The New Potential for Understanding Groundwater Contaminant Transport

Abstract

First off, we are honored that Dr. Neuman has chosen to engage over our paper. One of our key objectives for submitting the subject paper was to initiate a dialogue between remediation professionals and groundwater modelers. Dr. Neuman's input-as well as the kind words we have received directly from groundwater remediation professionals-suggests that to at least some degree we have accomplished this important objective.We would agree with Dr. Neuman that viewing deterministic models with a stochastic perspective provides an improvement. However, we disagree with his assertions that stochastic modeling is the answer to the historical shortcomings of the predictions made concerning groundwater remediation. Our rebuttal will not contain the elegant mathematics of Dr. Neuman's comment, but rather applies words, anecdotes, facts, and ideas to reaffirm our suggestion that it is time for a new path.

A lithofacies approach for modeling non‐Fickian solute transport in a heterogeneous alluvial aquifer

“…Despite significant theoretical, experimental, and computational advances, modeling of contaminant transport in heterogeneous aquifers is still challenging and subject of continuing debate in the scientific community [e.g., Hadley and Newell , ; Neuman , ; Molz , ]. Yet, accurate simulations of the fate of contaminants are needed to address an ever growing demand for clean groundwater resources and an increasing interest in the use of the subsurface for the storage of nuclear waste, CO 2 , and heat.…”

Field Tracer Test for the Design of LNAPL Source Zone Surfactant Flushing

“…The shape of this portion of the curve is also affected by both advection and dispersion and also by the solute exchange through diffusion between mobile and immobile porosities. Such exchange observed during the tracer solution washout is analogous to matrix diffusion and results in the tailing of the washout portion of the breakthrough curve (Payne et al ; Hadley and Newell ).…”

Vertical Discretization Impact in Numerical Modeling of Matrix Diffusion in Contaminated Groundwater

“…In some cases, remediation sites may be relatively unaffected by matrix diffusion. Examples of such sites can include the rare case of extremely homogeneous aquifers with nonsedimentary flow conditions with very weak low‐ k zones, as well as when evaluating groundwater plume stability with ongoing, strong biodegradation processes that can overcome the low‐level matrix diffusion flux (Hadley and Newell ). Other examples where conventional grids are likely to be sufficient are groundwater flow‐only applications such as evaluation of injection designs and capture zone studies.…”

“…While matrix diffusion (referring in general to contaminant storage then release) has been recognized for over four decades (e.g., Sudicky et al ), it was overshadowed for many years by a more focused concern about other source mechanisms (e.g., nonaqueous phase liquids) (Hadley and Newell ) and hampered by the lack of sufficient computational power to accurately simulate this process. Currently, it is recognized as a key reason to why contaminated sites exhibit sustained dissolved contaminant concentrations during long‐term natural attenuation monitoring after in‐situ remediation has been performed (Chapman and Parker ; AFCEE ; Sale et al ; Farhat et al ; Seyedabbasi et al ; Sale et al ; Hadley and Newell ).…”