Moving Ground Water Research Articles

The influence of pore-fluid in the soil on ground vibrations from a tunnel embedded in a layered half-space

A computationally efficient semi-analytical solution for ground-borne vibrations from underground railways is proposed and used to investigate the influence of hydraulic boundary conditions at the scattering surfaces and the moving ground water table on ground vibrations. The arrangement of a dry soil layer with varying thickness resting on a saturated poroelastic half-space, which includes a circular tunnel subject to a harmonic load at the tunnel invert, creates the scenario of a moving water table for research purposes in this paper. The tunnel is modelled as a hollow cylinder, which is made of viscoelastic material and buried in the half-space below the ground water table. The wave field in the dry soil layer consists of up-going and down-going waves while the wave field in the tunnel wall consists of outgoing and regular cylindrical waves. The complete solution for the saturated half-space with a cylindrical hole is composed of down-going plane waves and outgoing cylindrical waves. By adopting traction-free boundary conditions on the ground surface and continuity conditions at the interfaces of the two soil layers and of the tunnel and the surrounding soil, a set of algebraic equations can be obtained and solved in the transformed domain. Numerical results show that the moving ground water table can cause an uncertainty of up to 20 dB for surface vibrations.

Hieracium (Asteraceae) of sub‐alpine Dalarna, Sweden, revisited: decline in species richness attributable to both forestry and overgrowth

The Hieracium flora of westernmost Dalarna, comprising the southern fringe of the Scandes alps (central Scandinavia), is extremely rich in species. The area is dominated by species‐poor coniferous sub‐alpine and taiga forest, but within this matrix there are small and isolated sites with high species richness of both Hieracium and other plants. Both steep mountain slopes with outcrops of base‐rich bedrock and moving ground water, and old seasonal or permanant human settlements constitute such biodiversity hotspots. However, today the former are threatened by modern forestry practices and/or exploitation for winter tourism and the latter are commonly abandoned and subjected to severe overgrowth or dramatically changed land‐use. The area was thorougly surveyed in 1897–1921. In 2007, the same region and partly the same sites, were revisited. In 1897–1921, 15 Hieracium species were on average recorded from each site, but when the same sites were revisited in 2007 significantly fewer, only about 6 (40%) species per site, were refound. As far as the total species pool of the study area is concerned, it consisted of 168 species in 1897–1921, whereof only 117 (67%) were found in 2007. This remarkable reduction in species richness at both the local and the regional scale is attributable to both modern forestry practices and to the cessation of traditional agricultural practices like hay‐making on semi‐natural grasslands and extensive cattle‐grazing in the forests. It is concluded that to reduce the on‐going severe loss of biodiversity in the sub‐alpine and taiga regions, conservation efforts in these areas ought to be enhanced and concentrated not only on saving what still remains of old‐growth forest but also on managing remnants of grasslands and formerly grazed or mowed open forests around former settlements.

Wave propagation in layered dry, saturated and unsaturated poroelastic media

An exact stiffness formalism is presented to study harmonic and transient wave propagation in multilayered dry, saturated and unsaturated isotropic poroelastic media. Smeulders’ extension of Biot’s poroelastic theory is used to incorporate unsaturated porous media with a small gas fraction. A wide range of problems in geophysical and civil engineering can be treated, ranging from amplification of plane harmonic waves, dispersion and attenuation of surface waves to transient wave propagation due to a forced excitation. The effect of full or partial saturation on wave propagation in a poroelastic layered halfspace is demonstrated in a numerical example, in which the layering is caused by a moving ground water table.

In-situ alteration of minerals by acidic ground water resulting from mining activities: preliminary evaluation of method

