Jd. Marshall et al., Effect of temporal variability in infiltration on contaminant transport inthe unsaturated zone, J CONTAM HY, 46(1-2), 2000, pp. 151-161
A general methodology has been developed for investigating the effect of sh
ort-term temporal variability in infiltration on the long-term transport of
contaminants in soils. A one-dimensional, unsaturated transport model was
used to simulate the transport of a sorbing, nonvolatile solute, using eith
er steady-state or randomly varying infiltration. Concentration breakthroug
h curves are plotted against time and cumulative infiltration for constant
rainfall, and for five, random-rainfall realizations, The observed time-bas
ed breakthrough curves for an individual year depend significantly on the a
ctual rainfall pattern for that year. The average breakthrough curve, gener
ated from many years of randomly generated rainfall, approaches the constan
t infiltration time breakthrough curve. For an individual year, the cumulat
ive infiltration breakthrough curves for variable and constant infiltration
match closely, as suggested by Wierenga, P.J. [Wierenga, P.J., 1977. Solut
e distribution profiles computed with steady-state and transient water move
ment models. Soil Sci. Sec. nm. J., 41, 1050]. This indicates that, for the
conditions examined, cumulative rainfall can be used to predict adequately
contaminant transport for a given time period. Under more severe condition
s, increased variability in infiltration is expected to increase dispersion
. A dimensional analysis of the governing equations indicates two additiona
l explanations for the influence of infiltration variability on contaminant
transport. First, the hydraulic conductivity (and therefore, the velocity)
and retardation factor depend on the soil water content, which depends on
the infiltration pattern. Second, molecular diffusion dominates transport d
uring dry periods. The impact of this diffusion on the overall contaminant
transport depends on the: duration of dry periods. (C) 2000 Elsevier Scienc
e B.V. All rights reserved.