Complex Sites Highlight How Far We Have Come—And How Much Remains to be Done

Abstract

Confucius is credited with saying that life is really simple but we insist on making it complicated. Flip this upside down and we have a quote that might apply to contaminated sites: “Sites are complicated but we insist on making them simple.” A simple site is one that has not been studied. That being said, some sites present more challenges than others, and these are the ones researchers and practitioners have in mind when they talk about “Complex Sites.” The complexity arises from a number of factors that make up the pantheon of reasons simple site investigations or cleanup efforts fail: multiple contaminants, DNAPL presence, heterogeneous sediments that include low-permeability features, fractured rock or karst, fast flow, chemically aggressive groundwater, deep contamination, and the list goes on. In the early days of contaminant hydrogeology, many of these factors were underappreciated or unrecognized for the challenges they presented, and attempts to remediate sites were unsuccessful, to put it kindly. Since the turn of the millennium, the hydrogeological knowledge base has increased substantially, and new technologies and approaches have been introduced to fully remediate or at least significantly mitigate contamination in the subsurface. In this issue of GWMR, several of these technologies and approaches are presented.

Among the challenges that have been taken on are those of proper characterization and conceptual model development. Examples of this are featured in an article on in situ mineral samplers to track abiotic reactions with chlorinated solvents (Divine et al.) and two articles outlining approaches for developing three-dimensional geological and numerical site models (Lefrancois et al.) and modeling of multicomponent NAPL remediation for decision support (Stewart et al). Batch experiments are conducted to study strategies on how to handle mixed contaminants (Gavazza et al.). An insightful case study is presented to demonstrate how soil excavation can be used innovatively to address a multitude of logistical and technical challenges at a brownfield site (Cohen et al.). Articles describing the most recent developments in thermal remediation and electrokinetic treatment are also featured here (Heron et al.; Riis et al.). These are only a few examples of the articles and features presented in this issue.

The ultimate goal of contaminant hydrogeology is to understand the fate and transport of pollutants in groundwater, and to use that understanding to responsibly mitigate the risk these substances pose to humans and the environment. The complexity and dynamic nature of the subsurface constantly presents us with surprises and routinely drives us to come up with innovative solutions—either in the form of a single case workaround, or in the form of a broadly applicable new technology. The articles featured in this issue present a small sampling of that innovation and progress. The problem of complex sites remains a formidable one. While we can celebrate and share some of our “wins” in these pages, there is no doubt much room for many more contributions going forward. Contaminant hydrogeology promises to remain one of the most interesting fields and important vocations for many years to come.