Range Of Hydraulic Conductivities Research Articles

Analyzing slug tests in wells screened across the watertable: A field assessment

The slug test is the most widely used technique for the in situ estimation of hydraulic conductivityin confined and unconfined formations. Currently, there are no generally accepted methods in thegroundwater literature for the analysis of response data from slug tests performed in wells screenedacross the watertable. A field study was undertaken in an attempt to develop a set of practicalguidelines for tests conducted in such wells. Three wells, screened within unconsolidated materialexhibiting a range of hydraulic conductivities (.05–30.0 m/day), were installed to depths of up to9 m (30 ft) in Kansas River alluvium that ranges in thickness from 15 m to 21 m (50 ft to 70 ft)near Lawrence, Kansas. Intensive well-development efforts removed any drilling debris that couldinterfere with well-formation hydraulics. Once the wells were developed properly, a series of slugtests was performed at each well. The tests were designed to assess the role of the unsaturatedzone and the appropriateness of assuming a fixed hydraulic head upper boundary. The results ofthis investigation can be summarized as follows: (1) the sufficiency of well development shouldbe based on repeat slug tests and not the clarity of pumped water; (2) the effective screen radiusfor best model analysis should be based on a mass balance and not nominal screen dimensions;(3) the watertable can be represented as a constant head boundary and flow in the unsaturatedzone can be ignored in most situations; (4) conventional techniques for the analysis of slug-testdata seem to be reasonable for slug tests conducted in wells screened across the watertable, whenused with the appropriate effective screen radius and normalized head range; and (5) fluctuationsin the watertable elevation through time can be exploited to obtain some insight into the natureof vertical variation in hydraulic conductivity at a well. The results of this investigation indicatethat multiple slug tests should be performed at wells screened across the watertable in order toreliably assess the sufficiency of well development and the appropriateness of conventional theory.

Estimation of hydraulic conductivity in large-diameter, hand-dug wells using slug-test methods

To demonstrate the viability of using slug-test-analysis techniques to interpret recovery data in large-diameter, hand-dug wells, 37 wells representing a range of hydraulic conductivity and located in unconfined and weathered chalk and marl and confined alluvium in North-Central Texas were tested. Recovery data were analyzed by means of a numerical model, two semiempirical methods developed especially for interpreting recovery data from large-diameter hand-dug wells, and different slug-test-analysis methods that have different shape factors describing well geometry. Most hydraulic-conductivity values estimated by slug-test methods are within an order of magnitude of values that are estimated by using a numerical model or methods derived specifically for hand-dug wells. Because of the unique geometry of hand-dug wells (diameters on the same order as well lengths), care must be taken to ensure that the proper shape factors are used with slug-test methods. Because of the substantial well storage in hand-dug wells, considerable time may be required to lower the water level to the desired position, especially if pump capacity is limited. This pumping time results in a noninstantaneous withdrawal of water from the aquifer, which violates one of the assumptions of slug-test-interpretation methods. However, in low-permeability environments, reasonable results can still be attained if water removed from the well sources from well storage or if recovery time is considerably longer than pumping time.

Double-flow behavior observed in well tests of an extremely heterogeneous mine-spoil aquifer

A radial-flow investigation was performed to examine hydraulic characteristics of a heterogeneous unconfined mine-spoil aquifer formed by reclamation of surface-mine overburden. Slug test estimates of hydraulic conductivity ( K) range over four orders of magnitude (from 10 −6 to 10 −2 m/s) and display two prominent statistical modes, ascribed to fine matrix and coarse rubble zones, respectively. A large proportion of wells displayed either of two anomalous slug-test response patterns, attributable to zones of high K around or near the well. Slug-test estimates of matrix K appear unbiased, but those of high-conductivity zones are thought to contain error induced by local heterogeneity and drainage of storage from near the water table. Numerical simulation of slug tests suggests that high- K zones, vertically continuous to the water table and either in the annulus of (e.g. well skin) or in close proximity to the well, may produce response similar to that observed. It is not possible to distinguish well-skin from heterogeneity effects based on the nature of slug test response alone. Pumping yields, however, are generally higher for wells with anomalously rapid slug-test response and suggest that, in some cases, the heterogeneity extends to large distance from the well. Despite their local region of influence, slug tests in such extremely heterogeneous aquifers may encounter highly conductive zones that may reduce the reliability of their results if they permit water-table drainage to the well.

