On January 14, 2000, the EPA gave express notice of a regulatory interpretation that "slotted guidepoles at certain petroleum storage vessels and tanks may not comply with regulatory requirements. Slotted guidepoles are relatively simple devices for sampling the contents of a floating roof storage tank. Unless they are controlled, the slots, hollow core and the space between the guidepole and the tank's roof are observable emission pathways that violate the "no visible gap" prohibition in 40 CFR part 60, subparts Ka and Kb.

Based on these determinations, EPA Region IX brought enforcement actions against 5 California refineries that had tanks with slotted guidepoles and later issued a letter to the Western States Petroleum Association in which it provided a detailed analysis of the issue, determining that slotted guidepoles are subject to the no visible gap requirement. These enforcement matters were settled by the facilities installing controls (e.g., floats and wipers) at 20 NSPS Subpart Ka/Kb tanks and 27 non-NSPS tanks.

Also on January 14, 2000, the EPA proposed a "Storage Tank Emission Reduction Partnership Program". In the interests of promoting fast, efficient and widespread emission reductions, EPA intends to offer and enter into agreements with companies that installed or will install controls to reduce slotted guidepole emissions at their NSPS Subpart Ka/Kb tanks. As under EPA's policy concerning voluntary disclosure, this opportunity will be available only to owners/operators of affected NSPS Subpart Ka/Kb facilities that are not currently the subject of an enforcement action based upon their use of slotted guidepoles.