Section 13A. With respect to contracts for the recycling or composting of solid waste or the treatment, composting or disposal of sewage, septage or sludge authorized under the provisions of subsection (e) of section one, the governmental body may negotiate modifications and amendments to contracts for recycling services involving the addition of materials to be collected or processed, the deletion of materials to be collected or processed, the change in specifications with respect to materials to be collected or processed, and any price adjustments related to such modifications and amendments, where the contract is for a term of two years, or more, and where such changes are based upon changes in market conditions since the commencement of the contract, provided:
(1) after reasonable investigation of costs and benefits, the chief procurement officer has determined in writing that such modification is in the best interest of the governmental body; and
(2) where the modification involves the addition of materials and an increase in price to the governmental body, the chief procurement officer has determined in writing that the amendment is more advantageous than alternate means of procuring such services.