Coarse Sand Layer Research Articles

Effects of a semipervious lens on soil vapour extraction

We describe a theory for the removal of volatile organic chemicals from an unsaturated soil stratum consisting of highly porous coarse sand layers sandwiching a thin and semipervious lens. Each soil layer is modelled as a periodic array of spherical aggregates formed by solid grains and immobile water trapped by surface tension. Volatile chemicals are vaporized in the mobile air in pores between aggregates, dissolved in the intra-aggregate water, and adsorbed on the surface of soil grains. Using the effective transport equations derived for the aggregated soils, we consider shallow layers with sharp contrast in physical properties. An asymptotic analysis is developed for an axisymmetric geometry, yielding quasi-one-dimensional governing equations for individual layers. At the leading order the flow and the vapour transport are horizontal in the coarse layers but vertical in the semipervious lens. Numerical results are presented for a simple example to demonstrate the significance of the lens permeability, diffusivity and retardation factor, and the aggregate diffusivity in the coarse layers, on the vapour transport during the stages of contamination and air-venting.

Impact of Funnel Flow on Contaminant Transport in Sandy Soils: Numerical Simulation

AbstractAgrichemicals have played an essential role in maintaining the productivity of arable lands in modern agriculture. Recently, it was found that preferential flow could greatly enhance the leaching of agrichemicals into groundwater. This study investigated how contaminant transport would be influenced by funnel‐type preferential flow paths in a sandy vadose zone. Numerical simulations were conducted in four 12‐m‐wide by 6‐m‐deep two‐dimensional hypothetical soil profiles with embedded coarse sand layers. The soil layering structures in these profiles were generated according to what was observed in the vadose zone of a Plainfield sand (sandy, mixed, mesic Typic Udipsamment) in central Wisconsin. Corresponding simulations were conducted in one‐dimensional profiles as controls. Results showed that contaminant breakthrough time in the two‐dimensional profiles was only 25% of that in one‐dimensional homogeneous profiles. The ratio of the total mass leached from the two‐dimensional profile to that from the one‐dimensional profile increased exponentially as the water application rate decreased. This implies that: (i) the impact of funnel flow on contaminant transport is most drastic when the net infiltration is low; and (ii) minimizing excess leaching by carefully controlling the water budget alone might not prevent groundwater contamination. For a pesticide with a degradation coefficient of 3 × 10−7 s−1 and an adsorption coefficient of 0.5 cm3 g−1 in the top 30 cm and 0.05 cm3 g−1 from 30 to 600 cm, about 4% of the total mass would reach the groundwater through two‐dimensional funnel flow paths with an averaged daily net infiltration rate of 1.15 mm d−1.

Experimental Studies On Effects of Reservoir Heterogeneity On the Vapex Process

Abstract In thermal recovery processes, heat can penetrate by conduction through solids into low-permeability layers and shales. In the Vapex process, vapour is confined to the pore spaces and its ingress into fine pores can be limited by capillarity. In steam processes, heat can penetrate relatively rapidly beyond the interface and mobilize the oil at depth; in Vapex, the diffusion of vapour is much slower and the thickness of the mobilized oil is much less. Therefore, reservoir heterogeneity, such as that created by low-permeability layers and shales, becomes more important in affecting the performance of the Vapex process than with SAGD because it is more difficult for the gas phase to penetrate the low-permeability regions. In this study, experiments were carried out using a 2-D packed model to investigate the effects of low-permeability layers and lenses on Vapex. The model was packed in horizontal layers with two different sized sands. Crude from the Tangleflags North field, Lloydminster, was extracted with butane. The effects of both continuous, low-permeability layers and discontinuous, low-permeability lenses were investigated using different well configurations. The results using these models have been compared with those from uniformly packed models. All experiments involving low-permeability layers gave lower production rates than those involving uniformly high-permeability packing. When the horizontal low permeability layers were continuous, the production rate was even lower than that for a model uniformly packed with the same low-permeability sand. A higher oil production rate was found with discontinuous low-permeability lenses than with continuous layers. This is because the vapour chamber could rise around these lenses to penetrate further into the high-permeability material above; thus the oil could be drained concurrently from different heights. Capillarity, due to interfacial tension between the oil and solvent vapour phases, has a significant influence on the Vapex process. Its effects are both beneficial, because of the increased contact area between solvent vapour and oil, and detrimental, because of the resistance to the rising of vapour fingers, on a pore scale, from a coarse sand layer into a fine sand layer. This latter effect changes the shape and growth rate of the solvent chamber. A much higher residual oil saturation was found in the fine sands than in the adjacent coarse sands. Introduction Thermal methods are considered to be effective for the recovery of heavy oil and bitumen and they have been applied commercially world wide. They contribute 80% of the total production from all types of EOR. However, the large heat requirement makes thermal methods, such as steam injection, inefficient and uneconomic in many reservoirs. Reservoir characteristics that tend to reduce the performance of thermal processes are: thin pay zones, low porosity, high water saturation, low rock thermal conductivity and the presence of aquifers. A process using hydrocarbon vapours to extract bitumen or heavy oil, known as Vapex, has been described and studied(1,2,3) (Butler and Mokrys, 1989; 1991; 1993). The Vapex process, although an evolution of steam assisted gravity drainage (SAGD), is a non-thermal process.

