1.1 Introduction and overview
This section should briefly describe the submittal.
1.2 Site setting and description of structure(s)
This section should describe the site setting including the location, current and planned use, and current and future structures with proposed vapor mitigation. Include a description of the height, size, and general construction characteristics. For an existing building, a building survey should have been conducted. See Attachment 1 for an example of a building survey. The results of a building survey should identify specific building characteristics, features, and configurations that may affect the design, installation, and effectiveness of the AVMS. If the planned building is not yet constructed, this information should be evaluated from design plans, and discussions with the site development team.
Note: Many buildings (particularly larger commercial/industrial buildings) have multiple foundation types due to building additions over time; slab and sub-slab conditions often vary between building areas and foundation walls or changes in floor elevation may prevent airflow from one slab area to another. Other foundation features such as elevators, pits, sumps, floor drains, utilities, utility tunnels, and other structures located below the slab or floor level should be considered for their potential effect on the mitigation system design.
Key supporting information
- Topographic Site Location Map (from USGS or site plans as available)
- General Site Feature Map that includes existing and proposed structures to scale with any property lines, right-of-way (ROW), and major utilities.
- Figure(s) in plan view of the structure to be mitigated, including the room divisions, footings known and estimated, and other key features such as the location of pits, sumps, vents, basements
- Cross-sectional view figures and drawings may be helpful for depicting other key features relative to the proposed mitigation system.
- Appendix with Building survey that includes a photo log (see Attachment 1).
1.3 Site history
This section should describe the current and past site use, operational history as well as the type of hazardous or regulated substances currently and previously used at the property.
Note: Describing the site use and history aids in identifying the presence or likely presence of hazardous substances or petroleum products in, on, or at a property due to any release to the environment or conditions indicative of a release to the environment and may provide some general information on the concentrations of hazardous substances that could be expected to be encountered.
Key supporting information
- Table (optional depending on the complexity of the site) that provides a list of known activities or operational history that may have led to a release of hazardous substances into the environment.
- Figure that identifies the locations of current and past activities and operations that may have or are known to have led to a release of a hazardous substance into the environment. These areas are typically referred to as recognized environmental conditions (RECs).
1.4 Geology/hydrogeology
This section should describe the site geology and hydrogeology. Information should include a description of soil type(s) and depth to groundwater. Supporting data, including boring logs, should be provided. Soils may be described using either the USCS, USDA, or other soil classification system such as AASHTO/MDOT, but the classification system should be identified. The potential for known or estimated seasonal variations in groundwater should be described. The lithology and presence or absence of groundwater, including seasonal groundwater, should be evaluated to at least five (5') feet below the lowest part of the structure. The lowest part of the structure includes the maximum depth of any footings, sumps, drains, pits, and elevator shafts, etc. The potential for known or estimated seasonal variations in groundwater should be described where the groundwater needs to be evaluated.
A cross-section of the structure that is being mitigated should be provided with the site geology and hydrogeology information shown. Structures that have various footing depths, such as basements, elevators, tunnels, or pits and that are larger than 5,000 square feet may require more than one cross-section to clearly depict these features to aid in the review.
Soil that will be brought on-site beneath the structure, or as a component of the mitigation system, should also be identified and described including information on the type, characteristics, and where it will be placed.
Note: Engineered and construction soils should be described based on the available information and should include a description of the subgrade, sub-base, and base-course soils to a depth of at least 12” below the lowest part of the structure.
Key supporting information
- Figure identifying boring locations used to classify the geological and hydrogeological information.
- Boring logs.
- Cross-section(s) depicting the current or proposed structure, below grade site features (foundations, utilities, etc.) and geological and hydrogeological information.
- Tables, as necessary, identifying any monitoring wells installed, depth of the wells, and the elevation of the groundwater.
1.5 Detailed building information
1.5.1 Below grade building features and foundations
This section should describe the foundation type (i.e., footings, pier, columns, cast pilings, etc.) and building portions that are below grade (basements, crawlspaces, elevator sumps, pits, utilities, tunnels, etc.) that are in contact with the soil. If there are any foundations that are unknown, they should be discussed here and addressed in Section 2.2.
