Well Depth Shallow wells draw from the ground water nearest the land surface, which may be directly affected by farmstead activities. Polluted surface water can infiltrate into the soil and quickly affect a shallow well that was not properly constructed or is located in a coarse-textured soil that easily conducts water. Deeper wells are more protected from surface contamination by the soil. Many potential contaminants are sorbed by soil particles and degraded by soil microorganisms before reaching the groundwater tapped by a deep well. Local geologic conditions determine how susceptible an aquifer is to contamination from surface activities.
Aquifers located near the surface are more vulnerable to potential contamination.
The type of soil material overlying an aquifer also influences its vulnerability. Aquifers of sand and gravel allow water to pass through quickly and can be easily contaminated by polluted recharge water. In fractured bedrock, or karst areas, water moves between cracks and channels. Pollutants follow these same channels and enter directly into the aquifer. In contrast, water movement in deep bedrock aquifers is very slow.