sewer blowback

Sewer Blowbacks –Releasing the pressure!

Sewer Blowbacks – Releasing the pressure!

What is a Sewer Blowback?

A sewer blowback is when a combination of air/water/wastewater is ejected from a household wastewater fixture, such as a basin, floor drain, gully trap, and, most commonly a toilet.

This can occur when routine or reactive maintenance is being carried out on the utility’s sewer network with high-pressure water
jetting equipment. Water jetters are used to clear roots, debris and blockages in the sewer system and ensure flow occurs uninhibited. 

Blowbacks occur due to difference in pressure in both the main sewer line and the attached house plumbing. When jetting equipment is in use, water is forced into the sewer main under high pressure, this requires the displacement of a similar volume of air. The space behind the jetter is an area of high pressure, while there can be a negative pressure zone in front of the jetter nozzle. In most cases this air is forced along the sewer main or out private property vents. However, if there is insufficient ventilation, or a blockage in a house vent, this pressure will move to take the path of least resistance. This can result in pipe odors rising through floor drains, and if there is enough positive pressure the water seal in the toilet bed can be blown with force out of the fixture. 

The inverse of a ‘blowback’ can occur where negative pressure occurs in property plumbing, and the water seal in fitting bends can be sucked out, resulting in an atmospheric opening to the sewer causing the odour from the sewer to flow through the fixture into the room that it is located. In these cases, it can be rectified by adding additional water to the water seal 

sewer blowback process

Why do sewer blowbacks occur?

There are two factors that can be attributed to a sewer blowback within the property drain itself. 

A drainage vent can become blocked or restricted over time which can increase the likelihood of a sewer blowback. 

Blockages within the sewer main can also cause water to build up on the upstream side of them; when the jetter nozzle goes past the property connection the water can be forced up the connection pressurizing the property drain unless it has somewhere to go. 

sewer blowback

How can we prevent or minimise sewer blowbacks happening?

 There are several factors that contribute to sewer blowbacks that happen during the cleaning of the sewer main, some can be minimised/mitigated, and others cannot. 

  1.  Communicating to property owners that sewer main cleaning is scheduled, and it is recommended that they keep toilet lids closed. 
  2. Opening the upstream manhole to allow additional flow into the main being cleaned. 
  3. Using lower pressure and/or flow from the jetting truck.

    Most blowbacks consist of only the contents of the water volume within the trap/water seal and is usually clean water that is replaced on a regular basis by flushing the toilet and running a tap. Some utilities will keep a blowback register of historical occurrences. It is recommended to contact them if this happens to help inform future maintenance programs and minimise the potential of it happening again.  

     

About the author Anthony Woodhouse
lateral sewer pipes

Thinking laterally – Can lateral inspections supplement your inspection program?

Thinking laterally – Can lateral inspections supplement your inspection program?

The majority of any pipe network is made up of the smaller diameter lateral connecting pipe lengths (relative to mainline lengths), so it’s no surprise that lateral inspections are becoming more and more popular.

Let’s take a look at what you need to know about lateral inspections.

lateral sewer pipes

What are lateral inspections?

Lateral inspections are inspections that survey the connecting pipe to the main line. The inspection can either be done from an access point upstream of the connection back down to the mainline or from the mainline up through the lateral connection to a connection point or boundary point upstream.

Depending on where in the world you are, these connecting pipes to the main line are sometimes called house branch connections, junctions or taps. Similarly, there are also varying ways to undertake a lateral inspection or coding defects associated with the lateral. Some countries include lateral condition coding with mainline condition coding, whilst others treat the lateral condition coding separately.

Why are lateral inspections required?

Water authorities will do lateral inspections for several reasons. Most organisations undertake lateral inspections in their network because they own the lateral and are therefore required to maintain all or part of the lateral length. There are some organisations that proactively undertake lateral inspections to investigate unknown connectivity of the network.

When should I do a lateral inspection?

Funding an inspection program can be challenging sometimes. So, adding lateral inspections to your inspection program might sound like an extra burden. Let’s look at some of the reasons water authorities choose lateral inspections for their inspection program that make the investment worth it:

  1. Investigating reported customer issues – if a customer reports an issue and no problem can be identified with the mainline pipe.
  2. Investigating network connectivity – if there are suspected illegal connections in the lateral network, or if th
  3. As a workaround for upstream access restrictions

All of the above challenges cost the water authority’s money if left unresolved, which makes the business case for lateral inspections much easier. The magnitude to which this impacts your organisation will drive a cost-benefit ratio that makes sense for your organisation’s circumstances.

lateral inspection launch

Minicam lateral launch

How can I get a lateral inspections done?

