Sand Lenses Research Articles

Air and water entrapment in the vicinity of the water table.

A laboratory tank was used to study entrapment of water in coarse sand lenses above the water table and of air in coarse sand lenses below the water table. Monitoring of these experiments involved a combination of visual inspection, measurement of moisture content, and measurement of air/water pressure. The medium consisted of coarse sand lenses with various degrees of vertical connectivity embedded within a fine sand matrix. Experiments were performed under conditions of both drainage (from a fully saturated medium) and imbibition. Observations during drainage included: (1) water was trapped in the coarse sand zones above the water table at heights significantly greater than anticipated from consideration of capillary rise in the coarse sand; (2) rapid drainage of these same coarse zones occurred when air penetrated into these zones through the surrounding fine sands; and (3) prior to the time of penetration of the coarse sand by air, water pressure in the coarse zone dropped significantly below atmospheric pressure. Observations during imbibition included: (1) entrapment of air within coarse sands below the water table, (2) the pore fluids in these zones varied spatially from predominantly air to predominantly water, and (3) pressure in the trapped air phase was significantly greater than pressure in the water phase in the surrounding fine sand. Overall, these results demonstrated significant sensitivity to the geometry of the coarse sand inclusions, particularly the vertical connectivity of the coarse sand lens.

The very high alluvial formation of early Pleistocene age in the Creuse River Valley at Eguzon (Indre) : cryoturbation patterns, prehistoric occupation sites and absolute dating

Abstract Around twenty prehistoric sites of the very early Palaeolithic were discovered on the northern edge of the Massif Central, in the Creuse Valley between Crozant and the Paris Basin, and on the Aigurande crystalline plateau that borders it. Concentrated more particularly around Eguzon, the sites are all closely linked to fluviatile formations, whose study, despite difficult exploration conditions, revealed many remnants of alluvial deposits. Those of the very high formation, some up to 15 m thick, were the best preserved. The most significant site, at “Pont-de-Lavaud”, is in a thin bed of gravel made up mainly of quartz pebbles and debris with small, interbedded sand lenses. Tilted 6 to 7° in a small depression in the weathered foliated crystalline basement, the bed is at mid-slope of an interfluve between the Creuse River and one of its small tributaries. Excavation done between 1983 and 1995 uncovered many prehistoric artefacts carved out of quartz in the upper part of the sediment and, below this, various cryoturbation patterns (sorted circles, polygons, inclusions in the alluvium of alterite from the bedrock) and scattered, less abundant artefacts of the same type. Due to the outstanding state of conservation of these findings, they could be studied in a particularly detailed manner and, when coupled with the study of the alluvial formations, enabled us to : – place them at the base of the very high terrace, located 90–110 m above the river’s present-day low water level – attribute the unusual position of the outcrop to the tilting of a block of bedrock by new displacement of an old fault, thus confirming the role of recent tectonics in the regional morphology ; Absolute age dating by Electron Spin Resonance (ESR) of the best conserved outcrops of the very high alluvial formation gave an age of 1 to 1.2 million years, thus placing them at the end of the early Pleistocene. However, dating of alluvial remains near the site and of the site itself, gave ages between 0,9 and 1 million years. Differences are attributed to the role that greater erosion and pedogenic weathering might have played. Therefore, the “Pont-de-Lavaud” occupation sites are among the oldest presently known in Europe.

