DOI: 10.5061/dryad.ncjsxkt15
title: Data from: Using controlled subsurface releases to investigate the effect of leak variation on above-ground natural gas detection

description: Pipelines transport natural gas (NG) in all stages between production and
 the end user. The NG composition, pipeline depth, and pressure vary
 significantly between extraction and consumption. As methane (CH4­), the
 primary component of NG is both explosive and a potent greenhouse gas, NG
 leaks from underground pipelines pose both a safety and environmental
 threat. Leaks are typically found when an observer detects a CH4
 enhancement as they pass through the downwind above-ground NG plume. The
 likelihood of detecting a plume depends, in part, on the size of the
 plume, which is contingent on both environmental conditions and intrinsic
 characteristics of the leak. To investigate the effects of leak
 characteristics, this study uses controlled NG release experiments to
 observe how the above-ground plume width changes with changes in the gas
 composition of the NG, leak rate, and depth of the subsurface emission.
 Results show that plume width generally decreases when heavier
 hydrocarbons are present, the leak rate is reduced, and as leak depth
 decreases from 0.9 to 0.6 m. The above surface CH4 plume is undetectable
 when leaks are 1.8 m deep. As most survey methods typically prioritize
 leaks based on the leak size, this study shows that the effect of NG
 density on above-ground plume width is only 4%, equivalent to the effect
 of leak rate. This suggests that reported leaks in areas with heavier
 hydrocarbons could currently be missed or underestimated. Furthermore,
 this study shows that leaks from pipelines laid in covers meeting minimum
 depth requirements of 0.9 m could be easier to detect compared to those
 buried shallower. Overall, this study illustrates that leak survey
 protocols for flowlines and gathering lines should be different from
 distribution pipelines and tailored to the compositions of the transported
 NG to report emissions accurately.
description: The dataset is
 processed data for experiments that were conducted at conducted on the
 ‘rural testbed’ at Colorado State University’s Methane Emissions
 Technology Evaluation Center (METEC) in Fort Collins, CO, US, between
 April and June 2022. Four inlets were fixed at 0.5, 2, 5, and 7 m AGL on
 an 8 m stainless-steel mast 7 m northwest of the subsurface emission
 point. The four inlets were connected to the ABB LGR multiplexor  via 30 m
 lengths of PTFE tubing (1/8" ID x 1/4" OD x 1/16" Wall
 Tygon<sup>®</sup> 2375 Ultra Chemical Resistant Tubing) which
 sampled each height for one minute sequentially. The outlet of the
 multiplexer was connected to a VACUUBRAND GMBH + CO KG MD1 vacuum pump and
 then tee-ed to an ABB LGR-ICOS GLA 132 Ultraportable Greenhouse Gas
 Analyzer (UGGA). The UGGA is a laser absorption spectrometer measuring
 methane, carbon dioxide, and water mole fractions in an air sample. It
 reports mole fractions each second, with a stated precision of 1.4 ppb at
 1 Hz, 0 to 100 ppm linear measurement range, and 0.01 – 1 Hz measurement
 rate. Micrometeorological data is raw data measured at 10 Hz using RM
 Young 81000 ultrasonic anemometer  installed 6 m above the ground at
 METEC.  The sampled methane
 mixing ratios from the UGGA were aggregated into micrometeorological data.
 The Monin-Obukhov length (<em>L</em>) was calculated
 from<em> </em>the surface friction velocity
 (<em>u<sub>*</sub></em>, m
 s<sup>-1</sup>), the mean absolute air temperature
 (<em>T</em>, K), the von Kármán's constant
 (k<sub>v</sub>=0.41),  the gravitational acceleration
 (<em>g</em> = 9.8 m s<sup>-2</sup>) and the 3D
 horizontal/vertical wind vectors (<em>u</em>,
 <em>v</em>, and <em>w</em>, m
 s<sup>-1</sup>), respectively. For analysis, the
 <em>L</em> was converted to Pasquill-Gifford stability class
 (PGSC), where PGSC A is extremely unstable (−100≤?&lt;0), PGSC B/C
 is unstable (−500≤?&lt;−100), PGSC
 D is neutral (|?|&gt;500), PGSC
 E/F is stable (500≤?&lt;100), and
 PGSC G is extremely stable (0&lt;L≤100).
