>>12195721 (pb)
You could use an RV and it's drinking water tanks along with grey and sewage tanks to transport and deliver enough liquid explosive to do this damage. (actually enough to take out the block)
2 part liquid explosives are safe to transport before mixing and the components are available as not regulated as explosives.
If you located a vent or ground level elevator you could dump the tanks and let gravity fill the basement / bunker without ever needing to get into the building.