This study investigates the potential impact of climate change on residual contaminants in vadose zones and groundwater. We assume that the effect of climate changes can be represented by perturbations in the natural recharge through the aquifer system. We perform numerical modeling of unsaturated/saturated flow and transport and consider different performance metrics: contaminant concentrations at observation wells and contaminant export at the site's boundary. We evaluate the effect of increasing and decreasing recharge as well as the impact of potential failure of surface capping structures employed to immobilize vadose zone contaminants. Our approach is demonstrated in a real case study by simulating transport of non-reactive radioactive tritium at the U.S. Department of Energy's Savannah River Site. Results show that recharge changes significantly affect well concentrations: after an initial slight dilution we identify a significant concentration increase at different observation wells some years after t he recharge increase and/or the cap failure, as a consequence of contaminants' mobilization. This effect is generally emphasized and occurs earlier as the recharge increases. Under decreased aquifers' recharge the concentration could slightly increase for some years, due to a decrease of dilution, depending on the magnitude of the negative recharge shift. We identify trigger levels of recharge above which the concentration/export breakthrough curves and the time of exceedance of the Maximum Contaminant Level for tritium are remarkably affected. Moreover, we observe that the contaminant export at the control plane, identified as the risk pathway to the downgradient

18We investigate the way diverse groundwater extraction strategies affect the history of solute 19 concentration recovered at a pumping well while taking into account random spatial variability 20 of the system hydraulic conductivity. Considering the joint effects of spatially heterogeneous 21 hydraulic conductivity and temporally varying well pumping rates leads to a realistic

In 2009, the Sustainable Remediation Forum released a white paper entitled “Integrating sustainable principles, practices, and metrics into remediation projects” (Ellis & Hadley, 2009, Remediation, 19, pp. 5–114). Sustainable remediation was a relatively new concept, and the white paper explored a range of approaches on how sustainability could be integrated into traditional remediation projects. This paper revisits the 2009 white paper, providing an overview of the early days of the evolving sustainable remediation practice and an assessment of the progress of sustainable remediation over the last 10 years with a primary focus on the United States. The current state of the sustainable remediation practice includes published literature, current practices and resources, applications, room for improvement, international progress, the virtuous cycle that applying sustainable remediation creates, and the status of the objectives cited in the 2009 white paper. Over the last decade, several sustainable remediation frontiers have emerged that will likely be a focus in advancing the practice. These frontiers include climate change and resiliency, weighting and valuation to help better consolidate different sustainable remediation metrics, programmatic implementation, and better integration of the societal impacts of sustainable remediation. Finally, as was the case for the 2009 white paper, this paper explores how sustainable remediation may evolve over the next 10 years and focuses on the events and drivers that can be significant in the pace of further development of the practice. The events and drivers include transformation impacts, societal influences, and the continued development of new technologies, approaches, and tools by remediation practitioners. The remediation industry has made significant progress in developing the practice of sustainable remediation and has implemented it successfully into hundreds of projects. While progress has been significant, an opportunity exists to implement the tenets of sustainable remediation on many more projects and explore new frontiers to help improve the communication, integration, and derived benefits from implementing sustainable remediation into future remediation projects.

Our study is keyed to the analysis of the interplay between engineering factors (i.e., transient pumping rates versus less realistic but commonly analyzed uniform extraction rates) and the heterogeneous structure of the aquifer (as expressed by the probability distribution characterizing transmissivity) on contaminant transport. We explore the joint influence of diverse (a) groundwater pumping schedules (constant and variable in time) and (b) representations of the stochastic heterogeneous transmissivity ( ) field on temporal histories of solute concentrations observed at an extraction well. The stochastic nature of is rendered by modeling its natural logarithm, = ln , through a typical Gaussian representation and the recently introduced Generalized sub-Gaussian (GSG) model. The latter has the unique property to embed scaledependent non-Gaussian features of the main statistics of and its (spatial) increments, which have been documented in a variety of studies. We rely on numerical Monte Carlo simulations and compute the temporal evolution at the well of low order moments of the solute concentration ( ), as well as statistics of the peak concentration ( ), identified as the environmental performance metric of interest in this study. We show that the pumping schedule strongly affects the pattern of the temporal evolution of the first two statistical moments of , regardless the nature (Gaussian or non-Gaussian) of the underlying field, whereas the latter quantitatively influences their magnitude. Our results show that uncertainty associated with and estimates is larger when operating under a transient extraction scheme than under the action of a uniform withdrawal schedule. The probability density function (PDF) of displays a long positive tail in the presence of time-varying pumping schedule. All these aspects are magnified in the presence of non-Gaussian fields. Additionally, the PDF of displays a bimodal shape for all types of pumping schemes analyzed, independent of the type of heterogeneity considered. 1 Abstract 1Our study is keyed to the analysis of the interplay between engineering factors (i.e., transient 2 pumping rates versus less realistic but commonly analyzed uniform extraction rates) and the 3 heterogeneous structure of the aquifer (as expressed by the probability distribution characterizing 4 transmissivity) on contaminant transport. We explore the joint influence of diverse (a) Gaussian fields. Additionally, the PDF of displays a bimodal shape for all types of pumping 22 schemes analyzed, independent of the type of heterogeneity considered.

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