The chemical composition of the Cu-mining-related acidic ground water (pH ∼ 3.5 to near neutral) in Pinal Creek Basin, Arizona has been monitored since 1980. In-situ experiments are planned using alluvial sediments placed in the ground-water flow path to measure changes in mineral and chemical composition and changes in dissolution rates of subsurface alluvial sediments. The test results should help refine developed models of predicted chemical changes in ground-water composition and models of streamflow. For the preliminary test, sediment from the depth of the well screen of a newly drilled well was installed in three wells, the source well (pH 4.96) and two up-gradient wells (pHs 4.27 and 4.00). The sediment was placed in woven macrofilters, fastened in series to polyvinyl chloride (PVC) pipes, and hung at the screened level of each well. After interacting with the slowly moving ground water for 48 days, the test sediments were removed for analysis. There was no evidence that any of the materials used were biologically or chemically degraded or that the porosity of the filters was diminished by ferric hydroxide precipitation. These materials included 21-μm-pore (21PEMF) and 67-μm-pore polyester and the 174-μm-pore fluorocarbon Spectra/mesh macrofilters containing the in-situ sediment, the polypropylene (PP) macrofilter support structures, and the Nylon (NY) monofilament line used to attach the samples to the PVC pipe. Based on chemical and mineral composition and on particle-size distribution of the sediment before and after ground-water exposure, the 21PEMF macrofilter was chosen as the most suitable macrofilter for the long-term in-situ experiment. Tests also showed that the PP support structures and the NY monofilament line were sufficiently durable for this experiment.

In Situ Electromigration as a Method for Removing Sulfate, Metals, and Other Contaminants from Ground Water

AbstractElectromigration is proposed as an in situ method for preconcentrating contaminants in ground water prior to pumping and treating. In earlier investigations by the senior author and co‐workers, it was found that Cu in synthetic ground water migrated strongly to a Pt cathode and plated out as metallic copper. In the present study, carbon electrodes were inserted into a laboratory column of fine quartz sand that was saturated with a lower concentration of CuSO4 solution. A fixed potential of 2.5 V was applied, causing dissolved Cu and SO4 to accumulate strongly at the cathode and anode, respectively. Only minor plating‐out of Cu took place on the carbon electrodes. In addition to the use of carbon electrodes, the present research also investigated the effects of a lower concentration of metal, accumulation of SO4 adjacent to the anodes, adsorption of Cu on the sand, and competition by moving ground water.At an imposed voltage of 2.5 V and in the presence of 65 mg/L of dissolved Cu and 96 mg/L of SO4 (0.001 M CuSO4 solution), electrolysis of water caused large changes in the pH and speciation of the aqueous components, as well as precipitation of solid Cu‐hydroxides. Significant retardation of Cu occurred in the presence of ground water flowing at an average intergranular velocity of 0.2 m/day, but only minor retardation at water velocities of 1.9 and 2.9 m/day.Sulfate tends to migrate strongly to the anodes, suggesting that in situ electromigration may offer a useful new method for preconcentrating such highly soluble ions as SO4, NO3, and CI that are difficult to remove by conventional pump‐and‐treat methods. A number of potential problems exist that should be addressed in a field test.

Effects of Waste‐Water Irrigation on Aqueous Geochemistry Near Paris, Texas

AbstractA comprehensive assessment of the environmental impact of a full‐scale, operating overland flow (OLF) land treatment system was made at the Campbell Soup (Texas), Inc. facility in Paris, Texas. The system treats over 16,000 m3/d of waste water and has been in operation for over 25 years. Field samples of soil, waste water, OLF runoff, and ground water collected during the study and detailed long‐term process records maintained by Campbell Soup were used as part of the evaluation. Geochemical data indicated that sulfate‐chloride facies were dominant for the ground water collected at the OLF site. Field data and calculations indicated that the evapotranspirative concentration of salts in the applied waste water would be insufficient to produce the measured concentrations in the ground water. A pattern of increasing ionic concentration over time (1968 to 1989) with small changes in ionic ratios suggested a trend toward the dissolution and concentration of naturally present minerals (such as gypsum and sodium chloride) in the slow moving ground water. Predictions made with the aid of MINTEQA2, a thermodynamic equilibrium model, indicated that precipitation of carbonates and simultaneous ion exchange on clays could represent a significant mechanism for the removal of calcium and magnesium from solution and the addition of sodium. The development of a slightly saline, semiconfined aquifer was strongly suggested by the ground‐water geochemical data, soil data, the estimated rate of infiltration, field hydraulic conductivity, MINTEQA2 model predictions and the magnitude of the volume of waste water applied.

