Sewer Construction, Testing & Acceptance

New and rehabilitated sewers must be constructed so they can convey wastewater reliably for many years. Proper alignment, slope, bedding, joints, manholes, service connections, backfill, and testing all affect whether a sewer will perform as intended after it is placed in service.

Collection-system operators may not design every sewer project, but they need to understand construction and acceptance because poorly installed assets can create long-term problems such as infiltration, blockages, sags, root intrusion, structural damage, and repeated maintenance.

Purpose of Construction Inspection

Construction inspection helps confirm that installed sewers match approved plans and specifications.

Important items include:

• pipe material and diameter;
• alignment;
• grade;
• bedding;
• joint condition;
• manholes;
• service connections;
• backfill;
• testing;
• record documentation.

Approved Plans and Specifications

Before installation begins, construction personnel should work from current approved documents.

These documents define:

• pipe size;
• pipe material;
• elevations;
• slope;
• manhole locations;
• connection details;
• testing requirements.

Alignment

Alignment describes the horizontal path of the sewer.

Poor alignment can create:

• hydraulic restrictions;
• difficult cleaning;
• joint stress;
• future locating problems.

Grade

Grade describes the vertical slope of the sewer.

Gravity sewers depend on proper grade to maintain reliable flow.

Slope Calculation

A common calculation is:

Slope = Vertical Drop ÷ Horizontal Length

Slope as Percent

Slope, % = Vertical Drop ÷ Horizontal Length × 100

Slope Example

A sewer invert drops 3.0 feet over 750 feet.

Slope = 3.0 ÷ 750

Slope = 0.004 ft/ft

Slope = 0.4%

Why Grade Errors Matter

An incorrect grade can create:

• low velocity;
• solids deposition;
• sags;
• unexpected hydraulic restrictions.

Sewer Invert

The invert is the lowest internal point of the sewer pipe or flow channel.

Invert elevations are used to establish:

• slope;
• flow direction;
• connection elevations.

Pipe Bedding

Bedding supports the pipe and helps distribute loads.

Proper bedding helps maintain:

• alignment;
• grade;
• structural support.

Poor Bedding

Poor bedding can contribute to:

• settlement;
• pipe deformation;
• joint movement;
• sags;
• structural failure.

Foundation Conditions

Weak or unstable trench bottoms may require corrective measures before pipe installation.

Installing pipe directly on unsuitable material can lead to future settlement.

Pipe Installation

During installation, operators or inspectors should watch for:

• damaged pipe;
• debris inside the pipe;
• improper joint assembly;
• incorrect grade;
• poor bedding.

Keep Pipe Interiors Clean

Construction debris can create blockages before the sewer ever enters normal service.

Materials can include:

• soil;
• stone;
• concrete;
• wood;
• tools;
• other debris.

Pipe Joints

Joints should provide:

• proper alignment;
• structural continuity;
• watertight performance appropriate to the system.

Joint Problems

Defective joints can allow:

• infiltration;
• root intrusion;
• soil migration;
• misalignment.

Gaskets

Where gasketed joints are used, gaskets should be:

• clean;
• properly positioned;
• undamaged.

Service Laterals

Service laterals should be installed so they do not create:

• leaking connections;
• protrusions into the main;
• improper slopes;
• future blockage points.

Protruding Service Connections

A lateral that extends too far into the main sewer can:

• restrict flow;
• catch rags;
• interfere with cleaning and CCTV inspection.

Manhole Construction

Manholes should provide:

• structural integrity;
• proper channel configuration;
• appropriate benching;
• secure covers;
• watertight connections.

Manhole Channels

Channels should guide wastewater smoothly between connecting sewers.

Poor channels can create:

• solids deposits;
• turbulence;
• maintenance problems.

Manhole Benching

Benching should direct incidental water toward the channel rather than allow ponding across the manhole floor.

Manhole Leakage

Leaking manholes can become significant sources of infiltration.

Common leakage locations include:

• joints;
• pipe penetrations;
• frame connections;
• cracks.

Backfill

Backfill supports the pipe and restores the excavation.

Improper backfill can contribute to:

• pipe movement;
• surface settlement;
• pipe deformation;
• joint damage.

Compaction

Proper compaction helps reduce later settlement.

Compaction requirements depend on project specifications and site conditions.

Flexible Pipe Deflection

Some flexible sewer pipes can deform if:

• bedding is poor;
• backfill is improper;
• loads exceed expected conditions.

Deflection Testing

Deflection testing may be required for certain flexible pipes after installation.

The purpose is to verify that deformation remains within applicable project requirements.

Mandrel Testing

A properly sized mandrel may be pulled through a flexible sewer to identify excessive deformation where that testing method is specified.

