Meet Charles Hostetler, of SCS Engineers, at Session 4B Soil and Groundwater Characterization and Conceptualization on Tuesday, April 18, 3:30-5:50 for a discussion of CCR detection monitoring to minimize false positives.
CCR groundwater monitoring programs require routine detection monitoring around regulated units. Routine detection monitoring aims to identify situations where groundwater quality could be impacted by contaminants mobilized from CCR. Background data are collected to characterize the statistical distributions of groundwater quality parameters in the aquifer where there is no potential impact from regulated units. During operational, closure, and post-closure care activities, the same groundwater quality parameters are sampled periodically downgradient from the regulated unit and compared to these background data. Any statistically significant increases over background data spur an investigation of the potential result of CCR leachate impacting groundwater quality.
The procedure for designing and implementing a groundwater monitoring plan foresees that all routine detection monitoring programs will generate false positive results. The EPA’s Unified Guidance recommends that the design of monitoring plans minimize the site-wide false positive rate. For CCR detection monitoring programs, site-specific and regulatory requirements fix the number of well/parameter pairs and sampling frequencies, leaving the CCR permittee with two focus areas to minimize the site-wide false positive rate. The first is a robust background characterization that captures the site’s spatial and temporal variability. The second is a complete characterization of leachate composition, including unregulated constituents, and incorporating correlation into the statistical comparison to the background. These two focus areas can minimize costly assessment and corrective action activities.
Additional Information located on CCR and Utilities is on the SCS website.