Maintenance, Repair, and Construction of Distribution Infrastructure
Core concepts
Know the lifecycle of distribution work: planning, excavation, pipe laying, bedding, jointing, testing, disinfection, and backfill/compaction. Understand pipe bedding and trench requirements (proper bedding, cover, and compaction protect the pipe). Grasp pressure testing (hydrostatic test to specified pressure and duration) and disinfection of new mains (chlorine concentration and contact time, then flushing and bacteriological sampling before placing in service). Know valve and hydrant maintenance: exercising valves, hydrant flushing and inspection, and recordkeeping. Understand repair methods - clamp/repair sleeves, cut-in tees, tapping and line stops for live mains. Know traffic control and excavation safety (trench shoring, sloping, spoil placement). Understand asset management: preventive vs. corrective maintenance and leak detection.
Traps to watch
Questions test the order of operations - disinfection and testing must happen before a new main is placed in service, and sampling follows flushing. Another trap: confusing hydrostatic pressure testing with disinfection (different steps). Watch for trench safety specifics (spoil pile setback, shoring requirements) and for the requirement to exercise valves regularly.
Worked example
A new 8-inch main is installed. Correct sequence: pressure test at the specified test pressure for the required duration → flush → chlorinate to the required concentration and hold for the required contact time → flush → collect bacteriological samples → place in service only after satisfactory results. Skipping the sample step is the classic wrong answer.
Rule of thumb
New main: test → flush → disinfect → flush → sample → in service. Never energize a new main before satisfactory bacteriological results.