[en] The relative precision for groundwater analyses completed in the Basalt Materials Research Laboratory (BMRL) is typically on the order of 1--3% for inductively coupled plasma atomic emission spectroscopy measurements and better than 1% for anion analyses by ion chromatography. Excellent recoveries are found for known analyte additions to groundwater and synthetic Grande Ronde water. For the suite of elements currently under investigation, matrix effects do not pose a significant problem. The analytical results from the Basalt Waste Isolation Project laboratory for United States Environmental Protection Agency quality control standards are well within the 95% confidence interval as reported for the interlaboratory average. Results from BMRL participation in the United States Geological Survey Analytical Evaluation Program for Standard Reference Water Samples are presented. 9 refs., 6 tabs