What does Method TO-15 really mean? – July 2019


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What does Method TO-15 really mean? – July 2019

By: Henry Stahl

If you have been involved with a vapor intrusion (VI) investigation or air sampling, you are likely familiar with EPA Analytical Method TO-15. The “TO” stands for “toxic organics”. The first EPA compendium on this method was published in 1999 and refers to the sampling and analysis of any of 97 compounds identified as volatile organic compounds (VOCs). The compounds are taken from the hazardous air pollutants (HAPs) listed in Title III of the 1990 Clean Air Act Amendments. However, an investigator must exercise caution when requesting a TO-15 analysis from a laboratory; the compounds that are included in this analysis vary considerably between labs. This article will focus on the analytical portion separate from the sampling component of Method TO-15.

Differences in analyte lists can have drastic consequences, as seen in the following real-world example:

A consultant was conducting a vapor intrusion investigation at a former industrial site, using their preferred lab. Several sub-slab soil gas and air samples were taken. Several years later, a different consultant, using a different lab, took over the investigative work and began noticing detections of another chemical, acrolein, in sub-slab soil gas and indoor air samples, with concentrations exceeded screening levels. The facility had not been in operation between these two investigations, and the site conditions did not appear to change. Samples were collected by both clients using Vapor Pins® and stainless-steel evacuated canisters. Both consultants requested analysis by Method TO-15 from their respective labs.

Was there an unknown acrolein release during the interim? Unlikely. Acrolein did not suddenly “show up” in indoor air. It was always there, but due to the variance in the “TO-15 list” between labs, acrolein was not reported by the first laboratory.

When analyzing a sample via Method TO-15, labs do not analyze for all the compounds listed under the method. Often, a lab will report a “standard list” of common VOCs. This is done to keep costs down for the lab and the client. The usual VI suspects are among them: perchloroethylene (PCE), trichloroethylene (TCE), benzene, chloroform, xylenes, etc. Labs do not want to waste time and resources to calibrate an instrument for a compound that is rarely present. However, depending on the specific history of the site or industry, less common chemicals of concern, such as acrolein, could in fact be present. These chemicals may not be included in the lab’s “standard TO-15 list” and will not be reported in the analytical report unless specifically requested. The consultant must be diligent in their research of the site’s history and function and in requesting laboratory services. Some labs include additional analytes at no cost, but they must be specifically requested by the consultant. Other labs will include “non-standard” VOCs in their analyses for added cost, but again, these must be specifically requested, and may not be fully supported by QA/QC. Another important point worth noting is that an investigator must ensure that the reporting limits provided by the lab are sufficiently low enough to meet screening levels, however, this discussion is for another day.

Method TO-15 is an extremely rigorous and useful sampling and analytical method for gas media. However, when requesting this analysis, one must remember that no two laboratory TO-15 lists are alike. The onus is on the investigator to know what compounds will be included in the analysis from their lab and to understand the site’s historical usage well enough to know if other compounds should be added.

Published in the July 2019 Cox-Colvin & Associates Newsletter: Focus on the Environment


Henry Stahl is a Scientist with Cox-Colvin & Associates, Inc. and has been with the company since November 2017. He earned a B.S. with Research Distinction from the Ohio State University in 2017. Mr. Stahl has worked on several dozen vapor intrusion investigations during his time with Cox-Colvin, as well as other environmental investigation, monitoring, remediation, and mitigation projects under various regulatory programs.