1. pH It is defined as the negative common logarithm of the concentration of hydrogen ions [H + ] in moles/liter: pH = -log 10 [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.

2. 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.

3. Eh-pH predominance diagram for aqueous chromium at 25 °C (Cr tot = 1 µM).

4. 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. CriteriaValuesAuthority Total Dissolved Solids (TDS) 500 mg/l EPA 440/9-76-023 Sodium plus Potassium 200 mg/l EPA 440/9-76-023 Chloride250 mg/l EPA 440/9-76-023 Nitrate450 mg/l EPA 440/9-76-023 Total Hardness150 mg/l EPA 440/9-76-023 Specific Conductance 750 µmhos/cm or µS/cm U.S. Salinity Lab. Irrigation Recommendations

5. Alkalinity (AT) is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate.

6. Type of waters:Specific Conductance (µS/cm) Eh (millivolts) pH (pH units) rain water2 to 100+400 to +6004 - 7 freshwater lakes/streams 2 to 100+300 to +5006.5 - 8.5 ground water50 to 50,000-200 to +1006 - 8.5 brinesup to 500,000-300 to -600near neutral ocean water~ 50,000+300 to +5007.8 - 8.4 landfill leachate10,000variablenear neutral acid mine drainageup to 500,000+600 to +800below 5 wetlands / bogs50 to 50,000+100 to -100variable Typical ranges of values for some water field measurements. From: Sanders, L.L., 1998, A Manual of Field Hydrogeology: Prentice-Hall, NJ, 381p.