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 11-5-2-280.1-6.10 - Cathodic Protection Test Locations
Section 11-5-2-280.1-6.10.3 - Tanks Protected by Impressed Current
With impressed current cathodic protection systems, tank potentials are required to be measured with the reference electrode placed locally. Where the location of the anodes is known and they are relatively evenly distributed about the tank bed, the appropriate location to place the reference electrode would be in the soil at the middle of the tank (See Figure 9). However, if access to the soil is not available at the middle of the tank, the reference electrode may be placed in the soil at any point along the centerline of the tank similar to that described in Section 6.10.1.
As with the evaluation of any cathodic protection system, the location of the anodes in relation to reference electrode placement can be of critical importance. When selecting the appropriate local placement, it is necessary to place the reference electrode at the point over the structure that is the most distant from any active anode due to the effects of attenuation. Attenuation of the cathodic protection current may occur whereby effective protection is not achieved at some point along a UST system. For instance, if all of the active anodes are along one side of a tank bed, current distribution and attenuation may prevent sufficient protective current from reaching the side of the tanks away from the anodes. The preferred placement of the reference electrode would be along the centerline of the tanks at the end opposite to that where the anodes are installed (See Figure 10).
If it is not known where the anodes are installed, at least one measurement is required along the centerline of the tank. Testing should be conducted at as many locations along the centerline of the tank as are available. If soil access is available at each end of the tank and in the middle, all three structure-to-soil potentials should be recorded. If any one of the measured potentials does not meet one of the acceptable criteria, the structure should be failed.
In addition, if it is possible to measure the individual circuits in an impressed current system, a determination can be made as to which anodes are functional and how the current is distributed throughout the groundbed. How the current is distributed should be considered when choosing reference electrode placement when conducting a structure-to-soil potential survey. If for instance it is known that the majority of the rectifier output current is directed to only those anodes along one end of a tank bed, the reference electrode should be placed at the opposite end of the tank bed.
