you will compare this risk ranking with other farmstead management rankings. Worksheet #8 (MU publication WQ658) will help you identify your farmstead's site conditions (soil type, soil depth and bedrock characteristics) and Worksheet #9 (MU publication WQ659) will show you how these site conditions affect your risk rankings.
Look over your rankings for individual activities:
- Low-risk practices (4s): ideal; should be your goal despite cost and effort.
- Low- to moderate-risk practices (3s); provide reasonable groundwater protection.
- Moderate- to high-risk practices (2s); inadequate protection in many circumstances.
- High-risk practices (1s); inadequate; pose a high risk of polluting groundwater.
Regardless of your overall risk ranking, any individual rankings of "1" 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.
Find any activities that you identified as 1s and list them under "High-Risk Activities" in Worksheet #9 (MU publication WQ659).
Read MU publication WQ675,Improving Drinking Water Well Condition, and consider how you might modify your farmstead practices to better protect your drinking water.
These terms may help you make more accurate assessments when completing Worksheet #1. They may also help clarify some of the terms used in Fact Sheet #1 (MU publication WQ675).
- Abandoned water well
A permanently discontinued well or a well that is in such disrepair that its continued use for the purposes of obtaining groundwater is impractical or may be a health hazard.
- 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.
A water-bearing formation (soil or rock horizon) that transmits water in sufficient quantities to supply a water well.
- Bored wells
Wells constructed using augers, scoops, drag lines or similar equipment. These holes are usually of large diameter and are constructed in alluvial or glacial material.
An impervious durable pipe placed in a well to prevent the walls from caving and to keep out surface drainage or undesirable water, gas or other fluids.
A link or channel between pipes, wells, fixtures or tanks carrying contaminated water and those carrying potable (safe for drinking) water. Contaminated water, if at higher pressure, enters the potable water system.
- Drilled wells
Wells not dug or driven, including those constructed by a combination of jetting or driving. These wells are normally 4 inches to 8 inches in diameter.
- 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 smaller in diameter (2 inches or less), less than 50 feet deep and can be installed in areas of relatively loose soils, such as sand.
- Dug wells
A well in which the side walls may be supported by material other than standard weight steel casing. Water enters a dug well through the sides and bottom.
- Ground water
The water in the zone of saturation in which all of the pore spaces of the subsurface material are filled with water. The water that supplies springs and wells is groundwater.
Slurry of cement or bentonite clay used to seal the annular space between the outside of the well casing and the bore hole. Also used in sealing abandoned wells.
- Milligrams per liter (mg per liter)
The weight of a substance measured in milligrams contained in 1 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 1 million units of another.
- Pressure grout
Refers to the process of applying grout material under pressure to the annular space of a well for the purpose of sealing it and thus preventing vertical movement of fluids through the annular space. Grout must be introduced from the bottom of the annular space.
- 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 (seal)
A method or device used to protect a well casing or water system from the entrance of any external pollutant at the point of entrance into the casing.
The Missouri Farmstead Assessment System is a cooperative project of MU Extension; College of Agriculture, Food and Natural Resources; and the Natural Resources Conservation Service.
The National Farmstead Assessment Program provided support for development of the Missouri program. These materials are adapted from the Wisconsin and Minnesota prototype versions of Farm•A•Syst.
This material is based upon work supported by the Extension Service, U.S. Department of Agriculture, under special project number 91-EHUA-1-0055 and 91-EWQI-1-9271.
Adapted for Missouri from material prepared by Susan Jones, U.S. E.P.A., Region V, Water Division, and University of Wisconsin Cooperative Extension.
MU Extension Farm•A•Syst team members: Joe Lear, Regional Agricultural Engineering Specialist and Chief Editor; Beverly Maltsberger, Regional Community Development Specialist; Robert Kelly and Charles Shay, Regional Agricultural Engineering Specialists; Thomas Yonke, Program Director, Agriculture and Natural Resources; Jerry Carpenter, State Water Quality Specialist; and Bob Broz, Water Quality Associate.
Technical review provided by August Timpe, Missouri Department of Natural Resources; Charles Fulhage, MU Department of Agricultural Engineering; U.S. E.P.A. Region VII, Environmental Sciences Division; and Missouri Natural Resources Conservation Service.
WQ651, new October 1995