When a boulder is encountered at the tank elevation, which sequence of actions is recommended?

• A. Remove the boulder, then backfill the void with compacted granular fill
• B. Remove the boulder only
• C. Pave over the boulder
• D. Move the tank to another location

Answer: (A)

When installing a septic tank, the bed beneath the tank must be solid and level to provide uniform support. If a boulder sits at the tank elevation, the correct sequence is to remove the obstruction and then backfill the resulting void with compacted granular fill. Removing the rock eliminates a hard, concentrated load point that could crack or misalign the tank. After the rock is out, filling the space with compacted granular material restores a stable, even bearing surface and lets you compact in layers to the required density, reducing settlement and maintaining level support around the tank. Paving over the boulder wouldn’t give the needed internal bedding or uniform support, and moving the tank elsewhere isn’t necessary when the base can be properly prepared on site.