Groundwater Resource Investigation CVEN4503 Assignment 2
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Assignment 2 (individual assignment)
Complete all tasks and answer all questions contained in this document. Use graph paper
and additional sheets as necessary.
Assessment information and submission instructions:
This assignment is due on Friday 26 March at 9 am.
Fill in and sign the assignment cover sheet.
Submit using the hand-in box in Moodle.
This assignment is worth 30% of the course mark.
Please keep a copy of what you submit!
Do not send by email as this will not be accepted!
Workshop tasks and questions
Table 1 contain 19 groundwater quality analyses from 7 catchments across different
geological terrains in Australia as well as a surface seawater sample and two rainwater
samples (Figure 1).
1. Accuracy and units Hint: use an excel spreadsheet for these calculations.
(10% of mark)
(a) Recalculate the analytical data to the units mmol/L and then meq/L.
(b) Calculate for each water sample the Electrical Balance (E.B.). Include the major
ions in this calculation. Consider for each sample if other ions may contribute
significantly to the charge balance.
(c) The Electrical Conductivity (EC) is related to the sum of dissolved ions (in the units
of meq/L). For all samples calculate EC/100 and compare to both the sums of
anions and sums of cations (in the units of meq/L).
(d) The Electrical Balance for some samples is not good. For each of these samples
can you propose which parameters should be measured once again to improve
the balance? Qualify your answer.
(e) Some samples seem to show a consistent deviation between the sum of ions and
EC/100. Can you provide an explanation?
2. Piper Diagram (10% of mark)
(a) Convert the major ion concentrations in meq/L to percentages of the total for
cations and anions, respectively. The sum of cations should add up to 100% and
likewise the sum of anions should add up to 100%. Remember that per convention
the major ions included in a Piper diagram is fixed (for instance, you can’t include
nitrate).
(b) Plot the percentages in the provided Piper diagram template (Figure 2) or using
an online tool. Include the rainwater and seawater samples in the diagram.
(c) Divide the samples in the Piper plot into 4 groups and describe the characteristics
of the water composition for each group.
(d) Can you think of one advantage and one disadvantage of using Piper diagrams?
Groundwater Resource Investigation CVEN4503 Assignment 2
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3. Process interpretation (10% of mark)
(a) Calculate the contribution of ions from rainwater ions to the groundwater
composition by assuming that chloride (Cl) behaves as a conservative element
and that the two rainwater sample compositions are representative for Australia.
Hint: use ion ratios (e.g. Na/Cl, and SO4/Cl, etc.). Are there samples for which
using the rainwater composition is perhaps not appropriate?
(b) For the groundwater samples from the coastal catchments of Hat Head and
Rottnest Island: What is an obvious physical process that could be responsible for
most of the dissolved solids?
(c) For the samples from the inland catchments of Namoi Valley, Wellington, GAB,
Kingoonya, and Gippsland what is the likely main physical process responsible for
most of the dissolved solids? Can you quantify the effect of this process on the
water composition? Hint: consider the Cl concentrations again.
(d) Following the previous questions: What are the components in the water that
may also have a geochemical source (i.e. groundwater interacting with the
sediments and minerals)? Propose groundwater relevant chemical reactions that
could be responsible for the chemical contribution to the water compositions.
Please consider explanations for all the major cations and anions, and where
appropriate, other ions that you may deem important. Write the correctly
balanced chemical reactions for the processes that you consider. Hint: explore the
data by making bi-variate plots of relevant species (e.g. Na vs Cl, Ca vs HCO3, etc.).
(e) Does the water quality for each sample comply with the WHO drinking water
standards?
Groundwater Resource Investigation CVEN4503 Assignment 2
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Figure 1. Map of the locations of water quality samples from selected catchments across
Australia.
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Groundwater Resource Investigation CVEN4503 Assignment 2
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Groundwater Resource Investigation CVEN4503 Assignment 2
Page 5 of 5
Figure 2. Piper diagram template. Note template also available on Moodle.