Hydrogeological investigations at Morestead, Twyford, 2008-2009
Sorensen, J.P.R.; Butcher, A.S.; Stuart, M.E.. 2010 Hydrogeological investigations at Morestead, Twyford, 2008-2009. Nottingham, UK, British Geological Survey, 39pp. (OR/10/011) (Unpublished)Before downloading, please read NORA policies.
This report describes work undertaken at Morestead, Twyford as part of a BGS research project “Nitrate Fluctuations in Groundwater”. The project uses the same site as that described in Stuart et al. (2008a) for the project “Nitrate Mass Balance in the Saturated Zone”. A new borehole (Borehole B) was drilled in October 2008, located 10 m to the west of the existing one (Borehole A) to complement the existing infrastructure. During drilling the cuttings were inspected but no systematic recording of lithology was undertaken, as this information was already available in detail from the adjacent borehole. Borehole B was completed to a depth of 70 m and was cased to a depth of 12.7 mbgl; remaining unsupported below this. It should be stated that the casing protruded approximately 0.16 m above ground level. Initial geophysical characterisation was undertaken to evaluate the hole and its suitability for further testing. A multi-level sampler was installed in Borehole B during autumn 2008 when the groundwater level was low. The aim was to capture samples as the water table rose towards the anticipated spring 2009 high. The sampler worked well for most of the period, but there were issues with bottles not filling consistently, and the sampler length was insufficient to cope with rapid water level rise following heavy rainfall or snow melt. Samples retrieved were analysed for chloride, sulphate and nitrate (as NO3), which ranged between 16.9 and 68.8 mg/l, 11.7 and 29.9 mg/l, and <0.6 and 60.1 mg/l, respectively. Concentrations of nitrate appeared to increase as the water table rose above 20.5 mbgl; below this depth there is significant noise. Concentrations of sulphate and chloride both increased as the water table rose. Gamma and resistivity logs identified marl horizons which correlated with the Borehole A core as reported in Stuart et al. (2008a). Fluid and flow logs also indicate hydraulic layering within the Chalk. Temperature and conductivity logs suggested vertical flow below c. 25 m below casing top, which is was also supported by heat pulse flow meter (HPFM) and impeller flow logs. This flow regime was unaltered by pumping from a depth of 21.5 m indicating reasonable permeability in the Chalk above this depth. A nitrate sonde was also run before and during pumping. The results are currently awaiting calibration and are not available at the time of reporting. Groundwater levels were monitored in Borehole A and fluctuated over a range of 13.5 m, from around 10 to 23.5 mbgl, between December 2006 and the beginning of March 2009. However, numerous gaps in the data remain due to water levels exceeding the range of the pressure transducer initially installed in the borehole. Water levels were notably responsive to rainfall between December and February, for example between 25th January 2009 and 23rd February 2009 the water table rose by 8.7 m. The aquifer appears less responsive during summer and autumn when there is likely to be a greater soil moisture deficit.
|Item Type:||Publication - Report (UNSPECIFIED)|
|Programmes:||BGS Programmes 2010 > Groundwater Science|
|Additional Information. Not used in RCUK Gateway to Research.:||This item has been internally reviewed but not externally peer-reviewed|
|Additional Keywords:||GroundwaterBGS, Groundwater, Aquifer characterisation, Groundwater resources|
|NORA Subject Terms:||Earth Sciences|
|Date made live:||21 Jul 2010 09:05|
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