(1) Separate consumption levels will be determined for each partner in a jointly owned coal using facility.   Each partner will be allocated a portion of the facility's total consumption based either on actual coal consumed by each partner, electrical generation received, percentage ownership, or any other reasonable method determined by the department.   A joint owner's share of the consumption from a jointly owned coal using facility will be added to other Montana coal purchases by that purchaser to determine the total base level consumption for that purchaser.