A side-by-side comparison of bioaugmentation, biostimulation, and a recirculation-only control was implemented in a chloroethene-contaminated aquifer. The objective was to develop a contaminant mass balance based on the analysis of groundwater and aquifer solids and to quantify key dechlorinating populations during treatment to determine their relation to the rate of chloroethenes removed. The bioaugmentation strategy, using a Dehalococcoides-containing PCE-to-ethene dechlorinating inoculum enriched from the same aquifer, resulted in a nearstoichiometric dechlorination of both sorbed and dissolved chloroethenes to ethene within 6 weeks. In the biostimulation plot, continuous lactate and nutrient injection resulted in dechlorination but only following a 3-month lag period. Molecular tools targeting the 16S rRNA genes of Dehalococcoides and Desulfuromonas spp. were used to qualitatively monitor the distribution and quantitatively (Real-Time PCR) measure the abundance of the dechlorinating populations during the test. In the bioaugmentation plot, Dehalococcoides populations increased 3-4 orders of magnitude throughout the test area. Dehalococcoides populations also increased in the biostimulation plot but at a slower rate and immediately before the onset of rapid dechlorination. Terminal Restriction Fragment Length Polymorphism analysis indicated that the inoculum only impacted the bioaugmentation plot. This work extends the knowledge gained from previous field studies which reported qualitative relationships between the occurrence of Dehalococcoides populations and ethene production. Furthermore, the results demonstrate that bioreactive barriers capitalizing on reductively dechlorinating populations to control the migration of chloroethene plumes can be effectively designed once hydrologic information is incorporated.

No abstract

No abstract

Measurements of the oxidation (i.e., of aqueous Cr2+) and reduction (i.e., of aqueous Cr2072" and H202) capacities of aquifer solids and groundwater have been made on samples from a sand-and-gravel aquifer. The groundwater contributed less than 1% of the system oxidation or reduction poising capacity. Reduction capacities averaged 0.095, 0.111, and 0.136 mequiv/g of dry solids for oxic, transitional, and reducing Eh conditions, respectively. Measured oxidation capacities averaged 0.4 mequiv/g of dry solids over the range of redox intensity conditions.These capacities represent considerable resistance to the adjustment of redox conditions even at uncontaminated sites. Hydrogen peroxide reduction by aquifer solid samples proceeds rapidly relative to microbially mediated decomposition. This study indicates the need for closer scrutiny of the predictability and cost effectiveness of attempts to manipulate redox conditions in poorly poised aquifer systems.

An experiment was performed in a carbon tetrachloride (CT)- and nitrate-contaminated aquifer at Schoolcraft, MI, to evaluate bioaugmentation with Pseudomonas stutzeri KC, a denitrifying bacterium that degrades CT without producing chloroform (CF). A test section of the aquifer was treated to create pH conditions favorable for KC and then inoculated with culture grown aerobically on site. Activity was sustained with pulses of acetate-amended groundwater, followed by “chase” pulses of acetate-free water. In regions with effective substrate delivery, KC was detected, nitrate levels fell by 85%, pH levels increased, and CT levels decreased by ∼65%, with no significant increase in CF. After 3 weeks, denitrification and CT transformation activity decreased, and KC was no longer detected in groundwater from four wells. Loss of denitrification was attributed to the acetate-free chase. Upon eliminating the chase, CT transformation resumed, and KC was detected, but CF production was also observed, implicating indigenous organisms as agents of transformation. Final sediment analyses indicated 60−88% CT removal, little CF, and persistent KC. This work demonstrates subsurface pH adjustment, subsurface transport of KC, assimilation of KC into the aquifer community, CT removal without CF production after inoculation, and CF formation when KC activity declined.

Recent research has confirmed that low flow rate purging (i.e., ∼11/min) is a valid technique for 2 (5 cm) diameter monitoring wells with short screened intervals. The use of low flow, dedicated pumping devices for purging and sampling minimizes both the disturbance of stagnant water in the well casing and the potential for mobilization of particulate or colloidal matter which could lead to sampling artifacts. In addition, these techniques allow the use of purging indicator parameters (e.g., dissolved oxygen and specific conductance) to determine when to collect a sample for volatile organic compound (VOC) determinations. Detailed results from a monitoring network in a sand and gravel aquifer contaminated by organochlorine solvents support these findings. Recent publications on monitoring well hydraulic behavior and considerations of mass averaging effects due to pumping also support the use of low flow rate, minimal drawdown purging procedures to achieve reproducible sampling results. The suggested procedure includes documenting purging indicator parameters while purging with dedicated devices at low flow rates with minimal drawdown. This sampling method is less time‐consuming and reduces the need to handle large volumes of purge water since VOC concentrations, 02, and specific conductance values stabilized consistently in less than one bore volume.

No abstract

The impact of pollution on soil microbial communities and subsequent bioremediation can be measured quantitatively in situ using direct, non-culture-dependent techniques. Such techniques have advantages over culture-based methods, which often account for less than 1% of the extant microbial community. In 1988, a JP-4 fuel spill contaminated the glacio-fluvial aquifer at Wurtsmith Air Force Base, Michigan, USA. In this study, lipid biomarker characterization of the bacterial and eukaryotic communities was combined with polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis of the eubacterial community to evaluate correlation between contaminant (JP-4 fuel) concentration and community structure shifts. Vadose, capillary fringe and saturated zone samples were taken from cores within and up- and down-gradient from the contaminant plume. Lipid biomarker analysis indicated that samples from within the plume contained increased biomass, with large proportions of typically gram-negative bacteria. Outside the plume, lipid profiles indicated low-biomass microbial communities compared with those within the initial spill site. 16S rDNA sequences derived from DGGE profiles from within the initial spill site suggested dominance of the eubacterial community by a limited number of phylogenetically diverse organisms. Used in tandem with pollutant quantification, these molecular techniques should facilitate significant improvements over current assessment procedures for the determination of remediation end-points.