Precast Suds

New Housing Development ‘The Hamptons’, Newcastle-Under-Lyme, Staffs

suds — Mon, 27 Feb 2023 15:54:04 +0000

FP McCann has supplied and installed a 780 cubic metres precast concrete StormTank on behalf of housing developer Persimmon Homes and their civils ground worker M.V. Kelly in Newcastle-u-Lyme, Staffordshire. Sited under a landscaped area, the online attenuation tank is designed to alleviate flood risks in line with climate change conditions and storm surge events on ‘The Hamptons’ residential development
of 3 and 4 bedroom homes.

FP McCann’s StormTank is amongst a number of attenuation systems that are now accepted by Severn Trent Water and adoptable under the S104 approval process within Sewers for Adoption 6th and 7th Editions. StormTank is part of the FP McCann multi-purpose precast concrete tank range and can be designed and installed up to 6 metres high with overall dimensions to suit the client brief.

Measuring 36.8 metres long by 16.4 metres wide and at a height of 1.4 metres, ‘The Hamptons’ StormTank manages a storm event by capturing excess surface rainwater. The water can then released back into the online drainage system at a controlled rate thereby relieving the pressure on the main drainage network and reducing the risk of downstream flooding.

The StormTank designed as water class tightness 1, weighs 470 tonnes and has been constructed using over 200 individual steel reinforced precast concrete panels sections consisting of external (250mm thick) and internal (275mm thick) wall units and 120 solid roof slabs, 120mm thick. The tank is divided internally by special roof support walls with openings cast into them to allow water to flow freely between sections. Six man access opening points have been cast into designated roof sections to allow for entry for maintenance purposes. To comply with Severn Trent Water’s requirements, all elements of the StormTank have been positioned and constructed to achieve the required fall in the floor which in part is complete with a dry weather flow channel measuring 200mm wide by 50mm deep.

Prior to the pouring of the 250mm thick C40 concrete tank floor slab, a 100mm thick layer C20N/mm2 blinding was laid in conjunction with the precast concrete external wall installation. The panel sections manufactured at McCann’s state-of-the art precast facility in Byley, Cheshire were delivered to site over a period of 3 weeks for installation by the approved FP McCann specialist fixing team.

In conjunction with Persimmon and Manchester based EDGE consulting engineers, FP McCann value engineered the precast concrete tank system into the designated footprint by demonstrating increased performance efficiencies and associated commercial benefits over the originally detailed plastic pipe tank.

Commenting on the StormTank design and build, Peter Holker, Development Manager for Persimmon Homes (North West) says, “We had to take into consideration a number of factors on tank design. Robustness and long-life, low maintenance performance were key to our choice of attenuation tank. Having looked at and considered carefully a few options FP McCann’s StormTank fitted both the design and performance criteria. The McCann approved install team undertook the work in a timely, efficient and safe manner. On future projects, we will certainly consider similar FP McCann supply and install precast concrete StormTank systems.”

FP McCann’s 100 year design life StormTanks can be installed up to 6 metres high with no footprint size limitation and are designed for pedestrian loading through to LM1 highway loading. Internal design features can be added such as weir and baffle walls and penstocks or flap-valves can be pre-installed. Typical uses include:-
• Attenuation Tank
• StormBrake Chambers
• Pumping Stations
• Large CSO Chambers
• ASP Structures
• Basements
• Clean Water Storage Tank

Marshalls Civils & Drainage gets straight to the Point on pollution

suds — Mon, 27 Feb 2023 12:26:19 +0000

Pollution-resistant pipes from Marshalls Civils & Drainage help out at Gorsey Point.

Work is drawing to a close on a significant regeneration scheme in which bespoke concrete nitrile-seal drainage pipes by Marshalls Civils & Drainage have helped to mitigate potential contamination by pollutants.

Marshalls Civils & Drainage has supplied more than 140 precast concrete nitrile-seal pipes totaling 362m and in sizes ranging from 375mm to 675mm diameter to developer Marshall CDP’s Gorsey Point development in Widnes, Cheshire.

