User:Debra Tabron/sandbox

Permeable reactive barriers (PRBs) are in situ treatment zones created below ground to clean up contaminated groundwater. PRBs take advantage of natural groundwater migration to transport contaminants to a defined treatment zone. Contaminants are removed from groundwater in the PRB and treated groundwater passes through the permeable zone; eventually a “clean front” is created on the down-gradient side of the PRB. Zerovalent Iron (ZVI) was the first reactive material used in PRBs for groundwater remediation and it continues to be the primary material used in the construction of these treatment systems. ZVI PRBs can treat groundwater contaminated with chlorinated solvents and their breakdown products such as tetrachloroethene (PCE), trichloroethene (TCE), cis-1,2-dichloroethene (cis-DCE), vinyl chloride (VC), 1,1,1-trichloroethane (1,1,1-TCA), 1,1-dichloroethane (1,1-DCA), 1,2-dichloroethane (1,2-DCA), chloroform, and carbon tetrachloride; explosives such as TNT and RDX; cations of Pb, Cd, Ni, Zn, and Hg; and anions of Cr, As, Sb, Se, U, and Tc.

Related Article(s):

• Zerovalent Iron (ZVI) (Chemical Reduction - ISCR)
• Chemical Reduction (In Situ - ISCR)
• Metal and Metalloids - Remediation
• Chlorinated Solvents

CONTRIBUTOR(S):

Key Resource(s):

• Permeable Reactive Barriers: Lessons Learned/New Directions. Interstate Technology Regulatory Council (2005).
• Permeable Reactive Barrier: Technology Update. Interstate Technology Regulatory Council (2011)

Introduction

A PRB is commonly constructed using granular iron, limestone, organic-carbon, zeolites, apatite, or mixtures of these materials with sand or gravel . PRBs are installed hydraulically down-gradient from contaminant source zones to prevent off-site plume migration or to protect sensitive receptors. Design considerations for PRBs include:

1. understanding contaminant flux to determine the residence time requirement for effective treatment;
2. understanding geochemical conditions to identify compatibility issues between the selected reactive medium and site-specific groundwater; and
3. understanding groundwater flow to ensure the contaminant plume is intercepted for treatment (See Fig. 1) so contaminant flow beneath, around, or above the treatment system does not occur. PRBs are generally keyed into impermeable hydrostratigraphic units, such as clay layers or bedrock, to prevent underflow of contaminants beneath the treatment zone.