How can contaminants typically enter groundwater supplies?

Groundwater supplies are particularly vulnerable to contaminants that can enter through various pathways, with surface infiltration from agricultural runoff and septic systems being a primary method. This occurs when water from rain or irrigation percolates through the soil, carrying with it fertilizers, pesticides, pathogens, and other pollutants from agricultural practices and failing septic systems. As this water moves downward, it can reach the groundwater table, effectively introducing contaminants into the aquifer system.

In agricultural areas, runoff can accumulate a significant amount of chemicals used for crop production. When heavy rainfall occurs, these substances can be washed from the surface into the soil and subsequently into groundwater. Septic systems, particularly those that are poorly maintained or improperly sited, can leach bacteria and other harmful contaminants into the surrounding soil, eventually reaching the groundwater.

On the other hand, evaporation from water bodies does not contribute to groundwater contamination as it only leads to water vapor returning to the atmosphere. Direct discharge from treatment plants typically refers to surface water discharge rather than groundwater, while atmospheric deposition during rainfall can introduce some contaminants but is often less significant compared to surface runoff and septic system infiltration in terms of volume and impact on groundwater. Thus, surface infiltration from agricultural runoff and septic systems is recognized as a critical route for contaminants to enter