This manual describes a simplified methodology which can be used to assess the impact of urban stormloads on the quality of receiving waters, and to evaluate the cost and effectiveness of control measures for reducing these pollutant loads. The methodology is particularly appropriate for use at the planning level where preliminary assessments are made to define problems, establish the relative significance of contributing sources, assess feasibility of control, and determine the need for and focus of additional evaluations. It can also be used effectively in conjunction with detailed studies, by providing a cost-effective screening of an array of alternatives, so that the more detailed and sophisticated techniques can examine only the more attractive alternatives. The methodology is based on the determination of certain statistical properties of the rainfall history of an area. From these statistics, the desired information on loads, performance of controls, and receiving water impacts is generated directly. Procedures are quite simple to apply, using charts and graphs which facilitate screening alternate types or levels of control, testing sensitivity to assumptions concerning drainage area characteristics, stormwater contaminant levels and similar variable factors.

Cover title: A statistical method for assessment of urban runoff. Prepared for EPA Nonpoint Sources Branch, contract no. 68-01-3251. May 1979. Includes bibliographical references.