vvEPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA 832-F-99-031
September 1999
Collection Systems
O&M Fact Sheet
Sewer Cleaning and Inspection
DESCRIPTION
As sewer system networks age, the risk of
deterioration, blockages, and collapses becomes a
major concern. As a result, municipalities
worldwide are taking proactive measures to
improve performance levels of their sewer systems.
Cleaning and inspecting sewer lines are essential to
maintaining a properly functioning system; these
activities further a community's reinvestment into its
wastewater infrastructure.
Inspection Techniques
Inspection programs are required to determine
current sewer conditions and to aid in planning a
maintenance strategy. Ideally, sewer line
inspections need to take place during low flow
conditions. If the flow conditions can potentially
overtop the camera, then the inspection should be
performed during low flow times between midnight
and 5 AM, or the sewer lines can be temporarily
plugged to reduce the flow. Most sewer lines are
inspected using one or more of the following
techniques:
• Closed-circuit television (CCTV).
• Cameras.
• Visual inspection.
• Lamping inspection.
Television (TV) inspections are the most frequently
used, most cost efficient in the long term, and most
effective method to inspect the internal condition of
a sewer. Figure 1 shows the typical setup of
equipment for a TV inspection. CCTV inspections
are recommended for sewer lines with diameters of
0.1-1.2 m (4 - 48 inches.) The CCTV camera must
be assembled to keep the lens as close as possible
to the center of the pipe. In larger sewers, the
camera and lights are attached to a raft, which is
floated through the sewer from one manhole to the
next. To see details of the sewer walls, the camera
and lights swivel both vertically and horizontally. In
smaller sewers, the cable and camera are attached
to a sled, to which a parachute or droge is attached
and floated from one manhole to the next.
Documentation of inspections is very critical to a
successful operation and maintenance (O&M)
program. CCTV inspections produce a video
record of the inspection that can be used for future
reference.
In larger sewers where the surface access points are
more than 300 m (1000 linear feet) apart, camera
inspections are commonly performed. This
technique involves a raft-mounted film camera and
strobe light. This method requires less power than
the CCTV, so the power cable is smaller and more
manageable. Inspections using a camera are
documented on polaroid still photographs that are
referenced in a log book according to date, time,
and location.
Visual inspections are vital in fully understanding
the condition of a sewer system. Visual inspections
of manholes and pipelines are comprised of surface
and internal inspections. Operators should pay
specific attention to sunken areas in the
groundcover above a sewer line and areas with
ponding water. In addition, inspectors should
thoroughly check the physical conditions of stream
crossings, the conditions of manhole frames and
covers or any exposed brickwork, and the visibility
of manholes and other structures. For large sewer
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Source: Water Pollution Control Federation, 1989.
FIGURE 1 SETUP OF CCTV EQUIPMENT
lines, a walk-through or internal inspection is
recommended. This inspection requires the
operator to enter a manhole, the channel, and the
pipeline, and assess the condition of the manhole
frame, cover, and chimney, and the sewer walls
above the flow line. When entering a manhole or
sewer line, it is very important to observe the latest
Occupational Safety and Health Administration
confined space regulations. If entering the manhole
is not feasible, mirrors can be used. Mirrors are
usually placed at two adjacent manholes to reflect
the interior of the sewer line.
Lamping inspections are commonly used in low-
priority pipes, which tend to be pipes that are less
than 20 years old. Lamping is also commonly used
on projects where funds are extremely limited. In
the lamping technique, a camera is inserted and
lowered into a maintenance hole and then positioned
at the center of the junction of a manhole frame and
the sewer. Visual images of the pipe interior are
then recorded with the camera.
Several specialized inspection techniques have been
recently developed worldwide. AMTEC, a British
sewer inspection company, has deployed light-line-
based and sonar-based equipment that measures the
internal cross-sectional profile of sewer systems.
Karo, a German R&D company, is working on
enhancing CCTV technology with new sonar
sensors, but this method has yet to be proven
successful. Sonar technology could be very useful
in inspecting depressed sewers (inverted siphons),
where the pipe is continually full of water under
pressure. Melbourne Water and CSIRO Division
of Manufacturing Technology have introduced a
new technology called PIRAT, which consists of an
in-pipe vehicle with a laser scanner. This instrument
is capable of making a quantitative and automatic
assessment of sewer conditions. The geometric data
that is gathered is then used to recognize, identify,
and rate defects found in the sewer lines.
