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Sanitary Sewer System

Storm Sewer System

Combined Sewer Systems

Sewer Piping Material

• asbestos cement
• concrete
• vitrified clay
• polyethylene
• plastic
• ABS
• PVC
• polyolefin
• cast iron
• ductile iron
• stainless steel
• corrugated galvanized
• copper, and
• brass

ABS Pipe

PVC Pipe

HDPE pipe

Concrete pipe

Hazards Associated with Sewer Work

Responsibilities

Trenches

Confined Spaces

1. is enclosed or partially enclosed,
2. is not designed or intended for continuous human occupancy,
3. has limited or restricted means for entry or exit that may complicate the provision of first aid, evacuation, rescue or other emergency response service, and
4. is large enough and so configured that a worker could enter to perform assigned work.

• Preparation: Before workers can enter a confined space, employers must provide pre-entry planning. This includes:
  • Having a competent person evaluate the work site for the presence of confined spaces, including permit-required confined spaces.
  • Once the space is classified as a permit-required confined space, identifying the means of entry and exit, proper ventilation methods, and elimination or control of all potential hazards in the space.
  • Ensuring that the air in a confined space is tested before workers enter, and at specified intervals thereafter, for oxygen levels, flammable and toxic substances, and stratified atmospheres.
  • If a permit is required for the space, removing or controlling hazards in the space and determining rescue procedures and necessary equipment.
  • If the air in a space is not safe for workers, ventilating or using whatever controls or protections are necessary so that employees can safely work in the space.
• The employer must implement additional specific requirements in the OHS legislation regarding hazard assessment.
• Workers are responsible for carrying out their work in a manner that does not endanger them or their fellow workers. Workers must cooperate with their employer by following safe work procedures and using the equipment provided to complete the job safely.

Confined Spaces Air Quality Hazards

• insufficient amount of oxygen for the worker to breathe.
• toxic gases that could make the worker ill or cause the worker to lose consciousness.
• The presence of asphyxiants. Simple asphyxiants are gases which can displace oxygen in the air.  Low oxygen levels (19.5 percent or less) can cause symptoms such as rapid breathing, rapid heart rate, clumsiness, emotional upset, and fatigue. As less oxygen becomes available, nausea and vomiting, collapse, convulsions, coma and death can occur. Unconsciousness or death could result within minutes following exposure to a simple asphyxiant. Asphyxiants include argon, nitrogen, or carbon monoxide. It is important to note that wherever there is ferrous piping present, the rusting process can use up the available oxygen in a confined space, contributing to the likelihood of asphyxiation.

• Chemical exposures due to skin contact or ingestion (as well as inhalation of toxic gases).
• Fire hazard - An explosive or flammable atmosphere due to flammable liquids and gases and combustible dusts which, if ignited, would lead to fire or explosion.
• Process-related hazards - such as residual chemicals, or release of contents of a supply line.
• Biological hazards – viruses, bacteria from fecal matter and sludge, fungi, or molds.
• In warmer climates, the presence of dangerous animals and insects

Pinch Points

• Not paying attention to the location of hands and feet
• Walking or working in areas with mobile equipment and fixed structures
• Loose clothing, hair or jewelry getting caught in rotating parts of equipment
• Poor condition of equipment and guarding
• Dropping or carelessly handling materials or suspended loads
• Not using the proper work procedures or tools
• Reaching into moving equipment and machinery

