Project:Springfields, Spalding - Stormwater Management Design

Client: Interserve Projects

Date: 2003

Key Aspects:

SUDS Detailed Design, Stormwater detailed design, Hydraulic modelling, Best Value Engineering

Project Aims:

Development of a cost effective alternative stormwater drainage system to serve a new retail development. Utilising SUDS techniques to create cost savings and to reduce health and safety risks.

Project Summary:

The Springfields Outlet Shopping and Garden Festival development is located in Spalding, Lincolnshire. The entire site covers some 12 ha with 5.2 ha being paved and roofed area to be drained. Flooding protection up to 1 in 100 years protection was required.

Working in partnership with SEL Environmental, a conceptual SUDS design was developed as an alternative to a conventional stormwater drainage and storage scheme. Elevated groundwater levels precluded the use of infiltration drainage systems. The proposed scheme was based on providing discrete, shallow attenuation storage in the form of geocellular units with passive flow control. The system was modelled in InfoWorks to test compliance with the required design standards. The model was also used to optimise the required storage volumes and to check flood routeing during extreme rainfall events.

Ground conditions included high groundwater levels and unravelling soils at 2m depth. For these reasons, the scheme was designed
as a series of shallow storage tanks with shallow interconnecting pipework to reduce risk and to avoid delays during construction.
The properties of the geocellular storage units together with their very shallow depths were also utilised as sub-base replacement
to reduce the amount of imported material required.

Project : Nottingham Trent Park

Client : Trent Park Developments

Date : 2003

Key aspects

Assess risks posed by presence of methane and carbon dioxide in the ground and remove onerous conditions imposed by Local Authority, which were limiting the type of development.

Project aims

Demonstrate that the site is safe for residential housing redevelopment and obtain Local Authority Environmental Health Department agreement.

Project summary

The developer submitted a planning application for a luxury apartment block. The site investigation identified Alluvium below the site and low levels of methane were detected in an isolated borehole. The Local Authority stipulated that no residential development could commence until methane levels below 1% had been recorded for at least 2 years.

EPG were appointed to undertake a site risk assessment to demonstrate that the low levels of ground gas did not pose a risk. The source of the gas was organic material within the Alluvium which was trapped in the ground; significant active generation was not occurring.

The data enabled EPG to develop a conceptual ground and gas site model and a report derived from the available evidence clearly demonstrated there was no significant quantity of gas being generated. The report was presented to the Local Authority, which enabled a compromise to be reached regarding the gas problem. The project proceeded within a timescale that was acceptable to the developer.

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Project : Denton, Manchester

Client : SEL Environmental

Date : 2002

Key aspects

Design of in ground venting barrier system for prevention of landfill gas migration.

Project aims

To prevent the migration of landfill gas below the development site using a design incorporating an in ground barrier system, that permits the use of passive, rather than active, building protection measures

Project summary

The proposed site development of industrial units was hindered by gas migrating from an adjacent domestic and industrial landfill. Upon examination the gas migration was identified within a continuous sand layer in 6m depth Glacial Till deposits.

Gas migration within a discrete sand layer

The design comprised a virtual curtain barrier, which was installed using high capacity geocellular vents placed in a double overlapping row configuration to an 8m depth. The graph below clearly demonstrates the effect on gas levels within the migration layer provided by the installation of the virtual curtain barrier system; the system not only offered the client considerable cost savings over conventional barrier systems but also allowed the use of passive building protection measures as opposed to the active measures originally proposed

Figure 3 Gas concentrations in sand layer at 6m

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