14.3 Collection System Maintenance, Pipeline Inspection (CCTV) & Trench Safety

7.3 Collection System Maintenance, Pipeline Inspection (CCTV) & Trench Safety

Preserving the hydraulic carrying capacity and physical longevity of a municipal collection network requires continuous preventive maintenance, rigorous condition assessment, and unwavering adherence to occupational safety standards. Collection operators are tasked with dislodging heavy grease, cutting intrusive tree roots, extracting abrasive grit, and cataloging underground pipe defects using robotic camera systems.

Furthermore, collection system repairs demand frequent excavation and trenching in hazardous subterranean environments. Under OSHA 29 CFR 1926 Subpart P and Oregon OSHA (OAR Chapter 437, Division 3), operators must possess the technical competency to classify soil types, install engineered protective shoring systems, and protect crews against lethal cave-ins.

---

Collection System Cleaning Methodologies

Collection mains accumulate heavy deposits that restrict flow and cause blockages if left unaddressed. Utilities employ two primary cleaning methodologies: hydraulic cleaning and mechanical cleaning.

                 HYDRAULIC JETTING DIRECTION OF CLEANING

     [Upstream Manhole]                             [Downstream Manhole with Vac-Truck]
            │                                                       │
     ═══════╪═══════════════════════════════════════════════════════╪══════════════════
            │    ◄── Nozzle propelled UPSTREAM against flow         │   ▲
            │                                                       │   │ Vacuum Tube
            │        ══════════════════════════════════════►        │   │ Extracts Debris!
            │        Normal Sewage Flow                             │   │
            │        Rear water jets scour pipe walls and drag      │   ▼
            │        gravel/grease BACKWARD to downstream vac ─────►┴── [Catch Debris]
     ═══════╪══════════════════════════════════════════════════════════════════════════

1. Hydraulic Cleaning (High-Velocity Jetting)

High-velocity hydro-jetting is the universal industry standard for routine collection maintenance. A jetter truck utilizes a positive displacement triplex water pump delivering $40\text{ to }80+\text{ gpm}$ at pressures between $2,000\text{ and }2,500\text{ psi}$ through a continuous thermoplastic high-pressure hose.

• Direction of Operation (Clean Against the Flow): Jetting must always proceed from the downstream manhole working upstream against the normal flow of wastewater.
  • The jetting truck is positioned at the downstream manhole, and the hose nozzle is pointed into the upstream pipe barrel.
  • High-pressure water discharged through rearward-angled orifice jets ($15^{\circ}\text{ to }30^{\circ}$) creates tremendous thrust that propels the nozzle forward up the sewer line against gravity and incoming sewage flow.
  • Once the nozzle reaches the upstream manhole, the operator engages the hydraulic hose reel, slowly pulling the nozzle back downstream. The rearward water jets scour the pipe walls, peeling off grease rings and carrying loosened rocks, gravel, and sand downstream ahead of the nozzle.
• Crucial Rule: Vacuum Extraction at the Downstream Manhole: A combination vacuum truck (Vac-Con or Vactor) must be positioned at the downstream manhole with its heavy vacuum intake tube submerged in the manhole invert channel to continuously suck up all flushed debris. Flushed debris must NEVER be washed downstream into the next pipe reach. Pushing debris downstream consolidates gravel and grease into an unyielding mega-plug or forces heavy grit directly into downstream lift station pump impellers.
• Nozzle Selection:
  • Penetrator / Chisel Nozzles: Feature one or more forward-facing high-velocity cutting jets to bore through solid blockages and ice plugs.
  • Flushing / Radial Cleaning Nozzles: High-thrust rear-facing jets designed to maximize tractive force for transporting heavy gravel and sand out of flat pipes.
  • Rotating Chain Cutters & Milling Cutters: Driven by water turbine motors rotating stainless-steel chains or carbide teeth to shave encrusted calcium deposits, scale, and heavy root balls flush with the pipe wall.