Hydrothermics in the Wyoming Overthrust Belt

A thermal study was made across a 25 km (15.5 mi) traverse of the Overthrust belt in southwestern Wyoming. Estimates of relative heat flow from temperature measurements made in shallow (< 30 m or 98 ft) boreholes reveal a systematic variation of at least 400 mW/m2 (10 µcal/cm2 sec) magnitude across the study area. The cause of this variation is believed to be forced convection of heat by moving ground water. Two relative heat-flow highs coincide with zones where structurally related faults, possibly providing avenues for vertical water flow, project to the surface. Between those two zones in a topographically elevated area, low and predominately negative temperature gradients were observed in opposite seasons. These shallow negative gradients are believed to exist seasonally in quasisteady state and could be indicative of a broad zone of ground-water recharge. The association of two relative heat-flow highs with the two major deep geologic structures implies either a direct vertical communication of deep and shallow ground water or a coupling of deeper and shallower ground-water systems. The two structures studied are hydrocarbon bearing and associated with Whitney Canyon and Ryckman Creek fields. The thermal measurements support the possibility that ascending waters have influenced the hydrocarbon migration and accumulation in these structures. Such measurements may be useful in delineating and understanding similar features in other areas.

Heat Flow in Geophysical Exploration of Sedimentary Basins: ABSTRACT

In continental heat-flow studies, sedimentary basins are usually avoided because of difficulties in obtaining thermal conductivity measurements and because temperature gradients may contain advective signals caused by moving ground water. These problems are superimposed in the Denver and Williston basins where complex geothermal gradients derive both from large contrasts among thermal conductivities of strata and from regional ground-water flow. Detailed heat-flow studies may solve these problems and provide data relevant to basin hydrology: the occurrence and nature of geothermal resources, oil source rock maturation and secondary migration of petroleum, and formation and deposition of strata-bound ores. End_of_Article - Last_Page 849------------

The Bottom Heat Loss of a Solar Pond in the Presence of Moving Ground Water

The bottom heat loss from a solar pond in the presence of moving ground water was determined under steady state conditions. A simplified pond model was used which restricts the results to long, narrow, shallow ponds. The analysis was based on the steady two-dimensional energy equation utilizing an effective thermal conductivity. The ground was modeled as a porous soil consisting of two distinct regions; one above the water table and one below where the ground water was assumed to flow in the horizontal direction. Solutions were obtained by the finite-difference direct method utilizing matrix concepts. The bottom heat loss is represented by a conductance coefficient whose values are plotted as a function of Peclet number, water table level, and the thermal conductivity ratio of the two distinct soil regions. The results indicate that the heat loss rate significantly increases as the water table level moves closer to the pond bottom. At water table levels close to the pond bottom, the heat loss rate increases significantly with increasing Peclet number.

Convective Heat Transfer in Selected Geologic Situations

ABSTRACTThere are many geological situations where moving ground water transfers a significant amount of heat. Yet, while convective heat transfer is a common phenomenon, it is very difficult to treat analytically. In this paper we present a simple model of convective heat transfer in porous materials and a numerical method of solving the model. The model is then applied to three diverse field situations: (1) a thermal anomaly on the Hartville uplift in eastern Wyoming; (2) a fault‐controlled hydrothermal system near Monroe, Utah; and (3) the Luanshya copper mine in the Republic of Zambia. In each case heat transfer by moving ground water is shown to explain the observed thermal anomalies satisfactorily. Our results indicate that in certain situations the effect of ground‐water flow needs to be considered in making local and regional assessments of heat‐flow data. Furthermore, temperature measurements can be very useful in estimating aquifer recharge, particularly when thermal conductivity and structural information are available.

Theoretical Analysis of Forced Convective Heat Transfer in Regional Ground-Water Flow

Among the numerous processes that will cause anomalous temperature distributions in geologic basins is the spatial redistribution of heat by moving ground water. This problem is examined by solving the energy equation for the simultaneous transport of water by hydraulic gradients and heat by forced convection. The factors that affect the temperature distribution in a given basin include the intrinsic properties of the medium and contained fluid—namely, the thermal diffusivity of the solid-fluid complex and the hydraulic conductivity, the water-table configuration, and the ratio of basin depth to basin length. The severity of an anomalous geothermal gradient or temperature measurement depends primarily on the relative magnitude of the ratio of hydraulic conductivity to thermal diffusivity, and on the geometry of the flow field. A dimensionless group may be formulated from these parameters, and provides a relative measure of the simultaneous transport of heat by the bulk motion of the fluid to that by pure conduction. Solutions to the equation itself indicate that convective heat losses in ground-water recharge areas are balanced by convective heat gains in discharge areas. The geothermal gradient accordingly increases with increasing depth in recharge areas, decreases with increasing depth in discharge areas, and is a manifestation of pure conduction at the hinge line separating areas of recharge and discharge.

