Showing papers in "Quarterly Journal of Engineering Geology and Hydrogeology in 1991"

Behaviour of radon in the geological environment: a review

Abstract: A review of the behaviour of radon in the geological environment is presented. The general geochemistry of the element is described and the factors controlling its emanation from minerals and rocks and into the disperse phases itemized. A brief summary of analytical procedures for the analysis of the radon isotopes in waters and soil gases is given. The emanation of radon depends upon the source term uranium concentration, the nature of the host mineralogy, the permeability of the host rock and soil and the characteristics of the transporting medium. Weather can have a profound effect upon the concentration of radon in soil gas but often the variation due to the geological substrate is greater. Radon is not a problem unless it collects in buildings and underground structures. Some guidelines are given for identifying areas of high radon emanation based upon existing data sets.

Evaluating the strength and deformability of sandstones

Abstract: The mineralogy, texture and wave velocity characteristics of a range of sandstones were studied to aid the understanding and prediction of geotechnical properties. From a consideration of volumetric strain variations it is apparent that the weaker rocks display a behaviour markedly different from the stronger rocks. In the weaker rocks, the elastic range is limited to very low stress levels. The sensitivity of the strength and volumetric strain to sample moisture content has also been evaluated and shown to be an important variable in rock deformability behaviour; a decrease in moisture content tends to suppress the onset of dilatancy and microcracking, leading to an increase in peak strength. Microscopic characteristics, in particular in the areas of grain contact and cementation, were successfully used to explain the strength and deformability behaviour of a wide range of sandstones. Practical index parameters for assessing the strength and deformability of sandstones are outlined. Characterization by S waves shows potential as a complement to the index tests of saturated moisture content and point load for weak and strong sandstones respectively.

Lessons from Loscoe; the uncontrolled migration of landfill gas

Abstract: In March 1986 a house at Loscoe in Derbyshire was completely destroyed by a methane gas explosion, badly injuring the three occupants. Eight months later at a Public Inquiry, the sequence of events leading up to the incident was established and evidence produced to ascertain the origin of the methane. During the proceedings it became apparent that signs of ground heating had been detected approximately 100 m beyond the boundary of a near-by landfill some years before the explosion but that the phenomenon had been misinterpreted as a shallow burning coal seam. Had the geology of the area and the geochemistry of methane been known to the investigators at that time, it is possible that the landfill would have been identified as the source of methane and the Loscoe area protected from the dangers of uncontrolled gas migration.

Stabilization of a dispersive soil by blending with fly ash

Abstract: This paper is concerned with the influence of fly ash (pozzolanic) on the stabilization of a dispersive soil commonly found in northeast Thailand. The effect of various proportions of fly ash on the rate of erosion, dispersiveness, strength and frictional properties and the compaction and consolidation characteristics, are discussed. It is noted that in general the addition of fly ash not only inhibits erosion and dispersiveness but also contributes to a significant improvement in strength and deformation characteristics. Nevertheless, excessive quantities of fly ash (>8%) generate diminishing returns and in fact promote segregation (erosion) of the stabilized soil again due to insufficient cohesion. Mineralogical studies based on X-ray diffraction analysis indicate that the reduction in the rate of erosion of the blended soil is associated with fine particle flocculation. The long term properties, however, are directly linked with the self-hardening nature of fly ash which contributes to time-dependent strengthening of the stabilized soil.

Concrete petrography : a review

Abstract: Concrete strength depends on the amount, composition and quality of the hydrated binder to the fine and coarse aggregate. This paper reviews the way in which concretes can be examined with the petrographic microscope using both thin sections and polished plates. It reports observations made on actual samples, noting the similarity between the densities obtained by petrographic assessment and those established in laboratory tests. The paper highlights the value of carrying out a petrographic investigation to obtain quantitative information in support of and prior to the conventional chemical investigation, including aggregate/cement paste ratio and void content, assessment of the weight fractions of water, cement and aggregate; assessment of the composition of the binder including the slag to Portland cement ratio, assessment of the PFA to Portland cement ratio and possibly the assessment of the type of Portland cement employed in the mixture. Attention is also drawn to the implications of aggregate shape and grading.

An introduction to geological aspects of methane occurrence and control in British deep coal mines

Abstract: Practical methods for measuring the in situ gas contents of coal seams, modelling seam gas content trends, determining rates of methane emission from strata disturbed by mining and assessing the likelihood of unusual emissions are outlined. The constraints imposed by methane on coal production are highlighted and attention drawn to its attendant hazards. Successful planning for the control and exploitation of colliery methane cannot be achieved without a sound knowledge and understanding of the geology with which the mine interacts.

