It's called a "bund". Tanks farms / storage tanks often have such a feature. If there is a spill or catastrophic leak, the wall will contain the fluid until it can be disposed of appropriately, instead of just running into the storm drains. Added to which, it makes for a good defensive position!I've pictured it here against another I made. You can see clearly how the spill has been contained.Both of these will complement this small processing plant. I need to add a few more pipes and I'm thinking of adding some hand railing at some future point. But it does make for interesting gaming areas.The large tank in the finished bunded area is a toilet systen ball. Check out B&Q for a few great shapes!Again, use of the Ainsty dished ends as well as oil storage tanks (in the bunded area) and small generator (red thing) are by them.