16.2 New Construction Inspection, Pressure Testing & Utility Locating

16.2 New Construction Inspection, Pressure Testing & Utility Locating

Two distinct duties appear together in the Need-to-Know Criteria: inspecting what contractors install and locating what is already buried. Both protect the system and, in the second case, protect people.

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Construction Inspection

The utility inspector's job is to confirm that what gets buried matches the specification, because once backfilled nothing can be verified without re-excavation.

[!NOTE] Pipe ends must be plugged whenever work stops. An open main overnight admits rodents, debris, and contaminated stormwater, and this is one of the most common causes of a new main failing its bacteriological clearance and requiring re-disinfection.

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Hydrostatic Pressure and Leakage Testing

New mains are tested before disinfection and before being placed in service.

Procedure:

1. Backfill sufficiently to restrain the pipe, leaving joints exposed where practical.
2. Fill slowly and expel all air through hydrants and air valves — trapped air makes the test unreliable and is a serious hazard if the line fails.
3. Raise to the specified test pressure, commonly 150 psi or 1.5 times working pressure.
4. Hold for the specified duration, typically 2 hours.
5. Measure the make-up water required to restore test pressure.

Allowable leakage is not zero. Gasketed joints seep slightly, and the standard formula recognizes that:

$L = \frac{S \times D \times \sqrt{P}}{148,000}$

where L is allowable leakage in gallons per hour, S is the number of joints, D is nominal diameter in inches, and P is test pressure in psi.

Worked example. 1,200 ft of 8-inch main in 20-ft lengths gives 60 joints, tested at 150 psi.

$L = \frac{60 \times 8 \times \sqrt{150}}{148,000} = \frac{60 \times 8 \times 12.25}{148,000} = \frac{5,880}{148,000} = 0.040\text{ gal/hr}$

If make-up water exceeds the allowable figure, the contractor must locate and repair the leak and retest. Failing a pressure test after backfill is expensive, which is the incentive for careful joint assembly.

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Underground Utility Locating

Striking a buried utility injures and kills people every year. Locating is a legal obligation, not a courtesy.

The One-Call System

Before excavating, the excavator must notify the one-call center by dialing 811 (Arizona Blue Stake) within the statutory notice period, generally at least two working days before digging. Member utilities then mark their facilities in the requested area. Marks are valid for a defined period and must be re-requested if they expire or are destroyed.

The National Color Code

[!IMPORTANT] Memorize this table. Blue is potable water, green is sewer, purple is reclaimed water, yellow is gas, red is electric. The color code appears on essentially every distribution and collection exam. Note that white is used by the excavator to outline the dig area before locates are requested — it is not a utility color, and confusing it with a facility marking is a common error.

Locating Methods

Non-metallic pipe is the core difficulty. PVC and HDPE are invisible to electromagnetic locators, which is why tracer wire or detectable marking tape must be installed with every non-metallic main and service. Tracer wire is only useful if it is continuous, properly spliced, and brought up to an accessible test station or valve box — a broken or unterminated tracer wire is functionally the same as none.

Potholing

Marks show an approximate horizontal position, generally within a defined tolerance zone, and say nothing reliable about depth. Potholing — carefully exposing the utility, most safely by vacuum or hydro-excavation — is the only way to positively verify location and depth.

Standard practice is that mechanical excavation is prohibited within the tolerance zone on either side of a mark; work within that zone must be done by hand digging or vacuum excavation until the facility is exposed. Striking a marked line because a backhoe was used inside the tolerance zone is not an accident; it is a procedural failure.