Alluvial architecture of the human-influenced river Rhine, The Netherlands

The alluvial architecture of the embanked Rhine distributaries in The Netherlands is largely controlled by human interference with fluvial processes. Embankment, straightening, and stabilization of the rivers have influenced both in-channel and overbank sedimentation. Embanked river floodplain deposits are lithologically and sedimentologically different from natural (not human-influenced) floodplain deposits. After the embankments between 1050 and 1350 AD, the dominant process remained lateral within-channel accretion. However, the morphology of the point bars changed: in the natural situation, the bars had a convex shape (as seen from the channel), whereas in the embanked situation, they are concave (as seen from the channel). The latter is due to the development of bars along the downstream end of a previous formed bar. Deposits associated with lateral within-channel accretion are typically very fine to medium or coarse sand. The infill of residual channels is characterized by the absence of peat. After the normalization of the river channel to a fixed width (1850 AD), concave bank erosion, and development of scroll bars were constricted, and overbank deposition became the dominant embanked floodplain-forming process. Thick layers of sandy and clayey deposits were deposited on the embanked floodplain. Splay-like sand lenses are present in the overbank deposits. In case of dyke failures, a deep scour-hole was formed. Typical deposits associated with dyke-breaches are sandy dyke-breach deposits and scour-hole fills consisting of silty to sandy clay within the embanked floodplain and gyttja within the polder.

Sedimentology of the Bengal shelf, Bangladesh: comparison of late Miocene sediments, Sitakund anticline, with the modern, tidally dominated shelf

Characterisation of latest Miocene facies of the Bay of Bengal reveals a range of tidal and fluvially dominated sediments that represent sedimentation on a broad, shallow shelf that was strongly influenced by tidal and seasonal cyclicity. These tidally influenced sediments are excellently exposed within growth anticlines of the westward-migrating Chittagong–Tripura Fold Belt (CTFB), and permit detailed study of the late Miocene Bengal shelf for comparison with the modern subaqueous deltaic sediments. At the outcrop scale, facies associations record a subtidal shelf, migrating intertidal/subtidal bedforms, tidal and incised channels. The subtidal shelf comprises extensive sand sheets interbedded with thick clay horizons, while the migrating intertidal/subtidal bedforms exhibit a decrease in bedform size from large dunes to small ripple-scale cross-stratification that reflect a decrease in current velocity and sand/silt grade sediment supply as the bedforms migrated. Rootlet horizons within these intertidal/subtidal bedforms may represent a lower delta plain environment. The tidal channel facies consists of metre-scale sandstone beds that are rich in locally derived clay clasts, with up to 0.5 m of incision into a rhizolith horizon below. Incised channel facies records a coarse, pebbly sandstone with clasts derived from a reworked clastic source, with metre-scale scour at the base of this facies association into laminated and rhizolith clays. A 534-m one- and two-dimensional section within the Sitakund anticline, north of Chittagong, is characterised by 20–100-m thick, tidally dominated, progradational parasequences. Mudstones with isolated sand lenses and abundant trace fossils of the Cruziana ichnofacies, coarsen upwards to fine–medium-grained sandstones deposited in shallower, high-energy environments. These sands were deposited under both uni-directional and bi-directional currents resulting in dune-scale cross-stratification, and are overlain by 2–5-cm thick clay drapes, considered to be of a thickness greater than that typical of deposition from a single slackwater episode. The main controls on sedimentation are the seasonally influenced river and sediment discharge onto the shelf from the Himalayan source region, combined with the influence of daily, spring–neap tides, channel and bedform migration and minimal wave action over the shallow shelf. The modern Bay of Bengal shelf provides an analogue for interpreting processes recorded within the Miocene succession, allowing construction of a depositional model for the late Miocene shelf of the Brahmaputra/Ganges delta system, with sedimentation dominated by tidal and seasonal cyclicity.

The Role of Sequential Well Testing in Improving Oil Recovery From a Closed Sand Lens in the Bahrain Field

Summary The Ac zone refers to the sandstone facies of the Wara formation, which belongs to the Wasia group of the Middle Cretaceous age.* Owing to variable shale to sand ratios, the Ac zone is realized as different isolated sand lenses scattered all over the field. Owing to the complexity of the geology and the flow mechanism, well testing was used to manage the reservoir. The concept of a sequence of well tests on the same well was found to be essential in improving the oil recovery. Conducted on a specific well situated within a closed sand lens, sequential well testing yielded valuable information that assisted in understanding the drive mechanism and the deteriorating reservoir parameters, permeability, and skin. Such a method was crucial in improving the recovery from the sand lens as well as from the single-well-treatment perspective. This paper presents an example of how such a technique aided in improving the oil recovery from a small sand lens.