Depending on the reason for the inspection, and that site access conditions, lateral inspections are usually undertaken in one of two ways.

  1. Starting from the mainline – The first, is from the mainline using specialist inspection camera technology. This involves a type of camera that has ‘lateral launch’ functionality, which basically means a camera can be ‘launched’ up the lateral up to a length of 150 ft or 45.72 meters.  There are restrictions on the use of these types of cameras, such as lateral and camera angles. This type of inspection can help with access issues, and investigations of network connectivity.
  2. Starting from an upstream point in the lateral – The second way to do an inspection of the lateral starting from an upstream point in the lateral down towards the mainline. Its possible to do this type of inspection with a standard CCTV inspection camera (either crawler or pushrod). This type of inspection can help with investigations of customer issues.

Conclusion

The increased demand for lateral inspections can be attributed to a number of things, not least of which the availability of the technology, and increased customer reporting capability and more. Either way, these inspection methods are a great way to supplement your upcoming inspection programs where the needs arise.

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pipe inclination in roman aqueducts

Pipe inclination – What goes up must come down.

Pipe inclination - What goes up must come down?

What is pipe inclination?

Most of the world’s sewers and storm pipes operated as gravity pipe network. What that means is that the water in the pipes drain to the outlet point under gravity. For this to happen, the entire pipe network needs to be laid on a slight incline in the direction of the downstream outlet.

This is the most efficient method of transporting water from one point to another and has been a method used since ancient times. The Roman aqueducts brought water from the various springs in the Anio valley and its uplands to Rome, over 92000 metres or 301837.27 ft away, entirely using this method; slowly declining the aqueduct over the length of it so that water would fall in the direction of Rome.

roman aqueduct

Roman aqueducts crossing a valley

That is why when aqueducts needed to cross valleys, the Romans made every effort to keep the level of the structure constant, as dropping the level to match the valley would eventually require some sort of pumping action.

Why is inclination in pipes so important?

Pipes have inclination for the same reason as the Roman aqueducts do, water transport efficiency. The degree of inclination in pipes is a subject of much debate and is an ongoing engineering design and maintenance challenge. The more inclined the pipe, the faster the water will flow, the slighter the incline, the slower the water will flow. An interesting thing happens when water moves fast; it starts to pick up debris in the flow. Conversely, when the same flow starts to slow down, the debris that was once swept up in the flow begins to settle out.

For this reason, design engineers try to maximise inclination of the pipe network to encourage ‘self-cleaning’ velocities in the pipe network as a low-cost way to prevent blockages in the network. Anecdotally, a reasonable self-cleaning inclination would be between 1-2% grade depending on the diameter. A grade of 2.00% is the same as a ratio of 1 in 50. This means over a distance of 50 m the trench or pipe will slope down or fall 1 m from the horizontal.
However, in a flat catchment, there may not be a big enough difference in height between the top of the catchment and the bottom. When this happens, there is an increased risk of blockages and flooding because the water is not able to move itself (or debris) to the outlet as efficiently.

How can I test for inclination?

Testing for inclination can be done a couple of ways, but the most common are:

  1. Using pipe lengths and elevations between access points – Measuring the reduced level of the pipe from an upstream node and subtracting it from the reduced level of the downstream node would give you the elevation drop. Dividing that elevation drop by the length of the pipe would give you the indicative inclination of that pipe. The reason this method is only indicative is that there may be other dips and changes in direction of the pipe between the two access points that would affect the exact calculation.
  2. Using dynamic inclination measurements during CCTV inspections – Most standard CCTV camera crawler systems come with inclinometers as part of the equipment and the inclination is logged as part of the camera telemetry data. For water authorities to access this information, they will need to request and have the ability to decode this telemetry data. Or asking your CCTV contractor to display inclination on the on-screen display (OSD) as part of the inspection will also provide you with the information you need.

Conclusion

For gravity pipe networks, the inclination is very important for the efficiency of the network performance. Introducing additional debris, such as wet wipes or any other items that should not be flushed, into the sewer or storm pipe network only adds to the challenges that gravity networks have, which has the unfortunate impact of increases operational and maintenance costs for water authorities.

Effective public awareness campaigns to reduce sewer misuse such as #binthewipe and #weirdthingsinpipes can help to raise awareness about sewer misuse in the community to ensure we keep our pipes running as efficiently as possible.

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Sewer vent

What are sewer vents for and how do they work?

What are sewer vents for and how do they work?

Sewer vent

Inspecting sewer vent

Transporting more than wastewater

The process of transporting wastewater from houses to treatment facility is a journey through pipes and pumps of various type and size. When designing and optimising the transport of this fluid, there is another key factor that must be considered by engineers – ventilation of the sewer network. 

