Using a new approach to estimate the origins of nitrate contamination in groundwater, UC Davis scientists believe they have found a more effective way to quantify the origins and relative ages of groundwater arriving at points such as wetlands or wells. Though land-use practices and water-quality trends have been observed for some time now, few models have existed to determine accurately how long it takes pollutants to travel from the point of origin to levels where water supplies are drawn. But, supported by the U.S. Environmental Protection Agency, the U.S. Geological Survey and Monterey County, UC Davis researchers have developed a model to estimate the ages and origins of water pumped at wells, thereby assessing relative vulnerability of different parts of a groundwater system to contamination, says Graham Fogg, principal investigator on a study of nitrate contamination in the Salinas Valley. The researchers' model indicates that nitrates typically take from 40 to 60 years to make their way from the surface of a field to water 180 feet below the ground's surface in much of the Salinas Valley -- a finding consistent with observed water-quality trends. Describing the model as the first estimate of its kind, Fogg says, "This provides a scientific basis for answering how might land-use changes today affect future Salinas Valley groundwater quality and what is the likely time lag between the cause and the effect."