Q557. For blowdown vent stacks the preamble indicates that blowdowns from containers less than 50 cubic feet total physical volume are exempt from reporting. However, requirements under 98.233(i) refer to "50 standard cubic feet", which could imply a gas volume rather than a physical container volume. In comments to the proposed Subpart W, GPA had suggested a threshold of 50 cubic feet of physical container volume and we assume that is the intent here. Please clarify.

A557. The unique physical volume between isolation valves should be considered against the 50 cubic feet threshold for blowdown vent stacks. As stated in 40 CRF § 98.233(i)(2), unique physical volumes smaller than 50 cubic feet are exempt from reporting under § 98.233(i). Please see EPA-HQ-OAR-2009-0923-1018-27 in Response to Comments (pages 1464-1465) (http://www.epa.gov/climatechange/emissions/downloads10/Subpart-W_RTC_part2.pdf).