Mean Hydraulic Conductivity Research Articles

Site Characterization Using 3H/3 He Ground‐Water Ages, Cape Cod, MA

AbstractExploratory drilling to locate new water‐supply wells on Cape Cod, Massachusetts encountered fuel‐related organic contaminants in a shallow unconfined aquifer. However, the plume could not be traced back to the water table and estimates of ground‐water velocities were not consistent with plausible contaminant releases, and thus the source of contamination was not located. In conjunction with an expanded hydrogeologic investigation, tritium and helium isotope analyses were performed to delineate ground‐water ages and flow rates. Vertical profiles of ground‐water age were used to determine recharge rates that range from 70 to 115 cm/yr. The age of water near the leading edge of the contaminant plume along with estimates of dispersion were used to estimate when the contaminant release occurred (1975 ± 3 years). Recharge estimates, the geometry of the aquifer, and contaminant data were used in a simple mass balance model to determine both the location of the contaminant source and the horizontal ground‐water velocity (ranging from 20 ± 12 m/y to 90 ± 20 m/y across the site). Concurrent site investigations revealed fuel floating on the water table within the area (± 250 m) determined by the model. The configuration of the water table and recharge estimates were used to estimate a horizontal hydraulic conductivity of 130 ± 30 m/d. The mean hydraulic conductivity from a subsequent 72 hr, 12 well pumping test was 100 m/d.

Assessing flow systems in carbonate aquifers using scale effects in hydraulic conductivity

Counter to intuition, small-scale measurements of hydraulic conductivity do not average to regional values. Instead, mean hydraulic conductivity increases with measurement scale up to a critical distance termed the range, beyond which a constant regional value prevails. Likewise, variance in log hydraulic conductivity increases with separation distance between measurement points as the spatial correlation decreases. As dissolution proceeds in carbonate aquifers, heterogeneity and the volume necessary for an equivalent homogeneous medium (EHM) both increase. As these variables increase, the range of scale increase in both mean hydraulic conductivity and variance increases proportionately. Consequently, the range in scale effects is a reliable measure of the degree of secondary dissolution. By correlating the numeric value of range with independently measured hydraulic properties, the prevalent type of flow system, diffuse, mixed or conduit can be determined.

When enough is enough: The worth of monitoring data in aquifer remediation design

Given the high cost of data collection at groundwater contamination remediation sites, it is becoming increasingly important to make data collection as cost‐effective as possible. A Bayesian data worth framework is developed in an attempt to carry out this task for remediation programs in which a groundwater contaminant plume must be located and then hydraulically contained. The framework is applied to a hypothetical contamination problem where uncertainty in plume location and extent are caused by uncertainty in source location, source loading time, and aquifer heterogeneity. The goal is to find the optimum number and the best locations for a sequence of observation wells that minimize the expected cost of remediation plus sampling. Simplifying assumptions include steady state heads, advective transport, simple retardation, and remediation costs as a linear function of discharge rate. In the case here, an average of six observation wells was needed. Results indicate that this optimum number was particularly sensitive to the mean hydraulic conductivity. The optimum number was also sensitive to the variance of the hydraulic conductivity, annual discount rate, operating cost, and sample unit cost. It was relatively insensitive to the correlation length of hydraulic conductivity. For the case here, points of greatest uncertainty in plume presence were on average poor candidates for sample locations, and randomly located samples were not cost‐effective.

Minimum Thickness of Compacted Soil Liners: II. Analysis and Case Histories

The stochastic models described in a companion paper were used to analyze compacted soil liners with a variable number of 15 cm (6 in.) thick lifts. No optimum number of lifts could be defined based on first‐passage time; first‐passage time increased as the thickness increased. Both models showed that the flux through the liner and the equivalent hydraulic conductivity decreased and the mean hydraulic conductivity (modeled as a lognormally distributed random variable) of lifts decreased. There was little benefit to increasing the number of lifts beyond four to six lifts. An analysis of case histories of in situ hydraulic conductivity also showed little reduction in hydraulic conductivity when the number of lifts was increased beyond four to six. Based upon hydraulic conductivity considerations, the recommended minimum thickness of compacted soil liners is four to six lifts, or 60 cm to 90 cm (2 ft to 3 ft).

