Hepworth Geolight stormwater management water attenuation units

GEOlight – Stormwater Management

GEOlight is an ultra lightweight honeycombed modular structure made from recycled PVC.The units are assembled to provide underground storage for control of stormwater and may also be used as a soakaway. The high void rate, high compressive strength and low resistance to water flow make GEOlight an ideal material for efficient and rapid underground water storage during storm conditions.

High compressive strength – can be located underroads, car parks and amenity areas
Reduced excavation costs – the very high void rate (95%) minimises the required volume of earthworks

Speed of installation – 1000m3 reservoir completed in one week

The honeycombe structure is highly permeable,offering low resistance to water flow

Geolight’s unique lateral and vertical filling arrangement requires a minimum amount of stone

Depth of attenuation units reduced by using patented lateral supply

Simplified distribution pipe network – dispensing with costly and complicated pipework configurations

Modular format offers flexibility in capacity and geometry of reservoir to overcome topographical restraints and architectural requirements

Greatly reduces the risk of flooding when used as stormwater storage

Can also be used for water recycling and combining with irrigation systems

Can virtually eliminate pollution when used in combination with petrol/oil separators

Design service available, including calculations

GEOlight applications

The Environment Agency is keen to promote the wider use of sustainable drainage systems, which reduce the impact of surface-water run-off. There are two main ways of storing surface water for stormwater management:
Stormwater attenuation
Soakaways

Stormwater attenuation

This consists of water storage capacity that holdsexcess surface water during periods of peak rainfall.
The stored water is gradually released in a controlled manner into the surface water drainage system or directly into watercourses, reducing the risk of flooding downstream.

Soakaways

Soakaways are designed to store surface water run-off until it can be gradually absorbed by the surrounding ground.

GEOlight

GEOlight has been specially designed to form underground water storage reservoirs in stormwater management schemes. It’s honeycombed structure gives it certain characteristics that make it ideal for this purpose:
The high void rate (95%) of GEOlight means that the maximum volume of water is stored in the minimum overall volume.
High compressive strength. GEOlight is available in two strengths as standard; 200 and 400 kN/m2.
Note: Higher compressive strengths available from 600 to 1000 kN/m2 – please contact Hepworth Technical Advisory Service for further details.

The graph on the right shows the results of a compression test, where samples of GEOlight 400 were compressed at 1mm per minute.The deformation at 400 kN/m2 is about 1.6%.

Other uses

The water storage ability of GEOlight lends itself to a number of other uses:
Water recycling combined with irrigation systems – this is increasingly popular: GEOlight is used to retain stormwater which is then pumped as required to a network of standpipes for irrigation.
Drainage channels – the natural permeability of GEOlight lends itself for use as an underground drainage channel that collects and drains away groundwater.
Pollution control – when used in combination with oil/petrol separators, GEOlight can replenish groundwater without the risk of contamination from oil, chemicals or suspended solids.
To form lightweight embankments – GEOlight can be used to quickly form the base of embankments that only weigh a fraction of earth embankments. GEOlight – an efficient and economic solution for stormwater management

The costs in the table below have been complied by independent cost consultants using data provided directly by the companies who supply the products.

*Excavating and backfilling not included

Stormwater Attenuation – an explanation

The GEOlight Stormwater Attenuation System consists of two manholes (inspection chambers) connected by a length of perforated distribution pipe which feeds the stormwater storage reservoirs on either side formed from GEOlight.

The distribution pipe is normally from 225mm up to 500mm diameter, generally covered in a trench filled with draining material, such as 15/25 clean graded stone, free from fines.

The reservoirs and distribution pipe are wrapped in a waterproof membrane, such as butyl, to prevent seepage of water into the surrounding ground.The top of each GEOlight reservoir has a vent which is connected back to the upstream manhole.

A geotextile or 10 mm mesh geogrid is laid between the distribution pipe and GEOlight to prevent the GEOlight units being clogged by the draining materials.

How does it work?

1. In normal conditions, water enters a back drop manhole.This is the upstream manhole and any silt or sediment will collect in the bottom of the chamber. The water then flows along the distribution pipe into the downstream manhole.
The upstream pipework is sized to cope with normal flow conditions.The distribution pipe and attenuation tank are sized to cope with storm conditions.The outflow pipe is sized to cope with the permissible discharge.

2. In storm conditions the flow restrictor (vortex flow control or orifice plate) in the downstream manhole limits the amount of water flowing out of the manhole.This causes the water level in the distribution pipe to rise and water to spill into the GEOlight reservoirs on either side. As the water level rises in the reservoirs, air is forced out of the high level vents into the upstream manhole.

