S.D. Codified Laws § 31-14-21
In lieu of accepting any bids received on any bridge, approach, or abutment, or repair to bridge, or in case of emergency, the board of county commissioners may, if in the board's judgment the bridge or piece of work may be procured for less money than the amount of any bid submitted, cause the same to be built by day labor by regular county labor and county-owned equipment. The county highway superintendent shall be in charge of the construction. The superintendent shall hire a foreman, purchase the necessary material, and hire the necessary labor for the construction of each bridge, or piece of work. The work shall be done in accordance with plans and specifications furnished by the department or a registered engineer, the same as any other bridge or piece of work let by contract.
SDCL 31-14-21