title: Transport ofE. coliin Aquifer Sediments of Bangladesh: Implications for Widespread Microbial Contamination of Groundwater.
abstract: Fecal bacteria are frequently found at much greater distances than would be predicted by laboratory studies, indicating that improved models that incorporate more complexity are might be needed to explain the widespread contamination of many shallow aquifers. In this study, laboratory measurements of breakthrough and retained bacteria in columns of intact and repacked sediment cores from Bangladesh were fit using a two-population model with separate reversible and irreversible attachment sites that also incorporated bacterial decay rates. Separate microcosms indicated an average first order decay rate of 0.03 log10/ day for free bacteria in both the liquid phase and bacteria attached to the solid phase. Although two-thirds of the column results could be well fit with a dual deposition site, single population model, fitting of one third of the results required a two-population model with a high irreversible attachment rate (between 5 and 60 hr-1) for one population of bacteria and a much lower rate (from 5 hr-1to essentially zero) for the second. Inferred attachment rates for the reversible sites varied inversely with grain size (varying from 1 - 20 hr-1for grain sizes between 0.1 and 0.3 mm) while reversible detachment rates were found to be nearly constant (approximately 0.5 hr-1). Field simulations based on the fitted two-population model parameters predict only a two-fold reduction in fecal source concentration over a distance of 10 m, determined primarily by the decay rate of the bacteria. The existence of a secondary population of bacteria with a low attachment rate might help explain the observed widespread contamination of tubewell water withE. coliat the field site where the cores were collected, as well as other similar sites.
authors.affiliation: Department of Earth and Environmental Engineering, Columbia University, New York, USA.
authors.forename: John
authors.initials: J
authors.lastname: Feighery
authors.affiliation: Department of Environmental Sciences, Barnard College, New York, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Mailloux
authors.affiliation: Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Ferguson
authors.affiliation: Department of Geology, University of Dhaka, Dhaka, Bangladesh.
authors.forename: Kazi Matin
authors.initials: KM
authors.lastname: Ahmed
authors.affiliation: Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: van Geen
authors.affiliation: Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, USA.
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Culligan