January 2017 Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2015: Update Under Consideration for Storage Segment Emissions Incorporating an estimate for the Aliso Canyon Leak This memo was posted and open for stakeholder feedback in January 2017. Many of the updates discussed in the memos below were implemented in the 2017 Inventory. For information on the revisions implemented in the 2017 Inventory, please see Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2015: Revisions to Natural Gas Storage Segment Emissions, available at https://www.epa.aov/ahaemissions/natural-aas-and- petroleum-svstems-aha-inventorv-additional-information-1990-2015-aha. In fall of 2015, a well in a California storage field began leaking methane at an initial average rate of around 50 metric tons (mt) of methane (CH4) an hour, and continued leaking until it was permanently sealed in February of 2016.1 The EPA is considering options for including this emission source in its 2017 GHGI (which includes estimates from 1990-2015).2 The EPA is considering applying the California Air Resources Board (ARB) estimate of the methane release from the leak.3 ARB calculated emissions for two phases of the leak. The first phase corresponds roughly to the first month of the leak (late October-late November 2015), a time of heightened activity at the well. ARB's estimate for emissions in Phase I is 48,450 (+/- 8,810) metric tons of methane. Phase II covers the remainder of the leak period (around 2.5 months), when less site-level activity was occurring. ARB's estimate for emissions in Phase II is 51,200 (+/- 2,970) metric tons of methane. The resulting total estimate of emissions for the duration of the leak is 99,650 (+/- 9,300) metric tons of methane. For the 2015 estimate in the 2017 GHGI, the EPA is considering calculating emissions from Aliso Canyon as the sum of Phase I emissions (48,444 metric tons) and the portion of Phase II emissions that occurred in 2015. Table 1. Use of ARB leak calculations to develop 2015 estimate for U.S. GHGI4 1 For more information, please see Ensuring Safe and Reliable Underground Natural Gas Storage, Final Report of the Interagency Task Force on Natural Gas Storage Safety, available at http://www.energv.gov/sites/prod/files/2016/10/f33/Ensuring%20Safe%20and%20Reliable%20Underground%20 Natural%20Gas%20Storage%20-%20Final%20Report.pdf. 2 In this memo, "2016 GHGI" refers to the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990- 2014, published April 15, 2016, and "2017 GHGI" refers to the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2015, to be published by April 15, 2017. 3 For more information on the leak measurements and calculations, please see California Air Resources Board. Determination of Total Methane Emission from the Aliso Canyon Natural Gas Leak Incident. October 21, 2016. https://www.arb.ca.gov/research/aliso canvon/aliso canyon methane emissions-arb final.pdf. 4 Adapted from California Air Resources Board. Determination of Total Methane Emission from the Aliso Canyon Natural Gas Leak Incident. October 21, 2016. Table 4: Methane Emission Estimates of the Aliso Canyon Natural Gas Leak. 1 ------- January 2017 Phase Measurement Leak Rate Assumed number Leaked methane Flight Date (mt CH4 per of days at this leak for this period hour) rate (mt CH4) Phase 1 Three flights over 11/7-11/28/2015 46.9-60.4 37.0 (10/23-11/27) 48,445 Phase II 2015 11/28/2015 54.7 3.0 (11/29-12/1) 3,938 12/4/2015 48.8 7.0 (12/2-12/8) 8,198 12/12/2015 38.0 9.5 (12/9-12/18) 8,664 12/23/2015 28.1 13.5 (12/18-12/31) 9,104 Phase II 2015 29,905 total emissions Sum of Phase 78,350 1 and Phase II 2015 emissions Phase II 2016 1/8/2016 22.7 10.0 (1/1 -1/10) 5,448 1/12/2016 20.7 6.5 (1/11-1/17) 3,229 1/21/2016 19.1 7.0 (1/17-1/24) 3,208 1/26/2016 19.0 7.0 (1/24-1/31) 3,192 2/4/2016 22.5 11.5 (1/31-2/11) 6,210 Phase II 2016 21,288 total emissions The EPA is considering applying this estimate of 78,350 metric tons of methane to its estimate for 2015. This would result in a total 2015 storage well emission estimate of 92,590 metric tons of CH4 or 2.3 MMT C02e (using AR45 GWP of CH4, consistent with GHGI), and total transmission and storage segment emissions of around 34 MMT C02e, compared with the 2014 estimate of 32 MMT C02e. Table 2. Potential update to storage well emissions estimate in the 2017 GHGI, mt CH4 1990 2000 2005 2010 2014 2015 Storage wells 13,565 15,433 14,910 14,772 15,714 92,590 Storage well emission estimates in the 2018 GHGI The EPA plans to include in the 2018 GHGI both the estimate of the Aliso Canyon leak for 2015, and an estimate for the portion of the leak that occurred in 2016. It is estimated that 21,288 (99,638 total 5 AR4 refers to the Fourth Assessment Report by the Intergovernmental Panel on Climate Change. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K. and Reisinger, A. (eds)]. IPCC, Geneva, Switzerland, 2007. 2 ------- January 2017 minus 78,350 in 2015) metric tons of methane were emitted from the Aliso Canyon leak in 2016. This value would be applied to the 2016 estimate using the same approach selected for the 2015 estimate. Request for stakeholder feedback 1. The EPA seeks feedback on including this source under the storage well category. 2. The EPA seeks feedback on whether adjustments to the estimate are needed to take into account other sources of methane potentially included in the measured data (calculated to be <0.1% of total). The measurement results from studies conducted to assess the well leak at Aliso Canyon also included emissions from other sources at the storage site. In addition to other storage wells, the Aliso Canyon site had various CH4-emitting equipment. The data reported to GHGRP from the Aliso Canyon site included equipment counts of 100 pneumatic controllers (intermittent bleed), 10 reciprocating and 3 centrifugal compressors, and meters, valves and connectors.6 Adding the estimate from the Aliso leak measurements to the existing storage well estimate would result in some minor double counting, for the fraction of emissions that are likely included in the ARB leak estimate. The EPA has assessed 2015 GHGRP subpart W data reported by the facility to develop an estimate of other emissions occurring at the time of the leak. Total GHGRP CH4 emissions reported by the facility in 2015 were 1360 metric tons.7 For the duration of the leak, no compressors were used as no natural gas was being injected into the storage field. Deducting the emissions estimates for compressors (1065 metric tons of CH4) from the total reported to GHGRP results in emissions of 295 metric tons of CH4, and includes emissions from meters, valves and connectors. Apportioning these GHGRP-reported non-compressor CH4 emissions to the 70 days of the leak in 2015 results in 57 metric tons (295 x 70 / 365). The EPA could reduce the Aliso Canyon estimate by 57 tons, assuming that those tons are accounted for in the other estimates in the GHGI, or could make no adjustment, due to the small size of the emissions (calculated to be <0.1% of the total) and the uncertainty range of the Aliso leak. The EPA seeks comment on these approaches. 6 The GHGRP subpart W data used in the analyses discussed in this memorandum are those reported to the EPA as of August 13, 2016. 7 The facility's actual 2015 emissions were higher than those reported to the GHGRP. The GHGRP provides well- vetted average emission factors to calculate emissions. The facility followed these GHGRP calculation methods for 2015 reporting. Actual emissions differ from those reported due to the Aliso Canyon leak event. 3 ------- |