Lincolnshire Limestone Research Articles

A large pterosaur from the Middle Jurassic (lower Bajocian) of Rutland, United Kingdom

An incomplete, but large hollow bone is identified as pterosaurian on account of its pneumatic nature, thin bone wall, palaeohistology and the characteristic surface texture of the peridermal bone. Despite being incomplete it is tentatively identified as a ?left ulna, and is remarkable for its size. Coming from the lower Middle Jurassic Lincolnshire Limestone Formation of Rutland, eastern England, this is the first record anywhere in the World of a Bajocian pterosaur, and probably the first pterosaur recorded from Rutland. It is most likely from Discites to Laeviuscula zones part of the lower Bajocian succession, and represents one of the largest Jurassic pterosaurs yet recorded, with a wingspan tentatively estimated at between 3.5 and 4.0 m. The taxonomic identity of the new specimen is uncertain, but it is likely allied to the Pterodactyloidea on account of its size, although presently it remains Pterosauria fam. et gen., et sp. indet.

A metagenomic analysis of the bacterial microbiome of limestone, and the role of associated biofilms in the biodeterioration of heritage stone surfaces

There is growing concern surrounding the aesthetic and physical effects of microbial biofilms on heritage buildings and monuments. Carboniferous stones, such as limestone and marble, are soluble in weak acid solutions and therefore particularly vulnerable to biocorrosion. This paper aims to determine the differences and commonalities between the microbiome of physically damaged and undamaged Lincolnshire limestone, an area of research which has not been previously studied. A lack of information about the core microbiome has resulted in conflicting claims in the literature regarding the biodeteriorative potential of many microorganisms. To address this, we used metagenomics alongside traditional microbiological techniques to produce an in-depth analysis of differences between the bacterial microbiomes found on deteriorated and undamaged external limestone surfaces. We demonstrate there is a core microbiome on Lincolnshire limestone present on both damaged and undamaged surfaces. In addition to the core microbiome, significant differences were found between species isolated from undamaged compared to damaged surfaces. Isolated species were characterised for biofilm formation and biodeteriorative processes, resulting in the association of species with biodeterioration that had not been previously described. Additionally, we have identified a previously undescribed method of biofilm-associated biomechanical damage. This research adds significant new understanding to the field, aiding decision making in conservation of stone surfaces.

A new ammonite discovery from the Lincolnshire Limestone Formation (Lower Bajocian) of Eastern England

A newly discovered ammonite of the genus Hyperlioceras from the Lincolnshire Limestone Formation of Eastern England enables the biostratigraphical position of the principal building stone of Lincoln Cathedral: the ‘Silver Bed’ variant of Lincoln Stone (Lower Lincolnshire Limestone) to be precisely dated as subsectum biohorizon of the Lower Bajocian, Discites Zone. Ammonites are extremely rare in this formation thus the impetus to record it here and provide a firm date for strata in which it occurred following its discovery. The lithostratigraphical provenance of the specimen is briefly discussed and evidence provided to support the conclusion.

MINIMAL GEOLOGICAL DATA FOR MODELLING COMPLEX HYDROGEOLOGICAL SYSTEM USING GIS

Geological model is part of groundwater modelling processes. 3D geological models such as GSI3D and GOCAD are used extensively for modelling subsurface geology. These models require multiple input datasets from boreholes, geology maps, and geophysical data. However, due to insufficient definitive data, widely spaced data points that are interpolated were usually used for representation of a geological unit. Since the requirement of extensive data is always the main issue, a geological model is only applied for an area with sufficient data. In this study, minimal and accessible spatial datasets were used in the model for representation of the geological unit. These datasets were chosen to allow the model to be applied in areas of limited datasets. Via the GIS platform, the methodology was developed for the representation of geology in particular the aquifer unit. The raster surface of the geological layer was created in GIS using the information of dip, strike and faults displacement taken from the geological map. The developed GIS based geological model is capable of viewing a geological cross section, modelling the thickness and outcrop boundary of an aquifer unit. The model was tested by reconstruction of the geology map for the Slea catchment, in the United Kingdom and prediction of the thickness of the Lincolnshire Limestone aquifer.

