A state, county, or local governmental agency or authority, or an official or employee thereof, may not engage in the practice of engineering or land surveying involving either public or private property without the project being under the responsible charge of a professional engineer for engineering projects or a professional land surveyor for land surveying projects as provided for the practice of the respective professions by this chapter; provided, that nothing in this chapter shall be held to apply to any public work wherein the expenditure for the complete project of which the work is a part does not exceed $20,000.