In Situ Treatment Performance Monitoring: Issues and Best Practices

The U.S. EPA recently released an issue paper (EPA 542-F-18-002) that describes how in situ treatment technologies may impact sampling and analysis results.  The paper discusses the best practices to identify and mitigate issues that may affect sampling and analysis.

The utility of monitoring wells for performance or attainment monitoring is based on the premise that contaminant concentrations measured in the wells are representative of aquifer conditions. However, during in situ treatment, various biogeochemical and hydrogeological processes and sampling and analysis procedures may affect the representativeness of the monitoring well and sample quality, which may not be adequately considered in current remediation practice.

A properly designed monitoring network that anticipates the distribution of amendments after injection would minimize impacts to monitoring wells.  However, predicting amendment distribution prior to injection is challenging such that impacts to monitoring wells are likely.

The purpose of The U.S. EPA issue paper is to:
• describe how in situ treatment technologies may impact sampling and analysis results used to monitor treatment performance; and
• provide best practices to identify and mitigate issues that may affect sampling or analysis.

The U.S. EPA issue  paper discusses eight potential sampling or analytical issues associated with groundwater monitoring at sites where in situ treatment technologies are applied. These issues are grouped under three topic areas:
• Issues related to monitoring wells (Section 2).
• Representativeness of monitoring wells (Section 3).
• Post-sampling artifacts (Section 4).

The paper presents issues that pertain to collecting water samples directly from a monitoring well and does not discuss the use of other sampling techniques, such as passive diffusion bags or direct push groundwater sampling.