Preservation of aeolian genetic units by lava flows in the Lower Cretaceous of the Paraná Basin, southern Brazil

The Lower Cretaceous geological record of the intracratonic Paraná Basin in southern Brazil comprises a thick succession of aeolian sandstones and volcanic rocks. The intercalation between aeolian sandstone and volcanic floods allowed the preservation of distinct aeolian genetic units. Each genetic unit represents an accumulation episode, bounded by supersurfaces, that coincides with the base of lava flood events. The entire package can be subdivided into a Lower Genetic Unit, which corresponds to aeolian sandstones preserved below the initial lava flows (Botucatu Formation), and an upper set of genetic units, which comprises interlayered aeolian deposits and lava floods (Serra Geral Formation). The Lower Genetic Unit is up to 100 m thick. Its base is composed of ephemeral stream and aeolian sand sheet deposits that are overlain by cross‐bedded sandstones whose origin is ascribed to simple, locally composite, crescentic and complex linear aeolian dunes. Aeolian accumulation of the lower unit was possible as a result of the existence of a wide topographic basin, which caused wind deceleration, and a large sand availability that promoted a positive net sediment flux. The Upper Genetic Units comprise isolated sand bodies that occur in two different styles: (1) thin lenses (<3 m thick) formed by aeolian sand sheets; and (2) thick sand lenses (3–15 m) comprising cross‐bedded cosets generated by migration and climbing of simple to locally composite crescentic aeolian dunes. Accumulation of the aeolian strata was associated with wind deceleration within depressions on the irregular upper surface of the lava floods. The interruption of sedimentation in the Lower and Upper Genetic Units, and related development of supersurfaces, occurred as a result of widespread effusions of basaltic lava. Preservation of both wind‐rippled topset deposits of the aeolian dunes and pahoehoe lava imprints indicates that lava floods covered active aeolian dunes and, hence, protected the aeolian deposits from erosion, thus preserving the genetic units.

Multiphase flow and transport in fractured clay/sand sequences

A numerical model (Queen's University Multi-Phase Flow Simulator, QUMPFS) was used to assess the rate of trichloroethylene (TCE) dense, non-aqueous phase liquid (DNAPL) migration through fractured clay, with special attention focused on the influence of interbedded sand lenses. The presence of these sand lenses was found to increase the time required for the non-wetting phase to migrate through the full 30 m vertical extent of the clay sequence from a few days to several years. Applied vertical hydraulic gradients were found to be moderately influential in systems consisting solely of fractured clays, yet one of the dominant factors controlling speed of vertical migration when sand lenses were present. Larger displacement pressure of the sands relative to that of the fractures leads to slower DNAPL migration rates, due to the delays that occur during build-up of capillary pressures. Dissolution of DNAPL and subsequent matrix diffusion of the aqueous phase has little effect on the rate of DNAPL migration through systems consisting of fractured clay only, yet slows the rate of migration in systems containing sand lenses. In all cases examined, the rate of DNAPL loading to the lower aquifer far exceeded the rate of aqueous phase mass loading. It was also found that DNAPL reaches the lower aquifer at approximately the same time as the aqueous phase plumes even for systems experiencing downward groundwater flow due to the attenuation of the aqueous phase through matrix diffusion.

Mass transport and scale-dependent hydraulic tests in a heterogeneous glacial till–sandy aquifer system

