Troubleshooting Post-ISCO Performance Using Geochemical Data
John Valkenburg, Senior Engineer & Technical Sales Manager, Evonik
Given heterogeneous site conditions and other challenges, In Situ remediation technologies result in varied responses, especially when applied via injection. Many factors influence performance variations, including dosing, distribution / contact, contact time, sorbed mass / non-target demand, and even recontamination from inflowing groundwater. Following activated persulfate applications, monitoring several geochemical parameters enables distinguishing these various remediation response factors. Essentially, post-ISCO geochemical data review enables a perceptual recalibration of the working conceptual site model (CSM) using data-derived post-remediation lessons learned. Site learnings then enable remedial action plan changes where needed. This presentation overviews our approach to reviewing post-ISCO site geochemical response performance data. Several project site’s data are used to demonstrate concepts.
Key geochemical parameters used to assess persulfate applications include direct measurements of persulfate, electric conductivity (EC), sodium, potassium, sulfate, pH, and ORP. Geochemical response timing is used to evaluate monitoring location impacts over time, whether by persulfate itself and/or its activation, degradation, and dissolution products. Dissolved concentrations of persulfate, sodium, potassium, and sulfate are compared to application rates to validate substrate distribution and longevity. Sodium is a conservative tracer, rendering itself particularly useful in assessing distribution and flow paths.
Reviewing treatment performance relative to geochemical parameter changes often enables determining the root cause of ambiguous and/or mixed results. Variations in EC / sodium concentrations over time can help distinguish between true rebound versus recontamination. The ‘disappearance’ of an injectate geochemical footprint over time may suggest that new, untreated groundwater migrated into an area, re-contaminating groundwater. Conversely, contaminant concentrations ‘rebounding’ while EC and sodium remain elevated suggests a true rebound: desorbed mass re-equilibrating with groundwater post-ISCO and indicates an insufficient reagent dose. Making such data-driven distinctions guided further actions at our example sites: 1) a second application being recommended (a case of true rebound) and 2) expanding the treatment to include a source (a case of inflowing groundwater recontamination). Post-ISCO groundwater geochemistry also revealed where mixed results are best explained by substrate distribution variations, requiring application approach modifications enabling more homogeneous reagent placement, better contact, and more complete treatment.
John has over 35 years industry experience, including 5 as environmental chemist, 16 as environmental consultant, and over 15 years in his current engineer & technical sales role. He's a professional engineer in Michigan and University of Illinois graduate (BS in Dietetics & MS in Environmental Engineering). John and his wife enjoy their horses, dog, and cats.