Page 399 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

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should be used to determine the rates and volumes. This text is not intended to teach
hydrology; there are many excellent references that already do that. Instead, it is
intended to guide the designers to approach stormwater management in a new evolving
and inclusive way for more sustainable results.
The field of stormwater management is rapidly growing for a number of reasons, of
which two important ones come to mind. The first is the ever-increasing development
of the land in both the United States and the rest of the world, as populations grow and
gain higher standards of living. This development usually translates to an increase in
impervious surfaces and changes to site hydrologics and thus usually increases
stormwater runoff. The second reason is based on the concern about global climate
change, which may result in alterations to precipitation and weather patterns in many
areas of the world and then could impact the hydrology and subsequent runoff, even
from existing developments.

10.1 Nonpoint Source Pollution, BMPs, and LID
Most of the focus in the last century has been on collecting stormwater runoff and
discharging it somewhere else to prevent flooding in the immediate area caused by
development. However, in the last few decades it has been recognized that this general
design may not be the best alternative in all cases. Collecting stormwater can cause
powerful flows off-site that may result in property and ecological damage in addition
to poor water quality. This pollution from stormwater runoff is commonly referred to as
nonpoint source (NPS) pollution, as it has areal sources.
In response to the concerns about stormwater runoff and NPS pollution, the United
States has adopted a permitting program, with the intent that it will help decrease off-
site impacts of stormwater runoff. It is called the National Pollutant Discharge
Elimination System (NPDES). Phases of NPDES have slowly been implemented in the
1990s and early 2000s, and the practices and policies resulting from their implementation
are considered to be important for stormwater management sustainability, both in the
construction phase and during the operational life of a facility.
There is no standard set of solutions to manage stormwater and NPS pollution.
Each site and each watershed has its own needs and special conditions. Therefore,
stormwater management design in the 1990s developed into a concept called Best
Management Practices (BMPs). BMPs are a compilation of various methods and policies
to choose from that are intended to serve as stormwater quantity controls and stormwater
quality control measures. Several BMPs together may “best” serve to reduce stormwater
impacts of construction and development.
BMPs are frequently subdivided into several broad categories. They can be grouped
by project phase, by the form they take, and by function. Differentiation by project
phase is whether they serve to reduce NPS pollution during the demolition and
construction phase, or whether they are used to manage stormwater and reduce water
quality impacts during the operational phase of a facility, as depicted in Fig. 10.1.1.
BMPs can also be differentiated by form, that is, whether they are structural or
nonstructural, as noted in Fig. 10.1.2. A structural BMP is one that is physically put in
place, such as a detention pond, swale, or a catch basin. A nonstructural BMP is a policy
or practice. (Note that the LEED-NC 2.2 Reference Guide tends to put the more natural
BMPs such as swales also in the nonstructural category.) An example of a BMP that is a
policy might be a regulation that all facilities which change motor oil also have facilities