After the surface drainage areas are divided into areas based on slope and drop in elevation, the environmental engineer must segregate and run them to the proper sewer classification.
The divided areas are provided with a sewer box or catch basin. The separate sewer systems must now be connected to the proper classified sewer. The outlet connections at the sewer box or catch basin can be at the bottom or side depending on the limits of sewer inverts (see Figure 7.10.2). The invert is the elevation of the bottom inside surface of the sewer pipe.
The sewer design should provide for ample future expansion of the plant and unit areas. Sewer mains, in particular, should be sized to include the estimated flow of any expansion.
Storm water runoff is calculated in rainfall in based on 100% runoff for all paved areas and 50% runoff for un-paved areas. Obtain design rainfall in amount of in per hr for the specific area where the plant is to be located; oth-
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