A better understanding f groundwater-surface water interactions is urgently required o underpin the implementation of the Water Framework Directive and to increase our knowledge of environmental processes in relation to base flow, chemical and nutrient fluxes, contaminated groundwater-surface water transfers, the selection of spawning sites by Atlantic salmon( Salmos alar) and the abstraction of groundwater. This project assessed a range of methods, other than the time-consuming technique of flow gauging, as fast and effective indicators of groundwater-surface water interactions over a catchment-wide scale.The study was aided by the results of two high resolution catchment-wide flow-accretion surveys. Physical and chemical tracers were shown to be ineffective when compared against the results of the flow-accretion surveys. A number of factors, such as long reach lengths, anthropogenic discharges, other in-stream processes and similar groundwater and surface water composition, appeared to diminish the signals produced by groundwater inputs to below detectable levels. A detailed reach-scale investigation assessed a range of methods over different temporal and spatial scales. The direct measurement of groundwater and surface water levels were 100% accurate in the identification of groundwater-surface water interactions, but this method would be impractical for catchment-scale assessment. Three methods for predicting groundwater-surface water interaction sites were assessed based on hydrogeological theory, such as groundwater flow systems, dry valley inputs and localised aspects of the solid geology. The effectiveness of the predictions were compared against the results of the Frome and Piddle flow-accretion surveys. The method using the localised aspects of the solid geology showed relatively high accuracy (60-70%)and was quite fast for catchment-scale assessment. The final investigation showed a statistically insignificant correlation between groundwater inputs and the location of Atlantic salmon( Salmos alar) redds. However, lower densities of Atlantic salmon redds were observed a long certain survey reaches that were subjected to surface water losses.

The Permo-Triassic sandstone aquifer is one of the most important drinking water resources in the UK. Beneath the Four Ashes site, the aquifer is contaminated with toxic levels of phenolic compounds and inorganic species. Although the hydrochemistry of the groundwater has been fully characterised, no research has assessed contaminant plume development with time using full groundwater profiles. Also, studies have investigated the aerobic microbial ecology at the site, but no research has assessed the anaerobic communities. Anaerobes are important for the remediation of the contamination, as the majority of the contaminated groundwater is anoxic. Furthermore, research has demonstrated that the structure of planktonic (free-living) eubacterial communities at 30m below ground level (mbgl) differ significantly from the community attached to quartz sand suspended in the aquifer at the same depth. However, the diverse mineralogical matrices in sandstones may influence microbial attachment, and therefore the communities attached to quartz may not be representative of the true indigenous attached communities. The aim of this thesis was to update the knowledge on the groundwater hydrochemistry, and to investigate the effects of contaminant load and substratum properties on microbial attachment and anaerobic microbial ecology. Groundwater samples were taken from multiple depths using 2 depth-discrete boreholes. Concentrations of phenolic compounds in the groundwater were measured using high performance liquid chromatography, and inorganic species were measured by ion chromatography. Chemical profiles show that the groundwater hydrochemistry at borehole 59 (130m from source) remained stable between 1998 and July 2009. However, the data reveals that the distribution of the contaminants changed in August 2009, due to the onset of the pump and treat remediation strategy implemented at the site. Data from borehole 60 (350m from source) shows that the concentration of total phenolics increased markedly at 42- 45mbgl between 1998 and 2009, due to variations in contaminant spillage on site, potentially resulting in the plume extending further than the deepest sampling point (45mbgl). Denaturing gradient gel electrophoresis (DGGE) of amplified 165 rRNA, napA (nitrate-reductase) and dsrB (dissimilatory sulphate reductase) reveal that the structure of eubacterial and anaerobic communities varied with depth down the groundwater profile, and were therefore influenced by contaminant load. The DGGE profiles of planktonic communities were compared to the communities attached to 3 different geological substrata suspended in the aquifer under the same hydrochemical conditions (i.e. same depth). Profiles reveal that the planktonic communities were highly dissimilar to the attachment communities on all surfaces, and at all samplings. Furthermore, DGGE profiles of the attached communities were compared. Results reveal that the communities attached to 5hap granite and sandstone cluster separately to the community attached to quartz, suggesting that substratum properties are an important control governing microbial attachment. This was investigated by quantifying microbial attachment to 6 different geological coupons (apatite, 5hap granite, hematite, orthoclase, quartz and shale) suspended in the aquifer. Each coupon provided different physiochemical conditions (hydrophobicity, surface charge and nutrient chemistry) to the system. Results indicate that the most extensive attachment was on coupons that contained at least one microbial growth nutrient (Ca, P, K, Na, Fe, Mn); hematite, apatite, orthoclase and particularly 5hap granite, which contains the most nutrients. The least attachment was witnessed on the quartz surface, which contains no microbial nutrients. Quartz has similar surface charge and roughness to orthoclase, and a similar hydrophobicity to the 5hap granite. The only difference between the surfaces is nutrient availability. This confirms that substratum chemistry, in particular nutrient content, is a major control on microbial attachment.

