title: Use of pretreatment zones and zero-valent iron for the remediation of chloroalkenes in an oxic aquifer.
abstract: Pretreatment zones (PTZs) composed of sand, 10% zero-valent iron [Fe(0)]/sand, and 10% pyrite (FeS2)/sand were examined for their ability to prolong Fe(0) reactivity in above ground column reactors and a subsurface permeable reactive barrier (PRB). The test site had an acidic, oxic aquifer contaminated with tetrachloroethylene (PCE) and trichloroethylene (TCE). The 10% FeS2 and 10% Fe(0) PTZs removed dissolved oxygen and affected the pH and E(h) in the PTZ. None of the PTZs had any effect on pH or E(h) in the 100% Fe(0) zone. Nitrate and sulfate were removed more quickly in the Fe(0) zones preceded by either the 10% Fe(0) PTZ or 10% FeS2. PCE first-order degradation rate constants (k(obs)) decreased significantly (> 80%) with increasing column pore volumes regardless of the PTZ material used. k(obs) finally leveled off after approximately 1 yr of operation. The column results predict that the PRB will experience a breakthrough of PCE in 3-5 yr and illustrate the importance of incorporating temporal variations in degradation rate constants when designing PRBs.
authors.affiliation: National Exposure Research Laboratory, Ecosystems Research Division, U.S. Environmental Protection Agency, Athens, Georgia 30605-2700, USA. kenneke.john@epa.gov
authors.forename: John F
authors.initials: JF
authors.lastname: Kenneke
authors.forename: Steven C
authors.initials: SC
authors.lastname: McCutcheon
mesh_terms: D001673:Biodegradation, Environmental; D003691:Delaware; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D016014:Linear Models; D010084:Oxidation-Reduction; D010539:Permeability; D012822:Silicon Dioxide / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*; D013750:Tetrachloroethylene / Q000032:analysis*; D013995:Time; D014241:Trichloroethylene / Q000032:analysis*; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D013440:Sulfides; D014874:Water Pollutants, Chemical; C011342:pyrite; D014241:Trichloroethylene; D012822:Silicon Dioxide; D007501:Iron; D013750:Tetrachloroethylene