Soil Vapor Intrusion Updates

Throughout this web page, reference is made to the final guidance. This refers to the Guidance for Evaluating Soil Vapor Intrusion in New York State, October 2006.

The updates provide herein will be incorporated, as applicable, into the guidance document itself upon its periodic revision. If you have suggestions you would like us to consider during the next revision process, please share them with us at

May 2017: Updates to Soil Vapor / Indoor Air Decision Matrices


Based on reviews of toxicity data, risk assessments, and soil vapor intrusion data collected in New York State over the past decade, NYSDOH has assigned eight volatile chemicals to three newly revised and renamed Soil Vapor / Indoor Air Decision Matrices. These assignments and SVI Decision Matrices supersede those provided in the final guidance and in subsequent updates to the guidance (please note: the June 2007 update is no longer posted on this web page).  The assignments are summarized in the following table:

Soil Vapor/Indoor Air Matrix Volatile Chemical

Matrix A

carbon tetrachloride

Matrix B

methylene chloride

Matrix C

vinyl chloride

These modifications to the SVI Decision Matrices should not be interpreted as reflecting changes in the recommended approach for how, when, and where to collect soil vapor or soil vapor intrusion samples during the investigation of a contaminated site.

An overview of the Decision Matrices and factors NYSDOH considers when developing and assigning chemicals to them is provided in Section 3.4 of the 2006 guidance.


August 2015: New Ambient Air Guideline for Trichloroethene


NYSDOH has lowered their guideline for trichloroethene in ambient air from 5 micrograms per cubic meter (mcg/m3) to 2 mcg/m3 and developed a recommended immediate action level of 20 mcg/m3. The air guideline identified in Table 3.1 of the final guidance is no longer applicable.

September 2013: New Ambient Air Guideline for Tetrachloroethene


NYSDOH has lowered their guideline for tetrachloroethene in ambient air from 100 micrograms per cubic meter (mcg/m3) to 30 mcg/m3 and their recommended immediate action level from 1000 mcg/m3 to 300 mcg/m3. The air guideline identified in Table 3.1 of the final guidance is no longer applicable.

May 2010: Update on Building Questionnaires and Product Inventories

The Indoor Air Quality Questionnaire and Building Inventory Form in Appendix B of the final guidance (as revised March 2007) is provided to aid with the evaluation of indoor air sampling results by collecting pertinent building and household product information that may influence soil vapor intrusion and indoor air quality.


Based on comments received from field personnel and homeowners, as well as a review of indoor air evaluations at remedial sites, the NYSDOH and New York State Department of Environmental Conservation (NYSDEC) have created an abbreviated Indoor Air Quality Questionnaire and Building Inventory Form.

The abbreviated form is intended to decrease the amount of time spent gathering and reporting the supplemental building information while still collecting the most relevant information necessary for conducting a soil vapor intrusion investigation. It is intended to supplement, rather than replace, the original form. When completed properly, the abbreviated form will capture the information needed to perform the data evaluation process in most cases. However, in the event that a complete evaluation cannot be conducted or additional information is needed, the NYSDEC and NYSDOH may recommend a return to the structure to collect the additional information and complete the original form (as revised March 2007).

April 2010: Clarification on Data Validation

Reference is often made to "third-party data validation" of soil vapor, sub-slab vapor, indoor air and outdoor air results. While the purpose is the same, validation of these soil vapor intrusion data does not mean the same as formal "third-party data validation," which is typically associated with litigation activities. A NYSDEC Analytical Service Protocol Category B format data deliverable for the sample analyses is still reviewed by a qualified individual not directly associated with the project or the analytical laboratory and the output of the review is in the form of a Data Usability Summary Report (DUSR) rather than a validation report containing detailed evaluation of every piece of information generated by the analysis. More information about DUSRs and the qualifications necessary to prepare a DUSR is available in the NYSDEC's DER-10: Technical Guidance for Site Investigation and Remediation (May 3, 2010).

January 2010: Update to Section 2.7.2

Section 2.7.2(d) of the final guidance contains the following recommendation: during the construction of sub-slab implants and probes, porous, inert backfill material (e.g., glass beads, washed #1 crushed stone, etc.) should be added to cover about 1 inch of the probe tip for permanent installations.


This recommendation is no longer applicable; however, care should be taken to prevent the sub-slab aggregate from blocking the sampling probe or tubing to ensure air flow into the sampling device.

