Impact of Temporally Variable and Uniform Pumping Regimes on Contaminant Transport in Heterogeneous Aquifers

Abstract:

We study and compare the effect of temporally variable and uniform pumping regimes on key features of contaminant transport in a randomly heterogeneous aquifer. Pumping wells are used for groundwater supply in the context of urban, agricultural, and industrial activities. Groundwater management agencies typically schedule groundwater extraction through a predefined sequence of pumping periods to balance benefits to anthropogenic activities and environmental needs. The impact of the spatial variability of aquifer hydraulic properties, such as hydraulic conductivity, on contaminant transport and associated solute residence times are widely studied. Only a limited number of studies address the way a given pumping schedule affects contaminant plume behavior in heterogeneous aquifers. In this context, the feedback between a transient pumping regime and contaminant breakthrough curves is largely unexplored. Our goal is to investigate the way diverse groundwater extraction strategies affect the history of solute concentration recovered at the well while accounting for the natural variability of the geological system, in the presence of incomplete information on hydraulic conductivity distribution. Considering the joint effects of spatially heterogeneous hydraulic conductivity and temporally varying well pumping rates, this work offers a realistic evaluation of groundwater contamination risk. The latter is here considered in the context of human health and is quantified in terms of the probability that harm will result from exposure to a contaminant found in groundwater. Two scenarios are considered: a pumping well that extracts a given amount of water operating (a) at a constant pumping rate and (b) under transient conditions. The analysis is performed within a numerical Monte Carlo framework. We probe the impact of diverse geostatistical structures to describe aquifer heterogeneity on solute breakthrough curves and the statistics of target environmental performance metrics, including, e.g., peak concentration and the time at which peak breakthrough at well occurs.