10.1 Wastewater Collection System Design, Lift Stations & Inflow and Infiltration (I/I)

10.1 Wastewater Collection System Design, Lift Stations & Inflow and Infiltration (I/I)

1. Collection System Hydraulics & Gravity Sewer Design

A municipal wastewater collection system is an extensive subterranean network of building laterals, branch sewers, submains, regional trunk sewers, interceptors, and pumping lift stations. Its core objective is to collect untreated domestic sewage, commercial wastewater, and permitted industrial discharges, conveying them to a centralized wastewater treatment facility without allowing sanitary sewer overflows (SSOs), system backups into structures, septic odors, or groundwater contamination.

Manning's Equation for Gravity Flow

Unlike pressurized drinking water mains, standard gravity sanitary sewers flow as open channels with a free water surface exposed to atmospheric air inside the pipe headspace. The hydraulic velocity of open-channel gravity flow is calculated using Manning's Equation:

$V = \frac{1.486}{n} \cdot R^{2/3} \cdot S^{1/2}$

Where:

• $V$ = Mean fluid velocity (feet per second, ft/sec)
• $n$ = Manning's roughness coefficient (dimensionless; typically 0.009–0.010 for smooth PVC/HDPE, 0.013 for clay/ductile iron, 0.015 for aged concrete)
• $R$ = Hydraulic radius ($R = A/P$, where $A$ is cross-sectional flow area in sq ft, and $P$ is wetted perimeter in ft)
• $S$ = Slope of the hydraulic grade line or energy gradient (ft/ft)

Critical Velocity Criteria: Self-Cleansing Scour vs. Abrasion

Gravity sewers must be engineered to operate within strict velocity bounds:

$\mathbf{\text{Minimum Self-Cleansing Velocity: } 2.0 \text{ ft/sec} \quad (0.6 \text{ m/sec})}$ $\mathbf{\text{High-velocity protection threshold: } > 15 \text{ ft/sec} \quad (\text{erosion control documentation} > 20 \text{ ft/sec})}$

• The 2.0 ft/sec Self-Cleansing Mandate: Raw sewage contains heavy mineral grit ($SG \approx 2.65$) such as sand, gravel, and coffee grounds, as well as dense settleable organic solids ($SG \approx 1.05$). If velocity drops below 2.0 ft/sec, boundary shear stress diminishes below the critical threshold required to move bed-load particles. Solids settle out onto the pipe invert, forming sludge blankets that restrict hydraulic capacity, induce anaerobic digestion, generate deadly hydrogen sulfide ($H_2S$) gas, and cause catastrophic blockages.
• The high-velocity thresholds: North Carolina's Gravity Sewer Minimum Design Criteria require that where design velocities are projected to be greater than 15 feet per second, the sewers and manholes be protected against displacement by erosion and impact, and that for velocities greater than 20 feet per second erosion control measures be documented on the record drawings and in the engineer's certification. Sewers on 20 percent slopes or greater must be anchored securely with concrete. High-velocity grit sandblasts pipe inverts and hydraulic jumps damage manhole benching.

Minimum Slopes for Standard Gravity Sewer Diameters

All sewers must be designed and constructed to give mean velocities, when flowing full, of not less than 2.0 feet per second based on Manning's formula using an n value of 0.013, and sewers are designed flowing half full at the average daily flow. North Carolina's Gravity Sewer Minimum Design Criteria, applied through the permitting rules in 15A NCAC 02T, set these minimum slopes:

[!NOTE] Minimum sizes and cover. No public gravity sewer conveying wastewater may be less than 8 inches in diameter; no private gravity sewer may be less than 6 inches. A minimum of three feet of cover is required over all sewers unless ferrous pipe is specified. Additional design requirements worth memorizing: sewers must have straight alignment between manholes; deflection testing is performed on all pipe installations after backfill has been in place at least 30 days (or with 95 percent compaction certification), and no pipe may exceed 5 percent deflection, tested with a rigid ball or mandrel at least 95 percent of the base inside diameter; and leakage by exfiltration or infiltration must not exceed 100 gallons per inch of pipe diameter per mile per day.

