Leak Survey Research Articles

Development of Company-Specific Emission Factors with Confidence Intervals for Natural Gas Customer Meters in Southern California.

Methane is both a significant and short-lived greenhouse gas compared to CO2, and reducing methane emissions from natural gas distribution systems may offer cost-effective reduction opportunities. We report substantial new direct leak rate measurements from customer meter set assemblies (MSAs) in Southern California. In a novel way, emission factors are defined in terms of aboveground Hazardous and Nonhazardous leak categories, which take direct advantage of readily available industry leak data. We also studied leaks that were not detected as part of normal leak survey procedures. As a result, this yields company-specific emission factors that can be used to track progress in reducing methane emissions. This approach also has the advantage of explicitly accounting for the skewed or fat-tail distribution of leak rates by treating high flow rate MSA leaks separately from low flow rate MSA leaks. The Southern California Gas (SoCalGas) methane emission factors, based on 485 leak rate measurements by direct enclosure, were 4.55 (95% confidence interval: 2.32 to 7.14) kg/day for Hazardous leaks, 0.149 (0.119 to 0.183) kg/day for Nonhazardous leaks, and 0.0039 (0.0003 to 0.0198) kg/day for Non-Detected leaks. The percentage of surveyed meters with nondetected leaks was 29.1% (24.3 to 34.6%). Based on a robust Monte Carlo analysis, total leak emissions from MSAs for the SoCalGas system were reduced by 35% based on data from 2015 to 2022. These reductions were attributed to surveying a larger number of MSAs and accelerated leak repair rates. In traditional population-based emission inventories, an individual emission factor for a given asset category is multiplied by the total population of MSAs within the category. This approach simply cannot capture the reduction in leak numbers and methane emissions resulting from leak mitigation and prevention programs.

Evolution in geosynthetics starts with utilizing data technology

This paper focuses on the automation of the geosynthetics installation QA/QC process by way of software integration in the field data entry and office data management. Technology is essential to the advancement of geosynthetic installations, especially data application. In its most basic form, data application is a means of gathering, storing, and utilizing information more easily than its predecessor(s). If implemented appropriately, data application technology improves process efficiency. Users and downstream stakeholders of process improvements can then capitalize by delivering quicker, higher-quality, more economical products. The geosynthetics industry is lagging in the area of data application. From a feasibility perspective and assessing practical implementation opportunities, many workflows widely used for tracking geosynthetic installations and its associated means and methods are antiquated and, furthermore, lack reliable authenticity verification. The current accountability requirements require a robust catalog of information reporting to substantiate this important environmental construction practice. The combination of room to evolve in practice and existing data requirements make the geosynthetics industry an ideal suitor for this technology integration. While advancements in materials manufacturing, welding equipment, and post-installation leak surveys already contribute to progress, there is a lack of universally accepted information infrastructure to aggregate all facets of an installation. Software automation creates a cyclical geosynthetics ecosystem that benefits the industry as a whole.

Using controlled subsurface releases to investigate the effect of leak variation on above-ground natural gas detection

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 study illustrates that heavy gas leaks from flowlines and gathering lines could currently be more challenging to detect than leaks from distribution pipelines as the plume is trapped close to the ground. Further, 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. The study aims to improve the understanding of flowline/gathering line leaks to prevent fatal accidents, such as the 2017 explosion from a gathering line in Firestone, Colorado, that resulted in two fatalities and one injury.

The Danish national effort to minimise methane emissions from biogas plants

In total, 69 biogas plants representing 59 % of Danish biogas production participated in a national effort to reduce methane (CH4) emission. Measurements in terms of total plant CH4 emissions, quantification of emissions from point sources, leak surveys and conceptual design plans to mitigate emissions were performed. Plant-level CH4 emission rates varied between 1.3 and 81.2 kg CH4 h−1, and CH4 losses expressed in percentages of production varied between 0.3 and 40.6 %. Agricultural plants generally had lower CH4 loss rates compared to wastewater treatment plants. Biogas plants with a smaller gas production emitted a larger fraction of their production compared to larger plants, which was partly explained by the absence of gas collection from digestate storage tanks at smaller plants. A very commonly observed source of emission was pressure relief valves, where this source of leakage was observed at 53 % of the plants. A national emission factor (sum of CH4 emissions/sum of CH4 productions) was determined at 2.5 % for the Danish biogas production, whereof it was 2.1 % for agricultural biogas production and 6.7 % for biogas production at wastewater treatment plants. Measurements of total CH4 emissions at six plants performed before and after implementation of mitigating actions showed that emissions were reduced by 46 % by carrying out relatively minor technical fixes and adjustments. An economic evaluation showed that, in some cases, mitigating actions could be economically beneficial for the biogas plant (positive net present value over a 10 year time frame), due to an increase in revenue.

