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 11-5-2-280.1-6.7 - Continuity Testing
When conducting an evaluation of a cathodic protection system, it is normally necessary to establish that the cathodically protected components of a UST system are either electrically isolated or electrically continuous depending on the type of cathodic protection system. Ohmmeters (continuity testers) such as those utilized to test automotive wiring circuits are not acceptable for use on buried metallic structures and should never be used for testing continuity of UST system components. The "fixed cell-moving ground" method and the "point-to-point" method are the two commonly utilized ways to test continuity and are discussed in more detail below.
Fixed Cell - Moving Ground Method - The most commonly accepted method of conducting a continuity survey is referred to as fixed cell - moving ground. In this method, the reference electrode is placed at a location remote from any of the cathodically protected structures. Potentials of all the metallic structures present at the site are then measured without moving the reference electrode (refer to Appendix E for a more complete description). Because the conditions found at the reference electrode/electrolyte interface can change over a short period of time (causing the observed potential to change), it is important to conduct this type of testing as quickly as possible.
When determining whether electrical continuity or isolation is provided, the following guidelines are generally accepted for fixed cell - moving ground surveys:
> If two or more structures exhibit potentials that vary by 2 m V or less, the structures are considered to be electrically continuous.
>If two or more structures exhibit potentials that vary by 10 mV or greater, the structures are considered to be electrically isolated.
> If two or more structures exhibit potentials that vary by more than 2 mV but less than 10 mV, the result is inconclusive and further testing (point-to-point) is necessary.
Point-to-Point Method - An easier and usually more accurate way to test continuity is the "point-to-point" method. With this method, a reference electrode is not utilized. The two structures that are to be tested are simply touched with each lead of the voltmeter and the voltage difference (if any) is observed. For example, if you are trying to establish that electrical isolation exists between a tank and the fill riser associated with that tank, you would simply touch the fill riser with one of the voltmeter leads and the tank shell with the other voltmeter lead and observe the voltage difference.
When conducting point-to-point testing, any current that is flowing through the UST components can cause an inaccurate test result. Impressed current systems must be turned off.
When determining whether electrical continuity or isolation is provided, the following guidelines are generally accepted for point-to-point surveys:
>If the voltage difference observed between the two structures is 1 mV or less, the two structures are considered to be electrically continuous with each other.
> If the voltage difference observed between the two structures is 10 mV or greater, the two structures are considered to be electrically isolated from each other.
> If the voltage difference observed between the two structures is greater than 1 mV but less than 10 mV, the result is inconclusive and further testing beyond the scope of this document is necessary.
