Cleaning & Blockage Control

Sewer cleaning keeps wastewater moving by removing grease, roots, grit, rags, wipes, sediment, and other materials that reduce pipe capacity or create blockages. Effective blockage control combines emergency response with preventive maintenance so recurring problems are corrected before they cause backups or sanitary sewer overflows.

Collection-system operators should understand different cleaning methods, how to locate a restriction, how to recognize the likely cause of a blockage, when cleaning is only a temporary solution, and how maintenance history can be used to develop an efficient preventive-cleaning program.

Why Sewers Need Cleaning

Wastewater carries solids and debris that can accumulate in collection-system piping.

Common materials include:

• fats, oils, and grease;
• roots;
• rags and wipes;
• grit and sand;
• settleable solids;
• construction debris;
• foreign objects.

Blockage Effects

A blockage can cause:

• higher upstream wastewater levels;
• reduced downstream flow;
• customer backups;
• manhole overflows;
• sanitary sewer overflows.

Partial Versus Complete Blockage

A partial blockage allows some wastewater to pass.

A complete blockage can stop normal flow entirely.

Partial Blockages Can Be Difficult to Detect

A partially restricted sewer may operate normally during low flow but surcharge during:

• morning or evening peaks;
• wet weather;
• high industrial discharge.

Common Blockage Causes

Operators should identify the likely cause rather than treating every blockage the same way.

Frequent causes include:

• grease;
• roots;
• wipes and fibrous material;
• grit;
• structural defects;
• low-velocity deposits.

Fats, Oils, and Grease

Fats, oils, and grease can cool and attach to sewer walls.

As deposits grow, they can:

• reduce pipe diameter;
• increase roughness;
• trap rags and debris;
• eventually block flow.

Grease Problem Locations

Grease problems may be more common downstream from:

• restaurants;
• food-service areas;
• commercial kitchens;
• other significant grease sources.

Root Intrusion

Roots enter sewers through openings such as:

• cracks;
• open joints;
• defective service connections.

Once inside, roots can grow into dense masses that trap solids and reduce flow.

Root Cutting Is Often Temporary

Mechanical root removal can restore flow, but roots may return if the entry defect remains open.

Repeated root problems can indicate the need for:

• joint repair;
• spot repair;
• lining;
• pipe replacement.

Rags and Wipes

Fibrous materials can:

• catch on roots;
• collect at rough joints;
• wrap around pump components;
• combine with grease.

Grit and Sediment

Grit and sediment tend to accumulate where velocity is low.

Possible causes include:

• low sewer slope;
• low wastewater flow;
• pipe sag;
• large pipe diameter relative to normal flow.

Hydraulic Cleaning

Hydraulic cleaning uses water movement to loosen and transport deposits.

One of the most common methods is high-pressure sewer jetting.

High-Pressure Jetting

A jetting nozzle directs high-pressure water against deposits and pipe surfaces.

Jetting can be effective for:

• grease;
• soft deposits;
• sediment;
• loose debris.

Jetting Nozzles

Different nozzle designs can be used for different objectives such as:

• general cleaning;
• grease removal;
• sediment movement;
• penetrating blockages.

Do Not Simply Push Debris Downstream

Cleaning should remove or properly manage loosened material whenever practical.

Moving a large blockage downstream can create another restriction.

Vacuum Equipment

Vacuum equipment is often used with hydraulic cleaning to remove:

• grit;
• sediment;
• debris;
• cleaning water.

Combination Cleaning Trucks

Combination units can provide both:

• high-pressure jetting;
• vacuum removal.

Mechanical Cleaning

Mechanical methods use tools that physically cut, scrape, or remove obstructions.

Possible applications include:

• root cutting;
• hard deposits;
• specific obstructions.

Mechanical Root Cutters

Root-cutting tools can reopen pipe area but should be used with knowledge of pipe condition.

A severely deteriorated pipe may be vulnerable to additional damage.

Rodding

Rodding equipment can be used to penetrate or remove certain localized obstructions.

Cleaning Method Should Match the Problem

Examples include:

• grease may respond well to jetting;
• heavy roots may require cutting;
• grit may require jetting plus vacuum removal;
• structural collapse cannot be corrected by cleaning.

Locating a Blockage

Operators can compare upstream and downstream manholes.

A common restriction pattern is:

• high wastewater level upstream;
• lower wastewater level downstream.

Work from Known Access Points

System maps and manhole identification help operators determine:

• flow direction;
• affected sewer segment;
• upstream customers;
• downstream access.

Emergency Blockage Response

A rapid blockage response can include:

1. identify affected locations;
2. protect the public and work area;
3. locate the restricted sewer segment;
4. remove the obstruction;
5. verify restored flow;
6. inspect for the underlying cause;
7. document the event.