Reactivity of pyrite and organic carbon as electron donors for biogeochemical processes in the fractured Jurassic Lincolnshire limestone aquifer, UK

In this study, the weathering profiles of limestone blocks in the Jurassic Lincolnshire limestone (UK) are used to determine the spatial variation in concentration of electron donors (organic carbon and pyrite) that might drive subsurface microbial respiration, including denitrification. Organic carbon concentrations were found to be constant throughout the block transects. In contrast, sulphur and pyrite–iron concentrations were significantly higher in the unweathered zones in comparison to the weathered zones. Moreover, acid-extractable iron concentrations were significantly higher in the weathered zones in comparison to those of the unweathered zones. This suggests that pyrite is operating as the main electron donor in this system and that organic carbon is unreactive. Therefore, potentially beneficial microbial processes such as denitrification of agrochemically-contaminated groundwater will be limited, not by availability of organic carbon, but by availability of pyrite.

Isotope and reactive transport modelling of denitrification in the Lincolnshire Limestone aquifer, eastern England

Abstract Groundwater within the outcrop area of the Lincolnshire Limestone aquifer in eastern England is characterized by high (>50 mg l −1 ) nitrate concentrations, whereas in the confined zone c . 15 km further east, nitrate concentrations are low ( −1 ) or undetected. The decrease in nitrate concentrations is associated with an increase in the 15 N/ 14 N ratio (or δ 15 N) of the residual nitrate, a feature characteristic of bacterially mediated denitrification. The calculated isotopic enrichment factor for the denitrification process of −1.8‰ is low when compared with literature reports of laboratory experiments and previous field investigations. Isotope evolution modelling shows that the low enrichment factor is related to complex mixing processes occurring within the aquifer as a result of the interactions between fissure flow, matrix diffusion and mixing with low-nitrate groundwater in the confined zone. The natural attenuation of nitrate is proved to occur and is further investigated with a finite-element reactive transport fractured media model influenced by denitrification. The model simulations show that oxygen and nitrate concentrations decrease with distance from the centre of a fracture to values of 0.2 mg l −1 and 1.0 mg l −1 , respectively, at a distance of 4 cm from the fracture walls, in agreement with field evidence. The bacterial consumption rates of oxygen and nitrate mass can be calculated by comparison of reactive and non-reactive simulations and are found to be 4.2 mg O 2 m −3 day −1 and 48.2 mg NO 3 m −3 day −1 . Assuming heterotrophic denitrification, the organic carbon substrate utilization rates are calculated to equal 0.13 mg l −1 day −1 at outcrop (equivalent to the left-hand boundary of the model domain) and 0.07 mg l −1 day −1 at the right-hand boundary of the domain at a distance of 6.5 km. From a consideration of the percentage of available organic carbon contained in the limestone, and with a consumption rate of 0.13 mg l −1 day −1 at outcrop, the whole reservoir of organic carbon in the model domain would be utilized in 209 years, thus suggesting an eventual limit on denitrification in the confined aquifer.

Modelling land-use scenarios to reduce groundwater nitrate pollution: the European Water4All project

The Water4All project funded by the EU InterregIIIB programme aimed to demonstrate groundwater protection in the context of spatial planning and the implementation of the EU Water Framework Directive. Through a series of workshops, the four partner countries (Denmark, Germany, the Netherlands and the UK) developed a handbook containing an approach for risk-based land and water management to reduce diffuse pollution of groundwater from agricultural sources. Best practice guidelines were catalogued as a matrix of compensated and non-compensated ‘soft’ to ‘hard’ measures and were supported by illustrative case studies. The Water4All project also showed that spatially targeted measures can have wider benefits as part of a ‘whole landscape’ approach to planning and management. As an example, this paper explores a set of theoretical land-use scenarios, developed in consultation with stakeholders, which could potentially decrease nitrate concentrations in the regionally important Lincolnshire Limestone aquifer in eastern England. The results of a combined export coefficient and numerical groundwater modelling approach showed that a decrease in groundwater nitrate concentrations can be achieved over several decades with the implementation of a groundwater protection zone in which there is a significant element of land conversion from arable to woodland and grass. Hence, a long-term commitment to land management is required if the alternative and expensive end-of-pipe water treatment is to be avoided.