A forced gradient tracer experiment indicated a rapid transport of a solute tracer, chloride, through a 13-m thick fractured till–silty sand lens system to an underlying sandy aquifer in Ringe, Denmark. Chloride was applied to a 4×4.8 m 2 area on the ground surface and chloride breakthrough was monitored in horizontal filters at depths of 2.5 m (till), 4 m (till), 5.5 m (silty sand lens), and 20–20.5 m (sandy aquifer). This paper is an extension of the research undertaken by Sidle et al. (Water Resources Research, 34 (1998) 2515) and focuses only on the chloride breakthrough data from the silty sand lens (embedded in the till) and the sandy aquifer, and on the scale dependency of saturated hydraulic conductivity tests. The rapid chloride transport shows that the fracture and macropore flow is significant in the non-weathered till between the silty sand lens and the sandy aquifer. The first arrival of chloride in the sandy aquifer occurred 8 days after the start of the tracer injection and the “peak concentration” was reached after 3 weeks. In addition, slug tests, free flow tests, and large-scale infiltration tests were conducted to assess the spatial variability of the hydraulic characteristics of the interconnected aquitard/silty sand lens system and the underlying aquifer. The large-scale infiltration tests and the free flow tests yielded substantially higher K values than the slug tests, where the slug tests represented a small-scale sampling volume and only a localized fracture network. The infiltration tests captured the decrease in bulk K from the uppermost, bioturbated till to the underlying fracture-dominated till. K values varied in the till with depth by up to 3 orders of magnitude from 1×10 −7 to 1×10 −4 m s −1 with the highest permeabilities in the uppermost 2.5 m. The high permeabilities explain the fast breakthrough of the solute in the underlying aquifer. The present study indicates that at high flow rates diffusive exchange of solute tracer mass did not significantly influence the solute transport, particularly in the non-weathered till.

New Life from an Old Field-PKCU #2 Waterflood

Abstract The Pembina Keystone Cardium Unit #2 is located on the eastern edge of the Pembina Cardium oilfield. PKCU #2 has been on primary depletion for over 40 years and was nearing the end of its economic life. In late 1995 the Pembina Exploitation Team within Canadian Oxy decided to review the area in detail one last time. The final result of the exhaustive work, which included core floods, geological review, a 3D simulation, facilities and production optimization review, and a reservoir depletion plan, was a large scale waterflood on a depleted field. It is expected that the recovery factor for the waterflood will be 20% as compared to the primary recovery factor of 11%. The over 10,000,000 BOEs of incremental reserves will be developed for < $3.00/BOE. Waterflood start up was anticipated for late summer 1998. Author's Note Since this paper was originally written the following actions have taken place. CanadianOxy and Working Interest Owner approval was granted in the third quarter of 1997. Facilities Engineering and Operations began the process of consultation with area residents and gaining pipeline right of ways. Construction was set to begin in the Summer of 1998. Within CanadianOxy at that time a review of our properties was conducted. It was decided that all of CanadianOxy's Pembina properties would be sold. All work in the field was suspended. PKCU #2, along with the rest of CanadianOxy's Pembina properties, were sold to Penn West Petroleum in December 1998. Penn West is currently reviewing a scaled down version of the Keystone Waterflood. Introduction With the discovery of the Pembina Oilfield in the mid-1950s rapid development drilling was followed by the implementation of a waterflood. Most of the Pembina Cardium was under waterflood by the mid-1960s. The main western portion of the Pembina Cardium, centered around the town of Drayton Valley, was developed using waterflood on 80-acre spacing 5-spots. The southeastern portion of the Pembina Cardium, centered around the Village of Breton, was anomalous. Most of it was developed on 160 acre spacing on primary depletion. PKCU #2 is located in the SE portion of the field. Historically any secondary recovery scheme at PKCU #2 was deemed to be too risky for some of the following reasons:The overlying conglomerate would act as a thief zoneThe low reservoir pressureThe old geologic model of the sandstone which consisted of independent sand lenses was poor for waterfloodingThe value of the gas and liquids The uncertainty and risk with waterflooding PKCU #2 meant that the project could never get corporate and partner approval until some of the following questions were answered:Can you successfully waterflood a reservoir with high gas saturation and low pressure?What is the true geologic model?What is the cost of implementing a waterflood?What production and recovery could be anticipated?What is the downside risk? The 1995 Waterflood study included the following elements which were meant to answer all questions and concerns:

Recharge Through a Regional Till Aquitard: Three‐Dimensional Flow Model Water Balance Approach

