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Transport of copiotrophic bacteria in oligotrophic coarse soils: a Monte Carlo analysis




Peterson, Thomas Charles, author
Ward, Robert C., advisor
Warner, James W., committee member
Hunt, H. William, committee member
Doxtader, Kenneth G., committee member

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On-site wastewater treatment systems placed in coarse-grained, oligotrophic soils such as those typically found in the mountainous regions of the West are designed and installed with the assumption that most pathogenic microorganisms will not pass unaltered through an unsaturated zone located in the soil below each system. Studies have shown that 0.6 to 1.2 m of unsaturated soil below an on-site system drainfield is sufficient to remove most bacteria and viruses in most environments. Little is known of the transport of pathogenic, copiotrophic bacteria in coarse-grained soils below on-site drainfields placed in mountainous soil environments thought to be oligotrophic. A stochastic bacterial transport model was developed to analyze bacterial translocation in coarse-grained, mountainous soils beneath a hypothetical drainfield/soil interface. Specific model parameters were randomly generated using a procedure known to produce either a normal or log-normal distribution of random numbers. Numerous computer simulation runs were completed for hypothetical sandy and loamy sand soils subjected to a 10 year and 100 year rain storm. The resulting output was used to generate cumulative frequency distributions. Results from these simulations indicate that copiotrophic, enteric bacteria have the potential to travel great distances in oligotrophic, coarse-grained soils. The copiotrophic bacteria are likely to travel beyond the arbitrary 1.2 m of soil under conditions typically occurring in mountainous regions. The extent of bacterial transport and the bacterial concentration at any point in the soil is largely the result of the initial bacterial concentration, the impact of straining and clogging by the soil, and the bacterial die-off.


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Soil microbiology
Soil pollution
Pathogenic bacteria


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