Section 37. The metropolitan district commission, or any city, town or other political subdivision which prior to the sixth day of September, nineteen hundred and sixty-six had constructed or had under construction a water pollution abatement project which qualifies as an approved project as hereinbefore provided, and which project was financed in whole or in part by the proceeds of serial bonds or notes issued on or after December thirty-first, nineteen hundred and fifty-seven, under any general law or special law, shall be annually reimbursed by the commonwealth in an amount equal to thirty per cent of the principal payments of such serial bonds or notes maturing each year beginning January first, nineteen hundred and sixty-eight; provided, however, that if grants under any federal law on or after January first, nineteen hundred and fifty-six, have exceeded thirty per cent of such project's construction cost, the percentage of the principal payments to be paid by the commonwealth shall be reduced by the number of percentage points by which the federal grant exceeded thirty per cent. Reimbursements under this section shall be paid from amounts appropriated therefor from the Local Aid Fund under section 18C of chapter 58.

Any public entity which has constructed abatement facilities shall be eligible, subject to appropriation, for reimbursement of up to fifty per cent of the annual costs involved in the purchase of chemicals used for chlorination, sludge dewatering, odor control and advanced waste treatment for phosphorous removal and nitrification during the operation and maintenance of said abatement facilities. Any such public entity seeking such reimbursement shall prior to the end of any calendar year submit a statement of the cost of such chemicals used by it for said facilities during the preceding fiscal year. The division shall verify the statements of costs submitted and report upon the same to the general court. Reimbursements under this program shall be paid from amounts appropriated therefor from the Local Aid Fund under the provisions of section 18C of chapter 58.