No description available.

A number of karst springs rise in the Carboniferous strata of the Mells Valley, Somerset which is an area surrounded by many active and disused quarries. Some of these karst springs actively deposit tufa, a secondary precipitate of calcium carbonate, and they have been identified by the Environment Agency as potentially vulnerable to the effects of local sub-water table quarrying. A comparative study of a tufa-depositing spring, Whitehole Farm Spring, and a non tufa-depositing spring, St. Dunstan's Well, was carried out in order to determine the influence of hydrogeology, hydrogeochemistry and environmental biology on the processes of tufa deposition. The two springs are approximately 2 km apart and located within the same outcrop of Carboniferous Limestone strata. A series of qualitative dye-tracing tests established a positive hydraulic connection between a feeder stream which rose in the Old Red Sandstone of the upper hydrological catchment, a sinkhole at the junction with the Lower Limestone Shales and Whitehole Farm Spring resurgence in the Carboniferous Limestone. The sinkhole was shown to have two separate channels to the water table. The tests demonstrated that structural geology and the water table had definable effects on the subterranean route and travel time of the allogenic recharge water. The recharge water to Whitehole Farm Spring was guided by the SE - NW Downhead Fault and did not follow the SW - NE course of the natural dry valley. The water velocity was dependent on the height of the local water table at the time of the tests. Hydrograph analysis of flow data combined with the dye-tracing tests illustrated the rapid response of the springs to storm events (< 24 hrs). The results gave an indication of the shallow nature of the Carboniferous Limestone aquifer and the different stages of development of fissures and conduits in the two spring systems, St. Dunstan's Well being a more mature karst system than Whitehole Farm Spring. Analysis of 18 monthly water samples from both springs at their resurgences and 100 metres downstream revealed temporal and spatial differences in the hydrogeochemistry of the springs and their streams. Ca 2+ and HCOs' were the dominant ions in both spring waters, however, neither of the spring resurgences were supersaturated with respect to calcite (Whitehole Farm Spring, mean -0.17 ± 0.08 Sic ; St. Dunstan's Well, mean -0.33 ± 0.08 Sic). The resurgence water at Whitehole Farm Spring was higher in Ca 2+ (mean 112 ± 3.35 mg I" 1 ) than at St. Dunstan's Well and became supersaturated as it flowed downstream (mean 0.43 ±0.10 Sic). Lower Ca 2+ levels at St. Dunstan's Well (80 ± 2.7 mg I" 1 ) were influenced by the degassing of recharge water and the deposition of calcite as speleothem within the open system of caves behind the resurgence. Downstream supersaturation was also lower (-0.011 ± 0.079 Sic). There was a highly significant difference (p <0.001) between mean daily flow at Whitehole Farm Spring (0.95 ±0.19 ML d" 1 ) and St. Dunstan's Well (11. 58 ± 1.93 ML d" 1 ). Electrical conductivity, total dissolved solids, alkalinity, Na, K, and NO 3 were also higher at Whitehole Farm Spring, the differences being significant (p < 0.01). There were major differences in the biodiversity and environment of the two sites. Petrographic examination of field-collected tufa samples from Whitehole Farm Spring demonstrated that the stream flora, in particular lower plants, and the surrounding riparian vegetation were a major influence on the formation and morphology of the tufa deposits. Newly accreted tufa which had formed on artificial substrates placed in the stream, revealed calcite crystals surrounding the empty moulds of filamentous cyanobacteria. Hydrological conditions within the stream also influenced the micromorphology of calcite crystals forming on two filamentous algal species, Vaucheria longata and Zygnema stellinum. Whitehole Farm Spring was also found to be the more stable environment where biodiversity was higher. The shaded conditions created by Whitehole Farm Spring's woodland environment were beneficial to the growth of filamentous algae, cyanobacteria and bryophytes. The dominant species upstream was a crustose epilithic red alga Hildenbrandia rivularis. Downstream, in and on the tufa deposits the dominant aquatic flora were a number of species of the filamentous yellow-green alga Vaucheria and the cyanobacterium Lyngbya and the moss species Palustriella (Cratoneuron) commutatum. These species were either absent or growing under different ecological conditions at St. Dunstan's Well where there was sparse woodland. The dominant species at St. Dunstan's Well was the filamentous green alga Cladophora glomerata which was not present at Whitehole Farm Spring. Debris from the surrounding riparian vegetation at Whitehole Farm Spring acted as substrates for colonisation by microorganisms which enhanced the nucleation and growth of tufa in the stream. Hydrological and environmental conditions at St. Dunstan's Well prevented the accumulation of organic debris within the stream flow. The study highlighted the need for conservation of the natural environment and biota in order to maintain actively-depositing tufa springs.

