The SUDS design comprises a multi-staged source control system and the perimeter gas protection measures include a 600m long Virtual Curtain no-dig in-ground gas interception and dilution system.  Work commenced on the 12 acre site in February and the retail complex is due to open in Easter 2013 and will include several major tenants including Marks & Spencer, Boots and ASDA.

There’s more to interpretation than looking for trends with changing atmospheric pressure.

Find out more by downloading the Technical Discussion Note “High frequency monitoring for LFG“.

The purpose of the meeting was to informally peer-review the map to assess its fitness for purpose.  EPG’s Steve Wilson spent an enjoyable and informative day working with the map and also exploring the other useful services  provided by the BGS.

All SuDS practioners who have to make decisions about whether infiltration is appropriate on a site, will find the map extremely useful.

Further information about the SuDS Infiltration Map can be found here.

The cost of annual calibration and servicing was a significant on-going cost for the council, which EPG has helped to reduce considerably.  This was achieved by a rigorous assessment of the geology and identification that gas migration was occurring along a preferential pathway.  Natural levels of background carbon dioxide were identified so that differentiation between natural sources and landfill gas could be made in the monitoring wells in the migration zone.  Gas modelling was used to confirm the extent of gas migration and the assessment also showed a reduction in migration over time.  This allowed the majority of the internal systems to be safely removed, except for a few houses located very close to the landfill.

As part of the review EPG also identified adjustments to be made to the gas extraction and flare systems to ensure that they continued to work effectively to limit gas migration from the landfill site.

Inchcape Ltd, who owns and operates the car showroom development at Slyfield Industrial Estate in Guildford, appointed EPG to review the options for maintaining the integrity of the gas venting and membrane system, whilst facilitating the slab settlement mitigation measures.

By working closely with Uretek, a solution was developed based on injecting Uretek expanding resin to a predetermined precision zoning arrangement that ensured the on-going efficacy of the gas protection layers.  The system was installed during November 2011, remedying the 200mm slab subsidence and returning the showroom to a much more functional facility.

Details of the Uretek slab lifting system can be found at www.uretek.co.uk/our_systems/slab_lifting/

Installation concept

Bardon’s remit includes construction of external paving to playgrounds and a MUGA and the installation of a surface water drainage system comprising several innovative source control SUDS components and incorporating Bardon SudsAgg, a sub-base modified to provide minimum 30% void ratio suitable for water attenuation beneath the impermeable pavements.

The installation is due for completion during November 2011.

The framework is to be used to determine a site specific consultation zone for each site outside which there is  reasonable confidence there is no risk to property from gas migration; for small, older sites this will be far less than the current default of 250m.

The approach will draw on EPG’s risk assessment skills and will also use guidance from other countries.   The approach should also be suitable for other areas  where there are many small infilled ponds, gravel pits or similar features that do not pose a significant risk of gas migration.

The system was designed for main contractor Cheetham Hill Construction and is currently under construction. Kirkby is the latest in an increasing list of HWRCs that have benefited from SUDS designed by EPG; the first being constructed at Barkers Lane for Bedfordshire County Council in 2005; the first to avoid a foul discharge by utilizing source control SUDS.

Installation Photographs

Shallow excavation blinded with granular bedding layer

Shallow excavation lined with protective geotextile layer

Robust welded impermeable geomembrane laid on geotextile

Plastic modular diffuser units incorporating floating oil treatment mats installed

This alternative method was presented at recent CIRIA and Environmental Protection UK seminars and also at the Scottish Contaminated Land Forum’s 2nd Conference in Advances in land Contamination Assessment and Remediation, held in Glasgow on 8^th September 2011.

The approach draws on Geoff and Steve’s experience, both in the UK and internationally, of ground gas investigation and assessment.  It should remove some of the uncertainty that currently can exist with gas monitoring results and also provides a faster and more robust method of assessment.  To date, consultation with leading consultants has received a favourable response to the approach.

The paper “A simplified approach to ground gas assessment” can be found on our technical forum.

The FRA demonstrates the suitability of the site from a flood-risk perspective and the report includes an outline sustainable drainage design that incorporates several source control techniques including pervious pavements, swales and dry retention basins with an emphasis on the amenity aspect of the system.