distribution origin and hydraulic influence of fractures in a clay rich glacial deposit in the unconsolidated clay rich glacial deposits underlying a site in southwestern ontario fractures and root casts greatly influence hydraulic conductivity and groundwater flow the fractures are

constraints on hydraulic parameters and implications for groundwater flux across the upland estuary interface abstract analyses of independent laboratory and field scale measurements from two sites on sapelo island georgia reveal heterogeneity in hydraulic parameters across the upland estuary interface regardless of the method used short duration pumping tests amplitude attenuation of tidal pumping data sediment grain size distributions and falling head permeameter tests we obtain hydraulic conductivity of 10 4 m s 1 for the fine grained well sorted clean sands that make up the upland areas proximal to the upland estuary boundary the tidal pumping analyses and permeameter tests suggest that hydraulic conductivities decrease by more than two orders of magnitude a result consistent with the presence of a clogging layer such a clogging layer may arise due to a variety of physical chemical or biological processes the extent and orientation of the layers of reduced hydraulic conductivity near the upland estuary boundary influence the nature of the aquifer s response to tidal forcing where the lower conductivity layer forms a relatively flat creek bank tidal pumping produces a primarily mechanical response in the adjacent aquifer where the creek bank is nearly vertical there is a more direct hydraulic connection between the tidal creek and the adjacent aquifer the clogging layer likely contributes to the development of complicated flow pathways across the upland estuary boundary effective flow paths calculated from tidal pumping data terminate within the marsh beyond the boundary of the upland aquifer suggesting a diffuse regime of groundwater discharge in the marsh we postulate that in many settings submarsh flow may be as important as seepage faces for groundwater discharge into the marsh estuary complex

observation and analysis of near surface pore pressure measurements in clay shales slopes clay shales largely outcrop in the northern apennines of italy where they are associated with frequent and widespread landslide activity the paper presents the results of monitoring activities carried out in two field sites and focused on the hydrology of clay shales prone to landsliding in the monitored slopes the water table is close to the ground surface throughout the year with seasonal fluctuations of tens of centimetres to a couple of metres shallow weathered soils or clay cover and unaltered material exhibit a much different behaviour although responses to single rainfalls are clearly identifiable as pressure pulses in the clay cover they are never observed in the underlying parental clay shales where downward gradients indicate recharge and only long term seasonal fluctuations are recorded short term variations of pressure head in the clay cover are ruled by downward propagation of a pressure wave in saturated conditions more than 400 pore pressure responses collected in the two sites are analysed in terms of lag time rate and amount of pressure increase and timing of pressure peaking it emerges that the linear diffusion theory can satisfactorily explain the observed behaviour in deeper unaltered material the barometric effect influences the measures similarly to what is observed in confined aquifers after its removal the corrected data exhibit regular seasonal fluctuations which are used to estimate the diffusivity of the material based on phase lag and attenuation of the downward propagating long term periodic pulse copyright 2011 john wiley sons ltd

a multiscale study of the permeability of a thick clayey till we describe and evaluate two previously undocumented methods of bulk permeability k determination and compare results obtained with results of conventional smaller scale tests on the same thick clayey till deposit analysis of the downward propagation of seasonal water table fluctuations yielded bulk k of approximately 10 10 m s 1 in close agreement with results of laboratory consolidation and permeameter tests slug tests and distribution of vertical hydraulic gradient with depth in the deposit this agreement suggests that for such materials high gradient tests conducted at small scales of distance and time can provide reasonable estimates of bulk k the results also imply groundwater residence times in the till of thousands of years the flow pattern observed near a large excavation in the till was consistent with the initial recoveries of piezometers installed in much smaller boreholes assuming perturbation of hydraulic head in the formation due to borehole excavation time scales of these perturbations which prevent interpretation of measured hydraulic head using conventional well hydraulic methods varied from months to tens of years

origin and movement of groundwater and major ions in a thick deposit of champlain sea clay near montreal at a site near montreal piezometers and core samples were used to assess the origin age and rate of groundwater movement in a 28 m thick deposit of champlain sea clay 3h occurs only within the upper 3 4 m which indicates that groundwater below this surficial weathered zone originated prior to 1952 concentrations of 18o na and cl in water from the deepest piezometer suggest that the deep clay was deposited in a mixture of about 33 seawater and 67 freshwater profiles of several major ions show a gradual increase in concentration with depth mathematical simulations of vertical migration of ca2 mg2 k na and cl provide close matches to the field profiles when only upward diffusion of these ions into the surficial freshwater zone is included in the model with a diffusion time of approximately 10 000 a when the downward advection rate of 0 13 cm a 1 obtained from field measurements of hydraulic gradient and hydraulic conductivity is included in the model the simulated major ion profile

hydrogeology of two saskatchewan tills i fractures bulk permeability and spatial variability of downward flow groundwater flow patterns were compared and contrasted in two deposits of clayey till of different thicknesses both of which overlie regional aquifers in a flat upland recharge area analysis of 67 field and laboratory hydraulic conductivity determinations indicated that conductive fractures in the unoxidized zone of the thinner till dalmeny site give rise to an isotropic bulk permeability of approximately 5 10 9 ms 1 which is two orders of magnitude greater than the bulk permeability of unoxidized till in the thicker deposit warman site vertical pore water velocities estimated using hydraulic and isotopic evidence vary greatly at dalmeny and appear to be of the order of 8 m in 10 000 yr at warman the association of vertical groundwater flux depth to water table and depth of oxidized zone at a given location is referred to as the flow regime there spatially detailed water level monitoring and test drilling indicated substantial variation of the flow regime at dalmeny on a horizontal scale of tens of meters no such variation exists at warman the differentiation of the flow regime at dalmeny is due to higher till permeability which permits a spatially variable response to microtopographically focussed infiltration of surface water recognition of the causes and symptoms of flow regime variability beneath flat till landscapes has implications for environmental assessment procedures agricultural practices wetland management and waste disposal