The Middle Jurassic succession at Ketton, Rutland

The cement quarry at Ketton is the most important Middle Jurassic locality in inland England. For many years it has exposed the Lincolnshire Limestone, Rutland and Blisworth Limestone Formations. Excavations in the lower quarry have allowed access to the Northampton Sand and Grantham Formations, and temporarily to the Whitby Mudstone Formation, while extensions of the upper quarry, and the effects of recently exposed faults, additionally reveal complete sections in the Blisworth Clay, Cornbrash and Kellaways Formations. The site therefore allows the description of the whole succession of the Aalenian to Lower Callovian strata developed in the East Midlands: the Inferior Oolite Group, the Great Oolite Group and the lowest part of the Ancholme Group. In this paper the succession is summarized, incorporating data from stratigraphic revisions by Bradshaw (1978) and Ashton (1980). Measured sections and logs for each formation are presented, in order to provide a basis for more interpretative investigations and for regional correlation. New members are defined: the Castle Member within the Rutland Formation, and the Grange, Tinwell Lodge and Ketton Heath Members within the Blisworth Clay Formation, in each case with Ketton as the type section. Appendices relate previous bed-numbering schemes to our stratigraphy, and assign the ostracod faunas recorded by Bate (1967) from the Rutland Formation to their precise horizons.

Clay mineralogy of the Jurassic strata of the British Isles

AbstractThe nature and origin of the clay mineralogy of the Jurassic strata of the British Isles are described and discussed within their lithological and biostratigraphical framework using published and unpublished sources as well as 1800 new clay mineral analyses. Regional clay mineral variation is described systematically for the following formations or groups:England and Wales(i)Hettangian-Toarcian strata (Lias Group): Redcar Mudstone Fm.; Staithes Sandstone Fm.; Cleveland Ironstone Fm.; Whitby Mudstone Fm.; Scunthorpe Mudstone Fm.; Blue Lias Fm.; Charmouth Mudstone Fm.; Marlstone Rock Fm.; Dyrham Fm.; Beacon Limestone Fm.; Bridport Sand Fm.(ii)Aalenian-Bajocian (Inferior Oolite Group): Dogger Fm.; Saltwick Fm.; Eller Beck Fm.; Cloughton Fm.; Scarborough Fm.; Scalby Fm. (in part); Northampton Sand Fm.; Grantham Fm.; Lincolnshire Limestone Fm.; Rutland Fm. (in part); Inferior Oolite of southern England.(iii)Bathonian (Great Oolite Group): Scalby Fm. (in part); Rutland Fm. (in part); Blisworth Limestone Fm.; Great Oolite Group of southern England; Forest Marble Fm.; Cornbrash Fm. (in part).(iv)Callovian-Oxfordian: Cornbrash Fm. (in part); Kellaways Fm.; Oxford Clay Fm.; Corallian Beds and West Walton Beds; Ampthill Clay Fm.(v)Kimmeridgian-Tithonian: Kimmeridge Clay Fm.; Portland Sandstone Fm.; Portland Limestone Fm.; Lulworth Fm.; Spilsby Sandstone Fm. (in part). Scotland(vi)Hettangian-Toarcian: Broadfoot Beds, Dunrobin Bay Fm. Aalenian-Portlandian: Great Estuarine Group (Dunkulm, Kilmaluag and Studiburgh Fm.s); Staffin Shale Fm.; Brora Coal Fm.; Brora Argillaceous Fm.; Balintore Fm.; Helmsdale Boulder Beds (Kimmeridge Clay Fm.).Dominating the Jurassic successions are the great marine mudstone formations — the Lias Group, Oxford Clay, Ampthill Clay and Kimmeridge Clay. These are typically characterized by a detrital clay mineral assemblage of mica, kaolin and poorly defined mixed-layer smectite-mica-vermiculite minerals with traces of chlorite. Detailed evidence suggests that this assemblage is derived ultimately from weathered Palaeozoic sediments and metasediments either directly or by being recycled from earlier Mesozoic sediments. A potassium-bearing clay is a persistent component and formed at approximately the same time as the deposition of the host sediment, either in coeval soils or during very early diagenesis.At three periods during the deposition of the Jurassic (Bajocian-Bathonian, Oxfordian and late Kimmeridgian-Tithonian), the detrital clay assemblage was completely or partially replaced by authigenic clay mineral assemblages rich in kaolin, berthierine, glauconite or smectite minerals. Associated with these changes are major changes in the lithofacies, with the incoming of non-marine and proximal marine strata. The authigenic clay assemblages rich in kaolin and berthierine are generally restricted to the non-marine and very proximal marine beds, those rich in glauconite or smectite are typical of the marine lithofacies. Clay mineral assemblages containing vermiculite and mixed-layer vermiculite-chlorite sometimes occur in the non-marine and proximal marine facies. The causes of these major changes in lithofacies and clay mineralogy are discussed, and present evidence favours an important volcanogenic influence and not climatic control. It is suggested that the Bajocian-Bathonian, Oxfordian and Late Kimmeridgian-Tithonian were periods of enhanced volcanic activity, with centres probably located in the North Sea and linked to regional tectonic changes which caused major modifications of the palaeogeography of the British Isles. The most important of these changes was the development of the central North Sea Rift Dome during the Bajocian and Bathonian. Volcanic ash was widespread in both the non-marine and marine environments and its argillization under different conditions provided the wide range of authigenic clay mineral assemblages.Metre-scale clay mineral cyclicity is widespread in most of the Jurassic mudstone formations that have been examined in sufficient detail. The cyclicity is defined by systematic variations in the mica/ collapsible minerals (mixed-layer smectite-mica-vermiculite) ratio. This variation is unrelated to changes in lithology and its possible origins are discussed in detail using data from the Kimmeridge Clay provided by Reading University's contribution to the Rapid Global Geological Events (RGGE) Project.

