Page 544 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch14_500-554.qxd 8/7/10 8:56 PM Page 502

502 Chapter 14 Design of Sewer Systems

Street line
Street line
Sidewalk Roadway
Sidewalk
Roadway
Service connection
Service connection 30° bend
Concrete chimney
Common sewer
Common sewer
Cross-section
Cross-section

Sidewalk
Sidewalk Roadway
Roadway
30° bend
Service connection Service connection
Concrete
Y branch chimney

Common
Common Street
sewer Flow sewer Flow Street
line line
Plan Plan

Figure 14.3 Service Connections to Public Sewer at Normal Figure 14.4 Service Connections to Public Sewer in Deep
Depth. Trench. Conversion factor: 1 1 ft 0.3048 m; 1 1 in.
2.54 cm 25.4 mm

In separate systems, connections to the wrong sewer, in violation of common regula-
tions, carry some stormwater into sanitary sewers and some domestic wastewater into
storm drains. The dry-weather flow of combined sewers is primarily wastewater and
groundwater; the wet-weather flow is predominantly storm runoff. The first flush of
stormwater will scour away deposited solids, including much putrescent organic matter.

14.2 GRAVITY SEWERS
Sewers are hydraulic conveyance structures that carry wastewater to a treatment plant or
other authorized point of discharge. A typical method of conveyance used in sewer systems
is to transport wastewater by gravity along a downward-sloping pipe gradient. These sew-
ers, known as conventional gravity sewers, are designed so that the slope and size of the
pipe are adequate to maintain flow toward the discharge point without surcharging man-
holes or pressurizing the pipe. Gravity sewers are the oldest and most common wastewater
transport system existing. Technology advancement is limited principally to improvement
in materials and methods of construction.
Sewers are commonly referred to according to the type of wastewater that each trans-
ports. For example, storm sewers carry stormwater, industrial sewers carry industrial wastes,
and sanitary sewers carry both domestic sewage and industrial wastes. Another type of sewer,
known as a combined sewer, is prevalent in older communities, but such systems are no longer
constructed. Combined sewers carry domestic sewage, industrial waste, and stormwater.