Technological avenues and market mechanisms to accelerate methane and nitrous oxide emissions reductions.

Strategies targeting methane (CH4) and nitrous oxide (N2O) emissions are critical to meeting global climate targets. Existing literature estimates the emissions of these gases from specific sectors, but this knowledge must be synthesized to prioritize and incentivize CH4 and N2O mitigation. Accordingly, we review emissions sources and mitigation strategies in all key sectors (fuel extraction and combustion, landfilling, agriculture, wastewater treatment, and chemical industry) and the role of carbon markets in reducing emissions. The most accessible reduction opportunities are in the hydrocarbon extraction and waste sectors, where half (>3 Gt-CO2e/year) of the emissions in these sectors could be mitigated at no net cost. In total, 60% of CH4 emissions can be mitigated at less than $50/t-CO2. Expanding the scope of carbon markets to include these emissions could provide cost-effective decarbonization through 2050. We provide recommendations for carbon markets to improve emissions reductions and set prices to appropriately incentivize mitigation.

Investigating detection probability of mobile survey solutions for natural gas pipeline leaks under different atmospheric conditions

The 2015 Paris agreement aims to cut greenhouse gas emissions and keep global temperature rise below 2 °C above pre-industrial levels. Reducing CH4 emissions from leaking pipelines presents a relatively achievable objective. While walking and driving surveys are commonly used to detect leaks, the detection probability (DP) is poorly characterized. This study aims to investigate how leak rates, survey distance and speed, and atmospheric conditions affect the DP in controlled belowground conditions with release rates of 0.5–8.5 g min−1. Results show that DP is highly influenced by survey speed, atmospheric stability, and wind speed. The average DP in Pasquill–Gifford stability (PG) class A is 85% at a low survey speed (2–11 mph) and decreases to 68%, 63%, 65%, and 60% in PGSC B/C, D, E/F, and G respectively. It is generally less than 25% at a high survey speed (22–34 mph), regardless of stability conditions and leak rates. Using the measurement data, a validated DP model was further constructed and showed good performance (R2: 0.76). The options of modeled favorable weather conditions (i.e., PG stability class and wind speed) to have a high DP (e.g., >50%) are rapidly decreased with the increase in survey speed. Walking survey is applicable over a wider range of weather conditions, including PG stability class A to E/F and calm to medium winds (0–5 m s−1). A driving survey at a low speed (11 mph) can only be conducted under calm to low wind speed conditions (0–3 m s−1) to have an equivalent DP to a walking survey. Only calm wind conditions in PG A (0–1 m s−1) are appropriate for a high driving speed (34 mph). These findings showed that driving survey providers need to optimize the survey schemes to achieve a DP equivalence to the traditional walking survey.

Characterizing detection probabilities of advanced mobile leak surveys

Advanced leak detection (ALD) to survey local natural gas distribution systems has reached a point in technological maturity where new federal regulations will require its use in compliance surveys. Because most of these deployments are conducted by commercial providers, there has been little publicly available data documenting characteristics of the underlying methane (CH4) plumes that are the core features measured in ALD surveys. Here, we document key features of CH4 plumes measured in ALD surveys of 15 U.S. metropolitan areas where we had deployed high-sensitivity CH4 analyzers on Google Street View cars. Our analysis reveals that CH4 concentration enhancements from CH4 sources exhibit high temporal variability, often differing by more than 10-fold among repeated observations. This variability introduces challenges for estimating source emission rates because the same source can appear to be large on one drive-by and small on the next. Additionally, the frequency distribution of CH4 enhancements from a given source generally has a strong positive skew that can lead to overestimation of leak size. The magnitude of CH4 enhancements from a source measured with a mobile sensor can also change quickly over time, as indicated by decreasing temporal correlation between mobile measurements longer than an approximately hourly time scale. To manage the uncertainty, we demonstrate how additional survey effort can help overcome this variability and instability to allow discrimination among the wide range of leak sizes. We quantify the probability of source detection, finding that it increases with estimated leak size. Combining these results, we develop a simulation that demonstrates the potential for ALD to detect leaks and quantify emissions as a function of sampling (driving) effort. Our results suggest that five to eight drives of each roadway in a target area would detect >90% of leaks and provide adequate emissions quantification for repair/replacement prioritization.