Vacuum extraction of a nonaqueous phase residual in a heterogeneous vadose zone

The fate of an infiltrating nonaqueous phase liquid (NAPL) in a heterogeneous vadose zone was evaluated under laboratory conditions. Vapor extraction was then used to remove the contaminant, and the rate of removal was compared with the predictions of simple mathematical models. The laboratory experiments were conducted in idealized soil systems in which a fine-grained, low permeability lens insert was located in a coarse-grained sand layer. The infiltration study indicated that an essentially saturated layer of NAPL was trapped at the base of a fine-grained lens. A model of this process showed that capillary forces were responsible for the observed retention. Entrapment of NAPL within the fine-grained lens was expected to reduce the effectiveness of any in-situ extractive technology such as soil vacuum extraction (SVE) for the removal of the NAPL. Simple models of the mass transfer from the lens-entrapped NAPL to an extracting vapor in the coarse sand layer were developed and applied to laboratory experiments in which toluene, either pure or in a mixture, was injected within an idealized low permeability lens. Mass transfer resistances in the extracting vapor-phase controlled the release of pure toluene from the fine lens at low air flowrate (Reynolds number, Re ≤ 0.5) while intra-lens diffusion resistances were dominant at higher air flow rate (Re ≥ 3). Liquid phase resistances were always important in the extraction of toluene from a NAPL mixture. The models were found to accurately predict the removal rate of the toluene from the low permeability lens under each of the experimental conditions.

Riparian nitrogen dynamics in two geomorphologically distinct tropical rain forest watersheds: subsurface solute patterns

Nitrate, ammonium, dissolved organic N, and dissolved oxygen were measured in stream water and shallow groundwater in the riparian zones of two tropical watersheds with different soils and geomorphology. At both sites, concentrations of dissolved inorganic N (DIN; NH4 +- and NO3 −-N) were low in stream water (< 110 ug/L). Markedly different patterns in DIN were observed in groundwater collected at the two sites. At the first site (Icacos watershed), DIN in upslope groundwater was dominated by NO3 −-N (550 ug/L) and oxygen concentrations were high (5.2 mg/L). As groundwater moved through the floodplain and to the stream, DIN shifted to dominance by NH4 +-N (200–700 ug/L) and groundwater was often anoxic. At the second site (Bisley watershed), average concentrations of total dissolved nitrogen were considerably lower (300 ug/L) than at Icacos (600 ug/L), and the dominant form of nitrogen was DON rather than inorganic N. Concentrations of NH4 + and NO3 − were similar throughout the riparian zone at Bisley, but concentrations of DON declined from upslope wells to stream water. Differences in speciation and concentration of nitrogen in groundwater collected at the two sites appear to be controlled by differences in redox conditions and accessibility of dissolved N to plant roots, which are themselves the result of geomorphological differences between the two watersheds. At the Icacos site, a deep layer of coarse sand conducts subsurface water to the stream below the rooting zone of riparian vegetation and through zones of strong horizontal redox zonation. At the Bisley site, infiltration is impeded by dense clays and saturated flow passes through the variably oxidized rooting zone. At both sites, hydrologic export of nitrogen is controlled by intense biotic activity in the riparian zone. However, geomorphology appears to strongly modify the importance of specific biotic components.

