Assessing groundwater quality trends in pumping wells using spatially

When implementing remediation programs to
mitigate diffuse-source contamination of aquifers, tools
are required to anticipate if the measures are sufficient to
meet groundwater quality objectives and, if so, in what
time frame. Transfer function methods are an attractive
approach, as they are easier to implement than numerical
groundwater models. However, transfer function approaches
as commonly applied in environmental tracer
studies are limited to a homogenous input of solute across
the catchment area and a unique transfer compartment.
The objective of this study was to develop and test an
original approach suitable for the transfer of spatially
varying inputs across multiple compartments (e.g. unsaturated
and saturated zone). The method makes use of a
double convolution equation accounting for transfer
across two compartments separately. The modified transfer
function approach was applied to the Wohlenschwil
aquifer (Switzerland), using a formulation of the exponential
model of solute transfer for application to subareas
of aquifer catchments. A minimum of information was
required: (1) delimitation of the capture zone of the outlet
of interest; (2) spatial distribution of historical and future
pollution input within the capture zone; (3) contribution of
each subarea of the recharge zone to the flow at the outlet;
(4) transfer functions of the pollutant in the aquifer. A
good fit to historical nitrate concentrations at the pumping
well was obtained. This suggests that the modified transfer
function approach is suitable to explore the effect of
environmental projects on groundwater concentration
trends, especially at an early screening stage.