Ambiguities in recharge estimates but also in understanding flow process in Poorly Productive Bedrock Aquifers (PPBA) are reported from many studies across the globe. These arise from structural complexities of the hardrock aquifers and are further complicated by variability of the till cover. In Ireland these studies are completely missing and thus concept of groundwater flow and recharge into the PPBA is not well understood. In recognising this, a comparative study of three well typified metamorphic catchments situated in North of Ireland is presented here, each with contrasting land use, geology, glaciation history and consequently till cover with overall aim to develop transferable conceptual model. Quick turnaround times and by-pass flow even in deep bedrock are suggested by water chemistry. Application of stable water isotopes (δ180 and δD) confirms the meteoric origin with rapid response times to precipitation from several days to few months depending on till cover and rainfall intensities. Groundwater flow can be narrowed down to following flow systems: (1) transition zone with rapid transit times of few months; (2) deep and shallow bedrock with significantly lower circulation times. Tritium dating yielded residence time estimates of up to 60 years. Absence of drift deposits and interference of added drainage through fault or weathered zone decreased the residence time by 10 years. Groundwater in till and alluvium is likely to be recharged within the past 5 years. Moreover developed conceptual model was validated by mass balance modelling using NETPATH and suggests that consideration of 3D lateral components are necessary to fully understand the flow in these heterogeneous aquifers.

No description available.

