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trash generation and identifying very high, high, moderate and low trash generating areas. <br /> The term “trash generation” refers to the rate at which trash is produced or generated <br />onto the surface of the watershed and is potentially available for transport via MS4s to receiving waters. Generation rates do not explicitly take into account existing control <br />measures that intercept trash prior to transport. Generation rates are expressed as trash volume/acre/year and were established via the Generation Rates Project. <br /> In contrast to trash generation, the term “trash loading” refers to the rate at which trash <br />from MS4s enters receiving waters. Trash loading rates are also expressed as trash volume/acre/year and are equal to or less than trash generation rates because they <br />account for the effects of control measures that intercept trash generated in an area <br />before it is discharged to a receiving water. Trash loading rates are specific to particular <br />areas because they are dependent upon the effectiveness of control measures <br />implemented within an area. Figure 1-2 illustrates the difference between trash <br />generation and loading. <br /> <br /> <br />Figure 1-2. Conceptual model of trash generation, interception and load <br /> Trash generation rates were estimated based on factors that significantly affect trash <br />generation (i.e., land use and income). The method used to the establish trash generation rates for each Permittee builds off “lessons learned” from previous trash <br />loading studies conducted in urban areas (Allison and Chiew 1995; Allison et al. 1998; Armitage et al. 1998; Armitage and Rooseboom 2000; Lippner et al. 2001; Armitage <br />2003; Kim et al. 2004; County of Los Angeles 2002, 2004a, 2004b; Armitage 2007). The method is based on a conceptual model developed as an outgrowth of these studies <br />(BASMAA 2011b). <br />Trash generation rates were developed through the quantification and characterization of trash captured in Water Board-recognized full-capture treatment <br />devices installed in the San Francisco Bay Area. Trash generation rates estimated from this study are listed for each land use type in Table 1-1. Methods used to develop trash <br />generation rates are more fully described in BASMAA (2011b, 2011c, and 2012). <br /> <br /> <br />327