Some observations on a comparative aerial photography interpretation of a landslipped area

Abstract: All aerial photography interpretation must be used with caution. When well done and supported by ground truth exercises they can be a valuable aid to site investigation, depending on the quality and scale of the aerial photographs and the skill and background of the interpreter. A rare situation has arisen where eight interpretations of a landslip complex in gently folded Tertiary marine sediments overlain by young colluvium and covered by dense equatorial rainforest were made by different professional interpreters. This is used as an opportunity to illustrate the potential difficulty in obtaining a reliable interpretation. Five of the interpretations were made without knowledge of a major new landslip which occurred in an area of existing landslips and three were made with knowledge of the new landslip, all using the same pre-major new landslip aerial photographs. Of the five made without knowledge of the new landslip, two did not identify existing landslips at the site and three partially identified landslips but each in a different configuration. With knowledge of the new landslip the interpreters identified old features in the aerial photographs similar to the features produced or exposed by the new landslip.

Fault detection using soil gas geochemistry

Abstract: Soil gas surveys have been carried out at research sites in Great Britain and Italy to test soil gas geochemistry as a site investigation technique for the detection of faults and discontinuities. At a site on Oxford Clay in Gloucestershire, soil gas anomalies of high He, Rn and CO 2 and low O 2 were shown to correspond to the outcrop of a fault, identified by drilling and geophysics. Other apparently random anomalies remained unexplained and lateral migration of gas through superficial horizons complicated interpretation. Using three parallel sample lines at the same distance apart as the sample spacing it has proved not only possible statistically to remove spurious anomalies, but also to enhance and concentrate clusters of high values resulting from gas migration. This method was used to investigate a fault in Neogene clay at Narni in Italy where a gas pathway permeable to Rn and CO 2 was identified, corresponding to a geoelectrical anomaly indicating displaced strata. Further work was carried out over a fault revealed by trenching in the Caithness Flags in Scotland. For each three-line traverse an integrated gas anomaly map was produced to aid interpretation by allowing both sharp and diffuse anomalies to be more easily identified.

Predictions of block size distribution for quarrying

Abstract: The in situ block size and shape parameters of a rock mass with discontinuities are of signifcance for determining whether an existing or virgin quarry is suitable for armourstone production and for designing an appropriate blast pattern. A method for predicting these parameters is presented in this paper, which includes a detailed discontinuity survey technique and computer determination of the blocks dissected by the discontinuities. The applications of the method to simulated discontinuity data and natural joint data are discussed.

Quality and durability of stone for construction

Abstract: The use of natural stone materials in construction is now experiencing a marked revival particularly for external claddings. In contrast with most other construction materials, there are few British Standard tests for natural stone or Standard specifications defining the minimum quality requirements for various purposes. The Code of Practice for cladding is inadequate in these respects. The range of test methods provided by ASTM and the complementary series of Standard specifications covering the major stone families are summarized but none of these directly address durability. Selected quality assessment procedures from German, Italian and other European practices and a number of different approaches to the evaluation of durability of stone are critically reviewed. The crucial importance of representative samples in such evaluations is recognized but the aspects of source selection and sampling are not discussed in detail.

Degradation model for rock armour in coastal engineering

Abstract: A degradation model specifically for rock armour in coastal structures is proposed. The objective is to give the coastal engineer a new design tool. The model provides a prediction of the armourstone weight loss with time on the structure. This information can help in the assessment of alternative design costings while taking account of the quality of rock from different possible sources. Factors affecting the degradation rate are the intrinsic material properties of the rock source, the production-influenced geometric properties of the armourstone, the environmental boundary conditions at the coastal site and the armour layer design concepts used. To apply the model to a given rock source, a sample of the material is tested in an abrasion mill simulation of the wear process. This gives a weight versus laboratory time plot. Laboratory time is converted to years on site using an equivalent wear time factor which is derived from a combination of nine weighted parameters. The effects of the other principal degradation mechanisms, fracturing and spalling, are included as well as abrasion. For example by using parameter estimates which couple meteorological climatic conditions with particular rock type susceptibilities, the influence of physico-chemical degradation can be assessed.