This thesis presents a study of the flow system in the unconfined Chalk aquifer in East Yorkshire, based on the behaviour of spring discharge during the recession period. Groundwater is an important natural water resource in the UK, nearly one-third of England’s water supplies are provided by groundwater (almost 60% of the total by the Cretaceous Chalk aquifer). Springs drain water from large areas of the Chalk aquifer in East Yorkshire, so the discharge is governed by cumulative effects from flow systems and recharge. This study investigates whether the recession curve of spring hydrographs can be used to identify the characteristics of aquifer flow system, e.g. the extent of fracture and conduit flows. For this purpose analytical, hydrochemical and numerical modelling approaches been used. Due to the complexity of the hydrogeological system in the study area, various data sets have been used to conceptualize two gauged catchments within the Chalk aquifer outcrop area. Therefore climatic, hydrological, geological information has been collated and field monitoring of groundwater level, groundwater temperature, stream water temperature, stream water electrical conductivity, spring water CFCs concentration and stream water discharge undertaken. Annual recharge and water balances were calculated and interpreted for the two catchments (Kirby Grindalythe and Driffield). Geological information has been used to construct geological models of the two gauged catchments; hydrological conceptual models have been developed through combining hydrogeological information with the geological models. Actual evapotranspiration and rainfall data have been used for calculating annual recharge and estimating the timing of the start of the spring recession period for each hydrological year (i.e. the cessation of groundwater recharge). A tabulation method technique was used for constructing a Master Recession Curve (MRC) for selected gauged springs over 15 hydrological year recession periods. The MRC approach averages out the variation in between recession curves from different hydrological years, thus removing the effects of recharge variations between years, to produce a recession curve reflecting mainly topographical and hydrogeological factors. The MRC were analysed using the Maillet method; the Kirby Grindalythe MRC can be represented by a single recession coefficient, whereas that for the Driffield catchment was better represented by a two-segment curve (i.e. two recession coefficients). This result showed that the springs in the Kirby Grindalythe catchment drain from an aquifer consisting of a single reservoir, whereas that in the larger Driffield catchment may indicate a dual-reservoir aquifer (probably a network of smaller fractures in the interfluves, with a network of larger fractures or conduits in the valley). In order to investigate whether the topographic divide represents the groundwater divide, and also to investigate whether the gauged springs were responsible for draining all recharge water from the catchments, water balance has been calculated for each catchment. The result revealed that in both study catchments the net rainfall recharge is always greater than outflow (spring discharge plus abstraction). This result showed that either there is uncertainty in the catchment size (ie the topographic divides are not the groundwater divides) or there is groundwater discharge from the study catchments. The ratio of net rainfall recharge/spring outflow from water balance was compared to the maximum flow rate during the recession for water years 2010-2014. The ratio was fairly constant for Driffield catchment with average value 3.5, but in Kirby Grindalythe catchment the ratio was about 5.6. The most probable reason for this difference is that a considerable portion of the groundwater is flowing out from both catchments in the form of subsurface flow. The concentration of CFC11 and CFC12 in the water samples during the recession period of the springs were monitored in order to estimate the residence time of the groundwater in the aquifer. The result showed that the groundwater is contaminated with CFCs; therefore, the concentration of CFCs in the water samples was not able to be used in the Groundwater age estimation. It was noticed that the concentration of the contaminated CFCs has a pattern; therefore its pattern was compared with the pattern of the stream flow rate. A correlation has been noticed between CFCs concentration and flow rate. Through the analysis of this correlation it has been found that this correlation can be used for estimating flow system in the aquifer. In addition, the mixing CFC-11 and CFC-12 model has been used for estimating the flow system in the studied catchments. The results showed that Driffield catchment includes two flow systems. It is also showed that Kirby Grindalythe catchment consists of two sub-catchments; one of the sub-catchments feeds Duggleby-1 spring and the second one feeds Duggleby-2 spring. The sub-catchment which feeds the Duggleby-1 contain two flow systems and the sub-catchment which feeds Duggleby- 2 contain single flow system. Transient three-dimensional numerical models were developed to simulate both Kirby Grindalythe and Driffield catchments. The aquifers in each catchment were simulated with the finite difference block centred groundwater model MODFLOW2000 using Groundwater Vistas version 6 (GV 6). The recession curves from the models were calibrated to the observed MRC in each case. The outcome confirmed that in Kirby Grindalythe catchment the chalk aquifer consists of a single reservoir flow system, whereas in the Driffield catchment the aquifer consists of a double reservoir flow system.

Radiocarbon (14C) is one of the most ubiquitous radionuclide contaminants due to its formation at every stage of the nuclear power generation process. Authorised discharges and accidental release from anthropogenic activity have meant the concentration of this radionuclide at nuclear contaminated sites can be many orders of magnitude higher than the naturally occurring levels of 14C. It is of interest as a contaminant due to its long half-life (5730 ±40a; Godwin, 1962) and bioavailability. This thesis investigates the processes affecting the behaviour of inorganic and organic forms of 14C in subsurface environments. The first section of this work identified the key attenuation mechanisms of inorganic 14C in subsurface environments. The precipitation of 14C carbonate minerals in subsurface environments is enhanced by the availability of Ca2+ and by the abundance of nucleation sites. Maximum 14C removal in solid isotopic exchange experiments occurred after approximately 2 weeks equilibration and the amount of 14C removed from solution was proportional to the amount of calcite surface area present. These results suggest that if inorganic 14C is released into subsurface environments, both precipitation and solid phase isotopic exchange can result in non-conservative 14C-labelled dissolved inorganic carbon transport and so 14C contamination may persist in groundwater for decades following accidental releases. The results of the experiments using 14C-labelled low molecular weight organic substances suggest that ubiquitous and diverse bacterial phyla are able to utilise a range of 14C-containing low molecular weight organic substances very rapidly, and thus such substances are unlikely to persist in aerobic or denitrifying shallow subsurface environments, however under iron reducing conditions there is potential that a proportion of 14C-formaldehyde and 14C-methanol may persist for longer in groundwater and therefore spread further in subsurface environments.

