N.J. Stat. Ann. § 27:16-16

If the cost of the improvement contemplated by section 27:16-15 of this Title exceeds the amount set forth in or the amount calculated by the Governor pursuant to, R.S. 27:2-1, bids shall be invited for the performance thereof by publication in one or more newspapers in the county, for two weeks prior to the time appointed for receiving the bids. The contract shall be awarded to the lowest responsible bidder, who shall furnish good and sufficient security for the performance thereof, to the satisfaction of the board of chosen freeholders.