Do Not Force a Mandrel Through

If a mandrel will not pass, investigate the cause rather than treating excessive force as proof of acceptance.

Leakage Testing

Leakage testing helps evaluate whether installed sewers and manholes meet specified watertightness requirements.

Infiltration Testing

Infiltration testing measures groundwater entering the sewer under applicable conditions.

Excessive infiltration can indicate:

• leaking joints;
• cracks;
• defective manholes;
• poor service connections.

Exfiltration Testing

Exfiltration testing evaluates water leaking outward from a filled sewer section where the approved test method calls for it.

Air Testing

Low-pressure air testing may be used for certain gravity sewer installations according to approved specifications.

Operators should follow the specified:

• test pressure;
• stabilization period;
• test duration;
• safety procedures.

Air-Test Safety

Compressed air stores energy.

Testing should be performed using approved procedures and equipment.

Manhole Testing

Depending on project requirements, manholes may be tested using methods such as:

• vacuum testing;
• water testing;
• visual leakage inspection.

Testing Does Not Replace Inspection

A sewer can pass one test and still contain:

• debris;
• poor alignment;
• service protrusions;
• structural defects.

CCTV Inspection

Closed-circuit television inspection allows visual examination of the pipe interior.

CCTV can identify:

• cracks;
• joint defects;
• debris;
• roots;
• standing water;
• protruding laterals;
• deformation.

Standing Water in a New Sewer

Standing water can indicate:

• sag;
• incorrect grade;
• settlement;
• temporary obstruction.

Why Standing Water Matters

Persistent sags can collect:

• solids;
• grease;
• debris.

This can create long-term maintenance problems.

Post-Construction Cleaning

Before final acceptance, new sewer lines may require cleaning to remove:

• soil;
• construction debris;
• sediment;
• foreign material.

Acceptance Inspection

A final acceptance review may include:

• record drawings;
• test results;
• CCTV records;
• manhole inspection;
• cleanup;
• correction of deficiencies.

Punch List

A punch list identifies items that must be corrected before final acceptance.

Examples include:

• damaged structures;
• leaks;
• incorrect elevations;
• debris;
• poor restoration.

Record Drawings

Record drawings should document the installed system as accurately as possible.

Useful information includes:

• pipe location;
• pipe size;
• pipe material;
• manhole locations;
• invert elevations;
• service connections.

Why Record Drawings Matter

Accurate records help future operators:

• locate assets;
• plan cleaning;
• investigate backups;
• plan repairs;
• understand flow direction.

Acceptance Should Occur Before Problems Become Operations Problems

Defects are usually easier to correct before the contractor leaves the project than years later after failures begin.

Construction Debris

A common avoidable problem is leaving debris inside the system.

Debris can become the starting point for:

• blockages;
• rag accumulation;
• reduced capacity.

Settlement After Installation

Settlement can change:

• pipe grade;
• joint alignment;
• surface condition.

Surface Settlement

Settlement above a sewer trench can indicate inadequate backfill or compaction.

Pipe Sag After Acceptance

If a new sewer develops standing water shortly after installation, investigate:

• bedding;
• backfill;
• soil conditions;
• construction records.

Connections to Existing Sewers

Connections should be made carefully to avoid:

• debris entry;
• flow interruption;
• leakage;
• damage to existing assets.

Bypass Pumping

Construction or rehabilitation may require temporary bypass pumping.

A bypass system should be capable of handling expected wastewater flow.

Bypass Failure

Failure can cause:

• backups;
• overflows;
• worksite flooding.

Bypass Planning

Planning can include:

• pump capacity;
• backup pump;
• power supply;
• hoses and piping;
• high-level monitoring.

Construction Near Active Sewers

Active wastewater flow creates additional hazards and operational concerns.

Operators should coordinate:

• flow control;
• customer impacts;
• pump-station operation;
• emergency response.

Trench Safety

Sewer construction can involve excavation and trench hazards.

Operators should recognize hazards such as:

• cave-ins;
• falling material;
• underground utilities;
• water accumulation;
• mobile equipment.

Do Not Enter an Unsafe Excavation

Applicable excavation and trench-safety procedures must be followed before entry.

Utility Location

Existing utilities should be located before excavation.

Potential conflicts include:

• water mains;
• gas lines;
• electric lines;
• communications;
• other sewers.

Construction Traffic

Sewer work often occurs in roadways.

Traffic control should protect:

• workers;
• drivers;
• pedestrians.

Example: New Sewer Has Standing Water

Investigate:

• surveyed grade;
• bedding;
• settlement;
• possible obstruction.

