Potential Emissions and Exposures of Toxic Organics from Storage Tanks for Chemical Additions in Hydraulic Fracturing: A Modeling Approach

Hydraulic fracturing has promoted the exploitation of natural gas in the United States (U.S.). However, the storing and emptying of chemical additives in hydraulic fracturing wells may pose adverse effects through inhalation exposures. Based on the information about hydraulic fracturing fluids, this study investigated: 1) water volumes used to mix chemical additives for making up the hydraulic fracturing fluids; 2) chemical species, concentrations and their degradability in the hydraulic fracturing fluids; 3) emissions of organics from chemical storage tanks; and 4) the occupational inhalation exposures by toxic and organic vapors.

Results shows for 80,047 wells fractured between 2008 and 2014 and located in the 14 states studied, the highest total amount of water was consumed in Texas with 457.42 Mm³ of water used to fracture 40,521 wells; followed by Pennsylvania with 108.67 Mm³ of water used to treat 5,127 wells. For 5,071 wells completed in 2008 through July 2014 and located in the Marcellus Shale Formation, there were totally 517 chemicals introduced into the hydraulic fracturing fluids. Although most of the added chemicals can be removed with the appropriate treatments, the degradation of some chemicals would produce more toxic and persistent degradation produces.

For 72,023 out of 80,047 wells, the median daily emission values were 0.221 kg d^-1 per well. Those emissions were primarily contributed by the non-methane volatile organic compounds (NMVOCs). Furthermore, 95.14% of emissions caused by all NMVOCs were due to 60 NMVOCs which belong to the 847 candidate substances for the Priority List of Hazardous Substances defined by Agency for Toxic Substances & Disease Registry (ATSDR) in 2011. Results shows there were 2,893, 8, 4,415, and 2,992 out of 60,644 wells with the possibilities of the acute exposure for non-cancer risks, the chronic exposure for non-cancer risks, the acute exposure for cancer risks, and the chronic exposure for cancer risks on workers. Methanol was the major organic causing the acute exposure for non-cancer risks in hydraulic fracturing. Formaldehyde was the dominant contributor to both the acute and chronic exposures for cancer risks.