Page 94 - Water and wastewater engineering

GENERAL WATER SUPPLY DESIGN CONSIDERATIONS 2-37

TABLE 2-17
Secondary maximum contaminant levels
Contaminant SMCL, mg/L a
Chloride 250
Color 15 color units
Copper 1
Corrosivity Noncorrosive
Foaming agents 0.5
Hydrogen sulfide 0.05
Iron 0.3
Manganese 0.05
Odor 3 threshold odor number units
pH 6.5–8.5
Sulfate 250
Total dissolved solids (TDS) 500
Zinc 5

a
All quantities are mg/L except those for which units are given.

Secondary Maximum Contaminant Levels (SMCLs). The National Safe Drinking Water
Act also provided for the establishment of an additional set of standards to prescribe maximum
limits for those contaminants that tend to make water disagreeable to use, but that do not have
any particular adverse public health effect. These secondary maximum contaminant levels are
the advisable maximum level of a contaminant in any public water supply system. The levels are
shown in Table 2-17 .

AWWA Goals. The primary and secondary maximum contaminant levels are the maximum
allowed (or recommended) values of the various contaminants. However, a reasonable goal may
be much lower than the MCLs themselves. The American Water Works Association (AWWA)
has issued its own set of goals to which its members try to adhere. These goals are shown in
Table 2-18 .

2-4 EVALUATION OF PROCESS OPTIONS
In the design process, the data gathered in the sections outlined to this point in the chapter would
be sufficient to begin screening alternative supply and treatment options. In most cases a number
of options will be available. The pros and cons of these selections are discussed in Chapters 3
through 16.

2-5 PLANT SIZING AND LAYOUT
Once the preliminary selection of the water treatment unit operations and processes has been
made (the screening process discussed in Chapter 1), rough calculations are made to determine
sizes to be used in examining feasibility of site locations and cost. The elements to be considered