Each probation and parole officer shall receive as compensation for his services a salary to be fixed in accordance with the standards of classification of Chapter 29 (§ 2.2-2900 et seq.) of Title 2.2. Each officer shall also be paid necessary traveling and other expenses incurred by him in the discharge of his duties. The salary and expenses herein provided for shall be paid by the Commonwealth and no part shall be paid by or chargeable to any county or city, except as hereinafter provided. The governing body of any county or city may add to the fixed compensation of probation and parole officers such amount as the governing body may appropriate with the total amount not to exceed fifty percent of the amount paid by the Commonwealth to probation and parole officers. No additional amount paid by a local governing body shall be chargeable to the Department of Corrections or the Parole Board, nor shall it remove or supersede any authority, control or supervision of the Department or Board.