Sonex has also designed a new technology called
the ROTATOR sonic caliper, which is capable of
taking a reading for every foot of pipe. This device
is pulled through the sewer pipes from one manhole
to the next and collects data that can be used to
calculate the volume of debris underwater, measure
the corrosion from the crown of the pipe to the
waterline, and determine the percent of deflection at
all points around a flexible pipe. The data collected
is based on the time it takes a sonic pulse to travel
to and from a target.
Cleaning Techniques
To maintain its proper function, a sewer system
needs a cleaning schedule. There are several
traditional cleaning techniques used to clear
blockages and to act as preventative maintenance
tools. When cleaning sewer lines, local communities
need to be aware of EPA regulations on solid and
hazardous waste as defined in 40 CFR 261. In
order to comply with state guidelines on testing and
disposal of hazardous waste, check with the local
authorities.
Table 1 summarizes some of the most commonly
used methods to clean sewer systems.
Hydraulic cleaning developments have also been
emerging on the international frontier. France and
Germany have developed several innovative
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flushing systems using a 'dam break' concept.
France has developed a flushing system called the
Hydrass. The design of the Hydrass consists of a
gate that pivots on a hinge to a near horizontal
position. As the gate opens and releases a flow, a
flush wave is generated that subsequently washes
out any deposited sediments. Germany has also
developed a similar system called GNA Hydroself®.
This is a flushing system that requires no electricity,
no maintenance and no fresh water. The
Hydroself® consists of a hydraulically-operated gate
and a concrete wall section constructed to store the
flush water. This system can be installed into a
large diameter sewer (>2000 mm or >79.4 inches).
There appears to be no limit on the flushing length,
as more flush water may be stored without incurring
any additional construction or operating costs.
Another example of such a technology is seen in the
Brussels Sewer System. A wagon with a flushing
vane physically moves along the sewer and disturbs
the sediments so that they are transported with the
sewer flow.
Although all of these methods have proven effective
in maintaining sewer systems, the ideal method of
reducing and controlling the materials found in
sewer lines is education and pollution prevention.
The public needs to be informed that common
household substances such as grease and oil need to
be disposed in the garbage in closed containers, and
not into the sewer lines. This approach will not only
minimize a homeowner's plumbing problems, but
will also help keep the sewer lines clear.
APPLICABILITY
In recent years, new methodologies and accelerated
programs have been developed to take advantage
TABLE 1 COMMON SEWER CLEANING METHODS
Technology
Mechanical
Rodding
(See Figure 2)
Bucket Machine
Hydraulic
Balling
Flushing
Jetting
Uses and Applications
• Uses an engine and a drive unit with continuous rods or sectional rods.
• As blades rotate they break up grease deposits, cut roots, and loosen debris.
• Rodders also help thread the cables used for TV inspections and bucket machines.
• Most effective in lines up to 300 mm (12 inches) in diameter.
• Cylindrical device, closed on one end with 2 opposing hinged jaws at the other.
• Jaws open and scrape off the material and deposit it in the bucket.
• Partially removes large deposits of silt, sand, gravel, and some types of solid waste.
• A threaded rubber cleaning ball that spins and scrubs the pipe interior as flow increases in
the sewer line.
• Removes deposits of settled inorganic material and grease build-up.
• Most effective in sewers ranging in size from 13-60 cm (5-24 inches).
• Introduces a heavy flow of water into the line at a manhole.
• Removes floatables and some sand and grit.
• Most effective when used in combination with other mechanical operations, such as
rodding or bucket machine cleaning.
• Directs high velocities of water against pipe walls.
• Removes debris and grease build-up, clears blockages, and cuts roots within small
diameter pipes.
• Efficient for routine cleaning of small diameter, low flow sewers.
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TABLE 1 (CONTINUED) COMMON SEWER CLEANING METHODS
Technology
Applications
Scooter
Round, rubber-rimmed, hinged metal shield that is
mounted on a steel framework on small wheels.
The shield works as a plug to build a head of
water.
Scours the inner walls of the pipe lines.
Effective in removing heavy debris and cleaning
grease from line.
