If the Request for Qualifications identified the general need for A&E services to assist in the Department's overall mission, the Chief may enter into contracts for such services through a requirements contract, commonly known as an “on-call” contract. Requirements contracts will provide a process for the development and execution of task orders for defined as-needed A&E services. Rates for such services shall be specified in a rate schedule to be attached to the original contract provided that rates may be modified and categories of services added by mutual agreement of the parties.