Sewer Operations & Maintenance Programs

Consistent and thorough maintenance of the collection system will enable the system to serve its stated life. Preventive maintenance is talked about, but seldom practiced by some agencies. Decades of neglect, or grossly inadequate maintenance of some systems, are two reasons why wastewater collection systems now require billions of dollars worth of rehabilitation and upgrading over the next 20 years.

  1. Collection systems and service connections were not installed as designed. Problems are caused by faulty construction, poor inspection and low-bid shortcuts.
  2. The pipe joints were made rigid. Earth movement, vibration from traffic, settling of structures and construction disturbance (all occur from time to time) require a flexible pipe material or joint that can maintain tightness. Joints had opened, cracked and/or sheared thus allowing debris and infiltration into the sewer.
  3. Corrosion of sewer pipes and manholes from either the trench bedding and backfill or the wastewater being transported by the collection system was a factor neglected during design. A major cause of corrosion in wastewater collection systems and treatment plants is hydrogen sulfide gas.
  4. Potential damage to pipe joints by plant roots was not known or was neglected during design. Although root intrusion into sewers was age-old, it was assumed that if the joint was watertight, it would be root tight. People did not realize that roots would be attracted by moisture and nutrient vapor unless the joints were vapor tight (which means airtight). Roots can enter a pipe joint or walls microscopically (through extremely small holes or cracks); thus, open or leaking joints are not necessary for root intrusion in collection systems.
  5. Collection system environments are ideal for root growth. In this environment, roots enter, expand and open joints and cracks. Root growth is a principal cause of pipe damage that allows INFILTRATION and EXFILTRATION. This creates a major concern for health and pollution control authorities because of wastewater treatment plant overload and groundwater pollution.
  6. The out of sight, out of mind nature of wastewater collection system. Local taxpayers have invested more money in underground sewers than in all the structures above ground owned by their local government. Why has this great taxpayer investment been so grossly neglected? Because it is out of sight, and so, out of mind.
Poor records regarding complaints from the public or the date and location of stoppages that had to be cleared can result in an ineffective maintenance program. Good records, regular analysis of the records, and use of this information can produce a cost-effective preventive maintenance program.

This discussion has explained why many wastewater collection systems now present such a mammoth problem to the taxpayer and governmental agencies.  Fortunately there exist today properly designed, constructed, operated and maintained collection systems that can serve as examples of how the job should be done.  Leakage should not be a problem in properly constructed and maintained sewers.

Operation and maintenance of wastewater collection systems on a trouble or emergency basis has been the usual procedure and policy in many communities and districts.  Planned operation and preventive maintenance of the collection system has been delayed or omitted, in spite of desires by collection system operators.  Municipal officials tended to neglect collection systems as long as complaints were not excessive.  To please constituents, officials often demanded street and sidewalk repair be done by collection system crews, but seldom have they ever demanded preventive work on collection systems.

(Source: Operation and Maintenance of Wastewater Collection Systems, Vol I, California State University, Sacramento, 1998)

Inspection and testing are the techniques used to gather information to develop operation  and maintenance programs to ensure that new and existing wastewater collection systems serve their intended purposes on a continuing basis.  Inspection and testing are necessary to do the following:

  • Identify existing or potential problem areas in the collection system,
  • Evaluate the seriousness of detected problems,
  • Locate the position of problems, and
  • Provide clear, concise and meaningful reports regarding problems.

Two major purposes of inspecting and testing are to prevent leaks from developing in the wastewater collection system and to identify existing leaks so they can be corrected.  The existence of leaks in a wastewater collection system is a serious and often expensive problem.  When a sewer is under a water table, infiltration can take place and occupy valuable capacity in the sewer and the downstream treatment plant.  Sewers located above a water table can exfiltrate, allowing raw wastewater to pollute soil and groundwater.

Guidance for manhole inspections and sewer inspections are presented herein.  The information provided if employed is a good starting point for an inspection.

Manhole inspections should yield a report with the following information at a minimum:

  • Exact location of the manhole;
  • Diameter of the clear opening of the manhole;
  • Condition of the cover and frame, including defects that would allow inflow to enter the system;
  • Whether cover is subject to ponding or surface runoff;
  • The potential drainage area tributary to the defects;
  • Type of material and condition of the chimney corbel cone and walls;
  • Condition of steps and chimney and frame-chimney joint;
  • Configuration of the incoming and outgoing lines (including drops); and
  • Signs of frame-chimney leakage or damage to the frame’s seal

Additionally, the following data can be obtained by entering the manhole and using equipment such as portable lamps, mirrors, rulers, and probe rods:

  • Type of material and condition of apron and trough;
  • Any observed infiltration sources and the rate of infiltration;
  • Indications of height of surcharge;
  • Size and type of all incoming and outgoing lines; and
  • Depth of flow indications of deposition and the characteristics of flow within all pipes.
  • The condition of the manhole shaft;
  • Any leakage in the channel;
  • Any leakage between the manhole wall and the channel;
  • Any damage or leakage where pipeline connects to the manhole; and
  • Any flow obstructions.

