How can old unlined waste ponds and lagoons threaten aquifers?

Old, unlined waste ponds and lagoons threaten aquifers primarily by allowing hazardous substances to migrate directly into the subsurface environment. Because these older sites lack the impermeable liners and leachate collection systems required for modern facilities, liquid waste can seep through the soil and percolate downward until it reaches and mixes with groundwater.123

The risk is particularly acute when these sites are located directly above aquifers used for public water supply. The permeability of the underlying soil formations plays a critical role in this process; highly permeable materials, such as sand or gravel, allow for the relatively free flow of contaminated liquids toward the water table. Once hazardous materials infiltrate an aquifer, they can compromise water quality, posing significant, long-term threats to public health and environmental integrity. Remediation of such sites often requires complex engineering solutions, such as the installation of subsurface cutoff walls or the removal and treatment of contaminated soil and groundwater, to prevent further migration of pollutants.312