AN IMPROVED NITRATE MODELLING TOOL FOR SOURCE WATER PROTECTION IN SAND AND GRAVEL AQUIFERS

Non-point source nitrate pollution is a pervasive concern in the upper Midwest and Great Lakes regions of the United States where many private and public supply wells are drawn from groundwater. Inline treatment systems can be cost-prohibitive and are difficult to monitor and maintain. These limitations underscore the importance of establishing land management and wellhead protection plans that effectively reduce nitrogen inputs to groundwater and obviate the need for additional treatment. In a previous study, we introduced a modelling tool that can benefit these efforts by predicting the impact of land cover on well nitrate concentrations using a time of travel capture zone, mean annual recharge, and land cover datasets. The model effectively predicted historical nitrate concentrations in two municipal supply wells serving the City of Waupaca, WI. Here, we present an updated version of the nitrate calculator model. Updates include: (1) the addition of a graphical user-interface (GUI) for data, (2) allowing the use of gridded recharge data, and (3) allowing gridded input data to vary in grid size and grid cell dimension. Model results for Municipal Well #5 and Municipal Well #6 in the City of Waupaca, WI, strongly agree with median annual nitrate measurements in these wells (2014–2021). To demonstrate the versatility of this product in sandy, unconfined aquifers, we also present and discuss the results of this model when applied to other municipal wells in central Wisconsin.