3. Once the storm has passed, the water level in the GEOlight reservoirs gradually falls as water passes through the flow restrictor in the downstream manhole.The vents now allow air to return into the GEOlight reservoirs. Gradually the reservoirs empty.

The flow restrictor prevents excess surges of flood water to pass downstream and uses the storage reservoirs to store the water for the period of the storm.

Calculating the storage capacity

The storage capacity of the GEOlight reservoirs isdetermined by the maximum outflow permitted, (set by the water company or Environment Agency), the impermeable area of the site and the rainfall return period – normally 1 in 30 years, but again can be dictated by the water company.

A full design service, including calculations, can be supplied via a third party consultant. Please contact Hepworth Advisory Service for details.

Stormwater Attenuation - Typical details

The details on these two pages illustrate the construction of a typical GEOlight Stormwater Attenuation System.The length and height of the GEOlight reservoirs is determined by the quantity of water to be stored.

On the right are three commonly used arrangements of distributor pipe and GEOlight reservoir.The layout of each scheme is purpose designed to suit the characteristics and limitations of the site.

The high performance waterproof membrane should be continuous around both GEOlight reservoirs and the distributor pipe and granular fill. It is protected by a heavyweight needle punched, non woven geotextile.
A high flow geotextile is placed between the granularfill and GEOlight reservoirs to prevent silt and particles being washed into the reservoirs.

Stormwater Attenuation – Installation

Excavation and preparation
Standard preparation involves excavation to theinvert level the of tank.The ground must be prepared to a level of ± 20mm. All sharp objects and protrusions should be removed and the surface should be blinded with sand if necessary.
Allow for at least one metre of work space around the perimeter of the tank, depending on the depth of excavation.

With GEOlight, the amount of excavation can be reduced by up to 50% compared with other systems. This is because the pipe inverts and the bottom of the tank are at the same level and no pipework or stone is required beneath the GEOlight tank.

Geotextile layer
Lay the protective geotextile over the excavated area ensuring enough material is prepared to completely encase the system with the minimum number of joints.

Lay an impermeable membrane over the geotextile layer.

GEOlight installation
Lay the GEOlight units to the layout plan provided. The units are light and easy to lift and place into position, keeping labour time on site to an absolute minimum.

The GEOlight units are laid to a bonded pattern until the full depth of the attenuation tank has been reached.

Pipework/stone
The distribution pipe is now installed.
Install the distribution pipe and connect, via rocker pipes, to the upstream and downstream manholes (inspection chambers) situated at either end of the tank.

All joints through the membrane should be made using preformed or site fabricated top hat connections.

Normally only one distribution pipe is required per attenuation tank.This dispenses with the configuration of pipework usually necessary with other systems, saving time and reducing cost.

Unlike any other modular system GEOlight’s unique lateral and vertical filling arrangement requires a minimal amount of stone.

Encasing membrane
On completion of the GEOlight units and distributor pipe, fold the waterproof membrane over the sides and top of the tank to completely encase it. Sealing the joints provides a watertight reservoir. Membrane should be jointed with at least a 100mm overlap and can be sealed either by double sided tape, or hot air weld (depending on the type of membrane specified).

Wrap the protective geotextile over the waterproofmembrane, allowing for a 300mm overlap at the joints.

Backfilling
Once the tank is completed to the layout drawing and completely encased with the appropriate membrane and geotextile (filter layer), backfilling using selected as dug type material or similar can be carefully carried out to the specification for the standard onsite drainage detail.

Anticipated installation time to prepared ground

Using evidence from onsite installation it is possible to install 1000m3 attenuation tank in one week using 4 operatives.

Wet site conditions (high water table)
A wet site is defined as one where groundwater rises above the base of the tank. Where difficult ground conditions are encountered, i.e. unstable ground or shrinking clay, it will also be necessary to allow for an additional depth (as much as deemed necessary by the supervising engineer) to be excavated below the tank to allow for hardcore and sand blinding to provide a firm base.
In poor soil conditions it will also be essential to make substantial provision for planks, struts and temporary shuttering and to provide for adequate pumps to keep the excavation free form groundwater at all times during the course of the work.

Flotation

It is important to ensure that the GEOlight system will not be subject to flotation caused by groundwater pressure.To overcome this, the weight of the soil covering the top of the GEOlight must be greater than the uplift force caused by the systems buoyancy in the water. Most fill types will achieve this if the depth of cover fill is equal to or greater than the depth of the groundwater from the base of the GEOlight units.

Final inspection

After installation and prior to handover, any silt collection chamber or control manholes should be examined to ensure they are free of debris or contamination.

