Any building or property within the LIZ (including those above a vapor source) requires an evaluation of the potential risks to human health. In some cases, it may not be possible to determine a final LIZ until the investigation is complete. The evaluation and screening process identified below should begin immediately for buildings within the preliminary or assumed LIZ once identified.
5.1 Identify properties, buildings, and utilities - step 3
All properties, buildings, utilities, and preferential pathways within the LIZ must be identified. The utilities consist of any conduits where a vapor source can enter, and the preferential pathways consist of any utility backfill that is more permeable than the surrounding materials that may alter the migration of the vapor source. Details on what information should be obtained is provided in Table 5-1. A building survey form is included as Attachment 1 in Appendix A.1 of Volume 5.
Table 5-1: Information on the Buildings, Properties, and Utilities Required
|
Building, Property, or Utility |
Information required |
|---|---|
|
Properties |
|
|
Buildings |
|
|
Utilities |
|
|
Backfill surrounding the Utilities |
|
5.2 Initiate screening process: step 4
The screening process is implemented by first evaluating if there is sufficient data to evaluate a building within the LIZ. To complete this evaluation, confirm that the following questions can be answered:
- What is the depth to groundwater?
- What is the depth of the building foundation below grade?
- What is the horizontal extent of and depth to the vapor source?
- What is the distance between the vapor source and the building?
- Where are conduits located in relation to the LIZ and the vapor source?
- Can the vapor source enter the conduit?
If the questions cannot be answered, additional data collection is warranted. If the questions can be answered, a person should then proceed to Step 5 and screen the building(s) using the appropriate criteria. Sampling methods are further described in Section 5.3 and Volume 2 – Investigation Methods for the Volatilization to the Indoor Air Pathway.
The amount of data required to complete the evaluation is provided in Attachment C.3 and additional on various sampling methods is provided in Volume 2 – Investigation Methods for the Volatilization to the Indoor Air Pathway.
Additional considerations
The VIAP can only pose an unacceptable risk if there is an occupied building present (see definitions and the differences identified in Section 1.4). Therefore, a person evaluating the risks from the VIAP should focus on any current, planned or potential future occupied buildings when evaluating the site. If there is a vacant parcel of land, it is assumed that an occupied building can be constructed on it in the future even if there are currently no plans for construction. See Attachment D.3 for when land and resource use restrictions may be needed.
Note: If a party is using the site-specific VIAC provided by EGLE: Under Sec. 20120b, alternate site specific evaluations that better reflect the best available information concerning the toxicity, exposure risk posed by the hazardous substance, or other factors that support an unacceptable risk will not occur may be proposed for review and approval to EGLE.
Vapor sources that will remain in the environment and that are deeper than the bottom of a future building are typically able to be evaluated. However, shallow vapor sources which are less than three (3) feet below the ground surface, are often difficult to assess with the anticipated variability in the data collected. In areas where a building is not present, but a shallow vapor source remains, a restricted closure or no-further action that relies on a land or use restriction may be appropriate.
5.3 Data collection and evaluation: step 5
If an occupied building or property is not able to be screened out in Section 5.2 or if there are any conduits that may directly transport a vapor source and vapors to a building, then representative soil gas and vapor data will need to be collected. The soil gas data collection should be based on where the vapor source is in relation to the building.
Additional information on data collection for the following scenarios is provided in Attachment C.3:
- Building over Vapor Source
- Vapor Source not in Contact with a Building
- Vapor Source in Contact with a Building
- Building adjacent to a Vapor Source
- Conduits
- Buildings are Not Currently Present
- Redefining the LIZ
5.4 Site management: step 6 (when warranted)
When warranted, most strategies and approaches are dependent upon site-specific factors and cannot universally be applied across the entire property. In several areas of the state, especially where groundwater is less than ten (10) feet below grade, the approach is very different than those where deeper vapor sources will remain. The approach will also be significantly different if there is a need to address conduits with a vapor source present. Furthermore, the need for land or resource use restrictions will be highly dependent on-site conditions, if a vapor source remains, and how and where representative soil gas samples are collected in relation to the vapor source.
Attachment D.3 can be used as a guide for the evaluation and when land or resource restrictions or an alternate evaluation is necessary. Detailed management strategies including the use of either a land and resource use restriction, when they may or may not be appropriate, response activity and more is further described in Volume 5 – Response Activity for the VIAP.