Ecological succession in a former meander of the Rhône River, France, reconstructed by Cladocera remains

A former meander of the Upper Rhone River, France, is completely filled with silt and occurs as a forested wetland. Bosminidae and Chydoridae (Crustacea, Cladocera) remains are analysed from a 6-m sediment core that reaches coarse sand and gravel layers deposited by running water. The lower layer of fine sediment, deposited by still water after the meander had been cut off, was dated at 1666±211 BC. The likely end of aquatic succession was dated at 800±150 AD. The results, processed using Factorial Correspondence Analysis, suggest 3 phases during the aquatic succession. Phase I, corresponding to open water conditions, is very short. The following phases, indicating the development of macrophyte stands, then a decrease in depth, extend much longer. The unexpectedly long duration (1000–2000 years) of these macrophyte-dominated and marshy phases may be explained by a progressive rise in the mean water level of the Rhone River. The causes of this water level rise may be related to climatic and/or fluvial dynamics changes.

Dependence of anisotropy on saturation in a stratified sand

A laboratory experiment was performed to investigate the movement of water infiltrating from a point source into a porous medium comprised of alternating layers of fine and coarse sand packed in a clear plastic tank. The purpose of the experiment is to demonstrate whether the effective anisotropy of stratified materials is dependent upon saturation. The noncolinearity of the specific discharge and hydraulic head gradient directions is used as a measure of anisotropy. Dyes were used to map the specific discharge direction and tensiometers were used to characterize the hydraulic gradient field under unsaturated, steady state conditions. The results indicate a divergence between the direction of the specific discharge and gradient which increases as the pressure head decreases. Anisotropy determined from the experiment exceeds that calculated from the hydraulic conductivities of the individual materials.

Coarse-sediment bands on the inner shelf of southern Monterey Bay, California

Bands of coarse sand that trend parallel to the shore, unlike the approximately shore-normal bands found in many inner shelf areas, occur in southern Monterey Bay at water depths of 10–20 m, less than 1 km from the shore. The bands are 20–100 m wide and alternate with bands of fine sand that are of similar width. The coarse-sand bands are as much as 1 m lower than the adjacent fine-sand bands, which have margins inclined at angles of about 20°. The mean grain sizes of the coarse and fine sand are in the range of 0.354–1.0 mm and 0.125–0.354 mm, respectively. Wave ripples that average about 1 m in spacing always occur in the coarse-sand bands. Over a period of 3 yrs, the individual bands moved irregularly and changed in shape, as demonstrated by repeated sidescan sonar surveys and by the monitoring of rods jetted into the sea floor. However, the overall pattern and distribution of the bands remained essentially unchanged. Cores, 0.5–1.0 m long, taken in coarse-sand bands contain 0.2–0.5 m of coarse sand overlying fine sand or interbedded fine and coarse sand. Cores from fine-sand bands have at least one thin coarse sand layer at about the depth of the adjacent coarse-sand band. None of the cores revealed a thick deposit of coarse sand. The shore-parallel bands are of unknown origin. Their origin is especially puzzling because approximately shore-normal bands are present in parts of the study area and immediately to the north.

Shallow-water propagation effects over a complex, high-velocity bottom

Shallow-water propagation experiments conducted on the Scotian Shelf in 1978 produced very high transmission losses at low frequency for a range of only 4 km. The bottom along the propagation track consisted of a thin layer of coarse sand over granite bedrock which protruded through the sediment in certain regions. The sources of the high losses at low frequency are investigated by varying the acoustic properties of the geoacoustic model. It is shown that neither scattering nor shear effects in the granite basement accounts for this loss, but that a third mechanism, excitation of shear waves in the sediment, can cause such high losses.

Quantitative extraction of living meiofauna from marine and brackish muddy sediments

A method for extracting living meiofauna from marine and brackish water mud is proposed and tested. Samples are fitted into tubes and covered with a 2 cm layer of clean coarse sand. Water of appropriate salinity is added until the sample is flooded and the sandy cover is just moist. Sample tubes are closed and stored in the dark. As the samples become anaerobic, the animals migrate upwards into the sandy layer. To extract them, the sandy cover is separated periodically and washed out by 10-fold shaking and rotating in a beaker. The supernatant is decanted through small funnels, and animals are retained on a 40 pm gauze. Total extraction of 1 sample takes about half a n hour. This extraction procedure is compared to grain-by-grain investigation of the whole sample. Within the sites tested, Plathelminthes, Polychaeta, Oligochaeta, Copepoda, and Ostracoda were extracted quantitatively. Extraction of Nematoda and Halacarida was not always complete. In some cases, extraction even yielded significantly higher numbers of Oligochaeta and Plathelminthes than control sorting.

