What is included as a minimum requirement in the pre-mitigation building investigation?

A minimum requirement in the pre-mitigation building investigation is to include a sketch of the building foundation indicating system location. This is crucial because understanding the layout of the foundation helps identify potential entry points for radon and assesses how radon could penetrate into the building. It also aids in determining the effectiveness of the mitigation strategy being employed. The sketch serves as a reference for both the mitigation specialist and the homeowner, illustrating where radon mitigation systems will be installed.

The other options, while they may provide valuable information about the building and its environment, do not constitute minimum requirements. A report on air quality levels may be useful for understanding existing radon levels but is not fundamental to the structural assessment necessary for developing a mitigation plan. Similarly, conducting a visual inspection of the neighborhood provides context about surrounding properties but does not directly inform mitigation efforts pertaining to the specific building. An estimate of costs for mitigation efforts is important for budgeting but is not a prerequisite in the assessment of the building's structural characteristics and radon pathways.