10    EVALUATION OF INTRINSIC REMEDIATION
PROCESSES IN SITE RESTORATION
Stanislaus J. Zagula, Chemical Engineer
Woodward-Clyde
Chicago, Illinois 60603
Timothy R. Marshall, Senior Project Manager
Woodward-Clyde
Santa Ana, California 92705
INTRODUCTION
Intrinsic remediation, also referred to as natural attenuation, is an innovative remedial approach that integrates naturally occurring biotic and abiotic processes into an overall treatment
system to remediate contaminants in the subsurface soil and groundwater. These processes include biodegradation, biotransformation, abiotic oxidation, adsorption, dilution, dispersion, and
volatilization. As with other remediation technologies, it is necessary to provide scientifically
defensible data and sufficient evidence to demonstrate the effectiveness of the technology and its
protection of human health and the environment. To that extent, the successful application of intrinsic remediation relies on a focused site investigation, an understanding of the interrelationship of hydrology, geology, and biogeochemistry, and the scientific evaluation of the naturally
occurring biotic and abiotic intrinsic remediation processes.
Intrinsic remediation offers several advantages over conventional technologies. First, the contaminants are ultimately transformed to innocuous by-products rather than transferred to another
phase or media. Intrinsic remediation is nonintrusive, so site operations may continue uninterrupted, soil is not excavated, groundwater is not pumped, and infrastructure is not disturbed. Finally, intrinsic remediation does not rely on treatment equipment; therefore, capital costs, operation and maintenance costs, and downtime is minimized. However, intrinsic processes are not a
panacea; there are limitations as well. Changes in local hydrogeologic conditions, such as
groundwater gradients, velocities, biogeochemistry, and contaminant concentrations may impact
the effectiveness of intrinsic remediation. Likewise, as with other remediation technologies, heterogeneity in the subsurface may make hydrogeologic and biogeochemical characterization of
the aquifer more difficult.
The processes and methodologies utilized in the assessment and remediation of contaminated
soil and groundwater have significantly evolved since their conception in the 1970s. In the past,
generic and overly conservative cleanup objectives were formulated by nonrisked based criteria
such as maximum contaminant levels, background levels, or nondetection. New and developing
remediation technologies could not consistently achieve these stringent cleanup objectives, and
the cost to achieve even incremental steps in effectiveness was often prohibitive. Consequently,
responsible parties were limited to choosing between costly remedial actions such as "dig and
haul," incineration, and "pump and treat" technologies, or challenging the cleanup objectives
through litigation.
Presently, the methodologies for determining cleanup objectives are being reevaluated and a
new approach is emerging called risk-based corrective action (RBCA). In the RBCA approach, a
framework is set up to integrate site assessment, risk assessment, risk management, remedial action, and cleanup objective decisions based on current and reasonable potential risks to human
health and the environment. Previous corrective action objectives focused on reducing the
amount of contaminant at the site, often with an ultimate goal of achieving background or no detectable levels. In RBCA, the objective is to reduce risk to a level protective of human health and
51st Purdue Industrial Waste Conference Proceedings, 1996, Ann Arbor Press. Inc., Chelsea, Michigan 48118.
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