This example demonstrates simulating pollutant accumulation and washoff in an urban area, considering different land uses and using Event Mean Concentrations (EMCs) and exponential functions for washoff. Surface runoff quality is crucial yet complex in wet-weather flow studies. SWMM can empirically model nonpoint source runoff quality and water treatment, offering flexible math functions for estimating pollutant buildup and release during dry and stormy periods. We’ll use the same study area as Examples 1 through 4 to illustrate this in a typical urban setting.