Gorsey Point is a new commercial development located on Gorsey Lane, approximately one mile from Widnes town centre. The 16-hectare site is located within the Widnes Waterfront area, a significant regeneration scheme that is transforming 145 hectares of low-quality industrial land into new commercial, residential and leisure facilities on the banks of the River Mersey, close to the new Mersey Gateway Bridge.

The former manufacturing site has been cleared to provide ‘oven-ready’ development opportunities and Marshall Construction is now constructing a three-phase development of warehousing and offices totalling approximately 700,000ft2 of space.

The site’s former industrial role has resulted in a legacy of contamination and, despite thorough remediation of the site, care still needs taking to ensure that any residual pollutants remaining underground do not leach out into the environment.

In particular, potentially aggressive petrochemical residues need preventing from compromising the site drainage system and entering local watercourses. Because of the need to protect against potential pollutants, Marshall CDP specified the use of precast concrete drainage pipes fitted with seals manufactured with nitrile rubber which is notable for being highly resistant to oil fuel and other chemicals.

The seals were manufactured for Marshalls Civils & Drainage by a specialist company in the Netherlands. Because they are specified infrequently, Marshalls Civils & Drainage offers them as a bespoke service which requires extended lead times to allow them to be produced, shipped to the UK and incorporated into the pipe manufacturing process.

Close liaison with the supply chain was therefore essential to ensure the 14-week lead time cause no disruption to the build programme. Efficient teamwork allowed site activities to be rescheduled to accommodate this without causing any delay.

In addition to the pipes, approximately 50 related pipe components, such as nitrile rockers, spigot and socket pipes for each pipe size were also supplied.

Marshall Construction’s project manager Tom Slattery said: “The pipes had to be nitrile sealed because of the contamination on the brownfield site. Everything went swimmingly – the pipes were no different to installing ordinary pipes, the only consideration was the long lead-time. “

“We were fully aware of this from the beginning and were able to make allowances in the build programme. Marshalls kept us fully informed at all times and by working closely with our supply chain we were able to plan and execute the installation smoothly and without any hiccups.”

For more information on concrete pipes please visit www.marshalls.co.uk/commercial/product/concrete-pipes

Elliptical pipe tank used at ‘Greenacres’ housing development, Pontefract

admin — Mon, 24 Jan 2022 17:01:51 +0000

Elliptical pipes were recently employed to offer a stormwater attenuation and storage solution for a new 48 property housing development in Pontefract. The £8M investment by Barrat Homes was built over a 3.2 acre site in a greenfield area. Therefore there was a need to ensure that the local environment was not impacted. This would require stormwater peak flows off site to mimic the existing situation.

Due to the site’s nature, and its steep landscape, there was limited depth available to install an underground tank. The need for vehicle loading to National Highways standards.

Luke Martin, engineer for Barratt Homes explained that circular storage pipes “… would not have large enough cross sectional area to keep attenuation within the lower part of the site. We would have needed very deep drainage with extensive costs associated”. Elliptical pipes also do not need any in-situ secondary inverting to form dry weather flow channels or additional jointing material due to its integrated watertight elastomeric gasket.

The Stanton Precast team then worked closely with design consultants on the set up and design of side entry manholes. A total 31 elliptical pipe units (DN2650 x 1500) were supplied, along with fittings and end walls. An addition, a further 22 DN1600 circular pipes were supplied to replace the originally specified plastic pipes.

The project contractors, PJ Towey Construction ltd, were also pleased with the level of support and site training offered to help with the management and installation of the elliptical pipes on site. Martin Towey (PJ Towey Construction Ltd) noted that Stanton Precast members of staddd, including technician Chris Taylor, were “…a great help to the guys on site and made it a lot easier to work with the elliptical pipes. Overall we were really happy with the products, services and ease of installation. Once the team got started the installation was quite quick”.