As wastewater is pumped up and flows down through the different pipes in the system, there is also a movement of air. Due to the atmospheric pressure differentials at pump stations and within the headspace in the top half of gravity pipes, the network itself needs to breathe. The system must move air, as well as fluid.  

Why do we need sewer vents?

Venting of the wastewater network is important for several reasons, this includes: 

  • Providing airflow and pressure equalisation between the home and the pipe network 
  • Reducing and controlling odour issues above ground.
  • Avoid creating corrosive environments below ground that reduce asset life 

The ins and outs of vents

House vent – Otherwise known as a drainage waste vent (DWV) consisting of a 50mm (2”) PVC for a single dwelling and up to 200mm (8”) PVC for multiple dwellings, which extends above a roof of a building. This is usually installed at the head (furthest point from the main drain) of your property’s drainage system to allow enough air movement for you to flush your toilets and use all fixtures within your house and still maintain the water seals within each fixture 

Pump Station Vents (induct & educt) and Discharge manhole ventAt the pump station, a vent stack will also be present. This usually extends above the tree line, or nearby property roof level.  Vents are often constructed at the discharge points of the rising/forced mains. With wastewater being forced into the gravity system between two points, both locations need to have an open flow of air as from one end it draws in and the other it exhausts as the wastewater is displaced from one to the other.  

sewer vent

Image: Sewer Ventilation Clearance Requirements 

Forced ventilation (e.g., tunnels)Mechanical ventilation using a powered fan generates airflow at a controlled rate to ensure a sufficient volume of fresh air is circulated to ensure critical structures do not experience accelerated material corrosion. . 

Odour control units

In instances within sewer networks where odour is problematic, activated carbon filters can be used as a replacement for vent stacks. Vent stacks can become an occupational health and safety risk due to their deteriorating condition over their lifetime. Activated carbon neutralises gasses before they exit the vent pipe. In some cases, they are reducing odours up to 99%.  

There is a move to replace vent stacks due to ageing infrastructure and the risk they can pose to the public if they fail/collapse. An example of this is here, where a vent stack located near Muswellbrook High School (Australia) was replaced following ongoing odour complaints and the risk that it posed to the surrounding neighbourhood. 

Installing vent stack

Vent stack replacement. Muswellbrook High School, Australia (before and after)

There are several different options available to suit the needs of the situation. However, the principle is the same. Air flows in or out of the sewer through the replaceable filter media removing unpleasant odours without restricting the air requirements for the sewer to operate as intended.

Examples of types of vent replacement options.

These units ensure that harmful gasses within our sewer networks are ventilated and treated, helping keep us safe and extend the life of the underground assets for the utilities of your local area. 

About the author Anthony Woodhouse
Cloacina

Ancient Roman Sewer – Cloaca Maxima

Cloaca Maxima

This ancient roman sewer is protected by a goddess!

Tiber river

Tiber River

Strolling along the Tiber River in Rome, you could be forgiven for missing this wastewater wonder of the ancient world. 

While there were many strollers and joggers along the neatly paved banks of the ancient river, my husband and I were bee-lining for our next stop on our Rome itinerary: Cloaca Maxima. 

What is Cloaca Maxima?

Cloaca Maxima is a large diameter drain built in Ancient Roman times in the 6th century BC.  The drainage structure was named after Cloacina, an ancient Roman deity that represented purification. A shrine to this deity was said to be near the original stream, which is said to be the inspiration for the name. The literal translation in Latin is ‘Greatest Sewer’. 

The design and construction

It was initially a stream that was lined with stone, aimed at draining the local marshes and removing waste from the city. By the 3rd century BC, it was enclosed with a stone barrel (semi-circular) vault so that the swampy land around the Roman sewers could be filled in.  

Cloaca Maxima Catchment area in Ancient Augustan Rome

Figure 1 Catchment area map created in 1886 of Cloaca Maxima in Ancient Augustan Rome (source: https://www.wikiwand.com/en/Cloaca_Maxima#Media/File:Roma_Plan.jpg) 

The sewer was said to be dimensions that allowed inspection boats and boats fully laden with hay to pass through. 

This post goes into more detail about the construction and history of the famous sewer for those that are keen to learn more: https://www.wikiwand.com/en/Cloaca_Maxima 

Cloaca Maxima today

Today, the sewer is still in use, though nothing more than a trickle comes out of the once ‘Greatest Sewer’, most likely groundwater, as the city’s sewage has been long diverted to more modern pipe systems.

Cloaca Maxima today

If you are looking to replicate this enviable photo opportunity, you can find Cloaca Maxima still visible where it joins the Tiber River near the Ponte Rotto and Ponte Palatino bridges. 

