Geophysics on target at MOD site

In the last few months Phase SI has surveyed several areas at an MOD site where redevelopment and new building work is due to take place. The survey areas were a mixture of large grassed areas and smaller areas adjacent to existing buildings.

To meet health and safety requirements and to assist in their design the client needed to know the precise locations of buried utility apparatus within and adjacent to the development areas. MOD sites now fall within the planning process and to obtain planning approval an archaeological survey was also required. Previous experience of working on this site had shown the client that there were often buried features, associated with former structures, which were not shown on historical plans. They therefore wanted to identify if any such features where present within the new development areas.

Radio frequency location (RFL) and ground penetrating radar (GPR) were used for the utility tracing. The GPR survey was carried out on a series of regular survey grids and the data was processed and interpreted in the office. This approach makes increases the reliability of identifying utility apparatus and also allows other types of sub-surface features to be detected.

A magnetic survey was carried out over several large grassed areas. This is the standard technique for rapidly identifying archaeological features (areas in excess of 1.5 ha can be surveyed in a one day by a single operative) but it can also detect buried structures. The magnetic technique cannot be used in close proximity to buildings but the approach that Phase used for the utility tracing survey meant that the GPR survey could be used to help identify the presence of buried obstructions and to determine if possible archaeological features were present in these areas.

By combining different techniques Phase was able to meet several survey objectives. Our breadth of experience meant that the same operators could be used for all of the survey elements which resulted in significant cost savings compared to having the surveys done at separate times. Another key benefit was that the data from one technique and application could be used to help with another; the utility tracing GPR data could be used for the archaeological survey and the magnetic survey could identify metallic utility features in areas which could not be covered by GPR.