2. Mechanical Cleaning Methods

• Power Rodders: Heavy truck-mounted machines that rotate continuous or sectional tempered spring-steel rods into the pipe. Various cutting tools (bullet bits, corkscrews, root augers) rotate to slice through solid obstructions, puncturing total blockages when water jetting cannot penetrate.
• Bucket Machines (Power Winches): Used primarily in large-diameter trunk sewers ($>24\text{ in}$) overwhelmed by heavy gravel, cobblestones, or industrial mining silt. Two cable winches set up over adjacent manholes pull an expandable clamshell bucket back and forth through the sewer. The bucket scrapes forward, fills with heavy sediment, closes its clamshell jaw, and is hoisted up to street level for disposal.
• Sewer Balls and Kites: Inflatable grooved rubber balls or canvas kites tethered to a winch cable. When water backs up behind the ball, water accelerates around the narrow annular gap between the ball and pipe wall, generating high-velocity localized scouring jets that push heavy grit forward.

---

Root Control & Vegetation Management

Tree and shrub roots are attracted to sewer lines by escaping moisture vapor, warmth, and concentrated plant nutrients (nitrogen, phosphorus). Hairline roots enter microscopic voids in cracked joints, service saddles, and manhole rings, rapidly developing into dense, braided root curtains.

Mechanical Cutting vs. Chemical Control

• The Mechanical Cutting Trap: Utilizing rotating root cutters provides instantaneous relief by clearing the pipe bore. However, mechanical cutting behaves exactly like pruning a hedge: it stimulates aggressive vegetative regrowth. Within $3\text{ to }6\text{ months}$, the severed root ends generate dense clusters of fine root filaments that trap toilet paper and grease faster than the original root.
• Chemical Foaming Control: Modern root management utilizes specialized foam application equipment. Liquid chemical concentrate is blended with water and compressed air in a foam generator, creating a rich shaving-cream-like foam that completely fills the entire cross-section of the sewer main. The foam coats root curtains hanging from the pipe crown above the normal water line.
  • Active Ingredients: Typically a blend of metam-sodium (a contact cellular disruptor that kills root tissue on contact) and dichlobenil (a pre-emergent root growth inhibitor that bonds to pipe joints, preventing root regrowth for $2\text{ to }3\text{ years}$). Dead roots decompose and wash away naturally within months.

---

Fats, Oils, and Grease (FOG) Management & Saponification

Fats, Oils, and Grease (FOG) entering sanitary sewers from commercial restaurants, bakeries, and food processing facilities represent the leading cause of collection system dry-weather blockages and SSOs.

                 THE SAPONIFICATION FATBERG REACTION

   Liquid Hot FOG Wastes                 Alkaline Calcium Ions (Ca2+)
   from Commercial Kitchens              from Concrete Pipes & Sewage
   ────────────────────────              ────────────────────────────
   Free Fatty Acids (Palmitic,           Leached from deteriorating pipe
   Stearic, Oleic Acids)                 walls and alkaline detergents
              │                                        │
              └───────────────────┬────────────────────┘
                                  ▼
                   SAPONIFICATION CHEMICAL REACTION
                                  │
                                  ▼
             INSOLUBLE CALCIUM SOAP DEPOSITS ("FATBERGS")
      Rock-hard metallic soaps bond to pipe walls and choke sewers!

The Chemistry of Saponification

When warm FOG wastes enter cool underground sewers ($50-60^{\circ}\text{F}$), free fatty acids hydrolyze. In the sewer environment, these fatty acids encounter calcium ($Ca^{2+}$) and magnesium ($Mg^{2+}$) ions leached from deteriorating concrete pipes or released from dishwashing detergents.

Through a chemical process known as saponification, fatty acids react with calcium to precipitate insoluble calcium soaps (calcium palmitate and calcium stearate). These deposits are not soft grease—they form rock-hard, cementitious white deposits ("fatbergs") that chemically adhere to pipe surfaces and cannot be dissolved by hot water or high-pressure flushing.