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2. Collection System Piping Materials, Manholes & Grease Management

Sewer Pipe Materials

Collection systems operate in an aggressive chemical and structural environment characterized by corrosive domestic sewage, industrial solvents, biogenic sulfuric acid, external ground overburden, and tree root intrusion.

• Polyvinyl Chloride (PVC - SDR 35, SDR 26, C900): The dominant material for gravity mains up to 15–18 inches. Exceptional hydraulic smoothness ($n=0.009$), lightweight, completely immune to sulfuric acid corrosion, and utilizes push-on elastomeric gasketed joints that resist root penetration. Vulnerable to deflection or crushing if trench bedding (ASTM D2321 Class I crushed stone) is improperly compacted.
• Ductile Iron Pipe (DIP): Specified where collection lines cross under high-load highways, shallow cover (< 3 feet), extremely deep trenches (> 20 feet), aerial creek crossings on piers, or water main separation conflicts.
  • Corrosion Lining: Bare or cement-lined ductile iron is rapidly corroded by raw domestic sewage and sulfuric acid. For wastewater service, DIP must be lined internally with Protecto 401 ceramic epoxy or thick polyurethane lining to shield the metallic barrel.
• Vitrified Clay Pipe (VCP): Historically prevalent in older North Carolina cities. Completely vitrified ceramic pipe that is 100% chemically inert to all acids (except hydrofluoric acid) and highly abrasion-resistant. However, VCP is brittle, comes in short 3- to 6-foot lengths with numerous rigid joints, and is highly prone to shear fractures from ground shifting and root penetrations through mortar joints.
• Reinforced Concrete Pipe (RCP): Utilized for major regional interceptor sewers exceeding 24 to 36 inches in diameter. High beam and structural load-bearing capacity. Must be protected with internal HDPE T-Lock liners, epoxy, or polyurea coatings in high-sulfide environments.

Manholes in the Hydraulic Picture

Manholes provide access, ventilation, and junctions, and they are where the operator actually observes the system. Hydraulically, three things matter here: the flow channel must carry flow through the structure without turbulence or deposition; an incoming sewer entering high above the invert creates a free fall that strips hydrogen sulfide into the manhole atmosphere and erodes the bench, which is why North Carolina requires a drop pipe above a 2.5-foot difference; and manhole spacing governs whether the line can be cleaned at all. The detailed North Carolina requirements — spacing, diameter, bench slope, channel shaping, drop connections, flood protection, and construction — are covered in the manholes, service taps, and laterals section of this chapter.

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

Fats, Oils, and Grease (FOG) discharged from commercial food service establishments (restaurants, cafeterias) is the leading cause of collection system blockages in North Carolina. When warm, emulsified liquid grease enters cold sewer mains, it cools and undergoes saponification—chemically reacting with calcium ions dissolved in domestic wastewater to form hard, insoluble metallic soap deposits. These deposits agglomerate with flushed non-biodegradable synthetic wipes to create monolithic fatbergs that completely seal off pipe diameters, inducing catastrophic SSOs. Utilities enforce FOG ordinances requiring commercial kitchens to install certified gravity grease interceptors (minimum 750 to 1,500 gallon capacity with 30-minute hydraulic detention) pumped out at minimum 30- to 90-day intervals.

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3. Wastewater Lift Stations & Wet Well Hydraulics

When topography prevents continuous gravity drainage, wastewater lift stations (pumping stations) collect sewage in an underground chamber and pump it through a pressurized force main over topographic ridges or directly into the treatment plant.

