Site Investigation – West Sussex

Summary

Omnia were commissioned by our client to undertake an intrusive site investigation at Ford Airfield in Arun, West Sussex. The site had historically been used as an airfield from 1918 up until 1980 with the military using the airfield during the Second World War up until 1958. Since 1980, the site was predominantly used for agriculture, but areas of the former runway are still present, as well as former Highways and Haulage yards.

The airfield is now the subject of a planning application to develop up to 1,500 residential dwellings as well as commercial and office spaces, a primary school, local centre and public open space.
The purpose of Omnia’s intrusive investigation was to provide information on potential sources of contamination on site as well as providing geotechnical characteristics of the soils beneath the site.

Scope of Works

Previous investigations had been undertaken at the site which were reviewed by Omnia, with areas requiring further investigation identified. Omnia identified the following areas where further investigation was required in order to obtain sufficient information:

• Geotechnical characteristics of the soils underneath proposed roadways.
• Geotechnical characteristics of the soils beneath proposed areas of residential development in the north and the south of the site.
• Chemical concentrations and composition of soils within areas of identified potential contamination sources. These areas included areas of the former runway, identified geophysical anomalies on-site, an infilled canal, the highways and haulage yards and an area of previously identified elevated concentrations.

The intrusive investigation was undertaken in October and December 2024 during which the following works were undertaken:

• Eighty-five trial pits were advanced to collect samples for CBR testing beneath proposed roadways to inform roadway design.
• Four Cable Percussion (CP) boreholes, thirty Window Sampling (WS) boreholes and thirteen trial pits were advanced to undertake in-situ geotechnical testing and to collect soil samples for laboratory geotechnical testing in areas of proposed residential development in the north and the south of the site to inform foundation design.
• Twelve WS boreholes, forty-nine trial pits, nine hand dug pits and four stockpile samples were advanced within areas of identified sources of potential contamination in order to obtain soil samples for chemical analysis and to determine the vertical and lateral extent of any visual contamination.

Ground conditions within all locations were logged and recorded in accordance with British Standard BS5930 by an Omnia engineer.

Outcome

All CBR data obtained from soils beneath the proposed roadways was reported to Omnia’s client via a Factual Report which could be used to inform the appropriate design of the roadways.

Interpretive reports were produced detailing the ground conditions encountered and the results of the in-situ and laboratory geotechnical testing within the two areas of proposed residential development. The reports included proposed design bearing capacities for foundation design, concrete classification of on-site soils and recommendations for further works.

A detailed interpretive report, including a Tier 1 risk assessment based on residential end use, was produced detailing the ground conditions encountered and the results of the laboratory chemical analysis of soils within areas of identified potential sources of contamination at the site. Elevated concentrations of contaminants were recorded in multiple areas across the site and the report included an analysis of the elevated concentrations and recommendations for further works required.

Next Steps

Based on the findings of Omnia’s intrusive site investigation on this site in West Sussex, we have recommended to our client that further investigation is required in areas of the site to determine the extent and potential impact of identified contamination. Where the extent of contamination has been suitably determined, it has been recommended that remediation is undertaken, following a remediation method statement, to make the site suitable for use.