May 05, 1992 · Obayashi Corporation is the primary contractor for the construction of the San Pedro Creek and San Antonio River Tunnel and Shaft Project in San Antonio, Texas. We are presently tunnelling a 16,080 feet tunnel, 27 feet in diameter at a depth of 150 feet. Pursuant to 1905.10 Subpart B Variance, and other relief under Section 6(b) (6)(A) of the Act.