Section 171.500 - How does BIA determine the annual operation and maintenance assessment rate for the irrigation facility servicing my farm unit?(a) We calculate the annual operation and maintenance assessment rate by estimating the following annual costs and then dividing by the total assessable acres for your irrigation facility: (1) Personnel salary and benefits for the facility engineer/manager and employees under their management or control;(2) Materials and supplies;(3) Vehicle and equipment repairs;(4) Equipment costs, including lease fees;(7) Maintenance of a reserve fund available for contingencies or emergency costs needed for the reliable operation of the irrigation facility infrastructure;(8) Maintenance of a vehicle and heavy equipment replacement fund;(9) Systematic rehabilitation and replacement of project facilities;(10) Contingencies for unknown costs and omitted budget items; and(11) Other costs we determine necessary to properly perform the activities and functions characteristic of an irrigation facility.(b) Annual operation and maintenance assessment rates may be lowered through the exercise of our discretion when items listed in (a) of this section are adjusted pursuant to our authority under 25 U.S.C. 385 , 386a and 389 .(c) If you subdivide your farm unit, you may be subject to a higher annual operation and maintenance assessment rate, which we publish annually in the FEDERAL REGISTER.(d) At projects where supplemental water is available, the calculation of your annual operation and maintenance assessment rate may take into consideration the total estimated annual amount to be collected for supplemental water deliveries.