Mapping the PM Emissions Exposure Risk due to Hydraulic Fracturing in Pennsylvania

In the past decade, the shale gas boom has led to increasing exploration and production of this strategic energy source with considerable potential economic and environmental benefits. However, there exist environmental health risks caused by emissions from shale gas development activities. Emission concentrations higher than the standard exposure limits can lead to acute diseases and chronic health impacts. Efforts aimed at controlling these risks from shale gas development have focused on residential setback limits, but few other restrictions on the timing or density of development. The evaluation of exposure risk caused by emissions from shale gas development would aid analysis of the need for and effectiveness of regulatory policy changes aimed towards mitigating exposure. This study seeks to estimate the exposure level of residents within the vicinity of the set of actual historical wells to evaluate the severity of this exposure experience.

Current studies have focused mainly on evaluation of health risk caused from exposure to ambient emissions (Pandey et al., 2005; Kalaiarasan et al., 2009). Here, we take advantage of a health risk model to quantify emission exposure risk from hydraulic fracturing to evaluate the severity of this exposure experience. For this purpose, this study uses Gaussian plume models for thousands of individual sources to calculate the exposure values of fine particulate matter (PM_2.5) across the Marcellus shale region of Pennsylvania, considering the density and timing of drilling and fracturing activities. Our model uses the real time hourly monitored wind data to simulate the changes in PM_2.5 concentration levels within vicinity of shale gas well sites. These exposure values serve as inputs to the creation of exposure maps that quantify the level of environmental health risk associated with PM_2.5 emissions.

Results reveal several areas that did not comply with EPA exposure standards which implies a failure of public health protection policy at these locations. We use the results to create exposure maps that quantify and locate the environmental health risk associated with these emissions. We then combine these exposure results with disease risk models and population density to create a series of maps that identify expected case numbers as a function of geographic area and time. Based on these risk maps, we evaluate policy alternatives for regulating the density of shale gas development activity in time and space to keep individual communities below the recommended exposure levels for future emissions. The result from the health risk model is used along with economic valuation information to perform a cost-benefit analysis for controlling the hazardous air emissions from shale gas development activities.

While shale gas activities might cause relatively small changes in the mean annual PM_2.5 concentration at regional scale (0.1 to 0.4 μg/m3 as reported by Roohani et al. (2017)), our results from pollutant dispersion simulation demonstrate significant variations in exposure values as a result of the specific timing and locations of shale gas activities at the local scale. These results suggest that for pollutants with more localized effects like PM, wide area models are insufficient to understand and estimate the level of risk. These risk assessment data and cost estimations can serve as guidance for better and more effective health risk reduction policy at local and state levels. These results also serve as a support for updated residential setback policy around gas wells.

Reference:

1. Kalaiarasan, M., Balasubramanian, R., Cheong, K.W.D., Tham, K.W., 2009. Traffic-generated airborne particles in naturally ventilated multi-storey residential buildings of Singapore: Vertical distribution and potential health risks. Building and Environment. 44, 1493-1500.
2. Pandey, J.S., Kumar, R., Devotta, S., 2005. Health risks of NO₂, SPM and SO₂ in Delhi (India). Atmospheric Environment. 39, 6868-6874.
3. Roohani, Y.H., A.A. Roy, J. Heo, A.L. Robinson, P.J. Adams. 2017. Impacts of natural gas development in the Marcellus and Utica shales on regional ozone and fine particulate matter levels. Atmos. Environ. 155: 11–20.