Protect Against Overflow

During a blockage response, operators should monitor:

• upstream manhole levels;
• customer backup risk;
• overflow locations;
• incoming flow.

Temporary Bypass

Severe blockages or structural failures may require temporary bypass pumping while the sewer is cleaned or repaired.

Verify Restored Flow

Opening a blockage is not the end of the response.

Operators should confirm:

• upstream level returns toward normal;
• downstream flow is restored;
• no secondary blockage remains.

Post-Cleaning Inspection

CCTV inspection after cleaning can help identify:

• roots;
• cracks;
• open joints;
• sags;
• deformation;
• protruding laterals.

Repeated Blockages Need Investigation

If the same sewer blocks repeatedly, possible underlying causes include:

• root entry;
• grease source;
• structural sag;
• low slope;
• damaged pipe;
• protruding connection.

Preventive Cleaning

Preventive cleaning is scheduled before a blockage occurs.

Its purpose is to reduce:

• emergency calls;
• backups;
• overflows;
• unplanned overtime.

High-Frequency Maintenance Sewers

Some sewer segments require frequent cleaning because of known recurring conditions.

These locations may be identified from:

• blockage history;
• overflow history;
• CCTV results;
• grease problems;
• root problems.

Use Maintenance History to Set Frequency

If a sewer historically blocks every six months, waiting nine months between cleanings may create unnecessary risk.

If inspection shows the underlying problem has been repaired, the cleaning interval may be reconsidered.

Do Not Clean Every Sewer at the Same Frequency

A risk-based cleaning program directs more resources toward:

• problem sewers;
• critical sewers;
• locations with serious overflow consequences.

Cleaning Frequency Should Be Evidence Based

Useful evidence includes:

• deposit accumulation;
• blockage history;
• CCTV condition;
• customer complaints;
• hydraulic performance.

Cleaning Too Frequently

Unnecessary cleaning can:

• increase labor cost;
• increase equipment wear;
• consume water and fuel;
• occupy crews that could address higher-risk assets.

Cleaning Too Infrequently

Insufficient cleaning can increase:

• blockages;
• backups;
• overflows;
• emergency response cost.

Grease-Control Programs

Grease problems may require more than sewer cleaning.

Long-term control can involve:

• source identification;
• customer education;
• grease-control requirements;
• inspection;
• targeted sewer maintenance.

Root-Control Programs

Root problems can be managed through combinations of:

• mechanical cutting;
• approved root-control methods;
• structural repair;
• rehabilitation.

Cleaning and Hydraulic Capacity

Deposits reduce effective flow area.

Removing deposits can:

• restore pipe area;
• reduce upstream depth;
• improve hydraulic capacity.

Cleaning Cannot Increase Original Pipe Size

If the sewer is fundamentally undersized for peak flow, cleaning alone will not solve the capacity problem.

Cleaning and Infiltration

Cleaning does not normally eliminate groundwater entering through:

• cracks;
• open joints;
• defective laterals.

Those defects may require rehabilitation or repair.

Cleaning and Structural Failure

A collapsed sewer cannot be permanently corrected with cleaning equipment.

Structural repair is required.

Cleaning Records

Useful cleaning records include:

• date;
• sewer segment;
• cleaning method;
• material removed;
• cause of blockage;
• equipment used;
• follow-up action.

Document Material Removed

The type of material removed can help identify the underlying problem.

Examples include:

• heavy grease;
• roots;
• grit;
• wipes;
• construction debris.

Trend Repeated Events

Maintenance records can show whether:

• cleaning frequency is increasing;
• blockages are becoming more severe;
• the same defect is repeatedly causing failures.

Example: Same Sewer Blocks Every Three Months

Do not simply continue emergency cleaning indefinitely.

Investigate:

• CCTV condition;
• roots;
• grease;
• sag;
• pipe damage.

Example: Heavy Grease Is Removed Repeatedly

Review upstream grease sources and whether source-control measures are needed.

Example: Roots Return After Cutting

The root entry point remains.

Inspect for:

• open joints;
• cracks;
• defective service connections.

Example: Grit Returns Quickly

Possible causes include:

• low velocity;
• structural sag;
• upstream grit source;
• infiltration carrying soil into the sewer.

Example: Sewer Is Clear but Upstream Level Remains High

Investigate:

• additional downstream restriction;
• hydraulic surcharge;
• pump-station limitation;
• incorrect flow-path assumption.

Example: Blockage Occurs Only During Rain

A partial restriction may become critical when wet-weather flow increases.

Example: Cleaning Removes Almost No Material

If hydraulic problems remain, review:

• pipe condition;
• downstream level;
• structural deformation;
• capacity limitations.

Example: Jetting Water Returns to the Upstream Manhole

This may indicate:

• severe restriction;
• incorrect nozzle progress;
• downstream blockage.

