The metric units of measurement chosen for use throughout this document follow the guidelines set forth in ASTM Designation E 380. Some of these units, such as the megapascal (MPa), the microsiemens (μS), and the kilowatt per square meter (kW/m²) may be unfamiliar to the United States reader, but their equivalence to the more familiar English units is clearly indicated by the accompanying presentation of all values in both systems of measurement. For the purposes of this document, the units mg/l and μg/l used for measurement are considered to be equivalent to ppm and ppb, respectively.