Hoists

• Unintentional contact with a moving load will often result in serious or fatal consequences due the masses involved. Examples include workers that are responsible for landing and stacking loads getting caught between a solid surface and the moving load, or loads being moved before all workers have moved clear of the lifting zone, and workers getting crushed by the load. This latter situation can also be exacerbated if the load’s centre of gravity is unsafe, causing it to start swinging unexpectedly and uncontrollably.
• Lifting equipment can overturn for a variety of reasons. A common cause involves not using or fully extending the outriggers to provide a solid platform or setting up a crane on non-compacted/disturbed ground. The ground underneath may appear to be solid, but it can be deceptive. As a load is moved and weight transfers over the outriggers, they can start to sink into the soil. [caption id="attachment_30" align="aligncenter" width="400"] Figure 10 Mobile Crane[/caption]
• Proximity to overhead power lines is one major factor that is either overlooked or not understood. The crane boom/forklift truck does not actually have to come into direct contact with the power line for a dangerous condition to occur. The electric current in the lines can “arc” through the air when a grounded point is within a certain distance. This distance is determined largely by the voltage - the higher the voltage the greater the arc distance. Therefore the available voltage in the lines will determine the safe “limits of approach” as shown below. [caption id="attachment_31" align="aligncenter" width="756"] Figure 11 Limits of approach[/caption]
• In many cases the operator sitting in the cab may be isolated from the current and will not typically feel anything, but they are at significant risk if they attempt to leave the lifting equipment while the current is still flowing, as once they grab the structure and place a foot on the ground the current may then pass through their body to earth.
• Mechanical failure doesn’t occur as frequently as do some of the events described previously but is still relevant. Installed safety devices such as a safe working load indicator can fail. Braking systems, hydraulic systems and electrical systems are all vulnerable to failure. The very nature of the way that lifting devices are typically used, moving between locations, working in a wide variety of environmental conditions all add significantly to the wear and tear on this equipment. The key factor here for prevention is the systematic inspection, testing and certification of lifting and hoisting equipment. Whilst a slightly different mechanism of failure, it is also worth considering the condition and integrity of lifting accessories such as slings, shackles and hooks. These devices can also fail with catastrophic results.
• Dropped objects is a hazard that can occur in several ways. Objects may fall off the crane, the load or parts of it could fall or objects hidden within it may fall. If not secured properly, it is quite common for items to shift once the load is raised and then fall to the ground. For example, where items are left on a load by mistake (e.g., hand tools) or are hidden from view (e.g., rocks or other solid materials in pallet pockets), once the load is airborne these objects may be dislodged and fall.
• Climbing onto a load as it is being lifting or set in place such as when riggers/slingers have to climb on top of loads to either attach a sling to a hook or vice versa. Climbing on top of the load can be problematic as there is normally no safe access and no fall protection in place.

Sewer System Types, Applications and Operations

Gravity Sewer Systems

• at both ends of horizontal curves
• at the intermediate point of a curve with angle greater than 90°
• at the point of reverse curve
• at abrupt change in vertical alignment
• at changes in pipe size, and
• at the confluence of three or more pipes.

Pressure Sewer Systems

Vacuum Sewer System

Small Diameter Gravity Sewer

Hybrid Sewer System

Self-Test 1

Media Attributions

• Figure 1 Sanitary building drain and sewer by ITA is licensed under a CC BY-NC-SA licence.
• Figure 2 Storm building drain and sewer by ITA is licensed under a CC BY-NC-SA licence.
• Figure 3 Combined building drain and sewer by ITA is licensed under a CC BY-NC-SA licence.
• Figure 4 Cellular core ABS pipe by Greg Wirachowsky is licensed under a CC BY-NC-SA licence.
• Figure 5 PVC sewer pipe by Greg Wirachowsky is licensed under a CC BY-NC-SA licence.
• Figure 6 HDPE sewer pipe by Greg Wirachowsky is licensed under a CC BY-NC-SA licence.
• Figure 7 Manhole components © Reliner, used with permission.
• Figure 8 Trench shoring and sloping examples by ITA is licensed under a CC BY-NC-SA licence.
• Figure 9 Examples of confined space air quality hazards by ITA is licensed under a CC BY-NC-SA licence.
• Figure 10 Mobile Crane was adapted from work by ITA is licensed under a CC BY-NC-SA licence.
• Figure 11 Limits of approach by ITA is licensed under a CC BY-NC-SA licence.
• Figure 12 PVC gravity sewer piping at substantial depth by Imprezzive1 has been released into the public domain.
• Figure 13 Vacuum sewer system by Srstevens3 is licensed under a CC BY-SA 4.0 licence.

