Performance Assessment for Pump-and-Treat Closure or Transition

Abstract

A structured performance assessment approach is useful to evaluate pump-and-treat (P&T) groundwater remediation, which has been applied at numerous sites. Consistent with the U.S. Environmental Protection Agency's Groundwater Road Map, performance assessment during remedy implementation may be needed, and should consider remedy optimization, transition to alternative remedies, or remedy closure. In addition, a recent National Research Council study examined groundwater remediation at complex contaminated sites and concluded that it may be beneficial to evaluate remedy performance and the potential need for transition to alternative approaches at these sites. The intent of this document is to provide a structured approach for assessing P&T performance to support a decision to optimize, transition, or close a P&T remedy. The process presented in this document for gathering information and performing evaluations to support P&T remedy decisions includes use of decision elements to distinguish between potential outcomes of a remedy decision. Case studies are used to augment descriptions of decision elements and to illustrate each type of outcome identified in the performance assessment approach. The document provides references to resources for tools and other guidance relevant to conducting the P&T assessment. v SummaryA structured performance assessment approach is useful to evaluate pump-and-treat (P&T) groundwater remediation, which has been applied at numerous sites. Consistent with the U.S. Environmental Protection Agency's Groundwater Road Map, performance assessment during remedy implementation may be needed, and should consider remedy optimization, transition to alternative remedies, or remedy closure. In addition, a recent National Research Council study examined groundwater remediation at complex contaminated sites and concluded that it may be beneficial to evaluate remedy performance and the potential need for transition to alternative approaches at these sites. The intent of this document is to provide a structured approach for assessing P&T performance to support a decision to optimize, transition, or close a P&T remedy.The performance assessment approach described in this document is organized to use a set of decision elements to help decision makers distinguish between several categories of decision outcomes associated with transition, optimization, or closure of P&T systems. The decision elements selected for use in the P&T performance assessment include information about:

Performance Assessment of Pump‐and‐Treat Systems

“…A summary of the decision logic described by Truex et al () for the P&T performance assessment, incorporating the decision elements and the decision outcomes, is presented in Figure . After updating the conceptual site model (CSM) and assessing whether RAOs have been met, the decision logic consists of several primary assessments that distinguish between outcomes.…”

“…In this case, the decision logic specifies either evaluating technologies to supplement P&T or switching to a different remedy approach to address factors inhibiting remediation (e.g., matrix diffusion). Site decision makers may also consider ARAR waivers or revisiting RAOs (e.g., using approaches to define objectives, as described in the Integrated DNAPL Site Strategy document [ITRC ]), depending on the conditions driving the need for an alternative remedy approach to P&T. As described by Truex et al (), evaluation of the above transitions includes assessment of remedy time and cost, and would need to be conducted consistently with the appropriate remedy decision documents for the site.…”

“…Implementation of a pump‐and‐treat (P&T) groundwater remedy can be generalized into three categories based on the functional purpose of the system (Truex et al ). Source control applications focus on eliminating or minimizing the flux of contaminants out of the contaminant source area and can be an important component of a remedy to diminish a downgradient plume.…”

“…Application of contaminant mass discharge (CMD) approaches (e.g., ITRC ; Brusseau et al ) may also be important in predicting post‐P&T downgradient contaminant behavior. To assist in the performance assessment process, a structured approach for P&T performance assessment was developed (Truex et al ) and is described herein, using analysis of three example P&T systems to highlight key aspects of the associated decision logic, supporting calculations, and several potential outcomes of an assessment. The performance assessment and decision logic in Truex et al () could also be used prior to selection of a P&T remedy to establish a basis for P&T system objectives and to develop an exit strategy for transition to other elements of a multistep remedy.…”

“…To assist in the performance assessment process, a structured approach for P&T performance assessment was developed (Truex et al ) and is described herein, using analysis of three example P&T systems to highlight key aspects of the associated decision logic, supporting calculations, and several potential outcomes of an assessment. The performance assessment and decision logic in Truex et al () could also be used prior to selection of a P&T remedy to establish a basis for P&T system objectives and to develop an exit strategy for transition to other elements of a multistep remedy. Case studies 2 and 3, in particular, highlight use of the approach to define an appropriate exit strategy for the P&T system with associated interim remedial objectives.…”