An In-Situ PermeableReactive Barrier for theTreatment of HexavalentChromium andTrichloroethylene inGround Water:Volume 3Multicomponent ReactiveTransport ModelingUnited StatesEnvironmental ProtectionAgencyOffice of Research andDevelopmentWashington DC 20460EPA/600/R-99/095cSeptember 19990 0.5 1 1.5 2 2.5 3 3.5 4distance [m]44.555.566.57depth [m]0 0.5 1 1.5 2 2.5 3 3.5 4distance [m]0 0.5 1 1.5 2 2.5 3 3.5 4distance [m]4567depth [m]8.4x10-057.0x10-055.6x10-054.2x10-052.8x10-051.4x10-050.0x10+00Cr(VI)[mol l-1]EPA/600/R-99/095cSeptember 1999An In-Situ Permeable Reactive Barrier forthe Treatment of Hexavalent Chromium andTrichloroethylene in Ground Water:Volume 3Multicomponent Reactive Transport ModelingDavid W. BlowesK. Ulrich MayerDepartment of Earth SciencesUniversity of WaterlooWaterloo, Ontario, CanadaCooperative Agreement No. CR-823017Project OfficerRobert W. PulsSubsurface Protection and Remediation DivisionNational Risk Management Research LaboratoryAda, OK 74820National Risk Management Research LaboratoryOffice of Research and DevelopmentU.S. Environmental Protection AgencyCincinnati, OH 45268iiNoticeThe U. S. Environmental Protection Agency through its Office of Research andDevelopment partially funded and collaborated in the research described hereunder Cooperative Agreement No. CR-823017 to University of Waterloo. It hasbeen subjected to the Agency's peer and administrative review and has beenapproved for publication as an EPA document. Mention of trade names orcommercial products does not constitute endorsement or recommendation for use.All research projects making conclusions or recommendations based onenvironmentally related measurements and funded by the Environmental Protec-tion Agency are required to participate in the Agency Quality Assurance Program.This project was conducted under an approved Quality Assurance Project Plan.The procedures specified in this plan were used without exception. Information onthe plan and documentation of the quality assurance activities and results areavailable from the Principal Investigator.iiiForewordThe U.S. Environmental Protection Agency is charged by Congress withprotecting the Nation’s land, air, and water resources. Under a mandate of nationalenvironmental laws, the Agency strives to formulate and implement actions leadingto a compatible balance between human activities and the ability of natural systemsto support and nurture life. To meet these mandates, EPA’s research program isproviding data and technical support for solving environmental problems today andbuilding a science knowledge base necessary to manage our ecological resourceswisely, understand how pollutants affect our health, and prevent or reduce environ-mental risks in the future.The National Risk Management Research Laboratory (NRMRL) is the Agency’scenter for investigation of technological and management approaches for reducingrisks from threats to human health and the environment. The focus of theLaboratory’s research program is on methods for the prevention and control ofpollution to air, land, water, and subsurface resources; protection of water quality inpublic water systems; remediation of contaminated sites and ground water; andprevention and control of indoor air pollution. The goal of this research effort is tocatalyze development and implementation of innovative, cost-effective environ-mental technologies; develop scientific and engineering information needed byEPA to support regulatory and policy decisions; and provide technical support andinformation transfer to ensure effective implementation of environmental regula-tions and strategies.Environmental scientists are generally familiar with the concept of barriers forrestricting the movement of contaminant plumes in ground water. Such barriers aretypically constructed of highly impermeable emplacements of materials such asgrouts, slurries, or sheet pilings to form a subsurface “wall.” The goal of suchinstallations is to eliminate the possibility that a contaminant plume can movetoward and endanger sensitive receptors such as drinking water wells or dischargeinto surface waters. Permeable reactive barrier walls reverse this concept ofsubsurface barriers. Rather than serving to constrain plume migration, permeablereactive barriers (PRBs) are designed as preferential conduits for the contaminatedground water flow. A permeable reactive subsurface barrier is an emplacement ofreactive materials where a contaminant plume must move through it as it flows,typically under natural gradient, and treated water exits on the other side. Thepurpose of this document is to provide detailed design, installation and perfor-mance monitoring data on a full-scale PRB application which successfully remediateda mixed waste (chromate and chlorinated organic compounds) ground-waterplume. It was also the first full-scale installation of this technology to use a trencherto install a continuous reactive wall to intercept a contaminant plume. The informa-tion will be of use to stakeholders such as implementors, state and federalregulators, Native American tribes, consultants, contractors, and all other inter-ested parties. There currently is no other site which has used this innovativetechnology and reported on its performance to the extent detailed in this report. Itis hoped that this will prove to be a very valuable technical resource for all partieswith interest in the implementation of this innovative, passive, remedial technology.Clinton W. Hall, DirectorSubsurface Protection and Remediation DivisionNational Risk Management Research LaboratoryivvAbstractReactive transport modeling has been conducted to describe the performanceof the permeable reactive barrier at the U.S. Coast Guard Support Center nearElizabeth City, N.C. The reactive barrier was installed to treat groundwater con-taminated by hexavalent chromium and chlorinated organic solvents. The concep-tual model of the Elizabeth City site described in Volumes 1 and 2 of this documentseries (Blowes et al., 2000) provide the basis for the modeling study. Themulticomponent reactive transport model MIN3P was used for the simulations. Theessential reactions contained in the conceptual model are aqueous complexationreactions, combined reduction-corrosion reactions between the treatment materialzero-valent iron and the contaminants or other electron acceptors dissolved in theambient groundwater and the precipitation of secondary minerals within the