Tracking the progress of in-situ chemical oxidation

Last year I presented the story behind the use of real-time monitoring to track the movement of an activated carbon fluid injected into groundwater.

This year I’m presenting another remediation story involving in-situ chemical oxidation (ISCO) and how the migration of the injection fluid (potassium permanganate) was successfully monitored in real time through an aquifer.

To get the complete picture, come along to Land Remediation Expo at the NEC in Birmingham, Wednesday 12th September at 1:15 pm in Seminar Theatre 21.

I thought I’d share a snapshot of the data record with you.

Background and Data Record

In November 2016, potassium permanganate was injected into an aquifer contaminated with low concentrations of chlorinated solvents.

 

HydroVu data record with annotated notes for ORP measurement recorded every hour in 3 monitoring boreholes.

Three In-Situ Aqua TROLL 600 Multiparameter Sondes were positioned into monitoring boreholes. In the time-series graphic above, well MW-7S is located 4 metres downgradient of one of the injection wells, MW-2S is 6 metres downgradient of another injection well and MW-4S is located outside the injection area and has been used to illustrate background conditions within the aquifer, largely unaffected by the injection fluid.

The AT600 sondes were programmed to collect data every hour commencing a few days before injection. The injection process was carried out over a period of 9 days in 14 wells. The graphic above shows the monitoring record of ORP (oxidation-reduction potentiol, or redox) from the three monitoring wells over a period of 5 months. Data was transmitted daily to In-Situ’s HydroVu web platform, and reviewed weekly by consultants managing the remediation programme.

Notes on Data Record

The main objective of monitoring was to try and identify the rate of migration and/or depletion of the oxidising fluid through the aquifer and the time taken for water quality to return to background conditions. Significant changes were recorded in temperature, pH and electrical conductivity, but the ORP records gave the most reliable indication of the movement and depletion of oxidising solution as it migrated past the monitoring wells.

For example, the ORP response in well MW-7S (grey line) shows the following:

  • An immediate and rapid rise in ORP from below 100 mV to in excess of 700 mV. This occurred 1 day following injection in a well 4 metres upgradient of MW-7S.
  • ORP remained at around 700 mV for 2 weeks then fell gardually over the next 2 weeks, plateauing at 400 mV for a further 3 weeks before falling sharply to background levels. This process took 50 days from the date of injection.
  • The changes of ORP in well MW-2S show a similar, but more prolonged period of elevated ORP, lasting 100 days.

The detailed, high-resolution record for ORP has provided consultants with clear evidence to be able to quantify the transport and depletion time of the oxidsing reagent within the aquifer, greatly enhancing their confidence in the success of the injection process.

Most importantly, quarterly sampling of monitoring wells has continued with results available for a 15-month period since remediation. These indicate a significant and sustained fall in solvent concentrations, providing cautious optimism that the remediation was targetted effectively and has worked. Monitoring continues at the site.

I hope this has piqued your interest, and I look forward to welcoming some of you to the seminar on 12th September.

©Peter Dumble 2018

Peter.Dumble@pdhydrogeology.com

Acknowledgements

Our thanks Brian Symons, Sharon Kozicki and Robert Kick of Foth Infrastructure and Environment (USA), who’s work this is, for permission to anonymously use the data presented in this blog.