              DUPLEX SUBMERSIBLE LIFT STATION

               Control Panel & RTU (SCADA)
               ┌────────────────────────┐
               │  Lead / Lag Alternator │
               └───────────┬────────────┘
                           │
  Influent Gravity         │    Discharge Force Main (To WWTP)
  ────────────────► ┌──────┴───────────────────┬──────►
                    │  WET WELL                │
                    │                          │ [Check & Plug Valves]
                    │  ● High Level Alarm      │
                    │  ● Lag Pump Start        │
                    │  ● Lead Pump Start       │
                    │  ● Pumps Off             │
                    │                          │
                    │    ┌───┐        ┌───┐    │
                    │    │ P1│        │ P2│    │ Guide Rails
                    └────┴─┬─┴────────┴─┬─┴────┘
                           ▼            ▼
                  Steeply Sloped Hopper Floor (1:1)

Lift Station Configurations: Submersible vs. Dry Well

• Submersible Duplex Stations: The modern municipal standard. Two identical heavy-duty submersible non-clog centrifugal pumps (equipped with single-vane, vortex, or cutter impellers) are submerged directly in the sewage at the bottom of the wet well. Pumps ride on stainless steel guide rails with automatic self-coupling discharge shoes. Maintenance crews can hoist pumps to the surface with an overhead davit crane for servicing without entering the hazardous permit-required confined space. Duplex redundancy ensures that if one pump fails, the second pump handles 100% of peak design flow.
• Dry Well / Wet Well Stations: Consists of two separate subterranean structures divided by a watertight wall. Sewage collects in the wet well, while centrifugal pumps, motors, piping manifolds, and valves are housed in the adjacent clean, dry well. Offers superior accessibility for visual inspection, mechanical seal monitoring, and packing adjustment, but requires higher initial capital expenditure and dedicated dry well ventilation and sump dewatering pumps.

Wet Well Design, Sizing & Pump Cycle Time Calculations

Wet well volumetric sizing requires a delicate engineering balance:

• If the wet well is too large, sewage detention time exceeds 30 to 60 minutes, inducing severe anaerobic septicity, hydrogen sulfide generation, and floating grease crusts.
• If the wet well is too small, pumps start and stop constantly (short-cycling), causing electric motors to overheat, breaking motor starter contacts, and destroying motor windings.

$\mathbf{\text{Minimum Pump Cycle Time: } 5 \text{ to } 10 \text{ minutes} \quad (\le 6 \text{ to } 10 \text{ starts per hour})}$

The total pump cycle time ($t$, in minutes) represents the elapsed time from one pump start to the subsequent start of the same pump:

$t = \frac{V}{Q_p - Q_i} + \frac{V}{Q_i} = \frac{V \cdot Q_p}{Q_i \cdot (Q_p - Q_i)}$

Where:

• $V$ = Operating storage volume of the wet well between the "Pump Off" and "Lead Pump On" levels (gallons)
• $Q_p$ = Pump discharge capacity (gpm)
• $Q_i$ = Inflow rate entering the wet well (gpm)

Mathematical Principle: The minimum cycle time (fastest cycle rate) occurs precisely when the incoming wastewater flow rate equals exactly half of the pump's discharge capacity ($Q_i = 0.5 \cdot Q_p$). Under this peak-cycling condition, the formula simplifies to:

$V = \frac{t_{\text{min}} \cdot Q_p}{4}$

Level Sensing & Automation Instrumentation

Modern lift stations rely on automated level sensors linked to programmable logic controllers (PLCs) or pump alternators:

• Mechanical Tilt Float Switches: Sealed chemical-resistant polypropylene bulbs containing mechanical ball microswitches or mercury contacts suspended at discrete elevations: Pumps Off, Lead Pump On, Lag Pump On, and High Level Alarm. Highly reliable and economical, but prone to false switching from grease encapsulation, rag fouling, and turbulent sloshing.
• Ultrasonic Level Transmitters: Non-contact acoustic sensors mounted on the wet well ceiling that bounce ultrasonic sound waves off the liquid surface. Immune to corrosion, but can be blinded by thick surface grease blankets, dense steam/condensation, or surface turbulence.
• Submersible Hydrostatic Pressure Transducers: Piezoresistive pressure sensors lowered to the wet well floor that measure the hydrostatic pressure head of the liquid column. Provides continuous 4–20 mA level signals, but requires periodic cleaning to remove ragging.
• Air Bubbler Tubes: A continuous stream of compressed air is purged through a submerged open pipe. The air pressure required to force bubbles out of the bottom equals the hydrostatic liquid depth. Highly robust in heavy grease and solids environments.