AbstractIn southern Ontario, vertical leakage through a regionally extensive till is the primary source of recharge to underlying aquifers used for domestic and municipal water supply. Since leakage is largely controlled by the bulk hydraulic conductivity (K) of the aquitard, accurate estimates of K are necessary to quantify the resource. Considerable controversy exists regarding estimates of K for this aquitard, which vary according to the scale of the test method. For the till matrix, estimates from core samples and slug tests consistently range from 10−11 to 10−10 m/s. Isotopic evidence (3H), on the other hand, indicates that nonmatrix structures such as sand lenses, erosional surfaces, joints, and fractures significantly enhance till permeability. This is confirmed by slug test, pump test, recharge, and water balance studies, which show that K varies over seven orders of magnitude (10−12 to 10−5 m/s).To provide a regional estimate of bulk K and a reliable estimate of vertical recharge through the Northern Till, a numerical ground water flow model was constructed for the Duffins and Petticoat Creek drainage hasin. The model was calibrated to measurements of hydraulic head and estimates and measurements of base flow throughout the basin. This model demonstrates that the vertical hydraulic conductivity (Kv) for the Northern Till ranges from 5 × 10−10 to 5 × 10−9 m/s, values that are up to 2.5 orders of magnitude greater than matrix K estimates. Regional recharge through the Northern Till is estimated to range from 30 to 35 mm/a.

Transport and biodegradation of creosote compounds in clayey till, a field experiment

The transport and biodegradation of 12 organic compounds (toluene, phenol, o-cresol, 2,6-, 3,5-dimethylphenol, naphthalene, 1-methylnaphthalene, benzothiophene, dibenzofuran, indole, acridine, and quinoline) were studied at a field site located on the island of Funen, Denmark, where a clayey till 10–15 m deep overlies a sandy aquifer. The upper 4.8 m of till is highly fractured and the upper 2.5 m contains numerous root and worm holes. A 1.5–2 m thick sand lens is encountered within the till at a depth of 4.8 m. Sampling points were installed at depths of 2.5 m, 4 m, and in the sand lens (5.5 m) to monitor the downward migration of a chloride tracer and the organic compounds. Water containing organic compounds and chloride was infiltrated into a 4 m×4.8 m basin at a rate of 8.8 m 3 day −1 for 7 days. The mass of naphthalene relative to chloride was 0.39–0.98 for the sampling points located at a depth of 2.5 m, 0.11–0.61 for the sampling points located at a depth of 4 m, and 0–0.02 for the sampling points located in the sand lens. A similar pattern was observed for eight organic compounds for which reliable results were obtained (toluene, phenol, o-cresol, 2,6-, 3,5-dimethylphenol, 1-methylnaphthalene, benzothiophene, and quinoline). This shows that the organic compounds were attenuated during the downward migration through the till despite the high infiltration rate. The attenuation process may be attributed to biodegradation.

Riparian Forest Restoration Along Large Rivers: Initial Results from the Sacramento River Project

AbstractRestoration of riparian vegetation along large rivers is complicated by the patchiness of the habitat and by conflicts with the societal need to control flooding. The Sacramento River Project, led by The Nature Conservancy in northern California, is testing whether it is possible to restore native forest along a large river without removing flood control. We conducted a post‐hoc analysis of monitoring data collected by the project on 1–4‐year old plantings of 10 native trees and shrubs at five sites. Two questions of general interest were: Can one identify types of species or sites that are especially suitable for restoration in such riparian habitats? To what degree must sites be treated as mosaics of patches, with different types of patches that are suited to different species? Plant performance as measured by height was better in species of Salicaceae or in species planted as cuttings than in species of other families or in species planted as seedings or seeds. Three within‐site factors, land form, soil depth to a buried layer of sand or gravel, and soil texture, affected the growth of several species, indicating that sites do need to be treated as patchy. However, there was little evidence that different species performed better on different types of patches. Instead, areas with deep or fine soils seemed to be favorable for a number of species. Results suggest that it is feasible to re‐establish native trees and shrubs along large, regulated rivers, at least at certain sites for an initial period of several years with the aid of weed control and irrigation. Shallowly buried layers or lenses of gravel or sand are a hidden, fine‐scale factor that can reduce plant growth on river terraces.