Sanitary Building Sewer Sizing

1. Determine the total number of fixture units from fixtures found in tables 2.4.9.3 and 2.4.10.2
2. Add the flow from any semi-continuous or continuous flow appurtenances draining into it. These loads are normally expressed in L/sec, so they have to be converted into FU by applying the conversion number given in 2.4.10.3 (1) of the NPC, which is 31.7 fixture units per litre/second.
3. Once a total flow rate of fixture units has been calculated, it is applied to Table 2.4.10.6.-C to establish the minimum size of sanitary building sewer required at the chosen grade.

• If a clear-water waste appliance or fixture discharges a semi or continuous flow to the storm system, multiply its load in litres per second by 900 (the number of seconds in 15 minutes) to obtain the hydraulic load in L/15 min.
• If flow control roof drains are used, compute the discharge rate based on rainfall intensity, retention duration, accumulation height and roof area from the roof drain manufacturer’s data.

Combined Building Sewer Sizing

1. Determine the total load in fixture units from all upstream plumbing fixtures, excluding the flow from any semi or continuous flow appurtenances or fixtures. If the fixture unit load is 260 FU or less, use 2,360 L/15 min to represent them. However, if there are more than 260 FU, multiply the fixture units by 9.1 to determine the equivalent hydraulic load in litres/15 min.
2. Add up the total flow rate in L/sec from any semi or continuous flow appurtenances or fixtures that are draining through the section of combined piping being sized. Multiply this by 900 (the number of seconds in 15 minutes) to get a hydraulic load in L/15 min; this is the same procedure used when sizing storm sewer pipes.
3. Determine the hydraulic load, in L/15 min, from roofs and paved surfaces using the same procedure employed when sizing storm drainage pipes [effective area (m2) × rainfall intensity (mm/15 min)].
4. Add the hydraulic loads calculated in Steps 1 through 3 to obtain the total hydraulic load on the combined drainage pipe in L/15 min and then consult Table 2.4.10.9 to select the pipe size at the chosen grade.

• Although the two traps have the same flow rate into them in L/sec and are sized from the same table using that flow rate, the load from them is dependent upon the pipe that they are draining through, which is expressed in L/15 min for storm or combined pipes and in FU for sanitary pipes
• The loads at “J” and “M” are the same, even though there are 175 FU more at “M” than at “J”. This is because we look for the total number of FU going through a combined building drain. At “G”, “J” and “M” the load from “unconverted” (original) FU had not yet reached or exceeded 260, so at those points the single conversion number of 2,360 L/15 min was used to represent them. At “P”, there were now more than 260 FU in that piece of combined building drain, so instead of using 2,360 L/15 min we now multiply the “unconverted” FU by 9.1 and use that number. It is an “either/or” situation when considering the load presented on a piece of combined building drain by fixture units; either 2,360 L/15 min or FU x 9.1, never both.
• Never include the converted FU from any semi or cont flow trap in the calculation for a combined building drain. Instead use the calculation “L/sec x 900 = L/15 min”
• Don’t take shortcuts in calculations of load on combined building drains! Whenever a new piece of combined building drain is to be sized, always look for the totals of the three possible types of flow going through it, which are:
  • Stormwater from roof drains and parking lot drains
  • “Unconverted” (original) FU, and
  • Semi or continuous flow from traps serving pumps or clear water waste

Grades

Self-Test 2

Media Attributions

• Figure 1 Semi or continuous flow fixture into a sanitary system vs a storm system adapted from image by ITA is licensed under a CC BY-NC-SA licence.
• Figure 2 Sample load conversion by Greg Wirachowsky is licensed under a CC BY-NC-SA licence.

Determine the Elevations

Pipe Path and Grade

Excavation

• the possibility of flooding the trench
• cave-ins/sloughing caused by ground water
• frozen trench bottoms and backfill
• safety hazard risks to workers and traffic

Trench Width

Preparation of Trench Bottom

Install the Pipe

Pipe Terminations

Backflow Prevention

Backfill the Trench

Trench Boxes (Trench Shields or Shoring)

How to Install Reinforced Concrete Pipe (RCP)

