Legal & Technical
LEGAL AND TECHNICAL
- This report is provided for the sole use of the named client. Waterways Drainage Specialists Ltd accept no responsibility whatsoever to any parties other than the client; any such parties rely on the report at their own risk.
- This Report and its style are the copyright of Waterways Drainage Specialists Ltd but the Client may take copies of the Report for their own personal use. However, the report may not be used as evidence in any legal proceedings in Court without the express permission of Waterways Drainage Specialists Ltd.
- This survey was undertaken, in order to assess the structural and service condition of the drains in question.
- The survey report is compiled by our Survey Engineer chiefly from the visual display on the CCTV monitor and from the results of other tests, however, necessarily due to the nature of the work, some of the information may be based on assumption, experience, and third party information. Whilst all information is provided in good faith, Waterways Drainage Specialists Ltd cannot accept any liability whatsoever for any errors or omissions. Any recommendations made by Waterways Drainage Specialists Ltd are provided in good faith and on the basis of information made available. However, no statement is deemed to be in any circumstance a representation undertaking warranty or contractual terms and no claim will lie against Waterways Drainage Specialists Ltd, its Directors or staff if such statement proves inaccurate.
- Linear measurements along a pipeline are provided for guidance purpose only. They should not be relied on for the purpose of excavation and other similar works. We strongly recommend that the drain be accurately located with Electro-location equipment before such works commence. All other measurements contained in the report are also for guidance purposes only.
- Our CCTV surveys are digitally recorded and are available on request within 30 days of the survey and at additional cost. Any photographs included in the Report are retained by us for at least 30 days from the date of the survey.
- Our standard Survey includes CCTV inspections of all accessible drain runs wherever possible. In addition, hydraulic (water) tests, or leak tests, are carried out whenever appropriate and possible.
- Salt-glazed clayware pipes are the traditional type of drain pipe and most commonly found at older, pre-1960’s, properties. These pipes have spigot and socket joints that are caulked with mortar/hemp to provide a very rigid pipeline. Hence the slightest movement can crack pipes and/or the mortar caulking compound, to allow the drain to leak. The mortar caulking is not visible by CCTV so the only practical way to test joints is by hydraulic (water) testing. Defects common with this pipe material include broken, fractured and cracked pipes, and displaced and open joints, and root ingress.
- From the late 1940’s, although predominately in the 1960’s, pitch fibre pipes were commonly used for house drainage and sewage pipes. Pitch fibre pipes tend to delaminate, blister, and deform to an oval shape; conditions that tend to gradually worsen until blockages become a problem. As the pipes lose their circular shape they lose their structural integrity; pipe collapse is the inevitable conclusion. When pitch fibre drains were laid, it was common for traditional salt-glazed clayware pipes to be used for any bends and junction pipes, WC connections, gullies and ‘tail pipes’ into and out of manholes. The joints between the two types of pipe are often porous, particularly if the pitch fibre has deformed.
- Modern drain pipes are usually of either vitrified clayware (VC) or plastic (PVC). Such pipes are joined with plastic pipe couplings that provide some flexibility to the pipeline. These pipe couplings normally have a neoprene type seal, to prevent leakage. However, these seals can easily become damaged during installation, particularly if workmanship is not to the highest quality. They usually deter penetration by tree or shrub roots if installed carefully. Pipe couplings are not visible during a CCTV inspection, so hydraulic testing is required to test for leaks.
COMMON DRAINAGE PROBLEMS
- Leaking drains are a common cause of subsidence. The water that leaks from defective drains can wash out or soften the load-bearing soil beneath pipes and foundations, to cause settlement. But it does not follow that a leaking drain will definitely lead to such a problem. It depends on several factors such as the type of sub- soil, the type of foundation, and the route that the leaking water actually takes through the ground. Nevertheless, it is obviously preferable for a drainage system to be watertight, particularly those in close vicinity to building or wall foundations.
- Blockages: Structural defects in drains, such as broken or fractured pipes, displaced or open joints, or root ingress can catch debris and cause blockages. Back falling drains or bellies in a drain’s level can also cause flow to slow down and contribute to blockages. If the sewage or other material in a blockage is dry, it suggests that the blockage is a longstanding problem and that much of the water content has managed to either slowly seep away through the blockage or to leak out of the drains into the sub-soil through any defects in the drains. Grease and non-biodegradable waste materials, such as baby wipes, should not be disposed into the drain because they will inevitably cause a blockage.
