What is Turbidity?
Turbidity is a measure of the cloudiness of water- the cloudier
the water, the greater the turbidity. Turbidity in water is caused
by suspended matter such as clay, silt, and organic matter and
by plankton and other microscopic organisms that interfere with
the passage of light through the water.
Is Turbidity a health risk?
Turbidity is closely related to total suspended solids (TSS),
but also includes plankton and other organisms. Turbidity itself
is not a major health concern, but high turbidity can interfere
with disinfection and provide a medium for microbial growth. It
may also indicate the presence of heavy metals
such as cadmium, mercury and lead or toxic organic contaminants.
Causes of Turbidity:
Flow Rate: The flow rate of a water body is
a primary factor influencing turbidity concentrations. Fast running
water can carry more particles and larger-sized sediment. Heavy
rains can pick up sand, silt, clay, and organic particles from
the land and carry it to surface water. A change in flow rate
also can affect turbidity; if the speed or direction of the water
current increases, particulate matter from bottom sediments may
be resuspended.
Soil Erosion: Soil erosion is caused by disturbance
of a land surface. Soil erosion can be caused by building and
road construction, forest fires, logging, and mining. The eroded
soil particles can be carried by stormwater to surface water.
This will increase the turbidity of the water body.
Soil has eroded over time into this lake in Michigan leaving mining
contaminant to discolor the water.
Urban Runoff: During storm events, soil particles
and debris from streets and industrial, commercial, and residential
areas can be washed into streams. Because of the large amount
of pavement in urban areas, natural settling areas have been removed,
and sediment is carried through storm drains to creeks and rivers.
Wastewater: The wastewater from our houses contains
food residue, human waste, and other solid material that we put
down our drains. Most of the solids and organic material are removed
from the water before being discharged to the stream, but residuals
can remain..
Decaying Plants and Animals: As plants and animals
present in a water body die and decay, suspended organic particles
are released and can contribute to turbidity.
Bottom-Feeding Fish: Bottom-feeding fish (such
as carp) can stir up sediments as they remove vegetation. These
sediments can contribute to turbidity.
Algal Blooms: Algal blooms can contribute to
turbidity. Algal production is enhanced when nutrients are released
from bottom sediments during seasonal turnovers and changes in
water current.
Standards:
The EPA Surface Water Treatment Rule requires systems using
surface water or ground water under the direct influence of surface
water to (1) disinfect their water, and (2) filter their water
or meet criteria for avoiding filtration. At no time can turbidity
go above 5 nephelometric turbidity units (NTUs). In the United
States, systems that filter must ensure that the turbidity go
no higher than 1 NTU in at least 95% of the daily samples in any
month.
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