The Geological Survey of Northern Ireland (GSNI) and the British Geological Survey (BGS) completed a regional geochemical survey of Northern Ireland's Stream Waters. Sampling and quality control were undertaken according to the G-BASE protocol of BGS. Stream waters were sampled in 1994-96 (2,908 sites in the west) and in 2004-06 (2,966 sites in the east). The sampling distribution averaged one site per 2.4 km2.
For methodology and detection limits see: https://www.opendatani.gov.uk/dataset/gsni-tellus-regional-stream-waters-icp/resource/96871e7f-3f5b-4f27-8d8e-192fe0f6919f