Impacts of changing agricultural land-use practices on municipal groundwater quality: Woodstock, Ontario

The primary groundwater supply for the City of Woodstock, Ontario is drawn from a well field situated in a rural setting outside the city limits. Nitrate concentrations in several of the wells have exceeded the Ontario Drinking Water Guidelines leading to significant concern regarding the long-term water quality of this key supply. The source of nitrate may be related to historical agricultural land-use practices. In an attempt to reduce nitrate levels in the municipal wells, nutrient loadings on the agricultural land within the immediate vicinity of the well field are being significantly reduced through alternative cropping and fertilizing practices. To evaluate the success of these pro-active agricultural land-use practices a multi-faceted investigative approach has been adopted. A key component of this approach involves a detailed hydrogeologic investigation to: (a) improve the conceptual model of the groundwater flow system; (b) estimate the nitrate mass present in the subsurface; and (c) quantify the spatial nitrate mass loading from the agricultural land under investigation. In concert with these data, a three-dimensional flow and transport model is currently under development with the objective of predicting the magnitude and timing of the influence of these land-use changes on the nitrate concentrations extracted by the municipal well field. This paper presents an outline of the novel land-use management strategy employed by the County of Oxford, which oversees the City of Woodstock water supply, hydrogeological details of the various field investigations, and preliminary field results.