Example: Sewer Blocks Soon After Cleaning

Possible causes include:

• incomplete cleaning;
• rapid grease accumulation;
• heavy root intrusion;
• structural defect.

Cleaning Equipment Inspection

Before use, inspect equipment such as:

• hoses;
• nozzles;
• reels;
• vacuum components;
• mechanical cutters.

High-Pressure Water Hazards

Jetting equipment can produce enough pressure to cause serious injury.

Operators should follow equipment-specific procedures and keep personnel clear of hazardous hose and nozzle locations.

Hose Control

Jetting hoses can move unexpectedly under pressure.

Proper equipment operation and hose control are important safety practices.

Manhole Safety

Cleaning work around manholes can involve:

• traffic;
• falls;
• hazardous atmospheres;
• heavy covers.

Confined-Space Hazards

Collection structures can contain:

• hydrogen sulfide;
• methane;
• oxygen-deficient atmospheres.

Entry should follow applicable confined-space procedures.

Biological Exposure

Wastewater and removed debris can contain microorganisms.

Operators should use appropriate:

• PPE;
• hand hygiene;
• equipment-cleaning practices.

Traffic Control

Sewer-cleaning equipment often occupies roadways.

Appropriate work-zone controls should protect:

• operators;
• drivers;
• pedestrians.

Common Cleaning and Blockage-Control Mistakes

• Removing the blockage without identifying the cause.
• Pushing debris downstream and creating a new blockage.
• Repeatedly cutting roots without investigating the root entry point.
• Using cleaning as a substitute for structural repair.
• Cleaning every sewer on the same schedule regardless of history.
• Ignoring grease-source control.
• Failing to verify restored downstream flow.
• Failing to inspect recurring blockage locations with CCTV.
• Failing to document the material removed and corrective action.
• Ignoring high-pressure water, traffic, confined-space, and biological hazards.

A Practical Blockage Response

1. Identify the affected area.
2. Establish safe traffic and work-zone controls.
3. Check upstream and downstream manholes.
4. Locate the restricted sewer segment.
5. Select the appropriate cleaning method.
6. Remove or recover the obstruction.
7. Verify restored wastewater flow.
8. Inspect for the underlying cause.
9. Document the event and follow-up action.

A Practical Preventive-Cleaning Review

1. Review blockage history.
2. Review overflow and backup history.
3. Review CCTV findings.
4. Identify high-frequency maintenance locations.
5. Set cleaning intervals based on observed accumulation and risk.
6. Record each cleaning event.
7. Adjust frequency when conditions change.

A Practical Recurring-Blockage Review

1. Review what material is repeatedly removed.
2. Review the time between blockages.
3. Inspect the sewer with CCTV.
4. Check for roots, grease, sags, and structural defects.
5. Review hydraulic conditions.
6. Determine whether cleaning, source control, repair, rehabilitation, or replacement is appropriate.

A Practical Cleaning-Program Review

1. Identify the highest-risk sewer segments.
2. Compare maintenance frequency among segments.
3. Review labor and equipment use.
4. Review whether repeated cleaning is solving or only delaying problems.
5. Move resources toward locations with the greatest operational risk.
6. Coordinate cleaning with condition assessment and rehabilitation planning.

What to Remember for the Exam

• Sewer cleaning removes grease, roots, grit, sediment, rags, wipes, and other materials that restrict flow.
• Partial blockages may cause problems only during peak or wet-weather flow.
• High upstream level with lower downstream level can indicate a blockage between those points.
• Grease reduces effective pipe area and traps debris.
• Roots usually enter through an existing crack, joint, or connection defect.
• Root cutting restores flow but does not repair the root entry point.
• Low velocity and pipe sags can contribute to grit and sediment accumulation.
• High-pressure jetting is commonly used for grease, sediment, and soft deposits.
• Vacuum equipment can remove loosened grit and debris from the collection system.
• Mechanical methods can be used for roots and other difficult obstructions.
• The cleaning method should match the type of blockage and pipe condition.
• After clearing a blockage, operators should verify that upstream levels fall and downstream flow is restored.
• Recurring blockage locations should be inspected for underlying hydraulic or structural causes.
• Preventive cleaning should be based on maintenance history, risk, and observed accumulation.
• Not every sewer needs the same cleaning frequency.
• Cleaning can restore capacity lost to deposits but cannot correct an undersized or structurally failed sewer.
• Cleaning records should document the sewer segment, material removed, method, cause, and follow-up action.
• Repeated grease, root, or grit problems provide useful evidence about the underlying cause.
• Sewer cleaning involves high-pressure water, traffic, biological exposure, manhole, and confined-space hazards.
• Good blockage control combines rapid response, proper cleaning, verification, condition assessment, preventive maintenance, source control, accurate records, and structural repair when needed.