1. 5.3 Non-Structural BMPs and Stormwater Methodological Issues

other process). Both Non-Structural BMPs in Chapter 5 and Structural BMPs in Chapter 6 are
rated in terms of their anticipated pollutant removal performance or effectiveness. The initial
BMP selection process analyzes the final site plan and estimates the potential NPS load, using
Appendix A. The targeted reduction percentage for representative pollutants (such as 85%
reduction in TSS and TP load and 50% reduction in the solute load) is achieved by a suitable
combination of Non-Structural and Structural BMPs. This process is described in more detail
in Chapter 8.
Non-Structural BMPs and Stormwater Methodological Issues
The methodological approach set forth in Chapter 8 provides a variety of straightforward and
conservative ways to take credit for applying Non-Structural BMPs, provided that the “specifications”
defined for each BMP in Chapter 5 are properly followed.
Because so many of the Non-Structural BMPs seem so removed from the conventional practice of
stormwater engineering, putting these BMPs into play may be a challenge. Many of these Non-
Structural BMPs ultimately require a more sophisticated approach to total site design. Some of the
Non-Structural BMPs don’t easily lend themselves to stormwater calculations as conventionally
performed. How do we get stormwater credit for applying any of these techniques? Taking BMPs 5.6.1
and 5.6.2 again as examples, minimizing impervious cover by reducing road width or impervious
parking area directly translates into reduced stormwater volumes and reduced stormwater rates of
runoff. Site planners and designers will also recognize that many of the other Non-Structural BMPs,
such as clustering of uses, conserving existing woodlands and other vegetative cover, and
disconnecting impervious area runoff flows, all translate into reduced stormwater volume and rate
calculations. As such, these BMPs are self-crediting.
363-0300-002 / December 30, 2006
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