The Texas Commission on Environmental Quality (TCEQ) last week said most of the readings in a study of air emission quality in the Barnett Shale natural gas play in North Texas were "well below" acceptable chemical exposure limits.
The anticipated survey followed complaints by residents living in the region who claimed that their air was fouled and their water was contaminated by gas drilling (see NGI, Dec. 21, 2009). TCEQ scientists analyzed more than 100 volatile organic compounds (VOC), but mainly focused on benzene, which is a human carcinogen.
In January the TCEQ released results of an air monitoring survey around 126 gas production sites in the city of Fort Worth, TX (see NGI, Jan. 18). That monitoring survey found no levels of concern for any compounds, and it is unrelated to the new Barnett Shale survey, which monitored air emissions data across the region.
In the newly issued survey, regulators monitored 94 drilling sites, and "at a majority of the tested sites, chemical levels were either not detected or were below levels of health concern," the TCEQ said. However, two of the monitored sites registered moderately high level of benzene. In addition, 19 sites monitored registered benzene concentrations higher than TCEQ regulators said they "would have liked."
Three surveys were conducted by the TCEQ's mobile monitoring organization in August, October and November 2009 in Denton, Wise, Parker, Hood, Johnson and Tarrant counties. The surveys measured air emissions around a "wide variety of natural gas and natural gas-related production facilities," regulators said. "Monitoring staff made every effort to collect emissions measurements downwind of the sources, moving around to stay in the plume where emissions would be most concentrated."
Staff used hand-held VOC monitors, gas chromatographic monitors mounted in specialized TCEQ vehicles, infrared cameras that detect VOC emissions invisible to the naked eye, and instantaneous VOC canisters that take samples that are later analyzed in the laboratory with high levels of accuracy.
"Although the results are complex, it is clear that gas production facilities can, and in some cases do, emit contaminants in amounts that could be deemed unsafe for lifetime (70 years) or long-term exposure," regulators said. "However, at only two monitoring sites were benzene levels found that would trigger immediate actions to reduce emissions."
At one monitoring site, the Targa Resources Inc.'s North Texas LP Bryan Compressor Station (monitoring site No. 8), "instantaneous benzene samples were collected at levels up to 1,100 parts per billion (ppb) approximately 200 yards from two residences," the survey found.
"Although these levels are less than the lowest levels shown to cause adverse health effects in short-term human and animal studies, the levels are of potential concern due to their contribution to long-term cumulative exposure levels."
The TCEQ provided the monitoring results to Targa, and the company reported that repairs had been completed, said regulators. In a test by the TCEQ during the week of Jan. 18, "VOC levels were below short-term effects screening levels (ESL), and benzene was at normal background levels, about 0.25 ppb."
In another measurement taken at a Devon Energy Corp. gas well (monitoring site No. 7), a sample was collected by the TCEQ with a benzene concentration of 15,000 ppb.
"Although this sample was collected at the wellhead and the general public would not be expected to be exposed to these levels, it clearly demonstrates that gas operations can contribute to benzene concentrations in ambient air," the study said.
"The TCEQ provided the monitoring results to Devon, and the company reported that repairs had been completed. Like monitoring site No. 8, testing done [during] the week of Jan. 18 showed VOC levels at the wellhead and at the fence line were below short-term effects screening levels, and benzene was at normal background levels, about 0.25 ppb."
Elevated levels of other VOCs, including carbon disulfide, ethane, 1,2-dibromoethane and isopentane, also were detected at some drilling sites, "but none at levels that would be expected to cause adverse health effects. In addition, several other compounds that can cause odors were detected," said regulators.
The TCEQ already has instituted updated complaint and investigation guidelines for drilling production areas, which require citizen complaints to be investigated within 12 hours (see NGI, Jan. 11). The investigations, said the TCEQ, "can result in enforcement actions against entities responsible for excessive emissions."
Two new long-term monitors, which perform continuous, near-real-time VOC monitoring, are to be installed in the Texas cities of DISH and Eagle Mountain Lake "to get a better understanding of long-term ambient air conditions, to help assess the effectiveness of the TCEQ's actions, and to provide information on how to focus future efforts," said regulators.
"The TCEQ will continue reconnaissance investigations in the area, using both ground and air-based monitoring assets, and conduct a special emissions inventory of sources including an actual gas analysis from each site."
The TCEQ also plans to investigate sources for proper permit authorizations and require sites to be tested that have "continued excessive emissions." State regulators already had launched a review of permitting rules that apply to oil and gas operations to "ensure that authorizations and permits are enforceable and protective of public health, and that they properly regulate all operations located at an oil and gas site."
The TCEQ also said it would continue to provide compliance assistance to small operators, focused initially on condensate producers.
Another survey is scheduled for the same area this spring, said regulators. More information and data from the new study, including the toxicology department memo and the monitoring report, are posted on the TCEQ's Barnett Shale website.
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