Effect of Sample Collection Techniques on the Analysis of Methane in Water

Oral Presentation

Prepared by M. McGarvey1, L. Molofsky2, J. Black1, T. Upadhyay1, P. Higgins1
1 - PA DEP Bureau of Labs, PO Box 1467, Harrisburg, PA, 17105, United States
2 - GSI Environmental, Inc., 2211 Norfolk Street, Suite 1000, Houston, TX, 77098, United States


Contact Information: mmcgarvey@pa.gov; 717-346-8638


ABSTRACT

Analysis of methane and other light hydrocarbon gases in water has been of increasing interest in recent years due to the increase in shale gas drilling. Migration of methane from drilling sites into nearby residential wells is a public concern with regards to the health and safety of U.S. citizens. Considerable variability in methane concentration results has been observed when comparing water samples taken from the same sampling location. Excluding the possibility of natural or seasonal fluctuations, it is unclear whether this variability is mainly due to analytical technique, sample collection technique, or a combination of these and/or other factors. This study compared the measurement of methane concentrations in water samples using three different sample collection techniques. In an open system, a Volatile Organic Analysis (VOA) vial is filled directly while in contact with the atmosphere (Direct Fill). In the semi-closed system, a VOA vial is filled while inverted under a head of water (Inverted Fill). In the closed system, a proprietary sample collection vessel is filled without exposure to the atmosphere (IsoFlaskŪ). At methane concentrations less than approximately 20 mg/L, all three collection techniques provided comparable results. However, at concentrations greater than 20 mg/L, the direct fill technique was superior to the inverted fill collection technique, but overall, sample collection using the IsoFlaskŪ provided the most accurate measurement of methane in water.