Air Emissions From Natural Gas Exploration And Mining In The Barnett Shale Geologic Reservoir

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Air Emissions From Natural Gas Exploration And Mining In The Barnett Shale Geologic Reservoir

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Title: Air Emissions From Natural Gas Exploration And Mining In The Barnett Shale Geologic Reservoir
Author: Rich, Alisa Larraine
Abstract: This study evaluates air emissions from natural gas mining and production in the Barnett Shale within the Dallas/Fort Worth Metroplex. Due to advances in horizontal drilling and hydraulic fracturing, natural gas production in the Barnett Shale increased from 3 wells in 2000 to almost 8,000 wells in six Metroplex counties by 2008. Currently, information regarding emissions from natural gas production, particularly regarding hazardous air pollutants, is lacking; this information is particularly important given that drilling and production is occurring in highly urbanized areas. The objectives of this study were thus:* To identify the `fingerprint' of chemicals associated with natural gas production in the Barnett Shale through passive air monitoring; and* To correlate the presence of the fingerprint chemicals to methane and to each other.Air sampling was conducted at 36 sampling sites in 6 counties, resulting in 50 sets of monitoring data for subsequent statistical analysis. Passive samples were collected using summa canisters with 24-hour flow valves according to ASTM Method D-1357. Canister contents were analyzed for Toxic Organics (TO-14A), Tentatively Identified Compounds (TICs) and Light Hydrocarbons by Gas Chromatography/Mass Spectrometer Analysis (GC-MS). Statistical analysis confirmed a statistically significant probability that other chemicals will be present with methane including toluene, m&p xylenes, dichlorodifluoromethane, benzene, o-xylene, chloromethane, ethylbenzene, C12hydrocarbon, 1,2,3-trimethylbenzene and carbon disulfide. A Pearson's correlation coefficient identified strong relationships between toluene and m&p xylene (r = 0.85), benzene and toluene (r = 0.89), benzene and xylene (r = 0.86).A Principal Component Analysis (PCA) identified specific chemicals associated with 2 significant factors. These factors were strongly associated to specific natural gas mining and production processes, including fracking, flaring, venting, compression, and tanks holding produced water/condensate, and injection of produced water into wells. An ANOVA F-test confirmed a significant difference of specific chemicals related to compression with a p-value of >0.05. Many of the chemicals identified in this study are hazardous air pollutants (HAPs), and are known/suspected carcinogens, mutagens, developmental toxicants and neurotoxicants. Thus, use of dispersion modeling is advisable to develop safe setback distances between natural gas drilling/production facilities and critical receptors, such as schools.
Date: 2011-10-11

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