Q500. What is the difference between the methods in 98.233(k) and 98.234(a)(1) for monitoring tank emissions?  How do we treat intermittent emission from the storage tank? Can we use an alternative method to quantify the emissions?

A500. The purpose of this detection and measurement is to determine and quantify any continuous gas emissions from condensate storage tanks.  The most common source of vapor emissions from a transmission compressor station condensate tank would be liquid transfer from compressor scrubber dump valves.  These sources operating properly would be intermittent transfer of liquids from high pressure vessels to an atmospheric storage tank, with a short term flashing of dissolved gas, which is assumed to be less than 5 minutes in duration.  Malfunction of scrubber dump valves can result in high pressure vapor leaking through the valve, into the condensate tank, and out the tank roof vent, which would vent indefinitely.  This continuous release of vapor is detected as a continuous blow of gas from the condensate tank roof vent using a leak imaging camera or by using an acoustic through-valve leak detection instrument.  Based on the current rule, when using an optical gas imaging instrument, the tank needs to be monitored to determine whether the tank vapors are continuous for 5 minutes; see section 98.233(k)(2).  So if a leak is detected per requirements of 98.234(a)(1) and is continuous per the requirements of 98.233(k)(2) then the reporter has to measure the emissions per requirements in 98.233(k)(2)(i)-(iv).  The reporter has the choice of using an acoustic leak detection device to detect and measure leaks per requirements in 98.234(a)(5).  You cannot use alternative methods to those outlined in the rule.