Drainability Characteristics of Granular Pavement Base Material

A study was undertaken to determine the drainability characteristics of several types of unbound granular materials that are used in pavement bases. From the literature, testing concerns were identified and analyzed. Hydraulic conductivity and effective porosity were determined for aggregates from two sources of crushed stone and two sources of gravel. For each material two open gradations were tested in a rigid wall permeameter. One dense gradation of each material, at two levels of compaction, was tested in a flexible wall permeameter as well. Efforts were made to reduce possible flow along the sides of the rigid wall permeameter and to eliminate problems with air bubbles. The average hydraulic conductivities for the open and dense-graded materials were 3.6 × 10\u-¹ and 3.0 × 10\u-\u4 cm/s (1,021 and 0.85 ft/d), respectively. The effective porosities for the open and dense-graded materials were 68 and 27% of the nominal porosities, respectively. Four regression equations representing a wide range of hydraulic conductivity were developed to estimate hydraulic conductivity based on the results of this study and others reported in the literature.

Experimental Evaluation of a Drive‐Point Ground‐Water Sampler for Hydraulic Conductivity Measurement

AbstractDrive‐point ground‐water samplers, designed to enable delineation of the vertical and areal extent of a contaminant plume, have been modified to obtain an in situ measurement of hydraulic conductivity in aquifers. The multlevel drive‐point sampler (MLDPS) consists of a 30‐cm long screen pushed to a desired depth within a retractable outer sleeve and a pressure transducer to monitor the rate of fill within a sample chamber. The accuracy and variability of a MLDPS to measure hydraulic conductivity was evaluated in a 50‐m3 laboratory aquifer comprised of a uniform medium sand. Twelve measurements were performed using the MLDPS followed by duplicate slug tests performed at identical locations and depths within the aquifer. MLDPS and slug test data were analyzed using the method of Widdowson et al. (1990). The MLDPS provided an estimation of hydraulic conductivity at least one order of magnitude below slug test‐derived hydraulic conductivity and the range of hydraulic conductivity associated with a medium sand. MLDPS‐derived hydraulic conductivity values also show greater variability and range relative to the slug test‐derived values. Hydraulic conductivity ranges from 0.072 to 2.3 m/d using the MLDPS (coefficient of variation = Cv= 1.3) compared to a range of 10 to 16 m/d (Cv= 0.14) for the slug test values. Variability and magnitude of the MLDPS‐derived hydraulic conductivity is attributed to disturbance of aquifer material and experimental factors inherent to the design of the instrument.

A field test of tracer transport and organic contaminant elution in a stratified aquifer at the Rocky Mountain Arsenal (Denver, Colorado, U.S.A.)

A tracer-elution experiment was conducted in a 9-m-thick alluvial sand aquifer at the Rocky Mountain Arsenal, Denver, Colorado, within an extensive 1,1,1-trichloroethene and trichloroethene plume. The forced-gradient flow field was controlled by an injection well and an extraction well separated by 8.4 m and aligned in the direction of the natural-gradient flow. Upon extraction, the contaminant-laden water was treated by air stripping and reinjected into the injection well. Iodide tracer was added to the injection flow during the initial 27.5 h of the experiment. Tracer transport and organic contaminant elution were monitored by four 0.15-m-screened drive points and a fully penetrating monitoring well. Relative permeabilities, dispersivities and retardation factors were estimated from tracer breakthrough and contaminant elution curves by the moment method and by curve-fitting with an advection-dispersion model. Tracer transport through the four strata sampled by the drive points indicated a permeability variation of three orders of magnitude. Contaminant elution was not observed in the lowest-permeability stratum monitored during the experiment. In all monitored strata, contaminant elution was controlled primarily by permeability effects on water flow and exhibited minimal retardation or desorption effects. The fully penetrating monitoring well exhibited a tracer response primarily from the more permeable strata with the addition of tracer from the less permeable strata producing an increased breakthrough spreading. This increased spreading or dispersion was reflected in a higher longitudinal dispersivity estimate (1.2 m assuming a homogeneous aquifer) than dispersivity estimates from the drive-point sampler tracer curves (ranging from 5 to 21 cm). Contaminant elution curves from the fully penetrating monitoring well exhibited an initial response primarily from the more permeable strata (rapid elution of contaminants) and provided no insight into the elution response of the majority of the aquifer strata. Low mass recoveries of tracer within low-permeability layers are suspected to be due to the initial transient flow field and/or the initially high range of hydraulic conductivities along the injection well screen.