The potential for methane emissions from groundwaters of the UK

Methane (CH 4) is only a trace constituent of the atmosphere but an important greenhouse gas. Although groundwater is unlikely to be a major source of atmospheric CH 4, its contribution to the CH 4 budget of the UK has up to now been poorly characterised. Groundwater CH 4 concentrations have been measured on 85 samples from water-supply boreholes and a further eight from other miscellaneous water sources. Concentrations in abstracted groundwaters ranged from <0.05–42.9 μg/l for Chalk, <0.05–22 μg/l for the Lower Greensand, 0.05–21.2 μg/l for the Lincolnshire Limestone and from <0.05–465 μg/l for the Triassic sandstone. Having the largest abstraction volume, the Chalk is likely to be the main UK groundwater contributor to global CH 4 emissions. A calculation to estimate the total emissions of CH 4 from water-supply groundwater sources based on the median and the maximum CH 4 concentrations gave values of 2.2×10 −6 and 3.3×10 −4 Tg/year. Estimates show groundwater contributes a maximum of 0.05% of all UK CH 4 emissions and a further two orders of magnitude less in terms of the global CH 4 budget. Other groundwater sources such as inflows to tunnels may have significantly higher CH 4 concentrations, but the volume of water discharged is much lower and the overall amount of CH 4 outgassed is likely to be of the same order as the aquifer release. The generally low concentrations of CH 4 in groundwater supplies suggest no threat of explosion, although groundwater released by excavations remains a hazard.

