Tier 1 Evaluation

Are there Tier 1 look-up tables for the indoor inhalation exposure route just as there are for the other exposure routes?

Yes. There are two new tables (namely, Tables H and I) in the TACO regulations at 35 Illinois Administrative Code (35 Ill. Adm. Code) 742.Appendix B that contain Tier 1 soil gas and groundwater remediation objectives for the indoor inhalation exposure route. Within each table is a set of remediation objectives that apply to residential property use and a set of remediation objectives that apply to industrial/commercial property use. Volatile chemicals are the only contaminants of concern for the indoor inhalation exposure route.

How are the Tier 1 remediation objectives for the indoor inhalation exposure route different from those of the other exposure routes?

The differences are:

  1. There are two tables of Tier 1 remediation objectives (Tables H and I).

  2. The sampling media involved are groundwater and/or soil gas.

  3. There are no remediation objectives for the construction worker population.

  4. There are no remediation objectives for Class II groundwater.

  5. Averaging of sampling results is not allowed.

  6. The provisions for similar acting chemicals do not apply.

For what kind of building were the Tier 1 remediation objectives developed?

The Tier 1 remediation objectives were developed for a slab-on-grade building. A slab-on-grade building is a more conservative scenario because there is less air available in the building to mix with the contamination. A building with a basement assumes there is mixing of the air between the basement and the first floor. The Tier 1 remediation objectives are applicable to both slab-on-grade buildings and buildings with basements.

Note: For full concrete floors with sumps, site evaluators may not use the J&E model under Tier 1 and Tier 2 and must either exclude the pathway, show that the soil gas concentrations meet the remediation objectives developed from Equations J&E1 and J&E2, meet building control technology requirements, or proceed to Tier 3.

Why are there no remediation objectives in Tables H and I that apply to the construction worker population?

Remediation objectives are not provided for the construction worker population because this receptor group is not at risk from indoor inhalation exposure. The exposure duration for indoor construction in almost all cases is less than the exposure duration for the residents and commercial workers. Thus, the protection of these two receptors will ensure protection of the construction worker during the period of indoor construction.

Why are there no remediation objectives in Tables H and I that apply to Class II groundwater?

There are no Class II groundwater remediation objectives because the determination as to whether the groundwater meets potable resource groundwater standards is not relevant for the indoor inhalation exposure route. The groundwater as a mode of transport of contaminant vapors is the concern, not its potability.

How do the industrial/commercial remediation objectives differ from the residential remediation objectives?

For the indoor inhalation exposure route, the parameter values used to calculate the industrial/commercial remediation objectives differ from the residential remediation objectives in three ways: exposure duration, building size, and air exchange rate.

If compliance is demonstrated using the remediation objectives for industrial/commercial properties, will a land use limitation apply to the property?

Yes. As with the other exposure routes, soil gas and/or groundwater remediation objective determinations relying on an industrial/commercial scenario require the use of institutional controls in accordance with 35 Ill. Adm. Code 742.Subpart J. If industrial/commercial remediation objectives are used to demonstrate compliance, the No Further Remediation Letter issued by the Illinois EPA (which must be recorded in the office of the recorder or the registrar of titles of the county in which the property is located) will carry with it the requirement that the use of the property is limited to industrial/commercial purposes.

Under what conditions must Table H be used?

Appendix B.Table H must be used when any soil or groundwater contamination is located five feet or less, vertically or horizontally, from the existing or potential building or associated man-made pathway. The soil gas and groundwater remediation objectives listed in Appendix B.Table H are based upon diffusion and advection, both of which apply in this scenario. Appendix B.Table H applies only when the existing or potential building has a full concrete slab-on-grade or a full concrete basement floor and walls. Soil gas or groundwater remediation objective determinations relying on Appendix B.Table H require the use of institutional controls—namely, that the existing or potential building has a full concrete slab-on-grade or a full concrete basement floor and walls.

Under what conditions may Table I be used?

Appendix B.Table I may be used only when all soil and groundwater contamination is located more than five feet, vertically and horizontally, from the existing or potential building or associated man-made pathway. The soil gas and groundwater remediation objectives listed in Appendix B.Table I are based upon diffusion only, which applies in this scenario. Appendix B.Table I applies only when the existing or potential building has a full concrete slab-on-grade or a full concrete basement floor and walls. Soil gas and groundwater remediation objective determinations relying on Appendix B.Table I require the use of institutional controls—namely, (1) it is required that no soil or groundwater contamination exceeding the most stringent Tier 1 remediation objectives be present within five feet (in the advection zone) of an existing or potential building or associated man-made pathway, and (2) it is required that the existing or potential building has a full concrete slab-on-grade or a full concrete basement floor and walls. As an alternative to using Appendix B.Table I, it is permissible to use Appendix B.Table H.

In order to use Appendix B.Table I, it must be demonstrated that all soil and groundwater located five feet or less, in the advection zone, from the existing or potential building or man-made pathway meets the most stringent Tier 1 remediation objectives listed in Appendix B.Table A and the Tier 1 remediation objectives for Class I groundwater listed in Appendix B.Table E, respectively.

What kind of institutional control is required if Table H is used?

The No Further Remediation Letter will require that the existing or potential building has a full concrete slab-on-grade or a full concrete basement floor and walls.

What kinds of institutional controls are required if Table I is used?