Standby Power & Emergency Bypass Pumping

Because wastewater continuously flows into collection networks regardless of weather or electrical grid status, lift stations are prime vectors for SSOs during power outages or equipment failure. North Carolina addresses this through the reliability provisions of 15A NCAC 02T .0305 and the Pump Station Minimum Design Criteria, which let an applicant satisfy reliability with multiple power sources, permanently installed standby generation, or a documented contingency plan built on portable generation — in which case the station must have a quick-connect receptacle, located outside any enclosure and weather protected, that mates with the utility's portable unit. Other rule-driven features:

1. Permanent Emergency Auxiliary Power: On-site diesel or natural gas engine generators equipped with an Automatic Transfer Switch (ATS) capable of starting within 10 to 60 seconds of grid failure, powering all pumps, ventilation fans, and telemetry under full peak hydraulic load.
2. Emergency Bypass Quick-Connects: Standardized external suction and discharge ports (camlock or Bauer fittings) isolated by valves on the force main header. Allows mobile, trailer-mounted diesel trash pumps to bypass the station during pump repairs or wet well structural cleaning.
3. Alarms and telemetry. Weather-proof audible and visual alarms external to the structure are required, operating from a continuously charged battery backup when power or the standby generator fails. At a minimum the alarm and telemetry systems must annunciate high water in the wet well, pump failure, loss of power supply, and failure of an automatically activated standby power source, and the telemetry must reach personnel able to respond 24 hours a day, 365 days a year. Level sensing must indicate all pumps off, lead pump on, lag pump on, and high-water alarm; where a non-float method such as a bubbler or ultrasonic meter is used, a float switch at the high-water alarm level is required as a backup.
4. Inspection frequency. Under 15A NCAC 02T .0305(h)(1)(E), pump stations not connected to a telemetry system must be inspected every day; stations connected to telemetry are inspected once per week.

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4. Hydrogen Sulfide ($H_2S$) Chemistry & Microbial Induced Corrosion (MIC)

Hydrogen sulfide gas is the most dangerous atmospheric hazard in wastewater collection and the primary agent of structural infrastructure destruction.

             THE BIOCHEMISTRY OF MICROBIAL INDUCED CORROSION (MIC)

 1. SUBMERGED SLIME LAYER (Anaerobic):
    Sulfate-Reducing Bacteria (Desulfovibrio)
    SO4(2-) + Organic Carbon ──► Dissolved Sulfide (S2-, HS-)

 2. SEWER ATMOSPHERE HEADSPACE:
    Turbulence / Drops strip dissolved sulfide ──► Gaseous H2S off-gassing

 3. MOIST CONCRETE CROWN (Aerobic):
    Sulfur-Oxidizing Bacteria (Thiobacillus)
    Gaseous H2S + 2 O2 ──► Concentrated Sulfuric Acid (H2SO4) (pH drops to < 1.0!)

 4. CONCRETE STRUCTURAL COLLAPSE:
    H2SO4 + Concrete (Ca(OH)2) ──► Gypsum (CaSO4) + Ettringite ──► Crown Collapses

The Multi-Stage Biogenic Mechanism

1. Stage 1: Anaerobic Sulfate Reduction in Submerged Slime Layers: In lengthy gravity mains with flat slopes, or in pressurized force mains where dissolved oxygen ($DO$) is completely depleted ($DO = 0.0 \text{ mg/L}$), facultative and obligate anaerobic bacteria thrive in the biological slime layer adhered to submerged pipe walls. Sulfate-Reducing Bacteria (SRB), primarily Desulfovibrio desulfuricans, utilize sulfate ions ($SO_4^{2-}$) naturally present in domestic water as terminal electron acceptors to metabolize organic carbon, reducing sulfate into dissolved sulfide ($H_2S, HS^-, S^{2-}$):

