Health-based evaluation of ambient air measurements of PM2.5 and volatile organic compounds near a Marcellus Shale unconventional natural gas well pad site and a school campus

Abstract

Background: Limited air monitoring studies with long-term measurements during all phases of development and production of natural gas and natural gas liquids have been conducted in close proximity to unconventional natural gas well pads.

Objective: Conducted in an area of Washington County, Pennsylvania, with extensive Marcellus Shale development, this study investigated whether operations at an unconventional natural gas well pad may contribute to ambient air concentrations of potential health concern at a nearby school campus.

Methods: Almost 2 years of air monitoring for fine particulate matter (PM_2.5) and volatile organic compounds (VOCs) was performed at three locations between 1000 and 2800 feet from the study well pad from December 2016 to October 2018. PM_2.5 was measured continuously at one of the three sites using a beta attenuation monitor, while 24-h stainless steel canister samples were collected every 6 days at all sites for analysis of 58 VOCs.

Results: Mean PM_2.5 concentrations measured during the different well activity periods ranged from 5.4 to 9.5 μg/m³, with similar levels and temporal changes as PM_2.5 concentrations measured at a regional background location. The majority of VOCs were either detected infrequently or not at all, with measurements for a limited number of VOCs indicating the well pad to be a source of small and transient contributions.

Significance: All measurement data of PM_2.5 and 58 VOCs, which reflect the cumulative contributions of emissions from the study well pad and other local/regional air pollutant sources (e.g., other well pads), were below health-based air comparison values, and thus do not provide evidence of either 24-hour or long-term air quality impacts of potential health concern at the school.

Keywords: Air monitoring; Marcellus Shale; Natural gas; PM2.5; Public health; VOCs.

Fig. 1. Map of the three air monitoring sites relative to the study well pad site, the school campus, and other local producing well pads.

Wind roses are also shown for Sites 1 and 2 where meteorological stations were operated.

Fig. 2. Time series of 24-h PM_2.5 measurements at study monitoring site 1 and the PADEP background Florence site.

PADEP Pennsylvania Department of Environmental Protection, PM_2.5 fine particulate matter less than 2.5 micrometers in diameter.

Fig. 3. Summary of maximum measured 24-h VOC concentrations by monitoring site and study well pad site development phase.

A benzene, B ethylbenzene, C toluene, and D xylenes. Acute health-based air comparison values (HBACVs) are shown in red dashed lines. ppb parts per billion, VOC volatile organic compound. Measurements for m-, p-, and o-xylenes are summed in this figure because the applicable acute HBACV is for mixed xylenes.

Fig. 4. Summary of mean VOC concentrations by monitoring site and study well pad site development phase.

A benzene, B ethylbenzene, C toluene, and D xylenes. Chronic health-based air comparison values (HBACVs) are shown in red dashed lines. ppb parts per billion, VOC volatile organic compound. Measurements for m-, p-, and o-xylenes are summed in this figure because the applicable chronic HBACV is for mixed xylenes. Mean concentrations, and not 95% UCLs of the means, are shown due to the small number of samples and high fraction of non-detects for some development phases.