Optimum Hydraulic Conductivity to Limit Contaminant Flux Through Cutoff Walls

AbstractCutoff walls are becoming increasingly attractive options for the control of solute migration from long‐term sources of contamination. The main advantage of low permeability enclosures is that they restrict advective transport of solutes away from the source. However, with high concentration source zones surrounded by cutoff walls, there exists the potential for notable mass fluxes outward due to diffusive transport. This paper shows, through the use of the steady‐state flux equations, that there is an optimal range of hydraulic conductivities for barrier materials which permit the outward diffusive flux to be counter balanced by an inward advective and dispersive flux. This concept of designing optimum contaminant containment using an inward advective flux to counter the outward diffusive flux is valid for sealable joint sheet pile walls, bentonite‐slurry walls and clay liners, but not synthetic membrane materials with extremely low hydraulic conductivities. The effective diffusion coefficient for the common chlorinated organic solvents such as TCE in water‐saturated clayey materials is approximately 1 × 10−6 cm2/sec, resulting in an optimum hydraulic conductivity ranging from 1 × 10−6 to 1 × 10−8 cm/sec. This range in hydraulic conductivity is within the range of common barrier materials but not the lowest achievable. The steady‐state concentration profile in a slurry cutoff wall can result in a substantial amount of contaminant mass stored within the wall which will need to be considered over the long term or dealt with during site remediation. Large inward advective fluxes reduce the total chemical mass stored within the low permeability barrier material.

Laboratory Study of Hydraulic Conductivity for Coarse Aggregate Bases

Inadequate drainage of pavement structures has been identified as a primary cause of pavement distress. Hydraulic conductivity is the most important factor controlling drainage capability. Coarse grained materials have high values of hydraulic conductivity. ASTM and AASHTO standard test methods are limited for coarse materials used in pavement bases and subbases because of their high permeability and large particle sizes and the horizontal flow in the field conditions. A large scale horizontal permeameter and a testing procedure were developed and the range of hydraulic conductivities of six base and subbase specifications made up of three material types provided by the Ohio Department of Transportation were evaluated. A horizontal permeameter (305 × 305 × 457 mm) and a testing procedure were developed to reduce errors produced by sidewall leakage, partial saturation, measurement of small head differences, and interpretation of turbulent flow as laminar flow. Fifty-four samples were tested, including various gradations of nonstabilized, portland cement stabilized, and asphalt stabilized bases made of limestone, gravel, or slag materials. The results obtained were analyzed and compared with previous research, empirical relations, and field test results of similar base and subbase materials. The comparisons and analyses indicate that the permeameter and the procedure produce representative results. Test results indicate a wide range of hydraulic conductivities for gradations at each extreme of a specification. Effective porosities were also found to be as low as 6 percent for the fine gradation of a common limestone base material.

Laboratory Study of Hydraulic Conductivity for Coarse Aggregate Bases

Inadequate drainage of pavement structures has been identified as a primary cause of pavement distress. Hydraulic conductivity is the most important factor controlling drainage capability. Coarse grained materials have high values of hydraulic conductivity. ASTM and AASHTO standard test methods are limited for coarse materials used in pavement bases and subbases because of their high permeability and large particle sizes and the horizontal flow in the field conditions. A large scale horizontal permeameter and a testing procedure were developed and the range of hydraulic conductivities of six base and subbase specifications made up of three material types provided by the Ohio Department of Transportation were evaluated. A horizontal permeameter (305 X 305 X 457 mm) and a testing procedure were developed to reduce errors produced by sidewall leakage, partial saturation, measurement of small head differences, and interpretation of turbulent flow as laminar flow. Fifty-four samples were tested, including vari...