Enantioselective biodegradation of mecoprop in aerobic and anaerobic microcosms

Natural attenuation of mecoprop has been studied by determining changes in enantiomeric fraction in different redox environments down gradient from a landfill in the Lincolnshire limestone. Such changes could be due to differential metabolism of the enantiomers, or enantiomeric inversion. In order to confirm the processes occurring in the field, microcosm experiments were undertaken using limestone acclimatised in different redox zones. No biodegradation was observed in the methanogenic, sulphate-reducing or iron-reducing microcosms. In the nitrate-reducing microcosm ( S)-mecoprop did not degrade but ( R)-mecoprop degraded with zero order kinetics at 0.65 mg l −1 day −1 to produce a stoichiometric equivalent amount of 4-chloro-2-methylphenol. This metabolite only degraded when the ( R)-mecoprop disappeared. In aerobic conditions ( S)- and ( R)-mecoprop degraded with zero order kinetics at rates of 1.90 and 1.32 mg l −1 day −1 respectively. The addition of nitrate to dormant iron-reducing microcosms devoid of nitrate stimulated anaerobic degradation of ( R)-mecoprop after a lag period of about 20 days and was associated with the production of 4-chloro-2-methylphenol. Nitrate addition to sulphate-reducing/methanogenic microcosms did not stimulate mecoprop degradation. However, the added nitrate was completely utilised in oxidising sulphide to sulphate. There was no evidence for enantiomeric inversion. The study reveals new evidence for fast enantioselective degradation of ( R)-mecoprop under nitrate-reducing conditions.

Changes in enantiomeric fraction as evidence of natural attenuation of mecoprop in a limestone aquifer

Natural attenuation of the chiral pesticide mecoprop [2-(2-methyl-4-chlorophenoxy)propionic acid] has been studied by determining changes in its enantiomeric fraction in different redox environments down gradient of a landfill in the Lincolnshire Limestone. Previous studies have shown that mecoprop degrades predominantly aerobically and that differences in the biological behaviour of the two enantiomers will change their relative proportions during biodegradation. Originally deposited as a racemic mixture, there has been no change in the enantiomeric fraction in the most polluted part of the landfill plume where conditions are sulphate reducing/methanogenic. In the nitrate-reducing zone, the proportion of ( S)-mecoprop increases, suggesting preferential degradation of ( R)-mecoprop; while in the aerobic zone, the proportion of ( R)-mecoprop increases, suggesting faster degradation of ( S)-mecoprop. Mecoprop persistence in the confined Lincolnshire Limestone further downdip is explained by inhibition of degradation in sulphate-reducing conditions, which develop naturally. Laboratory microcosm experiments using up to 10 mg l −1 of mecoprop confirm these inferences and show that under aerobic conditions, ( S)-mecoprop and ( R)-mecoprop degrade with zero-order kinetics at rates of 1.90 and 1.32 mg l −1 day −1, respectively. Under nitrate-reducing conditions ( S)-mecoprop does not degrade, but ( R)-mecoprop degrades with zero-order kinetics at 0.65 mg l −1 day −1 to produce a stoichiometric equivalent amount of 4-chloro-2-methylphenol. This metabolite only degrades when the ( R)-mecoprop has disappeared. The addition of nitrate to a dormant iron-reducing microcosm devoid of nitrate stimulated anaerobic degradation of ( R)-mecoprop after a lag period of 21 days. There was no evidence for enantiomeric inversion. The study demonstrates the sensitivity of changes in enantiomeric fraction for detecting natural attenuation, and reveals subtle differences in mecoprop degradation in different redox environments within the Lincolnshire Limestone aquifer.

Nitrate leaching from a shallow limestone soil growing a five course combinable crop rotation: the effects of crop husbandry and nitrogen fertilizer rate on losses from the second complete rotation

Abstract. The field experiment tested the effects of three management systems on nitrate leaching losses from a five crop rotation on the Lincolnshire Limestone in Eastern England. The Standard system was similar to farming practice in the area. The Protective system integrated individual practices which were expected to decrease nitrate losses (e.g. cover crops, cultivation delay in autumn and reduced intensity, manipulation of drilling dates and, during the first few years of the first rotation, straw incorporation). The Intermediate system was a compromise between the two extremes. All crops were grown at full and half recommended nitrogen rates. This paper reports data from the second full rotation (years 6–10), thus enabling the medium‐term effects of continued management practices to be investigated. Average annual nitrogen leaching losses at 49, 35 and 25 kg N ha–1 for Standard, Intermediate and Protective systems, respectively, were significantly different. The respective flow‐weighted average NO3 concentrations were 167, 131 and 96 mg l–1. Thus, adopting nitrate retentive practices through the rotation was able to substantially decrease losses. The Protective system was as effective as in the first full rotation, demonstrating that 10 years of such practices had not failed in the medium‐term. However, continued minimal cultivation caused serious problems of weed build‐up. The cost of weed control and yield loss caused by grass weeds made cereal production uneconomic in some years. Thus, rules for nitrate leaching control need to be tempered with practical and agronomic considerations. Also, few (if any) management techniques tested guaranteed that nitrate losses would be small in all years, as the interaction with winter weather, particularly rainfall, was of vital importance.

