10.4 Collection System Inspection & Acceptance Testing

10.4 Collection System Inspection & Acceptance Testing

The Collection Systems needs-to-know lists Testing Collection Systems and Sewer Main Inspection as distinct topics. They serve two purposes: accepting new construction, and deciding which existing pipe to fix.

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1. CCTV inspection

A tracked or wheeled camera is run through a cleaned line, usually manhole to manhole, recording video and still images with distance referenced from the launch manhole.

• Clean first. A camera run through a dirty line documents debris, not defects.
• Code consistently. NASSCO's Pipeline Assessment Certification Program (PACP) provides standardized defect codes and structural and operations and maintenance grades from 1 (minor) to 5 (imminent failure). Consistent coding is what makes a rehabilitation prioritization defensible.
• What the operator is looking for: offset and open joints, circumferential and longitudinal cracks and fractures, deformation, holes, root intrusion, mineral encrustation, active infiltration ("runners" and "gushers"), sags or bellies holding water, protruding taps, and failed or intruding lateral connections.
• Lateral launch cameras extend the inspection into service laterals, where a large share of infiltration and inflow actually originates.
• Alternatives: sonar for surcharged lines, laser profiling for deformation measurement, and acoustic screening to rapidly rank segments for blockage risk before committing to CCTV.

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2. Smoke testing

A blower forces non-toxic smoke into an isolated segment while crews walk the area looking for where it emerges.

• Finds inflow: roof downspouts connected to the sanitary sewer, area and yard drains, uncapped cleanouts, storm sewer cross-connections, and defective manhole frames and lids.
• Also finds broken laterals (smoke rising from lawns) and, occasionally, dry plumbing traps inside homes — which is why public notification before smoke testing is mandatory practice: notify residents and the fire department, and explain that smoke entering a house indicates a plumbing defect.
• Best conditions: dry weather with a slight breeze; wet soil seals the ground and suppresses the smoke.

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3. Dye testing

Fluorescent dye (uranine, rhodamine) is introduced into a suspected source — a downspout, a catch basin, a swale, a private plumbing fixture — and downstream manholes are watched for color. Dye testing is the confirmation tool: smoke testing suggests a connection; dye testing proves it, which matters when the utility is about to require a property owner to disconnect at their own expense.

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4. Acceptance testing under North Carolina's gravity sewer criteria

These are the numbers an operator is expected to know when accepting a developer-built extension — and the ones to insist on, because a 6 percent deflected or leaking line becomes the utility's permanent maintenance problem the day it is accepted.

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5. Manhole inspection and testing

Manholes are frequently the largest single infiltration source in a basin, because they sit in the street where storm runoff collects.

• Visual inspection: frame seating and frame-to-chimney seal, chimney and cone condition, active leaks, bench and channel corrosion, step condition, presence of roots, and evidence of surcharge (debris marks on the walls).
• Vacuum testing is the standard watertightness test for new and rehabilitated manholes.
• Common rehabilitation: chimney seals, cementitious or epoxy lining, hydraulic cement plugging of active leaks, and frame and cover replacement with gasketed or watertight covers where flooding occurs.

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6. Flow monitoring for I/I analysis

Area-velocity meters installed at basin boundaries record depth and velocity continuously. Comparing dry weather flow with wet weather flow produces:

• Peaking factor = peak wet weather flow ÷ average dry weather flow.
• Rainfall-derived infiltration and inflow (RDII) volume per basin per storm, normalized by rainfall and basin area, which ranks basins for investigation.
• Groundwater infiltration estimated from the sustained overnight minimum flow in wet seasons versus dry seasons.

A basin with a high peaking factor gets smoke testing and CCTV; a basin with high sustained night flow gets manhole and joint investigation. That sequencing — meter, then investigate, then rehabilitate, then re-meter — is what keeps an I/I program from becoming an expensive guess.

[!NOTE] Rehabilitation is not permit-exempt by default. North Carolina's gravity sewer criteria deem certain routine maintenance and rehabilitation work permitted without a site-specific permit, provided the work conforms to the design criteria, no new sources of wastewater are connected, and replacements stay in the same alignment and diameter — with prior notification to the regional office and a professional engineer's certification on completion. Change any of those conditions and a permit is required.