Project Specifics

Geosyntec developed a groundwater compliance strategy for an electric cooperative’s fleet of CCR disposal units to address constituents in groundwater samples with statistically significant increases (SSIs) above background concentrations.

The first task was to evaluate whether the SSIs were related to a leachate release from the lined regulated coal ash disposal unit or were due to an alternative source.

Geosyntec Scope of Services

Geosyntec designed and implemented a geochemical forensics testing program to address this critical decision point. We collected leachate from the regulated unit as well as groundwater samples from background and compliance monitoring wells for analysis of major solutes as well as stable isotopes of those solutes, using a multiple-lines-of-evidence approach to enhance the credibility of the findings to potential third-party litigation.  Forensics tools included solute ratios, Stiff Diagrams, stable isotope cross plots, and stable isotope mixing diagrams.

Our analyses indicated that the wells with SSIs had fingerprints that did not match those of the leachate samples. We also developed an updated conceptual site model that acknowledged detection of solutes in downgradient monitoring wells that are derived from an underlying saline groundwater horizon. Finally, we prepared a report documenting our findings that the client posted to an internet site for public viewing.

Notable Accomplishments

The successful demonstration resulted in the site remaining in the Detection Monitoring Program stage, helping our client avoid the possibility of a costly Assessment Monitoring Program and implementation of corrective measures.  The results also paved the way to changing the design of the site’s groundwater monitoring program from inter-well statistics to intra-well statistics, which established more reasonable background concentrations for future evaluation of potential indicator parameter SSIs.

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