Modified El Paso Method Monitoring
AIM™ Environmental performs Modified El Paso Method monitoring of cooling-water and heat-exchange systems — the air-stripping VOC test that refineries and chemical plants rely on to catch process leaks and stay compliant under the MON NESHAP and TCEQ Appendix P. It’s leak detection and repair, applied to your cooling towers and heat exchangers.
What the Modified El Paso Method Is
The Modified El Paso Method — formally the Air Stripping Method for the Determination of Volatile Organic Compound Emissions from Water Sources — measures VOCs that have leaked from a process stream into a cooling-water or heat-exchange system. A water sample is drawn from the system, volatile compounds are stripped out in an air-stripping column, and the stripped air is analyzed with a flame ionization detector (FID). The reading tells you, in real numbers, whether a heat exchanger is leaking process fluid into your cooling water — long before it becomes a reportable release or a violation.
Who Needs It
If your facility runs heat exchangers in organic-chemical or petroleum service, your cooling-water systems are almost certainly subject to heat-exchange-system leak monitoring. The requirement appears in the federal MON NESHAP (40 CFR 63, Subpart FFFF, §63.2490) and in TCEQ Appendix P for Texas sites, and it is increasingly written into consent decrees. Refineries, petrochemical plants, and miscellaneous organic chemical manufacturers all fall in scope.
What AIM Does
We run the full monitoring program for you: scheduled sampling of each covered cooling-water and heat-exchange system, on-site air-stripping FID analysis to the method’s specifications, leak determination against the applicable action level, and clear, audit-ready documentation of every reading, calibration, and data point. When a leak is found, you get the numbers you need to locate and fix it — and the records that prove you did.
Why AIM
This is leak detection and repair — just applied to cooling towers and heat exchangers instead of valves and flanges — and LDAR is what we do. We bring the same calibrated instruments, defensible chain of custody, and regulator-ready reporting to your heat-exchange monitoring that we bring to a full LDAR program. Independent, precise, and built to hold up in an audit.
El Paso Method FAQs
What is the Modified El Paso Method?
It is a monitoring procedure (TCEQ Sampling Procedures Manual, Appendix P) for finding VOCs that leak from process equipment into cooling water. A cooling-water sample is run through an air-stripping column and the stripped vapor is read on a flame ionization detector (FID).
Who has to do El Paso Method monitoring?
Refineries under the Refinery Sector Rule (40 CFR 63.654) and chemical plants under the HON/SOCMI rules (40 CFR 63.104), plus Texas sources under 30 TAC 115.760–.769. We run it as a companion to refinery and chemical plant LDAR.
What is the action level?
Under the federal Refinery Sector Rule, the action level is 6.2 ppmv of total strippable VOC in the cooling water; crossing it triggers leak investigation and corrective action.
How often is monitoring required?
It depends on the applicable rule and your heat-exchange configuration — often monthly, with reduced frequency available after a record of clean readings. We scope the schedule to your units.
How does this fit with our LDAR program?
Cooling-water VOC monitoring is a natural companion to component LDAR. See our LDAR compliance overview for how the pieces fit together.
Talk to AIM about El Paso Method monitoring
Tell us about your heat-exchange systems and we’ll scope a monitoring program that keeps you compliant. Request a consultation →
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