Handheld Double Packer Equipment for Water Sampling and Hydraulic Measurements in Deep Boreholes

AbstractThe need 10 characterize deep and shallow bedrock hydrogeologic conditions in remote terrain encouraged the development of an inexpensive, last, and easily transporrable double packer sampler. The principal objective was to combine water sampling and hydraulic measurement with the same equipment. Unconventional construction that does not create any large hydraulic pressure differences in the equipment allows light and inexpensive standard materials and components to be used. The low cost, lightweight equipment can thus be operated by a single person.The equipment is based on the principle of using soft, hydraulically expandable packers that isolate the required section of the borehole. The inflation and deflation of the packers is controlled by a single tube, through which the water sample is also withdrawn. The uppermost part of the tube branches into two tubes; the pumping action is generated by cyclic pressure pulses applied to one of these tubes.The equipment has mainly been used in narrow 1,8‐inch (46 mm) diameter boreholes down to a depth of about 3280 feet (1000 m); versions capable of operating in larger boreholes and with higher pump capacity have also been constructed. At one sampling site, the chemical composition of water from an isolated fracture zone was compared with open hole water at the same depth. The water from the fracture had a different chemical composition compared with the mixed water sample from the open hole. To collect representative ground water samples, double packers and long pumping limes are required.The equipment characterizes both the hydraulically conductive bedrock structures and the chemical compositions of bedrock ground water. Through comparison to K‐values and chemical constituents in other portions of the borehole, the collected data can be used to estimate transport pathways, aquifer yield, travel times, and ground water evolution. The range of hydraulic conductivity measured with the equipment in association with this research was 10‐10 to 10‐7 m/s.

Borehole water-level variations and implications for the subglacial hydraulics of South Cascade Glacier, Washington State, U.S.A.

AbstractBoreholes were drilled in South Cascade Glacier to investigate the hydraulics of subglacial water flow. Results indicate that subglacial water pressures are generally close to local ice-overburden pressures and that a subglacial debris layer probably exists. Calculations indicate that the range of hydraulic conductivity of this layer is 10−7-10−4m−1. The borehole water levels generally increased during the ablation season and may be caused by a seasonal evolution in the permeability of the debris layer. Water in the debris layer drains to a subglacial conduit, the existence of which is inferred by large diurnal variations in the water level of one borehole. These levels commonly reached the bottom of the glacier, indicating near-atmospheric pressures in the conduit.

Borehole water-level variations and implications for the subglacial hydraulics of South Cascade Glacier, Washington State, U.S.A.

AbstractBoreholes were drilled in South Cascade Glacier to investigate the hydraulics of subglacial water flow. Results indicate that subglacial water pressures are generally close to local ice-overburden pressures and that a subglacial debris layer probably exists. Calculations indicate that the range of hydraulic conductivity of this layer is 10−7-10−4m−1. The borehole water levels generally increased during the ablation season and may be caused by a seasonal evolution in the permeability of the debris layer. Water in the debris layer drains to a subglacial conduit, the existence of which is inferred by large diurnal variations in the water level of one borehole. These levels commonly reached the bottom of the glacier, indicating near-atmospheric pressures in the conduit.

Searching for a fracture as a two-person zero-sum game

Searching for a fracture of a given hydraulic conductivity in a fractured rock, by means of observation bodies such as bore holes, is similar to a decision problem in a two-person zero-sum game with incomplete information. The searcher and the hidden fracture are considered the two players of the game. There is a finite number of moves or pure strategies in the hands of each player, that is, the former may drill a finite number of bore holes and the latter may be located or not in a certain hydraulic conductivity range of interest. A game model corresponding to this situation, taking into consideration the log-normal fracture hydraulic conductivity distribution, consistent with the occurrence in nature, is presented. The probability of finding a fracture in the jth interval of the hydraulic conductivity probability density function (PDF) graph after i drillings is taken as the payoff matrix of the game. The presented game model provides a solution for finding the number of bore holes to be drilled for intersecting a fracture within a prescribed hydraulic conductivity range. The method is exemplified for a particular data set.