A note on undulatory extinction of quartz in granite

Abstract: Undulatory extinction of quartz has become important in engineering geology because of its supposed indication of an alkali-silica reactive aggregate. This note reviews the small amount of quantitative data that is available on undulatory extinction of quartz grains in granites and granitic rocks. It is considered that undulatory extinction of quartz occurs as a result of deformation of the rock after its formation and that the greater the cumulative deformation the larger the angle, hence it is a useful indicator of the orogenic history of the rock. Preliminary measurements are reported of the undulatory extinction angle of quartz in some British granites suggesting a field worthy of further study. The note concludes with a discussion of the practical implications of the subject.

The legacy of aquifer pollution by industrial chemicals: technical appraisal and policy implications

Abstract: The problem of groundwater contamination by the common chlorinated industrial solvents is becoming increasingly apparent in Britain. Pollution is known to have occurred widely as a result of casual or accidental discharge of such chemicals over many decades. Two case histories demonstrate that the combination of solvent physicochemical properties and Chalk hydrogeological characteristics can result in both extensive transport and extreme persistence in this aquifer. Adequately proving the source of groundwater contamination is onerous. Individual pollution problems are equally likely to be the legacy of past industrial activity as the effect of current industrial practice. At least in its most direct sense this renders the ‘polluter-pays’ principle ineffective. The situation is further complicated by the technical difficulty, excessive cost and inadequate definition of aquifer restoration. Modifications and clarifications to policy are required to provide a more rational basis for the alleviation of this ground-water pollution problem.

The Kaiapit Landslide : events and mechanisms

Abstract: The landslide at Kaiapit occurred on the morning of 6 September 1988 in the Finisterre Range of Papua New Guinea and resulted in 74 fatalities. The landslide involved an estimated 2 km 3 of debris which covered an area of 11.4 km 2 and left a back-scarp some 1600 m high. The debris ran out in three flows for approximately 6 km in 5 minutes and velocities of 180km/h have been estimated. No single cause for the initiation of the landslide has been determined. It is felt that its location in a tectonically and seismically active region, the tropical climate and an inherently weak rock mass were fundamental contributary factors. The failure mechanisms are considered to have been massive planar slides. The debris assumed a final angle of rest of 6°; this may be explained by a combination of the concepts of acoustic fluidization and air entrapment. The landslide debris resulted in the formation of four dams, which had all breached within eight months of the event. Active erosion of the debris is resulting in the aggrading of river bed levels in the area.

Geophysical investigations of photolineaments in southeast Zimbabwe

Abstract: The paper presents preliminary results of continuing studies in SE Zimbabwe aimed at understanding the role of fracturing in hard rock aquifers. This is a semi-arid region in which a high proportion of boreholes drilled for water supply are dry or provide minimal yields for hand-pump usage. Remote sensing, using satellite images and aerial photographs, provides a rapid means of identifying potential fracture systems but field evidence of the nature and precise location of such fractures is limited. Ground geophysical techniques such as resistivity, electromagnetic and magnetic surveying have been extensively tested over a few selected sites in an attempt to characterize their response where photolineaments occur. These data reveal the presence of anomalies, predominantly of shallow origin, some of which correspond with the lineaments. Initial results suggest that the lineaments studied do not represent major, open groundwater conduits. Drilling and borehole logging information confirms the view that fracturing is poorly developed in general. An interpretation of pump test data collected as part of hydraulic fracturing tests suggests that drilling itself results in the preferential opening of vertical fissures near the borehole but that background transmissivity is very low. The work is continuing with a programme of core drilling and cross-hole seismic tomography, the results of which will be incorporated in further modelling of the geophysical data.

Delineating concealed faults and shallow subsurface geology along the Wasatch Front, Utah, USA, by integrating geophysical and trench data

