Natural attenuation is the reduction of contaminant concentration or toxicity resulting from dispersion, dilution, biodegradation, volatilization, sorption, and other processes that occur naturally in the subsurface. The concept and use of natural attenuation is gaining in popularity in this new era of evaluation and remediation based on the risks posed by contaminants to human health and the environment.
State and federal program documents and other non-regulatory guidance documents recommend the evaluation of various chemical and biological parameters in soil and groundwater to indicate the occurrence of natural attenuation of petroleum hydrocarbons. The US Environmental Protection Agency, the American Society for Testing and Materials' Risk-Based Corrective Action standard, the Air Force Center for Environmental Excellence and the state programs all recommend common parameters, such as dissolved oxygen, nitrate, sulfate, and fraction of organic carbon, to indicate the presence of aerobic and anaerobic conditions in the subsurface.
Each guidance document identifies other evaluation criteria that may be useful based on that program's attenuation model. This presentation will provide a brief overview of the natural attenuation process, identify the evaluation criteria from each program, and recommend a basic list of evaluation that should be appropriate for most sites.
AAPG Search and Discovery Article #90926©1999 AAPG Eastern Section Meeting, Indianapolis, Indiana