investigation of a potential groundwater resource in glacial

INVESTIGATION OF A POTENTIAL GROUNDWATER RESOURCE IN GLACIAL SEDIMENTS AND DEVONIAN OLD RED SANDSTONE AT CAP GLAS, BETTWS,

MONMOUTHSHIRE

Mhairi Garner MSc AEG 2009-2010

Investigation of a Potential Groundwater Resource in Glacial Sediments and Devonian

Old Red Sandstone at Cap Glas, Bettws, Monmouthshire

1) Project Outline and Objectives2) Location/Site Description3) Literature Review4) Desk Study5) Techniques of Field Data Collection and Analysis6) Factual Report7) Interpretive Report8) Conclusions and Recommendations9) References



Project with the British Geological Survey (BGS) (Cardiff Office) and Cardiff University (SEOS).

Cap Glas Court: Wants water. Spring supplies 3 cottages. Previously drilling unsuccessful (42m sandy drift).

To involve GI to identify underlying geological conditions, glacial topography and history .

To determine if: there is a likely source of water and suitable geological conditions to provide sufficient yield for abstraction.

To identify the geomorphology and nature of the glacial features in the project area

To identify rockhead To identify water bearing

strata

1a) Project Outline 1b) Objectives

Investigation of a Potential Groundwater Resource in Glacial Sediments and Devonian Old Red Sandstone at Cap Glas,

Bettws, Monmouthshire

2a) Location

2b) Site Description

o Bettws /Gavenny Valleyo Black Mountainso Brecon Beacons National Parko Sandstone ridgeso Springso Streamso Groundwater flow Figure 1. Site Location (OS National Grid

References)



3) Literature Review Geology 1. Bedrock: Silurian Wenlock rocks (Usk); The Devonian Old Red Sandstone; Carboniferous SWAnglo-Welsh Basin. Lower ORS (red): almost entirely continental, fluvial deposits; coarsen upwards. Senni Beds/Brownstones form hills (Barclay et al. 2005, p. 3). 2. Quaternary Glacial DepositsPleistocene glaciations. Mid-Wales ice sheet maybe flowed into Black Mountains, Usk glacier to S (Lewis and Thomas, 2005). Barclay (1989) good summary of deposits.3. Other Minor Quaternary Deposits (Barclay 1989). Hydrogeology Devonian ORS minor aquifer (springs, important locally), CaHCO3 rich waters, main flow mechanism is fracture flow , drift (Moreau et al. 2004; Barclay 1989).

Figure 3. Moreau et al. 2004.

Figure 2. Williams et al. 2004



4) Desk Study Geography/Natural

Heritage Topography Geology Hydrogeology Hydrology and Meteorology Site History Services Geological Model Site Investigation

Figure 4.

Figure 5. Figure 6.

5) Techniques of Field Data Collection and Analysis1. EDM/GPS Topographic Surveying – Various EDM problems.

GPS (Topcon HiperPro GPS+).

2. Geomorphological Feature Mapping - Airphoto/stereoscopic analysis;

airborne radar (NEXTMap) /OS digimap data analysis; ground truthing.

3. Soil Sampling – Hand augering, BS5930.

4. Geophysical Investigation (McCann, 1997) Electrical Resistivity –Wenner-Schlumberger; 5m spacing. GPS. 2 lines. GW. Seismic Refraction - Frequency 10Hz, 48 channels/geophones, geophone

spacing 2m. Various shots. Depth to rockhead.

5. Rainfall Data – Environment Agency Tal-y-Maes rainguage and local residents data.





6) Factual report

1. Topographic Survey and Geomorphology

EDM/GPS Radar and OS

Digimap Data Feature Mapping

2. Soil Mapping3. Geophysical

Investigation Electrical

Resistivity Seismic Refraction

4. Rainfall

Figure 7. Geomorphological Map



6) Factual Report cont.... Figures 8 to 12



7) Interpretive report Geomorphological Setting1. Geomorphological /Topographic Features2. Slope angles3. Soil Sampling4. Seismic Refraction5. Land System Setting Water Movement1. Electrical resistivity2. Water flow Conceptual Model

Figures 13-14

Figure 15. Final Conceptual Model.

Conceptual Model



Constructional terminoglacial environment: terminal mounds; kame terrace; glaciofluvial deposits; regional terminoglacial deposits. Over Steepened W Valley side. Boundary between glaciers from N and S. Devonian ORS minor aquifer (SST presence), drift, Springs GW flow from large catchment area, fracture flow to 50m, regional groundwater flow SW, WT in bedrock (maybe drift).Problems: slope angles, ER error, wider SR shots, hand augering, ground truthing, more scope for hydrogeological investigation.

The study area is classed as a constructional terminoglacial land system setting.

Drilling into bedrock should yield a good sufficient water supply.

Bedrock conceptual modelling shows ~50m depth (perhaps to 70m or so) for drilling.

>1 attempt may have to be made to hit water.

Glacial drift may hold water.

Conclusions Recommendations



References Barclay, W. J. 1989. Geology of the South Wales Coalfield, Part II, the

country around Abergavenny. London: HMSO. Barclay, W. J. et al. 2005. The Old Red Sandstone of Great Britain.

Peterborough: JNCC. Lewis, C. A. and Thomas, G. S. P. 2005. The Upper Wye and Usk Regions. In:

Lewis, C. A. and Richards, A. E. Eds. The Glaciations of Wales and Adjacent Areas. Bristol: Arrowsmith. pp. 101-128.

McCann, D. M. Culshaw, M. G. and Fenning, P. J. 1997. Setting the standard for geophysical surveys in site investigation. Engineering Geology Special Publications 1997; 12; p. 3-34. London: Geological Society.

Moreau et al. 2004. Baseline Report Series: 12. The Devonian Aquifer of South Wales and Herefordshire. Solihull: Environment Agency. Keyworth: British Geological Survey.

Williams, B. P. J., Marriott, S. B., Hillier, R. D. 2004. Preface: The Lower Old Red Sandstone of the Anglo-Welsh Basin: an introduction. Geological Journal 39(3/4).

investigation of a potential groundwater resource in glacial

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