NITRATE CONTAMINATION OF GROUND WATER IN THE NEEPAWA-LANGRUTH AREA OF MANITOBA

Reports of methemoglobinemia of bottle-fed infants and nitrate poisoning of ruminants prompted an investigation of the cause and distribution of high levels of nitrate in ground water. The problem was found to be of common occurrence in areas where surface deposits consist of about 2 to 4 m of sandy-textured material overlying less permeable lacustrine clay or clay loam till. Although appreciable amounts of nitrate move to the ground water in fallow fields, a very high nitrate concentration occurs only in and around farmsteads or in the vicinity of towns and villages where human and animal wastes are concentrated. Ground water in the sites investigated moved laterally in a northeasterly direction, and a dilution of nitrate was observed in the slowly moving ground water to a level of less than 10 ppm within about 1/10 km in that direction. In contrast, ground water closely adjacent to the western and southern boundaries of the farmsteads, being up-grade from the source of contamination, was found to be free from toxic quantities of nitrate.

Geothermal Exploration for Ground Water

Since 1961, precise ground-temperature measurements have been made at shallow depth in a number of geological terranes and climates. The objective has been to investigate the effectiveness of shallow geothermal techniques in geological exploration. The thermal sensors used are thermistors individually calibrated to within .02°C. It was found that shallow-earth temperatures can be related to the occurrence of ground water. Shallow, moving ground water produces low temperatures and low annual drift rates, due to damping of the annual temperature wave. Conversely, dry shallow bedrock, because of higher conductivity and lower specific heat, produces relatively higher temperatures and higher drift rates. Other permutations of observed temperature and drift rate reflect intermediate conditions of bedrock and ground-water distribution. As a case study, the geothermal survey of Johnson Valley is described. This is a closed basin system in southern California, which shows a direct relationship between ground temperature and depth to water as measured in wells.

Some Field Observations Relating the Growth of Bog Plants to Conditions of Soil Aeration

Peat bogs of any size are often dissected by channels of moving water, and it is well known that the plant communities of such channels are usually very different in composition from those where the water is stagnant. One of the plants which seems to favour an environment with moving water is Molinia caerulea. Jefferies (1915), for example, noted that Molinia grew better on sloping than on flat ground, and concluded that Molinia favours soil maintained by an aerated water supply in preference to 'sour' soil produced under stagnation. Rutter (1955) observed improved growth of Molinia in the presence of a fluctuating water table, and suggested that moving ground water not only improved the oxygen supply to the roots, but also brought about a reduction in the concentration of toxic substances by sweeping them away. In addition he remarks on the possible importance of moving ground water in bringing about the continuous renewal of soluble bases or other plant nutrients, a suggestion which is supported by Newbould & Gorham (1956). Until quite recently it has been extremely difficult to take measurements of oxygen in waterlogged soils in situ, and data on the oxygen regimes of flushed and unflushed habitats are consequently lacking. Recently, however, Lemon & Erickson (1952, 1955) and Poel (1960) have described a polarographic method, in which a platinum microelectrode can be used to measure the oxygen regime in soils. This is a particularly useful technique for it gives a true indication of the potential availability of soil oxygen to plant roots, since oxygen diffusion rate, rather than oxygen concentration, is measured at the sampling points. It is also very suitable for recording the small local differences in oxygen status down soil profiles. A particularly striking example of a differential in Molinia growth between flushed and stagnant soil was noticed by the authors near Laxford Bridge in Sutherland, and a smallscale investigation of the soil oxygen and its relation to the Molinia was carried out in the autumn of 1962. This was followed by a further investigation on 'Fen Bogs', a valley bog on the North Yorkshire Moors where distribution of Molinia was patchy. The two bogs together, therefore, give a series from flushed to stagnant conditions, with and without Molinia, and the platinum micro-electrode was used to investigate whether there was a variation in oxygen content of the peat which corresponded with the distribution and vigour of Molinia. In an attempt to define soil aeration as comprehensively as possible, oxidationreduction potentials and measurements of hydrogen sulphide were made in addition to oxygen diffusion at the Fen Bogs site.

