Capture and release zones of permeable reactive barriers under the influence of advective–dispersive transport in the aquifer Harald Klammler a,b,⇑ , Kirk Hatfield a,b , Mohamed M. Mohamed c , Irina V. Perminova d , Mike Perlmutter e a Department of Civil and Coastal Engineering, University of Florida, Gainesville, FL, USA b Inter-Disciplinary Program in Hydrologic Sciences, University of Florida, Gainesville, FL, USA c Department of Civil and Environmental Engineering, United Arab Emirates University, Al Ain, United Arab Emirates d Department of Chemistry, Lomonosov Moscow State University, Moscow, Russia e CH2M HILL, Atlanta, GA, USA article info Article history: Received 20 May 2013 Received in revised form 27 March 2014 Accepted 28 March 2014 Available online 6 April 2014 Keywords: PRB Contaminant Plume remediation Capture efficiency Factor of safety Conformal mapping abstract The problem of permeable reactive barrier (PRB) capture and release behavior is investigated by means of an approximate analytical approach exploring the invariance of steady-state solutions of the advection– dispersion equation to conformal mapping. PRB configurations considered are doubly-symmetric funnel-and-gate as well as less frequent drain-and-gate systems. The effect of aquifer heterogeneity on contaminant plume spreading is hereby incorporated through an effective transverse macro-dispersion coefficient, which has to be known. Results are normalized and graphically represented in terms of a relative capture efficiency M of contaminant mass or groundwater passing a control plane (transect) at a sufficient distance up-stream of a PRB as to comply with underlying assumptions. Factors of safety FS are given as the ratios of required capture width under advective–dispersive and purely advective transport for achieving equal capture efficiency M. It is found that M also applies to the release behavior down-stream of a PRB, i.e., it describes the spreading and dilution of PRB treated groundwater possibly containing incompletely remediated contamination and/or remediation reaction products. Hypothetical examples are given to demonstrate results. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Permeable reactive barriers (PRBs) are a popular technique for passive long-term interception and treatment of contaminant plumes in aquifers due to their cost effectiveness compared to pump and treat systems [3,28,40]. PRBs basically consist of a type of reactive material, which is installed in the pathway of a contam- inant plume (e.g., in a trench across ambient groundwater flow dri- ven by a natural gradient) and which degrades or retains contamination through chemical, biological or physical processes during the contaminant residence (or travel) time inside the reac- tive material [8,22,23,30]. For an effective application it is impor- tant that the PRB captures the target portion of the contaminated groundwater plume and that the contaminant residence time within the reactive material is adequate to achieve treatment objectives. In order to meet both requirements under a variety of conditions, different PRB configurations have been applied or proposed including (a) funnel-and-gate (FG) PRBs with imperme- able funnel arms to increase the width of the capture zone; (b) velocity equalization walls (VEW) to achieve more uniform con- taminant residence times in a reactor; and (c) drain-and-gate (DG) PRBs using trench-like drains to capture and release ground- water before and after passing a reactor. While FG PRBs, which may be reduced to continuous wall PRBs by using zero funnel length, are predominant, DG PRBs are limited to a smaller number of field applications (e.g., [7,37,42]). To the best of our knowledge, VEW PRBs have so far only been proposed conceptually [39]. Examples of these PRB types with groundwater stream lines, potential lines and capture zones are shown in Fig. 1. Theoretical studies of aquifer hydraulics are complicated by the hydraulic conductivity contrast between aquifer and reactive materials as well as by the presence of impermeable (e.g., funnel) or highly permeable (e.g., drains) PRB structure elements. As a con- sequence, analytical solutions (e.g., [2,15,31–33]) are less frequent and numerical approaches have been applied predominantly (e.g., [29,36,39,43–45]). The hydrodynamic conditions are further com- plicated by the natural heterogeneity of the aquifer, most notably by the spatial variability of hydraulic conductivity. This spatial http://dx.doi.org/10.1016/j.advwatres.2014.03.010 0309-1708/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Civil and Coastal Engineering, Univer- sity of Florida, Gainesville, FL, USA. Tel.: +1 352 9537x1441. E-mail address: haki@gmx.at (H. Klammler). Advances in Water Resources 69 (2014) 79–94 Contents lists available at ScienceDirect Advances in Water Resources journal homepage: www.elsevier.com/locate/advwatres