Authors Alliance for Aquatic Resource Monitoring
License CC-BY-NC-ND-4.0
Stream Team
Data Reminders
Guide to Equipment Precision and Recording Data
Acceptable Precision Ranges: QA/QC
Thank you for volunteering your time to participate in the Stream Team initiative. We greatly
appreciate your role collecting data to help evaluate stream health. When collecting data
there are several approaches to ensure that values are credible. This document will help to
explore some of the practices you can use during your monthly analysis.
Quality Assurance/Quality Control (QA/QC)
Quality assurance and quality control are the backbone of any successful stream monitoring
effort and are the measures taken to demonstrate the accuracy and precision of your data. Quality
Assurance (QA) refers to the plan and general processes for maintaining quality in all aspects of a
program. Quality Control (QC) consists of the specific steps taken to determine the validity of specif-
ic sampling and analytical procedures. This document will hone in on key Stream Team techniques
to help ensure that the values obtained are close to reflecting the accurate values of stream health
and that data points are comparable to each other. You can find out more about the key quality
assurance and control measures Stream Team implements on page 4 of the Stream Team manual.
What is an acceptable precision range?
Replicates are important for catching potential errors that might occur while testing samples
such as residue in test tubes, undissolved nitrate tablets, or expired reagents. When testing two repli-
cates of the same water sample, you should expect the values to be relatively close together. When
the two replicates are close to each other in value they are precise. When two values are close to
each other and close to the true value of the water sample, they are considered both accurate and
precise. The acceptable replicate precision range is an approach to, based on the sensitivity of the
equipment, deciding if your two replicates are close enough to be precise. If two replicates are not
within the acceptable precision range of each other than a third replicate is needed.
Table 1.0 Acceptable precision ranges by parameter
Parameter Unit Precision Range
Water Temperature °C ± 0.5 °C
pH pH unit ± 1 pH unit
Conductivity μS/cm ± 10 μS/cm
0 – 2 mg/L = ± 1 mg/L
Nitrate-Nitrogen mg/L
2 – 10 mg/L = ± 2 mg/L
10 – 15 mg/L = ± 5 mg/L
Acceptable Precision Ranges: Averaging
Left: Watershed Coordinators Abby Kaija ‘20 and Katherine Altamirano ‘20 cleaning lab equipment
according to ALLARM’s acid-washing protocol
Above: ALLARM’s lab team conducts QA/QC on volunteer-provided samples for the parameter pH
What happens if my two replicates are not precise?
Firstly, double-check your values and whether or not they fall in the precision range
according to the Stream Team parameter you are testing (Table 1.0). If two replicates are
not within the acceptable precision range of each other, then a third replicate is needed.
Once the third replicate is complete, determine which two replicates fall within the accept-
able precision range of each other. Note which of the two replicates are in range of each
other on the datasheet and only enter these two values into the Chesapeake Data Explorer.
What happens if, after my third replicate, have none within the accept-
able precision range?
If after your third replicate, you still do not have two values within the acceptable
precision range, continue to a 4th or 5th replicate until two values fall within range. As above,
note which of the two replicates are in range of each other on the datasheet and enter only
these two values in the Chesapeake Data Explorer. Often times, if you are needed a 3rd or
4th replicate, consider examining whether there could be a problem with dirty glassware or
expired reagents.
If you need a reagent replacement, please contact us at allarm@dickinson.edu
Averaging Replicates
Just as important as making sure replicates are precise, it is also important to ensure
the average of those replicates reflect the accuracy of the equipment. This means round-
ing to significant figures. Rounding to significant figures is different for each parameter
based on the precision and detection limit of the equipment.
Data Reminders: pH
Figure 1.0: pH values
When recording values for pH, you
can select the number shown on the
LaMotte color comparison slide or
7.25 the values directly between, where
the bold black line indicates the
7.75 change in value (reference Figure
1.0 for those middle values).
8.25
Note: You should not be recording
8.75 any number not listed in this graphic.
If the average of your two replicates
9.25
is not one of these numbers, round
9.75 up to the next acceptable value
listed in this diagram.
10.25
If the average of your two replicates is not one of these numbers, round up to the next ac-
ceptable value listed in this diagram. For pH, this means the number recorded should have a
decimal unit of .25, .5 or .75.
If you and a partner are determining the color of a pH replicate together, write your values
down and decide upon a single value for the replicate. Only record the agreed upon value
on your datasheet. This value will then be uploaded to the Chesapeake Data Explorer.
Table 2.0: Examples of acceptable pH values
Replicate 1 Replicate 2 Within precision range/ Need Average
another replicate?
7.5 7.75 Yes/No 7.75 (rounded up from 7.625
8.0 8.5 Yes/No 8.25
5 6.25 No/Yes Third replicate needed be-
fore averaging
Data Reminders: Nitrate-Nitrogen
Figure 2.0: Nitrate-Nitrogen values
Similarly to choosing pH values,
when recording values for ni-
trate-nitrogen, you can select the
number shown on the LaMotte
color comparison slide or the val- 0.5
ues directly between. Again, this is
where the bold black line indicates 1.5
the change in value (reference
Figure 2.0 for those middle values). 3.0
5.0
Note: You should not be record-
ing any number not listed in these 7.0
graphics. If the average of your
two replicates is not one of these 9.0
numbers, round up to the next
acceptable value listed in this dia- 12.5
gram.
If you and a partner are determining the color of a nitrate replicate together, decided on
a value for each replicate and only record the agreed upon value on your datasheet. This
value will then be uploaded to the Chesapeake Data Explorer.
Table 3.0: Examples of acceptable Nitrate-Nitrogen values
Replicate 1 Replicate 2 Within precision range/ Need Average
another replicate?
1.0 mg/L 1.5 mg/L Yes/No 1.5 mg/L (rounded up
from 1.25 mg/L)
4.0 mg/L 5.0 mg/L Yes/No 5.0 mg/L (rounded up
from 4.5 mg/L)
12.5 mg/L 15.0 mg/L Yes/No 15.0 mg/L (rounded up
from 13.75 mg/L)
0.5 mg/L 2.0 mg/L No/Yes Third replicate needed
before averaging
Data Reminders: Conductivity
When do I record a decimal place?
For measurements under 200 µS/cm, there is one decimal place. If your average of
conductivity replicates is under 200 µS/cm and has two decimal places, round to one
decimal place.
When do I record in whole numbers?
For measurements above 200 µS/cm, the meter reads in whole numbers. If your aver-
age of conductivity replicates is over 200 µS/cm has a decimal place, round to the
nearest whole number.
Table 4.0: Examples of acceptable conductivity values
Replicate 1 Replicate 2 Within precision range/ Need Average
another replicate?
256 µS/cm 257 µS/cm Yes/No 257 µS/cm (rounded up
from 256.5 µS/cm)
111.2 µS/cm 111.3 µS/cm Yes/No 111.3 µS/cm rounded up
from 111.25 µS/cm)
198.8 µS/cm 201 µS/cm Yes/No 200 µS/cm(rounded up
from 199.9 µS/cm)
510 µS/cm 525 µS/cm No/Yes Third replicate needed
before averaging
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