sources and dynamics of sulfur in weathered till western glaciated plains of north america abstract at three sites in the western glaciated plains warman and luck lake in saskatchewan canada and bow river in alberta canada thick 30 m till sequences contain 0 3 0 8 s by dry weight in the unweathered zone depths 2 5 15 m 65 90 of this s is cr reducible pyrite the remainder largely organic s is enriched in 34 s by 6 12 relative to the pyrite at the bow river site both pyrite and organic s are enriched in 34 s by up to 9 relative to samples of the same fractions from the warman and luck lake sites this may reflect a higher content of non marine parent material in southern alberta till at the warman site the sources and dynamics of sulfur in the weathered zone were investigated during weathering of the floral formation till sulfate was produced by the oxidation of pyrite and to a lesser extent by mineralization of organic s based on the distribution of so 4 in the landscape at warman three settings have been distinguished upland leached channel depression and saline ring the upland setting has a 9 m thick weathered zone which contains abundant so 4 mainly as secondary gypsum sulfate has been leached downward from the upper 2 m creating a peak accumulation of gypsum at 3 m sulfate has been leached from the entire 2 5 m deep weathered zone in the channel depression setting by seasonal infiltration of snow melt and lateral flow in contrast at 3 4 m depth in the weathered zone at the edge of the channel so 4 has accumulated as a saline ring here the gypsum s is up to 1 of the soil dry weight in the weathered zone of upland and saline ring settings the 34 s values of the so 4 in sediment extracts water soluble and groundwater 13 1 to 9 0 are very similar to those of the total s 12 0 to 11 4 and pyrite s 16 0 to 10 1 of unweathered floral formation till this indicates an in situ weathering source of the so 4 in contrast the 34 s of so 4 in sediment extracts and groundwater from the leached weathered zone of the upland and channel depression settings 7 7 to 4 5 is enriched in 34 s relative to unweathered floral formation till s this enrichment may be attributed to either 1 isotope fractionation during oxidation of pyrite and or 2 mineralization of residual organic s which is 34 s enriched after pyrite was weathered away

use of vertical profiles of δ18o to constrain estimates of hydraulic conductivity in a thick unfractured aquitard vertical distributions of 18o were used to constrain hydraulic conductivity k in a thick unfractured aquitard previous investigations utilizing permeability tests at a variety of scales keller et al 1989 indicated that bulk k at the site ranges from 3 5 0 11 m s to 1 2 10 10 m s advective displacements calculated on the basis of these k values lead to a wide range of predicted distributions of natural tracers after 11 000 years comparison of 18o distributions and simulated advection diffusion profiles provide a more precise constraint on advective displacement and hence on k the simulations cast in terms of a peclet number p v2t d ranging in value from 0 to 12 indicate that transport is diffusion controlled and that k is actually less than 1 2 10 11 m s p greater than 0 1 k 1 2 10 11 m s overestimates transport this result indicates that conventional permeability tests in very tight media tend to overestimate k in practical terms advective transport at the site is negligible and transport can be simulated with diffusion only p o

ice sheet derived submarine groundwater discharge on greenland s continental shelf 1 isotopically light 1 to 8 and fresh pore fluids 300 520 mm cl were found in continental shelf sediments up to 100 km offshore of southeastern se greenland suggesting infiltration and mixing of ice sheet meltwater with seawater to depths of 260 m these geochemical anomalies may be associated with ice sheet derived submarine groundwater discharge smgd we present a continental scale reconstruction of the late pleistocene hydrogeology of se greenland using finite element analysis that incorporates ice sheet loading and solute and isotope transport results indicate that subglacial infiltration and smgd are of the same order of magnitude and are highly dependent on the permeability of the subaerial basalt simulated infiltration and smgd almost doubled during the last glacial maximum compared to ice free conditions much of the present day glacially induced groundwater discharge occurs on land subice infiltration on the continental shelf likely represents a mixture of seawater and meltwater during past glacial maximums simulated smgd during the most recent interval of glacial retreat is about 4 of the total ice sheet melting at present the simulated rate of smgd is about 11 of the estimated current melting rate

characteristics of high resolution hydraulic head profiles and vertical gradients in fractured sedimentary rocks summary accurately identifying the position of vertical hydraulic conductivity k v contrasts is critical to the delineation of hydrogeologic units that serve as the basis for conceptual and numerical models of groundwater flow high resolution head profiles have identified the position and thickness of k v contrasts in clayey aquitards but this potential has not yet been thoroughly evaluated in sedimentary rocks this paper describes an experiment in which head profiles with the highest technically feasible resolution were obtained using westbay multilevel systems mls installed in 15 cored holes at three sedimentary rock research sites with contrasting geologic and flow system conditions mlss were installed to maximum depths between 90 and 260 m with 2 5 monitoring zones per 10 m head profiles were measured over multiyear periods the vertical component of hydraulic gradient i e vertical gradient was calculated for each pair of adjacent monitoring intervals in every mls and then categorized based on its repeatability to facilitate interpretation of k v contrasts and comparisons within boreholes between boreholes at the same site and between sites the head and vertical gradient profiles from all three sites display systematic i e simple geometric shapes defined by repeatable intervals of no to minimal vertical gradient indicating relatively high k v units bounded by shorter depth intervals with large up to 50 m m vertical gradients indicating relatively low k v units the systematic nature of the profiles suggests flow in regular and interconnected fracture networks rather than dominated by a few key fractures with irregular orientations the low k v units were typically thin with their positions and thicknesses not predicted by lithostratigraphy or detailed lithologic geophysical and horizontal hydraulic conductivity data hence the position and thickness of units with contrasting k v would not be evident if mlss with the conventional number of monitoring zones had been used furthermore the detailed profiles can be strongly diagnostic of hydrogeologic unit boundaries or layers and can be used to improve the quantitative assessment of flow system conditions that is foundational to understanding contaminant plume migration

observation and analysis of pore pressure fluctuations in a thin colluvium landslide complex near cincinnati ohio abstract field observations in a thin colluvium landslide complex along the ohio river near cincinnati show that measurable late winter and spring pore water pressure increases occur when several centimetres of rain fall over a period of one or more days average pre storm fillable porosity of 9 suggests that the colluvium was near saturation during the period of record dimensional analysis of flow through a sloping homogeneous layer of uniform thickness shows that short term pore pressure fluctuations in very nearly saturated soils can be approximated by a one dimensional linear diffusion equation the concept of slope parallel and slope normal characteristic times is also introduced to determine the conditions under which slope parallel and slope normal flow will predominate analytical solutions to the diffusion equation are then used to investigate the effects of storm frequency and magnitude on pore pressure fluctuations comparison of solutions for layers of finite and infinite thickness shows that an impermeable substrate nearly doubles pore pressures along the substrate for storms of short duration however the effect of an impervious boundary vanishes with increasing duration finally measured rainfall values are incorporated into a finite difference simulation of the observed pore pressures with good results

