On the use of photobleaching to reduce fluorescence background in Raman spectroscopy to improve the reliability of pigment identification on painted textiles

Subjecting a specimen of red lead watercolour paint on silk to photobleaching was demonstrated to be a simple means by which to engineer a reduction in the magnitude of the fluorescent background that was approximately exponential with time, with a corresponding improvement in the signal to noise ratio of the Raman spectrum, thus rendering the characteristic peaks more easily visible and allowing more confident identification of the pigment. However, relative heights of the Raman peaks obtained from the sample were seen to alter progressively as a result of irradiation, indicating that some component of the sample was undergoing degradation that may result in longer-term damage to a fragile historic artefact. It was also shown that crystals of the lead monoxide pigment massicot were present in the samples ofred lead on a painted silk artefact dating from 1750. It is concluded that this was either due to deliberate mixing of pigments by the artist, contrary to historic records, or as a result of the roasting techniques used to create red lead pigments at the time and not due to thermal degradation of the pigment during Raman analysis

Simple methods for assessing groundwater resources in low permeability areas of Africa

In many areas throughout Africa, a staggering proportion of wells and boreholes fail. Failure can occur for a number of reasons – inadequate maintenance and community involvement, poor engineering or a lack of water. Often it can be difficult to work out the exact reason after the event. However, in many geological environments the impacts of poorly sited and designed boreholes and wells are a major concern to funding agencies, implementing institutions and local communities. In such areas, good supplies of groundwater cannot be found everywhere, and boreholes and wells must be sited and designed carefully to make use of the available groundwater. To appropriately site and design water sources, the groundwater resources of an area need first to be investigated to understand how water occurs in the ground. In this manual we present some techniques that allow a quick assessment of groundwater resources without requiring much expertise or expense. Some of the techniques are old and established while others are new. However, all techniques have been tested by BGS (and others) in assessing groundwater resources in Africa. This manual does not claim to be a detailed textbook for hydrogeologists – there are enough already (see reading list at the end of the chapter). Rather it is meant as a practicalaid for those involved in the practice of rural water supply, particularly in Africa. Little training or equipment is required for the tests and they can all be carried out in a short space of time. The manual is divided into six sections. The first gives an overview of the groundwater resources of sub-Saharan Africa (SSA) and discusses the scope and detail of investigations required in different geological environments. The remaining chapters describe simple techniques for assessing groundwater resources, from basic reconnaissance to assessing the yield of a borehole. In the appendix are summary sheets of the most common techniques which can be photocopied and used in the field

Using CFCs and SF6 for groundwater dating : a SWOT analysis

A knowledge of the residence time of groundwater is of importance in understanding key issues in the evolution of water quality. Chlorofluorocarbons (CFCs) and sulphur hexafluoride (SF6) offer a convenient way of dating waters up to ~60 yrs old. In contrast to tritium, these gases are well-mixed in the atmosphere so their input functions are much less problematic. While any one of these gases can in principle provide a groundwater age, when two or more are measured on water samples the potential exists to distinguish between different modes of flow including piston flow, exponential flow and simple endmember mixing. As with all groundwater dating methods, caveats apply. Factors such as recharge temperature and elevation must be reasonably well-constrained. Mainly for SF6, the phenomenon of ‘excess air’ also requires consideration. Mainly for the CFCs, local sources of contamination need to be considered, as do redox conditions. For both SF6 and the CFCs, the nature and thickness of the unsaturated zone need to be factored into residence time calculations. This paper attempts a balanced look at the pros and cons of the trace-gas dating method

UNICEF IWASH Project, Northern Region, Ghana : an adapted training manual for groundwater development

This report is an adapted training manual, with specific best practice recommendations for groundwater development practitioners working in the Northern Region, Ghana. It is designed to be used in conjunction with the existing comprehensive training manual ‘Developing Groundwater: a guide to rural water supply’ by MacDonald, Davies, Calow and Chilton (2005). The additional guidelines provided in this supplementary report are specific to the Northern Region of Ghana, and have been informed by a review of groundwater development in the region which BGS carried out on behalf of UNICEF in 2010-2011. The Northern Region is a difficult area in which to find and develop groundwater resources. For this reason, more resources – time and money – need to be focussed on careful borehole siting and development in order to maximise success. This includes detailed desk and field reconnaissance surveys; the effective use and interpretation of geophysical siting methods; collection of good quality data during drilling and test pumping; rigorous recording and management of data; and effective interpretation, sharing and use of hydrogeological information by all groundwater development practitioners. This report, and the associated manual ‘Developing Groundwater’, provide practical help for carrying out these activities effectively. The authors gratefully acknowledge those persons who contributed to the formation of these guidelines, who include: UNICEF Ghana – Othniel Habila, Kabuka Banda and David Ede Community Water and Sanitation Agency (CWSA), Ghana – John Aduakye Canadian International Development Agency (CIDA) – Hydrogeological Assessment Project (HAP) – James Racicot All participants at the UNICEF/BGS workshop and training programme held in Tamale, Northern Region, from 7 to 18 February 2011