Key supporting information
- All below grade building features and foundations should be identified in plan view.
- Subsurface features should be depicted on the cross sections developed in Section 1.4.
1.5.2 Heating, ventilation, and air conditioning (HVAC)
This section should describe the current or proposed HVAC system, including any of the location of air intakes and exhaust that are required for its operation.
Key supporting information
- Figure(s) – should depict the location of any air intakes, vents, and discharge points including components on the roof or side of the structure.
1.5.3 Floor slab and condition
For an existing building, this section should describe and document the current condition of the floor. It should identify cracks with a width greater than 1/2-inch that may impact the operation of the AVMS, areas where concrete is not present, or areas that the concrete needs repair or replacement. For new or proposed floor slabs, this section only needs to identify the type and thickness of the floors that will be installed as part of the development.
Key supporting information
- Figure(s) – identify the location, type and condition of the floor slabs including cracks with a width greater than 1/2-inch, areas that concrete is not present, or areas that the concrete is likely to need repair or replacement based on the information collected during the building survey.
- Appendix – if applicable, with building survey and photolog with representative photos, especially in areas that repairs to the slab or building may be warranted.
1.5.4 Utility penetrations and man-made preferential pathways
This section should describe and document the location of penetrations and sumps in which soil gas may enter and directly vent into the structure and utilities that directly come into contact with a vapor source. This evaluation is limited to those utilities that are in direct contact with a vapor source. For new construction, this section should identify any penetrations that are known or expected to occur.
Key supporting information
- Figure(s) and cross-section(s) – identify the location of penetrations, sumps, and preferential pathways.
1.5.5 Historic buildings (if applicable)
This section should describe any limitations to the system design or layout that may need to be considered and are imposed on the structure due to a historic designation.
1.6 Source areas and contaminant
1.6.1 Applicable criterion
This section should identify the applicable criteria used to demonstrate that the response activity or corrective action is necessary to protect the public health, safety, welfare, or the environment, and identify the assumptions used in their development.
- Generic Criteria or Risked Based Screening Levels (RBSLs): If the use of the generic criteria is appropriate, supporting information should be described and presented.
- Site Specific Volatilization to Indoor Air Criteria (SSVIAC) or Site-Specific Target Levels (SSTLs): When developed for the site or if VIAP Screening Levels (SLs) are used, the supporting documentation should be provided demonstrating the criteria are appropriate for use.
Key supporting information
- Table identifying the criteria used.
- Appendix providing supporting documentation for use of the VIAP Criteria, including any previous approvals and the evaluation for the use of the site-specific criteria.
1.6.2 Vapor source
This section should identify the concentrations of the volatile regulated or hazardous substances or regulated substances that pose an unacceptable risk to the structure(s). The text should include a discussion of how the sample data aligns with the site history (Section 1.3). Representative soil, groundwater, and soil gas concentrations include any samples collected above and near the vapor source where vapors may enter the structure. Soil gas and vapor samples should be collected when site conditions allow, to confirm that mitigation is necessary.
Data must be provided that supports the design of the AVMS, including a demonstration that mitigation is warranted. Sample data must also support delineation of soil gas impacts in any areas where an AVMS is not proposed (i.e., outside of the planned mitigation footprint).
Key supporting information
- Tables that provide representative soil, groundwater, and vapor data compared to the applicable criteria.
- Figure(s) that identifies where the data was collected, including the sampled media and location of samples depicted on a scaled figure(s) relative to the structure(s).
- Figure(s) depicting detections above applicable criteria relative to the structure(s).
- Appendix should include all analytical data sheets and field forms obtained during their collection.
- Cross-section(s) should include below grade features and show the chemical data that exceeds the appropriate criteria.
1.7 Man-made preferential pathway evaluation (if applicable)
This section should include an analysis of Section 1.5.4 and if there is a need to design or propose a mitigation strategy for man-made preferential pathways or other preferential pathways that may not be addressed through the operation of the AVMS.
Key supporting information (as warranted)
- Text should reference the Figures identified in Section 1.6.2, as necessary.