Lessons from the Ancient Romans

Whilst the sewer is still technically in operation today, its much-diminished role is reportedly due to the misuse of the sewer (people putting all sorts of solid waste down there, even some political execution victims!) and backflow from the Tiber. Over time the once ‘greatest sewer’ has been re-routed to more the modern sewer system that sends sewage to treatment plants for treatment before discharge.

It’s certainly interesting to see and learn about the challenges of legacy wastewater infrastructure. Design challenges such as back flow design can be accounted for with careful planning. Social challenges with sewer misuse can be accounted for with meaningful community awareness campaigns. Either way, engineers today are working to deal with similar challenges today, just manifested with a modern twist. 

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Patch repair needed in new pipe

Streamlining CCTV Pipe Acceptance Testing

Streamlining CCTV Pipe Acceptance Testing

What is a pipe acceptance test?

Utilities that manage sewer and stormwater networks increasingly have reticulation pipework extensions constructed by contractors as part of developer works. These pipes are commissioned and adopted by the utility. In many cases, the new pipes are built as part of a larger development that incorporates road, footpath, and lot divisions for sale. It is important for public utilities to have assurance that these new pipe assets have been constructed to their approved design and are defect free prior to them taking ownership.

This inspection, or CCTV acceptance test, is a critical part of the process that confirms the newly constructed pipe meets the requirements set out by the relevant authority. A CCTV inspection for acceptance is intended to focus on a range of areas, including:

  • Surface damage of internal surfaces
  • Cracking, breaking, or holes in the pipe wall
  • Obstructions or deposits within the pipe
  • Constructed grade (fall) of the pipe
  • Deformation
  • Joint defects
  • Ponding of water, or flat sections
  • Connection and junctions
  • Length of constructed pipe

Public utilities usually specify that these inspections be completed to the relevant inspection reporting code and must meet minimum standards to be approved for contributed asset handover.

Patch repair needed in new pipe

Figure 1- Cured-in-place patch to rectify a pipe defect in a new pipe

Who completes and approves an acceptance test?

Civil construction companies are usually required to engage an independent CCTV sub-contractor to complete an acceptance test, with a qualified engineer providing sign-off on the CCTV results and other accompanying reports where required.

When does the acceptance test occur?

Utilities may be descriptive around what stage the acceptance test can occur, with practical completion of various other on-site works a pre-requirement. Where specified, this detail is listed in a specification document or instruction issued directly from the approving authority.

Cause of Delays

Delays in the workflow when submitting acceptance inspections can occur due to:

  • The time it takes to supply the approving authority the specified video and associated report/s; or
  • In instances where a pipe does not pass the acceptance test, there will likely be some form of minor repair/maintenance required and a follow-up CCTV inspection to confirm any identified issues have been rectified. In most cases this will be jetting to remove construction debris/deposits, or patching a location with pipe wall damage

If the follow-up to a failed CCTV acceptance test is delayed due to the workflow that is setup between civil contractor, CCTV contractor, and reviewing engineer; the cost to the overall project can be significant. In some cases, this delay will fall on the critical path of other finalization works and negatively impact other teams working on the development project. VAPAR has specifically designed a workflow that ensures the time between the CCTV inspection and approval is minimized to reduce any unnecessary or costly delays. In instances that repair or maintenance is required, the details of this can be distributed to the required parties quickly.

deposits and debris in pipe

Figure 2- Deposits and debris that requires removal before acceptance

How can VAPAR assist in avoiding costly delays in your review and approval timeline?

Same day turn-around can be achieved with upload from site that only requires the video file and an internet connection to your internet browser. VAPAR’s AI processing time is measured in minutes, not days. Your reviewed inspection results can be shared in real time with clients you have invited into the VAPAR.Solutions platform in a structured library of current and past inspection projects.

Alternatively, you can choose to send your package of inspection results for the day, or week, as a pdf report set or spreadsheet summary. What does this mean in practical terms? Data and results (including access to the selected inspection video files) can be shared without the requirement for downloaded software or file sharing programs. The CCTV inspection videos, and associated results are available directly to your client in the method most convenient for your situation.

Keeping all your inspections organised and accessible

VAPAR’s cloud storage solution for inspections means cataloguing, finding, and viewing your past CCTV results is both user friendly, and eliminates the requirement for on-premises storage. No more lost files spread across different servers and cluttered folder structures. For utilities that would like to compare original acceptance inspections with end of defect-liability inspection, or condition assessment years down the line, this can be done directly from your internet browser by searching asset ID, or node, to bring up your matching results.

Image of VAPAR.Solutions

Figure 3- Searching past inspections of the same pipe asset

About the Author Mark Lee