Petroleum Vapor Intrusion Assessment for Leaking UST Program Sites

Only for releases from petroleum USTs

Is it required that the indoor inhalation exposure route be investigated during early action or site investigation?

Generally, no. Characterization of the site is required first -- defining the extent of soil and groundwater contamination, if applicable -- as has always been done. Depending upon information collected from the site characterization, the determination can be made regarding the need for investigation of petroleum vapor intrusion (PVI). See the flowchart for steps to assess the potential for PVI. The determination will be made on a case-by-case basis.

How is “free product” in groundwater monitoring wells defined?

The presence of free product in groundwater monitoring wells is defined at 35 Ill. Adm. Code 734.215(a) as free product exceeding one-eighth of an inch in depth as measured in the well.

In looking at the flowchart, what is Csat soil?

Csat (soil saturation concentration) soil contains a concentration of an indicator contaminant as a result of the release from the UST that exceeds the soil saturation limit as determined at 35 Ill. Adm. Code 742.220. At the soil saturation limit, the soil is not capable of holding additional amounts of contaminants. It is akin to free product in soil.

Csat soil must be removed before pathway exclusion can be considered pursuant to the Tiered Approach to Corrective Action Objectives at 35 Illinois Administrative Code 742. Its removal prevents potentially unacceptable risks from contaminants remaining in the soil.

Insofar as the flowchart is concerned, how is “contaminated groundwater” defined?

Contaminated groundwater is, based upon laboratory analytical results, groundwater that contains concentrations of indicator contaminants as a result of the release from the UST that exceed the Tier 1, Class I groundwater remediation objectives for the groundwater component of the groundwater ingestion route at 35 Ill. Adm. Code 742.Appendix B.Table E.

What is the vertical separation distance?

The vertical separation distance is the thickness of uncontaminated soil (i.e., concentrations of indicator contaminants do not exceed the most stringent Tier 1 remediation objectives at 35 Ill. Adm. Code 742.Appendix B.Table A or B) separating the contamination (either soil and/or groundwater) from the lowest point of an overlying receptor (building basement, foundation, slab, or crawl space -- or ground surface if there is no overlying receptor).

  • The vertical separation distance for contaminated groundwater (i.e., concentrations of indicator contaminants exceed the Tier 1, Class I groundwater remediation objectives) is five feet of uncontaminated soil.

  • The vertical separation distance for Csat soil or free product in groundwater monitoring wells is 15 feet of uncontaminated soil.

How are natural pathways defined?

Natural pathways are defined at 35 Ill. Adm. Code 742.200 as natural physical conditions that may allow for the transport of regulated substances including, but not limited to, soil, groundwater, sand seams and lenses, and gravel seams and lenses.

How are man-made pathways defined?

Man-made pathways are defined as constructed physical conditions that may allow for the transport of regulated substances including, but not limited to, sewers, utility lines, utility or elevator vaults, building foundations, basements (including earthen floors), crawl spaces, drainage ditches, previously excavated and filled areas, or sumps.

For the Illinois EPA site-specific Tier 3 evaluation shown on the flowchart, must the UST owner or operator provide extra documents or extra data for this step in the process?

No. This step in the process will occur whenever there is enough information from the investigation of the release and characterization of the site to make a site-specific decision about the need for a PVI investigation based upon information available to the Illinois EPA at that time.

For example, if the incident can be closed at early action in accordance with Part 734, details of the release and the site will be evaluated to determine whether there is a potential for PVI. If not and if there have been no reported petroleum vapors in buildings as a result of the UST release, the incident can be closed with issuance of a No Further Remediation Letter without soil gas sampling.

For another example, if early action and site investigation activities generated enough information for the Illinois EPA to make the determination that soil gas sampling is not required -- then, later, free product is found in a groundwater monitoring well -- the assessment process will be revisited to determine the potential for PVI.

If early action and site investigation activities have been conducted and it is found that investigation of PVI is required, should a soil gas sample be collected?

Yes. If at any time during site investigation there is information to indicate that a PVI investigation is needed, the subsequent plan should include collection and analysis of a soil gas sample. If this determination is not made until after the site investigation is performed, the collection and analysis of a soil gas sample should be included in the corrective action plan.

Where should the soil gas sample be collected?

A soil gas sample should be collected from native soil at a depth of three feet below ground surface in the area representative of the most contamination.

For what parameters should the sample be analyzed?

The soil gas sample should be analyzed for the volatile chemicals listed at 35 Ill. Adm. Code 742.Appendix A.Table J that are indicator contaminants for the release. Ensure that the laboratory detection limits are equal to or less than the indoor air remediation objectives calculated using Equation J&E1 or J&E2 in case those calculated remediation objectives are used as soil gas remediation objectives.

How would the laboratory analytical results of the soil gas sample be used in relation to the indoor air remediation objectives calculated using Equation J&E1 or J&E2?

If the laboratory analytical results of the soil gas sample are less than or equal to the indoor air remediation objectives (which would be used as soil gas remediation objectives), no further consideration of the indoor inhalation exposure route is required.