$SO_4^{2-} + 2 \text{CH}_2\text{O} \xrightarrow{\text{SRB}} H_2S + 2 \text{HCO}_3^-$

1. Stage 2: Atmospheric Stripping into Headspace: Dissolved hydrogen sulfide exists in dynamic equilibrium with hydrosulfide ions, controlled by wastewater pH:

$H_2S \text{ (gas/dissolved)} \rightleftharpoons HS^- + H^+ \rightleftharpoons S^{2-} + 2 H^+$

At normal wastewater pH (6.5 to 7.5), approximately 50% of sulfide exists as dissolved, un-ionized $H_2S$ gas. When the flow encounters turbulence (drops, manholes, force main discharges, high velocities), the dissolved $H_2S$ gas is stripped out of the liquid and released into the air-filled pipe headspace. 3. Stage 3: Aerobic Microbial Oxidation on the Pipe Crown: High humidity in the sewer creates moisture condensation on the un-submerged concrete crown and walls. Aerobic Sulfur-Oxidizing Bacteria (SOB)—predominantly Thiobacillus species (Acidithiobacillus ferrooxidans, Thiobacillus concretivorus)—colonize the damp concrete surface. These autotrophic bacteria absorb atmospheric $H_2S$ gas and oxygen, oxidizing the gas into concentrated sulfuric acid ($H_2SO_4$):

$H_2S + 2 O_2 \xrightarrow{\text{Thiobacillus}} H_2SO_4$

Microbial Acidification: Bacterial acid production drives the pH on the concrete crown surface down from its initial alkaline state (pH 11–12) to below pH 1.0 to 2.0—an environment equivalent to battery acid. 4. Stage 4: Structural Concrete Attack (Crown Corrosion): Concentrated sulfuric acid chemically attacks the alkaline calcium hydroxide ($Ca(OH)_2$) and calcium silicate hydrates in the Portland cement matrix:

$H_2SO_4 + Ca(OH)_2 \longrightarrow CaSO_4 \cdot 2H_2O \text{ (Gypsum)}$

The resulting gypsum and associated ettringite crystals expand by over 100% in volume within the concrete pores, exerting massive internal crystallization pressures. The concrete loses all compressive strength, converting into a soft, mushy, chalky paste. The structural crown of the pipe thins, rebar corrodes, and the sewer ultimately suffers catastrophic structural collapse, creating sinkholes in roadways.

Chemical and Operational Mitigation Strategies

Utilities combat $H_2S$ generation and MIC through targeted chemical injection and mechanical controls:

• Calcium Nitrate Addition (e.g., Bioxide): Injected into the upstream head of force mains. Facultative bacteria preferentially consume nitrate ($NO_3^-$) rather than sulfate ($SO_4^{2-}$), raising the oxidation-reduction potential (ORP) above $-100 \text{ mV}$ and biochemically suppressing sulfate-reducing bacteria.
• Iron Salts (Ferrous / Ferric Chloride, $FeCl_2 / FeCl_3$): Added to sewage to chemically react with dissolved sulfides, precipitating them as dense, insoluble black ferrous sulfide ($FeS$) crystals that pass harmlessly to the treatment plant without off-gassing.
• pH Elevation / Caustic Shock Dosing ($NaOH$): Raising wastewater pH above 9.0 converts virtually all dissolved sulfide into non-volatile hydrosulfide ions ($HS^-$), keeping sulfide dissolved. Shock-dosing caustic to pH 12.5 for 20 to 30 minutes effectively sterilizes the slime layer, inactivating SRB for weeks.
• Ventilation & Air Treatment: Mechanical exhaust fans pull corrosive sewer headspace air through packed-bed wet chemical scrubbers, bio-trickling filters (where harmless microbes consume $H_2S$), or virgin activated carbon adsorption beds.

