Large Multi-Disciplinary Site Investigation

Client / Cheshire West and Chester Council
Site / Baron's Quay, Northwich
Value / £255k
Timescale / May 2011 for 8 Weeks, plus monitoring

Summary

Sanctus Limited were employed by Cheshire West and Chester Council to undertake the intrusive ground investigation works for the proposed regeneration of the Baron’s Quay area of Northwich town centre. The investigation required a combination of different borehole and trial pitting techniques in order to achieve the objectives, within a busy town centre and car parking areas. Health and safety was a priority and strict controls were put in place to ensure safe working methods and that no danger was posed to the public at any time.

The work was required to assess potential environmental and structural issues at the site resulting from the industrial salt mining heritage of the local area in order to facilitate the proposed mixed commercial/residential development.

The investigation included deep rotary boreholes to a maximum depth of 56mbgl to investigate salinity of groundwater and the presence of voiding in the top halite bed. Relatively shallow light cable percussive to a maximum depth of 18.3mbgl, and windowless sample holes were drilled to investigate the shallow subsurface for structural and environmental issues. Sanctus also undertook the excavation of strategically placed slit trenches to determine the orientations and depths of underground utility apparatus within existing roads and pedestrian areas, and hand pits to determine the construction of the river wall.

Upon completion of the exploratory boreholes the positions and levels were surveyed, with coordinates related to Ordnance Survey Nation Grid References and Datum. Both two and three-dimensional plans were created.

A 3 month programme of gas monitoring was required on all cable percussive and windowless sample holes. Monitoring was carried out with a portable landfill gas meter (Geotechnical Instruments GA2000) with an external flow pod. A 6 month programme of groundwater and brine monitoring was also undertaken.

Sanctus carried out discreet interval no purge sampling. This method of sampling targets a defined depth in order to obtain the water samples required to determine the salinity of the natural deep groundwater without contaminating it with fresher groundwater above.

All field work was carried out in general accordance with BS5930: 1999 (amended 2007) and BS10175: 2011, the Construction Phase Health and Safety Plan and the CDM Regulations.