Consider the concentration of lead in a lake, using a simplified model. the lake has a river flowing into it and another flowing out of it, and the water level in the lake is constant. the major sources of lead in the lake are direct deposition from the atmosphere and surface runoff carried into the lake with the river. the major removal process is river outflow. leaded gas was widely used for about 35 years (roughly 1950 – 1985), leading to a high influx of lead into the lake during those years. use a cmfr representation of the lake to calculate the growth and decay of lead concentration in the lake.