Handover
The site owner/agent should be advised of the following:
the location of the GEOlight system
maximum vehicle weight which may be trafficked across the area
NB It may be necessary to install signage, traffic cones, barriers etc, to prevent heavy vehicles from trafficking over the the GEOlight installation, unless the system has been specifically designed for heavy loading.

Soakaway Applications

Soakaways are a simple and traditional way of dispersing surface water where connection to the surface water drainage system is impractical. However, as part of the move to Sustainable Urban Drainage Systems and changes in the Building Regulations, the use of soakaways is preferable, where soil conditions allow.Where this is not possible, other options must be considered, such as attenuation to discharge to sewer, with the water company’s consent.

Directing run-off from roofs and hard paved areas directly into the ground via soakaways helps replenish groundwater and can recharge aquifers. Soakaways reduce the burden on treatment works and, by slowly releasing water into the ground, they reduce the risk of flooding.

The modular form of GEOlight means that soakaways can be sized to serve any size of development from a single house to a large industrial/ commercial development. The use of soakaways to serve roads and car parks, where water can become contaminated, will only be acceptable where the water first passes through an oil/petrol separator.
A check should be made with the local authority and the Environment Agency for their requirements.

Sizing the soakaway
Hepworth Technical Advisory Service can estimate soakaway sizing based on EN 752-4, where no infiltration tests are known.

Alternatively a design to BRE Digest 365 can be supplied providing the following test results (see box below) and the area of the impermeable surfaces that drain into each soakaway are available.

Surface Water Soakaway Design

Soil Infiltration rate calculation

1. Excavate a hole in the same location and to the same depth as anticipated in the full size soakaway. The base should be a metre below the invert of the incoming drain connection. The trial pit should be 0.3 to 1m wide and 1 to 3m long. It should have vertical sides trimmed square and if necessary for stability, should be filled with granular material. If so, a length of perforated pipe should be placed vertically in the pit to the full depth to allow water levels to be measured.
The trial pit width, length and effective depth should then be measured.

2. Fill the trial pit as quickly as possible with water to the maximum effective depth. Measure the time in minutes for the water to drop between 75% and 25% full. Repeat the test three times and note the time for each.

3. Results-
Width (m)=
Length (m)=
Effective depth (m)=
Time to drain between 75% and 25% full:
Test 1 (mins)=
Test 2 (mins)=
Test 3 (mins)=

How does it work?

1. Surface water is collected from roofs and hard paved areas into a surface drainage system.This discharges into a silt pit, containing a silt collection bucket.The outlet from the silt pit is to a perforated distributor pipe, from which water discharges into the GEOlight reservoir directly below.

2. During periods of heavy rainfall, the rate at which water is flowing into the GEOlight reservoir is greater than the ground can absorb and the GEOlight reservoir gradually fills with water.

3. Once the flow from the distribution pipe has seized, the water level in the GEOlight reservoir falls as water gradually seeps into the surrounding ground.

Maintenance
The silt pit has a silt collection bucket, to prevent clogging of the soakaway with silt. The silt collection bucket should be checked every few months and any significant silting-up should be removed.

The silt pit and rodding access provide access to the distribution pipes for checking and if required cleaning by jetting.

Trafficked areas
It is important that infiltration below trafficked areas and close to structures (5m minimum from a building) will not soften the underlying or surrounding soils.This application should be checked with a Geotechnical Engineer and care taken not to cause settlement.

Soakaways – Typical details

Soakaways – Installation

Excavation and preparation

All sharp objects and protrusions should be removed and the surface should be blinded with sand if necessary.
Allow for at least one metre of work space around the perimeter of the tank, depending on the depth of excavation. Allow for 100mm granular bed.

Geotextile/filter layer
Lay the protective geotextile over the excavated area ensuring enough material is prepared to completely encase the system with the minimum number of joints.

GEOlight installation
Lay the GEOlight units to the layout plan provided. The units are light and easy to lift and place into position, keeping labour time on site to an absolute minimum.
The GEOlight units are laid to a bonded pattern until the full depth of the attenuation tank has been reached.

Encasing geotextile

On completion of the GEOlight units, fold the geotextile over the sides and top of the units, allowing for a 300mm overlap at the joints.

Distribution pipe
Lay the distribution pipe to the layout plan, including the required backfill.

Backfilling
Backfill with granular material around the sides of the soakaway units.Then carefully backfill using selected as dug material to the specification for the standard onsite drainage detail.

Final inspection
After installation and prior to handover, any silt collection chamber should be examined to ensure they are free of debris or contamination.

Handover

The site owner/agent should be advised of the following:
the location of the GEOlight system
maximum vehicle weight which may be trafficked across the area
NB It may be necessary to install signage, traffic cones, barriers etc, to prevent heavy vehicles from trafficking over the the
GEOlight installation, unless the system has been specifically designed for heavy loading.

