Acute and chronic risk assessment of BTEX in the return water of hydraulic fracturing operations in Marcellus Shale.

Environmental pollution caused by human activities is a pressing issue in developed countries. In this context, it is vital to establish methodologies for the early and reliable estimation of the health risks posed by potential pollutants. Flowback and produced water (return water) from shale gas operations can contain toxic compounds, of which BTEX (benzene, toluene, ethylbenzene, and xylenes) are of concern due to their toxicity and frequent presence above regulatory limits. The return water generated by these operations is stored in ponds or tanks before reaching its final destination. Over time, the composition of this water changes, and leaks or inadequate contact can harm the environment and human health. Here we developed a risk assessment framework to evaluate the temporal evolution of chronic and acute BTEX exposure risks caused by accidental return water leakage. We applied the approach to a hydraulic fracturing operation in the Marcellus Shale Formation. Starting with a time series of BTEX concentrations in the return water, our method deploys transport models to assess risk to health. Our approach compares exposure levels with regulatory limits for inhalation, ingestion, and dermal contact. By identifying the risk levels, exposure pathways, and control parameters in the case study for a range of periods after leakage, our study supports the implementation of appropriate risk mitigation strategies. In addition, by examining risk variation under arid, semi-arid, and humid climate scenarios, the study reveals the impact of climate change on soil characteristics and BTEX transport. The development and application of this methodology is an important step in addressing concerns regarding shale gas operations. The approach proposed paves the way for sustainable practices that prioritise the protection of human health and the environment.