Handling Reinforced Concrete Pipe

Excavating for Reinforced Concrete Pipe

Preparing Joining Surfaces of RCP

Installing RCP

Backfilling Reinforced Concrete Pipe

Self-Test 3

Media Attributions

• Figure 1 Builders level on tripod by Greg Wirachowsky is licensed under a CC BY-NC-SA licence.
• Figure 2 Geodetic benchmark by ITA is licensed under a CC BY-NC-SA licence.
• Figure 3 Pipe laser and target for pipe interior by ITA is licensed under a CC BY-NC-SA licence.
• Figure 4 Example of trench for pipe by ITA is licensed under a CC BY-NC-SA licence.
• Figure 5 Cable puller and “Tirfor”® by ITA is licensed under a CC BY-NC-SA licence.
• Figure 6 N.C. backwater valve and N.O. backwater valve by ITA is licensed under a CC BY-NC-SA licence.
• Figure 7 Proper trench construction by ITA is licensed under a CC BY-NC-SA licence.
• Figure 8 Trench with warning tape above pipe by ITA is licensed under a CC BY-NC-SA licence.
• Figure 9 Lifting reinforced concrete pipe section by ITA is licensed under a CC BY-NC-SA licence.
• Figure 10 Installing two pipes in one trench by ITA is licensed under a CC BY-NC-SA licence.

• Based on depth
• Based on construction material

Manholes based on depth

• shallow manholes
• normal manholes, and
• deep manholes

Shallow manholes

Normal manholes

Deep manholes

Manholes based on construction material

• precast concrete manholes
• plastic manholes, and
• fiberglass manholes

Precast concrete manholes

Plastic manholes

Fiberglass manholes

Manhole covers

Applications

Manhole Locations

Indoor Manholes

Storm Manholes

Sanitary Manholes

Specialty Manhole Types

Drop Manhole

Lamp Manhole

Media Attributions

• Figure 1 Tapered precast concrete barrel sections © Kohnen Concrete Products, Inc. Used with permission.
• Figure 2 Manhole lid and cover by SuSanA Secretariat is licensed under a CC BY 2.0 licence.
• Figure 3 Plastic manhole cover by Greg Wirachowsky is licensed under a CC BY-NC-SA licence.
• Figure 4 Triple-sealed access cover for interior manhole © Kent Stainless. Used with permission.
• Figure 5 Storm manhole by ITA is licensed under a CC BY-NC-SA licence.
• Figure 6 Sanitary manhole by ITA is licensed under a CC BY-NC-SA licence.
• Figure 7 Manhole components © Reliner, used with permission.
• Figure 8 Lamp manhole by Greg Wirachowsky is licensed under a CC BY-NC-SA licence.

Types of Residential Catch Basins

Lawn Catch Basins

Patio and Driveway Catch Basins

Self-Test 1

Media Attributions

• Figure 1 Curb inlet catch basin by ITA is licensed under a CC BY-NC-SA licence.
• Figure 2 Area inlet catch basin by ITA is licensed under a CC BY-NC-SA licence.
• Figure 3 Dry well by ITA is licensed under a CC BY-NC-SA licence.
• Figure 4 Residential area catch basins by Greg Wirachowsky is licensed under a CC BY-NC-SA licence.
• Figure 5 Driveway area catch basins by Greg Wirachowsky is licensed under a CC BY-NC-SA licence.

• 2.2.5.2.(5) – Concrete Pipe and Fittings: Precast reinforced circular concrete manhole sections, catch basins and fittings shall conform to CSA A257.4, “Precast Reinforced Circular Concrete Manhole Sections, Catch Basins and Fittings”
• 2.4.7.1.(4) – Where a cleanout is required on a building sewer 8 inches or larger in size, it shall be a manhole.
• 2.4.7.3 “Manholes”:
  1. A manhole, including the cover, shall be designed to support all loads imposed upon it.
  2. A manhole shall be provided with
     1. a cover that provides an airtight seal if located within a building
     2. a rigid ladder of a corrosion-resistant material where the depth exceeds 1m, and
     3. a vent to the exterior if the manhole is located within a building
  3. A manhole shall have a minimum horizontal dimension of 1m, except that the top 1.5m may be tapered from 1m down to a minimum of 600 mm at the top.
  4. A manhole in a sanitary drainage system shall be channeled to direct the flow of effluent.

