An OEI was estimated for each of the 15 facilities using traditional inventory methods augmented with supplemental sources, emission factors from recent studies, and other modications to assure the inventory captured all known sources (see the Emission Calculation Guidance Tool attached to the SI). The guidance tool informs how to augment routine emission factors with direct measurements for signicant sources. For example, stack tests were used to directly measure methane slip in combustion exhaust, in an as-found conditions.