A model of glacial tectonics, applied to the ice­pushed ridges in the Central Netherlands

During a detailed structural geological and geomorphological survey of ice-pushed ridges around the Gel­derse Vallei (centre of the Netherlands) several questions arose about the origin of these landforms. The Gelderse Vallei is a Saalian glacial basin filled with younger sediments, 40 km long and up to 20 km wide, running NNW-SSE. Thrust sheets which build up the ice-pushed ridges on either side of the valley were transported away from the centre of the basin. They are up to 25 m thick and are pushed to a level about 100 m above the decollement. The thrust sheets, mainly consisting of coarse sand layers, moved as rigid masses, while only the finegrained basal layers deformed by heterogeneous simple shear. Pore water pressure plays an important role by greatly reducing the sliding friction in the decollement layer. Once a glacial thrust sheet is formed, the weight of the upward moving frontal part (the toe) offers a resistance to movement, which can not be overcome by the basal shear stress of the glacier alone. Basal shear stresses in most glaciers are in the order of 0.1 MPa (1 bar) and appear to be incapable of lifting a toe of the size found in most ice-pushed ridges in the Netherlands. The article presents a model of a system ice lobe - substratum, which is to a large degree controlled by gravitational forces. The dilemma may be solved by the concept of the gradient stress field under the marginal area of an ice lobe. This concept was first formulated by Rotnicki (1976). Because ice thickness decreases towards the margin, the substratum is subjected to a decreasing load in the same direction. If the increments of stress difference under a slab of ice in the marginal zone are summed, a gradient stress is arrived at which is di­rected towards the ice edge. An estimate of the forces involved in the static equilibrium around the glacier margin indicates that the contribution by the gradient stress field is sufficient to move the toe. In the model proposed in the article, the energy to move and imbicate glacial thrust sheets around the margins of an ice lobe, is supplied by the continuous flow of ice into the ice lobe. The dimensions of ice­pushed ridges are thus to a high degree functions of the thickness of the ice lobe or icecap. The Gelderse Vallei ice lobe will have been at least 250 m thick to be able to form the ridges. The basal shear stress contributes less to the tectonic transport, the larger the thrust sheets and the high­er the ice-pushed ridges.

DRAINAGE OF AN IRRIGATED SALINE SOIL IN ALBERTA

A shallow subsurface drainage system effectively controlled a high water table and reduced salinity in an irrigated soil near Magrath, Alberta. Plastic corrugated tubing was installed in 1976 at depths of 1.1–1.5 m and spacings of 15 and 30 m in a moderately saline soil. During the irrigation period, the water table rose to within 0.3 m of the surface but was lowered to pre-irrigation levels within 48 h. The water table was maintained at, or below, the depth of the drains between irrigations. The 15- and 30-m spacings of the drain lines were equally effective in providing water table control in this lacustrine soil which was underlain by a coarse sand and gravel layer. Salinity levels were decreased substantially only within the surface 0.3-m soil depth. Quality of the drainage effluent remained constant throughout the growing season with only small dilution effects detected during irrigations. Barley yields increased to 3900 kg/ha in 1978, 2 yr following drainage of this saline soil which had been out of crop production for 20 yr.

The Electro-Osmotic Guillotine, a New Device for Core Cutting

ABSTRACT Cutting cores of unconsolidated sediments with a guillotine-like electro-osmotic core cutter minimizes distortion of sedimentary structures and makes additional core cosmetics unnecessary even if coarse sand layers, larger clasts or shells are intercalated with clayey sediments.

