Va. Code § 21-357
The superintendent in charge of construction or the engineer shall make monthly estimates of the amount of work done, and shall furnish one copy to the contractor and file the other with the board of viewers and the board shall, within five days after the filing of such estimate, meet and direct the secretary to draw a warrant in favor of such contractor for ninety per centum of the work done, according to the specifications and contract; and upon presentation of such warrant, properly signed by the chairman and secretary, to the treasurer, of the drainage fund he shall pay the amount due thereon. When the work is fully completed and accepted by the superintendent or the engineer, the engineer shall make an estimate for the whole amount due, including amounts withheld on the previous monthly estimates, which shall be paid from the drainage fund, as before provided.
Va. Code § 21-357