Cooling Tower Monitoring using the El Paso Method

Cooling tower monitoring describes the characterization of volatile organic air pollutants that are capable of being air-stripped from a water matrix. While generic or indicator monitoring may be required to identify the existence of volatile organic compound (VOC) emissions, speciated compound characterizations may also be required in some instances to characterize the specific compounds present. Historically, a method for cooling tower water characterization was developed for use by El Paso Products Company in the early 70's.


This method utilized a dynamic or flow-through system for air stripping a sample of the water and analyzing the resultant off-gases for VOC's using a common flame ionization detector (FID) analyzer, and has been the popular choice in Texas for many years. The El Paso Products method, however, has been overshadowed nationally by the use of purge and trap analysis of water samples utilizing gas chromatography and/or mass spectrometry techniques. While direct water analysis has been shown to be effective for cooling tower measurements of heavier molecular weight organic compounds with relatively high boiling points, Texas Commission on Environmental Quality (TCEQ) has determined that this approach may be ineffective for capture and measurement of volatile organic compounds with lower boiling points, such as ethylene, propylene, 1,3-butadiene, and butenes. VOC's with a low molecular weight and boiling point are generally lost in the sample collection step of purge/trap type analyses.

Consequently, TCEQ requires that the air stripping method presented in this manual be used for cooling tower and other applicable water matrix emission measurements of VOC's with boiling points below 140ºF. Specific procedures for cooling tower sampling and analysis for VOCs with boiling points of 140ºF and greater must be submitted to TCEQ for approval on a case-by-case basis. *The summary above is an excerpt from the: TCEQ "Cooling Tower Monitoring," Sampling Procedures Manual, Appendix P, Revision No. 1.

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