Kites, Bags, and Poly Pigs
Similar in function to the ball.
Rigid rims on bag and kite induce a scouring
action.
Effective in moving accumulations of decayed
debris and grease downstream.
Silt Traps
Collect sediments at convenient locations.
Must be emptied on a regular basis as part of the
maintenance program.
Grease Traps and Sand/Oil Interceptors
The ultimate solution to grease build-up is to trap
and remove it.
These devices are required by some uniform
building codes and/or sewer-use ordinances.
Typically sand/oil interceptors are required for
automotive business discharge.
Need to be thoroughly cleaned to function
properly.
Cleaning frequency varies from twice a month to
once every 6 months, depending on the amount of
grease in the discharge.
Need to educate restaurant and automobile
businesses about the need to maintain these
traps.
Chemicals
Before using these chemicals review the Material Safety
Data Sheets (MSDS) and consult the local authorities on
the proper use of chemicals as per local ordinance and the
proper disposal of the chemicals used in the operation. If
assistance or guidance is needed regarding the application
of certain chemicals, contact the U. S. EPA or state water
pollution control agency.
Used to control roots, grease, odors (H2S gas),
concrete corrosion, rodents and insects.
Roof Control - longer lasting effects than power
rodder (approximately 2-5 years).
H2S gas - some common chemicals used are
chlorine (CI2), hydrogen peroxide (H2O2), pure
oxygen (O2), air, lime (Ca(OH2)), sodium
hydroxide (NaOH), and iron salts.
Grease and soap problems - some common
chemicals used are bioacids, digester, enzymes,
bacteria cultures, catalysts, caustics, hydroxides,
and neutralizers.
Source: Information provided by Arbour and Kerri, 1997 and Sharon, 1989.
of the information obtained from sewer line
maintenance operations. Such programs
incorporate information gathered from various
maintenance activities with basic sewer evaluations
to create a system that can remedy and prevent
future malfunctions and failures more effectively and
efficiently. Garland, Texas, has attempted to
establish a program that would optimize existing
maintenance activities to reduce customer
complaints, sanitary sewer overflows, time and
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Source: Sharon, 1989.
FIGURE 2 EQUIPMENT SETUP FOR RODDING
money spent on sewer blockages, and other reactive
maintenance activities. Their plan is based on
maintenance frequencies, system performance, and
maintenance costs over a period of time. This plan
was developed using Geographical Information
System (GIS) and historical data to show areas of
complaints, back ups, and general maintenance
information for the area. The City of Garland was
able to determine that as the maintenance frequency
increased, there was an increase in system
performance. Garland recommended 70 inspections
and maintenance activities for every 30 cleanings.
Inspections are considered more important because
they help define and prevent future problems.
A study performed by the American Society of Civil
Engineers reports that the most important
maintenance activities are cleaning and CCTV
inspections. Table 2 shows the average frequency
TABLE 2 FREQUENCY OF
MAINTENANCE ACTIVITIES
Activity
Average (% of system/year)
Cleaning
Root removal
Manhole inspection
CCTV inspection
Smoke testing
29.9
2.9
19.8
6.8
7.8
A maintenance plan attempts to develop a strategy
and priority for maintaining pipes based on several
of the following factors:
• Problems- frequency and location; 80
percent of problems occur in 25 percent of
the system (Hardin and Messer, 1997).
• Age- older systems have a greater risk of
deterioration than newly constructed
sewers.
• Construction material- pipes constructed of
materials that are susceptible to corrosion
have a greater potential of deterioration and
potential collapse. Non-reinforced concrete
pipes, brick pipes, and asbestos cement
pipes are examples of pipes susceptible to
corrosion.
• Pipe diameter/volume conveyed- pipes that
carry larger volumes take precedence over
pipes that carry a smaller volume.
• Location- pipes located on shallow slopes or
in flood prone areas have a higher priority.
• Force main vs. gravity-force mains have a
higher priority than gravity, size for size,
due to the complexity of the cleaning and
repairs.
• Subsurface conditions- depth to
groundwater, depth to bedrock, soil
properties (classification, strength, porosity,
compressibility, frost susceptibility,
credibility, and pH).