Relation Between Hydraulic Conductivity and Texture in a Carbonate Aquifer: Observations

AbstractBased on analysis of over 300 injection‐pressure tests and their assignment to logged stratigraphic intervals, it is argued that the Silurian dolomite aquifer in Milwaukee County, Wisconsin, behaves as both a fractured and porous medium. This paradox is resolved by examining the aquifer's individual stratigraphic units and their respective sedimentologic characteristics. Like many carbonates, the aquifer contains shoaling upward sequences and cycling through a variety of depositional environments and textures. Most of the stratigraphic units are fine‐grained mudstones, but interbeds with porous coarsegrained packstones and grainstones are also present.The packstone and grainstone units have unimodal distributions of hydraulic conductivity with geometric means between 10 4 and 10 3 cm/sec. The high matrix porosity masks any effects of jointing in these deposits, and they behave as porous high conductivity media. In contrast, hydraulic conductivities within the mudstones are bimodal, with one mode of very low matrix conductivities and a second higher mode controlled by jointing. Mudstone conductivities increase logarithmically with joint frequency, but never attain the magnitude of the values for the coarse‐grained units. Because the geometric mean hydraulic conductivities of the porous units are up to 1000 times greater than the thicker mudstones, the aquifer's bulk hydraulic conductivity is controlled by the thinner porous zones. Therefore, as a whole, the aquifer behaves as a porous medium even though most of the section is fracture‐dominated.Only the large number of hydraulic conductivity measurements isolated within specific stratigraphic units has allowed recognition of the importance of porous medium conditions in this aquifer. Because upward shoaling sequences are common within carbonates, a similar combination of porous and fractured medium conditions may be present, but unnoticed, in other carbonate aquifers. Investigators working in dolomites with minimal tectonic deformation should be particularly alert for porous medium effects.

Aquifer/aquitard Units of the Dakota Aquifer System in Kansas: Methods of Delineation and Sedimentary Architecture Effects on Ground-water Flow and Flow Properties

ABSTRACT In the near future, the demand for water in many parts of central and western Kansas will exceed the supply available from near-surface aquifers, forcing exploitation of the underlying Dakota aquifer. The Dakota aquifer framework consists of discontinuous sandstone aquifers confined by mudstone aquitards belonging to the Cretaceous Cheyenne Sandstone and the Kiowa and Dakota Formations. These strata were deposited in a variety of nonmarine through marine settings associated with several cycles of sea-level rise and fall. The aquifer comprises two entire and one partial unconformity-bounded sequences recognized in the Western Interior: Cheyenne-Kiowa, lower Dakota J sequence, and upper Dakota D sequence. Scale-dependent heterogeneity characterizes the Dakota aquifer, because of the inf uence of sedimentary processes on the arrangement and geometry of sandstone bodies and on the fabric of the sandstones. A multidisciplinary approach is being employed in the Dakota Aquifer Program of the Kansas Geological Survey to delineate aquifer/aquitard units and characterize scale-dependent heterogeneity using a variety of techniques. Colorized images of the subsurface from gamma-ray logs in cross sections reveal the complex arrangement of sandstone bodies within the Dakota due to deposition in fluvial and deltaic/estuarine to marine settings. At the more local scale, borehole geophysical logs are being used both to delineate local aquifer zones and to estimate overall ground-water quality. Pumping test results indicate that the contrast of hydraulic properties between a sandstone aquifer and its surrounding mudstone aquitard significantly channels the flow of ground water through the aquifer. he geometric mean hydraulic conductivity of fluvial sandstones is generally higher than in deltaic/estuarine sandstones in either the Dakota or Kiowa Formations. Overlapping ranges of hydraulic conductivity values in fluvial and deltaic/estuarine sandstones may be due to the uniformity of the sediment supplied from source areas combined with variations in the energy of transport and winnowing within each of these depositional systems. Permeameter tests of coreplugs and gamma-ray response on logs indicate that the better sorted, coarser, and less radioactive sandstones make the most permeable aquifer units in two cores of fluvial and deltaic/estuarine sandstones. Experimental variograms using coreplug data indicate that bedding is a significant control on the partitioning of hydraulic con uctivity within sandstone bodies. Succeeding efforts will focus on using the results presented in this paper combined with techniques, such as indicator kriging and geologic process modeling, to map the distribution of sandstone aquifers and their properties in the subsurface within small geographic areas of manageable size where detailed information is needed.

