title: Importance of Reversible Attachment in PredictingE. ColiTransport in Saturated Aquifers From Column Experiments.
abstract: Drinking water wells indiscriminatingly placed adjacent to fecal contaminated surface water represents a significant but difficult to quantify health risk. Here we seek to understand mechanisms that limit the contamination extent by scaling up bacterial transport results from the laboratory to the field in a well constrained setting. Three pulses ofE. colioriginating during the early monsoon from a freshly excavated pond receiving latrine effluent in Bangladesh were monitored in 6 wells and modeled with a two-dimensional (2-D) flow and transport model conditioned with measured hydraulic heads. The modeling was performed assuming three different modes of interaction ofE. coliwith aquifer sands: 1) irreversible attachment only (best-fit ki=7.6 day-1); 2) reversible attachment only (ka=10.5 and kd=0.2 day-1); and 3) a combination of reversible and irreversible modes of attachment (ka=60, kd=7.6, ki=5.2 day-1). Only the third approach adequately reproduced the observed temporal and spatial distribution ofE. coli, including a 4-log10lateral removal distance of ∼9 m. In saturated column experiments, carried out using aquifer sand from the field site, a combination of reversible and irreversible attachment was also required to reproduce the observed breakthrough curves andE. coliretention profiles within the laboratory columns. Applying the laboratory-measured kinetic parameters to the 2-D calibrated flow model of the field site underestimates the observed 4-log10lateral removal distance by less than a factor of two. This is promising for predicting field scale transport from laboratory experiments.
authors.affiliation: Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964.
authors.forename: P S K
authors.initials: PS
authors.lastname: Knappett
authors.affiliation: Civil Engineering and Engineering Mechanics, Columbia University, New York, NY 10027.
authors.forename: J
authors.initials: J
authors.lastname: Du
authors.affiliation: Civil Engineering and Engineering Mechanics, Columbia University, New York, NY 10027.
authors.forename: P
authors.initials: P
authors.lastname: Liu
authors.affiliation: Department of Environmental Science, Barnard College, New York, NY 10027.
authors.forename: V
authors.initials: V
authors.lastname: Horvath
authors.affiliation: Department of Environmental Science, Barnard College, New York, NY 10027.
authors.forename: B J
authors.initials: BJ
authors.lastname: Mailloux
authors.affiliation: Civil Engineering and Engineering Mechanics, Columbia University, New York, NY 10027.
authors.forename: J
authors.initials: J
authors.lastname: Feighery
authors.affiliation: Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964.
authors.forename: A
authors.initials: A
authors.lastname: van Geen
authors.affiliation: Civil Engineering and Engineering Mechanics, Columbia University, New York, NY 10027.
authors.forename: P J
authors.initials: PJ
authors.lastname: Culligan
keywords: E. coli; filtration theory; groundwater; microbial transport; reversible attachment