If the base test pressure is 3.5 psi and the water table is 2 feet above the sewer line, what is the total pressure in the pipe?

If the base test pressure is 3.5 psi and the water table is 2 feet above the sewer line, what is the total pressure in the pipe?

• A. 3.5 psi
• B. 4.5 psi
• C. 5.0 psi
• D. 6.0 psi

Answer: (B)

Pressure in the pipe during this test is the sum of the base pressure and the hydrostatic pressure from the water column above the line. Water exerts about 0.433 psi per foot of depth, so 2 feet of water adds 2 × 0.433 ≈ 0.866 psi. Add that to the base 3.5 psi: 3.5 + 0.866 ≈ 4.366 psi, which rounds to about 4.5 psi. The total is therefore higher than the base value because of the water head above the sewer line.

Pressure in the pipe during this test is the sum of the base pressure and the hydrostatic pressure from the water column above the line. Water exerts about 0.433 psi per foot of depth, so 2 feet of water adds 2 × 0.433 ≈ 0.866 psi. Add that to the base 3.5 psi: 3.5 + 0.866 ≈ 4.366 psi, which rounds to about 4.5 psi. The total is therefore higher than the base value because of the water head above the sewer line.