A PRELIMINARY STUDY OF PATTERNED GROUND ON SOME MOUNTAINOUS REGIONS OF CENTRAL AND NORTHERN JAPAN

There is a stringency about the existance of periglacial activities in some districts of Japan from the last glacial stage to recent. Some amounts of studies on periglacial pheno-mena relative to both fossil and recent types have already been made, and a few attempts were carried out to outline the palaeoclimatic zones or palaeogeographical features of Japanese Islands during the Wurm stage using some data indicating palaeoclimates by field observations about fossil patterned ground and other features distinguished as periglacial phenomena. While the concept that patterned ground indicates the palaeoclimate or palaeogeography has been accepted, there remained some confusions between terminology and genetical ideas about patterned ground in Japan. So, it was hoped that from the viewpoint of genetical ideas, re-checking of patterned grounds might provide profound data for palaeogeography, if the works would be carried out without confusions. In this preliminary study, the authors did on-the-spot investigations at such mountains as Mt. Kamikochi (2803m) and Mt. Chausu (2600m) in the Southern Alps and Mt. Kaun (1954m) of Taisetsu Volcano in Central Hokkaido. After these field works, we analysed the observed data and materials, and discussed on genetical ideas and environment, under which these patterned grounds develop. Conclusions are summarized as follows: (1) According to Washburn's classification of patterned ground, the patterned ground we observed is classified as “sorted circles” from its morphological feature, and there are two groups of different sizes, diameter 10-15cm and 100-150cm. (2) The places where sorted circles develop are fiat or gentle slopes covered with weathe-red debris without vegetation covers, or some depressions formed by snow patch erosion and dammed up shallow valleys. Larger size sorted circles develop at the bottom of depressions, which are sometimes filled with snow-melted water during summer and also with weathered materials from bedrock. The altitudes are usually around 2, 500m in the Southern Alps, and around 1, 600m on Mt. Kaun in Hokkaido. In these areas, the altitude is above the timber-line and nearly the some with the zone of pines montana. (3) The observations of soil profiles of sorted circles show two stratified layers, coarse sand and debris for the upper, fine well sorted sand and silt for the lower. The boundary of these two layers is sharp and not horizontal but waved. Careful taking off of the upper layer enables one to observe the three dimensional forms of the boundary, and it shows the exi-stance of mound-like forms. There is an obvious relationship between this mound form and sorted surface features. The center of sorted circles consisted of fine materials coincides with the top of the peak part of mound form. The fringed contour of sorted circles consisted of coarse materials concides with the outskirts of mound. So this mound form controls the size of sorted circles. (4) There are no fissures and no sand wedges which cut deep the fringed contours of sorted circles. But the mound form of boundary shows the process that the lower fine sand and silt layer extrudes into the upper coarse sand and debris layer without developing fissures. (5) The features of sorted circles mentioned above support the idea by A. E. Corte, that is, by the multicycles of freeze-thaw, the lower fine material layers extrude into the upper layers, and this differential movement of particles forms the mound form. The depth of lower fine layers, termed as active layer, controls the size of sorted circles. By other mecha-nical sorting processes, the surface sorted circles will develop. Of course, it is hard to explain all processes and mechanisms of sorted circles by restricted genetical ideas, but the further advanced fieldworks and laboratory methods are hoped to be carried out in some areas distinguished as periglacial regionss in Japan.

Thin Gravel Deposits on Wave-Eroded Cliffs Near Barrow, Alaska

The beach southwest of Barrow, Alaska, is limited to a foreshore which is backed by wave-eroded cliffs of the Quaternary Gubick Formation. These cliffs, which have an approximate elevation of 20 to 35 feet above mean sea level, are covered with a thin layer of coarse sand and gravel. This gravel unit ranges in thickness from a few inches to an intermittent covering of gravel. The unit extends inland about 10 feet in some places to about 300 feet in others. A gravel deposit of these dimensions is of little or no importance to most scientific disciplines. However, its presence and method of formation are of extreme importance to the unravelling of the archaeological sequence along the coast of Northern Alaska. The gravel units were first observed during the archaeological excavation of an Eskimo site at Walakpa, which is approximately 12 miles southwest of Barrow. At this location there is a sequence of gravel units interspersed throughout the stratigraphic column of the site. These gravel units were formed at the surface after a period of Eskimo occupation and then covered by a subsequent period of occupation, thus they served as a basis for separating one period of occupation from another either older or younger occupation level. ... The presence and method of deposition of the sand and gravel units at the Walakpa site give further evidence that vertical sorting has not occurred. This in turn suggests that the artifacts found in an occupation level belong only to that occupation level; i.e., the tool assemblages found can be attributed to a single period of cultural deposition. The observations are of extreme importance to the unravelling of the archaeological sequence along the arctic coast of Alaska. Owing to the uncommon occurrence of this phenomenon the author has only pieced together the sequence of events necessary for the deposition of these gravel units. However, they have been observed by Silas Negovanna who is a native of the area (personal communication).