• Corrosion potential- Hydrogen Sulfide
(H2S) is responsible for corroding sewers,
structures, and equipment used in
wastewater collection systems. The interior
conditions of the pipes need to be monitored
and treatment needs to be implemented to
prevent the growth of slime bacteria and the
production of H2S gases.
Source: ASCE, 1998.
of various maintenance activities.
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ADVANTAGES AND DISADVANTAGES
The limitations of various inspection techniques
used by sanitary sewer authorities are summarized
in Table 3. Table 4 shows the limitations of some of
the cleaning methods used by sanitary sewer
authorities.
TABLE 3 LIMITATIONS OF STANDARD
INSPECTION TECHNIQUES
Inspection
Technique
Limitation
Visual In smaller sewers, the scope of
Inspection problems detected is minimal because
the only portion of the sewer that can
be seen in detail in near the manhole.
Therefore, any definitive information on
cracks or other structural problems is
unlikely. However, this method does
provide information needed to make
decisions on rehabilitation.
Camera When performing a camera inspection
Inspection in a large diameter sewer, the
inspection crew is essentially taking
photographs haphazardly, and as a
result, the photographs tend to be less
comprehensive.
Closed This method requires late night
Circuit inspection ans as a result the TV
Television operators are vulnerable to lapses in
(CCTV) concentration. CCTV inspections are
also quire expensive and time
consuming.
Lamping The video camera does not fit into the
Inspection pipe and during the inspection it
remains only in the maintenance hole.
As a result, only the first 10 feet of the
pipe can be viewed or inspected using
this method.
Source: Water Pollution Control Federation, 1989.
The primary benefit of implementing a sewer
maintenance program is the reduction of SSOs,
basement backups, and other releases of wastewater
from the collection system due to substandard sewer
conditions.
Improper handling of instruments and chemicals
used in inspecting and maintaining sewer lines may
cause environmental harm. Examples include:
• Improperly disposing of collected materials
and chemicals from cleaning operations.
• Improperly handling chemical powdered
dyes.
Inadequately maintaining inspection devices.
Some instruments have a tendency to
become coated with petroleum based
residues and if not handled properly they can
become a fire hazard.
PERFORMANCE
Table 5 defines the conditions under which certain
cleaning methods are most effective. The following
case studies provide additional case study data for
sewer cleaning methods.
Fairfax County, Virginia
The Fairfax County Sanitary Sewer System
comprises over 3000 miles of sewer lines. As is the
case with its sewer rehabilitation program, the
county's sewer maintenance program also focuses
on inspection and cleaning of sanitary sewers,
especially in older areas of the system.
Reorganization and streamlining of the sewer
maintenance program, coupled with a renewed
emphasis on increasing productivity, has resulted in
very significant reductions in sewer backups and
overflows during the past few years. In Fiscal Year
1998, there were a total of 49 such incidents
including 25 sewer backups and 24 sewer
overflows.
The sewer maintenance program consists of visual
inspections, scheduled sewer cleanings based on
maintenance history, unscheduled sewer cleanings as
determined by visual or closed circuit television
inspections, and follow-up practices to determine
the cause of backups and overflows. Visual
inspections are carried out by using a mirror
attached to a pole; however, use of portable
cameras has been recently introduced to enhance the
effectiveness of visual inspections. Older areas of
the sewer system are inspected every two years;
whereas, the inspection of relatively new areas may
be completed in 3 to 4 years.
Cleaning is an important part of pipe maintenance.
Sewer line cleaning is prioritized based on the age of
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TABLE 4 LIMITATIONS OF CLEANING METHODS
Cleaning
Method
Limitation
Balling, In general, these methods are only successful when necessary water pressure or head is maintained
Jetting, without flooding basements or houses at low elevations. Jetting - The main limitation of this technique
Scooter is that cautions need to be used in areas with basement fixtures and in steep-grade hill areas.
Balling - Balling cannot be used effectively in pipes with bad offset joints or protruding service
connections because the ball can become distorted.
Scooter - When cleaning larger lines, the manholes need to be designed to a larger size in order to
receive and retrieve the equipment. Otherwise, the scooter needs to be assembled in the manhole.
Caution also needs to be used in areas with basement fixtures and in steep-grade hill areas.
Bucket This device has been known to damage sewers. The bucket machine cannot be used when the line is
Machine completely plugged because this prevents the cable from being threaded from one manhole to the next.
