Option for Increased Units of Service. The Department has the option to modify the Contract, by exercising the option to increase units of service by an amount not to exceed an additional fifty percent (50%) of the base number of units of service in the original Contract. Any increase in units of service shall be evidenced by an amendment executed by both parties. The optioned services may not commence before execution of the amendment. Delivery of additional units of service shall be upon the terms, conditions and rate agreed in the exercise of the options of this Contract.