Abstract: Planning and development along the Wasatch front must compensate for the geological hazards associated with faulting. Studies show that future ruptures will probably occur along already existing zones of weakness. Although any surface faults can be detected by surficial geological mapping others have no visible expression and can only be located by subsurface investigations. Geophysical methods, such as seismic refraction, gravity, magnetic, and radar can be integrated with geotechnical engineering methods such as drilling and trenching to obtain a better understanding of the subsurface geology at a specific site. Seismic refraction, gravity and magnetic surveys conducted near Provo, Utah along the Wasatch Mountain front have helped delineate shallow, concealed faulting. The reduced, modelled gravity and magnetic data typically correlate well with the refraction depth sections generated using the General Reciprocal Method (GRM). Field observations coupled with the geophysical data facilitated the identification of a number of probable faults along Rock Canyon Road, allowing an estimate to be made of the magnitude and direction of throw on the fault. A normal fault associated with a prominent north–south scarp near Rock Canyon Road was chosen for a case study. This fault scarp was later trenched by the Utah Geological and Mineral Survey (UGMS) and provided a direct comparison with the geophysical data sets. As all the data sets at this site correlate well with the subsurface geology, confidence is increased in interpreting other parts of the line. The characteristics of subsurface deformation can be used to gain a better understanding of the potential for surface rupture at a site and thereby in planning and site development and in devising remedial measures to mitigate the effects of earthquakes in populated areas.

Rock quality in coastal engineering

Abstract: The majority of coastal and shoreline defence structures use large quantities of rock in their construction which will be subjected to environmental conditions quite different from rock used for other purposes. Such materials are required to conform to specific size, shape and grading criteria by the designers of coastal defence structures and rock properties such as density will also be required for the design equations. The severity of the marine environmental conditions will also necessitate adequate levels of strength, abrasion resistance and durability. A quality assurance scheme for marine structures must take account of all these requirements. Test evaluations must be carried out at an early stage in the design process when alternative materials are being compared and again at the quality control stage of extraction as well as during the construction. Tests can be divided into four groups: those concerned with the geometric properties such as size, shape and grading; those concerned with intact rock strength and resistance to abrasion; with the intrinsic properties of the rock; and those related to durability characteristics such as weathering degradation. Many of the tests used to evaluate these properties were originally designed for aggregate materials, but recently two tests have been developed specifically for rock to be used in coastal defence structures. These procedures attempt to test those characteristics of the rock materials most affected by the degradation processes found in the marine environment and to offer a method of predicting the in-service performance of the rock with time.

Defining the catchment of a borehole in an unconsolidated valley aquifer with limited data

Abstract: Borehole catchments need to be defined for groundwater protection in general and for the control of nitrates in particular. There are rarely enough data to make an accurate definition. The catchment of a borehole which draws from the glacial infill aquifer in a Shropshire valley has been studied, with emphasis on how sensitive the catchment is to variations in hydrological and hydrogeological parameters. The amount and distribution of recharge are the most important controls on the catchment. In this example, 250f the borehole abstraction is derived from valley side recharge, that is runoff from the valley sides which recharges the margins of the aquifer. Thus part of the catchment lies off the aquifer. Despite the limited data available, a zone which probably accounts for about 650f the borehole9s abstraction can be defined, which would be sufficient to justify a nitrate control scheme. The complete catchment cannot be accurately defined however and the area covered by the possible range of catchment boundaries is 25% larger than the ‘best’ estimate. Additional field data would be needed to narrow this range significantly.

Radon in the surface waters of southwest England and its bearing on uranium distribution, fault and fracture systems and human health

Abstract: Radon is a natural radioactive gas produced by the decay of uranium and thorium in rocks and soils. High surface radon concentrations are commonly associated with high levels of uranium in underlying rocks. High radon levels can also occur in groundwater, even in rocks with normal crustal uranium concentrations. The discharge of groundwater via faults and fractures can produce radon anomalies unrelated to the distribution of uranium. The surface distribution of radon is therefore influenced by the distribution of uranium and of transport pathways along faults and fractures. The principal radon isotope (Rn-222, half-life 3.825 days) is capable of migrating significant distances from its source, both as a gas and in solution. In the gaseous form radon can migrate into houses where, in high concentrations, it can represent a health hazard. The distribution of radon in streams in several areas of southwest England has been investigated. The results show a clear association of high radon levels with the uranium-enriched granite of the region, although this may simply reflect the high fracture permeability of the granite rather than its uranium enrichment with a strong influence of major fracture systems. With regard to radon as a potential health hazard, both source and transport pathways must be identified if high-risk areas are to be located. Surveys of radon in surface waters may provide a useful and speedy technique for the broad identification of such areas.

