2018-194 Gas Well Setback Distance StudyDate: December 21, 2018 Report No. 2018-195
INFORMAL STAFF REPORT
TO MAYOR AND CITY COUNCIL
SUBJECT:
During the concluding items portion of the December 3, 2018 City Council meeting, Council
Member Meltzer requested information regarding conducting a scientific study to evaluate gas
well setback distances for the City of Denton.
DISCUSSION:
As mentioned in the gas well setback presentation during the City Council work session on
September 11, 2018, one of the most comprehensive studies specific to potential public health
impacts due to emissions of compounds leaving gas well sites within the Barnett Shale was
commissioned by the City of Fort Worth in 2010 through 2011. The specific goal of this study
was to evaluate whether the 600-foot setback from protected uses established by the City of Fort
Worth was adequate for protecting public health. The City of Fort Worth selected the Eastern
Research group (“ERG”) to conduct this study. ERG began the study during August 2010 and
provided a final report approximately 1 year later. Results of the study indicated that the 600-
foot setback used by the City of Fort Worth was protective of public health according to the
parameters used by the ERG to evaluate public health impacts. Although the study had some
critics, the information was subsequently used by several other cities as a basis for setback
distances, and today the 600-foot setback remains the most common setback distance used within
the Dallas – Fort Worth Metroplex.
The ERG study offers a framework for partially addressing the council request. However, the
study conducted by ERG for the City of Ft. Worth was designed to determine if an established
distance (600 feet) was sufficient for protecting public health. The current council request
appears to be to facilitate research to determine “what is a safe setback distance”, which is a
much more difficult issue to address since a defined distance is not implicit. With this in mind,
the basic design of the ERG study is still valid for addressing the research request, but
substantially more work will be needed to consider multiple distances.
Using the ERG study as a framework, staff suggests the following approach:
1. Complete ambient air monitoring and associated research to establish a baseline.
Complete ambient air monitoring to determine the prevalence and magnitude of specific
compounds in ambient air and complete an assessment of other potential sources of
emissions in proximity to gas wells. The City of Fort Worth established 8 monitoring
sites to assess ambient air quality, and measurements were taken over a two-month
period. Information obtained from this ambient air monitoring network was used to
provide context for point source sampling and analysis efforts, characterize exposure to
selected air toxics in ambient air at various locations in the city, establish concentrations
of air toxics (such as benzene) present in the ambient air in the area, and as a component
of the subsequent public health evaluation. Analyses of other potential sources of
Date: December 21, 2018 Report No. 2018-195
emissions unrelated to gas wells will help in sample collection design and ensure that
quantified emissions can be defensibly demonstrated to be from gas well pad sites.
2. Complete a point source emissions study to characterize emissions from natural gas-
related point sources located within the City of Denton. Data collected during this
phase can be used to derive total emissions profiles for each point source site. This point
source testing must be comprehensive, since emissions at any individual site can fluctuate
depending on day-to-day operating and equipment conditions. The variation in emissions
over the entire population must be captured to determine the likely range of emission
profiles, and the sampling will need to be done for multiple distances.
3. Use accepted, defensible analytical methods to perform monitoring. Analyze volatile
organic compounds (VOCs) using established protocols, which include the
Environmental Protection Agency’s (EPA' s) method TO-15, Carbonyl compounds
identified by EPA' s method TO-11A (including formaldehyde), speciated non-methane
organic compounds (SNMOC), as identified by ERG/SNMOC Analysis Method, and
Methane as identified by EPA' s method TO-14. This approach will provide
information for over 130 compounds, including 45 hazardous air pollutants such as
benzene, ethylbenzene, toluene, and xylenes (BTEX compounds), formaldehyde, and
acetaldehyde. It may also be advisable to consider newer passive methods for that use
sorbent tube technologies such as EPA method TO-17 and /or method 325A. From a
public health standpoint, concentrations of benzene should be of primary importance.
4. Complete air dispersion modeling. The results of elements 1-3 can be used to complete
air dispersion modeling to quantify downwind impacts from natural gas activities using
the latest EPA-approved models and methodologies. This information can then be used to
determine worst case exposure scenarios and to determine the adequacy of various
setback distances within the framework of a public health evaluation.
5. Use defensible and widely accepted heath based screening levels for public health
evaluation. Complete a public health evaluation by comparing the ambient air
monitoring data and the dispersion modeling results to the Texas Commission on
Environmental Quality (TCEQ) health-based screening levels with respect to distances
from pad sites. Evaluations should include both Effects Screening Levels (ESLs) and
Air Monitoring Comparison Values (AMCVs). The TCEQ has developed separate ESLs
for short-term and long-term exposure durations, where short-term values are typically
used for assessing 1-hour average concentrations and long-term values are typically used
for assessing annual average concentrations. Although ESLs are not regulatory
standards, they are often used to interpret potential exposures to air pollution predicted by
models. The TCEQ interprets ESLs as follows: “If predicted airborne levels of a
constituent do not exceed ESLs, adverse health or welfare effects are not expected. If
predicted ambient levels of constituents in air exceed the screening levels, it does not
necessarily indicate a problem but rather triggers a review in more depth.” Air
Monitoring Comparison Values (AMCVs) are pollutant-specific ambient air
concentrations that the agency has established to protect human health and welfare. In
contrast to ESLs, which are primarily used when evaluating air pollution levels predicted
Date: December 21, 2018 Report No. 2018-195
by models, AMCVs are used when conducting health screening evaluations of air
monitoring data. Depending on the sampling results, it is possible that Texas Risk
Reduction Program’s risk based exposure levels (RBELs) for residential inhalation may
also need to be considered.
It is staff’s opinion that the above approach will likely be able to address the Council request.
Staff obtained information on the ERG study via discussions with the City of Fort Worth staff
member that was the project manager for the study. The Fort Worth ERG study was completed
in approximately 1 year, and the total cost was $1,052,448. However, the study included a
$45,254 component for communication and outreach that could possibly be excluded, bring the
costs to $1,007,194 in 2010 dollars. Although the City of Denton has fewer gas well pad sites
than the City of Fort Worth, the request for the Denton study is to determine a specific public
health based setback distance, whereas the City of Fort Worth study was designed to determine if
a single distance (600 feet) was protective of public health. As a result, the City of Denton study
will require substantially more sampling, analytical, and modeling work. Applying a 5% per
year increase to the 2010 ERG study amount of $1,007,194 indicates that the cost of the ERG
study would be approximately 1.65 million in 2019. Considering the more extensive nature of
the Denton study as proposed, it is not unreasonable to expect the study to be in the 2 million
dollar range, and to take perhaps 1.5 to 2.5 years to complete. It is also worth noting that while
the proposed health based screening levels are derived from the TCEQ and the proposed methods
are supported by the EPA, if exceedences of standards are observed the TCEQ is unlikely to
accept those results without additional monitoring and evaluations being performed by the TCEQ
itself.
STAFF CONTACT(S):
Kenneth Banks
General Manager of Utilities
(940) 349-7165
Kenneth.Banks@cityofdenton.com