pH
It is defined as the negative
common logarithm of the
concentration of hydrogen ions
[H+] in moles/liter:
pH = -log10 [H+].
The concentration of hydrogen
ions is commonly expressed in
terms of the pH scale. Low pH
corresponds to high hydrogen
ion concentration and vice versa.
a Pourbaix diagram, also known
as a potential/pH diagram or
Eh/pH diagram. The diagrams
are named after Marcel Pourbaix
(1904–1998), the Russian-born
chemist who invented them.
In sedimentary environments the
concept of geochemical facies is
best illustrated on an Eh-pH
diagram, a diagram delineating
the stability field of certain
minerals in terms of the proton
concentration (pH) and electron
concentration (Eh).
Eh and REDOX: the ability of an
environment to supply electrons
to an oxidizing agent, or to take
up electrons from a reducing
agent.
Eh-pH predominance diagram for aqueous
chromium at 25 °C (Crtot = 1 µM).
Specific conductance (SpC) is a measure of the
concentration of soluble salts in solution.
Conductance is also a readily available field test which
enables a worker to compare a new sample with previously
analyzed samples quickly and easily.
Irrigation Recommendations
Criteria
Values
Authority
Total Dissolved
Solids (TDS)
500 mg/l
EPA 440/9-76-023
Sodium plus
Potassium
200 mg/l
EPA 440/9-76-023
Chloride
250 mg/l
EPA 440/9-76-023
Nitrate
450 mg/l
EPA 440/9-76-023
Total Hardness
150 mg/l
EPA 440/9-76-023
Specific
Conductance
750 µmhos/cm
or µS/cm
U.S. Salinity Lab.
Alkalinity (AT) is a measure of the ability of a solution to
neutralize acids to the equivalence point of carbonate
or bicarbonate.
Typical ranges of values for some water field measurements.
From: Sanders, L.L., 1998, A Manual of Field Hydrogeology: Prentice-Hall, NJ, 381p.
Type of waters:
rain water
freshwater
lakes/streams
ground water
brines
ocean water
landfill leachate
acid mine drainage
wetlands / bogs
Specific
Conductance
(µS/cm)
2 to 100
Eh
(millivolts)
pH
(pH units)
+400 to +600
4-7
2 to 100
+300 to +500
6.5 - 8.5
50 to 50,000
up to 500,000
~ 50,000
10,000
up to 500,000
50 to 50,000
-200 to +100
-300 to -600
+300 to +500
variable
+600 to +800
+100 to -100
6 - 8.5
near neutral
7.8 - 8.4
near neutral
below 5
variable