Dual stable isotope analysis comprising nitrogen-15 and oxygen-18 ratios for groundwater samples collected every 2-3 months over one hydrogeological year from the East Riding of Yorkshire. Isotopic ratios for nitrogen-15, oxygen-18 are both presented as raw and processed to NAIR and VSMOW, respectively. The data are in the form of a Microsoft Excel workbook containing Isotope Ratio Mass Spectrometer runs. The data were collected to understand key sources of nitrate contamination in Chalk groundwater and the dominant processes they undergo, and the extent of any attenuation. The Chalk catchments and the River Terrace Gravel catchment were compared, allowing conclusions to be drawn on the role of nitrate transformation, and the dominant location of transformations, to increase understanding of nitrate dynamics in agricultural systems. Groundwater samples were collected by the University of Leeds, the Environment Agency, Yorkshire Water and South East Water. Nitrate isolation and data interpretation carried out by Josephine McSherry, supervised by L. Jared West and Simon Bottrell. Mass spectrometry was carried out by Rob Newton and Bob Jamieson at the University of Leeds. No isotopic data are absent from the dataset, however oxygen contamination (resulting from the isolation method and since resolved) severely affected run O34b-O. Hydrochemical data relevant to the groundwater samples are not included as they are the property of the Environment Agency, Yorkshire Water or South East Water.