An enhanced procedure for urban mobile methane leak detection

Leaked methane from natural gas distribution pipelines is a significant human and environmental health problem in urban areas. To assess this risk, urban mobile methane leak surveys were conducted, using innovative methodology, on the streets of Hartford, Danbury, and New London, Connecticut, in March 2019. The Hartford survey was done to determine if results from a 2016 survey (Keyes et al., 2019) were persistent, and surveys in additional towns were done to determine if similar findings could be made using an identical approach. Results show that Hartford continues to be problematic, with approximately 3.4 leaks per road mile observed in 2016 and 4.3 leaks per mile estimated in 2019, similar to that previously found in Boston, Massachusetts (Phillips et al., 2013). A preliminary estimate of methane leaks in Hartford is 0.86 metric tonnes per day (or 313 metric tonnes per year), equivalent to 42,840 cubic feet per day of natural gas, and a daily gas consumption of approximately 214 U.S. households. Moreover, the surveys and analyses done for Danbury and New London also reveal problematic leaks, particularly for Danbury with an estimated 3.6 leaks per mile. Although road miles covered in New London were more limited, the survey revealed leak-prone areas, albeit with a range of methane readings lower than those in Hartford and Danbury. Data collection methods for all studies is first reported here and are readily transferable to similar urban settings. This work demonstrates the actionable value that can be gained from data-driven evaluations of urban pipeline performance, and if supplemented with a map of leak-prone pipe geo-location, and information on pipeline operating pressures, will provide a spatial database facilitating proactive repair and replacement of leak-prone urban pipes, a considerable improvement compared to reactive mitigation of human-reported leaks. While this work pertains to the selected urban towns in the Northeast, it exemplifies issues and opportunities nationwide in the United States.

Measurement of Apparent Electrical Impedance of Soil with Water Flow Inside

Understanding the flow of groundwater is very important, not only for water management but also for the prevention and mitigation of natural disasters. The electrical resistivity method has been established as an effective groundwater exploration method in geological surveys. The purpose of this study is to develop an accurate investigation method for groundwater flow using soil impedance fluctuations. As a preliminary experiment, the apparent soil impedance was measured by applying a low-frequency current through a soil column with water flow inside. The apparent impedance showed fluctuations due to water flow at frequencies above 20 Hz, and the fluctuation range increased with the flow rate of water. It has been proposed that groundwater flow can be detected by measuring impedance fluctuations, and it is considered that this method can be applied to groundwater surveys and embankment and reservoir leak surveys.

Compressed Air as Energy Savings, Leak Survey and Recognizing Right Fittings to Show Cost Benefits

Compressed Air as Energy Savings, Leak Survey and Recognizing Right Fittings to Show Cost Benefits

Detection limits of optical gas imagers as a function of temperature differential and distance

