INTRODUCTION - Water Quality Engineering in Natural Systems - page 3

age channel. In most countries, these (point) sources
are regulated, their control is mandated, and a permit
is required to operate waste discharge systems. Point
sources of contamination that are of concern in manag-
ing surface waters include domestic wastewater dis-
charges, industrial discharges, and accidental spills.

These overflows, called CSos, contain not only storm-
water but also untreated human and industrial waste,
toxic materials, and debris.

1.2.1.3 Stormwater Discharges. Stormwater dis-
charges are generated by runoff from pervious areas,
such as lawns, and impervious areas, such as paved
streets, parking lots, and building rooftops, during rain-
fall events. Stormwater runoff often contains pollutants
in quantities that could adversely affect the quality of
the receiving water. A typical stormwater outlet into a
drainageway (that leads to a receiving water) is shown
in Figure 1.3. The stormwater outlet discharges runoff
from the heavily traveled highway shown in the back-
ground. Although stormwater runoff is commonly dis-
charged through a single outfall pipe, such discharges
are more accurately classified as nonpoint pollutant
sources since they collect and transport contaminants
from an entire catchment area. The primary method to
control the quality and quantity of stormwater dis-
charges

1.2.1.1 Domestic Wastewater Discharges. Most
domestic wastewater treatment plants discharge their
effluent into rivers, lakes, or oceans. For river discharges
of treated domestic wastewater, the effect on the dis-
solved oxygen, pathogen levels, and nutrient levels in
the river are usually of most concern. Decreased oxygen
levels in rivers can cause harm to the aquatic life, patho-
gens can cause illness in humans, and increased nutrient
levels stimulate the growth of algae, which consume
oxygen (during nighttime and for decay) and make the
water undesirable for recreational use and as a source
of drinking water. For ocean discharges of treated
domestic wastewater, pathogen and heavy metal con-
centrations are usually of most concern. In particular,
pathogenic microorganisms discharged into the ocean
can infect humans who come in contact with the ocean
water in recreational areas, such as beaches. Domestic
wastewater discharged below ground from septic tanks
contains large numbers of pathogenic microorganisms,
with viruses of particular concern because of their
ability to move considerable distances in groundwater.
Properly designed, operated, and maintained sani-
tary sewer systems collect and transport domestic
sewage to publicly owned treatment works (PoTWs).
However, occasional unintentional discharges of raw
sewage from municipal sanitary sewers occur in almost
every system. These types of discharges, collectively
called SSos, have a variety of causes, including but not
limited to extreme weather, improper system operation
and maintenance, and vandalism. The untreated sewage
from SSos can contaminate receiving waters and cause
serious water-quality problems. These SSos can also
back up into basements, causing property damage and
threatening public health.

is through the use of best management

practices.

1.2.1.4 Industrial Discharges. There is a wide variety
in the types of industrial wastewaters, and elevated
levels of nutrients, heavy metals, heat, and toxic organic
chemicals are common in industrial wastewaters. Some
industries provide pretreatment prior to discharging
their wastewaters either directly into surface waters or
into municipal sewer systems for further treatment in
combination with domestic wastewater. In many coun-
tries outside the united States, industries are permitted
to discharge their wastewater without adequate pre-
treatment, and the resulting human and environmental
impacts are usually noticeable.

stormwater outlet

1.2.1.2 Combined Sewer Overflows. Combined sewer
systems are designed to collect rainwater runoff, domes-
tic sewage, and industrial wastewater in the same pipe.
Most of the time, combined sewer systems transport all
of their wastewater to a sewage treatment plant, where
it is treated and discharged to a receiving water body.
During periods of heavy rainfall or snowmelt, the waste-
water volume in a combined sewer system can exceed
the capacity of the sewer system or treatment plant. For
this reason, combined sewer systems are designed to
overflow occasionally and discharge excess wastewater
directly to nearby streams, rivers, or other water bodies.

drainageway

Figure 1.3. Stormwater outlet into drainageway.