Example: Air Test Fails

Possible causes include:

• leaking joint;
• damaged pipe;
• service-connection leak;
• test-equipment problem.

Example: Manhole Vacuum Test Fails

Review:

• joints;
• pipe penetrations;
• frame area;
• structural cracks;
• test setup.

Example: CCTV Shows Protruding Lateral

The protrusion should be evaluated and corrected according to project requirements before acceptance.

Example: Mandrel Does Not Pass

Possible causes include:

• excessive pipe deflection;
• debris;
• joint offset;
• incorrect test equipment.

Example: New Manhole Leaks During Wet Weather

Review:

• barrel joints;
• pipe penetrations;
• frame and cover area;
• surrounding groundwater conditions.

Example: New Sewer Blocks Repeatedly

Investigate:

• construction debris;
• sag;
• protruding lateral;
• incorrect slope;
• joint offset.

Example: Road Surface Settles Along Sewer Trench

This can indicate backfill or compaction problems.

Example: Treatment-Plant Flow Increases After New Sewer Is Connected

Review whether the increase is caused by:

• new customer flow;
• infiltration;
• unexpected stormwater inflow.

Acceptance Documentation

Useful project records include:

• inspection reports;
• test results;
• CCTV video;
• survey information;
• record drawings;
• repair documentation.

Good Records Reduce Future Troubleshooting Time

When a future blockage or structural problem occurs, construction records can help identify:

• pipe material;
• depth;
• joint type;
• previous repairs;
• installation conditions.

Common Sewer-Construction Mistakes

• Accepting incorrect grade because wastewater still flows.
• Ignoring standing water in CCTV inspection.
• Failing to remove construction debris.
• Accepting leaking joints or manholes.
• Ignoring protruding service connections.
• Assuming one successful test proves all construction quality.
• Failing to verify flexible-pipe deflection where required.
• Using inaccurate record drawings.
• Ignoring trench, traffic, and utility hazards.
• Accepting defects that later become routine maintenance problems.

A Practical Sewer-Construction Review

1. Verify approved plans and specifications.
2. Verify pipe size and material.
3. Check alignment and grade.
4. Inspect bedding and joints.
5. Inspect service connections.
6. Inspect manholes.
7. Review backfill and restoration.
8. Complete specified testing.
9. Review CCTV inspection.
10. Correct deficiencies before final acceptance.

A Practical Acceptance-Test Review

1. Confirm the required test method.
2. Verify test equipment condition.
3. Verify the test section and setup.
4. Perform the test according to approved procedure.
5. Record the result.
6. Investigate failures.
7. Correct defects.
8. Retest before acceptance.

A Practical CCTV Review

1. Confirm the sewer has been cleaned.
2. Inspect the entire pipe length.
3. Look for standing water.
4. Look for cracks and joint defects.
5. Check service connections.
6. Check for debris or obstructions.
7. Document defect locations.
8. Require correction of unacceptable defects.

A Practical Record-Transfer Review

1. Verify final pipe locations.
2. Verify manhole locations.
3. Verify invert elevations.
4. Verify pipe size and material.
5. Verify service connections.
6. Attach testing and CCTV records.
7. Enter the new assets into the collection-system maintenance records.

What to Remember for the Exam

• Proper sewer construction depends on alignment, grade, bedding, joints, manholes, connections, backfill, testing, and documentation.
• Gravity sewer grade controls flow direction and strongly affects hydraulic performance.
• Slope equals vertical drop divided by horizontal length.
• Poor bedding can cause settlement, deformation, joint movement, and sags.
• Defective pipe joints can allow infiltration, root intrusion, and soil migration.
• Protruding service laterals can restrict flow and catch debris.
• Manholes should have sound structures, smooth channels, appropriate benching, and watertight connections.
• Improper backfill and compaction can damage pipe and cause surface settlement.
• Flexible-pipe deflection may require testing before acceptance.
• Leakage testing can identify defective pipe, joints, manholes, and connections.
• Low-pressure air testing is one possible gravity-sewer test method when specified.
• CCTV inspection can identify cracks, debris, standing water, joint defects, deformation, and protruding laterals.
• Standing water in a new sewer can indicate a sag or grade problem.
• Testing does not replace visual and CCTV inspection.
• New sewers should be cleaned before final acceptance.
• Record drawings should show installed pipe locations, sizes, materials, manholes, invert elevations, and service connections.
• Bypass pumping must be capable of handling expected wastewater flow during construction or rehabilitation.
• Sewer construction can involve excavation, utility, confined-space, traffic, and wastewater hazards.
• Defects are usually easier to correct before final acceptance than after the sewer enters normal operation.
• Good acceptance procedures prevent construction defects from becoming permanent collection-system maintenance problems.