Page 452 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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12.4 Best Management Practices 411
One screening method involves applying screening criteria to each nonstructural prac-
tice to determine its applicability to the conditions in the watershed. The screening criteria,
which are specific to the watershed and depend on the program goals, include the following:
1. Pollutant removal: Because different regulations and source control practices are de-
signed to address different pollutants, the program team should ensure that the screened
list of controls includes practices designed to address the pollutants of primary concern.
In addition, some practices might not provide sufficient pollutant removal.
2. Existing government structure: Some practices implemented throughout the coun-
try require a specific government structure. For example, while a strong county
government might be important for implementing a specific regulatory control, the
role of county governments can vary from one section of the country to another.
Practices requiring specific government structures that do not exist in the area of
concern therefore could be eliminated from the list.
3. Legal authority: For regulatory controls to be effective, the legal authority to im-
plement and enforce the regulations must exist. If municipal boards and officials
lack this authority, they could be required to obtain it through local action.
4. Public or municipal acceptance: Implementing certain practices could be difficult
because of resistance from the public or an involved municipal agency. These prac-
tices can be eliminated from the list.
5. Technical feasibility: The municipal BMPs that require large expenditures and ex-
tensive efforts might not be suitable for small municipalities that lack the required
resources.
Another method of screening involves the use of a comparative summary matrix. Such
a matrix can be used to screen nonstructural control practices. In the matrix, various regu-
latory and source control practices are listed and their abilities to meet various criteria are
compared. The criteria to be listed include ability to remove specific pollutants, such as nu-
trients and sediments, maintenance requirements, longevity, community acceptance, sec-
ondary environmental impacts, costs, and site requirements. For each practice and crite-
rion, an assessment of effectiveness is indicated; for instance, on a scale of 1 to 5, with 1
indicating the highest effectiveness and 5 the lowest. This type of matrix can provide a
basis for an initial assessment of practices and their applicability to the program.

12.4.2.2 Structural Practices Because structural practices generally are more site spe-
cific and have more restrictions on their use than nonstructural practices, the initial screening
step for these practices can be more precise than that for nonstructural practices. Table 12.5
outlines some of the more important criteria for the screening of structural BMPs, includ-
ing their typical pollutant removal efficiencies, land requirements, the drainage area that
each BMP can effectively treat, the desired soil conditions, and the desired groundwater
elevation. By using these criteria and the information obtained during data collection and
analysis and problem identification and ranking, the program team can narrow the list of
BMPs to be further assessed in the BMP selection step.
The initial screening criteria for structural control practices include the following:

1. Pollutant removal: The municipality should ensure that the BMPs selected address
the primary pollutants of concern to the level of removal desired.
2. Land requirements: Large land requirements for some of the aboveground structural
BMPs can often restrict their use in highly developed urban areas. Land requirements
vary depending on the BMP.