4. (12 points) Consider the dispersion of a contaminant plume in a river that undergoes a firstorder decay. Assume the plume is introduced to the river as a slice input (i.e., complete mixing in the y and z directions). For the graphs that follow, sketch the conceptual plume profile to indicate the change described relative to the profile shown. Note: the sketch does not need to be exact, but must show the important trends in plume height, width, and/or position. If you need to recreate these graphs for your submittal, be sure to clearly indicate which profile is provided and which profile corresponds to the change indicated. (a) (2 points) The plume mass is halved (i.e., Mo decreases twofold): (b) (2 points) The first-order rate constant kl is halved (i.e., kl decreases twofold): (c) ( 2 points) The dispersivity is doubled (i.e., Ex increases twofold): (d) (3 points) The observation time is doubled (i.e., t increases twofold): (e) (3 points) The flowrate is doubled (i.e., Q increases twofold)