User guide : Aquifer Productivity (Scotland) GIS Datasets. Version 2

This report describes a revised version (Version 2) of the aquifer productivity (Scotland) datasets produced by the British Geological Survey (BGS). There are two maps: bedrock aquifer productivity and superficial deposits aquifer productivity. Version 1 of these datasets was produced in 2004. Version 2 uses updated geological linework and a slightly modified methodology. The aquifer productivity maps describe the potential of aquifers across Scotland to sustain various levels of borehole water supply, and the dominant groundwater flow types in each aquifer. The bedrock aquifer productivity map has five aquifer productivity classes (very high, high, moderate, low and very low); and three groundwater flow categories (significant intergranular flow; mixed fracture/intergranular flow; and fracture flow). The superficial deposits productivity map has four productivity classes (high; moderate to high; moderate; and a category to signify that a deposit is ‘not a significant aquifer’). All superficial deposits aquifers in Scotland are assumed to have primarily intergranular groundwater flow. The aquifer productivity maps are a tool to indicate the location and productivity of aquifers across Scotland. They have been used to help characterise groundwater bodies as required by the Water Framework Directive, and may have several other uses, including in policy analysis and development; to prioritise aquifer and site investigations; to inform planning decisions; and to improve awareness of groundwater in general. The complexity and heterogeneity of geological formations means that the maps are only a guide. They are designed to be used at a scale of 1:100,000, and not to assess aquifer conditions at a single point

Developing a preliminary recharge model of the Nile Basin to help interpret GRACE data

GRACE data provides a new and exciting opportunity to gain a direct and independent measure of water mass variation on a regional scale, but the data must be combined with hydrological modelling to indicate in which part of the water cycle the mass change has occurred. Processing GRACE data through a series of spectral filters indicates a seasonal variation to gravity mass (±0.005 mGal) thought to relate to the downstream movement of water in the catchment, and delayed storage from groundwater, following the wet season in the upper catchment. To help interpret these data a groundwater recharge model was developed for the Nile Catchment using the model ZOODRM (a distributed modelling code for calculating spatial and temporal variations in groundwater recharge). ZOODRM was an appropriate model to use for this work, due to the lower data demands of the model, relative to other groundwater models, the ability of the model to use entirely remotely-sensed input data, and the added functionality of runoff routing. Rainfall (NOAA data) and ET data were sourced from the FEWS NET African Data Dissemination Service. Geological data was sourced from the digital geology map of the world, landuse data from the USGS and the DEM data from ESRI. Initial model results indicate groundwater recharge across the basin of 0-4mma-1, with obvious considerable spatial variability. The results indicate the importance of groundwater in storing rainfall, and releasing it slowly throughout the year in different parts of the catchment. Only by modelling this process can GRACE data be reliably interpreted hydrologically. Despite only a qualitative interpretation of the GRACE data having been achieved within this preliminary study, the work has indicated that the ZOODRM model can be used with entirely remotely-sensed data, and that sufficient data exists for the Nile Basin to construct a plausible recharge model. Future work is now required to properly calibrate the model to enable closer comparison of the Nile GRACE data

Relating in situ hydraulic conductivity, particle size and relative density of superficial deposits in a heterogeneous catchment

Estimating the permeability of superficial deposits is fundamental to many aspects of catchment science, but can be problematic where insufficient in situ measurements are available from pumping tests in piezometers. Consequently, common practice is to estimate permeability from the material description or, where available, particlesize distribution using a formula such as Hazen. In this study, we examine the relationships between particlesize, relativedensity and hydraulicconductivity in superficial deposits in Morayshire, Northern Scotland: a heterogeneous environment typical of many catchments subject to previous glaciations. The superficial deposits comprise glaciofluvial sands and gravels, glacial tills and moraines, raised marine sediments, and blown sands. Thirty-eight sites were investigated: hydraulicconductivity measurements were made using repeated Guelph permeameter measurements, cone resistance was measured in situ with a Panda dynamic cone penetrometer; material descriptions were made in accordance with BS5930:1999; and disturbed samples were taken for particlesize analysis. Overall hydraulicconductivity (K) varied from 0.001 m/d to >40 m/d; glacial till had the lowest K (median 0.027 m/d) and glacial moraine the highest K (median 30 m/d). However, within each geological unit there was great variability in measured hydraulicconductivity values. Multiple linear regression of the data indicated that log d10 and relativedensity (indicated by cone resistance or BS5930:1999 soil state description) were independent predictors of log K and together gave a relationship with an R2 of 0.80. Material description using the largest fraction (e.g. sand or gravel) had little predictive power. Therefore, in heterogeneous catchments, the permeability of superficial deposits is most strongly related to the finest fraction (d10) and relativedensity of the material. In situ Guelph permeameter measurements at outcrops with good geological characterisation provide an easy and reliable method of determining the permeability of particular units of superficial deposits

BGS Consultancy : UNICEF IWASH project, Northern Ghana : visit report 25/10-5/11/2010

BGS have been commissioned to investigate the low drilling success rates encountered by the UNICEF IWASH programme in the Northern region of Ghana. The work is split into three phases: (1) situation analysis and information collation on current methods of groundwater development; (2) the development of a preliminary groundwater development map and suggestions for improving siting methods; and (3) a workshop and training course on groundwater development in N region. The project started on October 15th 2010 and is scheduled to finish by February 28th, 2011. Phase 1 involves a visit to Ghana, Phase 2 will occur mainly in the UK; and Phase 3 is scheduled to take place in Ghana during February 2011. This short note reports on the data collection visit 25th October – 5th November 2010. An itinerary, list of contacts and summary of data collected is given in the Appendices