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12 -foot -diameter tanks], or 18 inches of backfill [36 inches for 12 -foot -diameter tanks] plus 6 inches of reinforced concrete or 9 inches of asphalt. (See FIGURE 5-1.) In a wet condition, sufficient overburden and/or an appropriate anchoring system must be present to offset buoyancy of the tank. FIGURE 5-1 5.2.3.2. Tanks not subjected to traffic loads must have a cover depth of at least 24 inches of backfill [48 inches for 12 -foot - diameter tanks], or 12 inches of backfill [36 inches for 12 -foot - diameter tanks] plus 4 inches of reinforced concrete or 6 inches of asphalt. (See FIGURE 5-2.) In a wet condition, sufficient overburden and/or an appropriate anchoring system must be present to offset buoyancy of the tank. FIGURE 5-2 11 C] ®WARNING In a nontraffic installation, ensure that the areas above the tanks are not subjected to traffic or other types of loads, which could cause tank damage and result in death or serious injury. 5.2.3.3. The maximum burial depth is 7 feet of cover over the top of the tank. Deviation from this may be permissible with prior written authorization from Xerxes. Call your Xerxes representa- tive for a special quotation prior to tank purchase if the burial depth is to be greater than 7 feet. 5.2.3.4. Asphalt and concrete pads must extend a minimum of 12 inches beyond the tank in all directions. 5.2.3.5. If there is an unattached manway riser, it must not transmit load from the concrete slab to the tank. A minimum space of 6 inches must exist between the bottom of the riser and the top of the tank. 5.2.3.6. Traffic loads from the top slab must not be transmitted to an attached sump or riser. A minimum space of 3 inches must exist between the riser or sump and the slab. 5.3. TANK SPACING 5.3.1. GENERAL 5.3.1.1. The following are minimum spacings and must be increased as needed to accommodate deadmen or anchor slabs. (See SECTION 6.) 5.3.1.2. Always provide sufficient clearance to allow the deadmen to be set outside of the tank "shadow." (See FIGURE 5-3.) FIGURE 5-3 5.3.2. STABLE IN SITU (NATIVE) SOIL CONDITIONS 5.3.2.1. Where shoring is not required to maintain a vertical wall from top to bottom of the excavation, and where the soil is stable, the minimum spacing between the sidewall or endcap of the tank and the side of the excavation must be 18 inches [24 inches for 12 -foot -diameter tanks]. 5.3.2.2. If more than one tank is to be installed in the same hole, allow for at least 18 inches between the tanks. (See FIGURE 5-4.)