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5. Inflow and Infiltration (I/I): Diagnostic Testing & Assessment

Inflow and Infiltration (I/I) is extraneous, non-sanitary water that enters the wastewater collection network. I/I consumes collection pipe capacity, floods lift stations, causes sanitary sewer overflows (SSOs), washes out biological secondary treatment processes, and forces utilities to expand multimillion-dollar treatment facilities to process clean rainwater.

                  HYDROGRAPH RESPONSE: INFLOW vs. INFILTRATION

 Flow Rate (MGD)
    ▲
    │                     INFLOW (Sharp, violent peak matching rainfall)
    │                       ╭─╮
    │                      ╭   ╮
    │                     ╭     ╮
    │                    ╭       ╮     INFILTRATION (Slow, prolonged elevation)
    │                   ╭         ╮         ╭───────────────────────╮
    │                  ╭           ╮       ╭                         ╮
    │  Base Flow ─────●             ●─────●                           ●────
    └─────────────────┴─────────────┴─────┴───────────────────────────┴───► Time
                           Rainfall Event

Defining Inflow vs. Infiltration

• Inflow (Direct Stormwater): Extraneous water that enters the collection system directly from surface or atmospheric sources. Characterized by an immediate, sharp spike in collection flow occurring simultaneously with rainfall, followed by a rapid decline as soon as runoff ceases.
  • Sources: Roof downspouts directly tied into building laterals; outdoor area and driveway drains; unsealed manhole pick holes and submerged rim covers in low-lying roadways; cross-connections with storm drain pipes; foundation French drains; and residential basement sump pumps.
• Infiltration (Subterranean Groundwater): Extraneous water that seeps into collection pipes through defective subterranean infrastructure. Characterized by a gradual, delayed increase in flow as the groundwater table elevates following prolonged precipitation, followed by a very slow, sustained recession that can persist for weeks or months.
  • Sources: Cracked, fractured, or crushed pipe barrels; displaced, open, or offset pipe joints; deteriorated mortar brickwork in manholes; deteriorating building service laterals; and mechanical root penetration through pipe joints.

Diagnostic Inspection Methodologies

1. Closed-Circuit Television (CCTV) Inspection:
   • A robotic, motorized crawler camera is lowered into a cleaned sewer main and propelled through the conduit. A pan-tilt-zoom camera records high-definition video of pipe wall conditions.
   • Certified operators log defects according to national NASSCO PACP (Pipeline Assessment Certification Program) codes: quantifying joint offsets, hairline cracks, structural fractures, sags (bellies), active groundwater gushers, mineral encrustation, and root intrusions.
2. Smoke Testing:
   • An essential diagnostic methodology utilized specifically to detect Inflow and illicit surface cross-connections.
   • A high-capacity blower is positioned over an open manhole, and non-toxic, odorless, white or colored chemical smoke bombs (or liquid aerosol generators) are ignited. Sewer segments are isolated using sandbags or pneumatic test balls. The blower forces smoke under pressure through the isolated main.
   • Operators walk the neighborhood observing where smoke emerges: smoke emerging from residential roof gutters, driveway grates, ditch lines, or patio drains immediately pinpoints illegal inflow connections. Smoke venting from lawns indicates broken building laterals.
3. Dye Flooding / Dye Testing:
   • Fluorescent non-toxic dyes (uranine, rhodamine) are introduced into suspected inflow sources (storm catch basins, parking lot drains, foundation swales) and flooded with water while monitoring downstream sanitary manholes with UV lamps to confirm direct hydraulic interconnectivity.
4. Acoustic Inspection:
   • Sound wave transmitters and receivers lowered into adjacent manholes analyze acoustic reflection signatures, rapidly scoring pipe blockage and structural condition within seconds without water jetting or CCTV cameras.
5. Flow Monitoring & Peaking Factors:
   • Area-velocity ultrasonic flow meters installed in strategic trunk lines continuously record velocity and depth to compute diurnal flow. Comparing Dry Weather Flow (DWF) with Wet Weather Flow (WWF) establishes the Peaking Factor:

$\text{Peaking Factor} = \frac{\text{Peak Wet Weather Flow Rate (MGD)}}{\text{Average Dry Weather Base Flow Rate (MGD)}}$

In systems suffering from severe I/I, peaking factors can exceed 4.0 to 10.0:1, instantly overwhelming lift stations and causing SSOs.

