Stiff Diagram

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Stiff Diagram

Stiff diagrams are graphical presentations of the cation and anion content of water presented in milliequivalents per liter. More information on the application of Stiff diagrams can be found in the USGS Water Supply Paper 2254, Study and Interpretation of the Chemical Characteristics of Water available at http://pubs.usgs.gov/wsp/wsp2254/.

 

50131-stiff_diagram 50131-stiff_diagram_mean

 

By convention, cations are plotted on the left side of the Stiff Diagram and anions on the right. The Equivalent Weight field in the constituents table is used to convert between the measured mass concentration and the concentration in equivalents or milliequivalents 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

 

 

Click here to view a training video on generation of stiff diagrams in EnviroInsite here.

 

Stiff diagrams may be generated as either georeferenced plots (small diagrams with a leader to the well location) or as full page Stiff diagrams.  In the full page Stiff diagram plot, the diagrams are lined up vertically along the centerline of the page. To create georeferenced Stiff diagrams, select Plot> 2D data> Stiff Diagrams. The Stiff Diagram dialog box opens. Modify the properties of the Stiff diagram plot on the Query tab, Select Ions tab, Options tab, Labels tab, and EQuIS Query tab as desired. Click the OK button to save changes.

 

Query Tab

 

50131-query_stiff_diagram

 

 

Select Ions Tab

 

The anions and cations to be plotted in the Stiff diagram are selected on the Select Ions tab of the Stiff Diagram dialog box. Each line on the Stiff diagram can represent a single ion or the sum of two ions. Leave the second ion blank to plot a single ion or leave both ions blank to not plot a particular line.

 

50131-select_ions_stiff_diagram

 

 

Options Tab

 

In addition to the query options, the Stiff diagram dialog box offers the following options to customize the appearance of the plot.

 

50131-options_stiff_diagram

 

 

Labels Tab

 

50131-labels_stiff_diagram