A Comparison of Pumping and Slug Tests for Estimating the Hydraulic Conductivity of Unweathered Wisconsian Age Till in Iowa

AbstractThe low conductivity of glacial till is usually thought to preclude pumping tests, which has led to the predominate use of laboratory permeameter and single well response (slug) tests for estimating hydraulic conductivity. Slug tests only sample a small region around the well and may be more representative of the disturbance of well installation or development than in situ conductivity. To provide a larger scale comparison to slug test estimates of hydraulic conductivity for unweathered Wisconsin age till in Iowa, a pumping test was performed, with both the pumping and monitoring wells placed in unweathered till. Maintaining a constant drawdown of 439 cm in the pumping well for over five days yielded an average flowrate of only 26.3 ml/min, but produced a maximum drawdown of 104 cm at a radial distance of 178 cm. Assuming radial and vertical flow, least‐squares parameter estimation yielded a hydraulic conductivity estimate of 7.5 · 10‐7 cm/s and a specific storage estimate of 6.6 · 10‐6 cm‐1. Slug test results compared favorably, with geometric mean hydraulic conductivity estimates of 4.9 · 10‐7 cm/s from a Cooper et al. (1967) analysis and 7.1 · 10‐7 cm/s from a Hvorslev (1951) analysis. For this relatively low clay till (20% clay fraction), borehole smearing does not appear to have a significant impact on slug tests. The results indicate pumping tests can be performed, on an appropriate scale, in some unweathered tills.

Field study of dispersion in a heterogeneous aquifer: 1. Overview and site description

Results are presented for a large‐scale natural gradient tracer experiment conducted in a heterogeneous alluvial aquifer at a site near Columbus, Mississippi. The study was initiated with a 48‐hour pulse injection of 10 m3 of groundwater containing bromide and three organic tracers (pentaflourobenzoic acid, o‐trifluoromethylbenzoic acid, and 2,6‐diflourobenzoic acid). Over a 20‐month period, seven comprehensive samplings of the tracer plume were performed at approximately 1‐ to 4‐month intervals using an extensive three‐dimensional sampling well network. The dominant feature of the tracer plume that evolved during the study was the highly asymmetric concentration distribution in the longitudinal direction. This asymmetry was produced by accelerating groundwater flow along the plume travel path that, in turn, resulted from an approximate 2‐order‐of‐magnitude increase in the mean hydraulic conductivity between the near‐field and far‐field regions of the site. The Columbus study is distinct from previous natural gradient experiments because of the extreme heterogeneity of the aquifer, the large‐scale spatial variations in groundwater velocity, and the extensive set of hydraulic conductivity measurements for the aquifer.

Falling-head ponded infiltration with evaporation

The problem of falling-head ponded infiltration with evaporation is solved using the Green-Ampt (or delta-function) model. A significant parameter is ε K ̄ , the ratio of evaporation rate to mean hydraulic conductivity in the wetted region. An illustrative example with ε K ̄ = 1.633 gives a time for disappearance of water from the soil surface only 45.6% of that for the case ε K ̄ = 0 . When ε K ̄ = 1.633 , only 57.8% of the water infiltrates, with 42.2% lost by evaporation.

