University of Connecticut Cooperative Extension System: Water Quality and the Home Landscape

Well Water

Factors for Testing Water

Karen Filchak

There are a variety of factors that affect well water quality.

Factors that are considered of key importance in protecting the quality of well water include:

Location of the well

  • Type, age and integrity of well
  • Construction of the well
  • Soil and bedrock geology
  • Activities near the well

Location is determined by state and local regulations.  State and local regulations dictate well location and construction standards.  State minimums are set by statute and enforced by the Connecticut Department of Public Health. Local regulations can override state requirements only if they increase required distances from potential pollution sources.

The greatest protection of a well exists when the well is high in the landscape, the pipe is at least 6  inches above ground level, the land slopes away and water drains away from the wellhead . 

Well type, age and integrity must be included in the evaluation of the well. There are three main types of wells.  They include dug, driven and drilled.

 A dug well  has a large diameter cap, is shallow, older and presents a high risk of contamination since water is drawn from groundwater nearer the land surface.   Also, the condition of the well structure is likely to be compromised with age.

A driven well has a smaller diameter cap, is less than 50 feet deep, is driven into sand or loose soils and presents a moderate risk of contamination. 

A drilled well has a cap of 4-6”, is deeper (drilled through bedrock), presenting a lower risk for contamination of water.

The older the well, the greater is the likelihood that there can be problems.  Wells constructed over 50 years ago are likely to be shallow and poorly constructed.  Lubricating oils may be leaking; casings may be cracked or corroded.


The condition or integrity of the well is a factor no matter what the age of the well.  Activities near the well or frost may dislodge or crack the casing, or a damaged or unsecured well cap can result in contamination regardless of the type or age of the well.

Private drinking water wells must meet construction standards and be approved by the local health department


Proper construction of the well includes well type, height of casing above the land surface, condition of the casing and well cap (seal)as well as the casing depth relative to the land surface.  The local health department is a source of information for the homeowner or builder regarding construction concerns or questions.

In addition to sound initial construction, a well should be maintained with inspections every 10 years or so.

Soil and bedrock geology address conditions such as soil type, soil depth, type of bedrock and depth to the water table.

Soil is an important factor in determining where and how water moves.  Water and fluids move through most soils but at varying rates, depending upon the type of soil that the liquid is traveling through. 

Soil type determines the rate of flow to groundwater and the ability of soil to break down contaminants.  There are three basic types of soils, based on the size of the soil particles.  They are clay, which has small particles; silt/loam, which has medium sized particles; and sand/gravel, which has large particles.  Soil type is important because soil particle size will influence which pollutants are able to reach groundwater.  For example, sandy soils allow a more rapid downward movement of water allowing a faster and more direct potential for transmission of pollutants. 

Soil depth influences risks to groundwater.  The deeper the soil the greater the chance of breaking down or filtering surface contaminants before they reach groundwater.

The type of bedrock addresses whether the bedrock is impermeable (ex. shale or granite) or permeable (ex. limestone).  Fractures in bedrock affect potential for contamination as fractures cause water to move in unpredictable directions.  Therefore, even impermeable bedrock like granite does not guarantee protection from pollutants.

Depth to water table (the boundary between the unsaturated soil where pore spaces between soil or rock contain air, roots, soil organisms and some water and the saturated soil, where groundwater is drawn from drinking water wells) is a factor as well.  The closer the water table is to the surface of the land, the greater the susceptibility of groundwater to contamination from activities on the land. 

Activities near the well are important considerations when determining a wells susceptibility to contaminants.

Activities near the well can result in the introduction of contaminants to the well.  Practices such as use of fertilizers and chemicals, auto maintenance and leaks, animal waste or a failing septic system can all impact the quality of well water.

No one can predict with absolute certainty the likelihood of a contaminant entering groundwater.  A variety of factors need to be considered.  They include:


               Characteristics of the pesticide product

    • Solubility
    • Half life (persistence)
    • Adsorption rate
    • Characteristics of the Soil                    
    • Texture
    • Structure
    • Organic matter content
  • Applicator practices
  • Location of groundwater – water table
  • Type of geological formations above the groundwater
  • Condition of the well
  • Other Considerations:
    • Depth to groundwater fluctuates throughout the year
    • Often with turf pesticides, the quality of the turf makes a difference.  A strong stand of turf acts as a good biological filter for many pesticides

Proper well construction can help prevent contaminants from entering the well