(a) The board of supervisors may, by ordinance, resolution, or board order, authorize the county engineer, or other county officer, to order changes or additions in the work being performed under construction contracts. When so authorized, any change or addition in the work shall be ordered in writing by the county engineer, or other designated officer, and the extra cost to the county for any change or addition to the work so ordered shall not exceed five thousand dollars ($5,000) when the total amount of the original contract does not exceed fifty thousand dollars ($50,000), nor 10 percent of the amount of any original contract that exceeds fifty thousand dollars ($50,000), but does not exceed two hundred fifty thousand dollars ($250,000).
(b) For contracts whose original cost exceeds two hundred fifty thousand dollars ($250,000), the extra cost for any change or addition to the work so ordered shall not exceed twenty-five thousand dollars ($25,000), plus 5 percent of the amount of the original contract cost in excess of two hundred fifty thousand dollars ($250,000). In no event shall any such change or alteration exceed two hundred ten thousand dollars ($210,000).