Geohydrology and water quality in the vicinity of the Silver Creek tailings site, Summit County, Utah : Mason, J L Proc Symposium on Geology and Hydrology of Hazardous-Waste, Mining-Waste, Waste-Water and Repositories Sites in Utah, Salt Lake City, 1989P135–148. Publ Salt lake City: Symposium and Field Conference, 1989 (Utah Geological Association Publication 17)

Abstract The Silver Creek tailings site is in Prospector Square, a commercial development and residential community in Summit County, Utah. The movement and the extent of metal contamination in ground water from the unconsolidated valley fill were assessed in the area. Estimated values of hydraulic conductivity range from 1 to 14 feet per day for the poorly sorted clay, silt, sand, and gravel in the unconsolidated valley fill. An aquifer-interference test indicated that water in the valley fill did not move from the tailings site toward the pumped municipal well completed in the consolidated-rock aquifer. During low flow, concentrations of dissolved and suspended cadmium, manganese, and zinc in surface water downstream from the tailings were substantially greater than background concentrations. Concentrations of dissolved cadmium, manganese, and zinc were greater than background concentrations in water from at least three wells and a drain.

XYLEM ANATOMY AND HYDRAULIC CONDUCTANCE OF COSTA RICAN BLECHNUM FERNS

Hydraulic conductivities of stems, stipes, and elongate leaf stipes were determined for greenhouse‐grown Blechnum (B. fraxineum, B. fragile, B. buchtienii, B. sprucei) and Salpichlaena (S. volubilis) plants collected in tropical rain forests of Costa Rica. Organ conductivity was examined in relation to morphology and tracheid characteristics in order to gain an understanding of factors influencing water flow. Hydraulic conductivity of plant organs was determined by measurement of transpiration rates, leaf areas, and water potential gradients. Erect stemmed species develop larger whole plant water potential gradients than elongate stemmed species for a similar transpiration rate. Elongate leaves develop even smaller water potential gradients for a given transpiration rate. Stems have larger hydraulic conductivities but smaller leaf‐specific conductivities (LSCs) than stipes. Small conductivities and small LSCs are associated with short, erect stems. Elongate structures have large conductivities and large LSCs. Of the tracheid characteristics examined, the most important characteristics determining the magnitude of organ hydraulic conductivity are diameter, pit aperture area between tracheids, taper length, and cell length. Large conductivities of S. volubilis climbing leaf stipes are associated with very large‐diameter tracheids (some > 200 μm), large tracheid number, exceptionally long tracheids (some > 4 cm), large pit aperture area between tracheids, short tracheid taper, and smooth tracheid lumen walls. Hagen‐Poiseuille estimates of hydraulic conductivity range from 1.1 to 3.3 times the measured values. Conductivity of stipes is highly correlated with leaf area supplied by stipes. Conductivities of stems and elongate leaf stipes also correlate with leaf area supplied by these structures. Estimated hydraulic conductivities of field‐grown Blechnum and Salpichlaena demonstrate that larger conductivities are associated with larger plants. This study contributes toward our knowledge of fern water relations and extends previous growth form/hydraulic architecture characterizations by providing a more comprehensive comparison of closely related species. In addition, this study provides evidence for the relative importance of tracheid characteristics in determining the magnitude of organ hydraulic conductivity.

Experimental testing of transient unsaturated flow theory at low water content in a centrifugal field

Experimental measurements and theoretical predictions of transient moisture conditions have been compared for a sandy soil approaching hydrostatic equilibrium in a centrifugal field. Starting near saturation, samples were centrifuged at constant speed with a constant suction at the outflow boundary. Water flowed freely out of the sample through a porous plate. Step increases in centrifuge speed produced transient moisture conditions suitable for comparison between experiment and theory. Measurements of electrical conductivity by a direct contact four‐electrode technique indicated the water content according to a calibration based on known moisture conditions at various equilibrium states. A specially modified centrifuge permitted electrical measurements during centrifugation. For comparison, the transient water contents were computed by a finite‐difference solution of Richards' equation (modified by replacing gravitational with centrifugal potential), using soil characteristics measured previously by steady state techniques. The time dependence of water content changes, used as the basis for comparison between experiment and theory, shows agreement which is reasonable given the degree of uncertainty of the measurements. The experiment confirms, within a factor of 4, the validity of Richards' equation for moisture conditions as dry as 25% of saturation, over a hydraulic conductivity range of 5 × 10−11 to 1 × 10−8 m/s, and in a centrifugal field up to about 200 g.