Saturated Hydraulic Conductivity of Scandinavian Tills

There is a distinctive difference in hydraulic properties between the upper horizons of Scandinavian till soil and the deeper C-horizon. The hydraulic conductivity has been studied in different soil profile types, mainly Podzolic variants. In the topsoil there are correlations from grain size and porosity to hydraulic conductivity. Both porosity and hydraulic conductivity are stratified with depth. Often high conductivity appears in the upper soil horizons decreasing with depth to low values at about one metre. This pattern varies with soil type. The soils vary with topographic location as does the groundwater level. Published data on hydraulic conductivity in the C-horizon of sandy-silty tills in Scandinavia covers a wide range, from about 5 × 10−9 m/s to 5 × 10−4 m/s, with a mean of 3 × 10−6 m/s. The correlation between porosity and hydraulic conductivity, as well as between mean grain size and hydraulic conductivity, is weak in the C-horizon. It is concluded that the sediment structure has a decisive influence on the hydraulic conductivity of till. A model of the relationship between fabric (in relation to water flow direction), the porosity in the poresize interval 30-95 μm and the hydraulic conductivity is presented.

A two-step method for permeabilization of Drosophila eggs

As a first step in developing a procedure for the cryopreservation of Drosophila melanogaster embryos, we have established a method for permeabilization of the eggcase and have initiated studies of the hydraulic conductivity of permeabilized embryos and the permeation of selected cryoprotective agents. The eggcase of D. melanogaster embryos has a wax layer that precludes any flux of water. A two-step procedure employing organic solvents was developed to effect removal of the wax layer with minimal deleterious effects on the embryos. Dechorionated embryos (Oregon-R strain P2, 12 to 13 hr old) were rinsed sequentially in isopropanol and hexane. After removal of solvent, embryos were held in a modified cell culture medium for further manipulation. This procedure routinely yielded 80 to 95% of the eggs permeabilized (as determined by osmotic contraction in 1 M sucrose) and 75 to 90% survival (incidence of hatching). Hydraulic conductivity of permeabilized embryos and permeation of cryoprotectants were determined using a microdiffusion chamber and computerized video microscopy. Regression analysis of the volumetric data from individual embryos yielded the Boyle-van't Hoff function FV eq = 0.124 (osm −1) + 0.541 with the standard deviations of slope and intercept ( V b) being 0.010 and 0.040, respectively. Permeabilized embryos exhibited ideal osmotic behavior over the range of 0.265 to 2.00 osm. The mean hydraulic conductivity coefficient ( L p) was 0.722 ± 0.366 (μm/(min · atm) at 20 °C, based on observations of contraction following a step change in concentration of Ringer's solution. The time course for the transient volumetric change of permeabilized embryos subjected to a step change to isotonic Drosophila Ringer's solution containing 1 M DMSO, ethylene glycol, propylene glycol, or glycerol demonstrated that all four cryoprotectants permeated the embryos. DMSO permeated embryos at the highest rate, followed closely by ethylene glycol and propylene glycol, while glycerol permeated very slowly.

Harmonic Mean Conductivity in Declining Rate Filters

Harmonic mean conductivity equations for deep bed filters are developed. Differences between harmonic mean conductivity and hydraulic conductivity based on arithmetic average of specific deposit are explained.

Reclamation of a fine clayey montmorillonitic soil with high‐salt water under laboratory conditions

AbstractAn impermeable fine clayey montmorillonitic soil (Aquic Xerofluvent) was reclaimed using high‐salt water and the addition of a constant quantity of Ca at each step in successive dilutions. The soil attained the theoretically expected values of ESP and the depth of water which passed through the soil was close to the theoretical level. The leachate was studied throughout the process of reclamation and the following results obtained: At the end of the reclamation all ions were seen to be decreasing. The percolation rate of the soil and the „valence‐dilution”︁ effect of the reclaiming water permitted a satisfactory exchange of Na by Ca and Mg keeping the quantity of water close to the theoretically expected levels. The mean hydraulic conductivity (MHC) is strongly depended on the electrolyte concentration and the sodium/total concentration (Na/C) or Ca+Mg/total concentration (R) values of the leachate.

