Results of the U.S. Geological Survey's analytical evaluation program for standard reference samples : T-153 (trace constituents), M-146 (major constituents), N-57 (nutrient constituents), N-58 (nutrient constituents), P-30 (low ionic strength constituents), GWT-3 (ground-water trace constituents), GWM-3 (ground-water major constituents), and Hg-26 (mercury) distributed in April 1998 / - Farrar, Jerry W. (U.S. Dept. of the Interior, U.S. Geological Survey, 1998)