Will the tank be built to any particular code requirements? Since it is oily water and the volume is 10000 liters, you have to make sure it doesn't leak petroleum product into the ground or groundwater.
QA would be the same as any concrete structural system. Control the concrete, control the rebar placement, control the dimensions, make sure the waterproofing/leakproofing are intact, etc.
Concrete strength will depend on the design. Test the concrete for compliance. Do a leak test when the tank is built....not sure what your acceptance criteria will be, but you might check leak criteria under API code.