hydrogeochemistry of a clayey till 1 spatial variability the spatial variability of hydrogeochemical processes was studied within an 18 m thick unit of clayey till beneath a flat prairie landscape models of major element mass transfer constrained by chemical mineralogical and isotopic measurements on waters and solids were developed for two end member water quality types occurring within the unit the observed pattern of chemical variation which is predominantly lateral on a scale of tens of meters is caused by microtopographically controlled differences in the ratio of vertical water flux to oxidation rate associated with depression focused recharge such variation is to be expected where dynamic flow regimes develop in thin surficial tills containing chemically reduced constituents observed depletions of major elements from oxidized zones of the till support the mass transfer models and demonstrate that the time scales of persistence of hydrogeochemical variability in the till and of water quality evolution in the aquifer beneath range from 104 to 105 year na and s concentrations in such aquifers will depend primarily on ratios of influxes of end member water quality types from the till above while ca mg and inorganic c concentrations will remain high as long as partial pressures of co2 in the till remain high co2 generation in the till is discussed in the companion paper keller this issue

multiple scale hydraulic characterization of a surficial clayey aquitard overlying a regional aquifer in louisiana abstract the vertical hydraulic conductivity k v of a 30 m thick surficial clayey aquitard overlying a regional aquifer at an industrial site in the mississippi river valley in louisiana was investigated via intensive hydraulic characterization using high resolution vertical hydraulic head profiles with temporal monitoring and laboratory tests a study area was instrumented with a semi circular array of piezometers at many depths in the aquitard at equal distance from a large capacity pumping well including replicate piezometers profiles showed negligible head differential to 20 m bgs below which there was an abrupt change in vertical gradients over the lower 8 10 m of the aquitard hydraulic characteristics are strongly associated with depositional environment the upper zone of minimal head differentials with depth and minimal variation over time correlates with paleo mississippi river backswamp deposits while the lower zone with large head differentials and slow but moderate head changes correlates with lacustrine deposits the lower zone restricts groundwater flow between the surface and underlying regional aquifer which is hydraulically connected to the mississippi river lab tests on lacustrine samples show low k v 8 10 11 4 10 9 m s bracketing field estimates 6 10 10 m s from 1 d model fits to piezometric data in response to large aquifer head changes the slow response indicates absence of through going open fractures in the lacustrine unit consistent with geotechnical properties high plasticity normal consolidation suggesting high integrity that protects the underlying aquifer from surficial contamination the lack of vertical gradients in the overlying backswamp unit indicates abundant secondary permeability features e g fractures rootholes consistent with depositional and weathering conditions 2 d stylized transient flow simulations including both units supports this interpretation other published reports on surficial aquitards in the gulf coast region pertain to pleistocene deposits that lack laterally extensive lacustrine units and where k v is enhanced by secondary permeability features resulting in clayey aquitards with poor integrity

infiltration and hydraulic connections from the niagara river to a fractured dolomite aquifer in niagara falls new york abstract the spatial distribution of hydrogen and oxygen stable isotope values in groundwater can be used to distinguish different sources of recharge and to trace groundwater flow directions from recharge boundaries this method can be particularly useful in fractured rock settings where multiple lines of evidence are required to delineate preferential flow paths that result from heterogeneity within fracture zones flow paths delineated with stable isotopes can be combined with hydraulic data to form a more complete picture of the groundwater flow system in this study values of d and 18 o were used to delineate paths of river water infiltration into the lockport group a fractured dolomite aquifer and to compute the percentage of river water in groundwater samples from shallow bedrock wells flow paths were correlated with areas of high hydraulic diffusivity in the shallow bedrock that were delineated from water level fluctuations induced by diurnal stage fluctuations in man made hydraulic structures flow paths delineated with the stable isotope and hydraulic data suggest that river infiltration reaches an unlined storm sewer in the bedrock through a drainage system that surrounds carrying river water to hydroelectric power plants this findings is significant because the storm sewer is the discharge point for contaminated groundwater from several chemical waste disposal sites and the cost of treating the storm sewer s discharge could be reduced if the volume of infiltration from the river were decreased

a landslide in till near warman saskatchewan canada little information is available about typical shear strength parameters of tills in southern saskatchewan even though till is the most common earth material used for construction in this region the warman landslide in the south saskatchewan river valley provides some insight into the shear strength characteristics of a till and the results are compared with laboratory tests the till is from the upper till of the sutherland group which has a high clay content relative to the underlying and overlying tills a back analysis of the landslide produced 27 assuming c 0 comparison with laboratory test data and results from a similar landslide near lebret saskatchewan suggests that 22 5 with c 7 kpa may be appropriate residual shear strength parameters a rising water table appears to have been the main contributing factor to instability between 1969 and 1984 there is a possibility however that at the 1 50 return interval for flood levels on the river erosion at the toe of the landslid

controls on the distribution of major ions in pore waters of a thick surficial aquitard transport and geochemical processes controlling the chemical and isotopic composition of pore waters in the upper 45 m of a thick surficial clay rich till battleford formation were studied the upper 3 m of the till is oxidized and fractured the remaining 77 m of the till the aquitard is nonfractured and unoxidized concentrations of total dissolved solids so42 na mg2 and k decrease with depth through the unoxidized zone to a depth of about 15 m below ground below which the concentrations remain constant a similar trend was observed for alkalinity however the decrease in concentration occurs over 20 m in contrast to these ions ca2 concentrations increase with depth through the upper 20 m unoxidized zone below which the concentrations remain relatively constant the distribution of dissolved ions shows the presence of two end members elevated solute concentrations in the oxidized zone attributed to geochemical weathering that occurred since the start of the holocene and connate pleistocene age water at depths between 20 and 45 m abiotic and biotic geochemical reaction rates in the aquitard were shown to be extremely slow or not occurring

geology geochemistry and genesis of the cretaceous and paleocene sandstone and conglomerate hosted uragen zn pb deposit xinjiang china a review abstract the uragen zn pb deposit in wuqia county xinjiang china is hosted in sandstones and conglomerates of the lower cretaceous kezilesu group and argillaceous dolomite of the paleocene aertashi formation in the kashi sag northwestern tarim basin the deposit is characterized mainly by low grade zn pb 3 wt and large tonnage 3 mt metals in the southern ore zone potentially 10 mt metals for the whole deposit with an average zn pb ratio of about 5 8 the orebodies are tabular and stratiform mainly distributed in a syncline the ores are characterized by disseminated sulfides with minor massive veinlet patchy structures and fine grained locally colloform and framboidal textures the main primary metallic minerals are sphalerite galena pyrite and marcasite and minor supergene minerals include smithsonite hydrozincite anglesite calamine jarosite and limonite the ore minerals mainly occur as replacement of cements matrix and framework grains of the host rocks and as open space filling to a lesser extent based on the fact that orebodies straddle across a hiatus between the lower cretaceous and paleocene host rocks and on the replacement and open space filling textures and structures the mineralization is interpreted to be epigenetic the tightly clustered pb isotopic values of the main stage ore minerals 206 pb 204 pb ranging from 18 608 to 18 663 207 pb 204 pb from 15 619 to 15 669 208 pb 204 pb from 38 677 to 38 839 suggest that a single source supplied the metals whereas the wide range of s isotopes 34 s from 27 9 to 14 6 vcdt indicates multiple sources of reduced sulfur including those from thermal sulfate reduction tsr and bacterial sulfate reduction bsr the organic matter in the ores is characterized by relatively low concentrations of saturated hydrocarbons high concentrations of aromatic hydrocarbons asphaltenes and non hydrocarbons and low maturity compared to that in the host rocks and equivalent strata away from mineralization both hydrocarbons in the ores and host rocks show little biodegradation these characteristics of organic matter suggest that the site of mineralization was buried to significant depths and heated to above 80 c before the charging of hydrocarbons thus non development of biodegradation that some of the hydrocarbons were consumed in mineralization thus decreased maturity probably used as reducing agents for sulfate reduction in situ and that bacteria derived sulfur in the ores was not generated in situ mineralization probably resulted from mixing of a metal rich fluid with multiple fluids carrying reduced sulfur from different sources including some reduced sulfur from in situ tsr however it remains unclear whether the metal carrying fluid was derived from a near surface groundwater system and flowed downward to the site of mineralization at burial conditions or was derived from deeper parts of the basin and flowed up to the site of mineralization as part of a hydrothermal system the distinction of the two models requires a better understanding of the thermal profile across the deposit

