01. Medmenham Project
Background: RGS has worked with a major national flood risk consultant to assess the dangers presented at a historic site, on the banks of the River Thames in Buckinghamshire.
The assessment was necessary to enable the client to assess the site – which is in close proximity to the river and underlain by an aquifer - and involved installing boreholes, with standpipes, to undertake pumping tests as part of a hydraulic assessment and to assist preparation of a remedial action plan.
Contract requirements: Provide a cut-down light cable percussive rig for the second visit due to access restrictions. Pre-start site visits were undertaken by RGS Operations Director, Chay Rogers, who liaised with the client to establish access requirements and to establish a detailed knowledge of site characteristics.
The technical requirements included provision of:
- 1 pumping well with monitoring standpipes
- 7 observation wells with monitoring standpipes
- Full time professional attendance
- Second visit – installation of further monitoring standpipes using a cut-down drilling rig.
Boreholes were excavated using a light cable percussive drilling rig (cut down rig on the second visit) and standpipes installed at each location. Water was pumped from the main well, and levels taken simultaneously from the observation wells, in order to establish the hydraulic gradient, determine the potential yield of the main well, and assess the regional permeability of the aquifer.
Outcome: Successful risk flood risk assessment that included pump testing of an observation well to determine its potential yield and also the regional permeability of an aquifer.
Illustrations: Couple of photos (chosen to preserve site anonymity). Pump testing diagram if copyright restrictions allow, as below:
Please see pumping test diagram (taken from Foundations of Engineering Geology, A C Waltham, Blackie Academic and Professional, 1996, p37).