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Grab
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Sample
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Turbidity
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Testing
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In
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order
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to
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test
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the
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accuracy
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of
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the
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turbidimeters,
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a
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grab
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sample
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method
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has
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been
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developed.
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The
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results
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of
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this
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method
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will
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be
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compared
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to
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the
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results
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from
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the
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turbidimeters.
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The
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sample
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container
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will
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be
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a
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500
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mL
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glass
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beaker.
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It
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is
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very
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important
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that
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the
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water
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undergo
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minimal
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shear
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when
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entering
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the
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beaker
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so
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that
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flocs
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are
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not
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broken
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in
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the
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process.
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Therefore,
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the
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following
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procedure
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will
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be
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followed
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to
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collect
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a
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sample.
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First,
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the
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beaker
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will
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be
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gently
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emerged
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while
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angled
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downward
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(at
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approximately
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30
...
degrees),
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so
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that
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the
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area
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that
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the
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incoming
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water
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can
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pass
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through
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to
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enter
...
the
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beaker
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is
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as
...
large
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as
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possible.
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This
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can
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be
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seen
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in
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Grab
...
Sample
...
Procedure
...
...
Then,
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the
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beaker
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will
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be
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rotated
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downward
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until
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it
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is
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horizontal
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as
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seen
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in
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Grab
...
Sample
...
Procedure
...
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It
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will
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be
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further
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rotated
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until
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fully
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submerged
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as
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seen
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in
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Grab
...
Sample
...
Procedure
...
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The
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purpose
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of
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steps
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2
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and
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3
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are
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to
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let
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the
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water
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enter
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the
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beaker
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without
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allowing
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air
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to
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be
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trapped
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in
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the
...
beaker.
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If
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air
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bubbles
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are
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trapped
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in
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the
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beaker,
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then
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they
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may
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break
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flocks
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when
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the
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beaker
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is
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righted
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and
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they
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escape.
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Then
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it
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will
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be
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fully
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submerged
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into
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the
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water
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and
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rotated
...
so that the beaker is upright as seen in Grab Sample Procedure #Picture 4. Then, finally, the beaker will be lifted vertically from the water, so that it remains full.
| Wiki Markup |
|---|
{float:right|border=2px solid black|width=200px} {anchor:Picture 1}[!Pilot Plant^GrabSample1.jpg|width=200px!|Pilot Plant^GrabSample1.jpg] h5. that the beaker is upright as seen in Grab Sample Procedure Picture 4. Then, finally, the beaker will be lifted vertically from the water, so that it remains full.The water will be allowed to settle for 20 minutes to approximate the settling that should occur in the tube settlers. The length of time that the water should be allowed to settle was determined in the following way. First, I back-calculated from the flow that we had been running through the tube settlers in the past (40mL/min) to find the critical velocity, Vc, associated with that flow. Unable to find DVI conversion log file. LaTeX Markup: \large $$ V = {Q \over A} $$ This gives a Velocity through the settler tube, or Valpha, to be 0.1358 cm/sec, or 117.3 m/day. Then Vup was determined using the following equation: Unable to find DVI conversion log file. LaTeX Markup: \large $Vup = V_\alpha \sin \alpha $ Vup, for this case is 0.1176 cm/s or 101.6 m/day. Vc is the critical velocity that a floc must have to drop to the bottom of the tube settler and settle out. The following equation from Weber-Shirk was used to determine Vc. Vc = 0.01032 cm/s = 8.92 m/day This value is acceptable because it is below the threshold of 10m/day. Then, the time that the water in the beaker would need to be allowed to settle was calculated as follows: Unable to find DVI conversion log file. LaTeX Markup: \large $T = {{H_{_{bea\ker } } } \over {V_C }}$ T = 1 {float} |
| Wiki Markup |
|---|
{float:right|border=2px solid black|width=200px}
{anchor:Picutre 2}[!Pilot Plant^GrabSample2.jpg|width=200px!|Pilot Plant^GrabSample2.jpg]
h5. Grab Sample Procedure Picture 2
{float} |
| Wiki Markup |
|---|
{float:right|border=2px solid black|width=200px}
{anchor:Picutre 3}[!Pilot Plant^GrabSample3.jpg|width=200px!|Pilot Plant^GrabSample3.jpg]
h5. Grab Sample Procedure Picture 3
{float} |
| Wiki Markup |
|---|
{float:right|border=2px solid black|width=180px}
{anchor:Picutre 4}[!Pilot Plant^GrabSample4.jpg|width=150px!|Pilot Plant^GrabSample4.jpg]
h5. Grab Sample Procedure Picture 4
{float} |
The water will be allowed to settle for 20 minutes to approximate the settling that should occur in the tube settlers.
The length of time that the water should be allowed to settle was determined in the following way.
First, I back-calculated from the flow that we had been running through the tube settlers in the past (40mL/min) to find the critical velocity, Vc, associated with that flow.
| Include Page | ||||
|---|---|---|---|---|
|
This gives a Velocity through the settler tube, or Valpha, to be 0.1358 cm/sec, or 117.3 m/day.
Then Vup was determined using the following equation:
| Include Page | ||||
|---|---|---|---|---|
|
Vup, for this case is 0.1176 cm/s or 101.6 m/day.
Vc is the critical velocity that a floc must have to drop to the bottom of the tube settler and settle out. The following equation from Weber-Shirk was used to determine Vc.
| Include Page | ||||
|---|---|---|---|---|
|
Vc = 0.01032 cm/s = 8.92 m/day
This value is acceptable because it is below the threshold of 10m/day.
Then, the time that the water in the beaker would need to be allowed to settle was calculated as follows:
| Include Page | ||||
|---|---|---|---|---|
|
T = 12cm/(0.01032cm/s)
...
=
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19
...
minutes
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23
...
seconds
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,
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or
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about
...
20
...
minutes.
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Finally,
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the
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settled
...
water
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turbidity
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of
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the
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grab
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samples
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is
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tested
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using
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the
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bench
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turbidimeter
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in
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the
...
CUWTP
...
lab.
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This
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turbidimeter
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is
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calibrated
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regularly
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by
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CUWTP
...
staff.
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Results
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of
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grab
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sample
...
testing
...
The
...
above
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procedure
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was
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performed
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for
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two
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of
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the
...
turbidimeters
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on
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April
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2,
...
2008
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to
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test
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if
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the
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tube
...
settler
...
set-up
...
was
...
functioning
...
properly.
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The
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following
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were
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the
...
results
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from
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this
...
test:
...
| Turbidimeter 3 | Turbidimeter 2 |
|---|---|---|
| (NTU) | (NTU) |
Turbidimeter | 40.4 | 54.2 |
Grab Test | 61.4 | 82.3 |
Grab Test % Higher than Turbidimeter | 52% | 52% |
As can be seen from this data, the grab test had a settled turbidity that was, in both tests, 52% higher than the turbidity readings from the tube settler/turbidimeter combination. This suggests that the tube settler/ turbidimeter set-up was functioning as it should be. To verify this in another way, we changed the incoming lines between the turbidimeters, and observed that the values from the different turbidimeters agreed.