Quicksand and Water Wellsa

AbstractQuicksand is no myth, nor is it a rare phenomenon, either on the surface or in the subsurface. There is probably quicksand in every State of the U.S.A. where enough gradient is available to produce upward moving ground water. Surface quicksand is likely to occur in hilly country, especially in regions of calcareous rocks which often con‐tain solution openings and favor the occurrence of springs. It is often present near stream banks and stream beds, either along their shorelines, under water, or occasionally in the bottom of an apparently “dry” river.Subsurface qurcksand rs found in loosely consolidated or uncemented alluvial, fluvio‐glacial, or lacustrine sediments, which are usually well sorted and clean. It has been reported to depths as great as several hundred feet, and from a few feet to as much as 200 feet thick.In water wells, a “quick” or “heaving” condition may exist (as much as 150 feet) if a confined, permeable, loose silt, sand or gravel stratum is continuous to distant higher ground, and is subject to a greater head of water existing at the higher elevation, i. e., if artesian conditions exist.Similar material may heave in a water‐table (unconfined) well, due to the natural tendency of granular materials to move toward a drill hole when lateral support is removed (the drill cuttings). Heaving results from a loss of shearing strength as pressure is reduced when a drill hole upsets natural equilibrium. Suction produced by suddenly withdrawing bailer or tools further contributes to disturbing natural conditions.Quicksand is commonly sand (usually fine to medium grained) with an effective size ranging from less than 0.001 inch to 0.005 inch. It is often finer than sugar, which has an average effective size of 0.008 inch, to which it is often compared by drillers. Stoke's Law explains why fine, round‐ ed grains become “quick” much more readily than coarser sand or gravel.If sufficiently permeable, quicksand aquifers can successfully be used for water supplies, providing proper screening devices are available. However, representative driller's samples; sieve analyses; choice of(or omission of) sand filter pack; proper slot selection; low (0.1 fps) en‐ trance velocity; and careful, patient development techniques are important prerequisites.Permeability of quicksand varies widely, but might range from approximately 50 gpd/ft to 800 gpd/ft, and average between 100 or 175 gpd/ft2. From a 5‐feet thick quicksand bed, and at shallow depths, 1 to 10 gpm may be obtained for domestic or farm supplies using screened wells and drive points. Sufficient yields (250 gpm or more) for municipal wells are also possible.Drilling and completion problems with cable‐tool wells can usually be overcome by: 1) watching casing alignment; 2) running bailer slowly; 3) keeping a continual high head of water inside casing; 4)using a heavy string of drill tools; 5) allowing controlled sand‐heaving; 6) using short casing drives; 7) jetting with high‐pressure water to wash‐free tools if seized by a sudden heave; 8) avoiding thin‐walled casing; 9) drilling with a mixture of bentonite or native clay and water sludge; and 10) casing above the surface if the well is flowing.Rotary drilling and completion problems are minimal, but unless unusual pressures are encountered, quicksand aquifers may be overlooked. Caving can be prevented by providing sufficient hydrostatic differential pressure, and by using a heavy weighted drilling fluid.Well screens can be set by bailing them down through a quicksand “plug” which may have formed, and completing using the standard pull‐back method. A self‐closing bottom (washdown fitting) can also be used to jet‐down a screen while utilizing a high‐velocity water flow.In some cases a sand filter‐pack surrounding a continuous‐slot well screen may not be advisable in quicksand, especially if the aquifer's effective grain size is approxi‐mately 0.004 inch. A naturally developed well completed with a screen having a slot as narrow as 0.005 inch may be preferable, allowing 50 to 60 percent of the aquifer to be developed slowly and carefully through the screen. A case history comparing two well design methods is presented.Both cable‐tool and rotary sampling methods in quick‐ sands are discussed. The techniques are basically similar, whether the material is “quick” or stable.