Page 450 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch12_398-456.qxd 8/4/10 9:37 PM Page 409

12.4 Best Management Practices 409
During this step, program responsibilities must be clearly delineated. All involved en-
tities must be familiar with and accept their role in implementing and enforcing the plan.
Continuing activities also should be clearly defined and monitoring schedules should be
set to determine the program’s effectiveness in meeting its goals. Maintenance programs
should be developed so that structural practices continue to operate as intended. Finally,
the municipality should be aware of available federal and state technical assistance that
could help throughout implementation of the plan.

12.4 BEST MANAGEMENT PRACTICES
12.4.1 Best Management Practice Overview
Urban runoff problems are more difficult to control than steady-state, dry-weather point
source discharges because of the intermittent nature of rainfall and runoff, the number of
diffuse discharge points, the large variety of pollutant source types, and the variable nature
of the source loadings. Because the expense of constructing facilities to collect and treat
urban runoff is often prohibitive, the emphasis of stormwater management should be on
developing a least cost approach, which includes nonstructural controls and low-cost struc-
tural controls.
Nonstructural controls include regulatory controls that prevent pollution problems by
controlling land development and land use. They also include source controls that reduce
pollutant buildup or lessen its availability for washoff during rainfall.
Low-cost structural controls include the use of facilities that encourage uptake of pol-
lutants by vegetation, settling, or filtering. Because of the variability of pollutant removal,
these controls can be used in series or in parallel combinations. The concept of implement-
ing a “treatment train” might, for example, include initial pretreatment, primary pollutant
removal, and final effluent polishing practices to be constructed in series.
Table 12.4 lists several categories of methods that are commonly used as urban
runoff and CSO best management practices. The next sections describes methods of
BMP screening then give a brief overview of some of the more important characteris-
tics of these BMPs, including the types of pollutants controlled, the pollution removal
mechanisms, limitations on their use, maintenance requirements, and general design
considerations.

12.4.2 Best Management Practice Screening
The goal of BMP screening is to reduce the comprehensive list of BMPs to a more manage-
able list for final selection. Because this step is an initial screening, methods used are gener-
ally qualitative and require professional judgment. Although extensive knowledge about
specific design criteria is not necessary at this stage in the screening process, understanding
each individual BMP’s effectiveness and applicability to the program area’s problems is
crucial.
The BMPs are divided into two general categories: nonstructural and structural.
Nonstructural BMPs—which include regulatory practices, such as those that limit imper-
vious area or protect natural resources, and source controls, such as street sweeping or
solid waste management—are typically implemented throughout an entire community,
watershed, or special area. While structural BMPs, such as detention ponds or infiltration
practices, may be designed to address specific pollutants from known sources, they also
can be implemented throughout an area. In addition, structural BMPs can be required in
new developments or redevelopments.