Purge-and-Trap GC Analysis of Water Samples Associated wtih Hydraulic Fracturing and Natural Gas Extraction0 pages

Purge-and-Trap GC Analysis of Methane in Water
Samples Associated with Hydraulic Fracturing
Application Note 37920312

Keywords
Eclipse 4660 Purge-and-Trap
Sample Concentrator
Hydraulic Fracturing
Methane
Natural Gas
Underground Sources of Drinking
Water (USDW)

Introduction
Shale gas reservoirs, such as the Marcellus shale reserve in Pennsylvania
and Barnett shale reserve in Texas are a growing source of natural gas in
the United States. The U.S. Energy Information Administration (EIA)
estimates that the total natural gas resource base of the United States to be
2,553 trillion cubic feet (Tcf).(1) Shale gas production represents greater
than 20% of the current U.S. supply an increase from 1% in 2000.
Hydraulic fracturing or “fracking” involves pumping water, sand, and
chemicals at extremely high pressure into deep underground wells to
crack open hydrocarbon-rich shale formation and extract natural gas.
Chemicals used for hydraulic fracturing include potentially toxic
substances such as diesel fuel and disinfectants, which can contaminate
underground sources of drinking water (USDW).
In some cases, methane has been detected in household drinking water
from wells. A study conducted in the Marcellus and Utica shale
formations found methane concentrations were 17-times higher on
average (19.2 mg CH4 L-1) in wells from active drilling and extraction
areas then in non-active areas (1.1 mg L-1 on average).(2) The average
methane concentration found in shallow groundwater in areas of active
drilling and hydraulic fracturing fell within the defined action level (1028 mg L-1) for hazard mitigation recommended by the U.S. Department of
Interior.(2)
Methane is not a regulated contaminant under U.S. National Drinking
Water Regulations. In fact, a provision in the Safe Drinking Water Act
passed in 2005 exempts hydraulic fracturing from regulation under the
USEPA’a Underground Injection Control Program (except in cases where
diesel fuel is employed for fracking). Consequently, there are no USEPAapproved testing methods for measuring methane in drinking water and
groundwater.
The application note describes the use of a purge-and-trap gas
chromatography system to analyze methane, ethane, ethene, and propane
hydrocarbons (C1-C3) in drinking water samples.

Presented at the 2012 Pittsburgh
Conference on Analytical
Chemistry and Applied
Spectroscopy, Orlando, Florida,
March 12–15, 2012

Experimental
Instrumentation used for this study was an OI Analytical Eclipse 4660
Purge-and-Trap sample concentrator (Figure 1) with a proprietary trap
specifically designed to trap methane. The P&T was interfaced to an
Agilent 7890 GC/FID with a split/splitless injector and a SUPEL-QPLOT
column (30-meter x 0.32-mm I.D.).
A primary, saturated analytical standard was prepared by chilling 1 liter of