- Damp: Water leakage from drains can cause rising damp. However, we cannot prove that water leakage from drains has caused damp at specific sites, nor can we guarantee that repairing the drains would cure the damp problem. Damp can also enter buildings through disused drains.
- Vermin: Rats can use disused drains as nests. The solution is to clean and then properly cap off the disused drains.
- Foul Smells: There are numerous possible drainage problems which could cause foul smells to occur at buildings and sites. Possible problems include: blockages in the drains; detritus backed-up and holding in disused drains; disused drains which have not been properly capped off; foul water leaked from drains and soaking into the sub-soil; drainage systems which are not properly vented, such as through a Soil Vent Pipe to the atmosphere; defective Air Admittance Valves; internal manholes not being fitted with properly sealed and screwed down inspection covers; and poorly designed or constructed above ground plumbing.
- Waterways Drainage Specialists Ltd are very experienced in CIPP drain relining. This process provides very effective repair to defective and leaking drains. However, it is sometimes more suitable and economical to resort to conventional excavation and drain renewal.
- If a drain only has an occasional structural defect along its line, it is possible to install a shorter localised Patch Repair/ Sectional Liner over the defect rather than reline the entire drain. Patch/Sectional repair liners are installed per 1000mm. In a rare instance, when a patch repair liner is installed in a vitrified clayware drain with longitudinal cracks and fractures, it can cause the pipe to split, in this case a full length liner is more appropriate.
- We install Bluelight Lining with our Bluelight LED Lining System we can install DN100 – DN500 diameter. This Bluelight LED cured liner is odour free, styrene free vinylester impregnated needle felt liner and glass liner, water research centre certified, with a minimum of 50 year guarantee.
- Waterways Drainage Specialists Ltd operate a No-Dig process for reforming blistered and deformed pitch fibre drains. Essentially, the process consists of mechanical de-blistering and re-rounding, followed by relining with a CIPP liner. The process is effective in the vast majority of cases but sometimes there is no option but to resort to conventional excavation and drain renewal. Access at both ends of the drain is usually required to accomplish the ‘reforming’ process but if a drain just suffers from blistering, with no significant ‘oval’ deformation, then sometimes a satisfactory result can be achieved by working from one end only. Unfortunately, this service is not available in drains less than 100mm- diameter, so in the case of the defective 75mm diameter drains the most suitable and economical repair will be conventional excavation and drain renewal.
- Where a lateral drain junction or connection joins a main drain, we can reline over it and then cut a hole in the liner to remake the junction or connection. The lateral cutting is carried out using our Picote cutter or Dancutter on a flexible shaft that is fed into the lateral drain where access is available; then a hole is cut in the liner to the size of the original pipe. However, it is sometimes more suitable and economical to resort to conventional excavation and drain renewal.
- We cannot guarantee that repairing the drains will cure certain drainage problems, such as bellies, foul smells or damp. Although repairs are generally worthwhile to ensure the future structural integrity, improve flow rates and water-tightness of drains.
- Debris can cause flow problems in drains and can hinder drainage surveys. We can clean drains using our high-pressure water jetter, robotic Dancutter or electro-mechanical cutters. Ideally a drain should be jetted in an upstream direction, so that the debris can be dragged downstream. Jetting a drain in a downstream direction – otherwise known as “back-jetting” – can be time-consuming and less effective.
- Significant leakage of water to ground often occurs at gullies and in masonry manholes. Misaligned plumbing waste pipes or downpipes from roof guttering can cause erosion and voiding of the concrete and subsoil that surrounds the gully hopper, water can then run into the voiding to soak into the sub-soil. Similarly, the concrete benching or mortar jointing in masonry manholes often gradually erodes over the years, to allow water to leak out.
- Interceptor Traps or Buchan Traps were a Victorian idea primarily to stop fumes entering houses, but modern drains usually vent through a soil vent pipe, so these traps are generally no longer required. Such traps are prone to blocking. Defective or troublesome traps can be removed and replaced with straight pipes to eliminate the threat of them blocking. If a drain downstream of an interceptor trap is to be relined, the trap needs to be firstly removed to allow access for the relining equipment.