Record breaking FP McCann StormCleanser TM system installed at a Norfolk Recycling and Waste Management Facility

admin — Fri, 14 Jan 2022 12:42:19 +0000

FP McCann has supplied its largest precast StormCleanser system to date to a recycling and waste management facility in Norwich.

The PSH Environmental ltd recycling facility is based on the Rackheath Industrial Estate. As part of its site extension plan, the onsite surface drainage network was upgraded to help deal with increased surface water run-off and improve interception and prevention of contaminants within the surface water run-off washing out into the site’s holding lagoon.

The 3600mm wide StormCleanser hydrodynamic separator unit was supplied from FP McCann’s Ellistown precast concrete plant in Leicestershire. The unit was installed by civil engineering contract MB Plant & Civils with DN900 pipes for the unit’s inlet/ outlet.

Surface rainwater and any pollutants enter the StormCleanser chamber via the inlet pipe where the internal layout then enables low energy vortex flow patterns to form. This allows floatable materials such as plastics, paper and other light debris to gather at the top of the system and heavier sediment to settle at the bottom of the treatment chamber for removal by standard gully suction equipment. A baffle plate located above the sediment storage sump prevents the re-suspension of solids. Treated water then flows out of the system back into the main drainage network.

Commenting on StormCleanser, Matthew Body Managing Director of MB Plant and Civils says, “FP McCann delivered the 3600mm precast concrete StormCleanser chamber and the internal stainless steel components. It was then a simple task for our onsite team to assemble the unit which comfortably sits within the online drainage system”.

StormCleanser can be installed in precast concrete drainage chambers ranging from DN1200 up DN4000mm accommodating pipe diameters from DN150 up to DN900. Modular and bespoke designs are available for multiple inlet orientation with a choice of flow direction providing optimum configuration performance.

Stanton Precast Elliptical Pipes provide effective, long term stormwater solution for Pentland View housing development

admin — Fri, 14 Jan 2022 12:24:58 +0000

Stanton Precast provided up to 330 metres of 2650x 1500mm elliptical pipes, with a number of side entry manhole units, for the Pentland View housing development in Bilston, Edinburgh.

Situated in Midlothian, Pentland View, a new 190 unit housing development, is surrounded by countryside and has a striking background of the Pentland Hills. The development is located only 7 miles from the centre of Edinburgh and will include both, private and affordable housing units.

Analysis was carried out by Scottish Water engineers and the consultant Ironside Farrar into the DIA (drainage impact assessment) and the best solution for Scottish Waters combined sewer for storm and foul water. This included assessment of area, ground conditions and specific needs of the project. Stanton Precast Elliptical Pipes were then specified as they met the project criteria, which required more storage with efficient self-cleansing properties.

Advance Construction Scotland Ltd were awarded the contract and started DIA work on site in July 2021.

Over 330 metres of elliptical pipe were ordered to create two runs to sit parallel on a sloped area. Included in this were integrated side entry manhole units cast in to some of the elliptical pipes during manufacture. This eliminated the need for large diameter chambers to be constructed for man entry and maintenance as well as contributed to a quicker and easier installation. Again these were specified along with end walls for some of the end units.

Providing integrated products during manufacture ensures that quality and durability is maintained and there is less time, materials and waste on site.

A total of 69 loads were delivered in just 20 days to meet the installation scheduling – on time and in spec.

Advance Construction Scotland Ltd were impressed with the elliptical pipe and support from Stanton Precast.

Marc Watson, Technical Manager for ACS Ltd said: “Stanton Precast were really helpful with installation data, off loading and turning, elliptical installation literature to assist site with works. Delivery schedule with timings were agreed prior to the first delivery, so that site were fully aware when they were due, so that they could work around other site deliveries. Stanton Precast were able to double the amount of units being delivered to site per day to assist with speeding up installation on site. Lifting clutches were provided to assist with off- loading and placing units.