field variable head test in low permeability materials assessing the effects of trapped gas pocket and cavity expansion trapped gas and cavity expansion may affect the data of a variable head test in a monitoring well in a low permeability material some gas may be trapped in the top of the filter pack presence of a gas pocket may be alleged when the initial change in water level in the pipe is less than the theoretical value due to the slug volume a variable head test with trapped gas is described by three equations to be solved simultaneously the gas pocket contraction leads to an underestimation of the hydraulic conductivity k especially for small pipes used to test natural or compacted clay it must be considered however that the difference between the theoretical and measured changes in initial water level is due to the sum of trapped gas contraction plus cavity expansion falling head or trapped gas expansion plus cavity contraction rising head this difference cannot be used to assess the volume of trapped gas unless an independent mechanical test has established the material deformability for example p

monitoring of total soil moisture on a scale of hectares using groundwater piezometers a method has been developed for continuous measurement of total soil moisture on a scale of hectares the method is based on accurate measurement of groundwater pressures in thick clay formations and depends on the principle that changes of mechanical load result in changes of groundwater pressure the resulting data are similar to those obtained by conventional weighing lysimeters but on a much larger scale and with no significant hydrologic disturbance of the site several years of field testing show the method to be practicable

annual fluctuations of groundwater levels as a result of loading by surface moisture abstract long term hydrographs for deep confined aquifers in southern saskatchewan canada show annual fluctuations characterized by a gradual rise in head from october to may june and a rapid drop from may june to october these fluctuations are distinctly different from the seasonal fluctuations observed in surficial and shallow semi confined aquifers which reflect the response of these aquifers to recharge derived from snow melt and early spring rains on the basis of field data and theoretical considerations it is demonstrated that seasonal fluctuations of the water table are not transmitted down to the deep aquifers provided the confining layers are thick and have sufficiently low hydraulic diffusivity the annual fluctuations in the deep aquifers thus do not reflect seasonal recharge to these aquifers plots of moisture accumulation i e precipitation minus calculated areal evapotranspiration are strikingly similar to the observed hydrographs for the deep aquifers in timing and magnitude of the annual fluctuations it is postulated that the annual head fluctuations in the deep confined aquifers reflect changes of the mechanical load on the formations caused by seasonal changes of the soil moisture snow and storage at the water table the deep confined aquifers thus act as large scale inexact weighing lysimeters

fracture effects in the shallow groundwater zone in weathered sarnia area clay the sarnia area of southwestern ontario is underlain by thick deposits of clay rich glacial till from ground surface to between 4 and 6 m depth the clay till is fractured oxidized and penetrated by root holes the water table fluctuates seasonally between the ground surface and the bottom of the weathered zone water level response tests in conventional piezometers installed in augered holes in the weathered zone typically provide very low values of hydraulic conductivity 10 7 10 9 cm s which are similar to values obtained from the deeper unweathered and unfractured till the augering process creates a smeared clay zone along the borehole walls that significantly reduces measured hydraulic conductivity values in this study the weathered zone hydraulic conductivity was measured using unconventional piezometers a large diameter well and a tracer experiment between two test pits the smeared zone was removed or reduced around these installations and the measured weathered zone hydraulic conductivi

a new technique for obtaining high resolution pore pressure records in thick claystone aquitards and its use to determine in situ compressibility 1 laboratory tests are commonly used to determine properties vertical compressibility specific storage ss and vertical hydraulic conductivity kv of claystone aquitards however whether data representative of in situ conditions can be obtained from disturbed samples is questionable here we present a method to determine the in situ and ss of a thick sequence of cretaceous aged claystone by estimating the loading efficiency of a formation from pore pressure responses to barometric pressure fluctuations we installed 10 vibrating wire pressure transducers at different depths 25 325 m below ground in a thick claystone aquitard by placing them directly within the cement bentonite grout two years of continuous transducer records using this method appeared to provide pore pressure data with a resolution of better than one part in 105 equivalent to millimeter of hydraulic head change pore pressure responses to barometric pressure changes earth tides and precipitation events can be clearly identified and the barometric responses can be easily analyzed the resulting values of 0 6 0 93 2 5 10 7 to 2 2 10 6 kpa 1 and ss 2 6 10 5 to 4 5 10 6 m 1 all decrease with depth the results are comparable with the limited existing data for in situ estimates of ss and are as much as an order of magnitude smaller than laboratory estimates of ss for similar aquitard deposits our findings suggest that the fully grouted transducer method can provide an accurate and reliable means to monitor pore pressure changes and to determine in situ parameters for bedrock aquitard systems

comparison of methodological uncertainties within permeability measurements permeability measurements are critical to the calculation of water flow within hillslopes despite this errors in permeability measurements are often ignored and can be very large particularly in disturbance sensitive gley soils this work compares the uncertainties associated with six field methods of permeametry applied to a gleyed soil in upland britain slug tests constant head borehole permeametry and falling head borehole permeametry were undertaken on established piezometers additionally ring permeametry and two types of trench tests were evaluated method related uncertainty due to proximity of impeding layers of high sorptivity soils produces under and over estimates of permeability by a factor of up to 0 2 and 5 respectively this uncertainty band is smaller than the observed effects of anisotropy and temporal variability had smearing and soil ring leakage errors not been minimized the methodological uncertainties would have been so large that they would have distorted the true spatial field of permeability and its estimated impact on the balance of vertical and lateral flow

