TWENTY YEARS OF PREJUDICE TOWARD CONTAMINANT HYDROLOGY

Twenty years ago the geohydrology research community was drawn by need and opportunity toward the study of contaminant hydrology. What has this prejudice wrought, besides an enhanced ability to both characterize contaminant sites and to design containment and remediation, and how well has it done that? Before this diversion we viewed aquifers as monoliths, recharge as constant, rivers as fixed boundaries, chemistry as abiotic and inorganic, and subsurface life as unimportant. The focus on contaminant hydrology changed this and more. In our understanding, characterization efforts, and models aquifers are now heterogeneous, recharge is a function of time and space, former boundaries are the site of much of the action, chemistry is biotically mediated and organic, and life is everywhere. Then the word scale meant simply the size of the area you were studying, while now it describes how processes and properties change across all the time and space scales within your study. Then characterization meant a pump or borehole test, while now it means data assimulation of joint hydrologic and geophysical data sets, together with remote sensing products. Although an early infatuation with simulation studies and theory was initially misleading, its later full integration with field observations and laboratory experiments define the modern model of quantitative hydrogeology. These are broad science and technology contributions that benefit all aspects of physical and chemical hydrogeology, and related biological sciences. While prejudice toward contaminant hydrogeology may have led to the temporary and relative neglect of other aspects of hydrogeology, these scientific gains are now having broader impact, especially at the interfaces of hydrogeology with other scientific disciplines such as ecology. Today we are drifting away from the contaminant focus, not because we have nothing left to learn or because we have solved all the problems, but because need and opportunity lie elsewhere, and because through this temporary prejudice we have been reinvigorated.