The impact of thermally and chemically enhanced biostimulation of indigenous bacteria in a fractured rock aquifer and the resulting changes in hydraulic properties of the discrete fracture network were investigated at the field scale in this study. A field trial was conducted using five 30 m deep vertical boreholes drilled into limestone and granite geological units in a 100 m2 section of a field in Kingston, Ontario. Prior to a 14 day biostimulation experiment, pulse interference tests and tracer experiments were conducted between the various boreholes to characterize the fracture permeability and connections. Biostimulation methods were applied using a semi-passive injection withdrawal flow field. During periods of injection withdrawal, groundwater was recirculated at 15 ±2 Lpm through an aboveground reservoir (460 L) and gravity drainage system. Recirculating groundwater temperature was raised to 20°C - 25°C and a 4.5 L sodium lactate based nutrient solution was injected once daily. During biostimulation the groundwater temperature, geochemistry, microbiology and fracture hydraulic properties between the recirculating borehole pair were monitored. Hydraulic testing results showed that borehole transmissivity was reduced by up to 92% (injection borehole) of pre-biostimulation values and transmissivity of multiple borehole connections had been reduced by up to five orders of magnitude. The results of the tracer experiments showed an increase in solute tortuosity and arrival time and a decrease in peak concentration following biostimulation. The changes in transport observed in the tracer experiments are corroborated by heat transport measurements in the recirculation borehole pair. Microbiological and geochemical evidence of biological growth were observed in recirculating groundwater, but absent in the groundwater samples analyzed. Visual observations confirmed the increase in biological growth, although no direct characterization of the microbial community was performed. This study indicates the semi-passive operation of thermally and chemically enhanced biostimulation can provide a successful method for bioclogging a discrete fracture network. Pulse interference tests and tracer experiments were necessary to effectively evaluate the growth and distribution of the biobarrier, which developed beyond the influence of the injection well. Additional research is required to develop a better understanding of the factors governing biobarrier formation and longevity prior to industrial application. / Thesis (Master, Civil Engineering) -- Queen's University, 2010-12-03 14:19:33.755

A biostimulation field trial was conducted to determine the effect of nutrient addition on microbial populations in a fractured rock environment. The ultimate goal of this research is to induce bioclogging in rock fractures as a method of in situ containment and remediation of contaminated groundwater. This trial focused on biostimulation of indigenous bacteria in a single fracture through the addition of bioavailable carbon, nitrogen and phosphorus sources. Bench-scale experiments were conducted to determine the optimal source and concentration of nutrients for microbial growth. The final mixture selected for the field trial consisted of sodium lactate plus two liquid fertilizers, resulting in a 100:9:4 molar solution of bioavailable carbon, nitrogen, and phosphorus with a carbon source concentration of 8.9 g/L. The field trial was conducted in an uncontaminated area adjacent to an abandoned quarry in southern Ontario, Canada. The geology of the site consists of flat-lying dolostone pervaded by bedding plane fractures, with minimal overburden. An arrangement of three boreholes isolated a single fracture at a depth of 17m using straddle packer systems. A groundwater recirculation system was created with groundwater withdrawal at BH7 and reinjection of amended water at BH9. Throughout the three-week biostimulation experiment, general groundwater parameters, including temperature, dissolved oxygen and electrical conductivity, were monitored frequently. Geochemical and microbiological conditions including available electron acceptors, biochemical oxygen demand, heterotrophic plate counts, and microbial diversity were evaluated before and after the experiment. Monitoring results for the withdrawal well confirmed that nutrient delivery was occurring, albeit with substantial mass loss due to incomplete flow field development. Numerical modelling of the system estimated a nutrient mass loss of 29%. Geochemical monitoring of key electron acceptors suggested that redox conditions in the isolated fracture were greatly affected by nutrient addition. Biological data indicated significant changes in the microbial populations, with heterotrophic plate counts increasing significantly in the isolated fracture. Changes in microbial diversity were also observed through 16S rDNA analysis. Denaturing gradient gel electrophoresis results indicated substantial diversification and growth of the microbial community following biostimulation. Further research will investigate the potential for bioclogging at a NAPL-contaminated fractured bedrock site. / Thesis (Master, Civil Engineering) -- Queen's University, 2008-09-17 12:37:48.16

Biofilm growth is a significant factor in subsurface processes governing fluid flow and contaminant transport. Biobarriers are known to reduce hydraulic conductivity, as well as to immobilise metals in the matrix of the exopolymeric substances (EPS) produced by bacterial cells. It is therefore necessary to develop understanding of how bioclogging and related mechanisms occur in porous media, and how contaminants interact with biofilms at the laboratory scale, which ultimately can be scaled up to field scenarios. The aims of the laboratory experiments were to a) enable uniform biofilm growth in columns packed with different types of porous media, b) develop methods of quantifying and visualising biofilm distribution in porous media, and c) measure transport of zinc oxide (ZnO) nanoparticles in columns with and without biofilm growing on the porous media. Experiments were conducted with columns and batch tests. Biofilms were grown by inoculating columns with Pseudomonas putida. Biofilm distribution was quantified by biomass extraction and visualised using X-ray computed microtomography (μCT) imaging. Colorimetric methods were used predominantly to quantify protein and polysaccharide content in biofilms. However, these methods possess several major disadvantages, which were highlighted using experimental data from batch tests. X-ray computer microtomography is a non-destructive method of visualising biofilm growth and illustrating flow paths in porous media. Particular components of μCT images (porous media, biofilm, tracer) were subtracted from images based on density contrasts. Reconstructed images of small, bio-clogged columns show that clogging occurs not only as a result of abundant biofilm growth but also air bubbles. Nanoparticle transport in porous media involved the injection of bare and capped ZnO nanoparticle suspensions into columns packed with glass beads, sand and calcite with and without inoculation of bacteria. Results, as well as modelled predictions, showed that ZnO nanoparticles generally possess low mobility, and that biofilm impedes nanoparticle transport. Porous media surface charge, as well as the extent of biofilm growth, play an important role in nanoparticle transport.

Microorganisms have played a critical role in geological processes and in the formation of soils throughout geological time. It is hypothesized that biological activity can also affect soil properties in short engineering time-scales. Bioactivity in sediments is determined by the classical limiting factors (i.e., nutrients, water, C for biomass, temperature and pH) as well as by pore-size geometrical limits and mechanical interactions between bacterial cells and soil particles. These constraints restrict the range of grain size and burial depth where biomediated geochemical processes can be expected in sediments, affect the interpretation of geological processes and the development of engineering solutions such as bioremediation. When biological, geometrical and mechanical limiting factors are satisfied, bioactivity can be designed to alter the mechanical properties of a soil mass, including lowering the bulk stiffness of the pore fluid through controlled gas bio-generation, increasing the shear stiffness of the soil skeleton by biomineralization, and reducing hydraulic conduction through biofilm formation and clogging. Each of these processes can be analyzed to capture the bio-chemo-hydro-mechanical coupling effects, in order to identify the governing equations that can be used for process design. Design must recognize the implications of spatial variability, reversibility and environmental impacts.