Measurements of Head Variations within Observation Boreholes and their Implications for Groundwater Monitoring

Brassington, F. C.

doi:10.1111/j.1747-6593.1992.tb00742.x

Cited by 22 publications

(11 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Rushton & Salmon (1993) demonstrated the importance of low-permeability beds, especially mudstones, in controlling vertical head gradients in the sandstones. Vertical head gradients of a few per cent are often seen in boreholes (Brassington 1992;Taylor et al 2003), and usually most head change is seen across mudstone beds (Segar 1993). An extreme example is seen at a location in the southern Cheshire Basin where head differences of approximately 65 m have been recorded in wells of different depths at effectively the same location (Voyce pets.…”

Section: The Effect Of Mudstone Permeability On Flowmentioning

confidence: 99%

Towards prediction of saturated-zone pollutant movement in groundwaters in fractured permeable-matrix aquifers: the case of the UK Permo-Triassic sandstones

Tellam

Barker

2006

View full text Add to dashboard Cite

Abstract:The UK on-shore Permo-Triassic sandstones are fluvial and aeolian red beds showing a nested cyclic architecture on scales from millimetres to 100s of metres. They are typical of many continental sandstone sequences throughout the world. Groundwater flows through both matrix and fractures, with natural flow rates generally of less than 200 m year -1. At less than 30 m horizontal distances, below important minimum representative volumes for both matrix and fracture network permeability, breakthroughs are likely to be multimodal, especially close to wells, with proportionately large apparent dispersivities. 'Antifractures' -discontinuities with permeability much less than that of the host rockmay have a dominating effect. Where present, low-permeability matrix (e.g. mudstones) will significantly affect vertical flow, but will rarely prevent eventual breakthrough. Quantitative prediction of breakthrough is associated with large uncertainty. At scales of 30 to a few 100s of metres, multimodal breakthroughs from a single source become less common, although very rapid fracture flow has been recorded. At distances of hundreds of metres to a few kilometres, there is evidence that breakthroughs are unimodal, and may be more immediately amenable to quantitative prediction, even in some cases for reacting solutes. At this and greater scales, regional fault structures (both slip surfaces and granulation seams) can have major effects on sub-horizontal solute movement, and mudstones and cemented units will discourage vertical penetration. The aquifer has limited oxidizing capacity despite the almost ubiquitous presence of oxides, limited reductive capacity and limited organic sorption capacity. It has a moderate cation-exchange capacity, and frequently contains carbonate. Mn oxides are important for sorption and oxidation, but are present in limited quantity. Relationships between hydraulic and chemical properties are largely unknown. 'Hard' evidence for the solute transport conceptual model presented above is relatively limited. To be able to predict to a reasonably estimated degree of uncertainty requires knowledge of: the geological, and thence the hydraulic and geo-chemical, structure of the complex sandstone architecture (including the correlations between these properties); the development of suitable investigation techniques (especially geophysical) for mapping the structures; and the development of modelling tools incorporating matrix, fractures, 'antimatrix' and antifracture elements, each with associated hydraulic and possibly geochemical properties. In common with solute movement studies in most aquifer types, much more geological characterization needs to be undertaken. Although new investigation and modelling tools are being developed specifically for (shallow) hydrogeological applications with some considerable success, much greater advantage could be taken of importing techniques from other disciplines, and in particular from oil exploration and development.

show abstract

Section: The Effect Of Mudstone Permeability On Flowmentioning

confidence: 99%

Towards prediction of saturated-zone pollutant movement in groundwaters in fractured permeable-matrix aquifers: the case of the UK Permo-Triassic sandstones

Tellam

Barker

2006

View full text Add to dashboard Cite

show abstract

“…This flow means that conventional depth samples are representative of formation water from the inflow horizons rather than from the horizon opposite the sampling point. 2. The vertical flows, although too small t o be detected even with a sensitive (heat-pulse) flowmeter, nevertheless appear to have caused a significant change in formation-water chemistry in less than a month, as water from higher levels flowed down the borehole and into lower strata, displacing their natural groundwater.…”

Section: Discussionmentioning

confidence: 99%

The Influence of Unlined Boreholes on Groundwater Chemistry: A Comparative Study Using Pore‐Water Extraction and Packer Sampling

Price¹,

Williams

1993

Water & Environment J

View full text Add to dashboard Cite

In the consolidated formations which form most of the major aquifers in the UK, many monitoring boreholes are left unlined (open) for their effective length. They therefore provide pathways for groundwater to flow from one part of the aquifer to another. A borehole was core‐drilled through Triassic sandstones into Permian mudstones at a site in North Yorkshire. Pore water was extracted from the core and compared with conventional depth samples and with samples taken from intervals isolated using packer systems: (a) during drilling, (b) about one month after drilling, and (c) two years after drilling. The study revealed that natural flow down the borehole led to rapid changes in the quality of water in some parts of the formation. The implication is that open boreholes can act as conduits to allow flow to take place from one part of the aquifer to another. They are therefore not reliable as sampling points, and may actually accelerate the vertical spread of pollutants. However, this last effect should not be over‐stated; in this study, the flow down the borehole was equivalent to the natural flow through only a relatively small area of land.

show abstract

“…This appears to be consistent with the general trend of decreasing tracer recovery with depth. Such vertical head gradients are not uncommon in the UK Permo-Triassic sandstones [e.g., Brassington, 1992;Segar, 1993;Rushton and Salmon, 1993;Stagg et al, 1998;Streetly et al, 2002;Taylor et al, 2003;Furlong et al, 2011].…”

Section: Experimental Mass Recoverymentioning

confidence: 99%

Convergent tracer tests in multilayered aquifers: The importance of vertical flow in the injection borehole

Riley

Tellam

Greswell

et al. 2011

Water Resources Research

View full text Add to dashboard Cite

[1] A mathematical model describing the steady state flows in a forced gradient tracer test between an injection and pumping borehole in a multilayered sandstone aquifer has been developed that includes the effect of vertically variable background heads. A second model describing the recovery of tracer from a layer in which there are discharges due to vertical flow in the injection borehole is also presented. Application of the models to field tracer test data indicates that the observed recoveries, which are not proportional to the abstraction rate in each layer, are consistent with the hydraulic behavior of the aquifer when natural vertical head gradients are taken into account. Investigation with the models illustrates that the vertical distribution of tracer recovery depends strongly upon the background heads and that tracer tests conducted in the same aquifer, but at different times, may interrogate different aquifer layers. It is also shown generally that for a given abstraction rate the vertical distribution of tracer recovery in small-scale tracer tests is controlled largely by the transmissivity distribution but that as the spatial scale of the test increases, the distribution of recovery becomes proportional to the discharges from the injection borehole because of vertical flows within it, which may be natural or induced by pumping in the monitoring borehole. Uncertainties inherent in the design of forced gradient tracer tests in multilayered aquifers and the problems of applying the results of such tests to natural gradient contaminant migration are discussed.

show abstract

Measurements of Head Variations within Observation Boreholes and their Implications for Groundwater Monitoring

Cited by 22 publications

References 8 publications

Towards prediction of saturated-zone pollutant movement in groundwaters in fractured permeable-matrix aquifers: the case of the UK Permo-Triassic sandstones

Towards prediction of saturated-zone pollutant movement in groundwaters in fractured permeable-matrix aquifers: the case of the UK Permo-Triassic sandstones

The Influence of Unlined Boreholes on Groundwater Chemistry: A Comparative Study Using Pore‐Water Extraction and Packer Sampling

Convergent tracer tests in multilayered aquifers: The importance of vertical flow in the injection borehole

Contact Info

Product

Resources

About