NATURAL ATTENUATION OF DISSOLVED CHLORINATED SOLVENTS ALONG A FLOW PATH FROM AN OXIDIZED KARSTIC AQUIFER TO AN ANAEROBIC HYPORHEIC DISCHARGE ZONE

In-situ natural attenuation is an effective remedial alternative for addressing many groundwater contamination problems. Under ideal conditions, this method can be inexpensive, flexible, and minimally interruptive of normal site activities. Yet natural attenuation is a notoriously unsuccessful way of remediating chlorinated solvent plumes at many sites. Though these common degreasing agents, such as trichloroethene, trichloroethane, tetrachloroethene, and carbon tetrachloride, are among the most frequently encountered groundwater contaminants, they are often present in aquifers where less than ideal conditions for chlorinated solvent biodegradation pervade. One of the most common chlorinated solvent biodegradation reactions, Natural Reductive Dechlorination, occurs most readily in aquifers with high organic loads and low redox potential; conditions not seen in many aquifers, but known to be widespread in riparian zones along the banks of streams, lakes, rivers, and other surface water bodies. Documented here is a case where chlorinated solvent biodegradation occurs naturally as a plume flows from an oxygen-rich karstic aquifer system to a stream surrounded by anaerobic and organic-rich subsurface sediments.