Our contracts manager John Irving has advised that these works are currently progressing ahead of programme and without any issues. Our site supervisor on site had said that the units were very easy to move around site and place in excavation despite their awkward size.”

The key benefits of using elliptical pipes:

Backfill and minimal aggregate required so less materials, less truck movements
Can be installed at shallow depths due to structural profile
Internal profile allows a constant self-cleansing flow velocity, even with low flows, negating the need for a secondary dry weather flow channel to be installed
Cast in lifting anchors provide safer offloading and handling

Stanton Precast (formerly Stanton Bonna Concrete Ltd) are widely recognised as a leading UK manufacturer of precast concrete pipes, manholes, culverts and linear drainage as part of a comprehensive range of precast offsite solutions for water, highways, rail, housing, commercial, telecom and power sectors of the construction industry.

This, together with being part of Sateba, a European specialist in precast concrete rail and infrastructure, gives confidence that our knowledge and experience of precast concrete products is extensive and professional.

Sateba’s aim is to be the leaders in sustainability within our industry and ensure precast concrete will play its part in the circular economy. We are looking forward to working on building the future in a more sustainable way.

More information can be found at Stanton Precast’s website:

https://www.stantonprecast.co.uk/

Marshalls supply box culvert attenuation tank for industrial estate in Skelton

admin — Fri, 14 Jan 2022 12:12:01 +0000

Castlehouse Construction has the £7m main contract to build three industrial units totalling 29,950 sq ft for Carnworth Estates adjacent to the Pheasant Fields Lane retail park in Skelton. The project also included the construction of a car park for approximately 70 vehicles, plus soft and hard landscaping. Each industrial unit will have its own surface‐water management system to collect rainwater and surface water run‐off. These all feed into a central sub surface attenuation tank located under the road near the development’s main entrance.

Marshalls Civils & Drainage supplied 32 precast concrete MC2010 STKA box culverts laid in a double run to create the attenuation tank for storage and management of surface water from the three units. From receiving the order to delivery of the first units, Marshalls had a tight lead‐in time of less than 10 weeks. Marshalls was selected to supply the precast units for the attenuation tank on two main criteria: quality and availability.

The ability to supply standard units from existing stock was a key factor in keeping construction of the attenuation system on schedule.

The underground tank comprises 32 MC2010 culverts laid in a double row. Twenty of the culverts were standard designs which could be delivered immediately ex‐stock, while the remaining 12 were bespoke units manufactured to order. “Being able to use a stock product allowed us to speed up the programme,” explains Marshall’s Business Development Manager (Special Projects) Billy Fairhurst.

Castlehouse dug the excavation and cast the base slab for the attenuation tank and was able to start installing the standard MC2010 culverts without delay. Meanwhile Marshalls began manufacturing the 12 bespoke units for delivery on a just‐in‐time basis. The bespoke units included four end‐wall culverts with custom designed access holes and connections plus another eight units manufactured with special penetrations to connect the two parallel runs and to collect water flowing in from gulleys.

Dave Crozier, Project Manager with Castlehouse Construction, praised the quality of the Marshalls product as well as the support provided by Marshalls during the installation phase: “Marshalls kept us fully up‐to‐date with the manufacture of the specials and provided helpful advice to make the installation easier for us,” he says. It only took seven days to install all of the units, backfilling the excavation as we went,” he noted, “It took us only two weeks to finish the entire job.”

Update to BS 5911 offers further assurance about the durability of precast SuDS solutions

admin — Tue, 04 Jan 2022 14:32:23 +0000

A recent revision of precast drainage standard, BS 5911, offers more certainty about the intended working life of precast concrete SuDS solution.

BSI has published a revised edition of BS 5911-1, specification standard for unreinforced and reinforced concrete pipes, with a number of amendments which will improve how specifiers understand the durability of precast drainage systems, including precast SuDS components.

