The runoff of water from streets, lawns, and construction sites is a major source of pollutants for our lakes and streams.Various methods are available for controlling runoff and improving water quality? some cheap, others more costly. In the diagram draw the marginal social cost line that illustrates this. Add a marginal social benefit line that shows how the additional benefits of control decrease. Identify the optimal level of water quality. Suppose the government mandates control efforts that result in a higher level of quality. Illustrate the social waste associated with making the water too clean.