March 2009: Modification to the Recommended Use of Tracer Gas

The NYSDOH, in consultation with the NYSDEC, recommends in Section 2.7.5 of the final guidance that a tracer gas be used when collecting soil vapor samples as a quality assurance/quality control measure to verify the integrity of the soil vapor probe seal. A similar recommendation is not provided for sub-slab vapor samples.

Modified Recommendation

Based on the NYSDEC and NYSDOH's experience, we are modifying this recommendation to include the use of a tracer gas when collecting sub-slab vapor samples.

This modification is based on tracer gas testing in over 100 buildings to ensure that the sub-slab vapor sampling results were not biased by leakage of the sub-slab vapor probe seals. The results of this testing indicate that the routine use of tracer gas testing is valuable for verifying the integrity of the sub-slab vapor probe seal. The sub-slab vapor tracer gas tests revealed that approximately 10% of the seals were inadequate and had to be improved prior to sample collection. The tracer gas data also provide greater confidence that the sampling results from probes where little tracer gas was detected are representative of sub-slab vapor concentrations.

Based on our experience, inclusion of tracer gas testing as part of the sub-slab vapor protocol does not appreciably increase the cost of sampling. It typically adds 15 to 20 minutes to the sub-slab sampling process. Because structure-specific decisions are often based on a single sub-slab vapor sample from a single point in time, the use of tracer gas will reduce the possibility that decisions will be biased by faulty data. We therefore recommend its use.

October 2008: Notice Pertaining to the United States Environmental Protection Agency Building Assessment and Survey Evaluation Database

The U.S. Environmental Protection Agency (USEPA) has set up a website for their Building Assessment and Survey Evaluation (BASE) Database, which is discussed in Appendix C of the final guidance. Readers may note differences between the data presented by the USEPA in their report on the study and the data summarized by the NYSDOH in the guidance document. These differences are related to the USEPA using data from air samples collected with both multisorbent tubes and Summa® canisters. The USEPA provides a discussion of how these data were selected for each compound. The NYSDOH's compilation uses data obtained from the Summa® sampling methodology only.

February 2008: Modification to Indoor Air Sampling Recommendations

The NYSDOH, in consultation with the NYSDEC, recommends in Section 2.6.3 of the final guidance that indoor air samples be collected from both the basement and lowest level living space.

Modified Recommendation

A comparison of the results for basement and first floor air samples from structures located across the state indicate that concentrations of site-related contaminants in the air sample collected from the basement are typically less than or comparable to the concentrations in the corresponding first floor air sample. Exceptions to this observation were due to the presence of indoor or outdoor air sources of the contaminants. Overall, the data indicate that, in most cases, the basement result provides a conservative estimate of what may be present in the first floor air and sampling the lowest livable space is sufficient for determining whether actions are needed to address exposures related to soil vapor intrusion. This means one indoor air sample from the basement is expected to be adequate in most cases. However, the NYSDOH and NYSDEC reserve the right to request additional sampling (e.g., first floor air) if the information is needed for us to complete our evaluation.

This modification to the recommended indoor air sampling locations applies to structures with basements. We continue to recommend the collection of first floor air samples in slab-on-grade structures and in structures with living spaces over crawlspaces, as well as the collection of crawlspace air samples where applicable.

December 2007: New Fact Sheet on Volatile Organic Compounds in Indoor Air

The NYSDOH is pleased to announce the development of a new fact sheet, Volatile Organic Compounds (VOCs) in Commonly Used Products. This fact sheet focuses on volatile organic compounds or VOCs that are found in many products that we commonly use. It is designed to help the reader think about what VOCs may be present in their indoor air and steps they can take to reduce them.

March 2007: Correction to the Indoor Air Quality Questionnaire and Building Inventory Form in Appendix B

The Indoor Air Quality Questionnaire and Building Inventory form provided in Appendix B of the final guidance incorrectly lists "Stream radiation" as a type of heating system in Question 6 on page 3.


This typographical error has been corrected to indicate "Steam radiation" in a revised Indoor Air Quality Questionnaire and Building Inventory Form. In addition, in response to several requests, North arrows have been added to the Floor Plans and Outdoor Plot sections of the form.

December 2006 Correction to Table C.1 in Appendix C

The final guidance provides two entries for o-xylene in Table C1, Outdoor air.


The name of a compound, methyl-tert-butyl ether, was inadvertently omitted from the table and the name "o-xylene" was listed twice. This typographical error has been corrected in a revised Table C1, Outdoor air. The correction affects methyl-tert-butyl ether through o-xylene.