The Flower Mound community will spend the next two months waiting for results of a state investigation to learn if the number of cancer cases in the town is above the expected range.
The Texas Department of State Health Services (DSHS) is performing another cancer cluster study in Flower Mound after Rachael Rawlins, a University of Texas lecturer, published a study in the Virginia Environmental Law Journal that questions federal and state guidelines related to natural gas drilling and its possible health effects.
In her study, she questioned results of a 2010 cancer cluster investigation conducted by the DSHS, which was conducted following concerns of what Flower Mound residents called a growing number of cancer cases in the town.
The DSHS study, which included data from 1998 to 2007, concluded that the number of cases of childhood leukemia, all-age leukemia, non-Hodgkin’s lymphoma and childhood brain/central nervous system cancers in Flower Mound was within the expected ranges. The study did note an elevated number of breast cancer cases, but it attributed that to an increase in population and more mammograms.
“We have reviewed the law journal paper and stand by our original study,” said Carrie Williams, spokeswoman for the DSHS. “Our study was done and reviewed by doctorate and master’s level epidemiologists and scientists with decades of experience in analyzing cancer data.”
Williams added that Rawlins' analysis was not a cancer study or a scientific review.
“It contains a selective mix of information from various sources to form opinions about the state's regulatory structure and includes a critique of our methodology and findings,” Williams said.
Rawlins’ study points out the 99-percent confidence interval the DSHS study used. Her study used a 95-percent confidence interval. Confidence intervals are used to measure the reliability of the study.
Williams said the 99-percent confidence interval is more reliable.
“A 95-percent confidence interval can be problematic when multiple comparisons are made in a small population,” Williams said, adding the 99-percent interval has been used almost exclusively in cancer cluster investigations. “It can lead to a false positive.”
Still, the 2014 DSHS study is expected to run the data using both confidence intervals.
Williams said the 2014 cancer cluster investigation, which should be complete by June, will look at statistics from the same types of cancers and possibly additional ones.
Williams said the study will include both a 95 percent confident level, which Rawlins' analysis used, and a 99 percent confidence level, which the 2010 study used. But she added that, “the 99 percent confidence interval offers greater confidence that the result is real.”
"We take the community’s concerns and feelings to heart, but we can’t adjust our standards to find something that isn’t there," Williams said.
The study will include data through 2011, Williams said. She said there is typically a lag in data when conducting studies like this.
“It can take two or more years to work with the data to ensure we meet the National Cancer Reporting Standards, which require cancer registries to collect complete, timely and accurate data from the time of diagnosis through first course treatment on every cancer case that is diagnosed or treated in Texas,” Williams said.
Williams said when conducting a cancer cluster study, there is a four-step approach taken in accordance to Centers of Disease Control (CDC) guidelines. The first step is initial response, followed by assessment, which is the current investigation.
Williams said if there is evidence of a cancer cluster, the department will then assess the feasibility of performing an epidemiologic study to examine the association between the cancer cluster and a particular environmental contaminant.
She said factors that go into whether an environmental study would be feasible include the magnitude of difference between what was observed and what was expected, the number of cases, evidence of exposure, availability of environmental data, causes of the type of cancer being discussed, resources and the availability of partners to collaborate with.
If feasible, the final step would be a recommended study design that would be carried out in collaboration with community, environmental and other partners. When asked if that could include gas drilling activities, Williams said it’s hard to speculate beyond the current phase but said, as in any study, there would have to be access to evidence of exposure and environmental data.
While Rawlins questioned state and federal guidelines, she did praise Flower Mound’s efforts in protecting the community against potential environmental impacts of gas drilling.
Flower Mound’s gas drilling ordinance, updated in 2011, increased the setback requirements from a pad site to a residence from 1,000 feet, or 500 feet with mineral interest, to 1,500 feet. The same distance was established to a school, religious institution and a hospital.
In addition, the town performs monthly air monitoring at three drilling pad sites each month. It also has an ambient air monitoring station that rotates quarterly. The town also has a permanent monitoring station from the Texas Commission on Environmental Quality (TCEQ) at Fire Station No. 2 on Shiloh Road.
Matt Woods, the town’s director of environmental services, said the results have been favorable so far.
“There have not been any readings that exceed the monitoring values at our pad sites,” Woods said. “The goal of our program is to check for minor issues before they turn into major ones, and our gas operators have done a really good job at addressing those.”
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