ABSTRACT
Traditional ground-water monitoring strategies have relied on a process of collecting samples from wells and determining if there is evidence of contamination. This approach is arguably illogical, because if the purpose of monitoring is preventing aquifer contamination, the evidence comes only after contaminants have reached the resource we are trying to protect. Monitoring in the vadose zone, on the other hand, can provide early detection of contaminant migration and the opportunity to actually prevent ground-water contamination. Because this fact has been increasingly recognized in the regulatory arena, ground-water students and professionals need training in vadose zone hydrogeology. While the relative hydrologic importance of the vadose zone is much greater in the western United States, it remains a largely misunderstood portion of the geologic profile across the country. The vadose zone, sometimes saturated but more often not, is complicated by textural heterogeneities, flow instabilities, and preferred pathways. Reliable prediction of contaminant migration is lacking. Thus, ongoing monitoring is the only viable option and development of innovative monitoring techniques should be encouraged in both the public and private sectors. For example, deployment of monitoring techniques such as neutron moderation, dielectric measurements, and soil gas screening represent efficient, low-cost methods for improving monitoring coverage in space and time.
