This package contains data to an article about denitrification in groundwater. The data included are: 1. continuously analyzed (noble) gases and excess air model results of three different piezometers over a six-month period; 2. hydraulic conductivity and microbial activity analyzed at the piezometers (and the stream); 3. key parameters associated with denitrification (nitrate, alkalinity, O2, DOC, sulfate); 4. precipitation data and water level data of the stream and two piezometers.