Flow is an important parameter in the measurement of selenium, boron and salt loads in the Grassland Basin. Loads are calculated by multiplying the concentration of the contaminant of concern (expressed in ppb or ppm) by the flow (in cubic feet/second) and then multiplying by an appropriate constant to convert the mass flux into lbs or tons, depending on the constituent. In previous monitoring programs, flow has been the most inconsistently monitored parameter. Flows within the Basin can fluctuate quite widely and are especially susceptible to rainfall runoff events.