Durability is one of the main characteristics considered in the design of stormwater storage and attenuation tanks and other SuDS systems. There is no single agreed service life period for SuDS infrastructure. But SuDS solutions would be expected to perform effectively and with robust structural integrity throughout the life of the housing estate, retail or commercial development it serves. CIRIA’s Benefits of SuDS Tool (BeST) suggests a 100 years’ service life for a SuDS scheme. Many industry specifications, such as highway standards and PAS 2080, target a minimum design life of 120 years for infrastructure assets.

Defra’s SuDS Non-Statutory Technical Standards require SuDS solutions to be structurally robust throughout the design life of the development. For attenuation tanks, structural design requirements, and its associated working life, are specified in a number of ways: For example, Box culverts are designed to Eurocodes (EN 1992) with a clear reference to an intended working life of 100 years. Geocellular tanks are designed to CIRIA’s C737, but its design life advice can be found in testing standards EN 17152-1 or in products’ BBA certificates (usually 50 to 60 years). In the past, concrete pipeline products standards did not make any clear reference to a specific intended working life. The 100 years intended working life for concrete pipes was mainly based on reinforcement cover and exposure class design for 100 years as specified in the concrete specification standards and National Highways specification for concrete infrastructures. However, this has now changed following the update to BS 5911:

The new standard introduces a clearer justification explaining the link between specification of a DC-4 exposure class concrete mix to a 100 years’ Intended Working Life for pipes. As noted above, that link already existed in the past as all precast drainage is already specified to standards such as Special Digest 1 “Concrete in Aggressive Grounds” and BS 8500. But following the latest amendment, there is now a direct reference to a 100+ years in the pipes standard. The direct reference to a 100 years’ working life would not only help with asset management and Whole Life cost planning, but also with Design for Circular Economy, carbon footprinting and long-term performance.

The new BS 5911-1: 2021 can be purchased from the BSI website. For any further information on the new standard please contact email@precastdrainage.co.uk

Combined attenuation system meets flood prevention requirement

admin — Tue, 30 Nov 2021 10:14:47 +0000

Marshalls Flood prevention was a key requirement of planning permission for a 475-home development on agricultural land in the Vale of Glamorgan. The project also includes a new primary school and a roundabout being constructed as part of a link road.

The main contractor, Lewis Civil Engineering, specialises in deep sewer and water main pipelines and worked closely with Marshalls Civils & Drainage. Precast concrete dry-weather-flow pipes are suited to areas prone to flooding as they can reduce over-pumping costs by up to 15 per cent.

A three-line attenuation tank using 1500mm dry weather flow pipes was specified. This was combined with Hydro-Brake Optimum flow-control chambers, as part of the sustainable drainage system (SuDS), which Marshalls Civils & Drainage also supplied.

Les Vile, specifications manager for Marshalls Civils & Drainage said: “Using the precast dry-weather-flow pipes concentrates the flow of stormwater into a channel at the bottom of the attenuation system. This increases velocity and prevents the settlement of solids or water in the tank.

Jo Wallace-Blaker, Marshalls Civils & Drainage’s trading manager said, “There are multiple benefits to using a precast concrete solution like the one deployed here. It reduces onsite construction time, in turn reducing health and safety risk.

“In addition, heavyweight concrete has the ability to withstand ground movement and water jetting, making the system more resilient. By aligning modern precast drainage with Hydro-Brake flow control as part of the SuDS, it has been possible to mirror the natural watercycle at this site.”

FP McCann multi-purpose precast concrete panel tank installed on Northumberland Housing Development

admin — Tue, 30 Nov 2021 09:54:13 +0000

FP McCann has supplied and installed a 1,000m³ precast concrete panel attenuation tank on behalf of housing developer Miller Homes and their main drainage infrastructure contractor Esh Construction. Once complete the ‘Roman Fields’ development in Corbridge, Northumberland will consist of 123 prestigious properties. The attenuation tank is designed to alleviate flood risks from the site and to cater for a 1 in 100 year storm surge event.

