Compliance and Performance Monitoring for Permeable Reactive Barrier WallsCompliance monitoring determines whether the contaminant concentration levels required by the regulators are being met. Usually the compliance monitoring criteria will be set by the state where the site is located. Normal compliance monitoring parameters include:

the contaminants of interest

potential contaminant daughter products

• pH
• alkalinity
• specific conductance
• temperature, etc.

In general, several monitoring wells should be installed to determine:
are regulatory goals are being achieved?
does contaminant breakthrough occur (immediately or over time)?
is the contaminant flowing around the wall?
Typical well locations would include:
immediately downgradient of the reactive zone discharge

• at each end of the wall
• below the wall, and
• above the reactive zone (if possible)

In addition to monitoring the contaminants, their products, and the routine water quality parameters listed above, performance monitoring of permeable reactive barriers is needed. Performance monitoring is to assure that the reactive barrier is functioning as designed and to allow evaluation of whether it continues to function properly over time. Changes in the monitored parameters should alert the investigator to potential problems with the barrier. For a reactive iron barrier the performance monitoring parameters should include:

•hydrologic parameters (baseline and changes over time)
•precipitates on the iron surfaces (and rate of buildup)
• Eh
• dissolved oxygen, and
•ferrous iron

Knowledge of these parameters help confirm emplacement as well as address and detect:
• loss of reactivity
• decrease in permeability
• decrease in reaction zone residence time
• short circuiting of the reactive zone (i.e. preferential pathways), and
• funnel wall leakage

Increases in the hydraulic head across the barrier could, for example, indicate that plugging is occurring. Coring the barrier and evaluating the buildup of precipitates on the iron surfaces could confirm this suspicion. When functioning properly, Eh in the iron barrier should be low, oxygen should be undetectable, and ferrous iron should be present.

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Powell & Associates
(248) 738-3860
Email: rpowell@powellassociates.com

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