Alpine Debris-Flows in Leirdalen, Jotunheimen, Norway, with Particular Reference to Distal Fans, Intermediate-Type Deposits, and Flow Types

The landforms and deposits associated with AD 1996 debris-flows at three sites in the low-alpine zone, Jotunheimen, southern Norway, are described and analyzed. Parallel levées, composed of diamicton, occur on the valley-side slopes but distinct frontal lobes are absent: instead, low-angle fans, up to about 50 m wide and ca. 500 m long have overridden vegetation in the footslope zone and in the valley bottom. Five facies are recognized in the fans: (1) cobble-rich diamicton, up to 50 cm thick; (2) pebble-rich diamicton, typically up to 30 cm thick; (3) pebbly sand lenses, up to about 15 cm thick; (4) massive silty sand or sandy silt (intermediate-type deposits) of thickness 5–15 cm; and (5) laminated fine sands and silts (typically a few cm thick). These succeed one another in a vertical and lateral sense. The landform-sediment assemblage and proximal-distal trends are explained by a four-stage model of an integrated debris-flow event in which (1) slope failure and sediment disaggregation are followed sequentially by (2) debris flow sensu stricto (cohesive debris flow), (3) wet mudflow or hyperconcentrated flow, and (4) water flow. Debris flow sensu stricto accounts for an estimated 48 to 51%, wet mudflow/hyperconcentrated flow 21 to 26%, and water flow 24 to 31%, by volume of material mobilized during each debris-flow event at two of the sites. Results highlight the potential complexity of debris-flow events and the importance of the associated relatively fine-grained intermediate-type deposits with little or no structure, which are attributed here to wet mudflow and/or hyperconcentrated flow. Water-lain deposits, also integral to the debris-flow event, tend to be thinner and finer, better sorted, and distinctly laminated.

Alpine Debris-flows in Leirdalen, Jotunheimen, Norway, with Particular Reference to Distal Fans, Intermediate-type Deposits, and Flow Types

The landforms and deposits associated with AD 1996 debris-flows at three sites in the low-alpine zone, Jotunheimen, southern Norway, are described and analyzed. Parallel levées, composed of diamicton, occur on the valley-side slopes but distinct frontal lobes are absent: instead, low-angle fans, up to about 50 m wide and ca. 500 m long have overridden vegetation in the footslope zone and in the valley bottom. Five facies are recognized in the fans: (1) cobble-rich diamicton, up to 50 cm thick; (2) pebble-rich diamicton, typically up to 30 cm thick; (3) pebbly sand lenses, up to about 15 cm thick; (4) massive silty sand or sandy silt (intermediate-type deposits) of thickness 5–15 cm; and (5) laminated fine sands and silts (typically a few cm thick). These succeed one another in a vertical and lateral sense. The landform-sediment assemblage and proximal-distal trends are explained by a four-stage model of an integrated debris-flow event in which (1) slope failure and sediment disaggregation are followed sequentially by (2) debris flow sensu stricto (cohesive debris flow), (3) wet mudflow or hyperconcentrated flow, and (4) water flow. Debris flow sensu stricto accounts for an estimated 48 to 51%, wet mudflow/hyperconcentrated flow 21 to 26%, and water flow 24 to 31%, by volume of material mobilized during each debris-flow event at two of the sites. Results highlight the potential complexity of debris-flow events and the importance of the associated relatively fine-grained intermediate-type deposits with little or no structure, which are attributed here to wet mudflow and/or hyperconcentrated flow. Water-lain deposits, also integral to the debris-flow event, tend to be thinner and finer, better sorted, and distinctly laminated.

