THE VALUE OF FIELD OCCURRENCE STUDIES OF FECAL CONTAMINATION IN AQUIFERS AND WELLS

Field-scale investigations of the occurrence of fecal contamination in aquifers and wells play an important role in developing a better understanding of the potential health impacts of exposure to contaminated groundwater. These kinds of studies are often challenging, time consuming and expensive, partly because of spatial and temporal variability in many of the factors (societal and physical) that influence occurrence of microbial contaminants. As a result, it is often difficult to obtain funding for such studies, especially over the multi-year time periods necessary to evaluate the influence of seasonal factors, such as precipitation, or to relate contaminant occurrence to disease. Journal editors are sometimes hesitant to publish these kinds of manuscripts, especially studies at the village or local scale, out of concern that the results may not have broad applicability to other areas. The authors respectfully submit that such studies are essential, because they help distinguish what “is” occurring from what might be “predicted” to occur. In some respects, they are like medical “case histories”, which can provide important new insights, especially when studies from multiple patients (field sites) are compared. These observations can then be used to inform newly designed laboratory or modeling experiments, which together with the field studies form a valuable type of meta-analysis. Field occurrence studies can also identify unexpected transport mechanisms, pathways or sources of microbial contamination, which may lead to changes in water resource management or health policy. The authors recently completed a 3-year study of fecal contamination in a series of rural villages in Bangladesh. The study was hypothesis-driven (related to geologic controls on occurrence of arsenic and fecal bacteria), but some of the most exciting findings were not a central part of the original experimental design. A few of these are briefly discussed and include: a) the role of village ponds as sources of fecal contamination, b) the influence of pumping duration on concentration of fecal bacteria, and c) cast-iron hand pumps as reservoirs of fecal bacteria. These findings and subsequent publications, which support (or do not support) conventional wisdom, point out the importance of field occurrence studies.