The No Further Remediation Letter will require that (1) no soil or groundwater contamination exceeding the most stringent Tier 1 remediation objectives be present within five feet, vertically or horizontally, of an existing or potential building or associated man-made pathway, and (2) the existing or potential building has a full concrete slab-on-grade or a full concrete basement floor and walls.

If soil and groundwater contamination is located more than five feet from the existing or potential building or man-made pathway but the institutional control associated with the use of Table I is not wanted, can Table H be used instead of Table I?

Yes. As an alternative to using Appendix B.Table I, it is permissible to use Appendix B.Table H. However, the use of Table H still carries with it an institutional control—namely, that the existing or potential building has a full concrete slab-on-grade or a full concrete basement floor and walls.

With respect to distance of contamination from a building and decisions on when to use Appendix B.Table H or I, can one building be considered to be representative of other buildings on a site, or does each building need to be addressed?

Each building would need to be addressed. There would not be a representative building.

For a site with varying depths of contamination, can the most conservative building location be used as being representative of site conditions?

No. Each area of contamination and existing or potential building must be addressed and concentrations of contaminants compared to the remediation objectives at Appendix B.Table H or I, as appropriate.

Must compliance with both the soil gas and the groundwater remediation objectives be demonstrated?

It depends upon which Tier 1 table is used:

  • If Appendix B.Table H is used, compliance is determined by meeting either the soil gas remediation objectives or the groundwater remediation objectives.

  • If Appendix B.Table I is used, compliance is determined by meeting both the soil gas remediation objectives and the groundwater remediation objectives.

The remediation objectives in Appendix B.Table I are considerably higher than those in Appendix B.Table H, but, in order to use the higher remediation objectives, the property owner must agree that at least five feet of uncontaminated soil and groundwater will be maintained. The reason for this is to ensure there are stable conditions on the property to keep vapors from getting into a building or associated man-made pathway by way of advection. A five-foot clean building zone of influence must be maintained for existing and potential buildings and associated man-made pathways so that advective transport of vapors into the building does not occur.

In addition, because the remediation objectives in Appendix B.Table I are considerably higher than those in Appendix B.Table H—hence, less conservative—more lines of evidence are required. As such, then, compliance with both the soil gas remediation objectives and the groundwater remediation objectives is required.

If contamination is located five feet or less from the existing of potential building or man-made pathway (hence, Table H must be used) and groundwater analytical results demonstrate compliance with the groundwater remediation objectives listed in Table H—but soil gas analytical results do not demonstrate compliance with the soil gas remediation objectives in Table H—is any further investigation of the indoor inhalation exposure route required?

No. If the use of Appendix B.Table H is applicable, compliance may be demonstrated by meeting either the soil gas remediation objectives or the groundwater remediation objectives.

If there is a groundwater monitoring well at the property boundary with contaminant concentrations that exceed the Appendix B.Table H groundwater remediation objectives for the indoor inhalation exposure route, will the site still qualify for an NFR Letter? The site may not have any buildings, and, presumably, the groundwater contamination extends off-site.

Yes, if soil gas samples were collected, if the laboratory analytical results of soil gas sampling meet the soil gas remediation objectives at Appendix B.Table H, and if no other pathways are a concern, then the site is eligible for an NFR Letter. This is because soil gas data is a more reliable indicator than groundwater data for predicting exposure from the indoor inhalation exposure route. Although there are no existing buildings, potential future buildings—on-site and off-site—are a factor when considering the indoor inhalation exposure route.

If a site has no soil contamination (i.e., contaminant concentrations meet the most stringent Tier 1 soil remediation objectives for the other pathways) within the 5-foot advection zone and groundwater has not been encountered at a reasonable depth, can the remediation objectives at Appendix B.Table I be used?

No. If using Appendix B.Table I, compliance is determined by meeting both the soil gas and groundwater remediation objectives. If groundwater was not encountered, Appendix B.Table I cannot be used. Either the remediation objectives at Appendix B.Table H may be used, the proposal may be submitted under a Tier 3 evaluation, or pathway exclusion in accordance with 35 Ill. Adm. Code 742.312 may be used.

Can soil data be used to address the indoor inhalation exposure route?

Yes. Proposals to use soil data must be submitted under a Tier 3 evaluation.

Can the laboratory analytical results be averaged and used to demonstrate compliance with the remediation objectives?

No. Averaging is not allowed.

What remediation objectives should be used for volatile chemicals not listed in Table H or I?

For volatile chemicals not listed in Appendix B.Table H or I, site-specific remediation objectives may be requested from the Illinois EPA, or site-specific remediation objectives may be proposed under a Tier 3 evaluation in accordance with 35 Ill. Adm. Code 742.Subpart I.

Can a Tier 1 evaluation be used to evaluate soil gas samples collected from a location four to five feet beneath a building foundation?

Yes. A Tier 1 or Tier 2 evaluation may be used so long as the samples are not collected sub-slab. Proposals to use sub-slab soil gas sampling data must be submitted under a Tier 3 evaluation.

If compliance with the Tier 1 remediation objectives is demonstrated, is there need for further action?

Further action is not required so long as compliance with the remediation objectives is demonstrated for all applicable exposure routes and any required institutional controls, if any, are in place.

If compliance with the Tier 1 remediation objectives is not demonstrated, what options are available to address the indoor inhalation exposure route?

As with the other exposure routes, options available include Tier 2 evaluation, Tier 3 evaluation, exposure pathway exclusion, and remediation.

Where can I get more information?

You may contact the project manager on-call for your remediation program at 217-524-3300 for further information regarding vapor intrusion.

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

June 2013