Contamination

Contamination of streams and wells is a serious problem in karst regions. In the case of surface streams, a high degree of natural purification takes place. Flowing water is aerated as it tumbles over riffles, is exposed to UV sunlight, and is filtered to some extent by trickling through sandbars and small rocks.

However, when water is diverted underground no natural purification takes place. This is because the water runs in smooth cave conduits, like pipes. Cave streams are usually smooth and placid instead of tumbling. There's no sunlight in a dark cave. As a result, a raw sewage spill or any contamination into a cave system can kill the long-lived and unique aquatic cave organisms.

Due to the nature of the open flow in these underground conduits, contaminants travel in karst systems at rates of feet per second as compared to rates of feet per year for groundwater travel in normal soils. This results in rapid contamination of a local groundwater system in a karst area. A spill can enter a cave system and emerge miles downstream where the cave spring joins a river.

Fish can easily be wiped out by such raw sewage contamination due to depletion of dissolved oxygen in the water—causing the fish to suffocate and die.

Rather than putting karst regions at risk through the contruction of additional waste treatment facilities, often a better answer is to retrofit existing facilities with immersed membrane technology (see Immersed Membrane Technology In Action).