Controls on bacterial sulphate reduction in a dual porosity aquifer system: the Lincolnshire Limestone aquifer, England

Chemical and sulphur isotopic analyses are presented of fissure-waters and pore-waters in the deep confined zone of a dual porosity carbonate aquifer. Some of the fissure-waters show good evidence for bacterial sulphate reduction, with low concentrations of sulphide present which is strongly to moderately depleted in 34S relative to sulphate. The sulphur geochemistry is best interpreted as mixing between: (i) a reduced water with sulphide ∼60‰ depleted in 34S relative to sulphate; and (ii) a sulphate-rich water from up-dip in the aquifer. In addition, sulphide oxidation occurs where sufficiently oxidizing water is drawn in by abstractions. The large isotope fractionation factor associated with the sulphidic waters is probably the result of redox cycling of sulphur with little net reduction, rather than a true kinetic fractionation factor. By contrast, pore-waters in the “sulphate reducing zone” show little or no evidence for the effects of sulphate reduction, despite the fact that the pore-waters represent a significant reservoir of sulphate for reduction. Some pore-waters have been modified recognizably by diffusional exchange with the fissure-waters, but the aquifer matrix has not been colonized by sulphate reducing bacteria, probably because porethroats in the limestone are too small for bacteria to pass. Physical exclusion of bacteria from the aquifer matrix and limited diffusional exchange are likely to exert fundamental controls on bacterial redox processes in dual porosity aquifer systems and other systems with low permeability due to small pore interconnections.

Migration and attenuation of agrochemical pollutants: insights from isotopic analysis of groundwater sulphate

Existing hydrochemical and hydrogeological models of pollution migration and attenuation in the Lincolnshire Limestone aquifer of eastern England have been examined in the light of the results of a groundwater sulphate sulphur isotope investigation. This has allowed the distinction of different sources of sulphate and their relative importance in different parts of the aquifer. The principal sources are 34S-depleted inputs, derived from the oxidation of pyrite within both the aquifer matrix material and the overlying mudstone deposits, and 34S-enriched anthropogenic inputs which are derived from acid rain fallout augmented by agrochemicals. Groundwaters sampled over the outcrop zone of the aquifer have sulphate δ 34S dominated by contemporary acid rain inputs in the recharge waters. A down-dip decrease in the 34S content of groundwater sulphate over the unconfined and shallow confined areas of the aquifer is indicative of a progressive increase in the significance of pyrite-derived sulphate in the system. The contribution of sulphate from this source is large and indicates that pollution front penetration (previously based on total sulphate concentrations) is more restricted than previously thought. Moreover, the extent of pyrite oxidation is greater than can be accounted for by dissolved O 2 and the additional component corresponds to that which would be expected from reduction of nitrate using pyrite as the electron donor. We suggest that this mechanism is responsible for denitrification in the aquifer, but that it will be ultimately limited by pyrite availability near fissure surfaces where the reaction takes place.

Total catchment conditions in relation to the Lincolnshire Limestone in South Lincolnshire

Abstract Hydrogeological studies of the Lincolnshire Limestone aquifer in south Lincolnshire combined with the development of mathematical models were reported in the 1970s. However, these studies concentrated on the aquifer and did not consider the total catchment conditions of both the groundwater and surface water systems. Greater importance is now placed on understanding total stream and river flows and preparing models which can predict the change in flows due to different abstraction scenarios; this has required a complete review of ‘the catchment’ of the Lincolnshire Limestone and the associated models. This review has led to the development of improved methods of estimating the recharge due to runoff, identifying locations such as inliers of the Lincolnshire Limestone in the river valleys where runoff can enter the aquifer system, improving the representation of wild bores (uncapped overflowing artesian boreholes) and representing leakage through the overlying strata in the east of the study area. These developments now allow the simulation of total river flows, especially low flows. A novel type of diagram has been devised for representing inflows, outflows and changing flow conditions along the streams and rivers.

