Assessing groundwater quality trends in pumping wells using spatially varying transfer functions

Baillieux, A.; Moeck, C.; Perrochet, P.; Hunkeler, D.

Assessing groundwater quality trends in pumping wells using spatially varying transfer functions | Estimer l’évolution de la qualité d’une eau souterraine par fonctions de transfert Evaluación de las tendencias de la calidad del agua subterránea en los pozos de bombeo utilizando funciones de transferencia espacialmente variables 利用空间上变化的传递函数评价抽水井地下水水质趋势 Avaliação de tendências na qualidade da água de poços de bombeamento utilizando funções de transferência variantes no espaço

2015

Baillieux, A. | Moeck, C. | Perrochet, P. | Hunkeler, D.

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.

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