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 × 10−5 m2∙s−1. Geochemical patterns, tritium data, and measured seepage fluxes from an ephemeral pond also indicate that the vertical conductivity of the unweathered till is much higher than the value obtained from the consolidation tests. The data thus show that the unweathered till has significant vertical and horizontal fracture permeability. Key words: till, permeability, fracture, groundwater recharge, contaminant transport.

Grouting as a Remedial Technique for Buried Low‐Level Radioactive Wastes

AbstractSeven grout formulations were tested in the laboratory for their ability to penetrate and to reduce the hydraulic conductivities of soils used as backfills for shallow land burial trenches. Soils from two sites, in Oak Ridge, TN, and Maxey Flats, KY, were used and both are classified as Typic Dystrochrepts. Three soluble grout formulations (sodium silicate, polypropenamide [polyacrylamide], and 1,3‐Benzenediol [resorcinol]‐formaldehyde) were able to both penetrate soil and sand columns and reduce hydraulic conductivities from initial values of ca. 10−4 m s−1 to < 10−8 m s−1. Three particulate grouts (lime [calcium oxide]‐fly ash, fly ash‐cement‐bentonite, and bentonite alone) could not penetrate columns; such formulations would, therefore, be difficult to inject into closed burial trenches. Field demonstrations with both sodium silicate and polyacrylamide showed that grout could be distributed throughout a burial trench and that waste‐backfill hydraulic conductivity could be reduced several orders of magnitude. Field grouting with polyacrylamide reduced the mean hydraulic conductivity of nine intratrench monitoring wells from 10−4 to 10−8 m s−1. Grouting of low‐level radioactive solid waste in situ, therefore, should be an effective technique to correct situations where leaching of buried wastes has or will result in groundwater contamination.

Effect of Disturbed Soil Thickness on Soil Water Use and Movement under Perennial Grass

AbstractPrevious research has shown that plant growth on minespoil of lower plant productivity is dependent upon thickness of soil replaced. Sodium‐affected strip‐mine spoils are a significant reclamation problem in the northern Great Plains. The purpose of this work was to develop understanding of plant growth response to soil thickness over sodic minespoils by measurement of water movement, water use, and root growth. Soil water storage and use were measured in each of three growing seasons under crested wheatgrass (Agropyron desertorum) grown on 0.25‐, 0.5‐, 0.75‐, and 1.0‐m thicknesses of disturbed soil. Soil profiles were constructed from Haploboroll topsoil (0.2 m for all treatments), placed over varying thicknesses of subsoil (B and C horizon materials), which in turn was placed over sodic (Sodium adsorption ratio = 30) drag‐line spoil at a semiarid, steppe‐land site in western North Dakota. Forage yield was 2‐ to 3.5‐fold greater on 1.0 m soil thickness than on 0.25 m. Both total soil water potentials and root weight densities were similar in minespoil and in subsoil at the same profile depths. Root water uptake was much less from the minespoil (mean saturated hydraulic conductivity (HC) = 1 × 10−3 cm/d) than from subsoil (mean HC = 0.2 cm/d). Low HC per se appeared to be the dominant factor limiting sodic minespoil as a plant growth medium because low HC resulted in less use of stored soil water from minespoil compared to subsoil. Depletion from a 120‐cm profile was 0.2, 3.3, 7.9 and 9.8 cm for 0.25‐, 0.50‐, 0.75‐ and 1.0‐m soil thickness, respectively. Relative differences in evapotranspiration (ET) between the 0.25‐m and 1.0‐m soil thickness treatments were much less than yield differences, reflecting progressively reduced water use efficiency with less soil thickness.

