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 11-5-2-280.4 - GUIDELINES FOR THE PERMANENT CLOSURE OF PETROLEUM UNDERGROUND STORAGE TANK SYSTEMS
Section 11-5-2-280.4-5 - SAMPLING LOCATIONS FOR DISPENSER ISLANDS & PIPING
Section 11-5-2-280.4-5.3 - Piping Trenches
Section 11-5-2-280.4-5.3.3 - Closure in Place of Piping
Since potentially contaminated soils cannot be seen during closure in place activities as when excavating, the sampling requirements for closure in place are more conservative. All sampling schemes must follow the exact guidelines given in this document unless special circumstances do not allow such. Any alternative sampling plan must be submitted to the UST Branch for approval.
When piping is to be closed in place, sampling along the piping trench is not required if the location of the dispenser island sample is within 25 feet of the nearest tank excavation sample. The 25 foot distance is measured in a straight line as depicted in Figure 12.
If you are conducting a piping closure in place but the tanks are remaining active, the 25 foot distance referenced above has no significance. Under these circumstances, a sample must be collected from the dispenser island and from the end of the piping trench where it enters the tank bed. If there is more than 25 feet of piping trench located between these two sampling points, additional samples must be collected such than no more than 25 feet exists between any two sample points.
If the distance between the dispenser island sample and the nearest tank bed sample is greater than 25 feet, soil samples must be collected along the piping trench such that no more than 25 feet of piping exists between any two sampling points as shown in Figure 13. This means that some excavation is required in order to locate the piping trench since sampling must occur underneath or immediately adjacent to the trench. All soil borings must extend to a depth of at least one foot below the bottom of the piping trench and into the native soil. Samples must be collected from each boring following the field screening practices as described in Section 4.4.4.
If "true" groundwater (refer to Section 3.2) is encountered during soil boring activities, groundwater samples must be collected from each boring that contains groundwater and each sample must be analyzed separately. Soil sampling must be conducted from those borings that do not have groundwater. In addition, regardless of whatever soil and/or groundwater sampling that is conducted, one soil sample must be collected from the boring that exhibited the highest level of petroleum contamination during the field screening process.
