Who does your municipality require to sign off on it? A Civil Engineer? Architect? Landscape Architect? Different municipalities have different reporting requirements for handling water runoff. What testing do they require for that specific report? A soil permeability report and a topographical map showing the natural flow is usually the minimum. That allows the City Engineer to review the proposed addition of impermeable structures on the land and the affect it will have on the adjacent properties.

You will need multiple disciplines involved for all of the approvals that you will need. Septic is different than drainage, and that is different than a soils study for foundation purposes. If you're not working with an architect familiar with all of the red tape, you need to hurry up and find one.

A civil engineer.