The Texas Commission on Environmental Quality has completed the Health Effects Review of Barnett Shale Formation Area Monitoring Projects, including Phase I (August 24 – 28, 2009), Phase II (October 9 – 16, 2009), and Phase III (November 16 – 20, 2009).
All chemicals monitored at the majority of monitoring sites were either not detected or were detected below levels of immediate health concern. At two monitoring sites in one geographic area, benzene was measured above the TCEQ short-term, health-based comparison value of 180 parts per billions (ppb) and the Toxicology Division (TD) recommends a reduction in volatile organic compound (VOC) emissions in this area. While not an immediate health concern, benzene was measured at short-term levels that could cause concern about long-term cumulative exposure levels at an additional 19 monitoring sites in 11geographic areas. The TD recommends additional stationary long-term monitoring in the Barnett Shale area to better assess the influence of oil and gas activity on ambient concentrations of VOCs, particularly benzene, on a regular basis over a long period of time.
Key Findings
• Thirty-five chemicals were detected above appropriate short-term comparison values in one instantaneous canister sample collected at a Devon Energy natural gas well -head (monitoring site 7) with a benzene concentration of 15,000 ppb. Multiple chemicals were detected at levels that could cause adverse health effects if short-term exposure were to occur. However, this sample was collected on-site, directly at the source, and the general public would not be expected to be exposed to these chemical concentrations from this source. This type of sample can help characterize the presence of benzene in some field gas prior to processing.
• In addition to the benzene concentration in the sample collected at the natural gas well-head, benzene was detected above the short-term health-based comparison value of 180 ppb at one of the 64 monitoring sites sampled for VOCs. Three Rea l-Time Gas Chromatograph (RTGC) samples collected predominantly downwind of the Targa North Texas LP Bryan Compressor Station (monitoring site 8) approximately 200 yards from two residences had instantaneous concentrations of 220 ppb, 1100 ppb, and 300 ppb benzene, with a maximum one-hour average of 370 ppb. Although the reported benzene concentrations in samples collected downwind of monitoring site 8 are less than the lowest levels shown to cause adverse health effects (e.g., hematological, neurological) in short-term human and animal studies, elevated short-term levels are of potential concern due to their contribution to long-term ( i.e., lifetime) cumulative exposure levels because benzene is a known human carcinogen. The TD recommends a reduction in the VOC emissions near monitoring site 8.
• Due to concern s about elevated short-term levels of benzene contributing to long-term cumulative exposure levels, the TD has some concerns about areas where benzene was detected above the long-term health-based comparison value of 1.4 ppb. Benzene was detected above the long-term health-based comparison value at 21 monitoring sites, including sites 7 and 8, in 12 different areas (Map I). Because of these concerns, the TD recommends additional stationary long-term monitoring in the area to better assess the influence of oil and gas activity on ambient concentrations of VOCs, particularly benzene, on a regular bas is over a long period of time.
• Carbon disulfide, ethane, isopentane, and 1,2-dibromoethane exceeded short-term health-based comparison values at some monitoring sites. However, the measured concentrations of these chemicals were all well below known health effects levels, so short-term exposure to these concentrations would not be expected to cause adverse health effects.
• None of the 20 monitored Reduced Sulfur Compounds (RSCs) were detected in any RTGC sample at
15 monitoring sites sampled for RSCs.
• Six monitoring sites were samples for Oxides of Nitrogen (NOx ). Although NOx, was detected in multiple samples, the monitored concentrations would not be expected to cause adverse health effects.
• Several chemicals were detected at concentrations that could cause odorous conditions. This is consistent with Texas Commission on Environmental Quality (TCEQ) staff reporting odors during this investigation as well as citizen reports of odors in the area. Persistent or recurrent exposure to levels which significantly exceed the odor threshold may cause odor-related effects such as headache and nausea.
• Existing TCEQ fixed-site VOC monitors near oil and gas activity in the Dallas/Fort Worth Metroplex have not reported annual averages of any VOCs, including benzene, above long-term health comparison values since monitoring began in 2000.
For more information on the completed study, please visit: http://www.tceq.state.tx.us/implementation/barnettshale/bshale-main