Chemical Hydrogeology

We hydrogeologists have waited for many years and some 70 volumes of the series of Benchmark Papers in Geology (Hutchinson Ross) for a definitive review of the theoretical development of hydrogeology. Our patience has been rewarded with two volumes, Physical Hydrogeology (edited by R.A. Freeze and W. Back) and Chemical Hydrogeology ). From a historical perspective, this appears to be a logical division of the subject. The two branches of hydrogeology evolved along separate pathways for many years. In the 1960s the influence of the groundwater flow regime on the geochemical nature of groundwater was first described in a qualitative way. In a 1970 Meinzer Award‐winning paper, the synergisms of groundwater flow, chemical thermodynamics, and mineral equilibria were eloquently described by Back and Hanshaw. The 1970s saw mass transport equations developed whereby physical flow of groundwater and transport of conservative solutes were quantitatively linked. Current research driven by the need to understand contaminant transport and attenuation mechanisms in groundwater is so linking physical and chemical hydrogeology that future review volumes may not be so conveniently divisible as these.