Manhole Installation

Delivery, Handling, and Storage

• Once the concrete sections have been delivered to site the installer must inspect the components for damage during shipping and unloading, and any non-compliance to approved shop drawings.
• Manhole components shall only be handled with appropriately rated handling equipment from the safe lift points designated by the manufacturer of the precast manhole sections. Manhole ladders, steps or appurtenances are not to be used as lifting points.
• When lifting manhole bases and risers, make sure the chain or cable lengths are long enough to prevent contact with the manhole joint area and are kept at appropriate lifting angles. Where safe lifting angles cannot be achieved, use appropriately rated spreader bars.
• If manhole product(s) need to be stored onsite, it is the installer’s responsibility to ensure the product is placed on level ground and free from unnecessary mud or debris to prevent damage to the manhole components.
• If any damage or non-compliance is identified, the installer shall take corrective action by notifying the manufacturer. Upon inspection if the damage may affect the performance of the manhole structure, the area shall be repaired. If the damaged manhole component cannot be repaired that component shall not be installed.
• If furnished, special joint materials, such as gaskets, lubricant, and mastic shall be stored securely and in accordance with manufacturer’s recommendations.

Excavation and Bedding Preparation

• Shoring if utilized for construction shall be in accordance with all national, regional, and local regulations.
• If shoring is to be removed, the installer shall use the appropriate lifting equipment to safely remove the shoring and to prevent any disturbance or damage to the manhole.
• The manhole foundation should be moderately firm to hard stabilized soil, or compacted fill material with adequate bearing capacity to support the manhole structure.
• A minimum 3 inches [75 mm] thick leveling course shall cover an area not less than manhole base area but preferably 6 inches [150mm] beyond the outside radius of the manhole base. The nominal maximum aggregate size within the leveling course shall not be greater than 1 inch.
• The soil foundation area or bedding under incoming and outgoing pipes should be treated the same as the manhole base section to prevent settlement or shearing of pipes and to provide proper alignment for the watertight connector/pipe interface if resilient rubber connectors are being used.

Installing and Joining

• During installation, set the manhole base on the leveling course making sure the manhole base section is firmly in place and the connectors or pipe openings match design orientation. Verify the top of the manhole base is level in two directions perpendicular to each other.
• Verify the manhole base section pipe openings and/or connectors are at proper grade for pipe inverts to match design elevations.
• Assemble multi-section manhole structures by lowering each section into the excavation. As they are installed, verify each additional riser section is plumb and the joint homed before installing the next riser, conical top or flat slab top.
• Ensure any seals or gaskets are installed correctly. The graphic below shows three common types of manhole rubber seals. [caption id="attachment_70" align="aligncenter" width="595"] Figure 2 Manhole section seals[/caption]
• Adjacently placed manhole sections shall be aligned to match the step placement of the preceding section if steps are provided.
• To ensure joint integrity when assembling the manhole structure, the installation contractor is responsible to maintain clean joint surfaces, removing all foreign materials that could damage or impair the jointing surfaces or gasket materials.

Connecting Pipes to Manholes and Field Cutting or Coring

• Any field cut of the manhole structure required for a pipe opening shall be approved by the engineer
• Lifting holes (full penetration “see through”) shall be sealed by inserting into the hole a rubber or plastic plug, precast plug with mastic sealant or with an approved cementitious material (or filling the opening with non-shrink grout from inside or outside or both).
• Embedded or cast-in lift anchors (“non-see through”) shall have the exposed small pocket volumes filled with non-shrink grout or with an impervious mastic material.