Product Data

* Note higher compressive strengths available

Decision tree

1. Building Research Establishment, Soakaway Design, Digest 365, September 1991
2. Roger Bettess, Construction Industry Research and Information Association, Infiltration Drainage –
Manual of good practice, CIRIA Report 156, 1996
* GEOlight can be used in areas trafficked by commercial and HGV vehicles, however, specific design advice should be sought from Hepworth for these applications.

COSHH and Handling Information

1. Composition/Information on ingredients
Hazardous Ingredients:
None as finished goods and products
Types of materials:
Polyvinyl chloride (PVC)
MEK

2. Hazards Identification
Nature of Hazard:
There are no health risks from the products during normal use.
The products may contain various pigment colours and stabilisers that may be toxic.These chemicals are, however, bound within the product material and not easily extracted.

3. First- Aid Measures
Eye Contact:
Plastic materials may cause physical irritation in the eyes.Wash out with large amounts of water. If irritation persists, seek medical advice.
Skin Contact: Not applicable
Inhalation: Not applicable
Ingestion: Not expected to have any toxic effects

4. Fire-Fighting Measures
Extinguishing Media:
On small fires use any hand-held extinguisher type.
On large fires use water.
Fire and Explosion Hazards:
Melting plastics may flow and spread in a large fire.
Products of fire will be thick black toxic smoke.
Material Characteristics:
PVC products will burn in the presence of a flame but are classed as self – extinguishing.
Protective Equipment:
Wear self-contained breathing apparatus and protective clothing.

5. Handling and Storage
Handling:
There are no hazards associated with the finished products. However, when cutting GEOlight, we recommend that the correct tools are used e.g. Handsaw or Alligator saw.When cutting dusts may be created. Avoid inhaling these dusts.
Take care of heat build-up within materials during cutting etc.
The pallets of GEOlight units should be placed on level ground and should not be stacked on site.
The maximum weight of the pallet of GEOlight units as delivered to site is 650kg, including packaging.
Machines used to lift the pallet should be able to lift this weight safely.
Loose individual units should not be stored more than three units high.
GEOlight units are lightweight ranging from 23kg to 55kg and can be easily handled – one or two person lift.
Storage:
GEOlight units will resist the effects of UV light for up to six months. However, prolonged storage in direct sunlight should be avoided.

GEOlight units should not be stored near to any fuel storage areas or any other solvents.
GEOlight units are very robust and resistant to damage during normal handling. However, they should be secured in areas where impacts from vehicles or construction plant will be avoided.

6. Exposure Controls/Personal Protection
Respiratory Protection:
Not required under normal conditions of use.
Where cutting, etc, creates dusts, wear a disposable half-mask to the standard FFP2S.
Hand Protection:
Wear impervious strong gloves to prevent cuts to the hands while handling,cutting,etc.
Eye Protection: Wear safety glasses when cutting,etc.
Skin Protection: Wear overalls

7. Site Hazards
Other Hazards for consideration:
Working in excavations and trenches - GEOlight may be designed with a shallow invert for infiltration (soakaway) or attenuation (storage) system.This negates the need for deep excavations or trenches.
Excavation near services e.g gas,electricity
Contaminated soil areas.

N.B. All risk assessments should be undertaken by the main contractor
relating to fire, lifting the units by excavator/forklift, access to and working in
excavations and trench support.

8. Stability and Reactivity
Decomposition Products:
Major thermal decomposition products are oxides of carbon. Relevant differences are (in addition):
PVC may produce amounts of Hydrogen Chloride.
Stability:
These materials are stable at temperatures up to normal operating limits (moulding parameters)

9. Ecological information
Biodegradability:
Plastic products are not readily biodegradable but are not detrimental to terrestrial wildlife.
Aquatic Toxicity:
Non-toxic to marine life.

10. Disposal Considerations
Method:
The preferred method is collection and re-cycling.
Plastics can safely be placed with regular industrial or household wastes where re-cycling is not available.

11. Other Information
This data sheet has been compiled by Hepworth Building Products, using the original manufacturer’s information.This information is provided without any representation to its accuracy and does not constitute a guarantee of the product or its properties.
As the handling,storage ,use and disposal of the product are beyond our control , Hepworth Building Products disclaim all liability for loss,damage,injury or expense in any way connected with such activities and further make no warranties ,express or implied ,as to the suitability of the product for any particular use.

Advisory Services

Technical Advisory Service
This service covers all aspects of Hepworth products from design through to maintenance.
- Hydraulic and structural design
- Quantity take offs and material scheduling
For any advice or assistance on these matters contact the Technical Advisory Service on:
Tel: 0870 4435551 Fax: 0870 4435552

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