There is authorized to be appropriated for fiscal years beginning after September 30, 1983, $31,000,000 (October 1990 price levels) plus or minus such amounts, if any, as may be required by reason of ordinary fluctuations in construction costs as indicated by engineering cost indexes applicable to the type of construction involved herein to carry out phase II. Amounts shall be made available pursuant to the authorization contained in this section in sums for individual projects based on findings of feasibility by the Secretary.