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6. Trenchless Collection System Rehabilitation Technologies

Traditional "dig-and-replace" sewer excavation in urban environments creates massive traffic disruptions, tears up paved roadways, damages adjacent utility mains, and carries extreme civil costs. Utilities increasingly rely on trenchless rehabilitation.

                  TRENCHLESS REHABILITATION METHODOLOGIES

1. CURED-IN-PLACE PIPE (CIPP):           2. PIPE BURSTING:

   Existing Cracked Host Pipe               Existing Fragile Host Pipe (Shattered)
   ┌───────────────────────────┐            ░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
   │  Flexible Resin Felt Tube │ ◄── Hot    ◄── [Expansion Cone] ◄── Pull Cable
   │  Cured into Hard Composite│     Water/ ░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
   └───────────────────────────┘     Steam/UV  New Continuous HDPE Pipe Pulled In

1. Cured-In-Place Pipe (CIPP) Lining

• Operational Process: A flexible, resin-impregnated non-woven polyester felt or fiberglass tube is inserted into the damaged host pipe from an existing manhole. The liner is inverted (turned inside out) or pulled in using hydrostatic water head or compressed air pressure. Once pressed tightly against the host pipe walls, the tube is cured by circulating hot water, injecting pressurized steam, or pulling an ultraviolet (UV) light train through the line. The thermosetting resin (polyester, vinyl ester, or epoxy) polymerizes and cross-links, hardening into a jointless, structural, smooth "pipe-within-a-pipe."
• Advantages: Eliminates excavation; completely seals all leaking joints and cracks; restores structural integrity; and despite a minor reduction in internal diameter, the ultra-smooth surface ($n=0.009$ vs. $n=0.015$ for aged pipe) often increases total hydraulic flow capacity.
• Reinstatement: A robotic cutter crawler is driven into the cured liner to mechanically mill out and reinstate lateral service connections from the inside without digging.

2. Pipe Bursting

• A pneumatic, hydraulic, or static expansion bursting head is pulled through the deteriorated host pipe (commonly vitrified clay, cast iron, or unreinforced concrete) by a heavy steel winch cable.
• The bursting head shatters the old host pipe, radially forcing the broken fragments outward into the surrounding soil matrix. Simultaneously, the head pulls a new, continuous string of butt-fused High-Density Polyethylene (HDPE) or fusible PVC pipe of equal or larger diameter (upsizing) directly into the vacated tunnel.
• Advantage: Unlike lining, pipe bursting allows utilities to upsize old 8-inch mains to 10- or 12-inch pipes to increase hydraulic capacity without trenching.

3. Sliplining

• A smaller-diameter continuous carrier pipe (HDPE, PVC, fiberglass) is pushed or pulled inside the host pipe. The annular space remaining between the outside of the carrier pipe and the inside of the host pipe is completely filled with pressurized, low-density cellular grout to anchor the pipe and seal out groundwater. Considerably reduces internal diameter.

4. Manhole Structural Rehabilitation

• Infiltration through deteriorated manholes accounts for 30% to 50% of total collection system infiltration.
• Rehabilitation involves high-pressure water blasting to remove grease and loose mortar, hydraulic cement water-plugs to halt active groundwater leaks, application of structural calcium-aluminate or fiber-reinforced cementitious mortar, and top-coating with 100% solids multi-layer monolithic epoxy, polyurethane, or polyurea spray liners to resist future biogenic sulfuric acid attack.