(a) Annual base charges. Owners of conventional run-of-river hydroelectric power plants that benefit from water storage facilities owned or partially owned by the Commission shall pay an annual base charge to the Commission. The amount of the base annual charge shall be one dollar per kilowatt of installed capacity.

(b) Annual variable charges. In addition to the base charge established in (a) of this section, annual charges based on power generated at each facility will be assessed as follows:

(1) Owners of hydroelectric power plants that benefit from increased hydraulic head available to the hydroelectric project as a result of investments by the Commission shall be charged one mill per kilowatt-hour of energy produced.

(2) Owners of hydroelectric power plants that derive additional benefits from increased flows available to the hydroelectric project that would not have been available without the Commission-sponsored project shall be charged one-half mill per kilowatt-hour of energy produced. No charges for increased flows will be required when charges for increased hydraulic head are in effect.

(3) Charges for the use of any facilities such as pipe conduits, outlet works, and so on, installed in, on or near a Commission-sponsored project that benefit the hydroelectric project in any way will be determined on a case-by-case basis as approved by the Commission.

(c) Credits. The owner of any hydroelectric generating facility shall receive a credit against the current year water use fee otherwise payable to the Commission for any amount which the Commission receives from the U.S. Army Corps of Engineers or from the Federal Energy Regulatory Commission for each calendar year.

(d) Exemptions. No payment will be required when hydroelectric power facility water use charges would amount to less than $25 per year. Retroactive charges will not be assessed for facilities which have already obtained Commission approval pursuant to Section 3.8 of the Delaware River Basin Compact. All hydroelectric generating projects that do not benefit from storage owned or partially owned by the Commission are exempt from these Commission water charges.

(e) Payment of bills. The amount due each year shall bear interest at the rate of 1% per month for each day it is unpaid beginning 30 days after the due date. Payments are due within 30 days of the end of each calendar year. Annual base charges will be prorated for periods less than a year.