We were contracted to seal a large warehouse floor for life longevity. Concrete, like our skin, has pores. When it is power troweled, those pores are generally closed. Some materials (oils, dirts, greases, chemicals) can penetrate those over time, and will stain or seep into a porous concrete.
Environmental safety is a big reason why Millennium does the work we do. Here on the Gulf Coast, our water tables are very close the surface. When concrete, a porous material, is set below the water tables, passage of fluids like water, or anything less viscous, can certainly happen.
Installation of a new pump and motor typically also requires filling a void caused to perfectly align pump flanges to avoid pipe stress. The void created below a machined baseplate or skid should ideally be filled with a material that is multipurpose- example; a resinous grout.