ABSTRACTOptical gas imaging (OGI) is an effective tool for detecting gas leaks from process equipment. Despite the fact that OGI has been used for leak detection for over a decade, its detection limit is an elusive performance metric and has not been systematically characterized and quantified like other detection instruments. A substantial body of research has been performed that has shed some light on the OGI detection limits and the factors that dictate the detection limits. The OGI detection limit expressed as ppm-m and ppm now can be quantified as a function of ΔT (differential temperature between the gas plume and the background), the OGI camera type, and the specific gas in question. Furthermore, the OGI detection limit expressed as grams per hour can be calculated based on the ΔT and the distance from the OGI camera to the leak location under common leak survey conditions. For the same OGI camera, the detection limit can vary by several orders of magnitude due to ΔT and distance. The present work has demonstrated how different OGI detection limits can be. More importantly, this work has, for the first time, formulated equations that can be used to determine OGI detection limits with a given set of leak detection conditions. Being able to quantify OGI detection limit and understand the variables that dictate the detection limit is a significant advancement. It will help OGI to become accepted as a mature field instrument. The variables characterized in this work should have an impact on the development of OGI leak survey protocols, such as Appendix K to Code of Federal Regulations 40 CFR Part 60 in the United States. Established detection limits will also help emission inventory for fugitive emissions when OGI is used as the sole leak detection method.Implications: Optical gas imaging (OGI) has been used for leak detection and control of fugitive volatile organic compound (VOC) emissions and methane emissions due to equipment leaks. However, detection limits of OGI have not been characterized and quantified like other detection instruments. The lack of well-understood detection limits has hindered broader applications of OGI. The work presented in this paper represents important steps that will enable OGI users and policymakers to establish (1) OGI detection limits under various conditions, (2) OGI leak survey criteria for a desired minimum detectable leak size, and (3) maximum potential emissions from the nondetect sources in emission inventory studies.

Rapid, Vehicle-Based Identification of Location and Magnitude of Urban Natural Gas Pipeline Leaks.

Information about the location and magnitudes of natural gas (NG) leaks from urban distribution pipelines is important for minimizing greenhouse gas emissions and optimizing investment in pipeline management. To enable rapid collection of such data, we developed a relatively simple method using high-precision methane analyzers in Google Street View cars. Our data indicate that this automated leak survey system can document patterns in leak location and magnitude within and among cities, even without wind data. We found that urban areas with prevalent corrosion-prone distribution lines (Boston, MA, Staten Island, NY, and Syracuse, NY), leaked approximately 25-fold more methane than cities with more modern pipeline materials (Burlington, VT, and Indianapolis, IN). Although this mobile monitoring method produces conservative estimates of leak rates and leak counts, it can still help prioritize both leak repairs and replacement of leak-prone sections of distribution lines, thus minimizing methane emissions over short and long terms.

Estimation of Area Leakage in Water Distribution Networks: A Real Case Study

Leakage detection in water distribution networks has attracted attention in the water supply industry. To prioritise leak surveys in water distribution networks, a method for estimating area leakage was proposed. This paper shows the results of a real case study to evaluate the proposed method. In two sets of test conditions, the method correctly identified areas where additional leakage of 3.5% of average system flow was simulated by discharge from fire hydrants. By comparing estimated area leakage with and without simulated leakage, the estimation error of area leakage was evaluated to be about 2% of average system flow.

Estimating Area Leakage in Water Networks Based on Hydraulic Model and Asset Information

Abstract This paper proposes a method of estimating area leakages in virtual areas of a water network to prioritize leak surveys for the areas. It estimates the leakage within the areas by minimizing the difference between the measured and the hydraulic-model-estimated pressure and flow rates. Leakage is distributed around junctions with risk models based on asset information around junctions such as pipe length. The accuracy was evaluated by a simulation study, where the impact of head measurement error was considered by a Monte-Carlo-type method. The mean absolute error of area leakage was less than 2 percent of the system flow.

Risk reduction through advanced leak management

Leaks of hydrocarbon to the atmosphere can be a major facility safety risk and personnel occupational health and safety (OHS) risk for oil and gas producing and processing facilities. Normally closed valves that pass or leak in-line are also a major contributor to product loss and facility risk. Component failures of these types have two common and challenging features: they are hard to find among the tens of thousands of potential leak sources, and the leakage rates either to the atmosphere or in-line can vary from minor to potentially catastrophic. In the past seven to eight years, advanced methods for finding and managing leaks resulting from poor component integrity have been developed. This paper covers some of ATMECO’s accumulated knowledge developed over many leak surveys of both onshore and offshore oil and gas facilities. Typical statistical profiles of leaks from uncontrolled facilities are presented. The types of component failure that lead to leaks are discussed along with probabilistic analyses relating to the next likely failure. Technologies of leak detection are reviewed, highlighting benefits and problems. Also discussed are the prerequisite data capture and management systems needed for a competent, robust and auditable system to manage component integrity. Gas imaging technology is becoming one of the core hydrocarbon leak detection tools and also assists greatly in the analyses of leaks and in providing valuable input to remedial actions. Survey design requirements for continuing and cost-effective component leak risk management are reviewed. Recommendations are provided about the preferred methods and management structures for programs designed to minimise component integrity risks.