the radial diffusion method 1 using intact cores to determine isotopic composition chemistry and effective porosities for groundwater in aquitards a new method is described for the determination of the isotopic composition and chemistry of groundwater in aquitards the effective porosities for each component can be determined concurrently the method is based on diffusive exchange of water and solutes between groundwater in a cylindrical core of aquitard material and water in a reservoir placed along the axis of the cylinder the method was tested for 2h cl and so4in an aquitard consisting of clay rich glacial till the 2h in aquitard core samples as determined by radial diffusion agreed closely with 2h in groundwater obtained from corresponding piezometers installed in the aquitard for the concentrations of cl and so4 the agreement was less close but still satisfactory the effective porosities were equal to the total porosities for 2h and were less than the total porosities for cl and so4 ions

combining unsaturated and saturated hydraulic observations to understand and estimate groundwater recharge through glacial till summary although there has been much previous research into various aspects of the flow mechanisms through glacial till an integrated analysis of the flow system from the ground surface to the aquifer is lacking this paper describes such an approach with reference to a detailed field study of the hydraulic processes controlling groundwater recharge through lodgement till in shropshire uk a fieldsite was instrumented with tensiometers and piezometers at a range of depths through the profile and the geology investigated in detail through field and laboratory testing the median matrix hydraulic conductivity of the 6 m thick till is found to be around 2 10 10 m s on the basis of laboratory measurements using the barometric efficiency of the till derived from on site pressure responses the specific storage for the till is found to be in the range 2 10 6 6 10 6 m 1 and approximately 3 10 6 m 1 for the underlying permo triassic sandstone the regional aquifer the hydraulic data indicate that till water table responses to rainfall occur during the summer period even when large tensions are present higher in the profile this is thought to be due to preferential flow through hydraulically active fractures in the till which were observed in a test pit dug on site the field evidence indicates that the fractures are usually infilled with a variety of materials derived and transported from clasts within the till the bulk hydraulic conductivity of the till seems to be greatly enhanced by these features and it is shown on the basis of hydraulic testing and numerical modelling that the bulk hydraulic conductivity of the till is orders of magnitude greater than that of the till matrix and reduces with depth below ground surface the paper furthers understanding of the hydraulic processes contributing to recharge through till and makes the link between the detail of these processes and simplified models of recharge estimation which may be needed for larger scale water resource studies the results are relevant also to contaminant migration studies and aquifer vulnerability assessments

fracture permeability and groundwater flow in clayey till near saskatoon saskatchewan field and laboratory studies of a clayey unweathered glacial till have shown that its bulk permeability exceeds its matrix permeability by two orders of magnitude such findings are common for weathered till but are rare for unweathered till and have important implications for groundwater recharge and contaminant transport the till in question is 6 m thick and appears to be unweathered and unfractured it is overlain by 12 m of weathered and highly fractured till results of consolidation tests on the unweathered till indicate a mean vertical hydraulic conductivity of 3 5 10 11 m s 1 and a mean specific storage of 1 3 10 4 m 1 results of slug tests yield a horizontal hydraulic conductivity of about 5 10 9 m s 1 drawdowns in the till in response to pumping from the aquifer below indicate a vertical hydraulic diffusivity of 4 5 10 5m2 s 1 the slug test results combined with specific storage results from consolidation tests indicate a similar value for horizontal hydraulic diffusivity of 4 10

multi scale hydrogeologic characterization of a leaky till mantled fractured bedrock aquifer system the paper presents hydrogeologic properties for a leaky till mantled fractured bedrock aquifer system based on geophysical and hydraulic tests performed at a drumlin located in northeastern massach

hydrogeology of two saskatchewan tills ii occurrence of sulfate and implications for soil salinity abstract the occurrence of sulfate salts in groundwater and solids was documented at two sites named dalmeny and warman where clayey tills overlie regional aquifers at dalmeny the till is thinner and approximately two orders of magnitude more permeable than at warman samples for sulfur and sulfate determinations were collected to depths of approximately 14 m and at horizontal spacings of a few tens of meters large numbers of indirect measurements of bulk salt content were obtained with a noncontacting earth conductivity meter results showed that the bulk sulfur and sulfate contents of solids could not in general be adequately characterized with point or grab samples from boreholes at dalmeny measurements representing larger averaging volumes revealed a spatially intricate pattern of sulfate abundance and depletion which extends vertically through the oxidized and unoxidized zones of the till to the underlying aquifer similar measurements at warman suggest that sulfate variability there is limited to the oxidized zone these findings and the observed coincidence of sulfate patterns with the groundwater flow patterns documented in part i2 show that the bulk permeability of the till controls the manner in which the subsurface sulfate reservoir is affected by microtopographic focussing of surface water input conceptual analysis of the responses of these systems to various land management practices indicates that where tills are relatively permeable these practices would primarily affect the quality of groundwater recharge to underlying aquifers where tills have low permeability the same practices would have no effect on aquifer water quality but they would affect the potential for surface and soil salinization

groundwater flow velocity and age in a thick fine grained till unit in southeastern wisconsin abstract piezometer nests were installed at study sites in each of five north south trending end moraines of the late pleistocene oak creek formation in southeastern wisconsin the formation is composed primarily of a fine grained glacial diamicton till and laterally continuous and discontinuous coarse grained lake and meltwater stream sediment it overlies the silurian dolomite aquifer which is a source of drinking water to rural areas the average vertical linear velocity and age of ground water in the oak creek formation were estimated by three methods darcy s law environmental isotopes including 3 h 2 h 18 o and 14 c dissolved inorganic carbon and solute transport modeling of 18 o the f 1 and metro sites in the tinley moraine showed excellent agreement among the three estimates of vertical velocity and showed the lowest velocity values 0 3 0 5 cm year 1 downward which suggests that diffusion controls vertical mass transport at these sites although the extrapolated maximum age of ground water is 35 000 years ground water below 75 m at these sites is probably not older than 15 000 years which is the maximum age of the formation estimates of velocity showed less agreement at study sites in the lake border moraine system to the east and ranged from about 0 2 to 20 7 cm year 1 maximum groundwater age could range from 213 to 6000 years higher and more variable velocities perhaps owing to thinner and more heterogeneous sediment in these areas suggest that diffusion may not dominate vertical mass transport heterogeneity and fractures may also promote the development of groundwater flow systems dominated by lateral flow because of the uncertainty about the nature of groundwater flow velocity and age in the formation east of the tinley moraine future waste disposal activity in southeastern wisconsin should be confined to the thickest parts of the tinley moraine near the present f 1 and metro sites

