In the end it is always cheaper and easier to manage your environmental responsibilities well . Ironically good environmental performance , and compliance with licence conditions , may become a point of difference between the company and their competitors , and save money .
OGI : What should a client expect with a typical air quality assessment , for example when assessing a gas field collection system and gas processing facility ?
Balch : There are many steps to follow when assessing air quality impacts for a proposed gas field and processing facility . From the beginning , it is important to clearly define the project area and identify the receptors that will be sensitive to the development , whether these are people in the local community or other environmental receptors . Also , both operational and construction related emissions need to be considered for the assessment .
Early in the project baseline ambient air quality and meteorological monitoring should be conducted . It is important to develop a good data set for the existing state of the air environment , including local meteorology . Many proponents ignore this requirement at the start , which can hurt the project later down the track and lead to delays and other important impact assessment issues . Air quality monitoring for gas field developments should focus on the critical operational pollutant , nitrogen dioxide , but also secondary pollutants like ozone , which will be important for assessing nitrogen dioxide impacts in the air quality impact assessment . Particulate matter ( PM10 ) will be the main concern for the construction phase , so it is also a good idea to monitor dust to assess the baseline for the construction air assessment .
The third most critical pollutant worth monitoring is not a health concern but an important greenhouse gas emission . Understanding the background methane concentrations in the project area and the natural and anthropogenic sources of these emissions has become an important requirement in coal seam and shale gas developments . CSG developments are often close to coal mines , which have significantly greater methane emissions than CSG production areas . Also , cattle feedlots , wastewater treatment plants and waste management facilities and landfills are also methane sources . Understanding the differences in methane emissions between these local sources and CSG developments has been important in recent projects I have conducted .
Estimating the air emissions inventory for the gas development is a critical step , including how the project will be powered and the gas processing approach . I have found that the source with the greatest emissions is not always the greatest contributor to ground level air quality impacts . Consequently , plant layout and stack design are also important considerations along with emission inventory development and emission control technology selection . The main operational emissions sources are gas compressors and power generators , regenerative boilers , pipeline compressor stations , flares and wellhead engines . Other fugitive emission sources can include fugitive emissions from the gas gathering network . While these emissions are primarily methane , other trace hydrocarbons are also present .
This information is then used to assess the potential impact to air quality using an atmospheric dispersion model . Care should be taken to select the most appropriate model for this application . Meteorological modelling is also conducted prior to the development of the dispersion model , and this step is greatly enhanced if a year of good quality local meteorological data is available .
Gas field projects are geographically large and dispersed , and emission sources and impact areas change throughout the life of the project as gas wells are commissioned and decommissioned . So planning how you will model and assess these impacts is critical . Through our vast experience in assessing these large projects , we have developed a thorough and robust method to assess the air impacts , while covering the entire project and allowing for the flexibility required .
OGI : And the work you do with LNG plants ?
Balch : Assessing the air impact of LNG plants is more in line with typical industrial facilities . While their footprint is large , they are typically confined to a single site and not spread out like gas fields with sensitive receptors situated between various emission sources .
As with gas field assessments , an assessment of the baseline air quality is important for LNG plant studies . However , unlike the gas fields , which are geographically spread out in rural areas with few other similar emission sources , many LNG plants are situated in industrial hubs with neighbouring industries emitting similar pollutants . In a similar way to the gas fields , air emissions sources comprise mainly fuel combustion processes so the most important pollutant for the assessment is nitrogen dioxide . A good understanding of the baseline levels of nitrogen dioxide and ozone , and the local meteorology is therefore crucial for a comprehensive air impact assessment .
Emission sources comprise routine processes such as gas turbines and power generators and non-routine processes like flares . These have very different uses and operating cycles that need to be considered carefully in the assessment scenarios . While these emissions are typically released from tall stacks , there are critical differences with modelling and assessing air quality impacts from rows of stacks in an LNG train and safety flares . Furthermore , some LNG plants operate with a ground flare , which is very different to the more common stack flare . These are important considerations when modelling and assessing LNG plants and not all atmospheric dispersion models can adequately account for these differences .
OGI : How does odour emissions monitoring work ?
Balch : Developing an odour monitoring plan for any site is inherently more complex than the standard emissions monitoring program for compliance with a site ’ s environmental
Gas Sampling From a Coal Seam Gas Well .
license . Compliance monitoring programs are typically focused only on stack emissions , while odour impacts are more commonly , but not always , caused by near ground fugitive emissions and smaller , less obvious stack sources .
Odour emissions can also be highly variable across a site and from each source . For instance , fugitive area source emissions from liquid and solid surfaces such as wastewater treatment tanks or compost stockpiles can vary spatially and temporally . These variations need to be measured and understood before developing an emissions inventory for a dispersion model . Industrial processes can also operate continuously or in batch mode , with both producing variable odour emission profiles from stack sources . The point in time at which grab samples are collected for odour analysis from each of these scenarios can dramatically affect the assessment of the odour impact .
Odour monitoring requires the collection of air samples from an emission point in sample bags . Samples are then transported to the odour laboratory for analysis within 30 hours of collection . The process of analysing odour is known as dynamic olfactometry and the standard test is to determine the concentration of the odour sample in ‘ odour units ’. Other odour attributes can also be measured using olfactometry including the intensity of the odour relative to its concentration above detection threshold and its hedonic tone , or pleasantness and unpleasantness . A description of the character of each sample is also provided .
Dynamic olfactometry is a process whereby a panel of trained and calibrated ( or screened ) human assessors are presented an odour to assess at varying amounts of dilution . The dilution of the odour sample is controlled by a device called an olfactometer , which is a sophisticated instrument designed to accurately and precisely mix the odour sample with clean air and present that air to the odour assessors at a series of dilutions . This allows the detection threshold of the odour sample to be determined .
Air Environment operates a state-of-the art odour laboratory from its Brisbane offices . We are able to successfully collect and analyse odour samples from sites all over Australia within timeframes mandated by relevant Australian standards .
OGI : Thank you for your time . • Air Environment T : + 61 7 3186 4420 E : andrew @ airenvironment . com . au
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