(53f) The Air Quality Impacts of Hydraulic Fracturing Flowback Fluid

Natural
gas production in the United States has increased dramatically in recent years
due to hydraulic fracturing. The cost to harvest natural gas from shale
formations has greatly decreased thanks to this process. The developments of
this technology have led to cheaper energy for many people but we do not yet
know the full scope of the environmental impacts of the process, including the
effects that these large scale operations have on air quality. A poorly
characterized source of volatile organic compounds (VOCs) and other emissions
from hydraulic fracturing are atmospherically vented storage tanks for
hydrocarbons and flowback water. Pollutants such as
VOCs can vent from these tanks during flowback period
as well as the time of normal well operation (the water is then considered
?produced? rather than flowback).

In this work
12 samples of hydraulic fracturing flowback fluid are
analyzed for their potential to affect atmospheric chemistry. The primary
emissions of concern are VOCs, which affect the production of both ozone and
particulate matter. Two indicators are used to assess the air quality
implications of these samples of flowback fluid:
total volatile organic carbon (TVOC) and volatile carbon emission rate.

The total
volatile organic carbon is measured by allowing a volume of 200-800 µL of a
sample to evaporate into a 60 L Teflon® bag filled with clean air and then
sampling the total gas-phase carbon with a flame ionization detector. The
results are shown in Figure 1. A wide range of concentrations is observed
(0-114 mgC/L), highlighting the range of potential
concentrations that can occur at different times and locations in the flowback process. The total volatile organic carbon for
many of these samples is quite high considering that the total organic carbon
(volatile + non-volatile) of normal surface waters do not typically exceed 10 mgC/L (World Health Organization).

Figure 1. Total volatile organic carbon
(TVOC) for 12 samples of flowback fluid.

The emission
rate of organic carbon is measured for each sample by slowly blowing clean air
over the top and sampling with a flame ionization
detector. 10 mL of each sample was used, with ~5 cm² of the sample
exposed to a stream of 1.5 LPM clean air. Figure 2 shows results on volatile
carbon emission rates (mgC/min) per the amount of
fluid and the surface area of the exposed surface. This measurement could be
used to estimate a range of emissions for flowback
fluid storage tanks, as long as fluid volume and exposed surface area are
known. Again, it should be noted that there is a wide range of measured rates,
which indicates that there can be a lot of variation in the composition of flowback fluid.

Figure 2. Evaporation rates for the
12 flowback fluid samples.

We conduct
additional experiments and quantify the potential effects of flowback fluid evaporation on  concentrations of ozone and
particulate matter. Ozone and particulate matter are both EPA criteria
pollutants which have threshold levels that are costly to meet for certain
areas, and they adversely affect human health. A single hydraulically fractured
well uses 2-5 million gallons of water (www.epa.gov)
which means that for a region with large hydraulic fracturing activity the
implications of these emissions on air quality are important to understand.