1.1 Introduction and overview
This section should briefly describe the purpose of this document.
1.2 Site setting and description of structures
This section should describe the site setting including the location, use, and current structures with a PVMS. This section should also include a description of the height, size, and general construction characteristics of the structure.
The results of a building survey should identify specific building characteristics, features, and configurations that affect the design and effectiveness of the PVMS. See Appendix 1 of Addendum A for an example of a building survey that should be performed immediately after the installation of the PVMS.
Note: Many buildings (particularly larger commercial/industrial buildings) have multiple foundation types and locations due to building additions over time; slab and sub-slab conditions often vary between building areas, and foundation walls or changes in floor elevation which 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 effect on mitigation designs.
Key supporting information
- Topographic Site Location Map (from USGS or site plans as available).
- General Site Feature Map that includes structures to scale with any property lines, right-of-way (ROW), and major utilities.
- Figure(s) in the plan view of the structure to be mitigated and that identifies 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 for depicting other key features relative to the PVMS.
- Appendix with building survey that includes a photo log (see Appendix 1 of Addendum A).
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 or regulated substances 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 historical operations that may have led to a release of hazardous or regulated substances into the environment.
- Figure that identifies the locations of current and historical operations that may have or are known to have led to a release of a hazardous or regulated substance into the environment. These areas are typically referred to as RECs.
1.4 Geology/hydrogeology
This section should describe the site geology and hydrogeology information. Information should include a description of soil types 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; regardless, 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.
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 those that are larger than 5,000 square feet, may require more than one cross-section clearly depicting 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 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 that may impact the function of the PVMS, they should be identified here and addressed in Section 2.2.
Key supporting information
- All below grade building features and foundations should be identified in the 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 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
This section should describe and document the current condition of the floor.
Key supporting information
- Figure(s) that identify the location, type, and condition of the floor slabs.
- Appendix with building survey and photolog with representative photos.
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.
Key supporting information
- Figure(s) and cross-sections should 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 are imposed on the structure due to a historic designation.
1.6 Source areas and contamination
1.6.1 Applicable criterion
This section should identify the VIAP screening levels and/or criteria used to demonstrate that the response activity is necessary to protect the public health, safety, or welfare, or the environment, and identify the assumptions used in their development, the supporting information that the criteria are appropriate for use, and the values.
- Generic criteria or RBSLs: If the use of the generic criteria is appropriate, supporting information should be described and presented.
- SSVIAC or 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 that identifies the criteria used.
- Separate appendix that provides supporting documentation for use of the VIAP Criteria, including any previous approvals for the use of the site-specific criteria.
1.6.2 Vapor source
This section should identify the concentrations of the volatile hazardous or regulated substances that pose an unacceptable risk to the structures(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 structure.
Data that supports the design of the PVMS must be provided, including demonstrating that mitigation is warranted. Vapor data must support delineation of soil gas impacts in any areas where a PVMS is not proposed (i.e., outside of the mitigation footprint) though PVMS are typically installed across the entire footprint of a structure.
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).
- Representative detections above criteria relative to the structure should also be depicted on the figures.
- Appendix should include all analytical data and field forms.
- Cross sections should include below grade features with the chemical data depicted.
1.6 Man-made preferential pathways evaluation (if applicable)
This section should include an analysis of Section 1.5.4 above 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 PVMS.
Key supporting information (as warranted)
- Text should reference the Figures identified in Section 1.6.2, as necessary, to identify preferential pathways that may pose an unacceptable risk due to their location within a source of vapors.