Notwithstanding the provision of any statute or ordinance or any regulation made under authority thereof, whenever the legislative body of a county shall determine that the whole or a portion of public utility facilities that are privately owned shall be located underground within an improvement district established pursuant to improvement by assessment statutes or ordinances, the utility engineering, placing of cables and splicing work shall be performed by the public utility concerned notwithstanding that a portion of the cost of the installation of such utility facilities underground may be borne by the county within which such improvement district is situated or the properties specially benefited within such improvement district or both.