Hydrogeological investigations at an experimental site in granite, south west England, in relation to the transport of radionuclides through fractured rock

Constant head injection tests and radioactive tracer experiments at an experimental site in the Carnmenellis granite in Cornwall have revealed a fracture permeability in which water movement is confined to discrete fractures separated by rock of low permeability. Data on flow path frequency, orientation, and effective hydraulic aperture, required for network modelling, have been obtained for a 700-m borehole, with additional hydraulic data from three other boreholes. In addition to fractures of “average” hydraulic conductivity, a small number of major hydraulic features (“main drains”) with major implications for radionuclide migration have been identified. A mean hydraulic conductivity for the granite investigated of 1.57 x 10 −7 msec −1 has been obtained, 2.08 x 10 −8 msec −1 if the major hydraulic features (with hydraulic conductivities as high as 10 −5 msec −1) are excluded.

The influence of abscisic acid on the water relations of leaf epidermal cells of Rhoeo discolor

The water relations of individual Rhoeo discolor (Commelinaceae) leaf epidermal cells were measured using the micro pressure-probe. Cell turgor pressure, volumetric elastic modulus (ϵ) and hydraulic conductivity (Lp) were determined. The influence of ABA on these parameters was studied by both immersion and vacuum infiltration of the leaf in 100 μM abscisic acid (ABA) solution (containing 100 μM dimethylsulphoxide (DMSO)). ABA treatment slightly, but significantly, raised the mean hydraulic conductivity of the cell membranes following both treatments. With infiltration the effect was immediate, with immersion the effect followed a lag period of about 4 h. ABA had no effect on cell turgor pressure or elastic modulus. In several cells in which a large number of individual Lp measurements were performed over a 30-min period a gradual increase of relaxation half time was observed, corresponding to a decreasing Lp.

Calculation of hydraulic conductivities and steady state capillary rise in peat soils from bulk density and solid matter volume

AbstractValues of the three constants in a convenient formula for the calculation of capillary conductivities of peat soils can be evaluated from bulk density and solid matter volume. Though some of the relative equations have a low significancy, they provide a means to calculate in a simple way a mean hydraulic conductivity function for peat soils with given values of the soil properties mentioned above. Examples of such functions are shown. The height of steady state capillary rise in homogeneous fen peats and high bog peats of increasing bulk density are comprised in some diagrams.

Hydraulic Conductivity of a Glacial Till in Albertaa

ABSTRACTSoils underlain at shallow depths (less than 1 m, 3 ft) by glacial till are generally considered undesirable for irrigation because of their unfavourable internal drainage characteristics. In some areas of southern Alberta, Canada, soils developed upon shallow tills have been irrigated successfully for over 60 years with no adverse effects on the soil. An investigation was conducted to describe the hydro‐geologic properties of till under one of these areas and to assess the properties with regard to drainage. Study techniques consisted of detailed test drilling and sampling, excavation of test pits, installation and monitoring of ground‐water instrumentation, field and laboratory hydraulic conductivity testing and tritium analyses of ground‐water samples. Two fracture sets were found in this till. Both sets of fractures produce secondary permeabilities which mask the low hydraulic conductivity of the till matrix (10−10 m·s−1). Small‐scale fractures which have a fracture spacing of approximately 10 mm (0.4 in.) have an apparent mean hydraulic conductivity of 5 × 10−9 m·s−1, whereas large‐scale fractures which have fracture spacings from 20 mm (0.8 in.) to over 630 mm(2 ft) have an apparent mean hydraulic conductivity of approximately 2 × 10−7 m·s−1. The high hydraulic conductivity of the large‐scale fractures was corroborated by tritium analyses of ground‐water samples. Tritium analyses also indicate the presence of recent water at depth in the till. The large‐scale fractures, which control the bulk hydraulic conductivity of this till, provide conduits through which infiltrating water can be transmitted to the ground‐water regime. These fractures are believed to be the reason why this land has remained irrigable for over 60 years.