Set-up of this equipment is time-consuming.
Flushing This method is not very effective in removing heavy solids. Flushing does not remedy this problem
because it only achieves temporary movement of debris from one section to another in the system.
High Velocity The efficiency and effectiveness of removing debris by this method decreases as the cross-sectional
Cleaner areas of the pipe increase. Backups into residences have been known to occur when this method has
been used by inexperienced operators. Even experienced operators require extra time to clear pipes of
roots and grease.
Kite or Bag When using this method, use caution in locations with basement fixtures and steep-grade hill areas.
Rodding Continuous rods are harder to retrieve and repair if broken and they are not useful in lines with a
diameter of greater than 300 mm (0.984 feet) because the rods have a tendency to coil and bend. This
device also does not effectively remove sand or grit, but may only loosen the material to be flushed out
at a later time.
Source: U.S. EPA, 1993.
the pipe and the frequency of the problems within it.
The county uses rodding and pressurized cleaning
methods to maintain the pipes. Bucket machines are
rarely used because cleaning by this method tends to
be time consuming. The county uses mechanical,
rather than chemical, methods to remove grease and
roots. Introducing chemicals into the cleaning
program requires hiring an expert crew, adopting a
new program, and instituting a detention time to
ensure the chemicals' effectiveness.
Record keeping is also vital to the success of such
a maintenance program. The county has started
tracking the number of times their sewer lines were
inspected and cleaned and the number of overflows
and backups a sewer line experienced. This
information has helped the county re-prioritize
sewer line maintenance and adapt a more
appropriate time schedule for cleaning and
inspecting the sewer lines.
The cost per foot for maintaining the Fairfax facility
has decreased over the years because of
streamlining and increasing efficiency and
productivity of field staff. In 1998, pressurized
cleaning cost $ 1.44/meter ($0.44/foot); rodding cost
$2.82/meter($0.86/foot); and television inspections
cost $3.18/meter ($0.97/foot). These costs include
labor costs, fringe benefits, equipment and material
costs, and overhead charges for administrative
services.
City of Fort Worth, Texas
The City of Fort Worth has started to use sewer
cleaning as a diagnostic tool, rather than just a
maintenance task. The city's sewer system
comprises 3540.5 kilometers (1850 miles) of line
and serves approximately 1.2 million customers.
The diameter of the sewer pipes ranges from 0.1 -2.4
meters (3.9-.4.5 inches). The sewer system in the
city is currently diagrammed in a series of hard-copy
map books; the City hopes to establish a GIS system
within the next year.
In the last three years, the City of Forth Worth has
extensively upgraded its sewer systems. As a result
their sewer maintenance group has expanded to
include three new divisions, which include:
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TABLE 5 EFFECTIVENESS OF CLEANING TECHNIQUES
Solution to
Problem
Emergency
Stoppages
Grease
Type of Problem
Roots
Sand, Grit,
Debris
Odors
Balling
High Velocity
Cleaning
Flushing
Sewer Scooters
Bucket Machines,
Scrapers
Power Rodders
Hand Rods
Chemicals
• = Most effective solution for a particular problem
• = Least effective solution for a particular problem
Source: U.S. EPA, 1993.
• Sewer Cleaning and Stoppage Section- this
section responds to customer complaints,
pinpoints problems within the lines, and
clears all blockages.
TV Section- this section locates defects and
building sewer connections (also referred to
as taps) within the system.
• Preventive Maintenance Section- this
section cleans and inspects the lines and also
provides for Quality Assurance and Quality
Control (QA/QC).
Most of Fort Worth's inspections use the CUE
CCTV system. However, about 40 percent of the
lines in the worst and oldest sections of the system
are inspected visually. Visual inspections are also
used in the most recently installed lines and
manholes.
The city uses a variety of cleaning methods
including jetting, high velocity cleaning, rodding,
bucket machining, and using stop trucks (sectional
rods with an attached motor). As part of their
preventive maintenance approach, the city has also
been using combination trucks with both flush and
vacuum systems. To control roots, the city uses a
vapor rooter eradication system which can ensure
that no roots return to the line for up to five years.
