|Performance Monitoring of MNA Remedies for VOCs in Ground Water (EPA/600/R-04/027) April 2004
Environmental monitoring is a major component of any remedy that relies on natural attenuation processes. The objective of this document is to identify data needs and evaluation methods useful for designing monitoring networks and determining remedy effectiveness.
Effective monitoring of natural attenuation processes involves a three-dimensional approach to network design and clearly defined performance criteria based on site-specific remedial action objectives. Objectives for the monitoring program will be met through routine evaluations of institutional controls and measurements of contaminant, geochemical, and hydrologic parameters. These data are used to evaluate changes in three-dimensional plume boundaries, contaminant mass and concentration, and hydrological and geochemical changes that may indicate changes in remedy performance.
Data interpretation focuses on detection of spatial and temporal changes, and assessment of their impacts on the achievement of site-specific goals. Particular changes of interest include:
Decisions regarding remedy effectiveness and the adequacy of the monitoring program will generally result in continuation of the program, program modification, implementation of a contingency or alternative remedy, or termination of the performance monitoring program. Such decisions are appropriately based on specific, quantifiable performance criteria defined in the monitoring plan.
Continuation of the program without modification would be supported by contaminant concentrations behaving according to remedial expectations, while ground water flow and geochemical parameters remain within acceptable ranges.
Modification of the program, including increases or decreases in monitoring parameters, frequency, or locations, may be warranted to accommodate changing conditions or improved understanding of natural attenuation processes at the site. Situations that may trigger implementation of a contingency or alternative remedy include:
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