Pub. Contract Code, § 20723

All work authorized to be done under this article, exceeding in cost the sum of five thousand dollars ($5,000) shall be awarded upon competitive bidding, except that work consisting solely of new construction is required to be awarded upon competitive bidding only if it exceeds in cost the sum of ten thousand dollars ($10,000). Notice of the proposed letting of such a contract shall be given by advertisement for a period of two weeks or published pursuant to Section 6066 of the Government Code, in a newspaper of general circulation, published, printed, and circulated, in the district. The board may authorize additional publication in other newspapers of general circulation in the district when it deems that such publication would best serve the public interest. The contract shall be awarded to the lowest responsible bidder.

The board may, without advertising for bids, negotiate with the government of the United States for the purpose of assisting the board in the performance of any of the work authorized by this article, and the board may contribute to the United States all or any portion of the estimated cost of any work authorized by this part which is to be done by or under contract with the United States.