Analytical Methods for Testing Reactive Cap Composition – A Case Study and Challenge to the Industry
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Background/Objectives: A current focus in the sediment remediation community is the use of reactive caps as a cost-effective remediation tool.  The use of reactive caps has been researched in laboratory and pilot scale projects and is now being taken into the field through remedy design and implementation.  Designers rely on the in-place caps having sufficient mass of reactive component to provide the required mitigation of human health and ecological risk.

But how can the designer determine if the caps were constructed with the required reactive mass?  To date, the assessment of in-place cap composition has been based on a mass balance, tracking the amount of reactive component mixed with sand or other specified material used in the cap.  This presumptive approach does not account for variability in mixing or separation of the reactive material during installation.  This presentation describes the analytical method developed to assess the composition of an installed reactive cap built as part of the remediation of Reaches 6 and 7 of the West Branch of the Grand Calumet River (WBGCR) in Northern Indiana.  This work was conducted by the Ryba Marine Construction Company/Terra Contracting Service, LLC, A Joint Venture (RTC JV) as a Great Lakes Legacy Act (GLLA) project for the EPA Great Lakes National Program Office (GLNPO).

Approach/Activities: RTC JV first considered the contract requirements for analytical methods to evaluate in situ mass for the two reactive components, Organoclay and granular activated carbon (GAC).  RTC JV reviewed the literature for test methods, and approached reactive component manufacturers and laboratories to get their input.  RTC JV then obtained GLNPO approval of the vendor-recommended analytical methods and began testing.  Problems arose in implementing these methods in the field, requiring RTC JV to develop alternate approaches for verifying in situ concentrations of reactive components.

Results/Lessons Learned: RTC JV was able to identify and implement an effective cap sampling and analysis program.  The selected sand/GAC test method was a loss on ignition (LOI) process modified to ensure complete GAC ignition.  RTC JV attempted to utilize a similar LOI procedure for testing the sand/Organoclay layer but found the method was unreliable.  Instead, a heavy liquid separation method was used to analyze the sand/Organoclay cap layer composition.  This presentation describes the test methods, required modifications, and key field implementation factors.

Accurate methods of analysis are needed to assess whether installed active caps have the designed amount of reactive component in order to effectively mitigate environmental risk.  The test methods developed for the WBGCR project were acceptable for assessing the GAC and Organoclay components of the cap layer; however, further research into analytical methods would benefit the industry.  The presentation concludes with this challenge and lists key attributes of an acceptable testing protocol for assessing reactive cap composition.