Lithostratigraphy and paleomagnetism of pre-Fraser glacial deposits in south-central British Columbia

Lithostratigraphic records spanning considerable parts of the Pleistocene were studied at three sites in south-central British Columbia. A sedimentary succession near Pavilion includes three distinctly different till units. While the surface till can be associated with the last glaciation (the Fraser Glaciation δ18O stage 2), the ages of the two older till units are presently unknown. However, optical dating of outwash silt resting on the oldest till indicates that this outwash unit and all the overlying units are younger than ~160 ka. In Big Bar Creek valley, about 50 km north of Pavilion, an aggradational sequence of indurated glaciofluvial sand, gravel, and till is exposed. A silt unit and a sand lens within an overlying till bed near the top of the section have reversed magnetization, indicating deposition prior to 780 ka, probably during the Matuyama chron. The Big Bar Creek sequence also includes glacio(?)fluvial sediments near the base that are normally magnetized, suggesting that they were deposited, at the latest, during the Jaramillo subchron (~1.0 Ma), but probably during the Gauss chron, before 2.6 Ma. Reversely magnetized glacio(?)fluvial gravel and sand also occur along Jesmond Road between the Marble Range and Edge Hills. These units give support for the development of at least one Cordilleran ice sheet in the Early Pleistocene or Late Pliocene.

Movement and remediation of trichloroethylene in a saturated heterogeneous porous medium: 1. Spill behavior and initial dissolution

An intermediate-scale flow cell experiment was conducted to study the flow of liquid and the transport of dissolved trichloroethylene (TCE) in a saturated, heterogeneous porous medium system. The 1.67-m long by 1.0-m high by 0.05-m wide flow cell was packed with three layers and five lenses consisting of four different sands. All lenses and layers had horizontal interfaces, except the lowest interface, which was pointed down in the middle. Groundwater flow was imposed by manipulating the water levels in two head chambers. Over 500 ml of dyed TCE was allowed to infiltrate at a constant rate into the porous medium from a narrow source located on the surface. A dual-energy gamma radiation system was used to determine TCE saturations at 1059 locations. Fluid samples were collected from 20 sampling ports to determine dissolved TCE concentrations. The TCE migrated downwards in the form of several relatively narrow (3–8 mm) fingers. Visual observations and measured TCE saturations indicated that the spilled TCE accumulated on top of, but did not penetrate into, fine-grained sand lenses and layers but that some TCE infiltrated into medium-grained sand lenses. This behavior is a result of the different nonwetting-fluid entry and permeability values of the sands. Most of the TCE finally pooled on top of a fine-grained sand layer located in the bottom part of the flow cell. A multifluid code (STOMP: subsurface transport over multiple phases), accounting for TCE entrapment, was used to simulate the movement of liquid TCE. Using independently obtained hydraulic parameter values, the code was able to qualitatively predict the observed behavior at the interfaces of the lenses and sand layers. Simulation results suggest that most of the liquid TCE at the lowest interface was in free, continuous form, while most of the other TCE remaining in the flow cell was entrapped and discontinuous. A simple pool dissolution model was used to predict observed dissolved TCE concentrations. Results show that the measured concentrations could only be predicted with unrealistically high transverse dispersivity values. The observed TCE concentrations are a result of a combination of entrapped and pool dissolution.

Lithostratigraphy and paleomagnetism of pre-Fraser glacial deposits in south-central British Columbia

Lithostratigraphic records spanning considerable parts of the Pleistocene were studied at three sites in south-central British Columbia. A sedimentary succession near Pavilion includes three distinctly different till units. While the surface till can be associated with the last glaciation (the Fraser Glaciation δ18O stage 2), the ages of the two older till units are presently unknown. However, optical dating of outwash silt resting on the oldest till indicates that this outwash unit and all the overlying units are younger than ~160 ka. In Big Bar Creek valley, about 50 km north of Pavilion, an aggradational sequence of indurated glaciofluvial sand, gravel, and till is exposed. A silt unit and a sand lens within an overlying till bed near the top of the section have reversed magnetization, indicating deposition prior to 780 ka, probably during the Matuyama chron. The Big Bar Creek sequence also includes glacio(?)fluvial sediments near the base that are normally magnetized, suggesting that they were deposited, at the latest, during the Jaramillo subchron (~1.0 Ma), but probably during the Gauss chron, before 2.6 Ma. Reversely magnetized glacio(?)fluvial gravel and sand also occur along Jesmond Road between the Marble Range and Edge Hills. These units give support for the development of at least one Cordilleran ice sheet in the Early Pleistocene or Late Pliocene.

