The Barnett Shale in Northeast Texas is one of the largest and most productive shale gas plays in the U.S. . It has seen an explosion in natural gas production due to advances in drilling technology and the use of hydraulic fracturing (‘fracking’) – technologies that have also prompted widespread concern about their potential health impacts.
A new study measured air quality at playgrounds located in close proximity to natural gas wells and related infrastructure in the Barnett Shale region cities of Fort Worth, Denton, Mansfield, and DISH. Using standardized EPA methods the study found measurable levels of benzene at play areas in 3 of the 4 cities. Benzene is a known carcinogen (e.g., leukemia) and short- and long-term exposure to it can cause a range of other health effects, including rapid and irregular heart rate, tremors, confusion, and unconsciousness .
Photo credits: Cathy McMullen via www.resource-media.org
While no level of exposure to carcinogens is totally safe, the measured benzene concentrations at McKenna Park in Denton, Delga Park in Fort Worth, and City Park in DISH exceeded the Effect Screening Level (ESL) and the Air Monitoring Comparison Value (AMCV) for benzene established by the Texas Commission on Environmental Quality (TCEQ) (see table). TCEQ uses ESLs in its air permitting process and AMCVs in ambient air quality monitoring. Both are chemical-specific air concentrations set to protect human health and welfare .
Exceeded ESL and AMCV*
Below Method Reporting Limit**
Measured above Method Reporting Limit
Exceeded ESL and AMCV
Exceeded ESL and AMCV
Table notes: *The long-term ESL and long-term AMCV values set by TCEQ for health effects of benzene are both 4.5 micrograms/m3 (1.4 ppb-V). ** The Method Reporting Limit is the minimum concentration of the chemical or compound that can be confidently determined by the laboratory method used.
At all of the playgrounds where measurements exceeded ESL and AMCV levels, the natural gas developments were within 500 feet. In 2013 the city of Denton adopted a revised ordinance regulating natural gas development that, among other things, requires a 1,200 feet setback distance between gas wells and ‘protected uses’ such as playgrounds. However, most of the city’s 270 active gas wells are grandfathered (vested) under older regulations and still allow activities such as hydraulic fracturing to occur within 250 feet of homes. Fort Worth requires setback distances of 600 feet (at least 300 feet for multiple well sites), while DISH ordained a 1,000 feet distance to buildings (reduction to a minimum of 500 feet at discretion of Town Board of Commissioners). The study’s results indicate how important adequate setback distances are to protect human health, especially that of children and other vulnerable population groups.
The air quality monitoring data also identified a host of other volatile hydrocarbons and compounds at the playgrounds, albeit in concentrations below TCEQ values. Some of these chemicals are known components of hydraulic fracturing fluids and can be harmful to human health [4-8]. The fact that the individual chemicals were detected below applicable monitoring and health-protective levels, does not exclude the possibility that their presence as a mixture can have cumulative impacts on human health.
This study illuminates once more the need for more routine monitoring of air quality in areas where oil and gas development collides with human settlements, stronger regulation of emissions, and adequate setback distances to keep children out of harm’s way.