ABSTACT La Réduction Chimique In Situ Offre la Réclamation sans Séquestrer les Contaminants ou Accumuler les Catabolites In Situ Chemical Reduction (ISCR) offers Remediation without Contaminant Sequestration or Catabolite Accumulation James Mueller*, David Hill and Alan Seech (The Adventus Group - Europe) ISCR Technology Development / Lessons Learned ISCR Modes of Action 2871 W. Forest Road, Suite 2  Freeport, IL  Tel: Fewster Drive  Mississauga, Ontario  Canada L4W 2A5  Tel: EHC, EHC-O, and O-Sox are registered trademarks of Adventus Intellectual Property Inc. Cost and Contact Information EHC = € 3.1/kg EHC-M = € 3.5/kg (delivery from within the EU; volume discounts may apply) ADVENTUS EUROPE Franz-Plattner Str. 28F 6170 Zirl, Tirol, Austria tel (+43) fax (+43) MNA ERD ZVI ABIOTIC MNA ISRM ISCR MNA * Chlorinated compounds degrade under reduced conditions * Sequential dechlorination * Biologically mediated * Dead-end intermediates common ERD (organic amendments) * Conditions can be manipulated to enhance reductive dechlorination * Hydrophobic carbon substrates sorbs COIs. * Biologically mediated by resident Dehalococcoides sp. *Sequential dechlorination is the norm; dead-end intermediates common Zero Valent Iron (ZVI) * Chlorinated solvents can be chemically reduced * Non-sequential dechlorination * Acetylene formation via Beta-elimination reactions = mineralization * Surface mediated reactions Abiotic MNA * Other forms of chemical reduction occur via non-sequential dechlorination, but less kinetically active compared to ZVI * Chlorinated solvents can be reduced by ferrous minerals In Situ Redox Manipulation= ISRM *Conditions can be otherwise manipulated to enhance abiotic reduction processes * Specifically, chemical reductants (dithionite; polysulfide, sodium sulfide) may be Used to manipulate reduced minerals (Fe, Al, Zn, Mn, etc) to enhance their reactivity * Szecsody et al, 2004; Nzegung et al., 2001 In Situ Chemical Reduction = ISCR * Synergistic physical, chemical and microbiological reactions * Yields thermodynamics <-500 mV that facilitate unique redox reactions; * Unique microbiology likely (extremophiles) * Persistent, oxidized compounds rapidly degrade under reduced Eh conditions * Appears to include surface catalyzed reactions * Does NOT accumulate dead-end intermediates / catabolites * ZVI performs better than natural minerals and non-ferrous co-reductants * Seech et al., 1995, 2000; Dolfing et al 2007 In situ chemical reduction (ISCR) describes the combined effect of stimulated biological oxygen consumption (via fermentation of added organic carbon sources), direct chemical reduction with zero-valent iron (ZVI) or other reduced metals, and the corresponding enhanced thermodynamic decomposition reactions that are realized at the lowered redox (Eh) conditions. There also exists a number of enhanced reductive dehalogenation (ERD) and other accelerated anaerobic bioremediation technologies that offer purportedly similar responses. DARAMEND® and EHC® are commercially available, patented ISCR reagents that have been used at hundreds of sites around the world to treat over 4 million tons of soil/sediment and millions of gallons of groundwater. These products contain controlled-release, complex carbon plus zero valent iron (ZVI) or other metal that uniquely exhibits the recognized benefits of ISCR. These substrates are unique in their ability to provide ZVI and thus yield Eh values as low as -550 mV. Hence, they integrate physical, geochemical and microbiological degradation processes that conventional enhanced bioremediation technologies cannot. The use of ISCR technologies has recognized potential for managing soil and groundwater environments contaminated by chlorinated solvents, pesticides, heavy metals and other constituents of interest (COI). A number of factors have been identified as important variables in remedial design and ISCR technology selection. These include: Primary mechanism: beta elimination Limited by: diffusion Distance: equivalent to physical injection of EHC injected zone (1 to 3 m for direct injection, 5 to 7 m for hydraulic fracturing) Duration: > 15 years for microscale iron Direct ZVI Effects Indirect ZVI Effects ISCR Effects Biostimulation Primary mechanisms: EHC fermentation produces VFAs and H+ to stimulate dehalogenators Limited by: groundwater flow rate, diffusion Distance: > 20 m downgradient of injection location Duration: > 5 years Primary mechanisms: low redox, high partial pressure of H+ and e- Limited by: natural redox and competing electron acceptors Distance: overlaps between injection zones Duration: 3 to 5 years Primary mechanism: reactive surface areas due to dissolved iron and ZVI Limited by: precipitation due to return to natural redox Distance: 8 to 10m downgradient of injection location Duration: >15 years for microscale iron