Abstract: Using a Geographic Information System to Determine the Chicot Aquifer System Surficial Confining Unit's Thickness and Location of Sand Lenses, Southwestern Louisiana 

ABSTRACT The Chicot aquifer system in southwestern Louisiana has a surficial confining unit that is undifferentiated from overburden material near the surface. This confining unit is composed of fine sand, silt, and clay, through which recharge flows to the underlying aquifer units. The thickness of the confining unit was mapped suing water-well and petroleum-well data from federal and state agency databases, and supplemental information from previous publications. thicknesses were estimated from 128 petroleum-well geophysical logs, 260 water-well geophysical logs, and 1,705 water-well driller's logs. Although an abundance of petroleum-well geophysical logs are available from southwestern Louisiana, logging commonly did not start at or near the ground surface, which rendered the logs unusable. Water-well driller's logs vary in quality, and those used were complied from paper-files of more than 10,000 well records. Thickness values from driller's logs were not used if the values did not match thickness values from other nearby geophysical and driller's logs. The thickness of the confining unit was estimated using kriging, and interpolation method. Kriging can handle spatial variability, smooth out random noise, and mitigate the impact of hot spots where there is a great quantity of data. Universal kriging was used instead of ordinary kriging because the data were highly correlated in a particular direction. The distribution of shallow domestic wells completed in sand lenses within the Chicot surficial confining unit was compared to the distribution of sand lenses obtained from the log data. This provided independent corroboration of areas where sufficient water is available for rural domestic use. End_of_Record - Last_Page 5-------

Non–aqueous phase liquid dissolution in heterogeneous systems: Mechanisms and a local equilibrium modeling approach

Experiments quantifying rates of non–aqueous phase liquid (NAPL) dissolution from heterogeneous media are presented and compared with model simulations. This work specifically addresses the overall dissolution of NAPL entrapped in a coarse sand lens at a high saturation. To explore the mechanisms governing dissolution rates, mathematical models describing the hydrodynamics of flow through the heterogeneous system were developed and coupled with a mass balance equation and a local equilibrium assumption (LEA) to quantify interphase mass transfer processes. Variations in the effective permeabilities as a function of NAPL saturation and the intrinsic permeabilities of the sands were employed to characterize the hydrodynamic aspects of flow through the heterogeneous system. Relative to errors generated by the ill‐defined aqueous phase relative permeabilities at high NAPL saturations, the model incorporating the system hydrodynamics as the sole rate‐limiting process provided a reasonable first estimate of effluent concentrations. With the representative elemental volume defined here, rate‐limited dissolution becomes important for low‐NAPL saturations (Sn < ∼0.05–0.15) causing tailing in the observed dissolution data and deviations between these data and the LEA model.

Application of directional filtering in lineament mapping for groundwater prospecting around bhinmal — A semi arid part of thar desert

The significance of neotectonic lineaments for groundwater prospecting was studied for the area around Bhinmal — a semi-arid part of Thar desert. The application of Directional Filtering procedures on IRS LISS I Band 4 digital image of the study area revealed NE-SW, NW-SE and E-W trending lineaments which are very subtle and in two cases, even unnoticed otherwise. The use of exploratory borehole lithologs and field evidences indicated that the identified lineaments are long rectilinear buried and partly exposed channels and the intersection zones are characterised by thick lenses of coarse sand and gravel. These buried channels and zones of coarse sediments thus represent potential sites for the accumulation of freshwater during rain. The present work has highlighted the suitability of Directional Filtering procedures for lineament mapping and buried channel studies in a desertic terrain.