Measuring and Modeling Air Pollution and Noise Exposure Near Unconventional Oil and Gas Development in Colorado

Rapid growth in unconventional oil and gas development (UOGD), driven by improvements in directional drilling and hydraulic fracturing technologies, has made the United States the world's largest producer of oil and natural gas. Rapid UOGD expansion in Colorado's Denver-Julesburg (DJ) Basin, often intersecting with a growing population, has elevated local concerns about noise and air quality impacts. Independent near-pad observations of hazardous air pollutants (HAPs) exposure and noise are uncommon, particularly during well drilling and completions, where evolving technologies and practices continue to alter emissions. The chief goals of this study were to identify potential impacts of UOGD HAPs emissions on nearby communities, characterize A- and C-weighted noise impacts from UOGD operations, and contextualize air and noise pollution measurement and modeling results at health-relevant temporal and spatial scales. Our focus was on the DJ Basin, where a changing regulatory environment has driven innovation to better protect human health and the environment, and past observations facilitate examining whether new operational practices have reduced impacts.

Air quality and noise impacts of UOGD operations conducted by three major DJ Basin operators were studied at four large well pads at three locations across the basin. Studied operations included well drilling, hydraulic fracturing, coiled tubing/millout operations, flowback, and early production. Methane and speciated volatile organic compound (VOC) measurements were made at near-pad and background locations to characterize increases in concentrations associated with specific UOGD activities. Air dispersion modeling was conducted to assess impacts as a function of distance from well pad operations. A- and C-weighted noise levels were monitored at multiple locations.

Near-pad concentration increases of UOGD-related VOCs were most prominent on short timescales, with the most concentrated plumes often one to two orders of magnitude more concentrated than regional background concentrations but typically persisting for less than an hour at a given location. Benzene and, during drilling operations, n-nonane levels came closest to their respective chronic noncancer inhalation health guideline values (HGVs) but remained well below these levels. One-hour benzene levels exceeded 9 parts per billion by volume (ppbv), the acute HGV, on several occasions during different operational phases. Analyses of VOC emissions from specific operational practices provide the first estimate of speciated VOC emission rates from coiled tubing/millout operations, revealed increased emission of C₈-C₁₀ n-alkanes from use of low-odor synthetic drilling muds, and indicated that implementation of closed-loop, tankless fluid-handling systems can reduce flowback emissions of benzene by more than 98% relative to other, recent green completion operations. A TRACER (TRAcking Community Exposures and Releases) UOGD preproduction emission model was developed to provide stakeholders with a new tool to forecast HAPs and other VOC emissions from planned well drilling and completion operations and to test strategies to reduce air quality impacts.

Noise parameters for A- and C-weighted noise consistently exceeded Colorado Energy and Carbon Management Commission (ECMC) thresholds for chronic noise at the minimum compliance point (350 feet) during all activities monitored. At the maximum compliance point (1,975 feet), A-weighted noise no longer exceeded ECMC chronic thresholds during drilling and coiled tubing/millout activities and only sporadically exceeded ECMC chronic thresholds during hydraulic fracturing. However, C-weighted noise consistently exceeded ECMC chronic thresholds during drilling and hydraulic fracturing and sporadically exceeded ECMC chronic thresholds during coiled tubing/millout operations.

Consistent with prior work in the DJ Basin, noise from UOGD operations poses a concern during well drilling and completions, while the greatest air pollutant exposure risk is associated with acute exposure to benzene. This finding highlights the importance of high time-resolution monitoring to document risk near UOGD preproduction operations. Increased utilization of improvements to preproduction operational practices, including the use of grid-powered, electrified drill rigs, synthetic drilling muds, and closed-loop, tankless fluid-handling systems, has reduced air quality and some noise impacts around the DJ Basin UOGD, while Colorado's implementation of a 2,000-foot setback distance has increased protection from HAPs exposure for those living near new well pads. UOGD operations in many other basins are not conducted using the same emission-reducing operational practices, and residents elsewhere often do not enjoy the protection of a 2,000-foot setback; our analyses find considerably higher risk at 500 feet.