Consider a hilly area in which new homes are being constructed. As rain falls on the site, without any controls, water running off the site would carry eroded soil particles to a nearby creek, polluting it badly. A detention pond is built to catch the particle-laden runoff at the bottom of the hill, to allow the soil particles to accumulate in the bottom of the pond while cleaner water overflows out of the pond and into the creek. For simplicity, assume that the rain is steady, all flows are steady, and ignore any transient effects on pond and water concentrations of soil particles. The water generated by the rain storm has a flow rate of 5.00 m3/min and entrains a concentration of particles of 4000. mg/L as it runs over the land. The nearby creek has a flow rate of 120. m3/min and normally carries an ambient concentration of 15.0 mg/L of soil particles. The detention pond will catch and remove most of the soil particles from the runoff, leaving outflow water (the water exiting the pond and flowing to the creek) with a concentration of 400. mg/L. Assume that 5% of the water that comes into the pond will seep down through the bottom (filtering out all particles), while the rest will over flow into the creek. a. Calculate the mass of mud accumulated in the detention ponds after three hours of this rainfall/runoff.
b. Calculate the concentration of particles in the creek after mixing with the overflow from the pond.