Once the delineation of the vapor source is complete, a 100-foot LIZ can be applied from the edge of the delineated vapor source. The LIZ is used to evaluate whether a building or a property is close enough to a vapor source to be considered a potential risk to the VIAP and require further evaluation. The LIZ includes the extent of the soil, groundwater, and/or NAPL as well as the screening distances beyond the delineated extent of the vapor source.
A 100-foot LIZ are measured from the outermost edge of the vapor source. Given the nature of environmental investigations, the exact location of the outmost edge is unknown, so this will require professional judgement. There are two ways that this can be accomplished: 1) start the LIZ from the soil or groundwater sampling location that are below SSVIAC or screening levels (most conservative); or 2) Interpolate the extent between sampling locations. As with all risk-based decision making as the potential for exposure to occur increases, so does the precision in the data collection.
As the LIZ is the theoretical maximum distance the vapor can migrate for screening, a person may wish to reduce the LIZ distance. In lieu of establishing a LIZ from the extent of the vapor source, a soil gas or vapor investigation may be conducted to delineate the extent of soil vapor above SSVIAC or screening levels.
Note: EGLE recommends that where possible, sufficient delineation of the extent of soil gas exceeding SSVIAC or screening levels is completed instead of using the LIZ.
Note: The LIZ cannot be less than the extent of the vapor source which is defined by an exceedance of applicable unrestricted residential VIAC. If an evaluation is made in accordance with Rule 299.14(5) or Rule 299.24(5) using more representative data such as soil gas, the soil gas data can be used to show compliance with the VIAC. In other words, there is no longer an exceedance in soil or groundwater, and does not represent a vapor source.