When I design a system, I don’t include risers on top of my tanks. What’s a riser? The green things in the image above. You can see the concrete tanks are buried, and where the surface of the ground will be. In operation, what this winds up looking like it this:
This one isn’t so bad, but you can clearly see accessing anything in this tank will be difficult without getting in there. Here is another example:
You can see how hard it is to access anything besides this filter. Filters are a bad idea too, but that’s another story.
How I normally design a wastewater tank is for the lid of the tank to be flush with the surface, like this:
The concrete slab is shown transparent, but you get the idea. Lid of the tank is flush with the surface. Not that you want to, but you can lay on your belly and access things. Pumps, junction boxes, strainers, valves, etc. You want to do everything you can to avoid getting in this tank, doing what you can in the design phase to prevent the need for entry is good. Of course it’s a wastewater tank and no one wants to go in there. But the other issue is a tank like this is a permit required confined space. You can die in there (CO2 asphyxiation), or drown… So having everything easily accessible from above is important.
Here is a complicated explanation of permit required confined spaces, and here is a simple one:
Breweries are full of permit required confined spaces (brew house, fermenters, brite tanks, wastewater tanks, etc.). Learn what you can about this important topic, choice ignorance will come back to bite you.