ENGINEERING AND HYDROGEOLOGICAL PROBLEMS ASSOCIATED WITH IN-SITU TREATMENT

Most organic materials that contaminate soil and the subsurface enviro nment are readily degraded by natural biological processes. To this de gree, in situ bioremediation can be thought of as a highly successful purification process. However, some organic molecules are naturally re fractory to biodegradation, or other environmental factors induce mole cular recalcitrance such as the absence of a proper microbial populati on or the presence of unsuitable environmental conditions. Examples of recalcitrant groundwater contaminants are soluble components of petro leum hydrocarbons (BTEX) and chlorinated aliphatic hydrocarbons (CAHs) . Organic recalcitrance may be changed through introduction of degradi ng populations of microorganisms or by changing the environmental cond itions through introduction of nutrients or other chemicals. The most significant engineering deficiency in in situ bioremediation is the ab sence of proven methods to introduce such materials into the subsurfac e environment for efficient mixing with microorganisms and the contami nants of concern.