Note: The use of indoor air remediation objectives calculated using Equation J&E1 or J&E2 as soil gas remediation objectives carries with it no institutional controls.

After defining the extent of soil gas contamination, what corrective action options are available to address the indoor inhalation exposure route?

The following options are available to address the indoor inhalation exposure route:

  • A Tier 1 evaluation using Appendix B.Table H. Either the soil gas or the groundwater remediation objectives in Table H must be met. The use of Table H carries with it the institutional control that the existing or potential building must have a full concrete slab-on-grade or a full concrete basement floor and walls.

  • A Tier 1 evaluation using Appendix B.Table I (which has remediation objectives that are considerably higher than those in Table H). In order to use Table I, soil and groundwater located five feet or less, vertically and horizontally, from the existing or potential building or associated man-made pathway must meet the most stringent Tier 1 remediation objectives listed at 35 Ill. Adm. Code 742.Appendix B. Tables A and E, respectively. Then, both the soil gas and the groundwater remediation objectives in Table I must be met. The use of Table I carries with it two institutional controls -- namely, (1) the existing or potential building must have a full concrete slab-on-grade or a full concrete basement floor and walls, and (2) no soil or groundwater contamination exceeding the most stringent remediation objectives can be present within five feet, vertically or horizontally, of an existing or potential building or associated man-made pathway.

  • Calculation of site-specific Tier 2 soil gas and/or groundwater remediation objectives for the indoor inhalation exposure route for volatile chemical indicator contaminants. The use of the equations carries with it the requirement for the institutional control that the existing or potential building must have a full concrete slab-on-grade or a full concrete basement floor and walls. Additional institutional controls may be required, depending upon conditions specific to the site that are used as the basis of the Tier 2 evaluation.

  • A Tier 2 evaluation comparing laboratory analytical results of soil gas samples, near-slab soil gas samples collected outside of an existing building, or exterior soil gas samples collected at the footprint of a potential building to calculated indoor air remediation objectives using Equation J&E1 or J&E2. If compliance is demonstrated, an institutional control is not required.

  • A Tier 3 evaluation in accordance with 35 Ill. Adm. Code 742.935.

  • Agreement to a land use restriction prohibiting a building or associated man-made pathway above the contaminated soil gas or groundwater. In order to use this pathway exclusion option, the extent of soil gas and groundwater contamination must be defined.

  • Installation and maintenance of an approved building control technology in accordance with 35 Ill. Adm. Code 742.Subpart L. Maintenance requirements, as well as provisions for inoperability, must be included in an institutional control.

  • A demonstration of active biodegradation. This exclusion option is available if the indicator contaminants are BTEX only. Its use will carry with it the requirement that an institutional control be placed upon the property to ensure that active biodegradation is allowed to occur (i.e., that “x” feet of soil [specific to the demonstration] no more contaminated than that present at the time of the demonstration of active biodegradation shall be maintained). If volatile chemical indicator contaminants other than BTEX are present, pathway exclusion via a demonstration of active biodegradation can be pursued under a Tier 3 evaluation.

  • Remediation of soil and/or groundwater.

Are there other considerations that should be taken into account when investigating the indoor inhalation exposure route?

Besides the concentrations of indicator contaminants, the location of contamination, and the media impacted, other considerations that should be taken into account are the presence/absence of an existing or potential building with a full concrete slab-on-grade or a full concrete basement floor and walls, as well as natural and man-made pathways from the subsurface (including, but not limited to, a sump in the basement floor). Neither the Tier 1 tables nor the Tier 2 equations (except J&E1 and J&E2) apply when the existing or potential building has an earthen crawl space, an earthen floor, a stone foundation, a partial concrete floor, or a sump. In such cases, available options include excluding the exposure route under 35 Ill. Adm. Code 742.312, meeting the building control technology requirements under 35 Ill. Adm. Code 742.Subpart L, or proposing an alternative approach under Tier 3.

NOTE: Equations J&E1 and J&E2 may be used to calculate soil gas remediation objectives even when the existing or potential building has an earthen crawl space, an earthen floor, a stone foundation, a partial concrete floor, or a sump, and, if compliance is demonstrated, no institutional control would be imposed.

Does the requirement to use industrial/commercial remediation objectives apply for this exposure route?

Yes, if the UST owner or operator is seeking payment from the UST Fund. Pursuant to Section 57.7(c)(3)(A)(ii) of the Environmental Protection Act, corrective action activities required to meet the minimum requirements of Title XVI shall include the use of industrial/commercial property remediation objectives, unless the UST owner or operator demonstrates that the property being remediated is residential property or being developed into residential property.

Where can I get more information?

You should contact the assigned Leaking UST Section project manager or the project manager on-call for the Leaking UST Section at 217-524-3300.

Reference: Petroleum Vapor Intrusion Assessment for Leaking UST Program Sites

This fact sheet is for general information only and is not intended to replace, interpret, or modify laws, rules, or regulations.

June 2013