These are groundwater geochemical data taken from two sites in the Kien Svay district of northern Kandal Province, Cambodia, southeast of Phnom Penh. These sites are referred to as “clay-dominated” and “sand-dominated” in reference to the known lithology and are known for high arsenic concentrations (Richards et al., 2017). Each site contained four 18 m boreholes installed in January 2019 using manual drilling described in Richards et al (2015), spaced evenly about ~1.5 m apart. The boreholes that were located at the clay-dominated site are referred to NB01, NB02, NB03 and NB04. The boreholes that were located at the sand-dominated site are referred to as NB05, NB06, NB07 and NB08. Two sampling campaigns were carried out: 6th-12th May 2019 (pre-monsoon season), and 27th-31st January 2020 (post-monsoon season). References: Richards, L. A., Magnone, D., Sovann, C., Kong, C., Uhlemann, S., Kuras, O., van Dongen, B. E., Ballentine, C. J., Polya, D. A. High Resolution Profile of Inorganic Aqueous Geochemistry and Key Redox Zones in an Arsenic Bearing Aquifer in Cambodia. Science of The Total Environment 2017, 590–591, 540–553. Richards, L. A., Magnone, D., van Dongen, B. E., Ballentine, C. J., Polya, D. A. Use of Lithium Tracers to Quantify Drilling Fluid Contamination for Groundwater Monitoring in Southeast Asia. Applied Geochemistry 2015, 63, 190–202.