Assessing groundwater transport of non-point source pollutants to surface waters and wells: Nitrates in the Maurice Watershed, New Jersey

Future changes in agricultural land use will alter input concentrations of non-point source pollutants (e.g. nitrates) to a watershed. While the water quality of surface waters within the watershed may begin to respond very quickly to land use changes due to surface runoff and other fast transport pathways, some of the pollutants may enter groundwater, which moves slowly through an aquifer. Thus, the impacts of land use change on surface water quality may take years to fully manifest, creating the need for a tool that will assess the long term response of contaminants reaching a stream based on changes in contaminant applications. Current modeling methods for groundwater contaminant transport, however, are intensive and require many site specific data. We propose an exponential lumped parameter model which only uses generally available field data to provide a quick assessment of the long term impacts of land use change on surface water quality. The exponential lumped parameter model was applied to the Maurice River watershed in New Jersey to estimate nitrate response in the river. Despite the complex hydrology of the Maurice watershed, the long term nitrate response generated by the lumped parameter model is very similar to the nitrate responses generated by both a more intensive MODFLOW model and field data. Furthermore, this study demonstrates that the same exponential lumped parameter model can be used to generate nitrate responses for high capacity pumping wells. Based on the Maurice watershed results, we will also discuss the validity of the exponential lumped parameter model under various factors, including weak sinks (sinks which do not draw water from the entire depth of the aquifer), seasonal recharge rates, spatially variable nitrate application rates, and subsurface denitrification.