- Blockages can form in manholes. Common causes for blockages include poor manhole construction (e.g. concrete channels or no chamber benching); defective manholes (e.g. eroded and voided chamber benching or channel seams, or root ingress); or poor drainage design (e.g. stacks being situated very close to manholes or entering a manhole on a branch channel rather than the main ‘straight through’ inlet, both of which can result of sewage dropping from height into the manholes).
- Manhole covers are sometimes buried; this is a very poor practice because it prevents access into the drainage system for monitoring and maintenance purposes. Manhole covers are most commonly buried under house extensions, decking, patios or garden areas. It is not possible to CCTV survey or leak test drains from buried manholes. Our general advice is that buried manholes should be made accessible to allow for the monitoring and maintenance of their drains.
- It is best practice for proprietary clayware channels to be installed in masonry built chambers. However, different channel materials are commonly used instead and this can sometimes cause problems. Pitch fibre channels can become blistered and deformed, resulting in debris collecting and causing blockages. Concrete channels can become porous with age, causing leakage to ground, and its roughness can cause blockages. Plastic channels, if not specifically designed for masonry chambers and expertly installed, they are likely to become loose and detached as masonry is an inert material and plastic is a reactive material.
SURFACE / RAIN WATER DRAINAGE
- Rainwater downpipes are sometimes installed directly into the ground with no access into their downstream drains for inspection or maintenance purposes. This is not best practice because (1) unless the drain runs to a manhole, there will be no access into it for the CCTV survey camera; and (2) debris could wash straight into the drain, with the potential for causing blockages. An improvement is to install a trapped access gully at the base of the downpipe; the gully would allow for further investigation of the drain and would prevent debris from washing into the drain and potentially causing a blockage.
- Surface/rain water drains sometimes run to sub-soil soakaways. Where the outfall of a surface/rain water drain cannot be proved, it may be assumed that the drain runs to a soakaway. Building Regulations state that soakaways should be situated at least 5 metres from any building. As far as possible, debris should be prevented from running to a soakaway because it will clog the soakaway, lead to blockages and premature failure of the soakaway. Where possible, we flow test a drain and its soakaway; this involves flushing water down the drain to monitor how quickly it flows away. The flow test may find the drain and soakaway to be free- flowing; however, the flow test involves just a few buckets of water and how the drain would cope under prolonged heavy rain is unknown. Or the flow test may find the drain to be slow flowing or to not flow at all, possible causes for this poor flow are: (1) a blockage in the drain, or more frequently at the soakaway entrance; or (2) an inadequate or failed soakaway.
- Rainwater downpipes sometimes discharge directly onto the ground. This is not best practice because it could cause damp, slippery surfaces, algae growth and erosion of ground surfaces.
- Rainwater downpipes sometimes discharge into water butts. If there is no gully close to the water-butt, any excess water from the water-butt will overflow onto the ground. This is not best practice because it could cause damp, slippery surfaces, algae growth and erosion of ground surfaces. Overflow pipes should be fitted flowing to a suitable area.
SOUTH WEST WATER OWNERSHIP
- South West Water has ownership for all public sewers marked on their Sewer Record Plan. Also, since the 1st October 2011, under the Transfer of Private Sewers, the statutory water companies (e.g. South West Water) have been responsible for all shared drains/sewers and for all private drains from where they leave a property’s boundary (otherwise known as lateral drains); in short, from this date onwards a property has only been responsible for those drains/sewers which just serve it and lie within its curtilage.
- We advise you clarify ownership with the water company. The client is free to show the water company a copy of this report. If the water company accept ownership, they are responsible for any blockage clearances and repairs in the public sewers, shared drains/sewers and the lateral drains.
- The public sewers, shared drains/sewers and the lateral drains are marked as green lines on our site diagram.
- Standard Notes 1 to 34 inclusive apply to this survey report.
- The appended site diagram illustrates the drainage layout.
- Our investigations included iTouch CCTV surveys of the drains. Appended to this report are detailed survey reports of each individual drain section.
- The school is served predominantly by separate foul and surface water systems, with the foul discharging to the main SWW sewer, and the surface water discharging to soakaways, a significant proportion of the surface water is un-accounted for, as it was not possible to inspect, due to the debris within the drains.
- We recommend the defective drains are repaired.