Volatile Organic Compound (VOC) Concentrations in the Northern Colorado Front Range and the Potential Impact of Future Oil and Natural Gas Activities in the Area

Recent advances in unconventional extraction of oil and natural gas (O&NG) have caused an increase in the number of wells in the Northern Colorado Front Range which has doubled Colorado’s natural gas production over the last 15 years. Growth in O&NG activity can lead to increased emissions of ambient Volatile Organic Compound (VOC) which may negatively impact air quality and human health. This study looks at 5 sites (school, gas station, residential area and 2 natural areas) in the City of Fort Collins and the Town of Timnath in order to provide a useful baseline of VOC concentrations for assessing the impact of future O&NG development activities. In this study samples were collected using an evacuated 6L stainless steel canister equipped with a calibrated flow controller that samples at a constant flow rate for approximately 1 week. Sampling began at the school and gas station in the summer of 2015 and is currently ongoing. Sampling at the 2 natural areas and the residential area took place in the fall of 2015. VOC concentrations were analyzed using an online gas chromatography flame ionization detector (GC-FID) system.

A suite of VOCs were measured in this study; however, the main compounds presented here are Benzene, Toluene, Ethylbenzene and Xylenes (BTEX compounds) because they have been well established as emissions association with O&NG and other petroleum products. BTEX compounds are of particular concern due to their carcinogenic effects and toxicity. Median BTEX concentrations found in this study are summarized in Table 1. Furthermore, the ratio of Toluene to Benzene was used to investigate the source and relative age of the sampled air masses.

The ratio of i-pentane to n-pentane was used to ascertain the influence of current O&NG emissions at each site. Ratios less than 1.0 are typical of O&NG while ratios from urban and combustion sources are typically higher (>2.0). The school, residential area and one of the natural areas were determined to have a similar influence from O&NG by displaying an i-pentane to n-pentane ratio of 0.97, 0.90 and 1.0, respectively. In contrast the gas station, having a mainly combustion influence, displayed a ratio of 2.27. The other natural area was determined to be a mixture of O&NG and urban emissions displaying a ratio of 1.19.

Development of new unconventional O&NG wells is ongoing in the Northern Colorado Front Range and there are plans to develop wells in close proximity to some of the sites in this study. The Environmental Protection Agency (EPA) steady-state dispersion model AERMOD was utilized to project the potential impacts of these developments. The model was run at the sites near future O&NG development locations to evaluate the potential emissions impacts from the addition of 1 or 4 wells. The AERMOD runs showed that the addition of new wells increase the concentration of VOCs near the source; however, concentrations beyond 1,000 ft. were near levels currently measured in this study. Sampling is ongoing at 2 of the sites and the results of the canister samples from this study will provide a detailed comparison in order to evaluate the AERMOD experiments and to accurately ascertain the in situ VOC increases as a result of additional O&NG development.