Channeling and Benching

Field-Poured Manhole Benching

• For precast manhole bases, the area underneath the manhole base must be excavated to the required elevation. The soil below the base should not be disturbed, or if fill is required it should be properly compacted. The manhole base is then lowered into the trench and checked for proper bearing on the sub-grade, proper elevation, and orientation to receive the incoming and outgoing sewers at the designated invert elevation. The base should be set to the invert elevations specified on the plans. If the base is not set within plan specifications, it may have to be removed and reset.
• The concrete inverts will be formed after connecting the sewer pipes to the manhole. The invert must be true to the sewer pipe invert elevations, with smooth channels of uniform cross section and slope, either straight or with a continuous curve between the inlet and outlet of the pipes. The concrete invert should be placed based on the dimensions and details of the contract plans and specifications. Some installers use dirt, brick, and other loose material as the foundation of the invert and then add a thin coat of concrete on the surface. This method should not be used because it does not produce a durable invert, which could lead to future maintenance problems.
• As with invert channels manufactured at the plant, field-poured channels and benching must be constructed only with high-quality concrete. The channels should then be consolidated, finished, cured, and properly placed. The minimum concrete thickness must be 2 inches.
• For onsite-constructed channeling, some installers use pipe of the same dimensions as the intended channel as the form for the channel. The pipe is coated with form oil and pressed halfway into the concrete benching to create a uniform path. The pipe is then removed, and the channel is troweled to a smooth finish.

Backfilling and Restoration

• Excavations shall be backfilled with an approved or specified soil material free from large stones, rocks, pavement, and other items that could damage the installed manhole structure. Expansive soil material shall not be used as backfill around the structure.
• When a precast concrete manhole structure is placed in an unpaved area, slope the area around the entrance frame and cover to provide drainage away from the entrance cover. Slope the final grading upward to within 1 inch (25 mm) of the top surface of the frame and cover.
• Backfilling shall be achieved by using lifts (layers) and compaction efforts or flooding (jetting) the excavation to meet the required soil density requirements.
• The installer must take special care and placement of bedding and backfill material under and surrounding pipe connections to manholes to provide firm, uniform support of the pipe at these junctions. This compaction effort is to reduce the potential of pipe shear at the manhole interface due to differential settlement of the surrounding soil.

Media Attributions

• Figure 1 Concrete sanitary manhole by ITA is licensed under a CC BY-NC-SA licence.
• Figure 2 Manhole section seals © photo courtesy of the National Precast Concrete Association.
• Figure 3 Manhole components © Reliner, used with permission.
• Figure 4 Precast channeling  © Kohnen Concrete Products, Inc. Used with permission.
• Figure 5 Examples of suggested directional changes through a manhole © photo courtesy of the National Precast Concrete Association.

Catch Basin Location and Layout

Pick the Location

Install the Catch Basin

Create the Trenches

Lay the Pipe

Testing and Back-Fill

Self-Test 2

Self-Test 1

1. a. At the property line
2. c. Drainage
3. d. Combined
4. a. Vitrified clay
5. b. ABS
6. b. Trench cave-ins
7. a. Air quality
8. c. Pinch point hazard
9. c. It pumps sewage from a deep sewer to a higher elevation
10. b. Gravity

Self-Test 2

1. c. On private property only
2. b. 1 ft³ of water through a 1 ¼″ OD pipe in 1 minute
3. b. Litres per 15 minutes
4. c. National Building Code of Canada
5. d. The manufacturer
6. a. Fixture units
7. d. 2,360 litres per 15 minutes
8. c. 2,730 L/15 min
9. c. A sanitary building drain
10. c. 2%

Self-Test 3

1. d. A benchmark elevation
2. d. 2.5%      72.875 – 71.350 = 1.525m             1.525m ÷ 60m = 0.025m/m = 2.5%
3. b. 12 inches
4. a. Bell holes
5. b. It is accessible and installed on a branch
6. c. Lay warning tape on top of the first lift of compacted spoils
7. b. RCP
8. b. Bulldoze the spoils back into the trench once haunching has been compacted

Competency A2

Self-Test 1

1. b. A normal manhole
2. c. Steel cable loops
3. a. Its weight
4. a. A vent
5. b. A trapping hood
6. d. Sculpted channels
7. a. A drop manhole
8. b. An interceptor
9. b. A drywell
10. d. A driveway catch basin

Self-Test 2

1. a. 1 m
2. b. 1 m
3. b. 3 inches (75 mm)
4. c. 6 inches (150 mm)
5. d. Benching
6. a. Pipe that is the same diameter as the channel
7. b. 2 inches (50 mm)
8. b. 1% ([latex]\dfrac{1}{8}[/latex]″/ft)
9. a. A “French” drain
10. d. A flow-through type

Resources

Resources