Piper Diagram

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Piper Diagram

A Piper diagram is a graphical representation of the chemistry of water samples in the form of the trilinear diagram. The relative abundance of common ions (cations and anions) are shown by separate ternary plots. The Piper diagram is comprised of three components as shown in the image below:

1) The lower left ternary plot representing cations (magnesium, sodium plus potassium, and calcium);

2) The lower right ternary plot representing anions (carbonate plus bicarbonate, sulfate, and chloride); and

3) A middle diamond plot, which is a matrix transformation of the two ternary diagrams.

The plots display the relative concentrations of each sample (i.e., sum of cations = 100 and sum of anions = 100). The data points in the center diamond are located by extending the points in the lower triangles to the point of intersection in the center plot.  The axis values at the top and bottom of the center diamond are 100; the axis values on the left and right side of the center plot are 0.

 

50174-piper_diagram

 

 

The Piper diagram is based on parameter concentrations expressed in equivalents per volume. The Equivalent Weight field in the constituents table is used to convert between the measured mass concentration and the concentration in equivalents or milliequivalents (meq) per liter. Equivalent weight is the mass per charge. Charge concentration is the mass concentration of an ion in water divided by the equivalent weight. The equivalent weight field should be entered as positive for cations and negative for anions. If the concentration values are entered as milligrams per liter or parts per million then the following values in the equivalent weight field will convert the concentrations to meq per liter.

 

Cation / Anion

Equivalent Weight

Na

22.9898

K

39.098

Ca

20.04

Mg

12.1525

Fe (II)

27.97

Fe (III)

18.65

Mn

27.469

CI

-35.453

HCO3

-61.016

SO4

-48.03

CO3

-30.004

NO3

-62.04

NH4

-18.039

PO4

-31.66

 

In each sample, the three cation/anion results (in milliequivalents) are divided by the sum of the three values to produce a percent of total cations. For example, if Ca= 0.80 meq, Mg =0.26 meq, and Na+K = 0.89 meq, then %Ca = 41, %Mg = 13, and %[Na+K] = 46.

 

Create Piper Diagram

 

View a training video on creating Piper diagrams in EnviroInsite here.

 

Open the Tasks Pane on the right-hand side of the EnviroInsite interface, select Create Window and then select Piper Diagram. Piper diagrams can also be created by selecting Window> New> Piper Diagram from a plan view map. A new view window is generated and the Piper Diagram dialog box opens. Modify the diagram properties on the Query tab, Select Ions tab, Options tab, Labels tab, TDS Circles tab, and EQuIS Query tab as desired. The most commonly selected anions are (1) Cl, (2) HCO3 + CO3 and (3) SO4 and selected cations are (1) Na + K, (2) Ca and (3) Mg. Click the OK button to save changes.

 

One of the unique features of Piper diagrams generated in EnviroInsite is the ability to post the well and screen label. Individual well labels may be turned on or off by deselecting the check box associated with each label from the tree control menu.

 

For EQuIS EnviroInsite clients, if the diagrams are not displaying as expected, check to see if DT_FACILITY.ELEV_UNIT is populated. If it is not, consider populating this information. Although it is not a required field for this report, it is recommended.