mineralogy of lead in a soil developed on a pb mineralized sandstone largentiere france lead speciation was determined in a soil developed on a geochemical anomaly arising from a pb zn stratabound deposit in largentiere ardeche france this geological setting offers the opportunity to determine the preferred form s of pb following soil formation on this unique anomaly in the soil profile studied pb concentrates in the b horizon 2055 mg kg pb relative to both the a 1330 mg kg pb and c 1874 mg kg pb horizons plumbogummite pbal 3 po 4 2 oh 5 h 2 o is the main host of pb in the soil profile pb also appears to be associated with mn hydr oxides as shown by micro analyses empa sem eds and sxrf in the form of inner sphere pb 2 complexes as suggested by pb l iii edge exafs spectroscopy linear least squares fitting of background subtracted k 3 weighted pb l iii edge exafs functions derived from bulk soil samples was carried out using pb l iii exafs spectra of 22 pb containing model compounds quantitative assessment of pb speciation revealed that whereas plumbogummite is the most abundant pb phase in the soil profile pb 2 mn hydr oxide surface complexes are gradually replaced by pb 2 surface complexes with other phases possibly pb 2 organic complexes upward in the soil profile the presence of large amounts of pb phosphate in the largentiere soil suggests that low solubility phosphates may be important long term hosts of pb in pb contaminated soils that have sufficiently high phosphorous activities to cause formation of these phases

characterizing the hydrogeology of a complex clay rich aquitard system using detailed vertical profiles of the stable isotopes of water abstract high resolution 1d profiles of the stable isotopes of porewater 2h and 18o obtained by direct porewater equilibration of core samples were used to identify hydrogeologic zones in a thick complex till aquitard system in saskatchewan canada detailed 1d isotope profiles revealed the presence of three distinct hydrogeological zones an upper 5 10 m an intermediate 10 30 m and a lower 30 62 5 m till zone the upper hydrogeological zone was controlled by a sand layer having a high hydraulic conductivity k the lack of vertical variability in the stable isotope data in the intermediate zone suggested groundwater flow and solute transport was controlled by a system of interconnected vertical fractures and lateral sand layers the curved shape of the isotope profile in the lower till zone suggested that solute transport in this zone was controlled mainly by molecular diffusion we show that high resolution vertical stable isotope profiles of porewater obtained from core samples and direct equilibration yield cost effective and invaluable hydrogeologic information on groundwater flow in aquitard systems that cannot be realistically obtained by construction of costly conventional piezometer bundles i e 2h and 18o analyses of water samples and k determinations further the direct equilibration approach overcomes the problem of piezometer leakage in low k aquitards

three dimensional imaging of aquifer and aquitard heterogeneity via transient hydraulic tomography at a highly heterogeneous field site abstract previous studies have shown that geostatistics based transient hydraulic tomography tht is robust for subsurface heterogeneity characterization through the joint inverse modeling of multiple pumping tests however the hydraulic conductivity k and specific storage ss estimates can be smooth or even erroneous for areas where pumping observation densities are low this renders the imaging of interlayer and intralayer heterogeneity of highly contrasting materials including their unit boundaries difficult in this study we further test the performance of tht by utilizing existing and newly collected pumping test data of longer durations that showed drawdown responses in both aquifer and aquitard units at a field site underlain by a highly heterogeneous glaciofluvial deposit the robust performance of the tht is highlighted through the comparison of different degrees of model parameterization including 1 the effective parameter approach 2 the geological zonation approach relying on borehole logs and 3 the geostatistical inversion approach considering different prior information with without geological data results reveal that the simultaneous analysis of eight pumping tests with the geostatistical inverse model yields the best results in terms of model calibration and validation we also find that the joint interpretation of long term drawdown data from aquifer and aquitard units is necessary in mapping their full heterogeneous patterns including intralayer variabilities moreover as geological data are included as prior information in the geostatistics based tht analysis the estimated k values increasingly reflect the vertical distribution patterns of permeameter estimated k in both aquifer and aquitard units finally the comparison of various tht approaches reveals that differences in the estimated k and ss tomograms result in significantly different transient drawdown predictions at observation ports

relating in situ hydraulic conductivity particle size and relative density of superficial deposits in a heterogeneous catchment summary estimating the permeability of superficial deposits is fundamental to many aspects of catchment science but can be problematic where insufficient in situ measurements are available from pumping tests in piezometers consequently common practice is to estimate permeability from the material description or where available particle size distribution using a formula such as hazen in this study we examine the relationships between particle size relative density and hydraulic conductivity in superficial deposits in morayshire northern scotland a heterogeneous environment typical of many catchments subject to previous glaciations the superficial deposits comprise glaciofluvial sands and gravels glacial tills and moraines raised marine sediments and blown sands thirty eight sites were investigated hydraulic conductivity measurements were made using repeated guelph permeameter measurements cone resistance was measured in situ with a panda dynamic cone penetrometer material descriptions were made in accordance with bs5930 1999 and disturbed samples were taken for particle size analysis overall hydraulic conductivity k varied from 0 001 m d to 40 m d glacial till had the lowest k median 0 027 m d and glacial moraine the highest k median 30 m d however within each geological unit there was great variability in measured hydraulic conductivity values multiple linear regression of the data indicated that log d 10 and relative density indicated by cone resistance or bs5930 1999 soil state description were independent predictors of log k and together gave a relationship with an r 2 of 0 80 material description using the largest fraction e g sand or gravel had little predictive power therefore in heterogeneous catchments the permeability of superficial deposits is most strongly related to the finest fraction d 10 and relative density of the material in situ guelph permeameter measurements at outcrops with good geological characterisation provide an easy and reliable method of determining the permeability of particular units of superficial deposits

origin age and movement of pore water in argillaceous quaternary deposits at four sites in southwestern ontario hydrogeologic information in the form of textural properties field and laboratory determined hydraulic conductivity values vertical hydraulic gradients from piezometer nests and major ion and isotopic contents 18o 2h 3h 13c 14c was obtained from four sites located in southwestern ontario on thick deposits of clayey till and glaciolacustrine clay at each site the piezometers were installed from the water table zone situated 1 4 m below the surface to a maximum depth between 20 and 35 m below the surface values of hydraulic conductivity determined in the laboratory by consolidometer and triaxial methods are in the order of 10 8 10 7 cm s and are similar to values calculated from rates of water level rise in piezometers mean values of average vertical groundwater velocity calculated with the measured values of hydraulic conductivity porosity and hydraulic gradient using the darcy equation for a saturated non fractured porous medium range from 0 13 to 0 26 cm yr tritiated pore waters only occur within 3 6 m of ground surface thereby indicating that groundwaters below this depth recharged prior to at least 1952 18o in the pore waters exhibit a distinctive regular shift with depth from water table values of 9 to 10 smow characteristic of present day precipitation to values between 14 and 17 at depths of 20 40 m which are characteristic of much cooler waters corrected 14c ages of the groundwater are greater than 8000 yr b p thereby suggesting that the groundwaters at depth entered these deposits during or after the formation of these deposits approximately 11 000 to 14 000 yr ago 18o 2h and cl concentration profiles were simulated with a one dimensional model for transport by advection and diffusion in a saturated porous medium reasonable agreement between the model and the field profiles was obtained with values of effective diffusion coefficients of 3 0 10 6 cm2 s for 18o 2h and cl and with groundwater velocities between 0 03 to 0 05 cm yr based on these results it is concluded that the pore water in these deposits is a mixture of late pleistocene and modern waters and that the distribution of 18c 2h and cl in these deposits is influenced predominantly by molecular diffusion apparently more so than by hydraulic flow

