AirToxScreen data overestimates risk in Weld County

Published on October 17, 2024

Recent data from AirToxScreen for the years 2017 and 2020 showed that cancer and non-cancer health risks in southwest Weld County were higher than what the Environmental Protection Agency (EPA) considers acceptable for human health. This finding prompted further investigation to confirm the actual levels of air toxics on the ground.

What is AirToxScreen?

AirToxScreen is a screening tool developed by the EPA and used by the Colorado Department of Public Health and Environment (CDPHE) to identify areas that might have higher health risks from air toxics—pollutants that can pose serious health concerns. The EPA uses computer models to estimate the concentrations of these air toxics. This helps in understanding potential risks to human health from pollutants in the air.

What Did the Investigation Reveal?

In 2022, CDPHE, working with Weld County, collected air samples for four weeks at 10 locations across the region — from Dacono to Platteville and Windsor to Kersey. They focused on three specific air toxics: acrolein, benzene, and formaldehyde — those AirToxScreen estimated to pose the highest risk.

Air sampling revealed the actual concentrations of these air toxics were lower than the 2017 and 2020 AirToxScreen estimates, aligning more closely with the 2019 AirToxScreen estimates. The difference in estimates was due to the EPA using a different basis for emissions and activity levels in 2019, which led to overestimations of air toxic levels for the other years.

Why Were the Measurements Overestimated?

An in-depth investigation by CDPHE and the EPA identified three main issues leading to the overestimation:

1. Overestimated Emissions: Incorrect assumptions about flaring and the use of condensate or storage tanks led to higher estimates.
2. Outdated Information: Emissions from well pad engines were overestimated due to outdated engine type data.
3. Double Counting: Emissions from around 60 facilities, mostly in Weld County, were counted twice.

What Does This Mean for Weld County?

The corrections made to the estimates show that the actual formaldehyde emissions are about 38% lower than initially estimated. The EPA now believes that the cancer risks in Weld County for 2020 are below the upper limit of acceptable risk, which is 100 excess cancer cases per million people.

Moving Forward

The EPA has updated its AirToxScreen website to reflect these corrections and provide a clear understanding of the revised health risks. These updates will be applied to other oil and gas areas in future releases of the AirToxScreen model. Weld County Environmental Health Services will continue to work closely with CDPHE and the EPA to ensure accurate data and better health risk estimates for the future. If you have questions, feel free to contact Dr. Annareli Morales with our Department Public Health and Environment: amorales@weld.gov

Keeping our air clean and safe is crucial for everyone’s health, and these efforts are part of ongoing work to ensure that our environment is as healthy as possible. For more details, you can explore the EPA’s list of corrections and CDPHE’s announcement on the Colorado State web portal.