Granular iron has been determined to be a potentially useful reductant for the removal of common organic contaminants from groundwater. This research is aimed at improving our understanding of the processes that control the reactivity and longevity of the iron particles when they are used for groundwater treatment. A suite of nitroaromatic compounds (NACs) including 4-chloronitrobenzene (4ClNB), 4-acetylnitrobenzene (4AcNB), nitrobenzene, 2-methylnitrobenzene (2MeNB), and 2,4,6-trinitrotoluene (TNT) was used to investigate granular iron reactivity in anoxic pH 10, 0.008 M KNO 3 solution. Master Builder's brand of granular iron with a surface area of about 1 m 2 /g was used in all experiments. The NACs were reduced rapidly to anilines that were found to sorb reasonably strongly to the solid particles and to interfere with the reduction of NACs. The granular iron was found to lose reactivity quite rapidly over the first few days of exposure and then more slowly over the next several months. Reactivity loss due to reversibly sorbed products was minimized by flushing the system with background electrolyte between experiments. Competition experiments with binary mixtures of 4ClNB and each one of the other NACs were performed to investigate relative affinities of these compounds for the solid surface. Despite the overall loss in reactivity observed for the granular iron, the relative rate constants in the competition experiments appeared to remain constant in time.

A novel method of measuring small-scale groundwater velocities in unconsolidated noncohesive media uses the travel time of a tracer pulse between an injection port and two detectors located on the surface of a cylindrical probe, called a point-velocity probe (PVP), as the basis for velocity estimation. The direction and magnitude of the water velocity vector were determined to within +/- 9% of magnitude and +/- 8 in direction, on average, in ten laboratory tank tests conducted with the PVP, when the velocities were between 5 and 98 cm/ day. Numerical simulations supported the accuracy of the underlying theory for interpretation of the PVP data and indicated that the technology is capable of measuring velocity at a very fine scale (0.5 cm around the circumference). The benchtop and modeling investigations indicated that the probe is moderately sensitive to the condition of the porous medium immediately next to the cylinder surface, suggesting that challenges exist for the deployment of the instrument in the field.

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A substantial cost of granular iron permeable reactive barriers is that of the granular iron itself. Cutting the iron with sand can reduce costs, but several performance issues arise. In particular, reaction rates are expected to decline as the percentage of iron in the blend is diminished. This might occur simply as a function of iron content, or mass transfer effects may play a role in a much less predictable fashion. Column experiments were conducted to investigate the performance consequences of mixing Connelly granular iron with sand using the reduction kinetics of trichloroethylene (TCE) to quantify the changes. Five mixing ratios (i.e., 100%, 85%, 75%, 50%, and 25% of iron by weight) were studied. The experimental data showed that there is a noticeable decrease in the reaction rate when the content of sand is 25% by weight (iron mass to pore volume ratio, Fe/Vp = 3548 g/L) or greater. An analysis of the reaction kinetics, using the Langmuir‐Hinshelwood rate equation, indicated that mass transfer became an apparent cause of rate loss when the iron content fell below 50% by weight (Fe/Vp = 2223 g/L). Paradoxically, there were tentative indications that TCE removal rates were higher in a 15% sand + 85% iron mixture (Fe/Vp = 4416 g/L) than they were in 100% iron (Fe/Vp = 4577 g/L). This subtle improvement in performance might be due to an increase of iron surface available for contact with TCE, due to grain packing in the sand‐iron mixture.

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iii A volume of sand containhg mal tar creosote was emplaced below the water table at CFB Borden to investigate nahiral attenuation processes for cornplex biodegraâable mamires. Cod tar creosote is a mixture of more than 200 polycyclic arometic hydrocarbons, heterocyciic compounds and phenolic compounds A representative group of seven cornpounds was sdected for detailed study: phenol, m-xylene? naphthalene, phenantiuene, 1-methylnaphthalene, dibenzohan and carbazole. Movememt of groundwater through the source led to the development of a dissolved orgmic plume, which was studied over a four year paiod.Qualitative plume obsemations and mass bahce caiculations indiateci two key d u s i o n s : 1) compounds nom the same source can display distmctiy different patterns of plume development and 2) m a s transformation was a major iafluence on plume behaviow for aü observed compounds. M e r being wmpletdy leached fiom the source eariy in the study, phenol rnigrateû as a discrete slug plume and ahost completely disappeared &er two years. The m-xylene plume migrated outward to a maximum distance a approximately two yean, and then receded back towards the source as the rate of mass flux out ofthe source decreased to below the overall rate of plume transformation Carbazole showed similar behaviour, dthough the reversai in plume development occurred more slowly.The dibenzofùran plume remainecl relatively constant in extent and mass over the last two years of monito~g, despite that constant source input over this period. This indicated that the rate of mass input was approximately equal to the rate of plume transfomation and is the fist conclusive documentation of a "steady state" plume, ofwhich the author is aware. Meanwhile, the naphthalene and 1-methyhaphthalene p l u m wntinued to advance over the observation p e n d although decreases in the rate of mass input nom the source to the plume were noted for both. The phenanthene plume was also subject to transformation, although rneasuement ofthe rate was less conclusive due the higher proportion of sorbed mass for this compound.Multiple lines of evidence were used to evahiate whether the observed plume mas loss was due to microbial b i d e g r a d a h . Cornparison of sterile and active laboriatory rnicrocosm using aquifer material indicated that aquifer microbes were able to metabolize plume compow1ds. Measurement of redox-sensitive parameters in the vicuiity of the plume showed the types of changes that would be expected to occur due to plume bidegradation: diss01ved oxygen and S0,'-decreased in groundwater within the plume wbiie signincant increases were noted for Fe2+, Mn2+ and methane. Further evidence that plume mass l o s was microbially-mediated was provided by the accumulation of aromatic acids within the plume. Measurements of phosphoiipid fatty acids (PLFA) in aquifer matenal indicated that microbial biomass and turnover rate were eteater within the plume: also consistent with biodegradation. CICornputer modeliing confinneci that mass trsnsfomtion was a strong idu...

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A field experiment was conducted in which carbon tetrachloride (CT) was found to transform to chloroform (CF) and carbon disulfide (CS2) in a ratio of about 2:1. Subsequent laboratory work was undertaken to better define the conditions required for this product ratio and to investigate its use as a means of distinguishing biologically driven and abiotic transformations in aquifers. The field experiment was conducted to assess the efficacy of a bioremediation scheme for treating CT in groundwater. The test section of the aquifer was taken to sulfate reducing conditions by the periodic addition of acetate from a nutrient injection wall (NIW). Under these conditions, CT was observed to transform completely producing primarily CF and CS2 at a ratio of approximately 2:1. In laboratory columns designed to mimic the field conditions, low-input concentrations of CT (<70 μg/L) resulted in complete dechlorination of the molecule, while higher input concentrations (>400 μg/L) led to the production of CF and CS2 in the same ratio as observed in the field. It was determined that amorphous iron sulfide had precipitated on the sand grains during the column experiments. Stertile laboratory batch experiments were conducted to test CT reactivity with various iron sulfide solids. A narrow ratio of 2:1 ± 0.4 CF to CS2 was only observed for CT reacting with freshly precipitated, amorphous FeS in near pH neutral solutions. The 2:1 ratio may be a useful tool for distinguishing abiotic transformations from biodegradation in sulfate reducing environments where FeS is actively precipitated.