hydraulic head in a clayey sand till over multiple timescales this paper presents an analysis of hydraulic head data measured every 2 h for 2 years in the leading edge of a drumlin that consists of weathered brown clayey sand till and underlying unweathered

hydrogeology and geochemistry of low permeability oil shales case study from hashfela sub basin israel abstract low permeability rocks are of great importance given their potential role in protecting underlying aquifers from surface and buried contaminants nevertheless only limited data for these rocks is available new appraisal wells drilled into the oil shale unit osu of the mt scopus group in the hashfela sub basin central israel provided a one time opportunity for detailed study of the hydrogeology and geochemistry of this very low permeability unit methods used include slug tests electrical logs televiewer imaging porosity and permeability measurements on core samples chemical analyses of the rock column and groundwater analyses slug tests yielded primary indication to the low permeability of the osu despite its high porosity 30 40 hydraulic conductivities as low as 10 10 10 12 m s were calculated using both the hvorslev and cooper bredehoeft papadopulos decoding methods these low conductivities were confirmed by direct measurements of permeability in cores and from calculations based on the kozeny carman approach storativity was found to be 1 10 6 and specific storage 3 8 10 9 m 1 nevertheless the very limited water flow in the osu is argued to be driven gravitationally the extremely slow recovery rates as well as the independent recovery of two adjacent wells despite their initial large head difference of 214 m indicate that the natural fractures are tight and are impermeable due to the confining stress at depth laboratory measured permeability is similar or even higher than the field measured values thereby confirming that fractures and bedding planes do not form continuous flow paths the vertical permeability along the osu is highly variable implying hydraulic stratification and extremely low vertical hydraulic conductivity the high salinity of the groundwater 6300 8000 mgcl l within the osu and its chemical and isotopic compositions are explained by the limited water flow suggesting long residence time of the water prolonged water rock interaction and mixing with ancient trapped salty water the current study demonstrates that targeted and detailed research of low permeability rocks can produce reliable hydraulic parameters using slug tests and accompanying methods the data produced is of upmost importance for quantitative risk evaluations such as models for waste burial in low permeability units

the permeability of natural soft clays part ii permeability characteristics reply the permeability characteristics of a number of intact natural soft clays from quebec the usa and sweden have been investigated in the laboratory the variation of permeability with void ratio is best represented in terms of a linear e vs lg k relation which is generally valid in the range of volumetric strains encountered in engineering practice the permeability at the in situ void ratio is shown to be a complex function of such parameters as the void ratio the clay fraction the plasticity index and the fabric of the clay permeability anisotropy is negligible in marine clays the e vs lg k relationships of the various clays tested are well ordered in terms of an empirical parameter ip clay fraction irrespective of the geological origin of the clay the slope of the e vs lg k relationship referred to as permeability change index ck is simply related to the initial void ratio by ck 0 5eo keywords permeability clays laboratory tests permeability anisotropy permeability void ratio re

water flow and swelling pressure in non saturated bentonite based clay barriers abstract the water uptake of 10 and 20 bentonite sand mixtures and of 100 pure bentonite was studied experimentally the results were compared with calculated water content distributions to study the usefulness of the diffusion equation the relation between the swelling pressure and the degree of saturation of a bentonite was also studied

37cl 35cl variations in a diffusion controlled groundwater system abstract groundwaters in the low permeability quaternary glacial deposits of southwestern ontario commonly exhibit increasing cl concentrations with depth because these deposits were formed in a freshwater glacial environment and because cl is not derived from weathering of these deposits previous investigations hypothesized that upward diffusion of saline formation waters from the shallow bedrock caused this cl trend this hypothesis was tested by measuring 37 cl 35 cl ratios in the groundwaters from two typical sites and comparing the results with theoretically derived isotopic distributions produced by diffusion 37cl measurements expressed relative to standard mean ocean chloride smoc ranged from 0 8 to 2 2 and vertical profiles showed a gradual enrichment in 35cl relative to 37cl with increasing distance upward from the bedrock till interface 537cl distributions were simulated with a mathematical solute transport model incorporating the effects of kinetic isotopic partitioning a sensitivity analysis indicated that the model results were affected by the groundwater velocity the isotope enrichment factor and diffusion times agreement between the simulated and observed cl isotope profiles was obtained using a groundwater velocity of 0 an isotopic enrichment factor of 1 0012 and diffusion times ranging from 14 000 to 16 000 years based on these results we conclude that the isotopic enrichment in 35cl was caused by upward diffusion over a period of about 15 000 years this diffusion period is consistent with what is known about the quaternary history of the area

water and solute transfer between a prairie wetland and adjacent uplands 2 chloride cycle the quality of water in lakes and wetlands depends on the exchange of solutes with adjacent uplands in many prairie wetlands the input of water is dominated by snowmelt runoff and the outputis dominated by groundwater flow we use chloride as a tracer to quantify the mass transfer processes associated with surface runoff and groundwater flow between a wetland in saskatchewan canada and the surrounding upland snowmelt runoff transports 4 5 kg yr 1 of chloride from the upland to the wetland most of this chloride infiltrates under the wetland and moves laterally to the upland with shallow groundwater under the upland chloride moves upward in the vadose zone with soil water and accumulates near the surface as water is consumed by evapotranspiration part of this chloride mixes with snowmelt runoff and moves back to the wetland therefore chloride is cycled between the wetland and the upland at an approximate rate of 5 kg yr 1 the chloride cycle occurs within 5 6 m of the ground surface a small amount of chloride escapes from the cycle with the downward flow of groundwater into the deep aquifer the estimated flux of chloride leaving the cycle is 0 1 0 6 kg yr 1 which is of the same order of magnitude as the rate at which the catchment receives atmospheric deposition of chloride because the atmospheric input is reasonably well known over the prairie region the concentration of chloride in groundwater under recharge wetlands can be used to estimate the recharge rate of deep aquifers