Previous studies of the hydrogeology of the Lower Greensand of the London Basin have suggested that recharge from the north and south is insufficient to balance current abstractions. Studies of the Lower Greensand have demonstrated the existence of a number of depositional troughs / tidal channels, the significance of which have been largely overlooked by previous hydrogeologists. Sedimentological studies show that these troughs consist of well sorted uncemented almost pure quartz coarse sands and act as conduits enabling rapid recharge of the London Basin from outcrops to the north and west. This study uses noble gas and uranium groundwater geochemistry to determine groundwater migration and mixing in the Lower Greensand. The noble gases were determined by mass spectrometry and the radioelements by alpha and gamma spectrometry and scintillation counting. Uranium disequilibrium and noble gas data have been used to confirm the existence of a zone of ancient (up to 50,000 years old) saline water in the central and deep basin. This data has also confirmed that recharge must occur from the Chalk and that this water is of considerable age ( -115, 000 years). The uranium data shows these waters are mixing in the south with very rapidly recharged water and in the north with recent recharge water. The volumes of these recharge waters are insufficient to support current abstractions and therefore saline water is being drawn from the deep aquifer to account for this short fall. This water in tum draws into the deep aquifer water recharged at the western outcrops, through the tidal channels. It is predicted that this western outcrop groundwater will have an age of -8000 years and in time will be detected, mixing with the deep saline water. There is some evidence from the dissolved radioelements to suggest that another trough may allow recharge from the south.

The distribution of hydrochemical types in the Sandringham Sands of west Norfolk is used to test a conceptual model of groundwater recharge and flow. Measurements of dissolved noble gases and strontium (Sr) isotope ratios were integrated into the study as specific tracers of recharge and water:rock interaction processes respectively. Recharge to the unconfined Sandringham Sands aquifer is affected by the patchy distribution of Quaternary sediments, especially glacial till. Groundwater recharged through the till can be distinguished from that recharged to outcrop areas by having higher Ca2+and HCO, concentrations (greater than 80 and 200 mg L \ respectively) and lower Mg2+and K+ concentrations (less than 5 mg L I for both species). Pyrite oxidation during recharge in both settings creates acidity that is consumed by calcite dissolution where the till is present but by glauconite weathering at outcrop, giving rise to the hydrochemical differences observed. Weathering of glauconite releases radiogenic Sr into the outcrop recharged water resulting in H7Sr/H6Sr ratios greater than 0.7087. Groundwater in the unconfined aquifer is reducing and commonly sulphidic as SO/ is reduced by oxidation of sedimentary organic matter disseminated throughout the aquifer matrix. The aquifer is confined to the east of its outcrop by the Gault and Snettisham Clays, separating the Sandringham Sands from the overlying Chalk. The oxygen isotope ratios (8IHO) of water from both the Chalk and the confined Sandringham Sands are depleted relative to those from the unconfined aquifer (::;-7.5%0 and ~-7.3%0 VSMOW respectively) indicating that the confined aquifer is mainly recharged from the Chalk. Two groundwater types are evident in the confined aquifer. The more northerly type is distinguished from the southerly type by having SO/ concentrations less than 20 mg LI and Si02 and Mg2t concentrations greater than 8 and 3 mg LI respectively. The northerly type is significantly supersaturated with respect to atmospheric noble gases, indicating the presence of a large concentration of "excess air". Excess air entrainment occurs during recharge and is proportional to the magnitude of annual water table fluctuation in the recharge area. The high concentrations measured require annual water table fluctuations of between 5 and 8 m, as observed over the drift-free Chalk outcrop in the north of the region. The Gault Clay is absent in this area allowing water recharged to the Chalk to flow into the Sands beneath. Lower concentrations of excess air are found in the southern groundwater type indicating a different recharge mechanism. This groundwater is recharged through the base of an incised channel infilled with Quaternary deposits, which provides a permeable conduit from the Chalk into the Sands, bypassing the confining clays. Therefore, the hydrochemical differences between the types result from different recharge mechanisms. This study is able to directly link observed water table fluctuations with the measured degree of neon supersaturation (~Ne) in groundwater for the first time. The results show excellent agreement to the theoretical relationship.