Hazardous substances as the dominant non-methane volatile organic compounds with potential emissions from liquid storage tanks during well fracturing: A modeling approach

Chemical additives used in hydraulic fracturing fluids (HFFs) are made up of various organic compounds that are potential human carcinogens. To estimate the emissions from these organic constituents in on-site liquid storage tanks, studies were performed using the AP-42 model on data collected from 72,023 wells put into production using hydraulic fracturing between 2008 and 2014 in the United States. Results show that a total of 8.11 × 10⁵ kg volatile organic compounds (VOCs) were potentially emitted from liquid storage tanks during fracturing operations, which was relatively low compared to other sources/activities in well fracturing. The median well emission roughly increased from 0.110 to 0.786 kg per well in 2008 and 2014, respectively, and was primarily due to the increase in the volume of chemical additives for fracturing one well. Of NMVOC emissions, 95.1% was contributed by 60 compounds listed on the priority list of hazardous substances defined by the Agency for Toxic Substances & Disease Registry (ATSDR), while 16.7% was caused by 15 carcinogenic compounds. Specially, methanol, formaldehyde, 2-propanol, and ethanol accounted for 55.5%, 16.6%, 11.7%, and 8.31% of NMVOC emissions. Our study highlights methanol, formaldehyde, 2-propanol, and ethanol as the targeted compounds for reducing organic emissions and occupational inhalation exposures related to storage tank operations.