Permeability reduction in saturated unconsolidated sediment using controlled microbial growth

This project focused on determining whether the addition of a carbon substrate to an aquifer, and the resulting growth of the facultative microorganisms, will produce a controllable decrease in hydraulic conductivity of the granular porous medium. A total of 28 laboratory experiments were performed in the laboratory. The experiments assessed the ability of the common facultative soil bacteria Pseudomonas aeruginosa to produce extracellular polysaccharides within the pore space of a model aquifer.;The information collected as part of this study indicated that the hydraulic conductivity of an aquifer could be reduced by up to two orders of magnitude by providing a continuous low concentration source of carbon substrate within a 30-day period. The type of microorganisms present, the hydrogeologic characteristics of the porous medium, and the ground water chemistry will likely limit the hydraulic conductivity reduction. In the experiments performed, it was observed that a coarser, better-sorted, better-rounded porous medium with a greater initial hydraulic conductivity would record the greater hydraulic conductivity reduction. This appears to be relative to the ability of the medium to distribute the carbon substrate and the nutrients needed by microorganisms for their growth. Furthermore, it is likely that the ground water velocity in the interconnected pores may also be a factor affecting the ability of microorganisms to successfully grow in the pore space, by limiting the ability of microorganisms to adhere to the porous medium.;The primary parameters that controlled the hydraulic conductivity for a given porous medium were the carbon substrate concentration and the duration of the injection period. The experiments showed that higher carbon substrate concentration (>0.01% at the injection point) resulted in greater, more rapid hydraulic conductivity reduction. The duration of the injection controls the amount of biomass present in the porous medium. A longer injection period resulted in higher total organic carbon concentration.;Two of the experiments performed were carried out using a water supply with a higher nutrient concentration. These resulted in a more rapid and greater decrease in hydraulic conductivity, and a greater accumulation of biomass.;Based upon the results of this study, it can be established that the hydraulic conductivity reduction and recovery of a coarse-grained porous medium injected with a source of carbon can be predicted using the hydrogeologic characteristics of the medium. The results of the experiments performed as part of this study show that it is possible to create a lower hydraulic conductivity barrier (biobarrier) by simply injecting a low concentration of carbon substrate. (Abstract shortened by UMI.).