Commercial Grease Interceptors & The "25% Rule"

To prevent FOG from entering the public collection grid, commercial kitchens must install approved pretreatment devices:

• Hydromechanical Grease Interceptors (HGIs): Small compact units installed indoors directly beneath individual three-compartment warewashing sinks ($20\text{ to }50\text{ gpm}$). HGIs utilize baffling and air entrainment to float grease, but have minimal storage capacity and require weekly manual cleaning.
• Gravity Grease Interceptors (GGIs): Large outdoor multi-compartment subterranean reinforced concrete vaults ($750\text{ to }2,000+\text{ gallons}$) located in exterior drive lanes. Raw kitchen waste enters the vault, where extended hydraulic detention time ($>30\text{ minutes}$) allows low-density FOG to float to the surface while dense food particles settle into a bottom sludge layer.
• The Regulatory 25% Rule: Under standard municipal sewer ordinances, a gravity grease interceptor must be pumped and cleaned whenever the combined thickness of the floating grease layer plus the bottom settled sludge layer exceeds $25\%$ of the total liquid operating depth. Once grease and sludge occupy more than $25\%$ of the tank volume, hydraulic retention time drops below the critical separation threshold, allowing greasy effluent to escape directly into the municipal sewer main.

---

Closed-Circuit Television (CCTV) Inspection & NASSCO PACP

To prioritize capital rehabilitation and track structural degradation, utilities deploy robotic crawler camera systems to inspect sewer interiors. North American pipeline inspection is standardized under the National Association of Sewer Service Companies (NASSCO) Pipeline Assessment Certification Program (PACP).

Robotic CCTV Crawler Equipment

• Pan-Tilt-Zoom (PTZ) Cameras: High-definition color cameras mounted on motorized multi-wheel tractors capable of traversing debris and standing water. The camera head rotates $360^{\circ}$ and tilts $270^{\circ}$ to inspect pipe barrels, service lateral connections, and pipe crowns.
• Laser Profiling Rings: Projects a calibrated ring of laser light onto the interior pipe wall while traversing. Digital image processing calculates the exact ovality and percentage of pipe deflection (critical for verifying flexible PVC pipes, which must not exceed $5\%$ deflection under ASTM standards).

NASSCO PACP Defect Classifications

PACP establishes a standardized alphanumeric coding lexicon to eliminate subjectivity among operators, dividing pipeline conditions into two core defect families:

PACP Condition Grading Scale (Grades 1 through 5)

Every observed defect is assigned a severity grade from 1 to 5 based on its likelihood of structural failure or hydraulic blockage:

• Grade 1 (Minor Defect): Hairline crack or superficial surface etching; little impact; reinspect on standard multi-year cycle.
• Grade 2 (Minor-to-Moderate Defect): Marginal defect; slight deterioration; monitor routinely.
• Grade 3 (Moderate Defect): Defect requiring maintenance or rehabilitation within $10\text{ to }20\text{ years}$.
• Grade 4 (Significant Defect): Severe fracture, heavy root intrusion, or deep acid etching; failure likely within $5\text{ to }10\text{ years}$; schedule for planned repair.
• Grade 5 (Critical Structural Failure): Broken pipe with missing fragments, soil void visible outside barrel, pipe deformation $>10\%$, or pipe collapsed. Failure is imminent or occurring; requires immediate emergency excavation or trenchless lining.

---

Trenching & Excavation Safety (OSHA Subpart P & Oregon OSHA)

Excavating and repairing buried sewers is inherently dangerous. Soil collapse occurs without warning, making trench cave-ins one of the leading causes of worker fatalities in utility operations.

                  TRENCH EXCAVATION SAFETY PROFILES

            SLOPING (TYPE C SOIL - 1.5 : 1)                 TRENCH SHIELD (BOX) IN TRENCH

                   ◄────── 1.5 ──────►                     Spoil Pile ≥ 2 ft Back
           ▲      ┌───────────────────                ┌───┐            │
           │      │                                   │   │            ▼
           │      │  (34° angle)                      │   │        ┌───────┐
         1.0      │                                   └───┘        │ Spoil │
           │      │                                 ═══════════════┴───────┴══
           ▼      └──────────┐                               │   ▲
                             │ Trench Base                   │   │ Shield extends ≥ 18"
                             └────────────                   │   │ above sloped cut!
                                                             │   ▼
                                                             │ ┌───────────┐
                                                             │ │ Trench    │
                                                             │ │ Box       │
                                                             │ │           │
                                                             └─┴───────────┴────────

The Physics of Soil Mechanics & Trench Collapse

One cubic yard ($27\text{ cu ft}$) of soil weighs between $2,700\text{ and }3,000\text{ pounds}$ ($1.35\text{ to }1.5\text{ tons}$)—roughly equivalent to a passenger automobile. A worker buried in a trench collapse is subjected to massive crushing forces. Even if the victim's head remains above ground, the weight of soil compressed against the chest wall prevents lung expansion, causing mechanical suffocation within 3 to 5 minutes.