description: # Using controlled subsurface releases to investigate the effect of leak
 variation on above-ground natural gas detection The dataset is a
 combination of methane measurements from the Ultraportable Greenhouse Gas
 Analyzer and meteorological data from the ultrasonic anemometer. This
 dataset is processed from the raw data in the following order: 1. The
 meteorological data was converted from the epoch time to the George date;
 the original sonic data was split into separate dates. 2. The 3D wind
 vectors u, v, and w were calculated from wind direction, wind speed, and
 wind elevation. 3. The UGGA raw data were unzipped, converted to TXT
 files, then to CSV files. 4. From the processed UGGA data, the following
 were extracted: Time,[CH4]\_ppm, MIU valve, and MIU desc variables. 5. For
 each experiment, multiple files were combined into daily files. 6. The
 Monin-Obukhov length was calculated every 15 minutes and converted to
 Pasquill-Gifford classification. Files *
 Experiment\_1.UGGA.MET.2022-04-25.csv: Day 1 data for the Baseline
 Experiment, 10 slpm of total natural gas (NG), 85% methane (CH4) 15% air,
 released at 0.9 m leak depth. * Experiment\_1.UGGA.MET.2022-04-26.csv: Day
 2 data for the Baseline Experiment, 10 slpm of total NG, 85% CH4 15% air,
 released at 0.9 m leak depth. * Experiment\_2.UGGA.MET.2022-05-10.csv: Day
 1 data for a gas composition experiment, 10 slpm of total NG, 70% CH4 30%
 ethane (C2H6), released at 0.9 m leak depth. *
 Experiment\_2.UGGA.MET.2022-05-11.csv: Day 2 data for a gas composition
 experiment, 10 slpm of total NG, 70% CH4 30% C2H6, released at 0.9 m leak
 depth. * Experiment\_3.UGGA.MET.2022-05-12.csv: Day 1 data for a gas
 composition experiment, 10 slpm of total NG, 70% CH4 10% C2H6 10% propane
 (C3H8) 10% butane (C4H10), released at 0.9 m leak depth. *
 Experiment\_3.UGGA.MET.2022-05-13.csv: Day 2 data for a gas composition
 experiment, 10 slpm of total NG, 70% CH4 10% C2H6 10% C3H8 10% C4H10,
 released at 0.9 m leak depth. * Experiment\_4.UGGA.MET.2022-04-04.csv: Day
 1 data for a leak rate experiment, 5 slpm of total NG, 85% CH4 15% air,
 released at 0.9 m leak depth. * Experiment\_4.UGGA.MET.2022-04-05.csv: Day
 2 data for a leak rate experiment, 5 slpm of total NG, 85% CH4 15% air,
 released at 0.9 m leak depth. * Experiment\_5.UGGA.MET.2022-06-02.csv: Day
 1 data for a leak rate experiment, 1 slpm of total NG, 85% CH4 15% air,
 released at 0.9 m leak depth. * Experiment\_5.UGGA.MET.2022-06-03.csv: Day
 2 data for a leak rate experiment, 1 slpm of total NG, 85% CH4 15% air,
 released at 0.9 m leak depth. * Experiment\_6.UGGA.MET.2022-05-25.csv: Day
 1 data for a leak depth experiment, 10 slpm of total NG, 85% CH4 15% air,
 released at 0.6 m leak depth. * Experiment\_6.UGGA.MET.2022-05-26.csv: Day
 2 data for a leak depth experiment, 10 slpm of total NG, 85% CH4 15% air,
 released at 0.6 m leak depth. * Experiment\_6.UGGA.MET.2022-05-27.csv: Day
 3 data for a leak depth experiment, 10 slpm of total NG, 85% CH4 15% air,
 released at 0.6 m leak depth. * Experiment\_7.UGGA.MET.2022-04-12.csv: Day
 1 data for a leak depth experiment, 10 slpm of total NG, 85% CH4 15% air,
 released at 1.8 m leak depth. * Experiment\_7.UGGA.MET.2022-04-13.csv: Day
 2 data for a leak depth experiment, 10 slpm of total NG, 85% CH4 15% air,
 released at 1.8 m leak depth. * Experiment\_7.UGGA.MET.2022-04-14.csv: Day
 3 data for a leak depth experiment, 10 slpm of total NG, 85% CH4 15% air,
 released at 1.8 m leak depth. NAN Values * The dataset contains NaN values
 for seconds when the analyzer did not report concentration values. This
 missing data is handled through listwise deletion. Due to the large
 dataset for the experiment, the listwise deletion does not significantly
 affect the overall result. Variables * Date: Date the experiment was
 conducted. * Time: The time the drawn air was sampled. * [CH4]\_ppm: CH4
 mole fraction in parts per million (ppm). * dis\_m: Distance from the
 release point to the mast in meters (m). * wdirecenter\_deg: Wind
 direction corresponding to the mast position from true North in degrees. *
 hgt\_m: Sampled height in meters (m). * Air temp(degC): Air temperature in
 degrees centigrade. * Air pressure(hPa): Air pressure in Hectopascal. *
 RH%: Relative humidity. * Sonic temp(degC): Sonic temperature in degrees
 centigrade. * WD(degN): Wind direction from true North in degrees. *
 WE(deg): Wind elevation in degrees. * WS(m/s): Wind speed in meters per
 second. * U(m/s): horizontal wind component calculated from the wind speed
 and wind direction in meters per second. * V(m/s): horizontal wind
 component perpendicular to U calculated from the wind speed and wind
 direction in meters per second. * W(m/s): vertical wind component
 calculated from the wind speed and wind elevation in meters per second. *
 L: Monin-Obukhov length. * PG: Atmospheric stability class <br>