The passivity of steel in concrete

Abstract: This paper describes the chemical nature of concrete and the internal environment in which the steel reinforcement is situated. The electrochemical basis for passivity of iron in aqueous solution is discussed and the anodic and cathodic reactions which occur are detailed in relation to pH-potential (Pourbaix) and current-potential (Evans) diagrams. The observed behaviour of iron in solution is compared to the behaviour of reinforcement in concrete. The breakdown of the passive film is discussed in relation to the commonly observed causes of deterioration of reinforced concrete i.e. carbonation of concrete, the presence of chloride ions at the steel surface and sulphate attack. Results of an SEM-EDS study of chloride-induced breakdown of the passive film are presented. The effects of the surface condition of the reinforcement prior to its inclusion in concrete and the use of latent hydraulic binders and thermosetting plastic coatings (fusion bonded epoxy) in relation to passivity and corrosion behaviour are discussed.

The problem of quality control and selection of armourstone

Abstract: The successful use of naturally occurring rock as an armourstone depends on the selection of suitable material which will perform the function for which it was designed. Two recent case histories of coast protection works with a combined total of about 200 000 tonnes of rock armour demonstrates that adequate quality and selection control procedures were not utilized and as a result substantial quantities of rock were rejected, and in one case costly arbitration procedures were involved. In each case the contractor for the works was responsible for the provision of armourstone in compliance with the specification and had simple engineering geological controls been used substantial savings could have been made.

Hydrogeological investigation of a fault in clay

Abstract: Measurements of groundwater head and hydraulic conductivity have been made around a fault in the Oxford Clay in order to examine the effect of a fault on the hydraulic properties of a clay and on groundwater flow. Pulse tests performed in the clays gave values of hydraulic conductivity ranging from 5 × 10 -12 to 2 × 10 -8 ms -1 . Although showing some overlap with the unfaulted clays, the hydraulic conductivity in the fault zone appears to be enhanced with respect to the adjacent unfaulted clays by up to one or two orders of magnitude. The groundwater heads in the mudrocks/clays are high compared with those in the underlying aquifers and appear to be relics from the period before major groundwater abstraction. Some outline numerical modelling suggested that both changes in fault geometry and varying fault properties could be invoked to explain adequately the measured head profiles using the traditional assumptions of Darcian flow. However, it is recognized that coupled flow processes may be of great significance in clay formations; in particular, the measured heads may result from hydraulic effects coupled with chemical and mechanical potentials.

A low-cost dedicated multi-level groundwater sampling system

Abstract: An important aspect of any detailed groundwater quality study is determining the vertical distribution of pollutants. This may be achieved by multi-level sampling from purpose designed boreholes. This study describes a relatively inexpensive system of dedicated sampling where gas-driven water samplers (incorporating vibrating wire piezometers) and unsaturated zone gas samplers are installed in conventional plastic water well casing. One important advantage of this system is that all functional units are housed within a protective screen, which offers both protection and improved potential for satisfactory backfilling. Experiments to determine the performance of gas-driven samplers when collecting water contaminated with chlorinated hydrocarbon solvents indicated that quantitatively accurate results are obtained using short lengths of nylon tubing. However, long lengths of nylon tubing introduced significant negative bias in solvent concentrations and it is recommended that a material with lower absorption properties be chosen to collect deep samples. The system was successfully installed on a contaminated industrial site. Significant variations in solvent pollution profiles together with a substantial vertical hydraulic gradient were defined and such hydrochemical and hydraulic information may be simply collected on a routine basis. Such data could not easily be gained from open boreholes, indicating the potential of the dedicated system in groundwater quality investigations.

The use of dating techniques to constrain the age of fault activity: a case history from north Somerset, United Kingdom

Abstract: Attempts were made to obtain absolute ages constraining the most recent episode of fault activity in the North Somerset Coastal Fault Belt as part of the seismic hazard assessment for the proposed Hinkley Point ‘C’ power station. Radiometric (uranium series, 14 C) and palaeomagnetic dating techniques were applied to calcite from vein systems which cut the Hinkley Point Fault and 14 C dating was applied to bone material from undeformed Quaternary gravel deposits overlying faults in Liassic bedrock at Helwell Bay. Detailed field mapping and microscopy indicated that the samples chosen for dating had not undergone any significant fault-related deformation. Dates obtained from the radiometric techniques ranged from c . 33 ka to greater than 300 ka and reflect the influences of isotopic exchange and contamination as well as the inherent age limitations of the techniques. Palaeomagnetic dating techniques identified reverse polarizaton in a calcite sample from the Hinkley Point Fault, indicating an age greater than 730 ka, the time of the last geomagnetic field reversal. Palaeomagnetic vectors suggest a pre-Pliocene (and conceivably an early Jurassic) age for the calcite vein emplacement.