Soil Classification System (OSHA 29 CFR 1926 Subpart P, App. A)

Oregon OSHA requires that all soil be classified based on at least one visual test and at least one manual field test (e.g., thumb penetration test, pocket penetrometer, or shear vane):

Protective Systems Mandate

Under OSHA rules, an engineered protective system is mandatory for any trench excavation $5\text{ feet}$ or greater in depth (or any excavation less than $5\text{ ft}$ if the Competent Person identifies evidence of a potential cave-in):

1. Sloping and Benching:
   • Type A Soil: Sloped at a maximum angle of $3/4:1$ ($53^{\circ}$ from horizontal). Benching permitted.
   • Type B Soil: Sloped at a maximum angle of $1:1$ ($45^{\circ}$ from horizontal). Benching permitted in cohesive soils only.
   • Type C Soil: Sloped at a maximum angle of $1.5:1$ ($34^{\circ}$ from horizontal). Benching is STRICTLY PROHIBITED in Type C soil (granular soils will not hold a vertical bench face!).
2. Trench Boxes (Shielding Systems):
   • Heavy welded steel or aluminum trench boxes placed in the excavation to shield workers from collapsing walls. Trench shields do not prevent wall movement; they withstand cave-in impact loads.
   • When sloping begins above a trench shield, the top of the shield must extend at least $18\text{ inches}$ ($0.45\text{ m}$) above the vertical trench wall to catch rolling rocks and sloughing soil.
   • Workers are permitted no more than $2\text{ feet}$ of earth undercut beneath the bottom of the shield, and only if soil conditions are stable and there is no evidence of soil boiling or running.
3. Hydraulic Shoring:
   • Aluminum hydraulic cylinders connected to vertical rails pressurized against trench walls using a manual hand pump. Fluid pressure applies continuous horizontal compressive stress against the trench wall, preventing soil movement before a collapse can initiate.

The OSHA "Competent Person"

Every excavation site must have a designated Competent Person on site. A Competent Person is defined as an individual who:

1. Possesses specific training in soil mechanics, hazard identification, and protective system engineering.
2. Is capable of identifying existing and predictable hazards in the surroundings or working conditions.
3. Has full, prompt authorization to take immediate corrective measures, including the absolute authority to immediately halt all excavation work and order workers out of the trench.

• Mandatory Inspection Frequency: The Competent Person must conduct formal trench inspections daily prior to the start of every shift, throughout the shift as conditions change, and immediately following every rainstorm, freeze/thaw cycle, or seismic tremor.

Access, Egress & Spoil Setback Regulations

• Trench Egress (Ladders / Ramps): A stairway, ladder, or ramp is mandatory in all trenches $4\text{ feet}$ ($1.2\text{ m}$) or greater in depth.
• Maximum Lateral Travel Limit: Workers inside the trench must never be required to travel more than $25\text{ feet}$ ($7.6\text{ m}$) laterally to reach an egress ladder (meaning ladders must be spaced no further than $50\text{ feet}$ apart).
• Ladder Extension Rule: Egress ladders must extend at least $3\text{ feet}$ ($36\text{ inches}$ / $0.9\text{ m}$) above the top surface edge of the excavation and be securely tied off at the top.
• Spoil Pile Setback: Excavated spoil dirt, rocks, paving slabs, and heavy construction equipment must be kept a minimum of $2\text{ feet}$ ($24\text{ inches}$ / $0.6\text{ m}$) back from the edge of the excavation lip. If a 2-foot setback cannot be achieved due to physical space constraints, retaining barriers or toeboards must be installed to prevent loose rocks from rolling onto workers.