hydrogeology and hydrochemistry of an aquifer aquitard system within glacial deposits saskatchewan canada abstract the hydrology and hydrochemistry of an aquifer aquitard system within glacial drift has been studied utilizing data for the aquitard as well as the aquifer the study area lies in the western glaciated plains near saskatoon saskatchewan canada hydrological and chemical processes within the overlying till control the recharge rate major ion chemistry and isotopic composition of the water in the aquifer the bedrock is hydraulically isolated from the system and does not affect the groundwater chemistry reaction products generated in the till are fed into the aquifer by advection and diffusion the aquifer acts as a chemically inert lateral transmission and mixing zone hydrochemical patterns in the aquifer are regional in extent and appear to be related to the geochemical conditions within the till and the flow pattern in the aquifer the system is evolving geochemically on a time scale of thousands of years

hydrogeology of a thick clay till and cretaceous clay sequence saskatchewan canada clay rich glacial till and cretaceous clay are common throughout the interior plains of north america quantifying groundwater flow through these aquitards has implications for solute transport in aquitards and protection of underlying aquifers groundwater flow through a two tiered aquitard system was investigated using laboratory and field methods at a test site in saskatchewan canada the aquitard system consists of 80 m of uniform plastic clay rich battleford till deposited 12 18 ka bp disconformably overlying 77 m of late cretaceous plastic marine clay snakebite member deposited 70 72 ma bp the upper 3 4 m of till is oxidized and fractured whereas the remainder is unoxidized for the scales investigated results suggested that hydraulic conductivity k is independent of scale for relatively thick till and clay bedrock deposits analysis of slug tests in the unoxidized till and laboratory tests on cores of unoxidized till yielded geometric mean k values of 5 4 10 11 and 2 7 10 11 m s res

hydrogeochemistry of prairie pothole region wetlands role of long term critical zone processes abstract this study addresses the geologic and hydrogeochemical processes operating at a range of scales within the prairie pothole region ppr the ppr is a 750 000 km2 portion of north central north america that hosts millions of small wetlands known to be critical habitat for waterfowl and other wildlife at a local scale we characterized the geochemical evolution of the 92 ha cottonwood lake study area cwlsa located in north dakota usa critical zone processes are the long term determinant of wetland water and groundwater geochemistry via the interaction of oxygenated groundwater with pyrite in the underlying glacial till pyrite oxidation produced a brown iron oxide bearing surface layer locally over 13 m thick and an estimated minimum of 1 3 1010 g sulfate so42 at cwlsa we show that the majority of this so42 now resides in solid phase gypsum caso4 2h2o and gypsum saturated groundwater results from the cwlsa were scaled up to a 9700 km2 area surrounding cwlsa using 1800 drill logs and literature data on wetland water chemistry for 178 wetlands within this larger area the oxidized brown zone depth and wetland water compositional trends are very similar to the cwlsa additionally surface water data from 176 southern canadian pothole wetlands that conform to the same wetland water geochemical trends as those recorded in the cwlsa further corroborate that so42 accumulation driven by pyrite oxidation is a nearly ubiquitous process in the prairie pothole region and distinguishes ppr wetlands from other wetlands worldwide that have a similar overall hydrology

microdepression focused recharge in a coastal wetland la plata argentina depression focused recharge dfr has been well documented for the clay till plains of western canada kettle lakes of southeastern wisconsin the sandhills region of nebraska and elsewhere in this study the importance of dfr in a fine grained estuarine coastal plain environment with extremely low topographic relief is shown the southwestern coastal plain of the rio de la plata near the city of la plata argentina extends 8 9 km inland from the river and ranges in elevation from 0 to 3 m above sea level the holocene postpampeano sediments predominantly composed of silty clay in the study area mantle the coastal plain and exert a major control on the hydrodynamics of groundwater of the region the average hydraulic conductivity of the unit ranges from 1 0 10 9 m s 1 when estimated on a small scale single well and oedometer tests to approximately 1 0 10 8 m s 1 when estimated on a larger scale tritium profiles and seepage meters a study of the groundwater flow system has established that recharge is occurring in the marshes of the central coastal plain which are 0 5 1 0 m lower than the surrounding land a broad 50 cm high groundwater mound a significant feature in the context of a regional hydraulic gradient of 0 0005 was documented below the marshland using nests of monitoring wells recharge rates are further controlled by subtle 10 40 cm elevation variations within the marsh four nests of six monitoring wells each were installed in the marsh and sampled for tritium recharge rates were then estimated through calibration simulations using a 1 d analytical solute transport model in the two nests in the lower wetter areas recharge rates were estimated at 4 6 cm year 1 whereas estimated recharge rates in the higher drier areas ranged from 0 3 cm year 1 these differences are consistent with 1 near neutral vertical hydraulic gradients in higher areas vs persistent downward gradients in lower areas 2 chloride concentrations almost an order of magnitude lower in groundwater underlying lower areas than in that of higher areas due to flushing of older more saline groundwater in the lower areas and 3 isotopic evidence for evapotranspiration only in the higher areas the present study suggests that ponding of surface water in local depressions can lead to significant recharge from coastal wetlands this finding has implications for the study of water balance soil salinity and nutrient budgets in these environments 1997 elsevier science b v all rights reserved

a new type curve method for estimating aquitard hydraulic parameters in a multi layered aquifer system summary we propose a new type curve method for estimating the hydraulic conductivity k and the specific storage s s of an aquitard in a multi layered aquifer system theoretical type curves of rate of aquitard compaction versus time are obtained through drawdown time series in the aquitard under a condition that the drawdown history of the underlying aquifer can be approximated as piecewise linear segments pls in each of which the drawdown shows a linear increase trend with time comparing with previous analytical solutions which are limited by the assumption of a constant head in the overlying unconfined aquifer the superposition principle can be called when water levels fluctuate with time in both upper and lower aquifers adjacent to the aquitard when applying the new pls method to estimate k and s s values of an aquitard the starting point of drawdown history at adjacent aquifers should be determined at first after that the drawdown history is approximated as pls to obtain drawdown rate of change for each linear stage and turning points of drawdown history the new pls method is demonstrated at a field site in changzhou city jiangsu province of china estimated results show that k and s s are respectively 9 80 10 10 m s and 4 46 10 4 m 1 for a thick aquitard and 2 34 3 50 10 10 m s and 2 28 10 4 m 1 for a thin aquitard estimated field k values as well as s s values through the new pls method are generally in accordance with the results obtained from the geologic method by konikow and neuzil 2007 they are also in agreements with the numerically calibrated results of shi et al 2008a at the regional scale and the laboratory experimental values of in situ soil samples collected by geological survey of jiangsu province of china