Human Health Risk Assessment for Oil and Gas Operations In Colorado

“We also estimated chronic exposures for production operations, which can continue for up to 30 years after well development, as well as for some large flowback operations that can last 14–15 months. At the 500-foot distance from the facility, chronic exposures during the 14–15-month flowback activities were far below guideline levels for individual chemicals and only slightly
above guideline levels for combined exposures to multiple chemicals with neurotoxicity or hematological critical effects (which include n-nonane, benzene, m+p-xylene, and trimethylbenzenes). Extending the exposure period to also include the preceding drilling and fracking activities led to similar results. The chronic exposures during production operations were generally the lowest, relative to guideline levels, from among all simulated exposures in the assessment. At the 500-foot distance from the facility, all chronic non-cancer exposures during production activities were below guideline levels, and the average incremental lifetime
cancer risk from chronic benzene exposure was 5-in-one million or less (dropping below 1-inone million before the 2,000-foot distance). When estimates of chronic exposure include exposure to development activities occurring sequentially with exposure to production activities, exposures were only slightly higher than those estimated during the production activities alone.”