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. 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 is related to potential contamination risks. Dug wells large diameter, usually shallow, highest risk of contamination. Drilled wells casing diameter between 4 and 8 inches, lower contamination risk. Well depth depends on depth of the well casing below the water table and local geologic conditions.