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 › Appendix 11-5-2-280.1-G

Current through June 25, 2024
STRUCTURE-TO-SOIL TEST PROCEDURE FOR IMPRESSED
							 CURRENT CATHODIC PROTECTION SYSTEMS
1. Inspect rectifier for proper operation and document
							 necessary information. This includes measurement of output voltage/amperage
							 with a multimeter (do not rely on rectifier gauges) and measurement of
							 individual anode circuits (if installation allows such). Record all necessary
							 information under Section XI and XII of MDEQ impressed current form.
2. Place voltmeter on 2 volt DC scale.
3. Connect voltmeter negative lead to reference
							 electrode.
4. Place reference electrode in clean soil directly
							 over the structure that is being tested. At least one measurement must be taken
							 for each tank - the preferred test point is usually the center of the tank.
							 Piping normally requires measurement at each end of the pipe (see Section
							 6.10.3 and 6.10.4 of MDEQ guidance document for further explanation).
* The reference electrode may not be placed on
							 concrete or other paving materials.
* Ensure that the reference electrode is placed
in
a vertical position (tip down).
* Ensure that the soil where the reference electrode
							 is placed is moist - add tap water if necessary.
* Ensure that the soil where the reference electrode
							 is placed is not contaminated with hydrocarbons.
* Ensure that the reference electrode window is not
							 exposed to direct sunlight.
5. Connect voltmeter positive lead to structure that
							 is to be tested.
* Ensure that good metal-to-metal contact is made
							 between the test lead clip/probe and the structure.
* Ensure that no corrosion exists where the test lead
							 makes contact with the structure.
* Ensure that your body does not come into contact
							 with the electrical connections.
* Ensure that test leads are not submerged in any
							 standing water.
* Ensure that test lead insulation is in good
							 condition.
6. Obtain voltage potential with the protective
							 current applied and record in the on column on the MDEQ impressed current
							 cathodic protection evaluation form.
7. Without moving reference electrode from the
							 position it was in during step 6 above, obtain voltage potential with the
							 protective current temporarily interrupted and record in the instant off column
							 on the MDEQ impressed current cathodic protection form.
* The instant off potential is the
2
nd value that is observed on a
							 digital voltmeter the instant the power is interrupted. The first number that
							 appears immediately after power interruption must be disregarded. After the
							 second number appears, a rapid decay (depolarization) of the structure will
							 normally occur.
* In order to obtain instant off potentials, a current
							 interrupter or a
2nd
person is necessary. If a current
							 interrupter is not available, have the second person throw the power switch at
							 the rectifier off for 3 seconds and then back on for 15 seconds. Repeat this
							 procedure until you are sure an accurate instant off reading has been obtained.
8. Conduct 100 mV polarization decay if you are unable
							 to obtain an instant off potential of -850 mV or more negative in step 7 above.
							 (Note: While not a requirement of this guidance document, consideration should
							 be given to adjusting the rectifier output until an instant off potential of
							 -850 mV is achieved or the maximum safe output is reached.) It is only
							 necessary to conduct 100 mV polarization where the lowest (most positive)
							 instant off potential is observed on the UST system.
* 100 mV of polarization is determined by leaving the
							 power interrupted on the structure until a change of at least 100 mV in the
							 structure-to-soil potential is observed. In calculating the 100 mV decay, the
							 instant off potential obtained in Step 7 above is utilized as the starting
							 point (e.g. if instant off = -800 mV, power must be left off until decayed to
							 -700 mV).
* Calculate voltage change by subtracting final (or
							 ending) voltage from the instant off voltage and record these values in the
							 appropriate columns on the MDEQ impressed current cathodic protection
							 evaluation form.
Data Interpretation
(for a more complete
							 discussion refer to Appendix D of this guidance document)
* If the instant off potential is -850 mV or more
							 negative, the 850 off criterion is satisfied and it is judged that adequate
							 cathodic protection has been provided.
* If the instant off potential is more positive than
							 -850 mV, the tank may or may not be adequately protected and a 100 mV
							 polarization test is necessary.
* If the structure exhibits more than 100 mV
							 polarization, the 100 mV polarization criterion is met and it is judged that
							 adequate cathodic protection has been provided.
* If you are unable to meet either the 850 instant off
							 or the 100 mV polarization criteria, it is judged that adequate cathodic
							 protection has not been provided and repairs/modification are indicated.
							 Alternatively, a person qualified as a corrosion expert could evaluate/conduct
							 the survey and determine that cathodic protection is adequate based on their
							 interpretation.