The Effect of Borehole Sealing on the Southern Lincolnshire Limestone Catchment

ABSTRACTThe Southern Lincolnshire Limestone is an important groundwater resource; however, for many years water has been lost from the aquifer system through uncontrolled artesian flow from wild‐bores in the Fenland area. During 1991–92, there was an extensive programme of sealing or controlling the wild‐bores, and compensation flows for ecological and farming purposes were provided at some sites.This paper describes a field study which was designed to identify the important features of part of the catchment; this was followed by the development of an existing groundwater model to provide an improved representation of the uncontrolled and controlled wild‐bores. The model is used to assess the consequences of controlling or sealing the wild‐bores.

Estimating runoff–recharge in the Southern Lincolnshire Limestone catchment, UK

This article addresses the problem of aquifers where recharge can arise from runoff from less permeable areas. A distributed model is described which is used to estimate the runoff from various strata, this runoff can subsequently infiltrate into the aquifer as the water flows onto the permeable areas of the aquifer system. The approach is illustrated by a Limestone aquifer; in the model, direct percolation, infiltration, soil moisture storage, minor aquifer storage etc. are considered for areas of 1km2. Runoff directed down the catchment, infiltration into the aquifer system can occur at the margins of the low permeability areas or when the streams pass onto the aquifer outcrop. Parameters of the runoff model are selected to reflect the physical processes, subsequently they are modified to match field measurements of runoff at three gauging stations located on the less permeable sub-catchments. The water balance and runoff calculations are carried out each day, the averaged values over half-monthly periods are used as input to a regional groundwater model.

The micro-scale hydrogeological properties of the Lincolnshire Limestone, UK

Abstract As part of an integrated study of the ‘dual porosity’ hypothesis, a detailed micro-scale hydrogeological study was conducted of the rock material from a quarry excavated in the Lincolnshire Limestone. Permeability and porosity determinations allow comparisons to be made with the lithostratigraphy and show that the matrix hydraulic conductivities are inconsequential in terms of groundwater flow. The relatively high porosities typical of these limestones, combined with large surface areas associated with the major bedding plane fissures, provide a mechanism in which diffusive transport can become a significant factor in contaminant migration. The diffusion coefficients ( D *) of three tracers used in field investigations (bromide,fluorescein and amino g acid) were measured in each of the main rock materials from the site using both double reservoir and reservoir depletion techniques. In addition, an assessment was made of D * estimation using an electrical resistivity method. Alteration of the matrix due to calcite dissolution of the fissure faces creates a zone of enhanced permeability and porosity. The presence of a fissure fill results in a ‘multiporosity’ interface between the fissure and the matrix that may significantly increase the mass of contaminant entering the pore fluid by diffusion in comparison with a simplistic conceptualization of this zone.

Migration of dissolved petroleum hydrocarbons, MTBE and chlorinated solvents in a karstified limestone aquifer, Stamford, UK

Abstract Two incidents of hydrocarbon contamination to the Lincolnshire Limestone in east Stamford, UK, have been investigated. No evidence of LNAPL contamination of groundwater was observed, suggesting that the spills may largely have been retained in the unsaturated zone. Some groundwater contamination by dissolved hydrocarbons occurred, apparently especially at times of high recharge. Rapid flow paths were proven to nearby springs in the River Welland (with groundwater flow velocities of up to 240 m day −1 ), and dissolved hydrocarbon and MTBE contamination appears to have been flushed rapidly from these systems. MTBE contamination at Tallington Pumping Station (5 km east of the site) is not clearly linked to these incidents. Of potentially more concern was the discovery of dissolved chlorinated solvent contamination in the groundwater at the spill sites, possibly related to a landfilled quarry and/or a nearby engineering works. No direct evidence of DNAPL was observed. A conceptual model of solvent distribution suggests independent sources of TCE, PCE and TCA.