19.2 CCTV Inspection, Condition Assessment & FOG Control
Key Takeaways
- PACP provides a standardized defect coding system so that condition ratings are comparable between inspectors, contractors, and years.
- Structural defects such as cracks, fractures, and deformation are coded separately from operation and maintenance defects such as roots, deposits, and grease.
- Smoke testing finds inflow sources including illegal downspout and area drain connections, while dye testing confirms a specific suspected connection.
- Grease interceptors work by retention time and cooling that allow FOG to separate, so an undersized or unmaintained interceptor passes grease straight through.
- The 25 percent rule requires a grease interceptor to be pumped when the combined floating grease and settled solids reach one quarter of the working depth.
19.2 CCTV Inspection, Condition Assessment & FOG Control
You cannot manage what you have not seen. Closed-circuit television inspection converts a buried pipe into a documented, coded, and rankable asset.
CCTV Inspection
A camera is transported through the pipe on a self-propelled tractor (mainline) or a push camera (laterals and small diameter), transmitting video with distance measurement to a recording van.
| Feature | Purpose |
|---|---|
| Pan-and-tilt head | Look directly at a defect and up a lateral rather than only straight ahead |
| Zoom | Detail on distant defects |
| Footage counter | Locates the defect precisely for excavation or spot repair |
| Lateral launch | Deploys a secondary camera up a service lateral from the mainline |
| Sonar | Profiles the submerged portion in surcharged lines |
| Laser profiling | Measures ovality and deformation quantitatively |
| Zoom camera (manhole-deployed) | Rapid screening from the manhole without entering the pipe |
The line must be cleaned before inspection. A camera driving through grease and debris documents the debris, not the pipe.
PACP Defect Coding
The Pipeline Assessment Certification Program (PACP), developed by NASSCO, is the industry-standard coding system. Its value is consistency: a defect coded by one certified inspector means the same thing as the same code from a different inspector in a different year, which is what makes condition data usable for trending and for capital planning.
PACP separates defects into two families, and the distinction drives the response:
| Category | Examples | Response |
|---|---|---|
| Structural | Cracks, fractures, broken pipe, holes, deformation, collapse, joint offsets, surface damage | Rehabilitation or replacement |
| Operation and maintenance (O&M) | Roots, deposits (attached, settled), grease, infiltration, obstructions | Cleaning, root control, source control |
Defects are graded 1 (minor) through 5 (most severe), and a grade 5 structural defect indicates imminent or actual collapse. Segment scores derived from the individual defect grades allow the utility to rank hundreds of reaches by condition and build a defensible rehabilitation priority list.
[!IMPORTANT] The structural versus O&M distinction is the practical point. Cleaning a reach every six months because it fills with roots treats the symptom; the roots are entering through a structural joint defect, and lining the pipe eliminates both. Conversely, rehabilitating a structurally sound pipe that simply accumulates grease from an upstream restaurant wastes capital that source control would have solved.
Smoke Testing
Non-toxic smoke is blown into a sewer segment with a blower at a manhole. Smoke escapes wherever there is an opening to the surface.
What it finds:
- Illegal inflow connections: roof downspouts, area and yard drains, foundation drains, sump pumps
- Broken or missing cleanout caps
- Defective manhole covers and frames
- Cracked laterals and pipe defects near the surface
- Dry or missing plumbing traps inside buildings — smoke entering a home indicates a real sewer gas pathway
Practical requirements: notify residents and the fire department in advance, work when the ground is relatively dry (saturated soil blocks smoke), photograph and log every finding with an address, and be prepared to explain to alarmed residents that the smoke is non-toxic.
Limitation: smoke testing finds inflow — direct surface connections — but does not find infiltration, which is groundwater entering through defects below the water table.
Dye Testing
Fluorescent dye is introduced at a specific fixture, downspout, drain, or surface feature, and downstream manholes are observed for the color.
Dye testing confirms one suspected connection, whereas smoke testing screens broadly. The two are complementary: smoke testing generates a list of suspect locations, and dye testing proves the specific connection before the utility asks a property owner to disconnect it.
Other Inspection Methods
| Method | Application |
|---|---|
| Acoustic inspection | Rapid screening; sound transmitted between manholes indicates whether a blockage is developing. Cheap and fast, used to prioritize CCTV |
| Manhole inspection | Frame and cover, chimney, corbel, barrel, bench and invert, steps, and evidence of surcharge — the "grease ring" high-water mark |
| Visual/surface inspection | Depressions, odors, standing water, vegetation anomalies over the alignment |
| Flow monitoring | Depth and velocity meters quantifying wet-weather response |
| Drone and multi-sensor platforms | Large-diameter and difficult-access inspection |
Manhole inspection deserves attention because manholes are a major inflow pathway. A vented or perforated cover in a street that ponds accepts enormous inflow during a storm, and defective frame seals and deteriorated chimneys are among the most cost-effective inflow repairs available.
Fats, Oils, and Grease Control
FOG is the leading cause of sanitary sewer blockages nationally. Warm grease flows freely; as it cools it congeals on the pipe crown and walls, building up until it forms a dam that catches everything else.
Grease Interceptors and Traps
| Type | Location | Capacity |
|---|---|---|
| Under-sink grease trap | Inside, near the fixture | Small; frequent cleaning |
| In-ground grease interceptor | Outside, buried | Large; the standard for food service |
| Automatic grease removal unit | Inside | Mechanically skims |
How they work: wastewater enters and slows, giving time for the grease to cool and float and for solids to settle, so that relatively clear water is drawn from the middle and passes on. Everything about their performance depends on retention time.
Why they fail:
- Undersized for the flow — the water passes through too fast to separate
- Not maintained — a full interceptor has no separation volume left
- Hot water discharge — dishwashers and high-temperature sanitizers keep grease liquid so it passes straight through
- Emulsifiers — detergents, degreasers, and additives keep grease suspended
- Garbage disposals — food solids overwhelm the settling volume
[!IMPORTANT] The 25 percent rule is the standard maintenance trigger: an interceptor must be pumped when the combined thickness of the floating grease layer and the settled solids layer reaches 25 percent of the total working depth. Beyond that point the effective retention volume has shrunk enough that separation efficiency falls sharply. Many ordinances also impose a maximum interval, commonly 90 days, regardless of measured depth.
Program Elements
An effective FOG program combines an ordinance requiring interceptors at food service establishments, permitting and inspection, manifest tracking of pumping records, enforcement with escalating penalties, public education on residential grease disposal, and targeted cleaning of the sewer reaches downstream of known FOG-generating clusters. Correlating blockage history with food service locations in GIS is how utilities identify where enforcement will pay.
A CCTV inspection codes a reach with multiple grade 4 root intrusions at joints and grade 3 longitudinal cracking. The utility has been jetting this reach every six months for years. What does the coding suggest?
A utility suspects that roof downspouts in an older neighborhood are connected to the sanitary sewer, contributing to wet-weather overflows. Which investigation method screens the area most efficiently?
An inspector measures a grease interceptor with a working depth of 48 inches and finds 7 inches of floating grease and 6 inches of settled solids. What action is required?