What is identified as the biggest cause of groundwater contamination from a leaching bed?

• A. Installing the leaching bed too far from high groundwater table.
• B. Installing the leaching bed too close to the high groundwater table.
• C. Using fine sand as fill.
• D. Building the bed away from water sources.

Answer: (B)

The key factor is the amount of soil between the leaching bed and the groundwater to allow natural filtration and treatment of effluent. When the bed is placed too close to a high groundwater table, there isn’t enough unsaturated soil for contaminants to be attenuated before reaching groundwater. Pathogens, nitrates, and other pollutants can move quickly into the groundwater, making proximity to the water table the primary risk for contamination. Seasonal rises in the water table can further reduce the available treatment zone and increase vulnerability.

Keeping the bed at a greater depth relative to the water table reduces this risk by providing more soil for filtration. Building away from water sources is also protective. While the fill material can influence drainage and clogging behavior, it doesn’t explain the dominant cause as much as insufficient vertical separation from the groundwater.