Mississippi Administrative Code › Title 11 - Mississippi Department of Environmental Quality › Part 5 - Underground Storage Tank Regulations › Chapter 2 - Mississippi Commission on Environmental Quality Underground Storage Tanks Regulations Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks (UST) (Adopted March 22, 1989; Amended August 25, 2011, Last Amended August 23, 2018) › Appendix 11-5-2-280.1 - GUIDELINES FOR THE EVALUATION OF UNDERGROUND STORAGE TANK CATHODIC PROTECTION SYSTEMS › Section 11-5-2-280.1-6 - CATHODIC PROTECTION TESTING › Section 11-5-2-280.1-6.1 - Equipment › Section 11-5-2-280.1-6.1.2 - Reference Electrode

Current through June 25, 2024
A standard copper/copper sulfate reference electrode
						  (also known as a half cell or reference cell) must be utilized in order to
						  obtain structure-to-soil potentials. The reference electrode must be maintained
						  in good working condition and must be placed in the soil in a vertical position
						  when conducting a test.
On those sti-Ps tanks that have a PP4 test station, a
						  reference electrode is permanently buried in the tank pit. Since it is
						  generally not possible to determine where the permanent reference electrode was
						  installed on these types of systems, it is also necessary to conduct
						  structure-to-soil potential measurements in the conventional manner (i.e. with
						  a portable reference electrode in the soil directly over the tank and at a
						  remote placement). A tank may not be passed on the basis of a structure-to-soil
						  potential obtained with a PP4 test station. Both the local and the remote
						  potential obtained in the conventional manner must indicate that adequate
						  cathodic protection has been provided regardless of what the PP4 test station
						  indicates.
Maintenance of the reference electrode is important for
						  accurate results and includes:
a. The
						copper-sulfate solution inside the reference electrode should be clear. If the
						solution appears cloudy, this may indicate that the solution has become
						contaminated and the reference electrode should be compared with the known
						standard as described in paragraph e below. Should it be necessary to replace
						the solution, only distilled water and new copper-sulfate crystals should be
						used. Excess copper-sulfate crystals must be present in order to assure a
						saturated solution. Under average conditions, it is usually a good idea to
						empty and replace the solution every 2 or 3 months.
b. The porous ceramic tip must be maintained
						moist at all times. If the tip is allowed to dry out, it may lose its porosity
						and a good low resistivity contact with the soil will not be possible. Periodic
						replacement of the tip may be necessary.
c. The copper rod inside the reference
						electrode should periodically be cleaned with non-metallic sandpaper. Do not
						use black metal oxide sandpaper, steel wool or any other metallic abrasive as
						this can cause the copper rod to become contaminated. If the copper rod becomes
						contaminated, it is best to replace the reference electrode.
d. The copper-sulfate solution must be free
						of contamination or errors will be introduced in the readings you observe. If
						the reference electrode is submerged in water or placed in moist soils that are
						contaminated, it is likely that the solution will become
						contaminated.
e. The reference
						electrode that is used in the field must be periodically calibrated. How often
						the reference electrode needs to be calibrated depends upon several different
						factors. Among the more important factors that should be considered are the
						frequency of use and the exposure of the reference electrode to contaminants.
						As a general rule, calibration should be checked once every week if the
						reference electrode is used daily. If the reference electrode is only
						periodically used, calibration should be checked prior to each use.
Calibration of the reference electrode is accomplished
						  by comparing it with another reference electrode that has never been used. The
						  unused reference electrode that is to act as the calibration standard should be
						  properly set up (ready for use) and must not have ever been used in the field
						  so that no chance of contamination exists.
To calibrate the field electrode:
1. Place the voltmeter on the 2 volt DC scale
						(or lower) and connect the leads to the reference electrodes as shown in the
						illustration below.
2. Place both
						the field electrode and the standard electrode in a shallow nonmetallic
						container that has one to two inches of tap water in the bottom of it. Do not
						use distilled water. The reference electrodes must be placed vertically in the
						container with the ceramic tip of each submerged in the water.
3. Observe the potential measurement
						displayed on the voltmeter. If more than 10 mV potential exists between the two
						reference electrodes, the field reference electrode should be properly cleaned
						and refilled with new solution until the potential difference is 10 mV or less.
						If you are unable to achieve a 10 mV or less potential difference after
						cleaning/reconditioning, the field electrode must be replaced.
4. In order to lessen the chance of cross
						contaminating the calibration electrode, you should leave the calibration
						electrode in the water for the shortest time necessary to complete the test.
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