SEDIMENTATION IN SAN DIEGO TROUGH AND CONTRIBUTING SUBMARINE CANYONS

SUMMARYThere are a series of basins off southern California, all presumably due to faulting of the broad continental borderland. Of these, San Diego Trough is the only one where sedimentation has gone on sufficiently to fill the basin depressions so that there is a continuous slope southward to where the trough connects with the deeper San Clemente Basin. This deposition has apparently come to a very great extent from turbidity currents moving down submarine canyons developing channeled fans at the canyon bases. All along the canyons and channels as well as across the fans and in San Diego Trough there are sequences of turbidite sands alternating with muddy sediments that represent the normal deep water sedimentation. Comparison of the coarse fraction from the sands and from the interbedded muds shows that the former are predominantly terrigenous in character whereas a large proportion of the latter are biogenous. Mica is quite low in the coarser sand layers but is abundant in the coarse fraction of the muds. Diatoms and radiolarians are largely confined to the mud layers where they may constitute a large percentage of the sand fraction.Study of the heavy and light minerals shows that the sediments of San Diego Trough are derived largely from the nearby land masses rather than having a considerable admixture from the north as would be the case if sediments were being brought down by turbidity currents coming into the trough from the north. The alterites are appa‐rently lower in San Diego Trough than in the near shore source area which suggests that a supply of sediments may be picked up from the canyon or channel walls along the way to the trough. Also the finding of the only coarse sands in the middle reaches of the channels suggests local sources as does the general make up of these coarse sands. Despite these locally derived coarse sands the prevalence of very fine sand and the “mud” layers between sand layers suggest that the turbidity currents supplying sediments to San Diego Trough have low velocities or at any rate little erosive capacity.

Schliemann's Trojan Excavations

THE Times of Tuesday contains several letters from Dr. Schliemann, describing the researches he has been recently making in the Trojan country in company with Dr. Virchow of Berlin, and M. Burnouf, of Athens. They endeavoured to ascertain the geological character of the plain of Troy, by sinking shafts in different parts between Mount Hissarlik and the Hellespont. Dr. Schliemann states:—“We obtained every where the same result—viz., below the clay soil a thick layer of coarse or fine river sand, and below it the very compact dark-brown clay of the plain. But the most important result was obtained by the shaft we sunk in the Stomalimne, mentioned by Strabo, which is an easily recognisable swamp, situate between the mouths of the rivers; it slopes abruptly from the plastic clay of the plain to a field of sand which is nearly on a level with the sea. Excavating there, we found below the layer of sand, which is hardly an inch thick, a layer of plastic clay, about 16 inches thick, which is perfectly the same as in the plain, and below it a dark-blue sand containing putrified vegetable matter, which can leave no doubt that here existed a swamp. The upper part of this layer of blue sand is exactly on a level with the sea and with the adjoining inlet, the water of which is brackish and has no current. Having dug in this blue sand a large hole two feet deep, we saw the water filtering from all sides through the sand and soon filling the hole completely, and thus the water's surface was on a level with both inlet and sea; but this water was sweet and drinkable. In no one of our shafts sunk elsewhere did we discover the slightest trace of the sea having ever sojourned there; everywhere we found only the produce of sweet water. Thus it is evident that the soil of the plain of Troy has been produced by sweet water, and that this deposit is anterior to the existence of both the Scamander and the Simois, the more so as the modifications produced by these rivers are but very slight.” Therefore he maintains the theory that at the time of the Trojan war the sea formed a deep gulf in the Plain of Troy, that the later Ilium (Hissarlik) was too near the Hellespont, and no space left for the great deeds of the “Iliad”; that consequently the two cities could not possibly be identical—is now exploded and can never be revived again. Both Professor Virchow and Mr. Burnouf have accepted Dr.Schliemann's theory that the immense bed of the small and insignificant rivulet Kalifatli-Asmak, which has no running water except during the inundations in winter—that this river-bed, which has in many places a breadth of from 660 ft. to 825 ft.—is identical with the ancient bed of the Scamander.