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### Relation of electrochemical potentials and iron content to 
ground-water flow patterns

#### Professional Paper 498-C

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- Document: **Report**                                 (4.44 
  MB pdf)
- Plates:
- **Plate 1**                                
    (pdf)
- **Plate 2**                                
    (pdf)
- **Plate 3**                                
    (pdf)
- Paper 
  version: **USGS Store**
- Download citation as:  RIS

#### Abstract

This study was undertaken to develop means of measuring oxidation potentials 
in aquifer systems and to use the measured values in interpreting the behavior 
of iron in ground water. Anne Arundel County, Md., was selected as the area of 
study because of the wide range of concentration of iron-nearly zero to about 35 
ppm-in the ground water and the rather complete information on the geology and 
hydrology. The regional geology consists of coastal plain sediments ranging in 
age from Early Cretaceous through the Recent. Most of the pH and 
oxidation-potential measurements were made in nonmarine Cretaceous deposits, 
only a few in the marine Eocene. Iron-bearing minerals in the area are primarily 
hematite or limonite and glauconite with a small amount of pyrite.

Equipment was developed that permits the measurement of oxidation potentials 
by use of saturated calomel and platinum electrodes in ground-water samples 
uncontaminated by oxygen of the atmosphere. Measured Eh values range from about 
+700 mv to -40 mv. Approximately 2 to 3 hours are required to measure a stable 
or nearly stable oxidation potential.

The mineralogy and organic content of the deposits and the ground-water flow 
pattern are the primary controls on the oxidation potential and pH of the water. 
A correlation exists between the oxidation potential and the concentration of 
iron in ground water; the higher concentrations occur in waters with the lowest 
values of Eh. The concentration of iron in the water tested shows little 
correlation with the pH of the water. The highest oxidation potentials were 
measured in water produced from shallow wells and those wells in recharge areas. 
The lowest potentials were measured farthest downgradient in water associated 
with gray and green sediments. The Eh values measured in the field are between 
values predicted from the solubility of Fe(OH)2(c) and values 
predicted from the solubility of hematite.

#### Study Area



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