Once a municipal public construction contract has been entered into, the contract cannot be modified with regard to the quantity of construction required unless there is an increased quantity clause in the contract. However, an increased quantity clause is statutorily limited to an amount not exceeding 15 percent of the original contract price. Wis. Stat. sec. 62.15(1c); Probst v. City of Menasha, 345 Wis. 90, 13 N.W.2d 504 (1944). If the cost of additional work exceeds 15% of the original contract price, the work should be treated as a separate contract and competitively bid. Contracts #366.