The cleaning and inspection crews consists of two
members to operate each of the combination trucks
and TV trucks. The City of Forth Worth has
cleaned approximately 239 kilometers (145 miles) of
line and has TV inspected approximately 70
kilometers (44 miles) of line from 1996 to 1998.
The cleaning cost for 1998 was determined to be
$1.38/meter ($0.42/foot) and the TV inspection
cost was determined tobe$1.28/meter($0.39/foot).
The City of Fort Worth is working on cleaning its
entire system every seven to eight years. The
cleaning frequency of the lines is prioritized based
on the number of complaints received in each area.
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City of Los Angeles, California
The Los Angeles Wastewater Collection System is
one of the largest and most complex systems in the
world. It serves approximately four million people
over 600 square miles. The system is made up of
6,500 miles (6950 kilometers) of sewer lines. The
diameter of the sewer lines ranges from 6 to 150
inches (0.1-3.8 meters) and about half of the system
is more than 50 years old.
The continuing success of this system has been
attributed to a preventive and proactive operation
and maintenance program. This program has
implemented a computerized maintenance
management plan emphasizing preventive and
corrective maintenance; this system tracks all
maintenance activities.
For preventive maintenance, Los Angeles has
adopted a Sewer Condition Assessment Program.
This program prioritizes the inspection, cleaning,
and rehabilitation of the sewer system, based on a
scoring system that uses the age, size, and the
construction material of the pipe to schedule
inspections. Scores are determined using GIS and
specially-designed computer and logic programs.
High-priority inspections are conducted using
CCTV; lower-priority ones use the lamping
technique. Lamping may be followed up by a
CCTV inspection if more information is required.
Los Angeles performs approximately 145 kilometers
(90 miles) of CCTV inspections per year. The cost
of CCTV inspections is approximately $1.00/foot,
including labor and equipment. The City also
performs about 4506 kilometers (2800 miles) of
visual inspections per year at $0.07/foot.
Los Angeles cleans about 2,032 kilometers (1,900
miles) of sewer per year. The cleaning frequency is
based on inspections and field conditions. The City
removes roots by means of mechanical rodding
machines ($1.71/meter or $0.52/ft), chemical
applications, hydraulic winch machines, and hand
rods ($3.12/meter or $0.95/foot). Los Angeles's
Corrosion Abatement Maintenance Program uses
magnesium hydroxide crown spraying to treat about
129 kilometers (80 miles) of sewer per year at a cost
of $700,000 to prevent corrosion. Los Angeles's
program to control H2S odor uses caustic shock
dosing, which costs about $l,000,000/year.
COSTS
Table 6 summarizes the annual maintenance costs
per mile for cleaning and inspecting.
TABLE 6 NATIONAL SUMMARY OF MAINTENANCE COSTS
Identifier
Total O&M cost/mile/year
Labor (cost/mile/year)
Fringe Benefits (cost/mile/year)
Chemicals (cost/mile/year)
Hydroflush Cleaning (cost/mile)
Television Inspection (cost/mile)
Preventive Maintenance
Range of Costs
$951-$46,9731
$695-$19,8311
$192-$9,0331
$0.3-$7,6161
$475 -5.2302
$1,000-$11,4502
63% of Total Maintenance
Average Cost
$2,8233
$3,6261
$1,1851
$5121
$1,7001
$4,6001
Costs (excludes depreciation)
Source: 1 Water Environment Research Foundation, 1997.
2 Arbour and Kerri, 1997.
3ASCE, 1998.
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ADDITIONAL INFORMATION
California State University, Sacramento
Ken Kerri
6000 J Street
Sacramento, California 95819
Fairfax County, Virginia
Ifty Khan
Department of Public Works
6000 Freds Oak Road
Burke, Virginia 22015
City of Fort Worth, Texas
Cory Hanson
Fort Worth Water Department
1608 11th Avenue
Fort Worth, Texas 76102
City of Los Angeles, California
Barry Bergren
Los Angeles Bureau of Sanitation
2335 Dorris Place
Los Angeles, California 90031
City of Topeka, Kansas
Tim Green
Department of Public Works
515 S. Kansas Avenue
Topeka, Kansas 66603
The mention of trade names or commercial products
does not constitute endorsement or recommendation
for the use by the U.S. Environmental Protection
Agency.
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
401 M St., S.W.
Washington, D.C., 20460
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