Hydrostatic Test Failure on a 4-Inch PVC Building Drain
A plumbing contractor is testing a new 4-inch PVC underground sanitary building drain, 120 feet long with 1/8-inch-per-foot slope, serving a 24-unit apartment building. The line has 14 solvent-welded joints and two long-sweep 90s. The contractor fills the line through a 10-foot standpipe at the upstream manhole, bringing the water level to 10 feet above the highest point of the line, and lets it stand. After 15 minutes, the water level in the standpipe has dropped 3 inches. There are no visible leaks at the joints or at the test plugs. The ambient temperature is 88°F and the pipe was in direct sun before backfill. The inspector is due in an hour. The contractor wants to add water and call it a pass because no water is on the ground.
1. Is this a passing hydrostatic test? Explain your reasoning.
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No. A 3-inch drop in the standpipe over 15 minutes is not a passing result, even if no water is visible on the ground. The adopted code requires the test to hold without a drop for the specified period, commonly a 10-foot head for 15 minutes. Adding water and calling it a pass conceals the reason for the loss and would be a false test. The loss could be a leaking test plug, a defective valve or cleanout, a joint that is not leaking visibly because water is traveling along the trench, trapped air being absorbed, or evaporation from the standpipe. The direct sun and warm pipe are relevant because temperature changes can move the water level, but that is an explanation to investigate, not a reason to ignore the result. The line must be retested after the cause is found and corrected.
2. What diagnostic steps would you take before the inspector arrives?
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First, verify the test setup: check the standpipe for leaks, confirm the test plugs are tight, and make sure no valve or cleanout is passing. Mark the water level, refill, and observe for another 15 minutes to see whether the drop repeats at the same rate. Isolate the line in sections with test plugs to determine whether the loss is in the main run, a branch, or the test equipment. If water testing is inconclusive, use the code-approved air test at 5 psi with a gauge and soap solution on the joints, or a smoke test if permitted. Inspect the solvent-welded joints for gaps, especially at the long-sweep 90s, and check for pipe deflection or damage from backfill. Do not backfill or cover any portion until the source is identified and the line passes.
3. What records and retest procedure should be followed once the cause is corrected?
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Document the original failure, the diagnostic steps, the repair, and the retest with photos and a signed test report. Repair the defective joint or fitting using the manufacturer's solvent-cement procedure, allow proper cure time, and then repeat the hydrostatic test at the required head for the full duration with the inspector present. If an air test is used instead, hold 5 psi for the required period with no gauge drop and apply soap solution to all joints. Record the test pressure, duration, water level, ambient temperature, and the tester's certification. Do not accept a test that was topped off during the observation period, and do not backfill until the inspector signs off.