Acoustic Leak Survey of the Underground Potable Water System at a CONUS Army Installation

U. S. Army Corps of Engineers Engineer Research and Development Center, Construction Engineering Research Laboratory (ERDC-CERL), and Carlyle Consulting’s John Carlyle conducted a leak detection survey at a U.S. Army Installation. The age of pipes in the distribution system ranged from 20 to 60 years. The thrust of the work was to acoustically survey all of the underground pipelines constituting the installation’s potable water distribution system and find any leaks. The results of the survey were that 6 leaks were discovered in the main lines, 63 leaks associated with fire hydrants, freeze proof hose bibs, water meters, etc., and 33 leaks inside buildings. Over two thousand acoustic measurements were made in order to obtain these results.

Sci‐AM Fri ‐ 06: Boxes, locks and talks: Making Class II compliance in a regulated environment

Class II facilities in general and cancer centers running a radiation therapy program in particular, are being subjected to increasingly more rigorous regulation by the Canadian Nuclear Safety Commission (CNSC). The mission of the CNSC to regulate the use of nuclear energy and materials to protect health, safety, security and the environment can sometimes run counter to the day‐to‐day reality of running a cancer clinic. The recent division of our hospital radiation safety program into two distinct components: Class II (radiotherapy) and other (diagnostic radiology, nuclear medicine, research and laboratories, and consolidated), resulted in a significant improvement in the organization and delivery of radiation safety services. Performing the duties of a Class II Radiation Safety Officer to meet compliance requires a delicate balance of paper‐pushing and common sense: two activities that are often at odds with each other. License activities covered by CNSC document C‐120, such as applications and renewals as well as annual compliance reports, will be discussed. Devices we have installed to facilitate compliance for teletherapy and brachytherapy (HDR and manual) licenses will be presented. Procedures accepted by the CNSC for in‐house leak testing and survey meter calibration (R‐116 and R‐117) and suggestions for facilitating CNSC inspections and audits will also be discussed. Finally, a description of our approach to meeting several recent compliance requirements by the CNSC Nuclear Security Division (within the scope of Prescribed Information limitations) at our cancer center will be reviewed.

Practical Steps to Reduce Apparent Water Losses

This article discusses water loss and categorizes it into either real losses or apparent losses. A case study is presented of the Kansas City (MO) Water Services Department (KCWSD) where, in 2001, high rates of water loss and accompanying loss of revenue were experienced. A detailed water audit identified several factors leading to both real and apparent water losses. The Water Recovery Committee was formed to address these issues, creating a leak survey crew to accelerate the rate of repair of water main leaks and breaks, and dividing the apparent losses into four main areas. The article discusses several process improvements to further reduce apparent water losses, along with the success of the water recovery measures that were instituted.

Surveys Uncover Undetected Leaks

This article discusses leak detection and the use of a leak survey to pinpoint the location of the leak. A leak survey uses sensitive electronically amplified sensors that allow the technician with headphones to hear leaks through pipes from fire hydrants, main line valves, and service valves and meters up to several hundred feet away from the leak, depending on pipe size, material, and pressure on the system.

Leaks in Pipe Networks

Leak detection in water‐distribution systems can be accomplished by solving an inverse problem using measurements of pressure and/or flow. The problem is formulated with equivalent orifice areas of possible leaks as the unknowns. Minimization of the difference between measured and calculated heads produces a solution for the areas. The quality of the result depends on number and location of the measurements. A sensitivity matrix is key to deciding where to make measurements. Both location and magnitude of leaks are sensitive to the quantity and quality of pressure measurements and to how well the pipe friction parameters are known. The overdetermined problem (more measurements than suspected leaks) gives the best results, but some information can be derived from the underdetermined problem. The variance of leak areas, based on the quality of system characteristics and pressure data, indicates the likely accuracy of the results. The method will not substitute for more traditional leak surveys but can serve as a guide and supplement.