LEACHING OF A HIGHLY SALINE-SODIC SOIL IN SOUTHERN ALBERTA: A LABORATORY STUDY

Moderate to highly saline-sodic soil cores extracted from a Brown Solodized Solonetzic soil were leached in the laboratory using good-quality irrigation water to determine relative salt removal with time. Leaching curves comparing the relative concentration of salts against the relative depth of leaching water applied were similar over a wide range of salinities and hydraulic conductivities. The time required to transmit an equivalent depth of water through the soil core and achieve a salinity reduction of about 75% ranged from less than 2 d to an estimated 15 mo. The primary limitation to reclamation in these soils was the low hydraulic conductivity rather than the initial salt content or depth of leaching water required. Key words: Reclamation, leaching, hydraulic conductivity, saline-sodic soil

ESTIMATING UNSATURATED HYDRAULIC CONDUCTIVITY FROM EASILY MEASURED SOIL PROPERTIES

We measured hydraulic conductivity (saturated and unsaturated) on 127 soil cores, which were taken in different horizons of a wide variety of Belgian soil series. The hot air method (Arya et al. 1975) and the crust method (Bouma et al. 1983) were combined to obtain the complete range of hydraulic conductivity from saturation to air-dry. The textural composition in nine fractions, the organic carbon content, and the dry bulk density were determined for each of the sample horizons as well. Four different empirical models were evaluated on their performance in describing the measured hydraulic conductivity curves. The model parameters were estimated by linear and nonlinear regression techniques. It is concluded that the Gardner equation (1958) with three parameters best described the hydraulic conductivity for the given soils. Regression equations for estimating the Gardner parameters were established from simple soil properties, such as soil texture, carbon content, bulk density, and saturated hydraulic conductivity. We found that the three parameters can reasonably well be estimated from the textural composition and the saturated hydraulic conductivity. A one-dimensional sensitivity analysis indicates that the n parameter, representing the slope of the hydraulic conductivity pressure head relation in log-log scale, is most sensitive.

Suitability of Marine Clays as Hazardous Waste Site Liners

Marine clays of Maine may be more resistant to physico-chemical alteration when permeated with solvents than are other more mineral-rich clays used in previous studies. This conclusion is preliminary. Long duration permeameter testing and chemical analysis of the effluent would produce a more definitive statement on the long-term suitability of these clays as liners at hazardous waste disposal sites. It is found that the marine clays of Maine are different from clays used in similar studies in two ways, mineralogically and physico-chemically. The clay mineral content (if any) is very small. Clay size particles consist of ground-up rock minerals (mica, chlorite, feldspar, quartz). The cation exchange capacity is very low for clay and the ability to swell and shrink is very small, both properties related to the lack of clay minerals like montmorillonite. Hydraulic conductivities range from 2 × 10−8 to 5.2 × 10−8cm/s for the six columns of this study. No major increases or decreases in hydraulic conductiviti...

In Situ Hydraulic Conductivity at Four Hillslope Locations in a Closed Drainage System

AbstractVirtually no information has been published concerning the hydraulic properties of large acreages of till plain soils associated with “Potholes” in Northcentral United States and Canada. The objectives of this research were to measure and compare in situ hydraulic conductivities and selected soil physical properties at several depths in four soil profiles on a till plain in southeastern North Dakota. In addition, theoretical hydraulic conductivity values were calculated and compared with the in situ conductivities.Unsaturated soil hydraulic conductivity vs. depth was measured in situ at four sites on a toposequence developed from a glacial till. Water was allowed to infiltrate the soil at each site and the soil surface covered to prevent evaporation. During the ensuing drainage periods soil water pressure was monitored with triplicate tensiometers at each of six depths. These depths were not arbitrary as in previously reported studies but were selected on the basis of soil morphology. Soil water characteristics, determined on triplicate 7.6‐ by 7.6‐cm cores taken from the same depth as the tensiometer cups, were used in conjunction with the soil water pressure data to compute hydraulic conductivities. Hydraulic conductivity generally increased with depth to about 90 cm. Below this depth, hydraulic conductivity tended to decrease. In addition, hydraulic conductivity values at each depth for each site were computed by the Green and Corey Method. When the matching factor was selected from the midpoint of the measured hydraulic conductivity range, the conductivities computed by Green and Corey's method compared favorably with those measured in situ.