How are basements considered at Tier II?
If a basement exists, the site-specific depth to contaminated soil or groundwater should be calculated from the basement floor, not the ground surface. If you conduct Tier II calculations on a building with a basement you should consider the buried sections of walls that can transmit vapours to the interior. This can be done by considering the sum of the basement wall and floor area in contact with soil as the modified floor area and recalculate a new Building Volume / Area Ratio (Screen 8.4). When calculating the building volume, only the basement height should be used since complete mixing of basement air and first floor air is unlikely. Ensure that the Building Volume / Area figure is placed in the correct exposure box for your site (Residential or Commercial).
