For purposes of this chapter, any reference to the term gallon with respect to liquefied natural gas means diesel gallon equivalent (DGE) and any reference to the term gallon with respect to compressed natural gas or liquefied petroleum gas means gasoline gallon equivalent (GGE). For any gaseous product for which a conversion factor is not provided for in this chapter, based on the best information available, the department shall establish a temporary conversion factor to determine the gallon equivalent. The department shall subsequently submit to the General Assembly a recommended legislative change for this conversion factor.