Q617. I am trying to determine Subpart W applicability for a facility that falls under source category onshore natural gas transmission compression. The calculation utility for onshore natural gas transmission compression makes note of the fact that GHG emissions from transmission storage tanks are not included in the calculation utility spreadsheet. The Subpart W preamble and rule, and EPA guidance document for this source category list transmission storage tanks as requiring direct measurement of emissions. Does EPA offer guidance on how to estimate a worst case scenario for GHG emissions from transmission storage tanks for purpose of determining applicability? Is there a default or assumed value for emissions from transmission storage tanks and that is why it was left out of the calculation utility?

A617. EPA does not have sufficient data to characterize an average emissions factor for scrubber dump valve leakage through transmission storage tanks. Therefore, the calculation tool does not have this source built in. Hence, it is left to the facility to consider whether this is a significant source, including use of an acoustic detection device that has algorithms to quantify through-valve leakage from scrubber dump valves to determine applicability.