The attenuation tank is amongst a number of precast concrete products that are now accepted by Northumbrian Water within Sewers for Adoption 6th and 7th Editions and is part of the FP McCann multi-purpose StormStore panel tank range which can be designed and installed up to 6 metres high with overall dimensions to suit the client brief. Measuring 23 metres long by 17 metres wide at a height of 3 metres, the online drainage precast concrete panel tank sited under the access road, manages a storm event by capturing excess surface rainwater. The water can then be released back into the drainage system at a controlled rate, thereby relieving the pressure on the main network and reducing the risk of downstream flooding into the nearby Cor Burn.

Prior to the construction of the tank, a 75mm thick blinding layer of concrete formed the hardstand to receive the poured floor slab; a 250mm thick layer of C40 reinforced concrete. The panel sections manufactured at FP McCann’s state-of-the-art precast facility in Byley, Cheshire were then delivered to site over a period of 4 days for installation by the approved FP McCann specialist fixing team.In total, 22 external walling panels were fixed and 24 internal wall units to form four special internal support walls. Large openings in the internal walls allow water to flow freely between each section. Covering the tank are 70 individual precast cover slabs. 4 manhole openings have been cast into 4 end slabs to give easy access for maintenance purposes.

The tank has been set on a 1:400 fall towards the outlet and the base is complete with a dry weather flow channel. To complete the tank, in-situ concrete was pumped onto the roof slabs to provide an additional protection layer.

Commenting on the panel tank design and build, Steve Morris, Senior Quantity Surveyor for Esh Construction says, “With final adoption under the Northumbrian Water S104 approval process, we had to take into consideration a number of factors on tank design. Robustness and long-life, low maintenance performance was key to our choice of attenuation tank. FP McCann’s multi-purpose panel tank system fitted both the design and performance criteria. The FP McCann approved installation team undertook the work in a timely, efficient and safe manner. On future projects, we will certainly consider similar FP McCann supply and install precast concrete StormStore panel tanks systems.”

In addition to the tank, FP McCann has also supplied standard precast concrete spigot and socket pipes, manhole chamber rings and cover slabs to the Corbridge housing development.

FP McCann’s multi-purpose panel tanks have a 100-year design life and can be installed up to 6 metres high with no footprint size limitation and are designed for pedestrian loading through to LM1 highway loading.

Internal design features can be added such as weir and baffle walls and penstocks or flap-valves can be pre-installed. Typical uses include:

Attenuation Tank
StormBrake Chambers
Pumping Stations
Large CSO Chambers
ASP Structures
Basements
Clean Water Storage Tank

Adoption of attenuation tank system: Five reasons why precast attenuation tanks offer the best option

admin — Wed, 07 Apr 2021 09:06:08 +0000

As we celebrate one year since the new sewers’ adoption code came into force, we look at the new code’s requirements and identify five main reasons why a precast concrete attenuation tank should be the number one option for most SuDS applications.

The new sewers’ adoption Design & Construction Guide (DCG) came into force in April 2020. What is unique about this new ‘Sewers for Adoption’ guide is that it allows Sustainable Drainage Systems (SuDS), such as ponds, swales and underground stormwater attenuation tanks, to be adopted by water authorities in England.

There is a very wide range of underground attenuation tank systems available. It is important to understand that not all these systems meet the strict requirements of adoption under the DCG. In this article, we explore a number of these requirements. We also look at other factors usually considered by Water Companies and other asset owners. We identify five main reasons why a precast concrete attenuation tank is likely to be the safe, appropriate option for most SuDS applications.

1. Access for inspection & cleaning

Clause 3, of C7.8 in the new DCG code, requires tanks to have provisions for access for inspection and cleaning. More crucially, the DCG states that this should also include means of removing any sediment and preventing it from being washed downstream.

