Methane Analysis in Waters

Ask the Expert Question:

Water samples were collected from wells that were believed to be impacted by methane due to hydraulic fracturing and analyzed by two different laboratories. Two different analytical methods were run, RSK-175 and EPA Method 18. The results from the same sample source were about an order of magnitude different. Both methods used the analysis of headspace. Do you know why such a large difference would occur?

Experts Response:

In response to your question about large differences in results from two methods - RSK-175 and EPA method 18, I suspect that the differences relate to differing approaches in purging methane from each sample. RSK-175 is intended to measure dissolved gases, such as methane, in water samples, whereas EPA method 18 is designed for analyzing volatiles in air samples. The results for EPA 18 will depend on the how the laboratory created the headspace vapor sample, as that step is not defined in the method.

I suggest you evaluate how the methane in the water sample was converted to a gaseous sample, and also evaluate how standardization was performed for EPA 18. Another contributing factor is how the integrity of the water sample was maintained from collection to time of analysis. Unless the samples remained tightly sealed until analysis was performed, some methane could have been lost prior to analysis.

In summary, both methods should provide accurate methane analysis, so the main issues to investigate are the sample preservation and handling prior to analysis, and particularly how the EPA 18 headspace was created.

View Dr. Jack Tuschall's expert profile