Pipeline (C-34) · Lesson 4 of 6

Leakage Testing a Gravity Pipe: Exfiltration and Air Test

"Leakage Testing a Gravity Pipe: Exfiltration and Air Test" is lesson 4 of 6 in the Pipeline (C-34) Learning Hub. It opens with "When and How Much Gets Tested" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. When and How Much Gets Tested
  2. The Exfiltration Limit and Its Head Rules
  3. Turn the Limit Into Gallons for Your Run
  4. Low-Pressure Air Test (Pipe 30 Inches or Smaller)
  5. When the Line Fails

The worked example in the course applies this lesson to a realistic job in 4 steps, from "Convert the length to miles" through "Check the head limit".

What you'll be able to do

  • Explain the main idea of "Leakage Testing a Gravity Pipe: Exfiltration and Air Test" in plain language you can use on the exam.
  • Apply this step with confidence: "Turn the Limit Into Gallons for Your Run".
  • Apply this step with confidence: "Low-Pressure Air Test (Pipe 30 Inches or Smaller)".
  • Apply this step with confidence: "When the Line Fails".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Leakage Testing a Gravity Pipe SystemUPPER MHLOWER MHwater level in upper manhole6 ft min above crownhead at lower invert6 + 1 + 12 = 19 ft12-in, 1,200 ft, 12 ft fall (not to scale)LOW-PRESSURE AIR TEST (pipe 30 in or smaller)12-in pipe: 1.8 min per 100 ft12 x 1.8 = 21.6 min for 1,200 ftPass: drop under 1 psi from the 3.5 psi startEXFILTRATION TESTLimit: 1,000 gal per inchof diameter, per mile, per dayD = 12 in, L = 1,200 ft1,200 / 5,280 = 0.2273 mile1,000 x 12 x 0.2273= 2,727 gal per day2,727 / 24= 113.6 gal per hourHead check at lower end:6 + 1 + 12 = 19 ft19 ft is not over 20 ft: OKTest at least 1 hour.Exfiltration limit: 113.6 gal per hour for 1,200 ft of 12-in pipeAir test alternative: under 1 psi drop for 21.6 minCaltrans Standard Specifications 2025, section 61-2.01D(3)(b) exfiltration and (c) low-pressure air testCC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: When and How Much Gets Tested

The 2025 Caltrans Standard Specifications, section 61-2.01D(3), require each pipe system to be cleaned and tested with the exfiltration, infiltration, low-pressure air, or negative air pressure method, and the field leakage test is run after backfilling. Infiltration needs the Engineer's approval if the groundwater table is low, and you use only one test method on a contiguous pipe system. Pipe systems under 1,500 feet have every joint tested; longer systems are tested at a rate of 50 joints per 100 for runs under 1 mile, 30 per 100 for 1 to 3 miles, and 20 per 100 above 3 miles. The Engineer does not accept an installation that fails, and you must stop all obvious leaks even if the total is below the allowable quantity.

Step 2: The Exfiltration Limit and Its Head Rules

For an exfiltration (water) test, section 61-2.01D(3)(b) limits leakage to 1,000 gallons per inch of nominal pipe diameter per mile of pipe per day. The minimum test pressure is 6 feet of water column above the pipe crown at the upper end (or above the active groundwater table, whichever is higher). Limit the length you test so the pressure on the invert of the lower end does not exceed 20 feet of water column. The allowable leakage goes up 8 percent for each 1.5 feet of pressure above the basic 6 feet. The test must run at least 1 hour. If you fill the pipe to let it absorb water, start the test within 72 hours after filling and finish within 24 hours after that; plastic and metal pipe need no absorption period.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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