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In Situ Permeable Reactive BarriersGeoSierraGeoSierraResidence Time (hours)IRON REACTIVE WALL07000100020003000400050006000LIRON REACTIVETCE1,1,1-TCA1,1,1-TCAVCVCVCVC04862Concentration(ppb)In Situ Permeable BarriersIn situ reactive barriers, i.e. treatment walls, are replacingpump and treat remedies for contaminated groundwater withcost savings greater than 75%. Iron reactive permeable barriersremediate chlorinated solvent contaminated groundwater byabiotic degradation of the halogenated volatile organic com-pounds into harmless daughter products. Azimuth orientatedvertical hydraulic fracturing is an alternate mode of placing ironreactive barriers in situ, resulting in significant cost savings andallows reactive barriers to be installed at greater depths thanconventional technologies. Orientated vertical fracturingtechnology has installed permeable iron reactive barriers at anumber of sites in highly permeable sands and gravel down tomoderate depths and a number of cases greater than 100*.The advantages of orientated hydraulic fracture placed reactivebarriers are:• cost savings• minimal site disturbance• no excavation of contaminated material• deep application of treatment technology• minimal impact on groundwater flow regimeThe in situ reactive barriers are constructed froma series of wells installed along the barrieralignment. A controlled vertical fracture isinitiated in each well at the required azimuthorientation and depth. Iron filings are injectedinto the wells in a highly viscous cross linkedproprietary HPG gel, to form a continuouspermeable iron reactive barrier. The barrier’sgeometry is monitored in real time by theactive resistivity method to ensure the barrier is constructed as designed.Monitoring of Barrier GeometryThe reactive barrier installation is monitored in real timeduring injection to determine its geometrical extent and toensure fracture coalescence or overlap occurs. The gel ironmixture is energized by a 100Hz low voltage source. Downhole resistivity receivers are monitored to detect changes ininduced voltages by the propagation of the fracturing fluid.From these induced voltages and utilizing an incrementalinverse integral method, the fracture geometry is displayedin real time during the installation process.02550750255075DEPTH (Feet)Column Reactivity TestsLaboratory column reactivity tests performed on sitespecific groundwater quantify degradation rates ofthe contaminants. The column tests determine theapplicability of a particular reactive barrier systemfor a site. Column tests conducted both in house andat UW/ETI and AFCEE have determined that the gel,hydroxypropylguar (HPG) —a natural polymer usedin the food industry as a thickener, has minimalimpact on barrier reactivity and upon degradationleaves an extremely low residue with no measuredimpact on barrier permeability.Pulse Interference TestsThe hydraulic continuity of the reactive barrier isquantified by pulse interference tests, with pulse sourcewells on one side of the wall and high precision receivertransducers installed in wells on the opposite side.The test involves a cyclic injection of fluid into thesource well and high precision measurement of thepressure pulse in a neighboring well. The time delayand attenuation of the hydraulic pulse enables thehydraulic effectiveness and continuity of the wall tobe assessed.The pulse interference test is also ideal for thehydraulic characterization of complex flow systems,such as fractured bedrock, braided stream and eskerdeposits. Being a transient hydraulic test, transmissivityand storativity can be determined, and hydraulic flowregimes can be clearly delineated.UW/ETI—University of Waterloo/Envirometal Technologies Inc.AFCEE—USAF Center for Environmental ExcellenceTime (minutes)ReceiverPressure(psi)SourceFlowRate(gals/min)0 1 2 3 4 500.010.020.030.040.050.060.070.080.090.10102030405060708090100PW-2 MatchedPW-2 MeasuredPW-3Pulse Well PW-3 at 100'-105'Confined Aquifer 35' to 110' bgsHydraulic Conductivity = 105 ft/daySpecific Storage = 5.2x10-6 /ft0500100015002000250030000 0.5 1 1.5 2 2.5 3 3.5 4 4.5Column Residence Time (hrs)Concentration(ppb)TCEc-DCEGeoSierraGeoSierraGeoSierraGeoSierraEnvironmentalServicesM Field InvestigationM Site AssessmentM Risk AssessmentM Remedial Investigation/Feasibility Study (RI/FS)M Site Remediation(Design/Build)M Performance Monitoring & Site Closure3730 Chamblee Tucker Rd.Atlanta, GA 30341(678) 406-0094(770) 934-9476 (Fax)www.geosierra.comGeoSierra LLCGeoSierra, a privately owned company, is based in Atlanta, GA. GeoSierra concentrates on technological driven products andservices in geotechnical, environmental and earthquake engineering. GeoSierra typically turnkeys projects from investigation,through to design and build. GeoSierra has been successful in modifying soil and groundwater remedies, to save costs, eliminateO&M, and reduce the time to site closure.