Q500. What is the difference between the methods in 40 CFR 98.233(k) and 40 CFR 98.234(a)(1) for monitoring tank emissions? How do we treat intermittent emissions from the storage tank? Can we use an alternative method to quantify the emissions?

Q500. What is the difference between the methods in 40 CFR 98.233(k) and 40 CFR 98.234(a)(1) for monitoring tank emissions?  How do we treat intermittent emissions from the storage tank? Can we use an alternative method to quantify the emissions?

A500. The purpose of the detection and measurement methods is to determine and quantify any continuous gas emissions from condensate storage tank vent stacks. The most common source of vapor emissions from a transmission compressor station condensate tank would be liquid transfer from compressor scrubber dump valves. When operating properly, these sources 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. 40 CFR 98.233(k)(1) specifies several methods that may be used to detect a continuous release of vapor from the condensate tank roof vent. Two options simply determine either the presence or absence of a leak. These methods are based on the use of a leak imaging camera (in accordance with 40 CFR 98.234(a)(1)) or by using an acoustic through-valve leak detection instrument. If a leak is detected using either of these methods, the rule requires that another method (such as a flow meter) be used to determine if the emissions are continuous for 5 minutes and to quantify the emissions if they are continuous for 5 minutes; see 40 CFR 98.233(k)(2). Alternatively, determination of continuous emissions and quantification of the emissions could be determined by using a continuous measurement method without first using a leak detection method. You cannot use alternative methods to those specified in the rule.