The UK has an average rainfall of 1,254mm per annum, and has an increased threat of flooding and persistent rain in the next few decades due to climate change. Despite silt traps, significant amount of sediment and debris enter attenuation tanks every year. The process of removing and retrieving that sediment from inside tanks could be a major challenge for some attenuation tank systems. Despite the fact that some geocellular systems are accessible via CCTV and remote-controlled maintenance equipment, it is not clear how sediment trapped inside such systems can be effectively collected and retrieved without being washed downstream. Only piped systems and modular attenuation tanks can offer sufficient access for maintenance and removal of sediment.

Some plastic pipe systems can be used for attenuation and offer man-entry for maintenance. But the ability of such systems to take sufficient water jetting pressure during cleaning remains uncertain. Within piped attenuation tank systems, only concrete pipeline systems can offer effective water jetting resistance (≥ 4,000 psi) sufficient to remove hardened sediment, grease and FOG.

2. Structural integrity and reliability

attenuation tanks are expected to be installed under fields, car parks and minor roads where a wide range of loads would be presumed. The strength of a tank and its ability to maintain structural integrity over its lifetime is key for its use. Concrete attenuation tanks made of modular precast units, box culvert units and concrete pipes have a long track record and proven performance over their expected design life. The units are designed to Eurocodes and BS 9295, and would account for lateral forces, such as acceleration and braking forces, where applicable.

Lightweight alternatives, such as geocellular tank, may not have such proven track record. Unless strictly designed to C737, the long-term performance of such units against a wide range of loads is yet to be understood fully. Decades after the installation of an underground concrete attenuation tank, articulated trucks can brake over that tank multiple times without any fear of collapse. It is not clear if a decades’ old lightweight tank can offer the same guarantees.

3. Life Expectancy

The expectation within the industry is for any infrastructure to last and function for 100-120 years. This is the life expectancy used in Susdrain’s B£ST tool to assess the sustainability and functionality of SuDS projects. It is a life expectancy that most lightweight attenuation systems, including geocellular tanks, do not meet. The main European standard for geocellular tanks, EN 17152-1, suggests a design life of 50 years. Some plastic pipeline standards, such as EN 13598, offer testing to fulfil a service life of 50 years or more. For concrete attenuation tanks made of modular units, box culverts or concrete pipes, Series 1700 of the Specification for Highway Works in England (NG 1704) suggests that such products are deemed as highway structures capable of fulfilling a design life of 120 years.

4. Carbon footprint

Despite concrete attenuation tanks being significantly heavier than plastic alternatives, there is a significant difference between both systems on embodied and operational carbon emissions. Most geocellular tank systems are made of mould injected polypropylene, which has a cradle-to-grave carbon footprint 30-40 times higher than an equivalent mass of precast drainage products. This massive difference is likely to double if a 100+ years SuDS development service life is considered. The end-of-life impacts of a precast concrete attenuation tank are also likely to be lower. A precast concrete tank can be dismantled and reused after the end of life. Even if demolished after the end of its service, the crushed concrete will absorb significant amounts of carbon dioxide and will be used as aggregates. On the other hand, a geocellular tank retrieved after 50 or 60 years will need to be recycled or incinerated, leading to further emissions which may exceed 900 kg CO2/t and 1340 kg CO2/t respectively. Leaving the plastic tanks underground after use will cause the plastic to decompose over hundreds of years, leading to further Greenhouse gas emissions.

5. Space constraints

Not all sites in need of SuDS can afford sufficient space for ponds or wetlands. Underground tanks are likely to be used in most existing urban sites as tanks can be built under estate roads and car parks. Precast concrete tanks offer a superior option in terms of space constraints as units can be installed in the tightest of places adjacent to existing structures without any concerns over structural integrity. Concrete attenuation tanks can also be installed with lower cover depths and can be installed much deeper compared to geocellular tank alternatives.

SuDS is still a relatively new concept. There have been lots of high-profile applications for almost all attenuation tank systems, but only time can tell whether these applications are successful and offer the asset owners value for money. As the use of attenuation tanks grows over the next few years, it will be possible for the industry to learn more about the strengths and flaws of each attenuation tank solution.