For the first revision, and any subsequent revision, of a source reduction and recycling element of a countywide integrated waste management plan which is required to be submitted to the board pursuant to Section 41770, the county waste characterization component shall identify the constituent materials which comprise the solid waste disposed of within the unincorporated area of the county. The information shall be statistically representative of the solid waste disposed of within that area and shall reflect seasonal variations. The constituent materials shall, to the extent practicable, be identified by volume, percentage in weight, or its volumetric equivalent, material type, and source of generation, which includes residential, commercial, industrial, governmental, or other sources.