Determination of the influence of joint orientation on rock mass classification for tunnelling using a stereographic overlay

Abstract: Rock mass classification systems are commonly employed during exploration for rock tunnels. Joint orientation is an important input, affecting blasting, span widths, roof support and groundwater flow. When using Bienawski9s geomechanics classification system, the favourability of joint orientations with respect to tunnel drive direction must be selected. As joint populations are generally plotted stereographically, an overlay has been prepared on which sectors defining favourability in terms of the geomechanics classification are delineated. Superimposition of the favourability overlay on a joint pole counter plot allows easy assessment of the effects of joint set orientations.

The significance of faults for the Afulilo hydro scheme in Upolu, Western Samoa

Abstract: The geologically young Samoan Islands are situated in a seismically active area in the Pacific Ocean, at the northern end of the Kermadec-Tonga Trench. The paper discusses two faults not shown on the 1: 100 000 geological maps of the area. One of the faults, trending northwest/southeast, has been postulated as passing through the Afulilo dam site. The other fault trends northeast/southwest, displacing the line of the recent volcanic cones by up to 2.5 km. Any movement along this fault could affect the integrity of the hydroelectric powerhouse and a possible future intake structure.

Assessment of the potential for tectonic fault rupture for high-level nuclear waste repositories

Abstract: Active faults that extend to near the Earth9s surface may pose a direct threat to the safety of engineered structures. Usually the threat can be mitigated by taking appropriate siting or design actions. Such actions require a thorough understanding of the characteristics and magnitude of the faulting hazard based on detailed field investigations of the site locality and an adequate assessment of the characteristics of past faulting in the site9s tectonic regime. An active fault may be defined in purely geological terms as one that has exhibited displacement in the present tectonic regime. However, for engineering considerations an active fault is usually defined in terms of a specified time of most recent movement, or a longer time in which multiple movements have taken place. Deterministic or probabilistic approaches are used to assess faulting hazard for the purpose of engineering design consideration. Support is building for the use of probabilistic procedures alone or combined with deterministic procedures to assess faulting hazard for design of critical facilities.

Sandstones as geomaterials

Abstract: The lithological characteristics and dynamic and static test results are presented for six sandstone types ranging in age from Lower Old Red Sandstone to Triassic. Attention is drawn to the differing geomechanical properties of these sandstones and hence the variation in their suitability as construction geomaterials. Comparisons are made between a number of the static properties of the sandstones and their geomechanical performance. The paper emphasizes the importance of considering those sandstone properties relevant to particular applications. An indication is given of the suitability of the six examples of sandstones to the main construction geomaterial uses: building stone, armourstone, rip-rap, aggregate sub-base, aggregate dressing and concrete.

A new system for the objective interpretation of third-party data in assessments of regional sand and gravel resources

Abstract: A comprehensive desk study was recently carried out to assess the potential resources of sand and gravel in the drift deposits of County Durham. The study was based on published information, limited field observations and the analysis of 6000 subsurface datapoint references and over 1700 particle size distribution results. It was necessary, therefore, to devise a system of analysis which could provide an objective and repeatable assessment of the sand and gravel deposits and their resource potential on a regional basis. The evaluation system previously adopted by the Industrial Minerals Assessment Unit (IMAU) for the sand and gravel resource assessments conducted by the British Geological Survey was reviewed. This system comprises a statistical procedure to classify the investigation data and gives arbitrary physical criteria to determine whether a deposit can be regarded as ‘potentially workable’. The principal data available to the IMAU for each of their resource assessments were specifically gathered for the project under their direct supervision. The IMAU system could not be applied to the Durham study because data for this study were obtained totally from third-party sources. A system of analysis was designed which was sensitive to the variation in data quality. It is based on a flow chart comprising both question/answer and action elements and incorporates the arbitrary physical criteria adopted by the IMAU. The system is described in this paper and the effectiveness and limitations are demonstrated with reference to the Durham study.

Chemical reaction between concrete and natural groundwaters and its implications for the commissioning of observation boreholes in chalk

Abstract: Four purpose-constructed observation boreholes in chalk were found to contain water with pH of 10-11.5 and abnormal chemistry within fourteen months of commissioning. Experiments show that this was due to contamination by alkaline porewater solutions from the concrete grout used in construction. Contamination was still detectable nearly three years after construction but was cleared by pumping. A six-hour pumping test is recommended as standard procedure during commissioning of observation boreholes.