Modified EPA SOP RSK-175 Using a Teledyne Tekmar Purge and Trap Concentrator

The US is in the midst of a “gas” rush from Colorado to New York State. Gas containing shale sites will become common vernacular with names such as, Barnett, Devonian, Marcellus, Utica, Antrim, Haynesville, and New Albany. Several regions have what are known by the energy companies as stacked plays, that is, areas where two or more gas shale regions overlap resulting in huge potential output. For instance Marcellus, Utica and Devonian have significant overlap in Pennsylvania making that state a prime location for drillers. Concern over natural gas finding its way into drinking water was confirmed by the Dimock Case where 14 homes had well water contaminated with methane.** Another case involved bubbling water on the Susquehanna River where it is believed that gas was migrating from gas wells that are located 2 to 3 miles away. Methane in private drinking water was detected in six homes near the river and ranged in concentration from 2.2 ppm to 55.8 ppm (mg/L). The Pennsylvania Department of Environmental Protection (PA DEP) has warned that concentrations over 28 ppm are of concern since the methane may partition out of the water and into the home with risk of explosion.

Many states are expected to adopt a variation of RSK-175 for the analysis of natural gas in drinking water. The PA DEP has developed a method based on a paper published which calculates the saturation point of methane for standard preparation. Both techniques are done using headspace with flame ionization (FID) as the preferred method of detection. Tekmar recently presented a modified technique at the Eastern Analytical Symposium (EAS) which used Purge and Trap and a proprietary trap in the concentrator. A Stratum PTC and AQUATek 100 Autosampler were coupled to the GC-FID. The Rt-U Plot column was used in a 30m x 0.53mm ID column. Restek offers an improved version of this column the Rt-U-Bond column (cat#19750) that offers lower bleed and less particle generation compared to the Rt-U-Plot columns. Calibration standards were made from stock standards by calculating the saturation of the gases at 0°C. For instance methane’s concentration after bubbling through chilled water for 2 hours is 39.59 ppm, ethane is 131.7 ppm and ethylene is 281 ppm. Samples were also run by headspace to compare the results between the two approaches. Calibration for methane ranged from 20 ppb to 40,000 ppb with an average RSD of 10%. Real world drinking water samples were run by the PA DEP using this method.  This method met the criteria outlined in both the RSK175 and the BOL6019 methods.

*Correction 12/13/2011: The pressure was listed in the figures as 19.44 psi. The pressure should be listed as 4.82 psi. I made changes today to the blog to reflect the correct pressure. Thank You Blog Readers for your comments and help with this article.

**Correction 3/17/2012: There are still questions relating to the Dimock Case and its cause.