Sewer pipe inspections of small diameter sewers for infiltration are most effective when a closed circuit television camera is employed. Television inspections should provide the following information:

  • Definitions of problem(s)
  • Determine if problem is in municipal sewer or private property sewer
  • Effectiveness of existing cleaning program
  • Future sewer cleaning requirements
  • Sewer rehabilitation needs
  • Ability to assess whether trenchless technology or excavation and replacement can solve the problem
  • Ability to project repair budget
  • Information to plan a permanent solution

Planning is required to define the inspections goals.  Inspections are performed to:

  • Identify maintenance problems
  • Determine general sewer conditions
  • Identify extraneous flows

The following data is useful to have prior to beginning the inspection:

  • Sewer map or as-built plans to locate sewer
  • Site specific data
  • accessibility of deploying equipment at manholes
  • depth of flow in sewer
  • pipe diameter
  • traffic connections
  • safety requirement
  • sewer cleaning
  • sewer backup records
  • sewer cleaning records
  • influence of pump station discharges
  • influence of industrial discharges

If such records are not available or kept, then a system to retain such information should be established.

During the CCTV inspection the following information should be obtained:

Pipe structural condition Pipe material Joints
Joint interval distance Pipe cracks Root intrusion
Debris, sediment and/or oil and grease Service connections type
quadrant location building number active or inactive
rate of infiltration Infiltration and inflow Alignment
Sewer types Sewer location Sewer surface cover (depth)
Roadway surface material Time of day Weather conditions

Inspection for sources of inflow are most readily achieved through smoke testing and/or dye testing.  Smoke testing of sewers is done to determine:
  • stormwater sewer connections
  • proof that buildings or residences are connected to the sanitary sewer
  • illegal connections such as roof leaders or downspouts, yard drains and industrial drains
  • location of broken sewers due to settling of foundations, manholes and other structures
  • location of uncharted manholes and diversion points

Dye testing can be used to verify connections of drains to sanitary or storm sewers.  Dye testing can be used to verify the findings of smoke testing.

Suggested Inspection And Maintenance Frequencies
Task Frequency in Years
Video inspection/line testing (typical) 3 to 15
Video inspection/line testing (problem area) 1 to 3
Field check (problem area) 1
Walk alignment 1
Manhole/line lamping (typical) 3 to 15
Manhole/line lamping (problem area) 1 to 3
Cleaning (typical) 3 to 15
Cleaning (problem area) 0.5 to 3
System assessment 1
Source: Nelson, Richard E. “Collection System Maintenance: How Much is Enough?” Operation Forum, July 1996

Cleaning. The purpose of sewer cleaning is to remove foreign material from the sewer and generally is undertaken to alleviate one of the following conditions:

  • Blockages (semisolid obstructions resulting in a virtual cessation of flow).  These generally are dealt with on an emergency basis, although the underlying cause can be treated preemptively.
  • Hydraulic capacity.  In some cases, sediment, roots, intrusions (connections or other foreign bodies), grease, encrustation and other foreign material restrict the capacity of a sewer, causing surcharge or flooding.  Cleaning the sewer may alleviate these problems permanently, or at least temporarily.
  • Pollution caused by either the premature operation of combined wastewater overflows because of downstream restrictions to hydraulic capacity or pollution caused by the washing through and discharge of debris from overflows during storms.
  • Odor caused by the retention of solids in the system for long periods resulting in, among other things, wastewater turning septic and producing hydrogen sulfide.
  • Sewer inspections, where the sewer needs to be cleaned before inspection.  This requirement most often occurs when using in-sewer CCTV inspection techniques.
  • Sewer rehabilitation where it is necessary to clean the sewers immediately before the sewer being rehabilitated.

Common cleaning methods include jet rodding, manual rodding, winching or dragging, cutting, and manual or mechanical digging.  The method usually is determined in advance and is normally contingent on the pipe type and size and on the conditions expected in the pipe.

Jet Rodding This method depends on the ability of high-velocity jets of water to dislodge materials from the pipe walls and transport them down the sewer. Water under high pressure (approximately 2000 psi) is fed through a hose to a nozzle containing a rosette of jets sited so the majority of flow is ejected in the opposite direction of the flow in the hose. These jets propel the hose through the sewer and dislodge the materials on the sewer walls. A range of nozzles is available to cope with the different pipe diameters and materials encountered. The hoses, nozzles, water supply and necessary pumps usually are incorporated in a purpose-built vehicle. Equipment for removing and storing discharge material also is provided on some cleaning units.

Rodding This method is generally a manual push-pull technique used to clear blockages in smaller-diameter, shallow sewer systems typically not exceeding (10 in. in diameter or 6 ft. in depth. For sewer greater than 10 in. in diameter, the rods tend to wander are not very effective. The distance from the access point is limited to approximately 60 ft.

Dragging. This is a technique where custom buckets are dragged through the sewer and the material deposited into skips.

Cutting. This method generally is used for removing roots from sewers. High-pressure water jet cutters have been developed for removing even more solid intrusions, such as intruding connections. Care is required to eliminate damage to the existing sewer structure.

Manual or Mechanical Digging. Traditionally used in larger-diameter sewers, this method involves manually excavating the material and placing it in buckets for removal. As the sewer system can be hazardous, the technique now is used infrequently. High-pressure jet equipment also can be used manually in larger sewers.

Record Keeping

Record keeping of sewer maintenance, inspections and repairs meets several needs of the sewer system. Records help simplify and improve work planning and scheduling, including integrating recurring and on-demand work. Measuring and tracking of workforce productivity and developing units costs for various activities are a few of the record keeping benefits. Records of sewer maintenance, service line maintenance, and sewer main and service line repairs should be kept and maintained. Examples of record forms are found herein.